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Zhou H.,Central South University | Zhou H.,Hunan Province Zhengyuan Energy Storage Materials and Devices Research | Li Y.,Central South University | Li J.,Central South University | And 2 more authors.
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | Year: 2013

The surface of graphite was coated with amorphous carbon in phenol-formaldehyde resin mixing in a liquid phase. Then the graphite samples were carbonizated at 1 000 °C. The carbon-coating samples were prepared by three different process including one time coating, double coating and the improvement of interface properties by adding cyclohexanol. The surface structure and morphology of samples were investigated by XRD, Raman, SEM, TEM and BET. Electrochemical behaviors of samples were studied by galvanostatic charge/discharge test. The results show that the flake particles of the spherical graphite exhibits smooth surface with the decrease of graphitization and a enhancement of isotropic. Specific surface area increases from 6.934 m2/g to 10.877 m2/g. The sample by adding cyclohexanol shows the best electrochemical property with lower irreversible capacity from 98.0 mA·h/g to 37.3 mA·h/g, higher coulomb efficiency from 73.2% to 90.2%, and the specific capacity keeping at 98.7% after 50 cycles with charging and discharging in 0.2C. Source


Zhou H.,Central South University | Zhou H.,Hunan Province Zhengyuan Energy Storage Materials and Devices Research | Geng W.,Central South University | Li J.,Central South University | And 4 more authors.
Cailiao Yanjiu Xuebao/Chinese Journal of Materials Research | Year: 2014

The compatibility of lithium difluoro(oxalato)borate (LiODFB) electrolyte with LiNi0.5Mn1.5O4 as high-voltage cathode material was investigated by cyclic voltammetry, charge-discharge test and AC impedance. The results show that the LiNi0.5Mn1.5O4/Li half cells with LiODFB or LiPF6 as electrolyte all have simple REDOX peak at 25℃ and 60℃, and the battery has an excellent reversibility. The battery with LiODFB has better cycle performance than that with LiPF6 at 25℃ and 60℃. Their 0.5C initial discharge specific capacities at 25℃ are 126.3 mAh∙g-1 and 131.6 mAh∙g-1, and the capacity retention ratios by the 100th cycle are 97.1% and 94.7% respectively. The 0.5 C initial discharge specific capacities at 60℃ are 132.6 mAh·g-1 and 129.1 mAh·g-1, and capacity retention ratios by the 100th cycle are 94.1% and 81.7% respectively. AC impedance plots also show that the battery with LiODFB has a lower chargetransfer resistance than that with LiPF6 at 60℃, indicating that the battery with LiODFB has excellent cyclic performance at high temperature. © Copyright. Source

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