杂原子掺杂氮化碳的可控制备及其锂硫电池性能研究

Lithium-sulfur batteries with high energy density and low cost are recognized as the most possibly commercialized rechargeable battery candidates, which would replace the currently used lithium-ion batteries, and the key step is to explore high performance lithium sulfur battery cathode materials. This project proposes a new sulfur host called boron doped graphitic carbon nitride (B-g-C3N4) to improve cycling performance of lithium-sulfur battery, which strongly hinders its commercial application. In this project, B-g-C3N4 with high surface area and high conductivity will be prepared, and the electrochemical performance of the B-g-C3N4 cathode will be discussed in details. Boron doping is employed to increase the limited conductivity of intrinsic carbon nitride, therefore the obtained B-g-C3N4 can be used as a sulfur cathode, in which the abundance nitrogen sites (57%) can chemically adsorb lithium polysulfides during charge-discharge. Due to the much strong interaction of chemical adsorption than physical adsorption, the “shuttle effect” aroused from the dissolution of polysulfides in the electrolyte will be blocked, resulting in the enhancement of cycling performance of lithium sulfur batteries. Through the research, it is expected to solve the problem of low cycling life of lithium-sulfur batteries. As a result, the lithium-sulfur batteries with high energy density, low cost and long cycling life will be achieved, which can significantly promote the commercialization of lithium-sulfur batteries.

锂硫电池因其能量密度高和成本低而被认为是目前最有可能商业化，并取代锂离子电池的二次电池，开发高性能锂硫电池正极材料是成功的关键。本项目针对锂硫电池循环寿命短，阻碍其商业应用的问题，旨在开发一种新型的电极材料硼掺杂的石墨相氮化碳(B-g-C3N4)，来提高锂硫电池的循环稳定性。拟开展高比表面积高导电性的石墨相氮化碳的硼掺杂可控制备和B-g-C3N4锂硫电池性能及其固硫机制等研究。项目采用硼掺杂的方法来提高石墨相氮化碳的导电性，从而充分利用石墨相氮化碳中高达57%的活性氮来化学吸附充放电过程中的多硫化锂，这种化学吸附作用远强于常规的物理吸附吸附作用，可以更好地抑制多硫化锂的溶解，从而提高锂硫电池的循环稳定性。通过本项目的研究，可以从根本上解决锂硫电池循环寿命短这一科学难题，使得所制备的锂硫电池能量密度高、价格低，循环寿命长，这对推动锂硫电池的商业化具有重要的意义。

锂硫电池因其高能量密度和低成本有望取代锂离子电池，但由于多硫化锂的穿梭效应导致锂硫电池的循环寿命短，制约其商业化发展，针对这一难题，本项目提出可控制备高比表面积和高导电性的极性硼掺杂的石墨相氮化碳(B-g-C3N4)，来抑制充放电过程中多硫化锂的穿梭效应，从而提升锂硫电池的循环稳定性。围绕上述研究内容，本项目制备了系列掺杂的氮化碳材料，探索了前驱体、掺杂源及热处理温度等硼掺杂氮化碳结构和形貌的影响规律。讨论分析了硼掺杂量对B-g-C3N4电导率及其锂硫电池性能的影响。实验和DFT计算研究表明B-g-C3N4电导率较未掺杂氮化碳有了极大的提升。而且，对B-g-C3N4改性的锂硫电池性能进行了系统研究。采用B-g-C3N4改性的锂硫电池其比容量和循环寿命等都得到极大提升，这主要是因为：(1) B-g-C3N4中大量的C-N和B-N极性键，能够牢固地化学吸附多硫化锂，抑制多硫化锂在电解液中的溶解；(2) 高电导率，加速了电子转移并提高了硫利用率；(3)高比表面积，不仅提供了丰富的活性位点吸附多硫化锂，而且使硫均匀负载在上面。本项目的研究有效解决了锂硫电池循环寿命短这一科学难题，使得所制备的锂硫电池能量密度高、价格低，循环寿命长，这对推动锂硫电池的商业化具有重要的意义。本项目总计发表SCI论文15篇，国内外学术会议论文/口头报告多次，培养博士生1名，硕士生2名。