Poly(Vinylidene Fluoride)-Wrapped LiFePO₄ Microspheres as Highly Stable Dual Functional Cathode for Solid-State Lithium Batteries

Solid polymer electrolytes hold great promise for achieving improved processability and safety in solid-state lithium-ion batteries (LIBs); however, several inherent challenges arise from the use of polymers. One critical issue is the ultrahigh interfacial resistance between the cathode and electrolyte, which has emerged as a main research focus in recent years. In this study, a dual functional cathode (DFC) is developed by uniformly dispersing the cathode material (LiFePO₄) into the polymer electrolyte poly(vinylidenfluorid-co-hexafluorpropylene):lithium bis(trifluoromethanesulfonyl)imide, resulting in a conformable lamella structure with embedded microspheres. Simultaneous enhancement of the interfacial contact and the ion transport efficiency is observed. Solid-state LIBs incorporating the proposed DFC demonstrate exceptional electrochemical performance at room temperature, exhibiting a high discharge capacity of 138 mAh g⁻¹ at 1 C, along with an impressive capacity retention of over 80% after 250 cycles, all while preserving the intricate spherical structure. The discharge capacity reaches 98 mAh g⁻¹ even at a high rate of 5 C. At an elevated temperature of 60 °C, a capacity retention of 80% is obtained after 500 cycles. Therefore, this work provides a simple but effective design concept for improving interfacial compatibility between the cathodes and polymer electrodes in solid-state LIBs.