Operando XRD analysis of self-discharge induced by elevated temperature for sulfide-based all-solid-state Li-ion batteries

Operando XRD in elevating temperature was performed on an all-solid-state Li-ion battery consisting of LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), argyrodite-type solid electrolyte (SE), and graphite in a charged and stacking states. The XRD patterns were obtained for the positive electrode (PE), SE and negative electrode (NE) layers, respectively. Multiphase Rietveld analysis was performed on the XRD data of each layer obtained every 10 °C to evaluate the temperature dependence of the lattice parameters of NCM523 and each SE. It was found that the delithiation in NE gradually occurred from 60 °C onwards, and the LiC 6 and LiC 12 transformed into graphite, fully delithiation, at 110 °C. The SEs showed different behavior in each layer up to 110 °C, and significant a -axis expansion occurred in the order NE, the SE, and the PE layers. Above 110 °C, NCM523 showed a -axis expansion and c -axis contraction just like lithiation. The sudden expansion of the a -axis in SE is suggested to be Li insertion into SE via a redox reaction between the LiC x or lithiated SEs and the SEs. Through this mechanism, the lithiated graphite and delithiated NCM523 gradually react with SE and reaches a discharge states at 140 °C, and then can be considered to have self-discharge. • Operando XRD for each electrode layer was performed while elevating temperature. • Above 110 °C, NCM523 in charged state gradually started lithiation. • Above 60 °C, LiC 6 and LiC 12 delithiated and transformed graphite at 110 °C. • Up to 110 °C, SE showed different expansion mode in each layer. • Complete self-discharge reached at 140 °C via gradual reduction of SEs.