Neil P. Dasgupta

High Resolution Image Download MS PowerPoint Slide Sodium (Na) batteries are of growing interest due to the higher earth abundance of sodium than lithium, as well as their promising theoretical energy density when metallic Na anodes are used. However, Na plating and stripping are heavily influenced by the physicochemical properties of the solid electrolyte interphase (SEI), which is directly influenced by the solvent and salt used for the electrolyte. While most studies focus on the SEI that forms on the surface of Na metal after plating, we expand this analysis by identifying a nanoscale “pre-plating” SEI that forms on the current collector (CC) prior to the onset of Na plating. Here, we systematically investigate an array of Na salt and glyme solvents in the electrolyte and determine the associated impacts on pre-plating SEI formation on aluminum CCs. By combining analytical electrochemistry approaches with a multimodal suite of spectroscopy techniques (X-ray, infrared, and Raman), supported by density functional theory calculations, we reveal a direct correlation between the Na + coordination environment and pre-plating SEI composition. We find that longer-chain glymes produce larger proportions of organic alkoxide products in the interphase, consistent with increased Na + –glyme interactions, while the fraction of salt-derived inorganic products (e.g., NaF) correlates with Na + –anion coordination. These insights highlight the critical influence of electrolyte composition─particularly solvent identity and Na + coordination─on the initial SEI formation in anode-free Na batteries.

ABSTRACT Perovskite solar cells (PSCs) are traditionally fabricated using sequential layer‐by‐layer deposition, in which each layer of the device is processed on top of the preceding layer. This constrains the processing techniques and selection of transport layer materials that can be used in the solar cell. To overcome these challenges, two half‐cells can be processed independently and then diffusion‐bonded through a lamination process. However, current lamination processes for perovskite solar cells suffer from relatively long process times, which can limit throughput when moving toward high‐volume manufacturing. In this study, a custom platform was designed for rapid‐joule heating of perovskite materials and devices. This enabled more than a 99% reduction in lamination time from 26 min to 1 s. Perovskite samples that were laminated in 1 s exhibited comparable values of percent bonded area, interfacial toughness, grain domain size, and X‐ray diffraction spectra to those laminated in greater than 10 min. As a proof‐of‐concept, 18.3% efficient devices were successfully laminated in 5 s. A transient heat transfer model was developed to describe the relationship between the perovskite temperature and the electrical power supplied to the heaters, establishing a baseline for predicting processing conditions in large‐scale manufacturing systems. Ultra‐fast lamination provides a pathway toward scalable roll‐to‐roll or sheet‐to‐sheet manufacturing of PSCs.

High Resolution Image Download MS PowerPoint Slide Electrochemical reactive carbon capture (eRCC) is a promising route for carbon utilization, but its performance is limited by fundamental constraints in conventional membrane electrode assembly (MEA) configurations. The key steps of eRCC, such as CO 2 desorption, mass transport, and conversion, are detrimentally coupled at the zero-gap MEA interface. Here, we demonstrate that incorporating a dedicated stripping compartment enables the direct supply of CO 2 -laden solution to the membrane interface without electrode obstruction, and effectively decouples the mass transport of desorbed CO 2 from its conversion in an interface-modulated three-compartment flow cell (3CFC), by modulating the pressure differential across compartments to drive directed CO 2 transport. The in situ/operando Raman spectroscopy revealed its unique pH-buffering capability near the electrode, contributing to high C 2+ selectivity and enhanced eRCC performance. This unique platform achieves remarkable stability and selectivity in the direct conversion of bicarbonate across diverse catalysts. At −200 mA/cm 2, a Cu(OH) 2 -derived catalyst achieved an unprecedented C 2+ selectivity of 52.0%, representing a 17-fold increase from 3.1% in the MEA cell. Moreover, Ag electrodes exhibit long-term stability for more than 155 h at −100 mA/cm 2 from bicarbonate conversion, in contrast to the rapid increase in H 2 observed in the MEA configuration. The CO selectivity of a Ni single-atom-catalyst from eRCC was dramatically enhanced to 96.7% utilizing 3CFC, compared to 38.0% in the MEA cell. This work presents a new principle for controlling the interfacial chemical environment in complex electrochemical systems.

Solid-state batteries with lithium (Li) metal anodes experience stability issues at the Li|solid electrolyte (SE) interface during stripping due to void formation. In this work, an operando detection strategy for void formation at the Li|SE interface is developed based on galvanostatic electrochemical impedance spectroscopy (GEIS). The stripping behaviors of in situ-formed Li on Li 6 PS 5 Cl and Li 7 La 3 Zr 2 O 12 SEs in an “anode-free” configuration are studied. By comparing the impedance data in the frequency domain to the cell voltage trace in real time, we identify descriptors that enable early detection of void formation. It is found that the imaginary component of the impedance in specific frequency ranges enables earlier detection of void formation compared to other descriptors. To describe these trends, a three-dimensional (3-D) model of the interfacial void geometry is developed to predict the impedance response, which agrees well with experiments. Informed by these GEIS results, we demonstrate the potential of an operando impedance measurement using only one frequency to enable early detection of voids, without the need for broadband impedance equipment or real-time fitting with equivalent circuit models. This approach can be integrated into a control system to enable early diagnosis of interfacial degradation in solid-state batteries.

This dataset supports the work “Current-controlled Zinc Electrodeposition Morphology in Ionic Liquid Electrolytes using Microelectrode Arrays”. It includes experimental data from zinc electrodeposition and stripping performed on gold ultramicroelectrode (UME) arrays at different current densities. The data also contains scanning electron microscopy (SEM) images used to analyze deposition morphology as well as Coulombic efficiency comparison data for different current densities. The microelectrode arrays were fabricated using nanofabrication techniques, and zinc deposition experiments were carried out using a zinc-based slurry counter electrode and Au UME arrays as the working electrodes. Each UME was sequentially subjected to zinc deposition and/or stripping, enabling a high-throughput investigation of electrochemical behavior across the array. In addition to the experimental data, the work also includes modeling performed in COMSOL Multiphysics to support interpretation of mass transport and deposition behavior.

The solid electrolyte interphase (SEI) is known to play an essential role in battery performance. However, for highly reactive components such as Li metal anodes, additional side reactions may also contribute to interfacial stability. In particular, for solid-state batteries (SSBs), there exists a unique interface where exposed Li metal surfaces come into contact with the surrounding gas-phase molecules during operation, which is distinct from the solid-liquid interface that exists in a liquid electrolyte system. In this work, we study the dynamic formation of a solid-gas interphase (SGI) layer on the exposed surfaces of the Li metal anode during plating, stripping, and open-circuit rest periods. A customized environmental chamber was fabricated to allow for control of the background gas composition and pressure while cycling SSBs under stack pressure. The formation of an SGI was found to depend on the plated Li capacity, ambient gas composition, and aging time, which has a direct impact on Coulombic efficiency. To reveal the dynamic formation of the SGI layer with trace background reactant gases, operando X-ray photoelectron spectroscopy (XPS) was performed under ultrahigh vacuum conditions. Solid-state pouch cells were assembled in a commercially relevant dry room environment, revealing the influence of SGI formation on calendar life in practical cell configurations. These findings highlight the importance of SGI formation, which is distinct from the classical SEI layer that arises from electrolyte decomposition, in the analysis of SSBs.

Understanding and controlling the microstructure of zinc (Zn) metal electrodeposits are critical for advancing the next generation of rechargeable Zn batteries. In this study, we develop microelectrode arrays to systematically investigate the relationship among current density, morphology, and Coulombic efficiency (CE) during Zn electrodeposition from an ionic liquid electrolyte. By independently controlling the current density or voltage on each microelectrode, we identify three key deposition regimes. At lower current densities, Zn electrodeposition forms soft, loosely packed mossy structures with moderate CE between 80 and 90%. Increased current densities yield more compact morphologies, representing a transition zone where growth becomes more uniform and achieves 98-99% CE. Under constant voltage deposition, the Zn salt in the electrolyte near the microelectrode depletes, leading to sharp, filament-like dendrites with CE below 50%. These findings demonstrate the ability to control Zn electrodeposition morphology in nonaqueous electrolytes while highlighting the diffusion-limited kinetics that dictate deposition behavior and reversibility. The methodology provides mechanistic insights and offers viable strategies for designing dendrite-free Zn anodes for stable and efficient ZIBs.

The rapid electrification of the transportation sector has catalyzed the investigation of direct recycling of lithium-ion batteries (LIBs) to reduce the socioeconomic and environmental impacts of LIB production. Most direct recycling methods break down the electrode into its constituent active materials and employ some combination of heat and chemical treatment to recover the active material in the battery while preserving its structure and morphology [1]. This process removes the solid-electrolyte interphase (SEI) layers, which are formed during the initial few cycles of a battery’s life and are important for battery stability and safety [2]. In particular, the formation of the SEI at the surface of the anode is an important factor that contributes to the initial loss of lithium inventory (LLI) in a cell [3], [4]. To overcome these challenges, electrode-level direct recycling is an alternative technique that reuses battery active materials without removing them from their current collectors. This technique can potentially preserve the SEI that is formed on the graphite anode during the first life of the cell. Preserving the natural SEI is beneficial because this would mitigate the initial LLI of a second-life battery, thus prolonging its second lifetime. However, using the natural SEI from a first-life battery could decrease the performance of the second life battery, since the SEI builds up during cycling and increases the cell resistance [2]. Therefore, the goal of this study is to understand the role of the SEI layer in electrode-level direct recycling. To study the role of the SEI layer, in this study, pouch cells were assembled, cycled, and then disassembled. The lithium nickel manganese cobalt oxide cathode was extracted from the pouch cell, and remanufactured into second-life cells with different types of graphite anodes. In particular, we compare a pristine (uncycled) graphite anode, a second-life (cycled) anode, and an anode with an artificial SEI layer deposited by atomic layer deposition (ALD). The artificial SEIs produced via ALD can mitigate initial LLI by preventing the reductive side reactions with the electrolyte that form the SEI [5]. These layers can also decrease the cell’s resistance due to their higher ionic conductivity than that of the natural SEI. We observe distinct differences in the initial Coulombic efficiency (ICE) between these anode groups, where the use of an artificial SEI can improve the ICE by at least 5% compared to a pristine graphite anode in the second-life cell, while avoiding the unnecessary buildup of the natural SEI from the first life. This technique thus serves as a method to reduce the initial LLI in a battery’s second life, and also has the potential to be deployed at scale. [1] T. Yang et al. , “An Effective Relithiation Process for Recycling Lithium-Ion Battery Cathode Materials,” Adv Sustain Syst , vol. 4, no. 1, Jan. 2020, doi: 10.1002/adsu.201900088. [2] E. Peled and S. Menkin, “Review—SEI: Past, Present and Future,” J Electrochem Soc , vol. 164, no. 7, pp. A1703–A1719, 2017, doi: 10.1149/2.1441707jes. [3] S. J. An, J. Li, Z. Du, C. Daniel, and D. L. Wood, “Fast formation cycling for lithium ion batteries,” J Power Sources , vol. 342, pp. 846–852, 2017, doi: 10.1016/j.jpowsour.2017.01.011. [4] H. Zhou, F. Xin, B. Pei, and M. S. Whittingham, “What Limits the Capacity of Layered Oxide Cathodes in Lithium Batteries?,” Aug. 09, 2019, American Chemical Society . doi: 10.1021/acsenergylett.9b01236. [5] E. Kazyak, K. H. Chen, Y. Chen, T. H. Cho, and N. P. Dasgupta, “Enabling 4C Fast Charging of Lithium-Ion Batteries by Coating Graphite with a Solid-State Electrolyte,” Adv Energy Mater , vol. 12, no. 1, Jan. 2022, doi: 10.1002/aenm.202102618.

Solid state batteries (SSBs) are a promising alternative to state-of-the-art Li-ion batteries, owing to their improved safety and high energy density. However, Li-metal SSBs experience Li dendrite and void formation at the Li/solid electrolyte (SE) interface at high current densities and cycle numbers, leading to capacity loss and catastrophic cell failure [1]. There is a need to understand the origin and growth mechanisms of these degradation modes; however voids are difficult to study because they exist at the buried SE/Li interface [2, 3]. To overcome this limitation, in this study, we used a transparent Al-doped Li7La3Zr2O12 (LLZO) SE to facilitate real-time visualization of void formation and growth through operando video microscopy synchronized with electrochemical cycling. Al-doped LLZO SE was fabricated by hot pressing and the transparency of 1mm pellets was examined using both ultraviolet visible spectroscopy and optical microscopy. Features as small as 2 μm in resolution could be optically resolved through these transparent LLZO pellets. In-plane Li metal symmetrical cells were fabricated on LLZO pellets and assembled in a custom-built visualization cell platform for o perando video microscopy tests during electrochemical cycling. Using this platform, void formation was observed at the Li/SE interface during stripping. Voids <10 μm in size were observed, which increased over time in both number and size. Image segmentation was performed on the operando optical images to analyze the coupled electrochemical-morphological effects on void formation and growth. This allowed for quantification of the void size, shape, and position throughout cycling. The void morphology was further confirmed by cross-sectional scanning electron microscopy (SEM). This work further enhances our understanding of how, when, and whyvoid formation occurs and presents a powerful operando method to study phenomena with as small as a 2μm resolution at buried interfaces in SSBs.

Given concerns about the low earth abundance of lithium (Li) in Li-ion batteries, there is growing interest in developing a beyond-Li materials basis for rechargeable batteries. Batteries based on sodium (Na) are a compelling alternative due to the ~1000-fold higher concentration of Na in the earth’s crust, along with high charge capacities (1166 mAh/g, 1128 mAh/cm 3 ) if Na is used as a metallic anode. A major issue with Na metal, however, is its chemical reactivity. Conventional carbonate-based battery electrolytes react with Na to form a thick, heterogeneous, and organic-rich solid electrolyte interphase (SEI) that exacerbates plating nonuniformity and capacity loss during cycling. [1,2] In comparison, ether-based electrolytes have been observed to promote the formation of a relatively compact, inorganic-rich SEI on plated Na, which can enable extended cycle life in certain formulations such as NaPF 6 in glyme. [1,2] One important yet underexplored aspect of Na electrochemistry, however, is the “pre-cycling” SEI, which forms on the current collector (CC) via electrolyte decomposition before Na plating onset. In Li metal systems, for example, chemical inhomogeneities on the CC can cause current focusing during Li nucleation, intensifying the heterogeneity of Li deposits, [3] and plated Li has even been found to chemically react with surface oxide species on the CC [4] — which is of elevated concern for Na. This study quantitatively examines the pre-cycling SEI formation in a range of relevant ether-based Na electrolytes; we systematically examine various Na salts in glymes of different lengths in order to explore the relationship between the Na + coordination environment, SEI composition, and ensuing electrochemical behavior. The electrolytes examined herein are 1 M of a Na salt (NaPF 6 , NaBF 4 , NaFSI, or NaTFSI) in either 1,2-dimethoxyethane (G1), bis(2-methoxyethyl) ether (G2), triethylene glycol dimethyl ether (G3), or tetraethylene glycol dimethyl ether (G4), if soluble. Raman spectroscopy measurements in different glymes demonstrate varying degrees of ion pairing, providing an avenue for quantitative comparison between Na + --anion coordination and SEI formation products. Na-Al cells are utilized for electrochemical analysis; both galvanostatic reduction and linear sweep voltammetry (LSV) at slow rates reveal small but significant reductive capacities (~0.005 mA/cm 2 ) before Na plating onset in each electrolyte. Cyclic voltammetry is then performed between 0 and 2 V vs. Na, revealing that roughly half of the 1 st cycle reductive capacity can in fact be attributed to irreversible electrolyte decomposition. LSV of G3- and G4-based electrolytes in three different Na salts exhibit distinct current density peaks, providing electrochemical signatures of enhanced decomposition for these particular glymes. Next, Al electrodes are systematically polarized to different positive potentials vs. Na; XPS and FTIR analyses reveal both anion and solvent decomposition products on the CC surface. Interphase composition is dependent on polarization potential, which suggests the presence of different electrolyte decomposition pathways. Finally, the impact of the pre-cycling SEI on ensuing electrochemistry is examined. This work further reveals the impact that electrolyte composition can have on the very early stages of battery operation, with lessons relevant to both Na metal and Na-ion battery research. [1] Seh, Z. W., Sun, J., Sun, Y. & Cui, Y. A Highly Reversible Room-Temperature Sodium Metal Anode. ACS Central Science 1 , 449-455 (2015). [2] Sayahpour, B. et al. Quantitative analysis of sodium metal deposition and interphase in Na metal batteries. Energy & Environmental Science 17 , 1216-1228 (2024). [3] Sanchez, A. J. & Dasgupta, N. P. Lithium Metal Anodes: Advancing our Mechanistic Understanding of Cycling Phenomena in Liquid and Solid Electrolytes. Journal of the American Chemical Society 146 , 4282-4300 (2024). [4] Yoon, J. S. et al. Thermodynamics, Adhesion, and Wetting at Li/Cu(-Oxide) Interfaces: Relevance for Anode-Free Lithium–Metal Batteries. ACS Applied Materials & Interfaces 16 , 18790-18799 (2024).

Nanomaterials offer several advantages for electrochemical energy storage, devices including high surface areas, short transport distances, and tunable material properties. However, the ability to precisely control the chemical, structural, and physical properties of surfaces and heterogeneous interfaces limits the performance of many applications. To address these challenges, in this talk, I will describe recent advances from our group in the application of Atomic Layer Deposition (ALD) for the atomically-precise modification of surfaces and interfaces in both liquid and solid-state batteries. In Li-ion batteries with liquid electrolytes, I will discuss the application of glassy Li 3 BO 3 -Li 2 CO 3 (LBCO) films as “artificial SEI” layers on graphite anodes. These LBCO layers have the highest ionic conductivity reported to date for an ALD-deposited lithium solid electrolyte (2 * 10 -6 S/cm), with a wide electrochemical stability window [1]. When deposited on the surface of graphite anodes after calendaring, the ALD-modified electrodes enable extreme fast charging at 4-6C rates, at both room temperature and down to sub-zero temperatures (-10 °C), without lithium plating [2-3]. This illustrates the critical role of interfacial impedance in fast charging applications, which is decoupled from mass transport effects using 3-electrode measurements In solid-state batteries, I will describe the use of a rotary-bed ALD system to coat single-crystalline NMC particles with ~5 nm thin amorphous Nb 2 O 5 layers [4]. Remarkably, these coatings improve both the first-cycle Coulombic efficiency and extended cycle life when charged up to voltages of 4.5-4.7 V vs. Li/Li + . High-resolution transmission electron microscopy analysis reveals the suppression of structural changes in the layered NMC structure in coated cathodes at these high voltages, which also prevents intra-particle cracking that otherwise occurs at these high voltages. These findings illustrate the important coupling of interfacial electrochemistry and chemo-mechanical stability in composite cathodes for solid-state batteries. References E. Kazyak et al., J. Mater. Chem. A 6 , 19425 (2018) E. Kazyak et al., Adv. Energy Mater. 12 , 2102618 (2022) T. H. Cho et al., Joule 9 , 101881 (2025) M. K. Jangid et al., Nature Commun. 15 , 10233 (2024)

Solid-state batteries have emerged as a promising technology for next-generation energy storage systems, offering enhanced safety and higher energy densities compared to conventional liquid-electrolyte batteries. However, the practical realization of solid-state cells—particularly anode-free designs—remains hindered by the persistent challenge of dendrite formation. These filament structures can compromise performance and safety by inducing internal short circuits, accelerating capacity fade, and posing the risk of battery failure. Understanding and controlling dendrite formation is crucial to unlocking the full potential of solid-state batteries. [1] [2] [3] This work presents a model of the spatial distribution of ionic flux during electrodeposition in battery systems to elucidate the conditions that govern dendrite initiation. The model employs an electro-quasi-static framework with nonlinear boundary conditions representing charge transfer kinetics, implemented within ABAQUS software. The analysis reveals that dendrite onset is intimately tied to the formation of singular current fields at the electrode surface. This phenomenon is governed by the interplay between electrode geometry and an intrinsic electrochemical length scale, which arises from the balance of ionic conductivity and interfacial charge transfer kinetics described by the Butler–Volmer equation. When the electrode dimension greatly exceeds this length scale, a pronounced current density singularity develops at the electrode edge. In contrast, when the electrode size is comparable to the electrochemical length scale, the singularity is suppressed, leading to a more uniform flux profile. These relationships between electrode length scales and the current density distribution along the interface reveal how geometrical effects could influence the probability of local dendrite initiation. These findings are further explored through experimental observations of electrodes with different sizes. By elucidating this mechanism, the results offer new insights into understanding the underlying mechanisms that influence dendrite formation in solid-state batteries. [1] Kazyak, E., Garcia-Mendez, R., LePage, W. S., Haslam, C., Sakamoto, J., & Dasgupta, N. P. (2020). Li Penetration in Ceramic Solid Electrolytes: Operando Microscopy Analysis of Morphology, Propagation, and Reversibility. Matter, 2(4), 1025–1048. [2] Choudhury, R., Wang, M., & Sakamoto, J. (2020). The Effects of Electric Field Distribution on the Interface Stability in Solid Electrolytes. Journal of The Electrochemical Society, 167(14), 140501. [3] Swamy, T., Park, R., Sheldon, B. W., Rettenwander, D., Porz, L., Berendts, S., Fleig, J., & Wilkening, M. (2018). Lithium Metal Penetration Induced by Electrodeposition through Solid Electrolytes: Example in Single-Crystal Li 6 La 3 ZrTaO 12 Garnet. Journal of The Electrochemical Society, 165(16), A3648–A3655.

Anode-free solid-state batteries (SSBs) are a promising alternative to traditional lithium-ion batteries (LIBs) with higher energy density, better manufacturability, and improved safety. The key challenge associated with the widespread use of anode-free batteries lies in the irreversible cycling of lithium metal. The nucleation of lithium on a bare copper surface occurs stochastically due to “hot spots”, resulting in uneven plating and lithium dendrite growth which causes cell failure. While significant efforts have been devoted to improving the uniformity of lithium plating in LIBs by modifying the current collector using patterned interlayers and 3D geometries [1,2], it is unclear if these techniques are directly translatable to solid-state batteries due to the uniquely complex chemo-mechanics of the solid-solid interface. Therefore, in this study we explore the use of patterned ALD deposited interlayers to control in situ lithium metal formation at the current collector and argyrodite (Li 6 PS 5 Cl) solid electrolyte interface. ALD thin films that range from lithiophilic to lithiophobic (ZnO, Al 2 O 3 , and LiF) were patterned spatially on copper current collectors using photolithography. Molten lithium contact angle measurements were obtained to quantify wetting behavior of the ALD interlayers [3]. Lithium metal nucleation and early growth selectivity on the resulting patterns were studied at various current densities, stack pressures, and areal capacities using post-mortem optical microscopy and focused ion-beam/scanning electron microscopy (FIB-SEM) techniques. Lithium selectivity was quantified by comparing deposition on active (lithiophilic) and inactive (lithiophobic) regions of the current collector through image segmentation. Lithium was observed to preferentially deposit on lithiophilic regions in single material patterns, and selectivity was significantly improved using dual patterns that employed ZnO in active areas and Al 2 O 3 in inactive regions. The highly customizable process of patterning which was developed allows for the design of interlayers with complex 2D shapes, enabling controlled area selective deposition of lithium. This platform opens the possibility of investigating challenging phenomena in SSBs, such as void formation during fast discharge. [1] Jung, W.-B. et al. ACS Appl. Mater. Interfaces 13 , 60978–60986 (2021) [2] Chen, K.-H., Sanchez, A. J., Kazyak, E., Davis, A. L. & Dasgupta, N. P. Adv. Energy Mater. 9 , 1802534 (2019) [3] J. S. Yoon, D. W. Liao, S. M. Greene, T. H. Cho, N. P. Dasgupta, D. J. Siegel, ACS Appl. Mater. Interfaces 16 , 18790 (2024)

Fast-charging capabilities greater than 4C is required for wider adoption of electric vehicles. In this work, we combine cell-scale simulations of the charging process and their analysis to elucidate the limiting factor for fast charging and to identify approaches to address these limitations. Two anode designs are considered. The first is the highly ordered laser-patterned electrode, wherein a periodic array of channels are introduced to graphite anode to facilitate ionic transport. The second is the hybrid anode, in which a mixture of graphite and hard carbon are used as the active material. Both of these types of anodes have exhibited fast-charge capability and excellent capacity retention. We examined the effect of the two designs on the homogeneity of the reaction current density distribution using finite-element-based modeling. Through these simulations, the observed improvements in the rate performance were determined to be a result of the homogenization of the reaction current density distribution within the anodes. Such an improvement in the homogeneity enables higher electrode utilization and therefore a lower overpotential required for fast charge. As a result of the reduction in the peak reaction current density, the propensity for Li plating is diminished in the anode, which ultimately lead to the superior capacity retention of cells with the modified anodes. We employ the second Damköhler number for the anodes to quantify this effect, and we develop a semi-analytical model that is computationally efficient. Finally, for the hybrid anode, we apply the regression tree analysis (RTA) to determine the important factors that enable the fast charging. The RTA result indicates that, for this system, the effective electrolyte transport properties of Li ions and the open circuit voltage profiles of the active materials are important.

Due to the low price and abundance of sodium, researchers have gained interest in developing sodium-ion batteries as a more sustainable energy storage option to lithium-ion batteries. Although the energy density of sodium-ion batteries is relatively lower than lithium, the “anode-free” battery (AFB) has the potential to be competitive with lithium-ion energy densities. In the anode-free configuration, sodium is entirely sourced from the cathode and is plated/stripped directly on the aluminum current collector (CC). However, plating of sodium on the current collector can be inhomogeneous in morphology, lowering the coulombic efficiency and decreasing cycle life. The incorporation of a metaling alloying interlayer on the CC has been previously shown to promote homogeneous deposition due to the enhanced sodium wetting on the substrate, resulting in reduced plating overpotentials and improved cycle life.[1,2] However, there has been a general lack of in situ/operando observations of the morphological evolution of sodium in the presence of an alloying interlayer, or quantitative analysis of sodium contact angles on these interlayers. Additionally, these interlayers are reported to delaminate from the CC throughout cycling and expose the underlying CC surface, which is detrimental to battery performance over time. In this work, we explore the sodium morphological evolution and adhesion on nanoscale gold interlayers that were deposited on an aluminum CC, to better understand how the interlayer improves sodium AFB performance. We further introduce an intermediate adhesion bi-layer structure to mitigate delamination and promote improved stability. To observe the morphological evolution of sodium on the interlayers compared to an uncoated CC, we utilized operando video microscopy,[3] together with complimentary post-mortem optical imaging and scanning electron microscopy (SEM). Sodium exhibited increased adhesion and uniformity on the gold interlayer compared to the uncoated CC; however, sodium preferentially plates onto microstructural features on the CC surface, suggesting there is current focusing in these regions. The alloying interlayer elements were also observed to migrate along the surface during plating, exposing the underlying aluminum foil. To further analyze sodium adhesion, quantitative contact angle measurements between molten sodium and these substrates were performed,[4] which revealed increased sodiophilicity and a higher work of adhesion on the interlayer. We further performed quantitative peel tests, which suggests that the interfacial toughness of gold on the CC substrate is poor. Therefore, to increase the adhesion of the gold to the CC to prevent interlayer delamination during subsequent cycling we introduce a bi-layer structure. Preliminary results suggest that the bilayer provides stronger interfacial toughness of the interlayer on the CC, which can circumvent the limitations of a pure gold layer. These fundamental studies will inform design requirements for metallic interlayers for sodium AFBs, and highlight the coupled importance of wetting, adhesion, and nucleation. [1] Tang, S.; Qiu, Z.; Wang, X.-Y.; Gu, Y.; Zhang, X.-G.; Wang, W.-W.; Yan, J.-W.; Zheng, M.-S.; Dong, Q.-F.; Mao, B.-W. A Room-Temperature Sodium Metal Anode Enabled by a Sodiophilic Layer. Nano Energy 2018 , 48 , 101–106. https://doi.org/10.1016/j.nanoen.2018.03.039. [2] Tang, S.; Zhang, Y.; Zhang, X.; Li, J.; Wang, X.; Yan, J.; Wu, D.; Zheng, M.; Dong, Q.; Mao, B. Stable Na Plating and Stripping Electrochemistry Promoted by In Situ Construction of an Alloy‐Based Sodiophilic Interphase. Adv. Mater. 2019 , 31 (16), 1807495. https://doi.org/10.1002/adma.201807495. [3] Sanchez, A. J.; Kazyak, E.; Chen, Y.; Chen, K.-H.; Pattison, E. R.; Dasgupta, N. P. Plan-View Operando Video Microscopy of Li Metal Anodes: Identifying the Coupled Relationships among Nucleation, Morphology, and Reversibility. ACS Energy Lett. 2020 , 5 (3), 994–1004. https://doi.org/10.1021/acsenergylett.0c00215. [4] Yoon, J. S.; Liao, D. W.; Greene, S. M.; Cho, T. H.; Dasgupta, N. P.; Siegel, D. J. Thermodynamics, Adhesion, and Wetting at Li/Cu(-Oxide) Interfaces: Relevance for Anode-Free Lithium–Metal Batteries. ACS Appl. Mater. Interfaces 2024 , 16 (15), 18790–18799. https://doi.org/10.1021/acsami.3c19034.

Lithium metal anodes are a promising pathway to achieving higher energy densities than current state-of-the-art Lithium-ion batteries. The highest theoretical energy densities can be obtained in an anode-free configuration, where the Lithium metal anode is formed on the current-collector (CC) in situ. However, the relative instability of the lithium metal anode poses challenges for liquid electrolytes due to the interface between CC and liquid electrolyte being unrestricted. Solid-state batteries (SSBs) are a promising alternative to Li-ion batteries due to the potential for higher energy and power densities as well as improved safety by eliminating the flammable liquid electrolyte . However, the initial Li nucleation, plating, and stripping processes on the CC surface in anode-free SSBs are influenced by both interfacial electro-chemistries and mechanical stresses [1]. For this reason, an external stack pressure is typically applied to ensure intimate contact between SSB interfaces. The majority of research on SSBs only reports nominal stack pressure as a static and singular variable, which is defined by the nominal applied force and surface area. However, stack pressure has been shown to be variable across cell surface area and throughout cycling. Therefore, there is increasing awareness that stack pressure must be treated as a spatially and temporally varying quantity, which can have a significant impact on the heterogeneity of the Li metal/solid electrolyte interface during cycling [2]. In this work, we utilize an operando thin-film pressure mapping sensor to analyze the spatial and temporal pressure distributions within anode-free SSBs during cycling. We examine the underlying the mechanisms of pressure evolution throughout Li plating and stripping with 200-µm spatial resolution. This system allows us to characterize evolving interfacial stress in situ and synchronize the pressure maps with electrochemical data. Consistent with our recent report, operando pressure mapping is used to show that elastomeric interlayers can be used to circumvent the inherent inhomogeneities in stack pressure throughout cycling [2]. We additionally show that the presence of alloying interlayers on the CC surface can promote improved wetting of Li metal across the anode-free interface. Leveraging the high spatial resolution of the sensor, we observe the evolution of pressure during plating and stripping at and around point contacts as Li metal creeps across the anode-free interface. The operando pressure evolutions are further correlated with ex situ plasma focused-ion beam (PFIB) imaging and optical microscopy to reveal the detailed microstructure and morphology of the interface. This work provides valuable insights into the dynamic pressure evolution within SSBs, which can inform future design decisions that promote pressure regulation.

Solid-state batteries (SSBs) have emerged as a promising alternative to lithium-ion batteries (LIBs), offering inherent safety, higher energy density and high-temperature operation [1] . LiFePO 4 (LFP), an olivine cathode material, can further enhance safety and stability of a SSBs owing to its outstanding thermal stability and flat discharge voltage profile (~3.45 V vs Li⁺/Li) [2] . However, the LFP cathode has not been extensively explored for SSBs with sulfide solid electrolytes (SSEs). To address this knowledge gap, we optimize the operation of LFP composite cathode in SSBs by investigating the effect of composition, capacity loading (i.e., thickness) on initial Coulombic efficiency (ICE) and cycling stability by using single-layer (Li 6 PS 5 Cl SSE; LPSC) and bilayer (an additional thin layer of Li 3 InCl 6 attached to the cathode side; LIC) solid electrolyte (SE) configurations. Typically, thinner electrodes perform better than thicker ones. Interestingly, in the single-layer SE design, the thinner electrode (1 mAh/cm 2 ) demonstrated lower ICE and poor capacity retention compared to the thicker electrode (3 mAh/cm 2 ). The inferior performance of thinner electrodes in single-layer SE design is attributed to the unstable LFP/LPSC interface [3] , which accelerates LPSC degradation and interfacial side reactions, contributing to inferior ICE. These unwanted reactions were mitigated by incorporating a thin layer of LIC SE in between the bulk LPSC SE and the LFP composite. The effect of stack pressure was also investigated, which showed reduced polarization, especially at high C-rates, highlighting the need for mechanical compliance in SSBs. At higher stack pressure (17 MPa), the discharge capacity improved by >80% compared to lower stack pressure (1 MPa) at higher rate. The higher stack pressure results in better particle-particle contacts and kinetics. Overall, this study provides a comprehensive understanding of the electro-chemo-mechanics at multi-layered interfaces and highlights the critical role of cell architecture, electrode parameters, interfacial engineering, and stack pressure optimization in achieving high ICE and long-term cycling stability in SSBs with LFP cathodes. References [1] B. S. Vishnugopi, E. Kazyak, J. A. Lewis, J. Nanda, M. T. McDowell, N. P. Dasgupta, P. P. Mukherjee, ACS Energy Lett. 2021 , 6 , 3734. [2] L.-X. Yuan, Z.-H. Wang, W.-X. Zhang, X.-L. Hu, J.-T. Chen, Y.-H. Huang, J. B. Goodenough, Energy Environ. Sci. 2011 , 4 , 269. [3] A. Cronk, Y.-T. Chen, G. Deysher, S.-Y. Ham, H. Yang, P. Ridley, B. Sayahpour, L. H. B. Nguyen, J. A. S. Oh, J. Jang, D. H. S. Tan, Y. S. Meng, ACS Energy Lett. 2023 , 8 , 827.

Laminated perovskite solar cells (L-PSCs), which can be fabricated by independently processing the hole and electron transport sides of the solar cell on separate substrates and then bonding them together, offer unique passivation, transport, and contact-layer combinations. Lamination also facilitates inherent self-encapsulation between two glass substrates, which can be leveraged to improve stability. However, the impacts of this glass-glass encapsulation on the mechanical properties and thermal stresses that arise during operation have not been previously studied. Here, we measured the thermal cycling stability and interfacial toughness of L-PSCs for the first time. L-PSCs withstood thermal cycling (TC50 protocol, -40 to 85 °C) without failure, with all devices exhibiting an increase in power conversion efficiency after cycling. To quantify their mechanical properties, the interfacial toughness values of device stacks were measured, and minimal changes were observed after TC50 cycling. An analytical framework was developed to describe the mechanical failure criterion for the self-encapsulated L-PSC system under thermal cycling, showing that using substrates with the same material properties on both sides makes the device system robust to thermal cycling. This study demonstrates that L-PSCs exhibit strong thermal and mechanical stability without the need for additional encapsulation.

Atomic layer deposition (ALD) is a powerful technique for modifying the surface chemistry and properties of substrates with complex and nonplanar topologies. However, achieving uniform and conformal deposition on ultrahigh-aspect-ratio substrates remains challenging, typically requiring large quantities of precursors and long exposure times. Furthermore, process optimization is often performed empirically and involves substantial trial and error. In this work, we perform a combined experimental and computational study of ALD Al2O3 infiltration into silica aerogel monoliths (aspect ratio >105). A reaction-diffusion model is used to explore the effects of key processing parameters, namely, exposure time per dose, precursor source temperature, number of aerogels in the reactor, and reactor volume. The model is based on quasi-static mode ALD, where the dosed precursor is held in the chamber for a fixed period of time before purging. We analyze the trade-offs between process throughput and precursor utilization for each of these parameters. Furthermore, we investigate the co-optimization and interactions between multiple process parameters, demonstrating the potential for further improvements. This physics-based model can be used to identify a set of process parameters for high-aspect-ratio ALD that meet specific manufacturing objective functions, including throughput, cost, and sustainability.

In recent years, there has been a tremendous increase in research on solid-state batteries, as they have the potential to enable lithium (Li) metal anodes with improved safety and stability compared to liquid electrolytes. In the early days, much of the research focused on the plating half-reaction during charging; in particular, there has been a large focus on understanding the formation and propagation of dendrites/filaments at fast charging rates. However, recent work has drawn increasing attention to the stripping (discharge) half-reaction, where contact loss can occur along the solid-solid interface between the Li metal anode and solid electrolyte, especially at high current densities. In particular, there have been many observations of inhomogeneous stripping along the interface, resulting in localized void formation. These voids, in turn, can result in increased current focusing as the interfacial morphology evolves, resulting in an unstable system. Despite the significant increase in recent attention paid to void formation during stripping, there remain several unanswered questions about the mechanisms that guide void nucleation, growth, and recovery during cycling. Furthermore, the majority of research on void formation has relied on ex situ analysis of the interface, which often requires destructive tear-down and post-mortem analysis of the batteries. Therefore, there is a need to develop new and improved diagnostic methods for solid-state batteries to enable early, robust, and sensitive detection of voids as they dynamically for and evolve in real time during cycling. In this talk, I will describe our recent efforts to understand the nucleation, growth, and recovery of voids during stripping of Li metal anodes against inorganic solid electrolytes, such as the garnet LLZO and sulfide LPSCl systems. A combination of in situ and ex situ analytical techniques will be employed to gain a more complete understanding of the void growth phenomena. In particular, we will focus on operando methods that enable high temporal resolution, while minimizing perturbations of the system.By combining these direct and indirect observations of void growth with continuum scale modeling, we demonstrate the relationships between cell polarization, impedance, and void morphology. Finally, we will discuss methods to reduce void formation, including recovery of interfacial contact during battery operation.

Perovskite solar cells are traditionally made using sequential layer-by-layer deposition, which constrains the processing techniques and selection of transport layer materials that can be used in the solar cell. To overcome these challenges, two half-cells can be processed separately and laminated together. Lamination exhibits numerous manufacturing advantages, including self-encapsulation, and compatibility with a wider range of processing conditions. However, current lamination processes for perovskite solar cells suffer from high cycle times of 5- 30 min. In this work, we demonstrate lamination of halide perovskite (HP) interfaces and devices in 1 second, demonstrating more than a 99% reduction in processing time compared to previous reports. In situ photoluminescence imaging of HP films during lamination elucidates the unique evolution of defects in the film, motivating the use of in-line metrology in future manufacturing environments. Furthermore, we demonstrate the first example of lamination of HP layers using a customized rolling system, allowing for continuous sheet-to-sheet processing. Overall, the results of this study show that lamination is a promising alternative manufacturing pathway for PSCs.

Perovskite solar cell (PSC) operational lifetimes have increased, but stability remains a major challenge for commercialization. Key stability issues for PSCs include chemical instability under light and heat, and mechanical failure modes such as delamination or fracture. Laminated PSCs (L-PSCs), created by independently processing the hole and electron transport sides of the solar cell and laminating them together, offer unique passivation, transport, and contact layer combinations. This processing method minimizes thermal and chemical stresses on the perovskite layer during processing of other layers in the cell and provides inherent self-encapsulation between two glass substrates, which can be leveraged to improve stability. However, to date, the thermal and mechanical properties of L-PSCs have not been widely studied. In this study, we measured the thermal cycling stability and interfacial mechanical properties of L-PSCs for the first time. L-PSCs withstood thermal cycling testing (TC50) without failure, with all the devices increasing in power conversion efficiency post-TC50. The champion device increased from an initial electrical performance of 18.4% to 20.0% after TC50. To quantify the mechanical properties of the device stack, we measured the interfacial toughness of aged (non-thermally cycled) and TC50 tested device stacks. Minimal changes in the interfacial toughness of the device stacks were observed with TC50 testing (0.27 ± 0.05 J/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> non-TC50 and 0.20 ± 0.04 J/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> post-TC50). This study demonstrates the impressive thermal and mechanical stability of L-PSCs with no additional encapsulation. Even after thermal cycling, the L-PSCs are on par in electrical performance and mechanical toughness with pristine non-laminated PSCs and can be a route to avoid critically weak interfaces that hamper commercialization, like C60 in high performing devices.

Carbon interlayers have been implemented in "anode-free" solid-state batteries to improve the uniformity and reversibility of lithium deposition by controlling the location of Li plating. However, there remains a lack of fundamental understanding of the detailed role of how these interlayers function during in situ Li formation. In this study, the relationships between the interfacial adhesion of the carbon interlayer to the solid electrolyte and the location of Li plating are investigated. By varying the lamination pressure used during manufacturing, the ability to systematically tune the resulting interfacial adhesion is demonstrated. Mechanical peel tests are performed, and a 4-fold increase in interfacial toughness is measured as the lamination pressure increases from 100 to 400 MPa. Post-mortem electron microscopy revealed that the location of Li plating with respect to the carbon interlayer transitions from the interface with the solid electrolyte to the current collector above a threshold interfacial toughness, which is consistent when the interlayer material is changed from amorphous to hard carbon. These findings highlight the role of electro-chemo-mechanical relationships in systematically controlling Li deposition in solid-state batteries when interlayers are present.

Solid-state batteries unlock possibilities for using energy-dense anodes such as lithium metal while addressing key degradation challenges. However, unresolved issues at the material and cell levels have hindered their commercialization, including variability in mechanical control and testing methodologies, a limited understanding of material behavior under operating conditions, and performance and design gaps between cells for benchtop testing and cells for advanced characterization. This perspective highlights the current state-of-the-art in testing and characterizing solid-state batteries, focusing on mechanical monitoring and controls, benchtop diagnosis and characterization techniques, and advanced operando synchrotron imaging. We emphasize the need for uniform experimental standards, scalable and practical battery cell designs to match commercial operating conditions, and integrated approaches to design advanced in situ and operando experiments to reflect realistic battery operating conditions.

Conspectus The ability to synthesize nanoarchitected materials with tunable geometries provides a means to control their functional properties, with applications in biological, environmental, and energy fields. To this end, various bottom-up and top-down synthesis processes have been developed. However, many of these processes require prepatterning or etching steps, making them challenging to scale-up to complex, nonplanar substrates. Furthermore, the ability to integrate nanomaterials into hierarchical arrays with precise control of feature spacing and orientation remains a challenge. One approach to overcome these patterning challenges is the use of surface modification layers to guide the resulting geometry of nanomaterial architectures grown from the substrate. A powerful strategy to accomplish this is what we will refer to as “surface-directed assembly,” where the resulting geometric parameters (feature size, shape, orientation) are predetermined by the initial surface layer. In particular, the use of Atomic Layer Deposition (ALD) to form a surface layer, followed by solution-based growth processes, has the ability to synthesize architected structures with tunable geometries on complex, nonplanar surfaces. Over the past decade, we have reported a series of studies where surface-directed assembly is used to synthesize ZnO nanowires (NWs) on top of a variety of substrates. In this case, a thin film of ZnO is deposited onto the substrate using ALD, which can guide the NW diameter, spacing, and angular orientation with respect to the substrate by controlling epitaxial relationships. Furthermore, we have shown that by depositing a submonolayer overcoat of a secondary material (e.g., amorphous TiO 2 ), nucleation sites are partially blocked, which can further tune the spacing between nanowires while minimizing changes to their other geometric properties. This approach can be used to generate multilevel hierarchical structures, such as hyperbranched NW arrays with tunable control of each level of hierarchy using ALD. Finally, we have demonstrated that the tunable control of geometric parameters can be scaled-up to curved, nonplanar substrates. This highlights the power of ALD to conformally and uniformly deposit the seed layers on complex substrates with subnanometer precision. To complement these seeded hydrothermal approaches, we expanded this strategy to include conversion chemistry of the initial ALD seed layers. For example, by replacing ZnO with Al 2 O 3 as the seed layer without changing the hydrothermal growth conditions, Al–Zn layered-double hydroxide nanosheets can be formed instead of nanowires. In another example of conversion chemistry, a solution anion-exchange process was used to incorporate sulfur into ALD metal oxide films. In both of these conversion processes, the properties of the initial ALD film enabled tuning of the resulting nanostructure geometry. In this Account, we describe the use of ALD to guide the growth of diverse nanomaterial systems, with tunable control over their geometry and composition. We further show how these approaches can be used to tune functional properties for a range of applications, including superomniphobic surfaces, antibiofouling coatings, and photocatalysis. We conclude with an outlook on how the combination of ALD and solution synthesis can enable future directions in scalable nanomanufacturing to overcome the limitations of traditional top-down and bottom-up approaches.

“Lithium–metal-free” manufacturing of solid-state battery cells could simplify cell assembly and increase the energy density. However, the performance of these cells benefits from a more homogeneous anode formation. The use of thin alloying interlayers in “lithium–metal-free” cells can improve cycle life, but their influence on the morphology and microstructure of plated lithium is yet unknown. Gold and silver interlayers allow for lithium plating at higher current density (0.25 mA cm –2 ) without short-circuiting compared to cells without interlayers. The lithium homogeneity is substantially improved, as shown by optical microscopy and 3D profiling. In addition, electron backscatter diffraction determined that the grain size and grain boundary orientation can be controlled by changing the lithium layer composition in the case of silver or by introducing inert particles when using gold interlayers. These findings further the understanding of how thin alloying interlayers can substantially alter the cycling performance of lithium in “lithium–metal-free” solid-state batteries.

The sodium super-ionic conductor (NaSICON) has versatile applications as a ceramic electrolyte for energy storage, where it can serve as an impermeable separator in solid-state batteries and redox flow systems. In particular, NaSICON systems have been proposed to be relatively stable in contact with water, making them compatible with aqueous battery chemistries. However, owing to their brittle nature and metal oxide constituents, stress-corrosion cracking (SCC) is an important failure mechanism that has not been previously explored. In this study, we assess the fracture toughness of NaSICON membranes in contact with aqueous solutions that are relevant to redox flow systems. Microindentation was performed to generate visible surface cracks and residual stress, which were observed to grow in length after exposure to aqueous solutions. This allows for a quantitative measurement of fracture toughness, which decreases after exposure to water. To contextualize these results, we develop a simplified model of the fracture behavior in aqueous redox-flow batteries that incorporate NaSICON membranes, illustrating the importance of SCC in cell design. This work provides quantitative insights into SCC as a failure mode in NaSICON, enhancing our understanding of the chemo-mechanical behavior of ceramic electrolytes in contact with aqueous solutions.

Realizing solid electrolytes with low grain-boundary (GB) resistance is critical for advancing all-solid-state batteries. High GB resistance in SEs is often attributed to deficiencies in mobile ions at these boundaries; yet, when and how these deficiencies form during synthesis remain unclear. Here, we use a unique in situ scanning transmission electron microscopy setup to guide solid electrolyte crystallization during annealing, enabling real-time observation of GB formation at the atomic scale, with Li 0.33 La 0.56 TiO 3 as a model SE. We reveal an ultrathin, less than 1.5 nm thick, lithium-deficient layer that emerges at the crystallization front upon crystallization and persists as two adjacent crystals fuse to form a GB. We offer two hypotheses for the origin of the lithium-deficient layer, one based on thermodynamic stabilization and the other on kinetic constraints. Our results provide guidelines for designing synthesis strategies to reduce GB resistance in solid electrolytes.

Spatial atomic layer deposition (SALD) is a powerful thin-film deposition technique to control surfaces and interfaces at the nanoscale. To further develop SALD technology, there is need to deepen our understanding of the effects that process parameters have on the deposited film uniformity. In this study, a 3D computational model that incorporates laminar-flow fluid mechanics and transport of diluted species is developed to provide insight into the velocity streamlines and partial-pressure distributions within the process region of a close-proximity atmospheric-pressure spatial atomic layer deposition (AP-SALD) system. The outputs of this transport model are used as the inputs to a surface reaction model that simulates the self-limiting chemical reactions. These coupled models allow for prediction of the film thickness profiles as they evolve in time, based on a relative depositor/substrate motion path. Experimental validation and model parameterization are performed using a mechatronic AP-SALD system, which enable the direct comparison of the simulated and experimentally measured geometry of deposited TiO2 films. Characteristic features in the film geometry are identified, and the model is used to reveal their physical and chemical origins. The influence of custom motion paths on the film geometry is also experimentally and computationally investigated. In the future, this digital twin will allow for the capability to rapidly simulate and predict SALD behavior, enabling a quantitative evaluation of the manufacturing trade-offs between film quality, throughput, cost, and sustainability for close-proximity AP-SALD systems.

Hybrid anodes formed by blending graphite and hard carbon have been demonstrated to be an effective method of overcoming the inherent tradeoff between the energy density and fast-charging capability for Li-ion battery electrodes. However, owing to the complex interplay between the constituent active materials, a fundamental understanding of the electrode parameters that enable the fast-charging performance in hybrid anodes has remained elusive. Such understanding is crucial for an effective electrode design. In this work, we employ continuum-scale modeling and analyze the results using the regression tree algorithm and the second Damköhler number to quantify the impact of material and electrode properties on the SOC achieved at the anode voltage of 0 V vs. Li/Li + . Our results show that the effective electrolyte transport properties of Li ions and the open circuit voltage profiles of the active materials are two key parameters that determine the fast-charging (4C) performance of the hybrid anode.

Anode-free solid-state batteries could have high energy densities and simplified manufacturing since excess lithium metal is not needed during cell assembly. However, the factors that control lithium growth/stripping at the anode current collector are not well understood. Here, we use operando X-ray microcomputed tomography to comprehensively image and quantify lithium deposition and stripping under various conditions in three different Li|Li6PS5Cl|current collector cells, revealing diverse behavior. A cell with high impedance exhibits extensive lithium filament growth, with filaments that grow around pre-existing pores in the solid-state electrolyte (SSE) rather than lithium filling these pores. Lithium filament formation is partially reversible, with the cracks shrinking as lithium metal is stripped. Uniform lithium deposition is achievable at low current densities in low-impedance cells, whereas higher current densities cause an increase in interfacial roughness, which is correlated with filamentary growth. These results provide insight into filamentary vs. planar lithium growth and highlight that the evolution of lithium is sensitively dependent on SSE microstructure and electrochemical process.

Anode-free solid-state batteries contain no active material at the negative electrode in the as-manufactured state, yielding high energy densities for use in long-range electric vehicles. The mechanisms governing charge–discharge cycling of anode-free batteries are largely controlled by electro-chemo-mechanical phenomena at solid–solid interfaces, and there are important mechanistic differences when compared with conventional lithium-excess batteries. This Perspective provides an overview of the factors governing lithium nucleation, growth, stripping and cycling in anode-free solid-state batteries, including mechanical deformation of lithium, the chemical and mechanical properties of the current collector, microstructural effects, and stripping dynamics. Pathways for engineering interfaces to maximize performance and extend battery lifetime are discussed. We end with critical research questions to pursue, including understanding behaviour at low stack pressure, tailoring interphase growth, and engineering current collectors and interlayers. Anode-free batteries contain no active material at the negative electrode when manufactured, and this can enable them to have high energy density. This Perspective presents a critical overview of the mechanisms governing the behaviour of anode-free solid-state batteries and provides guidance to improve this type of battery.

production and shift towards CO selectivity, which is attributed to changes in the chemical state of the surface. Our findings demonstrate the impact of atomically-precise surface modifications on electrocatalyst selectivity.

Abstract Lithium solid-state batteries offer improved safety and energy density. However, the limited stability of solid electrolytes (SEs), as well as irreversible structural and chemical changes in the cathode active material, can result in inferior electrochemical performance, particularly during high-voltage cycling (&gt;4.3 V vs Li/Li + ). Therefore, new materials and strategies are needed to stabilize the cathode/SE interface and preserve the cathode material structure during high-voltage cycling. Here, we introduce a thin (~5 nm) conformal coating of amorphous Nb 2 O 5 on single-crystal LiNi 0.5 Mn 0.3 Co 0.2 O 2 cathode particles using rotary-bed atomic layer deposition (ALD). Full cells with Li 4 Ti 5 O 12 anodes and Nb 2 O 5 -coated cathodes demonstrate a higher initial Coulombic efficiency of 91.6% ± 0.5% compared to 82.2% ± 0.3% for the uncoated samples, along with improved rate capability (10x higher accessible capacity at 2C rate) and remarkable capacity retention during extended cycling (99.4% after 500 cycles at 4.7 V vs Li/Li + ). These improvements are associated with reduced cell polarization and interfacial impedance for the coated samples. Post-cycling electron microscopy analysis reveals that the Nb 2 O 5 coating remains intact and prevents the formation of spinel and rock-salt phases, which eliminates intra-particle cracking of the single-crystal cathode material. These findings demonstrate a potential pathway towards stable and high-performance solid-state batteries during high-voltage operation.

Lithium (Li) metal anodes are widely studied as replacements for current graphite anodes as they have projected higher energy density. However, Li-metal batteries face issues with dendrite propagation and the eventual formation of dead Li. Solid-state batteries (SSBs) are a promising pathway to realize Li-metal batteries, which is attributed to their ability to improve safety and stability through the use of solid-state electrolytes. In particular, “anode-free” SSBs can enable high energy densities by forming a Li metal anode in situ. The initial Li nucleation, plating, and stripping behaviors in anode-free SSBs is influenced not only by the interfacial electrochemistry, but also by the mechanical stresses present along the current collector interface. Mechanical stress also plays a key role in Li metal anode deformation, where creep is the dominant deformation mechanism. However, to date, stack pressure is typically reported as a singular value, rather than considering the temporal and spatial variations in interfacial stress as the battery cycles. This work investigates the role of inhomogeneous stack pressure on Li anode formation and dissolution against a sulfide solid electrolyte. To compensate for this inhomogeneous stack pressure, elastomeric interlayers are used to increase the uniformity of stress along the interface, and thus improve electrochemical cyclability. To analyze the impact of elastomeric interlayers on areal Li plating coverage, post-mortem optical microscopy images of the current collector are captured, showing an improvement in areal coverage from 49% to 70%. The reversible capacity also increases from 89% to 94% with inclusion of an elastomer layer. To confirm the trends in an elastomer layer on increasing stack pressure homogeneity, the mechanical stress at the anode-free interface is modeled using finite-element simulations under different stack pressure geometries. System-level simulations illustrate tradeoffs with respect to the uniformity of mechanical stress and energy density. This work demonstrates the importance of studying external auxiliary components and packaging in SSBs to optimize anode-free SSB performance.

Recent efforts have explored the use of sodium super ionic conductors (NaSICON) in aqueous redox flow batteries (RFBs) because of their ability to selectively conduct sodium ions while effectively preventing the crossover of active species, thereby enhancing the performance and longevity of RFBs. However, despite the potential of NaSICON membranes in enhancing the electrochemical performance of RFBs, the use of dense and thick ceramic membranes results in increased cell resistances. Modak et al. recently suggested that NaSICON membranes with thicknesses below 100 mm may achieve equivalent power densities to RFBs with polymer membrane and meet the resistance criterion. 1 Therefore, to realize the commercial application of these thin ceramic films, careful attention must be paid to the membrane’s mechanical properties, especially fracture strength and toughness. Stress-corrosion cracking (SCC) is particularly important for ceramics when they are exposed to water, 2 which is defined as the growth of cracks due to the simultaneous action of a stress and a reactive environment. During cell operation, the NaSICON membrane is immersed in corrosive liquid electrolytes and is simultaneously subject to a pressure gradient due to the uneven electrolyte flow. Consequently, understanding the interaction at solid-liquid interface and its impact on NaSICON is crucial as it may affect the fracture toughness of NaSICON and cause unexpected failure. In this study, the toughness of the samples was determined using Vickers indentation. The indentations were imaged using an optical microscope, allowing for measurement of the crack lengths. To assess the evolution of fracture toughness of NaSICON in the presence of typical RFB reactants, the pellets were soaked in selected aqueous solutions. The influence of solution composition, pH value, and molarity are investigated as well as soaking time. Significant crack propagations were observed in all pellets when immersed in solutions, suggesting a decrease in the fracture toughness of the NaSICON pellet after interacting with these liquids. Measurable crack growth was observed to occur mainly within the first 24 hours of immersion, suggesting a equilibrium had been reached between the driving forces for crack propagation (such as stress intensity and corrosive environment) and the resisting material properties (material toughness). To model the influence of SCC during operation of an aqueous RFB, theoretical analysis was conducted to quantify the relationships between the pressure gradient that a NaSICON membrane can withstand under a given geometry, and the evolution of its fracture toughness. These fundamental mechanical studies will provide valuable insights to understand and manage stress corrosion cracking of NaSICON membranes in contact with liquid electrolytes. Modak, S., Valle, J., Tseng, K. T., Sakamoto, J. &amp; Kwabi, D. G. Correlating Stability and Performance of NaSICON Membranes for Aqueous Redox Flow Batteries. ACS Appl Mater Interfaces 14, 19332–19341 (2022). Spearing, S. M., Zok, F. W. &amp; Evans, A. G. Stress Corrosion Cracking in a Unidirectional Ceramic‐Matrix Composite. Journal of the American Ceramic Society 77, 562–570 (1994).