LiNi0.6Co0.2Mn0.2O2 Cathodes Coated with Dual-Conductive Polymers for High-Rate and Long-Life Solid-State Lithium Batteries

High-energy density and safe solid lithium batteries call for cathodes with high capacity and good kinetic properties. In this work, LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathodes are coated with the ionic-electronic dual-conductive polymers composed of poly(ethylene glycol) (PEG)-doped polyaniline (PANI). Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, and thermogravimetric analysis reveal that the dual-conductive polymers are homogeneously coated on the surfaces of NCM622 cathodes with a thickness of approximately 10 nm. The solid-state lithium batteries consisting of the NCM622 cathodes coated with PANI-PEG show a specific capacity of 158 mA h g^-1 and a retention rate of 88% after 100 cycles at the rate of 0.1 C and room temperature, which are superior to the discharge capacity of 153 mA h g^-1 and capacity retention of 59% after 100 cycles for the batteries with the pristine NCM622 cathodes. Moreover, the cells with the coated cathodes display a better rate performance of 84 mA h g^-1 at 1 C than those with the uncoated ones which show a rate performance of 11 mA h g^-1 at 1 C.