基于氧化还原型电解液添加剂的金属锂负极保护及高能锂硫电池的构建

Lithium-sulfur (Li-S) batteries have become one of the most attractive candidates for the next-generation of high-energy lithium batteries due to their high theoretical energy density. However, the generation of lithium dendrites on the surface of lithium anodes from uneven Li-ion deposition can increase safety risks. Additionally, the dissolution-discharge mechanism of the sulfur cathode will consume lots of electrolyte when compared with conventional commercial lithium-ions batteries. Thus, not only do the scientific problems require solving, but also the key barriers preventing the commercial implementation of Li-S batteries must be overcome. To address all these issues, a novel modification strategy based on multifunctional redox electrolyte additives is proposed in this project, and the research plan is classified as follows. 1) Study the effect of redox additives on the characteristics of the electrolyte; investigate the matching mechanisms between various additives and the selected electrolytes, as well as the compatibility between the modified electrolyte and the lithium anode, such as the formation of SEI film. 2) Study the effect of the electrolyte with redox additives on the electrochemical performance of Li-S batteries; investigate their interface reaction mechanisms via in-situ digital holographic method, and further propose a selection rule of redox electrolyte additives for Li-S batteries. 3) Investigate the electrochemical performance of soft-packed Li-S batteries with the developed novel electrolyte to fabricate high-energy and safe Li-S batteries.

锂硫电池由于其高能量密度而成为下一代高能锂电池的首选。但是锂离子的不均匀沉积会产生锂枝晶进而带来安全隐患，同时硫正极的溶解放电机制则会带来电解液用量大的问题；这些不仅是亟需解决的科学问题，也是推进锂硫电池实际应用需要克服的关键问题。针对以上问题，本项目创新性地提出了采用多功能氧化还原型电解液添加剂来解决上述问题的研究思路，具体研究内容如下：1）系统考察氧化还原型电解液添加剂对电解液基本特性的影响，研究各种添加剂和不同基底电解液的匹配机制，以及所配制电解液与金属锂负极的相容性，比如表面膜的构建；2）考察不同氧化还原型电解液添加剂对锂硫电池电化学性能的影响，并采用原位的数字全息技术探究其界面反应机制，提出氧化还原型电解液添加剂的优选原则；3）研究优选的含有氧化还原型添加剂的电解液在实际电池体系（软包装）下的综合性能，进而构建具有长寿命的高能量密度的锂硫电池，推进其实际应用。

锂硫电池由于其高能量密度一直备受关注，被认为是最接近实用化的下一代高能二次电池技术。本项目主要针对锂硫电池中金属锂负极的枝晶和粉化问题，聚焦于电解液改性的策略，并辅以三维高亲锂骨架和高比能硫基复合正极的研究，以期大幅提升锂负极的循环寿命，进而构筑高性能锂硫软包电池。具体研究内容如下：（1） 系统考察了多种电解液添加剂对金属锂负极的保护作用，阐明了其表界面反应机制，并筛选出了酞菁钴和辛基酚聚氧乙烯醚等多种高效添加剂，可以实现金属锂负极在3mAh/cm2的大充放容量下，稳定循环1800h以上；（2）制备了聚合物硫/碳纳米管复合材料，阐明了对多硫化物的限定机制以及长链硫的可逆性；系统研究了不同减水剂对硫正极分散性的影响以及对多硫化物的限定作用，在5mg/cm2的高面载量下，可呈现>6mAh/cm2的高可逆面容量；（3）设计和系统研究了一系列高亲锂三维载锂骨架的机械和电化学性能，主要包括金属/碳和金属氧化物/碳复合骨架材料，达成了厚度可控（<50微米）、低膨胀率（5.4%）和高面载量等应用指标；（4）对数字全息原位监测技术进行改进，实现了对金属锂复合负极表界面沉积行为的动态监测，并拓展应用到锌离子电池等领域。项目执行期内共发表研究论文18篇，申请专利14项，授权5项，完成了项目的预期指标。

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