| Summary: | Solid polymer electrolytes (SPEs) are seen as the key component in the development of solid-state lithium batteries (SSLBs) by virtue of their good processability and flexibility. However, poor mechanical strength, low room-temperature lithium-ion (Li-ion) conductivity and unsatisfactory interfacial compatibility with electrodes limit their practical application. In this work, a composite electrolyte consisting of polyvinylidene fluoride and polyvinylidene carbonate with a Li<sub>6.4</sub>La<sub>3</sub>Zr<sub>1.4</sub>Ta<sub>0.6</sub>O<sub>12</sub>(LLZTO) active filler (PFPC: LLZTO-SPE) is reported to achieve excellent ionic conductivity (4.25 × 10<sup>−4</sup> S cm<sup>−1</sup> at 30 °C), a wide electrochemical window (>4.6 V), a high Li-ion transference number (<i>t<sub>Li<sup>+</sup></sub></i> = 0.49) and good interfacial compatibility with the electrode. Incorporating LLZTO as an active filler not only increases the ionic conductivity of the electrolyte, but also homogenizes Li-ion flux and stabilizes the electrode/electrolyte interface, thereby preventing lithium dendrites from piercing the electrolyte. As a result, Li/Li symmetrical cells using PFPC: LLZTO-SPEs deliver more than 800 h of cyclability at 0.1 mA cm<sup>−2</sup> and a high critical current density (CCD) of 2.6 mA cm<sup>−2</sup>. The assembled Li/PFPC: LLZTO/LFP SSLBs achieve 87% capacity retention after 150 cycles at 0.2 C and 89% capacity retention for 100 cycles at 0.5 C. This work inspires new insights into designing high-performance SPEs.
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