硅负极材料电化学容量自补偿功能的建构及其电化学反应结构演变机理研究

Lithium-ion battery is the most promising in the transferring and storing of clean regenerative energy for its high density energy storage. High-packed lithium ion batteries are becoming one of the most important underwater batteries, which attributes definitely to the voyage range and the smart operating system of unmanned underwater vehicle. Silicon has the highest capacity anode material of all-known anode materials and thus has received intense attention for many years, but the issues of capacity fading and poor lifetime caused by the severe volume changes (4X) during lithium insertion/extraction, which results in pulverization thus electronic disconnection of silicon, have not been addressed Furthermore, the volumetric changes can also disrupt the solid electrolyte interphase (SEI) layer resulting in dramatic lithium consumption in the electrolyte. The project proposed here is emphasizing on the designing of self-healing interface and the consructing of self-compensation mode for silicon-containing composite anode materials. The purpose of the project is to overcome the performance fading caused by volumetric effect. This proposal is for the development of silicon microstructure that enables excellent synergy effect on the mechanical/electrochemical properties and thus long life for silicon electrode. Highly interconnected SiNW network should be formed rather than the forest of isolated SiNWs to alleviate the mechanical failure. The microstructure design of the interface/surface of silicon composite anode on the molecular level with click chemistry mechanism is the key factor and route to gain the self-healing property so as to prompt the stability of SEI film. The obtaining of self-capacity compensating depends on the embedding of lithium-rich compound, which could provide lithium ions quantitatively on cycling to compensate the loss of the lithium ions trapped by defects or dangling bonds irreversibly. The purpose of the project is to explore and find the new method to improve the long-term performance of silicon-containg anode material. Furthermore, the understanding of the fundamental mechanisms for lithium insertion/extraction in/from the fabricated silicon composites and the correlation between different architecture with different microstructure and the mechanical stress-elimination of the material employed in highly moist and salty sea environment need more research. The successful implementation of the proposed research will contribute to a new area of designing advanced Si-based anodes for lithium ion batteries and getting breakthrough for commercialization. This improved lithium ion batteries with higher energy density, and higher power will be competitive in the power sources of underwater vehicles

高性能锂离子电池是水下电源的重要组成部分。锂离子电池高容量负极材料的研究对于锂离子电池的性能提升具有重大意义。硅负极材料在电化学脱嵌锂过程严重的体积膨胀与收缩是造成"死锂微区"、结构及界面不稳定的重要原因，是阻碍其性能提高的难题。课题以构筑具有容量自补偿与界面自愈性能的硅复合负极材料为基，以构建材料界面的电化学微观自修复性和容量自补偿特性为研究重点，原创性地提出基于具有锂源缓释特性的富锂化合物的植入，实现材料电化学反应中的锂源原位微补偿功能，从而建立负极活性材料的锂源电化学自补偿新途径；通过分子和介观层面的调控，使材料界面及表面具备电化学自愈合能力，解决材料电化学脱嵌锂过程中由于结构不对等产生的不稳定性，建立该类复合材料实现长效稳定的新途径；阐释所构筑的硅复合负极材料在复杂海洋环境中的电化学动力学规律，揭示其在海水环境中电池滥用条件下的安全性能，为水下电源的升级换代提供理论基础与实践先导。

锂离子电池高容量硅负极材料在电化学脱嵌锂过程中严重的体积效应是阻碍其性能提升的难点。项目以构建具有容量自补偿与自愈能力的界面为切入点，进行了一系列的探索性研究。取得的进展如下：1）构建了具有富锂过渡层的硅/铌酸（富）锂/氧化铌。以氧化物为表面与结构稳定剂，通过富锂过渡层的原位生长，达到有效传递应力，富锂补偿不可逆锂源消耗的目的。在硅与基体材料的界面处构造锂源过渡层，以构建锂离子传输的连续通道，增强氧化物基体与增强体硅活性中心的协同效应。详细研究了其微结构及过渡层对复合材料电化学脱嵌锂性能的影响。2）原创性建立了非贵金属复合催化剂非平衡VLS生长相互连接的3D硅纳米线网络结构的生长工艺。采用Cu-Al复相纳米催化层体系实现硅三维纳米或微米网络的微结构的构筑，利用相界面与主相的性能差异实现Si-Al-Cu晶核的分级，从而使得材料在催化沉积过程中实现微结构的分级，使得沉积的目标材料不同结构之间实现相互连接。3）对硅与基体材料界面构造锂源过渡层进行了深入及系统研究，建立了原位氧化物/富锂硅酸盐双壳层结构调控硅的电化学嵌脱锂的路径，对锂源补偿进行有效调控。4）设计了以构建纳米惰性位点、建立3D弹性骨架、改善离子/电子传输通道为基础的硅复合体系，通过N的掺杂使得体系传输界面得以有效增强，从而成功制备了具有稳定结构的硅/氮化炭/石墨烯多相复合材料，将硅的寿命提高到1000个循环以上。通过惰性位点调控锂离子的嵌入量，从而协调硅的体积膨胀与嵌锂能力之间的矛盾，从而提高其电化学循环性能。通过红外光谱、拉曼光谱的测定，系统分析了所制备的复合材料的键合特点，发现由于Si-C、Si-N等惰性化学键的引入，复合材料的性能较硅单体得到了极大的提高，在0.5C的倍率下，其循环寿命提高到1000循环以上。5）在海水模拟环境下，进行了补偿型硅复合材料用于锂离子电池的环境耐受性初期研究。研究结果表明，温度震荡相对于其他因素更为直接地影响锂离子电池的充放电性能。