阴离子-石墨嵌层化合物型高电势正极材料及其相关储能器件的研究

Graphite can reversibly intercalate many anions with a considerable capacity from nonaqueous electrolyte solutions at a high potential near 5V against lithium metal. Therefore, anion-graphite intercalation compounds are promising candidates for high potential positive electrode materials in many kinds of electric energy storage devices. Moreover, most of the anions as charge carriers are composed of multiple atoms, their storage mechanisms within graphite positive electrodes are much more complexed than those of single-atom ions involved in the common electric energy storage devices. Therefore, they are worthy of intensive study. This project aims at the investigation on the intercalation behavior of anions into graphite and the related applications in some electric energy storage devices. The electrochemical processes including the intercalation of anions from the electrolyte solution into graphite electrode (the charge transfer across the interface), the movement of anions in the bulk phases of solutions and graphite electrode, respectively, will be studied from various aspects such as molecualr design and tailoring of anions, the modifications of solvation environments, graphite structures, and ambient influences. By the combination of different powerful electrochemical in situ techniques, the storage pattern of anions inside the graphite electrode may be probed. On the other hand, some negative electrode materials capable of accommodating cations will be picked up to couple with graphite positive electrode materials. Some electric energy storage devices will be constructed and be tested for practical application. This project helps for the further understanding of charge storage mechnism of complicated ions, and widening the research field of new electric energy storage devices and related materials.

石墨可以在非水电解液中可逆插嵌多种阴离子，其电势相对于锂金属高达5V,并且具有可观的容量。所以阴离子-石墨层间化合物有望在多种储能器件中担当高电势正极材料。另外，作为电荷载体的阴离子大都由多个原子构成，其在石墨正极中的储能机制远比一般储能器件中所牵涉的单原子离子更为复杂，值得深入探究。本项目致力于探索阴离子插嵌石墨的电化学行为及其在储能器件中的应用。试图从分子设计和剪裁、溶剂化环境修饰、石墨结构调控以及外界条件影响等多个方面研究阴离子插嵌石墨电极的界面电荷转移过程，以及阴离子分别在溶液或石墨体相中的传输规律。同时通过一些有力的电化学原位表征方法的联用，深入揭示石墨电极材料存储阴离子的方式。此外，择选能高效存储阳离子的负极和电解液材料与该类正极材料匹配，组装成储能器件考察综合性能。本研究将加深对复杂结构的离子在石墨电极材料中存储机制的认识，进一步拓宽新型储能器件和材料的领域。

阴离子-石墨嵌层化合物是双离子电池中最为普遍使用的正极材料。阴离子在石墨正极中的电化学存储行为会受到多种因素的制约,进而对双离子电池的储能特性发挥重大的影响。本项目结合多种常规电化学测试和原位电化学表征，解析了电解液组分、石墨种类及构造等关键因素与阴离子在石墨电极中存储行为之间的内在关联。揭示了溶剂化和离子对效应在阴离子插嵌石墨电极过程中的支配作用。基于六氟磷酸锂-甲基乙基碳酸酯开发了有望获得实用化的二元溶剂电解液体系，并将该类电解液适配石墨正极的原因归结为甲基乙基碳酸酯溶剂和六氟磷酸根阴离子之间的优先络合及其共插嵌。首次发现阴离子在石墨电极的存储过程中，某些溶剂和阴离子的同步逆向传输现象。首次证实甲基乙基碳酸酯和碳酸乙烯酯可以协同溶剂化六氟磷酸根阴离子，共同参与插嵌石墨正极。在四氟硼酸锂-甲基乙基碳酸酯基溶液中，发现锂离子和四氟硼酸根阴离子之间强烈的离子对作用抑制了阴离子插嵌石墨正极，通过添加具有高介电常数和高给体数的溶剂或者替换较大尺寸阳离子，这一状况得以改善。另一方面，本项目提出了三种负极材料能够分别存储锂、钠和季铵盐阳离子，并和石墨电极配伍组装了新型的双离子电池。硅锂合金负极的储锂容量大，工作电势较低，整体电池的能量密度得以显著提升，通过对硅负极的预锂化处理以及控制充放电截止电压，可以兼顾长循环寿命。采用磷酸铁作为储钠负极材料，解决了锂资源有限、价格高昂的问题。活化的中间相炭微球可以存储较高容量的季铵盐阳离子，规避低电势下金属沉积所造成的安全隐患。本项目为双离子电池的发展奠定了基础。