锂离子电池负极中空锗纳米管电极的稳定性研究

Capacity of lithium ion battery can be improved by germanium nanowire array with large theoretical specific capacity. However, mechanical stresses induced by the volume changes during cycling result in capacity fading and poor cycling life. Hollow germanium nanotube was used to improve the cyclic stability of electrode by easing volume expansion. The effect of composition, morphology and structure of nanotube on the stability and electrochemical performance of electrode were studied, and the mechanism of improving the germanium electrode stability was revealed. On this basis, polymer nano diaphragm coated hollow germanium nanotube structure were designed to improve the structure and interface stability of germanium nanotube array electrode. The relationship between structure (morphology, thickness, glass transition temperature) and the properties (electrochemical, interfacial compatibility, stress change, charge/discharge volume evolution) were explored. Mechanism of electrode stabilization was studied by online observation of morphology ,structure and stress combined with the finite element simulation, which provided theoretical basis and design method for the design and development of lithium ion battery with high capacity and stability.

锗纳米线阵列电极具有可利用其高质量和体积比容量以及纳米线阵列结构提高电池容量的优势，然而存在由于充放电体积膨胀和纳米线结构形变引起的电极循环和结构稳定性差的缺陷。本课题组设计中空锗纳米管结构，利用中空结构缓解锗负极材料的体积膨胀，提高电极的循环稳定性，探索纳米管组成、形貌及结构与电极稳定性以及电化学性能之间的内在联系，揭示中空纳米管结构提高锗电极稳定性的作用机制。在此基础上，为提高锗纳米管阵列电极的结构与界面稳定性，设计高分子纳米隔膜包覆中空锗纳米管结构，探索高分子纳米隔膜厚度、凝聚态结构、玻璃化温度等对电极充放电过程中体积演变、应力变化、界面相容性以及电池电化学性能之间的内在联系，并通过在线观测电极体积、形貌/应力分布动态变化，结合有限元模拟计算，揭示核壳包覆结构实现电极稳定化的机理，为高容量、高稳定性锂离子电池的发展与设计提供理论依据和设计方法。

作为锂离子电池负极材料，锗纳米线阵列电极能够提高电池容量，然而存在锗锂合金化过程中体积膨胀引起的充放电循环稳定性差及纳米线本身结构稳定性差的缺陷。本项目围绕锗纳米线电极的稳定化开展实验和理论模拟研究。（1）利用模板内化学气相沉积法结合高温退火处理制备锗纳米管负极，并提出了利用柯肯达尔效应制备锗纳米管的反应机理。循环100次之后，可逆容量在800 mAhg-1，库伦效率均保持在99%以上，循环性能远高于纳米线负极，表明纳米管结构能够提高负极稳定性，并提出了纳米管结构提高负极稳定性的机理，主要与纳米管空腔结构缓解体积膨胀相关。（2）在纳米管负极基础上，利用微扩孔和原位浸润高分子溶液的方法制备了PEO包覆锗纳米管结构负极，循环100次之后，可逆容量约在1000 mAhg-1，库伦效率均保持在99%以上，循环性能进一步改进，并提出了聚合物提高纳米管稳定性的机理，主要跟聚合物提高SEI膜的稳定性和聚合物柔性缓解体积膨胀有关。（3）基于纳米球负极材料，考虑实心球与空心球两种情况，建立锂离子电池充放电过程中浓度、位移等方程，模拟了锂离子电池充放电过程中负极材料应力分布变化。结果表明空心球的径向和环向应力远低于实心球，在循环过程中应力不易达到强度极限而产生裂纹以致失效，极大地降低了负极材料充电过程中的应力破坏风险，理论证实了内部空腔结构具有更好的力学稳定性。