A method for recycling dry electrode membranes

Abstract

This application relates to the technical field of lithium-ion battery electrode membranes, and specifically relates to a method for recycling dry electrode membranes, including: freezing the recycled materials into a solid state at a first preset temperature, and then performing vacuum drying treatment; performing low-temperature coarse crushing on the materials at a second preset temperature, where the second preset temperature is greater than the first preset temperature; performing low-temperature airflow crushing on the materials at a third preset temperature to obtain recycled powder; mixing the recycled powder with new powder as a preparation raw material, and preparing a dry electrode membrane by the preparation process of the dry electrode membrane; the first preset temperature, the second preset temperature, and the third preset temperature are all less than 0°C. Through the recycling treatment of the trimmed scraps after rolling the dry electrode membrane into a film, this application can be mixed with new powder to prepare a dry electrode membrane, with a recovery rate of 100%, avoiding material waste and also reducing the environmental pollution problem caused by the discarded scraps.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion battery electrode membranes, and specifically relates to a method for recycling dry-process electrode membranes. Background Art

[0002] The electrode provides a site for charge storage / release and becomes a key core component of electrochemical energy storage devices such as lithium-ion batteries, supercapacitors, and lithium-ion capacitors. The preparation methods of electrodes can be divided into two types: wet method and dry method. The wet method is to uniformly mix electrode active materials, conductive agents, binders, etc. in water or organic solvents to obtain a viscous slurry; then it is compounded with a metal current collector by methods such as roll coating, blade coating, and spraying; finally, the solvent is removed through processes such as rolling, drying, and finishing to obtain the electrode. The wet method for preparing electrodes has the advantages of uniform mixing of electrode components, simple process, and strong continuity, but it also has deficiencies such as more water / solvent residues, binder clogging of charge channels, and low volumetric energy storage density. The dry electrode preparation process is to obtain a uniformly mixed electrode masterbatch by mixing electrode active materials, conductive agents, and binders through a mixing device; then, through a fibrillating device, the binder is fibrillated to form a three-dimensional network structure, and then through a calendering process, granular inorganic particles are formed into a self-supporting electrode membrane; finally, the self-supporting electrode membrane is compounded with a metal current collector through a conductive binder to obtain the electrode. The dry process has the advantages of no solvent residue, high utilization rate of electrode active substances, and a wide adjustable range of electrode thickness, and has become an advanced electrode preparation method.

[0003] In the dry electrode preparation process, the calendering process is a process in which the heated binder electrode powder containing a three-dimensional network structure passes through the gap between a pair or more pairs of horizontally rotating rollers facing each other, so that the material is subjected to extrusion and extension, and becomes a self-supporting electrode membrane with a certain thickness, width, and smooth surface. During the calendering process, when the binder passes through the roller gap, the rollers apply a large transverse pressure to the powder material. Coupled with the weight of the rollers themselves, during the film-forming process, the powder undergoes viscous flow on the one hand and elastic deformation on the other hand, resulting in a wavy edge at the edge of the self-supporting electrode membrane, which cannot be used in subsequent processes. Therefore, usually after the electrode membrane is formed and shaped, a trimming device is added before winding to trim the irregular parts at the edge of the electrode membrane. This part of the material cannot be directly reused and is usually discarded directly, resulting in waste of raw materials. Moreover, this part of the powder contains lithium, cobalt, nickel, manganese, or lithium iron phosphate compounds, which is likely to cause certain pollution to the environment. Summary of the Invention

[0004] In order to reduce the waste of electrode membrane materials and the pollution caused to the environment after the electrode membrane materials are discarded, this application provides a method for recycling dry-process electrode membranes.

[0005] The present application provides a method for recycling dry electrode membranes, wherein the trimmed portion of dry electrode powder after calendering into membranes is recycled as a recovered material, comprising the following steps:

[0006] Step S10, freezing the recycled material into a solid state at a first preset temperature, and then performing a vacuum drying process;

[0007] Step S20, coarsely crushing the material obtained in step S10 at a second preset temperature, wherein the second preset temperature is greater than the first preset temperature;

[0008] Step S30, subjecting the material obtained in step S20 to low-temperature airflow pulverization at a third preset temperature to obtain regenerated powder;

[0009] Step S40, mixing the regenerated powder obtained in step S30 with new powder as a preparation raw material, and preparing a dry electrode membrane using a dry electrode membrane preparation process;

[0010] Wherein, the first preset temperature, the second preset temperature and the third preset temperature are all less than 0°C.

[0011] By adopting the above scheme, the edge material trimmed after the electrode membrane is formed is frozen into a solid state in a low-temperature environment, then dried in a high vacuum environment, and then subjected to two low-temperature crushing treatments to obtain regenerated powder. By mixing the regenerated powder with the new powder, it can be used as a raw material for preparing a dry electrode membrane.

[0012] Since the raw material composition of the dry electrode membrane is simple and there is no water or other solvents, the scraps of the dry electrode membrane are dried and then crushed twice to different degrees from coarse to fine, and these steps are all carried out in an environment below 0°C. The recycled material becomes more brittle and easier to crush, so it is easier to obtain a powder with uniform particle size and fineness. There is no volatilization or loss of components during the processing of the recycled powder. Under the premise that the raw material components are fully mixed before calendering and film formation, the ratio of each raw material component in the recycled powder hardly changes. Therefore, the recycled powder can be mixed with the new powder to form the raw material for preparing the dry electrode membrane.

[0013] Optionally, the ratio of each component in the powder derived from the recycled material is consistent with the ratio of each component in the new powder.

[0014] Since the ratio of each raw material component in the recycled powder hardly changes, the ratio of each component in the powder from the recycled material is kept consistent with the ratio of each component in the new powder, which facilitates the performance control of the electrode membrane material mixed with the recycled powder and ensures the consistency of the product.

[0015] Optionally, the first preset temperature in step S10 is -20 to -10 °C, and the vacuum degree of the vacuum drying treatment is 0.1 to 130 Pa.

[0016] By freezing the recycled material into a solid state in a low-temperature environment of -20 to -10 °C and performing vacuum drying in a high-vacuum environment of 0.1 to 130 Pa, the recycled material can be frozen more thoroughly and dried more completely, facilitating more thorough crushing of the recycled material in the subsequent crushing step.

[0017] Optionally, the second preset temperature in step S20 is -10 to 0 °C; the third preset temperature in step S30 is -10 to 0 °C.

[0018] By controlling both crushing processes in a low-temperature environment of -10 to 0 °C, the material can always maintain low-temperature brittleness, which is beneficial for thorough crushing of the material.

[0019] Optionally, the mass ratio of the recycled powder to the new powder in step S40 is 3 - 6:4 - 7.

[0020] Optionally, the new powder in step S40 includes the following components in parts by weight:

[0021] 91 - 95.7 parts of active substance,

[0022] 3 - 6 parts of conductive agent,

[0023] 0.3 - 0.5 part of dispersant,

[0024] 1 - 2.5 parts of binder.

[0025] Optionally, the binder is a fluoropolymer.

[0026] Specifically, the fluoropolymer includes, but is not limited to, polymers such as PTFE, FEP, PFA, and PVDF. As a preferred embodiment, the above binder is PTFE resin, i.e., polytetrafluoroethylene resin. This binder is convenient for improving the tight adhesion between substances in the powder, thus facilitating that the powder will not disperse and is difficult to form a self-supporting film during the calendering process.

[0027] Optionally, the dispersant is nano-magnesium oxide, fumed silica, or fumed aluminum oxide.

[0028] By selecting a suitable dispersant, it is convenient for substances in the powder to be mixed more uniformly, improving the uniformity of the electrode film product.

[0029] Optionally, the conductive agent includes one or more of acetylene black, carbon black, carbon nanotubes, and graphene.

[0030] Optionally, in the step S40, the preparation process includes:

[0031] Step S41, performing a first premixing process on the active material, the conductive agent, and the dispersant;

[0032] Step S42, performing a second premixing process on the material obtained in the step S41 and the recycled powder;

[0033] Step S43, adding a binder to the material obtained in the step S42, and then performing a third premixing process;

[0034] Step S44, performing a heat preservation process on the material obtained in the step S43;

[0035] Step S45, performing a fibrillation process on the material obtained in the step S44 to obtain a powder for preparing a dry electrode film.

[0036] Optionally, in the step S45, a high-shear fibrillation device is used for the fibrillation process, and the shear rate of the fibrillation process is 1.3 - 1.65 Mach, and the processing temperature is 80 - 130 °C.

[0037] Through the above technical solution, using a high-shear fibrillation device can fibrillate the solid binder resin in the electrode powder material. The three-dimensional network structure is formed by the fibrillation of the solid binder, so that the electrode powder is cross-linked by this three-dimensional network structure, and then is pressed into a self-supporting electrode film through a calendaring process. Subsequently, the electrode film is thermally laminated on both sides of the current collector to finally obtain a dry electrode sheet. In this way, an electrode sheet with a higher tap density and higher energy density can be prepared. The electrode sheet with this three-dimensional network structure can prevent the active material particles from falling off during the charge and discharge cycles of the battery, and has good cycle stability.

[0038] The beneficial technical effects of this application:

[0039] 1. In this application, by recycling the trimmed scraps after calendering the dry electrode film into a film, they can be mixed with new powder to prepare a dry electrode film, with a recovery rate of 100%. This avoids waste of materials and also reduces the environmental pollution problem caused by the disposal of scraps.

[0040] 2. The utilization rate of the raw materials for preparing the dry electrode film in this application can reach 100%, reducing the production cost of lithium batteries.

[0041] 3. Compared with the dry electrode film prepared from brand-new raw materials, for the lithium battery prepared from the dry electrode film prepared from recycled materials, its electrochemical performance does not decrease. Therefore, through the recycling method of this application, the recycled materials can be restored to the same performance as brand-new raw materials. Description of the Drawings

[0042] Figure 1 It is a schematic flow chart of the dry electrode film recycling method of the embodiment of the present application. Specific implementation manners

[0043] The technical solutions of the present application will be described in detail below in conjunction with specific embodiments. In the following embodiments, unless otherwise specified, the raw materials used are commercially available products. Information such as ratios, equipment, and parameters not mentioned in Embodiments 1 to 4 are kept consistent.

[0044] The active materials involved in the present application include positive electrode active materials and negative electrode active materials. Among them, the positive electrode active materials include, but are not limited to, any one or at least two combinations of LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMn2O4, LiTi5O 12 , Li(Ni 0.5 Mn 1.5 )O4, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, LiNbO3 or a sulfur-carbon composite material; the negative electrode active material materials include, but are not limited to, any one or a combination of two or more of graphite, silicon, silicon-graphene, silicon-aluminum alloy, tin-based materials, graphene, asphalt carbon microspheres, activated carbon, carbon fiber, graphene, carbon nanotubes, carbon aerogels, transition metal oxides, conductive polymers, lithium-containing compounds, hard carbon materials or soft carbon materials.

[0045] Figure 1 It is a schematic flow chart of the dry electrode film recycling method of the embodiment of the present application. Refer to Figure 1 , an embodiment of the present invention provides a dry electrode film recycling method, which is used to recycle the trimmed part after calendering the dry electrode powder into a film as a recycling material, and specifically includes the following steps:

[0046] Step S10, freeze the recycling material into a solid state at a first preset temperature, and then perform vacuum drying treatment. Exemplarily, in specific implementation, the above treatment is carried out using a vacuum dryer. Exemplarily, in specific implementation, the first preset temperature is -20 to -10 °C, and the vacuum degree of the vacuum drying treatment is 0.1 to 130 Pa.

[0047] Step S20, perform low-temperature coarse crushing on the material obtained in step S10 at a second preset temperature, and the second preset temperature is higher than the first preset temperature. Exemplarily, in specific implementation, the low-temperature coarse crushing is carried out using a low-temperature crusher. Exemplarily, in specific implementation, the second preset temperature is -10 to 0 °C.

[0048] Step S30: Subject the material obtained in Step S20 to low-temperature airflow pulverization at a third preset temperature to obtain a regenerated powder. Exemplarily, in specific implementation, the low-temperature airflow pulverization treatment is carried out using a low-temperature airflow mill. Exemplarily, in specific implementation, the third preset temperature is -10 to 0 °C.

[0049] Step S40: Mix the regenerated powder obtained in Step S30 with a new powder as a preparation raw material, and prepare a dry electrode film by the preparation process of the dry electrode film.

[0050] Exemplarily, in specific implementation, the proportion of each component in the powder from the recycled material source is the same as the proportion of each component in the new powder.

[0051] Exemplarily, in specific implementation, the mass ratio of the regenerated powder to the new powder is 3-6:4-7. The new powder includes the following components in parts by weight: 91-95.7 parts of active material, 3-6 parts of conductive agent, 0.3-0.5 part of dispersant, and 1-2.5 parts of binder.

[0052] In this embodiment, the above-mentioned binder is a fluorine-containing polymer, including but not limited to polymers such as PTFE, FEP, PFA, and PVDF. As a preferred embodiment, the above-mentioned binder is PTFE resin, that is, polytetrafluoroethylene resin. This binder can facilitate the control of the production quality of the electrode.

[0053] In this embodiment, the above-mentioned dispersant is nano-magnesium oxide, fumed silica, or fumed aluminum oxide.

[0054] In this embodiment, the preparation process includes Step S41 to Step S45. Specifically,

[0055] Step S41: Perform a first premixing treatment on the active material, conductive agent, and dispersant. Exemplarily, in specific implementation, the first premixing treatment is carried out in a high-energy mixer, the cooling temperature ≤ 20 °C, the treatment time is 20-90 min, and the rotation speed is 300-1400 rpm.

[0056] Step S42: Perform a second premixing treatment on the material obtained in Step S41 and the regenerated powder. Exemplarily, in specific implementation, the second premixing treatment is carried out in a low-temperature mixer, the temperature is 0-5 °C, the treatment time is 5-10 min, and the rotation speed is 500-1300 rpm.

[0057] Step S43: Add the binder to the material obtained in Step S42, and then perform a third premixing treatment. Exemplarily, in specific implementation, the third premixing treatment is carried out in a low-temperature crusher, the temperature is 0-5 °C, the treatment time is 1-15 min, and the rotation speed is 200-600 rpm.

[0058] Step S44: Insulate the material obtained in step S43. In a preferred example, the above material can be insulated with a temperature adjustment of 30~100°C, and the insulation time is 5~40 min.

[0059] Step S45: Fibrize the material obtained in step S44 to obtain the powder for preparing the dry electrode film. Exemplarily, in specific implementation, a high-shear fibrilization device is used for fibrilization treatment. The shear speed of the fibrilization treatment is 1.3~1.65 Mach, the treatment temperature is 80~130°C, and the treatment time is 30~120 s.

[0060] The technical solution of the present invention will be further described below through specific embodiments.

[0061] Example 1

[0062] Example 1 is 2 positive electrode sheets prepared from brand-new raw materials, and the preparation steps are as follows:

[0063] S1: Weigh the cathode active material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, conductive agent carbon black, and dispersant nano-magnesium oxide, and mix them in a mass ratio of 94:3:0.5 to obtain the initial mixed material;

[0064] S2: Add binder PTFE to the initial mixed material obtained in S1 and mix them. The mass ratio of the cathode active material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 to the binder PTFE is 94:2.5;

[0065] S3: Insulate the material obtained in S2, with the insulation temperature being 80°C and the insulation time being 120 min;

[0066] S4: Use a high-shear fibrilization device to fibrilize the material in S3, and the shear speed of the fibrilization treatment is 1.5 Mach, and the treatment temperature is 100°C to obtain the target material;

[0067] S5: Use a heating roller to perform hot pressing on the target material to form a positive electrode film;

[0068] S6: Use a heating roller to press the positive electrode film and the current collector aluminum foil together, and trim to obtain the positive electrode sheet.

[0069] Example 2

[0070] Example 2 is two negative electrode sheets prepared using entirely new raw materials. The preparation steps are basically the same as those in Example 1, except that in Example 2, carbon nanotubes are used as the negative electrode active material, and copper foil is used as the current collector.

[0071] Example 3

[0072] Example 3 is two positive electrode sheets prepared by mixing the trimmed scraps after pressing in Example 1 with new powder. The specific steps are as follows:

[0073] S1: Freeze the trimmed scraps after pressing in Example 1 at -20 °C into a solid state, and perform vacuum drying treatment under a vacuum degree of 10 Pa;

[0074] S2: Coarsely crush the material obtained in S1 at -10 °C;

[0075] S3: Perform low-temperature airflow pulverization on the material obtained in S2 at -10 °C to obtain recycled powder;

[0076] S4: Weigh the positive electrode active material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, conductive agent carbon black, and dispersant nano-magnesium oxide, and mix and process them according to a mass ratio of 94:3:0.5 to obtain new powder;

[0077] S5: Mix the recycled powder obtained in S3 with the new powder in S4 according to a mass ratio of 3:4;

[0078] S6: Add binder PTFE to S5, and the mass ratio of the positive electrode active material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 to the binder PTFE is 94:2.5;

[0079] S7: Perform heat preservation treatment on the material in S6, with the heat preservation temperature being 80 °C and the heat preservation time being 120 min;

[0080] S8: Perform fibrillation treatment on the material in S7 using a high-shear fibrillation device, and the shear speed of the fibrillation treatment is 1.5 Mach, and the treatment temperature is 100 °C to obtain the target powder;

[0081] S9: Use a heating roller to perform hot pressing and forming treatment on the target powder to form a positive electrode film;

[0082] S10: Use a heating roller to press and bond the positive electrode film and the current collector aluminum foil, and trim to obtain the positive electrode sheet.

[0083] Example 4

[0084] Example 4 involves preparing 2 negative electrode sheets by mixing the trimmed scraps after lamination in Example 2 with new powder. The preparation steps are basically the same as those in Example 3, except that in Example 4, carbon nanotubes are used as the negative electrode active material and copper foil is used as the current collector.

[0085] Example 5

[0086] Example 5 is a battery assembled with the positive electrode sheets prepared in Examples 1 - 2 and the negative electrode sheets prepared in Examples 3 - 4. The specific assembly method is as follows:

[0087] Wind and stack the positive electrode sheet, negative electrode sheet, and separator to form an electrode core. The separator can be a PP / PE composite separator. Place it into the aluminum plastic film with punched pits, inject the electrolyte, perform a primary encapsulation, let it stand. After negative pressure formation, pierce the aluminum plastic film, vacuum extract the gas generated during formation, supplement the electrolyte, cut off the air bag, and perform a secondary encapsulation.

[0088] The specific battery products obtained by assembly are shown in Table 1.

[0089] Table 1

[0090]

[0091] Performance Test

[0092] Perform a cycle performance test on Battery A, Battery B, Battery C, and Battery D. The test method for the cycle performance test is as follows:

[0093] At an ambient temperature of 25°C, charge at a constant current of 1C with a constant voltage until 4.4V, with a cut-off current of 0.03C. Then discharge at a constant current of 1C until 3.0V. Repeat this cycle 500 times, record the discharge capacity in the 1st week, 100th week, 200th week, 300th week, 400th week, and 500th week, and calculate the capacity retention rate according to the following formula. The test results are shown in Table 2.

[0094] Capacity retention rate (%) = (discharge capacity in the last cycle / discharge capacity in the 1st cycle) × 100%

[0095] Table 2

[0096]

[0097] As can be seen from the data in Table 2, whether it is after 100 cycles or 500 cycles, the capacity retention rates of Battery A, Battery B, Battery C, and Battery D are basically the same. This shows that using the trimmed part after calendering into a film as the recycled material and mixing it with new powder to prepare the electrode film does not reduce its electrochemical performance. That is to say, the recycled material does not have a negative impact on the performance of the battery. This also indirectly shows that it is feasible to reuse the recycled material to prepare the electrode film after appropriate treatment.

[0098] This specific embodiment is only an interpretation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment that do not contribute creatively as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for recycling a dry electrode film, characterized in that, The trimmed part after calendering the dry electrode powder into a film is recycled as recycled material, including the following steps: Step S10: Freeze the recycled material into a solid state at a first preset temperature, and then perform vacuum drying treatment; Step S20: Coarsely crush the material obtained in Step S10 at a second preset temperature, where the second preset temperature is higher than the first preset temperature; Step S30: Grind the material obtained in Step S20 by low-temperature air flow at a third preset temperature to obtain recycled powder; Step S40: Mix the recycled powder obtained in Step S30 with new powder as a preparation raw material, and prepare a dry electrode film by the preparation process of the dry electrode film; Among them, the first preset temperature, the second preset temperature, and the third preset temperature are all less than 0°C; The new powder in Step S40 includes the following components in parts by weight: 91 - 95.7 parts of active material, 3 - 6 parts of conductive agent, 0.3 - 0.5 part of dispersant, 1 - 2.5 parts of binder.

2. The dry electrode film recycling method according to claim 1, wherein The ratio of each component in the powder from which the recycled material is derived is the same as the ratio of each component in the new powder.

3. The dry electrode film recycling method according to claim 1, characterized in that The first preset temperature in Step S10 is -20 to -10°C, and the vacuum degree of the vacuum drying treatment is 0.1 - 130 Pa.

4. The dry electrode film recycling method according to claim 1, characterized in that, The second preset temperature in Step S20 is -10 to 0°C; the third preset temperature in Step S30 is -10 to 0°C, and the second preset temperature and the third preset temperature are not 0°C.

5. The dry electrode film recycling method according to claim 1, characterized in that The mass ratio of the recycled powder to the new powder in Step S40 is 3 - 6:4 - 7.

6. The dry electrode film recycling method according to claim 1, characterized in that, The binder is a fluorine-containing polymer.

7. The dry electrode film recycling method according to claim 6, characterized in that, The dispersant is nano magnesium oxide, fumed silica, or fumed aluminum oxide.

8. The method for recycling the dry electrode film according to claim 6, characterized in that, In Step S40, the preparation process includes: Step S41: Perform a first premixing treatment on the active material, the conductive agent, and the dispersant; Step S42: Perform a second premixing treatment on the material obtained in Step S41 and the recycled powder; Step S43: Add a binder to the material obtained in Step S42, and then perform a third premixing treatment; Step S44: Perform a heat preservation treatment on the material obtained in Step S43; Step S45: Perform a fibrillation treatment on the material obtained in Step S44 to obtain powder that can be used to prepare a dry electrode film.

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