Time-resolved XRD study on the thermal decomposition of Li _1-xNi_0.8Co_0.15Al_0.05O₂ cathode materials for Li-ion batteries

Time-resolved X-ray diffraction (XRD) studies were used to monitor structural changes in charged Li_1-xNi_0.8Co _0.15Al_0.05O₂ cathodes in the presence of electrolyte as a function of temperature. The electrolyte accelerated thermal decomposition of the ' charged cathode material. The presence of the electrolyte changed the paths of the structural changes and lowered the temperatures for onset of the reactions. As the degree of Li-ion deintercalation increased, the thermal decomposition took place at less elevated temperature. At low states of charge (x < 0.5) the XRD pattern of Li,_1-xNi_0.8Co _0.15Al_0.05O₂ cathode heated at 450°C is similar to NiO structure. The formation of the NiO-like rock salt structure is accompanied by the formation of Li₂CO₃. In the presence of electrolyte the solvent acts as a reducing agent and also lithium extracted from the structure reacts with the solvent resulting in the formation of Li ₂CO₃. Time-resolved XRD results for Li _1-xNi_0.8Co_0.15Al_0.05O₂ at higher states of charge (x > 0.5), when heated from 25 to 450°C, show the conversion to a disordered spinel structure from a layered structure at elevated temperature. When subsequently heated at higher temperature, the disordered spinel structure converts to NiO-like rock salt structure.