基于锂离子电池材料用四氧化三钴的绿色制备技术基础

High-performance cobaltosic oxide (Co3O4) is not only the key raw material of cathode materials for lithium ion batteries, but also its application in anode materials for lithium-ion batteries is one of the hotspots. Our country's yield of Co3O4 is more than 13000t per year and is also increasing at an annual average rate of 20%. However, there are still some problems that have not been solved, for example the ammonia nitrogen pollution. Besides, relationships among the structure and morphology of Co3O4 for lithium ion battery anode materials and electrochemical performance are not very clear now. In this project the green synthetic process of micro-/nano- Co3O4 will be explored. The effects of solution concentration, pH value, temperature and mixing speed etc. on the grain diameter will be investigated. The influence of polymer additive type and its dosage on Co3O4 morphology, crystal texture, microstructure and imperfection will be primarily studied. Based on these studies, effects of Co3O4 particle size and its distribution, morphology (such as spherical, fibrous, flaky, polyhedron-shaped) and element doping vario-property on the electrochemical performance such as initial capacity, capacity retention, high/low temperature change resistant will be discussed and corresponding regularities will be revealed. The precipitation thermodynamics and kinetics, controlled thermal decomposition behavior of Co(OH)2 and Co3O4 crystal growth mechanism in the CoCl2-NaOH-Na2CO3-H2O reaction system will be studied and the correlation model of "synthetic process-micro-morphology -Charge and discharge mechanism-electrochemical performance" will be established. The research achievements through these studies are of a great significance for developing Co3O4 green synthetic technology, realizing function-oriented structure design and controllable preparation, enriching the electrochemical mechanism of micro/nano- cobaltosic oxide.

高性能四氧化三钴是锂离子电池正极材料的关键原材料，也是锂离子电池用负极材料的研究热点。我国的四氧化三钴产量大且增长快，但现有工艺却存在品质难以精准控制和氨氮污染严重等问题，且人们对钴盐-碱-水系合成四氧化三钴的反应机理及其颗粒粒度/形貌、晶体结构与电化学性能关系尚存争议。本项目拟研究无氨体系的微/纳米级Co3O4的绿色合成工艺；探讨溶液浓度、pH、温度、搅拌速率等参数与粒径大小、粒径分布、形貌等之间的关系；高分子添加剂种类及用量对Co3O4的形貌、晶体结构、微组织结构及缺位等的影响；揭示四氧化三钴粒径的大小与分布、形貌、元素掺杂改性等对初始比容量、容量保持率、耐高低温性能等电化学性能的影响规律和无氨反应体系的沉淀热力学与动力学、Co(OH)2的受控热分解行为及Co3O4晶体的生长机理，拟建立"合成工艺-微结构形貌-充放电机理-电化学性能"的关联模型，以实现功能导向的材料结构设计与可控制备。

过渡金属氧化物（如Co3O4、MnCo2O4等）因具有较高的理论比容量而成为当前的研究热点。针对Co3O4形貌等微观结构控制机理不明晰，且微观结构与电化学性能之间的影响机制研究不深入的现状，本项目采用绿色合成工艺合成了系列微/纳米级Co3O4、MnCo2O4等；阐明了溶液浓度、pH、温度等参数与粒径大小、粒径分布、形貌等之间的控制机制；明晰了高分子添加剂种类及用量等对Co3O4、MnCo2O4的形貌、晶体结构、微组织结构及缺位等的影响规律；揭示了产品粒径的大小与分布、形貌等对初始比容量、容量保持率等电化学性能的关联规律；明确了前驱体的受控热分解行为及Co3O4、MnCo2O4晶体的生长机理；推导了"合成工艺-微结构形貌-充放电机理-电化学性能"之间的内在规律，实现了功能导向的材料结构设计与可控制备。其主要成果如下：（1）采用液相沉淀法和水热法分别制备了片状和球形的CoCO3，并采用固相热分解法合成了对应形貌的Co3O4。结果表明：片状Co3O4的电化学性能要明显优于球形的，但水热法合成产品的形貌一致性更好。（2）通过改变表面活性剂的种类和溶剂配比，制备了不同形貌的CoCO3，经热处理后制备了一系列新颖的微/纳米Co3O4。结果表明：该类微米级的立方、多面体和纺锤体颗粒均是由相似的不规则的纳米粒子（直径约为20-200nm，厚度约为20-40nm）相互堆砌而成；煅烧后的Co3O4基本继承了前驱体CoCO3的形貌特征与尺寸大小；该类Co3O4均具有较高的首次放电比容量（在0.1C条件下约为1300.0mAh•g-1），在低倍率条件下容量保持率均较理想（在0.1C条件下循环50次后，容量保持率大于95.0%），其中纺锤体的倍率性能最优（在1C和2C条件下循环70次后，容量保持率高达90.1%和98.9%）。（3）通过改变表面活性剂种类和尿素的用量分别制备了不同形貌（椭球型和球型）微/纳米MnCo2O4。结果表明：椭球型MnCo2O4颗粒具有核壳结构和浓度梯度的结构特点，在0.4A•g-1条件下，50次循环后其放电比容量大于620.0mAh•g-1；且经多次充放电后，其椭球形貌、核壳结构与浓度梯度均能保持；具有浓度梯度和核壳结构的球型MnCo2O4的循环性能与倍率性能要优于不具备该结构特征的样品。