CN114464770A - Electrode plate and battery comprising same - Google Patents
Electrode plate and battery comprising same Download PDFInfo
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- CN114464770A CN114464770A CN202210039438.5A CN202210039438A CN114464770A CN 114464770 A CN114464770 A CN 114464770A CN 202210039438 A CN202210039438 A CN 202210039438A CN 114464770 A CN114464770 A CN 114464770A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
Abstract
The invention provides an electrode plate and a battery comprising the same. The electrode plate comprises a current collector, a first active material layer, a second active material layer and a functional coating, wherein the electronic conductivity of the second active material layer is greater than that of the first active material layer; when the battery assembled by the electrode plate is punctured by a foreign object, the functional coating can wrap the first active material layer and the second active material layer on the surface of the electrode plate due to the high extensibility and the electronic insulation property of the functional coating, so that short circuit of the positive electrode and the negative electrode can be greatly reduced or even avoided, and the needling safety of the battery is improved.
Description
Technical Field
The invention belongs to the technical field of batteries, and relates to an electrode plate and a battery comprising the same.
Background
At present, the development of batteries mainly advances towards high energy density and ultra-fast charge technology, such as application of high-nickel ternary positive electrode materials and silicon-carbon negative electrode materials, so that the intrinsic safety of the batteries is greatly deteriorated, and in addition, the safety accidents of the batteries are frequent due to abuse under various conditions, such as external uncontrollable factors of overcharge, high temperature, impact and the like, so that the improvement of the safety of the batteries is very necessary.
There are many ways to improve the safety of the battery, such as modification of a diaphragm coating, high-temperature-resistant diaphragms, polymer composite current collectors, use of electrolyte flame-retardant additives, coating of positive electrode materials, and the like. Although these methods have improved safety to some extent, there are many problems, such as limited improvement, difficulty in manufacturing, high cost, and deterioration of electrical properties of the battery.
Therefore, more and more new technologies for improving safety are being developed, such as coating layers on the surfaces of positive and negative electrodes to ensure lithium ion conduction and to exhibit electrical insulation properties, as disclosed in the prior art, so as to improve the safety of the battery.
Disclosure of Invention
During research, the inventors of the present application found that the greatest problem exists in the above manner of applying the coating slurry on the surface of the pole piece to form the coating layer is that: in the coating process, the coating slurry infiltrates into the pores inside the pole piece to form a package for the active materials, so that the electronic insulation among the active materials is caused, and the electrical performance of the battery is influenced. Therefore, although the manner of coating the ion conductivity and electronic insulation coating on the surface of the pole piece can improve the safety of the battery to a certain extent, the problem of obviously deteriorating the electrical performance of the battery needs to be solved.
In order to overcome the defects of the prior art, the invention provides an electrode plate and a battery comprising the same. Specifically, the invention provides the following technical scheme:
an electrode sheet comprising a current collector, a first active material layer provided on at least one side surface of the current collector, a second active material layer provided on a surface of the first active material layer, and a functional coating provided on a surface of the second active material layer; the electron conductivity of the second active material layer is larger than the electron conductivity of the first active material layer.
According to the invention, the electrode plate with the double-layer active substance layer is constructed in a double-layer coating mode, so that the safety of the battery when the battery is pierced by a foreign object can be improved, and the influence of the functional coating on the electrical performance of the battery can be reduced to the greatest extent. In the two-layer active material layer, the electron conductivity of the second active material layer close to the functional coating is larger than that of the first active material layer far from the functional coating. When the slurry for preparing the functional coating is coated on the surface of the second active material layer, the slurry can be infiltrated into the second active material layer, the electronic resistance of the second active material layer can be obviously increased due to the fact that the slurry for preparing the functional coating comprises an electronic insulating material (such as a polymer), but through a double-layer coating technology, the electronic conductivity of the second active material layer close to the functional coating is designed to be larger than that of the first active material layer far away from the functional coating, and the influence of the infiltration of the slurry of the functional coating on the increase of the internal resistance of the electrode plate can be reduced.
According to an embodiment of the present invention, the first active material layer has a compacted density that is less than a compacted density of the second active material layer.
According to the invention, the compaction density of the first active material layer is further made smaller than that of the second active material layer, namely the second active material layer has higher compaction density, so that the influence of internal permeation of functional coating slurry on the increase of the internal resistance of the electrode plate can be greatly reduced, the electrical property of the battery is further ensured, the safety performance of the battery can be improved, and the energy density of the battery is also considered. That is to say, through setting up such compaction density, reduce the internal infiltration of functional coating thick liquids, both realized promoting the effect of safety, furthest has reduced the problem that the internal resistance that the functional coating brought increases again.
According to an embodiment of the present invention, the first active material layer includes a first active material and a first conductive agent, and the second active material layer includes a second active material and a second conductive agent; and the content of the first conductive agent in the first active material layer is less than the content of the second conductive agent in the second active material layer.
According to an embodiment of the present invention, the first active material layer includes a first active material and a first conductive agent, and the second active material layer includes a second active material and a second conductive agent; and the content of the first conductive agent in the first active material layer is less than or equal to the content of the second conductive agent in the second active material layer, and the conductivity of the second conductive agent is greater than that of the first conductive agent, namely the electronic conductivity of the second conductive agent is greater than that of the first conductive agent.
According to an embodiment of the present invention, the compacted density of the second conductive agent is greater than the compacted density of the first conductive agent. The compaction density of the second conductive agent is greater than that of the first conductive agent, so that the compaction density of the second active material layer is greater than that of the first active material layer, the influence of internal permeation of functional coating slurry on the increase of internal resistance of the electrode plate can be greatly reduced, the electrical property of the battery is further ensured, the safety performance of the battery can be improved, and the energy density of the battery is also considered.
According to an embodiment of the present invention, the content of the first conductive agent is 0.5 to 5 wt%, and the content of the second conductive agent is 0.5 to 5 wt%.
In the invention, the content of the first conductive agent is the mass percentage of the mass of the first conductive agent in the total mass of the first active material layer; the content of the second conductive agent is the mass percentage of the mass of the second conductive agent to the total mass of the second active material layer.
According to an embodiment of the present invention, the first conductive agent and the second conductive agent are the same or different and are independently selected from at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.
Preferably, the first conductive agent is selected from conductive carbon black and the second conductive agent is selected from carbon nanotubes.
According to an embodiment of the present invention, the first active material layer further includes a first binder, and the second active material layer further includes a second binder.
According to an embodiment of the present invention, the first binder and the second binder are the same or different and are independently selected from at least one of sodium carboxymethylcellulose, styrene-butadiene latex, polytetrafluoroethylene, polyethylene oxide.
According to an embodiment of the present invention, the thickness of the first active material layer is larger than the thickness of the second active material layer.
According to an embodiment of the present invention, the thickness of the first active material layer is 1 μm to 100 μm.
According to an embodiment of the present invention, the thickness of the second active material layer is 0.1 μm to 20 μm.
According to an embodiment of the invention, the functional coating has a thickness of 0.1 μm to 20 μm.
According to an embodiment of the invention, the functional coating comprises a polymer.
According to an embodiment of the present invention, the functional coating further comprises a plasticizer and a lithium salt.
According to the embodiment of the invention, the functional coating comprises the following components in percentage by mass:
30-80% of polymer, 0-50% of plasticizer and 0-50% of lithium salt.
According to an embodiment of the present invention, the polymer includes, but is not limited to, at least one of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, and polymethyl methacrylate. The polymer has the main function of swelling electrolyte, so that the normal conduction of lithium ions is ensured; the coating comprising the polymer has high elongation at break, and can ensure that the functional coating wraps the active substance layer when a foreign object punctures, thereby improving the safety.
According to an embodiment of the present invention, the plasticizer comprises a small molecule material including, but not limited to, at least one of ethylene carbonate, succinonitrile, methyl methacrylate, ethyl methacrylate, and propyl methacrylate. The plasticizer mainly has the effects of improving the swelling performance of the polymer in the electrolyte, so that the ionic conductivity of the functional coating is improved, and meanwhile, the addition of the plasticizer can also reduce the crystallinity of the polymer and improve the fracture elongation of the functional coating.
According to an embodiment of the present invention, the lithium salt includes, but is not limited to, at least one of lithium bistrifluoromethylsulfonyl imide, lithium bistrifluorosulfonimide, lithium bisoxalato borate, and lithium difluorooxalato borate. The main function of the lithium salt is to improve the ionic conductivity of the functional coating.
According to an embodiment of the invention, the functional coating is a highly extended, lithium ion conducting, non-conducting coating.
According to an embodiment of the present invention, the functional coating is prepared by the following method:
and mixing a polymer, a plasticizer, a lithium salt and an organic solvent, coating the mixture on the surface of the active material layer, and drying to obtain the functional coating.
Wherein, the organic solvent comprises but is not limited to at least one of N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone.
According to an embodiment of the present invention, the electrode tab is a positive electrode tab or a negative electrode tab.
According to an embodiment of the present invention, when the electrode sheet is a positive electrode sheet, the current collector is a positive electrode current collector, the active material layer is a positive electrode active material layer, and the active material is a positive electrode active material.
According to an embodiment of the present invention, when the electrode sheet is a negative electrode sheet, the current collector is a negative electrode current collector, the active material layer is a negative electrode active material layer, and the active material is a negative electrode active material.
According to an embodiment of the present invention, the positive electrode current collector includes, but is not limited to, an aluminum material, an aluminum/polymer, an aluminum/carbon composite, and specifically, the aluminum material, the aluminum/polymer, the aluminum/carbon composite is a porous or non-porous aluminum material, an aluminum/polymer, an aluminum/carbon composite foil.
According to an embodiment of the present invention, the negative electrode current collector includes, but is not limited to, a copper material, a copper/polymer, a copper/carbon composite, and particularly, the copper material, the copper/polymer, the copper/carbon composite is a porous or non-porous copper material, a copper/polymer, or a copper/carbon composite foil.
According to an embodiment of the present invention, the positive electrode active material includes a composite oxide. Specifically, the composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel, and illustratively, the composite oxide includes at least one of lithium cobaltate, a lithium nickel manganese cobalt ternary material, lithium manganate, lithium nickel manganate and lithium iron phosphate.
According to an embodiment of the present invention, the negative active material is selected from natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO2Spinel-structured lithiated TiO2-Li4Ti5O12And one or more of Li-Al alloy.
The invention also provides a battery, which comprises the electrode plate.
According to an embodiment of the invention, the battery comprises a positive plate, a negative plate and a diaphragm arranged between the positive plate and the negative plate at intervals, wherein at least one of the positive plate and the negative plate is the electrode plate.
The invention has the beneficial effects that:
the invention provides an electrode sheet and a battery comprising the same. The electrode plate comprises a current collector, a first active material layer, a second active material layer and a functional coating, wherein the electronic conductivity of the second active material layer is greater than that of the first active material layer; when the battery assembled by the electrode plate is punctured by a foreign object, the functional coating can wrap the first active material layer and the second active material layer on the surface of the electrode plate due to the high extensibility and the electronic insulation property of the functional coating, so that short circuit of the positive electrode and the negative electrode can be greatly reduced or even avoided, and the needling safety of the battery is improved. Furthermore, the compaction density of the first active material layer is smaller than that of the second active material layer, namely, the second active material layer has higher compaction density, so that the influence of internal permeation of functional coating slurry on the increase of the internal resistance of the electrode plate can be greatly reduced, the electrical property of the battery is further ensured, the safety performance of the battery can be improved, and the energy density of the battery is also considered.
Drawings
Fig. 1 is a schematic structural view of an electrode sheet according to a preferred embodiment of the present invention.
Fig. 2 is a schematic structural view of an electrode sheet according to a preferred embodiment of the present invention.
Reference numerals: 1-current collector, 2-first active material layer, 3-second active material layer, 4-functional coating.
Detailed Description
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
In the description of the present invention, it should be noted that the terms "first", "second", etc. are used for descriptive purposes only and do not indicate or imply relative importance.
Example 1
Preparing a double-layer coating positive plate containing a functional coating:
1) the preparation method comprises the steps of uniformly mixing NCM811 (positive electrode active material), conductive agent conductive carbon black (Super-P) and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 97.5:1:1.5 to prepare lower-layer coating positive electrode slurry (used for forming a first active material layer with the thickness of 50 mu m), uniformly mixing NCM811 (positive electrode active material), conductive agent conductive carbon black (Super-P) and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 96.5:2:1.5 to prepare upper-layer coating positive electrode slurry (used for forming a second active material layer with the thickness of 10 mu m), coating the lower-layer coating positive electrode slurry on two surfaces of a current collector aluminum foil, coating the upper-layer coating positive electrode slurry on the surface of the lower-layer coating positive electrode slurry, and synchronously finishing the upper-layer coating and the lower-layer coating on double-layer coating equipment. Then drying the slurry at 100 ℃ to form a double-layer positive active material layer, and then carrying out cold pressing;
2) dissolving polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene carbonate and lithium bis (trifluoromethyl) sulfonyl imide in an organic solvent DMAC (dimethylacetamide) according to a mass ratio of 70:10:20, uniformly mixing to prepare functional coating slurry, coating the functional coating slurry on the surface of the double-layer positive active material layer, and performing air blast drying at 80 ℃ to obtain a functional coating with the thickness of 10 microns;
3) and (4) cutting edges, cutting pieces, slitting, and slitting to obtain the positive plate containing the functional coating.
Preparing a negative plate:
1) preparing graphite, conductive carbon black (Super-P) serving as a conductive agent, carboxymethyl cellulose sodium (CMC) serving as a thickening agent and Styrene Butadiene Rubber (SBR) serving as a binder into negative electrode slurry according to the mass ratio of 96.5:1.0:1.0:1.5, coating the negative electrode slurry on a current collector copper foil, drying the current collector copper foil at 90 ℃ to form a negative electrode active material layer with the thickness of 60 mu m, and cold pressing the negative electrode active material layer;
2) and trimming, cutting into pieces, slitting, and slitting to obtain the lithium ion battery negative plate.
Preparing an electrolyte: mixing lithium hexafluorophosphate (LiPF)6) The electrolyte solution was obtained by dissolving the above-mentioned compound in a mixed solvent composed of Ethylene Carbonate (EC), dimethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) (the mass ratio of the three components was 1:1: 1).
Preparing a lithium ion battery: and winding the positive plate, the diaphragm and the negative plate into a battery cell, wherein the battery cell capacity is about 5 Ah. The diaphragm is positioned between the adjacent positive plate and negative plate, the positive electrode is led out by aluminum tab spot welding, and the negative electrode is led out by nickel tab spot welding; then the electric core is placed in an aluminum-plastic packaging bag, the electrolyte is injected after baking, and the polymer lithium ion battery is finally prepared after the processes of packaging, formation, sorting and the like.
Example 2
Preparing a positive plate:
1) uniformly mixing NCM811 (positive active material), conductive carbon black (Super-P) serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder according to the mass ratio of 97.5:1:1.5 to prepare positive slurry, coating the positive slurry on two surfaces of a current collector aluminum foil, drying at 100 ℃ to form a positive active material layer with the thickness of 60 mu m, and then carrying out cold pressing;
2) and (4) trimming, cutting into pieces, slitting, and slitting to obtain the positive plate.
Preparing a negative plate containing a functional coating:
1) preparing graphite, conductive carbon black (Super-P) serving as a conductive agent, carboxymethyl cellulose sodium (CMC) serving as a thickening agent and Styrene Butadiene Rubber (SBR) serving as a binder into lower-layer coating negative electrode slurry (used for forming a first active material layer with the thickness of 50 mu m) according to the mass ratio of 96.5:1.0:1.0:1.5, preparing upper-layer coating negative electrode slurry (used for forming a second active material layer with the thickness of 10 mu m) from the graphite, the conductive carbon black (Super-P) serving as the conductive agent, the carboxymethyl cellulose sodium (CMC) serving as the thickening agent and the Styrene Butadiene Rubber (SBR) serving as the binder according to the mass ratio of 95.5:2.0:1.0:1.5, coating the lower-layer coating negative electrode slurry on two surfaces of a current collector copper foil, coating the upper-layer coating negative electrode slurry on the surface of the lower-layer coating negative electrode slurry, and coating the upper layer and the lower layer on a double-layer coating device synchronously. Coating the slurry on a current collector copper foil, drying at 90 ℃ to form a double-layer negative active material layer, and then carrying out cold pressing;
2) dissolving polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene carbonate and lithium bis (trifluoromethyl) sulfonyl imide in an organic solvent DMAC (dimethylacetamide) according to a mass ratio of 70:10:20, uniformly mixing to prepare coating slurry, coating the coating slurry in a negative electrode active material layer, and performing air drying at 80 ℃ to obtain a functional coating with the thickness of 10 microns;
3) and cutting edges, cutting pieces and strips, and preparing the negative plate containing the functional coating after the strips are cut.
Preparing an electrolyte and a lithium ion battery: as in embodiment 1, no further description is provided herein.
Example 3
Preparing a positive plate containing a functional coating:
1) the preparation method comprises the steps of uniformly mixing NCM811 (positive electrode active material), conductive agent conductive carbon black (Super-P) and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 97.5:1:1.5 to prepare lower-layer coating positive electrode slurry (used for forming a first active material layer with the thickness of 50 mu m), uniformly mixing NCM811 (positive electrode active material), conductive agent conductive carbon black (Super-P) and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 95.5:3:1.5 to prepare upper-layer coating positive electrode slurry (used for forming a second active material layer with the thickness of 10 mu m), coating the lower-layer coating positive electrode slurry on two surfaces of a current collector aluminum foil, coating the upper-layer coating positive electrode slurry on the surface of the lower-layer coating positive electrode slurry, and synchronously finishing the upper-layer coating and the lower-layer coating on double-layer coating equipment. Then drying the slurry at 100 ℃ to form a double-layer positive active material layer, and then carrying out cold pressing;
2) dissolving polyvinylidene fluoride-hexafluoropropylene copolymer, methyl methacrylate and lithium bis (trifluoromethyl) sulfonyl imide in an organic solvent DMF (dimethyl formamide) according to a mass ratio of 70:10:20, uniformly mixing to prepare functional coating slurry, coating the functional coating slurry on the surface of the double-layer positive active material layer, and performing air blast drying at 80 ℃ to obtain a functional coating with the thickness of 10 mu m;
3) and (4) cutting edges, cutting pieces, slitting, and slitting to obtain the positive plate containing the functional coating.
Preparing a negative plate: as in embodiment 1, the description is omitted here;
preparing an electrolyte and a lithium ion battery: as in embodiment 1, no further description is provided herein.
Example 4
Preparing a positive plate containing a functional coating:
1) the preparation method comprises the steps of uniformly mixing NCM811 (positive electrode active material), conductive agent conductive carbon black (Super-P) and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 97.5:1:1.5 to prepare lower-layer coating positive electrode slurry (used for forming a first active material layer with the thickness of 50 mu m), uniformly mixing NCM811 (positive electrode active material), conductive agent conductive carbon black (Super-P) and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 96.5:2:1.5 to prepare upper-layer coating positive electrode slurry (used for forming a second active material layer with the thickness of 10 mu m), coating the lower-layer coating positive electrode slurry on two surfaces of a current collector aluminum foil, coating the upper-layer coating positive electrode slurry on the surface of the lower-layer coating positive electrode slurry, and synchronously finishing the upper-layer coating and the lower-layer coating on double-layer coating equipment. Then drying the slurry at 100 ℃ to form a double-layer positive active material layer, and then carrying out cold pressing;
2) dissolving polyvinylidene fluoride-hexafluoropropylene copolymer, methyl methacrylate and lithium bis (trifluoromethyl) sulfonyl imide in an organic solvent DMF (dimethyl formamide) according to a mass ratio of 70:10:20, uniformly mixing to prepare functional coating slurry, coating the functional coating slurry on the surface of the double-layer positive electrode active material layer, and performing air blast drying at 80 ℃ to obtain a functional coating with the thickness of 5 mu m;
3) and (4) cutting edges, cutting pieces, slitting, and slitting to obtain the positive plate containing the functional coating.
Preparing a negative plate: as in embodiment 1, the description is omitted here;
preparing an electrolyte and a lithium ion battery: as in embodiment 1, no further description is provided herein.
Example 5
Preparing a positive plate: as in embodiment 4, the description is omitted here;
preparing a negative plate containing a functional coating:
1) preparing graphite, conductive carbon black (Super-P) serving as a conductive agent, carboxymethyl cellulose sodium (CMC) serving as a thickening agent and Styrene Butadiene Rubber (SBR) serving as a binder into lower-layer coating negative electrode slurry (used for forming a first active material layer with the thickness of 50 mu m) according to the mass ratio of 96.5:1.0:1.0:1.5, preparing upper-layer coating negative electrode slurry (used for forming a second active material layer with the thickness of 10 mu m) from the graphite, the conductive carbon black (Super-P) serving as the conductive agent, the carboxymethyl cellulose sodium (CMC) serving as the thickening agent and the Styrene Butadiene Rubber (SBR) serving as the binder according to the mass ratio of 95.5:2.0:1.0:1.5, coating the lower-layer coating negative electrode slurry on two surfaces of a current collector copper foil, coating the upper-layer coating negative electrode slurry on the surface of the lower-layer coating negative electrode slurry, and coating the upper layer and the lower layer on a double-layer coating device synchronously. Coating the slurry on a current collector copper foil, drying at 90 ℃ to form a double-layer negative active material layer, and then carrying out cold pressing;
2) dissolving polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene carbonate and lithium bis (trifluoromethyl) sulfonyl imide in an organic solvent DMAC (dimethylacetamide) according to a mass ratio of 70:10:20, uniformly mixing to prepare coating slurry, coating the coating slurry in a negative electrode active material layer, and performing air drying at 80 ℃ to obtain a functional coating with the thickness of 5 microns;
3) and cutting edges, cutting pieces and strips, and preparing the negative plate containing the functional coating after the strips are cut.
Preparing an electrolyte and a lithium ion battery: as in embodiment 1, no further description is provided herein.
Example 6
Preparing a double-layer coating positive plate containing a functional coating:
1) the preparation method comprises the steps of uniformly mixing NCM811 (positive active material), conductive agent conductive carbon black (Super-P) and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 97.5:1:1.5 to prepare lower-layer coating positive slurry (used for forming a first active material layer with the thickness of 50 mu m), uniformly mixing NCM811 (positive active material), conductive agent single-walled carbon nanotubes and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 97.5:1:1.5 to prepare upper-layer coating positive slurry (used for forming a second active material layer with the thickness of 10 mu m), coating the lower-layer coating positive slurry on two surfaces of an aluminum foil, coating the upper-layer coating positive slurry on the surface of the lower-layer coating positive slurry, and synchronously finishing the upper-layer coating and the lower-layer coating on double-layer coating equipment. Then drying the slurry at 100 ℃ to form a double-layer positive active material layer, and then carrying out cold pressing;
2) dissolving polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene carbonate and lithium bis (trifluoromethyl) sulfonyl imide in an organic solvent DMAC (dimethylacetamide) according to a mass ratio of 70:10:20, uniformly mixing to prepare functional coating slurry, coating the functional coating slurry on the surface of the double-layer positive active material layer, and performing air blast drying at 80 ℃ to obtain a functional coating with the thickness of 10 microns;
3) and (4) cutting edges, cutting pieces, slitting, and slitting to obtain the positive plate containing the functional coating.
Preparing a negative plate: same as in example 1.
Preparing electrolyte and lithium ion battery: as in embodiment 1, no further description is provided herein.
Comparative example 1
Preparing a positive plate:
1) uniformly mixing NCM811 (positive active material), conductive carbon black (Super-P) serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder according to the mass ratio of 97.5:1:1.5 to prepare positive slurry, coating the positive slurry on two surfaces of a current collector aluminum foil, drying at 100 ℃ to form a positive active material layer with the thickness of 60 mu m, and then carrying out cold pressing;
2) and (4) cutting edges, cutting pieces, slitting, and slitting to obtain the positive plate containing the bifunctional coating.
Preparing a negative plate: as in embodiment 1, detailed description thereof is omitted.
Preparing electrolyte and a lithium ion battery: as in embodiment 1, detailed description thereof is omitted.
Comparative example 2
Preparing a positive plate containing a functional coating:
1) uniformly mixing NCM811 (positive active material), conductive carbon black (Super-P) serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder according to the mass ratio of 97:1.5:1.5 to prepare positive slurry, coating the positive slurry on two surfaces of a current collector aluminum foil, drying at 100 ℃ to form a positive active material layer with the thickness of 60 mu m, and then carrying out cold pressing;
2) dissolving polyvinylidene fluoride-hexafluoropropylene copolymer, methacrylate and lithium bis (trifluoromethyl) sulfonyl imide in an organic solvent DMAC (dimethylacetamide) according to a mass ratio of 70:10:20, uniformly mixing to prepare coating slurry, coating the coating slurry on the surface of a positive active material, and performing air-blast drying at 80 ℃ to obtain a functional coating with the thickness of 10 microns;
3) and (4) cutting edges, cutting pieces, slitting, and slitting to obtain the positive plate containing the bifunctional coating.
Preparing a negative plate: as in embodiment 1, the description is omitted here;
preparing an electrolyte and a lithium ion battery: as in embodiment 1, no further description is provided herein.
Comparative example 3
Preparing a positive plate containing a functional coating:
1) the preparation method comprises the steps of uniformly mixing NCM811 (positive electrode active material), conductive agent conductive carbon black (Super-P) and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 97:1.5:1.5 to prepare lower-layer coating positive electrode slurry (used for forming a first active material layer with the thickness of 50 mu m), uniformly mixing NCM811 (positive electrode active material), conductive agent conductive carbon black (Super-P) and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 97.5:1:1.5 to prepare upper-layer coating positive electrode slurry (used for forming a second active material layer with the thickness of 10 mu m), coating the lower-layer coating positive electrode slurry on two surfaces of a current collector aluminum foil, coating the upper-layer coating positive electrode slurry on the surface of the lower-layer coating positive electrode slurry, and synchronously coating the upper layer and the lower layer by using a double-layer coating device. Then drying the slurry at 100 ℃ to form a double-layer positive active material layer, and then carrying out cold pressing;
2) dissolving polyacrylonitrile, methacrylate and acetylene black in an organic solvent DMAC (dimethylacetamide) according to a mass ratio of 50:10:40, uniformly mixing to prepare coating slurry, coating the coating slurry on the surface of a positive active material layer, and performing forced air drying at 60 ℃ to obtain a functional coating with the thickness of 10 microns;
3) and (4) cutting edges, cutting pieces, slitting, and slitting to obtain the positive plate containing the functional coating.
Preparing a negative plate: as in embodiment 1, the description is omitted here;
preparing an electrolyte and a lithium ion battery: as in embodiment 1, the description is omitted here;
comparative example 4
Preparing a positive plate:
1) uniformly mixing NCM811 (positive active material), conductive carbon black (Super-P) serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder according to the mass ratio of 97:1.5:1.5 to prepare positive slurry, coating the positive slurry on two surfaces of a current collector aluminum foil, drying at 100 ℃ to form a positive active material layer with the thickness of 60 mu m, and then carrying out cold pressing;
2) and (4) trimming, cutting into pieces, slitting, and slitting to obtain the lithium ion battery positive plate.
Preparing a negative plate containing a functional coating:
1) preparing graphite, conductive carbon black (Super-P) serving as a conductive agent, carboxymethyl cellulose sodium (CMC) serving as a thickening agent and Styrene Butadiene Rubber (SBR) serving as a binder into lower-layer coating negative electrode slurry (used for forming a first active material layer with the thickness of 50 mu m) according to a mass ratio of 96:1.5:1.0:1.5, preparing upper-layer coating negative electrode slurry (used for forming a second active material layer with the thickness of 10 mu m) from the graphite, the conductive carbon black (Super-P) serving as a conductive agent, the carboxymethyl cellulose sodium (CMC) serving as a thickening agent and the Styrene Butadiene Rubber (SBR) serving as a binder according to a mass ratio of 96.5:1.0:1.0:1.5, coating the lower-layer coating negative electrode slurry on two surfaces of a current collector copper foil, coating the upper-layer coating negative electrode slurry on the surface of the lower-layer coating negative electrode slurry, and synchronously coating the upper layer and the lower layer on double-layer coating equipment. Coating the slurry on a current collector copper foil, drying at 90 ℃ to form a negative active material layer, and then carrying out cold pressing;
2) dissolving polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene carbonate and lithium bis (trifluoromethyl) sulfonyl imide in an organic solvent DMAC (dimethylacetamide) according to a mass ratio of 70:10:20, uniformly mixing to prepare coating slurry, coating the coating slurry in a negative electrode active material layer, and performing air drying at 80 ℃ to obtain a functional coating with the thickness of 10 microns.
Preparing an electrolyte and a lithium ion battery: as in embodiment 1, no further description is provided herein.
Comparative example 5
Preparing a double-layer coating positive plate containing a functional coating:
1) the preparation method comprises the steps of uniformly mixing NCM811 (positive active material), a conductive agent single-walled carbon nanotube and a binder polyvinylidene fluoride (PVDF) according to the mass ratio of 97.5:1:1.5 to prepare lower-layer coating positive slurry (used for forming a first active material layer with the thickness of 50 mu m), uniformly mixing NCM811 (positive active material), a conductive agent conductive carbon black (Super-P) and a binder polyvinylidene fluoride (PVDF) according to the mass ratio of 97.5:1:1.5 to prepare upper-layer coating positive slurry (used for forming a second active material layer with the thickness of 10 mu m), coating the lower-layer coating positive slurry on two surfaces of an aluminum foil, coating the upper-layer coating positive slurry on the surface of the lower-layer coating positive slurry, and synchronously finishing the upper-layer coating and the lower-layer coating on double-layer coating equipment. Then drying the slurry at 100 ℃ to form a double-layer positive active material layer, and then carrying out cold pressing;
2) dissolving polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene carbonate and lithium bis (trifluoromethyl) sulfonyl imide in an organic solvent DMAC (dimethylacetamide) according to a mass ratio of 70:10:20, uniformly mixing to prepare functional coating slurry, coating the functional coating slurry on the surface of the double-layer positive active material layer, and performing air blast drying at 80 ℃ to obtain a functional coating with the thickness of 10 microns;
3) and (4) cutting edges, cutting pieces, slitting, and slitting to obtain the positive plate containing the functional coating.
Preparing a negative plate: same as in example 1.
Preparing electrolyte and a lithium ion battery: as in embodiment 1, no further description is provided herein.
And (4) performance testing:
the lithium ion batteries manufactured in the above examples and comparative examples were subjected to a needle punching test, an internal resistance test, and a capacity test.
1. Needling test conditions: in a test environment of (25 +/-5) DEG C, fully charging the battery to 4.2V, using a high-temperature-resistant steel needle with the diameter of phi 5mm (the conical angle of the needle point is 45-60 degrees, and the surface of the needle is smooth and clean and has no rust, oxidation layer and oil stain), penetrating the battery from the direction vertical to the large surface of the battery at the speed of (25 +/-5) mm/s, wherein the penetrating position is close to the geometric center of the punctured surface, and the steel needle stays in the battery core. And observing whether the battery is on fire or explodes, and recording the temperature rise and the pressure drop of the battery.
2. The internal resistance test is obtained by electrochemical impedance spectroscopy.
3. And (3) capacity testing: charging to 4.2V (100% SOC) at 0.33C constant current in a test environment at (25 +/-5) ° C, standing for 10min, discharging to 2.8V at 0.33C constant current, and recording the discharge capacity as C0Standing for 10min, charging to 4.2V (100% SOC) at 0.33C constant current, standing for 10min, discharging to 2.8V at 1C constant current, and recording discharge capacity as C1。
The results of the above tests are shown in Table 1.
Table 1 results of performance test of batteries of examples and comparative examples
As can be seen from the table above, the presence of the non-functional coating on the surfaces of the positive and negative pole pieces in the comparative example 1 results in the best electrical performance, the 1C discharge capacity is 96% of the 0.33C discharge capacity, but the safety performance of the battery is the worst, and the functional coating needs to improve the safety because of fire explosion caused by needle punching.
The positive electrode in the embodiment 1 is coated in a double-layer mode, the mass percentage of the conductive agent in the second active material layer is 2% and is higher than that (1%) of the conductive agent in the first active material layer, and the functional coating is coated on the surface of the pole piece, so that the manufactured battery does not ignite in a needling test, and compared with the comparative example 2, the battery has the advantages that although the battery does not ignite in the needling process in the comparative example 2, the positive pole piece is coated in a conventional single-layer mode, the functional coating slurry is easy to infiltrate into the pole piece, the electronic resistance of the pole piece is increased, the electrical property is poor, the 1C discharge capacity is 83.6% of the 0.33C discharge capacity, and the conductive agent content of the second active material layer is increased in the embodiment 1, so that after a small amount of the functional coating slurry enters in an infiltration mode, the increase of the electronic resistance can be relieved to a greater extent due to the increase of the conductive agent content, and the good electrical property is kept.
The negative electrode of example 2 was coated with two layers, and the mass ratio of the conductive agent in the second active material layer was 2% and higher than (1%) of the conductive agent in the first active material layer, and then the functional coating was applied to the surface of the electrode sheet, and the battery produced did not ignite in the needling test. Compared with the embodiment 1, the double-layer coating mode is used on the surface of the negative electrode, and the functional coating on the surface of the negative electrode is matched, so that the safety can be improved, and the electrical property loss of the battery is ensured to be small.
The positive electrode in example 3 is coated in a double layer mode, the mass percentage of the conductive agent in the second active material layer is continuously increased to 3%, the functional coating is coated on the surface of the pole piece, the battery needling safety can be improved, the electrical performance can be improved, and the 1C capacity is improved to 94.6% from 93.8% in example 1.
In comparative example 3, the content of the conductive agent in the first active material layer was controlled to 1.5%, but the content of the conductive agent in the second active material layer was reduced to 1%, and with the functional coating, the needling ensured that no fire occurred, but the electrical performance of the battery was significantly reduced, the 1C capacity was only 79.4%, and the internal resistance of the battery was significantly increased to 10.22m Ω.
Comparative example 4 is to control the content of the conductive agent in the first active material layer to 1.5%, reduce the content of the conductive agent in the second active material layer to 1%, cooperate with the functional coating, the acupuncture can guarantee not to fire, but the electrical performance of the battery is obviously reduced, the 1C capacity is only 80.2%, the internal resistance of the battery is obviously increased, up to 10.06m Ω.
The positive electrode in example 4 is coated in two layers, the mass ratio of the conductive agent in the second active material layer is 2% and is higher than that of the conductive agent in the first active material layer (1%), and then the functional coating is coated on the surface of the pole piece, the thickness of the functional coating is reduced to 5 μm, the manufactured battery can be guaranteed not to be ignited in a needling test, and it can be seen that the thickness of the functional coating is reduced, the internal resistance is obviously reduced, and the 1C capacity of the battery is improved to 95.6%.
In the embodiment 5, the positive electrode and the negative electrode are coated in double layers, the mass ratio of the conductive agent in the second active material layer is 2% and is higher than the mass ratio (1%) of the conductive agent in the first active material layer, and then the surfaces of the positive electrode plate and the negative electrode plate are coated with the functional coatings, the thickness of the coating is 5 μm, so that the battery can be ensured not to be ignited in a needling test, but the internal resistance of the battery is increased due to the fact that the surfaces of the positive electrode plate and the negative electrode plate are coated with the functional coatings, the influence on the electrical property of the battery is obvious, and compared with the embodiment 4, the 1C capacity is only 90.2% in performance.
The positive electrode in example 6 was coated with two layers, and the mass ratio of the conductive agent in the first and second active material layers was 1%, except that the second conductive agent was a single-walled carbon nanotube, the first conductive agent was conventional conductive carbon black, and the surface of the positive electrode sheet was coated with a functional coating having a thickness of 10 μm, it can be seen that the battery did not ignite in the needle punching test, but the electrical performance was significantly improved, and the 1C capacity was 94.1%.
The positive electrode of comparative example 5 was double coated, and the mass ratio of the conductive agent in the first and second active material layers was 1%, except that the first conductive agent was single-walled carbon nanotubes, the second conductive agent was conventional conductive carbon black, and the surface of the positive electrode sheet was coated with a functional coating having a coating thickness of 10 μm, it can be seen that the battery pin-prick test can ensure no fire, but the electrical properties are significantly deteriorated as compared to example 6, and therefore, a material having more excellent conductivity such as single-walled carbon nanotubes is selected in the second active material layer, under the same conductive agent content, the conductivity of the second active material layer can be obviously improved, and the compaction density of the single-walled carbon nano tube is higher than that of the conventional conductive carbon black, the higher compacted density of the second active material layer comprising single-walled carbon nanotubes under the same roll conditions may also reduce the functional coating slurry's interpenetration.
In summary, the embodiments and the comparative examples can be concluded that the functional coating on the surface of the pole piece is a necessary condition for ensuring the safety of needling, but the existence of the functional coating has an adverse effect on the electrical performance, mainly because the functional coating comprises an electronic insulating material to increase the internal resistance of the pole piece, and the conductive agent content is increased in the second active material layer of the pole piece in a double-layer coating manner of the pole piece to enhance the conductive capability of the second active material layer, so that the problem of the increase of the internal resistance caused by the functional coating can be alleviated, and the electrical performance loss of the battery can be reduced; or the second active material layer is selected to have better conductive capability, so that the conductive capability of the second active material layer is enhanced, the problem of internal resistance increase caused by the functional coating can be relieved, and the electrical property loss of the battery is reduced.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. An electrode sheet, comprising a current collector, a first active material layer provided on at least one side surface of the current collector, a second active material layer provided on a surface of the first active material layer, and a functional coating provided on a surface of the second active material layer; the electron conductivity of the second active material layer is larger than the electron conductivity of the first active material layer.
2. The electrode sheet according to claim 1, wherein the first active material layer has a compacted density that is less than the compacted density of the second active material layer.
3. The electrode sheet according to claim 1, wherein the first active material layer includes a first active material and a first conductive agent, and the second active material layer includes a second active material and a second conductive agent; and the content of the first conductive agent in the first active material layer is less than the content of the second conductive agent in the second active material layer.
4. The electrode sheet according to claim 1, wherein the first active material layer includes a first active material and a first conductive agent, and the second active material layer includes a second active material and a second conductive agent; and the content of the first conductive agent in the first active material layer is less than or equal to the content of the second conductive agent in the second active material layer, and the electronic conductivity of the second conductive agent is greater than that of the first conductive agent.
5. The electrode sheet according to any one of claims 1 to 4, wherein the compacted density of the second conductive agent is greater than the compacted density of the first conductive agent.
6. The electrode sheet according to any one of claims 3 to 4, wherein the content of the first conductive agent is 0.5 to 5 wt%, and the content of the second conductive agent is 0.5 to 5 wt%.
7. The electrode sheet according to any one of claims 1 to 4, wherein the thickness of the first active material layer is larger than the thickness of the second active material layer.
8. The electrode sheet according to any one of claims 1 to 4, wherein the functional coating comprises the following components in percentage by mass:
30-80% of polymer, 0-50% of plasticizer and 0-50% of lithium salt.
9. The electrode sheet according to any one of claims 1 to 4, wherein the electrode sheet is a positive electrode sheet or a negative electrode sheet.
10. A battery comprising the electrode tab of any one of claims 1-9.
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