Understanding Decomposition of Electrolytes in All-Solid-State Lithium–Sulfur Batteries

Abstract

The decomposition behavior of electrolytes affects the cycle stability and electrochemical redox activity in all-solid-state lithium−sulfur batteries (ASSLSBs). However, there is a sparse understanding of the electrochemistry of ASSLSBs involving the oxidative decomposition of sulfide solid electrolytes (SEs) due to the lack of fundamental studies. Herein, we unveil the redox chemistry related to Li 2 S/S conversion reaction, electrolyte decomposition, and redox reaction of the decomposition product, based on differential capacity curves. The oxidation reaction of Li 2 S proceeds simultaneously with a continuous oxidative decomposition of sulfide SEs. Raman spectroscopy of the cell after cycling shows that SEs in the cathode convert the thiophosphates with a S−S thiol bond via the decomposition behavior of the electrolytes. The implication of this reaction chemistry is expanded toward understanding the Li 2 S activation process in ASSLSBs. Additionally, we demonstrate that Li 2 S/SE interface modification by different rotation speeds of ball milling in SE mixing allows us to control the decomposition kinetics of electrolytes. The severe decomposition of electrolytes causes cycle fading instead of increasing the electrochemical redox activity in the early period. The findings of this work highlight the need for interface engineering to avoid severe degradation of electrolytes in the cathode and enhance the ability of SEs as a redox mediator.

Mechanism Exploration of Li2S–Li2O–LiI Positive Electrodes with High Capacity and Long Cycle Life via TEM Observation

“…Even so, few Li 2 S-based active materials in all-solid-state Li/S batteries have achieved both a high capacity and long cycle life. There are still two main reasons that Li 2 S cannot maintain high charge–discharge capacity in long-term cycling: (1) degradation of SEs at the interface between SEs and conductive carbons , and (2) inactivation due to Li 2 S grain enlargement . Narrow electrochemical windows of sulfide SEs cause the former.…”

Y2S3-Doped Li2S Active Cathode Materials for All-Solid-State Li–S Batteries

“…HCDF images and ED intensity profiles of the 99Li 2 S·1Y 2 S 3 cathode composite before and after the charge–discharge reaction were also identical to those of 99Li 2 S·1Y 2 S 3 active cathode material (Figure S6). Although Li 3 PS 4 can act as a redox mediator with reactions of Li 3 PS 4 itself and accelerate the redox reaction of the Li 2 S cathode in all-solid-state Li–S batteries, P-doped LiYS 2 has the catalyst effects without reactions.…”

“…27 Meanwhile, the reduction peak at 1.2 V and oxidation peak at 1.8 V result from the redox activity of the Li 2 S active cathode material. 27 Their intensities also increase after each cycle, indicating that the Li 2 S active cathode material is activated. The relative intensity of the peak at 1.2 V with respect to the peak at 1.3 V obtained for the 99Li 2 S•1Y 2 S 3 material is larger than that of Li 2 S, indicating that Y 2 S 3 doping promotes the redox reaction of the Li 2 S active cathode material, although it also promotes the reaction of the degradation product of the Li 5.5 PS 4.5 Cl 1.5 solid electrolyte.…”

“…The reduction peak at 1.3 V and oxidation peak at 1.8 V generated by the redox activity of the Li 5.5 PS 4.5 Cl 1.5 solid electrolyte degradation product increases after each cycle owing to the contribution of the degradation product. 27 Meanwhile, the reduction peak at 1.2 V and oxidation peak at 1.8 V result from the redox activity of the Li 2 S active cathode material. 27 Their intensities also increase after each cycle, indicating that the Li 2 S active cathode material is activated.…”

Li10GeP2S12 solid electrolytes synthesised via liquid-phase methods

“…20 À , which is similar to the previous report. 23 The use of EtOH with high polarity allows the stabilization of polysulfides, particularly S 3 À radical anions, which enhances the reaction kinetics and solubility in the Li 10 GeP 2 S 12 precursor solution. 23 EtOH, because no Li 3 PO 4 peaks were observed for the liquid shaking with THF solvent (Fig.…”