Abstract: A doping-coating surface modification method was used to improve the cycle performance of the lithium-ion battery cathode material spinel LiMn₂O₄. Al was chosen as the doping element and Al(NO₃)₃ as the raw material. We investigated Al³⁺ doping of 7.1%(atomic fraction) at the temperatures of 300, 400, 500, 600, 700, 750, and 800 °C. It was found that at increasing temperatures, the maximum specific capacity of the modified samples first increased and then decreased, with a maximum at 700 °C. The fading rate increased initially with temperature as well, and then decreased, followed by a small rise with temperature. This is because the coated layer gradually reacted with the LiMn₂O₄ granule at elevated temperatures and became a completely solid solution layer by 750 °C. The fading rate reached the minimum at the same time. Subsequently, the solid solution layer diffused into the LiMn₂O₄ granule, weakening the granule protection so that the fading rate slightly increased. Among these samples, the maximum specific capacity (133.6 mAh·g^-1) was for the sample treated at 700 °C for 5 h, and the fading rate was 3.4% after 50 cycles. It is shown that doping-coating surface modification with Al³⁺ may enable the commercial application of spinel LiMn₂O₄ cathode material for lithium-ion batteries.

Key words: Lithium-ion battery, Cathode material, Spinel LiMn₂O₄, Doping-coating surface modification, Solid solution