Composite Solid Electrolyte for High Voltage Solid‐State Li‐Metal Battery

Abstract A composite solid electrolyte (CSE) was prepared by incorporating Li 7 La 3 Zr 2 O 12 (LLZO) particles, lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), and different concentrations of a solid plasticizer in a poly(vinylidene fluoride hexafluoropropylene) (PVDF‐HFP) matrix. Subsequently, we investigated the ionic conductivity and electrochemical stability of the CSE, and its interfacial compatibility with a Li‐metal electrode. 30 wt.% plasticizer with CSE exhibits a high ionic conductivity of 4.23×10 −4 and 8.14×10 −4 S cm −1 at 25 and 60 °C, respectively, with an excellent stability of up to 4.76 V vs . Li/Li + . The CSE is sandwiched between the Li‐metal and NCM811 for the fabrication of a solid‐state battery (SSB), which delivers a discharge capacity (163 mAh g −1 ) at a rate of 0.2 C (60 °C). The LiNbO 3 (LNO) modification over the NCM811 cell delivers a high discharge capacity of 198 mAh g −1 , excellent rate capability, and good cycle life. Furthermore, the LNO coating on the surface of the NCM811 cathode, which effectively improves the contact between the cathode and electrolyte, eventually leads to an increase in the discharge capacity. Therefore, the prepared CSE is a good choice for use in SSB; moreover, the LNO coating noticeably improved the cycling stability, reversibility, and rate capability compared to an unmodified NCM811 cathode in the SSB configuration.