Aluminum Foil Anodes for Li-ion Rechargeable Batteries: The Role of Li Solubility within β-LiAl

Abstract

Li-ion battery (LIB) electrodes contain a substantial amount of electrochemically inactive materials, including binder, conductive agent, and current collectors. These extra components significantly dilute the specific capacity of whole electrodes, and thus have led to efforts to utilize foils, e.g., 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: 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 nanopore formation. Application-wise, the maturity of aluminum industry, combined with excellent sustainability prospects, makes this anode an important option for future devices.

Simplifying Electrode Design for Lithium-Ion Rechargeable Cells

“…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 The prepared electrode yields distinct peaks of crystalline β-LiAl and Al in the X-ray diffractogram (Figure 2b), while the bilayer nature of the prepared electrode is revealed by the scanning electron microscopy (SEM) images (Figure 2c,d). From a macroscopic view (Figure 2e,f), the lithiated surface exhibits a grayish color, while the back side of a single-side electrode remains the silvery white of aluminum metal.…”

“…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.…”

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

“…Because this study is the first to suggest cycling between the β-LiAl and the higher-order phases in the LIB cells that are expected to operate under ambient conditions, some practical implementation aspects should be acknowledged: Unlike conventional graphite anodes, β-LiAl itself serves as a Li reservoir (in the same way as the cathode), but prelithiation is essential to enabling this before final cell assembly. Various methods for lithiating Al (mechanical, 41,42 chemical, 43 and electrochemical 37 ) have all been demonstrated to be effective for this purpose. Naturally, a prelithiated surface must be sufficiently stable (at least in a dry room), such that the fabrication process can be significantly simplified.…”

Simplifying electrode design for lithium-ion rechargeable cells

“…Systematic prelithiation steps are done electrochemically to form a layer of the β-LiAl that homogeneously covers the Al foil surface and with a targeted thickness based on anticipated device capacity. [8] Alternatively, it has been shown elsewhere that simple mechanical rolling may also be similarly effective, although confirmation of the product composition is still needed. [9,10] From a macroscopic view (Figure 2c-d), the lithiated surface exhibits a greyish color while the back side of a single side electrode remains the silvery white of aluminum metal.…”