Lithium iron phosphate positive plate recovery method suitable for retired lithium ion power battery

Abstract

The invention discloses a lithium iron phosphate positive plate recovery method suitable for a decommissioned lithium ion power battery, which comprises the following steps: S1, safely disassembling the decommissioned lithium iron phosphate power battery to obtain a positive plate; s2, soaking the positive plate in an eluent at a constant temperature of 65-95 DEG C, taking out the current collector after an active substance is separated from the current collector, and filtering to obtain the active substance; s3, cleaning and drying the active substance and the current collector obtained in the step S2; the eluent is formed by dissolving an acidic chelating agent and a passivating agent in water, the acidic chelating agent comprises one or more of gluconic acid, nitrilotriacetic acid, ethylenediamine tetraacetic acid and pentetic acid, and the passivating agent is used as an additive and comprises one or more of sodium phytate, sodium acetate, sodium citrate, sodium oxalate and sodium phosphate. According to the invention, the retired lithium iron phosphate battery is recovered at low cost by using a low-energy-consumption, safer, green and environment-friendly efficient method, and a high-purity and more complete positive active material and current collector are obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery recycling, and in particular relates to a method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries. Background Art

[0002] With the development of new energy technology, the replacement of new energy vehicles on the market is also proceeding at a relatively fast pace, and the number of retired new energy vehicles has also increased sharply. The focus of recycling retired new energy vehicle resources is to recycle the power batteries, such as lithium-ion power batteries. The positive electrode material of the battery accounts for a relatively high proportion of the power battery cost, so the recycling of positive electrode materials has become an important part of the new energy recycling system.

[0003] Regarding lithium-ion power batteries, lithium iron phosphate is widely used in the field of power batteries due to its stability, safety, environmental friendliness, mature manufacturing process, and low manufacturing cost. The service life of lithium iron phosphate batteries as automotive power batteries is 5 to 8 years. As the power battery with the longest application history, lithium iron phosphate batteries began to enter the mass scrapping period as early as 2019, and the current retirement scale is still expanding.

[0004] Although the demand for recycling lithium iron phosphate is high, the current recycling methods for lithium iron phosphate cathodes of retired lithium-ion power batteries still have many shortcomings. For example, the existing conventional recycling methods are mainly hydrometallurgy and pyrometallurgy, accounting for 51% and 26% respectively. In the pre-processing stage, the cathode material generally needs to be crushed as a whole, or even the entire power battery is directly crushed, which has a great impact on the recycling efficiency, and hydrometallurgy and pyrometallurgy also have a great impact on the environment.

[0005] Although hydrometallurgy and pyrometallurgy have good performance in terms of recovery rate, the simple and rough treatment methods in the pre-treatment link increase the cost and complexity of the subsequent steps. At present, the industry has proposed a variety of methods for separating current collectors and active substances, such as the high-temperature method to decompose the binder to achieve the effect of separating the current collector and the active substance, the organic method uses organic solvents to dissolve the binder, and the chemical method uses acid or alkaline solutions to dissolve part of the current collector to separate the active substance. Among them, the high-temperature method has high energy consumption, and there will be emissions of harmful substances such as hydrogen fluoride, and it will also cause the purity of the active substance and the current collector to be low after separation; the organic method requires the use of a large amount of organic solvents, which is costly; the acidic chemical method will produce a large amount of hydrogen, which will also cause a large loss of active substances, and the alkaline chemical method will cause a large amount of current collector to dissolve, affecting the product state.

[0006] The recycling of lithium iron phosphate active materials and current collectors of retired lithium-ion power batteries is imperative, but the existing recycling methods in the industry are simple and crude, which is a serious waste of resources and serious damage to the environment, and reduces the quality of the final recycled products. The various current recycling methods have inevitable and significant shortcomings, which hinder the application of these methods in industry. Therefore, it is necessary to propose a new recycling method. Summary of the invention

[0007] In order to solve the above technical problems, the purpose of the present invention is to provide a method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries. Through a concise processing flow, retired lithium iron phosphate batteries can be recycled at low cost in a low-energy, safer, green and environmentally friendly manner to obtain high-purity and more complete positive active materials and current collectors.

[0008] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0009] A method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries comprises the following steps:

[0010] S1. Safely dismantle the retired lithium iron phosphate power battery to obtain the positive electrode sheet;

[0011] S2, immersing the positive electrode sheet in an eluent at a constant temperature of 65 to 95°C, taking out the current collector after the active material is separated from the current collector, and filtering to obtain the active material;

[0012] S3, washing and drying the active material and current collector obtained in step S2;

[0013] Wherein, in step S2, the eluent is formed by dissolving an acidic chelating agent and a passivating agent in water, the acidic chelating agent includes one or more of gluconic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid and pentetic acid, and the passivating agent is used as an additive and includes one or more of sodium phytate, sodium acetate, sodium citrate, sodium oxalate and sodium phosphate.

[0014] Preferably, in the eluent, the total concentration of the acidic chelating agent and the passivating agent is 0.01 to 3 wt.%.

[0015] Preferably, the molar ratio of the acidic chelating agent to the passivating agent is 2:1.

[0016] Preferably, in step S3, the active substance and the current collector are cleaned using a cleaning liquid, wherein the cleaning liquid includes any one of water, ethanol aqueous solution and weak alkaline solution.

[0017] More preferably, the pH value of the weakly alkaline solution is 8.0-8.5.

[0018] More preferably, the weak alkaline solution includes one or more of sodium carbonate solution, sodium bicarbonate solution, sodium dihydrogen phosphate solution, ammonia solution, sodium silicate solution, and sodium borate solution.

[0019] Preferably, in step S1, the discharge mode includes any one of short-circuit discharge, resistance discharge, load discharge and salt water immersion discharge.

[0020] Preferably, in step S3, the filtration method includes one or more of gravity filtration, vacuum filtration, pressure filtration, centrifugal filtration and membrane filtration.

[0021] Preferably, in step S3, the cleaning method includes one or more of soaking, rinsing, flushing or ultrasonic cleaning.

[0022] Preferably, in step S3, the drying method includes one or more of air drying, oven drying, vacuum drying, freeze drying, microwave drying or nitrogen purge drying.

[0023] Beneficial effects:

[0024] The eluent used in the present invention has low loss of active substances, significantly improves the recovery rate of each element and the structural integrity of the material, and the eluent with chelating and passivation properties can undergo chelating and passivation reactions with metal ions generated after the current collector is acid-etched. Its chelating products and passivation products can protect the current collector from continued acid etching, ensure that no active substances remain on the surface of the current collector, and at the same time ensure the integrity of the current collector, thereby achieving the purpose of high purity of active substances, low loss, and complete and pure current collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The picture shows a lithium iron phosphate positive electrode sheet disassembled from a retired lithium-ion power battery;

[0026] Figure 2 The picture shows the lithium iron phosphate positive electrode sheet disassembled from a new non-retired lithium-ion power battery;

[0027] Figure 3 The lithium iron phosphate active material recovered and obtained in Example 1 of the present invention;

[0028] Figure 4 The positive electrode current collector recovered from Example 1 of the present invention;

[0029] Figure 5 The relationship curve between the elution time required for separation of the active material from the current collector and the concentration of the eluent used in Comparative Examples 4 and Comparative Examples 13 to 21 of the present invention at room temperature (25° C.);

[0030] Figure 6The relationship curve between the elution recovery rate of the active substance and the concentration of the eluent used in Comparative Example 4 and Comparative Examples 13 to 21 of the present invention;

[0031] Figure 7 This is a scanning electron microscope image of the active material recovered by the present invention;

[0032] Figure 8 This is a scanning electron microscope image of the active material obtained in Comparative Example 3;

[0033] Fig. 9 X-ray diffraction patterns of the active substances of Example 1, Example 6, Example 7 and Comparative Example 22 of the present invention;

[0034] Fig.10 The relationship curve between the elution time required for separation of the active material from the current collector and the elution temperature used in Example 1, Example 2, Example 5, Comparative Example 1, and Comparative Examples 9 to 12 of the present invention is shown;

[0035] Fig.11 The graph is a relationship curve between the elution recovery rate of the active substance and the elution temperature used in Example 1, Example 2, Example 5, Comparative Example 1, and Comparative Examples 9 to 12 of the present invention. DETAILED DESCRIPTION

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings and other implementation methods can be obtained based on these drawings without creative work.

[0037] The present invention provides a method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries, comprising the following steps:

[0038] S1. Safely disassemble the retired lithium iron phosphate power battery to obtain the positive electrode sheet.

[0039] In the present invention, the lithium iron phosphate power battery includes retired lithium iron phosphate batteries, scrapped lithium iron phosphate batteries and various lithium iron phosphate batteries with residual power. The above lithium iron phosphate batteries are completely discharged and then disassembled to obtain positive electrode sheets, negative electrode sheets and separators. Among them, the positive electrode sheet is a lithium iron phosphate positive electrode sheet, which contains lithium iron phosphate active material, a binder and a current collector. The binder is generally an aqueous binder or an organic binder. The current collector is generally an aluminum foil or a carbon-coated aluminum foil. The negative electrode sheet includes a graphite negative electrode sheet, and the separator includes a single-layer polyethylene separator, a single-layer polypropylene film or a multi-layer composite separator.

[0040] Discharge the battery in known or unknown state to reduce safety risks and prevent thermal runaway caused by residual load. After full discharge, the concentration of high-value elements in the electrolyte is reduced and concentrated in the positive electrode sheet, which improves the recovery efficiency of lithium iron phosphate. Materials with different physical properties obtained by disassembling the battery can be recycled in a targeted manner later. The present invention mainly focuses on the recovery of lithium iron phosphate positive electrode materials.

[0041] In step S1 , the discharge mode is short-circuit discharge, resistance discharge, load discharge or salt water immersion discharge.

[0042] Among them, short-circuit discharge is 1 to 10 seconds, discharging to a safe voltage of 3V; resistance discharge is 10 to 100 hours, discharging with a discharge current of 0.5 to 1C by adjusting the resistance; load discharge is 1 to 10 hours, discharging with a discharge current of 0.2 to 1C by adjusting the load power; salt water immersion discharge is 5 to 100 hours, and the salt water immersion discharge uses a sodium chloride solution with a concentration of 5 to 10wt.%.

[0043] S2. Soak the positive electrode sheet in a constant temperature eluent until the current collector and the active material are separated. After the active material and the current collector are separated, take out the current collector and filter to obtain the active material.

[0044] In step S2, the eluent is formed by dissolving an acidic chelating agent and a passivating agent in water, wherein the molar ratio of the acidic chelating agent to the passivating agent is 2:1, specifically, the acidic chelating agent includes one or more of gluconic acid (GA), nitrilotriacetic acid (NA), ethylenediaminetetraacetic acid (EDTA) and pentetic acid (DTPA), and the passivating agent is used as an additive, including one or more of sodium phytate, sodium acetate, sodium citrate, sodium oxalate and sodium phosphate. The acidic chelating agent is dissolved in water to form an acidic environment, which has a corrosive effect on the surface of the current collector, and the chelating agent and the passivating agent have a protective effect on the surface of the current collector, that is, hydrogen ions corrode the surface of the current collector to achieve the effect of separating the current collector and the active substance, and the acid radicals provided by the chelating agent and the passivating agent can react with metal ions to protect the current collector from being further corroded by hydrogen ions.

[0045] The recycling method currently widely used in the industry will damage the current collector, making it difficult to recover the elements in the current collector or the recycling cost is high, and will also cause a large number of elements of the current collector to be mixed in the active material, making it difficult to separate and purify the high-value active material. The present invention adopts the immersion method to avoid damaging the current collector, and the active material falls off from the surface of the current collector during the immersion process.

[0046] Preferably, in the eluent, the total mass concentration of the acidic chelating agent and the passivating agent is 0.01-3 wt.%. When the concentration of the active ingredient in the eluent is 3 wt.%, after completing step S2, the eluent can be filtered and reused for more than or equal to 15 times.

[0047] The concentration of the eluent of the present invention is low, the loss of active substances of the positive electrode material is low, and the recovery rate of each element and the structural integrity of the material can be improved. The eluent mainly acts on the surface of the current collector to separate the current collector from the binder, etc. The acidic chelating agent and the passivating agent can react with the metal ions generated after the current collector is acid-etched to produce a chelation reaction and a passivation reaction, and the chelation product and the passivation product have a protective effect on the surface of the current collector to prevent the current collector from being further acid-etched, thereby ensuring that there is no active substance remaining on the surface of the current collector and ensuring the integrity of the current collector.

[0048] In step S2, the constant temperature of the eluent is 65-95°C. Specifically, the method of maintaining the constant temperature of the eluent includes any method of water bath insulation, oil bath insulation, thermostat insulation, heating plate insulation, heat block insulation or temperature-controlled circulating gas insulation. The eluent is in a constant temperature state to ensure the elution effect, effectively accelerate the solution to infiltrate the positive electrode sheet, speed up the speed of large-area contact between the eluent and the current collector, and also speed up the reaction speed of the elution-related reaction to avoid excessive temperature causing violent reactions that are difficult to control.

[0049] The present invention adopts a lower recovery temperature, and compared with the high temperature of several hundred degrees Celsius commonly used in the industry, the present invention also has obvious advantages in saving energy costs.

[0050] It is easy to understand that lithium iron phosphate is insoluble in water. After the separation of the current collector and the lithium iron phosphate active material is completed in step S2, the complete current collector is taken out first, and the lithium iron phosphate active material is mixed with the eluent. The filter residue after filtration is the active material, and the filtrate can be reused many times.

[0051] S3. The active material and the current collector obtained in step S2 are cleaned with a cleaning solution, and after drying, a positive electrode sheet elution product, namely, a high-purity lithium iron phosphate active material and a complete current collector, is obtained.

[0052] In step S3, the cleaning solution includes any one of water, ethanol aqueous solution and weak alkaline solution, wherein the weak alkaline solution includes sodium carbonate solution, sodium bicarbonate solution, sodium dihydrogen phosphate solution, ammonia solution, sodium silicate solution, sodium borate solution, etc. It is easy to understand that the cleaning solution does not react with the active substance or the current collector. The present invention does not limit the concentration of the ethanol aqueous solution and the weak alkaline solution. The cleaning solution can rinse the active substance and the eluent remaining on the surface of the current collector, and rinse and separate the active substance remaining on the surface of the current collector, collect the waste liquid after cleaning, and filter and recover the active substance again. Using water as the cleaning liquid, the residual acidic chelating agent and passivating agent can be dissolved in water and taken away, and the waste liquid can be added to the eluent for reuse; using ethanol as the cleaning liquid, according to the principle of like dissolves like, the cleaning effect of the acidic chelating agent can be improved, and the waste liquid is no longer added to the eluent for reuse; using a weak alkaline solution as the cleaning liquid, reacting with the acidic chelating agent, is conducive to removing the residual acidic chelating agent, and the waste liquid is no longer added to the eluent for reuse.

[0053] In step S3, the volume concentration of ethanol is 70%. The pH value of the weak alkaline solution is 8.0-8.5, and preferably, the weak alkaline solution includes a sodium bicarbonate solution with a concentration of 0.1 mol / L.

[0054] In step S3, the filtration method includes one or more of gravity filtration, vacuum filtration, pressure filtration, centrifugal filtration and membrane filtration.

[0055] When gravity filtration is used, the pore size of the filter paper is 1 to 25 μm. When vacuum filtration is used, the pore size of the filter paper is 0.1 to 25 μm, and the vacuum degree is 0.05 to 0.1 MPa. When pressure filtration is used, the pore size of the filter paper is 0.1 to 10 μm, and the pressure is 0.1 to 1 MPa. When centrifugal filtration is used, the speed is controlled to be 1000 to 15000 rpm, and the centrifugal force is 1000 to 20000 g. When membrane filtration is used, the filtration pore size is 0.1 to 0.45 μm, and the filtration pressure is 0.1 to 0.5 MPa.

[0056] In step S3, the cleaning method includes one or more of soaking, rinsing, flushing or ultrasonic cleaning. Specifically, the soaking cleaning time is 10 to 20 minutes, the rinsing cleaning time is 1 to 10 minutes, the flushing cleaning time is 1 to 10 minutes, the flushing flow rate is 1 to 5 m / min, the ultrasonic cleaning time is 1 to 2 minutes, the ultrasonic cleaning frequency is 20 to 80 kHz, and the power is 50 to 500 W.

[0057] In step S3, the drying method includes one or more of air drying, oven drying, vacuum drying, freeze drying, microwave drying or nitrogen purge drying. Among them, the air drying time is 1 to 3 days, the oven drying temperature is 50 to 120°C, the time is 2 to 6 hours, the vacuum drying temperature is 50 to 100°C, the time is 2 to 4 hours, the freeze drying temperature in the freezing stage is -40 to -80°C, the drying stage temperature is -20 to 0°C, the total time is 1 to 2 days, the microwave drying time is 5 to 30 minutes, and the nitrogen purge drying temperature is 25 to 40°C, and the time is 30 to 120 minutes.

[0058] The technical solution of the present invention is described in detail below with specific embodiments, wherein the lithium iron phosphate positive electrode sheet disassembled from retired lithium-ion power batteries is shown in FIG. Figure 1 As shown in the figure, the lithium iron phosphate positive electrode sheet disassembled from a new non-retired lithium-ion power battery is as follows Figure 2 shown.

[0059] The technical solution of the present invention is described in detail below with specific embodiments.

[0060] Example 1

[0061] Discharge the retired lithium iron phosphate power battery in a discharge cabinet at a rate of 0.2C to obtain a safely disassembled battery with a voltage lower than 3V, disassemble the safely disassembled battery to obtain a battery cell, disassemble the battery cell to obtain a positive electrode sheet, a negative electrode sheet and a separator;

[0062] The positive electrode sheet was immersed in an eluent in an oil bath at 90°C, wherein the eluent was a mixed solution of sodium phosphate and nitrilotriacetic acid with a concentration of 0.5wt.%, wherein the molar ratio of sodium phosphate to nitrilotriacetic acid was 1:2. After the active substance and the current collector were separated, the current collector was taken out and the solution was vacuum filtered to obtain the active substance. The filter paper had a diameter of 90mm, a pore size of 10μm, and a vacuum degree of 0.1MPa.

[0063] The current collector and active material are rinsed separately with a cleaning liquid, the cleaning liquid is deionized water, the flushing flow rate is 5m / min, and the flushing time is 10min; after flushing, it is dried in an oven at 120°C for 6h, thus completing the recovery of the lithium iron phosphate positive electrode sheet of the retired lithium-ion power battery.

[0064] Example 2

[0065] Discharge the retired lithium iron phosphate power battery in a discharge cabinet at a rate of 0.2C to obtain a safely disassembled battery with a voltage lower than 3V, disassemble the safely disassembled battery to obtain a battery cell, disassemble the battery cell to obtain a positive electrode sheet, a negative electrode sheet and a separator;

[0066] The positive electrode sheet was immersed in an eluent in an 80°C oil bath, wherein the eluent was a 0.5wt.% sodium phytate and gluconic acid mixed solution, wherein the molar ratio of sodium phytate to gluconic acid was 1:2; after the active substance and the current collector were separated, the current collector was taken out, and the solution was vacuum filtered to obtain the active substance, the filter paper had a diameter of 90mm, a pore size of 10μm, and a vacuum degree of 0.1MPa;

[0067] The current collector and active material are rinsed separately with a cleaning liquid, the cleaning liquid is deionized water, the flushing flow rate is 5m / min, and the flushing time is 10min; after flushing, it is dried in an oven at 120°C for 6h, thus completing the recovery of the lithium iron phosphate positive electrode sheet of the retired lithium-ion power battery.

[0068] Example 3

[0069] Discharge the retired lithium iron phosphate power battery in a discharge cabinet at a rate of 0.2C to obtain a safely disassembled battery with a voltage lower than 3V, disassemble the safely disassembled battery to obtain a battery cell, disassemble the battery cell to obtain a positive electrode sheet, a negative electrode sheet and a separator;

[0070] The positive electrode sheet was immersed in an eluent in an oil bath at 65°C, wherein the eluent was a mixed solution of sodium acetate and ethylenediaminetetraacetic acid with a concentration of 0.5wt.%, wherein the molar ratio of sodium acetate to ethylenediaminetetraacetic acid was 1:2; after the active material and the current collector were separated, the current collector was taken out, and the solution was vacuum filtered to obtain the active material, the filter paper had a diameter of 90mm, a pore size of 10μm, and a vacuum degree of 0.1MPa;

[0071] The current collector and active material are rinsed separately with a cleaning liquid, the cleaning liquid is deionized water, the flushing flow rate is 5m / min, and the flushing time is 10min; after flushing, it is dried in an oven at 120°C for 6h, thus completing the recovery of the lithium iron phosphate positive electrode sheet of the retired lithium-ion power battery.

[0072] Example 4

[0073] Discharge a new non-retired lithium iron phosphate power battery in a discharge cabinet at a rate of 0.2C to obtain a safely disassembled battery with a voltage lower than 3V, disassemble the safely disassembled battery to obtain a battery cell, disassemble the battery cell to obtain a positive electrode sheet, a negative electrode sheet and a separator;

[0074] The positive electrode sheet was immersed in an eluent in an oil bath at 80°C, wherein the eluent was a mixed solution of sodium phytate, sodium citrate and gluconic acid with a concentration of 0.5wt.%, wherein the molar ratio of sodium phytate, sodium citrate and gluconic acid was 1:1:4; after the active substance and the current collector were separated, the current collector was taken out, and the solution was vacuum filtered to obtain the active substance, the filter paper had a diameter of 90mm, a pore size of 10μm, and a vacuum degree of 0.1MPa;

[0075] The current collector and active material are rinsed separately with a cleaning liquid, the cleaning liquid is deionized water, the flushing flow rate is 5m / min, and the flushing time is 10min; after flushing, it is dried in an oven at 120°C for 6h, thus completing the recovery of the lithium iron phosphate positive electrode sheet of the retired lithium-ion power battery.

[0076] Example 5

[0077] Compared with Example 2, the eluent of this example is not kept in an oil bath at 80° C., but kept in an oil bath at 70° C. The rest of the operations are the same as those of Example 2.

[0078] Example 6

[0079] Compared with Example 2, the concentration of the eluent in this example is 1 wt.%. The remaining operations are the same as those in Example 2.

[0080] Example 7

[0081] Compared with Example 2, the concentration of the eluent in this example is 3 wt.%. The remaining operations are the same as those in Example 2.

[0082] Comparative Example 1

[0083] Compared with Example 2, the eluent of this comparative example is not kept in an 80° C. oil bath, but is kept in a room temperature environment of 25° C. The remaining operations are the same as those of Example 2.

[0084] Comparative Example 2

[0085] Compared with Example 2, this comparative example does not use an eluent but deionized water, and the positive electrode sheet is immersed in deionized water in an oil bath at 80° C. The remaining operations are the same as those in Example 2.

[0086] Comparative Example 3

[0087] Compared with Example 2, the concentration of the eluent in this comparative example is 10 wt.%. The remaining operations are the same as those in Example 2.

[0088] Comparative Example 4

[0089] Compared with Example 4, the eluent of this comparative example is not kept in an 80° C. oil bath, but is kept in a room temperature environment of 25° C. The remaining operations are the same as those of Example 4.

[0090] Comparative Example 5

[0091] Compared with Example 4, this comparative example does not use an eluent but deionized water, and the positive electrode sheet is immersed in deionized water in an oil bath at 80° C. The remaining operations are the same as those in Example 4.

[0092] Comparative Example 6

[0093] Compared with Example 2, the eluent of this comparative example is not a 0.5 wt.% sodium phytate and gluconic acid mixed solution, but a 0.5 wt.% gluconic acid solution. The rest of the operations are the same as those of Example 2.

[0094] Comparative Example 7

[0095] Compared with Example 2, the eluent of this comparative example is not a 0.5 wt.% sodium phytate and gluconic acid mixed solution, but a 0.5 wt.% sodium phytate solution. The rest of the operations are the same as those of Example 2.

[0096] Comparative Example 8

[0097] Discharge the retired lithium iron phosphate power battery in a discharge cabinet at a rate of 0.2C to obtain a safely disassembled battery with a voltage lower than 3V, disassemble the safely disassembled battery to obtain a battery cell, disassemble the battery cell to obtain a positive electrode sheet, a negative electrode sheet and a separator;

[0098] The positive electrode sheet was immersed in an eluent at room temperature (25°C), wherein the eluent was a mixed solution of sodium citrate and pentetic acid with a concentration of 3wt.%, wherein the molar ratio of citrate to pentetic acid was 1:2; after the active material and the current collector were separated, the current collector was taken out, and the solution was vacuum filtered to obtain the active material, the filter paper had a diameter of 90mm, a pore size of 10μm, and a vacuum degree of 0.1MPa;

[0099] The current collector and active material are rinsed separately with a cleaning liquid, the cleaning liquid is deionized water, the flushing flow rate is 5m / min, and the flushing time is 10min; after flushing, it is dried in an oven at 120°C for 6h, thus completing the recovery of the lithium iron phosphate positive electrode sheet of the retired lithium-ion power battery.

[0100] Comparative Example 9

[0101] Compared with Example 2, the eluent of this comparative example is not kept warm in an 80° C. oil bath, but in an ice-water bath at 5° C. The rest of the operations are the same as those of Example 2.

[0102] Comparative Example 10

[0103] Compared with Example 2, the eluent of this comparative example is not kept in an oil bath at 80° C., but kept in an oil bath at 40° C. The rest of the operations are the same as those of Example 2.

[0104] Comparative Example 11

[0105] Compared with Example 2, the eluent of this comparative example is not kept in an oil bath at 80° C., but kept in an oil bath at 50° C. The rest of the operations are the same as those of Example 2.

[0106] Comparative Example 12

[0107] Compared with Example 2, the eluent of this comparative example is not kept in an oil bath at 80° C., but kept in an oil bath at 60° C. The rest of the operations are the same as those of Example 2.

[0108] Comparative Example 13

[0109] Compared with Comparative Example 4, the concentration of the eluent in this comparative example is 10 wt.%. The remaining operations are the same as those in Comparative Example 4.

[0110] Comparative Example 14

[0111] Compared with Comparative Example 4, the concentration of the eluent in this comparative example is 50 wt.%. The remaining operations are the same as those in Comparative Example 4.

[0112] Comparative Example 15

[0113] Compared with Comparative Example 4, the concentration of the eluent in this comparative example is 30 wt.%. The remaining operations are the same as those in Comparative Example 4.

[0114] Comparative Example 16

[0115] Compared with Comparative Example 4, the concentration of the eluent in this comparative example is 20 wt.%. The remaining operations are the same as those in Comparative Example 4.

[0116] Comparative Example 17

[0117] Compared with Comparative Example 4, the concentration of the eluent in this comparative example is 7 wt.%. The remaining operations are the same as those in Comparative Example 4.

[0118] Comparative Example 18

[0119] Compared with Comparative Example 4, the concentration of the eluent in this comparative example is 5 wt.%. The remaining operations are the same as those in Comparative Example 4.

[0120] Comparative Example 19

[0121] Compared with Comparative Example 4, the concentration of the eluent in this comparative example is 3 wt.%. The remaining operations are the same as those in Comparative Example 4.

[0122] Comparative Example 20

[0123] Compared with Comparative Example 4, the concentration of the eluent in this comparative example is 1 wt.%. The remaining operations are the same as those in Comparative Example 4.

[0124] Comparative Example 21

[0125] Compared with Comparative Example 4, the concentration of the eluent in this comparative example is 0.3 wt.%. The remaining operations are the same as those in Comparative Example 4.

[0126] Comparative Example 22

[0127] Compared with Example 2, the concentration of the eluent in this comparative example is 10 wt.%. The remaining operations are the same as those in Example 2.

[0128] The test experiment is as follows.

[0129] Scanning electron microscopy analysis: The scanning electron microscopy results of the active material obtained in Example 2 are as follows Figure 7 As shown, the scanning electron microscopy results of the active material obtained in Comparative Example 3 are as follows Figure 8 As shown, by observing the surface morphology of the active substances obtained under different treatment conditions, it can be seen that high-concentration acidic solutions will dissolve part of the active substances, affecting the recovery rate and the quality of the recovered products.

[0130] X-ray diffractometer analysis: The X-ray diffraction results of the active materials obtained in Examples 2 and 4 and Comparative Examples are as follows: Fig. 9 As shown in Figure 2, as the concentration of the acidic eluent increases, the intensity of the diffraction peak decreases continuously, indicating that the crystallinity of the crystals continues to decrease and the lattice structure of lithium iron phosphate in the active material is destroyed.

[0131] Recovery effect index test: The recovery effect includes the time required for separation of the current collector and the active material, as well as the total recovery rate of the active material and the current collector. The test results of Examples 1-4 and Comparative Examples 1-5 and 8 are shown in Table 1 below.

[0132] Table 1 Recovery effect of Examples 1-4 and Comparative Examples 1-8

[0133]

[0134]

[0135] According to Table 1, through the recovery effect indicators of Examples 1-4, it can be seen that appropriately increasing the elution temperature within a certain range can effectively accelerate the separation speed of the active substance and the current collector, shorten the immersion time of the electrode, avoid the dissolution of the active substance and the current collector, and thus improve the recovery rate of the material; it can also reduce the concentration requirement of the eluent while avoiding the corrosion of the material by the high concentration eluent.

[0136] It can be seen from the recycling effect indicators of Example 2 and Example 4 that the recycling method can not only effectively recycle lithium iron phosphate pole pieces of retired lithium-ion power batteries, but also recycle other types of lithium iron phosphate pole pieces in different states.

[0137] By comparing the recovery effect indicators of Example 2 and Comparative Examples 1 and 7, it can be seen that eluting the electrode at a higher temperature can significantly accelerate the separation rate of the active material and the current collector, and improve the recovery rate by shortening the contact time between the electrode and the acidic eluent.

[0138] By comparing the recovery effect indicators of Example 2 and Comparative Example 2, and Example 4 and Comparative Example 5, it can be seen that using a lower concentration of eluent to separate the active material and the current collector on the electrode can save time without affecting the recovery rate.

[0139] By comparing the recovery effect indicators of Example 2 and Comparative Example 3, and Example 4 and Comparative Example 4, it can be seen that when the concentration of the eluent is too high, it is equivalent to the acid washing method in the industry, which has a serious impact on the recovery rate of the material.

[0140] By comparing the recovery effect indicators of Example 2 and Comparative Examples 6 and 7, it can be seen that when only one of the components in the eluent is used, the recovery rate or elution time will be significantly deteriorated. For example, in Comparative Example 6, only gluconic acid is used, and although the elution time is shorter, the recovery rate is significantly lower than that of Example 2. In Comparative Example 7, only sodium phytate is used, and the elution time is much longer than that of Example 2. Even though it has a higher recovery rate, it takes a very long time.

[0141] The active material and current collector obtained in Example 1 were subjected to an inductively coupled plasma test, and the steps are as follows.

[0142] Sample preparation: The sample is prepared into liquid form by acid dissolution, digestion or microwave digestion to ensure that the elements in the sample can be atomized and plasmatized.

[0143] Nebulization: Liquid samples are atomized into tiny droplets by a nebulizer and fed into the plasma.

[0144] Plasma source: The sample is dissociated at high temperature by passing it through a plasma (usually an argon plasma), atomizing and exciting or ionizing the elements.

[0145] Detection: ICP-OES: Quantitative analysis is performed by measuring the intensity of light emitted by an element at a specific wavelength; ICP-MS: Quantitative and qualitative analysis is performed by measuring the mass-to-charge ratio of different elements in an ionized sample.

[0146] The test data is shown in Table 2.

[0147] Table 2 Content of each element in the recovered active material and current collector

[0148]

[0149]

[0150] It should be noted that, for example, elements such as O and F account for a large proportion in the active substances, but this method cannot measure them, while other impurity elements are of many types but their contents are too low to be meaningful to display. Other impurity elements are of many types but their contents are too low to be meaningful to display.

[0151] According to the data in Table 2, the atomic ratio of active material Li:Fe:P is 0.78:0.97:1, which is close to 1:1:1, and is very beneficial for the subsequent repair and regeneration of lithium iron phosphate; the Al purity of the recovered current collector is extremely high, and the content of active material contained therein is extremely low, indicating that the active material and current collector recovered by this recycling method are of good quality and high value, and the active material and current collector are completely separated.

[0152] According to the attached Figure 5 The data show that at room temperature, using different eluent concentrations, it takes more than 20 minutes of elution time to achieve the separation of the active substance and the current collector, indicating that the elution separation efficiency of the active substance and the current collector is low at room temperature, and a higher temperature is required to shorten the elution time.

[0153] According to the attached Figure 6 The data shows that once the concentration of the eluent exceeds 3wt.% at room temperature, the elution rate will be lower than 80%. An elution rate lower than 80% will significantly affect the recovery rate of the active material and the current collector, which is not conducive to improving the recovery efficiency. This also shows that if you want to maintain a higher elution rate, you need to control the concentration of the eluent below 3wt.%.

[0154] According to the attached Fig. 9 The data shows that compared with the standard lithium iron phosphate PDF card, the diffraction characteristic peaks of the active material eluted with 0.5-3wt.% eluent can have a good correspondence, and the diffraction peak intensity is not low. If the diffraction peak intensity of the active material eluted with 10wt.% eluent is very low, it means that the eluent concentration is too high, which will cause structural damage to the lithium iron phosphate material, and the eluent concentration must be controlled in a lower range.

[0155] according to Fig.10 The data shows that the higher the temperature used during elution, the less time required for elution and the higher the elution efficiency. However, this does not mean that a higher temperature must be pursued during elution, because the higher the temperature, the more energy is consumed and the higher the cost of elution. The selection of elution temperature requires comprehensive consideration of elution effect, elution cost and elution efficiency.

[0156] according to Fig.11 The data show that the elution rate will decrease when the temperature is too low or too high, but the decrease is very small. In the temperature range of 5 to 90°C, the elution rate remains at a high level of 92%. Fig.10 Based on the experimental results, the selection of 65-95°C as the elution temperature range is a good balance between elution rate and elution speed.

[0157] The embodiments provided by the present invention are described in detail above. Specific examples are used herein to describe the principles and implementation methods of the present invention, and the description of the above embodiments is only used to help understand the core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries, characterized in that: The following steps are involved: S1. Safely dismantle the retired lithium iron phosphate power battery to obtain the positive electrode sheet; S2, immersing the positive electrode sheet in an eluent at a constant temperature of 65 to 95°C, taking out the current collector after the active material is separated from the current collector, and filtering to obtain the active material; S3, washing and drying the active material and current collector obtained in step S2; Wherein, in step S2, the eluent is formed by dissolving an acidic chelating agent and a passivating agent in water, the acidic chelating agent includes one or more of gluconic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid and pentetic acid, and the passivating agent is used as an additive and includes one or more of sodium phytate, sodium acetate, sodium citrate, sodium oxalate and sodium phosphate.

2. The method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries according to claim 1, characterized in that: In the eluent, the total concentration of the acidic chelating agent and the passivating agent is 0.01-3 wt.%.

3. The method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries according to claim 1, characterized in that: The molar ratio of the acidic chelating agent to the passivating agent is 2:

1.

4. The method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries according to claim 1, characterized in that: In step S3, the active material and the current collector are cleaned using a cleaning liquid, wherein the cleaning liquid includes any one of water, ethanol aqueous solution and weak alkaline solution.

5. The method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries according to claim 4, characterized in that: The pH value of the weak alkaline solution is 8.0-8.

5.

6. The method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries according to claim 4, characterized in that: The weak alkaline solution includes one or more of sodium carbonate solution, sodium bicarbonate solution, sodium dihydrogen phosphate solution, ammonia solution, sodium silicate solution, and sodium borate solution.

7. The method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries according to claim 1, characterized in that: In step S1 , the discharge mode includes any one of short-circuit discharge, resistance discharge, load discharge and salt water immersion discharge.

8. The method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries according to claim 1, characterized in that: In step S3, the filtration method includes one or more of gravity filtration, vacuum filtration, pressure filtration, centrifugal filtration and membrane filtration.

9. The method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries according to claim 1, characterized in that: In step S3, the cleaning method includes one or more of soaking, rinsing, flushing or ultrasonic cleaning.

10. The method for recycling lithium iron phosphate positive electrode sheets suitable for retired lithium-ion power batteries according to claim 1, characterized in that: In step S3, the drying method includes one or more of air drying, oven drying, vacuum drying, freeze drying, microwave drying or nitrogen purge drying.

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