亚熔盐体系高振实密度镍基多元正极材料的可控制备及高效稳定界面原位构筑

Layered Ni-rich cathode materials are considered as the most promising cathode materials for lithium ion batteries in electric vehicles (EVs) because of their advantages of high specific capacity and low cost. However, this kind of materials suffers sensitive to air and poor surface stability. Spray pyrolysis is advanced technique for short-process material preparation, but the as-obtained material has porous/hollow structure, leading to poor compactness and low tap density. This project proposes a novel synthesis of Ni-rich cathode materials by double fluidized atomization-fluidized bed pyrolysis followed by molten-assisted sintering (DFB-MS). The high-tap-density multi-metal oxides precursor is obtained by double-fluidized atomization and fluidized bed pyrolysis using chlorides sub-molten salt used as starting material. B2O3 is used as an additive to induce the grain growth and aggregation as well as react with lithium residue on the surface to form Li-ion conductive coating layer, resulting in increasing the tap density and in-situ constructing highly efficient and stable interface simultaneously. This project will establish the flow field model for the DFB process and clarify the morphological regulating principle of precursor in this process. The evolution rule of grain growth/aggregation and surface property will be cleared, and the relationship between the particle morphology, surface property and performance will be revealed. Finally, this project will provide a new thought and scientific basis for controllable preparation and interface modification of high tap density cathode materials.

层状镍基多元正极材料能量密度高、成本低，是最具发展潜力的锂离子动力电池正极材料。但该材料对空气敏感，界面稳定性差。喷雾热解是一种短流程制备材料的先进方法，但易形成多孔或空心结构，材料致密性差、振实密度低。针对这些问题，本项目提出亚熔盐体系“双流体雾化-流化床热解-助熔剂辅助烧结”新方法(DFB-MS法)制备镍基多元正极材料。氯化物亚熔盐经“双流体雾化-流化床热解(DFB)”，短流程制备高振实密度多元氧化物前驱体；以B2O3为烧结添加剂，诱导正极材料颗粒生长团聚，同时与颗粒表面锂残渣反应生成锂离子导体包覆层，同步实现镍基多元正极材料振实密度的提升与高效稳定界面的原位构筑。建立DFB过程流场模型，阐明该过程前驱体的形貌调控原理；明晰B2O3作用下正极材料晶粒生长团聚及界面性质演变规律，揭示颗粒形态及界面性质与性能之间的构效关系。本项目的开展可为高振实密度正极材料的可控制备及界面改性提供新思路。

针对高镍三元正极材料存在合成流程长、元素分布不均，界面副反应严重和晶间微裂纹等问题，开展了喷雾热解法制备前驱体、单晶形貌设计和硼元素多维度改性高镍正极材料的基础研究。阐明了氯化物体系中溶液浓度对前驱体晶粒结构、粒径、形貌、残氯含量和正极材料晶体结构、形貌和电化学性能的影响规律，确定了合适的氯化物溶液浓度，所得高活性前驱体在单晶材料合成方面具有显著优势；通过乙酸盐体系一步喷雾热解制备含锂前驱体，实现了锂元素与其他元素在前驱体中的均匀分布及正极材料的形貌调控；为高性能三元正极材料的合成提供了新方法。以喷雾热解制得前驱体为研究对象，揭示了高活性氧化物前驱体形成单晶材料的物相形貌演变规律，提升了喷雾热解材料的振实密度；以窄分布、小粒径的前驱体为原料，揭示了正极材料由多晶向单晶转变的影响因素，构建了制备条件-材料性质-电化学性能的多级联动关系，为单晶高镍正极材料的物相形貌精准调控奠定了基础。揭示了硼元素多尺度改性的作用机理，为硼元素改性正极材料物相组成、微区结构和电化学性能提供理论指导。系统地研究了喷雾热解、共沉淀前驱体中添加硼酸助熔剂对三元材料结构、形貌及电化学性能的影响，建立了硼元素掺杂、晶界浸润、表面包覆多尺度改善高镍三元正极材料的机理模型。以上研究为多元正极材在电池领域的进一步推广应用提供了理论依据和基础，推动了新材料、新能源和新能源汽车等战略性新兴产业的发展。