Improving the Electrochemical Performance of a Solid-State Battery with a LiFePO₄–Garnet-Based Composite Cathode

A solid-state electrolyte (SSE) is a core component of an all-solid-state battery with high safety and energy density. Among the various types of SSEs, garnet-type Li7La3Zr2O12 SSEs have an exceptionally high ionic conductivity (10–3 to 10–4 S/cm) and good chemical stability against Li metal, making them an excellent choice for solid-state Li-metal batteries. The main challenge impeding the development of solid-state batteries is the high interfacial resistance caused by poor solid–solid contact between the SSE and electrodes. When a solid electrolyte Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is used to coat LiFePO4, the interfacial impedance between the cathode material and the solid electrolyte is effectively reduced, ionic conductivity is increased, and interface stability is improved. The electrochemical test results show that when compared to that of unmodified materials, the performance of the modified materials is significantly improved. The initial specific discharge capacity of the modified materials reaches 147.6 mA h/g, and an excellent cycling performance with 82.5% capacity retention after 250 cycles at 0.5 C is observed, indicating that the modified materials, in particular, have better high-temperature performance. This is primarily due to the LLZTO-based solid electrolyte-modified cathode materials, which improve interface compatibility, accelerate Li-ion transmission, and reduce the interface side reaction.