Stable SEI Formation on Al-Si-Mn Metallic Glass Li-Ion Anode

Abstract

Alloying anodes such as silicon are of great interest for lithium-ion batteries due to their high lithium-ion storage capacities, but have only seen minimal commercial deployment due to their limited calendar life. This has been attributed to an intrinsically unstable solid electrolyte interphase (SEI) that is aggravated by mechanical failure. An amorphous structure can mitigate lithiation strains, and amorphous alloys, or metallic glasses, often exhibit exceptional fracture toughness. Additional elements can be added to metallic glasses to improve passivation. Splat quenching was utilized to prepare an amorphous Al 64 Si 25 Mn 11 Li-ion anode with a specific capacity >900 mAh/g that remains amorphous upon cycling. On this metallic glass electrode, parasitic electrolyte reduction is found to be much reduced in comparison to pure Si or Al, and comparable to that on Cu. The SEI is much thinner, more stable, and richer in fluorinated inorganic phases than the SEI formed on Si, while organic carbonate compounds such as lithium ethylene decarbonate (LiEDC) are notably absent. This study indicates that metallic glasses can become a viable new class of Li-ion anode materials with improved surface passivity. This work explores LIB anodes consisting of splat-quenched Si-based metallic glasses(17-19). These maintain Si, which can alloy with up to 3.75 Li(13,19), as the main Li-binding element, but distribute it homogeneously within an amorphous matrix. Alloying elements can be selected to maintain the amorphous structure, store more Li, or improve SEI stability. An additional consideration is that new LIB anode materials ought to have a viable large-scale synthesis route. Scalable manufacturing of amorphous alloys requires rapid solidification from the melt. Two common methods are melt spinning(20) and splat quenching(21-24), which have been used commercially in the production of amorphous Fe-Si-B based magnetic alloys(25-28), demonstrating that they can produce rapidly solidified material at scale.To facilitate freezing in the amorphous structure upon cooling, the melt should remain liquid down to as low a temperature as possible, and have a composition that does not crystallize readily. The lowest melt temperatures occur at eutectic alloy compositions, such as the Al-Si eutectic at 577°C and 12.2 at% Si(29). In this eutectic, the Al can also lithiate(30), increasing its specific capacity. The Al-Si eutectic alloy has been successfully employed as an LIB anode(31), but crystallizes and phase-separates on cooling. Addition of a third metal M impedes phase separation(16) and enables the formation of Al-Si-M metallic glasses (17,18). Prior studies on sputtered amorphous Al-Si-Mn(19) and Al-Si-Sn(13) thin films have established a region of amorphous compositions with good LIB cycling performance. Based on those studies, the Al 64 Si 25 Mn 11 composition was selected for this work. The composition was confirmed by energydispersive x-ray spectroscopy (EDX). Utilizing splat quenching, which enables cooling rates up

Understanding the Origin of the Nonpassivating Behavior of Si-Based Anodes during the Initial Cycles

“…An alternative path is to modify the electrode composition by including elements known to promote the formation of a stable SEI. As a proof of concept, we reported on the synthesis of an Al−Mn−Si-based amorphous glasses, 62 which shows a more stable SEI and lower parasitic currents than those observed on pure Si anodes.…”