新型锂硫电池硫正极水基粘结剂的制备研究

Preparation and Evaluation of a New Water-Based Binder for Sulfur Cathode in Lithium–Sulfur Batteries

硫正极材料因具有较高的能量密度而广受关注,但由于其在充放电过程中体积变化大、硫穿梭效应使其容量衰退快等原因,大大限制了其实际使用。本文通过RAFT乳液聚合首次设计合成了聚(苯乙烯-b-丙烯酸正丁酯-b-苯乙烯)(Sn BAS)三嵌段共聚物作为硫电极粘结剂。通过制备粘结剂薄膜测试其在醚类电解液的溶胀性,并进行多倍率充放电、电池寿命测试,与聚苯乙烯(PS)、聚丙烯酸正丁酯(Pn BA)及商用SBR对比,发现通过调配苯乙烯/丙烯酸正丁酯(St/n BA)质量比率可获得兼具高力学强度及高电解液溶胀率的电极粘结剂。将粘结剂Sn BAS100用于制备硫电极,所得硫正极分别在0.1C、0.2C、0.5C、1C、2C、0.1C倍率充放电后,再次以0.2C倍率充放电所得放电比容量为781 m Ah×g-1,与首次充放电时的放电比容量1061 m Ah×g^(-1)相比,容量保留率为73.6%。电极继续100次循环后放电比容量为740m Ah×g^(-1),容量保留率为94.7%,每次充放电的平均容量衰退率为0.05%。结果表明,水溶性嵌段结构的SnBAS粘结剂是一种极具应用潜力的水基硫正极粘结剂。

Sulfur cathode has attracted great interest in recent years due to its high energy density. However, dramatic reduction in cathode energy density and sulfur shuttle effects during charge and discharge processes result in poor battery performance. A new water-based sulfur cathode binder, poly（styrene-b-n-butyl acrylate-b-styrene）（SnBAS） was designed and synthesized via RAFT emulsion polymerization in this study. Polymer membranes of the prepared binder were employed to study swelling ratio of the material in an ether electrolyte. The properties of the binder were compared with those of PS, Pn BA and a commercial SBR binder, and the results show that Sn BAS binders with proper St/n BA weight ratios can significantly improve battery performance. Cathodes with SnBAS have satisfactory mechanical strength and appropriate swelling ratios in the electrolyte. The sulfur cathode prepared with the binder shows capacity of 781 mAh×g^-1 at 0.2C after charge and discharge cycles at 0.1, 0.2, 0.5, 1, 2, 0.1C, which has a capacity retention rate of 73.6%. The specific capacity is 740 mAh×g^-1 after additional 100 cycles at 0.2C, which corresponds to capacity decay of 0.05% per cycle and a capacity retention rate of 94.7%. This work demonstrates that Sn BAS is a promising water-based binder for sulfur cathode of lithium–sulfur batteries.