由於硫價格低廉、環境友好及高比電容量 (1675 mAh/g sulfur) 等優點，被視為非常有開發前景的高能量密度鋰電池正極材料。相對於一般鋰硫電池正極材料，硫-聚丙烯腈化合物 (S/PAN) 由於在充放電過程中不會有長鏈聚硫鋰化物之形成，可在一般商用鋰電池電解液 (LiPF6 in EC: DEC) 中維持良好電化學效能，然而，S/PAN仍存在許多缺點，諸如材料含硫量低導致電池整體電容量較低及在進行高速率充放電時導電度不佳等。
為改善上述問題，本研究使用溶解沉澱法將聚丙烯腈包覆在導電碳材 (super P) 上，並藉由調配聚丙烯腈/N-甲基咯烷酮 (PAN/NMP) 溶液濃度及聚丙烯腈與導電碳的比例，得到較高表面積且顆粒大小均一之聚丙烯腈-碳複合物 (rSP@PAN)。接著將硫 (S) 先溶於二硫化碳 (CS2 ) 溶劑中，利用液固混拌提升S與rSP@PAN的混合均勻度，再進行高溫熱處理，得到硫-聚丙烯腈-碳複合物(SCS2/rSP@PAN)。結果顯示，表面積提高之rSP@PAN複合物可使高分子PAN與S反應接觸面積增加，在與硫燒結後，形成之SCS2/rSP@PAN其含硫量最高可達54.5%，且其實際S/PAN化合物中的含硫量為66.5%，相較於一般商業化PAN與S之化合物僅有44.5%硫含量，明顯有所提高。此外，導電碳的摻入可彌補PAN及S的低導電度，提高在高速率充放電下的可逆電容量。實驗發現，SCS2/rSP@PAN正極材料在10 C 的充放電速率下，仍可得到511 mAh/gS的高可逆電容量，相較於一般商業化PAN與S之化合物僅能達約80 mAh/gS之電容量，顯示導電碳混摻有利於提升S/PAN化合物的電化學效能。本研究發展之硫-聚丙烯腈-碳複合物 (SCS2/rSP@PAN) 可有效提高硫含量及材料導電度，使其能量密度及功率密度皆有提高，更有潛力運用於鋰硫電池的陰極上。

Element sulfur, with the advantages of low cost, environmental friendly, and high theoretical specific capacity (1675 mAh/g) has been seen as a promising choice of high energy density cathode material for rechargeable lithium batteries. Relative to the ordinary lithium sulfur battery cathodes, the sulfur/polyacrylonitrile, without the formation of high-order lithium polysulfides during the charge/discharge process, exhibits better electrochemical performance using commercial electrolyte (LiPF6 in EC: DEC). However, several drawbacks exist in the S/PAN such as the lower sulfur content leading to the lower capacity of the battery and poor electrical conductivity of sulfur at high charge/discharge rate.
In order to overcome the problem as mentioned, in this study, dissolution/reprecipitation process was used to wrap the polyacrylonitrile onto conductive carbon (super P) and the polyacrylonitrile-carbon composite (rSP@PAN), with the higher surface area and uniform particle size, was obtained by adjusting the concentrations of the PAN/NMP solution and the ratio of PAN and the conductive carbon. Then, the sulfur was dissolved into CS2 solvent and mixed with rSP@PAN in which the uniformity can be improved via liquid-solid mixing, and the SCS2/rSP@PAN was obtained after the calcination. It was found that the contact area between PAN and S can be effectively increased by the higher surface area of rSP@PAN. After heat treatment with sulfur, the highest sulfur content of obtained SCS2/rSP@PAN reaches 54.5%, which is 66.5% sulfur content in only S/PAN compound, showing an obvious improvement in comparison to only 44.5% sulfur content in sulfur/commercial PAN compound. Moreover, the introduction of the conductive carbon can compensate the low conductivity of PAN and sulfur, which improves the reversible capacity at high charge/discharge rate. The result shows that SCS2/rSP@PAN can deliver a high reversible capacity of 511 mAh/gS at 10 C-rate, which is only 80 mAh/gS obtained in sulfur/commercial PAN compound. This reveals that the electrochemical performance can be improved by introducing the conductive carbon. In general, the sulfur content and the conductivity of material can be effectively enhanced by developed sulfur- polyacrylonitrile-carbon composite, leading a higher energy density and power density and providing a promising cathode material for lithium sulfur battery.

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