Evolution And Impact Of Impurities On The Directly Regenerated Spent Ternary Cathode Material

With the increasing popularity of electric vehicles,lithium-ion batteries,as the core of electric vehicles,are facing severe retirement problems.Developing recycling methods will help protect the environment and reduce resource waste.Direct regeneration has the advantages of short process and low energy consumption.In this thesis,waste Nickel-cobalt-Manganese ternary cathode material was selected to study the evolution behavior of two impurities F and Cu in the direct regeneration process and their influence on the structural properties of the repaired material.The main contents are as follows:（1）Mechanical crushing and solvothermal methods were used to construct two kinds of regeneration materials containing different amounts of F,and the evolution behavior of F element before and after direct regeneration treatment and its influence on the electrochemical properties of the materials were studied.The results show that the content of F has no obvious effect on the morphology and crystal structure of regenerated materials.PVDF was decomposed in the process of calcination and the impurity element F was introduced into the superficial lattice in the form of metal fluoride（Li F,Mn F₂ and Ni F₂）,and an obvious uneven F ion modification layer was formed on the surface of the regenerated high-fluoride material.The electrochemical tests showed that the regenerated high fluorine material（called GS-C）showed great electrochemical performances,and the specific discharge capacity of the first cycle at 1C was 138.0m Ah g^-1,which was obviously higher than the regenerated low fluorine material SC-C.The excellent electrochemical properties of the repaired materials can be attributed to the F ion modification layer formed on the surface of the repaired particles,which is conducive to the migration and diffusion of Li⁺.（2）This paper proposes a method of handling ammonia-ammonium carbonate solution,without introducing new impurities,effectively remove high Cu most Cu impurity in the recycled material.In this way the electrochemical properties of the repaired materials were guaranteed.The reversible discharge capacity of AR-NCM after Cu impurity removal and direct repair is 132.2m Ah g^-1 after 200 cycles at 0.5C current density,which proves the feasibility of ammonia-ammonium carbonate solution treatment.（3）The regenerated material with different content of Cu impurity was prepared.The analysis showed that Cu impurity evenly distributed on the surface of the particles,showing no obvious impact on the morphology and phase of regenerated materials;The electrochemical tests showed that the impurity Cu had a negative effect on the electrochemical performance of the repair materials,and it gradually aggravated with the increase of Cu content.Electrochemical tests also showed that the Cu impurity was not conducive to the migration and diffusion of Li⁺on the surface of the material,which would have a negative impact on the electrochemical properties of the material.