Improvement of the Cycling Performance of Aluminum Anodes through Operando Light Microscopy and Kinetic Analysis

Aluminum is an attractive anode material for lithium‐ion batteries (LIBs) owing to its low cost, light weight, and high specific capacity. However, utilization of Al‐based anodes is significantly limited by drastic capacity fading during cycling. Herein, a systematic study is performed to investigate the kinetics of electrochemical lithiation of Al thin films to understand the mechanisms governing the phase transformation, by using an operando light microscopy platform. Operando videos reveal that nuclei appear at random positions and expand to form quasi‐circular patches that grow and merge until the phase transformation is complete. Based on this direct evidence, models of the lithiation processes in Al anodes are discussed and reaction‐controlled kinetics are suggested. The growth rate of LiAl depends on the potential and increases considerably as higher overpotentials are approached. Lastly, improved cycling performance of Al‐based anodes can be realized by two approaches: 1) by controlling the lithiation extent, the cycling life of Al thin film is extended from 5 cycles to 25 cycles; 2) the performance can be optimized by adjusting the kinetics. Together, this work offers a renewed promise for the commercialization of Al‐based anodes in LIBs where the performance requirements are compatible with the proposed cycle life‐extending strategies. Step into the light: An operando light microscopy study is conducted systematically for electrochemical lithiation of Al thin film anodes under various driving forces. The nucleation is found to be highly inhomogeneous and the phase transformation grows from 3 D to 2 D. A new lithiation kinetics model is proposed to illustrate the β‐phase evolution. By controlling these kinetic parameters and the extent of lithiation, the cycle life of the Al anode is significantly improved.