Spherical layered Li-rich cathode material: Unraveling the role of oxygen vacancies on improving lithium ion conductivity

The commercialization of layered lithium-rich manganese oxide material (LLMO) suffers from low conductivity, poor cycling performance, and complicated synthetic techniques. Herein, we develop a low-cost, short-time, and simple low-temperature combustion synthesis (LCS) method for massive production of spherical LLMO material with high oxygen vacancy concentration. In our LCS method, the microstructure and oxygen vacancy concentration of the products are controllable by regulating the dosage of fuel (i.e., urea). Positron annihilation and electron paramagnetic resonance both accurately characterize oxygen vacancy in materials with different urea dosages. When the dosage of urea is 1.5 times of stoichiometric ratio, both the free electron density and oxygen vacancy concentration of the obtained U1.5@LLMO are the highest, which are favorable for rapid transfer of electrons and ions. At rate of 1 C, the average discharge capacity of U1.5@LLMO is 185 mAh g⁻¹ with a high capacity retention of 94.33% after 100 cycles. The corresponding lithium ion diffusion is 1.346*10⁻¹² cm² S⁻¹, much higher than those of other samples. DFT calculation demonstrated that the electrochemical activity of Li⁺ increased significantly with the increase of oxygen vacancy concentration. This powerful LCS method for the production of LLMO with excellent electrochemical properties shows great potentials for large-scale applications.