Modulating Anion Redox Activity of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂through Strong Sr-O Bonds toward Achieving Stable Li-Ion Half-/Full-Cell Performance

Controlled synthesis and compositional modification of Li-rich layered oxides (LLOs), Li1.2Mn0.54Co0.13Ni0.13O2, are considered as potential strategies to achieve high structural stability/reversibility and suppressed voltage/capacity fading for realizing stable cycle life performance in lithium-ion batteries (LIBs). In this study, the effect of strontium (Sr2+) doping in Li1.2-2xSrxMn0.54Co0.13Ni0.13O2 (0.0015 ≤ x ≤ 0.007) is systematically investigated by electrochemical studies. X-ray refinement studies reveal the occupancy of Sr2+ at Li+ (lithium) sites with larger oxygen-lithium-oxygen interslab spacing in the crystal structure. Investigation of Sr2+-doped materials in Li-ion cells furnishes up to ∼50% reduction in anionic redox activity during the first charge cycle compared to LLO. Ex situ structural analysis of LLO and Sr2+-doped samples shows suppressed layered to spinel phase transformation for the latter. The Sr2+-doped electrode (x = 0.005) delivers ∼70 W h kg-1 more energy (620 W h kg-1) than the LLO at 0.2 C. Besides, testing for 500 cycles at 1 C, the Sr2+-doped cathode (x = 0.005) retains ∼94% of its initial capacity as against LLO (68%). High temperature study at 55 °C shows better electrochemical performance, indicating good structural stability of Sr2+-doped samples. Moreover, in the full-cell configuration, the Sr2+-doped cathode (x = 0.005) retains ∼98% of its initial capacity at 0.5 C after 50 cycles unlike LLO (55%).