CN115472770A - Positive plate and preparation method thereof and secondary battery - Google Patents

Positive plate and preparation method thereof and secondary battery Download PDF

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Publication number
CN115472770A
CN115472770A CN202211027910.XA CN202211027910A CN115472770A CN 115472770 A CN115472770 A CN 115472770A CN 202211027910 A CN202211027910 A CN 202211027910A CN 115472770 A CN115472770 A CN 115472770A
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positive
inorganic filler
current collector
positive electrode
coating
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谭远高
魏小亮
黄旭
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Huizhou Liwinon Energy Technology Co Ltd
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Huizhou Liwinon Energy Technology 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
    • 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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/50—Current conducting connections for cells or batteries
    • H01M50/572—Means for preventing undesired use or discharge
    • H01M50/584—Means for preventing undesired use or discharge for preventing incorrect connections inside or outside the batteries
    • H01M50/586—Means for preventing undesired use or discharge for preventing incorrect connections inside or outside the batteries inside the batteries, e.g. incorrect connections of electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/50—Current conducting connections for cells or batteries
    • H01M50/572—Means for preventing undesired use or discharge
    • H01M50/584—Means for preventing undesired use or discharge for preventing incorrect connections inside or outside the batteries
    • H01M50/59—Means for preventing undesired use or discharge for preventing incorrect connections inside or outside the batteries characterised by the protection means
    • 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

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  • 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)
  • Secondary Cells (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a positive plate, a preparation method thereof and a secondary battery, wherein the positive plate comprises a positive current collector, a safety coating arranged on at least one surface of the positive current collector, and a positive active coating arranged on one side of the safety coating, which is far away from the positive current collector, and the resistance of the positive plate is 0.2-5 omega. The positive plate is provided with the safety coating and the positive active material layer, the negative active material layer is prevented from contacting with the positive current collector in the mechanical abuse safety test process, and meanwhile, the safety coating has certain internal resistance and can reduce heat generated in short circuit.

Description

Positive plate, preparation method thereof and secondary battery
Technical Field
The invention belongs to the technical field of secondary batteries, and particularly relates to a positive plate, a preparation method of the positive plate and a secondary battery.
Background
The lithium ion battery has the advantages of high specific energy, strong continuous running capability, long cycle life, wide working range, short charging time, capability of discharging with large current and the like, and is widely applied to the power fields of electric vehicles and the like and the consumption fields of mobile phones, watches, flat panels, notebooks and the like.
With the development of lithium ion batteries in the fields of fast charging, high energy density and the like, the safety problem caused by the battery core becomes the focus of attention of people gradually. Lithium ion battery mechanical abuse safety tests such as needling, unilateral extrusion, foreign body extrusion are one direction of concern for the major families.
In the testing process of needling, unilateral extrusion, foreign matter extrusion and the like, four contact short circuits can occur in the lithium ion battery, namely, a positive active material and a negative active material, a positive active material and a negative current collector, a positive current collector and a negative active material, and a positive current collector and a negative current collector. Among the four short-circuiting methods, the short-circuiting method in which thermal runaway is most likely to occur is a short-circuiting between the "positive electrode current collector and the negative electrode active material".
The existing diaphragm and electrolyte have limited capability of improving the safety of the battery core, are more used for improving the safety of thermal abuse such as thermal shock and the like, and have no obvious effect on improving the safety of mechanical abuse such as acupuncture, unilateral extrusion, foreign matter extrusion and the like.
Disclosure of Invention
The invention aims to: the positive plate is provided with the safety coating and the positive active material layer, the negative active material layer is prevented from contacting with the positive current collector in the mechanical abuse safety testing process, and meanwhile, the safety coating has certain internal resistance and can reduce heat generated when short circuit occurs.
In order to achieve the purpose, the invention adopts the following technical scheme:
the positive plate comprises a positive current collector, a safety coating arranged on at least one surface of the positive current collector and a positive active coating arranged on one side, far away from the positive current collector, of the safety coating, wherein the resistance of the positive plate is 0.2-5 omega.
Preferably, the compaction density of the positive active coating layer is 3.70-4.25 g/cm 3 。
Preferably, the tail part of the positive plate is also provided with an insulating layer, and the insulating layer and the safety coating are arranged in parallel.
Another object of the present invention is: aiming at the defects of the prior art, the method for preparing the positive plate is provided, the first slurry is coated on the surface of the positive current collector, the safe coating is formed by drying, the second slurry is coated on the surface of the safe coating, and the positive active coating is formed by drying to obtain the positive plate.
Preferably, the hardness of the security coating is 5 to 9.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a positive plate comprises the following steps:
step S1, mixing and stirring inorganic filler, a first conductive agent and a first binder according to the mass part ratio of 80-96;
and S2, mixing and stirring the positive active substance, the second conductive agent and the second binder according to the mass part ratio of 90-98 to 1-5.
Preferably, the tap density TD of the inorganic filler in the step S1 is more than or equal to 0.8g/cm 3 。
Preferably, the particle size of the inorganic filler in step S1 satisfies the following condition: d 10 ≥0.2μm，0.5μm≤D 50 ≤2.5μm，D 90 ≤5μm，D 99 ≤10μm。
Preferably, the inorganic filler in step S1 contains doping elements, the doping elements include sodium, calcium, iron and copper, the doping amount of sodium in the inorganic filler is less than or equal to 0.05%, the doping amount of calcium in the inorganic filler is less than or equal to 0.05%, the doping amount of iron in the inorganic filler is less than or equal to 0.005%, and the doping amount of copper in the inorganic filler is less than or equal to 0.0005%.
Preferably, the inorganic filler comprises one or more of alumina, boehmite, magnesia, titania, zirconia, silica and yttria.
Preferably, the first conductive agent is one or more of conductive graphite, conductive carbon black, carbon nano tubes and carbon nano fibers; the first binder is one or a combination of more of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene butadiene rubber, sodium carboxymethylcellulose and acrylate.
A secondary battery comprises the positive electrode plate.
Compared with the prior art, the invention has the beneficial effects that: the positive plate is provided with the safety coating and the positive active material layer, the negative active material layer is prevented from contacting with the positive current collector in the mechanical abuse safety testing process, and meanwhile, the safety coating has certain internal resistance and can reduce heat generated in the short circuit.
Drawings
Fig. 1 is a schematic view of the structure of the positive electrode sheet of the present invention.
Wherein: 1. a positive current collector; 2. a security coating; 3. a positive active coating layer; 4. an insulating layer.
Detailed Description
The present invention will be described in further detail with reference to the following detailed description and the accompanying drawings, but the embodiments of the invention are not limited thereto.
The positive plate comprises a positive current collector 1, a safety coating 2 arranged on at least one surface of the positive current collector 1 and a positive active coating 3 arranged on one side, far away from the positive current collector 1, of the safety coating 2, wherein the resistance of the positive plate is 0.2-5 omega.
The positive plate is provided with the safety coating 2 and the positive active coating 3, has a certain resistance, can reduce short-circuit batteries when short circuit occurs, reduces heat generation, reduces thermal shock, has mechanical strength, and can pass safety tests of mechanical abuse. The safety coating 2 not only has certain mechanical strength, but also has certain resistance, the resistance of the pole piece can be improved, the pole piece can pass various mechanical abuse tests due to the higher mechanical strength, and the pole piece cannot generate a large amount of heat under the condition of short circuit due to the higher resistance, so that the short-circuit current during short circuit is reduced.
In some embodiments, the positive active coating layer has a compacted density of 3.70 to 4.25g/cm 3 . Preferably, the positive electrode active coating layer 3 has a compacted density of 3.70 to 3.90g/cm 3 、3.90～4.10g/cm 3 、4.1～4.25g/cm 3 Specifically, the compacted density of the positive electrode active coating layer 3 was 3.70g/cm 3 、3.75g/cm 3 、3.80g/cm 3 、3.85g/cm 3 、3.90g/cm 3 、3.95g/cm 3 、4.00g/cm 3 、4.12g/cm 3 、4.18g/cm 3 、4.20g/cm 3 、4.25g/cm 3 。
In some embodiments, the tail of the positive plate is further provided with an insulating layer 4. The insulating layer 4 can further improve the safety performance of the positive plate, and contact short circuit is avoided in the test, so that the mechanical abuse performance test is improved. Preferably, the pole piece of the invention is applied to a winding battery cell, and the insulating layer 4 is positioned at the ending part of the battery cell, so that the safety performance at the end can be improved.
In some embodiments, the security coating 2 has a hardness of 5 to 9. Preferably, the hardness of the security coating 2 is 5, 6, 7, 8, 9.
According to the preparation method of the positive plate, the first slurry is coated on the surface of the positive current collector 1 and dried to form the safe coating 2, the second slurry is coated on the surface of the safe coating 2 and dried to form the positive active coating 3, and the positive plate is obtained.
A preparation method of a positive plate comprises the following steps:
step S1, mixing and stirring an inorganic filler, a first conductive agent and a first binder according to the mass part ratio of 80-96 to 1-10 to obtain a first slurry, coating the first slurry on at least one side surface of a positive current collector 1, and drying to form a safety coating 2;
and S2, mixing and stirring the positive active material, the second conductive agent and the second binder according to the mass part ratio of 90-98 to 1-5.
The positive plate mainly comprises a safety coating 2 and an active substance layer, and the resistance range of the double-sided membrane of the safety coating 2 is 0.1-3 omega. The safety coating 2 coats two sides of the current collector, the active substance layer covers the safety coating 2, and the thickness of the safety coating 2 is smaller than that of the active substance layer. The adhesion of the security coating 2 is greater than that of the active substance layer. The diaphragm resistance range of the positive pole piece is 0.2-5 omega, and the value range of the compacted density PD of the rolled positive pole piece is 3.70-4.25 g/cm 3 . An insulating coating layer is arranged at the tail part of the positive plate.
The safety coating 2 comprises an inorganic filler, a first conductive agent and a first adhesive, wherein the inorganic filler mainly comprises at least one or more of aluminum oxide, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide and yttrium oxide. The tap density TD of the inorganic filler is more than or equal to 0.8g/cm 3 Inorganic filler D 10 ≥0.2μm，D 50 Between 0.5 and 2.5 μm, D 90 ≤5μm，D 99 Less than or equal to 10 mu m. The impurity elements of the inorganic filler are less than or equal to 0.05 percent of Na, less than or equal to 0.05 percent of Ca, less than or equal to 0.005 percent of Fe and less than or equal to 0.0005 percent of Cu. The first adhesive mainly comprises one or a combination of more of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene butadiene rubber, sodium carboxymethyl cellulose and acrylate. The first conductive agent is one or a combination of more of conductive graphite, conductive carbon black, carbon nano tubes and carbon nano fibers. Preferably, the ratio of the mass of the first conductive agent to the mass of the inorganic filler in the security coating 2 is between 0.01 and 0.15; the ratio of the mass of the first conductive agent to the mass of the first adhesive is between 0.0025 and 3.
Wherein the active material layer includes an active material, a second conductive agent, and a second binder. The active substances mainly comprise: one or a plurality of lithium cobaltate, lithium iron phosphate, lithium manganese iron phosphate and lithium manganese oxide. The second conductive agent is one or a combination of more of conductive graphite, conductive carbon black, carbon nano tubes and carbon nano fibers. The second adhesive is one or a combination of more of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene butadiene rubber, sodium carboxymethylcellulose and acrylate.
The tail insulating layer 4 includes an insulating material and an adhesive. The insulating material mainly comprises one or more of PMMA, PET, alumina, boehmite, magnesia, titania, zirconia, silica and yttria. The adhesive mainly comprises one or a plurality of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene butadiene rubber, sodium carboxymethylcellulose and acrylic ester. Preferably, the ratio of the mass of the binder to the mass of the insulating material in the insulating layer 4 is between 0.05 and 0.4.
In some embodiments, the inorganic filler in step S1 has a tap density TD ≧ 0.8g/cm 3 . Preferably, the inorganic filler in step S1 has a tap density TD of 0.9g/cm or more 3 Specifically, the inorganic filler has a tap density of 0.8g/cm 3 、0.85g/cm 3 、0.89g/cm 3 、0.9g/cm 3 、0.95g/cm 3 。
In some embodiments, the particle size of the inorganic filler in step S1 satisfies the following condition: d 10 ≥0.2μm，0.5μm≤D 50 ≤2.5μm，D 90 ≤5μm，D 99 Less than or equal to 10 mu m. Preferably, D 10 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, D 50 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, D 90 2 μm, 3 μm, 4 μm, 5 μm, D 90 10 μm, 9 μm, 8 μm, 7 μm, 6 μm. The particle size of the inorganic filler is set within a certain range, so that the inorganic filler, the first conductive agent and the first binder are mixed more fully, the pole piece has a certain resistance value and mechanical strength, and meanwhile, the pole piece also has a certain electrochemical performance.
In some embodiments, the inorganic filler in step S1 contains doping elements including Na, ca, fe and Cu, wherein Na is doped in the inorganic filler in an amount of 0.05% or less, ca is doped in the inorganic filler in an amount of 0.05% or less, fe is doped in the inorganic filler in an amount of 0.005% or less, and Cu is doped in the inorganic filler in an amount of 0.0005% or less. The doping element is an element which can not be brought in the processing process of the raw material, the doping amount of the doping element in the inorganic filler is set, the doping amount is prevented from being too high, and the doping element is prevented from being separated out in the charging and discharging process to cause internal short circuit and influence on the performance of the battery cell.
In some embodiments, the mass ratio of the first conductive agent to the first binder in step S1 is in a range of 0.0025 to 3. The smaller the ratio, the less the content of the conductive agent, the larger the internal resistance of the safety coating 2, the better the safety performance and the worse the electrical performance; meanwhile, the smaller the ratio, the more the content of the adhesive is, the larger the viscosity of the slurry is, the more difficult the safety coating 2 is to coat, and the more difficult the processing is, but at the moment, the larger the adhesive force between the safety coating 2 and the current collector is, the more difficult the safety coating 2 is to fall off in the needling process, the better the safety performance is, the more the content of the adhesive is, the larger the swelling of the adhesive is in the use process in a high-temperature environment, the larger the internal resistance of the battery core is increased, and the poorer the performance of the battery core in the high-temperature environment is. The ratio is too large, the conductivity of the battery cell is good, the safety performance of the battery cell is poor, and the electrical performance is better.
In some embodiments, the inorganic filler comprises one or more of alumina, boehmite, magnesia, titania, zirconia, silica, and yttria.
In some embodiments, the first conductive agent is one or more combinations of conductive graphite, conductive carbon black, carbon nanotubes, carbon nanofibers; the first binder is one or a combination of more of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene butadiene rubber, sodium carboxymethylcellulose and acrylate.
3. A secondary battery comprises the positive electrode plate.
Specifically, a secondary battery includes positive plate, barrier film, negative pole piece, electrolyte and casing, the barrier film is used for separating positive plate and negative pole piece, the casing is used for installing positive plate, barrier film, negative pole piece and electrolyte.
Positive plate
The positive electrode current collector 1 in the positive electrode sheet is generally a structure or a part for collecting current, and the positive electrode current collector 1 may be any material suitable for use as a positive electrode current collector 1 of a lithium ion battery in the art, for example, the positive electrode current collector 1 may include, but is not limited to, a metal foil, and the like, and more specifically, may include, but is not limited to, an aluminum foil, and the like. The positive active coating 3 further comprises a binder and a conductive agent, wherein the binder is polyvinylidene fluoride, and the conductive agent is graphene.
Negative plate
The negative plate comprises a negative current collector and a negative active material layer arranged on at least one surface of the negative current collector, wherein the negative active material layer comprises a negative active material, and the negative active material can be one or more of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium titanate or other metals capable of forming alloys with lithium. Wherein, the graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite; the silicon-based material can be one or more selected from simple substance silicon, silicon-oxygen compound, silicon-carbon compound and silicon alloy; the tin-based material can be one or more selected from simple substance tin, tin oxide compound and tin alloy. The negative electrode current collector is generally a structure or a part for collecting current, and the negative electrode current collector may be any material suitable for use as a negative electrode current collector of a lithium ion battery in the art, for example, the negative electrode current collector may include, but is not limited to, a metal foil, and the like, and more specifically, may include, but is not limited to, a copper foil, and the like. The negative electrode active material layer further comprises a binder and a conductive agent, wherein the binder is polyvinylidene fluoride, and the conductive agent is conductive carbon.
Isolation film
The separator may be any material suitable for a separator of a lithium ion battery in the art, and for example, may be a combination including, but not limited to, one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fiber, and the like.
The shell is made of one of an aluminum plastic film and stainless steel.
Example 1
1. The preparation method of the positive plate comprises the following steps:
step S1, mixing and adding an inorganic filler, a first conductive agent and a first binder into a stirring tank according to the mass part ratio of 90The thickness of the positive current collector 1 on both side surfaces of the positive current collector 1 is 9 μm, and the coating areal density is 14mg/1540.25mm 2 At the moment, the resistance of the membrane is measured to be 0.8 omega, the Mohs hardness is 7, and the safe coating 2 is formed after drying; coating the insulating slurry on the tail parts of the two side surfaces of the positive current collector 1, drying to form an insulating layer 4, arranging the insulating layer 4 and the safety coating 2 in parallel, and completely covering the two side surfaces of the positive current collector 1 by the safety coating 2 and the insulating layer 4 together;
step S2, mixing and stirring the lithium cobaltate positive electrode active substance, the conductive carbon black first conductive agent and the polyvinylidene fluoride first binder according to the mass part ratio of 96 3 And obtaining the positive pole piece with the diaphragm resistance of 2.0 omega, and carrying out cold pressing, trimming, cutting and slitting on the positive pole piece to obtain the positive pole piece, wherein the sheet resistance is shown in figure 1.
2. Preparing a negative plate: preparing a silicon-carbon negative electrode active substance, conductive agent superconducting carbon, binder polyvinylidene fluoride or Styrene Butadiene Rubber (SBR) into negative electrode slurry according to a mass ratio of 96; and cutting edges, cutting pieces, slitting, and preparing the cathode plate after slitting.
3. And (3) isolation film: a polyethylene porous film with the thickness of 16 μm is selected as the separation film.
4. Preparing a battery: and winding the positive plate, the isolation film and the negative plate into a battery cell, wherein the battery cell capacity is about 5Ah. The isolating film is positioned between the adjacent positive plate and negative plate, the positive electrode is led out by aluminum tab spot welding, and the negative electrode is led out by nickel tab spot welding; then placing the battery core in an aluminum-plastic packaging bag, baking, injecting the electrolyte, packaging, forming, grading and the like, and finally preparing the lithium ion battery.
Example 2
The difference from example 1 is that: in the step S1, the mass part ratio of the inorganic filler, the first conductive agent and the first binder is 83.
The rest is the same as embodiment 1, and the description is omitted here.
Example 3
The difference from example 1 is that: in the step S1, the mass part ratio of the inorganic filler, the first conductive agent and the first binder is 85.
The rest is the same as embodiment 1, and the description is omitted here.
Example 4
The difference from example 1 is that: in the step S1, the mass parts ratio of the inorganic filler to the first conductive agent to the first binder is 88.
The rest is the same as embodiment 1, and the description is omitted here.
Example 5
The difference from example 1 is that: in the step S1, the mass part ratio of the inorganic filler to the first conductive agent to the first binder is 92.
The rest is the same as embodiment 1, and the description is omitted here.
Example 6
The difference from example 1 is that: in the step S1, the mass part ratio of the inorganic filler to the first conductive agent to the first binder is 95.
The rest is the same as embodiment 1, and the description is omitted here.
Example 7
The difference from example 1 is that: the compacted density of the positive electrode active coating layer 3 was 3.70g/cm 3 。
The rest is the same as embodiment 1, and the description is omitted here.
Example 8
The difference from example 1 is that: the compacted density of the positive electrode active coating layer 3 was 3.95g/cm 3 。
The rest is the same as embodiment 1, and the description is omitted here.
Example 9
The difference from example 1 is that: the compacted density of the positive active coating 3 was 4.15g/cm 3 。
The rest is the same as embodiment 1, and the description is omitted here.
Example 10
The difference from example 1 is that: the compacted density of the positive active coating layer 3 was 4.25g/cm 3 。
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 1
The difference from example 1 is that: the positive plate has no safety coating 2.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 2
The difference from example 1 is that: the positive plate has no insulating layer 4.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 3
The difference from example 1 is that: the safety coating 2 comprises lithium iron phosphate, a first conductive agent and a first binder, wherein the mass part ratio of the first conductive agent to the first binder is 90.
The rest is the same as embodiment 1, and the description is omitted here.
The prepared pole piece and the secondary battery are subjected to performance test, and the test results are recorded in table 1.
And (3) needle punching test: completely puncturing the battery cell at one time by using a steel needle with the diameter of 2.65mm and the speed of 150mm/s and requiring the battery cell not to be pulled out, wherein the puncturing positions are positioned at the left, middle and right positions of the maximum surface of the battery cell;
foreign matter extrusion test: the cell is squeezed between two planes, a screw M1.4X 3.0 is placed on the surface of the cell, the maximum pressure is not less than 13kN, once the pressure reaches 13.0 +/-1 kN, the pressure is released immediately, and different cells are used for squeezing each time
45 ° needle punch test: and (3) completely puncturing the battery cell at one time by using a steel needle with the diameter of 2.65mm and the speed of 150mm/s, wherein the battery cell is required not to be pulled out, the angle between the battery cell and the steel needle is 45 degrees in the puncturing process, and the puncturing position is positioned in the center of the maximum surface of the battery cell.
And (3) hardness testing: the pole piece is sequentially scratched on the surfaces of diamond (10), corundum (9), topaz (8), quartz (7), feldspar (6), apatite (5), fluorite (4), calcite (3), gypsum (2) and talc (1), and the hardness grade corresponding to the mark appearing for the first time is recorded.
And (3) resistance testing: electrifying the pole piece by using the current I of 1A, testing the voltage value U at two ends of the pole piece, and calculating the resistance R = U/I.
TABLE 1
Figure BDA0003816468550000101
Figure BDA0003816468550000111
As can be seen from table 1 above, the pole piece and the battery cell of the secondary battery prepared by the present invention have better mechanical properties and safety properties compared with the pole piece and the secondary battery in the prior art. From comparison of examples 1 to 6, when the mass part ratio of the inorganic filler, the first conductive agent and the first binder in step S1 is set to be 90. From comparison of examples 1, 7 to 10, it is found that the compacted density of the positive electrode active coating layer 3 when set is 3.85g/cm 3 In this case, the prepared secondary battery has the best performance.
As can be seen from comparison of examples 1 to 10 with comparative example 1, comparative example 1 lacks the safety coating layer 2, resulting in a low mechanical property of the entire pole piece, and thus failing to pass the mechanical abuse safety test of the battery, particularly, the foreign substance compression test passage rate is 0, and is liable to cause short-circuiting in the case of foreign substance compression to cause thermal abuse.
Compared with the comparative example 2, the comparison of the examples 1 to 10 shows that when the pole piece has no insulating layer 4, the safety performance of the pole piece is reduced to some extent, so that the mechanical abuse performance test cannot pass 100%, and the overall resistance of the pole piece is low, so that when short circuit is caused by mechanical abuse, thermal runaway is easily caused, a large amount of heat is emitted, and serious safety accidents are caused.
The comparison between examples 1-10 and comparative example 3 shows that the pole piece uses inorganic filler to replace lithium iron phosphate, so that the overall hardness and the resistance of the pole piece are increased, the mechanical abuse passing rate of the pole piece can reach 100%, the resistance reaches 1.5-2 omega, and the mechanical performance and the safety performance are greatly improved.
Variations and modifications to the above-described embodiments may become apparent to those skilled in the art to which the invention pertains based upon the disclosure and teachings of the above specification. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious modifications, substitutions or alterations based on the present invention will fall 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 (11)

1. The positive plate is characterized by comprising a positive current collector, a safety coating arranged on at least one surface of the positive current collector and a positive active coating arranged on one side, far away from the positive current collector, of the safety coating, wherein the resistance of the positive plate is 0.2-5 omega.
2. The positive electrode sheet according to claim 1, wherein the positive electrode active coating layer has a compacted density of 3.70 to 4.25g/cm 3 。
3. The positive plate according to claim 1, wherein the tail part of the positive plate is further provided with an insulating layer, and the insulating layer is arranged in parallel with the safety coating.
4. The positive electrode sheet according to claim 1, wherein the safety coating layer has a hardness of 5 to 9.
5. The method for producing a positive electrode sheet according to any one of claims 1 to 4, comprising the steps of:
s1, mixing and stirring inorganic filler, a first conductive agent and a first binder according to the mass part ratio of 80-97 to 2-10 to obtain first slurry, coating the first slurry on at least one side surface of a positive current collector, and drying to form a safety coating;
and S2, mixing and stirring the positive active substance, the second conductive agent and the second binder according to the mass part ratio of 90-98.
6. The method for preparing the positive electrode sheet according to claim 5, wherein the tap density TD of the inorganic filler in the step S1 is not less than 0.8g/cm 3 。
7. The method for producing a positive electrode sheet according to claim 5, wherein the particle diameter of the inorganic filler in step S1 satisfies the following condition: d 10 ≥0.2μm，0.5μm≤D 50 ≤2.5μm，D 90 ≤5μm，D 99 ≤10μm。
8. The method for preparing the positive electrode sheet according to claim 5, wherein the inorganic filler in the step S1 contains doping elements including sodium, calcium, iron and copper, the doping amount of sodium in the inorganic filler is less than or equal to 0.05%, the doping amount of calcium in the inorganic filler is less than or equal to 0.05%, the doping amount of iron in the inorganic filler is less than or equal to 0.005%, and the doping amount of copper in the inorganic filler is less than or equal to 0.0005%.
9. The positive electrode sheet preparation method according to claim 5, wherein the inorganic filler comprises one or more of alumina, boehmite, magnesia, titania, zirconia, silica, and yttria.
10. The method for preparing the positive electrode sheet according to claim 5, wherein the first conductive agent is one or a combination of more of conductive graphite, conductive carbon black, carbon nanotubes and carbon nanofibers; the first binder is one or a combination of more of polyvinylidene fluoride, polyurethane, sodium polyacrylate, styrene butadiene rubber, sodium carboxymethylcellulose and acrylate.
11. A secondary battery comprising the positive electrode sheet according to any one of claims 1 to 4.
CN202211027910.XA 2022-08-25 2022-08-25 Positive plate and preparation method thereof and secondary battery Pending CN115472770A (en)

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CN115472770A true CN115472770A (en) 2022-12-13

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