Conductive paste, electrode sheet, preparation method thereof and application

Abstract

The present invention relates to a conductive paste, an electrode sheet, and a preparation method and application thereof. The conductive paste includes a conductive agent and an organic solvent. The conductive agent includes thick-diameter carbon nanotubes, thin-diameter carbon nanotubes, and reduced graphene oxide. The thick-diameter carbon nanotubes and the thin-diameter carbon nanotubes are interpenetrated with each other. The diameter of the thick-diameter carbon nanotubes is 50 nm to 200 nm, and the diameter of the thin-diameter carbon nanotubes is 6 nm to 12 nm. The thick-diameter carbon nanotubes, the thin-diameter carbon nanotubes, and the reduced graphene oxide jointly form a three-dimensional network structure. Coating the positive electrode paste prepared by using this conductive paste on a microporous foil material to obtain an electrode sheet can greatly improve the adhesion of the electrode sheet, greatly improve the energy density of the battery cell prepared, and at the same time, it will not affect the kinetic performance of lithium ions.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a conductive paste, an electrode sheet, and a preparation method and application thereof, and in particular to the application of the electrode sheet in lithium-ion batteries. Background Art

[0002] As a new type of energy, lithium-ion batteries have attracted much attention for their advantages such as light weight, high capacity and long cycle life. Among them, ternary lithium batteries are increasingly being paid attention to and recognized by the industry due to their dual advantages of comprehensive performance and cost. They have surpassed lithium iron phosphate and lithium cobalt oxide to become the mainstream technology route for lithium batteries.

[0003] The energy density of ternary lithium batteries on the market is about 180Wh / kg on average, and it is difficult to reach more than 300Wh / k, which is far from meeting the requirements of electric vehicles for driving range. The development of batteries with higher energy density has always been the focus of the lithium battery field. At present, existing lithium-ion battery manufacturers generally use SP compounded carbon nanotubes as conductive agents, which have a perfect conductive network and improve the conductivity of the battery. The energy density of the battery is mainly improved by increasing the electrode load and reducing the weight of auxiliary materials such as foil in the electrode, such as making microporous copper foil, aluminum foil, etc. However, due to the increase in the load of high-energy-density batteries, the amount of binders such as PVDF is relatively small, resulting in a decrease in the adhesion of the electrode sheet, which is not conducive to electronic conduction, and further affects the conductivity of the battery, resulting in a decrease in the rate discharge performance of the battery. Therefore, how to prepare an electrode sheet with good adhesion, high energy density, and will not affect the kinetic properties of lithium ions has always been a difficult problem for technicians in this field to overcome. Summary of the invention

[0004] Based on this, the present invention provides a conductive slurry and a preparation method thereof, and further provides an electrode sheet and a preparation method thereof. The electrode sheet has good bonding properties, and the energy density of the battery cell assembled from the electrode sheet can reach 350Wh / kg, and will not affect the kinetic properties of lithium ions.

[0005] The technical solution of the present invention is as follows.

[0006] One aspect of the present invention provides a conductive paste, which includes a conductive agent and an organic solvent. The conductive agent includes thick-diameter carbon nanotubes, thin-diameter carbon nanotubes and reduced graphene oxide. The thick-diameter carbon nanotubes and the thin-diameter carbon nanotubes are interspersed with each other. The diameter of the thick-diameter carbon nanotubes is 50nm to 200nm, and the diameter of the thin-diameter carbon nanotubes is 6nm to 12nm. The thick-diameter carbon nanotubes, the thin-diameter carbon nanotubes and the reduced graphene oxide together form a three-dimensional network structure.

[0007] In the above conductive paste, the ratio of the total mass of the above-mentioned thick-diameter carbon nanotubes and the above-mentioned thin-diameter carbon nanotubes to the mass of the above-mentioned reduced graphene oxide is (4-100):1.

[0008] In the above conductive paste, the mass ratio of the above-mentioned thick-diameter carbon nanotubes to the above-mentioned thin-diameter carbon nanotubes is 1:(4-10).

[0009] The present invention also provides a preparation method of the above conductive paste, which includes the following steps:

[0010] Disperse the reduced graphene oxide in an organic solvent to form a suspension;

[0011] Add the thick-diameter carbon nanotubes and the thin-diameter carbon nanotubes to the above suspension, and disperse them by ultrasonic waves to obtain the conductive paste.

[0012] Furthermore, the present invention also provides an electrode paste, which includes the above conductive paste, an electrode active material, and a binder; the weight ratio of the conductive agent, the electrode active material, and the binder in the above conductive paste is (1-4):(92-98):(1-5).

[0013] Another aspect of the present invention provides an electrode sheet, which includes a microporous foil and an electrode material layer provided on the microporous foil, and the preparation raw materials of the electrode material layer include the above electrode paste.

[0014] The present invention further provides an electrode sheet, which includes a microporous foil, a first coating provided on the microporous foil, a second coating provided on the first coating, and a third coating provided on the second coating. The first coating and the third coating are prepared from the above electrode paste, and the second coating is prepared from a conductive paste prepared from the above conductive agent.

[0015] In the above preparation method, the thickness of the above first coating is 30μm-200μm, the thickness of the above second coating is 5μm-25μm, and the thickness of the above third coating is 30μm-200μm.

[0016] Furthermore, the present invention also provides a preparation method of an electrode sheet, which includes the following steps:

[0017] Provide the above conductive paste;

[0018] Provide the above electrode paste;

[0019] Coat the above electrode paste on the microporous foil to form a first coating;

[0020] Coat the above conductive paste on the above first coating to form a second coating;

[0021] Coat the above electrode paste on the above second coating to form a third coating.

[0022] The present invention also provides a battery, which includes the above-mentioned electrode sheet or the electrode sheet prepared by the above-mentioned method for preparing the electrode sheet.

[0023] Beneficial effects

[0024] In the present invention, a conductive paste is prepared by compounding carbon nanotubes with a thick tube diameter of 50 nm to 200 nm, carbon nanotubes with a thin tube diameter of 6 nm to 12 nm, and reduced graphene oxide. Among them, the carbon nanotubes with a thick tube diameter and the carbon nanotubes with a thin tube diameter are interpenetrated in the gaps between the carbon nanotubes of each other, and the carbon nanotubes of these two tube diameters and the reduced graphene oxide jointly form a three-dimensional network composite structure. This conductive paste is used to prepare the electrode paste, which can greatly improve the bonding performance of the electrode paste, and thus is beneficial to improving the rate discharge performance of the battery cell.

[0025] Furthermore, an electrode paste is prepared by using this conductive paste, an electrode active material, and a binder, and an electrode sheet is obtained by coating on a microporous foil. The carbon nanotubes with a thin tube diameter and the carbon nanotubes with a thick tube diameter can penetrate through the microporous foil, and the three-dimensional network conductive network formed by the carbon nanotubes and the reduced graphene oxide adheres the electrode paste on both surfaces of the microporous foil, greatly improving the bonding property of the electrode sheet; moreover, both the carbon nanotubes and the reduced graphene oxide have porous structures, which can absorb the electrolyte and improve the conduction rate of Li + , thereby reducing the concentration polarization inside the battery cell, and the rate discharge performance of the battery cell prepared is also significantly improved.

[0026] Furthermore, the above-mentioned electrode paste is coated on the microporous foil, and then a layer of the above-mentioned conductive paste is coated, and then another layer of the above-mentioned electrode paste is coated. By coating two layers of electrode paste with the conductive paste as an intermediate layer, the areal density of the electrode plate can be increased, and at the same time, the bonding property of the electrode material on the prepared electrode sheet is good. Coating the above-mentioned conductive agent paste in the middle can enhance the long-range conductivity of the electrode sheet and further improve the bonding property between layers. This electrode sheet can be used as a positive electrode sheet or a negative electrode sheet for preparing a battery, greatly improving the energy density of the battery cell prepared, and at the same time not affecting the kinetic performance of lithium ions. Description of the drawings

[0027] Figure 1 SEM image of the conductive paste obtained in Example 1;

[0028] Figure 2 SEM image of the carbon nanotubes in the conductive paste obtained in Example 1. Detailed implementation manners

[0029] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are given. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0031] An embodiment of the present invention provides a conductive paste, which includes a conductive agent and an organic solvent. The conductive agent includes thick-diameter carbon nanotubes, thin-diameter carbon nanotubes, and reduced graphene oxide. The thick-diameter carbon nanotubes and the thin-diameter carbon nanotubes are interpenetrated with each other. The diameter of the thick-diameter carbon nanotubes is 50 nm to 200 nm, and the diameter of the thin-diameter carbon nanotubes is 6 nm to 12 nm. The thick-diameter carbon nanotubes, the thin-diameter carbon nanotubes, and the reduced graphene oxide together form a three-dimensional network structure.

[0032] In one embodiment, in the above-mentioned conductive paste, the mass ratio of the above-mentioned thick-diameter carbon nanotubes to the above-mentioned thin-diameter carbon nanotubes is 1:(5 - 10).

[0033] In one embodiment, in the above-mentioned conductive paste, the ratio of the total mass of the above-mentioned thick-diameter carbon nanotubes and the above-mentioned thin-diameter carbon nanotubes to the mass of the above-mentioned reduced graphene oxide is (4 - 10):1.

[0034] In one embodiment, in the above-mentioned conductive paste, the ratio of the total mass of the above-mentioned thick-diameter carbon nanotubes and the above-mentioned thin-diameter carbon nanotubes to the mass of the above-mentioned reduced graphene oxide is (7 - 10):1.

[0035] In one embodiment, the above-mentioned organic solvent is N-methylpyrrolidone.

[0036] In one embodiment, the viscosity of the above-mentioned conductive paste is 5000 mPa·s to 16000 mPa·s.

[0037] It can be understood that the thick-diameter carbon nanotubes and the thin-diameter carbon nanotubes of the present application can be single-walled carbon nanotubes or multi-walled carbon nanotubes, and the tube lengths of the thick-diameter carbon nanotubes and the thin-diameter carbon nanotubes can be the same as those of commonly used carbon nanotubes in the art.

[0038] The diameter of the thin carbon nanotubes is much lower than the pore diameter (50 μm - 500 μm) of commonly used microporous foils, which can increase conductivity. The thick-diameter carbon nanotubes and thin-diameter carbon nanotubes interpenetrate each other, forming a three-dimensional network composite structure with reduced graphene oxide, and the formed network conductive network adheres the electrode slurries on both sides of the electrode sheet, greatly improving the adhesion of the electrode sheet. Moreover, both graphene and carbon nanotubes have porous structures, which can absorb electrolytes and improve the conduction rate of Li+, thereby reducing the concentration polarization inside the battery cell. The adhesion performance of the obtained electrode sheet is greatly improved, and the rate discharge performance of the prepared battery cell is also significantly improved.

[0039] An embodiment of the present invention further provides a preparation method of the above conductive slurry, including the following steps S1 - S2:

[0040] S1. Disperse reduced graphene oxide in an organic solvent to form a suspension.

[0041] In one embodiment, the above organic solvent is N-methylpyrrolidone. Further, the concentration of the above suspension is 0.5 wt% - 2 wt%.

[0042] It can be understood that the above reduced graphene oxide can be directly purchased or prepared by oneself by using methods such as the graphite oxide reduction method.

[0043] Graphene oxide is obtained as reduced graphene oxide through a reduction reaction. The specific surface area of reduced graphene oxide is relatively large, which is beneficial to absorbing and retaining electrolytes.

[0044] S2. Add thick-diameter carbon nanotubes and thin-diameter carbon nanotubes to the suspension obtained in the above step S2, and perform ultrasonic dispersion to obtain a conductive slurry.

[0045] In one embodiment, the conditions for the above ultrasonic treatment are: ultrasonic treatment at 20 KHz - 40 KHz for 3 h - 4 h.

[0046] Reduced graphene oxide and carbon nanotubes are prone to agglomeration and delamination, which affect conductivity and service life. By making reduced graphene oxide into a suspension, the flaky reduced graphene oxide is evenly dispersed and not prone to agglomeration. Then, carbon nanotubes are added. Through ultrasonic treatment, on the one hand, the carbon nanotubes can be evenly dispersed, and the thick carbon nanotubes are inserted into the gaps between the thin carbon nanotubes, interpenetrating each other to form carbon nanotubes similar to cross-linking, avoiding agglomeration. On the other hand, the carbon nanotubes are evenly dispersed in the suspension and combined with reduced graphene oxide to form a three-dimensional network structure. The above conductive agent can be used in the positive electrode slurry or the negative electrode slurry, and correspondingly can be used to prepare the positive electrode sheet or the negative electrode sheet.

[0047] Further, an embodiment of the present invention further provides an electrode slurry, which includes the above conductive slurry, an electrode active material, and a binder.

[0048] It is understandable that the above electrode paste can be a positive electrode paste or a negative electrode paste. When the electrode paste is a positive electrode paste, the active material therein is a positive electrode active material; similarly, when the electrode paste is a negative electrode paste, the active material therein is a negative electrode active material. Correspondingly, the positive electrode material or the negative electrode material in the formed positive electrode sheet or negative electrode sheet contains the above conductive agent. In one embodiment, when the above electrode paste is a positive electrode paste, the above electrode active material is selected from at least one of lithium cobaltate, lithium iron phosphate, and ternary materials. Further, the above electrode active material is preferably a ternary material.

[0049] The ternary material is inexpensive, has stable performance, good cycle performance, is balanced in terms of capacity and safety, has good overcharge resistance, and is easy to synthesize.

[0050] In one embodiment, the above binder is selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber latex, and carboxymethyl cellulose. Further, it is preferably selected from polyvinylidene fluoride.

[0051] Polyvinylidene fluoride has strong electrochemical corrosion resistance, which is beneficial to improving the service life of the battery.

[0052] In one embodiment, in the above electrode paste, the weight ratio of the conductive agent, the electrode active material, and the binder in the above conductive paste is (1-4):(92-98):(1-5).

[0053] In one embodiment, the viscosity of the above electrode paste is 5000 mPa·s to 16000 mPa·s.

[0054] Using the above conductive paste, electrode active material and binder to prepare an electrode paste, which is coated on a microporous foil. Currently, the pore diameter of the commonly used microporous foil is 50 μm to 500 μm. Carbon nanotubes with thin diameters and carbon nanotubes with thick diameters can pass through the microporous foil and form a three-dimensional network conductive structure with reduced graphene oxide. The formed network conductive network adheres the electrode paste on both sides of the electrode sheet, greatly improving the adhesion of the electrode sheet. Moreover, both reduced graphene oxide and carbon nanotubes have a porous structure, which can absorb the electrolyte and improve the conduction rate of Li + , thereby reducing the concentration polarization inside the battery cell, and the rate discharge performance of the battery cell prepared is also significantly improved.

[0055] The present invention also provides a preparation method of the above electrode paste, including the following steps:

[0056] Mix the electrode active material, the binder, and the above conductive paste to obtain an electrode paste.

[0057] In one embodiment, the viscosity of the above electrode paste is 5000 mPa·s to 16000 mPa·s.

[0058] It is understandable that in the above steps, organic solvents commonly used for preparing electrode paste can be further added according to the actual required viscosity of the electrode paste.

[0059] In one embodiment, the organic solvent is N-methylpyrrolidone.

[0060] Another embodiment of the present invention provides an electrode sheet, which includes a microporous foil and an electrode material layer provided on the microporous foil, and the preparation raw materials of the electrode material layer include the above-mentioned electrode paste.

[0061] One embodiment of the present invention further provides an electrode sheet, which includes a microporous foil, a first coating provided on the microporous foil, a second coating provided on the first coating, and a third coating provided on the second coating. The first coating and the third coating are prepared from the above-mentioned electrode paste, and the second coating is prepared from the above-mentioned conductive paste.

[0062] In one embodiment, the thickness of the first coating is 30 μm to 200 μm, the thickness of the second coating is 5 μm to 25 μm, and the thickness of the third coating is 30 μm to 200 μm.

[0063] Furthermore, one embodiment of the present invention provides a method for preparing an electrode sheet, which includes the following steps S10-S50.

[0064] S10: Provide the above-mentioned conductive paste.

[0065] S20: Provide the above-mentioned electrode paste.

[0066] S30: Coat the above-mentioned electrode paste on the microporous foil to form a first coating;

[0067] In one embodiment, the thickness of the above-mentioned first coating is 30 μm to 200 μm.

[0068] S40: Coat the above-mentioned conductive paste on the above-mentioned first coating to form a second coating.

[0069] In one embodiment, the thickness of the above-mentioned second coating is 5 μm to 25 μm.

[0070] S50: Coat the above-mentioned electrode paste on the above-mentioned second coating to form a third coating.

[0071] In one embodiment, the thickness of the above-mentioned third coating is 30 μm to 200 μm.

[0072] It should be noted that the thickness of the above-mentioned coating is the thickness of the coating formed after drying.

[0073] In one embodiment, the pore diameter of the microporous foil is 50 μm to 500 μm.

[0074] In one embodiment, transfer coating or extrusion coating is used for coating.

[0075] The above electrode paste is coated on the microporous foil, then a layer of the above conductive paste is coated, and then another layer of the above electrode paste is coated. By using the conductive paste as an intermediate layer to coat two layers of electrode paste, the areal density of the electrode sheet can be increased, and at the same time, the adhesion of the electrode material on the prepared electrode sheet is good. Coating a layer of the conductive agent of the present invention in the middle can enhance the long-range conductivity of the electrode sheet and further improve the adhesion between layers; the electrode sheet can be used as a positive electrode sheet or a negative electrode sheet for preparing a battery, so that the energy density of the battery cell prepared can be greatly improved without affecting the kinetic performance of lithium ions.

[0076] The present invention also provides a battery, which includes the above electrode sheet or the electrode sheet prepared by the above method for preparing an electrode sheet.

[0077] The present invention will be described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. It should be understood that the appended claims define the scope of the present invention, and those skilled in the art should realize that certain changes made to the embodiments of the present invention will be covered by the spirit and scope of the claims of the present invention. Specific Embodiments

[0079] Here are examples of the conductive agent, electrode sheet and its preparation method and application according to the present invention, but the present invention is not limited to the following embodiments.

[0080] Example 1

[0081] 1) Prepare a reduced graphene oxide suspension: Add 1 g of reduced graphene oxide to 100 mL of NMP and ultrasonicate for 6 h to obtain a reduced graphene oxide suspension.

[0082] 2) Add 8 g of carbon nanotubes with a small diameter (diameter: 6 nm to 12 nm, tube length: 5 μm to 20 μm), 1 g of carbon nanotubes with a large diameter (diameter: 50 nm to 200 nm, tube length: 5 μm to 20 μm) to the above reduced graphene oxide suspension, and ultrasonically disperse for 4 h at 20 KHz to 40 KHz. The viscosity of the slurry is 8000 mPa·s.

[0083] 3), Mix the conductive paste, ternary material, and polyvinylidene fluoride prepared above. The weight ratio of the conductive agent, ternary material, and polyvinylidene fluoride in the conductive paste is 1.5:96.5:2. Then add an appropriate amount of NMP to adjust the slurry viscosity to 10,000 mPa·s, stir and mix evenly to obtain the electrode slurry.

[0084] 4), Using the transfer coating method, coat the above electrode slurry on a microporous foil (foil pore diameter 50 μm to 500 μm), and the coating thickness is 190 μm to obtain an electrode sheet.

[0085] 5), Use the obtained electrode sheet as the positive electrode sheet of the battery to assemble and manufacture the battery cell.

[0086] Take the electrode sheet obtained in step 4) after rolling for a 180° steel plate peel test, and the peel strength of the electrode sheet is measured to be 0.371 kN / m.

[0087] Example 2

[0088] In Example 2, the mass ratio of the thin-diameter carbon nanotubes to the thick-diameter carbon nanotubes is 6:1, and other conditions are the same as in Example 1.

[0089] Take the rolled electrode sheet for a 180° steel plate peel test, and the peel strength of the electrode sheet is measured to be 0.372 kN / m.

[0090] Example 3

[0091] In Example 3, the mass ratio of the thin-diameter carbon nanotubes to the thick-diameter carbon nanotubes is 4:1, and other conditions are the same as in Example 1.

[0092] Take the rolled electrode sheet for a 180° steel plate peel test, and the peel strength of the electrode sheet is measured to be 0.322 kN / m.

[0093] Example 4

[0094] In Example 4, the mass ratio of the thin-diameter carbon nanotubes to the thick-diameter carbon nanotubes is 10:1, and other conditions are the same as in Example 1.

[0095] Take the rolled electrode sheet for a 180° steel plate peel test, and the peel strength of the electrode sheet is measured to be 0.372 kN / m

[0096] Comparative Example 1

[0097] 1), Compound SP and thin carbon nanotubes (the mass ratio of SP and thin carbon nanotubes is 1:8, the tube diameter: 6 nm to 12 nm, and the tube length: 5 μm to 20 μm) in NMP to obtain an SP-compounded carbon nanotube slurry.

[0098] 2), Mix the SP compounded carbon nanotube slurry, ternary material, and polyvinylidene fluoride. The weight ratio of the conductive agent (note: the conductive agent refers to SP and fine carbon nanotubes), ternary material, and polyvinylidene fluoride in the SP compounded carbon nanotube slurry is 1.5:96.5:2. Then add an appropriate amount of NMP to adjust the slurry viscosity to 10,000 mPa·s, and stir for 0.5 - 5 h to mix evenly, thus obtaining the electrode slurry.

[0099] 3), Adopt the transfer coating method to coat the above electrode slurry on the microporous foil (the pore diameter of the foil is 50 μm - 500 μm), and the coating thickness is 190 μm to obtain the electrode sheet.

[0100] 4), Use the obtained electrode sheet as the positive electrode sheet of the battery to assemble and prepare the battery cell.

[0101] Take the rolled electrode sheet obtained in step 4) for a 180° steel plate peel test, and the peel strength of the electrode sheet is measured to be 0.273 kN / m.

[0102] Comparative Example 2

[0103] Comparative Example 2 is basically the same as Example 1, the difference is that: in step 2), 9 g of fine carbon nanotubes (tube diameter is 6 - 12 nm, tube length is: 5 μm - 20 μm) are added as the conductive agent, and no thick carbon nanotubes are added.

[0104] Take the rolled electrode sheet for a 180° steel plate peel test, and the peel strength of the electrode sheet is measured to be 0.301 kN / m.

[0105] Comparative Example 3

[0106] Comparative Example 3 is basically the same as Example 1, the difference is that: in step 2), 9 g of thick carbon nanotubes (tube diameter is 150 nm, tube length is: 5 μm - 20 μm) are added as the conductive agent, and no fine carbon nanotubes are added.

[0107] Take the rolled electrode sheet for a 180° steel plate peel test, and the peel strength of the electrode sheet is measured to be 0.321 kN / m, but the specific surface area of the thick tube diameter carbon nanotubes is small and the conductivity is poor; the conductivity of the prepared electrode sheet is very poor and it is not suitable for lithium batteries.

[0108] Comparative Example 4

[0109] 1), Prepare a dispersion slurry by ultrasonicating 8 g of fine tube diameter carbon nanotubes (tube diameter is: 6 nm - 12 nm, tube length is: 5 μm - 20 μm), 1 g of thick tube diameter carbon nanotubes (tube diameter is: 50 nm - 200 nm, tube length is: 5 μm - 20 μm), 100 mL of NMP at 20 KHz - 40 KHz for 4 h.

[0110] 2), Add 1 g of reduced graphene oxide to 100 mL of NMP and sonicate it at 20 KHz - 40 KHz for 6 h to obtain a reduced graphene oxide suspension.

[0111] 3), Stir and mix the above dispersion, reduced graphene oxide suspension, ternary material and polyvinylidene fluoride. The weight ratio of the conductive agent (note: the conductive agent refers to graphene oxide, carbon nanotubes with small diameters and carbon nanotubes with large diameters), ternary material and polyvinylidene fluoride is 1.5:96.5:2. Then add an appropriate amount of NMP to adjust the slurry viscosity to 10000 mPa·s to prepare an electrode slurry.

[0112] 4), Using the transfer coating method, coat the above electrode slurry on a microporous foil (the pore diameter of the foil is 50 μm - 500 μm), and the coating thickness is 190 μm to obtain an electrode sheet.

[0113] 5), Use the obtained electrode sheet as the positive electrode sheet of the battery to assemble and prepare a battery cell.

[0114] Take the electrode sheet obtained in step 4) after rolling and perform a 180° steel plate peel test.

[0115] In step 3), it is difficult to evenly disperse the raw materials. It is difficult for carbon nanotubes with two diameters to form a complete three-dimensional network composite structure with reduced graphene oxide. The conductivity of the prepared battery cell is not good, and the peel strength of the electrode sheet is measured to be 0.263 kN / m.

[0116] Example 5

[0117] 1), Take the conductive slurry prepared in Example 1.

[0118] 2), Coat the electrode slurry prepared in Example 1 on a microporous foil (the pore diameter of the foil is 50 μm - 500 μm). After the electrode sheet is dried (the coating thickness after drying is 150 μm); then coat a layer of the above-prepared conductive slurry (the coating thickness after drying is 15 μm), and then coat a layer of the electrode slurry prepared in Example 1 (the coating thickness after drying is 150 μm). Use the transfer coating method to obtain an electrode sheet.

[0119] 3), Use the obtained electrode sheet as the positive electrode sheet of the battery to assemble and prepare a battery cell.

[0120] Take the electrode sheet obtained in step 2) after rolling and perform a 180° steel plate peel test. The peel strength of the electrode sheet is measured to be 0.370 N / m.

[0121] Take the battery cell obtained in step 3) for energy density testing. The energy density of this battery cell reaches 350 Wh / kg. Since a conductive paste layer of the present invention is introduced, it can improve the long-range conductivity of the electrode sheet, and while increasing the energy density of the battery cell, it will not affect the kinetic performance of lithium ions.

[0122] Example 6

[0123] 1), Take the conductive paste prepared in Example 1.

[0124] 2), Coat the electrode paste prepared in Example 1 on a microporous foil (the pore diameter of the foil is 50 μm to 500 μm). After the electrode sheet is dried (the coating thickness after drying is 120 μm); then coat another layer of the above-prepared conductive paste (the coating thickness after drying is 15 μm), and then coat another layer of the electrode paste prepared in Example 1 (the coating thickness after drying is 180 μm). Adopt the transfer coating method to obtain the electrode sheet.

[0125] 3), Use the obtained electrode sheet as the positive electrode sheet of the battery to assemble and obtain the battery cell.

[0126] Take the rolled electrode sheet obtained in step 2) for 180° steel plate peeling test. The peeling strength of the electrode sheet is measured to be 0.367 kN / m.

[0127] Take the battery cell for energy density testing. The energy density of this battery cell reaches 352 Wh / kg.

[0128] Example 7

[0129] In Example 7, the middle conductive paste coating is not coated on the electrode sheet, and other conditions are the same as those in Example 5.

[0130] Take the rolled electrode sheet obtained in step 2) for 180° steel plate peeling test. The peeling strength of the electrode sheet is measured to be 0.358 kN / m.

[0131] Take the obtained battery cell for energy density testing. The energy density of this battery cell reaches 305 Wh / kg. However, due to the poor long-range conductivity of the electrode sheet, the volume resistance of the battery cell is large and the conductivity decreases.

[0132] Example 8

[0133] In Example 8, the middle coating of the electrode sheet is prepared from the SP compounded carbon nanotube paste prepared in Comparative Example 1, and other conditions are the same as those in Example 5.

[0134] Take the rolled electrode sheet for 180° steel plate peeling test. The peeling strength of the electrode sheet is measured to be 0.352 kN / m.

[0135] The obtained battery cells were subjected to energy density tests, and the energy density of the battery cells reached 325 Wh / kg. Rate performance tests

[0136] Rate performance

[0137] Furthermore, the battery cells prepared in Example 1 and Comparative Examples 1 and 2 were subjected to rate performance tests. The test method referred to the enterprise standard, and the test results are shown in Table 1.

[0138] Table 1

[0139]

[0140] It can be seen from the results in Table 1 that when the electrode paste prepared from the conductive agent prepared by the present invention is used to prepare the positive electrode sheet, the adhesiveness of the prepared positive electrode sheet is improved, and the rate performance is improved. Especially, it has outstanding advantages under high-rate discharge conditions. Moreover, the energy density of the battery cells prepared with this positive electrode sheet can reach 350 Wh / kg, and at the same time, it will not affect the kinetic performance of lithium ions, greatly improving the utilization rate of auxiliary materials such as foil and separator.

[0141] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0142] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A conductive paste, characterized in that, the conductive paste comprises a conductive agent and an organic solvent, the conductive agent comprises thick-diameter carbon nanotubes, thin-diameter carbon nanotubes and reduced graphene oxide, the thick-diameter carbon nanotubes and the thin-diameter carbon nanotubes are interpenetrated with each other, the diameter of the thick-diameter carbon nanotubes is 50nm - 200nm, the diameter of the thin-diameter carbon nanotubes is 6nm - 12nm, the thick-diameter carbon nanotubes, the thin-diameter carbon nanotubes and the reduced graphene oxide jointly form a three-dimensional network structure, and both the carbon nanotubes and the reduced graphene oxide have porous structures; the preparation method of the conductive paste comprises the following steps: Disperse the reduced graphene oxide in the organic solvent to form a suspension; Add the thick-diameter carbon nanotubes and the thin-diameter carbon nanotubes into the suspension and disperse them by ultrasonic waves to obtain the conductive paste.

2. The conductive paste according to claim 1, characterized in that, the ratio of the total mass of the thick-diameter carbon nanotubes and the thin-diameter carbon nanotubes to the mass of the reduced graphene oxide is (4 - 10):

1.

3. The conductive paste according to claim 1 or 2, characterized in that, the mass ratio of the thick-diameter carbon nanotubes to the thin-diameter carbon nanotubes is 1:(4 - 10).

4. A preparation method of a conductive paste according to any one of claims 1 - 3, characterized in that, comprises the following steps: Disperse the reduced graphene oxide in the organic solvent to form a suspension; Add the thick-diameter carbon nanotubes and the thin-diameter carbon nanotubes into the suspension and disperse them by ultrasonic waves to obtain the conductive paste.

5. An electrode paste, characterized in that, the components of the electrode paste comprise an electrode active material, a binder and the conductive paste according to any one of claims 1 - 3; the weight ratio of the conductive agent, the electrode active material and the binder in the conductive paste is (1 - 4):(92 - 98):(1 - 5).

6. An electrode sheet, characterized in that, the electrode sheet comprises a microporous foil and an electrode material layer provided on the microporous foil, and the preparation raw materials of the electrode material layer comprise the electrode paste according to claim 5.

7. An electrode sheet, characterized in that, the electrode sheet comprises a microporous foil, a first coating provided on the microporous foil, a second coating provided on the first coating and a third coating provided on the second coating, the first coating and the third coating are prepared from the electrode paste according to claim 5, and the second coating is prepared from the conductive paste according to any one of claims 1 - 3.

8. The electrode sheet according to claim 7, characterized in that, the thickness of the first coating is 30μm - 200μm, the thickness of the second coating is 5μm - 25μm, and the thickness of the third coating is 30μm - 200μm.

9. A preparation method of an electrode sheet, characterized in that, comprises the following steps: Provide the conductive paste according to any one of claims 1 - 3; Provide the electrode paste according to claim 5; Coat the electrode paste on the microporous foil to form a first coating; Coat the conductive paste on the first coating to form a second coating; The electrode paste is coated on the second coating to form a third coating.

10. A battery, characterized in that the battery includes the electrode sheet as described in claim 6, or the electrode sheet as described in claim 7 or 8, or the electrode sheet prepared by the preparation method as described in claim 9.

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