The use of new three-dimensional (3D) porous graphene-metal oxide composite microspheres as an anode material for Li-ion batteries (LIBs) is first introduced here. 3D graphene microspheres are aggregates of individual hollow graphene nanospheres composed of graphene sheets. Metal oxide nanocrystals are uniformly distributed over the graphene surface of the microspheres. The 3D porous graphene-SnO₂ microspheres are selected as the first target material for investigation because of their superior electrochemical properties. The 3D porous graphene-SnO₂ and graphene microspheres and bare SnO₂ powders deliver discharge capacities of 1, 009, 196, and 52 mAh·g^-1, respectively, after 500 cycles at a current density of 2 A·g^-1. The 3D porous graphene-SnO₂ microspheres exhibit uniquely low charge transfer resistances and high Li-ion diffusivities before and after cycling.

In this study, for the first time, polymeric precursors have been used in the preparation of yolk-shell powders using a large-scale spray drying process. An esterification reaction between the carboxyl group of citric acid and the hydroxyl group of ethylene glycol inside the droplet produced organic polymers during the drying process of the droplet. During the spray drying process, the polymeric precursors enabled the formation of multi-shell cobalt oxide yolk-shell powders with superior electrochemical properties. The maximum number of shells of the particles in the yolk-shell powders post-treated at 300, 400, and 500 ℃ were six, five, and four, respectively. The initial discharge capacities of the cobalt oxide yolk-shell powders post-treated at 300, 400, and 500 ℃ were 1, 188, 1, 331, and 1, 110 mAh·g^-1, and their initial charge capacities were 868, 1, 005, and 798 mAh·g^-1, respectively. The discharge capacities of the powders post-treated at 300, 400, and 500 ℃ after 100 cycles were 815, 958, and 670 mAh·g^-1, respectively, and their corresponding capacity retentions measured after the first cycles were 92%, 93%, and 82%, respectively. The pure phase Co₃O₄ yolk-shell powders post-treated at 400 ℃ had low charge transfer resistance and high lithium-ion diffusion rate.