Combined effect of high voltage and large Li-ion flux on decomposition of Li6PS5Cl

Abstract

High voltage has been considered the primary factor causing electrolyte decomposition in all-solid-state lithium batteries. However, whether high voltage is the only decisive factor in sulfide electrolyte decomposition is an open question. Herein, we redefined the decomposition conditions of sulfide electrolytes under the combined effect of high voltage (≥5 V vs. Li⁺/Li) and large Li⁺ flux by recording the decomposition process of Li₆PS₅Cl via in situ Raman spectroscopy during cyclic voltammetry measurement. The result shows that under the combined action of high voltage and large Li⁺ flux, PS₄ ^3- anions of Li₆PS₅Cl undergo much more severe deformation and decomposition than they do only at high voltage or large Li⁺ flux. At the same time, it also suggests that the much severe decomposition of Li₆PS₅Cl located near the surface of cathode particles compared to that in the bulk region of Li₆PS₅Cl may be the combined result of electrochemical/chemical reactions and high voltage/large Li⁺ flux. Furthermore, the effect of large Li⁺ flux on the irreversible decomposition of Li₆PS₅Cl supplements our understanding of the electrochemical stability of solid electrolytes. This work redefines the stability of sulfide electrolyte and gives directions to design highly stable bulk and interfacial structures of sulfide electrolytes at high voltage and high current density.

Fig. 1. The CV curves of (a) LPSCl-VGCF|LPSCl|LiIn, (b) uncoated LNMO-LPSCl-VGCF|LPSCl|LiIn, (c) LTaP@LNMO-LPSCl-VGCF|LPSCl|LiIn and (d) LCO-LPSCl-VGCF|LPSCl|LiIn cells, respectively. The battery used for measurement is newly assembled.

Fig. 2. The in situ Raman spectra of (a and b) LPSCl-VGCF|LPSCl|LiIn, (c and d) uncoated LNMO-LPSCl-VGCF|LPSCl|LiIn, (e and f) LTaP@LNMO-LPSCl-VGCF|LPSCl|LiIn, and (g and h) LCO-LPSCl-VGCF|LPSCl|LiIn cells from two-dimensional and three-dimensional views, respectively. The positions for Raman signal collection are the LPSCl-rich area far from the cathode active particle/LPSCl particle interface in the composite cathode.

Fig. 3. (a) Micrograph of the in situ Raman surface scanning mode and selected points in the LTaP@LNMO-LPSCl-VGCF|LPSCl|LiIn cell. (b and c) Distribution of the cathode and sulfide electrolyte, distinguished by observing the local content distribution of PS₄³⁻ (420 cm⁻¹) and Ni²⁺–O (490 cm⁻¹) in the composite cathode, respectively. (d) Schematic diagram of position 1 and position 2 studied in the in situ Raman experiments. (e) The in situ Raman spectra of the LTaP@LNMO-LPSCl-VGCF composite cathode at position 2 from a two-dimensional view.