Enhancing the Electrochemical Performances of Disordered Li_1.23Ni_0.3Nb_0.3Fe_0.16O_0.85F_0.15 Cathode Material for Lithium-Ion Batteries by LiNbO_x Coating

For the next generation of lithium-ion batteries (LIBs), it is primary to seek high capacity and long-lifetime electrode materials. Li-excess disordered rock-salt structure (DRS) cathodes have gained much attention due to their high specific capacity. However, Li-excess can lead to a decrease in the structural stability of an electrode material. A new Li-rich DRS oxyfluorides, Li_1.23Ni_0.3Nb_0.3Fe_0.16O_0.85F_0.15 (F_0.15) with a series amounts of LiNbO_x (LN) coating (0, 5, 10, and 15 wt % denoted as F_0.15-LN₀, F_0.15-LN₅, F_0.15-LN₁₀, and F_0.15-LN₁₅, respectively), are successfully synthesized and evaluated as cathode materials in LIBs. Among them, F_0.15-LN₁₀ exhibits the highest initial discharge specific capacity of 296.1 mAh g^-1 (at a current density of 20 mA g^-1) with the capacity retention rate of 14% higher than that of the uncoated F_0.15 after 80 cycles. Even at 300 mA g^-1, F_0.15-LN₁₀ still delivers the highest discharge specific capacity of 130 mAh g^-1. After 20 cycles, the charge-transfer impedance of F_0.15-LN₁₀ remained the smallest. The characterizations indicate that LN coating reduces the surface polarization of the cathode materials, slows the interfacial side reactions between the electrolyte and the electrode, and speeds up the Li⁺ diffusion. These results demonstrate that LN coating is an effective strategy to improve the electrochemical performance.