Stabilized Performance of LiNi0.90Co0.07Al0.03O2 Cathodes via Zr4+ Doping upon 4.5 V Application due to the Suppression of H2-H3 Phase Transitions

The layered structured cathode material LiNi0.90Co0.07Al0.03O2 (NCA) has good prospects for its high energy density for the application in electric vehicles (EVs) but suffers from rapid capacity decay at a high working voltage. In this work, Zr-doped LiNi0.90Co0.07Al0.03O2 (Zr-NCA), with excellent performance at 4.5 V, has been successfully synthesized through a nano-milling-assisted solid-state reaction. The doped material presents an initial capacity of 225.9 mA h.g(-1) and a coulombic efficiency of 89.29% at 4.5 V, and an improved capacity retention by 22.84% after 100 cycles at 0.5 C is also observed. Such a big promotion can be ascribed to the fact that the irreversible phase transition from the second hexagonal to third hexagonal (H2-H3) phase is suppressed by strong Zr-O bonds. The substitution of zirconium ions also expands the thickness of the lithium slab, which thereafter causes a rapid Li-ion migration; thus, the doping of Zr4+ in the NCA cathode also creates a promoted rate behavior with a capacity of 144.7 mA h.g(-1) at 5 C. The method of lattice doping to improve electrochemical performance of NCA at 4.5 V has been displayed, showing high potential for the mass production of cathode materials with a high energy density.