Inorganic-organic competitive coating strategy derived uniform hollow gradient-structured ferroferric oxide-carbon nanospheres for ultra-fast and long-term lithium-ion battery.

The gradient-structure is ideal nanostructure for conversion-type anodes with drastic volume change. Here, we demonstrate an inorganic-organic competitive coating strategy for constructing gradient-structured ferroferric oxide-carbon nanospheres, in which the deposition of ferroferric oxide nanoparticles and polymerization of carbonaceous species are competitive and well controlled by the reaction thermodynamics. The synthesized gradient-structure with a uniform size of ~420 nm consists of the ferroferric oxide nanoparticles (4-8 nm) in carbon matrix, which are aggregated into the inner layer (~15 nm) with high-to-low component distribution from inside to out, and an amorphous carbon layer (~20 nm). As an anode material, the volume change of the gradient-structured ferroferric oxide-carbon nanospheres can be limited to ~22% with ~7% radial expansion, thus resulting in stable reversible specific capacities of ~750 mAh g after ultra-long cycling of 10,000 cycles under ultra-fast rate of 10 A g. This unique inorganic-organic competitive coating strategy bring inspiration for nanostructure design of functional materials in energy storage.