具有可反转内建电场的肖特基结石墨烯/氧化钛高倍率锂离子电池

It is known that the lithium storage performance of titania electrode at high charge-discharge rates is severely limited by poor chemical diffusion of lithium, resulting from both slow lithium ion diffusion and poor electronic conductivity. Hyriding titania with graphene has reached great improvement on electronic conductivity but very less on lithium ion diffusion. A major reason is that the band diagram of the graphene and titania is not in the favor of the liuthium diffusion. This project plans to form a Schottky contact between graphene and titania by controlling the graphene band diagram and introducing oxygen-deficiency in the titana. The direction of the Schottky heterojunction build-in electric field will point to the inner of the graphene and titania hybrids, which will facilitate the lithium ion diffusion into. The direction of the build-in electric field will reverse, based on the fact that the lithium ion will upmove the Fermi level of the graphene and dowmmove the fermi leverl of oxygen-dificiency titania after lithim insertation. The reversed build-in electric field will facilitate the lithium extraction during charging process. By this method, the graphene and titania hybrids will improve both lithium extraction and insertion kinetics and realize high-rate lithium ion battery material, because their build-in electric field will keep the same direction with the lithium ion diffusion direction all the time. The relationship between the band diagram of namomaterials, heterojunction interface with the lithium ion diffusivity will be researched. More significantly, this study will shed a new light on constructing hybrids materials for high performance lithium ion batteries.

常规的氧化钛与石墨烯复合，受到石墨烯和氧化钛能带结构的限制，电子电导率获得了极大的提高，而锂离子的扩散系数提高却非常有限，这严重地影响了材料的倍率性能。本研究拟通过贵金属掺杂降低石墨烯的费米能级，氧缺陷掺杂提高氧化钛费米能级，并构筑氧化钛包覆石墨烯的石墨烯/氧化钛肖特基异质结，形成指向材料内部的初始内建电场，促进锂离子在放电时的快速嵌入。此外，利用锂的嵌入提高石墨烯费米能级、降低具有氧缺陷的氧化钛费米能级的性质，通过对石墨烯/氧化钛初始势垒的调控，实现在锂离子完全嵌入后石墨烯与氧化钛的费米能级相对位置反转，内建电场方向也随之发生反转，促进锂离子在充电时的快速脱出。由此构建内建电场将在充电和放电均促进锂离子的扩散，实现高倍率的石墨烯/氧化钛锂离子电极材料。通过项目的研究，探索纳米材料能带结构，异质结界面性质与锂离子扩散之间的构效关系，为构建高倍率锂离子电池的复合电极材料提供新思路。

常规的氧化钛与石墨烯复合，受到石墨烯和氧化钛能带结构的限制，电子电导率获得了极大的提高，而锂离子的扩散系数提高却非常有限，这严重地影响了材料的倍率性能。本研究拟通过贵金属掺杂降低石墨烯的费米能级，氧缺陷掺杂提高氧化钛费米能级，并构筑氧化钛包覆石墨烯的石墨烯/氧化钛肖特基异质结，形成内建电场在充放电可以反转的电极材料，促进锂离子在充电时的快速脱嵌。本项目的研究率先进行了石墨烯的优化制备及其与氧化钛复合材料的可控制备研究，获得了纳米尺寸界面结合，石墨烯表面氧化钛均匀分布，尺寸在7-20 nm可控的复合物。利用Cs对石墨烯进行掺杂，调控了石墨烯的表面性能与功函数，并采用水热还原和在惰性气体下煅烧的方法来控制氧化钛的结晶及缺陷，构建的Cs-RGO复合物成功的用于锂离子电池的负极材料中进行测试，在10C的高倍率条件下充放电，性能达到108 mAh/g，相比于只经过惰性气体煅烧未进行Cs掺杂的石墨烯提高了30%，比未煅烧未进行Cs掺杂的石墨烯/氧化钛复合物提高了270%。为进一步提高电极的导电性能，我们在电极中引入了碳纳米管作为导电体并作为粘结剂，制备了自支撑的石墨烯氧化钛复合电极，制备的电极具有优良的导电性和柔韧性，所获得的电极在0.3C充放电倍率条件下达到210 mAh/g，在3C充放电倍率下达到140 mAh/g。. 本项目的开展为制备高倍率下优异性能的锂离子电池材料提供了新思路和实践基础，并对解决实际氧化钛石墨烯复合材料体系中的导电性能和倍率性能具有重要的意义。