基于纳米铁电体的锂硫电池正极性能调控与固硫新机制研究

There are several challenges need to be conquered for the elemental sulfur as a high-performance cathode material for lithium-sulfur batteries such as poor electronic conductivity, large volumetric change during lithiation/delithiation process, and dissolution of intermediate polysulphides. Among them, the dissolution of intermediate polysulphides and a series of related negative impacts are the crucial problems to be solved. Based on the recent progresses in ferroelectric materials and photocatalysis, as well as our previous research, we propose in this project to incorporate a ferroelectric material (BaTiO3 nanoparticle) into the BaTiO3/rGO/S composite cathode for lithium-sulfur batteries. In such a composite cathode, the BaTiO3 nanoparticle works as an absorbent to anchor soluble lithium polysulfides, due to the internal electric field originated from its spontaneous polarization. The relationship between the microstructure, ferroelectric and electrochemical performances of the BaTiO3/rGO/S composite cathode would be established in this study. Meanwhile, efforts will also be devoted to developing versatile fabrication technologies to control the structure and performance of the high-performance cathode materials. In addition, it would be of fundamental importance to understand the mechanism of how the BaTiO3 nanoparticles absorb the polysulfides and influence their dissolution and diffusion. The outcomes from this research project will provide new ideas and theoretical guidance for designing and synthesizing high-performance sulfur cathode.

单质硫存在电子电导率低、锂化前后体积变化大及中间产物多硫化物的溶解、扩散等诸多问题，特别是多硫化物的溶解与扩散及其带来的系列负面影响，是锂硫电池亟待解决的最关键问题。针对上述问题，本项目在借鉴纳米铁电材料与光催化领域最新研究进展及申请人前期研究工作的基础上，创新性地将“铁电效应”引入锂硫电池当中，利用纳米铁电材料BaTiO3自发极化产生的内建电场实现对极性多硫化物的锚定，制备具有固硫新机制的钛酸钡/还原石墨烯/硫（BaTiO3/rGO/S）复合正极材料。本项目通过材料制备工艺优化、物相与结构表征、铁电性能及电化学性能测试，揭示材料结构与铁电特性、储能特性的内在关联，实现兼具高比容量与高循环稳定性BaTiO3/rGO/S复合正极材料的可控制备；通过研究BaTiO3铁电特性对多硫化物锚定的影响规律，揭示其多硫化物锚定新机制，为高性能锂硫电池正极材料的设计合成与开发应用提供新的思路和科学依据。

针对高比能锂硫全电池面临的正极多硫化物溶解穿梭等系列问题，本项目创新性地提出多种正负极材料的设计与改性思路，包括在正极一侧利用纳米铁电体BaTiO3，小分子吡咯及单原子催化剂等增加多硫化物吸附和转化的动力学, 在负极一侧引入石墨烯，惰性α-Si3N4膜和共轭微孔聚合物等，实现了具有高能量密度、高安全性的锂硫全电池的构筑。项目研究建立结构、性能可控的正极材料制备技术，揭示材料微观结构与电化学性能间的构效关系，提出基于纳米铁电体“铁电效应”的多硫化物锚定策略，阐明一种全新的多硫化物的吸附固定机制；同时，在深入研究固硫机制和工艺探索的基础上，我们面向高比能锂硫全电池提出了一系列锂金属防护策略和锂硫专用电解液的设计准则。项目研究成果发表Advanced Materials、Advanced Energy Materials、Nano letter等SCI期刊论文15篇；申请发明专利10项，形成了具有自主知识产权的系列专利体系，部分成果支撑获得省部级奖励2项。项目的开展为高容量、长循环寿命锂硫电池正极材料的设计合成与高比能锂硫全电池开发应用提供新的思路和科学依据。