尖晶石相原位共生的富锂正极材料结构调控与电化学性能研究

Development of new-type cathode materials is the key to enhance the energy density of lithium-ion battery, while the properties of materials are closely related with their structural characteristics. Due to the combined advantages of high dynamic properties for spinel structure and the high capacity for lithium-rich cathodes, the multiphase of intergrowth structured spinel and lithium-rich structure become one important development direction of future new-type cathode material. However, current multiphase integrated structures are always quite difficult to be guaranteed on the nanometer scale because of their different characteristics. Therefore, it is assuredly a most important subject for searching and developing new preparation methods and its mechanism in research of lithium rich cathode materials with spinel phase intergrowth. Based on previous experiments, this study aims to construct multiphase structure cathode materials by spinel phase intergrowth. During this process, we’ll investigate the mechanism of spinel structure intergrowth with lithium-rich structure and the principle of micro-phase coalesce growth combined with theoretical calculation, form quantitative analysis method of multiphase intergrowth structure which can provide guidance for the controllable design and construction of multiphase integrated structure. On the basis of learning the mechanisms of synergetic multiphase intergrowth process as well as the relationship between the performance and structure for the cathode materials, we'll investigate the electrochemical synergetic of the intergrowth phases combined with evolution of structure and properties, and furthermore, illustrate the effect of the structure design, raw material selection and preparation conditions on the electrochemical performance of the cathode materials. Those explorations may provide new ideas and experiences for the development new-type multiphase intergrowth structure for high performance lithium-ion batteries cathode materials.

发展新型正极材料是提高锂离子电池能量密度的关键，而材料的性能与其结构特性密切相关。多晶相复合富锂正极材料结合了各自晶相结构的动力学优势和富锂正极高容量特点，成为未来新型正极材料发展的一个重要方向。但仍因其中不同晶相性质的差异很难保证多晶相纳米尺度上的复合。因此，探寻和发展新的制备方式及其形成机制，构建尖晶石相原位共生的富锂正极材料成为发展这类材料研究的重点。本课题在前期实验基础上，采用尖晶石相原位共生的方式构建多晶相复合材料，结合理论计算，探究多晶相原位共生机制和微相融合生长原理，形成多相结构量化研究方法，指导多晶相结构的可控设计和构建；在掌握协同作用晶相共生机制的基础上，依据结构与性能的相应关系，结合结构与性能演变规律,探究晶相之间的电化学协同效应，阐明结构设计、原料选择和制备条件的优化对材料电化学性能的影响，为具有多晶相共生结构高性能新型锂离子电池正极材料的开发与研究提供新思路和借鉴。

为响应国家“碳达峰”“碳中和”要求，研制新型高能量密度锂离子电池，开展高性能储能材料研究。项目针对富锂正极循环不稳定和持续电压衰减问题，通过设计局部贫锂和等锂半径原子取代构建含缺陷结构的富锂正极，经热处理过程调控缺陷结构原位形成尖晶石相，构建多相复合富锂正极材料，通过系统研究正极材料晶相生长过程中离子占位与元素价态演变规律，探究工艺条件与共生生长微相结构的内在联系，明晰晶相形成过程、共生晶相间化学协同效应及其对多晶相共生生长的影响。通过尖晶石相直接复合与离子掺杂、元素组成调节和聚合物诱导尖晶石相原位共生研究发现，Mg2+取代Li+会在富锂材料中形成尖晶石相原位复合和Mg2+掺杂的双重效应，显著减缓层状相向尖晶石相转变过程，电压降减缓至每循环0.0023V；以浸渍-干燥-烧结制备的尖晶石表面改性富锂正极材料在0.5C下循环容量稳定在203mAh·g-1；5wt%导电聚合物直接改性材料在2C和5C倍率容量分别为118 mAh·g-1和79.5 mAh·g-1，导电聚合物原位聚合法改性富锂材料在1C和2C倍率容量分别为205 mAh·g-1和165 mAh·g-1；以酚醛树脂为碳源原位诱导富锂材料表面形成尖晶石相，这种尖晶石、单斜、层状晶相共生的富锂正极材料在5 C倍率下放电比容量为135.1 mAh g-1（本征材料为80.4 mAh g-1）；以葡萄糖为碳源经水热法包覆改性富锂正极材料，经热处理制备碳/尖晶石/富锂复合正极，尖晶石相比例与葡萄糖含量相关，当含量为10%时，材料原位衍生尖晶石相含量为7.2%，改性后材料的0.2 C首次容量为245.8 mAh g-1（本征材料为199.6 mAh g-1），首次库伦效率提高近10%， 5 C容量达到了186.0 mAh g-1。研究结果表明，尖晶石相能提高初始放电电压，改善材料内部锂离子传输性能，三种晶相具有电化学协同作用，特别是在长循环过程中层状和尖晶石复合结构会在一定程度上减缓层状相的不可逆相转变，项目的研究为多晶相共生结构高性能锂离子电池新型正极材料的合成及应用提供规律性设计数据和基础理论，为发展其他多相结构新型材料提供思路和借鉴。