Aluminum Foil Anodes for Li-Ion Rechargeable Batteries: the Role of Li Solubility within β-LiAl

Tianye Zheng,Reiner Mönig,Dominik Kramer,Steven T Boles

doi:10.1021/acssuschemeng.1c07242

Abstract

Lithium-ion battery electrodes contain a substantial amount of electrochemically inactive materials, including binders, conductive agents, and current collectors. These extra components significantly dilute the specific capacity of whole electrodes and thus have led to efforts to utilize foils, for example, Al, as the sole anode material. Interestingly, the literature has many reports of fast degradation of Al electrodes, where less than a dozen cycles can be achieved. However, in some studies, Al anodes demonstrate stable cycling life with several hundred cycles. In this work, we present a successful pathway for enabling long-term cycling of simple Al foil anodes: the β-LiAl phase grown from Al foil (α-Al) exhibits a cycling life of 500 cycles with a ∼96% capacity retention when paired with a commercial cathode. The excellent performance stems from strategic utilization of the Li solubility range of β-LiAl that can be (de-)lithiated without altering its crystal structure. This solubility range at room temperature is determined to be ∼6 at %. Consequently, this design circumvents the critical issues associated with the α/β/α phase transformations, such as volume change, mechanical strain, and formation of nanopores. Application-wise, the maturity of the aluminum industry, combined with excellent sustainability prospects, makes this anode an important option for future devices.

Highlights

Aluminum has been explored as a candidate for the negative electrode in lithium-based rechargeable batteries since the 1970s.1 Generally, investigations of this system center around the phase transformations between the α phase and the β phase, which correspond to a high theoretical capacity of ∼993 mA h g−1 at room temperature
Our previous study suggests that the Al/LiAl/Al (α/ β/α) phase transformations might be intrinsically challenging to utilize due to the formation of nanopores, which cause a loss of electrolyte due to secondary solid electrolyte interphase (SEI) formation on a large surface area
While the α phase is present and overall α/β equilibrium is maintained, only β-LiAl is expected to form at relatively high potentials (>0.2 V vs Li/Li+; i.e., lithiation plateau), an overpotential is required to move the phase front

Summary

■ INTRODUCTION

Aluminum has been explored as a candidate for the negative electrode in lithium-based rechargeable batteries since the 1970s.1 Generally, investigations of this system center around the phase transformations between the α phase (fcc, Al) and the β phase (cubic, LiAl), which correspond to a high theoretical capacity of ∼993 mA h g−1 at room temperature. A novel anode structure has been developed by partly lithiating a metallic Al foil to form a monolithic electrode This prelithiation step is performed electrochemically here, other methods like simple mechanical rolling will be sufficient to fabricate such an electrode.[13] The β-LiAl and the α-Al layers function as the active material and the current collector, respectively. Scanning electron microscopy (SEM) has been performed to observe the morphologies of partly lithiated Al foils, providing insights into the Li−Al system Based on these observations, it is possible to electrochemically cycle the electrode such that the active layer (i.e., β-LiAl) of the anode stays within its Li solubility range. The current rate equivalent to C/10 (normalized to the LFP cathode; 0.1 mA cm−2) with a voltage window between 2 and 3.7 V was used for cycling performance assessment

■ RESULTS AND DISCUSSION

■ CONCLUSIONS AND PERSPECTIVES

■ ACKNOWLEDGMENTS

■ REFERENCES