CN117936686A

CN117936686A - Method for preparing thick electrode based on dry method film making process

Info

Publication number: CN117936686A
Application number: CN202410074336.6A
Authority: CN
Inventors: 郑俊生; 郎啸翰; 邵嘉诚
Original assignee: Tongji University
Current assignee: Tongji University
Priority date: 2024-01-18
Filing date: 2024-01-18
Publication date: 2024-04-26

Abstract

The invention relates to a method for preparing a thick electrode based on a dry-method membrane-making process, which comprises the following steps: (1) Weighing active materials, forming auxiliary agents, non-fibrosis and fibrosis binders, pore formers and leveling agents according to a certain proportion; (2) Respectively mixing an active material with a non-fibrous binder, a forming auxiliary agent, a pore-forming agent and a fibrous binder, and stirring and shearing at a high speed; (3) Regulating a roller press, and rolling the mixed powder to obtain an electrode film; (4) Placing the electrode film into a molding press for heating and pressurizing to remove pore-forming agent; (5) Uniformly smearing a proper amount of leveling agent on the surface of the electrode by using a spatula, and performing mould pressing again to improve the surface evenness of the electrode film and improve the binding force of the electrode film and the current collector; (6) And (3) adjusting the temperature and the wheelbase of the roller press, and laminating and rolling the current collector and the electrode film to obtain the thick electrode. Compared with the prior art, the invention can prepare the homogeneous thick electrode without cracks, improve the area loading capacity and the like.

Description

Method for preparing thick electrode based on dry method film making process

Technical Field

The invention belongs to the technical field of electrode materials, and relates to a method for preparing a thick electrode based on a dry-process membrane preparation process.

Background

The industry has proposed a number of strategies to increase the energy density of battery systems, accomplishing or achieving the goal of 500Wh kg ^-1 or even higher, such as developing electrode materials with high specific capacities at the material level, using lower porosity electrodes at the electrode level, developing "lean electrolyte" techniques at the battery level, and using CTP (Cell to Pack) and CTC (Cell to Chassis) techniques at the battery level to reduce the use of packaging materials. However, these energy densities are based on material level or electrode level, and the actual energy density of the battery system is still to be improved. Compared with other energy density lifting strategies, the energy storage mechanism of the lithium ion battery is not changed by the thick electrode design, so that the lithium ion battery is the easiest lifting strategy, the energy attenuation from the material layer to the electrode layer and from the electrode layer to the battery layer can be reduced, and the energy density of the battery is improved. Moreover, the thick electrode design has no repulsion with other lifting strategies, and can jointly lift the energy density of the battery with strategies such as new materials, new electrolyte and the like.

The key to the thick electrode design to increase battery energy density is to reduce the use of non-active materials such as separator, current collector, etc. within the overall battery system by increasing the area loading on a single pole piece. The mechanism of improving the energy density of the battery by the thick electrode design is that the space for improving the energy density of the battery by the thick electrode design is limited by the mass ratio of inactive components such as a diaphragm, a current collector and the like. Thus, further increases in electrode thickness may only increase a limited energy density at the expense of battery power performance. Therefore, thick electrode technology has an optimal interval to increase the energy density of the cell without compromising other cell performance.

In terms of preparation, the existing commercial battery pole piece mainly adopts a wet coating technology, namely electrode active materials and auxiliary agents are uniformly mixed in a solvent to prepare slurry, and the slurry is coated on a current collector. The essential step of the process is to dry the solvent in the pole piece, which is similar to other drying processes, and when the thickness of the pole piece is thicker, the pole piece cracking phenomenon can occur in the drying process. The preparation of thick electrodes requires breakthrough of this extreme value of thickness related to mechanical properties, namely critical cracking thickness (CCT, CRITICAL CRACKING THICKNESS).

In terms of use, as the thickness of the pole piece increases, the path of ions and electrons to all active sites inside the electrode is inevitably prolonged. Based on electrochemical energy storage mechanism, at higher rates, the ions may not reach the corresponding active sites due to slow diffusion kinetics, resulting in the failure of the electrode to exert full capacity. Thus, under certain conditions of magnification required by the operating conditions, the portion of the thick electrode that can contribute capacity may be limited to only the thickness interval of a conventional electrode. The design of thick electrodes requires the enhancement of this extreme thickness, the limiting diffusion depth (LPD, limited penetration depth), which is related to electrochemical performance.

Currently, the mainstream manufacturing process of lithium ion battery electrodes is usually a wet coating technology, which is difficult to match with thick electrode designs. In addition, wet coating techniques have the following problems: the energy consumption is huge; the pollution is serious; the cost is high; the mechanical and electrochemical properties of the electrode are easily destroyed.

In addition, there are also developed dry film forming techniques, such as typical powder spray film forming processes, which can be divided mainly into three steps. First, the active material, the conductive agent, and the binder powder are mixed into a uniform mixture. Then, the mixed powder is sprayed onto the current collector. Finally, the powder-loaded current collector is hot pressed, causing the binder to melt and adhere the powder to the current collector. Among these, critical spray processes have been achieved by various methods, such as pulsed laser and sputter deposition. By focusing the laser onto the material to be deposited, the material is evaporated and deposited onto the substrate, but the deposited film must be subjected to very high annealing temperatures (650-800 ℃), which can be reduced to 350 ℃ by sputter deposition. Although these two processes are representative of spray coating techniques, the removal of these two processes is subject to the effects of high temperatures, and the deposition rates are also very slow and not suitable for large-scale manufacturing.

The adhesive fibrillation is that under the action of shearing force, the adhesive forms a cross-linked network to fix the uniformly mixed electrode powder together, and the dry powder after the adhesive fibrillation can be directly calendered by a roll squeezer to prepare the electrode film with self-supporting performance and has good mechanical property. The adhesion between the electrode film and the current collector may affect the performance of the battery, and if the adhesion between the two is not strong, the electrode resistance may be increased. Currently, carbon-coated current collectors are often adopted to improve the adhesion between the current collector and the electrode film, however, the improvement of the adhesion performance by the current collector cannot well meet the production requirement, and the current dry electrode film on the market mostly causes electrode failure due to the stripping of the electrode film and the current collector.

Disclosure of Invention

The invention aims to provide a dry-method membrane-making method based on binder fibrillation, which can prepare a homogeneous thick electrode without cracks. The thick electrode can better improve the energy density of the lithium battery, and has higher loading capacity and larger specific surface capacity; the mechanical property and the electrochemical property of the electrode film can be improved by adding the non-fibrous binder which is crushed to form the microparticles; the pore-forming agent is added to form a pore canal structure in the electrode, so that the transmission rate of ions in the electrode is improved, and the energy density is improved; the leveling agent can fill surface micropores generated by pore forming, so that the surface flatness is improved, and meanwhile, the binding force between the electrode film and the current collector is improved. The traditional dry electrode pole piece is extremely easy to lose efficacy due to stripping of the electrode film and the current collector, and the bonding force between the electrode film and the carbon-coated aluminum foil current collector can be effectively improved by adding active carbon powder into the epoxy resin, so that the stripping strength of the electrode film is improved, and the electrode failure caused by stripping of the electrode film and the current collector is reduced.

The aim of the invention can be achieved by the following technical scheme:

a method for preparing a thick electrode based on a dry-method membrane preparation process comprises the following steps:

(1) Weighing active materials, forming auxiliary agents, non-fibrous binders, pore formers and leveling agents according to a certain proportion;

(2) Placing part of active materials and non-fibrous binder in a mashing cup, placing the mashing cup on a stirrer, and shearing and stirring the obtained mixed powder for a certain time at a certain rotating speed;

(3) Mixing the rest active materials with forming auxiliary agent, pore-forming agent and fiberizing binder powder, placing the mixture powder in a mashing cup, placing the mashing cup on a stirrer, and shearing and stirring the mixture powder for a certain time at a certain rotating speed;

(4) Uniformly mixing the two mixed powders obtained in the step (2) and the step (3), adjusting a roller press, rolling the mixed powder for a certain number of times to obtain an electrode film with a required thickness, and cutting the electrode film to obtain the electrode film with a proper size;

(5) Placing the cut electrode film into a rectangular mold, placing the mold into a hot press, and heating and pressurizing;

(6) Uniformly smearing a leveling agent on the surface of the electrode film after hot pressing by using a spatula, and heating and pressurizing the electrode film put into the die again;

(7) Shearing the current collector, adjusting the size of the sheared current collector, and attaching the current collector to the electrode film in the step (6) so that the electrode film can be completely pressed on the current collector;

(8) And (3) adjusting the temperature and the roll gap of the roll squeezer, attaching and rolling the current collector and the electrode film to obtain a composite electrode with proper thickness, and finally cutting and drying to obtain a thick electrode plate, namely the target product.

Further, the active material is lithium iron phosphate (LFP), ternary positive nickel cobalt manganese NCM622, a silicon carbon material, graphite or activated carbon (AC, model YP-50F).

Further, the molding aid is activated carbon (AC, model YP-50F).

Further, the non-fibrillating binder is carboxymethyl cellulose (CMC).

Further, the fiberizing binder is Polytetrafluoroethylene (PTFE).

Further, the pore-forming agent is ammonium bicarbonate (NH ₄HCO₃).

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

Further, the mass ratio of the active material, the forming additive and the binder is (8-9): (0.5-1): (0.5-1), and the mass ratio of non-fibrous binder to fibrous binder in the binder may be 1:4.

Further, the mass of the pore-forming agent NH ₄HCO₃ is 5% of the total mass of the active material, the forming additive and the binder.

Further, the leveling agent is an epoxy resin containing 0.1 to 0.5wt% of activated carbon, preferably 0.3wt%.

Further, the non-fibrous binder after the high-speed stirring and shearing treatment is in a pulverized state.

Further, the mixed powder containing the fiberized binder after the high-speed stirring and shearing treatment shows a cohesive state.

Further, the rotational speed of the shearing treatment is 20000 to 25000rpm, preferably 22000rpm; the treatment time is 8-12 min, preferably 10min, each stirring time is 2.5min, and cooling time is 1min.

Further, in the rolling process of the mixed powder, the thickness of the rolled electrode film is measured, the required thickness is compared, when the thickness of the rolled electrode film does not meet the requirement, the wheelbase of the roller press is adjusted, rolling is performed again, and the process is repeated until the electrode film with proper thickness is obtained.

Further, the thickness of the electrode film (i.e., the electrode film before the leveling agent is applied) obtained is 100 to 400 μm.

Further, the die is a rectangular steel plate with the size of 15cm×20cm.

In the step (5), the pressure is 20-50 MPa, the end temperature is 90-120 ℃, the heating rate is 1 ℃/s, and the time is 5-40 min when the pore-forming agent is removed by mould pressing.

Further, in the step (6), the coating amount of the leveling agent is 0.01-0.02 g/cm ².

Further, in the step (6), the pressure is 20-50 MPa, the end temperature is 60-90 ℃, the heating rate is 1 ℃/s, and the time is 10-30 min when the leveling agent is added in the die pressing.

Further, the current collector is a single-sided carbon-coated aluminum foil.

Further, the pressure at the time of bonding and rolling the current collector and the electrode film was 50MPa, the temperature was 180℃and the roll speed was 0.2 r.min ^-1.

Compared with the prior art, the method for thoroughly crushing and fibrillating the binder and smearing the leveling agent on the electrode film greatly improves the peeling strength between the electrode film and the current collector, thereby reducing the electrode failure condition caused by peeling the electrode film and the current collector. The self-supporting electrode film with good mechanical property and the electrode with greatly improved thickness can be prepared, and the area loading capacity, specific capacity and the like of the electrode can be improved.

Drawings

Fig. 1 shows electrode structures and equivalent models of a planar electrode (a) and a porous electrode (b).

Fig. 2 shows the variation of ion diffusion resistance (a) and charge transfer resistance (b) with electrode thickness.

Fig. 3 shows diffusion characteristics of electrodes having thicknesses of 108 (black), 210 (red), 305 (blue), and 410 (green) μm.

Fig. 4 shows the magnification performance of electrodes with thicknesses 108 (black), 210 (red), 305 (blue), 410 (green) μm: mass specific capacity (a), area specific capacity (b).

Fig. 5 is a graph of peel force versus peel displacement for a coated surface leveler (green) and a non-coated leveler (black).

FIG. 6 is an undried topography of an electrode coated with an 800 μm doctor blade.

FIG. 7 is a dried profile of an electrode coated with an 800 μm doctor blade (a) and 1000 μm doctor blade (b).

Fig. 8 is an active material: shaping auxiliary agent: binder=90:5:5, the roller temperature was preheated to 120 ℃ (a) and 110 ℃ (b) in mass ratio, and the mixed powder after shearing was shaped.

Fig. 9 is an active material: shaping auxiliary agent: binder=85:10:5, preheating roller temperature of 120 ℃ in terms of mass ratio, forming effect (a) of electrode film; further roll pressing to adjust the electrode film thickness, the electrode film is liable to tear tangentially along the direction of rotation of the parallel rolls (b).

FIG. 10 is a comparison of energy density of cells made from electrode films after changing the 180℃rolling temperature (dryYP-50-2) to 160℃rolling temperature (dryYP-50-3).

Fig. 11 is an illustration of the energy density of an electrode film cell made with modification of the binder, pore former, and leveler.

FIG. 12 shows the surface peeling of electrode films without the addition of leveling agent (a) and with the addition of leveling agent (b).

FIG. 13 is a flow chart of the preparation of a thick electrode of the present invention.

Detailed Description

The invention will now be described in detail with reference to the drawings and specific examples.

Electrochemical impedance spectroscopy is an effective method for studying internal resistance information of a battery. Regarding the internal resistance information of porous electrodes, many studies assume that the electrode/electrolyte interface is assumed to be a simple plane, thereby obtaining an apparent charge transfer impedance (R _ct), as in fig. 1a. However, due to the complex pore distribution in the porous electrode, the electrode/electrolyte interface in the porous electrode also has "porosity", as in fig. 1b, with which it is difficult to accurately interpret the rate performance of an actual battery. This means that the electrochemical process within a porous electrode is typically time dependent, whereas the prolonged charge transfer path in a thick electrode amplifies this characteristic even more.

FIGS. 2a and b are Navigator diagrams of LFP electrodes with 0% and 50% SOCs for different thickness thick electrodes prepared in example 2 below, respectively. In the Nahne plot with an SOC of 0%, the nearly vertical straight line in the low frequency region indicates the resistance phenomenon in the porous electrode without charge transfer (ELECTRICAL BLOCKING BEHAVIOR). The inclined line forming an angle of 45 degrees with the real axis in the high frequency region represents the ion diffusion resistance in the porous electrode, and the inclined line of 45 degrees reflecting R _ion is prolonged along with the increase of the thickness of the electrode, namely the ion diffusion resistance in the porous electrode is increased along with the increase of the thickness of the electrode. In the Navigator diagram with an SOC of 50%, the diameter of the semicircle in the low frequency region represents the magnitude of the charge transfer impedance within the porous electrode. Likewise, the semi-circle diameter reflecting R _ct increases with increasing electrode thickness, i.e., the charge transfer resistance in a porous electrode also increases with increasing electrode thickness.

The peak current of each electrode was plotted to the power of half the scan rate, and the slope of the straight line obtained by fitting was specifically shown in fig. 3. As the electrode thickness increases, the slope of the fitted line gradually decreases, representing a corresponding gradual decrease in the lithium ion diffusion coefficient. This also means that the ion diffusion behaviour in the electrode is increasingly limited as the thickness of the electrode increases.

The actual power for the different thickness thick electrodes prepared in example 2 below is shown in fig. 4. From the change condition of mass specific capacity, the specific capacity of each electrode can reach 160 mAh.g ^-1 at 0.05C; at 0.1C, the mass specific capacity of the 410 μm electrode was about 150 mAh.g ^-1, and the specific capacity of the thick electrode was lower than that of the other thick electrode. At a discharge current density of 0.5C, the electrode with a thickness of 108 μm has a high specific capacity of 145.6 mAh-g ^-1, but the electrode specific capacities with thicknesses of 210, 305, and 410 μm are 75.7%, 47.6%, and 34.2% of the former, respectively; at 1C, the specific capacities of the electrodes were 127.9, 61.6, 33.3, and 23.3 mAh.g ^-1, respectively. Further increasing the current density, the specific capacities of the 305 and 410 μm electrodes were already close to 0, while the 108 and 210 μm electrodes still had specific discharge capacities of 89.6 and 24.4 mAh.g ^-1, respectively. In combination with the area specific capacity performance of thick electrodes, the capacity that 305 and 410 μm electrodes can deliver at higher area current densities is already close to that of 205 μm electrodes, although the loading increases proportionally with thickness.

The traditional dry electrode pole piece is extremely easy to lose efficacy due to stripping of the electrode film and the current collector, and the bonding force between the electrode film and the carbon-coated aluminum foil current collector can be effectively improved by adding active carbon powder into the epoxy resin, so that the stripping strength of the electrode film is improved, and the electrode failure caused by stripping of the electrode film and the current collector is reduced. Fig. 5 is a graph of peel force versus peel displacement for a coated surface leveler (green) and a non-coated leveler (black).

The present embodiment is implemented on the premise of the technical scheme of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following examples.

In the following examples, specific sources of lithium iron phosphate, epoxy resin and other raw materials used are purchased by enterprises, such as LFP is taiwan rickai D50: 4+ -2 μm, active carbon AC YP-50F of Kuraray company, PTFE 60x DuPont, CMC NE-000243 of Japanese xylonite, NH ₄HCO₃ NH ₃ of Greagent:21.0-22.0%, and epoxy resin 6002. The remainder, unless specifically stated, is indicative of a conventional commercially available feedstock or conventional processing technique in the art.

Example 1:

(1) LFP, forming aid (AC, model YP-50F) and binder (CMC: ptfe=1:4) were weighed in a mass ratio of 85:8:7, and NH ₄HCO₃ was then weighed in an amount of 5% of the total mass of the mixture.

(2) Mixing 30% of LFP and CMC, placing in a mashing cup, shearing the mixed powder at 22000 r.min ^-1 for 10min, stirring for 2.5min each time, and cooling for 1min to finish the pulverization treatment of the non-fibrous binder.

(3) Mixing the rest LFP and AC, PTFE, NH ₄HCO₃, placing into a mashing cup, shearing the mixed powder at a speed of 22000 r.min ^-1 for 10min, stirring for 2.5min each time, and cooling for 1min to complete fibrillation of the fibrillating adhesive.

(4) After the mixing, the mixed powder is moved into a charging port of a roller press, the temperature of the roller is raised to 120 ℃, the roller spacing is set to 200 mu m, the pressure is 50MPa, and then the electrode film with self-supporting performance can be obtained by direct rolling. The roll spacing was adjusted stepwise to 200, 100 and 50 μm, and a 110 μm LFP electrode film could be obtained by repeated rolling (since the roll spacing of the roll presses used in the examples was difficult to maintain constant during rolling, and the lithium iron phosphate material was harder to roll to a thinner thickness, and thus repeated rolling was required at a roll spacing lower than the final thickness, depending on the specific thickness requirements).

(5) Cutting an electrode film, putting the electrode film into a steel plate rectangular die with the size of 15cm multiplied by 20cm, putting the die into a hot press for heating and pressurizing, wherein the hot pressing pressure is 50MPa, the end temperature is 120 ℃, the heating rate is 1 ℃/s, and the time is 30min. NH ₄HCO₃ can be completely decomposed at above 60 ℃, and the generated gas forms a pore canal inside the electrode film.

(6) Pouring a certain mass of epoxy resin into a 500ml beaker, dispersing AC (alternating current) into the epoxy resin, wherein the mass fraction of the AC is 0.3%, and stirring for 15min by using an electric stirrer to obtain the leveling agent. The leveling agent is uniformly smeared on the surface of the electrode by a spatula, and the smearing amount of the leveling agent is 0.0167/cm ² by taking an electrode film with the size of 15cm multiplied by 20cm as an example, the electrode placed in the die is heated and pressurized again, the pressure is 50MPa, the end point temperature is 90 ℃, the heating rate is 1 ℃/s, and the time is 20min.

(7) And cutting the carbon-coated aluminum foil current collector, and attaching the current collector to the LFP electrode film so that the electrode film can be completely pressed on the current collector.

(8) And selecting proper roller spacing according to the thickness of the obtained electrode film, adjusting the roller speed to be 0.20r.min ^-1, preheating the roller to 180 ℃, attaching the electrode film and the single-sided carbon-coated aluminum current collector, and rolling for one time to obtain the LFP thick electrode.

(9) The electrode plate with the diameter of 12mm is cut into the electrode plate by using a North circular sampler and is used for button cells. And transferring the cut electrode plate into a vacuum oven, and drying at 120 ℃ for 12 hours to take out the electrode plate for assembling the button cell.

The electrode sheet prepared in example 1 was further fabricated into a button cell, and the electrochemical performance test results are shown in FIG. 10 dryYP-50-1 and in the PTFE+CMC dotted line diagram of FIG. 11.

In addition, on the basis of the above example 1, as for the ternary electrode material, the process parameters to be adjusted are to adjust the roller spacing to 200, 50 and 0 μm step by step, and 105 μm NCM electrode film can be obtained by multiple rolling (the reason why the roller spacing is smaller than the final electrode film thickness is the same as above); for the silicon carbon material, the technological parameters to be adjusted are that the roller spacing is gradually adjusted to be 200 and 0 mu m, and a Si/C electrode film with the thickness of 100 mu m can be obtained by multiple times of rolling (the roller spacing is smaller than the thickness of a final electrode film for the same reason); for graphite materials, the technological parameters to be adjusted are that the mass ratio of dry powder is Gr: AC: binder=85:10:5, the roller spacing is adjusted to 200 and 0 μm step by step, and a graphite electrode film with the thickness of 100 μm can be obtained by multiple rolling (the reasons that the roller spacing is smaller than the thickness of the final electrode film are the same as above); for the activated carbon material, the technological parameters to be adjusted are that the mass ratio of the dry powder is controlled to be AC:binder=90:10, the roller spacing is adjusted to be 200 and 0 μm gradually, and an AC electrode film with the thickness of 60 μm can be obtained by multiple rolling (the reasons that the roller spacing is smaller than the thickness of the final electrode film are the same as above). The process steps (5) - (9) are identical to LFP.

Example 2:

A simplified method for preparing a thick electrode based on a dry-process membrane preparation process comprises the following steps:

(1) LFP, forming aid (AC, model YP-50F) and binder (CMC: ptfe=1:4) were weighed in a mass ratio of 85:8:7.

(3) Mixing the rest LFP, AC and PTFE, placing in a mashing cup, shearing the mixed powder at a speed of 22000 r.min ^-1 for 10min, stirring for 2.5min each time, and cooling for 1min to complete fibrillation of the fibrillating adhesive.

(4) After the mixing, the mixed powder is moved into a charging port of a roller press, the temperature of the roller is raised to 120 ℃, the roller spacing is set to 200 mu m, the pressure is 50MPa, and then the electrode film with self-supporting performance can be obtained by direct rolling. And (5) gradually adjusting the roller spacing, and repeatedly rolling for a plurality of times to finally obtain the LFP electrode films with four thicknesses of 108, 210, 305 and 410 mu m.

(5) And cutting the carbon-coated aluminum foil current collector, and attaching the current collector to the LFP electrode film so that the electrode film can be completely pressed on the current collector.

(6) And selecting proper roller spacing according to the thickness of the obtained electrode film, adjusting the roller speed to be 0.20r.min ^-1, preheating the roller to 180 ℃, attaching the electrode film and the single-sided carbon-coated aluminum current collector, and rolling for one time to obtain the LFP thick electrode.

(7) The electrode plate with the diameter of 12mm is cut into the electrode plate by using a North circular sampler and is used for button cells. And transferring the cut electrode plate into a vacuum oven, and drying at 120 ℃ for 12 hours to take out the electrode plate for assembling the button cell.

Comparative example 1:

a conventional electrode was used as comparative example 1, having a thickness of 70 μm, which was obtained from Kolu, and was a conventional lithium iron phosphate electrode.

Comparative example 2:

the traditional wet coating technology has the advantages that because the NMP toxic solvent is needed, drying is needed to remove the solvent, the cost in the drying and recycling aspects is high, meanwhile, because of the existence of critical cracking thickness, wet thick electrodes with no cracks and more than 200 mu m are difficult to prepare, the dry film making technology can avoid the use of the solvent, the solvent drying step is omitted, the cracking of the electrodes in the drying process is avoided, and the electrode thickness is greatly improved.

Preparing a wet electrode, taking an LFP positive electrode as an example, wherein the corresponding material ratio is LFP: super P (conductive agent): PVDF (binder) =90:4:6 in mass ratio. The corresponding LFP, super P and 5wt.% PVDF solution were first weighed in mass ratio in a 30ml stirred tank (total solid mass of single mix 10 g), and then NMP solvent was added to adjust the solids content of the whole system to 27%. Then the stirring box is moved into a planetary centrifugal stirrer, the stirring program is set to 700 r.min ^-1 for premixing for 30s, then 2000 r.min ^-1 is quickly mixed for 2 min, and finally 1000 r.min ^-1 is slowly mixed for 30s. After the mixing, a proper amount of slurry is taken by a medicine spoon and placed on a single-sided carbon-coated aluminum current collector, and the slurry is uniformly coated on the current collector by using 800 and 1000 mu m scrapers. After the coating was completed, the electrode was transferred to a blow-drying oven for drying to remove the solvent, the temperature of the blow-drying oven was set at 80 ℃ and the treatment was carried out overnight. The dried electrode was measured using a thickness gauge, and the 800 μm doctor blade coated electrode film was about 200 μm thick, and no significant crack presence was observed (see fig. 7 a); whereas the average thickness of the electrode film after blade coating with 1000 μm was about 300 μm, a significant crack was observed (see fig. 7 b).

Comparative example 3:

the ratio of the LFP dry electrode is adjusted to be LFP: AC: binder=90:5:5, other process parameters were the same as in example 1, and the sheared mixed powder could not be shaped by rolling, see fig. 8a.

Comparative example 4:

As a result of changing the rolling temperature to 110℃as compared with example 1, as shown in FIG. 8b, the mixed powder was improved in the molding effect after rolling but still had poor properties, and the rolled electrode film obtained at 110℃had a loose structure and an irregular and uneven shape.

Comparative example 5:

Compared to example 1, the formulation was adjusted to 85:10:5, the molding aid ratio was maintained at 10wt.%. Still, the electrode film forming effect was observed to be very good by rolling the sheared powder using a pre-heated roller temperature of 120 c, see fig. 9a. However, when the electrode film is subsequently rolled further to adjust the thickness of the electrode film to the experimentally required thickness, the electrode film is easily torn in a tangential direction parallel to the direction of rotation of the roller, see fig. 9b, and its mechanical properties still need to be improved. This degree of tearing means that the network formed by the fibrillation of the binder is unable to immobilize the active particles.

Comparative example 6:

As shown in FIG. 10, the energy density of comparative example 6 (dryYP-50-3) was lower than that of example 1 (dryYP-50-1) using 180℃rolled electrode sheets, as compared with example 1, most of which were the same, with the electrode film and current collector bonding temperature being changed to 160℃at 180 ℃.

Comparative example 7:

In comparison with example 1, the binder was made of PTFE in its entirety, and the other process parameters were the same as in example 1, and the energy density of the electrode film obtained was reduced at a low rate compared with example 1 (ptfe+cmc) as shown by the PTFE dotted line in fig. 11.

Comparative example 8:

Compared with example 1, the addition of pore formers and leveling agents is omitted, other process parameters are the same as those of example 1, the energy density of the obtained electrode film is shown as a without pore-forming agent dot line graph in fig. 11, and the energy density of the battery is obviously reduced compared with that of example 1 (PTFE+CMC).

Comparative example 9:

Compared with example 1, the leveling agent is not added with active carbon, namely, the leveling agent is all epoxy resin, other process parameters are the same as those of example 1, the energy density of the obtained electrode film is shown as a pore-forming agent without AC dotted line diagram in fig. 11, and the energy density of the battery is obviously reduced compared with that of example 1 (PTFE+CMC).

Comparative example 10:

Compared with example 1, the addition of the leveling agent was omitted, other process parameters were the same as in example 1, and as shown in fig. 12 (a), the adhesive tape was stuck on the surface of the electrode film active material to tear it by 180 °, the electrode film was extremely easily peeled off from the surface of the current collector, whereas fig. 12 (b) is the case of peeling off the electrode film to which the leveling agent was added, and was not peeled off as a whole.

The previous description of the embodiments is provided to facilitate a person of ordinary skill in the art in order to make and use the present invention. It will be apparent to those skilled in the art that various modifications can be readily made to these embodiments and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments, and those skilled in the art, based on the present disclosure, should make improvements and modifications without departing from the scope of the present invention.

Claims

1. The method for preparing the thick electrode based on the dry-method membrane preparation process is characterized by comprising the following steps of:

(3) Placing the mixed powder of the rest active materials, the forming auxiliary agent, the pore-forming agent and the fiberizing binder into another mashing cup, placing the mashing cup on a stirrer, and shearing and stirring the mixed powder for a certain time at a certain rotating speed;

(4) Uniformly mixing the mixed powder obtained in the step (2) and the step (3), adjusting a roller press, rolling the mixed powder for a certain number of times, and then cutting to obtain an electrode film with required thickness and proper size;

(6) Uniformly smearing a leveling agent on the surface of the electrode film after hot pressing by using a spatula, and continuously heating and pressurizing the electrode film placed in the die again;

(7) Shearing the current collector, adjusting the size of the sheared current collector, and attaching the current collector to the electrode film obtained in the step (6) so that the electrode film can be completely pressed on the current collector;

2. The method for preparing a thick electrode based on a dry-process film forming process according to claim 1, wherein the active material is lithium iron phosphate, ternary positive nickel cobalt manganese NCM622, silicon carbon material, graphite or activated carbon material;

The forming auxiliary agent is active carbon;

The non-fibrous binder is carboxymethyl cellulose;

The fiberizing binder is polytetrafluoroethylene;

The pore-forming agent is ammonium bicarbonate.

3. The method for preparing a thick electrode based on a dry-process film forming process according to claim 1, wherein the mass ratio of active material, forming aid and two binders is (8-9): (0.5-1): (0.5-1), wherein the mass ratio of the non-fibrous adhesive to the fibrous adhesive in the two adhesives is 1:4;

the pore-forming agent is 5% of the total mass of the active material, the forming auxiliary agent and the two binders.

4. The method for preparing a thick electrode based on a dry-process film forming process according to claim 1, wherein the leveling agent is a mixture of activated carbon and epoxy resin, and the mass content of the activated carbon is 0.1-0.5 wt%.

5. The method for preparing a thick electrode based on a dry-process film forming process according to claim 1, wherein in the high-speed stirring and shearing process: stirring in a time period, cooling for a period of time after each stirring, and continuing stirring;

The rotation speed of the high-speed stirring and shearing treatment is 20000-25000 rpm, and the treatment time is 8-12 min.

6. The method for preparing a thick electrode based on a dry film forming process according to claim 1, wherein in the step (4), the thickness of the electrode film after rolling is measured and compared with the required thickness in the rolling process of the mixed powder, and when the thickness of the electrode film after rolling is not satisfactory, the wheelbase of the roll squeezer is adjusted, rolling is performed again, and the above steps are repeated until the electrode film with a proper thickness is obtained.

7. The method for preparing a thick electrode based on a dry film forming process according to claim 1, wherein the hot pressing pressure in the step (5) is 20-50 MPa, the end-point temperature is 90-120 ℃, the heating rate is 1 ℃/s, and the time is 5-40 min.

8. The method for preparing a thick electrode based on a dry film forming process according to claim 1, wherein the hot pressing pressure in the step (6) is 20-50 MPa, the end-point temperature is 60-90 ℃, the heating rate is 1 ℃/s, and the time is 10-30 min.

9. The method for preparing a thick electrode based on a dry film process according to claim 1, wherein the current collector used is a single-sided carbon-coated aluminum foil.

10. The method for preparing a thick electrode based on a dry film forming process according to claim 1, wherein in the step (8), the pressure of the current collector and the electrode film when being laminated and rolled is 50Mpa, the temperature is 180 ℃, and the roll speed is 0.2 r.min ^-1.