过渡金属硼化物纳米材料的可控合成及其在锂硫电池中的应用

Lithium-sulfur (Li-S) battery has been recognized as one of most promising next generation high gravimetric energy density storage device. However, the commercial success and development of Li-S battery is mainly limited by the large volume expansion of sulfur, and a well-known shuttle effect caused by the dissolution of intermediate lithium polysulfides during charging-discharging processes in liquid electrolyte. This project proposes to achieve the controllable synthesis of transitional metal boride nanomaterials and their composites under relative mild experimental conditions, and then load sulfur and assemble into lithium sulfur batteries of high rate and long cycling performances. Through tuing the phases, elemental ratios, specific surface areas and micro&nano structures of the borides, the optimized cycling performance are expected to be obtained. And then full lithium- sulfur cells of high are planned to be assembled combined with Pre lithium-ion silicon materials and boride materials. This project also proposes to investigate and illustrate relationship between the structure, phases, compositions and absorption and suppression mechanism of shuttle effect of lithium polysulfides through the XPS spectra, density functional calculations and synchrotron radiation near edge absorption spectra analyses. Based on these studies, we plan to try to assemble full cells. This project will study new types of borides and beyond boride based new sulfur loading systems and their structure design and preparation method, which have great importance to the theoretical development and technique support for practical use and development of high performance new Li-S battery systems.

锂硫电池是极具发展前景的下一代高能量密度储能器件，然而其充放电过程中的体积膨胀效应以及中间产物多硫化锂的溶解等问题严重制约了其实际应用。针对以上问题，本项目拟在相对温和的实验条件下实现高导电性、高稳定性过渡金属硼化物材料微纳结构的调控及其复合材料的可控合成，将其载硫后组装锂硫电池并实现高倍率性能和长循环寿命；研究硼化物的物相、元素配比、比表面积、微纳结构等对其电化学性能的影响规律，进一步实现电池性能的调控与优化; 结合光电子能谱分析、密度泛函理论及同步辐射近边X-射线吸收谱等阐明硼化物的结构和物相、组分对多硫化锂的吸附和抑制穿梭效应的机理; 在此基础上，从所得硼化物中择优与富锂化的负极材料尝试组装成全电池；除硼化物外，还拟进一步探索锂硫电池电极材料新体系。本项目拟开展的锂硫电池正极载硫体系及其结构设计和性能优化有望为新型高性能的锂硫电池的发展和实际应用提供较重要的理论依据和技术支持。

硫的理论放电比容量是1675 mAh g-1，远高于商业化的锂离子电池正极的放电比容量；因硫在地壳中的储量丰富、价格低廉、环境友好及具有较高的理论能量密度（2600 Wh kg-1，是传统锂离子二次电池理论能量密度的3-5倍）等优点使其成为极具发展前景的下一代高能量密度储能器件。然而，锂硫电池充放电过程中的体积膨胀效应以及中间产物多硫化锂穿梭效应会造成正极活性物质的损失，导致容量的持续衰退等问题严重制约了其实际应用。另外，目前锂硫电池的研究主要集中在4 mg cm-2以下的低载硫量，在高硫含量（＞70 w％）和高面积载量下多硫化物的穿梭问题会严重加剧。因此，发展更加有效的多硫化物催化剂用以调控多硫化物的反应是锂硫电池急需要解决的问题.针对以上问题，本项目相对温和的实验条件下实现了系列高导电性、高稳定性过渡金属硼化物如硼化钛、硼化锆、硼化钴、硼化镍等纳米材料微纳结构的调控及其与碳的复合材料的可控合成，将其载硫后组装锂硫电池并实现高倍率性能和长循环寿命并实现了高面载量；系统研究了所得硼化物的物相、元素配比、比表面积、微纳结构等对其电化学性能的影响规律，进一步实现了电池性能的调控与优化。结合原位电池充放电测试、光电子能谱分析和密度泛函理论，阐明了硼化物的能带结构和物相、组分对多硫化锂的本征吸附和抑制穿梭效应的机理。在此基础上，从所得硼化物中择优组装成高软包电池，并成功点亮了多组LED灯、驱动了小型风扇。本项目开展的新型锂硫电池硼化物正极载硫体系及其结构设计和性能优化有望为高性能的锂硫电池的发展和实际应用提供较重要的理论依据和技术支持。到目前为止，本项目圆满完成了预期目标；我们已在本领域期刊发表标注国家基金资助的SCI 研究论文26篇，包括发表在国际著名期刊Nano Today (2篇)， Energy Storage Materials(3篇)，Angew. Chem. Int. Ed.（1篇），ACS Energy Letters（1篇）、Chemical Society Reviews (1篇)上的高水平论文多篇；获授权国家发明专利4项、获2020年度山东省自然科学二等奖1项（排第壹位）、培养了硕士研究生3名、博士研究生3名。