Title: Restraining oxygen release and suppressing structure distortion in single-crystal Li-rich layered cathode materials

Abstract

Li-rich oxides can be regarded as the next-generation cathode materials for high-energy-density Li-ion batteries since additional oxygen redox activities greatly increase output energy density. However, the oxygen loss and structural distortion induce low initial coulombic efficiency and severe decay of cycle performance, further hindering their industrial applications. Herein, the representative layered Li-rich cathode material, Li1.2Ni0.2Mn0.6O2, is endowed with novel single-crystal morphology. In comparison to its polycrystal counterpart, not only can serious oxygen release be effectively restrained during the first oxygen activation process, but also the layered/spinel phase transition can be well suppressed upon cycling. Moreover, the single-crystal cathode exhibits the limited volume change and persistent presence of superlattice peaks upon Li+ (de)intercalation processes, resulting in enhanced structural stability with absence of crack generation and successive utilization of oxygen redox reaction during long-term cycling. Benefiting from these unique features, the single-crystal Li-rich electrode not only yields a high reversible capacity of 257 mAh g−1, but also achieves excellent cycling performance with 92% capacity retention after 200 cycles. These findings demonstrate that the morphology design of single crystals can be regarded as an effective strategy to realize high-energy density and long-life Li-ion batteries.