钠离子电池空位调制阴离子氧化还原的P2型层状正极材料

Sodium-ion batteries (SIBs) are considered as the most promising alternative to lithium-ion batteries, but the performance of SIBs is restricted by cathode materials. The capacity of traditional cathode materials is limited, due to that their charge compensation is contributed from transition metals. Recent research found that anion could also contribute to charge compensation, supplying extra capacity for cathode materials. Until now, only several special oxygen coordination can trigger oxygen redox, such as Na-O-Li and Na-O-Mg. Developing new structure and coordination to enrich the cathode systems with oxygen redox has important scientific and practical significance. This project will try to introduce vacancy into the transition metal layers in P2-type layered cathodes. The Na-O-□ configuration will be constructed in this structure, thereby activating the redox reaction activity of O, and inducing the valence change of O during charge and discharge. By using various characterization methods such as synchrotron light source and electron microscope, the mechanism for the generation of transition metal vacancy will be studied in depth. The influence of different vacancy concentration on anion redox will be explored. The control factors of transition metal vacancy to trigger anion redox will be investigated. The results will provide new ideas and theoretical basis for the development of high capacity cathode materials for SIBs, which have important scientific significance and application value.

钠离子电池是有望替代锂离子电池的最具潜力的电池体系，而其性能主要受限于正极材料。传统的钠离子电池正极材料利用过渡金属进行电荷补偿，限制了其理论容量。近年来的研究发现，阴离子也能够参与电荷补偿，为正极材料提供额外容量。目前能够诱发阴离子变价的构型有Na-O-Li和Na-O-Mg，寻找新的结构和构型来丰富钠离子电池阴离子变价正极体系具有重要的科学价值和现实意义。本项目拟通过在钠离子电池P2型层状正极材料中的过渡金属层引入空位，在其结构中构建Na-O-□新构型，从而激活阴离子O的氧化还原反应活性，诱发O的变价。通过同步辐射光源和电子显微镜等多种表征手段，深入研究过渡金属空位产生机理，探索不同空位浓度对阴离子电荷补偿的影响，阐明过渡金属空位激发阴离子氧化还原的控制因素和机理。研究成果能够为开发高容量钠离子电池正极材料提供新的思路和理论依据，对开发新型高性能钠离子电池具有重要的科学意义和应用价值。

阴离子氧化还原反应可以极大提高二次电池的可逆容量，提升能量和功率密度。本项目拟通过在钠离子电池P2型层状正极材料中的引入本征过渡金属空位，构建Na-O-□新构型，从而激活阴离子O的氧化还原反应活性，诱发O的变价。通过同步辐射光源和电子显微镜等多种表征手段，实验结果结合理论计算，深入研究过渡金属空位产生机理，探索不同过渡金属空位浓度及空位位置对氧的变价提供电荷补偿的影响。利用原位X射线衍射和原位X射线吸收谱技术研究本征过渡金属空位影响储钠的结构变化和电荷补偿机理，利用非原位X射线吸收谱研究氧K边的变化，阐明过渡金属空位激发阴离子氧化还原的控制因素和机理。研究发现过渡金属空位可以通过固相合成法原位合成，本征过渡金属空位有利于提高空位附近氧的电荷密度，使得氧上具有较多的孤电子，有利于激发氧的氧化还原的活性，提高氧的氧化还原的容量和可逆性。本项目合成了过渡金属空浓度可调的Na0.7Mg0.2[Fe0.2Mn0.6□0.2]O2，不同过渡金属空位占据位点Na0.66Mn0.66-xMg0.33-y□x+yO2钠离子电池正极材料。Na0.7Mg0.2[Fe0.2Mn0.6□0.2]O2作为钠离子电池正极材料具有145 mAh g-1的可逆容量，空位周围未成键O 2p轨道上的孤对电子具有较高的能量，能够优先参与电荷补偿，发生可逆的氧变价，提供了除过渡金属变价外的可逆容量。而Na0.66Mn0.6Mg0.33□0.07O2具有190 mAh g-1可逆容量，只有占据Mn位点的空位可以提高其周围未成键氧2p轨道上的孤对电子，而位于Mg位点的空位则不会。本项目的实施为为开发阴离子氧化还原反应的高容量二次电池电池正极材料提供新的思路和理论依据，对开发新型高性能钠离子电池具有重要的科学意义和应用价值。