Study On Novel Cathode Materials And Binders For Lithium-Sulfur Battery

The lithium-sulfur (Li-S) batteries suffer from varieties of challenges, including the poor conductivity of active material S and its discharged product (Li2S), the expansion/contraction of cathode structure during the charging and discharging, shuttle effect caused by the dissolution and diffusion of polysulfide. These difficulties have hindered their commercial applications. Herein, we carry out the following researches focusing on the cathode materials and binders of Li-S batteries:(1)Cp-S@graphene(G) composites with network core/shell structure. After grafting polyaniline(PANI) on acetylene black, then elemental sulfur deposit in situ inside the PANI network to form Cp-S composite. Two methods have been employed to prepare the shell of graphene:the one method, the Cp-S@RGO composite with reduced oxide graphene as the shell by solution method. The another method, Cp-S@G composite based on expanded graphite(EG) via mechanical stripping method. Results show that (a) Cp-S@RGO composite has an initial discharge capacity of 1103mAhg-1 and remains 722mAhg’1 after 100 cycles at the current density of 100mAg-1, its cycle performance has been greatly improved compared with Cp-S and Cp-S@GO composites, (b) 5%,10%,15%-Cp-S@G composites have been prepared with different contents of EG. XRD result indicates that more content of EG, the more layers of G exfoliated from EG, the poorer electrochemical performance.5%-Cp-S@G composite has the best cycle performance.(2) Water-soluble binders. LA132, sodium alginate (named as SA), β-cyclodextrin (named as β-CD) and PVDF are used as binders in lithium-sulfur battery. The influence of these four binders on the electrochemical performance of sulfur electrode is investigated and results reveal that SA cathode displays the best cycle performance and rate performance. It exhibits a discharge specific capacity of 757 mAhg-1 and capacity retention of 70% after 115 cycles at a current density of 100 mAg-1, much higher than those of cathodes with other binders. Similarly, SA cathode showes the best rate performance. Therefore SA is expected to become potential binder for sulfur cathode in Li-S battery.