Fabrication of Ni-, Co- and NiCo-coated Graphite Microspheres by Heterogeneous Precipitation

The precursors with NiCO3.2Ni（OH）2.2H2O, Co2（OH）2CO3, or both NiCO3.2Ni（OH）2.2H2O and Co2（OH）2CO3 coated graphite microspheres were prepared respectively by the aqueous heterogeneous precipitation using nickel sulfate, cobalt nitrate, sodium carbonate, ammonium bicarbonate and graphite microspheres as the main starting materials. Subsequently, Ni-, Co- and NiCo-coated graphite microspheres were successfully obtained by thermal reduction of the as-prepared precursors at 500 ℃ for 2 h, respectively. These metal-coated graphite microspheres were characterized with a smooth, cohesive surface consisting of fine metallic particles. Optimized precipitation processing parameters of the concentration of graphite microspheres （10 g/L）, the rate of adding reactants （3 mL/min） and pH value （8.0） were determined by a trial and error method. The thermal analysis of the precursors was investigated by TG. Powders of the precursors and the resultant metal-（Ni, Co and NiCo alloy） coated graphite microspheres were characterized by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）.

Constructing mild expanded graphite microspheres by pressurized oxidation combined microwave treatment for enhanced lithium storage

The modified graphite anode materials have some prominent advantages over other anode materials in the industrial applications.A novel simple and gentle method is proposed to synthesize the mild expanded graphite microspheres(MEGMs) from flake graphite spheres through a combined modified pressurized oxidation combined with the microwave treatment.The microstructural results demonstrate that moderately expanded MEGMs with an expansion volume between 4 and 10 ml·g^(-1)exhibit a highly microporous structure with an enlarged interlayer spacing,a decreased microcrystalline size,as well as an increased number of functional groups on the surface,resulting in the increased storage sites and spaces for lithium ions and the enhanced diffusion rate of lithium ions.When used as the anode material for lithium-ion batteries,the MEGM-T75t30 obtained by oxidation treatment at 75℃ for 30 min followed by microwave irradiation for expansion displays a high reversible capacity of 446.7 mAh·g^(-1) at 100 mA·g^(-1) after 100 cycles and excellent rate performance(330 and 116 mAh·g^(-1) at 800 and 3200 mA·g^(-1),respectively).Therefore,the MEGMs prepared by this convenient and mild method show excellent electrochemical properties and good application potential.