Thermal stability enhancement through structure modification on micro-sized crystalline grains surface of lithium-rich layered oxides.

Lithium-rich layered oxides have been considered as the most promising candidate for offering the high specific capacity and energy density for lithium-ion batteries. However, the practical applications are still suffered by the cycle instability and also closely related thermal stability. Here, micro-sized crystalline grains with good dispersion of lithium-rich layered oxides are prepared by molten-salt method, while a spinel structure are also introduced on grains surface by following chemical oxidation and annealing process, and their thermal performance with different cut-off voltages during charge process are systematically studied using differential scanning calorimetry method. Results have shown that thermal stability of micro-sized crystalline grains are better than those of spherical secondary agglomerates, the spinel structure introduction on grain surface of micro-sized crystalline grains can contribute obviously for their thermal stability, in which the onset temperature of exothermic peak has been increased by 103 °C, and the thermal release value can be reduced as most as about 40 % when the battery was charged to 4.8 V. Furthermore, the electrochemical performance, especially cycle stability under high temperature has also been enhanced for spinel modified micro-sized crystalline grains. This work not only develops the micro-sized crystalline grains with good dispersion of lithium-rich layered oxides, confirming the advantages of these materials comparing to spherical secondary agglomerates, but also reveal the method to improve their thermal stability by grain surface structure modification, opening the way to optimize the comprehensive performance of electrode materials for batteries.