Preparation Of Two-dimensional Flake LiFePO₄/C And Recovery Of Spent LiFePO₄ Electrode Material

As an efficient green sustainable energy storage device,lithium-ion batteries have attracted extensive research.Olivine-structured lithium iron phosphate materials have been widely used in electric vehicles due to its low toxicity,low cost,long cycle life and high safety.In this paper,two-dimensional flake lithium iron phosphate with excellent electrochemical performances has been synthesized to meet the growing application needs.On the other hand,with the wide use of lithium iron phosphate batteries,more and more waste batteries after their span life will be produced.If these waste electrode materials are not properly handled,it will cause serious environmental pollution and waste of resources.Therefore,it is very important to make study on the recovery and reuse of spent LiFePO₄ electrode materials.The main research works include the following two parts:1.Two-dimensional flake LiFePO₄/C electrode materials were prepared with the assistance of surfactants.Specificly,FeCl₃·6H₂O and H₃PO₄ were used as raw materials,sodium dodecyl benzene sulfonate?SDBS?and hexadecyl trimethyl ammonium chloride?CTAC?were added to synthesize plate-like FePO₄·2H₂O precursors with uniform morphology by water bath method at relatively low temperature.Two-dimensional flake LiFePO₄/C was prepared by calcination the flake FePO₄·2H₂O precursors with lithium and carbon sources at high temperature.The effects of different surfactants SDBS and CTAC on the morphology and electrochemical properties of LiFePO₄/C were studied.The results of electrochemical tests showed that the discharge capacity of micro-plate LiFePO₄/C prepared by adding SDBS was 166.4 mAh g^-1 at 0.1C rate and the initial coulomb efficiency was 99.6%.After 500 cycles at 1 C rate,the capacity retention rate reached 99%with little attenuation.The discharge capacity of flake LiFePO₄/C synthesized by adding CTAC reached 168 mAh g^-1 at 0.1 C rate,which is close to the theoretical capacity of lithium iron phosphate,and it still delivered a discharge capacity of 127.2 mAh g^-1 at 10 C rate.After 800 cycles at 1 C rate,it matained a high capacity retention of 92.7%.Obviously,the flake LiFePO₄/C synthesized with the help of CTAC achieved better electrochemical performance.2.The recovery and reuse of spent LiFePO₄ cathode materials were investigated based on electric driven delithiation.Commercially available spent LiFePO₄ batteries after 1500 cycles were selected to recovery and reuse their cathode materials.The LiFePO₄ cathode materials were obtained by dismantling the spent lithium ion batteries.The collected LiFePO₄ materials were then mixed with polyvinylidene fluoride?PVDF?binder and coated on titanium mesh.And an electrolytic device was constructed using the titanium mesh coated with the spent LiFePO₄ materials as positive electrode,a bare titanium mesh as negetive electrode,and NaCl aqueous solution as initial electrolyze.Different voltages were applied by an externally connected adjustable power supplier,and iron phosphate?heterosite FePO₄?was obtained after the electric driven delithiation.Then,regenerated LiFePO₄/C materials were synthesized by calcining the recovered FePO₄ with lithium carbonate and glucose at high temperature.The results of electrochemical tests showed that the regenerated LiFePO₄/C electrode materials delieved specific discharge capacities of 148 mAh g^-1 and 79 mAh g^-1 at 0.1 C and 5 C rate respectively,and kept a high capacity retention rate of 96.3%after 300cycles at 1 C rate.The regenerated LiFePO₄/C exhibited much better electrochemical performance than the spent LiFePO₄ materials and it is promising to find practical application.