Pengjian Zuo

Nanosized core/shell silicon@carbon anode material for lithium ion batteries with polyvinylidene fluoride as carbon source

A nanosized anode material for lithium ion batteries with silicon as core and amorphous carbon as shell was synthesized by dispersing nanosized silicon in polyvinylidene fluoride solution and a subsequent pyrolysis process. The amorphous nature of the carbon in the composite was detected by X-ray diffraction and Raman spectroscopy. The core/shell structure was further identified by transmission electron microscopy. High reversible capacity and acceptable rate capability were exhibited compared with pristine silicon. The reversible capacity of the silicon@carbon nanocomposite at 50 mA g−1 after 30 cycles is 1290 mAh g−1 with a capacity retention of 97%. A stable reversible capacity of 450 mAh g−1 was delivered even at 1000 mA g−1. These improvements are attributed to the amorphous carbon shell, which suppresses the agglomeration of nanosized silicon, reduces the cell impedance, buffers the volume changes and stabilizes the electrode structure during charge/discharge cycles.

Effects of carbon on the structure and electrochemical performance of Li2FeSiO4 cathode materials for lithium-ion batteries

A Li2FeSiO4/C composite cathode material was prepared by a solid-state method with sucrose as a carbon source. The effect of carbon on the structure and electrochemical performance of Li2FeSiO4/C cathode materials for lithium-ion batteries was investigated. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests and electrochemical impedance spectroscopy (EIS). SEM images show that the obtained Li2FeSiO4/C materials consist of partially agglomerated nanoparticles with an average particle size of 100 nm. TEM images confirm that the carbon layer formed on the surface of Li2FeSiO4/C particles enhances the electronic conductivity and inhibits the agglomeration of the active particles during the annealing process. The electrochemical measurement results reveal that the Li2FeSiO4/C composite with 7.5 wt% carbon shows a good electrochemical performance with an initial discharge capacity of 141 mA h g−1 at 0.1 C. After 50 cycles, the discharge capacity of the Li2FeSiO4/C composite remains 94.2% of the initial capacity at a discharge rate of 0.5 C.

Effects of VC-LiBOB binary additives on SEI formation in ionic liquid–organic composite electrolyte

A safe electrolyte based on an ionic liquid–organic composite with binary additives was prepared. The stable solid electrolyte interphase (SEI) forms on the surface of a carbon anode by addition of vinylene carbonate (VC) and lithium bis(oxalato) borate (LiBOB) binary additives in ionic liquid–organic electrolyte mixture. The stable SEI effectively prevents the co-intercalation of PP13+ cations, thus leading to an obvious improvement in the performance of the cell.

Improved electrochemical performance of nano-crystalline Li2FeSiO4/C cathode material prepared by the optimization of sintering temperature

Li2FeSiO4/C cathode materials have been prepared using the conventional solid-state method by varying the sintering temperature (650xa0°C, 700xa0°C and 750xa0°C), and the structure and electrochemical performance of Li2FeSiO4/C materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, respectively. The results show that Li2FeSiO4 nano-crystals with a diameter of about 6–8xa0nm are inbedded in the amorphous carbon, and the Li2FeSiO4/C material obtained at 700xa0°C exhibits an initial discharge capacity of 195xa0mAu2009h g−1 at 1/16 C in the potential range of 1.5–4.8xa0V. The excellent electrochemical performance of Li2FeSiO4/C attributes to the improvement of conductivity and reduction of impurity by the optimization of the sintering temperature.