Recycling method of lithium iron phosphate positive electrode material

Abstract

The invention discloses a lithium iron phosphate positive electrode material recovery method, which comprises: (1) adding dilute phosphoric acid to positive electrode material powder to prepare a lithium iron phosphate slurry, and carrying out electrolysis extraction to recover the lithium element in the positive electrode material powder so as to obtain an iron phosphate slurry; and (2) adding concentrated sulfuric acid into the iron phosphate slurry obtained in the step (1) to carry out a dissolution reaction, then carrying out solid-liquid separation to obtain a ferric sulfate solution containing phosphoric acid, then adding iron blocks or iron powder to carry out a reaction, and then adjusting the iron-phosphorus ratio and the ferrous ion content of the system to obtain a ferrous solution meeting the requirements of ammonium-process iron phosphate. The recycling method of the lithium iron phosphate positive electrode material is simple in technological process, less in acid and alkali consumption, less in waste liquid and low in cost, valuable elements such as lithium, iron and phosphorus in the lithium iron phosphate positive electrode powder are recycled at low cost and high yield, and the extracted iron and phosphorus elements are presented in a ferrous solution and can be directly grafted with an existing ammonium-process iron phosphate device, so that the recycling method is suitable for industrial production. Good popularization prospects are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery recycling, and in particular to a method for recycling lithium iron phosphate positive electrode materials. Background Art

[0002] Lithium iron phosphate (LIFP) batteries are a new type of lithium-ion battery primarily used in the electric vehicle industry. Because the iron in LFP batteries is widely available, relatively inexpensive, and non-heavy metal, LFP batteries are relatively environmentally friendly. Furthermore, because LFP batteries can be recharged over 2,000 times and pose no explosion hazard under extreme conditions, they are considered the future of battery technology. According to data, LFP consumption reached 32,400 tons in 2015, accounting for over 65% of global LFP demand. Therefore, the recycling of spent LFP batteries will be an emerging research area and hot topic in the coming years. The cathode materials in LFP batteries often contain abundant resources of elements such as iron and phosphorus. Effective recycling and reuse of the cathode materials in spent LFP batteries could open up new avenues for recycling and repurposing spent LFP batteries. This, in turn, could promote the innovation and application of electrochemical catalytic materials and the development of clean energy technologies, contributing to sustainable development and environmental protection.

[0003] Lithium-ion battery cathode material recycling technologies are primarily categorized into two main categories: dry and wet methods. The dry method boasts large processing capacity and a simple process flow, but it also suffers from high energy consumption, low metal recovery rates, significant waste gas emissions, and a high impurity content in the recycled product. In the wet process, lithium iron phosphate cathode materials are typically dissolved into a solution using a strong acid and an oxidant. After solid-liquid separation, the pH of the solution is gradually adjusted by the addition of alkali. During this gradual pH change, useful elements such as lithium iron are precipitated in stages. These methods are characterized by complex process flows, low energy consumption, high metal recovery rates, and zero waste gas emissions, but their profitability is significantly affected by the market. With the large-scale retirement of lithium-ion batteries in recent years, the lithium-ion battery recycling industry has grown significantly to reduce the environmental impact of these waste batteries. Ternary cathode materials are primarily recovered through wet methods for precious metals such as nickel, cobalt, and lithium. Due to the significant profit margins offered by precious metal recycling, the recycling of ternary lithium battery cathode materials generally meets actual demand. For lithium iron phosphate battery positive electrode materials, the mainstream method can only recover lithium iron and other elements through wet methods. The profit margin is small and losses may occur due to market influences. This has led to the recycling of lithium iron phosphate battery positive electrode materials being in the early stages of industrialization, and its production capacity cannot meet actual demand. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for recycling lithium iron phosphate positive electrode materials, which reduces the recycling cost of lithium iron phosphate positive electrode materials and realizes the industrial promotion of recycling lithium iron phosphate battery positive electrode materials.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for recycling lithium iron phosphate positive electrode materials, disassembling waste lithium iron phosphate batteries to obtain positive electrode sheets, separating the positive electrode material and current collector in the positive electrode sheets, and preparing the obtained positive electrode material into positive electrode material powder, comprising the following steps:

[0006] (1) adding dilute phosphoric acid to the positive electrode material powder to prepare a lithium iron phosphate slurry, and then performing electrolytic extraction to recover lithium elements in the positive electrode material powder to obtain an iron phosphate slurry;

[0007] (2) adding concentrated sulfuric acid to the ferric phosphate slurry obtained in step (1) to carry out a dissolution reaction, and then performing solid-liquid separation to obtain a ferric sulfate solution containing phosphoric acid, and then adding iron blocks or iron powder to carry out a reaction, and then adjusting the iron-phosphorus ratio and ferrous ion content of the system to obtain a ferrous solution that meets the requirements of the ammonium process ferric phosphate.

[0008] Furthermore, the electrolysis system used in step (1) includes a cathode chamber, an anode chamber, and electrodes. The anode chamber and the cathode chamber are separated by an ion membrane, and the ion membrane only allows lithium ions to pass through. The electrodes are platinum electrodes or graphite electrodes, lithium iron phosphate slurry is added to the anode chamber, and dilute phosphoric acid is added to the cathode chamber. In order to reduce the impact of lithium iron phosphate slurry on the ion membrane, in addition to the anode chamber structural design and the anode liquid flow rate control, an ion membrane protective layer is added to the anode chamber side of the ion membrane. The ion membrane protective layer is made of wear-resistant and corrosion-resistant materials and has filter holes on the protective layer, which can prevent particles in the lithium iron phosphate slurry from passing through.

[0009] Furthermore, in step (1), direct current is introduced to electrolyze the lithium iron phosphate slurry, and the electrolysis temperature is controlled at 50° C. to 70° C.

[0010] Furthermore, the solid content of the lithium iron phosphate slurry in step (1) is 15% to 20%.

[0011] Furthermore, the cathode liquid extracted in step (1) is subjected to gas-liquid separation to obtain a 3% to 5% lithium phosphate solution and hydrogen. The cathode is controlled to obtain a 3% to 5% lithium phosphate solution according to the amount of lithium phosphate solution extracted and the amount of dilute phosphoric acid added; the lithium phosphate solution is evaporated and concentrated to obtain a lithium phosphate product or converted into a lithium carbonate product. The residence time of the anolyte is controlled according to the electrolysis current, and the residence time can be flexibly adjusted by adopting a large-scale circulation and small-scale extraction method; the amount of cathode lithium phosphate solution extracted is determined according to the circulation amount of the cathode solution, and generally the extraction amount is controlled to be 5% to 15% of the circulation amount, and the cathode liquid concentration is controlled to maintain the efficiency and stability of the electrolysis system; during the lithium phosphate extraction process, the pH is used as the basis for phosphoric acid supplementation. When the cathode liquid concentration is controlled to be 3% to 5% (corresponding to a phosphoric acid concentration value), once the cathode liquid pH approaches 3%, phosphoric acid solution needs to be added to the cathode liquid; after actual stable operation, continuous extraction and continuous replenishment are adopted to ensure that the phosphoric acid concentration of the cathode liquid is between 3% and 5%.

[0012] Furthermore, in step (2), concentrated sulfuric acid is added to the ferric phosphate slurry for a dissolution reaction, the temperature during the reaction is controlled to be 70° C. to 90° C., the molar ratio of iron in the ferric phosphate slurry to sulfuric acid in the concentrated sulfuric acid is 1:1.5, stirring is continued during the reaction, and stirring is continued for 30 to 120 minutes after the reaction is completed to obtain a dissolved slurry.

[0013] Furthermore, the dissolved slurry obtained in step (2) is pumped into a plate-and-frame filter press for solid-liquid separation to obtain a phosphoric acid-containing ferric sulfate solution and leaching residue, and the ferric sulfate solution is filtered and impurities removed to obtain a purified ferric sulfate solution.

[0014] Furthermore, the purified ferric sulfate solution in step (2) is pumped into a reduction reactor, and excess iron blocks / iron powder is added to the reduction reactor at a molar ratio of ferric ions to elemental iron of 1:0.5 based on the ferric ion content in the solution, to perform a reduction reaction on the ferric ions in the ferric sulfate solution; after the feeding is completed, stirring and heating steam are started to perform the reduction reaction, and the reaction temperature is maintained at 50°C to 70°C during the reduction reaction; when the solution turns green, the ferric ion content in the solution is detected, and when it reaches below 0.01%, stirring is stopped, and the reduction reaction is completed to obtain a ferrous sulfate solution; the ferrous sulfate solution after the reaction is subjected to solid-liquid separation, filtration, and impurity removal to obtain a purified ferrous sulfate solution.

[0015] Furthermore, the purified ferrous sulfate solution in step (2) is added with phosphoric acid to control the iron-phosphorus ratio of the phosphoric acid-containing ferrous sulfate solution to the requirement of 1:1 according to the requirements of the ammonium ferric phosphate raw material, and pure water is added to control the concentration of ferrous sulfate to 10% to 15%, thereby obtaining a ferrous solution that meets the requirements of the ammonium ferric phosphate. The initial pH of the raw material system can be adjusted by adding 20% ​​ammonia water to the ammonium ferric phosphate device, and then hydrogen peroxide is added to start the oxidation reaction to obtain hydroxy ferric phosphate. After adding the hydrogen peroxide, 20% ammonia water is added to adjust the system pH to within the control range.

[0016] Furthermore, the mass fraction of the dilute phosphoric acid is 5% to 10%, and the mass fraction of the concentrated sulfuric acid is 90 to 98%.

[0017] In the prior art, the recovery of lithium iron phosphate positive electrode materials is mainly done by electrode electrolysis, which is extremely complex and has poor operability. The present application can be electrolyzed directly after slurry preparation; the purity of lithium ions obtained by cationic membrane electrolysis is very high, and low-concentration phosphoric acid is used as the cathode liquid. On the one hand, the cathode can directly obtain lithium phosphate products. Since the purity of the supplemented cathode liquid and the transferred lithium ions are both very high, the obtained lithium phosphate solution is of high purity, which is convenient for subsequent lithium phosphate concentration and utilization as a product; on the other hand, a small amount of cathode liquid phosphate anions migrate to the anode without causing any impact on the operation of the electrolysis system. The anion phosphate radical is the same as the anode slurry anion, and has no effect on the subsequent slurry utilization, and the acidity of the phosphate radical has no solubility for lithium iron phosphate and iron phosphate; after lithium extraction, sulfuric acid is used to dissolve the electrolytic slurry, mainly dissolving iron phosphate and a small amount of lithium iron phosphate. Since the conductive agent and the binder are insoluble in sulfuric acid, this step, in addition to utilizing the iron and phosphorus elements , and a filter press is used to separate the conductive agent and the binder. The existing process requires calcination to remove organic matter such as the conductive agent and the binder before lithium extraction. This is a process with high energy consumption and unsatisfactory environmental protection effects; the dissolving liquid is reduced to ferrous ions in order to cooperate with the existing mainstream iron phosphate production process to use ferrous ions to produce iron phosphate, which is convenient for the grafting of iron-phosphorus elements with existing equipment. In the future, if the iron phosphate production technology is innovated, the process can be simplified to directly mix iron ions for utilization; the innovation of the utilization of iron-phosphorus elements, which is directly used as an ammonium method raw material, also makes up for the situation that the ammonium method iron phosphate utilizes insufficient by-products of sulfuric acid method titanium dioxide after the industry's production capacity is expanded in the future. Most of the existing technologies for utilizing iron-phosphorus elements generate corresponding iron phosphate. Since iron phosphate is a material precursor, the raw material stability and control requirements are much higher than those of chemical processes. The technology of directly generating iron phosphate is feasible in theory, but it is actually very difficult to implement and has low operability.

[0018] The beneficial effects of the present invention are as follows: the recovery method of the lithium iron phosphate positive electrode material of the present invention has a simple process flow, low acid and alkali consumption, low waste liquid, and low cost, the lithium element recovery rate is not less than 92%, the iron element recovery rate is higher than 95%, and the phosphorus element recovery rate is higher than 95%. The purity of the obtained lithium phosphate crystals is as high as 99.9%, and the purity of the obtained ferrous sulfate crystals is as high as 99%, realizing low-cost and high-yield recovery of valuable elements such as lithium iron and phosphorus in the lithium iron phosphate positive electrode powder, and the extracted iron and phosphorus elements are presented in a ferrous solution, which can be directly grafted with the existing ammonium method iron phosphate device, and has good promotion prospects. DETAILED DESCRIPTION

[0019] The present invention is further described below with reference to the embodiments.

[0020] The lithium iron phosphate batteries to be processed were disassembled to obtain positive electrode sheets, which were then subjected to multi-stage crushing and screening to obtain lithium iron phosphate positive electrode powder. The mass fractions of lithium and iron in the lithium iron phosphate positive electrode powder are shown in Table 1. The obtained lithium iron phosphate positive electrode powder was used for recycling in Examples 1-3 and Comparative Examples 1-6.

[0021] Table 1

[0022] Lithium mass fraction Iron mass fraction Phosphorus mass fraction Lithium iron phosphate cathode powder 8.5％ 17.2％ 12.3％

[0023] Example 1:

[0024] (1) The electrolysis system used in the electrolysis includes a cathode chamber, an anode chamber and electrodes. The anode chamber and the cathode chamber are separated by an ion membrane, and the ion membrane only allows lithium ions to pass through. The electrodes are graphite electrodes, lithium iron phosphate slurry is added to the anode chamber, and dilute phosphoric acid is added to the cathode chamber;

[0025] Pure water and 85% phosphoric acid are mixed to obtain 10% dilute phosphoric acid, and the dilute phosphoric acid is added to the cathode chamber of the electrolysis system; lithium iron phosphate positive electrode powder and 10% dilute phosphoric acid are mixed to obtain lithium iron phosphate slurry with a solid content of 20%, and the lithium iron phosphate slurry is added to the anode chamber of the electrolysis device, the electrolysis device adopts direct current electrolysis, the electrolysis temperature is controlled at 50°C, most of the anolyte in the anode chamber is circulated through electrolysis, the feed amount and the output amount ensure that the average residence time of the anolyte is 2 hours, and 15% iron phosphate slurry is obtained in the anode chamber; most of the cathode liquid in the cathode chamber is circulated, and the output catholyte is separated by gas and liquid to obtain a 5% lithium phosphate solution, and the amount of dilute phosphoric acid added is adjusted (0.5-1) according to the output amount and pH value of the lithium phosphate solution, and the output amount of the lithium phosphate solution is 10% of the circulation amount;

[0026] (2) The lithium phosphate solution produced in the cathode chamber is subsequently concentrated by evaporation and centrifugal drying to obtain a lithium phosphate product. The iron phosphate slurry produced in the anode chamber is uniformly collected in a leaching tank, and the stirring of the leaching tank is started. Based on the iron ion content in the iron phosphate slurry, an excess of 90% concentrated sulfuric acid is gradually added to the leaching tank at a molar ratio of iron to sulfuric acid of 1:1.6 to dissolve the iron phosphate slurry. After the concentrated sulfuric acid is added, the stirring operation is continued for 30 minutes to obtain a dissolved slurry. The reaction temperature is maintained at 70°C during the dissolution reaction. The dissolved slurry is pumped into a plate and frame filter press for solid-liquid separation to obtain a phosphoric acid-containing iron sulfate solution and a leaching residue. The purified iron sulfate solution is further obtained after impurities are removed by precise filtration;

[0027] (3) The purified ferric sulfate solution is pumped into a reduction reactor by a pump, and at the same time, excess iron powder is added to the reduction reactor at a molar ratio of 1:0.6 between ferric ions and elemental iron based on the content of ferric ions in the solution, and the ferric ions in the ferric sulfate solution are reduced. After the feeding is completed, stirring and heating steam are turned on to carry out the reduction reaction. The reaction temperature is maintained at 50°C during the reduction reaction. When the solution turns green, stirring is stopped when the content of ferric ions in the solution is detected to be below 0.01%. After the reduction reaction is completed, a ferrous sulfate solution is obtained, and the reacted ferrous sulfate solution is pumped into a plate and frame filter press for solid-liquid separation to obtain a ferrous sulfate solution containing phosphoric acid and unreacted iron blocks / iron powder. The purified ferrous sulfate solution is further obtained by removing impurities through precise filtration.

[0028] (4) The purified ferrous sulfate was transferred to a preparation kettle. According to the requirements of the ammonium ferric phosphate raw material, phosphoric acid was added to control the iron-phosphorus ratio of the ferrous sulfate solution containing phosphoric acid to be 1:1. At the same time, pure water was added to control the concentration of ferrous sulfate to 15% and pH 2.5. After passing the test, a ferrous solution that met the requirements of the ammonium ferric phosphate was obtained. The recovery rate of lithium ferrophosphide and the purity of the product were calculated. The results are shown in Table 2.

[0029] Example 2:

[0030] (1) The electrolysis system used in the electrolysis includes a cathode chamber, an anode chamber and electrodes. The anode chamber and the cathode chamber are separated by an ion membrane, and the ion membrane only allows lithium ions to pass through. The electrodes are graphite electrodes, lithium iron phosphate slurry is added to the anode chamber, and dilute phosphoric acid is added to the cathode chamber;

[0031] Pure water and 85% phosphoric acid are mixed to obtain 7% dilute phosphoric acid, and the dilute phosphoric acid is added to the cathode chamber of the electrolysis system; lithium iron phosphate positive electrode powder and 7% dilute phosphoric acid are mixed to obtain lithium iron phosphate slurry with a solid content of 17%, and the lithium iron phosphate slurry is added to the anode chamber of the electrolysis device, the electrolysis device adopts direct current electrolysis, the electrolysis temperature is controlled at 60°C, most of the anolyte in the anode chamber is circulated through electrolysis, the feed amount and the output amount ensure that the average residence time of the anolyte is 1.5 hours, and 18% iron phosphate slurry is obtained in the anode chamber; most of the cathode liquid in the cathode chamber is circulated, and the output catholyte is separated by gas and liquid to obtain a 4% lithium phosphate solution, and the amount of dilute phosphoric acid added is adjusted (0.5-1) according to the output amount and pH value of the lithium phosphate solution, and the output amount of the lithium phosphate solution is 6% of the circulation amount;

[0032] (2) The lithium phosphate solution produced in the cathode chamber is subsequently concentrated by evaporation and centrifugal drying to obtain a lithium phosphate product. The iron phosphate slurry produced in the anode chamber is uniformly collected in a leaching tank, and the stirring of the leaching tank is started. Based on the iron ion content in the iron phosphate slurry, an excess of 93% concentrated sulfuric acid is gradually added to the leaching tank at a molar ratio of iron to sulfuric acid of 1:1.55 to dissolve the iron phosphate slurry. After the concentrated sulfuric acid is added, the stirring operation is continued for 60 minutes to obtain a dissolved slurry. The reaction temperature is maintained at 80°C during the dissolution reaction. The dissolved slurry is pumped into a plate and frame filter press for solid-liquid separation to obtain a phosphoric acid-containing iron sulfate solution and a leaching residue. The purified iron sulfate solution is further obtained after impurities are removed by precise filtration;

[0033] (3) The purified ferric sulfate solution is pumped into a reduction reactor by a pump, and at the same time, excess iron powder is added to the reduction reactor at a molar ratio of 1:0.55 between ferric ions and elemental iron based on the content of ferric ions in the solution, and the ferric ions in the ferric sulfate solution are reduced. After the feeding is completed, stirring and heating steam are turned on to carry out the reduction reaction. The reaction temperature is maintained at 60°C during the reduction reaction. When the solution turns green, stirring is stopped when the content of ferric ions in the solution is detected to be below 0.01%. After the reduction reaction is completed, a ferrous sulfate solution is obtained, and the reacted ferrous sulfate solution is pumped into a plate and frame filter press for solid-liquid separation to obtain a ferrous sulfate solution containing phosphoric acid and unreacted iron blocks / iron powder. The purified ferrous sulfate solution is further obtained by removing impurities through precise filtration.

[0034] (4) The purified ferrous sulfate was transferred to a preparation kettle. According to the requirements of the ammonium ferric phosphate raw material, phosphoric acid was added to control the iron-phosphorus ratio of the ferrous sulfate solution containing phosphoric acid to be 1:1. At the same time, pure water was added to control the concentration of ferrous sulfate to 13% and pH 2. After passing the test, a ferrous solution that met the requirements of the ammonium ferric phosphate was obtained. The recovery rate of lithium ferrophosphide and the purity of the product were calculated. The results are shown in Table 2.

[0035] Example 3:

[0036] (1) The electrolysis system used in the electrolysis includes a cathode chamber, an anode chamber and electrodes. The anode chamber and the cathode chamber are separated by an ion membrane, and the ion membrane only allows lithium ions to pass through. The electrodes are graphite electrodes, lithium iron phosphate slurry is added to the anode chamber, and dilute phosphoric acid is added to the cathode chamber;

[0037] Pure water and 85% phosphoric acid are mixed to obtain 5% dilute phosphoric acid, and the dilute phosphoric acid is added to the cathode chamber of the electrolysis system; lithium iron phosphate positive electrode powder and 5% dilute phosphoric acid are mixed to obtain lithium iron phosphate slurry with a solid content of 15%, and the lithium iron phosphate slurry is added to the anode chamber of the electrolysis device, the electrolysis device adopts direct current electrolysis, the electrolysis temperature is controlled at 70°C, most of the anolyte in the anode chamber is circulated through electrolysis, the feed amount and the output amount ensure that the average residence time of the anolyte is 3 hours, and 20% iron phosphate slurry is obtained in the anode chamber; most of the cathode liquid in the cathode chamber is circulated, and the output catholyte is separated by gas and liquid to obtain a 3% lithium phosphate solution, and the amount of dilute phosphoric acid added is adjusted (0.5-1) according to the output amount and pH value of the lithium phosphate solution, and the output amount of the lithium phosphate solution is 15% of the circulation amount;

[0038] (2) The lithium phosphate solution produced in the cathode chamber is subsequently concentrated by evaporation and centrifugal drying to obtain a lithium phosphate product. The iron phosphate slurry produced in the anode chamber is uniformly collected in a leaching tank, and the stirring of the leaching tank is started. Based on the iron ion content in the iron phosphate slurry, an excess of 98% concentrated sulfuric acid is gradually added to the leaching tank at a molar ratio of iron to sulfuric acid of 1:1.5 to dissolve the iron phosphate slurry. After the concentrated sulfuric acid is added, the stirring operation is continued for 80 minutes to obtain a dissolved slurry. The reaction temperature is maintained at 90°C during the dissolution reaction. The dissolved slurry is pumped into a plate and frame filter press for solid-liquid separation to obtain a phosphoric acid-containing iron sulfate solution and a leaching residue. The purified iron sulfate solution is further obtained after impurities are removed by precise filtration;

[0039] (3) The purified ferric sulfate solution is pumped into a reduction reactor by a pump, and at the same time, excess iron powder is added to the reduction reactor at a molar ratio of 1:0.5 between ferric ions and elemental iron based on the content of ferric ions in the solution, and the ferric ions in the ferric sulfate solution are reduced. After the feeding is completed, stirring and heating steam are turned on to carry out the reduction reaction. The reaction temperature is maintained at 70°C during the reduction reaction. When the solution turns green, stirring is stopped when the content of ferric ions in the solution is detected to be below 0.01%. After the reduction reaction is completed, a ferrous sulfate solution is obtained, and the reacted ferrous sulfate solution is pumped into a plate and frame filter press for solid-liquid separation to obtain a ferrous sulfate solution containing phosphoric acid and unreacted iron blocks / iron powder. The purified ferrous sulfate solution is further obtained by removing impurities through precise filtration;

[0040] (4) The purified ferrous sulfate was transferred to a preparation kettle. According to the requirements of the ammonium ferric phosphate raw material, phosphoric acid was added to control the iron-phosphorus ratio of the ferrous sulfate solution containing phosphoric acid to be 1:1. At the same time, pure water was added to control the concentration of ferrous sulfate to 10% and pH 1.5. After passing the test, a ferrous solution that met the requirements of the ammonium ferric phosphate was obtained. The recovery rate of lithium ferrophosphide and the purity of the product were calculated. The results are shown in Table 2.

[0041] Comparative Example 1: (the cathode liquid obtained a 1% lithium phosphate solution, and the rest was the same as in Example 1)

[0042] (1) The electrolysis system used in the electrolysis includes a cathode chamber, an anode chamber and electrodes. The anode chamber and the cathode chamber are separated by an ion membrane, and the ion membrane only allows lithium ions to pass through. The electrodes are graphite electrodes, lithium iron phosphate slurry is added to the anode chamber, and dilute phosphoric acid is added to the cathode chamber;

[0043] Pure water and 85% phosphoric acid are mixed to obtain 10% dilute phosphoric acid, and the dilute phosphoric acid is added to the cathode chamber of the electrolysis system; lithium iron phosphate positive electrode powder and 10% dilute phosphoric acid are mixed to obtain lithium iron phosphate slurry with a solid content of 20%, and the lithium iron phosphate slurry is added to the anode chamber of the electrolysis device, the electrolysis device adopts direct current electrolysis, the electrolysis temperature is controlled at 50°C, most of the anolyte in the anode chamber is circulated through electrolysis, the feed amount and the output amount ensure that the average residence time of the anolyte is 2 hours, and 15% iron phosphate slurry is obtained in the anode chamber; most of the cathode liquid in the cathode chamber is circulated, and the output catholyte is separated by gas and liquid to obtain a 1% lithium phosphate solution, and the amount of dilute phosphoric acid added is adjusted (0.5-1) according to the output amount and pH value of the lithium phosphate solution, and the output amount of the lithium phosphate solution is 10% of the circulation amount;

[0044] (2) The lithium phosphate solution produced in the cathode chamber is subsequently concentrated by evaporation and centrifugal drying to obtain a lithium phosphate product. The iron phosphate slurry produced in the anode chamber is uniformly collected in a leaching tank, and the stirring of the leaching tank is started. Based on the iron ion content in the iron phosphate slurry, an excess of 90% concentrated sulfuric acid is gradually added to the leaching tank at a molar ratio of iron to sulfuric acid of 1:1.6 to dissolve the iron phosphate slurry. After the concentrated sulfuric acid is added, the stirring operation is continued for 30 minutes to obtain a dissolved slurry. The reaction temperature is maintained at 70°C during the dissolution reaction. The dissolved slurry is pumped into a plate and frame filter press for solid-liquid separation to obtain a phosphoric acid-containing iron sulfate solution and a leaching residue. The purified iron sulfate solution is further obtained after impurities are removed by precise filtration;

[0045] (3) The purified ferric sulfate solution is pumped into a reduction reactor by a pump, and at the same time, excess iron powder is added to the reduction reactor at a molar ratio of 1:0.6 between ferric ions and elemental iron based on the content of ferric ions in the solution, and the ferric ions in the ferric sulfate solution are reduced. After the feeding is completed, stirring and heating steam are turned on to carry out the reduction reaction. The reaction temperature is maintained at 50°C during the reduction reaction. When the solution turns green, stirring is stopped when the content of ferric ions in the solution is detected to be below 0.01%. After the reduction reaction is completed, a ferrous sulfate solution is obtained, and the reacted ferrous sulfate solution is pumped into a plate and frame filter press for solid-liquid separation to obtain a ferrous sulfate solution containing phosphoric acid and unreacted iron blocks / iron powder. The purified ferrous sulfate solution is further obtained by removing impurities through precise filtration.

[0046] (4) The purified ferrous sulfate was transferred to a preparation kettle. According to the requirements of the ammonium ferric phosphate raw material, phosphoric acid was added to control the iron-phosphorus ratio of the ferrous sulfate solution containing phosphoric acid to be 1:1. At the same time, pure water was added to control the concentration of ferrous sulfate to 15% and pH 2.5. After passing the test, a ferrous solution that met the requirements of the ammonium ferric phosphate was obtained. The recovery rate of lithium ferrophosphide and the purity of the product were calculated. The results are shown in Table 2.

[0047] Comparative Example 2: (the cathode liquid obtained a 7% lithium phosphate solution, and the rest was the same as in Example 1)

[0048] (1) The electrolysis system used in the electrolysis includes a cathode chamber, an anode chamber and electrodes. The anode chamber and the cathode chamber are separated by an ion membrane, and the ion membrane only allows lithium ions to pass through. The electrodes are graphite electrodes, lithium iron phosphate slurry is added to the anode chamber, and dilute phosphoric acid is added to the cathode chamber;

[0049] Pure water and 85% phosphoric acid are mixed to obtain 10% dilute phosphoric acid, and the dilute phosphoric acid is added to the cathode chamber of the electrolysis system; lithium iron phosphate positive electrode powder and 10% dilute phosphoric acid are mixed to obtain lithium iron phosphate slurry with a solid content of 20%, and the lithium iron phosphate slurry is added to the anode chamber of the electrolysis device, the electrolysis device adopts direct current electrolysis, the electrolysis temperature is controlled at 50°C, most of the anolyte in the anode chamber is circulated through electrolysis, the feed amount and the output amount ensure that the average residence time of the anolyte is 2 hours, and 15% iron phosphate slurry is obtained in the anode chamber; most of the cathode liquid in the cathode chamber is circulated, and the output cathode liquid is subjected to gas-liquid separation to obtain a 7% lithium phosphate solution, and the amount of dilute phosphoric acid added is adjusted (0.5-1) according to the output amount and pH value of the lithium phosphate solution, and the output amount of the lithium phosphate solution is 10% of the circulation amount;

[0050] (2) The lithium phosphate solution produced in the cathode chamber is subsequently concentrated by evaporation and centrifugal drying to obtain a lithium phosphate product. The iron phosphate slurry produced in the anode chamber is uniformly collected in a leaching tank, and the stirring of the leaching tank is started. Based on the iron ion content in the iron phosphate slurry, an excess of 90% concentrated sulfuric acid is gradually added to the leaching tank at a molar ratio of iron to sulfuric acid of 1:1.6 to dissolve the iron phosphate slurry. After the concentrated sulfuric acid is added, the stirring operation is continued for 30 minutes to obtain a dissolved slurry. The reaction temperature is maintained at 70°C during the dissolution reaction. The dissolved slurry is pumped into a plate and frame filter press for solid-liquid separation to obtain a phosphoric acid-containing iron sulfate solution and a leaching residue. The purified iron sulfate solution is further obtained after impurities are removed by precise filtration;

[0051] (3) The purified ferric sulfate solution is pumped into a reduction reactor by a pump, and at the same time, excess iron powder is added to the reduction reactor at a molar ratio of 1:0.6 between ferric ions and elemental iron based on the content of ferric ions in the solution, and the ferric ions in the ferric sulfate solution are reduced. After the feeding is completed, stirring and heating steam are turned on to carry out the reduction reaction. The reaction temperature is maintained at 50°C during the reduction reaction. When the solution turns green, stirring is stopped when the content of ferric ions in the solution is detected to be below 0.01%. After the reduction reaction is completed, a ferrous sulfate solution is obtained, and the reacted ferrous sulfate solution is pumped into a plate and frame filter press for solid-liquid separation to obtain a ferrous sulfate solution containing phosphoric acid and unreacted iron blocks / iron powder. The purified ferrous sulfate solution is further obtained by removing impurities through precise filtration.

[0052] (4) The purified ferrous sulfate was transferred to a preparation kettle. According to the requirements of the ammonium ferric phosphate raw material, phosphoric acid was added to control the iron-phosphorus ratio of the ferrous sulfate solution containing phosphoric acid to be 1:1. At the same time, pure water was added to control the concentration of ferrous sulfate to 15% and pH 2.5. After passing the test, a ferrous solution that met the requirements of the ammonium ferric phosphate was obtained. The recovery rate of lithium ferrophosphide and the purity of the product were calculated. The results are shown in Table 2.

[0053] Comparative Example 3: (electrolysis time is 0.5h, other conditions are the same as in Example 1)

[0054] (1) The electrolysis system used in the electrolysis includes a cathode chamber, an anode chamber and electrodes. The anode chamber and the cathode chamber are separated by an ion membrane, and the ion membrane only allows lithium ions to pass through. The electrodes are graphite electrodes, lithium iron phosphate slurry is added to the anode chamber, and dilute phosphoric acid is added to the cathode chamber;

[0055] Pure water and 85% phosphoric acid are mixed to obtain 10% dilute phosphoric acid, and the dilute phosphoric acid is added to the cathode chamber of the electrolysis system; lithium iron phosphate positive electrode powder and 10% dilute phosphoric acid are mixed to obtain lithium iron phosphate slurry with a solid content of 20%, and the lithium iron phosphate slurry is added to the anode chamber of the electrolysis device, the electrolysis device adopts direct current electrolysis, the electrolysis temperature is controlled at 50°C, most of the anolyte in the anode chamber is circulated through electrolysis, the feed amount and the output amount ensure that the average residence time of the anolyte is 0.5 hours, and 15% iron phosphate slurry is obtained in the anode chamber; most of the cathode liquid in the cathode chamber is circulated, and the output cathode liquid is subjected to gas-liquid separation to obtain a 5% lithium phosphate solution, and the amount of dilute phosphoric acid added is adjusted (0.5-1) according to the output amount and pH value of the lithium phosphate solution, and the output amount of the lithium phosphate solution is 10% of the circulation amount;

[0056] (2) The lithium phosphate solution produced in the cathode chamber is subsequently concentrated by evaporation and centrifugal drying to obtain a lithium phosphate product. The iron phosphate slurry produced in the anode chamber is uniformly collected in a leaching tank, and the stirring of the leaching tank is started. Based on the iron ion content in the iron phosphate slurry, an excess of 90% concentrated sulfuric acid is gradually added to the leaching tank at a molar ratio of iron to sulfuric acid of 1:1.6 to dissolve the iron phosphate slurry. After the concentrated sulfuric acid is added, the stirring operation is continued for 30 minutes to obtain a dissolved slurry. The reaction temperature is maintained at 70°C during the dissolution reaction. The dissolved slurry is pumped into a plate and frame filter press for solid-liquid separation to obtain a phosphoric acid-containing iron sulfate solution and a leaching residue. The purified iron sulfate solution is further obtained after impurities are removed by precise filtration;

[0057] (3) The purified ferric sulfate solution is pumped into a reduction reactor by a pump, and at the same time, excess iron powder is added to the reduction reactor at a molar ratio of 1:0.6 between ferric ions and elemental iron based on the content of ferric ions in the solution, and the ferric ions in the ferric sulfate solution are reduced. After the feeding is completed, stirring and heating steam are turned on to carry out the reduction reaction. The reaction temperature is maintained at 50°C during the reduction reaction. When the solution turns green, stirring is stopped when the content of ferric ions in the solution is detected to be below 0.01%. After the reduction reaction is completed, a ferrous sulfate solution is obtained, and the reacted ferrous sulfate solution is pumped into a plate and frame filter press for solid-liquid separation to obtain a ferrous sulfate solution containing phosphoric acid and unreacted iron blocks / iron powder. The purified ferrous sulfate solution is further obtained by removing impurities through precise filtration.

[0058] (4) The purified ferrous sulfate was transferred to a preparation kettle. According to the requirements of the ammonium ferric phosphate raw material, phosphoric acid was added to control the iron-phosphorus ratio of the ferrous sulfate solution containing phosphoric acid to be 1:1. At the same time, pure water was added to control the concentration of ferrous sulfate to 15% and pH 2.5. After passing the test, a ferrous solution that met the requirements of the ammonium ferric phosphate was obtained. The recovery rate of lithium ferrophosphide and the purity of the product were calculated. The results are shown in Table 2.

[0059] Comparative Example 4: (The stirring time after adding concentrated sulfuric acid was 20 minutes, and the rest was the same as in Example 1)

[0060] (1) The electrolysis system used in the electrolysis includes a cathode chamber, an anode chamber and electrodes. The anode chamber and the cathode chamber are separated by an ion membrane, and the ion membrane only allows lithium ions to pass through. The electrodes are graphite electrodes, lithium iron phosphate slurry is added to the anode chamber, and dilute phosphoric acid is added to the cathode chamber;

[0061] Pure water and 85% phosphoric acid are mixed to obtain 10% dilute phosphoric acid, and the dilute phosphoric acid is added to the cathode chamber of the electrolysis system; lithium iron phosphate positive electrode powder and 10% dilute phosphoric acid are mixed to obtain lithium iron phosphate slurry with a solid content of 20%, and the lithium iron phosphate slurry is added to the anode chamber of the electrolysis device, the electrolysis device adopts direct current electrolysis, the electrolysis temperature is controlled at 50°C, most of the anolyte in the anode chamber is circulated through electrolysis, the feed amount and the output amount ensure that the average residence time of the anolyte is 2 hours, and 15% iron phosphate slurry is obtained in the anode chamber; most of the cathode liquid in the cathode chamber is circulated, and the output catholyte is separated by gas and liquid to obtain a 5% lithium phosphate solution, and the amount of dilute phosphoric acid added is adjusted (0.5-1) according to the output amount and pH value of the lithium phosphate solution, and the output amount of the lithium phosphate solution is 10% of the circulation amount;

[0062] (2) The lithium phosphate solution produced in the cathode chamber is subsequently concentrated by evaporation and centrifugal drying to obtain a lithium phosphate product. The iron phosphate slurry produced in the anode chamber is uniformly collected in a leaching tank, and the stirring of the leaching tank is started. Based on the iron ion content in the iron phosphate slurry, an excess of 90% concentrated sulfuric acid is gradually added to the leaching tank at a molar ratio of iron to sulfuric acid of 1:1.6 to dissolve the iron phosphate slurry. After the concentrated sulfuric acid is added, the stirring operation is continued for 20 minutes to obtain a dissolved slurry. The reaction temperature is maintained at 70°C during the dissolution reaction. The dissolved slurry is pumped into a plate and frame filter press for solid-liquid separation to obtain a phosphoric acid-containing iron sulfate solution and a leaching residue. The purified iron sulfate solution is further obtained after impurities are removed by precise filtration;

[0063] (3) The purified ferric sulfate solution is pumped into a reduction reactor by a pump, and at the same time, excess iron powder is added to the reduction reactor at a molar ratio of 1:0.6 between ferric ions and elemental iron based on the content of ferric ions in the solution, and the ferric ions in the ferric sulfate solution are reduced. After the feeding is completed, stirring and heating steam are turned on to carry out the reduction reaction. The reaction temperature is maintained at 50°C during the reduction reaction. When the solution turns green, stirring is stopped when the content of ferric ions in the solution is detected to be below 0.01%. After the reduction reaction is completed, a ferrous sulfate solution is obtained, and the reacted ferrous sulfate solution is pumped into a plate and frame filter press for solid-liquid separation to obtain a ferrous sulfate solution containing phosphoric acid and unreacted iron blocks / iron powder. The purified ferrous sulfate solution is further obtained by removing impurities through precise filtration.

[0064] (4) The purified ferrous sulfate was transferred to a preparation kettle. According to the requirements of the ammonium ferric phosphate raw material, phosphoric acid was added to control the iron-phosphorus ratio of the ferrous sulfate solution containing phosphoric acid to be 1:1. At the same time, pure water was added to control the concentration of ferrous sulfate to 15% and pH 2.5. After passing the test, a ferrous solution that met the requirements of the ammonium ferric phosphate was obtained. The recovery rate of lithium ferrophosphide and the purity of the product were calculated. The results are shown in Table 2.

[0065] Table 2

[0066]

Claims

1. A method for recycling lithium iron phosphate positive electrode materials, comprising disassembling waste lithium iron phosphate batteries to obtain positive electrode sheets, separating the positive electrode material and the current collector in the positive electrode sheets, and preparing the obtained positive electrode material into positive electrode material powder, characterized in that: The following steps are involved: (1) adding dilute phosphoric acid to the positive electrode material powder to prepare a lithium iron phosphate slurry, and then performing electrolytic extraction to recover lithium elements in the positive electrode material powder to obtain an iron phosphate slurry; (2) adding concentrated sulfuric acid to the ferric phosphate slurry obtained in step (1) to carry out a dissolution reaction, and then performing solid-liquid separation to obtain a ferric sulfate solution containing phosphoric acid, and then adding iron blocks or iron powder to carry out a reaction, and then adjusting the iron-phosphorus ratio and ferrous ion content of the system to obtain a ferrous solution that meets the requirements of the ammonium process ferric phosphate.

2. The method for recycling lithium iron phosphate cathode material according to claim 1, characterized in that: The electrolysis system used in step (1) comprises a cathode chamber, an anode chamber and electrodes, wherein the anode chamber and the cathode chamber are separated by an ion membrane, and the ion membrane only allows lithium ions to pass through; the electrodes are platinum electrodes or graphite electrodes, lithium iron phosphate slurry is added to the anode chamber, and dilute phosphoric acid is added to the cathode chamber.

3. The method for recycling lithium iron phosphate cathode material according to claim 2, characterized in that: In the step (1), direct current is introduced to electrolyze the lithium iron phosphate slurry, and the electrolysis temperature is controlled at 50° C. to 70° C.

4. The method for recycling lithium iron phosphate cathode material according to claim 2, wherein: The solid content of the lithium iron phosphate slurry in step (1) is 15% to 20%.

5. The method for recycling lithium iron phosphate cathode material according to claim 2, characterized in that: The cathode liquid extracted in the step (1) is subjected to gas-liquid separation to obtain a 3% to 5% lithium phosphate solution and hydrogen. The cathode is controlled to obtain a 3% to 5% lithium phosphate solution according to the amount of lithium phosphate solution extracted and the amount of dilute phosphoric acid added. The lithium phosphate solution is evaporated and concentrated to obtain a lithium phosphate product or converted into a lithium carbonate product.

6. The method for recycling lithium iron phosphate cathode material according to claim 1, characterized in that: In the step (2), concentrated sulfuric acid is added to the ferric phosphate slurry for dissolution reaction, the temperature during the reaction is controlled to be 70° C. to 90° C., the molar ratio of iron in the ferric phosphate slurry to sulfuric acid in the concentrated sulfuric acid is 1:1.5, stirring is continued during the reaction, and stirring is continued for 30 to 120 minutes after the reaction is completed to obtain a dissolved slurry.

7. The method for recycling lithium iron phosphate cathode material according to claim 6, characterized in that: The dissolved slurry obtained in step (2) is pumped into a plate-and-frame filter press for solid-liquid separation to obtain a phosphoric acid-containing ferric sulfate solution and leached residue, and the ferric sulfate solution is filtered and impurities removed to obtain a purified ferric sulfate solution.

8. The method for recycling lithium iron phosphate cathode material according to claim 7, characterized in that: The purified ferric sulfate solution in step (2) is pumped into a reduction reactor, and excess iron blocks / iron powder is added to the reduction reactor at a molar ratio of ferric ions to elemental iron of 1:0.5 based on the content of ferric ions in the solution, to perform a reduction reaction on the ferric ions in the ferric sulfate solution; after the feeding is completed, stirring and heating steam are started to perform the reduction reaction, and the reaction temperature is maintained at 50°C to 70°C during the reduction reaction; when the solution turns green, the ferric ion content in the solution is detected, and when it reaches below 0.01%, stirring is stopped, and the reduction reaction is completed to obtain a ferrous sulfate solution; the ferrous sulfate solution after the reaction is subjected to solid-liquid separation, filtration, and impurity removal to obtain a purified ferrous sulfate solution.

9. The method for recycling lithium iron phosphate cathode material according to claim 8, characterized in that: Phosphoric acid is added to the purified ferrous sulfate solution in step (2) according to the requirements of the ammonium process ferric phosphate raw material to control the iron-phosphorus ratio of the ferrous sulfate solution containing phosphoric acid to be 1:1, and pure water is added to control the concentration of ferrous sulfate to be 10% to 15%, thereby obtaining a ferrous solution that meets the requirements of the ammonium process ferric phosphate.

10. The method for recycling lithium iron phosphate cathode material according to claim 1, characterized in that: The mass fraction of the dilute phosphoric acid is 5% to 10%, and the mass fraction of the concentrated sulfuric acid is 90 to 98%.

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