A method for preparing a thick electrode based on a dry film forming process

Abstract

The present application relates to a kind of methods for preparing thick electrode based on dry film preparation process, comprising the following steps: (1) according to certain proportion, active material, forming auxiliary agent, non-fibrous and fibrous binder, pore-forming agent, leveling agent are weighed;(2) active material and non-fibrous binder, active material and forming auxiliary agent, pore-forming agent, fibrous binder are respectively mixed to carry out high-speed stirring shear;(3) adjusting roller press, the mixed powder is rolled, and electrode film is obtained;(4) electrode film is placed into moulding press and heated and pressed, to remove pore-forming agent;(5) with spatula, even coating is applied on the surface of electrode, and again moulding is pressed, to improve the flatness of electrode film, and improve the bonding force of electrode film and current collector;(6) adjusting the temperature of roller press, axle distance, and electrode film is laminated and rolled with current collector, and thick electrode is obtained.Compared with prior art, the present application can prepare homogeneous thick electrode without crack, and improve area load capacity.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology and relates to a method for preparing thick electrodes based on a dry film-forming process. Background Technology

[0002] Industry and academia have proposed many strategies to improve the energy density of battery systems, achieving or realizing 500 Wh·kg⁻¹. -1 Even higher goals exist, such as developing electrode materials with high specific capacity at the material level, using electrodes with low porosity at the electrode level, developing "lean electrolyte" technology at the battery level, and employing CTP (Cell to Pack) and CTC (Cell to Chassis) technologies at the battery pack level to reduce the use of packaging materials. However, these energy density goals are all based on the material or electrode level, and the actual energy density of battery systems still needs to be improved. Compared to other energy density improvement strategies, thick electrode design does not change the energy storage mechanism of lithium-ion batteries and is the easiest to implement. It can reduce energy attenuation from the material level to the electrode level and from the electrode level to the battery level, thereby increasing the battery's energy density. Moreover, thick electrode design is not incompatible with other improvement strategies and can work together with new materials, new electrolytes, and other strategies to improve battery energy density.

[0003] The key to improving battery energy density through thick electrode design lies in increasing the areal load on a single electrode, thereby reducing the use of inactive materials such as separators and current collectors within the entire battery system. The mechanism by which thick electrode design improves battery energy density is by reducing the mass percentage of inactive components like separators and current collectors. However, the space available for thick electrode design to increase battery energy density is extremely limited. Therefore, further increasing electrode thickness may only result in a limited increase in energy density while compromising battery power performance. Thus, there exists an optimal range for thick electrode technology to improve battery energy density without compromising other battery performance characteristics.

[0004] In terms of preparation, existing commercially available battery electrodes mainly employ wet coating technology, which involves uniformly mixing electrode active materials and additives in a solvent to prepare a slurry and then coating it onto a current collector. An essential step in this process is drying the solvent in the electrode. Similar to other drying processes, when the electrode thickness is relatively large, cracking can occur during the drying process. The preparation of thick electrodes requires overcoming this thickness limit related to mechanical properties, namely the critical cracking thickness (CCT).

[0005] In terms of application, as the electrode thickness increases, the path for ions and electrons to reach all active sites within the electrode inevitably lengthens. Based on the electrochemical energy storage mechanism, at higher rates, ions may not reach the corresponding active sites in time due to slow diffusion kinetics, resulting in the electrode not utilizing its full capacity. Therefore, under certain required rate conditions, the capacity contribution of a thick electrode may be limited to the thickness range of a conventional electrode. The design of thick electrodes requires improving this thickness limit related to electrochemical performance, namely the limited penetration depth (LPD).

[0006] Currently, the mainstream fabrication process for lithium-ion battery electrodes is wet coating technology, which is difficult to match with thick electrode designs. In addition, wet coating technology also has the following problems: huge energy consumption; serious pollution; high cost; and easy damage to the mechanical and electrochemical properties of the electrode.

[0007] In addition, dry film-forming technologies have been developed, such as the typical powder coating process, which mainly consists of three steps. First, active materials, conductive agents, and binder powders are mixed into a homogeneous mixture. Then, the mixed powder is sprayed onto a current collector. Finally, the current collector carrying the powder is hot-pressed, causing the binder to melt and adhere the powder to the current collector. Key spraying processes have been achieved through various methods, such as pulsed laser and sputtering deposition. In pulsed laser deposition, the material is evaporated and deposited onto a substrate by focusing a laser on the material to be deposited. However, the deposited film must withstand very high annealing temperatures (650-800°C), while sputtering deposition can reduce this temperature to 350°C. Although these two processes are representative of spraying technologies, in addition to the effects of high temperatures, their deposition rates are also very slow, making them unsuitable for large-scale manufacturing.

[0008] Binder fibrillation involves the binder forming a cross-linked network under shear force, fixing the uniformly mixed electrode powder together. The dry-process powder after binder fibrillation can be directly calendered using a roll press to obtain a self-supporting electrode film with good mechanical properties. The adhesion between the electrode film and the current collector affects battery performance; weak adhesion leads to increased electrode impedance. Currently, carbon-coated current collectors are often used to improve adhesion between the current collector and the electrode film. However, improving adhesion solely through the current collector cannot adequately meet production requirements. Many dry-process electrode films on the market fail due to delamination between the electrode film and the current collector. Summary of the Invention

[0009] The purpose of this invention is to provide a dry film-forming method based on binder fibrillation, which can prepare crack-free, homogeneous, thick electrodes. Thick electrodes can better improve the energy density of lithium batteries, exhibiting higher load capacity and greater areal capacity. Adding a non-fibrous binder, which forms micron-sized particles after pulverization, can improve the mechanical and electrochemical properties of the electrode film. Adding a pore-forming agent can create a porous structure inside the electrode, which is beneficial for improving the ion transport rate within the electrode and increasing energy density. A leveling agent can fill the surface micropores created by pore formation, thereby improving surface smoothness and simultaneously enhancing the adhesion between the electrode film and the current collector. Traditional dry-process electrode sheets are prone to failure due to peeling between the electrode film and the current collector. By adding activated carbon powder to the epoxy resin, the adhesion between the electrode film and the carbon-coated aluminum foil current collector can be effectively improved, increasing the peel strength of the electrode film and reducing electrode failure caused by peeling.

[0010] The objective of this invention can be achieved through the following technical solutions: A method for preparing thick electrodes based on a dry film-forming process includes the following steps: (1) Weigh out the active material, molding aid, non-fibrous binder, fibrous binder, pore-forming agent, and leveling agent in a certain proportion; (2) Place some of the active material and non-fibrous binder into a crushing cup, place the crushing cup on a mixer, and shear and stir the resulting mixed powder at a certain speed for a certain time. (3) Place the remaining active material mixed with molding aid, pore-forming agent and fiber binder powder into a mortar cup, place the mortar cup on a mixer, and shear and stir the mixed powder at a certain speed for a certain time. (4) Mix the two mixed powders obtained in steps (2) and (3) above evenly, adjust the roller press, roll the mixed powder a certain number of times to obtain an electrode film of the required thickness, and then cut the electrode film to obtain an electrode film of appropriate size. (5) Place the cut electrode film into a rectangular mold, place the mold into a hot press, and heat and press it; (6) Use a spatula to evenly apply the leveling agent to the surface of the electrode film after hot pressing, and then heat and press the electrode film placed in the mold again; (7) Shear the current collector, adjust the size of the current collector, and attach the current collector to the electrode film of step (6) so that the electrode film can be completely pressed on the current collector. (8) Adjust the temperature and roller gap of the roller press, and roll the current collector and the electrode film together to obtain a composite electrode with a suitable thickness. Finally, after cutting and drying, a thick electrode sheet is obtained, which is the target product.

[0011] Furthermore, the active material is lithium iron phosphate (LFP), ternary cathode nickel cobalt manganese NCM622, silicon carbide material, graphite or activated carbon (AC, model YP-50F).

[0012] Furthermore, the molding aid is activated carbon (AC, model YP-50F).

[0013] Furthermore, the non-fibrous binder is carboxymethyl cellulose (CMC).

[0014] Furthermore, the fibrous adhesive is polytetrafluoroethylene (PTFE).

[0015] Furthermore, the pore-forming agent is ammonium bicarbonate (NH4HCO3).

[0016] Furthermore, the leveling agent is a mixture of activated carbon (AC, model YP-50F) and epoxy resin.

[0017] Furthermore, the mass ratio of the active material, molding aid, and binder is (8~9):(0.5~1):(0.5~1), and the mass ratio of the non-fibrous binder to the fibrous binder in the binder can be 1:4.

[0018] Furthermore, the mass of the pore-forming agent NH4HCO3 is 5% of the total mass of the above-mentioned active materials, molding aids and binders.

[0019] Furthermore, the leveling agent is an epoxy resin containing 0.1 to 0.5 wt% activated carbon, preferably 0.3 wt%.

[0020] Furthermore, the non-fibrous binder after high-speed mixing and shearing treatment is in a pulverized state.

[0021] Furthermore, the mixed powder containing fibrous binder after high-speed stirring and shearing treatment showed an adhesive state.

[0022] Furthermore, the rotation speed of the shearing process is 20,000 to 25,000 rpm, preferably 22,000 rpm; the processing time is 8 to 12 minutes, preferably 10 minutes, with a 1-minute cooling period after every 2.5 minutes of stirring.

[0023] Furthermore, during the rolling process of the mixed powder, the thickness of the electrode film after rolling needs to be measured and compared with the required thickness. If the thickness of the electrode film after rolling does not meet the requirements, the shaft distance of the rolling mill is adjusted and the rolling is performed again. This process is repeated until an electrode film of suitable thickness is obtained.

[0024] Furthermore, the thickness of the obtained electrode film (i.e., the electrode film before applying the leveling agent) is 100~400μm.

[0025] Furthermore, the mold is a rectangular steel plate with dimensions of 15cm × 20cm.

[0026] Furthermore, in step (5), the pressure during molding to remove the pore-forming agent is 20~50MPa, the final temperature is 90~120℃, the heating rate is 1℃ / s, and the time is 5~40min.

[0027] Furthermore, in step (6), the amount of leveling agent applied is 0.01~0.02 g / cm³. 2 .

[0028] Furthermore, in step (6), the molding pressure is 20~50MPa when the leveling agent is added, the final temperature is 60~90℃, the heating rate is 1℃ / s, and the time is 10~30min.

[0029] Furthermore, the current collector used is a single-sided carbon-coated aluminum foil.

[0030] Furthermore, the pressure during the current collector and electrode film bonding roll pressing is 50 MPa, the temperature is 180℃, and the roll speed is 0.2 r·min. -1 .

[0031] Compared with existing technologies, this invention significantly improves the peel strength between the electrode film and the current collector by thoroughly pulverizing and fibrillating the adhesive and applying a leveling agent to the electrode film, thereby reducing electrode failure caused by peeling between the electrode film and the current collector. It can prepare self-supporting electrode films with good mechanical properties and electrodes with significantly increased thickness, thereby improving their areal loading and specific capacity. Attached Figure Description

[0032] Figure 1 The electrode structures and equivalent models of the planar electrode (a) and the porous electrode (b) are shown.

[0033] Figure 2 The ion diffusion impedance (a) and charge transfer impedance (b) vary with electrode thickness.

[0034] Figure 3 Available in thicknesses of 108 (black), 210 (red), 305 (blue), and 410 (green). The diffusion characteristics of the electrode.

[0035] Figure 4 Available in thicknesses of 108 (black), 210 (red), 305 (blue), and 410 (green). Electrode rate performance: mass specific capacity (a), area specific capacity (b).

[0036] Figure 5The peel force versus peel displacement curves are shown for surfaces with and without surface leveling agent (green) and without surface leveling agent (black).

[0037] Figure 6 To adopt 800 The morphology of the doctor blade coated electrode before it is dried.

[0038] Figure 7 To adopt 800 scraper (a) and 1000 (b) Morphology of the doctor blade coated electrode after drying.

[0039] Figure 8 The ratio of active material: molding aid: binder is 90:5:5, by mass. The roller temperature is preheated to 120℃ (a) and 110℃ (b), and the molding effect of the mixed powder after shearing is observed.

[0040] Figure 9 The ratio of active material: molding aid: binder is 85:10:5 by mass. The preheating roller temperature is 120°C. The forming effect of the electrode film is (a). Further rolling is used to adjust the thickness of the electrode film. The electrode film is easily torn tangentially along the rotation direction of the parallel roller (b).

[0041] Figure 10 A comparison of the energy density of batteries fabricated with electrode films after changing the rolling temperature from 180℃ (dryYP-50-2) to 160℃ (dryYP-50-3).

[0042] Figure 11 The energy density of electrode film batteries made by modifying binders, pore-forming agents, and leveling agents.

[0043] Figure 12 The electrode film surface peeling is shown in the figures for (a) without leveling agent and (b) with leveling agent.

[0044] Figure 13 This is a flowchart illustrating the fabrication process of the thick electrode according to the present invention. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0046] Electrochemical impedance spectroscopy (EIS) is an effective method for studying the internal resistance of batteries. Regarding the internal resistance of porous electrodes, many studies assume the electrode / electrolyte interface is a simple plane, thus obtaining the apparent charge transfer impedance (R0). ct ),like Figure 1 a. However, due to the complex pore distribution in porous electrodes, the electrode / electrolyte interface in porous electrodes also exhibits "porosity," such as... Figure 1b. Using this assumption, it is difficult to accurately explain the rate performance of actual batteries. This means that the electrochemical processes within porous electrodes exhibit typical time dependence, and the extended charge-mass transfer pathways in thick electrodes amplify this characteristic.

[0047] Figure 2 a and b are Nyquist plots of LFP electrodes with different thicknesses prepared in Example 2 below, showing SOC at 0% and 50%, respectively. In the Nyquist plot at 0% SOC, the nearly vertical straight line in the low-frequency region indicates electrical blocking behavior within the porous electrode in the absence of charge transfer. The oblique line in the high-frequency region, forming a 45-degree angle with the real axis, represents the ion diffusion resistance in the porous electrode and reflects R... ion The 45-degree diagonal line lengthens with increasing electrode thickness, indicating that the ion diffusion resistance in the porous electrode increases with increasing electrode thickness. In the Nyquist plot at 50% SOC, the diameter of the semicircle in the low-frequency region represents the magnitude of the charge transfer resistance within the porous electrode. Similarly, the diameter of the semicircle in the low-frequency region reflects the magnitude of the charge transfer resistance within the porous electrode. ct The semicircular diameter increases with the increase of electrode thickness, meaning that the charge transfer impedance in the porous electrode also increases with the increase of electrode thickness.

[0048] Plot the peak current of each electrode against the half-power of the scan rate. The slope of the fitted line is shown in [reference needed]. Figure 3 As the electrode thickness increases, the slope of the fitted line gradually decreases, indicating a corresponding decrease in the lithium-ion diffusion coefficient. This also means that ion diffusion behavior in the electrode becomes increasingly restricted with increasing electrode thickness.

[0049] The actual magnification of the thick electrodes of different thicknesses prepared in Example 2 below is as follows: Figure 4 As shown in the figure, the specific capacity of each electrode can reach 160 mAh·g at 0.05C, based on the change in specific capacity. -1 At 0.1C, 410 The specific capacity of the electrode is 150 mAh·g -1 Around [a certain value], the specific capacity begins to fall below that of thicker electrodes of other thicknesses. At a discharge current density of 0.5C, the specific capacity of an electrode with a thickness of 108 [units unspecified] is [unspecified]. The electrode has a capacity of 145.6 mAh·g -1 High specific capacity, but with thicknesses of 210, 305 and 410. The specific capacities of the electrodes were 75.7%, 47.6%, and 34.2% of the former, respectively; at 1C, the specific capacities of each electrode were 127.9, 61.6, 33.3, and 23.3 mAh·g, respectively. -1 Further increase the current density, 305 and 410. The specific capacity of the electrodes is close to 0, while that of 108 and 210 is close to 0. The electrodes still have 89.6 and 24.4 mAh·g, respectively. -1 The discharge specific capacity. Considering the areal specific capacity performance of thick electrodes, although the load increases proportionally with thickness, at higher areal current densities, 305 and 410... The capacity that the electrode can release is close to 205. The electrodes.

[0050] Traditional dry-process electrode sheets are prone to failure due to peeling between the electrode film and the current collector. Adding activated carbon powder to the epoxy resin can effectively improve the adhesion between the electrode film and the carbon-coated aluminum foil current collector, increasing the peel strength of the electrode film and thus reducing electrode failure caused by peeling. Figure 5 The peel force versus peel displacement curves are shown for surfaces with and without surface leveling agent (green) and without surface leveling agent (black).

[0051] This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiment.

[0052] In the following embodiments, the raw materials such as lithium iron phosphate and epoxy resin used are specifically sourced from enterprises, such as LFP being Likai D50 from Taiwan, China: 4±2. The activated carbon AC was Kuraray YP-50F, the PTFE was DuPont 60x, the CMC was Daicel NE-000243, the NH4HCO3 was Greatent's NH3: 21.0-22.0%, and the epoxy resin was Mackerlin 6002. Unless otherwise specified, all other raw materials or processing techniques are commercially available and conventional in the field.

[0053] Example 1: A method for preparing thick electrodes based on a dry film-forming process includes the following steps: (1) Weigh LFP, molding aid (AC, model YP-50F) and binder (CMC:PTFE=1:4) in a mass ratio of 85:8:7, and then weigh 5% of the total mass of the above mixture of NH4HCO3.

[0054] (2) Mix 30% of the total mass of LFP with CMC in a blending cup and blend at 22000 r·min -1 The mixing powder was sheared at a certain speed for 10 minutes, and after every 2.5 minutes of stirring, it was cooled for 1 minute to complete the pulverization process of the non-fibrous binder.

[0055] (3) Mix the remaining LFP with AC, PTFE and NH4HCO3 in a crushing cup and crush at 22000 r·min -1 The mixing powder was sheared at a certain speed for 10 minutes, and after every 2.5 minutes of stirring, it was cooled for 1 minute to complete the fibrillation of the fibrous binder.

[0056] (4) After mixing, the mixed powder is transferred into the feed port of the roller press, the roller temperature is raised to 120°C, the roller gap is set to 200μm, the pressure is 50MPa, and then the electrode film with self-supporting properties can be obtained by direct roller pressing. By gradually adjusting the roller gap to 200, 100 and 50μm and performing repeated roller pressing, a 110μm LFP electrode film can be obtained (since the roller gap of the roller press used in the example is difficult to keep constant during roller pressing, and the lithium iron phosphate material is difficult to roll to a thinner thickness, it is necessary to repeat the roller pressing at a roller gap lower than the final thickness. The specific roller gap depends on the specific thickness requirement).

[0057] (5) After cutting the electrode film, place it into a rectangular steel plate mold with dimensions of 15cm × 20cm. Then, place the mold under a hot press for heating and pressurization. The hot pressing pressure is 50MPa, the final temperature is 120℃, the heating rate is 1℃ / s, and the time is 30min. NH4HCO3 will completely decompose above 60℃, and the generated gas will form pores inside the electrode film.

[0058] (6) Pour a certain mass of epoxy resin into a 500ml beaker, disperse AC in the epoxy resin, the mass fraction of AC is 0.3%, and stir with an electric stirrer for 15 minutes to obtain the leveling agent. Use a spatula to evenly apply the leveling agent to the electrode surface. Taking an electrode film with a size of 15cm×20cm as an example, the amount of leveling agent applied is 0.0167 / cm. 2 The electrodes placed in the mold were then heated and pressurized again at a pressure of 50 MPa, an end temperature of 90°C, a heating rate of 1°C / s, and a time of 20 min.

[0059] (7) Cut the carbon-coated aluminum foil current collector and attach the current collector to the LFP electrode film so that the electrode film can be completely pressed on the current collector.

[0060] (8) Select an appropriate roller spacing based on the obtained electrode film thickness, and adjust the roller speed to 0.20 r·min. -1 The roller is preheated to 180°C, and the electrode film and single-sided carbon-coated aluminum current collector are bonded together. After one rolling process, the LFP thick electrode can be obtained.

[0061] (9) Use a Norwegian circular sampler to cut the electrode sheet into 12 mm diameter electrode sheets for use in coin cells. Then, transfer the cut electrode sheets into a vacuum oven and dry them at 120°C for 12 h before taking them out for coin cell assembly.

[0062] The electrochemical performance test results of the electrode sheet prepared in Example 1, which was further fabricated into a coin cell, are as follows: Figure 10 dryYP-50-1 and Figure 11 The PTFE+CMC dot-line diagram is shown below.

[0063] Furthermore, based on the above embodiment 1, for ternary electrode materials, the process parameters that need to be adjusted are to gradually adjust the roller spacing to 200, 50, and 0. Multiple rolling processes can achieve 105. The NCM electrode film (the reason why the roll gap is less than the final electrode film thickness is the same as above); for silicon-carbon materials, the process parameters that need to be adjusted are to gradually adjust the roll gap to 200 and 0. Multiple rolling processes can achieve 100 The Si / C electrode film (the reason why the roller gap is less than the final electrode film thickness is the same as above); for graphite materials, the process parameters that need to be adjusted are to control the mass ratio of dry powder to Gr:AC:binder = 85:10:5, and gradually adjust the roller gap to 200 and 0. Multiple rolling processes can achieve 100 The graphite electrode film (the reason why the roller gap is less than the final electrode film thickness is the same as above); for activated carbon materials, the process parameters that need to be adjusted are to control the mass ratio of dry powder to AC: binder = 90:10, and gradually adjust the roller gap to 200 and 0. Multiple rolling processes can achieve a yield of 60. The AC electrode film (the reason why the roller gap is less than the final electrode film thickness is the same as above). Process steps (5) to (9) are the same as LFP.

[0064] Example 2: A simplified method for fabricating thick electrodes based on a dry film-forming process includes the following steps: (1) Weigh LFP, molding aid (AC, model YP-50F) and binder (CMC:PTFE=1:4) in a mass ratio of 85:8:7.

[0065] (2) Mix 30% of the total mass of LFP with CMC in a blending cup and blend at 22000 r·min -1 The mixing powder was sheared at a certain speed for 10 minutes, and after every 2.5 minutes of stirring, it was cooled for 1 minute to complete the pulverization process of the non-fibrous binder.

[0066] (3) Mix the remaining LFP with AC and PTFE in a crushing cup and crush at 22000 r·min -1 The mixing powder was sheared at a certain speed for 10 minutes, and after every 2.5 minutes of stirring, it was cooled for 1 minute to complete the fibrillation of the fibrous binder.

[0067] (4) After mixing, the mixed powder is transferred to the feed port of the roller press. The roller temperature is raised to 120°C, the roller gap is set to 200 μm, and the pressure is 50 MPa. Then, the electrode film with self-supporting properties can be obtained by direct roller pressing. The roller gap is gradually adjusted and repeated roller pressing is performed to finally obtain 108, 210, 305 and 410. Four thicknesses of LFP electrode film.

[0068] (5) Cut the carbon-coated aluminum foil current collector and attach the current collector to the LFP electrode film so that the electrode film can be completely pressed on the current collector.

[0069] (6) Select an appropriate roller spacing based on the obtained electrode film thickness, and adjust the roller speed to 0.20 r·min. -1 The roller is preheated to 180°C, and the electrode film and single-sided carbon-coated aluminum current collector are bonded together. After one rolling process, the LFP thick electrode can be obtained.

[0070] (7) Use a Norwegian circular sampler to cut the electrode sheet into 12 mm diameter electrode sheets for use in coin cells. Then, transfer the cut electrode sheets into a vacuum oven and dry them at 120°C for 12 h before taking them out for coin cell assembly.

[0071] Comparative Example 1: Using a conventional electrode as Comparative Example 1, its thickness is 70 mm. It was purchased from KELU and is a conventional lithium iron phosphate electrode.

[0072] Comparative Example 2: Traditional wet coating techniques are costly in terms of drying and recycling due to the use of toxic NMP solvent and the need for drying to remove the solvent. Furthermore, the presence of a critical cracking thickness makes it difficult to produce crack-free coatings exceeding 200 mm. The wet-process thick electrode is used, while the dry film-forming technology can avoid the use of solvents, eliminate the solvent drying step, avoid cracking of the electrode during the drying process, and greatly increase the electrode thickness.

[0073] To prepare a wet electrode, taking the LFP positive electrode as an example, the corresponding material ratio is LFP:Super P (conductive agent):PVDF (binder) = 90:4:6, based on mass ratio. First, weigh the corresponding LFP, Super P, and 5 wt.% PVDF solution into a 30 ml mixing container (the total solid mass of a single mixing is 10 g). Then, add NMP solvent to adjust the solid content of the entire system to 27%. Next, transfer the mixing container to a planetary centrifuge and set the stirring program to 700 r·min. -1 Premix for 30 seconds, then at 2000 r·min -1 Mix quickly for 2 minutes, then reduce to 1000 r·min. -1 Mix slowly for 30 seconds. After mixing, use a spatula to take an appropriate amount of slurry and place it on a single-sided carbon-coated aluminum current collector. Use 800 and 1000... A scraper evenly spreads the slurry onto the current collector. After coating, the electrode is transferred to a forced-air drying oven at 80°C to remove the solvent, and left overnight. The dried electrode is then measured using a thickness gauge at 800 mm. The electrode film coated by the doctor blade is approximately 200 μm thick. No obvious cracks were observed (see Figure 7 a); and after 1000 The average thickness of the electrode film after blade coating is approximately 300 mm. However, obvious cracks can be observed (see Figure 7 b).

[0074] Comparative Example 3: The ratio of LFP dry electrode was adjusted to LFP:AC:binder = 90:5:5 (by mass). Other process parameters remained the same as in Example 1. The sheared mixed powder could not be formed by roller pressing. See [link to example]. Figure 8 a.

[0075] Comparative Example 4: Compared to Example 1, the rolling temperature was changed to 110°C, and the results are as follows: Figure 8 b. The molding effect of the mixed powder after roller pressing is improved but still not good. The structure of the roller-pressed electrode film obtained at 110℃ is loose and the shape of the electrode film is irregular and uneven.

[0076] Comparative Example 5: Compared to Example 1, the formulation was adjusted to 85:10:5, while the proportion of molding aid remained at 10 wt.%. Using the same preheated roller temperature of 120°C, the sheared powder was rolled, and the electrode film forming effect was observed to be excellent. Figure 9a. However, during subsequent further rolling to adjust the electrode film thickness to the experimental requirements, the electrode film is prone to tearing tangentially along the direction parallel to the roller rotation direction, see... Figure 9 b. Its mechanical properties still need improvement. This degree of tearing means that the network formed by the fibrillation of the binder cannot fix the active particles.

[0077] Comparative Example 6: Compared to Example 1, most aspects are the same, except that the electrode film bonding temperature with the current collector is changed from 180°C to 160°C. The results are as follows. Figure 10 As shown, it can be seen that the energy density of Comparative Example 6 (dryYP-50-3) is less than that of the electrode sheet rolled at 180°C in Example 1 (dryYP-50-1).

[0078] Comparative Example 7: Compared to Example 1, the binder was entirely PTFE, and other process parameters were the same as in Example 1. The energy density of the resulting electrode film was as follows: Figure 11 As shown in the PTFE dot plot, the battery energy density decreases at low rates compared to Example 1 (PTFE+CMC).

[0079] Comparative Example 8: Compared to Example 1, the addition of pore-forming agent and leveling agent was omitted, while other process parameters remained the same as in Example 1. The energy density of the resulting electrode film was as follows: Figure 11 As shown in the dot-line graph without pore-forming agent, the battery energy density is significantly lower than that of Example 1 (PTFE+CMC).

[0080] Comparative Example 9: Compared to Example 1, no activated carbon was added to the leveling agent, i.e., it was all epoxy resin. Other process parameters were the same as in Example 1, and the resulting electrode film energy density was as follows: Figure 11 As shown in the dotted line graph of the pore-forming agent without AC, the battery energy density is significantly lower than that of Example 1 (PTFE+CMC).

[0081] Comparative Example 10: Compared to Example 1, the leveling agent was omitted, while other process parameters remained the same as in Example 1, such as... Figure 12 As shown in (a), when adhesive tape is applied to the surface of the active material of the electrode membrane and then peeled off at 180°, the electrode membrane is easily peeled off from the current collector surface. Figure 12 (b) The electrode film peeling condition after the addition of leveling agent, which was not completely peeled off.

[0082] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing thick electrodes based on a dry film-forming process, characterized in that, Includes the following steps: (1) Weigh out the active material, molding aid, non-fibrous binder, fibrous binder, pore-forming agent, and leveling agent in a certain proportion; (2) Place some of the active material and non-fibrous binder into a crushing cup, place the crushing cup on a mixer, and shear and stir the resulting mixed powder at a certain speed for a certain time. (3) Place the remaining active material mixed with molding aid, pore-forming agent and fiber binder into another mortar cup, place the mortar cup on a mixer, and shear and stir the mixed powder at a certain speed for a certain time. (4) Mix the powder obtained in steps (2) and (3) evenly, adjust the roller press, roll the powder a certain number of times, and then cut it to obtain an electrode film of the required thickness and appropriate size. (5) Place the cut electrode film into a rectangular mold, place the mold into a hot press, and heat and press it; (6) Use a spatula to evenly apply the leveling agent to the surface of the electrode film after hot pressing, and then continue to heat and press the electrode film placed in the mold again; (7) Shear the current collector, adjust the size of the current collector, and attach the current collector to the electrode film obtained in step (6) so that the electrode film can be completely pressed on the current collector; (8) Adjust the temperature and roller gap of the roller press, and roll the current collector and the electrode film together to obtain a composite electrode with a suitable thickness. Finally, after cutting and drying, a thick electrode sheet is obtained, which is the target product. The active material is lithium iron phosphate; The molding aid is activated carbon; The non-fibrous binder is carboxymethyl cellulose; The fibrous binder is polytetrafluoroethylene; The pore-forming agent is ammonium bicarbonate; The mass ratio of the active material, molding aid and the two binders is 85:8:7, and the mass ratio of the non-fibrous binder to the fibrous binder is 1:

4. The pore-forming agent comprises 5% of the total mass of the active material, molding aid, and two binders; The leveling agent is a mixture of activated carbon and epoxy resin, wherein the activated carbon content is 0.1~0.5 wt% by mass. In step (8), the pressure during the bonding and rolling of the current collector and electrode film is 50 MPa, the temperature is 180 °C, and the roller speed is 0.2 r·min. -1 .

2. The method for preparing thick electrodes based on a dry film-forming process according to claim 1, characterized in that, During high-speed mixing and shearing: mixing is carried out in time intervals, and after each mixing, the mixture is cooled for a period of time before mixing is continued. The high-speed stirring and shearing treatment speed is 20,000~25,000 rpm, and the treatment time is 8~12 min.

3. The method for preparing thick electrodes based on a dry film-forming process according to claim 1, characterized in that, In step (4), during the rolling process of the mixed powder, the thickness of the electrode film after rolling is also measured and compared with the required thickness. When the thickness of the electrode film after rolling does not meet the requirements, the shaft distance of the rolling mill is adjusted and the rolling is performed again. This process is repeated until an electrode film of suitable thickness is obtained.

4. The method for preparing thick electrodes based on a dry film-forming process according to claim 1, characterized in that, In step (5), the hot pressing pressure is 20~50MPa, the final temperature is 90~120℃, the heating rate is 1℃ / s, and the time is 5~40min.

5. The method for preparing thick electrodes based on a dry film-forming process according to claim 1, characterized in that, In step (6), the hot pressing pressure is 20~50MPa, the final temperature is 60~90℃, the heating rate is 1℃ / s, and the time is 10~30min.

6. The method for preparing thick electrodes based on a dry film-forming process according to claim 1, characterized in that, The current collector used is a single-sided carbon-coated aluminum foil.

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