Surface Modification of the LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Material by Coating with FePO₄ with a Yolk–Shell Structure for Improved Electrochemical Performance

Coating with FePO₄ with the size of 20-30 nm on the surface of a LiNi_0.8Co_0.10Mn_0.1O₂ (NCM811) cathode produces an LFP3@NCM811 cathode via a sol-gel method, which markedly reduces secondary crystal cracking. A stable particle structure greatly improves the cycling stability of the LFP3@NCM811cathode, which retains 97% of its initial discharge capacity compared to NCM811 (78%) after 100 cycles at 2.7-4.5 V. Furthermore, it retains 86 and 63% of its initial discharge capacity after 400 cycles for LFP3@NCM811 and NCM811, respectively. The initial discharge capacity of the LFP3@NCM811 cathode is 218.8 mAh g^-1 at 0.1 C, and the discharge capacity of the LFP3@NCM811 cathode is achieved to be 151.4 mAh g^-1 at 5 C, which is 15 mAh g^-1 higher than that of the NCM811 cathode. These are due to the reduction of cation mixing for a certain amount of Fe²⁺/Fe³⁺ or PO₄^3- doped into the NCM811 surface, and the yolk-shell structure formed by coating with FePO₄ helps improve the electronic conductivity and accelerate the Li⁺ transport. The cycling stability is mainly due to the secondary cleavage inhibition, which maintains the structural integrity of the cathode particles during the long cycle process and protects the inside of the particle from harmful electrolytes.