Method for preparing sodium ion battery positive electrode material from waste lithium iron phosphate

Abstract

The invention relates to the field of new energy materials, and discloses a method for preparing a sodium-ion battery positive electrode material from waste lithium iron phosphate. The method comprises the following steps: firstly, carrying out electrodialysis lithium extraction on the lithium iron phosphate waste by adopting an electrodialysis device taking an alkali metal group ion selective permeable membrane as a permeable membrane, and then carrying out solid-liquid separation on a mixed material in an anode chamber after lithium extraction; solid obtained after solid-liquid separation is iron phosphate slag, high-pressure alkaline leaching is conducted, and precipitated iron is calcined to prepare ferric oxide; the liquid is a sodium phosphate solution, and high-purity sodium phosphate is obtained through purification, impurity removal and crystallization and is used for preparing sodium dihydrogen phosphate; and finally, carrying out high-temperature calcination on ferric oxide and sodium dihydrogen phosphate to obtain the battery-grade ferric sodium pyrophosphate. The method is simple in process, easy to operate and low in recycling cost, lithium, phosphorus and iron are effectively recycled, meanwhile, interference of impurity elements of aluminum and fluorine is removed, and efficient resource utilization of waste residues is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of waste lithium ion battery recycling and the field of sodium ion battery, and in particular to a method for preparing a sodium ion battery positive electrode material from waste lithium iron phosphate. BACKGROUND

[0002] With the rapid development of renewable energy and electric vehicles, the demand for lithium ion batteries in China's new energy vehicle and energy storage market has increased dramatically. Among various lithium ion batteries, lithium iron phosphate (LFP) is favored by the market due to its high safety, abundant reserves, long cycle life, and low cost. It is estimated that the production will exceed 500 GWh by 2025. Although iron resources are abundant, the other main elements in LFP, lithium and phosphorus, are strategic resources due to their uneven distribution. So far, research has mainly focused on the recovery of metallic lithium from waste LFP. There is still a large amount of phosphorus and iron in the waste iron phosphate slag, which will cause environmental pollution and waste of resources if not properly disposed of, resulting in low utilization efficiency of phosphorus and iron resources. Therefore, it is of great significance to efficiently recover the waste iron phosphate slag obtained after lithium extraction from waste LFP.

[0003] At present, the main recovery method of waste iron phosphate slag is to completely dissolve it by high-concentration acid, and then generate iron phosphate by co-precipitation in the leaching solution. However, this method will cause the aluminum content in the co-precipitated iron phosphate product to exceed the standard and be difficult to remove, because the Ksp of aluminum phosphate (9.84×10 -21 ) is lower than that of iron phosphate (9.91×10 -19 ). Patent document CN116462232A discloses a similar method, but this method only reacts with sodium hydroxide solution at 90℃, so the removal of impurity aluminum is not complete, and the influence of impurity fluorine is not considered. CN115231537A discloses a method for preparing iron phosphate from phosphorus-iron slag, which consumes a large amount of acid and the removal of aluminum is not complete, resulting in phosphorus loss and high recovery cost. SUMMARY

[0004] In view of the problems that the current waste lithium iron phosphate recovery process consumes a large amount of acid and oxidant and subsequently generates a large amount of wastewater, the recovery rate of phosphoric acid slag is low, and the presence of impurities such as aluminum and fluorine interferes with the recovery of the product, resulting in poor quality of the recovered phosphoric acid iron product and high recovery cost, the present application proposes a method for preparing a sodium-ion battery positive electrode material from waste lithium iron phosphate, which first uses an alkali metal ion selective permeation membrane electrodialysis device to efficiently leach lithium from the waste lithium iron phosphate, then separates the lithium through a highly selective alkali metal ion selective permeation membrane, and the mother liquor is separated by solid-liquid separation to realize the recycling of the waste phosphoric acid iron slag, and the remaining mother liquor can be recycled. The method completely removes impurities, and the generated iron oxide and sodium phosphate have high purity, and can be further prepared into sodium iron pyrophosphate raw materials suitable for sodium-ion battery positive electrodes through high-temperature calcination, crystallization and other process flows, which is very suitable for large-scale production needs.

[0005] The technical solution of the present application is as follows:

[0006] A method for preparing a sodium-ion battery positive electrode material from waste lithium iron phosphate, characterized in that it comprises the following steps:

[0007] S1: lithium extraction by electrodialysis of lithium iron phosphate waste: dissolve the lithium iron phosphate waste in a neutral solution, place it in the anode chamber of an electrodialysis reaction device, introduce an acidic solution into the cathode chamber, use an alkali metal ion selective permeation membrane as the permeation membrane, and perform electrochemical electrodialysis under the constant voltage or constant current of a direct current power supply; during the electrodialysis process, Li + is continuously leached out, and Li + in the solution in the anode chamber passes through the alkali metal ion selective diaphragm into the cathode chamber; after a certain reaction time, the mixture in the anode chamber is subjected to solid-liquid separation, and the separated solid is phosphoric acid iron slag, and the cathode chamber obtains a lithium salt solution for preparing battery-grade lithium carbonate;

[0008] S2: high-pressure alkali leaching of the phosphoric acid iron slag and solid-liquid separation to obtain iron oxide and sodium phosphate solution;

[0009] S3: crystallization of the purified and impurity-removed sodium phosphate solution to obtain crystalline sodium phosphate, and the mother liquor after crystallization of the sodium phosphate solution can be continuously recycled, and the sodium phosphate is used to prepare sodium dihydrogen phosphate with dilute phosphoric acid;

[0010] The iron oxide is subjected to high-temperature oxidation calcination in an oxygen-containing atmosphere to obtain battery-grade nanometer iron red;

[0011] S4: the nanometer iron red is used as an iron source, the sodium dihydrogen phosphate is used as a sodium source and a phosphorus source, and the carbon source is mixed with the deionized water in a certain proportion, stirred, and then a dispersing agent is added, and the mixture is stirred at a temperature of 60-80 DEG C until a gel is formed, and then the gel is dried to obtain a dry gel, and the obtained dry gel precursor is subjected to high-temperature calcination in an argon atmosphere to obtain sodium iron pyrophosphate.

[0012] Further, the alkali metal ion selective permeable membrane is made by a dry film forming process, which is made of modified polyphenylene sulfide, inorganic filler and polymer polymer binder, and the modified polyphenylene sulfide powder and inorganic powder are dispersed in the polymer support net formed by the polymer; the modified polyphenylene sulfide particles in the alkali metal ion selective permeable membrane are in flat shape, the length of the modified polyphenylene sulfide particles in the vertical direction of the membrane is 1-10 μm, and the length in the horizontal direction of the membrane is 5-20 μm; the thickness of the membrane is 100-300 μm; the inorganic filler is one or more of zirconium hydrogen phosphate Zr(HPO4)2, barium sulfate BaSO4 and clay; the high molecular polymer is a composite of one or more of polytetrafluoroethylene, cellulose and derivatives, polyacrylic acid and polyvinylidene fluoride.

[0013] The modified polyphenylene sulfide is prepared from cross-linked polyphenylene sulfide, tetrachloro-p-benzoquinone and deionized water in a mass ratio of (15-20):1:(5-8) at a hydrothermal reaction temperature of 150-250℃ for 2-10h.

[0014] Further, in step S1, the anode of the electrodialysis reaction device is a titanium or nickel plate with an oxide having an electrocatalytic function attached to the surface, and the oxide having an electrocatalytic function is an oxide of titanium, zirconium, ruthenium, iridium, tin, tantalum or a mixture of two or more of the oxides; the current collector of the cathode of the electrodialysis reaction device is carbon felt, titanium or stainless steel, and the current collector surface is loaded with activated carbon or graphene.

[0015] Further, in step S1, the neutral solution is any one or a combination of lithium sulfate and lithium chloride solution, and the concentration is 0.5-1.5 mol / L; the solid-liquid ratio of the lithium iron phosphate waste to the neutral solution is 1g:10-15 mL; the acid solution is a sulfuric acid solution with a concentration of 0.1-1 mol / L.

[0016] Further, in step S1, in the electrodialysis process, the constant voltage is 3-8V or the constant current is 20-100mA / cm 2 , the reaction temperature is 25-30℃, and the reaction time is 1-12h.

[0017] Further, in step S2, the alkaline solution used in the high-pressure alkaline leaching process is one or a combination of 1-8 mol / L sodium hydroxide or sodium carbonate solution; the solid-liquid ratio of the phosphoric acid iron residue to the alkaline solution is 1g:3-10 mL, the alkaline leaching pressure is 1-6 MPa, the temperature is 100-300℃, and the time is 5-20h. After the reaction, the solid-liquid is separated, and the separated solid is iron oxide, which is a mixture of one or more of carbon-containing compounds of α-FeOOH, Fe3O4 and Fe2O3.

[0018] 2FePO4+6OH - →Fe2O3+2(PO4) 3- +3H2O / FePO4+3OH - →FeOOH+(PO4) 3- +H2O

[0019] 2Al+2OH - +2H2O→2(AlO2 - )+3H2↑

[0020] LiF+OH - →LiOH+F -

[0021] Further, the process of crystallizing sodium phosphate in S3 is: the sodium phosphate solution is cooled to -5℃ after high-temperature concentration and cooling, and solid sodium phosphate is precipitated;

[0022] The process of preparing sodium dihydrogen phosphate is: after the sodium phosphate solid is washed to be neutral, it is added into dilute phosphoric acid with a concentration of 2-2.3 mol / L according to a molar ratio of sodium phosphate: phosphoric acid of 1: (2-2.2), pH is kept at 3-4, temperature is kept at 40-90℃, stirring reaction is kept for 1-2 h, and sodium dihydrogen phosphate is obtained after crystallization, ethanol washing and drying of the crystal.

[0023] Further, in step S3, the calcination temperature of the iron oxide is 300-800℃, and the calcination time is 2-6 h, so that battery-grade nanometer iron red is obtained. The purity of Fe2O3 in the battery-grade nanometer iron red is ≥99.5%, the content of impurity elements Al, Fe, P and Na is less than 20 ppm, and the particle size is 0.1-0.5 μm.

[0024] Further, in step S4, the carbon source is one or more of sucrose, glucose and citric acid.

[0025] Further, in step S4, the nanometer iron red, sodium dihydrogen phosphate and carbon source are dissolved in deionized water according to a mass ratio of 1: (2.5-3.5): (0.15-0.2), the ratio of solute to water is 1 g: 10-15 mL, glycol is added as a dispersant after stirring for half an hour, the ratio of solute to glycol is 1 g: 0.8-1.2 mL, the solution is kept stirring at 60-80℃ until a gel is formed, and the gel is dried at 100-120℃ for 10-12 h to obtain a dry gel; the obtained dry gel precursor is pre-calcined at 250-300℃ for 4-5 h, then heated to 500-600℃ at a heating rate of 5℃·min -1 -1 under a stable argon gas flow, and calcined for 8-10 h.

[0026] 48NaH2PO4+12Fe2O3+C12 H 22 O 11 →24Na2FeP2O7+59H2O+6CO2+C

[0027] The particle size of the obtained solid sodium iron pyrophosphate is 45-75 mu m, and further grinding can obtain a particle size of 1-20 mu m.

[0028] Beneficial effects

[0029] The method for preparing a sodium-ion battery positive electrode material from waste lithium iron phosphate uses an alkali metal ion selective permeable membrane in an electro-dialysis reaction device, which is mainly formed by dispersing modified polyphenylene sulfide powder and Zr(HPO4)2 powder and other inorganic fillers in a polymer support net formed by a dry film forming technology, has high compactness, nanoscale transport channels and other characteristics, and has a large SO4 2- Anion is difficult to migrate.

[0030] The selective permeability of the alkali metal ion selective permeable membrane to metal ions is determined by the difference in the bonding ability between the sulfur site of polyphenylene sulfide and the cation, and the alkali metal monovalent cation with weak bonding ability has a higher diffusion coefficient. Through density functional calculation of the diffusion energy barrier of the ion, the diffusion ability is ranked as Fe 2+ , 1.2-1.4 eV) < Mg 2+ , 0.8-1.2 eV) < Al3+ (0.4-0.7 eV) < hydroxyl (OH - , 0.3-0.6 eV) < lithium (Li + , 0.2-0.3 eV) < hydrogen (H + , 0.1-0.3 eV) < sodium (Na + , 0.08-0.13 eV) < potassium (K + , 0.08-0.12 eV).

[0031] Due to the low migration energy barrier of monovalent metal, the sulfur site of polyphenylene sulfide and the monovalent metal cation in the solution undergo dipole adsorption, and the cation on the sulfur site can move along the adsorption site to form a continuous cation transfer path, thereby collectively constructing a nanoscale efficient cation transport channel in the membrane. High-valent metals have a high migration energy barrier and are difficult to pass through the membrane. Under the driving of the electro-dialysis electric field, efficient separation of monovalent metals and multivalent impurity ions (such as Al3+ and Fe 3+ ) is achieved.

[0032] Compared with the traditional slurry electrolysis, the electro-dialysis process in the present application uses an alkali metal ion selective permeable membrane to separate the anode chamber and the cathode chamber, and the Li +The iron phosphate is left in the anode chamber in the form of a precipitate by electric field driving through the diaphragm into the cathode chamber, and the whole process is green and economical.

[0033] The process of high-pressure alkali leaching treatment of the iron phosphate slag of the application on alkali liquor realizes high selectivity separation of iron and phosphorus in the iron phosphate slag, effectively removes impurity elements aluminum and fluorine, realizes high removal rate of aluminum, achieves high selectivity, and realizes effective recovery of phosphorus and iron. The iron phosphate slag of the application is converted into sodium iron pyrophosphate positive electrode material for sodium ion batteries by roasting and crystallization and other methods.

[0034] The method for preparing sodium ion battery positive electrode material from waste lithium iron phosphate of the application realizes secondary utilization of waste slag and solution after separation of iron and phosphorus, and prepares battery-grade sodium iron pyrophosphate suitable for sodium ion batteries, realizing efficient closed-loop recovery of waste LFP. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The process flow chart of the method for preparing sodium ion battery positive electrode material from waste lithium iron phosphate of the application.

[0036] Figure 2 The schematic diagram of the lithium electrodialysis device for waste lithium iron phosphate of the application.

[0037] Figure 3 The XRD graph of the diiron trioxide prepared in Example 5.

[0038] Figure 4 The XRD graph of the sodium iron pyrophosphate prepared in Example 5.

[0039] Figure 5 The SEM graph of the sodium iron pyrophosphate prepared in Example 5 DETAILED DESCRIPTION

[0040] The application will be further described below in combination with the drawings and specific examples, but the protection scope of the application is not limited thereto.

[0041] As shown in the drawings, Figure 1 the method comprises the following steps:

[0042] S1: lithium electrodialysis of lithium iron phosphate waste: the lithium iron phosphate waste is dissolved in a neutral solution, placed in the anode chamber of an electrodialysis reaction device, an acidic solution is introduced into the cathode chamber, an alkali metal ion selective membrane is used as a permeable membrane, and an electrochemical electrodialysis reaction is carried out under the constant voltage or constant current of a direct current power supply; in the electrodialysis process, Li + is continuously leached out, and Li +The alkali metal group ions are selected to pass through the selective diaphragm into the cathode chamber; after a certain reaction time, the mixture in the anode chamber is subjected to solid-liquid separation, and the separated solid is iron phosphate residue, and the cathode chamber obtains a lithium salt solution for preparing battery-grade lithium carbonate.

[0043] S2: The iron phosphate residue is subjected to high-pressure alkali leaching and solid-liquid separation to obtain iron oxide and sodium phosphate solution; the iron oxide is a mixture of one or more of carbon-containing compounds of α-FeOOH, Fe3O4 and Fe2O3.

[0044] S3: The sodium phosphate solution is subjected to purification and impurity removal and then crystallization to obtain crystalline sodium phosphate, and the sodium phosphate is used to prepare sodium dihydrogen phosphate with dilute phosphoric acid;

[0045] 2FePO4+6OH - →Fe2O3+2(PO4) 3- +3H2O / FePO4+3OH - →FeOOH+(PO4) 3- +H2O

[0046] 2Al+2OH - +2H2O→2(AlO2 - )+3H2↑

[0047] LiF+OH - →LiOH+F -

[0048] The iron oxide is subjected to high-temperature oxidation calcination in an oxygen-containing atmosphere, the calcination temperature is 300-800°C, and the calcination time is 2-6h to obtain battery-grade nanometer iron red; the battery-grade nanometer iron red has a purity of Fe2O3≥99.5%, the content of impurity elements Al, Fe, P and Na is less than 20ppm, and the particle size is 0.1-0.5μm.

[0049] S4: The nanometer iron red is used as an iron source, the sodium dihydrogen phosphate is used as a sodium source and a phosphorus source, and a carbon source is mixed with the nanometer iron red and the sodium dihydrogen phosphate in a certain proportion and dissolved in deionized water, a dispersing agent is added after stirring, and the mixture is stirred at a temperature of 60-80°C until a gel is formed, the gel is dried to obtain a dry gel, and the dry gel precursor is subjected to high-temperature calcination in an argon atmosphere to obtain sodium iron pyrophosphate.

[0050] The carbon source is one or more of sucrose, glucose and citric acid.

[0051] Specifically, the sucrose is used as a carbon source, and the sucrose is used as a chelating agent in the solution mixing stage and as a carbon source and a reducing agent in the high-temperature calcination stage. The dispersing agent is ethylene glycol.

[0052] 48NaH2PO4+12Fe2O3+C 12 H22 O 11 →24Na2FeP2O7+59H2O+6CO2+C

[0053] The particle size of the obtained powder sodium iron pyrophosphate is 45-75 μm, and further grinding can obtain a particle size of 1-20 μm.

[0054] The electrodialysis reaction device used in the application is shown in the figure Figure 2 The alkali metal ion selective permeable membrane is manufactured by a dry film forming process, and is made of modified polyphenylene sulfide, inorganic filler and high molecular polymer adhesive composite. The modified polyphenylene sulfide powder and inorganic powder are dispersed in the polymer support net formed by the high molecular polymer. The modified polyphenylene sulfide particles in the alkali metal ion selective permeable membrane are in a flat shape, the length of the modified polyphenylene sulfide particles in the vertical direction of the membrane is 1-10 μm, and the length in the horizontal direction of the membrane is 5-20 μm. The thickness of the membrane is 100-300 μm. The inorganic filler is one or more of zirconium hydrogen phosphate Zr(HPO4)2, barium sulfate BaSO4 and clay. The high molecular polymer is a composite of one or more of polytetrafluoroethylene, cellulose and derivatives, polyacrylic acid and polyvinylidene fluoride.

[0055] The modified polyphenylene sulfide is prepared from cross-linked polyphenylene sulfide, tetrachloro-p-benzoquinone and deionized water in a mass ratio of (15-20) : 1 : (5-8) at a hydrothermal reaction temperature of 150-250 ℃ and a reaction time of 2-10 h.

[0056] The anode of the electrodialysis reaction device is a titanium or nickel plate with an oxide having an electrocatalytic function attached to the surface. The oxide having an electrocatalytic function is an oxide of titanium, zirconium, ruthenium, iridium, tin, tantalum or a mixture of two or more of the oxides. The current collector of the cathode of the electrodialysis reaction device is carbon felt, titanium or stainless steel, and the surface of the current collector is loaded with activated carbon or graphene.

[0057] Example 1

[0058] The waste positive electrode material of the waste lithium iron phosphate battery, the elemental composition of the waste material is: Li: 4.02%, Fe: 28.12%, P: 12.13%, Al: 2.5%, F: 1.1%, C: 17%. 10g of the positive electrode material of the lithium iron phosphate battery is weighed and mixed with lithium sulfate solution according to the molar ratio of lithium iron phosphate to lithium sulfate of 0.6:1, the solid-liquid ratio is 1g:10mL, then it is added to the anode chamber, and 0.1mol / L of sulfuric acid solution is added to the cathode chamber. The electro-dialysis reaction is carried out at a constant voltage of 1V for 10h at a temperature of 30℃. After the reaction is completed, the mixture in the anode chamber is subjected to solid-liquid separation, the separated solution can be continuously used for electro-dialysis, and the separated solid is lithium phosphate residue B, and the cathode solution in the cathode chamber is lithium salt solution A, which is used for preparing battery-grade lithium carbonate.

[0059] The lithium salt solution A is sampled and analyzed by ICP, the leaching rate of lithium is 81.1%, and the lithium permeation rate in the cathode chamber is 99%. After the lithium salt solution A is purified, the pH value is adjusted to 11, and after filtration, the lithium salt solution A is heated to 95℃ to evaporate part of the solvent, and then CO2 is introduced to crystallize and precipitate lithium carbonate.

[0060] The lithium phosphate residue B is mixed with 2mol / L of sodium hydroxide solution, the solid-liquid ratio is 1g:15mL, and high-pressure alkali leaching reaction is carried out at 100℃ for 10h, the alkali leaching pressure is 1-6MPa, and after the reaction is completed, filtration is carried out to obtain sodium phosphate solution C and iron oxide D. Sampling is carried out in the sodium phosphate solution C, and ICP analysis is carried out, the leaching rate of aluminum is 62.6%, and the leaching rate of fluorine is 68.8%. After the sodium phosphate solution C is purified, sodium phosphate is obtained by concentration and crystallization. After the sodium phosphate crystal is washed to be neutral, according to the molar ratio of sodium phosphate to phosphoric acid of 1:2, it is added to 2mol / L dilute phosphoric acid, the pH value is kept at 3-4, the temperature is 60℃, and the stirring reaction is carried out for 2h, then the crystal is washed and dried to obtain sodium dihydrogen phosphate. And the iron oxide D is placed in an air atmosphere and calcined at 600℃ for 4h to obtain battery-grade nanometer iron red diiron trioxide.

[0061] 8g of diiron trioxide, 24g of sodium dihydrogen phosphate, and 1.42g of sucrose are dissolved in 400mL of deionized water, 30mL of ethylene glycol is added after stirring for half an hour, the solution is kept stirring at 80℃ until a gel is formed, and then it is dried at 120℃ for 12h to obtain a dry gel. The obtained dry gel precursor is pre-calcined at 250℃ for 5h, and then calcined at 600℃ for 10h in a stable argon gas stream to obtain sodium iron pyrophosphate.

[0062] Example 2

[0063] The positive electrode waste material of the waste lithium iron phosphate battery in this embodiment is the same as that in Example 1. 10 g of lithium iron phosphate positive electrode waste material is mixed with lithium sulfate solution at a molar ratio of lithium iron phosphate to lithium sulfate of 0.6:1, and the solid-liquid ratio is 1 g:10 mL. Then, the mixture is added to the anode chamber, and 0.1 mol / L sulfuric acid solution is added to the cathode chamber. The electrodialysis reaction is carried out at a constant voltage of 3 V at a temperature of 30°C for 10 h. After the reaction is completed, the mixture in the anode chamber is subjected to solid-liquid separation. The separated solution can be continuously used for electrodialysis, and the separated solid is phosphorus iron residue B. The cathode solution in the cathode chamber is lithium salt solution A, which is used to prepare battery-grade lithium carbonate.

[0064] The lithium salt solution A is sampled and analyzed by ICP. The leaching rate of lithium is 88.9%, and the lithium permeation rate in the cathode chamber is 99%. After the lithium salt solution A is purified, the pH value is adjusted to 11. After filtration, the lithium salt solution A is heated to 95°C to evaporate part of the solvent, and then CO2 is introduced to crystallize and precipitate lithium carbonate.

[0065] The phosphorus iron residue B is mixed with 2.5 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g:15 mL, and high-pressure alkali leaching reaction is carried out at a temperature of 150°C for 10 h. The alkali leaching pressure is 1-6 MPa. After the reaction is completed, the sodium phosphate solution C and iron oxide D are obtained by filtration. The sodium phosphate solution C is sampled and analyzed by ICP. The leaching rate of aluminum is 70.6%, and the leaching rate of fluorine is 79.7%. After the sodium phosphate solution C is purified, sodium phosphate is obtained by concentration and crystallization. The sodium phosphate crystals are washed to be neutral. According to the molar ratio of sodium phosphate to phosphoric acid of 1:2, they are added to 2 mol / L dilute phosphoric acid, the pH value is maintained at 3-4, the temperature is 60°C, and the stirring reaction is carried out for 2 h. After cooling, the crystals are washed and dried to obtain sodium dihydrogen phosphate. Iron oxide D is calcined at 600°C for 4 h in an air atmosphere to obtain diiron trioxide.

[0066] 8 g of diiron trioxide, 24 g of sodium dihydrogen phosphate, and 1.42 g of sucrose are dissolved in 400 mL of deionized water. After stirring for half an hour, 30 mL of ethylene glycol is added. The solution is kept stirring at 80°C until a gel is formed, and then dried at 120°C for 12 h to obtain a dry gel. The obtained dry gel precursor is pre-calcined at 250°C for 5 h, and then calcined at 600°C for 10 h in a stable argon gas stream to obtain sodium iron pyrophosphate.

[0067] Example 3

[0068] The positive electrode waste material of the waste lithium iron phosphate battery in this embodiment is the same as that in Example 1. 10 g of lithium iron phosphate positive electrode waste material is mixed with lithium sulfate solution at a molar ratio of lithium iron phosphate to lithium sulfate of 0.6:1, and the solid-liquid ratio is 1 g:10 mL. Then, the mixture is added to the anode chamber, and 0.1 mol / L sulfuric acid solution is added to the cathode chamber. The electrodialysis reaction is carried out at a constant voltage of 5 V. The reaction conditions are a temperature of 30°C and a time of 10 h. After the reaction is completed, the mixture in the anode chamber is subjected to solid-liquid separation. The separated solution can be continuously used for electrodialysis. The separated solid is phosphorus iron slag B, and the catholyte in the cathode chamber is lithium salt solution A, which is used to prepare battery-grade lithium carbonate.

[0069] The lithium salt solution A is sampled and analyzed by ICP. The leaching rate of lithium is 93.4%, and the lithium permeation rate in the cathode chamber is 99%. After adjusting the pH value of the impurity-removed and purified lithium salt solution A to 11, the solution is filtered, heated to 95°C, and then evaporated to remove part of the solvent. Then, CO2 is added to precipitate lithium carbonate.

[0070] The phosphorus iron slag B is mixed with 3 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g:15 mL, and high-pressure alkali leaching reaction is carried out. The reaction temperature is 200°C, the reaction time is 10 h, and the alkali leaching pressure is 1-6 MPa. After the reaction is completed, the phosphorus sodium solution C and the iron oxide D are obtained by filtration. The phosphorus sodium solution C is sampled and analyzed by ICP. The leaching rate of aluminum is 80.6%, and the leaching rate of fluorine is 84.7%. After purification and impurity removal, the phosphorus sodium solution C is concentrated and crystallized to obtain sodium phosphate. The sodium phosphate crystals are washed to be neutral. According to the molar ratio of sodium phosphate to phosphoric acid of 1:2, they are added to 2 mol / L dilute phosphoric acid, the pH is maintained at 3-4, the temperature is 60°C, and the stirring reaction is carried out for 2 h. After cooling and crystallization, the crystals are washed and dried to obtain sodium dihydrogen phosphate. The iron oxide D is calcined at 600°C in air for 4 h to obtain diiron trioxide.

[0071] 8 g of diiron trioxide, 24 g of sodium dihydrogen phosphate, and 1.42 g of sucrose are dissolved in 400 mL of deionized water. After stirring for half an hour, 30 mL of ethylene glycol is added. The solution is kept stirring at 80°C until a gel is formed, and then dried at 120°C for 12 h to obtain a dry gel. The obtained dry gel precursor is pre-calcined at 250°C for 5 h, and then calcined at 600°C in a stable argon gas stream for 10 h to obtain sodium iron pyrophosphate.

[0072] Example 4

[0073] In this embodiment, the waste positive electrode material of the waste lithium iron phosphate battery is the same as that of Example 1. 10 g of lithium iron phosphate positive electrode waste is mixed with lithium sulfate solution in a molar ratio of lithium iron phosphate to lithium sulfate of 0.6:1, and the solid-liquid ratio is 1 g:10 mL. Then, it is added to the anode chamber, and 0.1 mol / L sulfuric acid solution is added to the cathode chamber. The electrodialysis reaction is carried out at a constant voltage of 5 V. The reaction conditions are a temperature of 30°C and a time of 6 h. After the reaction is completed, the mixture in the anode chamber is subjected to solid-liquid separation. The separated solution can be continuously used for electrodialysis. The separated solid is phosphorus iron slag B, and the cathode solution in the cathode chamber is lithium salt solution A, which is used to prepare battery-grade lithium carbonate.

[0074] The lithium salt solution A is sampled and analyzed by ICP. The leaching rate of lithium is 90.1%, and the lithium permeation rate in the cathode chamber is 99%. After adjusting the pH value of the lithium salt solution A to 11 after impurity removal and purification, the solution is filtered, heated to 95°C, and then part of the solvent is evaporated. After adding CO2, lithium carbonate is precipitated by crystallization.

[0075] Phosphorus iron slag B is mixed with 3.5 mol / L sodium hydroxide solution, and the solid-liquid ratio is 1 g:15 mL. High-pressure alkali leaching reaction is carried out at a reaction temperature of 250°C and a reaction time of 10 h. After the reaction is completed, phosphorus sodium solution C and iron oxide D are obtained by filtration. The phosphorus sodium solution C is sampled and analyzed by ICP. The leaching rate of aluminum is 86.5%, and the leaching rate of fluorine is 91.2%. After purification and impurity removal, the phosphorus sodium solution C is concentrated and crystallized to obtain sodium phosphate. The sodium phosphate crystals are washed to be neutral. According to the molar ratio of sodium phosphate to phosphoric acid of 1:2, they are added to 2 mol / L dilute phosphoric acid, the pH is maintained at 3-4, the temperature is 60°C, and the stirring reaction is carried out for 2 h. After cooling and crystallization, the crystals are washed and dried to obtain sodium dihydrogen phosphate. Iron oxide D is calcined at 600°C in air for 4 h to obtain diiron trioxide.

[0076] 8 g of diiron trioxide, 24 g of sodium dihydrogen phosphate, and 1.42 g of sucrose are dissolved in 400 mL of deionized water. After stirring for half an hour, 30 mL of ethylene glycol is added. The solution is kept stirring at 80°C until a gel is formed, and then dried at 120°C for 12 h to obtain a dry gel. The obtained dry gel precursor is pre-calcined at 250°C for 5 h, and then calcined at 600°C in a stable argon gas stream for 10 h to obtain sodium iron pyrophosphate.

[0077] Example 5

[0078] In this embodiment, the waste positive electrode material of the waste lithium iron phosphate battery is the same as that in Example 1. 10 g of lithium iron phosphate positive electrode waste material is mixed with lithium sulfate solution according to the molar ratio of lithium iron phosphate to lithium sulfate of 0.6:1, the solid-liquid ratio is 1 g:10 mL, then it is added into the anode chamber, and 0.1 mol / L sulfuric acid solution is added into the cathode chamber. The electrodialysis reaction is carried out at a constant voltage of 5 V, the reaction conditions are temperature of 30℃ and time of 12 h. After the reaction is completed, the mixture in the anode chamber is subjected to solid-liquid separation, the separated solution can be continuously used for electrodialysis, and the separated solid is lithium phosphate residue B. The cathode solution in the cathode chamber is lithium salt solution A, which is used for preparing battery-grade lithium carbonate.

[0079] The lithium salt solution A is sampled and analyzed by ICP, the leaching rate of lithium is 96%, and the lithium permeation rate in the cathode chamber is 99%. After adjusting the pH value of the lithium salt solution A to 11, filtering, heating the solution to 95℃, evaporating part of the solvent, and adding CO2, lithium carbonate is precipitated.

[0080] The lithium salt solution A is sampled and analyzed by ICP, the leaching rate of lithium is 96%, and the lithium permeation rate in the cathode chamber is 99%. After adjusting the pH value of the lithium salt solution A to 11, filtering, heating the solution to 95℃, evaporating part of the solvent, and adding CO2, lithium carbonate is precipitated. Figure 3

[0081] 8 g of ferric oxide and 24 g of sodium dihydrogen phosphate, 1.42 g of sucrose are dissolved in 400 mL of deionized water, stirred for half an hour, then 30 mL of ethylene glycol is added, the solution is kept stirring at 80℃ until a gel is formed, and dried at 120℃ for 12 h to obtain a dry gel. The obtained dry gel precursor is pre-calcined at 250℃ for 5 h, then calcined at 600℃ in a stable argon gas stream for 10 h to obtain sodium pyrophosphate. The XRD spectrum and SEM image of sodium pyrophosphate prepared in this embodiment are shown in Figure 4 、 Figure 5 .

[0082] Comparative Example 1

[0083] ​In comparison with Example 5, the permeation membrane of the electrodialysis device does not use the modified polyphenylene sulfide alkali metal ion selective permeation membrane, but uses a cation exchange membrane (specification: CMB, Japan Astom), and sodium hydroxide solution is introduced into the cathode chamber instead of sulfuric acid solution, and direct electrodialysis oxidative leaching of valuable metal lithium is carried out, and the leaching efficiency of lithium is only 92%, and the permeation rate of lithium in the cathode chamber is only 96%, which shows that the polyphenylene sulfide alkali metal ion selective permeation membrane has a high extraction effect on lithium in the process, and the large amount of SO4 2- Anions are difficult to migrate to the anode chamber through the polyphenylene sulfide alkali metal ion selective permeation membrane.

[0084] Comparative Example 2

[0085] In comparison with Example 5, no high-pressure alkali leaching reaction is performed to treat impurity aluminum, and 10 g of positive electrode waste is directly subjected to electrodialysis oxidative leaching of valuable metal lithium, and then the method of high-temperature cooking with alkali solution is used for reaction, and finally the leaching residue obtained by solid-liquid separation is iron hydroxide, and after calcination, ferric oxide is obtained, and the ICP analysis shows that the content of aluminum element is 1.5%, and the content of fluorine element is 0.88%, which shows that the removal of impurities aluminum and fluorine is not complete in this process, and the content of impurity elements exceeds the standard.

[0086] Comparative Example 3

[0087] In comparison with Example 5, the commonly used ferric nitrate is used as the iron source to calcine to obtain sodium pyrophosphate iron, and a large amount of toxic and irritating nitrogen dioxide gas is generated in the process, which causes the obtained sodium pyrophosphate iron to present a fluffy and porous shape, and seriously affects the tap density. The tap density of the sodium pyrophosphate iron obtained by calcining the nanoscale ferric oxide obtained by oxidation roasting as the iron source is 1.89 g / cm 3 , and the tap density of the sodium pyrophosphate iron obtained by calcining the ferric nitrate as the iron source is 1.12 g / cm 3 .

[0088] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions implemented by those skilled in the art within the technical scope disclosed by the present application should be included in the protection scope of the present application.

Claims

1. A method of preparing a sodium-ion battery cathode material from spent lithium iron phosphate, characterized in that, The method comprises the following steps: S1: lithium extraction from lithium iron phosphate waste by electrodialysis: lithium iron phosphate waste is dissolved in a neutral solution and placed in an anode chamber of an electrodialysis reaction device, an acidic solution is introduced into a cathode chamber, an alkali metal ion selective permeable membrane is used as a permeable membrane, and an electrochemical electrodialysis reaction is carried out under a constant voltage or a constant current of a direct current power supply; during the electrodialysis process, Li + in the lithium iron phosphate waste in the anode chamber is continuously leached out, and Li + in the solution in the anode chamber passes through an alkali metal ion selective diaphragm into the cathode chamber; after a certain period of reaction, the mixture in the anode chamber is subjected to solid-liquid separation, the separated solid is iron phosphate slag, and the cathode chamber obtains a lithium salt solution which is used for preparing battery-grade lithium carbonate; S2: high-pressure alkali leaching is performed on the iron phosphate residue, and solid-liquid separation is performed, so as to obtain iron oxide and a sodium phosphate solution; S3: after the sodium phosphate solution is purified and impurities are removed, crystallization is performed, so as to obtain crystalline sodium phosphate; the sodium phosphate is used to prepare sodium dihydrogen phosphate with dilute phosphoric acid; The iron oxide is subjected to high-temperature calcination oxidation in an oxygen-containing atmosphere, so as to obtain battery-grade nanometer iron red; S4: the nanometer iron red is used as an iron source, the sodium dihydrogen phosphate is used as a sodium source and a phosphorus source, and a carbon source is uniformly mixed with deionized water in a certain proportion, is stirred, and then a dispersing agent is added; after stirring at a temperature of 60-80 DEG C until a gel is formed, drying is performed, so as to obtain a dry gel; the dry gel precursor obtained is subjected to high-temperature calcination in an argon atmosphere, so as to obtain sodium iron pyrophosphate.

2. The method of claim 1, wherein the method is characterized by, In step S1, the alkali metal ion selective permeation membrane is manufactured by a dry film forming process, and is composed of modified polyphenylene sulfide, inorganic filler and high molecular polymer adhesive. The modified polyphenylene sulfide powder and inorganic powder are dispersed in a polymer support net formed by the high molecular polymer. The modified polyphenylene sulfide particles in the alkali metal ion selective permeation membrane are in a flat shape, the length of the modified polyphenylene sulfide particles in the vertical direction of the membrane is 1-10 microns, and the length of the modified polyphenylene sulfide particles in the horizontal direction of the membrane is 5-20 microns. The thickness of the membrane is 100-300 microns. The inorganic filler is one or more of zirconium hydrogen phosphate Zr(HPO4)2, barium sulfate BaSO4 and clay. The high molecular polymer is a composite of one or more of polytetrafluoroethylene, cellulose and derivatives, polyacrylic acid and polyvinylidene fluoride. The modified polyphenylene sulfide is prepared from cross-linked polyphenylene sulfide, tetrachloro-p-benzoquinone and deionized water in a mass ratio of (15-20):1:(5-8) at a hydrothermal reaction temperature of 150-250 DEG C for 2-10 hours.

3. The method of claim 2, wherein the method is characterized by, In step S1, the anode of the electrodialysis reaction device is a titanium or nickel plate with an oxide having an electrocatalytic function attached to the surface. The oxide having the electrocatalytic function is an oxide of titanium, zirconium, ruthenium, iridium, tin, tantalum or a mixture of two or more oxides. The current collector of the cathode of the electrodialysis reaction device is carbon felt, titanium or stainless steel, and the surface of the current collector is loaded with activated carbon or graphene.

4. The method of claim 1, wherein the method is characterized by, In step S1, the neutral solution is any one or a combination of lithium sulfate and lithium chloride solution, and the concentration is 0.5-1.5 mol / L. The solid-liquid ratio of the lithium iron phosphate waste to the neutral solution is 1g:10-15 mL. The acid solution is a sulfuric acid solution, and the concentration is 0.1-1 mol / L.

5. The method of claim 1, wherein the method is characterized by: In step S1, the constant voltage is 3-8 V or the constant current is 20-100 mA / cm2 during the electrodialysis process 2 The reaction temperature is 25-30 °C, and the reaction time is 1-12 h.

6. The method of claim 1, wherein the method is characterized by: In step S2, the alkaline solution used in the high-pressure alkali leaching process is one or a combination of 1-8 mol / L sodium hydroxide or sodium carbonate solution. The solid-liquid ratio of the iron phosphate residue to the alkaline solution is 1g:3-10 mL. The alkali leaching pressure is 1-6 MPa, the temperature is 100-300 DEG C, and the time is 5-20 hours.

7. The method of claim 1, wherein the method is characterized by: In S3, the process of crystallizing the sodium phosphate is as follows: after the sodium phosphate solution is concentrated at a high temperature, it is cooled to-5 DEG C, and solid sodium phosphate is precipitated. The process for preparing sodium dihydrogen phosphate is as follows: after the sodium phosphate solid is washed to be neutral, the sodium phosphate is added into dilute phosphoric acid with a concentration of 2-2.3 mol / L according to a molar ratio of 1: (2-2.2), pH is kept at 3-4, temperature is kept at 40-90 ℃, and stirring reaction is carried out for 1-2 h, then the temperature is lowered to crystallize, and the crystal is washed by ethanol and dried to obtain sodium dihydrogen phosphate.

8. The method of claim 1, wherein the method is characterized by: In step S3, the calcination temperature of the iron oxide is 300-800 ℃, and the calcination time is 2-6 h.

9. The method of claim 1, wherein the method is characterized by, In step S4, nano iron red, sodium dihydrogen phosphate and carbon source are dissolved in deionized water according to a mass ratio of 1:(2.5-3.5):(0.15-0.2), and the ratio of solute to water is 1g:10-15mL. After stirring for half an hour, ethylene glycol is added as a dispersant, and the ratio of solute to ethylene glycol is 1g:0.8-1.2mL. The solution is kept stirring at 60-80°C until a gel is formed, and is dried at 100-120°C for 10-12h to obtain a dry gel. The obtained dry gel precursor is pre-calcined at 250-300°C for 4-5h, and then heated to 500-600°C at a heating rate of 5°C·min -1 under a stable argon gas stream, and calcined for 8-10h.

10. The method of claim 1, wherein the method is characterized by: In step S4, the carbon source is one or more of sucrose, glucose and citric acid.

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