锂氧气电池固相催化材料对放电产物结构的影响及其对液相催化充电过程的促进作用

Lithium-oxygen battery has received a lot of attention because of its ultra-high theoretic specific energy. In conventional lithium-oxygen batteries, solid state catalysts are needed to catalyze the formation/decomposition of solid discharge products during discharge/charge. However, it is hard to form good solid-solid contact between discharge product and cathode catalyst in the charge process, which causes low catalytic efficiency, high charge overpotential, serious electrolyte decomposition and poor cyclability. An effective solution to this problem is adding redox mediates in the electrolyte to catalyze the charge process via a liquid catalytic process. By doing so, the charge process doesn’t need solid-solid contact any more. Thus, the overpotential is suppressed. The efficiency of liquid phase catalysis is very much decided by the reaction rate between oxidized redox mediates and discharge product. And we noticed that this reaction rate is not only determined by the redox mediate species, but also related to the structural characterizations of the discharge product, such as its composition, crystalline, defects, morphology and spatial distribution. Effectively controlling the structure of the discharge product may be a way to raise the liquid phase catalytic efficiency significantly. Based on these knowledges, our project will systematically study the influence of discharge product structure to the liquid phase catalytic efficiency. Base on that, rational catalyst will be designed to control the structure of the discharge product, which makes it quickly oxidized by redox mediates during charge. As the result, the liquid phase catalytic efficiency will be raised, the overpotential of the lithium-oxygen battery will be lowered significantly and the cyclability will be improved.

锂氧气电池因其超高的理论比能量而广受关注。传统锂氧气电池正极的放/充电过程是靠固相催化材料催化固体放电产物的生成/分解，但充电过程中，放电产物与催化材料间很难形成良好的接触，导致催化效率低，过电位高，电解液分解严重，循环可逆性差。解决该问题的有效方法是在电解液中加入氧化还原介质，通过液相催化促进充电过程，摆脱对固固接触的依赖。液相催化的效率很大程度取决于充电过程中放电产物与氧化还原介质反应的速率，而我们意识到，这不仅与氧化还原介质的选择有关，也与放电产物的组成、晶体结构、缺陷、形貌、空间分布等结构特性密切相关，通过调控放电产物结构有可能大幅度提高液相催化的效率。基于以上认识，本项目将系统研究放电产物结构对液相催化效率的影响规律，进而通过设计催化材料调控放电产物的结构，使其在充电过程中快速地被氧化还原介质氧化，从而提高液相催化效率，大幅降低锂氧气电池的过电位，改善其循环可逆性。

锂氧气电池具有超高理论比能量，却由于放电产物是导电性不佳的固体，存在过电位高、循环可逆性差等问题。为了解决上述问题，本项目以放电产物的缺陷、形貌为纽带，研究了放电过程对放电产物结构的调控作用，进而改善放电产物导电性，降低其在后续充电过程中的氧化电位，促进液相催化的充电反应。研究成果集中在传质、传荷机理方面，不仅推动锂氧气电池相关理论发展，还促进其他电池体系技术进步，主要如下：.1..通过电子自旋共振、核磁共振、纳米探针等方法，发现放电条件对放电产物缺陷密度的影响规律，而高缺陷密度可以提升电子/离子电导率。放电产物的电子电导随放电电流的增加，会有3个数量级的提升；离子电导率相较于无缺陷过氧化锂，也高出2个数量级。.2..放电过程提高放电产物的缺陷密度可以降低充电过电位，比如定容循环中，增大放电电流，不改变充电电流，可将充电过电位降低0.8 V。.3..锂氧气电池充电过程液相催化效率受过氧化锂缺陷以及电解液的溶解能力影响。高AN电解液可以溶解更多的过氧化锂，但会氧化分解生成钝化膜，影响后续充放电。醚类电解液分解主要起始于的α-H提取反应，可通过全甲基化策略修饰抑制，将循环寿命延长3倍。.4..研发硼氧、铝氧人工SEI用于锂负极保护，可有效提升金属锂在含氧电解液中的循环稳定性，并匹配具有液相催化功能的活性电解液，协同提升能量效率、循环寿命。.5..开创超声方法检测电池内部电解液损耗以及产气相关的电化学过程，填补电池无损检测盲区；发明锂离子电池超声扫描仪，应用于华为、ATL、比亚迪、戴姆勒、通用汽车等十余家锂电池和新能源汽车企业。.6..将液相氧化还原过程放大，发明搅拌式自分层电池，具有热力学稳定的“液-液-固”架构，通过强制对流促进电池内部相间传质，循环稳定性和安全性俱佳，500次循环无任何衰减，且制造成本低廉，10秒即可完成组装，适用于大规模储能。