Perovskite-Type Oxide Coated-liMn₂O₄ Cathode Material For Li-Ion Batteries

Nowadays, environmental and energy problems have become increasingly serious, a new green energy, lithium-ion battery, has developed rapidly. In lithium-ion battery cathode materials, spinel LiMn₂O₄ is a promising cathode material because of its abundant in natural resources, excellent voltage profile characteristics, high safety and non-toxicity. However, its cycle performance and rate capability are still not ideal and remain to be further improved, which have limited its actual use in applications, especially in electric and hybrid electric vehicles.In our paper, spinel LiMn₂O₄ is prepared by high temperature solid-state reaction method. The sintering time and temperature are studied, and it finds that the sample calcined at 830 ? for 10 h shows the better crystallinity, which can deliver initial discharge capacity of 126 m Ah·g-1 at 0.05 C with coulombic efficiency of82.4%. The discharge capacity at 0.1 C is 120 mAh·g-1, with 70.5% of discharge capacity left after 100 cycles. The rate capability test demonstrates that discharge capacity is 111 mAh·g-1 cycled at 1 C again after 20 C with the capacity coverage of97.4%.La_0.7Sr_0.3Mn_0.7Co_0.3O₃ coated spinel LiMn₂O₄ is successfully prepared by a simple sol-gel method in this paper. The 3 wt.% La_0.7Sr_0.3Mn_0.7Co_0.3O₃ coated LiMn₂O₄ presents the best electrochemical performance. It can deliver 101 mAh·g-1at 1 C/10 C even after 100 cycles with a capacity retention of 93.5%. The rate capability of 3 wt.% La_0.7Sr_0.3Mn_0.7Co_0.3O₃ coated LiMn₂O₄ is also obviously enhanced, especially at high rates?10 C, 20 C and 30 C?. It can deliver 74.3 mAh·g-1at 30 C which is much higher than that of the bare sample?47.2 mAh·g-1?. XRD and XPS measurements show the formation of the La_0.7Sr_0.3Mn_0.7Co_0.3O₃, and it has no influence on the crystal structure of the pristine LiMn₂O₄. TEM tests show that La_0.7Sr_0.3Mn_0.7Co_0.3O₃ coating layer with good crystallinity can cover the surface of LiMn₂O₄ after cycling, which successfully protect bulk LiMn₂O₄ from electrolyte attack. EIS and CV tests demonstrate that the coating layer can improve the kinetics of LiMn₂O₄ electrodes.LaMnO3 coated LiMn₂O₄, La_0.7Sr_0.3MnO₃ coated LiMn₂O₄ and LaMn0.7Co0.3O3 coated LiMn₂O₄ are also prepared. At 0.5 C/0.5 C, the initial discharge capacity of uncoated LiMn₂O₄ and LaMnO3 coated LiMn₂O₄ are 106 mAh·g-1and 114 mAh·g-1,with the first coulombic efficiency of 89.1% and 95.0%. At 10 C/10 C,uncoated LiMn₂O₄, La MnO3 coated LiMn₂O₄, La_0.7Sr_0.3MnO₃ coated LiMn₂O₄ and LaMn0.7Co0.3O3 coated LiMn₂O₄ respectively exhibit discharge capacities of 53.6m Ah·g-1, 90.6 mAh·g-1, 93.0 mAh·g-1and 95.6 mAh·g-1 in sequence, which demonstrates perovskite-type oxide coating can improve the electrochemical performance of LiMn₂O₄ to varying degrees.