Method for recycling positive electrode material of retired lithium iron phosphate battery

Abstract

The application discloses a recycling method of retired positive electrode material of lithium iron phosphate battery, comprising the following steps: manually disassembling the retired lithium iron phosphate battery to obtain the positive electrode material; adding the positive electrode material, red mud and NaOH into water in proportion, and performing first stirring reaction; after the reaction is completed, filtering to obtain first filtrate and first filter residue; adding titanium white waste acid into the first filtrate, and filtering and separating to obtain Al(OH)3 precipitate; continuously adding titanium white waste acid into the first filtrate, and filtering and separating to obtain Fe(OH)2 precipitate; uniformly mixing titanium white waste acid, H2O2 and the first filter residue, and performing second stirring reaction; after the reaction is completed, filtering to obtain second filtrate and second filter residue; adding red mud or alkali liquor after the red mud is soaked into the second filtrate, adjusting the pH value of the second filtrate to neutral, filtering after the reaction to obtain third filtrate and Fe(OH)3 precipitate; adding Na2CO3 into the third filtrate, filtering after the reaction to obtain fourth filtrate and Li2CO3 precipitate; adding the fourth filtrate into the titanium white waste acid added into the first filtrate, removing Mg 2+ precipitate in the titanium white waste acid.

Description

Technical Field

[0001] This invention belongs to the field of cathode material recycling technology, specifically relating to a method for recycling cathode materials from retired lithium iron phosphate batteries. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Since the beginning of the 21st century, with increasing attention to environmental and energy issues, the market for power batteries, primarily lithium-ion batteries, has experienced explosive growth. As the supply of lithium-ion batteries continues to rise, the number of used lithium-ion batteries is also increasing rapidly, quickly reaching its peak retirement age. Currently, retired lithium iron phosphate batteries account for approximately 65% ​​of the total retired lithium-ion batteries, and a large number of lithium iron phosphate batteries are facing obsolescence.

[0004] As a highly integrated energy storage device, lithium-ion batteries have a complex internal structure and contain multiple components. Due to the late start of current recycling technology research and the incomplete development of the lithium battery recycling cycle, research on lithium battery recycling technology is unsystematic and immature. Current lithium-ion battery recycling processes include pretreatment and cathode material recovery. Among the cathode material recycling processes, pyrometallurgical recovery, hydrometallurgical recovery, and biological recovery processes have high industrial application value. Pyrometallurgical recovery involves providing a high-temperature environment to recover valuable metals, but it suffers from significant environmental pollution, low recovery rates, and high energy consumption. Hydrometallurgical recovery, which selectively extracts valuable metals by adding certain solvents, is currently the most common method. However, acid leaching, with its indiscriminate leaching behavior, increases the difficulty and cost of metal separation and causes severe environmental pollution. Alkaline leaching faces challenges such as additional wastewater discharge, and the binding mechanism between valuable metals and the leaching agent during ammonia leaching requires further in-depth research. Biological recovery mainly promotes the dissolution and leaching of valuable metals through the metabolic processes of certain microorganisms. This technology is still in its early stages and requires extensive research to improve efficiency and selectivity. All of the above technologies have significant limitations, hindering the development of lithium-ion battery recycling.

[0005] Meanwhile, the direct discharge of existing titanium dioxide waste acid and red mud in my country would cause environmental pollution and resource waste. Red mud, in particular, is characterized by its large volume, heavy metal ions, and strong alkalinity; its comprehensive utilization rate is only about 15%, and its disposal method still mainly involves damming and stockpiling, which occupies a large amount of land resources and may cause dust, soil pollution, and groundwater pollution. Titanium dioxide waste acid, on the other hand, has a low concentration and large quantity, making it difficult to utilize effectively. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for recycling cathode materials from retired lithium iron phosphate batteries.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] A method for recycling cathode materials from retired lithium iron phosphate batteries includes the following steps:

[0009] Waste lithium iron phosphate batteries with SOH < 40% were pretreated and then manually disassembled to obtain positive electrode materials.

[0010] The cathode material and red mud were added to water in a certain proportion, such that the mass ratio of cathode material, red mud and water was 0.5-1.5:2-5:15-25. The first stirring reaction was carried out. After the reaction was completed, the mixture was filtered to obtain the first filtrate and the first filter residue.

[0011] Titanium dioxide waste acid was added to the first filtrate to make the first filtrate neutral, and Al(OH)3 precipitate and Fe(OH)2 precipitate were obtained by filtration and separation.

[0012] Titanium dioxide waste acid, 20% H2O2 aqueous solution and first filter residue were mixed at a mass ratio of 4-8:2-5:1 and stirred for a second reaction. After the reaction was completed, the second filtrate and second filter residue (containing impurities such as SiO2, Mg3(PO4)2 and binder) were obtained by filtration.

[0013] Add red mud or alkaline solution after soaking red mud to the second filtrate, adjust the pH of the second filtrate to neutral, filter after reaction, and obtain the third filtrate and Fe(OH)3 precipitate;

[0014] Na2CO3 was added to the third filtrate. After the reaction, the fourth filtrate and Li2CO3 precipitate were obtained by filtration.

[0015] The fourth filtrate is added to the titanium dioxide waste acid used to add to the first filtrate, removing the Mg from the titanium dioxide waste acid. 2+ Precipitate removal.

[0016] The fourth filtrate is added to the titanium dioxide waste acid used to add to the first filtrate, removing the Mg from the titanium dioxide waste acid. 2+ Removing the precipitate can effectively prevent subsequent Al precipitation. 3+ This interference can help improve the purity of Al(OH)3.

[0017] When the capacity of lithium iron phosphate batteries decays to below 40%, physical and chemical methods are required to dismantle and recycle their cathode materials. Utilizing red mud and titanium dioxide waste acid—two types of industrial waste—to co-treat retired lithium iron phosphate batteries not only achieves the goal of coordinated treatment of waste, wastewater, and solid waste, but also reduces the consumption of acid and alkali resources, improving the utilization rate of resources and energy.

[0018] In some embodiments, the method for pretreating waste lithium iron phosphate batteries is as follows: the retired lithium iron phosphate batteries are placed in a sodium chloride solution to cause a short circuit and electrolysis reaction, producing hydrogen and chlorine gas, which are then collected and discharged.

[0019] Preferably, red mud is added to water, stirred, precipitated, and filtered to obtain an alkaline red mud solution. A mixture of collected hydrogen and chlorine gas is then passed into the alkaline red mud solution to absorb the chlorine. This method yields relatively pure hydrogen, effectively solving the environmental pollution problem caused by chlorine and providing hydrogen as a clean energy source. Hydrogen can then be used as an energy source in the energy-consuming parts of subsequent lithium battery processing, achieving the goal of reducing waste through waste disposal.

[0020] In a further preferred embodiment, the alkaline solution of red mud after chlorine absorption is added to the second filtrate to adjust the pH value of the second filtrate to neutral.

[0021] Preferably, the alkaline red mud solution is replaced with a sodium hydroxide solution. When sodium hydroxide solution is used to absorb chlorine gas, sodium hypochlorite and sodium chloride are produced. Sodium hypochlorite can be used for disinfection and sterilization.

[0022] In some embodiments, the temperature of the first stirring reaction is 50-70°C, and the time is 1-3 hours.

[0023] Preferably, the temperature of the first stirring reaction is 60°C and the time is 2 hours.

[0024] In some embodiments, the temperature of the second stirring reaction is 45-55°C, and the time is 2-4 hours.

[0025] In some embodiments, the mass ratio of Na2CO3 added to the third filtrate to the positive electrode is 1:3-5.

[0026] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0027] Acid-base leaching is currently the main method for recycling waste lithium batteries. However, this method consumes a large amount of acid and alkali resources and has a negative impact on the environment. This invention utilizes two difficult-to-treat industrial wastes—red mud (alkaline solid waste discharged after alumina extraction) and titanium dioxide waste acid generated during the sulfuric acid process for titanium dioxide production—to co-process retired lithium iron phosphate batteries. This achieves the recovery of metals such as aluminum, iron, and lithium from the cathode material, while simultaneously recycling a portion of the solution within the system. This not only reduces the consumption of acid and alkali resources during lithium battery recycling but also achieves the co-processing of three types of industrial waste, improving the utilization rate of resources and energy. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0029] Figure 1 This is a process flow diagram of an embodiment of the present invention;

[0030] Figure 2 This is an overall process flow diagram of an embodiment of the present invention. Detailed Implementation

[0031] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0032] Example 1

[0033] Chemical discharge pretreatment:

[0034] When retired lithium iron phosphate batteries are placed in a sodium chloride solution, the positive and negative electrodes are short-circuited and discharged, undergoing an electrolytic reaction with the solution to produce hydrogen and chlorine gas. Hydrogen is a clean energy source with high utilization value; however, chlorine is a toxic and harmful pollutant gas, and its direct emission would pollute the environment.

[0035] First, the chlorine and hydrogen gases generated during the discharge process are collected. These are then separated using a sodium hydroxide solution. The sodium hydroxide solution effectively absorbs the chlorine, producing sodium hypochlorite (NaClO) and sodium chloride (NaCl). The former can be used for disinfection, while the latter has some medical value, thus turning waste into treasure. Hydrogen, however, is insoluble in sodium hydroxide solution and does not react. After this process, the hydrogen and chlorine gases are separated, yielding hydrogen gas and effectively solving the environmental pollution problem caused by chlorine. Hydrogen, as a clean energy source, can be used in subsequent energy-consuming processes during lithium battery treatment, achieving the goal of preventing waste from accumulating.

[0036] Positive electrode material recycling:

[0037] First, artificial mechanical separation is performed to obtain the positive electrode material (specifically composed of: 90% lithium iron phosphate, 7% acetylene black conductive agent, 2% PVDF and 1% other materials by mass).

[0038] 1) Place the red mud (containing 28% silicon dioxide, 28.5% ferric oxide, 22% aluminum oxide, 11% sodium oxide, 8% calcium oxide, and 2.5% other materials by mass) and the separated positive electrode material into a beaker, add water and mix. The mass ratio of positive electrode material, red mud and water is 1:3:20. Stir thoroughly and filter to obtain filtrate 1 (containing AlO2). - The residue consists of Ca(OH)2 and filter residue 1 (containing impurities such as LiFePO4, Fe2O3, SiO2, and binder).

[0039] 2) Add the titanium dioxide waste acid (containing 25% sulfuric acid, 25.8% ferric sulfate, 49% water, and 0.2% other materials by mass) to a beaker containing filtrate 1, adjust the pH value to 7, filter and separate Al(OH)3 precipitate, Fe(OH)2 precipitate and filtrate, and recover aluminum and iron.

[0040] 3) Add the titanium dioxide waste acid, a 20% H2O2 aqueous solution, and the first filter residue to a beaker at a mass ratio of 6:3:1, and stir thoroughly. The H2O2 will decompose the Fe... 2+ Oxidized to Fe 3+ After filtration, filtrate 2 (containing Fe) was obtained. 3+ Li + SO4 2- PO4 2- (etc.) and filter residue 2 (containing impurities such as SiO2, Mg3(PO4)2, and binder).

[0041] 4) Add red mud to the obtained second filtrate, adjust the pH of the second filtrate to 7, and filter to obtain filtrate 3 (containing Li). + SO4 2- PO4 3- The iron is precipitated by reacting Fe(OH)3 with Fe(OH)3 to achieve the purpose of recovering iron.

[0042] 5) Add Na2CO3 to filtrate 3, and filter to obtain filtrate 4 (containing Na). + SO4 2- PO4 3- CO3 3- (etc.) and Li2CO3 precipitation are used to achieve the purpose of lithium recovery. Filtrate 4 is then added to the titanium dioxide waste acid used to treat filtrate 1, first removing the Mg from the titanium dioxide waste acid. 2+ Separation is achieved by precipitation of Mg3(PO4)2 to prevent interference with subsequent Al precipitation. 3+ This interference can help improve the purity of Al(OH)3.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recycling cathode materials from retired lithium iron phosphate batteries, characterized in that: Includes the following steps: Waste lithium iron phosphate batteries with SOH < 40% were pretreated and then manually disassembled to obtain positive electrode materials. The cathode material and red mud were added to water in a certain proportion, such that the mass ratio of cathode material, red mud and water was 0.5-1.5:2-5:15-25. The first stirring reaction was carried out. After the reaction was completed, the mixture was filtered to obtain the first filtrate and the first filter residue. Titanium dioxide waste acid was added to the first filtrate to make the first filtrate neutral, and Al(OH)3 precipitate and Fe(OH)2 precipitate were obtained by filtration and separation. Titanium dioxide waste acid, 20% H2O2 aqueous solution and first filter residue are mixed in a mass ratio of 4-8:2-5:1 and stirred for a second reaction. After the reaction is complete, the second filtrate and second filter residue are obtained by filtration. Add red mud or an alkaline solution of red mud impregnated into the second filtrate to adjust the pH of the second filtrate to neutral. After the reaction, filter to obtain the third filtrate and Fe(OH)3 precipitate. Na2CO3 was added to the third filtrate. After the reaction, the fourth filtrate and Li2CO3 precipitate were obtained by filtration. The fourth filtrate is added to the titanium dioxide waste acid used to add to the first filtrate, removing the Mg from the titanium dioxide waste acid. 2+ Precipitate removal.

2. The method for recycling the cathode material of retired lithium iron phosphate batteries according to claim 1, characterized in that: The method for pretreating waste lithium iron phosphate batteries is as follows: the retired lithium iron phosphate batteries are placed in a sodium chloride solution to cause a short circuit and electrolysis reaction, producing hydrogen and chlorine gas, which are then collected and discharged.

3. The method for recycling the cathode material of retired lithium iron phosphate batteries according to claim 1, characterized in that: After adding red mud to water and stirring, the mixture precipitates and is filtered to obtain an alkaline solution of red mud.

4. The method for recycling the cathode material of retired lithium iron phosphate batteries according to claim 2, characterized in that: The collected mixture of hydrogen and chlorine gas is passed into a sodium hydroxide solution to absorb the chlorine.

5. The method for recycling the cathode material of retired lithium iron phosphate batteries according to claim 1, characterized in that: The temperature for the first stirring reaction is 50-70℃, and the time is 1-3 hours.

6. The method for recycling the cathode material of retired lithium iron phosphate batteries according to claim 5, characterized in that: The temperature of the first stirring reaction was 60℃, and the time was 2 hours.

7. The method for recycling the cathode material of retired lithium iron phosphate batteries according to claim 1, characterized in that: The second stirring reaction was carried out at a temperature of 45-55℃ for 2-4 hours.

8. The method for recycling the cathode material of retired lithium iron phosphate batteries according to claim 7, characterized in that: The second stirring reaction was carried out at a temperature of 50°C for 3 hours.

9. The method for recycling the cathode material of retired lithium iron phosphate batteries according to claim 1, characterized in that: The mass ratio of Na2CO3 added to the third filtrate to the positive electrode is 1:3-5.

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