CN114883527A - Multilayer negative plate, preparation method thereof and secondary battery - Google Patents

Multilayer negative plate, preparation method thereof and secondary battery Download PDF

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CN114883527A
CN114883527A CN202210654490.1A CN202210654490A CN114883527A CN 114883527 A CN114883527 A CN 114883527A CN 202210654490 A CN202210654490 A CN 202210654490A CN 114883527 A CN114883527 A CN 114883527A
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coating layer
coating
active material
temperature
active substance
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CN114883527B (en
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曾朝智
黄志国
胡大林
廖兴群
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Huizhou Highpower Technology Co Ltd
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Huizhou Highpower 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
    • 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
    • H01M10/42—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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0416—Methods of deposition of the material involving impregnation with a solution, dispersion, paste or dry powder
    • 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
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • 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

Abstract

In order to solve the technical problem of insufficient energy density of a double-layer negative electrode in the prior art, the application provides a multilayer negative plate, wherein an ultrathin primer layer is coated on one side surface of a current collector, a first coating layer is coated on the surface of the ultrathin primer layer, and a second coating layer is coated on the surface of the first coating layer; the first coating layer comprises a first active substance, and the temperature of the first active substance for starting the thermal weight loss after being calcined in the air atmosphere is 500-600 ℃; the second coating layer comprises a second active substance, and the temperature of the second active substance for starting thermal weight loss after being calcined in the air atmosphere is 600-700 ℃. The application provides a multilayer negative pole piece has high energy load and fast ion transfer performance concurrently, not only improves the energy density of battery, also effectively prevents that the battery from analyzing lithium simultaneously, improves battery security performance, multiplying power performance and cyclicity ability.

Description

Multilayer negative plate, preparation method thereof and secondary battery
Technical Field
The invention belongs to the technical field of secondary batteries, and particularly relates to a multilayer negative plate, a preparation method thereof and a secondary battery using the multilayer negative plate.
Background
With the increasing degree of human industrialization, more and more greenhouse gases are emitted into the atmosphere. Extreme weather and adverse consequences caused by increasingly severe greenhouse effect cause wide attention of international society, so that development and development of new energy become important tasks for guaranteeing the full-blown development of various countries. The lithium ion battery has the advantages of small volume, light weight, high working voltage, high specific energy, long cycle life, low self-discharge, no memory effect, environmental protection and the like, and is widely applied to the fields of electric automobiles, power grid energy storage, portable equipment and the like, so that the lithium ion battery is rapidly developed. One of the first tasks is to develop high energy density lithium ion batteries to meet the rapidly growing demand of these devices. In addition, due to the demand of people for fast paced life, fast charging is also an important focus for developing lithium ion batteries. Therefore, the development of a lithium ion battery with high energy load and high charge rate performance is one of the focuses of the research and development.
One method for improving lithium ion diffusion of a high-energy load negative electrode at present is to adopt technologies such as particle size reduction to improve the lithium ion diffusion speed of the negative electrode, but the reduction of the particle size can cause low pole piece compaction and low first efficiency of a battery, and further cause the energy density of the battery to be reduced. The other is that a layer of soft carbon is coated on the surface of the high-energy graphite, the soft carbon has better compatibility with the electrolyte, the transmission of lithium ions is accelerated, but the soft carbon can reduce the specific capacity and the first effect of the graphite. Therefore, some patents disclose that two layers of graphite with different properties are coated on a copper current collector through double-layer coating, so that polarization and lithium precipitation of an electrochemical device can be improved from the direction of a negative electrode structure, and the energy density and the lithium ion diffusion speed of the electrochemical device are improved. However, due to the defects of the structural design, the energy density of the current double-layer cathode is not enough to meet the application requirements.
Disclosure of Invention
The invention aims to solve the technical problem that the energy density of a double-layer negative electrode is insufficient in the prior art, and provides a multilayer negative electrode plate, a preparation method thereof and a secondary battery.
In order to solve the technical problem, the application provides a multilayer negative plate, which comprises a current collector, an ultrathin bottom coating, a first coating layer and a second coating layer; the ultrathin primer coating is coated on one side surface of the current collector, the first coating layer is coated on the surface of the ultrathin primer coating, and the second coating layer is coated on the surface of the first coating layer;
the first coating layer comprises a first active substance, and the temperature of the first active substance for starting the thermal weight loss after being calcined in the air atmosphere is 500-600 ℃;
the second coating layer comprises a second active substance, and the temperature of the second active substance for starting thermal weight loss after being calcined in the air atmosphere is 600-700 ℃.
Preferably, the temperature of the first active substance for starting the thermal weight loss in the calcination in the air atmosphere is 500-510 ℃; the temperature of the second active substance for starting thermal weight loss after being calcined in the air atmosphere is 690-700 ℃.
Preferably, the thermal weight loss of the second active material is less than 5% at a temperature of 800 ℃.
Preferably, the thermal weight loss of the second active substance is 1-5% when the temperature of the thermal weight loss of the second active substance is 800 ℃.
Preferably, the ultrathin primer layer comprises a third active material, and the ultrathin primer layer is prepared from the third active material, a third binder and a third thickening agent according to the weight percentage (55-75%): (15-35%): (0-10%) is added into deionized water and mixed evenly to obtain the product.
Preferably, the third active substance is a carbon nanotube or graphene, the third binder is styrene-butadiene sol, and the third thickener is sodium carboxymethylcellulose; the thickness of the ultrathin bottom coating is 0.25-2 μm.
Preferably, the first coating layer comprises 97.5-98% by mass of a first active substance, 1.2-1.5% by mass of a first binder, 0-0.2% by mass of a first conductive agent, and 0.5-0.8% by mass of a first thickening agent, based on 100% by mass of the first coating layer;
the first active substance is graphite, soft carbon or hard carbon, and the first binder is one or more of polyvinylidene fluoride, butadiene rubber, polyethylene oxide, polytetrafluoroethylene, polyvinyl alcohol, vinylidene fluoride-hexafluoropropylene copolymer, styrene butadiene rubber and acrylonitrile multipolymer emulsion; the first conductive agent is one or more of Super P, conductive carbon black, conductive graphite, carbon nano tubes, acetylene black and graphite; the first thickening agent is sodium carboxymethyl cellulose;
the thickness of the first coating layer is 70-90 μm.
Preferably, the second coating layer comprises the following components by mass 100%: 98-98.5% of a second active substance, 0-2% of a second conductive agent, 0.7-1.0% of a second binder and 0.5-0.8% of a second thickening agent in percentage by mass;
the second active substance is graphite, soft carbon or hard carbon, and the second binder is one or more of polyvinylidene fluoride, butadiene rubber, polyethylene oxide, polytetrafluoroethylene, polyvinyl alcohol, vinylidene fluoride-hexafluoropropylene copolymer, styrene butadiene rubber and acrylonitrile multipolymer emulsion; the second conductive agent is one or more of Super P, conductive carbon black, conductive graphite, carbon nano tubes, acetylene black and graphite; the second thickening agent is sodium carboxymethyl cellulose;
the thickness of the second coating layer is 50-70 μm.
In another aspect, the present application provides a method for preparing a multilayer negative electrode sheet, including at least the following steps:
coating the slurry of the ultrathin primer coating on the surface of one side of a current collector to form the ultrathin primer coating;
coating the first coating layer slurry on the surface of the ultrathin base coating layer to form a first coating layer;
and step three, coating the second coating layer slurry on the surface of the first coating layer to form a second coating layer, so as to obtain the multilayer negative plate.
In another aspect, the present application provides a secondary battery using the above-described multilayered negative electrode sheet.
According to the multilayer negative plate provided by the application, the ultra-thin primer can effectively reduce the binder ratio in the first coating layer, improve the first active material ratio in the first coating layer, and improve the lithium loading capacity and the ion rapid diffusion capacity of the multilayer negative plate; the calcining temperature of the second active material in the second coating layer is higher than that of the first active material, the diffusion speed of lithium ions in the second coating layer is higher than that of the first coating layer, under the condition of large current or low temperature, the lithium ions can be rapidly diffused from the second coating layer and can be embedded into the first coating layer with high load capacity, and under the condition that the first coating layer also has high lithium load capacity, lithium metal can be effectively prevented from being separated out on the surface of the negative electrode. The application provides a multilayer negative pole piece has high energy load and fast ion transfer performance concurrently, not only improves the energy density of battery, also effectively prevents that the battery from analyzing lithium simultaneously, improves battery security performance, multiplying power performance and cyclicity ability.
Drawings
FIG. 1 is a schematic cross-sectional view of a multi-layer negative electrode sheet;
FIG. 2 is a graph showing the thermogravimetric curves of the calcination of the first active material in an air atmosphere in example 4;
FIG. 3 is a graphical representation of the thermal weight loss versus temperature curve for the calcination of a second active material in an air atmosphere in accordance with example 4;
FIG. 4 is a graph of the 1C/0.5C 500 cycle at 25 ℃ for example 1;
FIG. 5 is a 1C/0.5C 500 cycle plot at 25 ℃ for comparative example 1;
the reference numbers in the drawings of the specification are as follows:
1. a current collector; 2. an ultra-thin primer layer; 3. a first coating layer; 4. a second coating layer.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1, the multilayer negative electrode sheet provided by the present application includes a current collector 1, an ultrathin primer layer 2, a first coating layer 3, and a second coating layer 4; the ultrathin primer layer 2 is formed by coating ultrathin primer slurry on one side surface of the current collector 1, the first coating layer 3 is formed by coating first coating slurry on the surface of the ultrathin primer layer 2, and the second coating layer 4 is formed by coating second coating slurry on the surface of the first coating layer 3;
the first coating layer 3 comprises a first active substance, and the temperature of the first active substance for starting thermal weight loss after being calcined in an air atmosphere is 500-600 ℃;
the second coating layer 4 includes a second active material, and the temperature at which the second active material starts to lose weight by heat when calcined in an air atmosphere is 600 ℃ to 700 ℃.
The ultrathin primer layer 2 is coated on one side surface of the current collector 1, and the method has the advantages that the ratio of the binder in the first coating layer 3 is reduced, and the ratio of the active substance in the first coating layer 3 is improved, so that the energy density and the lithium ion diffusion speed of the multilayer negative plate are increased. The higher the calcination temperature of the active material is, the higher the decomposition degree is, and the higher the crystallinity of the active material is, the faster the diffusion speed of lithium ions in the active material structure is; the temperature ranges of the first active substance and the second active substance starting thermal weight loss are limited, the first active substance is calcined in an air atmosphere, the temperature range of the starting thermal weight loss is 500-600 ℃, the second active substance is calcined in the air atmosphere, the temperature range of the starting thermal weight loss is 600-700 ℃, the temperature range of the starting thermal weight loss of the second active substance is higher than the temperature range of the starting thermal weight loss of the first active substance, the diffusion speed of lithium ions in the second coating layer 4 is higher than the diffusion speed of the lithium ions in the first coating layer 3, the lithium ions can rapidly pass through the second coating layer 4 and are embedded into the first coating layer 3 under the condition of large current or low temperature, and particularly under the condition of low temperature, the lithium ions can more conveniently and rapidly pass through the second coating layer 4 and are embedded into the first coating layer 3 with high load; meanwhile, the binder proportion of the first coating layer 3 is reduced, the content of the first active material layer is increased, the load capacity of the first coating layer 3 is enhanced, a large amount of lithium ions can rapidly pass through the second coating layer 4 and be embedded into the first coating layer 3 with high load under a high-current condition or a low-temperature condition, the precipitation of lithium metal on the surface of a negative electrode is effectively avoided, the energy density of the battery is improved, and the cycle performance, the rate capability and the safety performance of the battery are improved.
According to the multilayer negative plate provided by the application, the ultra-thin primer layer 2 can effectively reduce the binder proportion in the first coating layer 3, improve the first active material proportion in the first coating layer 3, and improve the lithium loading capacity and the ion rapid diffusion capacity of the multilayer negative plate; the calcining temperature of the second active material in the second coating layer 4 is higher than that of the first active material, the diffusion speed of lithium ions in the second coating layer 4 is higher than that of the first coating layer 3, under the condition of large current or low temperature, the lithium ions can be rapidly diffused from the second coating layer 4 and can be embedded into the first coating layer 3 with high load capacity, and under the condition that the first coating layer 3 also has high lithium loading capacity, lithium metal can be effectively prevented from being separated out on the surface of the negative electrode. The application provides a multilayer negative pole piece has high energy load and fast ion transfer performance concurrently, not only improves the energy density of battery, also effectively prevents that the battery from analyzing lithium simultaneously, improves battery security performance, multiplying power performance and cyclicity ability.
In other embodiments, the temperature at which the first active material is calcined in an air atmosphere to begin thermal weight loss may be 500 ℃, 510 ℃, 515 ℃, 520 ℃, 530 ℃, 540 ℃, 550 ℃, 560 ℃, 570 ℃, 580 ℃, or 590 ℃; the temperature at which the second active material starts to undergo thermal weight loss upon calcination in an air atmosphere may be 600 ℃, 610, 620, 630, 640, 650, 660, 670, 680, 690, or 700 ℃.
In some preferred embodiments, the temperature of the first active material at which the calcination in the air atmosphere starts the thermal weight loss is 500 to 510 ℃; the temperature of the second active substance for starting thermal weight loss after being calcined in the air atmosphere is 690-700 ℃.
The temperature at which the first active material starts to undergo thermal weight loss by calcination in an air atmosphere may be 500 ℃, 501 ℃, 502 ℃, 503 ℃, 504 ℃, 505 ℃, 506 ℃, 507 ℃, 508 ℃, 509 ℃ or 510 ℃. The temperature of the first active material for starting the thermal weight loss after being calcined in the air atmosphere is preferably within the range of 500-510 ℃, and the lithium ion loading capacity of the first active material is improved as much as possible on the premise that the multilayer negative electrode sheet does not precipitate lithium, so that the energy density of the battery is improved. The temperature at which the second active substance starts to undergo thermal weight loss by calcination in an air atmosphere may be 691 deg.C, 692 deg.C, 693 deg.C, 694 deg.C, 695 deg.C, 696 deg.C, 697 deg.C, 698 deg.C, 699 deg.C or 700 deg.C. The temperature of the second active material at which the thermal weight loss starts when the second active material is calcined in the air atmosphere is preferably within the range of 690-700 ℃, so that the diffusion speed of lithium ions in the second coating layer 4 is effectively increased, particularly, the lithium ions are prevented from being accumulated and separated out on the surface of the negative plate to form lithium dendrites under the condition of large current or low temperature, and the safety performance, rate capability and cycle performance of the battery are improved by the cooperation of the first active material and the second active material.
In some embodiments, the second active agent has a weight loss on heating of less than 5% at a temperature of 800 ℃ for the weight loss on heating of the second active agent; when the thermal weight loss temperature of the second active substance is limited to 800 ℃, the thermal weight loss is less than 5%, the crystallinity of the second active substance is controlled, the ion diffusion rate is further improved, and lithium precipitation on the surface of the multilayer negative plate is effectively avoided.
In some preferred embodiments, the thermal weight loss of the second active material is 1-5% at a temperature of 800 ℃. The second active substance may have a thermal weight loss of 1%, 1.5%, 1.8%, 2.2%, 2.8%, 3.4%, 3.8%, 4.1%, 4.6%, 4.9% or 5% at a thermal weight loss temperature of 800 ℃; the thermal weight loss of the second active substance is within the range of 1% -5%, the crystallinity of the second active substance can be effectively controlled, the migration rate of lithium ions in the second coating layer 4 is improved, and the lithium ions are effectively prevented from being reduced and separated out on the surface of the second coating layer 4 and being stacked to form lithium dendrites.
In some embodiments, the ultra-thin primer slurry comprises a third active, the ultra-thin primer slurry is made up of the third active, a third binder, and a third thickener (55% to 75%): (15-35%): (0-10%) is added into deionized water and mixed evenly to obtain the product.
The third active substance is a carbon nano tube or graphene, the third binder is styrene-butadiene sol, and the third thickening agent is sodium carboxymethylcellulose; the thickness of the ultrathin bottom coating 2 is 0.25-2 μm.
The third active material is carbon nano tube or graphene, the carbon nano tube or graphene has high conductivity, and the thickness of the ultrathin primer layer 2 has high conductivity even in a small thickness. The thickness of the ultra-thin primer layer 2 may be 0.25 μm, 0.4 μm, 0.8 μm, 1.2 μm, 1.5 μm, 1.7 μm, 1.9 μm, or 2.0 μm, and the ultra-thin primer layer 2 may be applied in a specific thickness according to actual circumstances.
The thickness of the ultra-thin primer layer 2 is between 0.25 μm and 2 μm, which can improve the capacity density of the battery and the proportion of the first active material in the first coating layer 3. If the thickness of the ultrathin primer layer 2 is higher than 2 micrometers, the overall thickness of the multilayer negative plate is increased, and the energy density of the battery is reduced; if the thickness of the ultra-thin primer layer 2 is less than 0.25 μm, the ultra-thin primer layer 2 is thin, the coating process is not easily controlled, and the effect of increasing the proportion of the first active material in the first coating layer 3 cannot be obtained by the ultra-thin primer layer 2.
In some embodiments, the first coating layer slurry includes 97.5 to 98.0% by mass of a first active material, 1.2 to 1.5% by mass of a first binder, 0 to 0.2% by mass of a first conductive agent, and 0.5 to 0.8% by mass of a first thickener, based on 100% by mass of the first coating layer slurry;
the first active substance is graphite, soft carbon and hard carbon, and the first binder is one or more of polyvinylidene fluoride, butadiene rubber, polyethylene oxide, polytetrafluoroethylene, polyvinyl alcohol, vinylidene fluoride-hexafluoropropylene copolymer, styrene butadiene rubber and acrylonitrile multipolymer emulsion; the first conductive agent is one or more of Super P, conductive carbon black, conductive graphite, carbon nano tubes, acetylene black and graphite; the first thickening agent is sodium carboxymethyl cellulose;
the thickness of the first coating layer 3 is 70 to 90 μm.
Ultra-thin priming coat 2 coats on the 1 surface of mass collector, effectively reduce binder in the first coating 3 and account for than, thereby improve first active material quality in the first coating 3 and account for than, the first active material in the first coating 3 that this application provided has higher quality and accounts for than, only than in the second coating 4 the quality of second active material account for than about 1% low, make first coating 3 when guaranteeing to have higher cohesiveness with mass collector 1, can effectively improve the load-carrying capacity of first coating 3, promote the energy density of battery. The mass percentage of the first active material in the first coating layer 3 may be 97.5%, 97.6%, 97.7%, 97.8%, 97.9%, or 98%; the first binder may be 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, or 1.5% by mass. It should be noted that the mass contents of the first active material, the first binder, the first conductive agent, and the thickener, and the thickness of the first coating layer 3 may be defined according to actual specific requirements. In some embodiments, the second coating layer 4 comprises the following components by mass 100%: 98-98.5% of a second active substance, 0-0.2% of a second conductive agent, 0.7-1.0% of a second binder and 0.5-0.8% of a second thickening agent by mass;
the second active substance is graphite, soft carbon and hard carbon, and the second binder is one or more of polyvinylidene fluoride, butadiene rubber, polyethylene oxide, polytetrafluoroethylene, polyvinyl alcohol, vinylidene fluoride-hexafluoropropylene copolymer, styrene butadiene rubber and acrylonitrile multipolymer emulsion; the second conductive agent is one or more of Super P, conductive carbon black, conductive graphite, carbon nano tubes, acetylene black and graphite; the second thickening agent is sodium carboxymethyl cellulose;
the thickness of the second coating layer 4 is 50 to 70 μm.
The thickness of second coating 4 is less than the thickness of first coating 3, and lithium ion migration distance shortens, and lithium ion migration rate promotes, more is favorable to lithium ion from second coating 4 diffusion to first coating 3 in, especially under the heavy current condition, more is favorable to lithium ion from second coating 4 diffusion to first coating 3 in, promotes the fast ion transfer performance of multilayer negative pole piece, prevents effectively that the battery from analyzing lithium, improves battery multiplying power performance, cyclicity ability and security performance. The thickness of the second coating layer 4 may be 50 μm, 53 μm, 56 μm, 59 μm, 62 μm, 65 μm, 68 μm or 70 μm. The thickness of the first coating layer 3 may be 70 μm, 75 μm, 78 μm, 82 μm, 85 μm, 86 μm, 89 μm or 90 μm. The thickness of the first coating layer 3 is thick, more lithium ions can be loaded, and under the condition of large current, the lithium precipitation of the battery can be effectively prevented while the energy density of the battery is improved. In this embodiment, current collector 1 is a 4-6 μm copper foil.
In another aspect, the present application provides a method for preparing a multilayer negative electrode sheet, including at least the following steps:
coating the surface of one side of a current collector 1 with the ultrathin primer slurry to form an ultrathin primer 2;
coating the first coating layer slurry on the surface of the ultrathin primer layer 2 to form a first coating layer 3;
and step three, coating the second coating layer slurry on the surface of the first coating layer 3 to form a second coating layer 4, so as to obtain the multilayer negative plate.
The second coating layer 4 is positioned on the outermost surface of the multilayer negative plate, so that the diffusion speed of ions is ensured under the condition of high current, and lithium metal is effectively prevented from being formed on the surface of the multilayer negative plate through deposition of lithium ions; the ultrathin bottom coating slurry is coated on the surface of the current collector 1, and the first coating layer slurry is coated on the surface of the ultrathin bottom coating 2, so that the mass ratio of the first active substance in the first coating layer 3 can be improved, and the high load capacity and the battery energy density of the multilayer negative plate are improved.
In another aspect, the present application provides a secondary battery using a negative electrode sheet that is a multi-layered negative electrode sheet. The secondary battery using the multilayer negative plate can improve the energy density of the battery, prevent the lithium precipitation of the battery and improve the safety performance of the battery.
The present invention will be further illustrated by the following examples.
Example 1
The first active substance is calcined in the air atmosphere at the temperature of 500 ℃ for starting thermal weight loss of graphite 1, and the second active substance is calcined in the air atmosphere at the temperature of 600 ℃ for starting thermal weight loss of graphite 2; selecting a copper foil with the thickness of 6 mu m as the current collector 1; an acrylonitrile multipolymer emulsion.
The preparation method of the multilayer negative plate comprises the following steps:
(1) preparing ultrathin priming paint: adding a proper amount of deionized water into a stirring kettle, then adding 70 wt% of carbon nano tube, 27 wt% of styrene butadiene latex and 3 wt% of sodium carboxymethylcellulose, and fully stirring to obtain ultrathin primary coating slurry;
(2) preparing first coating layer slurry: adding 98.2 wt% of graphite 1, 0.3 wt% of acrylonitrile multipolymer emulsion, 0.5 wt% of sodium carboxymethyl cellulose, 1 wt% of conductive agent SP and a proper amount of deionized water into another stirring kettle, and fully stirring to obtain first coating layer slurry;
(3) preparing second coating layer slurry: adding 98.5 wt% of graphite 2, 0.2 wt% of acrylonitrile multipolymer emulsion, 0.3 wt% of sodium carboxymethyl cellulose, 1 wt% of conductive agent SP and a proper amount of deionized water into another stirring kettle, and fully stirring to obtain second coating layer slurry;
(4) preparing a multilayer negative plate: coating the ultrathin primer slurry on the surface of one side of a current collector 1 to form an ultrathin primer 2, wherein the thickness of the ultrathin primer 2 is 0.25-2 microns; coating the first coating layer slurry on the surface of the ultrathin primer layer 2 to form a first coating layer 3, wherein the thickness of the first coating layer 3 is 70-90 micrometers; and coating the second coating layer slurry on the surface of the first coating layer 3 to form a second coating layer 4, wherein the thickness of the second coating layer 4 is 50-70 mu m, and thus the multilayer negative plate is obtained.
Examples 2 to 4 and comparative examples 1 to 4
The other operation steps are the same as example 1, except that the temperature at which the first active material starts to undergo thermal weight loss upon calcination in an air atmosphere is different, the temperature at which the second active material starts to undergo thermal weight loss upon calcination in an air atmosphere is different, and the thermal weight loss of the second active material is different when the thermal weight loss temperature of the second active material is 800 ℃, as shown in table 1. The temperature at which the first active material of example 4 calcined in the air atmosphere started to lose weight by heat is shown in fig. 2, and the temperature at which the second active material calcined in the air atmosphere started to lose weight by heat is shown in fig. 3.
TABLE 1 data on specific parameters of examples 1-8 and comparative examples 1-4
Figure BDA0003688767100000091
Lithium secondary batteries were prepared by using the multi-layered negative electrode sheets prepared in examples 1 to 8 and comparative examples 1 to 4, and the batteries were subjected to electrical property tests, the specific test data of which are shown in tables 2 to 4.
And (3) testing the battery performance:
1. lithium separation degree test:
(1) normal temperature 2.5C lithium precipitation degree test:
discharging to 3.0V at 25 ℃ at 0.5 ℃, standing for 10min, then charging to 4.45V at 2.5C with constant current and constant voltage, stopping current at 0.05C, circulating for 20 times, fully charging the battery after the end, disassembling the battery cell in a drying room environment, and observing the lithium precipitation condition on the surface of the negative electrode. The lithium separation degree is divided into no lithium separation, edge serious lithium separation and surface lithium separation. The test results are shown in table 4. Slight lithium precipitation indicated the negative electrode.
(2) Normal temperature 2.0C lithium precipitation test:
discharging to 3.0V at 25 ℃ at 0.5 ℃, standing for 10min, then charging to 4.45V at 2.0C with constant current and constant voltage, stopping current at 0.05C, circulating for 20 times, fully charging the battery after the end, disassembling the battery cell in a drying room environment, and observing the lithium precipitation condition on the surface of the negative electrode. The lithium separation degree is divided into no lithium separation, edge serious lithium separation and surface lithium separation. The test results are shown in table 4.
(3)10 ℃ 1.3C lithium precipitation test:
the lithium ion batteries prepared in the example 1 and the comparative examples 1 and 2 are respectively discharged to 3.0V at 0.5C at 10 ℃, are kept for 10min, are charged to 4.45V at constant current and constant voltage at 1.3C, the cut-off current is 0.05C, are circulated for 20 times, are fully charged after the circulation is finished, are disassembled in a drying room environment, and the lithium precipitation condition on the surface of a negative electrode is observed. The lithium separation degree is divided into no lithium separation, edge serious lithium separation and surface lithium separation. The test results are shown in table 4.
(4)0 ℃ 0.7C lithium assay test:
the lithium ion batteries prepared in the example 1 and the comparative examples 1 and 2 are respectively discharged to 3.0V at 0 ℃ under 0.5 ℃, are kept for 10min, are charged to 4.45V under constant current and constant voltage at 0.7 ℃, the cut-off current is 0.05C, are circulated for 20 times, are fully charged after the circulation is finished, are disassembled in a drying room environment, and are observed for the lithium precipitation condition on the surface of a negative electrode. The lithium separation degree is divided into no lithium separation, edge serious lithium separation and surface lithium separation. The test results are shown in table 4.
2. Energy density:
at room temperature, 0.7C constant current and constant voltage was charged to 4.45V, the off current was 0.05C, and then 0.2C constant current was discharged to 3.0V. The cell volumetric energy density at 0.2C was calculated. Volumetric energy density-capacity × plateau voltage/(thickness × width × height); the test results are shown in Table 2.
3. 25 ℃ cycle test:
the battery is placed in an environment with the temperature of 25 ℃, the battery is charged to 4.45V according to the 3C, then the battery is charged to the cutoff current of 0.05C at the constant voltage of 4.45V, and then the battery is discharged to 3V at the temperature of 25 ℃ for charging and discharging circulation for 200 weeks by a charging system of 0.7C, so as to obtain the capacity retention rate. Capacity retention rate is 200 th discharge capacity/1 st discharge capacity × 100%. The test results are shown in Table 3.
4. DCR testing
1. The cell was left to stand at 0 ℃ and 25 ℃ for 10 min; charging to 4.45V at 2.0.2C constant current and constant voltage, and cutting off the current to 0.02C; 3. standing the battery for 10 min; 4.0.1C constant current discharge for 10 s; 5.1C constant current discharge for 10 s; 6.0.2C constant current discharge for 30 min; 7. standing for 30 min; repeating the steps for 4-7 times and 11 times, recording charge and discharge data, and setting the lower limit voltage to be 2.8V. The test results are shown in table 2.
5. Multiplying power charge-discharge test
At room temperature, 0.7C constant current and voltage was charged to 4.45V, the off current was 0.05C, and then constant current and voltage was discharged to 3.0V at 2.0C and 2.5C. The charge capacity was recorded and the test results are shown in table 2.
At room temperature, 2.0C and 2.5C were constant current charged to 4.45V, and then 0.5C was constant current discharged to 3.0V. The discharge capacity was recorded and the test results are shown in table 2.
6. Ambient temperature cycle of example 1, comparative example 1: the battery is placed in an environment with the temperature of 25 ℃, the battery is charged to 4.45V according to the 1C, then the battery is charged to the cutoff current of 0.05C at a constant voltage of 4.45V, and then the battery is discharged to 3V at the temperature of 25 ℃ for 500 cycles of charge and discharge, so as to obtain the capacity retention rate. Capacity retention rate is 500 th discharge capacity/1 st discharge capacity × 100%. The 500-week normal temperature cycle curve for example 1 is shown in fig. 4, and the 500-week normal temperature cycle curve for comparative example 1 is shown in fig. 5.
TABLE 2 examples 1-8 and comparative examples 1-4 Battery Performance test data
Figure BDA0003688767100000111
Table 3 examples 1-8 and comparative examples 1-4 cell performance test data
Figure BDA0003688767100000112
Figure BDA0003688767100000121
Table 4 performance test of degree of lithium deposition of examples 1 to 8 and comparative examples 1 to 4
Figure BDA0003688767100000122
From the above tables 2 to 4, it is understood that in examples 1, 2, 5 and 6, the temperature at which the first active material starts to undergo thermal weight loss upon calcination in the air atmosphere is between 500 ℃ and 510 ℃, and the batteries obtained therefrom have higher energy densities. Examples 2, 3, 7 and 8 show that when the temperature of the second active material at which the thermal weight loss starts to rise in the air atmosphere is between 690 and 700 ℃, the battery has a higher rate discharge capacity retention rate and a high capacity retention rate in a large-current charge cycle. In examples 1-8, compared with comparative examples 1 and 3, the temperature at which the first active material starts to lose weight with heat after being calcined in the air atmosphere is lower than or higher than 500-600 ℃, the temperature at which the second active material starts to lose weight with heat after being calcined in the air atmosphere is lower than or higher than 600-700 ℃, the lithium precipitation of the battery is serious under the charging and discharging of large current at low temperature or normal temperature, and the rate performance and the large current cycle performance of the battery are poor; the temperature of the first active material for starting the thermal weight loss during the calcination in the air atmosphere is between 500-600 ℃, and the temperature of the second active material for starting the thermal weight loss during the calcination in the air atmosphere is between 600-700 ℃, so that the diffusion rate of lithium ions is favorably improved, the lithium precipitation of the battery at low temperature or high current is prevented, and the rate performance and the cycle performance of the battery are improved. Compared with the examples 7 and 8, the temperature of the second active material in the comparative example 2, which starts to lose weight with heat after being calcined in the air atmosphere, is lower than 600 ℃, the impedance of the battery is increased, the rate discharge performance is poor, the cycle performance is poor, and the lithium precipitation of the battery is serious, which shows that the temperature of the second active material, which starts to lose weight with heat after being calcined in the air atmosphere, is between 600 and 700 ℃, and is beneficial to improving the diffusion rate of lithium ions in the second active material, thereby effectively preventing the lithium precipitation of the battery, reducing the impedance of the battery, and improving the rate performance, the safety performance and the large-current charging cycle performance of the battery. Examples 3, 4 in comparison with comparative example 4, the temperature at which the first active material starts to undergo thermal weight loss upon calcination in an air atmosphere was higher than 500-600 ℃, and the energy density of the cell was reduced.
The cycle data in fig. 5 shows that the temperature at which the first active material begins to be calcined in the air atmosphere is lower than 600-.
As shown in tables 1 to 4, when the temperature of the thermal weight loss of the second active substance is 800 ℃, the thermal weight loss mass percentage content of the second active substance is related to the temperature at which the thermal weight loss of the second active substance starts to be calcined in the air atmosphere, and the higher the temperature at which the thermal weight loss starts to be calcined, the lower the thermal weight loss mass percentage content; through examples 2, 3, 7 and 8, it is known that when the thermal weight loss temperature of the second active material is 800 ℃, the thermal weight loss of the second active material is between 1% and 5%, the rate discharge capacity retention rate of the battery is higher, the battery impedance is low, and the large current cycle performance is better.
Through comparison between examples 1-8 and comparative examples 1-4, it is known that when the temperature at which the first active material starts to be calcined in the air atmosphere is between 500-600 ℃ and the temperature at which the second active material starts to be calcined in the air atmosphere is between 600-700 ℃, the energy density of the battery can be improved and the diffusion rate of lithium ions through the second active material can be increased, thereby effectively preventing lithium precipitation of the battery, particularly lithium precipitation under low temperature conditions, reducing the impedance of the battery, and improving the rate capability, safety performance and cycle performance of the battery.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. A multilayer negative plate is characterized by comprising a current collector, an ultrathin bottom coating, a first coating layer and a second coating layer; the ultrathin primer coating is coated on one side surface of the current collector, the first coating layer is coated on the surface of the ultrathin primer coating, and the second coating layer is coated on the surface of the first coating layer;
the first coating layer comprises a first active substance, and the temperature of the first active substance for starting the thermal weight loss after being calcined in the air atmosphere is 500-600 ℃;
the second coating layer comprises a second active substance, and the temperature of the second active substance for starting thermal weight loss after being calcined in the air atmosphere is 600-700 ℃.
2. The multilayer negative electrode sheet according to claim 1, wherein the temperature at which the first active material begins to lose weight thermally when calcined in an air atmosphere is from 500 ℃ to 510 ℃; the temperature of the second active substance for starting thermal weight loss after being calcined in the air atmosphere is 690-700 ℃.
3. The multilayer negative electrode sheet of claim 1 or 2, wherein the thermal weight loss of the second active material is less than 5% at a temperature of 800 ℃ for the thermal weight loss of the second active material.
4. The multilayer negative electrode sheet of claim 3, wherein the thermal weight loss of the second active material is 1% to 5% at a temperature of 800 ℃ for the thermal weight loss of the second active material.
5. The negative electrode sheet of claim 1, wherein the ultra-thin primer layer comprises a third active material, and the ultra-thin primer layer is prepared from the third active material, a third binder, and a third thickener in a ratio of (55% to 75%): (15-35%): (0-10%) is added into deionized water and mixed evenly to obtain the product.
6. The multilayer negative electrode sheet according to claim 5, wherein the third active material is carbon nanotubes or graphene, the third binder is styrene-butadiene sol, and the third thickener is sodium carboxymethylcellulose; the thickness of the ultrathin bottom coating is 0.25-2 μm.
7. The multilayer negative electrode sheet according to claim 1, wherein the first coating layer comprises 97.5-98.0% by mass of the first active material, 1.2-1.5% by mass of the first binder, 0-2% by mass of the first conductive agent, and 0.5-0.8% by mass of the first thickener, based on 100% by mass of the first coating layer;
the first active substance is graphite, soft carbon or hard carbon, and the first binder is one or more of polyvinylidene fluoride, butadiene rubber, polyethylene oxide, polytetrafluoroethylene, polyvinyl alcohol, vinylidene fluoride-hexafluoropropylene copolymer, styrene butadiene rubber and acrylonitrile multipolymer emulsion; the first conductive agent is one or more of Super P, conductive carbon black, conductive graphite, carbon nano tubes, acetylene black and graphite; the first thickening agent is sodium carboxymethyl cellulose;
the thickness of the first coating layer is 70-90 μm.
8. The multilayer negative electrode sheet according to claim 1, wherein the second coating layer comprises the following components by mass 100%: 98-98.5% of a second active substance, 0-0.2% of a second conductive agent, 0.7-1.0% of a second binder and 0.5-0.8% of a second thickening agent;
the second active substance is graphite, soft carbon or hard carbon, and the second binder is one or more of polyvinylidene fluoride, butadiene rubber, polyethylene oxide, polytetrafluoroethylene, polyvinyl alcohol, vinylidene fluoride-hexafluoropropylene copolymer, styrene butadiene rubber and acrylonitrile multipolymer emulsion; the second conductive agent is one or more of Super P, conductive carbon black, conductive graphite, carbon nano tubes, acetylene black and graphite; the second thickening agent is sodium carboxymethyl cellulose;
the thickness of the second coating layer is 50-70 μm.
9. The method for preparing the multilayer negative electrode sheet according to any one of claims 1 to 8, characterized by comprising at least the following steps:
coating the slurry of the ultrathin primer coating on the surface of one side of a current collector to form the ultrathin primer coating;
coating the first coating layer slurry on the surface of the ultrathin base coating layer to form a first coating layer;
and step three, coating the second coating layer slurry on the surface of the first coating layer to form a second coating layer, so as to obtain the multilayer negative plate.
10. A secondary battery using the multilayer negative electrode sheet according to any one of claims 1 to 8.
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