多硫聚合物复合导电碳基体的形貌控制及其锂硫电池

Lithium-sulfur batteries are among the most promising energy storage technologies owing to their high energy density (up to 2600 Wh/kg) and favorable comprehensive performance. However, lithium-sulfur batteries mainly suffer from two problems. One is the extremely low electronic conductivity of sulfur and the products of discharge, the other is the dissolution of lithium polysulfides and the shuttling effect of polysulfides. One of the most widely adopted approaches to address the two issues is the physical encapsulation of elemental sulfur within porous carbon. The high conductivity of the porous carbon and the physical adsorption between the pores and lithium polysulfides could partially overcome the two problems of lithium-sulfur batteries. Owing to the weak adsorption of the polar lithium polysulfides on the nonpolar carbon surface, this approach could not fully inhibit the dissolution of lithium polysulfides. To solve this problem, this project designs an in-situ synthesis of polysulfide polymers within the pores of porous carbon. The lithium intercalation product of polysulfide polymers provides anchoring sites for chemically binding the lithium polysulfides. This strong adsorption and the physical adsorption of the pores provide a twofold adsorption to the lithium polysulfides, which could effectively inhibit the dissolution of lithium polysulfides and improve the performances of lithium-sulfur batteries. Because the conductivity of cathode materials plays an important role in the performances of lithium-sulfur batteries and it is closely related to their morphologies, porous carbon with spherical, tubular, flaky and three-dimensional coiled morphologies will be selected as carrier for polysulfide polymers. The successful synthesis of the composites with corresponding morphologies will demonstrate that this method simplifies the morphology control of polysulfide polymers to the morphology control of porous carbon. Supported by numerous studies on the morphology control of porous carbon, this design has wide options and significant research values.

锂硫电池以高能量密度（高达2600 Wh/kg）和良好的综合性能而成为最有前景的储能技术之一。然而，锂硫电池面临两个最主要的问题：一、硫及其放电产物的高度绝缘性；二、多硫化锂的溶解及其穿梭效应。以往最常采用的方案是利用多孔碳负载硫，多孔碳的高导电性及其孔道对多硫化锂的吸附作用能有效缓解锂硫电池的上述问题。但是，非极性的多孔碳对极性的多硫化锂吸附力弱，难以完全抑制多硫化锂的溶解。针对该科学问题，本项目拟在多孔碳的孔道中原位合成多硫聚合物，利用该聚合物的嵌锂产物对多硫化锂的强吸附作用再加上多孔碳的吸附作用，可有效抑制多硫化锂的溶解并改善锂硫电池的性能。由于导电性也影响锂硫电池材料的性能，而材料的导电性与形貌有关，本项目拟选用球状、管状、片状和三维线团状的多孔碳负载多硫聚合物，合成相应形貌的复合材料，将多硫聚合物的形貌控制简化成多孔碳的形貌控制，而后者已有大量成果可供选择，具有重要的研究价值。

目前，锂硫电池面临两个最主要的问题：一、硫及其放电产物的高度绝缘性；二、多硫化锂的溶解及其穿梭效应。以往最常采用的方案是利用多孔碳负载硫，多孔碳的高导电性及其孔道对多硫化锂的吸附作用能有效缓解上述问题。但是，非极性的多孔碳与极性的多硫化锂之间的吸附能低，难以完全抑制多硫化锂的溶解。本项目引入多硫聚合物，通过多硫聚合物对多硫化锂的强吸附作用来抑制多硫化锂的溶解，项目实施分为两个方面，一方面制备和合成新形貌的碳材料，并调控碳材料的孔结构和表面极性；另一方面，在所得碳材料中原位聚合形成多硫聚合物，总体形貌依旧保持原始碳材料的形貌。.采用简便的工艺及商业化原料一步反应合成了聚合物纳米带线团，碳化后再用CO2活化转变为三维碳纳米带线团（CsCNBs），研究了CsCNBs负载单质硫和多硫聚合物的性能，进一步优化孔结构和多硫聚合物的含量，最优化的复合材料在最高15C的倍率下比容量依然高达796mAh/g。.采用KOH活化法合成了亲水CsCNBs，并研究了其在锂硫电池及超级电容器中的应用。相比CO2活化制备的CsCNBs，KOH活化制备的CsCNBs对多硫化锂展现出较强的吸附能力，即使在4C的高电流密度下，其初始比容量也高达621mAh/g，并且1000次循环的衰减率仅为0.039%每个循环。所得CsCNBs的比电容在0.5A/g的电流密度下高达327.5F/g。更进一步，采用四氟硼酸四乙基铵的乙腈溶液做电解液，组装成对称超级电容器，在功率密度为345W/kg的电流密度下其能量密度高达29.8Wh/kg。.鉴于纳米带线团具有优异可压缩性，将其包覆在SiO颗粒的表面，可有效改善SiO负极材料的循环稳定性，包覆后的样品循环100次后，比容量保持率为104%，远高于未包覆样品的36%。.上述结果证明CsCNBs在锂硫电池和硅碳负极材料方面具有较大的理论研究价值和实用价值。