High temperature performance of surface-treated Li_1.1(Ni _0.15Co_0.1Mn_0.55) O_1.95 layered oxide

The electrochemical performance of pristine and AlF₃ -coated Li_1.1(Ni_0.15Co_0.1Mn_0.55) O _1.95 cathodes is reported for cells cycled at 25 and 55°C. In a half-cell configuration, a nanolayer coating of AlF₃ on the Li _1.1(Ni_0.15Co_0.1Mn_0.55) O _1.95 stabilizes the capacity on cycling. However, in cell tests with metallic lithium anodes, the initial coulombic efficiency decreased slightly at both 25 and 55°C for AlF₃ -coated Li_1.1(Ni _0.15Co_0.1Mn_0.55) O_1.95 in comparison to the pristine material. For cells constructed with graphite instead of lithium anodes, the capacity stability improved with cycling for the coated cathode materials. Transition-metal dissolution was more pronounced for the AlF₃ -coated sample when stored at 55°C in electrolytes. For both the pristine and AlF₃ -coated samples, there was no extra capacity loss due to the elevated temperature. Around 10% capacity gain of the cathode materials at elevated temperature is assumed to be due to improved thermodynamic activation.