Elucidating Reversible Electrochemical Redox of Li₆PS₅Cl Solid Electrolyte

Abstract

Sulfide-based solid electrolytes are promising candidates for all solid-state batteries (ASSBs) due to their high ionic conductivity and ease of processability. However, their narrow electrochemical stability window causes undesirable electrolyte decomposition. Existing literature on Li-ion ASSBs report an irreversible nature of such decompositions, while Li–S ASSBs show evidence of some reversibility. Here, we explain these observations by investigating the redox mechanism of argyrodite Li6PS5Cl at various chemical potentials. We found that Li–In | Li6PS5Cl | Li6PS5Cl–C half-cells can be cycled reversibly, delivering capacities of 965 mAh g–1 for the electrolyte itself. During charging, Li6PS5Cl forms oxidized products of sulfur (S) and phosphorus pentasulfide (P2S5), while during discharge, these products are first reduced to a Li3PS4 intermediate before forming lithium sulfide (Li2S) and lithium phosphide (Li3P). Finally, we quantified the relative contributions of the products toward cell impedance and proposed a strategy to reduce electrolyte decomposition and increase cell Coulombic efficiency.

Stack Pressure Considerations for Room‐Temperature All‐Solid‐State Lithium Metal Batteries

“…The low 1 st cycle Coulombic efficiency is attributed to initial electrolyte decomposition at the cathode. [26][27][28] Subsequent cycles present an average Coulombic efficiency over 99% and the cell does not exhibit any shorting behavior. In contrast, the cell using Li metal anode exhibits significant voltage drop during its 1 st charge cycle.…”

Toward Higher Voltage Solid‐State Batteries by Metastability and Kinetic Stability Design

“…Such lattice vector compression results in peak shifting caused by the externally applied uniaxial pressure and/or uniform (de)lithiation. Thus, the presence of strain broadening suggests that in addition to the expected peak shifting, due to (de)lithiation and uniaxial compression at certain experimental conditions, [ 12,14,24 ] there also exists sources of localized strains that distort particular unit cells away from normal position. The experimental step of discharging the high voltage scanned LGPS back to 2.5 V before taking SXRD was designed to maintain a constant Li composition in LGPS, so the effect of Li composition induced lattice parameter change and Bragg peak shift can be minimized, while the irreversible strain effect induced at high voltage can be most clearly observed.…”

“…Attempts to explain this have focused on interface contact or cathode coating, [ 9 ] electronic insulation, [ 10,11 ] and lithiation/delithiation of electrolyte. [ 12–14 ] However, it still lacks a quantitative explanation of the disparate results found in literatures in this field.…”

“…The results show direct evidences of LGPS straining during these electrochemical processes. In addition to LGPS straining due to (de)lithiation, which shifts XRD peaks, [ 12,14,24 ] strain broadening suggests the existence of small localized domains of highly strained regions. These small strained pockets inside LGPS particles are evidences of decomposed inclusions within the solid‐electrolyte, for the first time providing direct experimental evidences to prior predictions of nucleated decay morphologies.…”

4 V room-temperature all-solid-state sodium battery enabled by a passivating cathode/hydroborate solid electrolyte interface

“…Also, anodic currents during the next forward voltage scan remain low up to the upper cutoff voltage of the previous step. This demonstrates (i) that the electrochemical decomposition products of both [B 12 H 12 ] 2À and [CB 11 H 12 ] À ions are not redox active within the operating voltage range, in contrast to the redox activity of decomposed species in sulfide SEs, 24,55 and (ii) that the decomposition products prevent further oxidation of the electrolyte.…”