Optimized Al Doping Improves Both Interphase Stability and Bulk Structural Integrity of Ni-Rich NMC Cathode Materials

The nickel-rich transition metal oxide-NMC, LiNi1-x-yMxCoyO2, 1 - x - y >= 0.6-shows great potential for use in lithium-ion batteries that exhibit high energy densities; however, large-scale use of the material in batteries is hindered by technical challenges, including secondary particle cracking, interfacial instability, and cell degassing during cycling. In this paper, we report a strategy that employs minimal Al doping to improve the bulk integrity, structure, and interfacial stability of the cathode and, hence, the long-term cycling capability. With only 1 mol % Al doping, the Al-NMC76 electrode can retain 79.2% capacity after 500 cycles at 4.5 V, which is far better than the capacity retention for undoped NMC76 tested under similar conditions. The improved cycling can be attributed to the Al doping in the NMC76, which not only improves bulk structural stability by introducing the Al doping into the lattice but also suppresses chemical reactions with the acidic electrolyte.