WO2024060653A1 - Recycling process of lithium iron phosphate - Google Patents

Abstract

Provided is a recycling process of lithium iron phosphate, which comprises the following steps: S1, dispersing lithium iron phosphate black powder in a solution system, adding a sulfuric acid solution and hydrogen peroxide, and carrying out a reaction and filtration to obtain a filtrate A and a filter residue A; S2, dispersing the filter residue A in a sulfuric acid solution, and carrying out a reaction and filtration to obtain a filtrate B and a filter residue B; S3, dispersing the filter residue B in a sulfuric acid solution, and carrying out a reaction and filtration to obtain a filter residue C and a filtrate C; and S4, adding aqueous ammonia into the filtrate C, carrying out a hydrothermal reaction in a stirring state to obtain a green crystal and a filtrate D, and roasting the green crystal to obtain battery-grade iron phosphate. In S1, the pH value of the filtrate A is adjusted with lithium hydroxide to obtain a filtrate E and a filter residue E, the filtrate E passes through an electrochemical reactor to obtain a lithium sulfate solution, a lithium hydroxide solution and dilute sulfuric acid, and then the described liquid is reused in all the steps. In S1, the pH value is controlled to be 3-7, and the ORP of the solution system is controlled to be maintained at 350-500 mV. In S2, the pH value is controlled to be 0.5-2. In S3, the pH value is controlled to be 0-0.3. In S4, the pH value is controlled to be 1.6-3.5. By means of the process, recycling of iron phosphate and total-recycle utilization of each intermediate in the recycling process are achieved at the same time, and in a total-recycle process, no new substances need to be additionally added, no wastewater is generated, and thus the process is a green and environment-friendly regeneration process.

Description

A kind of recycling process of lithium iron phosphate Technical Field

The present invention relates to the technical field of recycling processing, and specifically, to a recycling process of lithium iron phosphate.

Background technique

With the development of my country's lithium-ion battery industry, the effective recycling and processing of used batteries is an important issue for the healthy and sustainable development of the industry. The structure of lithium-ion batteries generally includes positive electrode, negative electrode, electrolyte, separator, casing, cover, etc. The positive electrode material is the core of the lithium battery and accounts for more than 30% of the battery cost.

Waste lithium iron phosphate batteries contain a large amount of lithium element, and lithium element is an important component of the cathode material of lithium-ion batteries, so its recycling can better exert its important economic value. At the same time, waste lithium iron phosphate batteries contain a large amount of electrolyte, organic waste and other pollutants. Random disposal without treatment will inevitably cause serious environmental problems. Therefore, recycling waste lithium iron phosphate batteries has important economic and environmental significance.

There are three main methods for recycling lithium iron phosphate: one is the fire method, which directly re-sinters the black powder. However, this method does not effectively remove impurities, and the quality of the regenerated cathode obtained is not high; the other is the use of oxidants. Lithium, iron, and phosphorus are leached with acid, and iron and phosphorus are directly precipitated with alkali. During this process, impurities in the black powder, such as aluminum, copper, manganese, etc., precipitate together with iron and phosphate, and the impurities cannot be effectively removed. Moreover, most of the sediments are amorphous products, which are extremely difficult to remove by solid-liquid separation (filtration, washing); currently, there are also processes for long-term aging, but on the one hand, it takes a long time, and on the other hand, the effect of solid-liquid separation is not good; The third method is to use oxidants to leach lithium. However, the current method The leaching rate of lithium is low, some processes last for a long time and have low efficiency, and some processes have high iron and phosphorus dissolution rates and low overall efficiency.

Contents of the invention

The present invention provides a lithium iron phosphate recovery process, which can effectively solve the problems of low impurity removal rate and poor product quality in the recovery process in the prior art.

The embodiments of the present invention are implemented through the following technical solutions:

A recycling process for lithium iron phosphate, including the following steps:

S1 lithium iron phosphate black powder is dispersed in the solution system, sulfuric acid liquid and oxidant are added, and after reaction and filtration, A filtrate and A filter residue are obtained;

S2 disperses the A filter residue in the sulfuric acid solution, and after reaction and filtration, obtains the B filtrate and B filter residue;

S3 disperses the filter residue B in sulfuric acid solution, reacts and filters to obtain filter residue C and filtrate C;

S4 Add ammonia water to the C filtrate, and under stirring, undergo a hydrothermal reaction to obtain green crystals and D filtrate. The green crystals are roasted to obtain battery-grade iron phosphate.

The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

The invention simultaneously realizes the recovery of lithium iron phosphate and the full recycling of intermediates in the recycling process. During the full cycle, there is no need to add new substances and does not cause the generation of sewage. It is a green and environmentally friendly regeneration process. . At the same time, the lithium concentration obtained by lithium leaching is high, and lithium is effectively extracted; iron phosphate powder with low impurity content is also obtained, and the lithium iron phosphate cathode material obtained by this has good electrochemical properties.

Description of the drawings

In order to explain the technical solutions of the embodiments of the present invention more clearly, the drawings needed to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some aspects of the present invention. The embodiments should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without exerting creative efforts.

FIG1 is a schematic diagram of a lithium iron phosphate recovery process according to the present invention;

Figure 2 shows the XRD test curves of S1 and A1;

Figure 3 shows the typical x-ray diffraction pattern of recycled C-LiFePO ₄ material compared with materials on the market;

Figure 4 shows the charge and discharge characteristic curve of the button battery;

Figure 5 shows the rate performance curve of recycled materials;

Figure 6 shows the rate discharge performance curve of recycled materials.

Detailed ways

In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

First, the present invention provides a recycling process for lithium iron phosphate. The process route is shown in Figure 1. Specifically, it includes the following steps:

S1 lithium iron phosphate black powder is dispersed in the solution system, sulfuric acid liquid and oxidant are added, and after reaction and filtration, A filtrate and A filter residue are obtained;

S2 disperses the A filter residue in the sulfuric acid solution, and after reaction and filtration, obtains the B filtrate and B filter residue;

S3 disperses the B filter residue in the sulfuric acid solution, and after reaction and filtration, obtains the C filter residue and C filtrate;

S4 Add ammonia water to the C filtrate. Under stirring, the hydrothermal reaction produces green crystals and D filtrate. The green crystals are roasted to obtain battery-grade iron phosphate.

In the present invention, the oxidizing agent is hydrogen peroxide, hypochlorous acid, chlorine, or oxygen.

In the present invention, S(1) is also included. The pH of the A filtrate is adjusted with lithium hydroxide to obtain E filtrate and E filter residue. The E filtrate is passed through an electrochemical reactor to obtain lithium sulfate liquid, lithium hydroxide liquid and dilute sulfuric acid.

In the present invention, filtrate A is first adjusted to pH 5.5-6.5 with lithium hydroxide, filtered to obtain filtrate 1, filtrate 1 is then adjusted to pH 10-12 with lithium hydroxide, and filtered to obtain filtrate E; lithium hydroxide is used to adjust the pH. It comes from lithium hydroxide liquid obtained by electrochemical processor.

In the present invention, the lithium sulfate liquid obtained through the electrochemical processor is reused in the solution system in S1.

In the present invention, the sulfuric acid liquid in S1, the sulfuric acid liquid in S2, and the sulfuric acid liquid in S3 are derived from dilute sulfuric acid obtained by electrochemical treatment.

In the present invention, in S1, the pH value is controlled to be 3 to 7, and the ORP of the solution system is controlled to be maintained at 350 to 500 mV. Preferably, in S1, the pH value is controlled to be 4 to 5, or the pH value can also be around 4, such as 3.9, 4.1, etc.

In the present invention, in S1, hydrogen peroxide is added in batches, which may be added at the 0th minute, the 10th minute, the 20th minute, the 30th minute, and the 40th minute respectively. At the same time, the addition speed of hydrogen peroxide can also be controlled by adjusting ORP. By adding hydrogen peroxide in batches, the utilization rate of hydrogen peroxide is improved. If hydrogen peroxide is added all at once, it will cause the hydrogen peroxide to decompose and reduce the amount of hydrogen peroxide participating in the reaction.

In S1, the purpose of adding sulfuric acid and hydrogen peroxide at the same time is to consume the OH in the solution ^and promote the lithium leaching reaction of lithium iron phosphate. Hydrogen peroxide decomposes rapidly in an alkaline environment. Adding acid to control the reaction in a more acidic environment can improve the performance of hydrogen peroxide. Usage efficiency.

In the present invention, in S1, the stirring time is 0.25 to 5 hours. In S1, keep the temperature of the solution system at 35~60℃. You can also selectively choose 35~50℃, 35~55℃, 50~60℃, 35~60℃. At the same time, you can use a constant temperature water bath or a high and low temperature constant temperature machine. Maintain system temperature.

In the present invention, in S2, the pH value is controlled to be 0.5-2.

In the present invention, in S2 and S3, the reaction temperature is 50-80°C, and the stirring time is 0.5-3h.

In the present invention, in S3, the pH value is controlled to be 0 to 0.3.

In the present invention, in S4, the pH value is controlled to be 1.6 to 3.5.

In the present invention, in S4, ammonia water is added at normal temperature, and the reaction time is 1/6 to 2 hours. After the reaction, the temperature is raised to 80 to 160°C and maintained for 1 to 10 hours for crystallization.

In the present invention, in S(1), the lithium hydroxide liquid obtained by the electrochemical processor is crystallized, and the obtained water is reused into the sulfuric acid liquid in S2.

In the present invention, in S4, the D filtrate is removed and filtered with lithium hydroxide to obtain the F filtrate, and the F filtrate is reused in the solution system in S1; and/or in S3, the C filtrate is removed with lithium hydroxide. The filtrate is reused into the solution system in S1. The impurity removal here refers to using lithium hydroxide to adjust the pH value to 10-12, and the filtered filtrate is reused into the solution system in S1.

In the present invention, the solution system in S1 can be only deionized water, or it can be electrochemically recovered through the aforementioned S(1) to obtain dilute lithium sulfate for reuse, or the F filtrate in S4 can be reused, or it can be made from the aforementioned substances. composed solution.

In the present invention, in S1, the lithium iron phosphate black powder accounts for 1/5 to 1/2 of the mass of the solution system.

In the present invention, S1 is used to achieve the purpose of lithium leaching, which is to extract lithium from lithium iron phosphate. At the same time, the extraction amount of lithium is high, and most of the iron and phosphorus can be retained in the filter residue. middle. The concentration of lithium in the extraction solution after lithium leaching can reach 1.6 mol/L, which is a considerable concentration. After impurity removal, it can be directly entered into the electrochemical reactor to prepare lithium hydroxide and sulfuric acid. This operating method greatly improves the efficiency of the electrochemical reactor; at the same time, it can also directly extract the most economically valuable lithium, thereby increasing the flexibility of the process.

The invention provides a kind of lithium iron phosphate. The iron phosphate obtained through the aforementioned recovery process of lithium iron phosphate is used as raw material, glucose is used as the carbon source, Li ₂ CO ₃ is used as the lithium source, and carbon-coated lithium iron phosphate is obtained after roasting. Cathode material.

<Example>

Example 1

Add 1.5L deionized water to a 2L glass beaker, start stirring, and use a constant temperature water bath to maintain the system temperature at 35°C. After stirring for 10 minutes, add 500g of lithium iron phosphate black powder into the beaker. At the same time, add 200mL of 30% hydrogen peroxide. Use an online pH meter to control the addition rate of 37.8% sulfuric acid, and keep the pH value of the system between 4 and 5. Add 100 mL hydrogen peroxide after 10 minutes, add 100 mL hydrogen peroxide at 20 minutes, add 100 mL hydrogen peroxide at 30 minutes, add 50 mL hydrogen peroxide at 40 minutes, and add a total of 550 mL hydrogen peroxide. After 60 minutes of reaction, the reaction was stopped. At this time, a total of 385 mL of sulfuric acid was added. After filtering and washing the filter cake, 2480 mL of filtrate and 461.7 g of filter cake were obtained. The leaching rate was calculated from the Li remaining in the filter residue to be 95.05%, and the Li concentration of the leaching liquid was 1.13 mol. /L. Use the remaining lithium content in the filter residue ICP to detect the contents of Li, Fe, and P in each material. The results are shown in Table 1.

Example 2

Add 1.5L deionized water to a 2L glass beaker, start stirring, and use a high and low temperature thermostat to maintain the system temperature at 50°C. After stirring for 10 minutes, add 500g of lithium iron phosphate black powder into the beaker. Use an online pH meter to control the addition rate of 37.8% sulfuric acid, and keep the pH value of the system at 3.9. Use an online ORP meter to adjust the addition speed of 30% hydrogen peroxide, and keep the ORP value of the control system at 410mV. After reacting for 30 minutes, adjust the ORP to 380mV and continue the reaction for 30 minutes before stopping the reaction. At this time, a total of 371 mL of sulfuric acid and 468 mL of hydrogen peroxide are added. After filtering and washing the filter cake, 2303 mL of filtrate and 463.83 g of filter cake are obtained. Through the remaining Li in the filter residue, The calculated leaching rate is 95.2%, and the Li concentration of the leaching solution is 1.21 mol/L. The Li, Fe, and P contents in each material were detected by ICP using the lithium content remaining in the filter residue, as shown in Table 1.

Example 3

Add 1.5L deionized water to a 2L glass beaker, start stirring, and use a high and low temperature thermostat to maintain the system temperature at 55°C. After stirring for 10 minutes, add 500g of lithium iron phosphate black powder into the beaker. Use an online pH meter to control the addition rate of 37.8% sulfuric acid, and keep the pH value of the system at 7. At the same time, add 200mL of 30% hydrogen peroxide. After 10 minutes, add 100mL hydrogen oxygen water, add 100 mL of hydrogen peroxide at the 20th minute, 100 mL of hydrogen peroxide at the 30th minute, and 50 mL of hydrogen peroxide at the 40th minute, adding a total of 550 mL of hydrogen peroxide. After 60 minutes of reaction, the reaction was stopped. At this time, a total of 215 mL of sulfuric acid was added. After filtering and washing the filter cake, 2256 mL of filtrate and 468.5 g of filter cake were obtained. The leaching rate was calculated from the Li remaining in the filter residue to be 63.3%, and the Li concentration of the leaching liquid was 0.79 mol. /L. Use the remaining lithium content in the filter residue ICP to detect the contents of Li, Fe, and P in each material, as shown in Table 1.

Table 1 Lithium leaching results of Example 1-Example 3

Example 4

The first step: Lithium immersion

In a 50L reactor, add 14L of deionized water, start stirring, and use a high and low temperature thermostat to maintain the system temperature at 50°C. After stirring for 10 minutes, add 10kg of lithium iron phosphate black powder to the beaker. Use an online pH meter to control the addition rate of 20.6% sulfuric acid to control the pH value of the system to be maintained at 3.5-3.9. Use an online ORP meter to adjust the addition rate of 30% hydrogen peroxide to control the ORP value of the system to be maintained at 480mV. After 120 minutes of reaction, stop the reaction. At this time, a total of 14.934kg of sulfuric acid and 7.35kg of hydrogen peroxide are added. After filtering and washing the filter cake, 30650mL of filtrate and 9.395kg of filter cake are obtained. The leaching rate calculated by the residual Li in the filter residue is 95.1%, and the Li concentration of the leaching solution is 1.72mol/L.

The second step is to remove impurities

The impurity contents of the filtrate after two impurity removals are shown in Table 2. The Li concentration is 1.75 mol/L. 398 mL of 4 mol/L LiOH solution was consumed, and the volume of the filtrate after impurity removal was 31058 mL, which was directly passed through the electrochemical reactor as an intermediate liquid to obtain 10.87 L of 4 mol/L LiOH solution and 9.06 L of dilute sulfuric acid with a concentration of 20.6%. At the same time, 10.05 L of intermediate liquid remained, in which the lithium ion concentration was 0.35 mol/L, which was used to replace part of the deionized water in the lithium immersion reaction and was reused in the system.

The impurity removal process is: add LiOH solution to the filtrate (derived from the LiOH solution obtained after the intermediate liquid is treated in the electrochemical reactor), adjust the pH to 5.5~6.5, filter to obtain filtrate 1, and then use LiOH solution to adjust the pH value of filtrate 1 to 10-12, filter to obtain the aforementioned intermediate liquid.

The third step is to dissolve impurities

The lithium leaching filter residue undergoes an impurity dissolving process (temperature 85°C, dissolution end pH value 0.8), and the impurities are dissolved using 20.6% dilute sulfuric acid obtained from the electrochemical reactor. After dissolving impurities, the mass of the 9.395kg filter cake became 8.878kg. The Al content dropped from 0.21% to 0.029%, the removal rate was 86%, Fe was reduced by 150g, P was reduced by 75g, and the Fe loss rate was 4.9%. The P loss rate is 4.56%.

Step 4: Acid dissolution

The filter cake that has gone through the impurity dissolving process is completely dissolved with 20.6% dilute sulfuric acid at a temperature of 50°C and pH=0. The dissolution rates of Fe and P are 98.1% and 98.0%.

Step Five: Heavy Iron

Take 22L of the filtrate obtained by "acid dissolving", adjust the pH value of the solution to 1.9 with 27% ammonia water at room temperature, and react in a hydrothermal reactor at 105°C for 2 hours to obtain light green precipitate S1, whose Fe/P molar ratio is 1.01.

The light green precipitate was calcined at 650℃ to obtain _FePO4 powder.

The filtrate and residue obtained in each step were tested by ICP, and the contents of various elements are shown in Table 2.

Table 2 Content table of each process

Example 5

22L of the filtrate obtained by "acid dissolving" in the fourth step in Example 4 was adjusted to a pH value of 1.9 with 27% ammonia water at room temperature to obtain a white precipitate A1 with an Fe/P molar ratio of 0.87.

Example 6

Glucose was added as a carbon source and Li ₂ CO ₃ was added as a lithium source to the FePO ₄ powder in Example 4, and the mixture was calcined to obtain a carbon-coated lithium iron phosphate positive electrode.

Specifically, 6g iron phosphate, 1.47g Li ₂ CO ₃ and 0.99g glucose were added to water and mixed thoroughly to obtain a mixture, which was dried using a spray dryer.

The dried mixture was sintered in argon gas (5% hydrogen) at 700°C for 12 hours to obtain dark gray carbon-coated LiFePO4, in which the mass ratio of carbon was 3%.

<Test example>

Test example 1

The green precipitate S1 obtained in Example 4 and the white precipitate A1 obtained in Example 5 were analyzed by XRD to analyze the aforementioned S1 and A1, and the results are shown in Figure 2. It can be seen from the results that A1 is an amorphous precipitate and S1 is a ferrosite crystal. S is the characteristic peak spectrum line of ferrosite crystal.

Test example 2

The regenerated carbon-coated LiFePO ₄ obtained in Example 6 was used as the test raw material. The test raw material was fully mixed with carbon black (SuperP Li) and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1 to obtain a mixture. The mixture was then soaked in NMP and stirred at high speed in vacuum for 3 hours to obtain a positive electrode slurry.

The obtained positive electrode slurry was coated on an aluminum foil with a thickness of 20 μm. After NMP evaporation, the C-LiFePO ₄ electrode was rolled to a thickness of 60 ± 5 μm (including the thickness of the aluminum foil). Cut the C-LiFePO ₄ electrode into discs with a diameter of 10 mm.

In a glove box filled with Ar gas, the positive electrode sheet was installed into a button cell and electrolyte was injected, and the electrochemical performance was tested. The test results are shown in Figures 2-5.

Figure 3 shows the typical x-ray diffraction pattern of the recycled C-LiFePO ₄ material compared with the material on the market (Betteri). #40-1499 is the characteristic peak spectrum line of lithium iron phosphate. Usually a substance has multiple XRD characteristic peak spectrum lines, namely PDF cards. The #40-1499 card was selected for this experiment.

Figure 4 shows a button battery made from regenerated C-LiFePO ₄ cathode, which was cycled within a charge and discharge current of 0.1C and a voltage range of 2.5V-3.8V. Its initial capacity is 157.1mAh g ^-1 . The electrode exhibits a typical charging plateau at approximately 3.4V (vs. Li/Li ⁺ ), which corresponds to the redox of Fe ³⁺ /Fe ²⁺ .

Figure 5 shows the rate performance of recycled materials. At a high charge and discharge rate of 4C, the capacity still reaches 81mAh g ^-1 .

Figure 6 shows that the capacity retention rate of the recycled material is 88.5% after 800 cycles at a 1C charge and discharge rate.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (11)

1. A recycling process for lithium iron phosphate, which is characterized by including the following steps:

   S1 lithium iron phosphate black powder is dispersed in the solution system, sulfuric acid liquid and oxidant are added, and after reaction and filtration, A filtrate and A filter residue are obtained;

   S2 disperses the A filter residue in the sulfuric acid solution, and after reaction and filtration, obtains the B filtrate and B filter residue;

   S3 disperses the B filter residue in the sulfuric acid solution, and after reaction and filtration, obtains the C filter residue and C filtrate;

   S4 Add ammonia water to the C filtrate, and under stirring, undergo a hydrothermal reaction to obtain green crystals and D filtrate. The green crystals are roasted to obtain battery-grade iron phosphate;

   In S1, the pH value is controlled to be 3 to 7, and the ORP of the solution system is maintained at 350 to 500mV;

   In S2, the pH value is controlled to be 0.5~2;

   In S3, the pH value is controlled to be 0-0.3;

   In S4, the pH value is controlled between 1.6 and 3.5.
2. The recovery process of lithium iron phosphate according to claim 1, characterized in that it also includes S (1), adjusting the pH of the A filtrate with lithium hydroxide to obtain the E filtrate and the E filter residue, and the E filtrate is obtained through the electrochemical reactor Lithium sulfate liquid, lithium hydroxide liquid and dilute sulfuric acid.
3. The recovery process of lithium iron phosphate according to claim 1, characterized in that the oxidant is hydrogen peroxide, hypochlorous acid, chlorine, or oxygen.
4. The recovery process of lithium iron phosphate according to claim 2, characterized in that the A filtrate is first adjusted to a pH value of 5.5-6.5 with lithium hydroxide, filtered to obtain filtrate 1, and the filtrate 1 is then adjusted to a pH value of 10 with lithium hydroxide. ~12, filter to obtain the E filtrate; the lithium hydroxide used to adjust the pH comes from the lithium hydroxide liquid obtained through the electrochemical processor.
5. The recovery process of lithium iron phosphate according to claim 2, characterized in that the lithium sulfate solution obtained through the electrochemical processor is reused into the solution system in S1.
6. The recovery process of lithium iron phosphate according to claim 1, characterized in that the sulfuric acid liquid in S1, the sulfuric acid liquid in S2, and the sulfuric acid liquid in S3 are derived from dilute sulfuric acid obtained through an electrochemical processor.
7. The recovery process of lithium iron phosphate according to claim 1, characterized in that, in S1, the stirring time is 0.25 to 5 hours.
8. The lithium iron phosphate recovery process according to claim 1 is characterized in that, in S2 and S3, the reaction temperature is 50 to 80° C. and the stirring time is 0.5 to 3 h.
9. The recovery process of lithium iron phosphate according to claim 1, characterized in that, in S4, ammonia water is added at normal temperature, the reaction time is 1/6~2h, after the reaction, the temperature is raised to 80~160°C, and maintained for 1~ Crystallization was carried out for 10h.
10. The recovery process of lithium iron phosphate according to claim 3 or 4, characterized in that, in S(1), the lithium hydroxide liquid obtained by the electrochemical processor is crystallized, and the obtained water is reused into the sulfuric acid in S2 liquid.
11. The recovery process of lithium iron phosphate according to any one of claims 1 to 6, characterized in that in S4, the D filtrate is removed by lithium hydroxide and filtered to obtain the F filtrate, and the F filtrate is reused into the solution in S1 system; and/or, in S3, the filtrate of the C filtrate after impurity removal by lithium hydroxide, and the filtrate is reused into the solution system in S1.