Surface Li+/K+ Exchange toward Double-Gradient Modification of Layered Li-Rich Cathode Materials.

Surface coating and lattice doping are widely used to enhance the interfacial and structural stabilities of Li1.2Ni0.13Co0.13Mn0.54O2 (LNCM). In this paper, KF is used to modify LNCM for the first time. A Li+/K+ exchange in the Li slabs is realized via a high-temperature treatment. Consequently, subsurface K+ gradient doping and surface K1-xLixF gradient coating are obtained simultaneously on LNCM. Such an Li+/K+ exchange mechanism and double-gradient modification are clarified by X-ray diffraction, energy-dispersive spectrometry line scans, and high-resolution transmission electron microscopy analyses. As a result, the optimal 0.5 wt % KF-modified LNCM material shows markedly alleviated voltage degradation (0.0031 V@1 cycle), improved cycling stability (88%@100 cycles@0.5 C), and rate capability (108 mA h g-1@10 C), revealing large application potential in high-energy materials.