Surface modification with oxygen vacancy in LiNi0.5Co0.2Mn0.3O2 for lithium-ion batteries

Highlights: • Graphene-Oxide(GO) modified NCM with oxygen vacancy layer is formed. • Modification mechanism in sintering process is keenly studied by Raman spectra. • GO-modified NCM exhibits enhanced electrochemical performances at high rates. • Li-ion diffusion coefficient in the charging/discharging process is tested by GITT. • Theory of phase transformation is further expounded via XRD and HRTEM. -- Abstract: The well-distributed smaller sized Graphene-Oxide-treated LiNi_0.5Co_0.2Mn_0.3O₂ (GO-treated NCM) layered cathodes are successfully synthesized by hydrothermal method, which has truncated octahedral shape with evenly oxygen vacancy layer on the surface. With temperature ascends progressively, the cathode molding and the modification mechanism of Graphene-Oxide (GO) in the calcination process are keenly studied by Raman spectra. In addition, the synergistic effect of oxygen vacancy and cathode electrolyte interphase (CEI) layer at outer surface accelerates lithium diffusion coefficient during cycling. Especially, GO-treated NCM exhibits the optimal capacity retention as high as 78.8% after 150 cycles at 15 C, compared with NCM whose is only 38.4%. Even at full cell state, GO-treated NCM has better rate performance and displays excellent energy density as high as 310.5 Wh kg⁻¹ after 200 cycles at 1 C (1 C = 160 mAh g⁻¹). Ultimately, the theory of phase transformation of cycled cathodes is expounded in detail in combination with high resolution transmission electron microscopy (HRTEM) and the variation of X-ray diffraction (XRD) peaks positions.