锂硫电池导电涂层式凝胶电解质的设计构建与改性固硫机制研究

Lithium sulfur battery has been considered to be one of the most promising energy storage devices with high energy density. However, it suffers from poor cycle life, low coulombic efficiency and severe self-discharge due to the solubility of polysulfides in organic electrolyte. Herein, combining the advantages of conductive coating and gel electrolyte, we design and develop a novel gel polymer electrolyte as conductive coating on the cathode, which consists of a crosslink framework of polyacrylamide and conductive polymer, and a plasticizer based on ionic liquid capable of restraining sulfur. The project intends to take a technical route of “casting-evaporation-activation” to prepare the coated gel electrolyte controllably, and attempt to reveal the inner relationships among the electrolyte composition, structure, properties and cathode performance. Based on above researches, a coated gel electrolyte system with the ability of immobilizing sulfur effectively, stable structure and favorable electrical/ion conductivity is expected to be built, and then the overall cell performances are estimated to be improved. The project plans to master the principle and method of coordinating each component of the coated gel electrolyte and improving the compatibility among them, and build a balanced and synergistic operation system with multiple parts used for immobilizing sulfur. The project will further reveal the physically-chemically associated mechanism of fixing sulfur and interfacial reaction rule based on the coated gel electrolyte, which could be capable of providing new research ideas and design basis for developing advanced lithium sulfur battery with high specific energy and long life.

锂硫电池是一种极具发展潜力的高能量密度储能体系，但是其放电中间产物多硫化物易溶于电解质中并形成穿梭效应，导致电池循环性能差、库仑效率低、自放电率高。为此，本项目结合正极导电涂层与凝胶电解质二者的优点，设计开发一种位于硫碳复合正极表面的、基于聚丙烯酰胺/导电聚合物交联骨架和抑硫型离子液体作增塑剂的新型导电涂层式凝胶聚合物电解质。项目拟采取“流延刮涂-自然挥发-高温活化”技术路线，实现该涂层凝胶电解质的可控制备，并力求揭示其组成、结构、性质与电极储能特性之间的内在关联，掌握性能调控策略，以构筑一个固硫高效、结构稳定、电/离子双导的涂层电解质体系，综合改善锂硫电池的电化学性能。项目拟建立涂层凝胶电解质各组分的相容相适性协调机制，并构建多重固硫结构的平衡协同运作体制。项目最后阐明基于该涂层凝胶电解质的物理-化学联合固硫新机制与界面反应规律，为高比能、长寿命锂硫电池开发提供新的设计思路与理论依据。

锂硫电池是以硫-硫键的断裂/生成来实现电能与化学能相互转换的一类新型二次电池体系，具有能量密度高、原料来源丰富、对环境友好等优点，极具发展潜力，但是却存在活性物质利用率低、循环寿命短、自放电严重等一系列缺陷。究其原因，多硫化物在电解液中的溶解、扩散与穿梭是制约该电池性能及实用化进程的最核心问题。. 本项目提出设计开发一种新颖的导电凝胶电解质涂层，即在成型的硫正极表面以涂层方式构筑电/离子双导的凝胶电解质。其关键策略在于将正极导电涂层与凝胶电解质两个特色组分进行有效融合，充分发挥二者的优点，并尽可能摒弃各自缺陷，最终建立一个稳定、高效的协同改性固硫体系。项目取得的重要结果总结如下：1）聚丙烯酰胺在有机电解液中溶胀性良好，聚丙烯酸对多硫化物的化学吸附作用突出，两款功能聚合物结合使用可以有效提升硫正极反应动力学与稳定循环能力。2）利用丙烯酰胺和丙烯酸共聚物P(AM-co-AA)构筑硫正极表面的凝胶涂层，一方面限域了正极区的多硫化物，另一方面改善了正极/电解液界面的离子传输性质，因而显著提高了硫活性物质利用率和电池整体性能。3）聚环氧乙烷PEO、导电聚合物PEDOT:PSS和P(AM-co-AA)共混涂覆于硫正极表面形成的导电凝胶涂层，具有界面修饰(良好的离子传输通道和稳定的界面结构)、多硫化物吸附（物理限域和化学钳制联合作用）和氧化还原反应调控（PEDOT电活化与PSS原位催化）等多重功能，优化了多硫化物与硫化锂相互转化的整体反应进程。4）引入适中含量的离子液体作为导电凝胶涂层的增塑剂，不仅增强了溶液离子电导，而且抑制了多硫化物溶解，从而实现了更高效固硫和电池性能的进一步提升。. 本项目研究成果，有助于加深对锂硫电池工作原理与失效机制的理论认识，为高性能长寿命锂硫电池开发提供新的研究思路与设计依据，因此具备显著的创新性和重要的科学价值。