SiO₂-coated LiNi_0.915Co_0.075Al_0.01O₂ cathode material for rechargeable Li-ion batteries

We reported a one-step dry coating of amorphous SiO₂ on spherical Ni-rich layered LiNi_0.915Co_0.075Al_0.01O₂ (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.