单态氧在锂离子电池中的时间分辨光谱探测及反应动力学研究

The effort to save the modern society from energy crisis and environmental pollution has been made for years with challenges and hopes mutually emerging. Lithium ion batteries (LIBs) attract rapidly increasing research and industrial interest due to their high energy density, long cycle stability and environment-friendly compared to other alternatives. A promising class of cathode materials is lithium nickel cobalt manganese oxide (LiNixCoyMnzO2, x + y + z = 1, NCM) since the good performance in capacity. However, the phase changed will be taken place when charging NCM over 80% state of charge (SOC), accompany with the releasing of singlet oxygen (1O2), and then evolution of CO and CO2 which is harmful to the performance of LIBs and potential security problem. It is thus essential to understand the molecular mechanisms of the reaction between singlet oxygen and electrolyte. In this work, we plan to perform time-resolved phosphorescence (1270 nm) spectroscopy to detect the 1O2 in LIBs，directly. Our result will present directly the experimental evidence to reveal the existence of 1O2 in LIBs. Furthermore, we will perform time-resolved Fourier transform infrared spectroscopy (TR-FTIR) and UV-Vis transient absorption spectrum which can present directly the experimental evidence to reveal the reaction mechanism by detecting the key transient intermediates with model experiments and analyzing their kinetics to investigate the chemical oxidation mechanisms of 1O2 and electrolyte, and combined with the analysis of gassing, electrolyte, solid electrolyte interface (SEI) of the LIBs. These results will clearly provide the molecular reaction mechanism between 1O2 and electrolyte, which can provide a comprehensive and reliable reference for the LIBs research and development.

发展新能源汽车被广泛认为是有效应对能源与环境挑战的重要战略举措，锂离子电池凭借高比能、长循环、环境友好等优点而被广泛的研究和关注。高镍层状氧化物是最具商用前景的锂离子电池正极材料之一，但在高载荷态时，容易发生相变并释放寿命短、反应活性高的单态氧分子，进一步单态氧与电解液发生反应生成CO2和CO等气体，严重影响锂离子电池性能，同时有潜在安全风险。本项目拟采用时间分辨发射光谱技术实现对锂离子电池中单态氧进行直接探测；并通过动力学模型实验模拟锂离子电池中单态氧与电解液反应，采用时间分辨紫外可见光谱、时间分辨傅里叶变换红外光谱技术，结合锂离子电池循环过程中产气、电解液、固体电解质膜成分及含量的分析，多维度研究并揭示单态氧与电解液反应机理。本项目将为研究锂离子电池相关科学问题提供新方法和新思路，有望清晰给出单态氧与电解液的反应机制，为锂离子电池设计开发提供基础科学信息。

锂离子电池应用从便携式电子产品迅速扩张到电动汽车和储能，市场蓬勃发展。高比能层状氧化物正极材料提供了高比容量的优点，但热稳定性低、与电解质反应活性高、高脱锂态时结构不稳定等问题，同时氧的释放也成为近年来的另一个棘手问题，特别是高镍层状氧化物材料和富锂锰基层状氧化物材料。氧的释放不仅会加速阴极的结构破坏和容量衰退，还会引起气体的析出和与阳极的串扰效应，造成严重的安全隐患。然而，其氧释放机制和反应动力学尚不清楚，阻碍了层状氧化物正极材料的应用。本项目利用时间分辨光谱和设计带光学窗口的软包电池，我们原位检测到了锂离子电池中单态氧的在1270nm的磷光发射光谱信号，为确认锂离子电池中单态氧的存在提供直接的实验数据。进一步，对单态氧与电池电解液不同溶剂的反应动力学进行了研究，单态氧在环状碳酸乙烯酯溶剂中的衰减寿命24.1μs，说明碳酸乙烯酯与单态氧发生反应，而单态氧在链状碳酸二甲酯溶剂中的衰减寿命50.5μs，说明碳酸二甲酯对单重态氧无猝灭作用，表明链状碳酸二甲酯对单态氧比较友好。进一步研究了温度对富锂锰基层状氧化物正极材料充放电动力学研究，发现氧／锰离子本征动力学性能差使电荷转移过程具有较高的表观活化能是导致富锂锰基层状氧化物正极材料容量随温度降低而降低的主要原因，氧／锰离子参与电荷补偿反应诱导界面膜阻抗增加提升低电压区间界面锂离子传输和固相扩散的表观活化能增加也是影响极化增加的主要原因。此外，研究了高镍层状氧化物正极材料大容量、高比能锂离子电池内短路失效机制、产热及耗散机制，阐明电池内短路过程中电池内部组件变化与电池外部特征参数的关联作用，为电池安全预警设计提供数据支撑。本项目的研究方法和成果为开发高安全层状氧化物正极材料和高能量密度电池的设计提供有力支撑。在项目支持下，申请国家发明专利1项，发表论文3篇，正在整理待发表论文1篇。