Effects of strontium oxide on synthesis and performance of monocrystalline ultrahigh-Ni layered cathode materials for Li-ion batteries

Monocrystalline layered cathode is of particular interest owing to the satisfactory mechanical integrity against long-term cycling. However, the high-temperature calcination, which is perceived as the indispensable reaction condition, favors the formation of Ni²⁺ that triggers the Li⁺/Ni²⁺ disorder and the formation of electrochemically inactive NiO. Herein, we develop a SrO-assistant method to synthesize a monocrystalline ultrahigh-Ni LiNi_0.95Co_0.04Mn_0.01O₂ under a moderate calcination temperature. The addition of an appropriate amount of SrO (0.3 wt%, SCN95–Sr-3) facilitates the formation of monocrystalline LiNi_0.95Co_0.04Mn_0.01O₂ (grain size: 2–4 μm) under 790 °C. The obtained LiNi_0.95Co_0.04Mn_0.01O₂ represents excellent electrochemical properties with an initial discharge capacity of 240.5 mAh g⁻¹ and a Coulombic efficiency of 90.1 % at 0.1C (1C = 220 mA g⁻¹) in a Li-metal half cell. Upon long-term cycling, the monocrystalline feature with less crystallographic defect effectively enhances the structural stability and inhibits the formation of intergranular cracks, resulting in an enhanced cyclic stability (discharge capacity of 151.0 mAh g⁻¹ maintained after 300 cycles at 1C in a Li-metal half cell). Coupled with a graphite anode, the LiNi_0.95Co_0.04Mn_0.01O₂|| graphite full cell represents a stable cycling at 1C, with a capacity retention of 99.0 % after 100 cycles.