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

Highlights: • Co-doping with large K⁺/S²⁻ delays structural changes in Li_1.135K_0.03MNCOS_0.02. • Reduced transition metal migration with enhanced electrochemical performances. • K⁺/S²⁻-doped Li_1.135K_0.03MNCOS_0.02 exhibits exceptional structural stability. • Layered-to-spinel change, oxygen vacancies or irreversible capacity loss are curtailed. -- 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 Li_1.165Mn_0.495Ni_0.165Co_0.165O₂ (LMNCO; 0.5Li₂MnO₃-0.5LiMn_0.33Ni_0.33Co_0.33O₂) was prepared as the starting material, followed by synthesis of the optimized K⁺-doped L_1.135K_0.03Mn_0.495Ni_0.165Co_0.165O₂ (LKMNCO) and K⁺/S²⁻-doped L_1.135K_0.03Mn_0.495Ni_0.165Co_0.165O₂S_0.02 (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.