High-voltage and free-standing poly(propylene carbonate)/Li_6.75La₃Zr_1.75Ta_0.25O₁₂ composite solid electrolyte for wide temperature range and flexible solid lithium ion battery

Solid electrolyte is regarded as a perfect way to enhance safety issues and boost energy density of lithium batteries. Herein, we developed a type of free-standing poly(propylene carbonate)/Li_6.75La₃Zr_1.75Ta_0.25O₁₂ composite solid electrolyte for ambient temperature and flexible solid-state lithium batteries. The composite solid electrolyte exhibited excellent comprehensive performance in terms of high ionic conductivity (5.2 × 10⁻⁴ S cm⁻¹) at 20 °C, a wide electrochemical window (4.6 V), high ionic transference number (0.75) and satisfactory mechanical strength (6.8 MPa). When evaluated as solid electrolyte for an ambient-temperature solid lithium battery, such a composite electrolyte delivered excellent rate capability (5C) at 20 °C. This superior performance can be comparable to a liquid electrolyte-soaked PP separator-based lithium battery at room temperature. To our knowledge, this is the best rate capability of a solid composite electrolyte for a solid lithium battery at ambient temperature. Moreover, such a composite electrolyte-based flexible LiFePO₄/Li₄Ti₅O₁₂ lithium ion battery delivered excellent rate capability and superior cycling stability. All these fascinating features make poly(propylene carbonate)/Li_6.75La₃Zr_1.75Ta_0.25O₁₂ a very promising all-solid-state electrolyte for flexible solid lithium batteries. Our study makes a big step into addressing the challenges of ambient-temperature solid lithium batteries.