新型碳包覆锂化Li7Ti5O12/C负极材料的储锂机理与性能调控

The applications of lithiated anode materials which can supply Li+ to high-performance lithium-ion cells for energy storage can effectively improve safety or enhcance energy density, which make lithiated anode materials have an attractive prospect. However, the strong reduction ability of the lithiated anode materials makes them difficult to be synthesized. The applicant successfully developed a new facile method to fabricate carbon-coated lithiated Li7Ti5O12/C anode materials through solid-state reaction process using nanosized TiO as reductant and reactant. Preliminary study revealed that this lithiated anode materials had novel and unique electrochemical properties, and it was deduced that the lithiation mechanism had very close relation with occupation sites of Li+ in the lattice. Based on the above investigation results, in this project, a new type of carbon-coated lithiated Li7Ti5O12/C anode material will be fabricated by the new facile method developed by the applicant. The relationship between lithiation mechanism and Li+ occupation sites in the lattices will be systemically studied. Effects of fabrication parameters on microstructure and electrochemical properties of Li7Ti5O12/C will be investigated. In addition, the relationship between structure of the carbon layers and structural stability of Li7Ti5O12/C in air will be understood. Consequently,this new fabrication method will be further developed and optimized, and the new typy of lithiated Li7Ti5O12/C anode material with high performance and structural stability will be obtained. The results of this project are believed to make basis for developments of the high-performance lithium-ion cell for energy storage and new type of lithium-ion batteries.

可提供Li+的锂化负极材料应用于高性能锂离子储能器件可以有效提高安全性或提高能量密度，应用前景广阔。然而，锂化负极材料较强的还原性导致其制备困难。申请人研发出利用纳米TiO为还原剂和反应物通过固相反应制备碳包覆锂化Li7Ti5O12/C负极材料的新方法，并发现这种锂化负极材料的电化学性能新颖独特，推断其储锂机理与Li+的晶格占位相关。以此研究和认识为基础，本项目拟利用这种新方法制备新型Li7Ti5O12/C负极材料作为研究对象，系统研究并阐明Li+在Li7Ti5O12中的晶格占位与储锂机理的内在关联；揭示Li7Ti5O12/C的制备工艺对其结构和电化学性能的影响规律；构建碳层结构与Li7Ti5O12/C结构稳定性的构效关系。进而优化并完善这种新的制备方法，获得稳定性高且电化学性能优良的Li7Ti5O12/C锂化负极材料。本项目研究将为发展高性能锂离子储能器件及构建新体系锂离子电池奠定基础。

锂硫、锂空气电池具有高的能量密度，但其负极所采用的金属锂具有极大的安全隐患，因而研发替代锂负极的新型负极材料具有重要意义。本项目利用超细TiO2(5nm)和碳酸锂作为原料，通过原位碳热还原制备出Li4+xTi5O12（0<x<3）型钛酸锂，具有独特的电化学性能，其首次脱锂容量达到169 mAh/g （0.1C）。此外，通过镁热还原碳包覆的TiO2制备出碳包覆的TiO，以其作为反应物和还原剂，制备得到了Li1+xTi2O4负极材料，其锂离子在晶格中除了占据八面体16c位之外，还占据四面体间隙8a位。通过镁热还原的方法，得到了六角结构和立方结构的Li0.5TiO2负极材料，随着固相反应时间的延长，Li0.5TiO2由六角结构向立方结构发生了相变，且六角结构Li0.5TiO2具有更优越的储锂性能。通过固相反应制备了层状结构的Li1.20Ti0.44Cr0.36O2/C，利用X射线衍射和电化学阻抗谱重点研究了其晶体结构随着充放电循环的演化过程，即有序到无序的渐变过程。随着其晶体结构转变为无序态，电荷转移电阻增加，由此解释了循环性能的变化。. 在制备Li4+xTi5O12（0<x<3）的前驱体TiO2的过程中，本项目获得了一项突破性进展，研发出一种同时具有超高倍率性能、高容量和长寿命的超细TiO2/C复合球材料，TiO2的颗粒尺寸在1—6nm，平均尺寸3.3nm。作为锂离子电池负极材料，其在80C (45秒充电/放电)电流密度下，可逆容量仍达到理论容量的55%，600次循环后容量保持率达92%。作为钠离子电池负极材料，经过1800次循环后可逆容量仍达176 mAh/g（2C），展现出极佳的循环稳定性。对这种超细TiO2/C复合球材料的储锂/储钠机理进行了详细的分析和研究—赝电容储锂/储钠机理。赝电容所占的容量可达总储锂容量的79%，而比电容达到600 F/g，超过了文献中所报道的绝大多数电容器材料在有机电解液体系中的比电容值。. 本项目的科学意义在于（1）探索了替代应用于锂硫、锂空气电池锂负极或应用于锂离子电容器的一种新材料；（2）研发出一种通过尺寸效应导致的赝电容储锂/储钠机制使电极材料同时具备高倍率性能、比容量和长循环寿命，将锂离子电池的高能量密度和电容器的高功率密度长寿命有机结合在一起。