A simple, cost-effective approach is presented for producing exfoliated films of pure graphene or polymer–graphene composite with high yield, high conductivity, and processability. The approach combines supercritical CO2 with ultrasonics. Characterization by Raman spectroscopy combined with atom force field microscopy demonstrates that the graphene sheets were obtained with 24% as monolayers, 44% as bilayers, and 26% as trilayers. The layer number and lateral size of graphene sheets can be controlled by adjusting the process parameters. The yield of graphene sheets with a lateral size of about 0.5–5.0 μm is about 16.7 wt % under optimum conditions, which can be easily raised to 40–50 wt % by repeated exfoliation of the sediment that remained in the reactor. The resultant pure graphene film made by filtration has a high electrical conductivity of 2.8 × 107 S/m. The electrical conductivity of the film of polyvinyl alcohol–graphene composite is 300 S/m.

An artificial interface is successfully prepared on the surface of the layered lithium-rich cathode material Li1.2Ni0.13Mn0.54Co0.12O2 via treating it with hydrazine vapor, followed by an annealing process. The inductively coupled plasma-atomic emission spectrometry (ICP) results indicate that lithium ions are leached out from the surface of Li1.2Ni0.13Mn0.54Co0.12O2 by the hydrazine vapor. A lithium-deficiency-driven transformation from layered to spinel at the particle surface happens in the annealing process, which is proved by the results of X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). It is also found that the content of the spinel phase increases at higher annealing temperature, and an internal structural evolution from Li1-xM2O4-type spinel to M3O4-type spinel takes place simultaneously. Compared to the pristine Li1.2Ni0.13Mn0.54Co0.12O2, the surface-modified sample annealed at 300 °C delivers a larger initial discharge capacity of 295.6 mA h g(-1) with a Coulombic efficiency of 89.5% and a better rate performance (191.7 mA h g(-1) at 400 mA g(-1)).

A series of LiMn1−xFexPO4 (0 ≤ x ≤ 1) cathode materials with different Mn/Fe ratios have been successfully synthesized by a facile solvothermal method.

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Nano/micro-hierarchical-structured LiMn0.85Fe0.15PO4/C cathode materials were prepared by solvothermal synthesis combined with spray pyrolysis. XRD patterns and HRTEM images indicate that the LiMn0.85Fe0.15PO4/C are well crystallized and no impurity is observed. The as-prepared LiMn0.85Fe0.15PO4/C porous spherical (0.5-11 m) are accumulated by primary nanoparticles (~50 nm in width, 50-250 m in length). Adopting the sucrose as a carbon source, the cathode delivers a reversible discharge capacity of 171.2 mAh g-1 at 0.1C, almost exactly its theoretical capacity (~170 mAh g-1). Moreover, the composite exhibits high cycle stability without apparent capacity fading after 100 cycles at rates of 0.1C and 1C. The outstanding electrochemical performances are partially due to Fe2+ substituting and carbon coating which improve the electrical conductivity, and importantly due to its nano/micro-hierarchical structure, where primary nanoparticles exhibit high electrochemical activity, abundant mesopores benefit electrolyte penetration and hierarchical structure ensure the cycling stability.