Air‐Stable Li_xAl Foil as Free‐Standing Electrode with Improved Electrochemical Ductility by Shot‐Peening Treatment

Abstract

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.

Utilization of Li-Rich Phases in Aluminum Anodes for Improved Cycling Performance through Strategic Thermal Control

“…For instance, reducing the grain size in Al foils via a shot-peening treatment before prelithiation is reported to be helpful to make a LiAl electrode stable in ambient air for several hours. 45 Alternatively, SEI engineering is also demonstrated to be beneficial to the β-LiAl, giving better air compatibility as well as a more stable cycling performance. 43,45,46 The term "N-to-P ratio" (i.e., the capacity ratio of negative over positive electrode) is brought up to prevent Li plating from occurring on the surface of anodes.…”

“…45 Alternatively, SEI engineering is also demonstrated to be beneficial to the β-LiAl, giving better air compatibility as well as a more stable cycling performance. 43,45,46 The term "N-to-P ratio" (i.e., the capacity ratio of negative over positive electrode) is brought up to prevent Li plating from occurring on the surface of anodes. The possible short circuit induced by Li dendrites may lead to catastrophic incidents, e.g., explosions, fires, and so forth.…”

Simplifying Electrode Design for Lithium-Ion Rechargeable Cells

“…This eliminates the powder–slurry steps prior to dry room processing and replaces them with single prelithiation, which can be done either (electro-)­chemically or mechanically, perhaps even as reel-to-reel at a full scale. Although it is debatable to what extent a moisture-controlled environment (e.g., a dry room) is necessary for the prelithiation process (blue background in Figure a), it has been demonstrated elsewhere that LiAl could be quite stable in ambient air by artificially forming a solid electrolyte interface (SEI) layer or via shot peening treatment of Al foils before lithiation …”

“…Although it is debatable to what extent a moisture-controlled environment (e.g., a dry room) is necessary for the prelithiation process (blue background in Figure 1 a), it has been demonstrated elsewhere that LiAl could be quite stable in ambient air by artificially forming a solid electrolyte interface (SEI) layer 4 or via shot peening treatment of Al foils before lithiation. 5 …”

Simplifying electrode design for lithium-ion rechargeable cells

“…1a), it has been demonstrated elsewhere that LiAl could be quite stable in ambient air by artificially forming a solid electrolyte interface (SEI) layer, [5] or via a shot-peening treatment of Al foils. [6] While the dual functionality of an Al foil anode serving as both electronic conductor and lithium host represents a significant advancement for lithium-ion cells, the quest for a foilbased cathode may be more problematic since the use of ceramic oxides is largely unavoidable for high energy density devices. Indeed, a composite with a malleable metal matrix may be highly effective on the cathode side for realizing the construction of solvent-and binder-free full cells.…”