Insight into the integration way of ceramic solid-state electrolyte fillers in the composite electrolyte for high performance solid-state lithium metal battery

Reasonably combining ceramic solid-state electrolytes (SSEs) and polymer-based SSEs to create versatile composite SSEs has provided new enlightenment for the development of solid-state lithium metal batteries (SSLMBs). Here, different integration ways of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) with an electrospinned 3D polyacrylonitrile (PAN) nanofiber and a polymer electrolyte formed by in-situ polymerization reaction were investigated. Firstly blending LLZTO ceramic with 3D PAN nanofiber followed by filling with polymer electrolyte into the spaces can offer the composite SSE a higher ionic conductivity (2.06 × 10−3 S·cm−1), the highest lithium transference number (0.5), and the highest mechanical strength (2.85 MPa). It can operate in Li symmetric cells over 1000 h with the potential of 0.07 V under a current density of 0.2 mA·cm−2, and make Li-LiFePO4 solid-state batteries (SSBs) excellent cycling performance (86.3% retention after 500 cycles at 0.5 C). It also delivers excellent electrochemical performances in 4.3 V or 4.5 V high voltage SSBs. In contrast, when LLZTO is absent or added through simple mixing without integration into PAN network, the electrochemical performances of SSEs and SSLMBs are inferior. Mechanism study suggests that the direct contact of LLZTO and succinonitrile (SN) will initiate the decomposition of SN, leading to the formation of a C=N-C barrier layer and further degradation of electrochemical performance.