Dielectric Polarization in Inverse Spinel-Structured Mg2TiO4 Coating to Suppress Oxygen Evolution of Li-Rich Cathode Materials

High-energy Li-rich layered cathode materials (approximate to 900 Wh kg(-1)) suffer from severe capacity and voltage decay during cycling, which is associated with layered-to-spinel phase transition and oxygen redox reaction. Current efforts mainly focus on surface modification to suppress this unwanted structural transformation. However, the true challenge probably originates from the continuous oxygen release upon charging. Here, the usage of dielectric polarization in surface coating to suppress the oxygen evolution of Li-rich material is reported, using Mg2TiO4 as a proof-of-concept material. The creation of a reverse electric field in surface layers effectively restrains the outward migration of bulk oxygen anions. Meanwhile, high oxygen-affinity elements of Mg and Ti well stabilize the surface oxygen of Li-rich material via enhancing the energy barrier for oxygen release reaction, verified by density functional theory simulation. Benefited from these, the modified Li-rich electrode exhibits an impressive cyclability with a high capacity retention of approximate to 81% even after 700 cycles at 2 C (approximate to 0.5 A g(-1)), far superior to approximate to 44% of the unmodified counterpart. In addition, Mg2TiO4 coating greatly mitigates the voltage decay of Li-rich material with the degradation rate reduced by approximate to 65%. This work proposes new insights into manipulating surface chemistry of electrode materials to control oxygen activity for high-energy-density rechargeable batteries.