Betar M. Gallant

Highly reversible and long-cycling Na metal anodes would enable Na-based batteries to approach energy densities competitive with established Li-ion technologies while leveraging earth-abundant materials. While several Na electrolytes have demonstrated impressive cyclability with Coulombic efficiency (CE) exceeding 99%, the number of high-performance electrolytes is lower, and designs are more restrictive, than counterpart Li systems to date. Meanwhile, design principles for high-performance Na electrolytes and their derived Solid Electrolyte Interphases (SEI) are less well established. Here, we examine factors that differentiate Na cyclability across different salts (1 M NaPF6, NaOTf, NaClO4, and NaFSI) in an exemplar class of primarily diglyme (G2) electrolytes. We first examine the hypothesis, commonly encountered in literature, that elevated Na SEI solubility compared to Li is a strong driver of CE. Upon conducting solubility measurements of sodium and lithium fluoride, carbonate, oxide, and methoxide (i.e. MF, M2CO3, M2O, and MOCH3, with M = Na or Li) phases in neat solvent, we find that while solubilities are indeed elevated (e.g. Na2O in G2: 2.3×10-4 M) for Na SEI compared to Li SEI (e.g. Li2O in G2: 2.3×10-5M), the absolute solubility is expected to be exceedingly small in 1 M electrolytes (<10-9 M) due to the common ion effect. However, one notable exception is (Na, Li)OCH3 (e.g. NaOCH3 in 1 M Na+ G2: ~10-6 M), broadly representative of organic Na SEI phases. Looking beyond simple solubility, we find that OCH3

Lithium bis(fluorosulfonyl)imide (LiFSI) is widely regarded as the leading salt for stabilizing lithium metal anodes, owing to the formation of an inorganic-rich solid electrolyte interphase (SEI) and enabling Coulombic efficiencies (CE) >99.5%. Here, we identify sulfur–fluoride exchange (SuFEx) click chemistry as a previously unrecognized pathway governing the stability of FSI under cycling and aging conditions. We show that O-nucleophiles abundant at the lithium surface, including Li2O and lithium alkoxides, react with FSI to produce bis(sulfonato)imide derivatives, establishing a self-driven SEI degradation pathway. Through a detailed kinetic and crystallographic study, we isolate critical SuFEx intermediates and identify their chemical fingerprints in SEI layers. We demonstrate that methoxide-substituted FSI anions are particularly detrimental: being soluble and reduced at potentials less cathodic than FSI, they alter the SEI formation mechanism and decrease CE. These findings reframe electrolyte design strategies and suggest that suppressing SuFEx reactivity is essential for achieving sustained CE >99.9%.

Photochemical CO2 separation offers a low-temperature alternative to conventional thermal CO2 separation, replacing fuel-derived heat with light as the energy input. Although prior photoacid and photobase systems have shown promising light-driven CO2 capture–release behavior, continuous pure-CO2 generation from dilute feeds remains insufficiently developed. Here, we demonstrate light-driven pure-CO2 production from a 15% CO2 feed, reaching 3.2 sccm from 1.2 mL min−1 of circulating sorbent solution in a single lab-scale reactor, equivalent to 4.6 L day−1. In the dimethyl sulfoxide amine–photoacid platform, acidity matching allows each photoacid molecule to undergo repeated excited-state proton transfer, coupling carbamic acidforming CO2 capture to efficient release. The evolved CO2 forms self-generated bubbles without external sweep gas in the reduced-pressure continuous flow photoreactor developed in this work. Techno-economic analysis projects a minimum separation cost of $31.7 tCO2 −1 from 15% CO2 source. These results establish a practical foundation for scalable light-driven carbon capture.

Lithium bis(fluorosulfonyl)imide (LiFSI) is widely regarded as the leading salt for stabilizing lithium metal anodes, owing to the formation of an inorganic-rich solid electrolyte interphase (SEI) and enabling Coulombic efficiencies (CE) >99.5%. Here, we identify sulfur–fluoride exchange (SuFEx) click chemistry as a previously unrecognized pathway governing the stability of FSI under cycling and aging conditions. We show that O-nucleophiles abundant at the lithium surface, including Li2O and lithium alkoxides, react with FSI to produce bis(sulfonato)imide derivatives, establishing a self-driven SEI degradation pathway. Through a detailed kinetic and crystallographic study, we isolate critical SuFEx intermediates and identify their chemical fingerprints in SEI layers. We demonstrate that methoxide-substituted FSI anions are particularly detrimental: being soluble and reduced at potentials less cathodic than FSI, they alter the SEI formation mechanism and decrease CE. These findings reframe electrolyte design strategies and suggest that suppressing SuFEx reactivity is essential for achieving sustained CE >99.9%.

Lithium bis(fluorosulfonyl)imide (LiFSI) is widely regarded as the leading salt for stabilizing lithium metal anodes, owing to the formation of an inorganic-rich solid electrolyte interphase (SEI) and enabling Coulombic efficiencies (CE) >99.5%. Here, we identify sulfur–fluoride exchange (SuFEx) click chemistry as a previously unrecognized pathway governing the stability of FSI under cycling and aging conditions. We show that O-nucleophiles abundant at the lithium surface, including Li2O and lithium alkoxides, react with FSI to produce bis(sulfonato)imide derivatives, establishing a self-driven SEI degradation pathway. Through a detailed kinetic and crystallographic study, we isolate critical SuFEx intermediates and identify their chemical fingerprints in SEI layers. We demonstrate that methoxide-substituted FSI anions are particularly detrimental: being soluble and reduced at potentials less cathodic than FSI, they alter the SEI formation mechanism and decrease CE. These findings reframe electrolyte design strategies and suggest that suppressing SuFEx reactivity is essential for achieving sustained CE >99.9%.

CO 2 capture and release via a light-driven pH swing offers a promising route to carbon management by harnessing sunlight and reducing reliance on external energy inputs. Recent studies have explored diverse photoactive compounds, yet the engineering of light-driven CO 2 separation systems remains underexplored. We introduce a microfluidic slug flow reactor that couples efficient light delivery with molecular p K a alignment to drive separation. A synthesized polymeric photoacid with a high ground-state p K a (∼10) remains protonated in the dark during CO 2 absorption and deprotonates under illumination to drive CO 2 release. Since higher loadings attenuate light and confine activation near the surface, we tuned illumination depth and reactor geometry to maintain uniform activation and sustained operation, with stable performance over 125 h, releasing 34 mmol of CO 2 captured from a 5% CO 2 /3% O 2 feed while minimizing photothermal effects. Overall, this architecture provides a versatile platform for coupling with future advanced photoactive chemistries.