| The rapid increase in demand for lithium-ion batteries in recent years has led to a sharp increase in the number of used lithium-ion batteries.Spent lithium-ion batteries will cause serious pollution to the environment.On the other hand,the positive electrode materials of used batteries contain valuable metals such as cobalt and nickel,which need to be recycled.In this paper,the positive electrodes of the spent lithium nickel cobalt manganese oxide battery and the spent lithium iron phosphate battery are taken as the research objects.The leaching process of the positive electrode using sulfuric acid and /or reducing agent as the leaching agent is studied.The separation of the aluminum foil and the positive electrode material is realized.Aluminum is recovered in the form of metal with little loss,and all metals in the positive electrode material are leached in the form of ions.The main content of the study and the main conclusions obtained are as follows.1.The decomposition behavior of binder PVDF in sulfuric acid is studied.(1)The binder PVDF can be decomposed in concentrated sulfuric acid.The XRD,SEM and IR analysis of the reaction product,and the analysis of fluorine concentration in the solution indicate that the product of the PVDF decomposition reaction is HF and carbon.After the decomposition reaction occurs,the PVDF changes from the original sphere to an irregular small sphere.(2)In the 4mol/L sulfuric acid solution,PVDF is hardly decomposed.Even if the temperature is increased to 130? and the reaction time is increased to 4 h,the decomposition rate of PVDF is still very low.2.The leaching behavior of valuable metals in sulfuric acid solution from positive electrodes of spent lithium nickel cobalt manganese oxide batteries is studied.(1)The aluminum foil is dissolved in the dilute sulfuric acid solution,causing the loss of aluminum.While the aluminum foil is not dissolved during concentrated sulfuric acid leaching process,and the aluminum foil can be recovered in the form of metal,and there is no aluminum ion in the leach liquor,which is beneficial to the metal separation for the subsequent procedure.However,compared with the leaching with dilute sulfuric acid solution,it takes longer time for the separation of positive electrode materials from aluminum foils when leaching with concentrated sulfuric acid.(2)The temperature,the amount of sulfuric acid,and the leaching time have significant effects on the separation of positive electrode materials from aluminum foils,and the leaching rate of nickel,cobalt,manganese,lithium,and aluminum.(3)The suitable conditions for leaching the positive electrode with concentrated sulfuric acid are as follows.The liquid-solid ratio of concentrated sulfuric acid to the positive electrode sheet is 1.6 ml/g.The positive electrode is first leached at 50? for30 min,and then the aluminum foil is separated from the slurry.Then the slurry is heated to 80? and leached for 30 min.Under these conditions,lithium can be completely leached,and the leaching efficiencies of nickel,cobalt and manganese are about 20%.(4)The suitable conditions for leaching the positive electrode with the dilute sulfuric acid solution are as follows.The reaction temperature is 80 ?.The liquid-solid ratio of 4 mol/L sulfuric acid solution to the positive electrode is 8 ml/g.After reaction for 10 min,the aluminum foil is separated from the slurry,and the slurry is leached continuously for 50 min.Under these conditions,lithium is almost completely leached,and the leaching efficiencies of nickel,cobalt,and manganese can reach 25.4%,22.4%,and 17.4%.However,aluminum is also leached,and the leaching efficiency of aluminum reaches 50%.(5)When leaching the positive electrode with concentrated sulfuric acid at 80?,the acid consumption for the complete leaching of lithium is lower and decreased by 8%compared with the leaching with the dilute sulfuric acid solution,and decreased by 13%for the complete separation of the aluminum foil from the positive electrode material.(6)The decomposition reaction of the binder under concentrated sulfuric acid,the passivation of concentrated sulfuric acid to the aluminum foil,and the chemical reaction between the concentrated sulfuric acid and the positive electrode material are the main reasons for the separation of the aluminum foil from the positive electrode material.3.The reduction-leaching of positive electrodes of spent lithium nickel cobalt manganese oxide batteries is studied.(1)The XPS analysis show that there are metals with high valence in the leach residues obtained from the leaching of lithium nickel cobalt manganese oxide with sulfuric acid.Therefore,it is necessary to add a reducing agent to completely leach cobalt,manganese and manganese.(2)When the positive electrode sheets are leached with concentrated sulfuric acid-hydrogen peroxide or dilute sulfuric acid-hydrogen peroxide,the leaching efficiencies of nickel,cobalt,manganese and lithium all reach 100%.(3)When using glucose and ascorbic acid as the reducing agents,the suitable temperature for reduction-leaching is 80?,and the suitable reaction time is 60 min.The appropriate amounts of glucose and ascorbic acid are 1.4 g glucose/g positive electrode and 1.4 g ascorbic acid/ g positive electrode.4.The leaching behavior of valuable metals in sulfuric acid solution from positive electrodes of spent lithium iron phosphate batteries is studied.(1)The suitable conditions for leaching the positive electrode sheet by concentrated sulfuric acid are as follows.The liquid-solid ratio of concentrated sulfuric acid to the positive electrode sheet is 1.2 ml/g positive electrode sheet.The positive electrode is first leached at 50? for 12 min,at which the positive electrode material has been detached from the aluminum foil.The aluminum foil is then sieved out,and the remaining slurry is heated to 80? and leached continuously for 1 h.Under this condition,almost all of lithium,iron,and phosphorus are leached into the solution.(2)The suitable conditions for leaching the positive electrode sheet with dilute sulfuric acid are as follows.The liquid-solid ratio of 4 mol/L sulfuric acid and positive electrode sheet is 5 ml/g positive electrode sheet.The positive electrode is first leached at 25? for about 10 min,at which the positive electrode material has been detached from the aluminum foil.The aluminum foil is then sieved out,and the remaining slurry is heated to 80? and leached continuously for 50 min.Under this condition,almost all of lithium,iron and phosphorus are leached into the solution,and about 3% of the aluminum is lost into the leachate.(3)At 80?,the lithium iron phosphate cathode material should be completely leached,and the dilute sulfuric acid reduces the acid consumption by about 9% than the concentrated sulfuric acid.To completely separate the aluminum foil from the positive electrode material,dilute sulfuric acid reduces acid consumption by about 12%over concentrated sulfuric acid.When leaching the positive electrode with 4mol/L sulfuric acid at 80?,the acid consumption for the complete leaching of lithium is lower and decreased by 9%compared with the leaching with concentrated sulfuric acid solution,and decreased by12% for the complete separation of the aluminum foil from the positive electrode material.Leaching the positive electrodes of spent lithium ion batteries with concentrated sulfuric acid is a promising technology.The positive electrode materials are completely detached from aluminum foils at a lower temperature(below 50?)at the beginning leaching time(<30min).After sieving out the aluminum foils,the slurry is heated to 80? to continue leaching the positive electrode material.For lithium nickel cobalt manganese oxide,lithium is preferentially leached,and a reducing agent such as hydrogen peroxide is required to leaching all of the valuable metals such as nickel,cobalt and manganese.Compared with the traditional technology of leaching with dilute sulfuric acid or dilute hydrochloric acid,the technology proposed in this paper has less acid consumption,milder reaction conditions and lower energy consumption,and the separation of positive electrode materials from aluminum foils can be realized in the leaching process,which simplifies the recycling process of spent lithium-ion batteries. |
PDF Full Text Request