CN112467075B - Pole piece, electric core and secondary battery - Google Patents

Pole piece, electric core and secondary battery Download PDF

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Publication number
CN112467075B
CN112467075B CN202011220423.6A CN202011220423A CN112467075B CN 112467075 B CN112467075 B CN 112467075B CN 202011220423 A CN202011220423 A CN 202011220423A CN 112467075 B CN112467075 B CN 112467075B
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Prior art keywords
coating
pole piece
thickness
slurry
tap density
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CN112467075A (en
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游坤
黄天翔
宋贺
华秉杨
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Jiangsu Zenio New Energy Battery Technologies Co Ltd
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Dongguan Tafel New Energy Technology Co Ltd
Jiangsu Tafel New Energy Technology Co Ltd
Jiangsu Tafel Power System Co Ltd
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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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • 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
    • 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
    • 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
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Inorganic Chemistry (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a pole piece which comprises a current collector, a first coating and a second coating, wherein the first coating is arranged on at least one surface of the current collector, the second coating is arranged on the surface of the first coating, and the tap density of an active substance in the first coating is greater than that of an active substance in the second coating. In addition, the invention also relates to a battery cell and a secondary battery comprising the battery cell, wherein the battery cell comprises a positive plate, a negative plate, a diaphragm arranged between the positive plate and the negative plate and electrolyte, and the positive plate and/or the negative plate are/is the pole piece. Compared with the prior art, the pole piece has high porosity, is beneficial to adsorbing more free electrolyte and improves the cycle performance of the battery cell.

Description

Pole piece, electric core and secondary battery
Technical Field
The invention belongs to the technical field of batteries, and particularly relates to a pole piece, a battery cell and a secondary battery.
Background
The secondary battery has been widely used in the fields of consumer mobile phones, electric tools, medical electronics and the like due to its excellent performance, and simultaneously has also shown good application prospects in the fields of new energy automobiles, energy storage base stations and the like.
As the market demand of power batteries is gradually expanded, the demand of consumers on the electrochemical performance and the dynamic performance of the power batteries is higher and higher. Lithium ion secondary batteries are one of the major members of the power battery family, and improvements in energy density and cycle life are crucial to battery performance improvement.
The lithium ion secondary battery completes the charging and discharging process by the insertion and extraction of ions between the positive and negative active materials, wherein the design of the pole piece directly influences the performance of the lithium ion secondary battery. In the cycle process of the battery, the positive and negative materials are expanded to release and embed lithium ions, so that electrolyte between the pole pieces is extruded out, the poor liquid retention capability of the pole pieces causes poor cycle, and the service life is terminated in advance. At present, for the improvement of the service life of the lithium ion secondary battery, the content of the electrolyte in the electrode in the circulating process is ensured mainly by reducing the compaction density of the pole piece and improving the liquid absorption capacity of the pole piece or by adding the electrolyte with higher content. However, the reduction of the compaction density leads to the increase of the thickness of the pole piece and the reduction of the energy density, and the increase of the distance between active material particles on the pole piece can lead to the deterioration of contact and influence on electron conduction; the electrolyte with higher content is added, so that the internal pressure of the battery core is increased, the expansion problem is caused, the safety performance of the battery core is influenced, and the production material cost of the battery core is increased.
In view of the above, it is necessary to provide a new technical solution to solve the above technical problems.
Disclosure of Invention
One of the objects of the present invention is: aiming at the defects of the prior art, the pole piece is provided, has high porosity, is beneficial to the pole piece to absorb more free electrolyte, and improves the cycle performance of the battery core.
In order to achieve the purpose, the invention adopts the following technical scheme:
the utility model provides a pole piece, includes the mass flow body, first coating and second coating, first coating set up in at least one side of the mass flow body, the second coating set up in first coating surface, active material's tap density is greater than in the first coating active material's tap density in the second coating.
As an improvement of the pole piece, the tap density of the active substance in the first coating is M1The tap density of the active material in the second coating layer is M2，M1＝a·M2，1.01＜a＜1.3。
0.8g/cm is used as an improvement of the pole piece of the invention3≤M1≤3.5g/cm3，0.7g/cm3≤M2≤3.3g/cm3。
As an improvement of the pole piece, the thickness of the first coating is T1The thickness of the second coating layer is T2，T2＝b·T1，0.05＜a＜0.3。
T is more than or equal to 20 mu m and is an improvement of the pole piece1≤100μm，1μm≤T2≤30μm。
As an improvement of the pole piece of the present invention, the first coating layer and the second coating layer have the same composition, and the active material in the first coating layer and the active material in the second coating layer respectively include at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium titanate, lithium manganese oxide, graphite, and silicon carbon.
As an improvement of the pole piece, the porosity of the first coating is 10-25%.
As an improvement of the pole piece, the porosity of the second coating is 15-35%.
The second purpose of the invention is: the battery cell comprises a positive plate, a negative plate, a diaphragm arranged between the positive plate and the negative plate, and electrolyte, wherein the positive plate and/or the negative plate is the plate described in the specification.
The third purpose of the invention is that: the secondary battery comprises a shell and a battery cell encapsulated in the shell, wherein the battery cell is described in the specification.
Compared with the prior art, the beneficial effects of the invention include but are not limited to: in the invention, the tap density of the active substance in the second coating of the pole piece is less than that of the active substance in the first coating, wherein the second coating with the lower tap density of the active substance is more difficult to roll, and after the pole piece is rolled, the compaction density of the second coating is correspondingly lower, so that the second coating has higher porosity and can adsorb and store more free electrolyte; the first coating with the relatively high tap density of the active material has relatively high compaction density after rolling, so that the excessive increase of the thickness of the pole piece and the excessive reduction of the energy density can be avoided, and meanwhile, the distance between active material particles can not be excessively increased, and further, the influence on the electron conduction in the pole piece is avoided. Therefore, the pole piece can store more electrolyte, and the problems of lithium precipitation, poor circulation and the like caused by insufficient electrolyte are avoided.
Drawings
FIG. 1 is a schematic view of a pole piece according to the present invention.
FIG. 2 is a second schematic view of the structure of the pole piece of the present invention.
FIG. 3 is a graph showing the cycle curves of some of the batteries of examples and comparative examples of the present invention.
Wherein: 1-current collector, 2-first coating, 3-second coating.
Detailed Description
Embodiments of the present invention will be described in detail below. The examples of the invention should not be construed as limiting the invention.
1. Pole piece
The invention provides a pole piece, and referring to fig. 1-2, the pole piece comprises a current collector 1, a first coating 2 and a second coating 3, wherein the first coating 2 is arranged on at least one side of the current collector 1, the second coating 3 is arranged on the surface of the first coating 2, and the tap density of an active substance in the first coating 2 is greater than that of an active substance in the second coating 3.
In some embodiments, the tap density of the active material in the first coating 2 is M1The tap density of the active material in the second coating layer 2 is M2，M1＝a·M2A is more than 1.01 and less than 1.3. Specifically, a is 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29. Preferably, a is 1.10.
In some embodiments, 0.8g/cm3≤M1≤3.5g/cm3，0.7g/cm3≤M2≤3.3g/cm3. It should be noted that the tap density is small, and the corresponding compacted density is small, and too small compacted density may cause the occupied volume of the active material with the same mass to be too large, so that the volume density of the battery cell is reduced.
In some embodiments, the first coating 2 has a thickness T1The thickness of the second coating 3 is T2，T2＝b·T1A is more than 0.05 and less than 0.3. Specifically, b is 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29. Preferably, b is 0.1.
In some embodiments, 20 μm ≦ T1≤100μm，1μm≤T2Less than or equal to 30 mu m. Preferably, T1Is 50 μm, T2Is 5 μm. It should be noted that when the thickness of the second coating 3 is too small, the increase in porosity is limited; when the thickness of the second coating layer 3 is excessively thick, the energy density of the cell may be excessively reduced.
In some embodiments, the first coating layer 2 and the second coating layer 3 are the same in composition, and the active material in the first coating layer 2 and the active material in the second coating layer 3 each include at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium titanate, lithium manganese oxide, lithium oxygen compound, graphite, and silicon carbon. The active materials in the first coating layer 2 and the second coating layer 3 may be selected according to the properties required for the positive and negative electrode sheets in actual production, including but not limited to the above-listed materials.
In some embodiments, the first coating 2 has a porosity of 10 to 25%. Specifically, the porosity of the first coating layer 2 may be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%.
In some embodiments, the porosity of the second coating 3 is 15-35%. Specifically, the porosity of the second coating layer 3 may be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%.
2. Battery cell
The second aspect of the invention provides an electric core, which comprises a positive plate, a negative plate, a diaphragm arranged between the positive plate and the negative plate, and electrolyte, wherein the positive plate and/or the negative plate is the plate of the invention.
Positive electrode
The positive plate comprises a positive current collector, a positive first coating coated on at least one surface of the positive current collector and a positive second coating coated on the surface of the positive first coating. The material of the positive electrode current collector includes, but is not limited to, an aluminum foil, and the specific kinds of the positive electrode first coating layer and the positive electrode second coating layer are not particularly limited and may be selected according to the requirements.
In some embodiments, the positive electrode first coating layer and the positive electrode second coating layer each comprise a positive electrode active material comprising LiCoO2、LiNiO2、LiMnO4、LiCo1-yMyO2、LiNi1-yMyO4And LiNixCoyMnzM1-x-y-zO2Wherein M is at least one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, and y is more than or equal to 0 and less than or equal to 1, x is more than or equal to 0 and less than or equal to 1<1，0≤z≤1，x+y+z≤1。
In some embodiments, the positive electrode first coating layer and the positive electrode second coating layer further comprise a binder to improve the binding of the positive electrode active material particles to each other and also to the main body of the pole piece. Non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon, and the like.
In some embodiments, the positive first coating layer and the positive second coating layer further comprise a conductive material, thereby imparting conductivity to the electrodes. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.
Negative electrode
The negative plate comprises a negative current collector, a negative first coating coated on at least one surface of the negative current collector and a negative second coating coated on the surface of the negative first coating. The material of the negative electrode current collector includes, but is not limited to, copper foil, and the specific kinds of the negative electrode first coating and the negative electrode second coating are not particularly limited and may be selected as desired.
In some embodiments, the negative electrode first coating and the negative electrode second coating include a negative electrode active material including carbon, graphite, and SiO2One or a combination of two of (1).
In some embodiments, the negative electrode first coating layer and the negative electrode second coating layer may further include a binder that improves binding of the negative electrode active material particles to each other and binding of the negative electrode active material to the current collector. Non-limiting examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon, and the like.
In some embodiments, the negative electrode first coating and the negative electrode second coating further comprise a conductive material, thereby imparting conductivity to the electrodes. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.
Diaphragm
In some embodiments, the cell of the present invention is provided with a separator between the positive and negative electrodes to prevent short circuits. The material and shape of the separator used in the battery cell of the present invention are not particularly limited, and may be any of the techniques disclosed in the prior art.
For example, the separator may include a substrate layer and a surface treatment layer.
The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.
At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.
The inorganic layer comprises inorganic particles and a binder, wherein the inorganic particles are selected from one or more of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from one or a combination of more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
The polymer layer comprises a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).
3. Secondary battery
The third aspect of the invention provides a secondary battery, which comprises a shell and a battery cell encapsulated in the shell, wherein the battery cell is the battery cell disclosed by the invention.
Embodiments of the present invention are illustrated below with reference to examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the claimed invention.
Example 1
Preparing a positive plate:
1) stirring by taking lithium iron phosphate as an active substance, carbon black as a conductive agent, polyvinylidene fluoride as a bonding agent and NMP as a solvent, wherein the weight ratio of the lithium iron phosphate: carbon black: preparing slurry with the mass ratio of polyvinylidene fluoride (94: 3: 3) and NMP (N-methyl pyrrolidone) accounting for 40% of the weight of the slurry, wherein the tap density of the lithium iron phosphate in the first slurry is 1.3g/cm3The tap density of the lithium iron phosphate in the second slurry is 1.1g/cm3；
2) Coating the first slurry on an aluminum foil with the thickness of 13 mu m by using an extrusion coating process, drying to form a first coating, coating the second slurry on the first coating, drying to form a second coating, rolling, wherein the thickness of the first coating after rolling is 65 mu m, and the corresponding compaction density is 2.45g/cm3The thickness of the second coating was 10 μm, corresponding to a compacted density of 2.35g/cm3；
3) And performing the working procedures of die cutting, slitting and the like to obtain the positive plate.
Preparing a negative plate:
1) stirring by taking graphite as an active substance, carbon black as a conductive agent, styrene butadiene rubber as an adhesive, sodium carboxymethyl cellulose as a dispersant and deionized water as a solvent, wherein the weight ratio of graphite: carbon black: styrene-butadiene rubber: preparing slurry with the mass ratio of the sodium carboxymethylcellulose being 96:1:1.5:0.5 and the deionized water accounting for 50% of the weight of the slurry, wherein the tap density of graphite in the first slurry is 0.95g/cm3The tap density of the graphite in the second slurry is 0.85g/cm3；
2) Using an extrusion coating process, firstly coating the first slurry on a copper foil with the thickness of 6 mu m and drying to form a first coating, then coating the second slurry on the first coating and drying to form a second coating, and then rolling, wherein the thickness of the first coating after rolling is 50 mu m, and the corresponding compaction density is 1.65g/cm3The thickness of the second coating was 5 μm, corresponding to a compacted density of 1.6g/cm3；
3) And performing the working procedures of die cutting, stripping and the like to obtain the negative plate.
Preparing a diaphragm:
a PE porous film having a thickness of 12 μm was used as a separator.
Preparing an electrolyte:
mixing lithium hexafluorophosphate (LiPF)6) Dissolved in a mixed solvent composed of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) (the mass ratio of the three is 1; 2: 1) to obtain the electrolyte with the concentration of 1 mol/L.
Preparing a lithium ion battery:
winding the positive plate, the diaphragm and the negative plate into a battery cell, wherein the diaphragm is positioned between the positive plate and the negative plate, the positive electrode is led out by spot welding of an aluminum tab, and the negative electrode is led out by spot welding of a nickel tab; and then placing the battery core in an aluminum-plastic packaging bag, injecting the electrolyte, and carrying out processes such as packaging, formation, capacity and the like to prepare the lithium ion battery.
Example 2
The difference from example 1 is:
preparing a positive plate:
1) with phosphorusLithium iron phosphate is used as an active substance, carbon black is used as a conductive agent, polyvinylidene fluoride is used as a bonding agent, and NMP is used as a solvent for stirring, wherein the weight ratio of the lithium iron phosphate: carbon black: preparing slurry with the mass ratio of polyvinylidene fluoride (94: 3: 3) and NMP (N-methyl pyrrolidone) accounting for 40% of the weight of the slurry, wherein the tap density of lithium iron phosphate in the slurry is 1.3g/cm3；
2) Using an extrusion coating process, coating the slurry on an aluminum foil with the thickness of 13 mu m, drying, rolling, wherein the thickness of the rolled coating is 75 mu m, and the corresponding compaction density is 2.45g/cm3；
3) And performing the working procedures of die cutting, slitting and the like to obtain the positive plate.
The rest is the same as embodiment 1, and the description is omitted here.
Example 3
The difference from example 1 is:
preparing a negative plate:
1) stirring by taking graphite as an active substance, carbon black as a conductive agent, styrene butadiene rubber as an adhesive, sodium carboxymethyl cellulose as a dispersant and deionized water as a solvent, wherein the weight ratio of graphite: carbon black: styrene-butadiene rubber: the mass ratio of the sodium carboxymethylcellulose is 96:1:1.5:0.5, the deionized water accounts for 50% of the weight ratio of the slurry, and the slurry is prepared, wherein the tap density of graphite in the slurry is 0.95g/cm3；
2) Using an extrusion coating process, firstly coating the slurry on a copper foil with the thickness of 6 mu m, drying, then rolling, wherein the thickness of the coating after rolling is 55 mu m, and the corresponding compaction density is 1.65g/cm3；
3) And performing the working procedures of die cutting, stripping and the like to obtain the negative plate.
The rest is the same as embodiment 1, and the description is omitted here.
Example 4
The difference from example 3 is:
preparing a positive plate:
the tap density of the lithium iron phosphate in the first slurry is 1.3g/cm3The tap density of the lithium iron phosphate in the second slurry is 1.27g/cm3(ii) a The compacted density of the first coating layer after rolling was 2.45g/cm3The second coating had a compacted density of 2.42g/cm3。
The rest is the same as embodiment 3, and the description is omitted here.
Example 5
The difference from example 3 is:
preparing a positive plate:
the tap density of the lithium iron phosphate in the first slurry is 1.3g/cm3The tap density of the lithium iron phosphate in the second slurry is 1.18g/cm3(ii) a The compacted density of the first coating layer after rolling was 2.45g/cm3The second coating had a compacted density of 2.38g/cm3。
The rest is the same as embodiment 3, and the description is omitted here.
Example 6
The difference from example 3 is:
preparing a positive plate:
the tap density of the lithium iron phosphate in the first slurry is 1.3g/cm3The tap density of the lithium iron phosphate in the second slurry is 1.01g/cm3(ii) a The compacted density of the first coating layer after rolling was 2.45g/cm3The second coating had a compacted density of 2.3g/cm3。
The rest is the same as embodiment 3, and the description is omitted here.
Example 7
The difference from example 3 is:
preparing a positive plate:
after rolling, the thickness of the first coating was 65 μm and the thickness of the second coating was 4 μm.
The rest is the same as embodiment 3, and the description is omitted here.
Example 8
The difference from example 3 is:
preparing a positive plate:
after rolling, the thickness of the first coating was 65 μm and the thickness of the second coating was 6.5. mu.m.
The rest is the same as embodiment 3, and the description is omitted here.
Example 9
The difference from example 3 is:
preparing a positive plate:
after rolling, the thickness of the first coating was 65 μm and the thickness of the second coating was 13 μm.
The rest is the same as embodiment 3, and the description is omitted here.
Example 10
The difference from example 3 is:
preparing a positive plate:
after rolling, the thickness of the first coating was 65 μm and the thickness of the second coating was 18 μm.
The rest is the same as embodiment 3, and the description is omitted here.
Comparative example 1
The difference from example 1 is:
preparing a positive plate:
1) stirring by taking lithium iron phosphate as an active substance, carbon black as a conductive agent, polyvinylidene fluoride as a bonding agent and NMP as a solvent, wherein the weight ratio of the lithium iron phosphate: carbon black: preparing slurry with the mass ratio of polyvinylidene fluoride (94: 3: 3) and NMP (N-methyl pyrrolidone) accounting for 40% of the weight of the slurry, wherein the tap density of lithium iron phosphate in the slurry is 1.3g/cm3；
2) Using an extrusion coating process, coating the slurry on an aluminum foil with the thickness of 13 mu m, drying, rolling, wherein the thickness of the rolled coating is 75 mu m, and the corresponding compaction density is 2.45g/cm3；
3) And performing the working procedures of die cutting, slitting and the like to obtain the positive plate.
Preparing a negative plate:
1) stirring by taking graphite as an active substance, carbon black as a conductive agent, styrene butadiene rubber as an adhesive, sodium carboxymethyl cellulose as a dispersant and deionized water as a solvent, wherein the weight ratio of graphite: carbon black: styrene-butadiene rubber: the mass ratio of the sodium carboxymethylcellulose is 96:1:1.5:0.5, the deionized water accounts for 50% of the weight ratio of the slurry, and the slurry is prepared, wherein the tap density of graphite in the slurry is 0.95g/cm3；
2) Using an extrusion coating process, firstly coating the slurry on a copper foil with the thickness of 6 mu m, drying, then rolling, wherein the thickness of the coating after rolling is 55 mu m, and the corresponding compaction density is 1.65g/cm3；
3) And performing the working procedures of die cutting, stripping and the like to obtain the negative plate.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 2
The difference from example 3 is:
preparing a positive plate:
the tap density of the lithium iron phosphate in the first slurry is 1.3g/cm3The tap density of the lithium iron phosphate in the second slurry is 0.6g/cm3(ii) a The compacted density of the first coating layer after rolling was 2.45g/cm3The second coating had a compacted density of 1.96g/cm3。
The rest is the same as embodiment 3, and the description is omitted here.
Comparative example 3
The difference from example 3 is:
preparing a positive plate:
after rolling, the thickness of the first coating was 65 μm and the thickness of the second coating was 0.8. mu.m.
The rest is the same as embodiment 3, and the description is omitted here.
Comparative example 4
The difference from example 3 is:
preparing a positive plate:
after rolling, the thickness of the first coating was 65 μm and the thickness of the second coating was 32 μm.
The rest is the same as embodiment 3, and the description is omitted here.
Performance testing
The batteries prepared in the above examples and comparative examples were subjected to cycle performance tests, specifically, 0 to 100% DOD cycle charge and discharge tests at 60 ℃ with a charge and discharge current of 1C/1C. The test results are shown in Table 1. Further, the cycle curves of examples 1 to 3 and comparative example 1 are shown in FIG. 3.
TABLE 1 test results
Figure BDA0002761786580000121
As can be seen from the test results of table 1 and fig. 3, the battery (conventional battery) prepared in comparative example 1 was likely to have water jump when it was circulated for 900 cycles and to have completed when it was circulated for 1000 cycles. In addition, when the cycle reached 80% capacity retention, the number of cycles for comparative example 1, example 2 and example 3 was 1026, 1669, 1423 and 1295 cycles, respectively, and the cycle performance example 1 > example 2 > example 3 > comparative example 1. That is, the effect of the pole piece of the invention adopted by the positive pole piece and the negative pole piece is the best, and the effect of the pole piece of the invention used by the single negative pole piece is better than that of the pole piece of the invention used by the single positive pole piece. In addition, as can be seen from comparison of examples 3, 7 to 10 and comparative examples 3 to 4, when the thickness of the second coating layer is too small, the improvement effect is limited. If and only if the tap density of the active material in the second coating layer and the thickness of the second coating layer are within the reasonable range defined by the invention, the battery can be better ensured to have better cycle performance while having higher energy density.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (6)

1. A pole piece is characterized by comprising a current collector, a first coating and a second coating, wherein the first coating is arranged on at least one surface of the current collector, the second coating is arranged on the surface of the first coating, and the tap density of an active substance in the first coating is greater than that of an active substance in the second coating;
the tap density of the active material in the first coating is M1The tap density of the active material in the second coating layer is M2，M1=a·M2，1.01＜a≤1.11，0.8g/cm3≤M1≤3.5g/cm3，0.7g/cm3≤M2≤3.3g/cm3；
The thickness of the first coating is T1The thickness of the second coating layer is T2，T2=b·T1，0.06≤b≤0.19，20μm≤T1≤100μm，1μm≤T2≤30μm。
2. The pole piece of claim 1, wherein the first coating and the second coating are the same in composition, and the active material in the first coating and the active material in the second coating each comprise at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium titanate, lithium manganese oxide, graphite, and silicon carbon.
3. The pole piece of claim 1, wherein the porosity of the first coating is 10-25%.
4. The pole piece of claim 1, wherein the porosity of the second coating is 15-35%.
5. An electric core, comprising a positive plate, a negative plate, a diaphragm arranged between the positive plate and the negative plate, and electrolyte, wherein the positive plate and/or the negative plate is the plate of any one of claims 1 to 4.
6. A secondary battery comprising a casing and a cell encapsulated in the casing, wherein the cell is the cell of claim 5.
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CN114335419A (en) * 2021-12-23 2022-04-12 蜂巢能源科技股份有限公司 Lithium battery negative pole piece and lithium battery
CN116888798B (en) * 2022-10-17 2024-08-23 宁德时代新能源科技股份有限公司 Secondary battery and electricity device comprising same
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