CN117117090A - Negative electrode plate and preparation method and application thereof - Google Patents
Negative electrode plate and preparation method and application thereof Download PDFInfo
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- CN117117090A CN117117090A CN202311180691.3A CN202311180691A CN117117090A CN 117117090 A CN117117090 A CN 117117090A CN 202311180691 A CN202311180691 A CN 202311180691A CN 117117090 A CN117117090 A CN 117117090A
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- 238000002360 preparation method Methods 0.000 title description 16
- 238000000576 coating method Methods 0.000 claims abstract description 305
- 239000011248 coating agent Substances 0.000 claims abstract description 304
- 239000011230 binding agent Substances 0.000 claims abstract description 142
- 239000000463 material Substances 0.000 claims abstract description 130
- 239000006258 conductive agent Substances 0.000 claims abstract description 104
- 239000002131 composite material Substances 0.000 claims abstract description 68
- 239000007773 negative electrode material Substances 0.000 claims abstract description 57
- 239000013543 active substance Substances 0.000 claims abstract description 8
- 239000011247 coating layer Substances 0.000 claims description 42
- 238000003756 stirring Methods 0.000 claims description 20
- 238000005096 rolling process Methods 0.000 claims description 19
- 239000001768 carboxy methyl cellulose Substances 0.000 claims description 18
- 229920002134 Carboxymethyl cellulose Polymers 0.000 claims description 17
- 229920003048 styrene butadiene rubber Polymers 0.000 claims description 17
- 235000010948 carboxy methyl cellulose Nutrition 0.000 claims description 16
- 239000008112 carboxymethyl-cellulose Substances 0.000 claims description 16
- 239000002002 slurry Substances 0.000 claims description 16
- 238000001035 drying Methods 0.000 claims description 13
- 239000002904 solvent Substances 0.000 claims description 12
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 5
- 238000000034 method Methods 0.000 claims description 5
- 229920002239 polyacrylonitrile Polymers 0.000 claims description 5
- 229920002125 Sokalan® Polymers 0.000 claims description 3
- 238000000265 homogenisation Methods 0.000 claims description 3
- 229920000058 polyacrylate Polymers 0.000 claims description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 239000004584 polyacrylic acid Substances 0.000 claims 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 abstract description 9
- 229910052744 lithium Inorganic materials 0.000 abstract description 9
- 239000011888 foil Substances 0.000 description 21
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 15
- 239000002174 Styrene-butadiene Substances 0.000 description 14
- 239000011149 active material Substances 0.000 description 13
- 239000000203 mixture Substances 0.000 description 13
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 12
- 239000011889 copper foil Substances 0.000 description 12
- 229910002804 graphite Inorganic materials 0.000 description 12
- 239000010439 graphite Substances 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 9
- 239000002245 particle Substances 0.000 description 7
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 5
- 230000005540 biological transmission Effects 0.000 description 5
- 229910001416 lithium ion Inorganic materials 0.000 description 5
- 239000003792 electrolyte Substances 0.000 description 4
- 239000000919 ceramic Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 3
- 229920000049 Carbon (fiber) Polymers 0.000 description 2
- 229910013872 LiPF Inorganic materials 0.000 description 2
- 101150058243 Lipf gene Proteins 0.000 description 2
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 description 2
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 239000006183 anode active material Substances 0.000 description 2
- 239000010405 anode material Substances 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 239000004917 carbon fiber Substances 0.000 description 2
- 239000002041 carbon nanotube Substances 0.000 description 2
- 229910021393 carbon nanotube Inorganic materials 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
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- 238000001000 micrograph Methods 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 230000002441 reversible effect Effects 0.000 description 2
- 239000002356 single layer Substances 0.000 description 2
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 description 2
- 229920001027 sodium carboxymethylcellulose Polymers 0.000 description 2
- 229910001415 sodium ion Inorganic materials 0.000 description 2
- 230000008961 swelling Effects 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
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- 229910021389 graphene Inorganic materials 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
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Classifications
-
- 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
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
-
- 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
- H01M4/139—Processes of manufacture
- H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
-
- 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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
-
- 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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Inorganic Chemistry (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention belongs to the technical field of batteries, and discloses a negative electrode plate, which comprises a current collector and a composite coating coated on at least one side surface of the current collector, wherein the composite coating comprises a first coating and a second coating, and the first coating is positioned between the current collector and the second coating; the composite coating is prepared from a coating material, wherein the coating material comprises a negative electrode active substance, a conductive agent, a first binder and a second binder, and the first coating material for preparing the first coating comprises a negative electrode active substance I, a conductive agent I, a first binder I and a second binder I; the second coating material for preparing the second coating comprises a negative electrode active material II, a conductive agent II, a first binder II and a second binder II; wherein the amount of the conductive agent I of the first coating is larger than the amount of the conductive agent II of the second coating. The invention uses the negative electrode to carry out secondary coating, which not only can ensure the energy density of the battery, but also can improve the multiplying power performance of the lithium battery.
Description
Technical Field
The invention belongs to the technical field of batteries, and particularly relates to a negative electrode plate, a preparation method and application thereof.
Background
At present, the improvement of the rate performance of the lithium battery is improved from materials, formulas and coating surface density, and the rate performance of the lithium battery is improved by using a small-particle anode material to improve the quantity of a conductive agent in the formulas and performing a thin coating method during coating.
However, the use of a small particle of the negative electrode material, the increase in the amount of the conductive agent in the formulation, and the thin coating at the time of coating, although the rate performance of the lithium battery can be improved, cannot be compatible with the energy density of the lithium battery.
Disclosure of Invention
The invention aims to provide a negative electrode plate, a preparation method and application thereof, wherein the energy density of a lithium battery is ensured and the multiplying power performance of the lithium battery is improved by adopting a technology of preparing the negative electrode plate through secondary coating through the optimal design of a negative electrode active slurry formula.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a negative electrode tab comprising a current collector and a composite coating applied to at least one side of the current collector, the composite coating comprising a first coating and a second coating, the first coating being located between the current collector and the second coating; the composite coating is prepared from a coating material, wherein the coating material comprises a negative electrode active substance, a conductive agent, a first binder and a second binder, and the first coating material for preparing the first coating comprises a negative electrode active substance I, a conductive agent I, a first binder I and a second binder I; the second coating material for preparing the second coating comprises a negative electrode active material II, a conductive agent II, a first binder II and a second binder II; wherein the amount of the conductive agent I of the first coating is larger than the amount of the conductive agent II of the second coating.
Further, the negative electrode active material in the coating material of the composite coating layer is composed of the negative electrode active material I in the first coating material and the negative electrode active material II in the second coating material; the conductive agent in the coating material of the composite coating consists of a conductive agent I in the first coating material and a conductive agent II in the second coating material; the first binder in the coating material of the composite coating consists of a first binder I in the first coating material and a first binder II in the second coating material; the second binder in the coating material of the composite coating consists of the second binder I in the first coating material and the second binder II in the second coating material.
Further, the contents of the negative electrode active material, the conductive agent, the first binder and the second binder in the coating material of the composite coating are 90-97.5%, 0.5-5%, 1-2% and 1-4% in sequence by mass percent.
Further, the coating material of the composite coating comprises the following components in percentage by mass: 96% of negative electrode active material, 1% of conductive agent, 1.2% of first binder and 1.8% of second binder.
Further, the negative electrode active material I in the first coating material is 48-52% of the total mass of the negative electrode active materials in the coating material of the composite coating according to mass percentage; the conductive agent I in the first coating material is 78% -82% of the total mass of the conductive agent in the coating material; the first binder I in the first coating material accounts for 48-52% of the total mass of the first binder in the coating material; the second binder I in the first coating material accounts for 48-52% of the total mass of the second binder in the coating material.
Further, the negative electrode active material I (first active material for short) in the first coating material is 50% of the total mass of the negative electrode active material in the coating material of the composite coating; the conductive agent I (first conductive agent for short) in the first coating material is 80% of the total mass of the conductive agent in the coating material; the first binder I (binder 11 for short) in the first coating material accounts for 50% of the total mass of the first binder in the coating material; the second binder I (binder 12 for short) in the first coating material accounts for 50% of the total mass of the second binder in the coating material.
Further, the thickness of the first coating layer is 50 to 80 μm (e.g., 55 μm, 60 μm, 65 μm, 70 μm, or 75 μm).
Further, the negative electrode active material (which may be simply referred to as a second active material) in the second coating material is 48% -52% of the total mass of the negative electrode active material in the coating material; the conductive agent II (which can be simply called as a second conductive agent) in the second coating material is 18-22% of the total mass of the conductive agent in the composite coating material; the first binder II (which can be simply called as binder 21) in the second coating material accounts for 48% -52% of the total mass of the first binder in the coating material; the second binder II (which may be simply referred to as binder 22) in the second coating material accounts for 48% -52% of the total mass of the second binder in the coating material.
Further, the negative electrode active material in the second coating layer is 50% of the total mass of the negative electrode active material in the coating material of the composite coating layer; the conductive agent II in the second coating layer is 20% of the total mass of the conductive agent in the coating material of the composite coating layer; the first binder II in the second coating layer accounts for 50% of the total mass of the first binder in the coating material of the composite coating layer; the second binder II in the second coating layer accounts for 50% of the total mass of the second binder in the coating material of the composite coating layer.
Further, the thickness of the second coating layer is 20 to 50 μm (e.g., 25 μm, 30 μm, 35 μm, 40 μm, or 45 μm).
Further, the first binder includes one or more of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyacrylonitrile (PAN), and polyacrylate, and the second binder includes Styrene Butadiene Rubber (SBR).
Further, the current collector may employ a current collector conventional in the art, such as copper foil or aluminum foil.
The second aspect of the invention provides a preparation method of the negative electrode plate, which comprises the following steps:
and (3) primary coating: adding a negative electrode active material I, a conductive agent I, a first binder I, a second binder I and a first solvent into a stirring tank according to a formula of a first coating material for homogenization to obtain a first slurry; then coating the first slurry on at least one side surface of a current collector to obtain a current collector with a first coating;
and (3) secondary coating: adding a negative electrode active material II, a conductive agent II, a first binder II, a second binder II and a second solvent into a stirring tank according to the formula of the second coating material, and stirring and homogenizing to obtain a second slurry; then coating the second slurry on the first coating on the surface of the current collector, and drying to obtain the current collector with the composite coating of the first coating and the second coating;
and (3) rolling treatment: and rolling the current collector of the composite coating obtained by the secondary coating to obtain the negative electrode plate.
Further, the first solvent or the second solvent includes at least one of water or N-methylpyrrolidone (NMP).
The third aspect of the invention also provides an application of the negative electrode plate in the field of batteries.
Further, the battery includes a lithium ion battery and a sodium ion battery.
Compared with the prior art, the invention has the following beneficial effects:
(1) The invention uses the technology of secondary coating of the negative electrode, optimizes the formulation, can ensure the energy density of the battery, and improves the multiplying power performance of the lithium battery, thereby meeting the requirements of long-time endurance and quick charge of the battery;
(2) Compared with the prior art, the technical scheme of the invention does not need to add new process and equipment, and is easy to realize the mass production of the negative electrode plate.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
Fig. 1 is a scanning electron microscope image of a negative electrode sheet prepared in example 1 of the present invention.
Fig. 2 is a scanning electron microscope image of the negative electrode tab prepared in comparative example 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention. The process parameters for the specific conditions not noted in the examples below are generally as usual.
The endpoints of the ranges and any values disclosed in the present invention are not limited to the precise range or value, and the range or value should be understood to include values close to the range or value. For numerical ranges, one or more new numerical ranges may be obtained in combination with each other between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point values, and are to be considered as specifically disclosed in the present invention.
According to a first aspect of the present invention, a negative electrode tab comprises a current collector and a composite coating applied to at least one side of the current collector, the composite coating comprising a first coating and a second coating, the first coating being located between the current collector and the second coating; the composite coating is prepared from a coating material, wherein the coating material comprises a negative electrode active substance, a conductive agent, a first binder and a second binder, and the first coating material for preparing the first coating comprises a negative electrode active substance I, a conductive agent I, a first binder I and a second binder I; the second coating material for preparing the second coating comprises a negative electrode active material II, a conductive agent II, a first binder II and a second binder II; wherein the amount of the conductive agent I of the first coating is larger than the amount of the conductive agent II of the second coating.
In the present invention, the content of the conductive agent is different in the first coating layer and the second coating layer. The amount of conductive agent in the first coating near the foil face is higher than the amount of conductive agent in the second coating remote from the foil face. The amount of the coating conductive agent is increased on the first coating close to the foil surface, so that the conductivity of the pole piece can be increased, the tortuosity of the pole piece is smaller (or the ion conduction path is reduced), lithium ions are easier to be embedded, and the rate capability of the pole piece is improved.
The gradient distribution type conductive agent content at one side close to the current collector is increased, so that the electron transmission capability of the current collector and the active material is enhanced, the effective contact area between the active material and the current collector is increased, the electron conductivity is improved, and the interface resistance is further reduced.
Further analysis, the conductive agent coats the anode active material, so that better conductive capacity can be provided for the anode, resistance of electron transmission is reduced, insertion and extraction capacity of lithium ions is improved, reversible energy level of the battery is improved, polarization effect of the battery is reduced, internal impedance of the battery is further reduced, under the conditions that total conductive agent content is unchanged and current collector side is higher in conductive agent content, the electrode plate can provide more transfer paths for electrons, electrons can reach an external circuit more smoothly, and when the content of the conductive agent on the side is lower, the transmission of electrons is blocked, and the electrons cannot pass through the solid-phase anode material well, so that larger resistance is generated. Under high-rate conditions, the content of the conductive agent at the current collector side is reduced, and the load of large current cannot be borne, so that the battery performance is drastically reduced.
However, too much amount of the conductive agent on the current collector side reduces the electrode density, resulting in a decrease in capacity, while too little amount results in a low utilization of the active material in the electrode, and a decrease in high-rate discharge performance.
As an optional embodiment of the invention, the coating material of the composite coating comprises the following components in percentage by mass: 90% -97.5% (e.g., 91%, 92%, 93%, 94%, 95%, 96% or 97%), 0.5% -5% (e.g., 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or 4.5%), 1% -2% (e.g., 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8% or 1.9%) of a first binder, and 1% -4% (e.g., 1.2%, 1.5%, 2%, 2.5%, 3%, 3.5%, 3.6% or 3.8%) of a second binder; .
As an alternative embodiment of the present invention, the coating material of the composite coating layer comprises the following components in percentage by mass: 96% of negative electrode active material, 1% of conductive agent, 1.2% of first binder and 1.8% of second binder.
As an alternative embodiment of the present invention, the negative electrode active material I in the first coating material is 48% to 52% (e.g., 48.5%, 49%, 49.5%, 50%, 50.5%, 51% or 51.5%) of the total mass of the negative electrode active materials in the coating material of the composite coating layer in mass percent; the conductive agent I in the first coating material is 78% -82% (e.g., 78.5%, 79%, 79.5%, 80%, 80.5%, 81%, or 81.5%) of the total mass of conductive agents in the coating material; the first binder I in the first coating material comprises 48% -52% (e.g., 48.5%, 49%, 49.5%, 50%, 50.5%, 51% or 51.5%) of the total mass of the first binder in the coating material; the second binder I in the first coating material comprises 48% -52% (e.g., 48.5%, 49%, 49.5%, 50%, 50.5%, 51% or 51.5%) of the total mass of the second binder in the coating material.
As an alternative embodiment of the present invention, the negative electrode active material I (abbreviated as first active material) in the first coating material is 50% of the total mass of the negative electrode active material in the coating material of the composite coating layer; the conductive agent I (first conductive agent for short) in the first coating material is 80% of the total mass of the conductive agent in the coating material; the first binder I (binder 11 for short) in the first coating material accounts for 50% of the total mass of the first binder in the coating material; the second binder I (binder 12 for short) in the first coating material accounts for 50% of the total mass of the second binder in the coating material.
As an alternative embodiment of the invention, the thickness of the first coating is 50 to 80 μm (e.g. 55 μm, 60 μm, 65 μm, 70 μm or 75 μm).
The invention adopts the method that the composite coating is formed on at least one side surface of the current collector to prepare the negative electrode plate, and each coating contains the negative electrode active material in the composite coating of the negative electrode plate, so that the battery using the negative electrode plate has excellent energy density and multiplying power performance. If the first coating of the negative electrode tab does not contain an active material, it contains only a conductive agent and a binder, which results in a first coating thickness of less than 50-80 um. If the coating thickness of the present invention is intended, the use of the first coating layer containing only the conductive agent and the binder tends to increase the amount of the binder, and in addition, the first coating layer is too thick, which tends to cause powder dropping and cracking, which in turn leads to a large interface resistance.
In addition, if the active material is not contained in the first coating layer, only the active material is entirely disposed in the second coating layer, which may reduce the energy density and rate performance of the battery.
As an alternative embodiment of the present invention, the negative electrode active material (which may be simply referred to as a second active material) in the second coating material is 48% to 52% (e.g., 48.5%, 49%, 49.5%, 50%, 50.5%, 51% or 51.5%) of the total mass of the negative electrode active material in the coating material; the conductive agent II (which may be simply referred to as a second conductive agent) in the second coating material is 18 to 22% (e.g., 18.5%, 19%, 19.5%, 20%, 20.5%, 21% or 21.5%) of the total mass of the conductive agents in the composite coating material; the first binder II (may be simply referred to as binder 21) in the second coating material accounts for 48% -52% (e.g., 48.5%, 49%, 49.5%, 50%, 50.5%, 51% or 51.5%) of the total mass of the first binder in the coating material; the second binder II (which may be referred to simply as binder 22) in the second coating material is 48% to 52% (e.g., 48.5%, 49%, 49.5%, 50%, 50.5%, 51% or 51.5%) of the total mass of the second binder in the coating material.
As an alternative embodiment of the present invention, the negative electrode active material in the second coating layer is 50% of the total mass of the negative electrode active material in the coating material of the composite coating layer; the conductive agent II in the second coating layer is 20% of the total mass of the conductive agent in the coating material of the composite coating layer; the first binder II in the second coating layer accounts for 50% of the total mass of the first binder in the coating material of the composite coating layer; the second binder II in the second coating layer accounts for 50% of the total mass of the second binder in the coating material of the composite coating layer.
As an alternative embodiment of the invention, the thickness of the second coating is 20 to 50 μm (e.g., 25 μm, 30 μm, 35 μm, 40 μm or 45 μm).
In the present invention, the negative electrode active material may employ a negative electrode active material conventional in the art. The conductive agent may employ a conductive agent conventional in the art, for example, the conductive agent includes at least one of conductive graphite, graphene, conductive carbon black (SP), carbon Fiber (CF), or Carbon Nanotube (CNT).
As an alternative embodiment of the present invention, the first binder includes one or more of sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyacrylonitrile (PAN), and polyacrylate, and the second binder includes Styrene Butadiene Rubber (SBR). Preferably, the first binder is sodium carboxymethyl cellulose.
In the pole piece preparation process, the negative pole piece must be rolled due to the requirements of energy density and compaction density. Because CMC has brittleness, CMC is used alone as a binder in the rolling process, collapse of the structure of the negative electrode surface material after rolling is easy to cause, and the pole piece is seriously dropped powder and cannot be used; however, SBR is a rubber which does not have a suspension dispersion function, and the use of SBR alone as a binder causes sedimentation of slurry to be coated, making it difficult to prepare the slurry, and too much SBR causes swelling of the pole piece in an electrolyte.
In the invention, the CMC and SBR binders are combined, so that the problem of brittleness caused by singly using CMC in the rolling process, and the problems of slurry preparation and swelling caused by singly using SBR can be solved.
As an alternative embodiment of the present invention, the current collector may employ a current collector conventional in the art, such as copper foil or aluminum foil.
According to a second aspect of the present invention, a method for preparing the negative electrode sheet includes the steps of:
and (3) primary coating: adding a negative electrode active material I, a conductive agent I, a first binder I, a second binder I and a first solvent into a stirring tank according to a formula of a first coating material for homogenization to obtain a first slurry; then coating the first slurry on at least one side surface of a current collector to obtain a current collector with a first coating;
and (3) secondary coating: adding a negative electrode active material II, a conductive agent II, a first binder II, a second binder II and a second solvent into a stirring tank according to the formula of the second coating material, and stirring and homogenizing to obtain a second slurry; then coating the second slurry on the first coating on the surface of the current collector, and drying to obtain the current collector with the composite coating of the first coating and the second coating;
and (3) rolling treatment: and rolling the current collector of the composite coating obtained by the secondary coating to obtain the negative electrode plate.
As an alternative embodiment of the present invention, the first solvent or the second solvent includes at least one of water or N-methylpyrrolidone (NMP).
The third aspect of the invention also provides an application of the negative electrode plate in the field of batteries.
As an alternative embodiment of the present invention, the battery includes a lithium ion battery and a sodium ion battery.
The present invention will be described in further detail with reference to specific examples and comparative examples.
Example 1
The preparation method of the negative electrode plate comprises the following steps:
and (3) primary coating: the negative electrode active material graphite (particle diameter of 12-15 μm), the conductive agent SP, the binder 11 (CMC) and the binder 12 (SBR) are mixed in a ratio of 96% by 50%:1% 80%:1.2% 50%: adding 1.8% by 50% of the mixture into a stirring tank for homogenizing to obtain a first anode homogenate; then coating the first negative electrode homogenate on one side surface of the copper foil, and drying to obtain the copper foil with the first coating; the thickness of the first coating is 100mm;
and (3) secondary coating: the negative electrode active material graphite (particle diameter of 12-15 μm), the conductive agent SP, the binder 21 (CMC) and the binder 22 (SBR) are mixed in a ratio of 96% by 50% by mass: 1% 20%:1.2% 50%: adding 1.8% by 50% of the mixture into a stirring tank for homogenizing to obtain a second anode homogenate; then coating second anode homogenate on the two side surfaces of the foil with the first coating, and drying to obtain a copper foil with a composite coating of the first coating and the second coating, wherein the thickness of the second coating is 100mm;
and (3) rolling treatment: and rolling the foil with the composite coating obtained after the secondary coating to obtain the negative electrode plate. Fig. 1 shows a Scanning Electron Microscope (SEM) image of the negative electrode tab in example 1.
Example 2
The present example prepared a negative electrode sheet using the preparation method of example 1, except that the content of the conductive agent in the first coating layer was 1% by 78%, and the content of the conductive agent in the second coating layer was 1% by 22%.
Example 3
The present example prepared a negative electrode sheet using the preparation method of example 1, except that the content of the conductive agent in the first coating layer was 1% by 82%, and the content of the conductive agent in the second coating layer was 1% by 18%.
Example 4
This example prepared a negative electrode sheet using the preparation method of example 1, the only difference being that this example used 0.95% sp and 0.05% cnt as the total conductive agent in the coating material of the composite coating. Specifically, the preparation method of the negative electrode plate comprises the following steps:
and (3) primary coating: the negative electrode active material graphite (particle size of 12-15 μm), conductive agent, binder 11 (CMC) and binder 12 (SBR) are mixed in a mass percentage of 96% by 50%:1% 80%:1.2% 50%: adding 1.8% by 50% of the mixture into a stirring tank for homogenizing to obtain a first anode homogenate; then coating the first negative electrode homogenate on a copper foil material, and drying to obtain the copper foil material with the first coating; the thickness of the first coating is 100mm; wherein, the dosage of the first conductive agent is as follows: 1%. 80%. 0.95% sp+1%. 80%. 0.05% cnt;
and (3) secondary coating: the negative electrode active material graphite (particle size of 12-15 μm), conductive agent (0.95% sp and 0.05% cnt), binder 21 (CMC) and binder 22 (SBR) were mixed in mass percentage of 96% by 50%:1% 20%:1.2% 50%: adding 1.8% by 50% of the mixture into a stirring tank for homogenizing to obtain a second anode homogenate; then coating the second anode homogenate on the foil with the first coating, and drying to obtain the copper foil with the composite coating of the first coating and the second coating, wherein the thickness of the second coating is 100mm; wherein, the dosage of the second conductive agent is as follows: 1%. 20%. 0.95% sp+1%. 20%. 0.05% cnt;
and (3) rolling treatment: and rolling the foil with the composite coating obtained after the secondary coating to obtain the negative electrode plate. Fig. 1 shows a Scanning Electron Microscope (SEM) image of the negative electrode tab in example 1.
Comparative example 1
The preparation method of the negative electrode plate comprises the following steps:
the negative electrode active material graphite, the conductive agent SP, the first binder CMC and the second binder SBR are mixed according to the mass percentage of 96 percent: 1%:1.2%:1.8% of the mixture was added to a stirring tank to be homogenized, coated on one side surface of a copper foil material as a negative electrode sheet, the coating effect was as shown in fig. 2, and then assembled into a button cell.
Comparative example 2
The preparation method of the negative electrode plate comprises the following steps:
and (3) primary coating: the negative electrode active material graphite, the conductive agent SP, the binder 11 (CMC) and the binder 12 (SBR) were mixed in a mass percentage of 96% by 50%:1% by 40%:1.2% 50%: adding 1.8% by 50% of the mixture into a stirring tank for homogenizing to obtain anode homogenate; then coating the anode homogenate on one side surface of a copper foil, and drying to obtain a foil with a first coating; the thickness of the first coating is 100mm;
and (3) secondary coating: the negative electrode active material graphite, the conductive agent SP, the binder 21 (CMC) and the binder 22 (SBR) were mixed in a mass percentage of 96% by 50%:1% 60%:1.2% 50%: adding 1.8% by 50% of the mixture into a stirring tank for homogenizing to obtain anode homogenate; then coating the anode homogenate on the surface of the foil with the first coating, drying to obtain the foil with the composite coating of the first coating and the second coating,
and (3) rolling treatment: and rolling the foil with the composite coating obtained after the secondary coating to obtain the negative electrode plate.
Comparative example 3
The preparation method of the negative electrode plate comprises the following steps:
and (3) primary coating: the negative electrode active material graphite, the conductive agent SP and the binder SBR are mixed according to the mass percentage of 96% by 50%:1% 90%: adding 3% -50% of the mixture into a stirring tank for homogenizing to obtain anode homogenate; then coating the anode homogenate on one side surface of a copper foil, and drying to obtain a foil with a first coating;
and (3) secondary coating: the negative electrode active material graphite, the conductive agent SP and the binder CMC are mixed according to the mass percentage of 96% by 50%:1% 10%: adding 3% -50% of the mixture into a stirring tank for homogenizing to obtain anode homogenate; then coating the anode homogenate on the surface of the foil with the first coating, and drying to obtain the foil with the composite coating of the first coating and the second coating;
and (3) rolling treatment: and rolling the foil with the composite coating obtained after the secondary coating to obtain the negative electrode plate.
Comparative example 4
The preparation method of the negative electrode plate comprises the following steps:
and (3) primary coating: the negative electrode active material graphite, the conductive agent SP, the first binder CMC and the second binder SBR are mixed in a mass percentage of 96% by 50%:1% 70%:1.2% 50%: adding 1.8% by 50% of the mixture into a stirring tank for homogenizing to obtain anode homogenate; then coating the anode homogenate on one side surface of a copper foil, and drying to obtain a foil with a first coating;
and (3) secondary coating: the negative electrode active material graphite, the conductive agent SP and the binder CMC are mixed according to the mass percentage of 96% by 50%:1% by 30%:1.2% 50%: adding 1.8% by 50% of the mixture into a stirring tank for homogenizing to obtain anode homogenate; then coating the anode homogenate on the surface of the foil with the first coating, and drying to obtain the foil with the composite coating of the first coating and the second coating;
and (3) rolling treatment: and rolling the foil with the composite coating obtained after the secondary coating to obtain the negative electrode plate.
Battery assembly
The negative electrode piece prepared in the above examples and comparative examples was used as a negative electrode, a 12mm diameter lithium piece was placed in the negative electrode case of a button cell, and 1mol/L LiPF was dropped 6 The EC/DEC/DMC (volume ratio is 1:1:1) electrolyte of (1), a ceramic diaphragm with a diameter of 16mm (the ceramic diaphragm is formed by coating a ceramic layer with a diameter of 3 mu m on a 9 mu m PE base film) is placed on the electrolyte, and then 1mol/L LiPF is dripped 6 The electrolyte of EC/DEC/DMC (volume ratio is 1:1:1), the negative plate is punched into a wafer with the diameter of 14mm, the wafer is placed on a diaphragm, and the positive shell of the button cell is covered and sealed, so that the CR2025 button cell is assembled.
Performance testing
Electrochemical performance tests were performed on the coin cells obtained in the above examples and comparative examples on a battery test system. Gram capacities of button cells at 0.1C, 0.2C, 0.5C and 1C were tested at 25 ℃. The voltage range of the battery is 0.005V-2.0V.
Table 1 shows gram capacities at different charge rates of batteries prepared from the negative electrode tabs in examples 1 to 4 and comparative examples 1 to 4.
Table 1 gram capacity at different charging rates
As can be seen from fig. 1 and 2, the surface particle size of the negative electrode sheet of the composite coating of the present invention is more uniform and dense than that of the negative electrode sheet using a single-layer coating.
As can be seen from table 1, in the above embodiment of the present invention, the composite coating is coated on one side surface of the current collector, and the gram capacity of the negative electrode plate of the composite coating obtained under different multiplying power currents is larger than that of the negative electrode plate of the corresponding single-layer coating, so that the gram capacity of the negative electrode plate of the composite coating under high multiplying power currents is relatively higher, and the adoption of the negative electrode plate of the composite coating is beneficial to improving the multiplying power performance of the battery core.
In summary, according to the negative electrode plate adopting the composite coating, the content of the conductive agent on one side of the gradient distribution type current collector is increased, so that the electron transmission capability of the current collector and the active material is enhanced, the effective contact area between the active material and the current collector is increased, the electron conductivity is improved, and the interface resistance is further reduced.
Further, the conductive agent coats the anode active material, so that better conductive capacity is provided for the anode, resistance of electron transmission is reduced, intercalation and deintercalation capacity of lithium ions is improved, reversible energy level of the battery is improved, polarization effect of the battery is reduced, internal impedance of the battery is further reduced, and under the conditions that total conductive agent content is unchanged and higher conductive agent content is arranged on the side close to the current collector, the electrode plate can provide more transfer paths for electrons, so that the electrons can reach an external circuit more smoothly.
In addition, when the content of the conductive agent on one side of the current collector is higher, the battery can bear the load of larger current under the condition of high multiplying power, thereby improving the performance of the battery. However, too much amount of the conductive agent on the current collector side reduces the electrode density, resulting in a decrease in capacity, while too little amount results in a low utilization of the active material in the electrode, and a decrease in high-rate discharge performance.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (10)
1. A negative electrode tab comprising a current collector and a composite coating applied to at least one side of the current collector, the composite coating comprising a first coating and a second coating, the first coating being located between the current collector and the second coating; the composite coating is prepared from a coating material, wherein the coating material comprises a negative electrode active substance, a conductive agent, a first binder and a second binder, and the first coating material for preparing the first coating comprises a negative electrode active substance I, a conductive agent I, a first binder I and a second binder I; the second coating material for preparing the second coating comprises a negative electrode active material II, a conductive agent II, a first binder II and a second binder II; wherein the amount of the conductive agent I of the first coating is larger than the amount of the conductive agent II of the second coating.
2. The negative electrode sheet according to claim 1, wherein the contents of the negative electrode active material, the conductive agent, the first binder and the second binder in the coating material of the composite coating layer are 90% to 97.5%, 0.5% to 5%, 1% to 2% and 1% to 4% in this order by mass percent.
3. The negative electrode tab according to claim 1 or 2, characterized in that,
the negative electrode active material I in the first coating material is 48-52% of the total mass of the negative electrode active material in the coating material of the composite coating according to the mass percentage; the conductive agent I in the first coating material is 78% -82% of the total mass of the conductive agent in the coating material; the first binder I in the first coating material accounts for 48-52% of the total mass of the first binder in the coating material; the second binder I in the first coating material accounts for 48-52% of the total mass of the second binder in the coating material;
and/or the negative electrode active material in the second coating material is 48% -52% of the total mass of the negative electrode active material in the coating material; the conductive agent II in the second coating material is 18-22% of the total mass of the conductive agent in the composite coating material; the first binder II in the second coating material accounts for 48-52% of the total mass of the first binder in the coating material; the second binder II in the second coating material accounts for 48-52% of the total mass of the second binder in the coating material.
4. The negative electrode plate according to claim 2, wherein the coating material of the composite coating comprises the following components in percentage by mass: 96% of negative electrode active material, 1% of conductive agent, 1.2% of first binder and 1.8% of second binder.
5. The negative electrode tab of claim 3, wherein,
the negative electrode active material I in the first coating material is 50% of the total mass of the negative electrode active material in the coating material of the composite coating; the conductive agent I in the first coating material is 80% of the total mass of the conductive agent in the coating material; the first binder I in the first coating material accounts for 50% of the total mass of the first binder in the coating material; the second binder I in the first coating material accounts for 50% of the total mass of the second binder in the coating material;
and/or the negative electrode active material in the second coating layer is 50% of the total mass of the negative electrode active material in the coating material of the composite coating layer; the conductive agent II in the second coating layer is 20% of the total mass of the conductive agent in the coating material of the composite coating layer; the first binder II in the second coating layer accounts for 50% of the total mass of the first binder in the coating material of the composite coating layer; the second binder II in the second coating layer accounts for 50% of the total mass of the second binder in the coating material of the composite coating layer.
6. The negative electrode tab according to claim 1 or 2, wherein the thickness of the first coating layer is 50-80 μm; the thickness of the second coating is 20-50 mu m.
7. The negative electrode tab of claim 1 or 2, wherein the first binder comprises one or more of carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, and polyacrylate, and the second binder comprises Styrene Butadiene Rubber (SBR).
8. A method of producing a negative electrode sheet according to any one of claims 1 to 7, comprising the steps of:
and (3) primary coating: adding a negative electrode active material I, a conductive agent I, a first binder I, a second binder I and a first solvent into a stirring tank according to a formula of a first coating material for homogenization to obtain a first slurry; then coating the first slurry on at least one side surface of a current collector to obtain a current collector with a first coating;
and (3) secondary coating: adding a negative electrode active material II, a conductive agent II, a first binder II, a second binder II and a second solvent into a stirring tank according to the formula of the second coating material, and stirring and homogenizing to obtain a second slurry; then coating the second slurry on the first coating on the surface of the current collector, and drying to obtain the current collector with the composite coating of the first coating and the second coating;
and (3) rolling treatment: and rolling the current collector of the composite coating obtained by the secondary coating to obtain the negative electrode plate.
9. The method for producing a negative electrode sheet according to claim 8, wherein the first solvent or the second solvent includes at least one of water or N-methylpyrrolidone.
10. Use of a negative electrode sheet according to any one of claims 1-7 in the field of batteries.
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