Constructing highly functional oxygen defect Li7La3Zr2O12-polyacrylonitrile composite electrolytes for all-solid state lithium-ion batteries

Abstract

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) has excellent thermal stability, high ionic conductivity, and high Young's modulus, which can inhibit dendritic growth. However, the bottleneck of improving battery performance lies in the limitation of high electrolyte–electrode interface resistance. Constructing an interface between inorganic solid electrolyte fillers and polymer electrolyte matrices is an effective method to reduce interfacial impedance. In this work, oxygen deficient Li₇La₃Zr₂O₁₂-PAN solid composite electrolytes were synthesized. Oxygen-deficient LLZO-2, produced via 2 h of hydrogen treatment, when combined with polyacrylonitrile (PAN), forms a solid composite electrolyte, achieving an excellent ionic conductivity of 1.11 × 10⁻⁴ S cm⁻¹ at 25 °C and a broad electrochemical stability window of 4.29 V (vs. Li⁺/Li). The LLZO-2-PAN composite electrolyte exhibits good interfacial stability and an overvoltage of ±600 mV at a high current density of 0.3 mA cm⁻². Li|LLZO-2-PAN|LiFePO₄ cells demonstrate outstanding electrochemical performance, with an initial discharge capacity of 256.2 mA h g⁻¹ at 0.1C. After 90 cycles, the discharge capacity remains at 228 mA h g⁻¹, with a capacity retention rate of 90.0%. The oxygen vacancies in the material are adjusted by the duration of the hydrogen treatment, which significantly influences ionic conductivity and interfacial stability.