Air-stable and freestanding lithium alloy/graphene foil as an alternative to lithium metal anodes

Developing high-capacity anodes is a must to improve the energy density of lithium batteries for electric vehicle applications. Alloy anodes are one promising option, but without pre-stored lithium, the overall energy density is limited by the low-capacity lithium metal oxide cathodes. Recently, lithium metal has been revived as a high-capacity anode, but faces several challenges owing to its high reactivity and uncontrolled dendrite growth. Here, we show a series of Li-containing foils inheriting the desirable properties of alloy anodes and pure metal anodes. They consist of densely packed Li x M (M = Si, Sn, or Al) nanoparticles encapsulated by large graphene sheets. With the protection of graphene sheets, the large and freestanding Li x M/graphene foils are stable in different air conditions. With fully expanded Li x Si confined in the highly conductive and chemically stable graphene matrix, this Li x Si/graphene foil maintains a stable structure and cyclability in half cells (400 cycles with 98% capacity retention). This foil is also paired with high-capacity Li-free V 2 O 5 and sulfur cathodes to achieve stable full-cell cycling. Lithium alloy nanoparticles are encased inside few-layer graphene to yield a chemically stable, high-capacity anode with promising performance in a full-cell configuration.