Significance of gallium doping for high Ni, low Co/Mn layered oxide cathode material

Abstract

High Ni-low Co/Mn layered oxides are emerging as next-generation cathode materials, capable of providing high energy density at a reduced cost in lithium-ion batteries (LIBs). Conversely, the performance decay and structural degradation become more noticeable as the Ni content increases in high Ni cathodes due to the low content of Co and Mn that helps to stabilize the structure. To compensate for the loss of electrochemical performance, herein, we introduce gallium as a dopant to high-Ni, low Co/Mn layered oxide material. Gallium occupying TM site, partially occupies Li sites that enlarges the c-parameter and provides adequate Li/Ni antisite mixing, developing biphasic material that exhibits a well-ordered layered structure with a disordered layered phase on the surface and subsurface. Ga substitution significantly suppresses H2-H3 phase transition, and the disordered layered phase on the surface restrains the parasitic side reaction and enables robust electrochemical kinetics. Therefore, outstanding retention of 90.1% is achieved for NCMG-2 at 0.5C after 100 cycles under the voltage window of 2.7–4.3 V with excellent rate capability, compared to NCM with 68.5% retention. Ab-initio calculations also validate the structural stability, forming a robust oxygen network by the strong binding energy of Ga-O in Ni-rich layered structure. Hence, Ga doping preserved the structural and surficial integrity, which is a strategic approach to improving the electrochemical performance of high-Ni, low Co/Mn layered oxide material.