Synergetic effects of cation (K+) and anion (S2−)-doping on the structural integrity of Li/Mn-rich layered cathode material with considerable cyclability and high-rate capability for Li-ion batteries

Abstract Controlling structural deformations and rapid voltage decay during prolonged cycling has been considered the foremost challenge in improving the cycling and rate performance of Li-rich cathode materials for advanced lithium-ion batteries. In this work, we report an effective strategy for delaying structural variations and inhibiting transition metal migration by co-doping with a large-sized cation and anion. A Li-rich layered composite cathode, namely Li1.165Mn0.495Ni0.165Co0.165O2 (LMNCO; 0.5Li2MnO3-0.5LiMn0.33Ni0.33Co0.33O2) was prepared as the starting material, followed by synthesis of the optimized K+-doped L1.135K0.03Mn0.495Ni0.165Co0.165O2 (LKMNCO) and K+/S2−-doped L1.135K0.03Mn0.495Ni0.165Co0.165O2S0.02 (LKMNCOS) samples via a co-precipitation method. This co-doping strategy retarded structural deformations by significantly suppressing transition metal migration, as evidenced by ex-situ X-ray diffraction analysis at various cycle numbers for the sample cycled at 1.0 C-rate. The K+/S2−-doped sample, i.e., LKMNCOS, exhibited exceptional cycling stability and high-rate capability. Owing to the enhanced structural properties, the co-doped sample delivered an initial charge/discharge capacity of 341/295 mAh g−1 at 0.05 C, with the lowest irreversible capacity loss (ICL) compared to the pristine and K+-doped sample. A discharge capacity of ~129 mAh g−1 was also achieved even after 450 cycles at 1.0 C-rate, with the highest capacity retention ratio (65%) and lowest average capacity decay rate per cycle (~0.07%), suggesting excellent cycling performance. Overall, the results are prospectively beneficial for further development of advanced layered cathodes that undergo layered-to-spinel transformations and demonstrate the efficacy of co-doping for alleviating undesired structural defects.