LAUSR

Aluminum (Al) is an attractive anode material for lithium-ion batteries (LIBs) due to its low cost, light weight, and high specific capacity. However, utilization of Al-based anodes is significantly limited by the drastic capacity fading during cycling. We report a systematic study investigating the kinetics of electrochemical lithiation of Al thin films to understand the mechanisms governing the phase transformation, 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 the 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 via 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 cycle life-extending strategies proposed here.