Method for stripping waste lithium ion battery electrode material through ozone-assisted low-temperature pyrolysis

Abstract

The invention belongs to the technical field of lithium ion battery recovery, and particularly relates to a method for stripping a waste lithium ion battery electrode material through ozone-assisted low-temperature pyrolysis, which comprises the following steps of: putting a waste lithium battery or fragments obtained by crushing a waste lithium battery electrode plate into a heating furnace, then introducing ozone-containing gas, and carrying out heat treatment at 150-250 DEG C to degrade a binder, and separating the particles of the electrode material as well as the particles and the current collector to obtain the loose electrode material. Through the strong oxidation synergistic pyrolysis effect of ozone, the pyrolysis temperature of the binder is greatly reduced, and the molecular chain structure of the binder is directionally degraded, so that the binding power among active substance particles of the electrode material is reduced, and meanwhile, the damage of fluorine-containing substances generated by binder decomposition caused by high-temperature pyrolysis to the structure of the positive electrode material is inhibited; and due to directional degradation, electrode active substance particles are depolymerized and are stripped from the interface of the current collector, so that the efficient separation of the electrode material and the current collector is finally realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery recycling, and particularly relates to a method for ozone-assisted low-temperature pyrolysis stripping of waste lithium-ion battery electrode materials. Background Art

[0002] Due to core advantages such as high energy density, long life, and low maintenance cost, lithium-ion batteries have become a key carrier for energy transformation, and their shipments have increased explosively in the past decade. Among them, as the core component of lithium-ion batteries, electrode materials account for more than 60% of the total cost of lithium-ion batteries. At present, while the global number of lithium-ion batteries is increasing rapidly, the accelerating arrival of the lithium-ion battery retirement wave is also accompanied. Therefore, the development of efficient recycling of electrode materials has become a core issue in resource recycling and sustainable development.

[0003] In this context, the efficient stripping technology of electrode materials has become a key pre-process for realizing green recycling. Existing stripping schemes mainly rely on methods such as high-temperature pyrolysis (400 - 600 °C), organic solvent dissolution, and mechanical stripping. However, high-temperature pyrolysis easily leads to problems such as oxidation embrittlement of current collectors and lattice distortion of electrode materials; organic solvent dissolution is difficult to promote on a large scale due to problems such as solvent toxicity and cost; mechanical stripping can avoid problems such as material structure damage and environmental pollution, but the stripping rate is insufficient (<70%), and impurities such as Al and Cu are easily introduced. Therefore, the existing processes are difficult to balance in the "stripping rate - material integrity - environmental friendliness" triangular relationship, and the stripping process of electrode materials and current collectors still faces severe challenges, seriously restricting the economy and environmental protection of large-scale recycling.

[0004] In view of this, developing a method for stripping electrode materials with a high stripping rate, low material damage, and environmental friendliness has very important industrial promotion significance for promoting the recycling of resources of retired lithium-ion batteries. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for ozone-assisted low-temperature pyrolysis stripping of waste lithium-ion battery electrode materials. Through the strong oxidation and pyrolysis synergistic effect of ozone, the pyrolysis temperature of the binder is reduced, while the stripping rate is increased and the degree of material damage is reduced.

[0006] To achieve the above purpose, the present invention provides a method for ozone-assisted pyrolysis stripping of waste battery electrode materials, including: placing the fragments after crushing waste lithium-ion batteries or waste lithium-ion battery electrode sheets in a heating furnace, then introducing ozone-containing gas, and performing heat treatment at 150 - 250 °C to degrade the binder, so that the electrode material is separated from the current collector to obtain the stripped electrode material.

[0007] Ozone treatment, through the strong oxidizing property of ozone in synergy with pyrolysis, reduces the pyrolysis temperature of the binder. By promoting the breakage of the high - molecular chains of the binder, theoretically, only 5% of the binder chemical bonds need to be destroyed to reduce the degree of polymerization of the binder to 20, and it basically loses the ability to bond the electrode materials. Therefore, during the treatment process, the high - molecular binder will not decompose to generate small molecules such as HF, will not corrode the electrode materials, and the entire process will not damage the current collector, thus avoiding the introduction of impurities such as Al chips or Cu chips.

[0008] The components of the fragments after crushing the waste lithium - ion battery are a mixture of crushed aluminum - plastic shell, separator, positive electrode plate, and negative electrode plate. The components of the fragments after crushing the electrode plates of the waste lithium - ion battery are a mixture of positive electrode plate and negative electrode plate.

[0009] The binder used in the waste lithium - ion battery or the electrode plates of the waste lithium - ion battery includes one or more of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), styrene - butadiene rubber (SBR), and polyimide (PI).

[0010] Furthermore, the generation or introduction rate of the ozone gas, the heat - treatment time, and the heat - treatment temperature satisfy the following relational expression:

[0011]

[0012] where t is the heat - treatment time, with the unit of min; x is the generation or introduction rate of the ozone gas, with the unit of mg / min; V is the volume of the heating furnace, with the unit of m 3 ; T is the absolute heat - treatment temperature, with the unit of Kelvin (K); k is the concentration constant, and through a large number of experimental tests, the value range of k is 7.2 - 24.6 mg / m 3 .

[0013] Among them, the preferred range of the ratio of the ozone gas generation or introduction rate to the volume of the heating furnace is 15 - 200 mg / (m 3 ·min).

[0014] Furthermore, while introducing the ozone gas, water vapor is also introduced, and the molar ratio of the water vapor to the ozone is (0.1 - 1):1.

[0015] Furthermore, during the heat - treatment process, the crushed waste battery is subjected to a flipping treatment. For example, the heating furnace is equipped with a drum - type rotating device, and the rotation speed of the drum - type rotating device is 2 - 10 rpm. Through continuous tumbling, the surface of the electrode plate is fully contacted with the gas, and the separation of the electrode material particles is promoted by the collision between the electrode plates.

[0016] Further, the method further includes: subjecting the heat-treated material to ultrasonic screening or vibrating screening, with the screen aperture being 20 - 100 μm, and collecting the material passing through the screen as the positive and negative electrode material mixture.

[0017] The ultrasonic screening treatment refers to applying high-frequency ultrasonic vibration on the screen. The ultrasonic vibration causes the screen to produce tiny and rapid displacements, breaking up particle agglomerates and preventing particles from getting stuck in the screen holes, keeping the screen holes unobstructed to improve the screening efficiency.

[0018] The vibrating screening treatment refers to mechanically generating periodic vibrations to drive the movement of the screen surface. The purpose is also to break up large particles and prevent particles from getting stuck in the screen holes, keeping the screen holes unobstructed to improve the screening efficiency.

[0019] Further, the frequency of the ultrasonic treatment is 20 - 40 kHz, and the treatment time is 10 - 30 minutes; the amplitude of the vibrating screening treatment is 1 - 5 mm, and the treatment time is 5 - 20 minutes.

[0020] Further, the method further includes: mixing the positive and negative electrode material mixture with a eutectic salt, heating to a temperature above the eutectic point of the eutectic salt, collecting the upper solid substance to obtain the regenerated negative electrode material, and collecting the lower solid substance to obtain the regenerated positive electrode material;

[0021] The density of the eutectic salt is greater than that of the negative electrode material and less than that of the positive electrode material

[0022] Further, the method further includes: first cleaning the positive and negative electrode material mixture with ethanol and then drying it, and then mixing it with the eutectic salt.

[0023] Further, the mass ratio of the positive and negative electrode material mixture to the eutectic salt is 1:(3 - 5); the density of the eutectic salt is 2.5 g / cm 3 ~3.5 g / cm 3 , and the cations of the eutectic salt preferably include one or more of alkali metals and alkaline earth metals; the anions preferably include one or more of NO 3 - , Br - , I - , OH - , ClO 4 - and so on.

[0024] Further, the particle size of the fragments after crushing the waste lithium battery or waste lithium battery electrode sheet is 2 - 5 cm.

[0025] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0026] 1. A method for ozone-assisted pyrolytic stripping of waste battery electrode materials provided by the present invention skillfully utilizes the strong oxidizing property of ozone in synergy with pyrolysis, which can significantly reduce the pyrolysis temperature of the binder, directionally degrade the molecular structure of the binder, cause the active object particles of the electrode material to depolymerize and fall off from the current collector, and the stripping rate is increased to more than 95%. Moreover, after reducing the pyrolysis temperature, the structural damage of the cathode material caused by high-temperature pyrolysis can be inhibited and the energy consumption can be reduced. The reason is that ozone treatment promotes the breakage of the high molecular chain of the binder. Only by breaking 5% of the chemical bonds of the binder, the degree of polymerization of the binder will be reduced to 20, and it will basically lose the ability to bond the electrode material. Therefore, small molecules such as HF will not be generated during the treatment process, the electrode material will not be corroded, and the current collector will not be damaged during the whole process. Therefore, the introduction of impurities such as Al chips or Cu chips is avoided. High-temperature pyrolysis means that the high molecular structure of the binder is completely destroyed above the decomposition temperature of the binder (>350 °C). A large amount of fluorine-containing substances will be generated during the degradation process, severely etching the electrode material, resulting in the formation of a passivation layer on the surface, increasing the difficulty of subsequent regeneration and repair, and reducing the electrochemical performance. In short, the whole process of the present invention is simple and efficient, environmentally friendly, has great potential for industrial promotion, and can generate great benefits.

[0027] 2. By optimizing the relationship formula of the ozone gas generation or introduction rate, heat treatment time and heat treatment temperature, the present invention can reasonably design the stripping experimental parameters, achieve the best stripping effect, and prevent problems such as low stripping rate or decreased electrochemical performance caused by improper parameter setting.

[0028] 3. The present invention also generates hydroxyl radicals (·OH) and reactive oxygen species through the synergistic oxidation reaction of water vapor and ozone. The strong oxidizing property of the hydroxyl radicals further promotes the breakage of the binder molecular chain and improves the stripping rate.

[0029] 4. The present invention uses a eutectic salt with a density between the cathode material and the anode material to realize the separation and regeneration of the cathode and anode materials of waste lithium-ion batteries in one step, and the regenerated cathode and anode materials have good electrochemical performance. Description of the Drawings

[0030] Figure 1 The first charge-discharge curve of the ternary 523 material obtained by stripping under an ozone atmosphere at 200 °C.

[0031] Figure 2 The first charge-discharge curve of the graphite material obtained by stripping under an ozone atmosphere at 200 °C.

[0032] Figure 3 The positive electrode sheet after being treated in an air atmosphere at 200 °C.

[0033] Figure 4The positive electrode sheets are treated in an ozone atmosphere at 140°C, 150°C, and 260°C respectively.

[0034] Figure 5 The first charge-discharge curves of the ternary 523 material obtained by peeling under ozone atmosphere treatment at 160°C.

[0035] Figure 6 The first charge-discharge curves of the ternary 523 material obtained by peeling under ozone atmosphere treatment at 180°C.

[0036] Figure 7 The positive electrode sheet after being treated in an ozone atmosphere at 200°C for 100 min.

[0037] Figure 8 The first charge-discharge curves of the ternary 523 material obtained by peeling under air atmosphere treatment at 350°C. Specific embodiments

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] The present invention provides a method for ozone-assisted pyrolytic peeling of waste lithium-ion battery electrode materials, including: placing the fragments after crushing waste lithium-ion batteries or waste lithium-ion battery electrode sheets in a heating furnace, then introducing ozone gas, and performing heat treatment at 150-250°C to obtain peeled electrode materials.

[0040] In the temperature range of 150-250°C, the present invention uses the strong oxidizing ability of ozone to assist in the degradation of the binder, causing the binder polymer to crack, and making it easy to separate between the electrode material particles, so that it is easy to fall off from the current collector. The strong oxidizing property of ozone synergistically with the pyrolysis effect can reduce the pyrolysis temperature of the binder, directionally degrade the molecular chain structure of the binder, reduce the adhesion force between the active substance particles of the electrode material, and at the same time inhibit the phenomenon of electrode material structure damage caused by high-temperature pyrolysis. The directional degradation can depolymerize the active substance particles of the electrode material and peel off from the aluminum foil current collector interface, finally realizing the efficient separation of the positive electrode material from the current collector without introducing additional impurities, with a peeling rate ≥ 95% and a surface damage rate of the current collector ≤ 2%. The present invention can solve the problems of low peeling rate, serious damage to the material structure, and large environmental pollution in the prior art.

[0041] Ozone has a good degradation effect on common positive and negative electrode binders (such as polyvinylidene fluoride, polyacrylic acid, carboxymethyl cellulose, styrene-butadiene rubber, polyimide, etc.). This method is carried out at a relatively low temperature, with little damage to the electrode material and no large amount of fluorine-containing waste gas. In theory, ozone only needs to destroy 5% of the chemical bonds of the binder to reduce the degree of polymerization of the binder to 20, basically losing the ability to bond the electrode material, and will not turn into small gaseous molecules and will not corrode the electrode material.

[0042] In particular, the preferred temperature range for achieving a high stripping rate is 150-250°C. The reason is that when the temperature is lower than 150°C, the ozone oxidation capacity is insufficient, resulting in a decrease in the adhesive degradation efficiency; when the temperature is higher than 250°C, the ozone thermal decomposition intensifies, causing the effective ozone concentration to decrease, which also results in a decrease in the adhesive degradation efficiency.

[0043] The optimal temperature range for maintaining the electrochemical performance of the positive electrode material is 180-250°C. The reason is that when the temperature is lower than 180°C, although ozone treatment can pyrolyze part of the binder to achieve the stripping effect, some of the binder is still not completely decomposed, and the binder residue leads to an increase in the interface impedance of the positive electrode material and a decrease in the electrochemical performance.

[0044] Furthermore, the generation or introduction rate of the ozone gas, the heat treatment time and the heat treatment temperature satisfy the following relationship:

[0045]

[0046] Where t is the heat treatment time, in min; x is the ozone gas generation or introduction rate, in mg / min; V is the heating furnace volume, in m 3 ; T is the absolute temperature of heat treatment, in Kelvin (K); k is the concentration constant. After a large number of experimental tests, the value range of k is 7.2~24.6mg / m 3 ;The K in 2360K stands for Kelvin.

[0047] The preferred range of the ratio of ozone gas generation or introduction rate to the heating furnace volume is 15 to 200 mg / (m 3 ·min).

[0048] During the experiment, the heating furnace is in a flowing state, and the flow rate of ozone gas and the treatment time need to be reasonably adjusted. The reasons are as follows: When the ozone introduction rate is low, if the treatment time is too short, the binder will not decompose completely, and the stripping of the electrode material cannot be achieved; when the ozone introduction rate is high, if the ozone treatment time is too long, it will lead to a decline in the performance of the positive electrode, and the aluminum foil current collector will be pulverized. Therefore, through a large number of experiments, the present invention has summarized the relationship among the ozone generation or introduction rate, the heat treatment temperature, and the time under the ozone treatment scheme. Through this relationship, the experimental parameters can be designed quickly and reasonably, and the stripping effect can be ensured.

[0049] Further, while introducing the ozone gas, water vapor is also introduced, and the molar ratio of the water vapor to the ozone is (0.1 - 1):1. At a temperature of 150 - 250 °C, the water vapor and the ozone undergo a synergistic oxidation reaction to generate hydroxyl radicals (·OH) and reactive oxygen species. The strong oxidizing property of the hydroxyl radicals further promotes the breaking of the binder molecular chain and improves the stripping rate.

[0050] Further, during the heat treatment process, the broken waste batteries are subjected to a flipping treatment. For example, a drum - type rotating device is configured for the heating furnace, and the rotation speed of the drum - type rotating device is 2 - 10 rpm. Through continuous tumbling, the surface of the electrode sheet is fully contacted with the gas, and the separation of the electrode material particles is promoted by the collision between the electrode sheets.

[0051] Further, the method further includes: subjecting the heat - treated material to ultrasonic sieving or vibrating sieving treatment. The aperture of the sieve mesh is 20 - 100 μm. The positive and negative electrode material particles are smaller and are located under the sieve. The material collected under the sieve is the mixture of the positive and negative electrode materials.

[0052] The ultrasonic sieving treatment refers to applying high - frequency ultrasonic vibration on the sieve mesh. The ultrasonic vibration causes the sieve mesh to produce tiny and rapid displacements, breaks up the particle agglomeration, and prevents the particles from getting stuck in the sieve holes, keeping the sieve holes unobstructed to improve the sieving efficiency. For details, reference can be made to Patent CN202223023145.2.

[0053] The vibrating sieving treatment refers to driving the sieve surface to move by mechanically generating periodic vibrations. The purpose is also to break up the large - sized particles and prevent the particles from getting stuck in the sieve holes, keeping the sieve holes unobstructed to improve the sieving efficiency. For details, reference can be made to Patent CN202211443334.7.

[0054] Further, the frequency of the ultrasonic treatment is 20 - 40 kHz, and the treatment time is 10 - 30 minutes; the amplitude of the vibrating sieving treatment is 1 - 5 mm, and the treatment time is 5 - 20 minutes.

[0055] Further, the method further includes: mixing the positive and negative electrode material mixture with a eutectic salt, heating to a temperature above the eutectic point of the eutectic salt, collecting the upper solid material to obtain a regenerated negative electrode material, and collecting the lower solid material to obtain a regenerated positive electrode material;

[0056] The density of the eutectic salt is greater than the density of the negative electrode material and less than the density of the positive electrode material. For specific reference, please refer to the patent CN202411868086.X previously applied by the applicant.

[0057] Utilizing the density difference, after the eutectic salt melts, the electrode material with a larger density will sink, and the electrode material with a smaller density will float, thereby achieving the purpose of separating the positive and negative electrode materials.

[0058] For example, the density of the eutectic salt is designed in the range of 2.5 g / cm 3 ~3.5 g / cm 3 . When the negative electrode is graphite, since the density of the negative electrode material (2.2 g / cm 3 ~2.4 g / cm 3 ) is less than the density of the eutectic salt, it will float, and the density of the positive electrode material (usually above 3.6 g / cm 3 ) is greater than the density of the eutectic salt, so it will sink. In this way, the purpose of separating the positive and negative electrode materials is achieved. Finally, the upper solid material is collected to obtain a regenerated negative electrode material, and the lower solid material is collected to obtain a regenerated positive electrode material, thereby realizing the recycling of the positive and negative electrode materials of waste lithium-ion batteries.

[0059] The mass ratio of the positive and negative electrode material mixture to the eutectic salt is 1:(3 - 5).

[0060] The negative electrode material is not wetted by the eutectic salt. Therefore, the negative electrode material floating on the surface of the molten salt is in a loose granular form. With the help of an air suction filtration device, the floating negative electrode material is continuously collected by the method of air flow suction and filtration, so that the positive and negative mixed materials can be accurately separated to obtain pure positive and negative electrode materials. At the same time, due to the non-wetting property of the negative electrode material and the eutectic salt, the separation of the negative electrode material is very convenient, efficient and simple.

[0061] Further, the method further includes: first cleaning the positive and negative electrode material mixture with ethanol and then drying it to remove the residual oligomer components on its surface, and then mixing it with the eutectic salt; ethanol is a non-toxic and inexpensive organic solvent, but common battery binders have low solubility in ethanol and cannot be washed away with ethanol. Experiments in the present invention have found that after the binder is treated with ozone, some of its chemical bonds are broken and it becomes an oligomer, and its solubility in ethanol is greatly improved, and good washing effects can be achieved with ethanol.

[0062] The density of the eutectic salt is 2.5 g / cm 3~3.5 g / cm 3 , the cations of the eutectic salt preferably include one or more of alkali metals and alkaline earth metals; the anions preferably include NO 3 - , Br - , I - , OH - , ClO 4 - or more of them. The melting point of the eutectic salt is usually less than 500 °C, preferably less than 200 °C.

[0063] Further, the waste battery is a waste lithium-ion battery. Preferably, the positive electrode material is one or more of ternary materials, lithium cobaltate materials, and lithium iron phosphate materials, and the negative electrode material is graphite. The particle size of the crushed waste battery is 2 - 5 cm.

[0064] Example 1

[0065] The fragments obtained by crushing the waste ternary 523 (LiNi 0.5 Co 0.2 Mn 0.3 O 2 ) graphite-type lithium-ion battery were placed in a heating furnace with a roller device. Among them, the generation or introduction rate of the ozone gas, the heat treatment time, and the heat treatment temperature satisfy the following relationship:

[0066]

[0067] where t is the heat treatment time, in minutes; x is the generation or introduction rate of the ozone gas, in mg / min; V is the volume of the heating furnace, in m 3 ; T is the heat treatment temperature, in Kelvin (K), T(K) = T′(°C) + 273.15; k is the concentration constant, and the value range of k obtained through a large number of experimental tests is 7.2 - 24.6 mg / m 3 .

[0068] The preferred range of the ratio x / V of the ozone introduction rate to the heating furnace volume is 15 - 200 mg / (m 3 ·min).

[0069] When the volume of the heating furnace is 1 m 3Ozone gas was continuously introduced at a rate of 60 mg / min. Tests found that at 150 °C, a better stripping effect could be achieved after treatment for about 45 - 150 min (stripping rate > 95%, which was basically consistent with the theoretical time obtained from the above formula); when the temperature was increased to 200 °C, tests found that a better stripping effect could be achieved when the treatment time was 25 - 80 min (stripping rate > 95%, which was basically consistent with the theoretical time obtained from the above formula); when the temperature was increased to 250 °C, tests found that a better stripping effect could be achieved when the treatment time was 15 - 50 min (stripping rate > 95%, which was basically consistent with the theoretical time obtained from the above formula).

[0070] Next, based on the above formula, when the ozone gas introduction rate was 60 mg / min and the treatment temperature was 180 °C, the predicted result was that it would take 30 - 100 min. The next step was to conduct actual tests. Tests found that when the actual treatment time was 35 - 100 min, the stripping rate could reach more than 95%. In addition, based on the above formula, the treatment conditions when the ozone gas introduction rate was 45 mg / min were predicted. When the treatment temperature was 200 °C, due to the decrease in the ozone gas introduction rate, the predicted result was that it would take 35 - 125 min to achieve a better stripping effect. Then actual tests were conducted. Tests found that when the actual treatment time was 30 min, the stripping rate was only about 80%. When the treatment reached more than 35 min, the stripping rate could reach more than 95%. A good stripping effect could be achieved within the range of 35 - 120 min. The actual test results were within the range of the model calculation, indicating the reliability of the empirical equation of this model.

[0071] In addition, during the heating process, the rotation speed of the roller device was adjusted to 2 rpm to ensure full contact between the surface of the electrode sheet and the ozone gas, and to promote the separation of electrode material particles through the collision between the electrode sheets.

[0072] After heat treatment, the battery fragment mixture was passed through a 50 - μm sieve in sequence. During the screening process, ultrasonic treatment at 20 kHz was applied to the sieve for 5 minutes to promote the large pieces of electrode material that had fallen off to be crushed into fine particles and pass through the sieve. Then other battery components such as current collectors and battery cases were screened out to obtain a mixture of positive and negative electrode materials. Then the mixture after ozone treatment was washed with ethanol to remove the residual oligomer components on the surface. The washed mixture was in a loose powder state without large blocky particles.

[0073] Then the pure positive and negative electrode materials were separated by the method of eutectic salt. Specifically as follows:

[0074] Mix the obtained mixture above with the eutectic salt of lithium nitrate, cesium nitrate and potassium nitrate in a mass ratio of 1:3 to obtain the mixture to be separated. The molar content ratio of lithium nitrate, cesium nitrate and potassium nitrate in the eutectic salt is 1:2:1. At this ratio, the density of the eutectic salt is 2.84 g / cm 3 .

[0075] Heat the above-mentioned mixture to be separated to 150 °C. At this temperature, the eutectic salt melts. Since graphite is not wetted by the eutectic salt, graphite floats on the surface of the eutectic salt and is in a loose powder form. At this time, use a suction device to continuously suck the graphite floating on the surface into the collection bin for enrichment. After the graphite is completely collected, pour out the molten salt to collect the ternary 523 sedimented at the bottom, and collect and retain the poured molten salt for the next operation.

[0076] Wash the dispersed ternary 523 and graphite with deionized water twice respectively. After drying, anneal the ternary 523 in an oxygen atmosphere at 900 °C for 4 h to remove the residual lithium compounds (such as lithium carbonate) formed on the material surface during the water washing process. Anneal the graphite in an argon atmosphere at 800 °C for 2 h to eliminate a small amount of structural defects inside the graphite structure. Finally, obtain the NCM523 cathode material and graphite anode material that can be put into commercial use again.

[0077] Use inductively coupled plasma atomic emission spectrometry to analyze the impurities in the obtained cathode material and anode material. The content of Al impurity is less than 0.0032%, the content of Cu impurity is less than 0.0054%, the content of F impurity is less than 0.06%, and the content of P impurity is less than 0.04%.

[0078] Figure 1 The first charge-discharge curve of the obtained cathode material (NCM523) has a specific capacity of 160 mAh / g at a charge-discharge rate of 0.1C, indicating that the treatment process has little damage to the structure of the cathode material. Figure 2 The first charge-discharge curve of the obtained anode material (graphite) has a specific capacity of 365 mAh / g at a charge-discharge rate of 0.1C, indicating that the treatment process has no obvious effect on the performance of the anode material.

[0079] Example 2 (This example is to supplement the role of water vapor)

[0080] The waste ternary 523 (LiNi 0.5 Co 0.2 Mn 0.3 O 2)Place the fragments after crushing the graphite-type lithium-ion battery in a heating furnace equipped with a roller device. Adjust the ozone gas inlet rate to 60 mg / min and introduce water vapor simultaneously. The molar ratio of water vapor to ozone is 1:1. Thanks to the synergistic oxidation reaction between water vapor and ozone, the stripping rate can be increased by 10% - 30%. Therefore, it can be processed at 200 °C for about 20 - 60 min. During the heating process, adjust the rotation speed of the roller device to 2 rpm to ensure full contact between the surface of the electrode sheet and the ozone gas, and promote the separation of electrode material particles through the collision between the electrode sheets.

[0081] After heat treatment, pass the battery fragment mixture through a 50-μm sieve in sequence. During the screening process, apply ultrasonic treatment at 20 kHz on the sieve for 5 minutes to promote the large pieces of electrode material that have fallen off to be crushed into fine particles and pass through the sieve. Then, sieve out other battery components such as the current collector and battery case to obtain a mixture of positive and negative electrode materials. Then, wash the mixture after ozone treatment with ethanol to remove the residual oligomer components on the surface. The washed mixture is in a loose powder state without large blocky particles.

[0082] Then, use the same eutectic salt method as in Example 1 to separate and obtain pure positive and negative electrode materials.

[0083] Example 3 (This example is for supplementary comparison without ozone treatment)

[0084] Place the discarded ternary 523 (LiNi 0.5 Co 0.2 Mn 0.3 O 2 )After crushing the graphite-type lithium-ion battery, place it in a heating furnace equipped with a roller device. Under an air atmosphere, process it at 200 °C for 60 min. During the heating process, adjust the rotation speed of the roller device to 2 rpm to ensure full contact between the surface of the electrode sheet and the gas, and promote the separation of electrode material particles through the collision between the electrode sheets.

[0085] After heat treatment, pass the battery fragment mixture through a 50-μm sieve in sequence. During the screening process, apply ultrasonic treatment at 40 kHz on the sieve for 30 minutes. As Figure 3 shown in the positive electrode sheet, almost no positive electrode material falls off from the current collector at this time. This is mainly because the degradation temperature of the binder is not reached at this temperature, and the strong oxidation and pyrolysis synergistic effect of ozone is lacking. Therefore, the binder cannot be degraded, and the stripping of the electrode material cannot be achieved.

[0086] Example 4 (This example is for supplementary preferred temperature range of high stripping rate)

[0087] Place the discarded ternary 523 (LiNi 0.5 Co 0.2 Mn 0.3 O 2)After the graphite-type lithium-ion battery is broken, it is placed in a heating furnace with a roller device, and the ozone gas inlet rate is adjusted to 60 mg / min. Then, it is treated at 140 °C, 150 °C, 180 °C, and 260 °C for 100 min, 80 min, 60 min, and 45 min respectively. During the heating process, the rotation speed of the roller device is adjusted to 2 rpm to ensure sufficient contact between the surface of the electrode sheet and the ozone gas, and to promote the separation of electrode material particles through the collision between the electrode sheets.

[0088] After heat treatment, it is subjected to ultrasonic screening treatment at 40 kHz for 30 minutes, and the others are the same as in Example 1. As Figure 4 shown, almost no positive electrode material falls off the current collector for the positive electrode sheet treated at 140 °C, a large amount of positive electrode material falls off for the ones treated at 150 °C and 180 °C, and only a small amount of positive electrode material falls off for the one treated at 260 °C.

[0089] For the positive electrode sheet treated at 140 °C, almost no positive electrode material falls off the current collector mainly because the temperature is relatively low, and at this time the ozone oxidation ability is insufficient, resulting in a decrease in the degradation efficiency of the binder, and it is impossible to separate the positive electrode material particles from each other and fall off the current collector. For the one treated at 260 °C, only a small amount of positive electrode material falls off the current collector, mainly because the temperature is relatively high, and the effective ozone concentration decreases due to the intensification of thermal decomposition of ozone, and the degradation efficiency of the binder decreases. Therefore, the optimal stripping temperature range for ozone treatment is 150 - 250 °C.

[0090] Figure 5 The first charge-discharge curve of the positive electrode material (NCM523) separated at 150 °C is shown. At a charge-discharge rate of 0.1C, the discharge specific capacity is significantly reduced, only 134 mAh / g. This is attributed to the insufficient degradation efficiency of the binder at this temperature. Although partial degradation of the binder can promote the falling off of the positive electrode material, there is still some binder remaining on the surface of the positive electrode material, resulting in an increase in the interfacial impedance and thus a decrease in the electrochemical performance.

[0091] Figure 6 The first charge-discharge curve of the positive electrode material (NCM523) separated at 180 °C. At a charge-discharge rate of 0.1C, the discharge specific capacity is 158 mAh / g. Therefore, the optimized temperature range for maintaining the electrochemical performance of the positive electrode material is 180 - 250 °C.

[0092] Example 5 (This example is to supplement the example of the pulverization of the current collector caused by long-term ozone treatment)

[0093] The waste ternary 523 (LiNi 0.5 Co 0.2 Mn 0.3 O 2) After crushing the graphite-type lithium-ion battery, it is placed in a heating furnace equipped with a roller device. Adjust the feeding rate of ozone gas concentration in the heating furnace to 60 mg / (m 3 ·min). Treat it at 200 °C for 100 min. During the heating process, adjust the rotation speed of the roller device to 2 rpm to ensure full contact between the surface of the electrode sheet and the gas, and promote the separation of electrode material particles through the collision between the electrode sheets.

[0094] After heat treatment, perform ultrasonic screening treatment at 20 kHz for 15 minutes. At this time, it is found that the positive electrode material completely falls off from the current collector. However, at the same time, due to the long-term oxidation effect of the current collector, as Figure 7 shown, part of it is pulverized, and a large amount of aluminum powder is mixed into the mixed components of the positive and negative electrode materials.

[0095] Example 6 (This example is a supplementary comparison of high-temperature treatment without ozone)

[0096] Put the discarded ternary 523 (LiNi 0.5 Co 0.2 Mn 0.3 O 2 ) After crushing the graphite-type lithium-ion battery, it is placed in a heating furnace equipped with a roller device. Under an air atmosphere, treat it at 350 °C for 60 min. During the heating process, adjust the rotation speed of the roller device to 2 rpm to ensure full contact between the surface of the electrode sheet and the gas, and promote the separation of electrode material particles through the collision between the electrode sheets.

[0097] After heat treatment, pass the battery fragment mixture through a 50-μm sieve in sequence. During the screening process, apply ultrasonic treatment at 20 kHz on the sieve for 5 minutes to promote the large-piece electrode material that has fallen off to be crushed into fine particles and pass through the sieve, and then screen out other battery components such as the current collector and the battery case to obtain a mixture of positive and negative electrode materials. Then wash the mixture treated with ozone with ethanol to remove the residual oligomer components on the surface. The washed mixture is in a loose powder state without large-piece granular particles.

[0098] Then use the method of molten salt to separate and obtain pure positive and negative electrode materials.

[0099] Figure 8The first charge-discharge curve of the obtained cathode material (NCM523) is shown. At a charge-discharge rate of 0.1C, the discharge specific capacity is only 20 mAh / g. This is attributed to two aspects. Firstly, a large amount of fluorine-containing substances are generated during the high-temperature pyrolysis of the binder, resulting in damage to the structure of the cathode material and a decline in its electrochemical performance. Secondly, because the pyrolysis of the binder is incomplete and part of it remains on the surface of the cathode material. Different from the state where the binder decomposes into oligomers after ozone treatment, the decomposition products of the binder by high-temperature pyrolysis have low solubility in ethanol and are thus difficult to remove, leading to the influence of surface impurities on the cathode material, an increase in internal resistance, and a decline in electrochemical performance. Therefore, in the present invention, ozone-assisted pyrolysis can effectively maintain the electrochemical performance of the obtained electrode material while ensuring the stripping rate.

[0100] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for stripping waste lithium-ion battery electrode materials by ozone-assisted pyrolysis, characterized in that: include: The broken fragments of discarded lithium-ion batteries or discarded lithium-ion battery electrode sheets are placed in a heating furnace, and then ozone-containing gas is introduced to perform heat treatment at 150-250° C. to degrade the binder, so that the electrode material particles are separated from each other and from the current collector to obtain loose electrode materials.

2. The method according to claim 1, characterized in that The generation or introduction rate of the ozone gas, the heat treatment time and the heat treatment temperature satisfy the following relationship: Where t is the heat treatment time, in min; x is the ozone gas generation or introduction rate, in mg / min; V is the volume of the heating furnace, in m 3 ; T is the absolute temperature of heat treatment, the unit is Kelvin K; k is the concentration constant, the value range of k is 7.2~24.6mg / m 3 .

3. The method according to claim 1, characterized in that: Water vapor is introduced simultaneously with the ozone gas, and the molar ratio of the water vapor to the ozone is (0.1-1):

1.

4. The method according to claim 1, characterized in that: During the heat treatment, the waste lithium-ion batteries or the fragments of waste lithium-ion battery electrode sheets are turned over.

5. The method according to any one of claims 1 to 5, characterized in that: The method further comprises: subjecting the heat-treated material to ultrasonic screening or vibration screening, wherein the mesh size is 20 to 100 μm, and collecting the material under the mesh as a mixture of positive and negative electrode materials.

6. The method according to claim 6, characterized in that: The method further comprises: mixing the positive and negative electrode material mixture with a eutectic salt, heating to above the eutectic point of the eutectic salt, collecting upper solid matter to obtain regenerated negative electrode material, and collecting lower solid matter to obtain regenerated positive electrode material; The density of the eutectic salt is greater than the density of the negative electrode material and less than the density of the positive electrode material.

7. The method according to claim 6, characterized in that The method further comprises: firstly washing the positive and negative electrode material mixture with ethanol and then drying it, and then mixing it with the eutectic salt.

8. The method according to claim 7, characterized in that The mass ratio of the positive and negative electrode material mixture to the eutectic salt is 1:(3-5); the density of the eutectic salt is 2.5 g / cm 3 ~3.5g / cm 3 The cation of the eutectic salt preferably includes one or more of alkali metals and alkaline earth metals; the anion preferably includes NO3 - Br - ,I - OH - 、ClO4 - One or more of .

9. The method according to claim 1, characterized in that: The average particle size of the fragments after the waste lithium-ion batteries or waste lithium-ion battery electrode sheets are crushed is 2-5 cm.

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