Suppressing irreversible phase transition and enhancing electrochemical performance of Ni-rich layered cathode LiNi0.9Co0.05Mn0.05O2 by fluorine substitution

Abstract Ni-rich layered oxide LiNixCoyMn1-x-yO2 (x ≥ 0.8) is the most promising cathodes for future high energy automotive lithium-ion batteries. However, its application is hindered by the undesirable cycle stability, mainly due to the irreversible structure change at high voltage. Herein, we demonstrate that F substitution with the appropriate amount (1 at%) is capable for improve the electrochemical performance of LiNi0.9Co0.05Mn0.05O2 cathode significantly. It is revealed that F substitution can reduce cation mixing, stabilize the crystal structure and improve Li transport kinetics. The resulted LiNi0.9Co0.05Mn0.05O1.99F0.01 cathode can deliver a high capacity of 194.4 mAh g-1 with capacity retention of 95.5% after 100 cycles at 2.0 C and 165.2 mAh g-1 at 5 C. In-situ synchrotron X-ray technique proves that F ions in the cathode materials can suppress the irreversible phase transition from H2 phase to H3 phase in high voltage region by preventing oxygen gliding in a-b planes, ensuring a long-term cycle stability.