CN112151743A - A kind of hole making method of thick electrode and its product and use - Google Patents

Abstract

The present invention provides a method for making holes for thick electrodes, products and uses thereof. The method for making holes includes coating a slurry with a viscosity of 6000mPa·s～9000mPa·s on a current collector with a surface roughness Ra≥1μm. surface, drying to obtain the thick electrode; the active material layer of the thick electrode obtained by the above method includes an air channel from the surface of the pole piece to the surface of the current collector, which effectively solves the problem of poor electrolyte wettability of the thick electrode, long lithium ion migration path, The problem of large concentration polarization improves the electrochemical performance of thick-electrode lithium-ion batteries; and the above-mentioned pore-making method greatly simplifies the process of thick-electrode pore-making and reduces the cost of thick-electrode pore-making.

Description

A kind of hole making method of thick electrode and its product and use

technical field

The invention belongs to the field of batteries, and relates to a method for making holes for thick electrodes, products and uses thereof.

Background technique

At present, in order to solve the problem of cruising range of electric vehicles, improving energy density is an important direction for the development of lithium-ion batteries. The preparation of ultra-thick pole pieces with high coating weight is the most direct way to increase the specific energy of the battery, which can effectively reduce the proportion of inactive materials, such as current collectors, tabs, battery shells, etc. As the thickness of the pole piece increases, the specific energy of the battery increases correspondingly at lower rates; however, at higher rates, the kinetics of lithium ion diffusion is limited, the utilization of electrode active materials decreases, and the energy density of the battery is impaired. Therefore, for thick pole pieces, it is more important to design and optimize the microstructure of the electrode in order to ensure high loading while ensuring the diffusion rate of lithium ions and the full utilization of active materials. Due to its high specific capacity, the development of silicon-based anodes is also one of the most effective ways to improve the energy density of lithium-ion batteries. However, as an active material, the main problems of silicon materials include: volume expansion of 300% to 400% during charge and discharge; after alloying with lithium, the volume of crystalline silicon changes significantly, and such volume effects can easily cause silicon anodes. The material pulverizes and peels off the current collector. Moreover, the exfoliation caused by the silicon volume effect will cause repeated destruction and reconstruction of the solid electrolyte membrane (SEI), thereby increasing the consumption of lithium ions and ultimately affecting the capacity of the battery. High irreversible capacity and low Coulombic efficiency lead to low actual battery capacity and poor cycle life. At present, researchers are solving these problems by means of silicon powder nanoization, silicon carbon coating, doping and binder optimization, and the design of silicon-based electrodes also needs to optimize the microstructure.

In addition, the energy density and power density of the battery are two important parameters, but they are contradictory. How to balance the two through the optimal design of the electrode microstructure is also the key to electrode design. For example, the pole piece structures and manufacturing methods disclosed in CN2002351A and CN102694150A are both from the perspective of increasing the porosity of the pole piece along the thickness direction, improving the wettability of the electrolyte in the pole piece, and reducing the phenomenon of concentration polarization.

In view of the defects of thick electrode sheet thickness, low porosity, wettability and long ion migration path, researchers have innovated the traditional electrode process and developed a series of controllable preparation technologies; The microscopic distribution of the electrode is precisely controlled. The researchers add a small amount of magnetic material or pore-forming agent to the electrode slurry, and then apply an external magnetic field during the electrode coating process to control the electrode microstructure, or the pore-forming agent volatilizes on the pole piece during the coating process. Pores are generated; the above scheme reduces the tortuosity of pores in the thickness direction of the electrode by 4 times, and improves the electrochemical performance of the prepared battery. However, this solution requires the introduction of magnetic substances. On the one hand, the proportion of electrode active substances is reduced, and the energy density is sacrificed; Second, multi-layer structure electrodes such as pore gradient distribution and vertical distribution of conductive agents or active materials are beneficial to improve battery performance. For this reason, some researchers have developed multi-layer coating processes. At present, multi-layer coating is mainly realized by two process methods. The first is divided coating. First, a layer of electrode slurry is coated on the current collector, and then a second layer of slurry is coated after drying. The second method is to develop an extrusion-type multilayer coating die to realize the simultaneous coating of multiple layers of wet slurry to prepare electrodes. The main problem of this solution is that the processing technology is complex, and the coating needs to be carried out twice, resulting in low production efficiency and high processing difficulty. In addition, because this process requires the first layer to be coated and dried before the second layer is applied, a clear boundary is created between the two coatings, and the different interfaces expand and contract differently during the charging and discharging process, resulting in interface peeling or increase in interface impedance, electrochemical Performance deteriorates rapidly.

Therefore, it is still of great significance to develop a pore-forming method for thick pole pieces with simple process, low cost, and no introduction of magnetic substances and pore-forming agents.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for making holes for thick electrodes, products and uses thereof. The method for making holes includes coating a slurry with a viscosity of 6000-9000 mPa·s on a current collector with a surface roughness Ra ≥ 1 μm. surface, and drying to obtain the thick electrode; the active material layer of the thick electrode obtained by the above method includes an air channel from the surface of the pole piece to the surface of the current collector, which effectively solves the problem of poor wettability of the thick electrode electrolyte and long lithium ion migration path. The problem of large concentration polarization improves the electrochemical performance of thick-electrode lithium-ion batteries; and the above-mentioned pore-making method greatly simplifies the process of thick-electrode pore-making and reduces the cost of thick-electrode pore-making.

The medium-thick electrode in the present invention refers to that the surface density of the current collector surface active material layer on the electrode is ≥20 mg/cm ² , such as 25 mg/cm ² , 30 mg/cm ² or 35 mg/cm ² , etc.

In order to achieve this object of the invention, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a method for making a hole for a thick electrode, the method comprising adjusting the viscosity to 6000-9000 mPa·s, such as 6500 mPa·s, 700 mPa·s, 7500 mPa·s, 8000 mPa·s or 8500 mPa·s etc. slurry is coated on a current collector with surface roughness Ra ≥ 1 μm (for example, 1 μm, 1.5 μm, 2 μm or 3 μm, etc.), and dried to obtain the thick electrode.

In order to solve the problems of poor electrolyte wettability, long lithium ion migration path, large concentration polarization, cumbersome pore-making process and high cost in thick electrodes, the pore-making method for thick electrodes of the present invention adopts the above-mentioned slurry of specific viscosity The material (viscosity is 6000-9000mPa·s) is coated on the surface of the current collector whose surface roughness meets the above conditions. When the slurry is transferred to the surface of the current collector (for example, the slurry is transferred from the tank to the current collector), due to the slurry The viscosity is high, the air flow between the coating and the current collector is poor, and it cannot be discharged in time. During the subsequent drying process, the air bubbles are removed from the bottom, and an air channel is generated from the current collector to the coating surface, so as to improve the protection of the pole piece. The purpose of improving the ion migration ability during the charging and discharging process; and the above-mentioned pore-forming method is simple to operate, without adding pore-forming agents or magnetic substances, reducing electrode foreign matter and ensuring the design of thick electrodes with high active material ratio; in addition, the coating process It can be completed at one time, which is the same as the current electrode coating process, and the operation is simple and the process cost is low.

The pore making method of the invention greatly simplifies the process of making holes for the thick electrode and pole pieces, reduces the cost of making holes for the thick electrode pieces, and effectively solves the problems of poor electrolyte infiltration, long lithium ion migration path and large concentration polarization of the thick electrode pole piece. problem, improving the electrochemical performance of thick-electrode lithium-ion batteries.

Preferably, the coating method is transfer coating, and the principle of transfer coating is to adjust the amount of slurry transfer through the blade gap, and to transfer the slurry to the current collector by the rotation of the back roller and the coating roller. Transfer coating mainly includes two processes: First, the rotation of the coating roller drives the slurry to pass through the gap between the metering rollers to form a slurry layer with a certain thickness. The second is that the slurry layer of a certain thickness transfers the slurry to the foil through the rotation of the opposite coating roller and the back roller to form a coating. Selecting transfer coating is beneficial to ensure the formation of stable closed pores between the coating and the current collector during the coating process.

The transfer coating described in the present invention is the prior art, for example, it can be realized by using a commercially available model transfer coating machine. The model of the transfer coater includes at least one of commercially available HB-TBD750, DT600/750, Q_ZY 002-2017 and Q_HN 002-2017.

Preferably, the current collector surface comprises open pits.

The preferred surface of the current collector of the present invention is mainly open pits, which is beneficial to increase the number of air bubbles generated when the slurry is coated on the surface of the current collector.

Preferably, the fineness of the slurry is less than 30 μm, such as 5 μm, 15 μm, 20 μm or 25 μm, etc.

The fineness of the slurry of the present invention is within the above range, which is beneficial to ensure the consistency and uniformity of the closed pores, and to avoid the occurrence of agglomerated particles and the deterioration of the pore distribution.

Preferably, the slurry is obtained by mixing under vacuum conditions, preferably vacuum conditions are -60 to -90kPa, such as -65kPa, -70kPa, -75kPa, -80kPa or -85kPa, etc.

The slurry of the present invention is obtained by mixing under vacuum conditions, which is beneficial to ensure the coating quality, avoid excessive bubbles in the slurry, lead to the decrease of the coating quality of the pole piece, and affect the electrochemical performance.

Preferably, the mixing method includes stirring, preferably the revolution speed is 15-500rpm, such as 20rpm, 50rpm, 100rpm, 200rpm, 300rpm or 400rpm, etc., and the rotation speed is 500-1500rpm, such as 600rpm, 700rpm, 800rpm, 900rpm, 1000rpm , 1100rpm, 1200rpm, 1300rpm or 1400rpm, etc.

Preferably, the slurry includes positive electrode slurry or negative electrode slurry.

Preferably, the mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode slurry is (88-97):(1.5-6):(1.5-6), for example, 90:5:5, 92: 3:5 or 95:2:3 etc.

The pore-forming method of the present invention avoids adding a pore-forming agent or a magnetic substance, thereby helping to increase the proportion of active substances, thereby improving the electrochemical performance of the thick electrode.

Preferably, the mass ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode slurry is (90-96):(0.1-2):(2-5), for example, 90:2:5, 90: 1:5, 92:2:5, 92:2:2, 93:2:2, 93:0.5:5, 94:1:2, 94:1:3, or 96:2:5, etc.

Preferably, the current collector comprises carbon-coated foil, preferably carbon-coated copper foil or carbon-coated aluminum foil.

Preferably, the thickness of the current collector is 12-20 μm, for example, 13 μm, 15 μm, 17 μm, or 19 μm.

Preferably, the drying temperature is 70-90°C, for example, 75°C, 80°C, or 85°C.

The drying temperature of the present invention is within the above temperature range, which is conducive to the discharge of gas between the coating and the current collector, thereby improving the pore-forming effect, enhancing the liquid-holding effect of the thick electrode and the ion migration ability during charging and discharging.

Preferably, the drying further includes rolling and slitting.

Preferably, the preparation method of the slurry includes: stirring and mixing the glue, the conductive agent and the active material under vacuum conditions of -60kPa～-90kPa, for example, -65kPa, -70kPa, -75kPa, -80kPa or -85kPa, etc. , wherein the revolution speed of stirring is 15-500rpm, such as 20rpm, 50rpm, 100rpm, 200rpm, 300rpm or 400rpm, etc., and the rotation speed is 500-1500rpm, such as 600rpm, 700rpm, 800rpm, 900rpm, 1000rpm, 1100rpm, 1200rpm, 1300rpm or 1400 rpm, etc., to adjust the viscosity to obtain a slurry with a viscosity of 6000-9000 mPa·s, for example, 6500 mPa·s, 700 mPa·s, 7500 mPa·s, 8000 mPa·s, or 8500 mPa·s.

Preferably, the conductive agent is selected from any one or a combination of at least two of conductive carbon black SP, carbon nanotubes, single-walled carbon nanotubes, graphene, acetylene black or Ketjen black.

Preferably, the active material includes a positive active material or a negative active material.

Preferably, the positive active material is selected from any one or a combination of at least two of lithium iron phosphate, ternary material, lithium manganate or lithium cobaltate.

Preferably, the negative electrode active material is selected from one or more of artificial graphite, natural graphite, silicon carbon, and lithium titanate.

Preferably, the solid content of the glue solution is 7-10%, such as 8% or 9%.

The pore-making method of the present invention controls the solid content of the glue liquid to be within the above range, which is beneficial to ensure that the viscosity of the discharged material is within a relatively high range, thereby facilitating the formation of closed pores with the current collector.

Preferably, the preparation method of the glue solution comprises mixing the binder and the solvent, and stirring under the vacuum conditions of -60～-90kPa, such as -65kPa, -70kPa, -75kPa, -80kPa or -85kPa, etc.;

Preferably, the stirring time in the preparation process of the glue solution is 3-4 hours; for example, 3.5 hours and the like.

Preferably, the binder includes polyvinylidene fluoride.

The types of polyvinylidene fluoride herein include at least one of commercially available HSV900, HSV9100, solf5130 and 4300.

Preferably, the solvent is selected from N-methylpyrrolidone.

Preferably, the mass ratio of the binder to the solvent is 1:(18-20).

Preferably, the method of stirring and mixing the glue, the conductive agent and the active material under vacuum conditions of -60 to -90kPa, such as -65kPa, -70kPa, -75kPa, -80kPa or -85kPa, etc., is included in the glue Add the conductive agent and active material in turn, and stir and mix.

Preferably, the active substance is added in portions.

Preferably, after the conductive agent is added and before the active material is added, the stirring time is 1-2 hours, for example, 1.5 hours.

Preferably, after the active substance is added, the stirring time is 0.5-3 hours, for example, 1 hour, 1.5 hours, 2 hours or 2.5 hours.

Preferably, the method of adjusting viscosity includes adding a solvent.

Preferably, after adjusting the viscosity, filtering is further included.

Preferably, the mesh number of the filter screen used in the filtration is greater than or equal to 150 mesh, such as 200 mesh or 250 mesh.

As a preferred technical solution of the present invention, the hole-making method comprises the following steps:

(1) slurry preparation, specifically including the following steps:

(a) stirring and mixing the binder and N-methylpyrrolidone under vacuum conditions for 3 to 4 hours to obtain a glue solution with a solid content of 7 to 10%;

(b) adding a conductive agent to the glue solution in step (a), stirring and mixing for 1-2 hours under vacuum conditions;

(c) Add active substances to the materials in step (b), stir and mix for 0.5 to 1 h under vacuum conditions, scrape off the materials adhering to the walls, paddles and bottom corners of the mixing cylinder in the shutdown state, and continue Stir and mix under vacuum for 1-2 hours;

(d) adding N-methylpyrrolidone to the material in step (c) to adjust the viscosity to obtain a slurry with a viscosity of 6000-9000 mPa·s and a fineness of less than 30 μm;

(2) The slurry obtained in step (1) is coated on a current collector with a roughness Ra of 1.5 μm, dried in an oven at 70-90° C., rolled and cut to obtain a thick electrode.

In a second aspect, the present invention provides a thick electrode prepared by the method described in the first aspect.

The thick electrode of the present invention is prepared by the method described in the first aspect, and the obtained thick electrode has better liquid retention effect, and solves the problems of poor electrolyte wettability, long lithium ion migration path, and concentrated lithium ion existing in traditional thick electrodes. The problem of large differential polarization improves the electrochemical performance of thick-electrode lithium-ion batteries.

Preferably, the thick electrode includes a current collector and an active material layer on the surface of the current collector.

Preferably, the areal density of the thick electrode is 20-30 mg/cm ² , such as 20 mg/cm ² , 22 mg/cm ² , 24 mg/cm ² , 26 mg/cm ² or 28 mg/cm ² , and the like.

The surface density of the thick electrode of the present invention is limited to the above range, which is conducive to the formation of air channels during the drying process, thereby solving the problems of poor electrolyte infiltration, long lithium ion migration path, and large concentration polarization of the thick electrode, improving the Electrochemical performance of thick-electrode lithium-ion batteries.

Preferably, the active material layer of the thick electrode includes an air channel from the surface of the pole piece to the surface of the current collector.

Preferably, the thick electrode includes a positive pole piece or a negative pole piece.

Preferably, the active material layer of the thick electrode has a porosity of 25-45%, such as 25%, 27%, 28%, 30%, 35%, 37%, 40% or 45%, etc.

In a third aspect, the present invention provides a battery comprising the thick electrode of the second aspect.

The battery of the present invention adopts the thick pole piece as described in the second aspect, which has excellent electrochemical performance and excellent cycle performance.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The pore-making method of the thick electrode of the present invention does not need to add a magnetic substance or a pore-forming agent, the operation is simple, and the cost is low;

(2) The thick electrode obtained by the pore-making method of the thick electrode of the present invention solves the problems of poor electrolyte wettability, long lithium ion transmission path and large concentration polarization existing in the traditional thick electrode, and improves the electrochemical performance of the thick electrode. performance.

Description of drawings

FIG. 1 is a schematic diagram of the process principle of the pore-making method of the thick electrode according to the present invention;

Fig. 2 is the electron microscope image of the carbon-coated aluminum foil surface adopted in the embodiment of the present invention 1;

Fig. 3 is the electron microscope picture of the thick electrode obtained in the embodiment of the present invention 1;

4 is an electron microscope image of the active material layer of the thick electrode obtained in Example 1 of the present invention;

1- Carbon-coated aluminum foil, 2- Air, 3- Coating, 4- Airway.

Detailed ways

The technical solutions of the present invention are further described below through specific embodiments. It should be understood by those skilled in the art that the embodiments are only for helping the understanding of the present invention, and should not be regarded as a specific limitation of the present invention.

The schematic diagram of the process principle of the pore-making method of the thick electrode according to the present invention is shown in Figure 1. Taking the thick electrode of the positive electrode as an example, the current collector is made of carbon-coated aluminum foil 1, and its surface roughness Ra is greater than 1 μm; The carbon-coated aluminum foil 1 is coated on the carbon-coated aluminum foil 1 with a set areal density in the form of transfer coating; preferably, the slurry has a high viscosity and a high coating areal density. When the slurry is coated on the carbon-coated aluminum foil, the air 2 It cannot be discharged in time before entering the oven, and is sealed between the coating layer 3 and the carbon-coated aluminum foil 1 by the slurry; after the thick electrode enters the oven, the bubbles float from the bottom of the electrode piece at high temperature (70-90°C), and the solvent in the coating layer It volatilizes from the pole piece to form air passages 4 in the pole piece, which are generated by the floating of the bubbles, so that a thick electrode with uniform holes can be obtained.

Example 1

In this example, a thick positive electrode was prepared, wherein the current collector was made of carbon-coated aluminum foil, the surface roughness Ra was 1.5 μm, and the thickness was 12 μm. The coating surface density is 25mg/cm ² ;

The preparation method of the positive thick electrode:

(1) Preparation of positive electrode slurry:

(a) stirring and mixing polyvinylidene fluoride and N-methylpyrrolidone under vacuum for 3 hours to obtain a glue solution with a solid content of 8%;

(b) adding conductive carbon black SP to the glue solution of step (a), stirring and mixing for 1h under the vacuum condition of -70Kpa; the revolution rate of the stirring process is 100rpm, and the rotation rate is 1000rpm;

(c) adding lithium iron phosphate to the material of step (b), continuing to stir and mix for 1h under the vacuum condition of -70Kpa, and scraping off the materials adhering to the wall of the mixing cylinder, the paddle and the bottom corner under the shutdown state. materials, continue to stir and mix for 2h under the vacuum condition of -70Kpa;

(d) adding N-methylpyrrolidone to the material in step (c) to adjust the viscosity to obtain a slurry with a viscosity of 7500 mPa·s and a fineness of less than 30 μm;

Among them, the mass ratio of lithium iron phosphate, polyvinylidene fluoride and conductive carbon black SP is 95:2:3;

(2) Transfer coating the slurry obtained in step (1) on carbon-coated aluminum foil, drying in an oven at 80° C., rolling, and slitting to obtain a positive thick electrode.

The electron microscope image of the thick positive electrode obtained in this example is shown in Figure 3. It can be seen from Figure 3 that there are air channels extending from the surface of the current collector to the surface of the coating distributed between the current collector (carbon-coated aluminum foil) and the coating surface. . FIG. 4 is a partial enlarged view of the air channel; it can be seen from this that the air channel is formed in the active material layer of the thick electrode by using the pore-making method of the present invention.

Example 2

The difference between this example and Example 1 is that the viscosity of the slurry is 6000 mPa·s, and other parameters and conditions are exactly the same as those in Example 1.

Example 3

The difference between this example and Example 1 is that the viscosity of the slurry is 9000 mPa·s, and other parameters and conditions are exactly the same as those in Example 1.

Example 4

The difference between this example and Example 1 is that the surface roughness Ra of the carbon-coated aluminum foil is 2 μm, and other parameters and conditions are exactly the same as those in Example 1.

Example 5

The difference between this example and Example 1 is that the slurry preparation process is carried out under normal pressure, and other parameters and conditions are exactly the same as in Example 1.

Example 6

The difference between this example and Example 1 is that the vacuum condition in the slurry preparation process is -90 kPa, and other parameters and conditions are exactly the same as in Example 1.

Example 7

The difference between this example and Example 1 is that the drying temperature in step (2) is 60° C., and other parameters and conditions are exactly the same as those in Example 1.

Comparative Example 1

The difference between this comparative example and Example 1 is that the viscosity of the slurry is 4500 mPa·s, and other parameters and conditions are exactly the same as those in Example 1.

Comparative Example 2

The difference between this comparative example and Example 1 is that the viscosity of the slurry is 10000 mPa·s, and other parameters and conditions are exactly the same as those in Example 1.

Comparative Example 3

The difference between this comparative example and Example 1 is that the surface roughness Ra of the carbon-coated aluminum foil is 0.5 μm, and other parameters and conditions are exactly the same as those in Example 1.

Comparative Example 4

The patent CN109167020A was used to add a pore-forming agent, and a thick electrode pole piece was made as a comparison.

Performance Testing:

Electrolyte wettability test is carried out to the positive electrode thick electrode obtained in the embodiment and the comparative example, and the test method is usually: and compare the weight of different pole pieces immersed in the electrolyte after immersing in the electrolyte to absorb the weight of the electrolyte, and absorb the many pole pieces of the electrolyte to preserve the liquid. strong ability. The electrode pieces of the examples and comparative examples were immersed in the electrolyte to test the absorption of the electrolyte, and the weight of the electrolyte absorbed by different schemes was weighed.

The positive electrode thick electrode obtained in the embodiment and the comparative example is assembled into a battery, and the battery assembly method is as follows:

The positive thick electrode (that is, the positive pole piece), the separator, and the negative pole piece are stacked to form a battery cell, which is then welded with aluminum tabs and copper tabs respectively, and heat-sealed with aluminum plastic film. Bake for 24 hours under the condition of vacuum degree of -0.095Mpa. During the baking process, nitrogen is continuously replaced and vacuumized.

Among them, the diaphragm adopts 14μm polyethylene diaphragm;

Negative pole piece: the current collector is 6μm copper foil, and the negative electrode active material layer is composed of graphite: conductive agent: binder = 96%: 1%: 3%;

Electrolyte preparation and injection: The electrolyte uses lithium hexafluorophosphate (LiPF ₆ ) with a concentration of 1.0mol/L as the electrolyte; ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and carbonic acid are used as the electrolyte. A mixture of propylene esters (PC) is the solvent, wherein the weight ratio of EC, EMC, DEC and PC is 40:25:30:5.

After the battery core is baked, the electrolyte is injected into the battery at 5.2g/Ah. The cells after liquid injection are pre-packaged, left to soak for 24 hours, and then the cells are charged and formed. After the formation is completed, the cells are evacuated again. After packaging, the batteries are divided into volumes to obtain the lithium-ion battery with porous thick electrodes. .

The capacity and cycle performance of the above-mentioned batteries are tested. The capacity test conditions are: at a temperature of 25±2°C, after the battery is activated, it is charged to 4.2V with a constant current of 0.1C, and then charged with a constant voltage. , the cut-off current is 0.05C. After standing for 5 minutes, discharge at 0.1C, the cut-off voltage is 2.5V, and the measured value is the initial capacity of the battery. Divide the initial capacity by the mass of the positive active material contained in the battery to obtain the gram capacity of the corresponding positive active material. Cycle life test: the test temperature is 25℃±2℃, charge to 4.2V with 0.7C constant current, then charge with constant voltage, the cut-off current is 0.05C; leave it for 5 minutes, then discharge at 0.7C, the cut-off voltage is 2.5V , set aside for 5 minutes between charge and discharge, cycle 500 times, record the capacity and calculate the capacity retention rate, capacity retention rate=capacity after 500 cycles/initial capacity.

The above test results are shown in Table 1;

Table 1

Liquid retention, g Initial specific capacity, mAh/g 100-week cycle retention, % Example 1 0.7 159 99.5 Example 2 0.68 159 98.6 Example 3 0.75 158 98.3 Example 4 0.74 158 96.8 Example 5 0.72 159 95.2 Example 6 0.7 159 99.5 Example 7 0.71 158 96.1 Comparative Example 1 0.5 158 99.1 Comparative Example 2 0.72 155 96.6 Comparative Example 3 0.5 159 95.1 Comparative Example 4 0.68 159 98.5

As can be seen from Table 1 above, the thick pole pieces obtained by the pore-making method of the present invention all have good electrolyte wettability and excellent electrochemical performance;

Comparing Examples 1-3 and 1-2, it can be seen that the viscosity of the slurry is controlled in the range of 6000-9000 mPa·s during the pore making process, which is conducive to the formation of an air channel between the current collector and the surface of the pole piece. , which is beneficial to improve the wettability of thick electrodes and improve their electrochemical performance;

Comparing Examples 1, 4 and 3, it can be seen that the surface roughness of the current collector is controlled at Ra ≥ 1 μm, which is conducive to the formation of an air channel between the current collector and the surface of the pole piece, which in turn is conducive to improving the wettability of the thick electrode , improve its electrochemical performance;

Comparing Examples 1 and 5-6, it can be seen that during the hole making process according to the present invention, the vacuum condition is controlled to be -60-90Kpa, which is conducive to the formation of an air channel between the current collector and the surface of the pole piece, which is conducive to improving The wettability of thick electrodes improves their electrochemical performance;

Comparing Examples 1 and 7, it can be seen that when the drying temperature is in the temperature range of 70-90°C, the pore-forming effect is better.

Comparing Example 1 and Comparative Example 4, it can be seen that the pore-making method of the present invention has the characteristics of simple operation and low cost, and can achieve the equivalent electrochemical performance of Comparative Example 4 without introducing foreign matter, which is conducive to maintaining excellent electrochemical performance.

The applicant declares that the above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should Changes or substitutions that can be easily conceived within the technical scope all fall within the protection scope and disclosure scope of the present invention.

Claims (10)

1. The pore-forming method of the thick electrode is characterized by comprising the steps of coating slurry with the viscosity of 6000-9000 mPa & s onto a current collector with the surface roughness Ra being more than or equal to 1 mu m, and drying to obtain the thick electrode.

2. The pore-forming method of claim 1, wherein said coating is by transfer coating;

preferably, the surface of the current collector comprises open pits;

preferably, the fineness of the slurry is less than 30 μm;

preferably, the slurry is obtained by mixing under the vacuum condition, and the vacuum condition is preferably-60 to-90 kPa;

preferably, the mixing method comprises stirring, preferably, the revolution speed is 15-500 rpm, and the rotation speed is 500-1500 rpm;

preferably, the slurry comprises a positive electrode slurry or a negative electrode slurry;

preferably, the mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode slurry is (88-97): (1.5-6): 1.5-6).

3. The pore-forming method of claim 1 or 2, wherein the current collector comprises a carbon-coated foil, preferably a carbon-coated copper foil or a carbon-coated aluminum foil;

preferably, the thickness of the current collector is 12-20 μm.

4. The pore-forming method according to any one of claims 1 to 3, wherein the drying temperature is 70 to 90 ℃;

preferably, the drying further comprises rolling and slitting.

5. The pore-forming method of any of claims 1-4, wherein the slurry is prepared by a method comprising: stirring and mixing the glue solution, the conductive agent and the active substance under the vacuum condition of-60 to-90 kPa, wherein the stirring revolution speed is 15 to 500rpm, the rotation speed is 500 to 1500rpm, and the viscosity is adjusted to obtain the slurry with the viscosity of 6000 to 9000mPa & s;

preferably, the conductive agent is selected from any one or a combination of at least two of conductive carbon black SP, carbon nanotubes, single-walled carbon nanotubes, graphene, acetylene black or Ketjen black;

preferably, the active material includes a positive electrode active material or a negative electrode active material;

preferably, the positive electrode active material is selected from any one of lithium iron phosphate, ternary material, lithium manganate or lithium cobaltate or a combination of at least two of the above materials.

6. The pore-forming method according to claim 5, wherein the solid content of the glue solution is 7-10%;

preferably, the preparation method of the glue solution comprises the steps of mixing the binder and the solvent, and stirring under the vacuum condition of-60 to-90 kPa;

preferably, the stirring time in the preparation process of the glue solution is 3-4 h;

preferably, the binder comprises polyvinylidene fluoride;

preferably, the solvent is selected from N-methylpyrrolidone;

preferably, the mass ratio of the binder to the solvent is 1 (18-20).

7. The pore-forming method according to claim 5 or 6, wherein the method for stirring and mixing the glue solution, the conductive agent and the active substance under the vacuum condition of-60 to-90 kPa comprises the steps of sequentially adding the conductive agent and the active substance into the glue solution, stirring and mixing;

preferably, the active substance is added in divided portions;

preferably, after the conductive agent is added and before the active substance is added, the stirring time is 1-2 h;

preferably, after the active substances are added, the stirring is continued for 0.5-3 h;

preferably, the method of adjusting viscosity comprises adding a solvent;

preferably, the viscosity adjustment further comprises filtration;

preferably, the mesh number of the filter screen adopted for filtering is more than or equal to 150 meshes.

8. The pore-forming method of any of claims 1-7, comprising the steps of:

(1) the preparation of the slurry specifically comprises the following steps:

(a) stirring and mixing the binder and N-methyl pyrrolidone for 3-4 hours under a vacuum condition to obtain a glue solution with a solid content of 7-10%;

(b) adding a conductive agent into the glue solution obtained in the step (a), and stirring and mixing for 1-2h under a vacuum condition;

(c) adding active substances into the materials in the step (b), stirring and mixing for 0.5-1 h under a vacuum condition, scraping the materials adhered to the wall, the blades and the bottom corners of the stirring cylinder under a shutdown state, and continuously stirring and mixing for 1-2h under the vacuum condition;

(d) adding N-methyl pyrrolidone into the material obtained in the step (c) to adjust the viscosity, so as to obtain slurry with the viscosity of 6000-9000 mPa & s and the fineness of less than 30 mu m;

(2) and (2) coating the slurry obtained in the step (1) on a current collector with the roughness Ra of more than or equal to 1 mu m, drying in an oven at 70-90 ℃, rolling and cutting to obtain the thick electrode.

9. A thick electrode, wherein the thick electrode is prepared by the method of any one of claims 1 to 8;

preferably, the thick electrode comprises a current collector and an active material layer positioned on the surface of the current collector;

preferably, the surface density of the thick electrode is 18-30 mg/cm²；

Preferably, the active material layer of the thick electrode comprises an air channel from the surface of the pole piece to the surface of the current collector;

preferably, the thick electrode comprises a positive electrode plate or a negative electrode plate;

preferably, the active material layer of the thick electrode has a porosity of 25 to 40%.

10. A battery comprising the thick electrode of claim 9.

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