Differentiating chemical and electrochemical degradation of lithium germanium thiophosphate and the role of atomic layer deposited protection layers

Abstract

Li10GeP2S12 (LGPS) is a superionic conductor that has an ionic conductivity equivalent to conventional liquid electrolytes (~10-2 S cm-1) and thus shows exceptional potential to fulfill the promise of solid-state...

Suppression of Electrochemical and Chemical Degradation of Li10GeP2S12 by an Elastomeric Artificial Solid Electrolyte Interphase

“…We repeated the same lithiation process sequence in the LGPS system as a control for the systems with elastomeric ASEI (Figure S11). Similar to the previous literature, , excess Li atoms break PS 4 3– and GeS 4 4– bonds to form Li–S, Li–P, and Li–Ge, leading to decomposition of solid electrolytes. These results further support our experimental post-cycling XPS results, which showed that LPE is remarkably capable of preventing interface degradation reactions at the LGPS/Li interface.…”

“…We repeated the same lithiation process sequence in the LGPS system as a control for the systems with elastomeric ASEI (Figure S11). Similar to the previous literature, 26,60 excess Li atoms break PS 4 3− and GeS 4…”

“…19−25 Other efforts have focused on application of an ionically conductive, but an electrically insulating, artificial solid electrolyte interphase (ASEI) protection layer between the electrodes and the LGPS. 26 LGPS that has shown some effect of improvement. 28 The ASEI must block direct contact between LGPS and Li metal to suppress the spontaneous interfacial reactions but also needs to effectively bridge electrochemical stability gap between Li and…”

“…In 2011, Kamaya et al first identified the sulfide superionic conductor Li 10 GeP 2 S 12 (LGPS) with a theoretical ionic conductivity of 1.2 × 10 –2 S cm –1 , comparable or even higher than conventional carbonate liquid electrolytes. , However, while LGPS is superior in terms of ionic conductivity, it also has a very narrow thermodynamic electrochemical stability window from 1.7 to 2.5 V (vs Li + /Li) . Due to this narrow electrochemical stability window, LGPS will readily react with both Li metal anodes and nearly all Li-ion cathodes (Li 2 CoO 3 , LiNi x Mn y Co z O 2 , and LiNi x Al y Co z O 2 ) electrochemically and chemically. − Most of these degradation reaction products are mixed ionic and electronic conductors (MIEC), which form non-self-limiting interfaces that do not mitigate the interfacial degradation reactions. ,, Significant efforts to resolve this interfacial incompatibility issue to enhance the electrochemical stability of LGPS include substitution of Ge with Sn and halogenation of the constituent LPS electrolyte to further increase the ionic conductivity. − Other efforts have focused on application of an ionically conductive, but an electrically insulating, artificial solid electrolyte interphase (ASEI) protection layer between the electrodes and the LGPS. − Li et al have demonstrated that a dual layer initiated by LiDFOB and LiPO 2 F 2 can effectively elongate the cycle life of LGPS cells . Wang et al have shown the successful application of the LiNb 0.5 Ta 0.5 O 3 interlayer to enhance the performance of LGPS in full-cell batteries.…”

“…34−40 While most of battery studies have extensively and almost exclusively focused on the electrochemical degradation of the cells during cycling, another important set of reactions, the spontaneous chemical reactions at the electrode/electrolyte interfaces have received little attention. 26,28 However, these chemical degra-dation reactions are of critical importance, because as long as the components of the cells are in physical contact with each other, the reactions would continue to happen. Therefore, we named this set of degradation reactions as chemical aging or aging, as it is dependent on the duration of physical contact.…”