Lithium aluminum alloy anodes in Li-ion rechargeable batteries: Past developments, recent progress, and future prospects

Abstract

Aluminum metal has long been known to function as an anode in lithium-ion batteries owing to its capacity, low potential, and effective suppression of dendrite growth. However, seemingly intrinsic degradation during cycling has made it less attractive throughout the years compared to graphitic carbon, silicon-blends, and more recently lithium metal itself. Nevertheless, with the recent unprecedented growth of the lithium-ion battery industry, this review aims to revisit aluminum as an anode material, particularly in light of important advancements in understanding the electrochemical lithium-aluminum system, as well as the growth of activity in solid-state batteries where cell designs may conveniently mitigate problems found in traditional liquid cells. Furthermore, this review culminates by highlighting several non-trivial points including: 1) Prelithiatied aluminum anodes, with β-LiAl serving as an intercalation host, can be effectively immortal, depending on formation and cycling conditions; 2) the common knowledge of aluminum having a capacity of 993 mAh g-1 is inaccurate and attributed to kinetic limitations, thus silicon and lithium should not stand alone as the only ‘high-capacity’ candidates in the roadmap for future lithium-ion cells; 3) replacement of Cu current collectors with Al-based foil anodes may simplify lithium-ion battery manufacturing and has important safety implications due to the galvanic stability of Al at high potentials vs. Li/Li+. Irrespective of the type of Li-ion device of interest, this review may be useful for those in the broader community to enhance their understanding of general alloy anode behavior, as the methodologies reported here can be extended to non-Al anodes and consequently, even to Na-ion and K-ion devices.

Impact of LiAl Nucleation Kinetics on the Microstructural Evolution of Aluminum Foil Anodes in Lithium-ion Batteries

“…The Al foil anode undergoes a dramatic structural transformation during the first lithiation (i.e., formation), in which the top surface of the Al foil is converted to LiAl via a two-phase reaction (α-Al → β-LiAl). 17,24 This reaction begins with the nucleation of LiAl on the foil surface, which under galvanostatic conditions, manifests as a large initial overpotential due to the small initial surface area of LiAl available for interfacial charge-transfer reaction (Fig. 1a).…”

“…To realize improved energy density compared to graphite anodes, LIB cells with Al foil anodes must utilize a low N/P ratio (i.e., <1.5) and a high areal capacity (i.e., >3 mAh cm −2 ), and would have any significant excess Li + inventory in the cell. 17,44,45 To obtain a realistic assessment of the cycle life of Al foil anodes, and to facilitate a comparison of the cycle life data between published literature, we suggest that cycle life testing of Al foil anodes should only be conducted in full cells. Reasonable ranges for areal capacity and cycling rate are, respectively, 1.0-3.0 mAh cm −2 and C/10 to C/3.…”

“…In the literature, the poor cycle life of Al foil anodes has mainly been attributed to pulverization and subsequent SEI resulting from the large volume change upon (de) lithiation, despite the fact that the volume change of the α-Al → β-LiAl phase transition (∼96%) is significantly lower than that of other alloying anode materials (e.g., ∼ 280% for Si), which exhibit much better cycle life. [14][15][16][17] Recently, diffusional Li trapping caused by the poor Li diffusivity of α-Al has also been shown to contribute significantly to capacity loss of Al foil anodes. The literature on Al anodes for LIBs includes materials with various form factors including powders, nanowires, and thin films, which may exhibit vastly different electrochemical behaviors compared to foils.…”

Insights into the Sodiation Kinetics of Si and Ge Anodes for Sodium-Ion Batteries

“…Amongst the notable merits of SIBs, a lighter Al foil is used to replace Cu foil as the anode current collector (Al is inactive to Na), which may increase the gravimetric energy density to some extent. 2 Different from LIBs which are usually kept at 5%-30% stage of charge, SIBs can be stored and shipped in a fully discharged state with no concern of deterioration of the cell performance since the dissolution and precipitation of Cu is avoided due to the absence of Cu current collectors. 3,4 As for the operational safety, the risk of short-circuiting resulting from dendrite growth at fast charging may be reduced because Na dendrites are observed to be mossy 5 instead of needle-like, as with Li dendrites, 6 although this has yet to be proven in the public domain.…”

“…14 However, this method is technically and financially challenging due to its multi-step nature and high energy consumption. Disordered carbon (i.e., soft carbon and hard carbon), on the other hand, is naturally more preferable for Na storage due to an increased structural disorder in the sp 2 hybridized lattice (compared to graphite). 15 In contrast to the limited Na storage of graphitizable soft carbon (e.g., ∼90 mAh•g −1 ), 16 the non-graphitizable hard carbon was found to deliver a high capacity of ∼350 mAh•g −1 and hold great promise as a SIBs anode since the early 2000s.…”