电动汽车废旧电池中锂的高能活化络合机制与超临界固相萃取机理研究

This project focuses on the current prominent problem of largely discarded lithium-ion batteries from electric vehicles, of which the existing disposal approaches cause serious environmental problem. The study prepares to develop a green system for lithium recovery, in which high-energy activation will be combined with supercritical solidoid extraction. Specifically, the form of lithium is firstly changed, then subject to supercritical extraction process for lithium dissolving and separation. The changing properties and complexation mechanisms of lithium in the high-energy activation and supercritical extraction system will be clearified through thermodynamic calculation and density functional theoretical calculation. The interaction mechanisms of lithium with other metals will be elucidated, and the change and distribution properties of pollutants will be traced. The transforming properties of different phases in the activation and extraction processes will be clarified using the theories of interfacial diffusion, ion exchange, duplet rearrangement, complexation restructuring. The mechanisms of free radical formation and high-energy reaction induction will be analyzed. High-energy activation mechanism of lithium will be clarified through thermodynamic and dynamic simulating calculation during leaching process combining with energy and diffusion equations. The interphase transformation of activating lithium in the supercritical fluid will be clarified. The complicated coordination mechanisms of lithium compounds in the extraction system will be analyzed using hard-soft acid base theory and hybrid orbital theory. The lithium extraction mechanisms will be clarified and the operation method will be established. Accordingly, the theoretical foundation for green recovery of lithium from spent lithium-ion batteries and further industrial application will be established.

针对我国电动汽车锂离子电池大量报废，现行处理方法环境问题突出的现状，开展高能机械活化联合超临界流体固相萃取锂的绿色回收方法的基础研究。首先通过高能活化改变锂的形态，然后采用超临界流体固相萃取的方法使锂溶出分离回收。将通过热力学和密度泛函理论计算，解析高能活化和超临界萃取体系中锂的形态变化特征与络合机制，阐明不同金属与锂之间的交互作用机理，追踪污染物的变化和分布特征；利用界面扩散、离子交换、电子对重排、络合重组理论，解析活化与萃取过程中不同物相的变化特征；分析活化过程中自由基的生成及引发高能活化反应的机制，结合能量方程和扩散方程，通过浸出过程热力学和动力学方程模拟计算，阐明锂的高能活化机理；解析超临界流体中活性锂的物相转化过程，利用软硬酸碱理论和分子杂化轨道理论解析萃取系统中锂络合物的复合配位机理，阐明萃取机制，确立操作方法，为废旧动力电池中锂的绿色回收和产业化应用提供理论支持。

本研究采用机械化学活化协同超临界流体萃取方法，对废旧锂电池正极材料中锂的选择性回收效果与机制进行了探讨，确立了锂高效回收方法，阐明了相关反应机理。废旧锂电池中锂和钴的机械化学螯合回收方法与机制研究中，将LiCoO2粉末与金属螯合剂EDTA共磨后直接加水浸出，金属Li和Co的回收率达到99%和98%。在LiCoO2/EDTA共磨时，EDTA中的两个N原子、四个羧基O原子，均能进入金属Li和Co的空轨道，形成环状结构的螯合物，即LiCoO2/EDTA通过固-固反应形成了稳定的水溶性的五元环螯合物Li-EDTA和Co-EDTA。通过考察不同供氯体和操作参数对Li回收率和Co转化率的影响发现，共价类的供氯体不适于Li的回收和磁性功能材料的制备，离子类的供氯体具有高的反应活性，不仅可以促进Li的氯化，同时还可以保证Co完整地保留在反应残渣中转化为CoFe2O4。将LiCoO2/Fe/NaCl共磨，既可以保证将Li转化为水溶性的盐，又可以将Co与Fe进行晶格重组。利用机械化学活化协同超临界萃取工艺从LiFePO4粉末选择性回收锂的研究发现，最佳机械活化参数是：(NH4)2SO4:LiFePO4为1:1（摩尔比）、LiFePO4:H2O为5:2（质量比）、球料比10:1、湿磨时间30 min，转速为600 r/min，机械活化后LiFePO4的晶体结构被破坏，造成晶面错位；相应的最佳萃取条件是：温度为80 ℃、固液比为50:1、时间为50 min，浸出率为99.6%。选择性萃取锂的机理为，机械化学活化使得LiFePO4晶体尺寸减小，晶体缺陷与化学活性增强，从而在萃取过程中LiFePO4中的Fe2+成为Fe3+，Fe3+与PO43-结合生成FePO4沉淀，锂进入萃取液中，实现选择性提取。项目的研究结果对于废旧动力锂动力电池中锂的环境友好型回收和产业化应用具有积极的参考价值，可以有效支持我国锂电新能源产业的发展。