新型混合聚阴离子锂离子电池正极材料中空微球和有序介孔结构制备与电化学特性研究

More recently, an entirely new class of polyoxyanion cathodes based on the orthosilicates, Li2MSiO4 (where M=Mn, Fe, and Co), has been attracting growing interest. Silicate polyanions compounds Li2MSiO4 is a class high capacity, low cost cheap, sustainable and safe cathode materials. In Li2MSiO4, Fe or Mn and silicon are the most abundant and lowest cost elements, and hence offer the prospect of preparing cheap and safe cathodes. A key feature of the Li2MSiO4 system is that, in principle, extraction of two lithium ions is possible for a two electron redox process (i.e., operating on both M2+/M3+ and M3+/M4+ redox couples) especially for the Mn system; this should produce a higher capacity (e.g. above 300 mAhg-1 for Li2MnSiO4). However, compounds Li2MSiO4 has various structural polymorphs, their unstable structure, low conductivity resulting in capacity fading fast, cycle performance poor.Recent developments and future challenges of silicate cathode materials focus on their electrochemical behaviour and nanomaterials chemistry. Aiming at these problems, we propose mixed polyanions innovative ideas; combine the advantage of phosphate polyanions cathode materials with structure stability and silicate cathode materials with high capacity. In this project, we will study the structure and electrochemical characteristics of a new type high capacity mixed polyanions cathode materials Li2-xM[SiO4]1-x[PO4]x. Adopting cations doping means to substitute for part of the transition metal ions to stabilize the transition metal tetrahedral [MO4] structure, improve the cycle stability of cathode materials. Using SiO2 nanoparticle as a template prepare hollow microspheres structure mixed polyanions cathode materials by self-sacrificing template method to improve the rate performance of cathode material. This project will study the effect of different ratio SiO4 and PO4 tetrahedral on the phase structural and electrochemical properties of Li2-xM [SiO4]1-x [PO4] x; study the synthesis process of hollow microspheres and mesoporous structure and the rate performance of cathode materials with mesoporous structure; study dynamic stability of mixing polyanion cathode materials with mesoporous structure and conduction mechanism of lithium ion in this new type cathode materials.

本项目以具有近两年颇受关注的具有潜在高容量的低成本硅酸盐聚阴离子正极材料Li2MSiO4为基础，针对硅酸盐正极材料存在多种同质异构体，在电化学充放电过程中结构不稳定，容量衰减快，循环性能差，以及电导率低倍率性能差的关键问题。拟将磷酸盐聚阴离子结构稳定性定高的优势与硅酸盐正极材料具有高容量的优势相结合，提出混合聚阴离子的创新思路，探索新型高容量混合聚阴离子正极材料Li2-xM[SiO4]1-x[PO4]x。同时采用采用阳离子掺杂手段，通过取代部分过渡金属离子，进一步稳定过渡金属八面体[MO6]结构，提高正极材料的循环稳定性。利用体系组元之一的SiO2纳米微球作为模板，采用自牺牲模板法制备具有空心微球结构的混合聚阴离子正极材料微球，提高此类正极材料的倍率性能。本课题重点研究SiO4与PO4四面体混合聚阴离子不同比例和介孔结构对Li2-xM[SiO4]1-x[PO4]x结构和电化学特性的影响。

硅酸锰锂因其安全性好、成本低廉及理论比容量高(333m Ah/g)，被认为是下一代锂离子电池正极材料的有力竞争者。本项目针对硅酸锰锂正极材料在锂离子电池应用中存在的纯相制备困难，电子电导、离子电导低，循环过程中容量衰减快等关键问题，结合申请者课题组在锂离子电池正极材料方面十多年的研究基础，提出了两步法合成纯相，原位碳包覆提高电子电导，颗粒纳米化等改善离子电导及引入电化学活性和非活性的多面体抑制容量衰减等创新思路。课题探索了碳包覆的硅酸锰锂的纯相制备工艺，成功制备得到纯的硅酸锰锂纳米颗粒，实现了两个锂的脱出。课题重点研究了硅酸锰锂在循环过程中首圈库伦效率低、容量衰减快的原因，详细阐述了其在循环过程中的结构变化，并设计引入稳定的多面体作为支柱，形成支撑网络以支撑晶体结构，有效抑制了循环过程中的结构坍塌，提升了硅酸锰锂的循环稳定性。本项目所形成的研究结果为硅酸锰锂正极材料的后续研究和实用化打下了坚实基础。