Al-doping enables high stability of single-crystalline LiNi_0.7Co_0.1Mn_0.2O₂ lithium-ion cathodes at high voltage

LiNi_0.7Co_0.1Mn_0.2O₂ (NCM) is a kind of promising cathode material for lithium ion batteries because of its high capacities. However, the further commercialization of this material has been seriously hindered by the unstable structure at a deep de-lithiation state. Herein, it is identified that this drawback can be diminished by Al-doping, which is inherently stable in the lattice framework to restrain the structural collapse of LiNi_0.7Co_0.1Mn_0.2O₂ at a high cut-off voltage (4.4 V). As expected, the Al-doped NCM (NCM-0.2Al) material obtains the highest reversible capacity and capacity retention (144.69 mA h g^-1, 80.26%) after 90 cycles at 1C. The excellent performance demonstrates that Al-doping can effectively enhance the Li⁺-ion diffusion kinetic and structural stability of NCM, providing a feasible strategy for the further industrialization of Ni-rich materials.