Regulating the Charge Distribution of Oxygen by High-Entropy Doping to Stabilize Single-Crystal Ni-Rich Cathode Materials
Single-crystal Ni-rich ternary cathode materials (811), with their comprehensive advantage of high energy density and low manufacturing cost, have been considered the most promising materials for Li-ion batteries. Due to strong O-p/TM-d covalent hybridization, the complete oxidation of Ni ions during electrochemical cycling is often accompanied by inevitable oxygen loss, resulting in an irreversible surface phase transition, accumulated lattice stress, and poor thermal stability. Considering the fact that introducing heteroatoms into traditional doping systems can alter the electron density distribution around coordinated oxygen, compositionally complex systems based on high-entropy doping may have a more significant effect on stabilizing lattice oxygen. Herein, the high-entropy doping strategy was applied to design and synthesize single-crystal NCM811 cathodes (HE811) through the molten salt method. Compared to 811, HE811 cathodes show an excellent initial Coulombic efficiency of 90.74% at 0.2C and deliver a higher capacity retention of 80.79% after 300 cycles at 1C between 2.8 and 4.3 V. Owing to high-entropy doping, the oxygen electron densities around multidopants are increased, inhibiting the excessive oxidation of lattice oxygen and improving the stability of TMO6 coordination structures. This work could provide insights into the high-entropy doping effects in modulating oxygen charge distribution to design high-energy-density Ni-rich ternary cathode materials with long-term cycling.
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