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

Abstract

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.

Exploring the Reversibility of Phase Transformations in Aluminum Anodes through Operando Light Microscopy and Stress Analysis

“…For the other cell types, (Figure 1b c), although different rates were used, identical shapes are observed, strengthening confidence in the different cell designs. [14] The slightly different CV shape of the optical cell is not a result of cell architecture. Instead, CV scan rates ( Figure S1a) and electrode forms ( Figure S1b) should play a more important role here.…”

“…The same study also suggests that the stability and reversibility of Al thin film anodes can be improved if these β phase patches are surrounded by the ductile α phase. [14] Therefore, a partial lithiation is adopted to minimize the patch coalescence, and thus enabling several stable cycles for investigations of the delithiation and re-lithiation processes. The surfaces of Al films at the end of~45 % partial lithiation show no visible degradation, i. e., neither delamination nor pulverization at the chosen magnification is observed.…”

“…This behavior can also be supported by the analyses of our previous work, which suggests a reaction-controlled growth mechanism of the β phase patches. [14] To shed light on the Li pathways that govern the β phase patches evolution during fast and repetitive cycling, CV is used in addition to GCD. The evolution of the Al film surface during the initial CV cycles is shown in Figure 2c, where a clear expansion of the β phase is observed.…”

“…The (de-)lithiation processes during electrochemical cycling can be summarized: 1. Initial lithiation: This process was elaborated in our previous study, [14] including oxides lithiation, nucleation, and growth of the β phase ( Figure 4a-c). The important features such as random nucleation and quasi-circular growth generally remain under the GCD mode.…”

“…In our previous study, we explored the kinetics of the initial electrochemical incorporation of Li into Al, and highlighted the factors that may affect the electrode stability. [14] Although the potentiostatic techniques with fixed driving forces used can be ideal for conducting kinetic analyses, they may not fully represent the typical working conditions for LIB applications. It is therefore also necessary to explore how Al electrodes behave under various electrochemical conditions, such as galvanostatic charge and discharge (GCD) and cyclic voltammetry (CV).…”