具有高电导率和高安全性的新型锂离子电池高电压电解质研究

Lithium ion batteries are looked on as the most important power sources because of their high energy density and efficiency compared with other battery systems. However, for the electric vehicle and stationary energy storage markets, wider application of lithium ion battery technology has been impeded due to issues like safety and inadequate energy density. The conventional electrolytes composed of organic carbonates with high flammability, seriously lower the safety level of lithium ion batteries. To further increase the energy density, one general approach is to employ cathode materials with high specific capacity or high operating voltage. The conventional electrolytes decompose rapidly above 4.5 V vs. Li/Li+ which restricts their application in high-voltage lithium ion batteries. According to the analysis of current research-status on high-voltage electrolytes and the working experience of applicant in this research field, fluoroethylene carbonate (FEC) or fluorinated gamma-butyrolactone (F-GBL) with high flash point and strong ability of dissociation of lithium salt and non-flammable fluorinated linear carbonates or ethers are chosen to formulate new electrolytes with high conductivity and high safety for high-voltage lithium ion batteries in this project. By adjusting the components of solvents in electrolytes or adding the proper additives, this kind of electrolytes can support high-voltage batteries to realize a good overall performance.

由于比其他二次电池更高的能量密度和效率，锂离子电池已被视为最重要电源器件。随着锂离子电池应用领域的扩大（如电动车和固定能源存储），对电池的能量密度和安全性也提出了更高要求。传统碳酸酯电解质极易燃，严重地降低了电池的安全水平。应用高电压/高容量正极材料是提高电池能量密度重要途径，而传统碳酸酯电解质在电位超过4.5 V vs. Li/Li+时会快速氧化分解，限制了其在高电压电池中的应用。基于对高电压电解质研究现状的分析和自身前期研究积累，在本项目中，拟以高闪点、强锂盐解离能力的氟代碳酸乙烯酯（FEC）或氟代γ-丁内酯（F-GBL）与难燃或不易燃的氟代线性碳酸酯或氟代醚为溶剂，构造具有高电导率和高安全性的新型高电压电解质；并通过调节电解质溶剂组成和应用添加剂，实现高电压电池出色的综合性能。

随着锂离子电池应用领域的不断扩大，对电池的能量密度和安全性也提出了更高要求。传统碳酸酯电解液存在易燃和无法匹配高电压正极材料等问题，将严重阻碍了锂离子电池产业的发展。本项目中，基于高闪点、强锂盐解离能力的氟代碳酸乙烯酯（FEC）等溶剂与不易燃的氟代线性碳酸酯、氟代醚或氟代有机磷化物等溶剂，构造多种具有高电导率和高安全性的新型电解液，通过筛选合适添加剂帮助优化电解液/电极界面从而进一步提升电化学性能，表征各种电解液性质并分析各电解液组成对这些性质的影响；系统评估电池性能并与传统碳酸酯电解液的实验结果对比，利用各种表征手段研究电极表面电化学反应、电极表面膜性质等因素对电池性能的影响。FEC/不可燃氟代醚类安全电解液可支持5 V镍锰酸锂/石墨18650电池获得优异循环性能，室温1 C倍率下500次循环容量保持率超过93%；FEC/DMC/氟代磷腈阻燃类安全电解液的室温电导率可高于9 mS cm-1，支持4.45 V 钴酸锂/硅-石墨软包电池获得突出的循环和倍率性能，室温1 C倍率下300次循环容量保持率可达到82%，8 C倍率放电容量可达到1 C倍率放电容量59%。这些研究结果为后续探索可匹配高容量/高电压正极材料和高容量负极材料的新型安全电解液提供了重要的实验依据。