Which is the winner between the single-crystalline and polycrystalline LiNi0.80Co0.15Al0.05O2 cathode in the lithium-ion battery?

Ni-rich layered oxide LiNi0.80Co0.15Al0.05O2 (NCA) owing to its high discharge capacity has been deemed as a research focus of lithium-ion batteries (LIBs). However, the structural instability is still against its wide application. Herein, the single-crystal NCA is successfully synthesized by the flux-aiding step sintering method, and its improved electrochemical performance at 25 °C, especially at 55 °C, is studied by comparison with polycrystalline NCA. Results from structure, morphology characterization, and composition analysis indicate that the single-crystal cathode can restrain the generation of cracks and structural collapse, as well as suppress the phase transition. Moreover, it effectively reduces the electrolyte decomposition and the interface impedance. These make single-crystal NCA not only exhibit superior cycle performance and rate capability at 25 °C but also display preferable thermal stability at an elevated temperature of 55 °C with a capacity retention of 74.5% after 200 cycles. Furthermore, the fading mechanism of single-crystal NCA at 55 °C is systematically discussed from structural to interfacial stability, which affords insight into guiding the modification for single-crystal cathodes. The proposed synthesized method will also provide new perspectives on designing reversible and stable cathode materials to achieve high energy density LIBs.