Promoting homogeneous tungsten doping in LiNiO₂ through grain boundary phase induced by excessive lithium

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.

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Contact the author: Jiexi Wang (wangjiexikeen@csu.edu.cn).

National Energy Metal Resources and New Materials Key Laboratory, Engineering Research Center of the Ministry of Education for Advanced Battery Materials, Hunan Provincial Key Laboratory of Nonferrous Value-Added Metallurgy, School of Metallurgy and Environment, Central South University, Changsha 410083, P. R. China.

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