A nano-LiNbO₃ coating layer and diffusion-induced surface control towards high-performance 5 v spinel cathodes for rechargeable batteries

The surface of a spinel LiNi_0.5Mn_1.5O₄ cathode was modified with a nano-LiNbO₃ coating layer by employing a Nb citrate-coated Ni_0.25Mn_0.75(OH)₂ precursor and subsequent single calcination with LiOH at 900 °C. The facile formation of the LiNbO₃ coating layer in the earlier stage of the calcination process in the presence of abundant LiOH resulted in successful modification of the parent material with a thin and homogeneous coating layer. More importantly, the partial diffusion and subsequent substitution of Nb ions into the parent material beneath the coating layer resulted in a Mn³⁺-rich domain near the surface of the parent material, LiNi_0.5Mn_1.5O₄. This Mn³⁺-rich region effectively improved the kinetic properties of Li⁺ diffusion near the surface of the cathode, especially during fast discharging, and the LiNbO₃-coated spinel oxide cathode with a high loading level of around 10 mg cm^-2 exhibited a discharge capacity of 100 mA h g^-1 even at 10C at ambient temperature. In addition, it showed 90% capacity retention after 100 cycles at 60 °C owing to the LiNbO₃ coating layer acting as a protective layer.