Improved electrochemical performance of LiMn_1.5Ni_0.5O₄ electrode modified by AlPO₄ for lithium-ion batteries

LiMn_1.5Ni_0.5O₄ materials modified by AlPO₄ are prepared by a sol-gel method with citric acid to improve their electrochemical performance. The physical and electrochemical properties of the samples are characterized by various analytical techniques. The coated AlPO₄ layer completely covers the surfaces of the LiMn_1.5Ni_0.5O₄ particles and the thickness of the coated layer is ∼15 nm. Moreover, the surface and charge-transfer resistances of the modified electrode are much lower than those of the pristine sample, and the lithium diffusion rate of the modified electrode was also significantly enhanced. As a result, the modified materials demonstrate improved electrochemical properties, even under elevated temperature conditions. This improvement is attributed to minimization of the side-reactions between the cathode and electrolyte by the AlPO4 protecting layer, the suppression of the formation of an undesirable SEI layer, and the partial absorption of the stress caused by the volume change during cycling. Therefore, surface modification by AlPO4 is an effective way to improve the performance of LiMn_1.5Ni_0.5O₄ cathode materials for lithium-ion batteries.