锂离子电池高镍正极材料空气敏感机制原位研究及表界面多尺度修饰

The layered nickel-rich materials have been regarded as one of the most promising cathode candidate for lithium ion batteries for EVs due to the advantage of high energy density and low cost. However, they still have many difficulties in the commercialization with respect to chemical stability, especially for the air sensibility. Due to the limitation of the mechanism of air sensibility, in-situ Raman spectroscopy will be used in this proposal to study the evolution of surface chemistry of nickel-rich film during storage in air. Based on the chemical information inferred by spectroscopic features, the mechanism of the air sensibility is expected to be unraveled. Based on the mechanism, the multi-scale modification constructed by the in-situ coating of LiTi2(PO4)3-Li3PO4 and the gradient doping of Ti and the controllable synthesis will be investigated. Taking the advantage of the synergistic effect between Ti gradient doping, which is believed to can increase of Ni3+/2+, and LiTi2(PO4)3-Li3PO4 coating, the surface potential and air stability of the material will be enhanced. Ti doping can also play as electron compensator of Ni4+ at charge state, which can restrain the conversion of Ni4+/Ni2+ and then can improve the structural stability. Furthermore, Li3PO4 will consume the H2O and HF in electrolyte and the corresponding products will act as artificial SEI layer due to the similar component. The accomplishment of the project will be of great importance regarding to the study of air sensibility and multi-scale modification construction for other battery materials.

层状高镍材料因能量密度高和成本低的优点成为目前最有应用前景的锂离子动力电池正极材料，然而高镍材料面临化学稳定性不足，特别是空气敏感效应等挑战。针对目前空气敏感机理的局限，项目通过原位拉曼研究高镍薄膜材料在空气中表界面结构和成分变化，深层次揭示材料空气敏感机理。基于此，采用固相法对高镍材料进行LiTi2(PO4)3-Li3PO4原位包覆和Ti4+界面梯度掺杂的多尺度修饰来提高材料稳定性。Ti4+掺杂提高Ni3+/2+电对电势，增加材料界面电势，与防水包覆层协同增强高镍材料空气稳定性。Ti4+对充电态高镍中Ni4+进行电子补偿，抑制Ni4+/Ni2+转变；Li3PO4与电解液中HF、H2O反应，生成物附着在材料表面形成人造SEI膜；LiTi2(PO4)3抑制材料与电解液副反应；三者共同作用改善材料电化学性能。本项目材料空气敏感效应和表界面多尺度修饰的研究为其他材料表界面稳定性研究提供新思路。

层状高镍材料因能量密度高和成本低的优点，成为目前最广泛应用的锂离子动力电池正极材料，然而高镍材料面临化学稳定性不足，特别是空气敏感效应。项目通过原位拉曼揭示了新鲜高镍正极材料在空气中储存30小时过程中表界面结构和成分变化，结果表明，除了表面锂残渣LiOH/Li2O吸附水和二氧化碳外，首次发现无电子转移脱锂反应也是材料储存初期电化学性能下降的关键原因。.针对表面锂残渣吸水问题，项目提出改性水洗方式，将表面锂残渣转化为厚度为2-3nm的磷酸锂包覆层。与传统水洗材料相比，该包覆层不仅将高镍正极材料在空气中暴露7天后碳酸锂的含量从5.4%降低至2.4%，空气稳定性显著提升。此外，由于包覆层具有快离子导体、且能消耗电解液中的HF，因此，材料的10C倍率容量和100圈容量保持率较传统水洗高镍正极分别提升122.3%和25.2%，较空白高镍分别提升31.5%和14.5%。.为同时抑制高镍正极储存过程中Ni3+/Ni2+的自发转变以及表面锂残渣的吸水，本项目以高镍正极表面锂残渣为包覆层原料，成功在其表面构建LiTi2(PO4)3-Li3PO4包覆和Ti4+界面梯度掺杂的双重修饰层。Ti4+掺杂能提高Ni3+/2+电对电势，增加材料界面电势，与包覆层协同增强高镍材料空气稳定性；Ti4+对充电态高镍中Ni4+进行电子补偿，抑制Ni4+/Ni2+转变。在本项目研究中，还发现多组分包覆层构建的高密度晶界，能显著提升包覆层离子导电率，且将发现用于改善锂金属负极、石墨负极，其循环稳定性也得到答复提升。在双重修饰作用下，修饰后的高镍正极倍率性能较空白样品提升106.2%，高温和高电压循环稳定性分别提升24.6%和20.3%。.本项目所揭示的空气敏感机制和多尺度修饰技术将为高性能锂离子电池正极材料的改性提高新思路。