High volumetric capacity three-dimensionally sphere-caged secondary battery anodes

High volumetric energy density secondary batteries are important for many applications, which has led to considerable efforts to replace the low volumetric capacity graphite-based anode common to most Li-ion batteries with a higher energy density anode. Because most high capacity anode materials expand significantly during charging, such anodes must contain sufficient porosity in the discharged state to enable the expansion, yet not excess porosity, which lowers the overall energy density. Here, we present a high volumetric capacity anode consisting of a three-dimensional (3D) nanocomposite formed in only a few steps which includes both a 3D structured Sn scaffold and a hollow Sn sphere within each cavity where all the free Sn surfaces are coated with carbon. The anode exhibits a high volumetric capacity of ∼1700 mA h cm^-3 over 200 cycles at 0.5C, and a capacity greater than 1200 mA h cm^-3 at 10C. Importantly, the anode can even be formed into a commercially relevant ∼100 μm thick form. When assembled into a full cell the anode shows a good compatibility with a commercial LiMn₂O₄ cathode. In situ TEM observations confirm the electrode design accommodates the necessary volume expansion during lithiation.