A hydrolysis-hydrothermal route for the synthesis of ultrathin LiAlO2-inlaid LiNi0.5Co0.2Mn0.3O2 as a high-performance cathode material for lithium ion batteries

Abstract

We present a novel hydrolysis-hydrothermal approach to using lithium residues on the surface of LiNi_0.5Co_0.2Mn_0.3O₂ as raw materials to synthesize ultrathin LiAlO₂-inlaid LiNi_0.5Co_0.2Mn_0.3O₂ cathode materials, for the first time. High-resolution transmission electron microscopy (HRTEM) and fast Fourier transform (FFT) analysis indicate that the spherical particles of LiNi_0.5Co_0.2Mn_0.3O₂ are completely coated by crystalline LiAlO₂ with an average thickness of 4 nm; cross-section SEM and corresponding EDS results confirm that partial Al³⁺ ions are doped into the bulk LiNi_0.5Co_0.2Mn_0.3O₂ with gradient distribution. Electrochemical tests show that the modified materials exhibit excellent reversible capacity, enhanced cyclability and rate properties, combining with higher Li ion diffusion coefficient and better differential capacity profiles compared with those of the pristine material. Particularly, the 2 mol% LiAlO₂-inlaid sample maintains 202 mA h g⁻¹ with 91% capacity retention after 100 high-voltage cycles (with 4.6 V charge cut-off) at 1 C. The enhanced electrochemical performance can be ascribed to the removal of lithium residues and the unique LiAlO₂-inlaid architecture. The removal of lithium residues are believed to decrease side reactions between Li₂O and the electrolyte, while the unique LiAlO₂-inlaid architecture can buffer the volume change of core and shell during cycles, enhance the composite's lithium ion diffusion ability and inherit the advantages of LiAlO₂ coating and doping.