微米级金属硅化物负极材料的氢驱动表面调控、储锂特性及其机理研究

Micrometre-sized silicon materials can be potentially used in high-capacity lithium ion batteries, owing to their high volumetric energy density, ease of mass production, and low costs, as compared to those of silicon nanoparticles. However, they exhibit severe pulverisation and rapid capacity fading during cycling. In order to improve the structural and interfacial stability of micrometre-sized Si anode materials, in the present project, the synergistic strategy combining composition regulation with surface functional coating is adopted and the research focuses on alloying and the SiOx-based conformal coating of micrometre-sized Si. Based on the cross-over study of hydrogen and lithium storage，a new method, associating hydrogen-driven chemical reaction with gas-solid reaction-ball-milling, is proposed to synthesize surface coated metal silicides composite. The synthetic process is explored to analyze the formation mechanism of the metal silicide and their coating layer. Meanwhile, the structural characteristics, mechanical properties, electrical conductivity and electrochemical performances of the prepared composite materials are studied systematically. Furthermore, the microstructural and phase changes of the prepared composites upon electrochemical cycling are studied to reveal their lithium storage mechanism. The influences of structural and interfacial stability and conductivity of the metal silicide composites on their cyclability and kinetics performance are investigated, and mechanisms related to the improved performances are elucidated. The study will provide new avenues and valuable references for structure design and electrochemical properties improvement of micrometre-sized Si anode materials in LIBs.

具有高振实密度、高能量密度和较低成本的微米级硅基锂离子电池负极材料相较于纳米硅具有更好的实用化前景，但微米级硅电化学循环过程中表现出更为严重的颗粒粉化和急速的容量衰退。针对微米级粉体硅负极材料的结构和界面稳定性问题，本项目拟采用成分调控和表面功能包覆协同改性策略，重点围绕微米级硅合金化与表面SiOx基保形包覆的构建开展研究工作。利用储氢储锂交叉研究提出“氢驱动化学反应”结合“气固反应球磨”制备微米级包覆结构的金属硅化物复合材料的新方法，拟探究合金化与表面包覆层的形成过程，分析形成原理和机制。同时，探明复合材料组成结构、表面包覆层以及机械性能和导电性对其储锂特性的影响规律，揭示其内在储锂机制。重点阐明复合材料结构稳定性、界面稳定性以及导电性对其电化学循环性能和动力学性能的影响，揭示复合材料电化学性能改善机理，为微米级硅负极材料的结构设计和电化学性能的改善提供新思路和有价值的参考。

具有良好实用化前景的微米级硅基锂离子电池负极材料，在电化学循环过程中表现出严重的颗粒粉化和急速的容量衰退，针对其面临的结构和界面稳定性问题，本项目进行了以下几个方面的研究：（1）设计与制备分级共形包覆和金属纳米晶强化的微米硅复合物负极材料，研究其电化学性能及性能改善机制；（2）对微米级硅复合负极材料进行传统导电剂匹配与导电机制探究，并利用低熔点金属作为粘结剂构建电极导电网络，研究其储锂动力学；（3）扩展氢驱动法在负极材料制备中的应用。. 通过氢驱动辅助气固反应结合静电自装获得具有反应性保形涂层和石墨烯封装的微米级硅分层涂层结构，Li-Si-O层和石墨烯的协同作用，使得该复合材料具有良好机械稳定性的同时，表现出优异的离子/电子传输能力。在Li-Si-O保形包覆基础上原位引入高导电Cu和Cu3Si纳米晶，进一步提升了含氧硅基复合材料的导电能力，从而获得优异的电化学循环和倍率特性，微米级硅-铜基负极材料在200 mA/g的电流密度下经500次循环后可逆比容量仍高达1096 mAh/g。在此基础上，研究发现片层石墨类导电剂，由于与微米硅颗粒粒径相当，易于分散，电导电率高，机械性能良好，可在微米硅复合负极中构建具有优良导电和应力缓冲能力的网络，实现电荷均匀有效传输的同时，保证电极的结构稳定性。采用低熔点金属Sn为金属粘结剂，通过传统的浆料涂布工艺并结合后续煅烧和热压，获得Cu3Si或Na2CO3纳米晶掺杂碳与金属Sn协同强化的Si负极，优化了硅负极的剥离强度、结构强度、电荷传输特性和界面稳定性，使得复合电极在1500 mA/g电流密度下500次循环后，其可逆容量可保持1009 mAh/g。此外，利用氢驱动预锂化制备得到具有不同氧空位浓度的铁氧化物负极材料，提高了材料的电子导电性和电化学反应活性，获得了首次库伦效率超过90%的铁氧化物负极材料。项目研究为高性能微米级硅基负极材料的结构设计与电化学性能改善，以及氢驱动制备方法的深入探索提供了理论参考与实验依据。.