SiO2-coated LiNi0.915Co0.075Al0.01O2 cathode material for rechargeable Li-ion batteries.

We reported a one-step dry coating of amorphous SiO2 on spherical Ni-rich layered LiNi0.915Co0.075Al0.01O2 (NCA) cathode materials. Combined characterization of XRD, EDS mapping, and TEM indicates that a SiO2 layer with an average thickness of ∼50 nm was uniformly coated on the surface of NCA microspheres, without inducing any change of the phase structure and morphology. Electrochemical tests show that the 0.2 wt% SiO2-coated NCA material exhibits enhanced cyclability and rate properties, combining with better thermal stability compared with those of pristine NCA. For example, 0.2 wt% SiO2-coated NCA delivers a high specific capacity of 181.3 mA h g-1 with a capacity retention of 90.7% after 50 cycles at 1 C rate and 25 °C. Moreover, the capacity retention of this composite at 60 °C is 12.5% higher than that of pristine NCA at 1 C rate after 50 cycles. The effects of SiO2 coating on the electrochemical performance of NCA are investigated by EIS, CV, and DSC tests, the improved performance is attributed to the surface coating layer of amorphous SiO2, which effectively suppresses side reactions between NCA and electrolytes, decreases the SEI layer resistance, and retards the growth of charge-transfer resistance, thus enhancing structural and cycling stability of NCA.