Synergistic-effect of high Ni content and Na dopant towards developing a highly stable Li-Rich cathode in Li-ion batteries

Developing a stable layered Li-rich oxide (LLO) is of utmost importance to realize electric vehicles (EVs), which offer driving ranges similar to internal combustion engine. In this study, the Ni concentration in the transition metal (TM) layer of the LLOs is increased gradually from 13% to 32% and the synergistic effect of doping Na is systematically analyzed. X-ray refinement studies of Ni excess LLOs reveal that increasing Ni content and doping Na increases the “c” lattice parameter and reduces the cation mixing. Electrochemical analysis of Ni excess cathode in Li-ion cell confirms that increasing the Ni content suppresses the Li2MnO3 activation and the layered to spinel structural transition in LLOs. Ni excess cathode (32% Ni) showed > 99% capacity retention (at 0.2C) compared to 84% retention for the electrode with 13% Ni content. Increasing the Ni content in TM layer negatively affected the rate capability. Doping Na in Li layer further enhances the electrochemical properties of these Ni excess electrodes with improved rate capability. The Na doped Ni excess cathode (24% Ni) furnishes discharge capacities and energy densities of 180 mAhg−1 and 613 WhKg−1 compared to 154 mAhg−1 and 471 WhKg−1 of undoped cathode with 13% Ni. The pillaring effect of inactive Na suppress the voltage fading upon cycling; Na doped Ni excess cathode (24% Ni) retained 93% of its initial voltage after 200 cycles, which is ∼ 0.35 V higher than the 13% Ni counterpart. In full cell configuration, Na doped Ni excess (20% and 24% Ni) electrodes exhibit enhanced energy densities of ∼ 100 WhKg−1than the undoped electrode with 13% Ni.