Design of synergistic-coated layer of La₂O₃/Al₂O₃ in LiNi_0.5Mn_1.5O₄ cathode for enhanced cycling stability and rate capability

LiNi_0.5Mn_1.5O₄(LNMO) material has high theoretical capacity and high operating voltage. Nonetheless, LNMO has still many problems which include oxidative decomposition of electrolyte at high voltage and dissolution of transition metals into electrolyte. In this work, oxides of both La and Al (LAO) were coated on the surface LNMO by a wet chemical method. LAO is estimated to improve cycling performance (both room and elevated temperatures) and rate capability of LNMO due to the synergistic effect of La₂O₃ and Al₂O₃. Al₂O₃ can protect LNMO from the corrosion of HF that derives from decomposition of LiPF₆, which results in mitigating the solution of Mn²⁺. Al₂O₃ can also prompt electrochemical reversibility of LNMO. La₂O₃ can enhance electrical conductivity, availing to charge transfer. Furthermore, La₂O₃ presents splendid thermal stability, which may boost the interfacial stability of LNMO. La₂O₃ can also alleviate the formation of the passive layer. The effect of coating content on performances of LNMO was also studied in detail. The capacity retention of 94.0% for the optimal coating LNMO with 4.0 wt.% (mLa₂O₃/mAl₂O₃ = 3: 1) is shown at 1 C and 25 °C after 200 cycles, and its capacity retention of 95.0% is exhibited at 1 C and 55 °C after 100 cycles. Its remarkable discharge capacities at 10, 15, and 20 C are 107.4, 94.4, and 82.7 mAh g⁻¹, respectively, and its capacity retention of 93.3% is displayed at 5 C at room temperature after 500 cycles.