废旧锂离子电池锂镍钴锰系层状正极材料失效机制及直接修复研究

The layered LiCoO2 and Li-Ni-Co-Mn mixed oxides are used most as active cathodes for commercial lithium-ion batteries (LIBs) at present. Recycling of cathodes from spent LIBs has many advantages such as saving the mineral resouces and mitigation of environmental pollution. Since cobalt is a rare and precious metal in China, recycling of metals from spent LIBs is of great strategic significance and economic value.Up to now, most reserch has been focused on the recovery of metals using metallurgical technology at home and abroad. The conventional method consists of complicated multi-step procedures such as dissolution in mixed acid solution, precipitation, various extraction procedures using different organic solvents, re-synthesis of electrode materials from leaching solution, etc.They have many unfavorable points such as high cost, easily causing second pollution, etc.Moreover, the research on the recycling of cathode materials is still concerned about the technologies ignoring the theoretical basis. The innovative point of the study is applying the material science technology to solve the problem on the resource circulation area. Ralated scientific problems will be analyzed from microcosmic viewpoint. The layered structure of the cathode materials was not badly destroyed after long time charge-discharge cycles. Thus, it is hopeful to accomplish the renovation of the cathode materials directly. On this research, cathode materials are separated from the current collectors by destroying the adhesive substance, which avoids the acid leaching and reduces the second pollutant emission. Then we will use the advanced material test technologies (such as SEM, XRD, STEM, EELS, XPS, etc) to characterize the microstructure evolution of cathode materials during charging and discharging process.The influences of the microstructure evolution on the lithiation/delithiation performance of cathode materials will be emphatically investigated. Based on the comprehensive analysis of the experiment results, we can reveal the material failure mechanisms and then design the renovation methods, such as high temperature roasting and hydrothermal reaction.The mechanisms proposed for the direct renovation methods are based on chemical compositon restored mechanism and dissolution-precipitationn mechanism. It will establish the theoretical foundation for a new recycling and renovating technology that is short process, environment friendly and suitable for both spent LiCoO2 and other Li-Ni-Co-Mn mixed oxides.

商品化锂离子电池正极材料以钴酸锂和锂镍钴锰多元层状氧化物为主，对其回收再利用节约矿产资源，保护生态环境，尤其对于钴资源缺乏的我国具有重大战略意义和经济价值。目前国内外对其回收再利用研究集中于利用冶金工艺回收有用金属，采用先溶解浸出再处理浸出液的多步处理法，工艺复杂、二次污染严重。研究成果多为对工艺技术的探索，缺乏基础理论。本项目拟将材料科学学科应用于资源循环利用领域，从微观角度研究相关科学问题，充放电过程中正极材料层状结构并未遭到严重破坏，有望实现直接修复。通过研究粘结剂失效机理，破坏粘结剂直接回收正极材料,避免溶解浸出，减少二次污染物排放；利用先进的材料分析测试技术，研究充放电过程中材料结构变化对脱嵌锂性能的影响规律，揭示材料失效机制，利用高温焙烧修复化学组成及水热反应溶解再析出等原理直接修复正极材料，为发展短流程，环境友好，同时适用于锂镍钴锰系层状正极材料的直接修复新方法奠定理论基础。

随着锂离子电池需求量的急剧上升，对于废旧锂离子电池的回收再利用具有重要的意义。本项目主要针对Li-Ni-Co-Mn系层状正极材料进行了清洁回收研究，失效机制研究以及直接修复研究。通过本项目研究，可以实现清洁回收锂离子电池正负极材料。利用XRD、STEM、XPS等材料研究手段从微观角度研究锂离子电池层状正极材料失效机制，研究发现充放电过程中正极材料晶粒内部层状结构并未遭到严重破坏，但是晶粒边界结构发生转变，锂离子脱出后，过渡金属原子占据部分锂空位，价态发生转变，有序的层状结构变为无序的非晶结构，这种非晶结构中离子电导差，锂离子不容易再次嵌入，长期循环后边界层厚度变厚，成为正极材料的主要失效机制。利用高温补锂焙烧及水热反应溶解再析出等原理直接修复正极材料，修复正极材料表面非晶层消失，正极材料重新恢复充放电性能，与自制的Li-Ni-Co-Mn系正极材料的充放电性能相当。通过本项目研究有对发展短流程，环境友好，同时适用于锂镍钴锰系层状正极材料的直接修复再利用新方法奠定理论基础。