Air-stable Li${}_x$Al foil as free-standing electrode with improved electrochemical ductility by shot-peening treatment

A self-supporting Al foil anode should be attractive to the lithium-ion battery (LIB) industry. However, initial attempts at using thin Al foil directly as a LIB anode ends up with extremely large initial Coulombic inefficiency and gross mechanical failures in just a few cycles. This feels incongruent with the expectation that face-centered cubic Al should have good ductility. In this study, the discrepancy between "electrochemical ductility" and "mechanical ductility" is explained. Unlike "mechanical ductility" based on dislocation slip inside each grain, here it is proposed that "electrochemical ductility" of such high-capacity alloy foil electrodes should be related to grain boundaries (GB) activities. It is found that after reducing the grain size D > 50 µm of the starting Al foil by shot-peening treatment, higher GB density (e.g., smaller initial grain size D < 20 µm) greatly alleviates the initial porosity damage after the roll-to-roll mechanical prelithiation and significantly improves electrochemical ductility thereafter, with enhanced cycle life in various kinds of full cells. Li${}_x$Al foil also demonstrates surprising air stability with negligible capacity loss even after several hours' exposure to air. Such thin prelithiated metallic foil anodes are therefore highly competitive against pure Li metal foils. (© 2021 Wiley-VCH GmbH)