锂离子电池高镍系层状正极材料结构和热稳定性的优化设计

Ni-rich layered cathode materials (NRM) have been considered as ones of the most promising cathode materials for high-energy lithium-ion batteries owing to their merits of high capacity, low self-discharge, fairly compatibility with the electrolytes and good cycle & rate performance. Investigating the phase transition and thermal stability changes during Li+ insertion/extraction process have been the key scientific issues and challenges of Ni-rich layered cathode materials, which need to be solved urgently and perplexes both enterprise and academe. Much research has been carried out to clarify the intrinsic correlation between the atomic-scale phenomenon (i.e. Ni migration, Li/Ni cation mixing and the formation of rock-salt phase) and structural evolution with thermal stability changes, and to further improve the structural stability of Li-deficient NRM. This project plans firstly to establish a more stable hexagonal crystal system through doping Ti, Zr into the transition metal layers. According to crystal field splitting energy, their lower electronegativity will make them function as an electronic donor thus electrons can be transferred from Ti/Zr to Ni, resulting a more stable Ni2+ in the symmetrical NiO6 octahedral structure. Secondly, a pre-oxidation process for precursor will be applied to enable the surface Ni to reside in Li slabs and acts as pillar layers to establish the host structure. Finally, an ultrathin La compounds membrane as fast ionic conductor will combine organically with the lattice oxygen to fix them and thus suppressing the migration of Ni. It also has the advantages of better accommodation of the strain and fast Li+ transport kinetics. Through all of these comprehensive optimal designs in terms of bulk/skin layer doping, surface modification, and hierarchical structure, combing with physical and chemical properties characterizations, it’s eminently possible to develop novel methods and technology to enhance fundamentally the structural and thermal stability of Li-deficient Ni-rich layered materials.

高镍系层状正极材料具有比容量高，自放电率低，与电解液匹配性好，循环及倍率性能较佳等特点，是高比能量型锂离子动力电池拟采用的优选正极材料。研究高镍系层状材料在嵌脱锂过程中的结构转变与热稳定性，诠释镍迁移、锂镍混排、相转变等现象的发生机制，优化材料在欠锂态的结构和热稳定性，一直是产学界关注并渴望解决的关键科学问题。本项目以构筑高镍系层状材料更稳固六方晶系为目的，拟首先从晶体场分裂角度，通过引入电负性更低的Ti、Zr元素调控过渡金属层的电负性，以改善NiO6八面体结构的对称性和稳定性；然后应用硝酸锰预氧化新工艺，在材料表层预先让镍进入锂层形成纳米支撑层，以抑制材料表层结构的相转变；最后，应用La系快离子导体的梯度复合，在材料一次颗粒和二次颗粒表面形成晶格氧的稳定层和抑制裂缝产生的缓冲层。通过上述针对本体、表层和分级结构的优化设计，以期从根本上改善高镍系层状材料欠锂状态下的结构和热稳定性。

高镍系层状正极材料具有比容量高，自放电率低，与电解液匹配性好，循环及倍率性能较佳等特点，是高比能量型锂离子动力电池拟采用的优选正极材料。项目组按计划执行并完成了规定的研究内容，明晰了高镍系层状正极材料嵌脱锂过程中过渡金属元素的迁移规律和相转变特征，掌握了基于材料本体、表层和分级结构开展的有针对性的组分和结构设计方法，系统研究了Ti、Al、Zr、W、Ce等元素单掺杂或双掺杂对高镍层状材料结构稳定性的改善作用，在高镍正极材料表面设计了La2Ni0.5Li0.5O4、LiTaO3、LiHSeO4等多种超薄快离子导体层，构筑了多种可缓冲一次颗粒膨胀应力且锂离子嵌入脱出通道更为顺畅的材料分级结构，研制出了具有高结构和热稳定性的高性能高镍层状正极材料。相关成果获得2022年度中国有色金属工业科学技术奖二等奖（发明）。四年来，项目组共发表标注本项目资助SCI收录学术论文26篇，申请国家发明专利21项，授权14项，培养博士研究生6人，硕士研究生8人，圆满完成了项目研究任务和研究目标。