无钴Ni-Mn固溶结构强化高比容量镍基正极材料基础研究

Ni-based cathode materials was known for its high specific capacity advantage, which has potential prospect for the advancement of high energy density power battery. Traditional Ni-based cathode materials mainly belonged to the Ni-Co solid solution materials and its derived material of lithium-ion batteries. These materials were restricted to be used in power batteries as it was expensive and poor in stability and safety. The research of low-costed cobalt free Ni-based cathode material with Ni-Mn solid solution has long been neglected. In this project, Ni-Mn solid solution was used to strengthen the structure of cobalt free Ni-based cathode materials to obtain a high discharge capacity (200mAh/g) at 4.5 V charging potential, and good safety and the cycle performances. The emphasis research is the strengthening effect of non-reactive components such as Mn4+ to the structure of Ni-based cathode materials, the correspondence between high operating voltage and high discharge capacity, and the optimization design of cathode materials for the safe use of performance. In theory, the structure stability of the materials will be evaluated by quantum chemistry calculation method, and material structure strengthening will be verified with XRD refinement methods etc to achieve the optimization of structural properties of materials. Nickel and manganese resources are more abundant and the target material has the advantage of high discharge capacity, good safety performance and low cost. So this research has important theoretical and practical significance for promoting the new cathode material development of new power battery cathode material.

镍基正极材料以高比容量的优势著称，对发展高能量密度动力电池有潜在前景。传统锂离子电池镍基正极材料以Ni-Co固溶及其衍生材料为主，由于其安全稳定性欠佳且成本较高，在大容量动力电池中受到制约。具有低成本优势的无钴、Ni-Mn固溶镍基正极材料的研究长期来一直被忽视.本研究拟采用Ni-Mn固溶强化材料结构，以期获得在4.5V高电压下能安全使用、循环性好、放电容量>200mAh/g的正极材料。重点研究非活性Mn4+等组分的掺入对镍基正极材料结构的强化作用；研究高工作电压与高放电容量的对应关系；研究该正极材料安全性能的最优化设计。理论上采用量子化学理论计算方法对材料结构稳定性进行计算评价，采用XRD结构精修等分析测试手段对材料结构强化进行论证，从而实现材料结构性能的最优化。由于镍锰资源较为丰富，目标材料又具有能量密度高、安全耐用、价格低的优势，本研究对发展动力电池新型正极材料有重要理论和实际意义。

镍基正极材料因比容量高在动力电池有广阔应用前景，但其结构稳定性较差问题亟待解决。本研究目的是在保持正极材料高比容量前提下，通过Ni-Mn固溶和离子掺杂进行结构强化，进一步提升镍基材料的使用稳定性。本研究工作实施取得了以下研究结果：（1）量子力学第一性原理计算与实验论证表明：随着Mn/Ni固溶度的提高及Nb5+掺杂对镍基正极材结构有稳定强化作用。当Ni-Mn固溶镍基正极材料LiNixMn1-xO2中随Mn的减少，即Ni（x）由 0.6增加到0.7、0.8时，晶胞体积增加率为2%，脱锂电压从3.57V降到3.56V、3.52V，结构趋于不稳定。Nb5+掺杂会使材料的Gibbs自由能降低，Nb-O键的键布居比M-O键布居大，表明Nb-O结合较M-O键紧密，有利于稳定材料的结构。（2）部分掺杂离子（Co3+、Zr4+、Al3+等）对镍基正极材料的结构强化和性能改善有调控作用。Co3+掺杂对材料晶粒生长、减少离子混排、提高放电容量、改善导电性有促进作用。LiNi0.9-xCoxMn0.1O2分别掺入不同的Co（x=0.04、0.07、0.1），在2.75~4.35V下放电，放电比容量高达210mAh/g、203.4mAh/g和189mAh/g，但循环性能有待进一步提升。Zr4+掺杂LiNi0.8Mn0.2O2对离子混排有较好抑制效果，其中掺杂1%时对晶体结构的有序度控制效果最好，在2.75—4.3V、1C充放电，循环100次的容量保持率97%，放电容量为165 mAh/g，循环性能优异。Al3+掺杂也能提高材料的稳定性，添加1%Al3+，在25℃、2.75-4.3V、0.2C充放电条件下，首次放电比容量达180.2mAh/g，循环100次后，容量保持率达94.06%。（3）合成条件对镍基正极材料结构性能影响有一定规律。随着镍基材料中N含量的增加，合成温度向降低趋势发展；提高合成气氛的氧浓度有利于改善正极材料性能。