Na+ Lattice Doping Induces Oxygen Vacancies to Achieve High Capacity and Mitigate Voltage Decay of Li-Rich Cathodes.

Abstract

In this work, we synthesized 1D hollow square rod-shaped MnO2, and then obtained Na+ lattice doped-oxygen vacancy lithium-rich layered oxide by a simple molten salt template strategy. Different from the traditional synthesis method, the hollow square rod-shaped MnO2 in NaCl molten salt provides numerous anchor points for Li, Co, and Ni ions to directly prepare Li1.2Ni0.13Co0.13Mn0.54O2 on the original morphology. Meanwhile, Na+ is also introduced for lattice doping and induces the formation of oxygen vacancy. Therefrom, the modulated sample not only inherits the 1D rod-like morphology but also achieves Na+ lattice doping and oxygen vacancy endowment, which facilitates Li+ diffusion and improves the structural stability of the material. To this end, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and other characterization are used for analysis. In addition, density functional theory is used to further analyze the influence of oxygen vacancy generation on local transition metal ions, and theoretically explain the mechanism of the electrochemical performance of the samples. Therefore, the modulated sample has a high discharge capacity of 282 mAh g-1 and a high capacity retention of 90.02% after 150 cycles. At the same time, the voltage decay per cycle is only 0.0028 V, which is much lower than that of the material (0.0038 V per cycle) prepared without this strategy. In summary, a simple synthesis strategy is proposed, which can realize the morphology control of Li1.2Ni0.13Co0.13Mn0.54O2, doping of Na+ lattice, and inducing the formation of oxygen vacancy, providing a feasible idea for related exploration.