氢化反应制备轻金属硅化物的反应机理及其结构和电化学性能

Developing new-type lithium storage materials with high-capacity is one of the key techniques to further enhance the energy densities of Li-ion batteries. Si-based materials have been regarded as one of the most promising anode materials of Li-ion batteries due to their high capacity of 4200 mAh/g. However, the huge volume change during lithiation/delithiation leads to severe particle pulverization and fracture, consequently resulting in quite poor cycling stability. Alloying with other active/inactive elements is one of the effective approaches to improve the electrochemical lithium storage properties of Si-based anode materials of Li-ion batteries. However, it is rather difficult to prepare the high-purity metal silicides due to the big discrepancy between the melting points of Si and other constituent elements. To solve this problem, this project proposes a novel approach of hydrogen-driven chemical reaction (HDCR) to prepare Group IA-IIIA metal silicides. By replacing pure metals with the corresponding metal hydrides or complex hydrides, the new-type high-purity light metal silicides are able to be successfully synthesized. The mechanisms of HDCR will be revealed. The relationship between compositions, structures, morphologies and electrochemical lithium storage properties of materials will be studied. The change rules of compositions, structures and morphologies of materials during lithiation/delithiation will be elucidated. The mechanisms of electrochemical lithium storage and capacity degradation will be understood. Moreover, the lithium storage properties will be further improved by the size controlling and in-situ carbon coating. As a result, we hope that it can bottom the development of the next generation Li-ion batteries with high energy densities.

开发新型高容量储锂材料是进一步提高锂离子电池能量密度的关键技术之一。Si基材料具有高达4200 mAh/g的电化学储锂容量，被认为是最有发展前景的锂离子电池阳极材料之一，但其在嵌/脱锂过程中巨大的体积膨胀极易引起材料粉化、破裂，从而导致循环稳定性极差。合金化是改善Si基锂离子电池阳极材料性能的有效手段之一，但金属硅化物组成元素间巨大的熔点差异导致其合成困难，产物纯度较低。本项目针对这一问题，提出用金属氢化物或配位氢化物替代纯金属，通过"氢化反应"技术制备高纯度的IA-IIIA族金属硅化物，揭示"氢化反应"机理；系统研究材料的成分、结构和形貌与电化学储锂行为的关系，掌握材料在嵌/脱锂过程中的成分、结构和形貌变化规律，揭示材料的电化学储锂机理和循环容量衰退机制，并通过尺寸控制和原位碳包覆进一步改善材料的电化学储锂性能，为发展新一代高能量密度锂离子电池奠定基础。

本项目重点围绕Si合金锂离子电池负极材料的合成和表面改性开展研究工作，在二元和三元金属硅化物的氢化反应制备，材料的结构、形貌和性能的关系，以及微米Si颗粒表面改性及其作用机理等方面取得了一系列重要的研究成果。利用氢驱动的化学制备技术，成功制备了Li2Si7、Li12Si7、Mg2Si、Li2MgSi、Li5AlSi2、Li7Al3Si4等二元和三元金属硅化物，系统研究了其结构、形貌以及电化学储锂性能，揭示了其储锂机理和循环容量衰退机制；在此基础上，通过原位表面包覆，大幅度改善了Si基负极的循环稳定性。其中，通过加热摩尔比7:2的Si与LiH混合物，成功得到了Li12Si7包覆的微米颗粒Si，所得产物在CO2气氛中球磨12h后，形成了纳米晶SiC和Li2SiO3弥散强化的非晶SiOx/C包覆层，产物的弹性模量和硬度大幅度增加到了52.8/2.23 Gpa，较原始样品提高了5-6倍；在0.01-1.5V的电压窗口、100 mA/g的电流密度条件下，首次放电和充电容量分别为1824 mAh/g和1268 mAh/g，经400个循环后，可逆容量高达957 mAh/g，是商业化碳材料的2.5倍。相关技术也推广至金属氧化物负极材料的表面改性，通过在CO2气氛下球磨LiH和Fe2O3的混合物，成功在纳米晶Fe2O3(10 nm)表面共形包覆了一层1-3nm的Li2CO3层；同时，由于球磨过程重复的破碎和冷焊作用，共形包覆的Fe2O3进一步团聚为亚微米颗粒，这种共形包覆和分级结构共存的纳米晶Fe2O3在100 mA/g的放电电流密度下，400个循环后的容量保持在975 mAh/g，明显高于未包覆的纳米Fe2O3颗粒。发表论文18篇，获授权发明专利8项。相关结果对于推动Si和金属氧化物高容量负极材料的实用化具有重要的理论和实际意义。