Study On The Recycling Process Of Cathode Materials From Waste Lithium Iron Phosphate Batteries

With the rapid development of its cost-effective and environmentally protection performance,electric vehicles?EVs?have increased the output and usage of power batteries.Lithium iron phosphate is a typical cathode material for lithium ion batteries.A large number of lithium iron phosphate batteries will be wasted.If they can be recycled reasonably,the environmental pollution and the production cost of lithium-ion batteries can be reduced.At the same time,their recycling can alleviate the pressure of global lithium resource shortage.Therefore the recycling of lithium iron phosphate battery is imperative.The main research contents of this paper are as follows:Firstly,the waste lithium iron phosphate battery was pretreated to obtain its cathode.Organic solvent,alkali dissolution-ultrasound and high temperature calcination were used to separate active substance,and the experimental conditions were optimized to improve the separation rate.The separation rate of active substances reached 95.98%when the cathode was heated for 5 h in the atmosphere of N₂ at 500?C.The cathode with a surface area of 0.25 cm²was ultrasonically immersed in propylene carbonate solvent for 120 min at 60?C,liquid/solid ratio of 25:1 mL/g,the separation rate reached 68.6%.Through the comparison of the three methods,the alkali solution-ultrasonic method has higher separation efficiency and less impact on environment.The cathode reacts under the condition that the concentration of NaOH solution is 0.8 mol/L,the liquid-solid ratio is 20:1 mg/L,reaction time is 10 min,the temperature is 30?C,and then ultrasonic cleaning in water for 1 min,the separation of active substance realized 100%,meanwhile the recovery rate of aluminum was 75.7%.XRD analysis confirmed that the recovered product was lithium iron phosphate.After the binder PVDF was removed,the recovered active substance was repaired and regenerated by mechanical activation-carbothermal reduction.Using Li₂CO₃,Fe?NO₃?₃ and?NH₄?₂HPO₄ as reactants,the addition amount of the reagent is determined according to the mass difference between the recovered material and the commercial material,and sucrose is used as the reducer.The precursor obtained by ball milling at 500 r/min for 5 h,then it was calcined in N₂ atmosphere to obtain regenerated material with uniform particle size and better crystalline form.At the same time,the doping of new materials on recycled materials during mechanical activation was studied.With the doping ratio of 10%,The regenerated materials'first discharge specific capacity at 0.1 C is 148.62 mAh/g,and the capacity retention rate is85.78%after 60 cycles.For lithium iron phosphate which is difficult to repair,using acid leaching and chemical precipitation to recover lithium.The experimental results show that under the conditions of H₂SO₄ concentration 2.5 mol/L,reaction temperature 50?C,reaction time 150 min,liquid/solid ratio 25:1 mL/g,H₂O₂:Li=2:1?molar ratio?,stirring rate 300 r/min,90.25%lithium can be leached from active substance.Lithium and iron are separated by adjusting the pH value of leaching liquor.When saturated Na₂CO₃ is added to the filtered solution,Li₂CO₃ with purity over 95%can be obtained.