【作者】 饶睦敏；

【导师】 李伟善；

【作者基本信息】 华南理工大学 ， 材料物理与化学， 2012， 博士

【摘要】 单质硫理论比容量高，同时具有低成本、低毒性、环境友好等优点，可望成为新一代高能二次锂电池的正极材料。但是，单质硫作为正极材料也存在着一些问题，一方面单质硫所固有的电子绝缘性使其表现为电化学钝性；另一方面硫电极的放电中间产物多硫化物具有较高的溶解性，易造成活性物质的损失，并且破坏电池体系的循环稳定性。为了解决硫电极存在的关键问题，本文以不同形态的碳材料作为单质硫的载体，通过简单的化学沉积法制备了高容量单质硫-碳复合材料，该类材料导电性良好、电化学可逆性高。通过简单的静电纺织法制备高孔隙率的聚合物电解质膜，与离子液体电解液结合制备高安全性的凝胶聚合物电解质，能够有效抑制多硫化物在电解液中的溶解，提高锂硫电池的循环稳定性。分别以活性纳米碳和碳纳米纤维为单质硫的载体，通过化学沉积法制备了具有核壳结构的纳米碳-硫复合材料。活性纳米碳-硫复合材料与碳纳米纤维导电剂组成的电极首次放电容量高达1200mAh/g，50次循环以后保持为668mAh/g。碳纳米纤维-硫复合材料与羧甲基纤维素钠（CMC）+丁苯橡胶（SBR）粘结剂制备的电极首次放电容量达1313mAh/g，60次循环后仍然保持586mAh/g。高导电性的活性纳米碳与碳纳米纤维能够提高活性物质单质硫的导电性，碳纳米纤维能够为硫电极提供网状的导电网络结构。以高温碳化法制备多孔纳米碳和多孔碳纳米纤维，分别作为纳米硫的载体，通过简单的化学沉积法制备多孔纳米碳-硫复合物和多孔碳纳米纤维-硫复合物。以多孔纳米碳-硫复合材料为正极的锂电池在0.05C（1C=1672mA/g）下100次循环后的容量仍然保持为740mAh/g以上。硫含量为42%的多孔碳纳米纤维-硫复合物在0.05C（1C=1672mA/g）下30次循环后仍然保持其85%的容量。多孔纳米碳和多孔碳纳米纤维材料不但具有良好的导电结构，并具有较强的吸附能力能有效的阻住充放电过程中产生的多硫化物在电解液中溶解，从而提高电池性能。以氧化石墨烯为单质硫的载体，通过化学沉积法制备氧化石墨烯-硫复合材料。氧化石墨烯在热处理后具有更好的电导率，并且其独特的层状结构能够为硫提供良好的导电网络，有效的抑制多硫化物在电解液中的溶解，并能够缓冲电极充放电过程引起的体积变化。电池在0.1C（1C=1672mA/g）下首次放电容量为1000mAh/g，50次循环后容量保持954mAh/g。通过静电纺织法制备高孔隙率的聚合物电解质膜，并与不同的离子液体结合制备新型凝胶聚合物电解质。聚丙烯腈/聚甲基丙烯酸酯（PAN/PMMA）聚合物膜与离子液体N-甲基-N-丁基吡咯烷二（三氟甲基）酰亚胺(PYR₁₄TFSI)结合制备新型凝胶聚合物电解质应用于在锂/磷酸铁锂（Li/LiFePO₄）电池中，电池0.2C（1C=1672mA/g）首次放电容量高达134mAh/g，50次循环后保持其92%的容量；应用于锂/硫（Li/S）电池中，与传统有机电解液相比，容量得到极大的提高。以碳纳米纤维-硫复合物为正极和PAN/PMMA聚合物膜与电解液N-甲基-N-丁基哌啶二（三氟甲基磺酰）亚胺（PPR14TFSI）:聚乙二醇二甲醚（PEGDME）（1:1）组成的凝胶聚合物电解质组成新型锂硫电池系统，电池在0.1C（1C=1672mA/g）下50次循环后容量仍能保持760mAh/g。更多还原

【Abstract】 Elemental sulfur is a promising cathode material for the next generation ofhigh-specific-energy rechargeable lithium batteries due to its high theoretical specific capacity.In addition, sulfur is also inexpensive, nontoxic and environmentally benign. However, thelithium sulfur cell still faces several serious challenges. On the one hand, the low utilizationof active material sulfur due to the high electrical resistivity of elemental sulfur. On the otherhand, the rapid capacity loss due to the high solubility （in organic solvent electrolytes） of thepolysulfide ions that are formed during the discharge/charge processes. In order to addressthese challenges, various kinds of carbon materials have been used to accommodate sulfurand to prepare carbon-sulfur composites by simple chemical deposition. These carbon-sulfurcomposites here can overcome the challenges of sulfur as a cathode for lithium battery.Moreover, novel gel polymer electrolytes based on an electrospun polymer membraneincorporating with room-temperature ionic liquid were prepared here to suppress thedissolution of the polysufides generated during the discharge process and to improve the cyclestability of lithium sulfur cell.Carbon particle and carbon nanofiber supported carbon-sulfur composites were preparedby a chemical deposition method, respectively. The carbon particle-sulfur cathode withcarbon nanofiber as conductor exhibits an initial discharge capacity of1200mAh/g, andretains668mAh/g after50cycles. The carbon nanofiber-sulfur electrode prepared withcarboxy methyl cellulose （CMC） and styrene butadiene rubber （SBR） binder exhibits aspecific capacity of up to1313mAh/g at the initial discharge and a specific capacity of586mAh/g after60cycles. The carbon particle and carbon nanofiber can improve theconductivity of sulfur, carbon nanofiber can provide a more effective electronicallyconductive network for sulfur electrode.Porous carbon and porous carbon nanofiber were prepared by the carbonization of thepolymer mixture. Sulfur is uniformly incorporated into the porous carbon and porous carbonnanofiber via a new simple chemical deposition strategy. The novel porous carbon-sulfurcomposite maintains a stable discharge capacity of more than740mAh/g after100cycles at0.05C（1C=1672mA/g）. The porous carbon nanofiber-sulfur nanocomposite with42wt%sulfur maintains85%of its initial capacity after30cycles at0.05C（1C=1672mA/g）. Theporous carbon and carbon nanofiber provide an extremely high surface area to adsorb anddisperse sulfur and ameliorate its disadvantages, such as the insulating nature of sulfur and thesolubility of polysulfide intermediates in organic solvent based electrolytes. Sulfur was immobilized to graphene oxide to prepare graphene oxide-sulfur compositeby simple chemical deposition. The graphene oxides in the heat-treated composites have goodconductivity, extremely high surface-area, and provide a robust electron transport network.The graphene oxide network also accommodates the volume change of the electrode duringthe lithium-sulfur electrochemical reaction and effectively confines any polysulfides fromdissolving. The lithium sulfur cell exhibits a specific capacity of up to1000mAh/g at theinitial discharge and a specific capacity of954mAh/g after50cycles at0.1C（1C=1672mA/g）.Poly（acrylonitrile）/poly（methyl methacrylate）（PAN/PMMA） membrane with highporosity was prepared by electrospinning technique, and novel gel polymer electrolytes basedon this fibrous PAN/PMMA activated with room temperature ionic liquid were prepared. Agel polymer electrolyte based on electrospun PAN/PMMA and ionic liquidN-methy-N-butylpyrrolidinium bis（trifluoromethanesulfonyl） imide （PYR14TFSI） wasprepared and used for lithium/lithium iron phosphate（Li/LiFePO4） and lithium/sulfur（Li/S）cells. In Li/LiFePO4cell, it exhibits an initial discharge capacity of134mAh/g, and retainsretains92%of its initial discharge capacity after50cycles. In Li/S cell, it has higherdischarge capacity than that uses the traditional liquid electrolyte. A new lithium-sulfur cellsystem exhibits excellent performance with a unique combination of carbon nanofiber-sulfurelectrode and gel polymer electrolyte based on electrospun PAN/PMMA membrane andlithium bis （trifluoromethylsulfonyl） imide in N-methyl-N-butylpiperidiniumbis（trifluoromethanesulfonyl）imide （PPR14TFSI）-poly （ethylene glycol） dimethy ether(PPR₁₄TFSI-PEGDME,1:1, by weight) electrolyte. The discharge capacity of this cellremains at760mAh/g after50cycles.更多还原