具备聚硫离子多重锚定和三维锂离子传输网络的锂硫电池技术研究

Li-S battery is one of Li-ion batteries with very high capacity. Its gravimetric energy density reaches 2500 Wh/kg that is 3-5 times compared with commericialized Li-ion batteries. Li-S battery is one of most potential power batteries for electric vehicles. However, the formation of soluable lithium polysulphide in liquid elctrolyte during charging and discharging processes in Li-S battery, results in a quick cycling capacity decay. The insulation nature of sulpher leads to a poor rate discharge performance which can not meet the requirements from electric vehicles. Therefore, depression of lithium polysulphide dissolution, and conductivity improvement of sulpher electrode are the critical issues in the development of Li-S battery technology. This project aims at lithium polysulphide anchoring site construction on modified porous carbon surfaces to depress lithium polysulphide dissolution. The in-situ characterizations via electric microscope and XRD is applied to analyze the lithium polysulphide appearance and disapearance during charging and discharging to elucidate the type, composition and structure of the anchoring sites for understanding the sulpher capature mechanism at the anchoring sites. The porous carbon functions as an electron distributor in the sulpher electrode material. Li-type perfluorinated resin-sulfonic acid is used for fabricating Li-ion distributor in porous carbon and depressing lithium polyphide dissolution. Studing the lithiation and delithiation procedures, and understanding the electron and Li-ion pathways are very important to improve the rate performance of sulpher electrode. A sulpher electrode with high conductivity without lithium polysulphide dissolution will be developed through composition and structure designs and material and electrode optimization. An electrode membrane assembly will be fabricated to attempt to enhance the Li-ion conductivity further for the rate performance improvement of the Li-S battery. The core technology related to Li-S battery with high rate performance and performance stability will be developed through these research activities metioned above.

锂硫电池是一种大容量锂离子电池，其能量密度是商业化锂离子电池的3-5倍，是电动车动力电池的最佳候选之一。锂硫电池在充放电过程中形成溶解于电解液的聚硫化锂,导致电池容量循环衰退极快。硫的绝缘性使电池的高倍率放电性能难以满足电动车的要求。因此，抑制聚硫化锂溶解和改善硫电极导电性已成为锂硫电池技术发展的关键。本项目以改性多孔碳为硫载体构筑聚硫化锂锚定中心，抑制聚硫化锂溶解。通过原位分析充放电过程中聚硫化锂的形成和消失，明确锚定位的种类、成分和结构，揭示锚定位固硫作用机理。在硫电极材料中利用多孔碳构建快速电子传输通道，利用锂离子型全氟磺酸树脂构建离子传输通道并抑制聚硫化锂溶出，剖析硫脱嵌锂过程、电子和锂离子的传输途径。设计优化硫电极材料、硫电极及其膜电极的组成与结构，构筑三维离子传输网络，强化离子传导，提高膜电极导电性和高倍率放电性能，获得具备长寿命、高能量密度和功率密度的锂硫电池核心技术。

锂硫电池是一种大容量锂离子电池，其能量密度是商业化锂离子电池的3-5倍，是电动车动力电池的最佳候选之一。锂硫电池在充放电过程中形成溶解于电解液的聚硫化锂,导致电池容量循环衰退极快。硫的绝缘性使电池的高倍率放电性能难以满足电动车的要求。因此，抑制聚硫化锂溶解和改善硫电极导电性已成为锂硫电池技术发展的关键。. 本项目以改性多孔碳为硫载体构筑了孔内聚硫化锂锚定中心，抑制聚硫化锂溶解。通过线下分析充放电过程中聚硫化锂的形成和消失，明确了C-N、C-S、Co-N对聚硫化物具有化学键合锚定作用，揭示吸附作用和微孔作用是锚定固硫的化学和物理过程，其中化吸附作用在于形成N-Li、S-Li和Co-S的键合。通过开发锂离子型全氟磺酸树脂和PBI与PVP、PEO混合树脂，得到多功能粘结剂，构建锂离子传输通道，利用其吸附聚硫离子和抑制聚硫离子穿梭的功能，有效提高了硫电极循环稳定性。剖析硫脱嵌锂过程、电子和锂离子的传输途径，首次发现硫电极在充放电循环中发生硫化物顶升（sulfide heave）现象，通过设计优化硫电极材料、硫电极、功能化隔膜及其电极的组成与结构，构筑了三维离子传输网络，强化了离子传导，有效提高膜电极导电性和高倍率放电性能，获得了具备长寿命、高能量密度和功率密度的软包锂硫电池核心技术。基于多孔碳制备工艺的改良，获得性能优异的硫电极材料和膜电极，循环寿命达到了900次。通过研制改性隔膜，硫电极（49 wt%S）5C放电容量达到了825 mAh/g，显示出优异的动力学性能。尤其是通过加压软包锂硫电池以抑制硫化物顶升，使用含70 wt.%S的多孔碳载硫材料， 载硫量为15.125 mg/cm2 的硫电极面积能量密度达到了 19.24 mWh/cm2 为市贩锂离子电池正极面积能量密度的 1.7倍，达到世界领先水平。