Coating effect of LiFePO₄ and Al₂O₃ on Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode surface for lithium ion batteries

Lithium-manganese-rich cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ is prepared by combustion method, and then coated with nano-sized LiFePO₄ and nano-sized Al₂O₃ particles via a wet chemical process. The as-prepared Li_1.2Mn_0.54Ni_0.13Co_0.13O₂, LiFePO₄-coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ and Al₂O₃-coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The scanning electron microscopy shows the agglomeration of the materials and their nanoparticle size ∼100 nm. The transmission electron microscopy confirms that LiFePO₄ forms a rough mat-like surface and Al₂O₃ remain as islandic particles on the surface of the Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ material. The Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ coated with LiFePO₄ and Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ coated with Al₂O₃ exhibits improved electrochemical performance. The initial discharge capacity is enhanced to 267 mAhg⁻¹ after the LiFePO₄ coating and 285 mAhg⁻¹ after the Al₂O₃ coating compared to the as-prepared Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ material that has an initial discharge capacity of 243 mAhg⁻¹. Galvanostatic charge–discharge tests at C/10 display longer activation of Li₂MnO₃ phase and higher capacity retention of 88% after 20 cycles for Li_1.2Mn_0.54Ni_0.13Co_0.13O₂-LiFePO₄ compared to Li_1.2Mn_0.54Ni_0.13Co_0.13O₂-Al₂O₃ of 80% after 20 cycles and LMNC of 80% after 20 cycles. Meanwhile Li_1.2Mn_0.54Ni_0.13Co_0.13O₂-LiFePO₄ also shows higher rate capability compared to Li_1.2Mn_0.54Ni_0.13Co_0.13O₂-Al₂O₃.