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

Nickel-rich LiNi[Formula: see text]Co[Formula: see text]Mn[Formula: see text]O 2 (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(Ni[Formula: see text]Co[Formula: see text]Mn[Formula: see text]Ti[Formula: see text]O 2 powder was prepared using high temperature solid-state synthesis. The layered [Formula: see text]-NaFeO 2 -type structure of NCM811 survives in the doped samples, and the lattice parameters [Formula: see text] and [Formula: see text] 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 Ni[Formula: see text] 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 [Formula: see text] = 0.01–0.03 versus 64.1% for [Formula: see text] = 0 after 100 cycles at 0.1 C. Thus, the sample with [Formula: see text] = 0.01 delivers the high discharge capacity of 180.6 mAh g[Formula: see text] after 100 cycles, much greater than 116.5 mAh g[Formula: see text] of [Formula: see text] = 0. Nevertheless, more Ti doping with [Formula: see text] = 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[Formula: see text] diffusion, chemical composition and valence state of cations.