类流体技术制备碳包覆无定形多孔硅复合电极材料的界面特性及嵌锂机理研究

In order to meet the requirements of an extended range and long cycling life for new-energy vehicles, improving the energy density and cycle stability of power lithium-ion battery (LIB) further has been a research hotspot for the investigations of novel power battery and urgent demand for industrial development of electric vehicles. Silicon-based hybrid material is one of the most promising alternative anode materials for high-energy LIB, owing to its high gravimetric specific capacity. However, a rapid capacity fading always occurs during cycling process due to the large volume expansion of silicon electrode, resulting in poor electrode cyclic stability, which has greatly limited its application. In this project, we provided a new prospective on enhancing the surface and interface stability of Si/C composite. Through the solvent-free-fluids synthesis techniques, the buffer layer has been built on the surface of porous amorphous silicon. We investigated the charge-discharge behavior, interface features, and lithium storage ability of Si/C anode composite material. It is believed that this LIB has a reversible capacity more than 800 mAh/g, an initial coulomb efficiency higher than 88%, an energy density of 300 ~ 400 Wh/kg, and the reversible capacity remain above 90% after 1000 cycles. We further studied the SEI formation processes and its mechanism by acoustic emission technique for battery monitoring. According to the systematic investigation of the relationship between the structure design and surface/interface stability and electrochemical properties will promote us to develop a novel Si/C anode composite material with high initial coulomb efficiency, high specific capacity and long cycling life.

为满足新能源汽车对高续航里程数和长循环寿命的要求，进一步提升动力锂电池的能量密度和循环稳定性，已成为动力电池研究的重点方向和电动汽车产业发展的迫切需求。硅基杂化材料是锂电负极材料的未来发展方向，但其体积膨胀效应导致循环稳定性较差，极大限制了它的实际应用。本项目从加强硅碳复合材料表界面稳定性的角度出发，利用类流体制备技术在多孔无定形硅材料表面构建缓冲层，考察其作为锂电负极材料的充放电行为、界面特性及储锂性能。预期开发出可逆比容量高于800mAh/g，首次库仑效率高于88%，能量密度为300~400Wh/kg，且经1000次充放电循环后，容量保持率在90%以上的新一代锂离子动力电池。利用声发射检测技术，深入探究硅基负极材料表界面SEI膜的演化过程和作用机制，揭示硅碳复合材料的结构设计和表界面稳定性对材料电化学性能的影响规律，为发展高首效、大比容量、长循环寿命的新型硅碳负极复合材料提供新的思路。

本项目从加强硅碳复合材料表界面稳定性的角度出发，利用类流体制备技术在多孔硅材料表面构建缓冲层，考察其作为锂离子电池负极材料的充放电行为、界面特性及储锂性能。深入探究硅基负极材料表界面SEI膜的演化过程和作用机制，揭示硅碳复合材料的结构设计和表界面稳定性对材料电化学性能的影响规律，为发展高首效、大比容量、长循环寿命的新型硅基负极材料提供新的思路。电化学测试结果表明：碳化硅缓冲层有效改善了块体材料的结构稳定性及导电性能，该复合电极材料的首次可逆比容量超过1300 mAh·g-1，在200 mA·g-1的电流密度下循环200次后，比容量依然接近1000 mAh·g-1。可逆比容量达1200 mAh·g-1，且经过500次充放电循环后，容量保持率在95%以上，显示出优异的循环稳定性。此材料之所以表现出优异的电化学性能，主要归因于多孔结构为硅材料的体积效应提供了足够空间，有利于极片结构的稳定，除此之外，多孔结构还能促进更多电解液的浸润，提高了锂离子在固相材料中的传输效率，改善了电池的倍率性能。随后，我们开发了以生物质甲壳素为前驱体的氮掺杂多孔碳材料，并通过溶剂热法制备了氮掺杂多孔碳材料包覆的硅氧化物电极材料。由于其稳固的有序多孔碳结构缓冲了活性物质充放电过程中的体积膨胀，同时氮原子的掺杂为锂离子的嵌入提供了更多活性位点，该电极材料具有非常高的比容量和循环稳定性，展现了非常好的应用前景。上述研究成果对碳硅复合材料在锂离子电池负极中的应用提供了研究思路和理论基础，为开发高容量、大功率、长寿命和低成本锂离子电池具有重要的理论意义和实用价值。