Optimizing the electrochemical performance of LiCoO2 at 4.5 V via synergistic modification of Mg2+ ion doping and Li1.3La0.3Ti1.7(PO4)3 coating

Abstract Increasing the operating voltage can significantly increase the energy density of LiCoO2, but it is accompanied by severe structural damage and interface degradation. Especially at a high voltage above 4.5 V, LiCoO2 faces severe challenges, such as irreversible phase transition, lattice oxygen loss, and electrode–electrolyte interface evolution. Herein, a high-voltage LiCoO2 cathode material with bulk doping and surface coating synergistic modification was designed and prepared. The doped Mg2+ ions entered the lithium layers as pillars, stabilizing the layered framework. Meanwhile, Li1.3La0.3Ti1.7(PO4)3 was uniformly coated on the surface of LiCoO2, which is beneficial for suppressing Co3+/2+ ion leaching and interface side reactions during cycling. Furthermore, Li1.3La0.3Ti1.7(PO4)3 is a fast ion conductor, which facilitates the rapid transport of lithium ions on the surface of the cathode material. Owing to the synergistic effect of Mg2+ ion doping and Li1.3La0.3Ti1.7(PO4)3 coating, the orbitals of Co 3d and O 2p in LiCoO2 crystal are changed, and the irreversible phase transition and oxygen loss are inhibited. The modified material exhibited an excellent electrochemical performance. A discharge capacity of 175.5 mAh·g−1 at 10 C rate, as well as a capacity retention of 90.14% after 200 cycles at 1 C rate, was achieved in the modified material. This work supplies a new method for developing high-voltage oxide cathodes through bulk and interfacial modification.