WO2024045515A1

WO2024045515A1 - Recovery method and production line for lithium iron phosphate positive electrode waste slurry

Info

Publication number: WO2024045515A1
Application number: PCT/CN2023/077591
Authority: WO
Inventors: 陈嵩; 李长东; 阮丁山; 周游; 李强; 宁培超
Original assignee: 广东邦普循环科技有限公司; 湖南邦普循环科技有限公司
Priority date: 2022-08-31
Filing date: 2023-02-22
Publication date: 2024-03-07
Also published as: CN115513548A

Abstract

Disclosed are a recovery method and production line for lithium iron phosphate positive electrode waste slurry. The recovery method for lithium iron phosphate positive electrode waste slurry comprises: adding water into lithium iron phosphate positive electrode waste slurry to obtain a waste slurry mixed solution; adjusting the pH value of the waste slurry mixed solution to 5-8 by using a weakly acidic buffering agent, and separating a mixture to be separated to obtain lithium iron phosphate positive electrode filter residues and an NMP mixed filtrate; rectifying the NMP mixed filtrate to obtain an NMP product; mixing the lithium iron phosphate positive electrode filter residues with a lithium source to obtain a lithium iron phosphate positive electrode mixture; and drying and roasting the lithium iron phosphate positive electrode mixture to obtain a lithium iron phosphate positive electrode material. The recovery method for lithium iron phosphate positive electrode waste slurry achieves simple and efficient solid-liquid separation of the lithium iron phosphate positive electrode waste slurry, and also increases the recovery rate of NMP and the lithium iron phosphate positive electrode material, thereby mitigating the problem of environmental pollution.

Description

Recycling method of lithium iron phosphate cathode waste liquid and its recycling production line

Technical field

Embodiments of the present application relate to the technical field of lithium battery waste liquid treatment, such as a method for recycling lithium iron phosphate cathode waste liquid and its recycling production line.

Background technique

At present, the market share of lithium iron phosphate batteries is expanding, and cost control of lithium iron phosphate cathodes has become increasingly important. However, in the production process of lithium iron phosphate batteries, the lithium iron phosphate cathode slurry is easily affected by the storage time, resulting in substandard quality, resulting in discarded lithium iron phosphate cathode slurry, thereby increasing the production cost of lithium iron phosphate batteries. At the same time, phosphoric acid Lithium iron batteries will also produce a large amount of lithium iron phosphate cathode waste during the cleaning process. In order to reduce the production cost of lithium iron phosphate batteries, companies generally recycle the lithium iron phosphate cathode waste liquid.

In the process of recycling lithium iron phosphate cathode waste liquid, the main purpose is to recover lithium iron phosphate cathode materials and NMP (N-Methy-lpyrrolidone, N-methylpyrrolidone). In this way, it can not only effectively solve the problem of lithium iron phosphate cathode The problem of waste liquid discharge polluting the environment can also reduce the production cost of lithium iron phosphate batteries.

However, in the process of recycling the lithium iron phosphate cathode waste liquid in related technologies, due to the good colloidal stability of the lithium iron phosphate cathode waste liquid, it is difficult to achieve solid-liquid separation through filter press and centrifugation, that is, there are solid-liquid separations. The problem is that the liquid is difficult to separate, so the lithium iron phosphate cathode material and NMP in the lithium iron phosphate cathode waste liquid cannot be recovered well, that is, there is a problem of low recovery rate.

Contents of the invention

The following is an overview of the topics described in detail in this article. This summary is not intended to limit the scope of the claims.

The embodiments of this application provide a method for recycling lithium iron phosphate cathode waste liquid and its recycling production line to achieve efficient separation and recovery of lithium iron phosphate cathode material and NMP in the lithium iron phosphate cathode waste liquid, so as to improve the lithium iron phosphate cathode material. and NMP recovery rate.

The embodiments of this application are realized through the following technical solutions:

A method for recycling lithium iron phosphate cathode waste liquid, including:

Add water to the lithium iron phosphate positive electrode waste liquid and mix to obtain a waste liquid mixture;

Add a weakly acidic buffer to the waste liquid mixture to adjust the pH of the waste liquid mixture to 5 to 8 to obtain a mixture to be separated;

Separate the mixture to be separated to obtain lithium iron phosphate positive electrode filter residue and NMP mixed filtrate;

Perform rectification on the NMP mixed filtrate to obtain NMP products;

Mix the lithium iron phosphate positive electrode filter residue with a lithium source to obtain a lithium iron phosphate positive electrode mixture;

The lithium iron phosphate cathode mixture is dried and roasted to obtain a lithium iron phosphate cathode material.

In some other embodiments, the amount of water accounts for 15% to 20% of the total volume of the lithium iron phosphate cathode waste liquid.

In some other embodiments, the water includes at least one of deionized water and pure water.

In other embodiments, the weakly acidic buffer includes at least one of lithium dihydrogen phosphate, carbonic acid, and oxalic acid.

In some other embodiments, the separation method is filtration or centrifugation.

In some other embodiments, the temperature of the rectification is 90°C to 130°C.

In some other embodiments, when the lithium iron phosphate positive electrode filter residue and the lithium source are mixed, the mass ratio of the lithium iron phosphate positive electrode filter residue and the lithium source is 1:1.

In some other embodiments, the roasting conditions are: roasting at 650°C to 700°C and in a nitrogen atmosphere for 3h to 4h.

In some other embodiments, the drying temperature is 100°C to 150°C.

A lithium iron phosphate cathode waste liquid recovery production line is produced using the recovery method of lithium iron phosphate cathode waste liquid described in any of the above embodiments.

Compared with related technologies, the embodiments of the present application have at least the following advantages:

The recycling method of the embodiment of the present application first adds water to the lithium iron phosphate cathode waste liquid; in this way, on the one hand, the added water can deactivate the adhesive PVDF in the lithium iron phosphate cathode waste liquid, and the viscosity drops sharply, thereby It can destroy the stability of the colloid of lithium iron phosphate cathode waste liquid, making it easy for solid-liquid separation to occur in the lithium iron phosphate cathode waste liquid, effectively solving the problem of difficult solid-liquid separation of lithium iron phosphate cathode waste liquid; on the other hand, the added Water can inhibit the hydrolysis of NMP and improve the recovery rate of NMP. Next, this application uses a weakly acidic buffer to adjust the pH of the waste liquid mixture to 5 to 8. Since the added water can destroy the stability of the lithium iron phosphate cathode waste liquid colloid, the weakly acidic buffer can better enter the iron phosphate. On the surface of the lithium cathode material and in the NMP, the added weakly acidic buffer can not only neutralize the pH of the waste liquid, effectively inhibit the hydrolysis of NMP, and further improve the recovery rate of NMP; the cations of the weakly acidic buffer can also be adsorbed on phosphoric acid. The surface of the lithium iron cathode material particles causes an imbalance of charges within the colloid, thereby accelerating the agglomeration of the lithium iron phosphate cathode material particles, achieving rapid solid-liquid separation, and reducing the difficulty of solid-liquid separation. It can be effectively separated by conventional filter press or centrifugation. Lithium iron phosphate cathode material and NMP liquid phase, and the added weakly acidic buffer can also inhibit the hydrolysis of NMP and the dissolution of the lithium iron phosphate cathode material, thereby improving the recovery rate of lithium iron phosphate cathode material and NMP. Finally, the NMP product is recovered through distillation, and the lithium iron phosphate cathode filter residue is mixed with the lithium source to supplement the lithium ion content of the lithium iron phosphate cathode filter residue, and then dried and roasted to obtain a regenerated lithium iron phosphate cathode that meets the requirements. The material meets the requirements of recycled lithium iron phosphate cathode material. The recycling method of the present application is simple to operate, efficient in separation, has a high recovery rate of lithium iron phosphate and NMP, and the prepared regenerated lithium iron phosphate cathode material has good lithium iron phosphate morphology and good electrochemical performance.

Other aspects will be apparent after reading and understanding the drawings and detailed description.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application and therefore do not It should be regarded as a limitation of the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a flow chart of a method for recovering lithium iron phosphate cathode waste liquid according to an embodiment of the present application;

Figure 2 is an XRD pattern of a lithium iron phosphate cathode material according to an embodiment of the present application;

Figure 3 is an SEM image of a lithium iron phosphate cathode material according to an embodiment of the present application;

Figure 4 is an electrical performance test chart of a lithium iron phosphate cathode material according to an embodiment of the present application.

Detailed ways

In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are shown in the accompanying drawings. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and comprehensive understanding of the disclosure of the present application.

It should be noted that when an element is referred to as being "fixed" to another element, it can be directly on the other element or intervening elements may also be present. When an element is said to be "connected" to another element, it can be directly connected to the other element or there may also be intervening elements present. The terms "vertical,""horizontal,""left,""right" and similar expressions used herein are for illustrative purposes only and do not imply is the only way to implement it.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing specific embodiments only and is not intended to inhibit the present application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The embodiments of the present application also provide a method for recycling lithium iron phosphate cathode waste liquid. In order to better understand the technical solutions and beneficial effects of the present application, the present application will be further described in detail below with reference to specific examples. Please refer to Figure 1. An embodiment of a method for recovering lithium iron phosphate cathode waste liquid includes some or all of the following steps:

S110. Add water to the lithium iron phosphate positive electrode waste liquid and mix it to obtain a waste liquid mixture.

It can be understood that the general components of lithium iron phosphate cathode waste liquid include lithium iron phosphate, PVDF (Polyvinylidenefluoride, polyvinylidene fluoride), conductive carbon black and NMP. Since PVDF is an organic adhesive, it can make the lithium iron phosphate cathode slurry The viscosity is relatively high, reaching 8000mpa·S to 10000mpa·S, which makes it more difficult to separate NMP and lithium iron phosphate cathode materials in the lithium iron phosphate cathode waste liquid. Therefore, this application adds water to the lithium iron phosphate cathode waste liquid. Since PVDF is insoluble in water, the added water can quickly deactivate the adhesive PVDF in the lithium iron phosphate cathode waste liquid, causing the viscosity to drop sharply, thereby destroying the The stability of the colloid of the lithium iron phosphate cathode waste liquid makes it easy for solid-liquid separation to occur in the lithium iron phosphate cathode waste liquid, effectively solving the problem of difficult solid-liquid separation of the lithium iron phosphate cathode waste liquid. In addition, the added water can inhibit the hydrolysis of NMP to improve the recovery rate of NMP. On the other hand, the added water can also increase the fluidity of the lithium iron phosphate cathode waste liquid so that the water can be fully and quickly dispersed under the mixing operation. Contact with PVDF to achieve efficient and rapid destruction of the stability of the lithium iron phosphate cathode waste liquid colloid.

S120. Add a weakly acidic buffer to the waste liquid mixture to adjust the pH of the waste liquid mixture to 5-8 to obtain a mixture to be separated.

It can be understood that due to the presence of residual lithium in the lithium iron phosphate cathode waste liquid, the lithium iron phosphate cathode waste liquid is alkaline, that is, pH=9-12, and because NMP is prone to hydrolysis in a strongly alkaline or strongly acidic environment. Therefore, this application uses a weakly acidic buffer to adjust the pH of the waste liquid mixture to 5 to 8, so that the pH value is controlled in a near-neutral environment, thereby inhibiting the hydrolysis of NMP to a greater extent. Worth to talk about What is interesting is that the lithium iron phosphate cathode material in the lithium iron phosphate cathode waste liquid is positively charged in the waste liquid, that is, the surface of the lithium iron phosphate cathode material particles is positively charged, and it is easy to form a stable colloid in the lithium iron phosphate cathode waste liquid. , and the weakly acidic buffer added in this application enables the cations of the weakly acidic buffer to be adsorbed on the surface of the lithium iron phosphate cathode material particles, causing a charge imbalance within the colloid, thereby accelerating the aggregation of the lithium iron phosphate cathode material particles and achieving solid-liquid Rapid separation, thereby reducing the difficulty of solid-liquid separation, allows users to effectively separate lithium iron phosphate cathode materials and NMP liquid phases through conventional filter press and centrifugation, and the added weakly acidic buffer can also inhibit the hydrolysis of NMP and phosphoric acid The lithium iron cathode material is dissolved, thereby increasing the recovery rate of lithium iron phosphate cathode material and NMP. It is worth mentioning that the so-called weakly acidic buffer refers to an acidic solution with pH<7 and pH>4.

S130. Separate the mixture to be separated to obtain lithium iron phosphate positive electrode filter residue and NMP mixed filtrate, so as to achieve efficient and rapid separation of the separated mixture with good separation effect.

S140. Distill the NMP mixed filtrate to obtain an NMP product. It can be understood that by distilling the NMP mixed filtrate, not only ensures less loss of NMP to improve the recovery rate of NMP, but also recovers lithium ions in the NMP mixed filtrate to reduce the environmental pollution of lithium ions. .

S150. Mix the lithium iron phosphate cathode filter residue and a lithium source to obtain a lithium iron phosphate cathode mixture.

It can be understood that since the lithium ion content of the separated lithium iron phosphate cathode filter residue is lower than that of the commercially available lithium iron phosphate cathode material, if the lithium iron phosphate cathode filter residue is not mixed with the lithium ion-containing suspension, operation, it is impossible to ensure that subsequent regenerated lithium iron phosphate cathode materials that meet the requirements can be obtained. Therefore, this application mixes the lithium iron phosphate cathode filter residue with a lithium source to supplement the lithium ion content in the lithium iron phosphate cathode filter residue to ensure that the regenerated lithium iron phosphate cathode material that meets the requirements can be obtained after subsequent roasting.

S160: Dry and bake the lithium iron phosphate cathode mixture to obtain a lithium iron phosphate cathode material.

It can be understood that by drying the lithium iron phosphate cathode mixture, the moisture of the lithium iron phosphate cathode mixture can be effectively removed to obtain a powder of the lithium iron phosphate cathode mixture with a smaller particle size to avoid the appearance of lithium iron phosphate. The agglomeration phenomenon in the cathode mixture is beneficial to the subsequent roasting operation, so that the powder of the lithium iron phosphate cathode mixture with smaller particle size can absorb heat more fully, that is, the positive rate of lithium iron phosphate is improved. The contact area between the mixed powder and heat can be quickly obtained to quickly obtain the regenerated lithium iron phosphate cathode material that meets the requirements. Please refer to Figure 2. It can be seen that the lithium iron phosphate peak of the lithium iron phosphate cathode material is obtained. There are fewer impurity peaks and the main substance is Lithium iron phosphate, as shown in Figure 3, the grain size of the calcined lithium iron phosphate cathode material particles is between 0.6 and 1.8 μm, and the regenerated lithium iron phosphate has a good morphology. As can be seen from Figure 4, the calcined iron phosphate Electrical performance indicators of lithium cathode materials: 0.1C discharge capacity is 155mAh/g, 1C discharge capacity is 138mAh/g. In addition, the first charge and discharge efficiency of 0.1C was measured to be >95%, that is, the electrochemical performance of regenerated lithium iron phosphate is good, that is, Regenerated lithium iron phosphate cathode material that meets the requirements. In addition, the recycled NMP products and regenerated lithium iron phosphate cathode materials can be directly recycled and put into the production of lithium iron phosphate batteries, thereby reducing the production cost of lithium iron phosphate batteries.

The above-mentioned recycling method of lithium iron phosphate cathode waste liquid first adds water to the lithium iron phosphate cathode waste liquid; in this way, on the one hand, the added water can deactivate the adhesive PVDF in the lithium iron phosphate cathode waste liquid, making the viscosity A sudden drop, which can destroy the stability of the colloid of the lithium iron phosphate cathode waste liquid, making the lithium iron phosphate cathode waste liquid prone to solid-liquid separation, effectively solving the problem of difficult solid-liquid separation of the lithium iron phosphate cathode waste liquid; another On the other hand, the added water can inhibit the hydrolysis of NMP and improve the recovery rate of NMP. Next, this application uses a weakly acidic buffer to adjust the pH of the waste liquid mixture to 5 to 8. Since the added water can destroy the stability of the lithium iron phosphate cathode waste liquid colloid, the weakly acidic buffer can better enter the iron phosphate. On the surface of the lithium cathode material and in the NMP, the added weakly acidic buffer can not only neutralize the pH of the waste liquid, effectively inhibit the hydrolysis of NMP, and further improve the recovery rate of NMP; the cations of the weakly acidic buffer can also be adsorbed on the lithium iron phosphate positive electrode. The surface of the material particles causes an imbalance of charges within the colloid, thereby accelerating the agglomeration of the lithium iron phosphate cathode material particles, achieving rapid solid-liquid separation, and reducing the difficulty of solid-liquid separation. Lithium iron phosphate can be effectively separated by conventional filter press or centrifugation. The cathode material and NMP liquid phase, and the added weakly acidic buffer can also inhibit the hydrolysis of NMP and the dissolution of the lithium iron phosphate cathode material, thereby improving the recovery rate of the lithium iron phosphate cathode material and NMP. Finally, the NMP product is recovered through distillation. The lithium iron phosphate cathode filter residue is mixed with the lithium source to supplement the lithium ion content of the lithium iron phosphate cathode filter residue. The regenerated lithium iron phosphate cathode that meets the requirements can be obtained by drying and roasting. The material meets the requirements of recycled lithium iron phosphate cathode material. The recovery method of the present application is simple to operate, has high separation efficiency, has a high recovery rate of lithium iron phosphate and NMP, and the prepared regenerated lithium iron phosphate cathode material has good lithium iron phosphate morphology and good electrochemical performance.

It should be noted that compared with the related lithium iron phosphate cathode waste treatment methods, vacuum distillation and flocculation filter press are usually used to separate NMP and lithium iron phosphate cathode materials. Since the method of vacuum distillation is not only The energy consumption is large and the NMP recovery rate is low. Since the flocculation filter press improvement method uses a special acidity regulator, not only is the operation complicated, but the special acidity regulator accelerates the hydrolysis of NMP and the dissolution of the lithium iron phosphate cathode material, resulting in The hydrolysis of NMP and the recovery rate of lithium iron phosphate cathode materials are low, and the maximum efficiency of recycling cannot be achieved. Therefore, this application first adds water to the lithium iron phosphate cathode waste liquid for mixing operation, so that the water can quickly deactivate the adhesive PVDF in the lithium iron phosphate cathode waste liquid, and the viscosity drops sharply to destroy the lithium iron phosphate. Stability of the positive electrode waste liquid colloid, then add a weak acidic buffer to the waste liquid mixture, and adjust the pH of the waste liquid mixture to 5 to 8, so that the added weakly acidic buffer can inhibit the hydrolysis of NMP and iron phosphate The lithium cathode material dissolves, thereby increasing the recovery rate of lithium iron phosphate cathode material and NMP, and the cations of the added weakly acidic buffer can be adsorbed on the surface of the lithium iron phosphate cathode material particles, thereby accelerating the agglomeration of the lithium iron phosphate cathode material particles. , to achieve efficient and rapid separation of solid-liquid lithium iron phosphate cathode waste liquid, thereby reducing the difficulty of solid-liquid separation. It is not only simple and efficient to operate, but also has good separation effect, and improves the recovery rate of NMP and lithium iron phosphate cathode materials, thereby achieving Maximize recycling efficiency.

In some other embodiments, water is first added to the lithium iron phosphate positive electrode waste liquid and stirred to obtain a waste liquid mixture, and then a weakly acidic buffer is used to adjust the pH of the waste liquid mixture to 5-8 to obtain The mixture is to be separated. It should be further explained that adding water can not only destroy the adhesive of the lithium iron phosphate cathode waste liquid to achieve rapid destruction of the colloid stability, but also inhibit the hydrolysis of NMP and improve the recycling rate of NMP. Add a weak acidic buffer to make the pH of the waste liquid mixture 5 to 8, so that the surface of the lithium iron phosphate cathode material can absorb the cations of the weakly acidic buffer to accelerate the hydrolysis of the lithium iron phosphate cathode material and NMP, and the weakly acidic buffer can also It can neutralize the alkalinity in the waste liquid mixture to inhibit the hydrolysis of NMP and the dissolution of the lithium iron phosphate cathode material, thereby improving the hydrolysis of NMP and the recovery rate of the lithium iron phosphate cathode material.

If the order of adding the two is reversed, that is, adding the weak acidic buffer first and then adding water, the newly added weakly acidic buffer cannot destroy the adhesive quickly, and it is necessary to wait until water is added to destroy the adhesive more quickly. agent, resulting in the inability to efficiently and quickly separate the lithium iron phosphate cathode waste liquid, that is, reducing the lithium iron phosphate The speed of solid-liquid separation of positive electrode waste liquid. In addition, if you choose to add a weakly acidic buffer first and then add water, you will need to use a weakly acidic buffer again to adjust the pH of the lithium iron phosphate cathode waste solution. This not only increases the number of processing steps, but also makes the operation more complicated and the solid-liquid separation speeds up. It is slow and increases the usage of weakly acidic buffer, resulting in higher processing costs. Therefore, this application first adds water and mixes evenly before adding a weakly acidic buffer. In this way, the operation is simple and the solid-liquid separation speed is fast, so as to achieve efficient separation of lithium iron phosphate cathode waste liquid, and inhibit NMP hydrolysis and reduce the risk of lithium iron phosphate cathode waste. Materials dissolve, thereby improving NMP hydrolysis and recovery of lithium iron phosphate cathode materials.

Further, in some preferred embodiments, the pH of the waste liquid mixture is controlled to 6-7 to ensure that the waste liquid mixture is close to neutral, thereby effectively inhibiting the hydrolysis of NMP and reducing the dissolution of the lithium iron phosphate cathode material. It also helps the lithium iron phosphate cathode material to absorb the cations of the weak acid buffer to achieve efficient solid-liquid separation. It is not only simple and fast to operate, but also improves the recovery rate of NMP and lithium iron phosphate cathode materials to maximize the efficiency of recycling. And the finally obtained NMP products and lithium iron phosphate cathode materials can be directly recycled into the production of lithium iron phosphate batteries, thereby reducing the production cost of lithium iron phosphate batteries and solving the problem of environmental pollution caused by the discharge of lithium iron phosphate cathode waste liquid.

In some other embodiments, the amount of water accounts for 15% to 20% of the total volume of the lithium iron phosphate cathode waste liquid, that is, the amount of water accounts for 10% of the total volume of the liquid in the lithium iron phosphate cathode waste liquid. 15%~20%. It can be understood that if the amount of water used is less than 15%, the amount of water added will not be enough to quickly inactivate PVDF, and it will not be able to destroy the stability of the colloid efficiently and comprehensively, making it difficult to separate solid and liquid in the lithium iron phosphate cathode waste liquid. phenomenon, resulting in a low recovery rate of NMP and lithium iron phosphate cathode materials; if the amount of water is higher than 20%, on the one hand, it will accelerate the hydrolysis of NMP, resulting in an increase in the hydrolysis rate of NMP, thereby reducing the recovery rate of NMP. On the other hand, Not only will it cause a waste of water resources, but it will also increase the time for subsequent drying processing, thereby increasing the cost of recycling lithium iron phosphate cathode waste liquid. Therefore, this application controls the amount of water to account for 15% to 20% of the total volume of the liquid in the lithium iron phosphate cathode waste liquid, so that the added water can well destroy the adhesive in the waste liquid. In this way, not only Improve the efficient separation of lithium iron phosphate cathode waste liquid and control the hydrolysis rate of NMP to a minimum, thereby minimizing the hydrolysis loss rate of NMP to increase the recovery rate of NMP in the lithium iron phosphate cathode waste liquid.

In some other embodiments, the water includes at least one of deionized water and pure water. Reasonable Solution, since there are fewer impurities in deionized water and pure water, it ensures that the added water has a high purity, which can effectively avoid the introduction of new impurities, thereby ensuring that subsequent regenerated lithium iron phosphate cathode materials with a purity of up to 99.9% can be obtained , thereby enabling the obtained NMP products to be directly put into production to reduce the production cost of lithium iron phosphate batteries.

In other embodiments, the weakly acidic buffer includes at least one of lithium dihydrogen phosphate, carbonic acid, and oxalic acid. It can be understood that since the aqueous solutions of lithium dihydrogen phosphate, carbonic acid and oxalic acid are all weakly acidic, they can effectively neutralize the lithium iron phosphate cathode waste liquid OH ^- , thus providing a relatively neutral environment for NMP, thereby inhibiting the occurrence of NMP. Hydrolysis to improve NMP recovery. In addition, the surface of the lithium iron phosphate cathode material particles can adsorb the cations of lithium dihydrogen phosphate, carbonic acid and oxalic acid to cause an internal charge imbalance in the colloid to accelerate the agglomeration of the lithium iron phosphate cathode material particles to achieve high efficiency of the lithium iron phosphate cathode waste liquid. Rapid separation, thereby reducing the difficulty of solid-liquid separation.

It should be noted that the addition of lithium dihydrogen phosphate, carbonic acid and oxalic acid will not introduce new impurities into the lithium iron phosphate cathode waste liquid, ensuring that high-purity NMP products and lithium iron phosphate cathode materials can be obtained in the future. In other words, the reaction between the added lithium dihydrogen phosphate and the lithium iron phosphate cathode waste liquid is: 2LiOH+LiH ₂ PO ₄ → Li ₃ PO ₄ +2H ₂ O. It can be seen that Li ⁺ and H ₂ PO ₄ ^- react with lithium iron phosphate The Li ⁺ and H ₂ PO ₄ ^- of the positive electrode waste liquid are consistent to avoid the introduction of new impurities into the lithium iron phosphate positive electrode waste liquid. The reaction between the added carbonic acid and the lithium iron phosphate positive electrode waste liquid is: 2LiOH+H ₂ CO ₃ → Li ₂ CO ₃ +2H ₂ O; the reaction between the added oxalic acid and the lithium iron phosphate cathode waste liquid: 2LiOH+H ₂ C ₂ O ₄ →Li2C ₂ O ₄ +2H ₂ O; it can be seen that Li ₂ CO ₃ and Li ₂ C ₂ O ₄ will generate gas and water during the subsequent distillation, drying and roasting to avoid the introduction of new impurities into the lithium iron phosphate cathode waste liquid, thereby ensuring that higher purity NMP products and lithium iron phosphate cathode materials are obtained. In addition, the added water and weakly acidic buffer can also inhibit the hydrolysis of NMP and the dissolution of the lithium iron phosphate cathode material, thereby improving the recovery rate of the lithium iron phosphate cathode material and NMP.

In some other embodiments, the step of adding a weakly acidic buffer to the waste liquid mixture to adjust the pH of the waste liquid mixture to 5-8 to obtain the mixture to be separated includes the following specific steps: : Add the weakly acidic buffer to the waste liquid mixture while stirring, and adjust the pH of the waste liquid mixture to 5-8.

It can be understood that a weak acidic buffer is added to the waste liquid mixture while stirring to ensure that the Ensure that the added weakly acidic buffer can be quickly dispersed into the waste liquid mixture, effectively preventing the added weakly acidic buffer from easily agglomerating at the contact surface with the waste liquid mixture, thereby ensuring that the weakly acidic buffer can function well into the waste liquid mixture so that the weakly acidic buffer can fully contact the waste liquid mixture to achieve efficient and rapid solid-liquid separation of the waste liquid mixture and effectively solve the difficult problem of lithium iron phosphate cathode waste liquid Separation issues.

In a preferred embodiment, the carbonic acid is a saturated solution to ensure that the saturated carbonic acid can fully and comprehensively contact the lithium iron phosphate cathode waste liquid to achieve efficient and rapid separation of the lithium iron phosphate cathode waste liquid, which is not only simple to operate but also It is highly efficient and inhibits the hydrolysis of NMP and the dissolution of lithium iron phosphate cathode materials, thereby improving NMP and lithium iron phosphate cathode materials, and avoiding the introduction of new impurities into the lithium iron phosphate cathode waste liquid to ensure high purity NMP and phosphoric acid. The lithium iron cathode material enables the obtained NMP and lithium iron phosphate cathode materials to be directly put into production to reduce the production cost of lithium iron phosphate batteries.

Similarly, in a preferred embodiment, the oxalic acid is 0.1 mol/L to ensure that the 0.1 mol/L oxalic acid can fully and comprehensively contact the lithium iron phosphate cathode waste liquid to achieve efficient and rapid treatment of the lithium iron phosphate cathode waste liquid. Separation is not only simple and efficient to operate, but also inhibits the hydrolysis of NMP and the dissolution of lithium iron phosphate cathode materials, thereby improving NMP and lithium iron phosphate cathode materials, and avoiding the introduction of new impurities into the lithium iron phosphate cathode waste liquid to ensure that High-purity regenerated NMP and lithium iron phosphate regenerated lithium iron phosphate cathode materials with good morphology and good electrochemical properties enable the obtained NMP and lithium iron phosphate cathode materials to be directly put into production to reduce the production of lithium iron phosphate batteries. cost.

In a more preferred embodiment, the concentration of lithium dihydrogen phosphate is 200g/L to ensure that the addition of 200g/L lithium dihydrogen phosphate can fully and comprehensively contact the lithium iron phosphate cathode waste liquid to achieve the lithium iron phosphate cathode waste liquid. Efficient and rapid separation is not only simple and efficient to operate, but also inhibits the hydrolysis of NMP and the dissolution of lithium iron phosphate cathode materials, thereby improving NMP and lithium iron phosphate cathode materials, and avoiding the introduction of new impurities into the lithium iron phosphate cathode waste liquid. To ensure that high-purity regenerated NMP and lithium iron phosphate regenerated lithium iron phosphate cathode materials with good morphology and good electrochemical properties are obtained, so that the obtained NMP and lithium iron phosphate cathode materials can be directly put into production to reduce the cost of lithium iron phosphate batteries. production costs.

In some other embodiments, the separation method is filtration or centrifugation. It can be understood that filter press operation or centrifugation operation is used to separate the mixture to be separated, so that users can effectively separate the mixture through conventional methods. Separate the lithium iron phosphate cathode material and the NMP liquid phase, thereby achieving efficient and rapid separation of the lithium iron phosphate cathode waste liquid.

In some other embodiments, the centrifugation is performed using a centrifuge to obtain the lithium iron phosphate positive electrode filter residue and NMP mixed filtrate. Further, the rotation speed of the centrifuge is 1200r/min～2000r/min. It can be understood that by controlling the rotation speed of the centrifuge to 1200 r/min to 2000 r/min, efficient and rapid separation of the mixture to be separated can be achieved.

In some preferred embodiments, the filtration is performed through a filter press to obtain a mixed filtrate of lithium iron phosphate positive electrode filter residue and NMP. Furthermore, the filter press is a plate and frame filter press. It can be understood that the plate and frame filter press includes a filter press component and a mounting frame. The filter press component is movably mounted on the mounting frame. The mixture to be separated is input to the filter press component to perform press filter separation, and then passes through the filter press component to achieve the separation. Efficiently and quickly separate the mixture to be treated to obtain lithium iron phosphate positive electrode filter residue and NMP mixed filtrate for later use.

In some other embodiments, the filter press assembly device includes a plurality of filter bodies, each of the filter bodies includes a filter frame, a filter plate and a filter cloth, and the filter plate is movably arranged on the mounting frame, and the The filter cloth is covered with the filter plate, and the filter frame is used to fix the filter cloth on the filter plate, so that the user can input a larger volume of mixture to be separated at one time, and multiple filter bodies can be simultaneously The mixture to be separated is filtered to achieve efficient and rapid separation of the mixture to be separated.

It should be noted that since the pH of the mixture to be separated obtained by the present application is close to neutral, it is less corrosive to the plate and frame filter press, and especially plays a good protective role for the filter cloth, thereby extending the plate and frame. The service life of the filter press is reduced, thereby reducing the recycling cost of lithium iron phosphate cathode waste liquid, and significantly reducing the harsh conditions for the use of filter cloth of the plate and frame filter press, making the filter press operation simpler.

In some other embodiments, the mesh number of the filter cloth is 200 mesh to 500 mesh. It can be understood that by controlling the mesh number of the filter cloth to 200 mesh to 500 mesh, it is possible to ensure that the lithium iron phosphate cathode material and NMP can be separated efficiently and quickly.

In some other embodiments, the pressure of the plate and frame filter press is 0.6Mpa~0.7Mpa. It can be understood that since the use of weakly acidic buffers can cause charge imbalance within the colloid, the lithium iron phosphate cathode material particles are easy to agglomerate into clusters. Not only is the solid-liquid separation speed fast and effective, that is, more lithium iron phosphate is formed in the mixture to be separated. Lithium iron phosphate cathode material particles. Therefore, this application sets the pressure of the plate and frame filter press to 0.6Mpa~0.7Mpa to achieve efficient and rapid separation of the mixture to be separated. It should be noted that the pressure of the traditional plate and frame filter press is usually ≤0.5Mpa, which is relatively The pressure is lower than that used in this application, mainly because the added weakly acidic buffer can cause a charge imbalance within the colloid, making it easy for the lithium iron phosphate cathode material particles to agglomerate and form relatively large amounts of iron phosphate in the mixed liquid to be separated. Lithium cathode material particles. Therefore, this application increases the pressure of the plate and frame filter press to ensure efficient and rapid separation of lithium iron phosphate cathode filter residue and NMP mixed filtrate, thereby increasing the recovery rate of lithium iron phosphate cathode material and NMP, and The separation effect is good.

In some other embodiments, the temperature of the rectification is 90°C to 130°C. It can be understood that if the temperature is lower than 90°C, less NMP will precipitate in the NMP mixed filtrate, thereby reducing the purity of the NMP product. If the temperature is higher than 130°C, NMP will easily be lost, resulting in a lower recovery rate of NMP. Therefore , this application can effectively remove the water in the NMP mixed filtrate by controlling the distillation temperature to 90°C to 130°C, which is conducive to the precipitation of NMP in the NMP mixed filtrate, thereby obtaining a regenerated NMP product with a purity as high as 99.9 or above, so as to obtain NMP products can be directly put into the production of lithium iron phosphate batteries, thereby reducing the production cost of lithium iron phosphate batteries.

In some other embodiments, when the lithium iron phosphate positive electrode filter residue and the lithium source are mixed, the mass ratio of the lithium iron phosphate positive electrode filter residue and the lithium source is 1:1. It can be understood that since the lithium ion content in the lithium iron phosphate cathode filter residue obtained after filtering is lower than the lithium ion content of the commercially available lithium iron phosphate cathode material, this application is based on the comparison between the lithium iron phosphate cathode filter residue and the lithium source. The mixing operation is carried out at a mass ratio of 1:1 to supplement the lithium ion content of the lithium iron phosphate cathode filter residue, thereby ensuring that subsequent regenerated lithium iron phosphate cathode materials that meet the requirements can be obtained.

In other embodiments, the lithium source is a lithium ion suspension. By formulating the lithium source into a lithium ion suspension, the lithium ion suspension can be more fully mixed with the lithium iron phosphate cathode filter residue to ensure that subsequent regenerated lithium iron phosphate cathode materials that meet the requirements can be obtained, thereby improving the phosphoric acid Recovery rate of lithium iron cathode materials.

In some other embodiments, the lithium ion-containing suspension includes at least one of lithium carbonate and lithium hydroxide. It is understandable that since lithium carbonate and lithium hydroxide can not only provide lithium for the lithium iron phosphate cathode filter residue, ions, and also ensures that the added lithium-ion-containing suspension will not introduce new impurities, that is, the added carbonate ions and hydroxide ions can be used during subsequent drying and roasting to ensure that regenerated lithium iron phosphate that meets the requirements is obtained Cathode materials, so that the recycled lithium iron phosphate cathode materials can be directly recycled into the production of lithium iron phosphate batteries, further reducing the production cost of lithium iron phosphate batteries.

Further, the concentration of the lithium ion-containing suspension is 90g/L to 110g/L. It can be understood that because the lithium-ion-containing suspension of 90g/L~110g/L can provide sufficient lithium ions for the lithium iron phosphate positive electrode filter residue, and ensuring that the addition of 90g/L~110g/L lithium-ion-containing suspension can It fully reacts with the lithium iron phosphate cathode filter residue without producing waste. It not only obtains the regenerated lithium iron phosphate cathode material that meets the requirements, but also reduces the cost of recycling the lithium iron phosphate cathode waste liquid. In a preferred embodiment, the concentration of lithium carbonate is 100g/L to ensure that 100g/L lithium carbonate can fully react with the lithium iron phosphate positive electrode filter residue to obtain lithium iron phosphate with good morphology and electrochemical performance. Highly regenerable recycled lithium iron phosphate cathode material.

In some other embodiments, the step of mixing the lithium iron phosphate positive electrode filter residue and the lithium ion-containing suspension to obtain the lithium iron phosphate positive electrode mixture also includes the following steps: The lithium iron phosphate cathode mixture is mixed and stirred for 30 to 40 minutes to ensure that a uniformly mixed lithium iron phosphate cathode mixture is obtained.

In some other embodiments, the conditions of the roasting operation are roasting at 650°C to 700°C and in a nitrogen atmosphere for 3h to 4h. It can be understood that the lithium iron phosphate cathode mixture is roasted at a temperature of 650°C to 700°C and filled with nitrogen for 3h to 4h to ensure that the lithium iron phosphate cathode mixture can be obtained by roasting in a nitrogen atmosphere for 3h to 4h. High-purity lithium iron phosphate cathode materials can remove conductive carbon black and moisture from the lithium iron phosphate cathode mixture to obtain regenerated lithium iron phosphate cathode materials that meet the requirements. If the roasting temperature is lower than 650°C and the time is lower than 3 hours, the conductive carbon black in the lithium iron phosphate cathode mixture cannot be effectively removed, and thus the regenerated lithium iron phosphate cathode material that meets the requirements cannot be ensured. If the roasting temperature is higher than 700 ℃, and the time is greater than 4 hours, it is easy to cause the loss of lithium iron phosphate cathode material, thereby reducing the recovery rate of lithium iron phosphate cathode material in the lithium iron phosphate cathode waste liquid.

In some other embodiments, the drying temperature is 100°C to 150°C. It can be understood that by controlling the temperature during drying to 100°C to 150°C, the moisture of the lithium iron phosphate cathode mixture can be effectively removed to obtain a powder of the lithium iron phosphate cathode mixture with a smaller particle size to avoid the appearance of iron phosphate. Lithium cathode mixture appears knotted It also facilitates subsequent roasting. The powder of the lithium iron phosphate cathode mixture can be quickly and comprehensively roasted to quickly obtain high-purity lithium iron phosphate cathode material. Further, the drying operation can be one of spray drying, double cone drying, rake drying, and hot air drying, so as to achieve drying of the lithium iron phosphate cathode mixture and form a lithium iron phosphate cathode mixture with a smaller particle size. Material powder.

In a preferred embodiment, the drying method is spray drying, and the temperature is 150°C. It can be understood that after the lithium iron phosphate cathode mixture is spray-dried, a lithium iron phosphate cathode mixture powder with a smaller particle size can be obtained, thereby effectively avoiding the agglomeration of the lithium iron phosphate cathode mixture, which will lead to subsequent roasting. When the agglomerated lithium iron phosphate cathode mixture is roasted, incomplete roasting is likely to occur inside, and a higher purity lithium iron phosphate cathode mixture cannot be obtained. Therefore, this application spray-dries the lithium iron phosphate cathode mixture at a temperature of 150°C to achieve rapid drying of the lithium iron phosphate cathode mixture to ensure that the lithium iron phosphate can be enlarged during subsequent roasting. The transfer rate of the cathode mixture powder and heat ensures that the lithium iron phosphate cathode mixture powder can quickly remove moisture and conductive carbon black, thereby obtaining high-purity lithium iron phosphate cathode material and improving the efficiency of the lithium iron phosphate cathode mixture powder. Drying efficiency.

It is worth mentioning that this application can simultaneously recycle NMP and lithium iron phosphate cathode materials in the lithium iron phosphate cathode waste liquid, and put the obtained regenerated NMP products and regenerated lithium iron phosphate cathode materials into lithium iron phosphate at the same time. In battery production, it can greatly reduce the production cost of lithium iron phosphate batteries and effectively reduce the environmental pollution caused by the discharge of lithium iron phosphate cathode waste liquid.

The present application also provides a lithium iron phosphate cathode waste liquid recovery production line, which is produced using the recovery method of lithium iron phosphate cathode waste liquid described in any of the above embodiments. It can be understood that in order to realize the automated production of recycling lithium iron phosphate cathode waste liquid, the recycling method of lithium iron phosphate cathode waste liquid is used for production, so as to achieve efficient and rapid recovery of NMP and lithium iron phosphate cathode materials in the lithium iron phosphate cathode waste liquid. Recycling and utilization can quickly prepare high-purity NMP products and regenerated lithium iron phosphate cathode materials that meet the requirements, thereby improving the efficiency of recycling and treatment of lithium iron phosphate cathode waste liquid.

Compared with related technologies, this application has at least the following advantages:

The recycling method of this application first adds water to the lithium iron phosphate cathode waste liquid; in this way, on the one hand, the added water can deactivate the adhesive PVDF in the lithium iron phosphate cathode waste liquid, causing the viscosity to drop sharply, thereby destroying the The stability of the colloid of the lithium iron phosphate cathode waste liquid makes it easy for solid-liquid formation in the lithium iron phosphate cathode waste liquid. The phenomenon of separation effectively solves the problem of difficult separation of solid and liquid from lithium iron phosphate cathode waste liquid; on the other hand, the added water can inhibit the hydrolysis of NMP and improve the recovery rate of NMP. Next, this application uses a weakly acidic buffer to adjust the pH of the waste liquid mixture to 5 to 8. Since the added water can destroy the stability of the lithium iron phosphate cathode waste liquid colloid, the weakly acidic buffer can better enter the iron phosphate. On the surface of the lithium cathode material and in the NMP, the added weakly acidic buffer can not only neutralize the pH of the waste liquid, effectively inhibit the hydrolysis of NMP, and further improve the recovery rate of NMP; the cations of the weakly acidic buffer can also be adsorbed on the lithium iron phosphate positive electrode. The surface of the material particles causes an imbalance of charges within the colloid, thereby accelerating the agglomeration of the lithium iron phosphate cathode material particles, achieving rapid solid-liquid separation, and reducing the difficulty of solid-liquid separation. Lithium iron phosphate can be effectively separated by conventional filter press or centrifugation. The cathode material and NMP liquid phase, and the added weakly acidic buffer can also inhibit the hydrolysis of NMP and the dissolution of the lithium iron phosphate cathode material, thereby improving the recovery rate of the lithium iron phosphate cathode material and NMP. Finally, the NMP product is recovered through distillation. The lithium iron phosphate cathode filter residue is mixed with the lithium source to supplement the lithium ion content of the lithium iron phosphate cathode filter residue. The regenerated lithium iron phosphate cathode that meets the requirements can be obtained by drying and roasting. The material meets the requirements of recycled lithium iron phosphate cathode material. The recovery method of the present application is simple to operate, has high separation efficiency, has a high recovery rate of lithium iron phosphate and NMP, and the prepared regenerated lithium iron phosphate cathode material has good lithium iron phosphate morphology and good electrochemical performance.

Some specific examples are exemplified below. If % is mentioned, it is expressed as a percentage by weight. It should be noted that the following examples do not exhaust all possible situations, and the materials used in the following examples can all be obtained from commercial sources unless otherwise specified.

Example 1

Pour 56.7kg of deionized water into 1000kg of lithium iron phosphate cathode waste liquid (solid content: 62.20%). After stirring evenly, a waste liquid mixture is obtained. While stirring, add 200g/L diphosphate to the waste liquid mixture. Adjust the pH of the lithium hydrogen solution to 7, and then continue stirring for 10 minutes to obtain the mixture to be separated. Use a screw pump to drive the adjusted mixture to be separated into a plate and frame filter press for filtering operation. The pressure is 0.6Mpa. The volume of the filtrate is 330L, and the mesh number of the filter cloth is 300 mesh to obtain the lithium iron phosphate positive electrode filter residue and the NMP mixed filtrate. The NMP mixed filtrate is input into a 0.5 μm precision filter and filtered for distillation and purification. The distillation temperature is 90°C. , to produce high-purity NMP products with NMP concentration ≥ 99.9%, and lithium salt crystals are precipitated during the distillation process; 750kg of lithium iron phosphate positive electrode filter residue obtained by press filtration is poured into 750L, 100g/L In the suspension of lithium carbonate, stir for 30 minutes at room temperature at a stirring speed of 400 r/min to obtain a lithium iron phosphate cathode mixture; the prepared lithium iron phosphate cathode mixture is spray-dried at 150°C to make phosphoric acid Lithium iron phosphate cathode mixture powder, lithium iron phosphate cathode mixture powder was roasted at 700°C in a nitrogen atmosphere for 3 hours to obtain a regenerated lithium iron phosphate cathode material.

Example 2

Pour 55.35kg of deionized water into 1000kg of lithium iron phosphate cathode waste liquid (solid content: 63.10%). After stirring evenly, a waste liquid mixture is obtained. While stirring, add saturated carbonic acid to the waste liquid mixture to adjust the pH to 6. , and then continue stirring for 10 minutes to obtain the mixture to be separated. Use a screw pump to drive the adjusted mixture to be separated into a plate and frame filter press for filtration operation. The pressure is 0.65Mpa, the filtrate volume is 330L, and the filter cloth The mesh number is 200 mesh to obtain the lithium iron phosphate positive electrode filter residue and NMP mixed filtrate. The NMP mixed filtrate is input into a 0.5 μm precision filter and filtered for distillation and purification. The distillation temperature is 100°C to obtain high-purity NMP. product, its NMP concentration is ≥99.9%, and lithium salt crystals are precipitated during the distillation process; 745kg of the lithium iron phosphate positive electrode filter residue obtained by press filtration is poured into 745L, 90g/L lithium hydroxide suspension, and the product is heated at room temperature Stir for 35 minutes at a stirring speed of 450 r/min to obtain a lithium iron phosphate cathode mixture; spray-dry the obtained lithium iron phosphate cathode mixture at 120°C to prepare a lithium iron phosphate cathode mixture powder. The mixed powder was calcined at 680°C in a nitrogen atmosphere for 3.5 hours to obtain a regenerated lithium iron phosphate cathode material.

Example 3

Pour 74.6kg of deionized water into 1000kg of lithium iron phosphate cathode waste liquid (solid content: 62.7%). After stirring evenly, a waste liquid mixture is obtained. While stirring, add 0.1mol/L oxalic acid to the waste liquid mixture. Adjust the pH of the solution to 8, and then continue stirring for 10 minutes to obtain the mixture to be separated. Use a screw pump to drive the adjusted mixture to be separated into a plate and frame filter press for filtration operation. The pressure is 0.7Mpa and the filtrate volume is 0.7Mpa. is 330L, and the filter cloth has a mesh size of 500 to obtain the lithium iron phosphate positive electrode filter residue and the NMP mixed filtrate. The NMP mixed filtrate is input into a 0.5 μm precision filter and filtered for distillation and purification. The distillation temperature is 130°C to prepare A high-purity NMP product is obtained, with an NMP concentration ≥ 99.9%, and lithium salt crystals are precipitated during the distillation process; 740kg of the lithium iron phosphate positive electrode filter residue obtained by press filtration is poured into 748L, 110g/L lithium carbonate suspension. , stir at room temperature for 40 minutes, the stirring speed is 380r/min, to obtain lithium iron phosphate Cathode mixture; the prepared lithium iron phosphate cathode mixture is spray-dried at 100°C to prepare lithium iron phosphate cathode mixture powder, and the lithium iron phosphate cathode mixture powder is roasted at 650°C in a nitrogen atmosphere for 4 hours to obtain a regeneration cycle Lithium iron phosphate cathode material.

Comparative example 1

The difference from Example 1 is that an equal amount of pure water is used instead of the lithium dihydrogen phosphate solution.

Comparative example 2

The difference from Example 1 is that an equal amount of 0.1 mol/L phosphoric acid is used instead of the lithium dihydrogen phosphate solution.

Comparative example 3

The difference from Example 1 is that an equal amount of 0.1 mol/L LiOH is used instead of lithium dihydrogen phosphate solution.

Comparative example 4

The difference from Example 1 is that 60 kg of deionized water and lithium dihydrogen phosphate solution were not added to the lithium iron phosphate positive electrode waste liquid.

Comparative example 5

The difference from Example 1 is that an equal amount of pure water is used instead of 750L, 100g/L lithium carbonate suspension aqueous solution.

Comparative example 6

The difference from Example 1 is that air atmosphere is used instead of nitrogen atmosphere.

Statistics were made on the state of the mixture to be separated and the NMP loss rate, NMP recovery rate, and recovery rate of lithium iron phosphate cathode material in Examples 1, 2, 3 and Comparative Examples 1, 2, 3, and 4. The results are shown in Table 1

NMP concentration: detected by gas chromatograph

Solid content determination: using a solid content tester

NMP recovery rate: NMP mass after distillation/(1-solid content)1000*NMP concentration of raw solution

NMP loss rate = 1 - NMP mass after distillation / (1 - solid content) 1000 * raw solution NMP concentration

Recovery rate of lithium iron phosphate cathode material = mass of lithium iron phosphate cathode filter residue * solid content rate of lithium iron phosphate cathode filter residue / 1000 * solid content of lithium iron phosphate cathode waste liquid

Table 1

From the comparison between Examples 1 to 3 and Comparative Examples 1 to 4 in Table 1, it can be seen that adding water and weakly acidic buffer in Examples 1 to 3 can effectively destroy the colloidal stability of lithium iron phosphate cathode waste liquid, and is not only simple to operate , high efficiency, and good separation effect. It reduces the difficulty of solid-liquid separation of lithium iron phosphate cathode waste liquid and can achieve efficient and rapid separation of the mixture to be separated by using conventional filtration, filter press or centrifugation, especially in Examples 1 and 2. The comprehensive indicators are excellent, that is, when the pH of the mixture to be separated is between 6 and 7, not only the filtration speed is fast, but also the recovery rate of NMP is as high as 87.00%, the recovery rate of lithium iron phosphate cathode material is as high as 97%, and regenerated The purity of NMP products is as high as over 99.9%, and the lithium iron phosphate cathode material meets the regeneration requirements to maximize the efficiency of recycling lithium iron phosphate cathode waste liquid.

Further, the electrical properties of the regenerated lithium iron phosphate cathode materials of Examples 1, 2, 3 and Comparative Examples 5 and 6 were tested. The results are shown in Table 2.

Table 2

From Table 2, it can be seen that the various electrical performance indicators of the lithium iron phosphate cathode materials prepared in Examples 1 to 3 are good, and the regenerated lithium iron phosphate cathode materials that meet the requirements can be directly recycled into the lithium iron phosphate battery. During production, it not only alleviates the problem of environmental pollution caused by the discharge of lithium iron phosphate cathode waste liquid, but also reduces the production cost of lithium iron phosphate batteries.

The above-mentioned embodiments only express several implementation modes of the present application, and their descriptions are relatively specific and detailed, but this should not be understood as limiting the scope of the patent application. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all fall within the protection scope of the present application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

A method for recycling lithium iron phosphate cathode waste liquid, which includes:

Add water to the lithium iron phosphate positive electrode waste liquid and mix to obtain a waste liquid mixture;

Add a weakly acidic buffer to the waste liquid mixture to adjust the pH of the waste liquid mixture to 5 to 8 to obtain a mixture to be separated;

Separate the mixture to be separated to obtain lithium iron phosphate positive electrode filter residue and NMP mixed filtrate;

The NMP mixed filtrate is rectified to obtain NMP products;

Mix the lithium iron phosphate positive electrode filter residue with a lithium source to obtain a lithium iron phosphate positive electrode mixture;

The lithium iron phosphate cathode mixture is dried and roasted to obtain a lithium iron phosphate cathode material.
The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, wherein the amount of water accounts for 15% to 20% of the total volume of the lithium iron phosphate cathode waste liquid.
The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, wherein the water includes at least one of deionized water and pure water.
The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, wherein the weakly acidic buffer includes at least one of lithium dihydrogen phosphate, carbonic acid and oxalic acid.
The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, wherein the separation method is filter press or centrifugation.
The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, wherein the temperature of the rectification is 90°C to 130°C.
The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, wherein when the lithium iron phosphate cathode filter residue and the lithium source are mixed, the mass ratio of the lithium iron phosphate cathode filter residue and the lithium source is 1: 1.
The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, wherein the roasting conditions are: roasting at 650°C to 700°C and in a nitrogen atmosphere for 3h to 4h.
The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, wherein the drying temperature is 100°C to 150°C.
A lithium iron phosphate cathode waste liquid recovery production line, wherein the production is carried out using the recovery method of lithium iron phosphate cathode waste liquid according to any one of claims 1 to 9.