| While the energy storage technology represented by lithium-ion batteries(LIBs)promotes the development of science and technology,it also leads to a shift in resource demand from fossil fuels to battery materials.With the increasing demand of the entire battery industry,a large number of spent LIBs will be produced,and the heavy metal salts and electrolytes inside them will cause serious damage to the ecological environment and human health.In addition,graphite materials occupy an important position in LIBs.If spent graphite(SG)can be recycled and reused,the shortage of graphite resources will be alleviated,which is conducive to the sustainable development of the new energy industry.Aiming at the current problems of low recovery efficiency and serious pollution,this paper mainly studies the migration of metal ions in the discharge pretreatment process of spent LIBs,the corrosion of battery surfaces,the generation of pollutants,the efficient removal of metallic impurities in SG and characterization analysis of relevant properties.The main research content has the following three aspects:(1)For the discharging process,this paper focuses on the chemical evolution of the discharge process of spent LIBs in different concentrations of salt solutions.Here,migration of metal ions inside battery,galvanic corrosion on surface of battery,chemical evolution outside battery and morphological analysis of the cathode material were investigated to attain the comprehensive understanding of discharging process.The efficient and complete discharging can be achieved using 5 wt.%CuSO4 as salt solution,resulting in enrichment of Li in cathode material.The content of Li in the spent LIBs cathode material after complete discharging is 48.71 mg/g,the mobility of Li is 60.83%.Different galvanic corrosion phenomena on the surface of battery can be discovered in different salt solutions,involving with the corrosion of Al or Fe shells,and resulting in the leakage of organic electrolytes inside battery into salt solution.In addition,SEM morphology analysis of the cathode material further demonstrated the discharge excellence of the 5 wt.%CuSO4 solution and reduced reagent consumption.(2)In the repair and regeneration process of SG,this paper focuses on the application of different removal methods for different metal impurities.Under hydrothermal conditions,the influencing factors such as reaction time,reaction temperature and solid-to-liquid ratio were explored for efficient removal of Cu and Li,respectively.The effects of reaction time,reaction temperature,solid-liquid ratio and HCl concentration on the simultaneous and efficient removal of Co,Mn and Ni were investigated under water bath conditions.Finally,the effects of different temperatures and times on the removal of organic impurities from the SG surface were investigated.The results showed that under the suitable conditions,the highest leaching rates were 96.61%for Cu,98.94%for Li,96.34%,99.67%and 99.34%for Co,Mn and Ni,respectively.The SG was calcined at 500℃ and 2 h to maximize the removal of organic matter such as binder and electrolyte.(3)For the above obtained regenerated graphite(RG),it was characterized and analyzed by XRD,SEM,and Raman spectroscopy,and compared with the SG and commercial graphite(CG).Finally,the three kinds of graphite were prepared into button batteries and tested for comparison of electrochemical properties.The results showed that the interlayer distance of the RG after hydrothermal leaching and calcination increased,the surface impurities decreased and fine graphite fragments appeared,which was more favorable for the embedding and detachment of Li-ions in graphite.In terms of electrochemical properties,the first discharge specific capacity of RG at a current density of 0.1 C was 410.11 mAh/g and the discharge specific capacity after 100 cycles was 401.85 mAh/g with a capacity retention rate of 97.99%.After ten cycles at different current densities,the discharge specific capacity was 407.48 mAh/g when the current density returned to 0.1 C again,which was higher than the initial value,indicating that the RG had good electrochemical properties and this method achieved the restoration and regeneration of SG. |
