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

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.

Simplifying Electrode Design for Lithium-Ion Rechargeable Cells

“…After holding the Li/Al half-cell at 0.40 V versus Li/Li + for an hour, following the strategy described by Geronov et al, the potential is adjusted to a level as low as 0.01 V (V 2 ) to form a great amount of β-LiAl nuclei on the Al surface within only 15 min (Figure S1). When the potential jumps back to a moderate level at 0.15 V versus Li/Li + (V 3 ), the subsequent phase transformation will mostly take place at the positions where the β-LiAl nuclei already exist, resulting in a layer of β-LiAl that homogeneously covers the Al foil surface with a targeted thickness based on anticipated device capacity …”

“…90% capacity retention. Since the cycled capacity is limited by the ACF, the (de-)­saturation of the β-LiAl layer should prevail instead of the α/β/α phase transformations . Compared to the poor cycling lives of Al anodes reported by others, our device takes advantage of the solubility range of β-LiAl that circumvents the intrinsic problems arising from the phase transformations, such as mechanical strain and formation of nanopores .…”

“…When the potential jumps back to a moderate level at 0.15 V versus Li/Li + (V 3 ), the subsequent phase transformation will mostly take place at the positions where the β-LiAl nuclei already exist, resulting in a layer of β-LiAl that homogeneously covers the Al foil surface with a targeted thickness based on anticipated device capacity. 14 …”

“…Since the cycled capacity is limited by the ACF, the (de-)saturation of the β-LiAl layer should prevail instead of the α/β/α phase transformations. 14 Compared to the poor cycling lives of Al anodes reported by others, our device takes advantage of the solubility range of β-LiAl that circumvents the intrinsic problems arising from the phase transformations, such as mechanical strain 17 and formation of nanopores. 18 The device delivers ∼1.6 mWh cm –2 at an areal power of ∼5.6 mW cm –2 (single-side), or a gravitational energy of ∼25.6 mWh g –1 at a gravitational power of ∼88.3 mW g –1 , normalized to the total mass of both Al and ACF.…”

Unlocking the High Capacity and Stability of Aluminum Anodes for Lithium-Ion Batteries through Strategic Thermal Control

“…15 Like most alloy anode materials, these problems are intrinsically coupled to the host element/matrix, and thus challenging to resolve. Alternatively, smart strategies to circumvent the huge mechanical stress 16 or restrict the α/β phase transformation (i.e., limited to the solubility range of β-LiAl) 17 hold promise for enabling room temperature Al anodes for LIBs.…”