The Application Of Different Form Of Carbon In Li/S Batteries

At present, Lithium-ion battery is widely used and is the mostpromising clean energy source, and elemental sulfur with its hightheoretical capacity (1672mAh·g^-1) becomes one of the mostpromising cathode material. But due to the insulation and thedissolution of polysulfide in the traditional organic electrolyte whichis produced in the process of charging and discharging, its applicationis limited. This article attempts to solve the above problems throughthe composition of carbon and sulfur to improve the electricalconductivity of sulfur.The specific way is taking flake graphite as raw material, with theprocess of chemical oxidation and high-temperature treatment,expanded graphite is prepared. We characteristic the physicalproperties of the product of each stage with SEM, XRD, FT-IR.XRDtest results show that the product expanded graphite,compared tothe raw material flakes, the diffraction peak position is not changed,the graphite crystal form is not changed. The SEM images show thatthe distance between the graphite layers increased. The FT-IRresults show that the appearance of C-O functional group proves theformation of graphite oxide, in the product expanded graphiteobtained after the high temperature treatment, oxygen-containing functional group disappeared in part.By comparing mix proportion,calcination time, calcinationtemperature of sulfur and expanded graphite, we choosed the bestconditions of experiments and concluded that a mixture ratio of sulfurand expanded graphite is2:1, the calcination time is4h, thecalcination temperature is155℃, the electrochemical performanceof the composite material is best. Initial discharge capacity ofcomposite material after155℃calcinationis378.51mAh/g, after20cycles, the capacity is149.51mAh/g, the capacity retention rate is39.50%. Compared with elemental sulfur, capacity retention rateincreased by19.86%. Compared with the impedance of165℃composite and the optimum temperature composite, thetest results show that composite materials of the optimumtemperature have greatly improved the kinetics of sulfur, reducingthe impedance of the battery.We prepared rough graphite nanosheets by using differentgraphite as raw materials and composite them with sulfur, then withhot compound method, we got sulfur/graphite nanosheetscomposite materials with the different treatments. Theelectrochemical test results show, for the sulfur/graphitenanosheets composite and sulfur/flake graphite nanosheets withdifferent treatment methods, the electrochemical properties of thecomposites by ultrasonic treatment is better. The first dischargecapacity of sulfur/flake graphite nanosheets composite is398.11mAhg^-1, after20cycles, the capacity retention rate is40.61%.Compared with elemental sulfur, capacity retention rate increased by20.97%. Compared with the AC impedance of the sulfur/flake graphite nanosheets composite material after ultrasonic treatmentand the sulfur, test results show that the composite materialreduces the impedance of the battery, improves theelectrochemical kinetics of the sulfur.