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

Abstract

The present application provides a method for recycling lithium iron phosphate positive electrode waste liquid and its recycling production line. The above-mentioned method for recycling lithium iron phosphate positive electrode waste liquid includes adding water to the lithium iron phosphate positive electrode waste liquid to obtain a waste liquid mixture; using a weak acidic buffer to adjust the pH of the waste liquid mixture to 5-8, separating the mixture to be separated to obtain lithium iron phosphate positive electrode residue and NMP mixed filtrate; distilling the NMP mixed filtrate to obtain an NMP product; mixing the lithium iron phosphate positive electrode residue with a lithium source to obtain a lithium iron phosphate positive electrode mixture; drying and roasting the lithium iron phosphate positive electrode mixture to obtain a lithium iron phosphate positive electrode material. The above-mentioned method for recycling lithium iron phosphate positive electrode waste liquid makes the solid-liquid separation of lithium iron phosphate positive electrode waste liquid simple and efficient, and also improves the recovery rate of NMP and lithium iron phosphate positive electrode material to reduce the problem of environmental pollution.

Description

Technical Field

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

[0002] As the market share of lithium iron phosphate batteries continues to expand, cost control of lithium iron phosphate cathodes is becoming increasingly important. However, during the production process, the lithium iron phosphate cathode slurry is easily affected by storage time, resulting in substandard quality and waste lithium iron phosphate cathode slurry, which increases the production cost of lithium iron phosphate batteries. Furthermore, the cleaning process of lithium iron phosphate batteries also produces a large amount of lithium iron phosphate cathode waste liquid. To reduce the production cost of lithium iron phosphate batteries, companies generally recycle and process the lithium iron phosphate cathode waste liquid.

[0003] In the process of recycling lithium iron phosphate positive electrode waste liquid, the main focus is on recovering lithium iron phosphate positive electrode materials and NMP (N-Methy-lpyrrolidone). This not only effectively solves the problem of lithium iron phosphate positive electrode waste liquid discharge polluting the environment, but also reduces the production cost of lithium iron phosphate batteries.

[0004] However, in the process of recycling and treating lithium iron phosphate positive electrode waste liquid in the existing technology, due to the good colloidal stability of the lithium iron phosphate positive electrode waste liquid, it is difficult to achieve solid-liquid separation by filtration and centrifugation, that is, there is a problem of difficult solid-liquid separation, and thus the lithium iron phosphate positive electrode material and NMP in the lithium iron phosphate positive electrode waste liquid cannot be well recovered, that is, there is a problem of low recovery rate. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for recovering lithium iron phosphate positive electrode waste liquid and a recovery production line thereof, so as to achieve efficient separation and recovery of lithium iron phosphate positive electrode material and NMP in the lithium iron phosphate positive electrode waste liquid, so as to improve the recovery rate of lithium iron phosphate positive electrode material and NMP.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A method for recovering lithium iron phosphate cathode waste liquid, comprising:

[0008] adding water to the lithium iron phosphate cathode waste liquid and mixing to obtain a waste liquid mixture;

[0009] adding a weak acidic buffer to the waste liquid mixture to adjust the pH of the waste liquid mixture to 5 to 8, thereby obtaining a mixture to be separated;

[0010] Separating the mixture to be separated to obtain a lithium iron phosphate positive electrode residue and an NMP mixed filtrate;

[0011] The NMP mixed filtrate is distilled to obtain an NMP product;

[0012] Mixing the lithium iron phosphate positive electrode residue with a lithium source to obtain a lithium iron phosphate positive electrode mixture;

[0013] The lithium iron phosphate positive electrode mixture is dried and calcined to obtain a lithium iron phosphate positive electrode material.

[0014] In some other embodiments, the amount of water used accounts for 15% to 20% of the total volume of the lithium iron phosphate positive electrode waste liquid.

[0015] In some other embodiments, the water includes at least one of deionized water and pure water.

[0016] In some other embodiments, the weak acid buffer comprises at least one of lithium dihydrogen phosphate, carbonic acid, and oxalic acid.

[0017] In some other embodiments, the separation method is filtration or centrifugation.

[0018] In some other embodiments, the distillation temperature is 90°C to 130°C.

[0019] In some other embodiments, when the lithium iron phosphate positive electrode filter residue is mixed with a lithium source, the mass ratio of the lithium iron phosphate positive electrode filter residue to the lithium source is 1:1.

[0020] In some other embodiments, the calcination conditions are: calcination at 650° C. to 700° C. in a nitrogen atmosphere for 3 h to 4 h.

[0021] In some other embodiments, the drying temperature is 100°C to 150°C.

[0022] A lithium iron phosphate cathode waste liquid recovery production line adopts the lithium iron phosphate cathode waste liquid recovery method described in any of the above embodiments for production.

[0023] Compared with the prior art, the present invention has at least the following advantages:

[0024] The recovery method of the present invention first adds water to the lithium iron phosphate positive electrode waste liquid. In this way, on the one hand, the added water can inactivate the adhesive PVDF in the lithium iron phosphate positive electrode waste liquid, causing the viscosity to drop sharply, thereby destroying the stability of the lithium iron phosphate positive electrode waste liquid colloid, making the lithium iron phosphate positive electrode waste liquid prone to solid-liquid separation, effectively solving the problem that the lithium iron phosphate positive electrode waste liquid is difficult to separate the solid and liquid; on the other hand, the added water can inhibit the hydrolysis of NMP and improve the recovery rate of NMP. Next, the present invention uses a weakly acidic buffer to adjust the pH of the waste liquid mixture to 5-8. Since the added water can destroy the stability of the lithium iron phosphate positive electrode waste liquid colloid, the weakly acidic buffer can better enter the surface of the lithium iron phosphate positive electrode material and NMP, so that 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; but also the cations of the weakly acidic buffer can be adsorbed on the surface of the lithium iron phosphate positive electrode material particles, causing an imbalance in the internal charge of the colloid, thereby accelerating the coagulation of the lithium iron phosphate positive electrode material particles, realizing rapid solid-liquid separation, reducing the difficulty of solid-liquid separation, and effectively separating the lithium iron phosphate positive electrode material and the NMP liquid phase by conventional filter pressing or centrifugation. The added weakly acidic buffer can also inhibit the hydrolysis of NMP and the dissolution of the lithium iron phosphate positive electrode material, thereby improving the recovery rate of the lithium iron phosphate positive electrode material and NMP. Finally, the NMP product is recovered by distillation, and the lithium iron phosphate positive electrode residue is mixed with a lithium source to replenish the lithium ion content of the lithium iron phosphate positive electrode residue, and then dried and calcined to obtain a regenerated lithium iron phosphate positive electrode material that meets the requirements. The recovery method of the present invention is simple to operate, has high separation efficiency, and has a high recovery rate of lithium iron phosphate and NMP. The lithium iron phosphate of the prepared regenerated lithium iron phosphate positive electrode material has good morphology and electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is a flow chart of a method for recovering lithium iron phosphate cathode waste liquid according to one embodiment of the present invention;

[0027] Figure 2 This is an XRD pattern of a lithium iron phosphate cathode material according to one embodiment of the present invention;

[0028] Figure 3 This is a SEM image of a lithium iron phosphate cathode material according to one embodiment of the present invention;

[0029] Figure 4 This is a diagram showing the electrical performance of a lithium iron phosphate cathode material according to one embodiment of the present invention. DETAILED DESCRIPTION

[0030] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0031] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly attached to the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] The present application also provides a method for recycling lithium iron phosphate cathode waste liquid. In order to better understand the technical solution and beneficial effects of the present application, the present application is further described in detail below in conjunction with specific embodiments. Figure 1 The method for recovering lithium iron phosphate cathode waste liquid in one embodiment includes some or all of the following steps:

[0034] S110, adding water to the lithium iron phosphate positive electrode waste liquid to obtain a waste liquid mixture.

[0035] It is understood that the components of lithium iron phosphate positive electrode waste liquid generally include lithium iron phosphate, PVDF (Polyvinylidenefluoride, polyvinylidene fluoride), conductive carbon black and NMP. Since PVDF is an organic adhesive, it can make the viscosity of the lithium iron phosphate positive electrode slurry higher, reaching 8000mPa·s to 10000mPa·s, which increases the difficulty of separating the NMP and lithium iron phosphate positive electrode materials in the lithium iron phosphate positive electrode waste liquid. Therefore, the present invention adds water to the lithium iron phosphate positive electrode waste liquid. Since PVDF is insoluble in water, the added water can quickly deactivate the adhesive PVDF in the lithium iron phosphate positive electrode waste liquid, causing the viscosity to drop sharply, thereby destroying the stability of the lithium iron phosphate positive electrode waste liquid colloid, making the lithium iron phosphate positive electrode waste liquid prone to solid-liquid separation, effectively solving the problem of difficult solid-liquid separation of lithium iron phosphate positive electrode 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 fully and quickly contact with PVDF under the mixing operation, so as to achieve efficient and rapid destruction of the stability of the lithium iron phosphate cathode waste liquid colloid.

[0036] S120, adding a weak 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.

[0037] It is understood that the presence of residual lithium in the lithium iron phosphate cathode waste liquid results in an alkaline pH of 9-12. Furthermore, NMP is susceptible to hydrolysis in strongly alkaline or acidic environments. Therefore, the present invention employs a weakly acidic buffer to adjust the pH of the waste liquid mixture to 5-8, thereby keeping the pH close to neutral and thereby significantly inhibiting NMP hydrolysis. It is worth mentioning that, since 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, it is easy to form a stable colloid in the lithium iron phosphate cathode waste liquid, and the weak acid buffer added in the present invention enables the cations of the weak acid buffer to be adsorbed on the surface of the lithium iron phosphate cathode material particles to cause an imbalance of charge inside the colloid, thereby accelerating the agglomeration of the lithium iron phosphate cathode material particles and achieving rapid separation of the solid and liquid, thereby reducing the difficulty of solid-liquid separation, so that the user can achieve effective separation of the lithium iron phosphate cathode material and the NMP liquid phase through conventional filter pressing and centrifugation, and the added weak acid 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. It is worth mentioning that the so-called weak acid buffer refers to an acidic solution of the weak acid buffer with a pH <7 and a pH >4.

[0038] S130, separating the mixture to be separated to obtain lithium iron phosphate positive electrode residue and NMP mixed filtrate, so as to achieve efficient and rapid separation of the separation mixture with good separation effect.

[0039] S140, distilling the NMP mixed filtrate to obtain an NMP product. It is understood that by distilling the NMP mixed filtrate, not only is the loss of NMP ensured to be small, thereby improving the recovery rate of NMP, but also the lithium ions in the NMP mixed filtrate can be recovered to reduce the pollution of lithium ions to the environment.

[0040] S150, mixing the lithium iron phosphate positive electrode filter residue with a lithium source to obtain a lithium iron phosphate positive electrode mixture.

[0041] It is understandable that since the lithium ion content of the separated lithium iron phosphate positive electrode residue is lower than the lithium ion content of the lithium iron phosphate positive electrode material sold on the market, if the lithium iron phosphate positive electrode residue is not mixed with the lithium ion suspension, it is impossible to ensure that the regenerated lithium iron phosphate positive electrode material that meets the requirements can be obtained subsequently. Therefore, the present invention supplements the lithium ion content in the lithium iron phosphate positive electrode residue by mixing the lithium iron phosphate positive electrode residue with a lithium source, thereby ensuring that the regenerated lithium iron phosphate positive electrode material that meets the requirements can be obtained after subsequent calcination.

[0042] S160, drying and calcining the lithium iron phosphate positive electrode mixture to obtain a lithium iron phosphate positive electrode material.

[0043] It can be understood that by drying the lithium iron phosphate positive electrode mixture, the moisture of the lithium iron phosphate positive electrode mixture can be effectively removed to obtain lithium iron phosphate positive electrode mixture powder with smaller particle size, so as to avoid the agglomeration of the lithium iron phosphate positive electrode mixture. This is beneficial for the subsequent calcination operation, so that the lithium iron phosphate positive electrode mixture powder with smaller particle size can absorb heat more fully, that is, the contact area between the lithium iron phosphate positive electrode mixture powder and heat is increased, so as to quickly obtain the regenerated lithium iron phosphate positive electrode 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 positive electrode material is relatively small, and the main substance is lithium iron phosphate. Figure 3 It can be seen that the grain size of the calcined lithium iron phosphate cathode material is between 0.6 and 1.8 μm, and the regenerated lithium iron phosphate has a good morphology. Figure 4The calcined lithium iron phosphate cathode material exhibits electrical performance indicators: a 0.1C discharge capacity of 155 mAh / g and a 1C discharge capacity of 138 mAh / g. Furthermore, the measured 0.1C initial charge and discharge efficiency is >95%, indicating that the regenerated lithium iron phosphate exhibits excellent electrochemical performance and meets the requirements for a regenerated lithium iron phosphate cathode material. Furthermore, the recycled NMP product and regenerated lithium iron phosphate cathode material can be directly recycled and reused in lithium iron phosphate battery production, thereby reducing the production cost of lithium iron phosphate batteries.

[0044] The above-mentioned method for recovering lithium iron phosphate positive electrode waste liquid first adds water to the lithium iron phosphate positive electrode waste liquid; in this way, on the one hand, the added water can inactivate the adhesive PVDF in the lithium iron phosphate positive electrode waste liquid, causing the viscosity to drop sharply, thereby destroying the stability of the lithium iron phosphate positive electrode waste liquid colloid, making the lithium iron phosphate positive electrode waste liquid prone to solid-liquid separation, effectively solving the problem of difficult solid-liquid separation of the lithium iron phosphate positive electrode waste liquid; on the other hand, the added water can inhibit the hydrolysis of NMP and improve the recovery rate of NMP. Next, the present invention uses a weakly acidic buffer to adjust the pH of the waste liquid mixture to 5-8. Since the added water can destroy the stability of the lithium iron phosphate positive electrode waste liquid colloid, the weakly acidic buffer can better enter the surface of the lithium iron phosphate positive electrode material and NMP, so that 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; but also the cations of the weakly acidic buffer can be adsorbed on the surface of the lithium iron phosphate positive electrode material particles, causing an imbalance in the internal charge of the colloid, thereby accelerating the coagulation of the lithium iron phosphate positive electrode material particles, realizing rapid solid-liquid separation, reducing the difficulty of solid-liquid separation, and effectively separating the lithium iron phosphate positive electrode material and the NMP liquid phase by conventional filter pressing or centrifugation. The added weakly acidic buffer can also inhibit the hydrolysis of NMP and the dissolution of the lithium iron phosphate positive electrode material, thereby improving the recovery rate of the lithium iron phosphate positive electrode material and NMP. Finally, the NMP product is recovered by distillation, and the lithium iron phosphate positive electrode residue is mixed with a lithium source to replenish the lithium ion content of the lithium iron phosphate positive electrode residue, and then dried and calcined to obtain a regenerated lithium iron phosphate positive electrode material that meets the requirements. The recovery method of the present invention is simple to operate, has high separation efficiency, and has a high recovery rate of lithium iron phosphate and NMP. The lithium iron phosphate of the prepared regenerated lithium iron phosphate positive electrode material has good morphology and electrochemical properties.

[0045] It should be noted that, compared with the existing lithium iron phosphate cathode waste liquid treatment method, vacuum distillation and flocculation filter press improvement methods are usually used to achieve the separation of NMP and lithium iron phosphate cathode materials. The vacuum distillation method not only consumes a lot of energy but also has a low NMP recovery rate. The flocculation filter press improvement method uses a special acidity regulator, which is not only complicated to operate, but also the special acidity regulator accelerates the hydrolysis of NMP and the dissolution of lithium iron phosphate cathode materials, resulting in low NMP hydrolysis and lithium iron phosphate cathode material recovery rates, and cannot achieve maximum recovery efficiency. Therefore, the present invention first adds water to the lithium iron phosphate positive electrode waste liquid for mixing operation, so that the water can quickly inactivate the adhesive PVDF in the lithium iron phosphate positive electrode waste liquid, and the viscosity drops sharply, thereby destroying the stability of the lithium iron phosphate positive electrode waste liquid colloid, and then adds a weak acid buffer to the waste liquid mixture, and adjusts the pH of the waste liquid mixture to 5-8, so that the added weak acid buffer can inhibit the hydrolysis of NMP and the dissolution of the lithium iron phosphate positive electrode material, thereby improving the recovery rate of the lithium iron phosphate positive electrode material and NMP, and the cations of the added weak acid buffer can be adsorbed on the surface of the lithium iron phosphate positive electrode material particles, thereby accelerating the coagulation of the lithium iron phosphate positive electrode material particles, so as to achieve efficient and rapid solid-liquid separation of the lithium iron phosphate positive electrode waste liquid, thereby reducing the difficulty of solid-liquid separation, not only simple and efficient operation, and good separation effect, and improve the recovery rate of NMP and lithium iron phosphate positive electrode material, thereby achieving maximum recovery efficiency.

[0046] 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 weak acidic buffer is used to adjust the pH of the waste liquid mixture to 5 to 8 to obtain a mixture to be separated. It should be further explained that the addition of water can not only destroy the adhesive of the lithium iron phosphate positive electrode waste liquid to quickly destroy the stability of the colloid, but also inhibit the hydrolysis of NMP and improve the recovery rate of NMP. Then, the weak acidic buffer is added to make the pH of the waste liquid mixture 5 to 8, so that the surface of the lithium iron phosphate positive electrode material can adsorb the cations of the weak acidic buffer to accelerate the hydrolysis of the lithium iron phosphate positive electrode material and NMP, and the weak acidic buffer can also neutralize the alkalinity in the waste liquid mixture to inhibit the hydrolysis of NMP and the dissolution of the lithium iron phosphate positive electrode material, thereby improving the hydrolysis of NMP and the recovery rate of the lithium iron phosphate positive electrode material.

[0047] If the order of addition of the two is swapped, that is, water is added after adding a weakly acidic buffer first, because the weakly acidic buffer just added into fails to destroy adhesive quickly, and needs to wait until water is added before destroying adhesive more quickly, resulting in the inability to efficiently and quickly realize separation of lithium iron phosphate positive electrode waste liquid, i.e., reduce the speed of solid-liquid separation of lithium iron phosphate positive electrode waste liquid. In addition, if water is added after selecting to add a weakly acidic buffer first, subsequent weakly acidic buffer needs to be used again to adjust pH to lithium iron phosphate positive electrode waste liquid, not only increase the step of processing, cause operation to be more complicated and solid-liquid separation speed is slow, and improve the usage amount of weakly acidic buffer, cause processing cost to become higher. Therefore, the present invention adds weakly acidic buffer after first adding water to mix uniformly, like this, not only simple to operate and solid-liquid separation speed is fast, to realize lithium iron phosphate positive electrode waste liquid efficient separation, and suppress NMP hydrolysis and alleviate lithium iron phosphate positive electrode material dissolution, so as to improve the recovery rate of NMP hydrolysis and lithium iron phosphate positive electrode material.

[0048] Furthermore, in some preferred embodiments, the pH of the waste liquid mixture is controlled to be 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 positive electrode material, and helping the lithium iron phosphate positive electrode material to adsorb the cations of the weak acid buffer to achieve efficient solid-liquid separation. Not only is the operation simple and fast, but it also improves the recovery rate of NMP and lithium iron phosphate positive electrode materials to achieve maximum recovery efficiency, and the final NMP product and lithium iron phosphate positive electrode material 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 lithium iron phosphate positive electrode waste liquid discharge polluting the environment.

[0049] In some other embodiments, the amount of water used accounts for 15% to 20% of the total volume of the lithium iron phosphate cathode waste liquid, that is, the amount of water used accounts for 15% to 20% of the total volume of the liquid in the lithium iron phosphate cathode waste liquid. It is understood that if the amount of water used is less than 15%, the amount of water added cannot fully and quickly deactivate PVDF, and the stability of the colloid cannot be efficiently and comprehensively destroyed, resulting in the phenomenon that the solid and liquid in the lithium iron phosphate cathode waste liquid are still difficult to separate, thereby resulting in a low recovery rate of NMP and lithium iron phosphate cathode materials; if the amount of water used is higher than 20%, on the one hand, it will accelerate the hydrolysis of NMP, thereby increasing the hydrolysis rate of NMP and thus reducing the recovery rate of NMP. On the other hand, it will not only waste water resources, but also increase the time of subsequent drying treatment, thereby increasing the cost of recycling the lithium iron phosphate cathode waste liquid. Therefore, the present invention controls the amount of water to account for 15% to 20% of the total volume of the liquid in the lithium iron phosphate positive electrode waste liquid, so that the added water can effectively destroy the adhesive in the waste liquid. In this way, not only the efficient separation of the lithium iron phosphate positive electrode waste liquid is improved, but also the hydrolysis rate of NMP is controlled to the lowest, thereby minimizing the hydrolysis loss rate of NMP and improving the recovery rate of NMP in the lithium iron phosphate positive electrode waste liquid.

[0050] In some other embodiments, the water includes at least one of deionized water and pure water. As can be appreciated, since deionized water and pure water contain fewer impurities, the added water is ensured to have a higher purity, effectively avoiding the introduction of new impurities. This ensures that the subsequent regenerated lithium iron phosphate cathode material with a purity of up to 99.9% can be obtained, allowing the resulting NMP product to be directly put into production, thereby reducing the production cost of lithium iron phosphate batteries.

[0051] In some other embodiments, the weak acid buffer comprises at least one of lithium dihydrogen phosphate, carbonic acid and oxalic acid. It is understood that since the aqueous solutions of lithium dihydrogen phosphate, carbonic acid and oxalic acid are all weakly acidic, they can effectively neutralize the OH in the lithium iron phosphate cathode waste liquid. - , thereby providing a near-neutral environment for NMP, thereby inhibiting its hydrolysis and improving its recovery rate. Furthermore, the surface of the lithium iron phosphate cathode material particles can adsorb cations of lithium dihydrogen phosphate, carbonate, and oxalic acid, causing an internal charge imbalance in the colloid, accelerating the agglomeration of the lithium iron phosphate cathode material particles and achieving efficient and rapid separation of the lithium iron phosphate cathode waste liquid, thereby reducing the difficulty of solid-liquid separation.

[0052] 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, thus ensuring that high-purity NMP products and lithium iron phosphate cathode materials can be obtained later. In other words, the reaction between the added lithium dihydrogen phosphate and the lithium iron phosphate cathode waste liquid is: 2LiOH+LiH2PO4→Li3PO4+2H2O, so it can be seen that Li + and H2PO4 - Lithium iron phosphate cathode waste liquid + and H2PO4 - The reaction between the added carbonic acid and the lithium iron phosphate cathode waste liquid is: 2LiOH+H2CO3→Li2CO3+2H2O; the reaction between the added oxalic acid and the lithium iron phosphate cathode waste liquid is: 2LiOH+H2C2O4→Li2C2O4+2H2O; it can be seen that Li2CO3 and Li2C2O4 will generate gas and water during the subsequent distillation, drying and roasting, so as to avoid the introduction of new impurities by the lithium iron phosphate cathode waste liquid, thereby ensuring the production of high-purity NMP products and lithium iron phosphate cathode materials. In addition, the added water and weak acid 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.

[0053] 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 a mixture to be separated includes the following specific steps: adding the weakly acidic buffer to the waste liquid mixture while stirring, and adjusting the pH of the waste liquid mixture to 5-8.

[0054] It can be understood that by adding a weak acid buffer to the waste liquid mixture while stirring, it is ensured that the added weak acid buffer can be quickly dispersed into the waste liquid mixture, effectively avoiding the added weak acid buffer from easily agglomerating at the contact surface with the waste liquid mixture, thereby ensuring that the weak acid buffer can well enter the interior of the waste liquid mixture, so that the weak acid buffer can fully contact the waste liquid mixture, so as to achieve efficient and rapid solid-liquid separation of the waste liquid mixture, and effectively solve the problem that the lithium iron phosphate positive electrode waste liquid is difficult to separate.

[0055] 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 positive electrode waste liquid to achieve efficient and rapid separation of the lithium iron phosphate positive electrode waste liquid. It is not only simple and efficient to operate, but also inhibits the hydrolysis of NMP and the dissolution of the lithium iron phosphate positive electrode material, thereby improving the NMP and lithium iron phosphate positive electrode material, and avoids the introduction of new impurities into the lithium iron phosphate positive electrode waste liquid to ensure that high-purity NMP and lithium iron phosphate positive electrode material are obtained, so that the obtained NMP and lithium iron phosphate positive electrode material can be directly put into production to reduce the production cost of lithium iron phosphate batteries.

[0056] Similarly, in a preferred embodiment, the oxalic acid is 0.1 mol / L to ensure that 0.1 mol / L oxalic acid can fully and comprehensively contact the lithium iron phosphate positive electrode waste liquid to achieve efficient and rapid separation of the lithium iron phosphate positive electrode waste liquid. It is not only simple and efficient to operate, but also inhibits the hydrolysis of NMP and the dissolution of the lithium iron phosphate positive electrode material, thereby improving the NMP and lithium iron phosphate positive electrode material, and avoids the introduction of new impurities into the lithium iron phosphate positive electrode waste liquid, to ensure that high-purity regenerated NMP and lithium iron phosphate with good morphology and electrochemical properties are obtained. The regenerated lithium iron phosphate positive electrode material can be directly put into production to reduce the production cost of lithium iron phosphate batteries.

[0057] In a more preferred embodiment, the concentration of lithium dihydrogen phosphate is 200 g / L to ensure that the added 200 g / L lithium dihydrogen phosphate can fully and comprehensively contact with the lithium iron phosphate positive electrode waste liquid to achieve efficient and rapid separation of the lithium iron phosphate positive electrode waste liquid. It is not only simple and efficient to operate, but also inhibits the hydrolysis of NMP and the dissolution of the lithium iron phosphate positive electrode material, thereby improving the NMP and lithium iron phosphate positive electrode material, and avoids the introduction of new impurities into the lithium iron phosphate positive electrode waste liquid, to ensure that high-purity regenerated NMP and lithium iron phosphate with good morphology and electrochemical properties are obtained. The regenerated lithium iron phosphate positive electrode material can be directly put into production to reduce the production cost of lithium iron phosphate batteries.

[0058] In some other embodiments, the separation method is filter pressing or centrifugation. It is understood that the use of filter pressing or centrifugation to separate the mixture to be separated allows the user to effectively separate the lithium iron phosphate cathode material and the NMP liquid phase through conventional methods, thereby achieving efficient and rapid separation of the lithium iron phosphate cathode waste liquid.

[0059] In some other embodiments, the centrifugation is performed by centrifuging to obtain a lithium iron phosphate positive electrode residue and an NMP mixed filtrate. Furthermore, the rotation speed of the centrifuge is 1200 r / min to 2000 r / min. It is 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.

[0060] In some preferred embodiments, the pressure filtration is performed by a filter press to obtain a mixed filtrate of lithium iron phosphate positive electrode residue and NMP. Furthermore, the filter press is a plate and frame filter press. It is understood that the plate and frame filter press includes a filter press assembly and a mounting frame, and the filter press assembly is movably arranged on the mounting frame. The mixture to be separated is input into the filter press assembly for pressure filtration separation, and then the filter press assembly is used to achieve efficient and rapid separation of the mixture to be separated, thereby obtaining a mixed filtrate of lithium iron phosphate positive electrode residue and NMP for standby use.

[0061] In some other embodiments, the filter press assembly device includes multiple filter bodies, each of which includes a filter frame, a filter plate and a filter cloth. The filter plate is movably arranged on the mounting frame, and the filter cloth is covered on the filter plate. The filter frame is used to fix the filter cloth on the filter plate, so that the user can input a larger volume of the mixture to be separated at one time. Multiple filter bodies can filter the mixture to be separated at the same time, thereby achieving efficient and rapid separation of the mixture to be separated.

[0062] It should be noted that since the pH of the mixture to be separated obtained by the treatment of the present invention is close to neutral, it is less corrosive to the plate and frame filter press, especially has a good protective effect on the filter cloth, thereby extending the service life of the plate and frame filter press, and further reducing the recovery cost of lithium iron phosphate positive electrode waste liquid, and significantly reducing the harsh conditions for the use of filter cloth in the plate and frame filter press, making the filtration operation simpler.

[0063] In some other embodiments, the mesh size of the filter cloth is 200-500 mesh. It is understood that by controlling the mesh size of the filter cloth to be 200-500 mesh, the lithium iron phosphate positive electrode material and NMP can be separated efficiently and quickly.

[0064] In some other embodiments, the pressure of the plate and frame filter press is 0.6Mpa to 0.7Mpa. It can be understood that since the weak acidic buffer can cause an internal charge imbalance in the colloid, the lithium iron phosphate positive electrode material particles are easily condensed into agglomerates, which not only speeds up the solid-liquid separation but also has a good effect, that is, more lithium iron phosphate positive electrode material particles are formed in the mixture to be separated. Therefore, the present invention sets the pressure of the plate and frame filter press to 0.6Mpa to 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 lower than the pressure of the present invention. This is mainly because the added weak acidic buffer can cause an internal charge imbalance in the colloid, so that the lithium iron phosphate positive electrode material particles are easily condensed into agglomerates to form relatively more lithium iron phosphate positive electrode material particles in the mixed liquid to be separated. Therefore, the present invention increases the pressure of the plate and frame filter press to ensure efficient and rapid separation of the lithium iron phosphate positive electrode filter residue and the NMP mixed filtrate, thereby improving the recovery rate of the lithium iron phosphate positive electrode material and NMP, and having a good separation effect.

[0065] In some other embodiments, the distillation temperature is 90° C. to 130° C. It is understood that if the temperature is lower than 90° C., less NMP is precipitated in the NMP mixed filtrate, thereby reducing the purity of the obtained NMP product. If the temperature is greater than 130° C., NMP is easily lost, resulting in a low recovery rate of NMP. Therefore, the present invention controls the distillation temperature to 90° C. to 130° C. to effectively remove water from the NMP mixed filtrate, which is beneficial to the precipitation of NMP in the NMP mixed filtrate, thereby obtaining a regenerated NMP product with a purity of 99.9% or more. The obtained NMP product can be directly used in the production of lithium iron phosphate batteries, thereby reducing the production cost of lithium iron phosphate batteries.

[0066] In some other embodiments, when the lithium iron phosphate positive electrode filter residue is mixed with the lithium source, the mass ratio of the lithium iron phosphate positive electrode filter residue to the lithium source is 1:1. It is understandable that since the lithium ion content in the lithium iron phosphate positive electrode filter residue obtained after pressure filtration is lower than the lithium ion content of commercially available lithium iron phosphate positive electrode materials, the present invention supplements the lithium ion content of the lithium iron phosphate positive electrode filter residue by mixing the lithium iron phosphate positive electrode filter residue with the lithium source at a mass ratio of 1:1, thereby ensuring that a regenerated lithium iron phosphate positive electrode material that meets the requirements can be obtained subsequently.

[0067] In some other embodiments, the lithium source is a lithium ion suspension. By preparing the lithium source into a lithium ion suspension, the lithium ion suspension can be more fully mixed with the lithium iron phosphate cathode residue, thereby ensuring that a regenerated lithium iron phosphate cathode material that meets the requirements can be obtained later, thereby improving the recovery rate of the lithium iron phosphate cathode material.

[0068] In some other embodiments, the lithium ion-containing suspension includes at least one of lithium carbonate and lithium hydroxide. It is understandable that lithium carbonate and lithium hydroxide not only provide lithium ions to the lithium iron phosphate cathode residue, but also ensure that the added lithium ion-containing suspension does not introduce new impurities. That is, the added carbonate ions and hydroxide ions can be released during the subsequent drying and calcination, thereby ensuring that a regenerated lithium iron phosphate cathode material that meets the requirements is obtained. The recovered lithium iron phosphate cathode material can then be directly recycled into the production of lithium iron phosphate batteries, further reducing the production cost of lithium iron phosphate batteries.

[0069] Furthermore, the concentration of the lithium ion-containing suspension is 90g / L to 110g / L. It can be understood that since the 90g / L to 110g / L lithium ion-containing suspension can provide sufficient lithium ions for the lithium iron phosphate positive electrode filter residue, and ensure that the addition of 90g / L to 110g / L lithium ion-containing suspension can fully react with the lithium iron phosphate positive electrode filter residue without generating waste, not only can the regenerated lithium iron phosphate positive electrode material that meets the requirements be obtained, but also the cost of recycling the lithium iron phosphate positive electrode waste liquid is reduced. In a preferred embodiment, the concentration of the 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 a regenerated lithium iron phosphate positive electrode material with good lithium iron phosphate morphology and good electrochemical properties.

[0070] In some other embodiments, the step of mixing the lithium iron phosphate positive electrode filter residue with the lithium ion-containing suspension to obtain a lithium iron phosphate positive electrode mixture further includes the following step: mixing and stirring the lithium iron phosphate positive electrode mixture for 30 minutes to 40 minutes to ensure that a uniformly mixed lithium iron phosphate positive electrode mixture is obtained.

[0071] In some other embodiments, the calcination operation is carried out under conditions of 650°C to 700°C and a nitrogen atmosphere for 3h to 4h. It is understood that the lithium iron phosphate positive electrode mixture is calcined for 3h to 4h at a temperature of 650°C to 700°C and filled with nitrogen to ensure that the lithium iron phosphate positive electrode mixture is calcined in a nitrogen atmosphere for 3h to 4h to obtain a high-purity lithium iron phosphate positive electrode material, that is, the conductive carbon black and moisture in the lithium iron phosphate positive electrode mixture can be removed to obtain a regenerated lithium iron phosphate positive electrode material that meets the requirements. If the calcination temperature is lower than 650°C and the time is less than 3h, the conductive carbon black in the lithium iron phosphate positive electrode mixture cannot be effectively removed, thereby failing to ensure that a regenerated lithium iron phosphate positive electrode material that meets the requirements is obtained. If the calcination temperature is higher than 700°C and the time is greater than 4h, it is easy to cause the loss of the lithium iron phosphate positive electrode material, thereby reducing the recovery rate of the lithium iron phosphate positive electrode material in the lithium iron phosphate positive electrode waste liquid.

[0072] In some other embodiments, the drying temperature is 100°C to 150°C. It can be understood that by controlling the drying temperature to 100°C to 150°C, the moisture of the lithium iron phosphate positive electrode mixture can be effectively removed to obtain a lithium iron phosphate positive electrode mixture powder with a smaller particle size, thereby avoiding the occurrence of agglomeration of the lithium iron phosphate positive electrode mixture. At the same time, it is beneficial for the subsequent calcination, so that the lithium iron phosphate positive electrode mixture powder can be quickly and comprehensively calcined to quickly obtain a high-purity lithium iron phosphate positive electrode material. Furthermore, the drying operation can be one of spray drying, double cone drying, rake drying, and hot air drying, so as to achieve the drying of the lithium iron phosphate positive electrode mixture and form a lithium iron phosphate positive electrode mixture powder with a smaller particle size.

[0073] In a preferred embodiment, the drying method is spray drying at a temperature of 150°C. It can be understood that since the lithium iron phosphate positive electrode mixture can obtain a lithium iron phosphate positive electrode mixture powder with a smaller particle size after spray drying, the lithium iron phosphate positive electrode mixture can be effectively avoided from agglomerating, resulting in the subsequent incomplete baking of the agglomerated lithium iron phosphate positive electrode mixture during baking, and thus it is impossible to obtain a lithium iron phosphate positive electrode mixture with higher purity. Therefore, the present invention spray-dries the lithium iron phosphate positive electrode mixture at a temperature of 150°C to achieve rapid drying of the lithium iron phosphate positive electrode mixture, so as to ensure that the transfer rate between the lithium iron phosphate positive electrode mixture powder and heat can be increased during subsequent baking, thereby ensuring that the lithium iron phosphate positive electrode mixture powder can quickly remove moisture and conductive carbon black, thereby obtaining a high-purity lithium iron phosphate positive electrode material and improving the efficiency of drying the lithium iron phosphate positive electrode mixture powder.

[0074] It is worth mentioning that, since the present invention can simultaneously recover NMP and lithium iron phosphate positive electrode materials in lithium iron phosphate positive electrode waste liquid, and simultaneously put the obtained regenerated NMP product and regenerated lithium iron phosphate positive electrode material into the production of lithium iron phosphate batteries, the production cost of lithium iron phosphate batteries can be greatly reduced, and the problem of environmental pollution caused by the discharge of lithium iron phosphate positive electrode waste liquid can be effectively alleviated.

[0075] The present application also provides a lithium iron phosphate cathode waste liquid recovery production line, which adopts the lithium iron phosphate cathode waste liquid recovery method described in any of the above embodiments for production. It can be understood that in order to realize the automated production of lithium iron phosphate cathode waste liquid recovery, the lithium iron phosphate cathode waste liquid recovery method is adopted for production, so as to realize the efficient and rapid recovery and utilization of NMP and lithium iron phosphate cathode material in the lithium iron phosphate cathode waste liquid, so as to quickly prepare a high-purity NMP product and regenerated lithium iron phosphate cathode material that meets the requirements, thereby improving the efficiency of lithium iron phosphate cathode waste liquid recovery and treatment.

[0076] Compared with the prior art, the present invention has at least the following advantages:

[0077] The recovery method of the present invention first adds water to the lithium iron phosphate positive electrode waste liquid. In this way, on the one hand, the added water can inactivate the adhesive PVDF in the lithium iron phosphate positive electrode waste liquid, causing the viscosity to drop sharply, thereby destroying the stability of the lithium iron phosphate positive electrode waste liquid colloid, making the lithium iron phosphate positive electrode waste liquid prone to solid-liquid separation, effectively solving the problem that the lithium iron phosphate positive electrode waste liquid is difficult to separate the solid and liquid; on the other hand, the added water can inhibit the hydrolysis of NMP and improve the recovery rate of NMP. Next, the present invention uses a weakly acidic buffer to adjust the pH of the waste liquid mixture to 5-8. Since the added water can destroy the stability of the lithium iron phosphate positive electrode waste liquid colloid, the weakly acidic buffer can better enter the surface of the lithium iron phosphate positive electrode material and NMP, so that 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; but also the cations of the weakly acidic buffer can be adsorbed on the surface of the lithium iron phosphate positive electrode material particles, causing an imbalance in the internal charge of the colloid, thereby accelerating the coagulation of the lithium iron phosphate positive electrode material particles, realizing rapid solid-liquid separation, reducing the difficulty of solid-liquid separation, and effectively separating the lithium iron phosphate positive electrode material and the NMP liquid phase by conventional filter pressing or centrifugation. The added weakly acidic buffer can also inhibit the hydrolysis of NMP and the dissolution of the lithium iron phosphate positive electrode material, thereby improving the recovery rate of the lithium iron phosphate positive electrode material and NMP. Finally, the NMP product is recovered by distillation, and the lithium iron phosphate positive electrode residue is mixed with a lithium source to replenish the lithium ion content of the lithium iron phosphate positive electrode residue, and then dried and calcined to obtain a regenerated lithium iron phosphate positive electrode material that meets the requirements. The recovery method of the present invention is simple to operate, has high separation efficiency, and has a high recovery rate of lithium iron phosphate and NMP. The lithium iron phosphate of the prepared regenerated lithium iron phosphate positive electrode material has good morphology and electrochemical properties.

[0078] The following examples illustrate some specific embodiments, where percentages are expressed by weight. It should be noted that the following examples do not exhaust all possible situations, and that the materials used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0079] Example 1

[0080] Pour 56.7 kg of deionized water into 1000 kg of lithium iron phosphate positive electrode waste liquid (solid content of 62.20%), stir evenly to obtain a waste liquid mixture, add 200 g / L of lithium dihydrogen phosphate solution to the waste liquid mixture while stirring to adjust the pH to 7, and then continue stirring for 10 minutes to obtain a mixture to be separated, and the adjusted mixture to be separated is pumped into a plate and frame filter press with a screw pump for filtration operation at a pressure of 0.6 MPa, a filtrate volume of 330 L, and a filter cloth mesh of 300 meshes to obtain a lithium iron phosphate positive electrode residue and NMP mixed filtrate, and the NMP mixed filtrate is input into a 0.5 μm precision filter to pass through After filtration, rectification and purification are carried out at a distillation temperature of 90° C. to obtain a high-purity NMP product with an NMP concentration of ≥99.9%, and lithium salt crystals are precipitated during the distillation process; 750 kg of lithium iron phosphate positive electrode filter residue obtained by pressure filtration is poured into 750 L of a 100 g / L lithium carbonate suspension, and stirred at room temperature for 30 minutes at a stirring speed of 400 r / min to obtain a lithium iron phosphate positive electrode mixture; the obtained lithium iron phosphate positive electrode mixture is spray-dried at 150° C. to obtain a lithium iron phosphate positive electrode mixture powder, and the lithium iron phosphate positive electrode mixture powder is calcined at 700° C. in a nitrogen atmosphere for 3 hours to obtain a regenerated and recycled lithium iron phosphate positive electrode material.

[0081] Example 2

[0082] Pour 55.35 kg of deionized water into 1000 kg of lithium iron phosphate positive electrode waste liquid (solid content of 63.10%), stir evenly to obtain a waste liquid mixture, add saturated carbonic acid to the waste liquid mixture while stirring to adjust the pH to 6, and then continue stirring for 10 minutes to obtain a mixture to be separated, and use a screw pump to pump the adjusted mixture to be separated into a plate and frame filter press for filtration operation. The pressure is 0.65 MPa, the filtrate volume is 330 L, and the mesh number of the filter cloth is 200 meshes to obtain a lithium iron phosphate positive electrode filter residue and NMP mixed filtrate. The NMP mixed filtrate is input into a 0.5 μm precision filter for filtration and then fine filtration. The method comprises the following steps: 1. The NMP product is purified by distillation at a distillation temperature of 100° C. to obtain a high-purity NMP product with an NMP concentration of ≥99.9%, and lithium salt crystals are precipitated during the distillation process; 2. 745 kg of lithium iron phosphate positive electrode filter residue obtained by pressure filtration is poured into 745 L of a 90 g / L lithium hydroxide suspension, and the mixture is stirred at room temperature for 35 minutes at a stirring speed of 450 r / min to obtain a lithium iron phosphate positive electrode mixture; 3. The prepared lithium iron phosphate positive electrode mixture is spray-dried at 120° C. to obtain a lithium iron phosphate positive electrode mixture powder, and the lithium iron phosphate positive electrode mixture powder is calcined at 680° C. in a nitrogen atmosphere for 3.5 hours to obtain a regenerated lithium iron phosphate positive electrode material.

[0083] Example 3

[0084] Pour 74.6 kg of deionized water into 1000 kg of lithium iron phosphate positive electrode waste liquid (solid content of 62.7%), stir evenly to obtain a waste liquid mixture, add 0.1 mol / L oxalic acid solution to the waste liquid mixture while stirring to adjust the pH to 8, and then continue stirring for 10 minutes to obtain a mixture to be separated, and the adjusted mixture to be separated is pumped into a plate and frame filter press with a screw pump for filtration operation at a pressure of 0.7 MPa, a filtrate volume of 330 L, and a filter cloth mesh of 500 mesh to obtain a lithium iron phosphate positive electrode residue and NMP mixed filtrate, and the NMP mixed filtrate is input into a 0.5 μm precision filter for filtration. Then, distillation and purification are carried out at a distillation temperature of 130°C to obtain a high-purity NMP product with an NMP concentration of ≥99.9%, and lithium salt crystals are precipitated during the distillation process; 740 kg of lithium iron phosphate positive electrode filter residue obtained by pressure filtration is poured into 748 L of a 110 g / L lithium carbonate suspension, and stirred at room temperature for 40 minutes at a stirring speed of 380 r / min to obtain a lithium iron phosphate positive electrode mixture; the prepared lithium iron phosphate positive electrode mixture is spray-dried at 100°C to obtain a lithium iron phosphate positive electrode mixture powder, and the lithium iron phosphate positive electrode mixture powder is calcined at 650°C in a nitrogen atmosphere for 4 hours to obtain a regenerated and recycled lithium iron phosphate positive electrode material.

[0085] Comparative Example 1

[0086] The difference from Example 1 is that an equal amount of pure water is used instead of the lithium dihydrogen phosphate solution.

[0087] Comparative Example 2

[0088] 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.

[0089] Comparative Example 3

[0090] The difference from Example 1 is that an equal amount of 0.1 mol / L LiOH is used instead of the lithium dihydrogen phosphate solution.

[0091] Comparative Example 4

[0092] 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.

[0093] Comparative Example 5

[0094] The difference from Example 1 is that an equal amount of pure water is used instead of 750 L of the 100 g / L lithium carbonate suspension aqueous solution.

[0095] Comparative Example 6

[0096] The difference from Example 1 is that an air atmosphere is used instead of a nitrogen atmosphere.

[0097] The state of the mixture to be separated and the NMP loss rate, NMP recovery rate, and recovery rate of the lithium iron phosphate positive electrode material of Examples 1, 2, 3 and Comparative Examples 1, 2, 3, and 4 were statistically analyzed. The results are shown in Table 1.

[0098] NMP concentration: detected by gas chromatograph

[0099] Solid content determination: using solid content tester

[0100] NMP recovery rate: NMP mass after distillation / (1-solid content)1000*NMP concentration of stock solution

[0101] NMP loss rate = 1-NMP mass after distillation / (1-solid content)1000*NMP concentration of stock solution

[0102] Recovery rate of lithium iron phosphate positive electrode material = mass of lithium iron phosphate positive electrode filter residue * solid content of lithium iron phosphate positive electrode filter residue / 1000 * solid content of lithium iron phosphate positive electrode waste liquid

[0103] Table 1

[0104]

[0105]

[0106] From the comparison of Examples 1 to 3 and Comparative Examples 1 to 4 in Table 1, it can be seen that the addition of water and a weakly acidic buffer in Examples 1 to 3 can effectively destroy the colloidal stability of the lithium iron phosphate positive electrode waste liquid, which is not only simple and efficient to operate, but also has a good separation effect. The difficulty of solid-liquid separation of the lithium iron phosphate positive electrode waste liquid is reduced, that is, conventional filtration, filter pressing or centrifugation can be used to achieve efficient and rapid separation of the mixture to be separated. In particular, the comprehensive indicators in Examples 1 and 2 are better, that is, when the pH of the mixture to be separated is 6 to 7, not only the filtration speed is fast, but also the NMP recovery rate is as high as 87.00%, the recovery rate of the lithium iron phosphate positive electrode material is as high as 97%, and the purity of the regenerated NMP product is as high as 99.9% or more. The lithium iron phosphate positive electrode material meets the regeneration requirements to achieve maximum efficiency in the recovery of the lithium iron phosphate positive electrode waste liquid.

[0107] Furthermore, the electrical properties of the regenerated lithium iron phosphate cathode materials of Examples 1, 2, 3 and Comparative Examples 5 and 6 were tested, and the results are shown in Table 2.

[0108] Table 2

[0109]

[0110] From Table 2, it can be seen that the various electrical performance indicators of the lithium iron phosphate positive electrode materials prepared in Examples 1 to 3 are good. The regenerated lithium iron phosphate positive electrode materials that meet the requirements can be directly recycled into the production of lithium iron phosphate batteries, which not only reduces the problem of lithium iron phosphate positive electrode waste liquid discharge polluting the environment, but also reduces the production cost of lithium iron phosphate batteries.

[0111] The above-described embodiments merely represent several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for recovering lithium iron phosphate cathode waste liquid, characterized in that: include: Adding water to the lithium iron phosphate cathode waste liquid and mixing to obtain a waste liquid mixture; wherein the viscosity of the lithium iron phosphate cathode slurry is 8000 mPa·s to 10000 mPa·s; and the amount of the water accounts for 15% to 20% of the total volume of the lithium iron phosphate cathode waste liquid; adding a weak acidic buffer to the waste liquid mixture to adjust the pH of the waste liquid mixture to 5-8, thereby obtaining a mixture to be separated; wherein the weak acidic buffer is an acidic solution with a pH <7 and a pH >4; and the weak acidic buffer comprises at least one of lithium dihydrogen phosphate, carbonic acid, and oxalic acid; Separating the mixture to be separated to obtain a lithium iron phosphate positive electrode residue and an NMP mixed filtrate; The NMP mixed filtrate is distilled to obtain an NMP product; wherein the distillation temperature is 90° C. to 130° C.; mixing 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 positive electrode mixture is dried and calcined to obtain a lithium iron phosphate positive electrode material.

2. 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.

3. The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, wherein: The separation method is filter pressing or centrifugation.

4. The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, characterized in that: When the lithium iron phosphate positive electrode filter residue is mixed with a lithium source, the mass ratio of the lithium iron phosphate positive electrode filter residue to the lithium source is 1:

1.

5. The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, characterized in that: The calcination conditions are: calcination at 650° C. to 700° C. in a nitrogen atmosphere for 3 h to 4 h.

6. The method for recovering lithium iron phosphate cathode waste liquid according to claim 1, characterized in that: The drying temperature is 100°C to 150°C.

7. A lithium iron phosphate cathode waste liquid recovery production line, characterized in that: The production is carried out using the method for recovering lithium iron phosphate cathode waste liquid according to any one of claims 1 to 6.

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