Research On Modification Of Graphene Based Lithium Sulfur Battery

Lithium-sulfur(Li-S) battery has attract much more attention due to its ultra high theoretical energy density, and sulfur is inexpensive, aboudent and environmental friendly which makes the Li-S battery becomes one of the most promising energy storage system. However, the insulating nature of sulfur and its discharge end products, the solubility of intermediates into organic electrolyte and the huge volume changes during charge/discharge process cause low capacity, poor cycle stability. The modification of Li-S battery has become the research frontier of current energy storage field. In this thesis, modification of graphene-wrapped sulfur composite, separator modification and fabrication of new current-collector-free configuration of Li-S batteries electrode have been done to address above challenges. The main research contents and results are listed as follows.(1) The sulfur wrapped by reduced graphene oxide(r GO) which is reduced by hydrazine or benzyl disulfide has been explored. The results show that the sulfur cathode wrapped by benzyl disulfide reduced rGO has better performance. The sulfur composite cathode wrapped by hydrazine reduced r GO exhbites an initial capacity of 443 mAh/g and retains 299 mAh/g after 100 cycles at 0.2 C. The capacity decay rate is 0.325% per cycle. The sulfur composite cathode wrapped by benzyl disulfide reduced rGO shows an initial capacity of 628 mAh/g and retains 400 mAh/g after 100 cycles at 0.2 C. The capacity decay rate is 0.36% per cycle.(2) The separator modification performed by insulative oxide coating and conductive coating has been explored. The results shows that the Li-S battery with rGO-coated separator has the best electrochemical performance. The Li-S battery with GO-coated separator has an initial capacity of 368 mAh/g and maintains 305 mAh/g after 100 cycles at 0.2 C. The capacity decay rate is 0.17% per cycle. The Li-S battery with TiO2-coated separator shows an initial capacity of 510 mAh/g and retains 385 mAh/g after 100 cycles at 0.2 C. The capacity decay rate is 0.245% per cycle. The Li-S battery with graphite-coated separator shows a high initial capacity of 1148 mAh/g and retains 694 mAh/g at 0.2 C. The capacity decay rate is 0.395% per cycle. T he Li-S battery with rGO-coated separator has an initial capacity of 1067 mAh/g and maintains 878 mAh/g after 100 cycle at 0.2 C. The capacity decay rate is 0.18% per cycle.(3) The electrochemical performance of new configuration of Li-S battery electrode which is conventional-current-collector- free has been explored. The results show that the electrode with CNT-S/separator configuration has the best performance. The electrode with r GO-S/separator configuration has an initial capacity of 799 mAh/g and retains 535 mAh/g after 100 cycle at 0.2 C. The capacity decay rate is 0.33% per cycle. The electrode with Super P-S/separator configuration shows an initial capacity of 618 mAh/g and maintains 363 mAh/g after 100 cycle at 0.2 C. The capcity decay rate is 0.41% per cycle. The electrode with CNT-S/separator configuration shows an initial capacity of 815 mAh/g and maintains 650 mAh/g after 100 cylces at 0.2 C. the capacity decay rate is 0.20% per cycle.