Comprehensive recovery method of lithium iron phosphate black powder

Abstract

The invention relates to the technical field of lithium ion battery recovery, in particular to a lithium iron phosphate black powder comprehensive recovery method which is characterized by comprising the following steps: S1, mechanically activating waste lithium iron phosphate black powder to obtain activated powder; s2, (NH4) 2SO4 and MeS2O3 are mixed, and compound molten salt is obtained; s3, the activated powder and the compound molten salt are placed in reaction cavities which are separated from each other up and down in a reaction furnace, the two reaction cavities are communicated through a gas flow guide pipe, microwave pyrolysis is carried out in a non-contact atmosphere, and pyrolysis slag is obtained; and S4, the pyrolysis slag is subjected to ultrasonic water leaching and solid-liquid separation, and lithium extraction liquid and lithium extraction slag are obtained. The activation powder and the compound molten salt are arranged in a non-contact mode, and the method has the advantages that the treatment process is simplified, and the product purity is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery recycling, more specifically, it relates to a comprehensive recovery method for lithium iron phosphate black powder. BACKGROUND

[0002] With the rapid development of new energy vehicles and energy storage industry, the installed capacity of lithium ion batteries is showing explosive growth. Lithium iron phosphate batteries (LiFePO4) have a market share of more than 40% in the power battery field due to their high safety, long cycle life and low cost advantages. According to industry statistics, the total amount of retired lithium iron phosphate batteries worldwide in 2023 reached 250,000 tons, and it is expected to exceed 2 million tons by 2030. However, the lithium content in the positive material of lithium iron phosphate battery is low (about 4.5%), and it does not contain high-valence metals, which makes the traditional recycling mode based on the extraction of valuable metals less economical. If not properly disposed of, a large number of waste batteries will cause serious resource waste and environmental pollution risk.

[0003] For the recycling of waste lithium iron phosphate batteries, the current mainstream technical routes include pyrometallurgy, hydrometallurgy and direct regeneration method, but all have significant limitations. Pyrometallurgy is generally carried out at high temperature, which has high energy consumption and is easy to cause high-activity lithium to volatilize, affecting the recovery efficiency of lithium. The core step of hydrometallurgy needs to consume a large amount of inorganic acid for metal leaching, and then needs to use alkali for neutralization, which is costly; the separation and purification steps of iron, lithium, phosphorus and other metal ions in the leaching solution are complex. The direct regeneration method has extremely strict requirements on the purity of raw materials, and the repair of the lattice structure of lithium iron phosphate is highly sensitive to impurities, and it is extremely difficult to efficiently separate LiFePO4 positive materials that meet the regeneration purity requirements from complex waste batteries in actual operation, which seriously restricts the large-scale industrial application of this technology. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the present application is to provide a comprehensive recovery method for lithium iron phosphate black powder, which has the advantages of simplifying the process and improving the recovery efficiency.

[0005] The above technical purpose of the present application is realized by the following technical scheme: a comprehensive recovery method for lithium iron phosphate black powder, comprising the following steps: S1, mechanically activating waste lithium iron phosphate black powder to obtain activated powder; S2, mixing (NH4)2SO4 and MeS2O3 to obtain a compounded molten salt; S3, placing the activated powder and the compounded molten salt in the upper and lower isolated reaction cavities in the reaction furnace, and connecting the two reaction cavities through a gas flow guide pipe, and carrying out microwave pyrolysis under a non-contact controlled atmosphere to obtain a pyrolysis residue; S4, ultrasonic water leaching and solid-liquid separation of the pyrolysis residue to obtain a lithium extraction liquid and a lithium extraction residue.

[0006] In one of the embodiments, the waste lithium iron phosphate black powder comprises graphite and lithium iron phosphate cathode.

[0007] In one of the embodiments, the specific steps of S1 are as follows: ball milling beads and ethanol are added to the waste lithium iron phosphate black powder for ball milling treatment to obtain the activated powder; wherein the ball milling speed is 300-500 r / min, the ball milling time is 4-8 h, and the ball-to-material ratio is 5:1-10:1; the ball milling beads are zirconium oxide or stainless steel balls with a diameter of 5-25 mm; the amount of ethanol added is 5-10% of the total amount of the waste lithium iron phosphate black powder and the ball milling beads.

[0008] In one of the embodiments, the MeS2O3 comprises one or more of Na2S2O3, (NH4)2S2O3 and K2S2O3.

[0009] In one of the embodiments, the mass fraction of (NH4)2SO4 in the complex molten salt is greater than 70%.

[0010] In one of the embodiments, the specific steps of S2 are as follows: (NH4)2SO4 and MeS2O3 are ground, mixed, ultrasonically dispersed and pressure pelletized to obtain the complex molten salt pellets with a particle size of 2-5 mm.

[0011] In one of the embodiments, the non-contact gas atmosphere comprises one or more of argon and nitrogen.

[0012] In one of the embodiments, the mass ratio of the activated powder to the complex molten salt in S3 is 1:4-1:8, the pyrolysis temperature is 300-500°C, and the pyrolysis time is 20-60 min.

[0013] In one of the embodiments, the ultrasonic power of the ultrasonic water immersion is 50-70 W, the temperature is 20-40°C, the liquid-to-solid ratio is 5:1-10:1 ml / g, and the time is 0.5-1 h.

[0014] In one of the embodiments, the lithium extraction residue comprises amorphous FePO4 and graphite.

[0015] The above-mentioned lithium iron phosphate black powder comprehensive recovery method has the following beneficial effects: Firstly, the activated powder and the complex molten salt are arranged in a non-contact manner, which maximally reduces the interference of metal and non-metal elements in the molten salt on lithium iron phosphate, reduces the complexity of the subsequent purification process, simplifies the processing process, and improves the product purity. Secondly, the sulfate system can avoid strong corrosion to the equipment, prolong the service life of the equipment, and the excess SO2 and SO3 gas generated by the decomposition of the system can be further prepared into sulfuric acid product, so that the resources are efficiently utilized. Thirdly, the setting of the complex molten salt can reduce the gasification and decomposition temperature of (NH4)2SO4, and the slow release of the gas can be realized by combining the balling process, so that the gas utilization rate is effectively improved, and the reaction process is optimized. Fourthly, the lithium extraction residue of the present application is FePO4 and graphite, which can be regenerated into LiFePO4 positive material through lithium mixing roasting, so that the high-value utilization of Fe, P and C is realized. Fifthly, by controlling the use of the non-contact gas atmosphere, the direct decomposition of (NH4)2SO4 into SO2 and the loss of the oxidation effect on LiFePO4 can be avoided, the risk of graphite damage can be reduced, the formation of by-products such as iron red Fe2O3 can be inhibited, and the smooth progress of the subsequent LiFePO4 regeneration process can be ensured. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is the XRD pattern of the waste old lithium iron phosphate black powder used in the present application; Figure 2 is the XRD pattern of the pyrolysis residue in the comparative example 2 of the present application. DETAILED DESCRIPTION

[0017] The present application will be further described in conjunction with the examples below, it should be pointed out that the following examples are intended to facilitate the understanding of the present application, and do not limit the present application in any way. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as generally understood by those skilled in the art to which the present application belongs. When there is a conflict, the definition in the specification shall prevail.

[0018] The term "prepared from" as used herein is synonymous with "comprising". As used herein the terms "comprising" "including", "having" "with" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0019] The conjunction "consisting of" excludes any unrecited elements, steps, or components. If used in the claims, this phrase shall be construed to be a "closed" claim, meaning that it excludes any material not specifically named. When the phrase "consisting of" appears in a claim, it does not exist to limit the subject matter of the claim to the specific materials recited but to the materials specifically recited only. Other elements are not excluded from the claim as a whole.

[0020] When a range, preferably a range, or a series of upper preferred values and lower preferred values, is used to express an equivalent, concentration, or other value or parameter, it should be understood that all ranges formed by any pair of an upper range limit or preferred value and a lower range limit or preferred value, whether or not the range is expressly disclosed, are specifically disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include the end values and all integers and fractions within that range.

[0021] A comprehensive recovery method of lithium iron phosphate black powder, comprising the following steps: S1, mechanically activating the waste lithium iron phosphate black powder to obtain activated powder, the waste lithium iron phosphate black powder comprising graphite and lithium iron phosphate positive electrode; The specific operation steps of mechanical activation are: adding ball milling beads and ethanol to the waste lithium iron phosphate black powder, under the conditions of ball milling speed of 300-500 r / min, ball-to-material ratio of 5:1-10:1, ball milling treatment for 4-8 h, the ball milling beads being 5-25 mm zirconium oxide or stainless steel balls, and the amount of ethanol being 5-10% of the total amount of the waste lithium iron phosphate black powder and the ball milling beads; Mechanical activation of the waste lithium iron phosphate black powder can effectively destroy the crystal structure of lithium iron phosphate, directly reduce the activation energy of the subsequent reaction, and reduce the particle size of the black powder, so that the contact area between the raw materials in the subsequent reaction is increased, and the reaction kinetics is efficiently accelerated.

[0022] S2, mixing (NH4)2SO4 and MeS2O3 to obtain a compounded molten salt, MeS2O3 including one or more of Na2S2O3, (NH4)2S2O3 and K2S2O3, the mass fraction of (NH4)2SO4 being greater than 70%; The specific operation steps of mixing are: grinding, uniformly mixing, ultrasonic dispersing and pelletizing of (NH4)2SO4 and MeS2O3 to obtain compounded molten salt pellets with a particle size of 2-5 mm; Compared with the traditional chlorine salt system, the sulfate salt system adopted in the application significantly reduces the corrosion risk of the equipment (avoiding the strong corrosion effect of chlorine gas and chlorine ions), and the SO2 / SO3 gas generated by decomposition can be efficiently recycled and used as raw material for preparing sulfuric acid products, realizing the resource utilization of by-products; Meanwhile, the specific compound molten salt adopted by the application can effectively reduce the gasification and decomposition temperature of (NH4)2SO4, is beneficial to the subsequent reaction, and in combination with the pelletizing process, slow and controllable release of the gas in the molten salt is realized, the utilization efficiency of SO2 / SO3 gas is significantly improved, and favorable conditions are created for the subsequent preparation of sulfuric acid.

[0023] S3, the activated powder and the compound molten salt are placed in the upper and lower separated reaction cavities in the reaction furnace, and the two reaction cavities are communicated through the gas flow guide pipe, and the microwave pyrolysis is carried out under the non-contact controlled atmosphere to obtain pyrolysis residue; The non-contact controlled atmosphere includes one or more of argon and nitrogen, the mass ratio of the activated powder and the compound molten salt is 1:4-1:8, the pyrolysis temperature is 300-500 DEG C, and the pyrolysis time is 20-60 min; The activated powder and the compound molten salt are arranged without contact, which maximally isolates the possible metal and non-metal impurity elements in the molten salt from polluting the target product lithium iron phosphate, and significantly reduces the difficulty and cost of the subsequent purification process; The activated powder and the compound molten salt are crucially reacted under the protection of the non-contact controlled atmosphere (Ar / N2), which on the one hand effectively inhibits the direct decomposition of (NH4)2SO4 in the presence of oxygen to generate SO2 and lose the oxidizing agent function (avoiding the reaction of 2(NH4)2SO4+O2(g)→2N2(g)+4SO2(g)+8H2O(g)), and ensures the effective oxidation and activation of LiFePO4; on the other hand, significantly reduces the risk of oxidation damage of graphite at high temperature, and effectively inhibits the generation of by-products (such as Fe2O3 iron red) generated by the activated powder and the molten salt in the air atmosphere, thereby ensuring the purity and electrochemical performance of the final regenerated LiFePO4 product; The mass ratio of the activated powder and the compound molten salt is set to 1:4-1:8, which can ensure complete reaction of the activated powder and avoid waste and rising processing cost caused by excessive compound molten salt; the pyrolysis temperature is set to 300-500 DEG C, which can ensure complete reaction of the activated powder and the compound molten salt while preventing the increase of production energy consumption caused by too high temperature.

[0024] S4, the pyrolysis residue is ultrasonically immersed in water for 0.5-1 h under the conditions of ultrasonic power of 50-70 W, temperature of 20-40 DEG C, and liquid-solid ratio of 5:1-10:1 ml / g, and then solid-liquid separation is carried out to obtain a lithium extraction liquid and a lithium extraction residue, and the lithium extraction residue includes amorphous FePO4 and graphite; The lithium extraction residue mainly contains FePO4 and graphite, which can be directly regenerated into high-performance LiFePO4 cathode material through simple lithium mixing roasting, realizing efficient and high-value recycling of iron (Fe), phosphorus (P) and carbon (C) elements. In contrast, the chlorosalt system usually produces FeCl3, which not only needs a complex collection system, but also needs additional dechlorination treatment process before being reused for LiFePO4 regeneration, which is complex and high in cost.

[0025] The reaction between the above complex molten salt and the activated powder is: (NH4)2SO4 decomposition: (NH4)2SO4 = 2NH3(g) + SO3(g) + H2O(g) SO3 gas reacts with lithium iron phosphate: 2LiFePO4 + 2SO3(g) = 2FePO4 + Li2SO4 + SO2(g) Overall reaction: 2LiFePO4 + 2(NH4)2SO4 = 2FePO4 + Li2SO4 + SO2(g) + 4NH3(g) + 2H2O(g) Example 1

[0026] A comprehensive recovery method of lithium iron phosphate black powder, comprising the following steps: S1, mechanical activation: mix 5g of waste lithium iron phosphate black powder, 45g of zirconia balls with a diameter of 5-25mm and 5mL of ethanol, and add them into a ball mill tank, and mill at a speed of 500r / min for 6h to obtain activated powder; S2, complex molten salt preparation: grind 16g of (NH4)2SO4, 1g of Na2S2O3 and 3g of K2S2O3 uniformly, then disperse them in an ultrasonic disperser, and finally press them into balls by a ball press to obtain NH4)2SO4-Na2S2O3-K2S2O3 complex molten salt with a diameter of 2-5mm; S3, non-contact gas atmosphere microwave pyrolysis: 4g of activated powder and 16g of complex molten salt are respectively placed in different quartz cavities, wherein the activated powder is located in the upper layer and the complex molten salt is located in the lower layer, and a quartz tube is used for gas flow between them, argon is introduced and the atmosphere furnace is heated to 500℃, and after keeping the temperature for 30min, it is naturally cooled to obtain pyrolysis residue; S4, ultrasonic water immersion of pyrolysis residue: the above pyrolysis residue is added to deionized water according to the liquid-solid ratio (mL:g) of 10:1, the above solution is placed in an ultrasonic cleaning machine, the ultrasonic power is set to 50W, and the reaction is carried out at 30℃ for 1h, then filtered to obtain lithium extraction residue and lithium extraction liquid, and the Li leaching rate is 97.1%. Example 2

[0027] S1, mechanical activation: 10 g of waste lithium iron phosphate black powder, 90 g of zirconia balls with a diameter of 5-25 mm and 10 mL of ethanol were mixed and added to a ball mill tank, and ball milling was performed at a rotation speed of 400 r / min for 7 h to obtain activated powder; S2, preparation of complex molten salt: 40 g of (NH4)2SO4, 4 g of Na2S2O3 and 6 g of (NH4)2S2O3 were ground uniformly, then dispersed in an ultrasonic disperser, and finally pressed into balls by a ball press to obtain (NH4)2SO4-Na2S2O3-(NH4)2S2O3 complex molten salt with a diameter of 2-5 mm; S3, contactless atmosphere-controlled microwave pyrolysis: 8 g of activated powder and 40 g of complex molten salt were respectively placed in different quartz cavities, wherein the activated powder was located in the upper layer and the complex molten salt was located in the lower layer, a quartz tube was used to connect the middle part for gas flow, argon was introduced, and the atmosphere furnace was heated to 400℃, and after 40 min of heat preservation, it was naturally cooled to obtain pyrolysis residue; S4, ultrasonic water immersion of pyrolysis residue: the above pyrolysis residue was added to deionized water according to the liquid-solid ratio (mL:g) 8:1, the above solution was placed in an ultrasonic cleaning machine, the ultrasonic power was set to 60 W, and the reaction was carried out at 25℃ for 1 h, and then filtered to obtain a lithium extraction liquid, and the Li leaching rate was 96.7%. Example 3

[0028] S1, mechanical activation: 12 g of waste lithium iron phosphate black powder, 60 g of zirconia balls with a diameter of 5-25 mm and 7 mL of ethanol were mixed and added to a ball mill tank, and ball milling was performed at a rotation speed of 300 r / min for 8 h to obtain activated powder; S2, preparation of complex molten salt: 50 g of (NH4)2SO4, 3 g of Na2S2O3 and 7 g of (NH4)2S2O3 were ground uniformly, then dispersed in an ultrasonic disperser, and finally pressed into balls by a ball press to obtain (NH4)2SO4-Na2S2O3-(NH4)2S2O3 complex molten salt with a diameter of 2-5 mm; S3, contactless atmosphere-controlled microwave pyrolysis: 10 g of activated powder and 50 g of complex molten salt were respectively placed in different quartz cavities, wherein the activated powder was located in the upper layer and the complex molten salt was located in the lower layer, a quartz tube was used to connect the middle part for gas flow, argon was introduced, and the atmosphere furnace was heated to 400℃, and after 20 min of heat preservation, it was naturally cooled to obtain pyrolysis residue; S4, ultrasonic water immersion of pyrolysis residue: the above pyrolysis residue was added to deionized water according to the liquid-solid ratio (mL:g) 10:1, the above solution was placed in an ultrasonic cleaning machine, the ultrasonic power was set to 70 W, and the reaction was carried out at 40℃ for 0.5 h, and then filtered to obtain a lithium extraction liquid, and the Li leaching rate was 96.8%. Example 4

[0029] S1, mechanical activation: 8 g of waste lithium iron phosphate black powder, 80 g of zirconia balls with a diameter of 5-25 mm and 8 mL of ethanol were mixed and added to a ball mill tank, and the ball mill was operated at a speed of 500 r / min for 4 h to obtain activated powder; S2, preparation of complex molten salt: 50 g of (NH4)2SO4, 2 g of (NH4)2S2O3 and 8 g of K2S2O3 were ground uniformly, then dispersed in an ultrasonic disperser, and finally pressed into balls by a ball press to obtain (NH4)2SO4-(NH4)2S2O3-K2S2O3 complex molten salt with a diameter of 2-5 mm; S3, contactless atmosphere microwave pyrolysis: 6 g of activated powder and 42 g of complex molten salt were respectively placed in different quartz cavities, wherein the activated powder was located in the upper layer and the complex molten salt was located in the lower layer, and a quartz tube was used for gas flow between them. Argon was introduced and the atmosphere furnace was heated to 300℃, and after 50 min of heat preservation, it was naturally cooled to obtain pyrolysis residue; S4, ultrasonic water immersion of pyrolysis residue: the above pyrolysis residue was added to deionized water at a liquid-solid ratio (mL:g) of 5:1, and the above solution was placed in an ultrasonic cleaning machine, the ultrasonic power was set to 70 W, and the reaction was carried out at 30℃ for 1 h. Filtration was performed to obtain a lithium extraction solution, and the Li leaching rate was 97.8%.

[0030] Comparative Example 1 The other conditions and steps were consistent with those of Example 1, except that the complex molten salt was not prepared, and (NH4)2SO4 was directly used.

[0031] Comparative Example 2 The other conditions and steps were consistent with those of Example 1, except that the argon was replaced with air.

[0032] Comparative Example 3 The other conditions and steps were consistent with those of Example 1, except that the atmosphere furnace was heated to 200℃.

[0033] Figure 1 For Examples 1-4 and Comparative Examples 1-3, the XRD patterns of the waste lithium iron phosphate black powder showed that both graphite and lithium iron phosphate positive electrode were present in the waste lithium iron phosphate black powder. The pyrolysis residues of Comparative Examples 1-3 were detected, and the relevant results are as follows: the pyrolysis residue of Comparative Example 1 still contained unreacted lithium iron phosphate; as shown in FIG. 1, the pyrolysis residue of Comparative Example 2 contained LiFePO4 and iron red, indicating that the side reaction of the complex molten salt with air increased, resulting in incomplete reaction and the formation of iron red in the product; the reaction temperature of Comparative Example 3 was too low, resulting in incomplete reaction. Figure 2

[0034] ​The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for comprehensive recovery of lithium iron phosphate black powder, characterized in that, Includes the following steps: S1. Mechanically activate waste lithium iron phosphate black powder to obtain activated powder; S2. Mix (NH4)2SO4 and MeS2O3 to obtain a composite molten salt; S3. The activated powder and the compound molten salt are placed in separate reaction chambers in the reactor, and the two reaction chambers are connected by a gas guide pipe. Microwave pyrolysis is carried out under a non-contact controlled atmosphere to obtain pyrolysis residue. S4. The pyrolysis residue is subjected to ultrasonic water immersion and solid-liquid separation to obtain lithium extraction liquid and lithium extraction residue.

2. The method for comprehensive recovery of lithium iron phosphate black powder according to claim 1, characterized in that: The waste lithium iron phosphate black powder includes graphite and lithium iron phosphate cathode.

3. The method for comprehensive recovery of lithium iron phosphate black powder according to claim 1, characterized in that, The specific steps of S1 are as follows: The waste lithium iron phosphate black powder was ball-milled with grinding beads and ethanol to obtain the activated powder. The ball milling speed is 300-500 r / min, the ball milling time is 4-8 h, and the ball-to-material ratio is 5:1-10:

1. The grinding balls are zirconium oxide or stainless steel balls with a diameter of 5-25 mm; The amount of ethanol added is 5-10% of the total amount of the waste lithium iron phosphate black powder and the grinding beads.

4. The method for comprehensive recovery of lithium iron phosphate black powder according to claim 1, characterized in that: The MeS2O3 includes one or more of Na2S2O3, (NH4)2S2O3, and K2S2O3.

5. The method for comprehensive recovery of lithium iron phosphate black powder according to claim 1, characterized in that: The mass fraction of (NH4)2SO4 in the compound molten salt is greater than 70%.

6. The method for comprehensive recovery of lithium iron phosphate black powder according to claim 1, characterized in that, The specific steps of S2 are as follows: (NH4)2SO4 and MeS2O3 are ground, mixed, ultrasonically dispersed, and granulated to obtain the composite molten salt balls with a particle size of 2-5 mm.

7. The method for comprehensive recovery of lithium iron phosphate black powder according to claim 1, characterized in that: The contactless controlled atmosphere includes one or more of argon and nitrogen.

8. The method for comprehensive recovery of lithium iron phosphate black powder according to claim 1, characterized in that: The mass ratio of the activated powder to the compound molten salt in S3 is 1:4-1:8, the pyrolysis temperature is 300-500℃, and the pyrolysis time is 20-60min.

9. The method for comprehensive recovery of lithium iron phosphate black powder according to claim 1, characterized in that: The ultrasonic immersion process is performed with an ultrasonic power of 50-70W, a temperature of 20-40℃, a liquid-to-solid ratio of 5:1-10:1ml / g, and a time of 0.5-1h.

10. The method for comprehensive recovery of lithium iron phosphate black powder according to claim 1, characterized in that: The lithium extraction residue includes amorphous FePO4 and graphite.

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