面向高倍率高比容量正极材料粒内纳米导电框架构建的研究

The cathode materials has the worst conductivity in lithium-ion battery. Its resistivity is more than 10000 times of graphite negative electrode. The large internal resistance brings serious harm and influence to the power battery, which is shown by its poor rate performance, short driving mileage, short cycle life and poor safety etc.. In order to reduce the internal resistance, the traditional method is to add conductive agent to the surface of the material particle, refine the material particle size and increase the cobalt content of the material, etc.. However, the problem of large internal resistance of power battery is still unsolved. In this project, the nickel base cathode material with high specific capacity will be used as the research object, and nano-graphene, carbon nanotube and other conductive agents will be introduced into the interior of micrometer positive electrode particles. The project will focus on the following: (1) Effect of the conductive agent on the nucleation of the spherical cathode precursor and its dispersion mechanism; (2) Mechanism of high temperature antioxidant protection of conductive agents; (3) Influence of conductive agent and its interface on the diffusion of positive crystal; (4) The effect of in-particle conductive agent on battery performance and theoretical calculation simulation, etc...Through the research of this project, the nano-conductive framework for cathode materials with performance of fast charging/discharging and high specific capacity is constructed, and the inner resistance of positive electrode material is reduced by more than one to two orders of magnitude, which can realize the fast charging and discharging of power battery, high energy density, excellent cycling performance and good safety. Therefore, the research work of this project has important theoretical and practical significance to accelerate the development of new energy vehicles..

正极材料在锂离子电池中导电性最差，电阻率是石墨负极的10000倍以上，内阻大对动力电池带来严重危害，表现在倍率性能差、续驶里程短、循环寿命短、安全性差等系列问题。为了降低内阻，传统方法是在材料颗粒表面加入导电剂、细化材料粒度、增加材料钴含量等措施加于改善，但不能根本解决内阻大的问题。本研究拟以高比容量镍基正极材料为研究对象，在微米级正极颗粒内部引入纳米级石墨烯、碳纳米管等导电剂，重点研究：导电剂对促进球形正极前驱体成核的影响及其分散机理；导电剂的高温抗氧化保护机制；导电剂及其界面对正极结晶扩散的影响；以及粒内导电剂对电池性能的影响及计算模拟等。通过研究，构建快充放高比容量正极材料的粒内纳米导电框架，将正极内阻降低1-2个量级以上，实现动力电池快充放、能量密度高、循环性能好、安全性好、成本低的研究目标。由于粒内导电剂研究还未见文献报道，因此开展本研究对加快新能源汽车发展有重要的理论意义。

由于正极材料在锂离子电池中的电子导电性和离子导电性较差，势必对动力电池带来系列负面影响，比如放电比容量较低、循环寿命较差、倍率性能较差、安全性能较差等系列问题。为了改善电池导电性能，传统方法是在材料颗粒表面加入导电剂、增加材料钴含量提高导电性等措施，但仍不能从根本上解决问题。本研究以导电性能较差的无钴镍基正极材料（LiNi0.8Mn0.2O2）为研究对象，以改善其导电网络结构为抓手，从两方面提升电池的导电性能。一是在微米级正极颗粒内部引入导电剂，如纳米碳黑、纳米石墨烯和碳纳米管形成粒内导电剂，形成更紧密的导电网络；二是将正极材料颗粒进一步细化，从而使围绕细颗粒正极周边导电剂的分布间距进一步缩小，实现导电性能的提升。研究表明：（1）在制备过程中随着粒内导电剂的加入量的递增，会使前驱体的粒径和振实密度不断减小，导电剂不能发挥晶核剂的作用；正极材料在预氧化和高温合成过程中，随着导电剂含量增加，正极材料粒度更细小和松散，材料比表面增加；在正极材料中添加碳纳米管导电浆料有效提升了电池表现出更好的循环和倍率性能，可以实现动力电池快充放和高能量密度的研究目标。（2）通过将正极材料机械粉磨的进一步细化处理，分成粗、中、细三种不同粒级（（9.16、5.97、1.23µm），随着粒径减小，尤其是导电材料纳米碳黑和碳纳米管对正极材料的放电比容量、循环性能及倍率性能都有明显的改善作用。本项目共发表SCI论文20篇，授权发明专利8项，培养硕博研究生12名，圆满完成制定目标。本项目的应用可以实现动力电池快充放、能量密度高、循环性能好、安全性好、成本低的研究目标。