Improved cycling stability of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode materials by optimizing Ti doping

Nickel-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) oxide is a prospective cathode material of Li-ion batteries owing to its high energy density and affordable price, however, it suffers from the poor cycling performance. The doping for metal cations is considered as an effective way to enhance its cycling stability. In this work, titanium was chosen to partially substitute transition-metal ions, i.e. Ni, Co and Mn, and the Ti content was optimized to improve the electrochemical performance of NCM811. The Ti-doped Li(Ni0.8Co0.1Mn0.1)(1-x)TixO2 powder was prepared using high temperature solid-state synthesis. The layered alpha-NaFeO2-type structure of NCM811 survives in the doped samples, and the lattice parameters a and c increase linearly with the Ti content. XPS spectra indicate that the Ni ions show a mixing state of +2 and +3, and the portion of Ni2+ increases by the Ti doping. The cycling stability is improved evidently by a small amount of Ti doping, i.e. capacity retention of 88.3-96.9% for x = 0.01-0.03 versus 64.1% for x = 0 after 100 cycles at 0.1 C. Thus, the sample with x = 0.01 delivers the high discharge capacity of 180.6 mAh g(-1) after 100 cycles, much greater than 116.5 mAh g(-1) of x = 0. Nevertheless, more Ti doping with x = 0.04-0.05 deteriorates the electrochemical performance. It illustrates the presence of optimal Ti-doping range in NCM811, which was rationalized as the synergetic effects of bond strength, Li+ diffusion, chemical composition and valence state of cations.