The layered oxide material LiNiO2 (LNO) is one of the most promising cathode materials for lithium-ion batteries (LIBs). However, the serious cation mixing of Ni2+ and Li+ in LNO cathode leads to the transformation of the material structure from layered to electrochemically inert rock salt phase, hindering the diffusion of lithium ions. The harmful phase transition during charge-discharge process is another important factor leading to the decay of electrochemical performance. Therefore, it is crucial to suppress the H2↔H3 phase transition in the electrochemical process to reduce the generation of intergranular microcracks for improving the electrochemical cycling performance of secondary particle-type LNO.
Tungsten (W) element in enhancing the stability of LNO has been researched extensively. Although W6+is widely used in the doping modification of lithium nickelate, the mechanism of high-temperature doping reaction of W6+ and the existence of W6+ in the doping process are still not explicit.
In a study published in the KeAi journal Advanced Powder Materials, a team of researchers in China used W doping to modify the structure of LNO to improve its cyclic performance.
"Initially, the W atoms react with a lithium source, forming a Li–W–O phase concentrated at the grain boundaries of primary particles," shares Jiexi Wang, senior and corresponding author of the study. "As the lithium ratio increases, these tungsten atoms gradually diffuse inward, integrating into the layered structure. This process, termed grain boundary phase doping, has been validated using first-principles calculations, providing evidence for its feasibility."
Notably, the Li2WO4 grain boundary phase assumes a dual role. Acting as an excellent lithium-ion conductor, it safeguards the cathode surface while significantly enhancing the rate performance of the battery. Meanwhile, the W atoms embedded within the cathode structure mitigate the damaging H2↔H3 phase transition, resulting in a marked improvement in the battery's electrochemical performance.
"A 0.3 wt% W-doped sample demonstrated a vastly improved capacity retention of 88.5% after 100 cycles at 2.8–4.3 V under 1C, compared to the 80.7% retention of pristine LNO. This finding takes us a step closer to more reliable and efficient energy storage solutions," adds Wang.
