Selective Recovery Of Li And FePO₄ From Spent LiFePO₄ Cathode Material

Lithium-ion batteries(LIBs)have been widely believed in the best energy sources for electric vehicles(EVs),portable electronic devices,and hybrid electric vehicles(HEVs)due to their high voltage and high energy density.Particularly,LiFePO4-type LIBs occupy large market share in electric vehicles due to the long-life cycle,cost-effective,and nontoxicity.More and more spent LIBs may lead to a severe environmental issue and aggravate the concerns about the shortages of resources.Particularly,Li is an important strategic element.In the past decades,the rising demand and limited supply of lithium increase the cost of lithium compounds.To recycle the sharply growing spent lithium-ion batteries and alleviate concerns over shortages of resources,particularly Li,is still an urgent issue.In this thesis,state of the art for recycling spent LIBs are discussed,and a natural organic acid-based leaching approach at room temperature is proposed to recover Li and FePO4 from spent LiFePO4(LFP)cathode powder.Citrus fruit juices(CFJs),rich in organic acids,such as citric acids and malic acids,have been used as leaching agents in this work owing to its benign operation,and relatively high efficiency,where the natural organic acids are mainly responsible for metal leaching.In this work,the selective recovery of Li and FePO4 from spent LiFePO4 cathode has been investigated taking CFJs as leaching agents.The influence of coexistence metal ions of Cu and Al,different types of CFJs,leaching parameters,leaching mechanism,the purity of Li2CO3 products,regeneration of new active LiFePO4 cathode from the recovered FePO4,and the effect of crystalline carbon on the electrochemical properties have been discussed.Inductively coupled plasma optical emission spectroscopy(ICP-OES),X-ray powder diffractions(XRD)and scanning electron microscopy(SEM)equipped with an energy-dispersive X-ray spectroscope(EDS)have been used for characterization of metal composition in leachate,crystallinity and morphology of the recovered products.After experimental analysis,we concluded that among lemon,orange and apple,lemon juice shows the best leaching effect based on its suitable pH of the reaction system.Under the optimized conditions(i.e.,Citric juice percentage,reaction time,solid to liquid ratio and amount of hydrogen peroxide),the leaching rates of Li,Cu and Al can reach up to 94.83%,96.92%and 47.24%,while Fe and P remain as low as 4.05%and 0.84%,respectively.Li2CO3 and FePO4 can be recovered from the leachate and the leaching residue,respectively.The recovered FePO4 was used to prepare new cathode material LiFePO4.The crystalline carbon,present in the spent LFP cathode scraps,has a significant effect on the electrochemical performances of the regenerated LiFePO4.The regenerated LiFePO4 cathode material delivered a comparable discharge capacity of 155.3 mAh g-1 at 0.1 C and rate capacity to the fresh LiFePO4.For the cycling stability,it displays a capacity retention of 98.30%over 100 cycles at 1 C with a fading rate of 0.017%per cycle.In comparison with reported work,the proposed organic acid-based recycling strategy is much benign for recycling the spent LFP cathode materials and helpful to the sustainable development of LIBs.