Deconvolved First Cycle Capacity Loss Mechanisms in All-Solid-State Batteries

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Deconvolved First Cycle Capacity Loss Mechanisms in All-Solid-State Batteries All-solid-state batteries (SSBs) fail to compete with their traditional lithium-ion battery (LIB) counterparts due to severe capacity loss in their first cycle. While the key contributors to capacity loss have been identified, it remains unknown the relative contribution of each loss mechanism due to solid electrolyte (SE) redox and worsening kinetics which obscure the measure of capacity. For the chemically abundant sulfur-based composite electrodes in particular, these parallel processes present a formidable challenge to addressing first cycle Coulombic inefficiency.1 Using near-equilibrium electrochemical and X-ray techniques, we demonstrate a full accounting of the sources of capacity loss within our argyrodite SE (Li5PS6Cl) | uncoated Li(Ni0.5Mn0.3Co0.2)O2 (NMC) | carbon composite cathode. By modifying the components of the composite electrode, we differentiate between electrolyte redox at the electronic conductor (current collector + carbon)|SE and NMC|SE interfaces. Using these cell formats we investigate the persistence of electronic conductor interfacial redox across many cycles, as well as the impact of self-discharge on long-term cycling behavior. By modifying the cycling window, we also investigate sluggish discharge kinetics of cathode and oxidation reversibility. Using operando XRD, we compare LIBs and SSBs to track cathode redox throughout cycling, enabling us to differentiate and quantify sources of capacity loss. These findings highlight the need to address overlooked sources of resistance and active material loss in SSBs which are not mitigated by cathode coating solutions.[1] Janek, J., Zeier, W.G. Challenges in speeding up solid-state battery development. Nat Energy 8, 230–240 (2023).