Interfacial stability is regarded as one of the greatest challenges in the commercialization of Ni-rich layered cathode materials, especially at high voltage. In this study, amorphous silica modified LiNi0.6Co0.2Mn0.2O2 cathode materials (NCM622) are successfully prepared by chemical grafting method using silane coupling agent (KH550). As the cathode material for lithium ion batteries, the amorphous SiO2 modified NCM622 retains 98.96% capacity retentions over 3.0–4.3 V after 100 cycles and 91.68% over 3.0–4.6 V after 50 cycles, higher than those for the pristine NCM622, which are only 91.60 and 77.38%, respectively. Such significant improvements are mainly attributed that the uniformly amorphous SiO2 layers enhance the interfacial structure of NCM622 cathode materials. The homogenous SiO2 coating layer greatly inhibits the formation of the inactive LiF and NiF2 etc. which originate from the erosion of electrolyte to electrodes and decomposition of electrolyte at the elevated voltage. In addition, the structure degradation of NCM622 cathode materials is also effectively suppressed during cycling due to the scavenger of the HF by the amorphous SiO2. The chemical grafting method with silane coupling agent provides an optimized and effective modifying routine for high performance silica modified cathode materials, especially for the high voltage performance.