The fillers in the Composite Solid Electrolyte (CSES) are mainly responsible for enhancing the conductivity of lithium ions, but do little to regulate the formation of the solid electrolyte interface (SEI). 
Figure 1Preparation and characterization of CSE.
Kang Feiyu, He Yanbing, Liu Ming, Shenzhen International Graduate School, Tsinghua UniversityAn interfacial reaction strategy was proposed by using a unique dielectric Nanbo3 (NNO) filler combined with a polyvinylidene fluoride (PVDF) matrix (PNo) to customize a robust fluorinated Li-Na hybrid SEI at the Li-CSES interface. li0.025na0.975NBO3 (LNo) is formed by Li+ and Na+ substitution in NNO, and the substituted Na+ is involved in the formation of SEI. Robust SEIs enriched with NAF LIF exhibit excellent conductivity and high Young's modulus for Li+ migration (801GPA), which enables long-term lithium deposition stripping cycles at the high areal capacity of solid-state lithium metal batteries. In addition, dielectric NNO can induce the formation of a high-dielectric phase of PVDF to promote the dissociation of lithium salts and produce more mobile Li+, resulting in PNNO-5 (556 10-4 s cm-1). 
Figure 2Formation mechanism of LIF NAF-SEI hybridssystem
As a result, the Li Li symmetrical battery using the PNNO electrolyte maintained a long-term cycle of more than 3 hours at a high area capacity of 2 mAh cm-600. The solid-state NCM811 LI battery can be stably cycled 2200 times at 2C and exhibits excellent performance at -20. In addition, solid-state NCM811 LI batteries also show significantly improved cell stability when paired with a high-load cathode (10 mg cm-2), showing great promise for the commercialization of solid-state lithium-metal batteries. This work provides a new design principle for the development of safe and stable solid-state lithium-metal batteries, a filler for interface engineering in a composite solid-state electrolyte. 
Figure 3Electrochemical performance of solid-state NCM Li batteries.
dielectric filler-induced hybrid interphase enabling robust solid-state li metal batteries at high areal capacity. advanced materials 2023. doi: 10.1002/adma.202311195