新型介孔碳纤维复合纳米锗基电极材料的高性能化研究

Germanium-based electrode materials suffer large volume changes during charge-discharge process, resulting in dramatical capacity fading. To overcome this issue, several approaches have been considered, including the fabrication of mesoporous nanostructures and the coating carbon or other conductive agents on the surface of electrode materials. Therefore, it has becoming an important topic to enhance the structural and interfacial stability of germanium-based electrode materials during the Li+ insertion/extraction into/out of anode process. Using the mixture solution of sodium lignin sulfonate (LN) and polyacrylonitrile (PAN) as precursors, a series of mesoporous carbon fibers with appropriate pore sizes will be synthesized via an electrospinning route. Then, we will combine nanotechnology and composite methods to fabricate germanium-based nanocomposites with a high Li-ion storage capability using the mesoporous carbon fibers as a nano-reactor. In this study, it will be devoted to performing a systemic research on the mechanism for high dispersion of germanium-based nanostructure in mesoporous carbon fiber matrixs induced enhanced structural and interfacial stability with a long cycle lifetime. Simultaneously, various characterizations and electrochemical measurements will be performed to investigate the key factors for determining the structure and interface stability. The fundamental mechanisms will be explained by applying in-situ X-ray diffraction, electrochemical impedance spectra and so on. We wish this project can give rise to interesting and useful results to academic communities involved in the lithium ion batteries (LIBs), and a novel approach will be established to improve the long cycle lifetime of germanium-based electrode materials for LIBs by the utilization of mesoporous carbon fibers.

针对锗基电极材料在充放电过程中巨大的体积变化导致其锂电池性能难以提升的难题，拟开展介孔碳纤维复合纳米锗基电极材料的研制，利用其特殊结构(如介孔结构、壳核结构)的限域作用，以改善其电化学性能及稳定性。基于静电纺丝的技术，以木质素磺酸钠(LN)和聚丙烯腈(PAN)为前躯体制备具有高比表面积和合适孔径的介孔碳纤维，并作为纳米反应器用于合成新型纳米结构锗基复合电极材料。同时，研究影响锗基复合材料结构与表界面稳定性的关键因素，揭示这些材料在锂电池应用中热力学活性和动力学稳定性的协调作用及其与电化学性能之间的内在关系，为研制出高性能的介孔碳纤维纳米锗基复合电极材料提供理论基础。

锗基合金型材料因具有高的理论比容量而有望成为动力电池负极材料的优良选择。但是锗基电极材料在充放电过程中巨大的体积膨胀和较低的电导率成为限制这类材料实际应用的关键因素。针对锗基电极材料的上述问题，拟开展介孔碳/多级孔碳纤维复合纳米锗基电极材料的研制，利用其特殊结构(如介孔结构、壳核结构)的限域作用，以改善其储锂/钠性能及循环稳定性。分别从介孔碳纤维的孔结构调控（微孔-介孔结构即多级孔结构、孔径>10 nm的介孔结构）、异质原子掺杂改性介孔碳(氮、硫共掺杂的有序介孔碳)和介孔碳的孔道结构(二维有序介孔碳、三维有序介孔碳)等三方面来考察介孔碳/多级孔碳纤维材料作为导电骨架和限域载体复合纳米锗基电极材料的电化学储锂/钠性能。.1.以木质素磺酸钠(LN)作为绿色造孔剂，静电纺丝法制得孔径可调的(介孔孔径>10 nm)的介孔碳纤维和多级孔碳纤维，并作为纳米反应器制备锗-介孔碳纤维纳米复合物，作为锂电池负极材料时有效缓解了电化学储锂过程中材料的体积变化，确保了电极材料的稳定性。.2. 氮、硫共掺杂改性的有序介孔碳(OMC-N-S)，三维双连续孔道结构的介孔碳作为导电框架和限域载体，都可有效缓冲电极材料的体积膨胀，显著提升锗基材料性能。.3.以二维有序介孔碳和气相沉积碳层做为双空间碳源，包覆制得CMK/Ge-C复合物，表现出极其优异的储钠倍率性能。.通过系统研究，揭示了介孔碳/多级孔碳纤维孔道结构影响纳米锗基电极材料在储锂过程中结构演变的作用机制；阐释了介孔碳/多级孔碳纤维框架和无定型碳层协同限域纳米锗基电极材料的作用机制；揭示了介孔碳/多级孔碳纤维复合纳米锗基电极材料在储锂过程中热力学活性和动力学稳定性的协调作用；获知了木质素磺酸钠基多孔碳纤维的形成机理和造孔机制；同时，研究了影响锗基复合材料结构与表界面稳定性的关键因素，阐明了纳米锗基电极材料与电化学储锂/钠性能之间的内在关系，构建了介孔碳/多级孔碳纤维复合纳米锗基电极材料的低成本可控合成方法体系；为研制出高性能的介孔碳/多级孔碳纤维纳米锗基复合电极材料提供理论基础。