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 are noticeable 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 tends to occupy both Li/Ni sites to enlarge the c-parameter and provide adequate Li/Ni antisite mixing to develop a biphasic material exhibiting a well-ordered layered structure along with a disordered layered phase. Ga substitution significantly alleviates the anisotropic volume change by suppressing H2-H3 phase transition, restraining intragranular cracking and enabling robust electrochemical kinetics. Therefore, outstanding retention of 90.1% is achieved for NCMG-2 at 0.5 C 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 of Ga substituted structure by forming a powerful oxygen network by the strong binding energy of Ga-O. 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.

Keywords: Li-ion batteries, high-Ni, low-Mn/Co, layered oxide, gallium doping, robust stability.