CN114175306A - Electrochemical device and electronic device - Google Patents

Electrochemical device and electronic device Download PDF

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Publication number
CN114175306A
CN114175306A CN202180004684.0A CN202180004684A CN114175306A CN 114175306 A CN114175306 A CN 114175306A CN 202180004684 A CN202180004684 A CN 202180004684A CN 114175306 A CN114175306 A CN 114175306A
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active material
protective coating
material layer
electrochemical device
positive electrode
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李巍巍
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology 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
    • 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
    • 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
    • H01M2004/028—Positive 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
    • 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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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)
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Abstract

The present application provides an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode, the positive electrode comprises a positive current collector, a protective coating and a positive active material layer, the positive active material layer is arranged on at least one surface of the positive current collector, and the protective coating is arranged along the side edge, close to the lug part, of the positive current collector. The protective coating layer includes a first active material, and the positive electrode active material layer includes a second active material. The embodiment of this application is through setting up protective coating on anodal mass flow body, when guaranteeing electrochemical device's security performance, has promoted electrochemical device's energy density.

Description

Electrochemical device and electronic device
Technical Field
The present application relates to the field of electrochemical energy storage, and more particularly to electrochemical devices and electronic devices.
Background
As electrochemical devices (e.g., lithium ion batteries) are developed and advanced, increasingly higher requirements are placed on their safety, energy density and kinetic properties. In order to improve the dynamic performance of an electrochemical device, a pole piece is generally cut into a multi-pole-lug structure at present, and an insulating layer is coated near a cutting position to play a role in insulating and preventing burrs generated by cutting from piercing a separation film.
However, the insulating layer does not exert gram capacity, which affects the increase in energy density of the electrochemical device. Therefore, further improvements are desired.
Disclosure of Invention
Some embodiments of the present application provide an electrochemical device comprising a positive electrode comprising a positive current collector, a protective coating, and a positive active material layer disposed on at least one surface of the positive current collector, wherein the protective coating is disposed along a side of the positive current collector near an ear of the positive electrode. The protective coating includes a first active material including at least one of lithium iron phosphate or lithium manganese iron phosphate.
In some embodiments, the positive electrode active material layer includes a second active material including at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium nickel manganese oxide, or lithium cobalt manganese oxide. In some embodiments, the ratio of the width of the protective coating layer to the width of the positive electrode active material layer is 1% to 5%. In some embodiments, the protective coating has a width of 0.5mm to 5 mm. In some embodiments, the thickness H of the protective coating layer and the thickness H of the positive electrode active material layer satisfy: h is more than or equal to 10 mu m and less than or equal to (H-5) mu m. In some embodiments, the thickness h of the protective coating and the Dv99 of the first active material satisfy: 1.2Dv99 is less than or equal to h.
In some embodiments, the protective coating further comprises a conductive agent and a binder, and the mass ratio of the first active material to the conductive agent to the binder is (78% -98.5%): 0.5% -10%): 1% -12%. In some embodiments, the conductive agent comprises at least one of conductive carbon black, conductive graphite, carbon fiber, multiwall carbon nanotubes, single wall carbon nanotubes, hard carbon, soft carbon, ketjen black, or graphene, and the binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, lithium sodium carboxymethyl cellulose, polyacrylic acid, polyacrylate, modified polyvinylidene fluoride, modified styrene butadiene rubber, or polyurethane. In some embodiments, the protective coating has a resistance of 30 Ω or more in the fully charged state. In some embodiments, the adhesion between the protective coating and the positive current collector is 5N/m to 200N/m. In some embodiments, the protective coating partially overlaps the positive active material layer.
In some embodiments, the electrochemical device further comprises a negative electrode comprising a negative electrode current collector and a negative electrode active material layer on at least a portion of a surface of the negative electrode current collector, wherein an orthographic projection of the protective coating partially falls on the negative electrode active material layer or an outer edge of the protective coating is aligned with an outer edge of the negative electrode active material layer.
In some embodiments, an orthographic projection of an outer edge of the positive electrode active material layer at a side away from the electrode ear falls on the negative electrode active material layer, and a distance of the outer edge of the positive electrode active material layer from an outer edge of the negative electrode active material layer at the corresponding side is between 2mm and 4 mm.
Embodiments of the present application also provide an electronic device including the above electrochemical device.
According to the embodiment of the application, the protective coating is arranged on the positive current collector and comprises the active materials of lithium iron phosphate and/or lithium manganese iron phosphate, so that on one hand, the arrangement of the protective coating can prevent burrs generated by cutting tabs from piercing the isolating membrane, the direct contact between the positive current collector and the negative active material layer is avoided, and the safety performance of the corresponding electrochemical device is greatly improved; on the other hand, because lithium iron phosphate and lithium manganese iron phosphate have the olivine three-dimensional structure, under the full charge condition, the resistance increases, can prevent the inside short circuit of electrochemical device, and along with discharging's going on, the resistance reduces, and the protective coating polarization reduces, further releases the electric quantity, when satisfying electrochemical device's security performance, can promote electrochemical device's energy density again.
Drawings
Fig. 1 to 2 illustrate cross-sectional views of a positive electrode of some embodiments of the present application taken along a plane defined by a thickness direction and a width direction of a positive electrode current collector.
Fig. 3 and 4 illustrate cross-sectional views of electrode assemblies of electrochemical devices of some embodiments of the present application.
Detailed Description
The following examples are presented to enable those skilled in the art to more fully understand the present application and are not intended to limit the present application in any way.
In order to improve the charge and discharge performance of the electrochemical device, a multi-tab structure is generally used. In the production process, the multi-tab pole piece structure is generally realized by adopting physical cutting or laser cutting and other modes. In order to prevent short circuit caused by the fact that burrs generated during cutting pierce the isolation film, insulating layers or insulating glue are generally arranged on two sides of the cutting surface. The insulating layer and the insulating glue have good protection effect, but do not exert gram capacity; and the insulating layer and the insulating glue are swelled strongly in the electrolyte, so that the adhesive force between the insulating layer or the insulating glue and the current collector is weak, the insulating layer or the insulating glue is easy to fall off from the current collector, and the protection effect is lost. Generally, the short circuit mode between the positive electrode collector and the negative electrode active material layer is most dangerous because heat generation is large at the time of short circuit, and the negative electrode active material layer is easily thermally runaway. Therefore, in order to improve the safety of the electrochemical device, it is most effective to avoid such a short-circuit mode.
This application has promoted electrochemical device's capacity under the prerequisite that satisfies the security performance through the protective coating who contains lithium iron phosphate or lithium iron manganese phosphate at least. Simultaneously, the technical scheme of this application optimizes the adhesion force between protective coating and the mass flow body through the ratio of the different components in the protective coating to improve protective coating's the condition of droing, make when experiencing the exogenic action, still can bond on the mass flow body better, promote electrochemical device's security performance.
Some embodiments of the present application provide an electrochemical device including a positive electrode. In some embodiments, as shown in fig. 1, the positive electrode includes a positive electrode current collector 111, a protective coating 112, and a positive electrode active material layer 113, the positive electrode active material layer 113 being located on at least one surface of the positive electrode current collector 111. In some embodiments, the positive electrode collector 111 includes a tab portion 1111. In some embodiments, the tab portion 1111 may be connected with an external tab. In some embodiments, the portion of the tab portion 1111 may itself serve as a tab, thereby eliminating an external tab. In some embodiments, the protective coating 112 is disposed along the side of the positive current collector 111 near the tab portion 1111. As shown in fig. 1, the protective coating layer 112 is disposed adjacent to the tab portion 1111 and adjacent to the positive electrode active material layer 113. In some embodiments, the protective coating 112 includes a first active material and the positive active material layer 113 includes a second active material.
In some embodiments, the protective coating 112 includes lithium iron phosphate and/or lithium manganese iron phosphate, on one hand, the protective coating 112 can prevent burrs generated by cutting tabs from piercing the isolation film, so that direct contact between the positive current collector 111 and the negative active material layer is avoided, and the safety performance of the corresponding electrochemical device is greatly improved; on the other hand, because lithium iron phosphate and lithium manganese iron phosphate have the olivine three-dimensional structure, under the full charge condition, resistance increases, can prevent the inside short circuit of electrochemical device, and along with discharging, resistance reduces, and the polarization of protective coating 112 reduces, further releases the electric quantity, when satisfying electrochemical device's security performance, can promote electrochemical device's energy density again.
In some embodiments, the first active material comprises at least one of lithium iron phosphate or lithium manganese iron phosphate. In some embodiments, the first active material may further be added with at least one of lithium cobaltate, lithium manganate or lithium nickel cobalt manganate. The resistance of the lithium iron phosphate or the lithium manganese iron phosphate is increased under high voltage, so that the electrochemical device plays a role in protection during short circuit. As the discharge proceeds, the resistance decreases, the polarization of the protective coating 112 decreases, and the electric quantity is further discharged, so that the safety performance and the capacity of the electrochemical device are both considered. In some embodiments, the second active material comprises at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium nickel manganese oxide, or lithium cobalt manganese oxide. These active materials can provide capacity to the positive electrode.
In some embodiments, the ratio of the width W1 of the protective coating layer 112 to the width W2 of the positive electrode active material layer 113 is 1% to 5%. If the ratio of the width W1 of the protective coating layer 112 to the width W2 of the positive electrode active material layer 113 is too small, the effect of preventing burrs generated at the time of cutting from piercing the separator is relatively limited; if the ratio of the width W1 of the protective coating layer 112 to the width W2 of the cathode active material layer 113 is too large, the energy density of the electrochemical device is affected.
In some embodiments, the width W1 of the protective coating 112 is 0.5mm to 5 mm. Too small a width W1 of the protective coating layer 112 is liable to cause a skip coating situation and is difficult to be stably realized, while too large a width W1 may occupy the coating space of the positive electrode active material layer 113, resulting in a decrease in the energy density of the electrochemical device.
In some embodiments, the thickness H of the protective coating layer 112 and the thickness H of the positive electrode active material layer 113 satisfy: h is more than or equal to 10 mu m and less than or equal to (H-5) mu m. That is, the thickness H of the protective coating layer 112 is 10 μm or more and is at least 5 μm less than the thickness H of the positive electrode active material layer 113. In some embodiments, the protective coating 112 has a thickness of 10 μm to 50 μm. Too small a thickness of the protective coating 112 may cause less coverage of the positive electrode current collector burrs, while too large a thickness may affect edge cutting of the positive electrode, resulting in poor appearance of the electrochemical device, and too large a thickness of the protective coating 112 may adversely affect energy density of the electrochemical device. In addition, the thickness H of the protective coating 112 is too close to the thickness H of the positive electrode active material layer 113 or even greater than the thickness H of the positive electrode active material layer 113, which may cause a gap between the positive electrode active material layer 113 and the separator to exist, resulting in an increase in polarization.
In some embodiments, the thickness h of the protective coating 112 and the Dv99 of the first active material satisfy: 1.2Dv99 is less than or equal to h. The Dv99 of the first active material refers to the particle size corresponding to 99% cumulative volume distribution of the particles of the first active material. In some embodiments, the particle size of the first active material of the protective coating 112 directly affects the minimum thickness of the protective coating 112, the smaller the particle size is advantageous in that the protective coating 112 can be made thinner and coverage assured, the smaller the Dv99 of the first active material, the more layers of particles stacked in the same thickness of the protective coating 112, the better the protection, the larger the specific surface area, and the better the electrical performance of the electrochemical device.
The granularity of the active material is tested by a laser particle sizer: after the instrument is started, a blank background test is firstly carried out, and when the blank background has no obvious characteristic peak, a granularity test is carried out: taking a certain amount of active material (1g), adding a proper amount of surfactant (such as sodium dodecyl sulfate), adding a dispersing agent (water or alcohol or N-methylpyrrolidone (NMP)) for dispersing, carrying out ultrasonic treatment for 10min, adding the dispersed material into a sample bin, and starting testing to obtain the particle size distribution condition of the material, automatically outputting the particle size distribution of the material by related software, and calculating to obtain Dv99 (the corresponding particle size when the cumulative volume distribution of the sample reaches 99%).
In some embodiments, the protective coating 112 further includes a conductive agent and a binder, and the mass ratio of the first active material to the conductive agent to the binder is (78-98.5) to (0.5-10) to (1-12). The protective coating 112 in this mass ratio range has a higher active material ratio, improves the energy density of the electrochemical device, and simultaneously ensures appropriate conductivity and adhesion of the protective coating 112.
In some embodiments, the conductive agent in the protective coating 112 includes at least one of conductive carbon black, conductive graphite, carbon fiber, multi-walled carbon nanotubes, single-walled carbon nanotubes, hard carbon, soft carbon, ketjen black, or graphene. In some embodiments, the conductive agent in the protective coating 112 is present in an amount of 0.5% to 10% by mass. Thus, the rate capability of the electrochemical device is improved under the condition of ensuring the safety performance of the electrochemical device. In some embodiments, the conductive agent in the protective coating 112 is present in an amount of 0.3% to 8% by mass. In some embodiments, the binder in the protective coating 112 comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethylcellulose, lithium sodium carboxymethylcellulose, polyacrylic acid, polyacrylate, modified polyvinylidene fluoride, modified styrene butadiene rubber, or polyurethane. In some embodiments, the binder content in the protective coating 112 is 1% to 12% by mass.
In some embodiments, the protective coating 112 has a resistance of 30 Ω or more in the fully charged state. This ensures that the adverse effect on the rate performance of the electrochemical device is minimized. In addition, the resistance of lithium iron phosphate or lithium manganese iron phosphate increases under high voltage, so that the electrochemical device plays a role in protection during short circuit. As the discharge proceeds, the resistance decreases, the polarization of the protective coating 112 decreases, and the electric quantity is further discharged, so that the safety performance and the capacity of the electrochemical device are both considered. The resistance of the protective coating 112 can be tested by: disassembling the fully charged battery, and keeping a complete positive electrode; rinsing the positive electrode with dimethyl carbonate for 30min, and drying at 100 ℃ for 4 h; and then cutting the protective coating to a length of at least 1.5cm, testing by using a four-probe resistance instrument, wherein two cylindrical metal terminals with the diameter of 1.2cm are used as resistance testing terminals, the protective coating is placed in the middle of the plane of the metal terminals during testing, 0.4 ton of pressure is applied to two ends of each terminal, and the resistance value of the protective coating is obtained in the 5 th second. It should be understood that this method of testing the resistance is exemplary only, and not limiting, and that other suitable methods may also be employed.
In some embodiments, the adhesion between the protective coating 112 and the positive current collector 111 is 5N/m to 200N/m. The excessively low adhesion between the protective coating 112 and the positive electrode current collector 111 makes the protective coating 112 easily fall off from the positive electrode current collector 111, and it is difficult to achieve an effect of covering burrs of the positive electrode current collector 111, so that the electrochemical device is likely to be short-circuited, ignited, and smoke when being pressed or falling. If the adhesion between the protective coating 112 and the positive electrode current collector 111 is too large, an excessively high binder content is generally required, and the excessively high binder content may reduce the electrical properties of the protective coating 112 and also may not contribute to the increase in the energy density of the electrochemical device. The adhesion of the protective coating 112 to the positive current collector 111 can be tested using a tensile tester, but can also be tested using other suitable methods. The adhesion was tested as follows: cutting the protective coating 112 into a strip with a certain width and a length of 5cm, wherein the width is determined according to the actual coating width of the protective coating; measuring the width f of the cut strip of the protective coating 112, adhering one side of the protective coating 112 to a flat plate with a double-sided adhesive tape, tearing the strip of the protective coating 112 off the double-sided adhesive tape at a speed of 25mm/min in the direction perpendicular to the flat plate, and recording the force N used for tearing off, so that the adhesion force of the protective coating 112 and the positive current collector 111 is N/f.
In some embodiments, the protective coating 112 partially overlaps the positive electrode active material layer 113. In some embodiments, as shown in fig. 2, at least a portion of the protective coating 112 and the positive active material layer 113 overlap each other.
Fig. 3 and 4 illustrate cross-sectional views of an electrode assembly of an electrochemical device taken along a plane defined by the thickness and width of a separation film according to some embodiments of the present application. It should be understood that the sectional view is a sectional view of the electrode assembly in a wound structure, which is taken along a plane defined by the thickness and width of the separator after the electrode assembly is unfolded. In some embodiments, as shown in fig. 3, the negative electrode includes a negative electrode current collector 121 and a negative electrode active material layer 122 on at least a part of a surface of the negative electrode current collector 121. In some embodiments, the tab 1111 may or may not have a protective coating disposed thereon. In some embodiments, the orthographic projection of the protective coating 112 partially falls on the negative active material layer 122. In some embodiments, as shown in fig. 4, the outer edge of the protective coating 112 is aligned with the outer edge of the negative active material layer 122. As such, even if the separator 10 is pierced, the presence of the protective coating 112 can prevent a short circuit between the positive electrode collector 111 and the negative electrode active material layer 122, improving the safety performance of the electrochemical device.
In some embodiments, as shown in fig. 4, an orthogonal projection of an outer edge of the cathode active material layer 113 at a side opposite to the tab 1111 falls on the anode active material layer 122, and a distance d between the outer edge of the cathode active material layer 113 and an outer edge of the anode active material layer 122 at the corresponding side is between 2mm and 4 mm. By making the orthographic projection of the outer edge of the positive electrode active material layer 113 fall on the negative electrode active material layer 122, that is, d is positive, lithium ions released from the positive electrode upon charging can be easily inserted into the negative electrode active material layer 122, reducing the loss of lithium ions. If d is too small, it may cause a problem that more lithium ions are not sufficiently inserted into the anode active material layer 122 to cause loss of lithium ions; if d is too large, lithium intercalation property is not exerted by an excessive amount of the anode active material layer 122, reducing the energy density of the electrochemical device.
In some embodiments, separator 10 generally has some ductility, which may provide some protection during current collector burr puncture. Since the protective coating 112 is located between the positive electrode collector 111 and the separator 10, there is a certain adhesion between the protective coating 112 and the separator 10 after being pressed into contact, which is advantageous for further protecting the separator 10 from being punctured. In some embodiments, the adhesion between the protective coating 112 and the release film 10 is greater than or equal to 5N/m.
In some embodiments, the surface of the positive electrode collector 111 or the surface of the protective coating 112 may be subjected to a patterning or roughening treatment to improve the adhesion between the protective coating 112 and the positive electrode collector 111 or the adhesion between the protective coating 112 and the separator 10.
In some embodiments, the positive electrode active material layer 113 may further include a conductive agent. In some embodiments, the conductive agent in the positive electrode active material layer 113 may include at least one of conductive carbon black, ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the positive electrode active material layer 113 may further include a binder, and the binder in the positive electrode active material layer 113 may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinyl pyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer 113 may be (78-99): (0.1-10). In some embodiments, the thickness of the positive electrode active material layer 113 may be 10 μm to 200 μm. It should be understood that the above description is merely an example, and the positive electrode active material layer 113 of the positive electrode may employ any other suitable material, thickness, and mass ratio.
In some embodiments, the positive current collector 111 of the positive electrode may be an Al foil, but other current collectors commonly used in the art may be used. In some embodiments, the thickness of the positive current collector 111 of the positive electrode may be 1 μm to 200 μm. In some embodiments, the positive electrode active material layer 113 may be coated only on a partial area of the positive electrode collector 111 of the positive electrode.
In some embodiments, the negative active material layer 122 includes a negative active material, which may include at least one of graphite, hard carbon, silicon, silica, or silicone. In some embodiments, a conductive agent and a binder may also be included in the negative active material layer 122. In some embodiments, the conductive agent in the negative active material layer 122 may include at least one of conductive carbon black, ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the binder in the negative active material layer 122 may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. In some embodiments, the mass ratio of the anode active material, the conductive agent, and the binder in the anode active material layer 122 may be (78 to 98.5): (0.1 to 10): (0.1 to 10). It will be appreciated that the above description is merely exemplary and that any other suitable materials and mass ratios may be employed. In some embodiments, the negative electrode current collector 121 of the negative electrode may employ at least one of a copper foil, a nickel foil, or a carbon-based current collector.
In some embodiments, the separator 10 comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect. In some embodiments, the thickness of the isolation film is in the range of about 5 μm to 500 μm.
In some embodiments, the surface of the separator may further include a porous layer disposed on at least one surface of the substrate of the separator, the porous layer including inorganic particles selected from alumina (Al) and a binder2O3) Silicon oxide (SiO)2) Magnesium oxide (MgO), titanium oxide (TiO)2) Hafnium oxide (HfO)2) Tin oxide (SnO)2) Cerium oxide (C)eO2) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO)2) Yttrium oxide (Y)2O3) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator film have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The porous layer on the surface of the isolating membrane can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the adhesion between the isolating membrane and the pole piece.
In some embodiments of the present application, the electrode assembly of the electrochemical device is a wound electrode assembly, a stacked electrode assembly, or a folded electrode assembly. In some embodiments, the positive electrode and/or the negative electrode of the electrochemical device may be a multilayer structure formed by winding or stacking, or may be a single-layer structure in which a single-layer positive electrode, a single-layer negative electrode, and a separator are stacked.
In some embodiments, the electrochemical device comprises a lithium ion battery, but the application is not so limited. In some embodiments, the electrochemical device may further include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution including a lithium salt and a non-aqueous solvent. The lithium salt is selected from LiPF6、LiBF4、LiAsF6、LiClO4、LiB(C6H5)4、LiCH3SO3、LiCF3SO3、LiN(SO2CF3)2、LiC(SO2CF3)3、LiSiF6One or more of LiBOB or lithium difluoroborate. For example, LiPF is selected as lithium salt6Because it has a high ion conductivityThe electric rate and the cycle characteristics can be improved.
The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.
The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.
Examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), or a combination thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1, 2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.
Examples of carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonic lactone, caprolactone, methyl formate, or combinations thereof.
Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.
Examples of other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.
In some embodiments of the present application, taking a lithium ion battery as an example, a positive electrode, a separator, and a negative electrode are sequentially wound or stacked to form an electrode member, and then the electrode member is placed in, for example, an aluminum plastic film for packaging, and an electrolyte is injected into the electrode member for formation and packaging, so as to form the lithium ion battery. And then, performing performance test on the prepared lithium ion battery.
Those skilled in the art will appreciate that the above-described methods of making electrochemical devices (e.g., lithium ion batteries) are merely examples. Other methods commonly used in the art may be employed without departing from the disclosure herein.
Embodiments of the present application also provide an electronic device including the electrochemical device described above. The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.
In the following, some specific examples and comparative examples are listed to better illustrate the present application, wherein a lithium ion battery is taken as an example.
Example 1
Preparation of the positive electrode: the method comprises the steps of adopting an aluminum foil as a positive current collector of a positive electrode, dissolving positive active material lithium cobaltate, conductive agent conductive carbon black and polyvinylidene fluoride in N-methyl pyrrolidone (NMP) solution according to the weight ratio of 97.8: 1.4: 0.8 to form slurry of a positive active material layer, coating the slurry on the positive current collector with the coating thickness of 80 mu m to obtain the positive active material layer, coating a layer of protective coating slurry on the positive current collector adjacent to the positive active material layer to obtain a protective coating, and specifically dissolving lithium iron phosphate (Dv90 is 5.16 mu m), conductive agent conductive carbon black and polyvinylidene fluoride in N-methyl pyrrolidone (NMP) solution according to the weight ratio of 95: 2: 3 to form protective coating slurry. And then drying, cold pressing and cutting to obtain the anode. Wherein the thickness of the protective coating is 30 μm, and the width is 4 μm; the thickness of the positive electrode active material layer was 50 μm.
Preparation of a negative electrode: dissolving artificial graphite, sodium carboxymethylcellulose (CMC) and styrene butadiene rubber serving as a binder in deionized water according to the weight ratio of 97.7: 1.3: 1 to form negative electrode slurry. And (3) adopting copper foil with the thickness of 10 mu m as a current collector of the negative electrode, coating the negative electrode slurry on the current collector of the negative electrode, drying and cutting to obtain the negative electrode.
Preparing an isolating membrane: the base material of the isolation film is Polyethylene (PE) with the thickness of 8 mu m, two sides of the base material of the isolation film are respectively coated with an alumina ceramic layer with the thickness of 2 mu m, and finally, two sides coated with the ceramic layer are respectively coated with polyvinylidene fluoride (PVDF) as a binder with the thickness of 2.5mg, and the base material of the isolation film is dried.
Preparing an electrolyte: under the environment that the water content is less than 10ppm, LiPF6Adding non-aqueous organic solvent (ethylene carbonate (EC):propylenecarbonate (PC): 50, weight ratio), LiPF6The concentration of (A) is 1.15mol/L, and the electrolyte is obtained after uniform mixing.
Preparing a lithium ion battery: and sequentially stacking the anode, the isolating membrane and the cathode in sequence to enable the isolating membrane to be positioned between the anode and the cathode to play an isolating role, and winding to obtain the electrode assembly. And (3) placing the electrode assembly in an outer packaging aluminum-plastic film, dehydrating at 80 ℃, injecting the electrolyte, packaging, and performing technological processes such as formation, degassing, edge cutting and the like to obtain the lithium ion battery.
The examples and comparative examples were carried out by changing the parameters in addition to the procedure of example 1, and the specific changed parameters are shown in the following table.
The following describes a method of testing various parameters of the present application.
Volumetric energy density test:
standing at 25 + -3 deg.C for 30min, charging with 0.5C (1C is the rated capacity of the lithium ion battery) current until the battery voltage reaches 4.45V (rated voltage), charging with the lithium ion battery at constant voltage, and stopping charging when the current reaches 0.05C; standing the lithium ion battery for 30 min; discharging the lithium ion battery to 3.0V at a current of 0.2C, and standing for 30 min; and taking and placing the capacitance as the actual capacity of the lithium ion battery. And multiplying the actual capacity of the lithium ion battery by the actual voltage platform of the electrode assembly, and dividing by the volume of the lithium ion battery to obtain the actual volume energy density of the lithium ion battery.
And (3) extrusion testing:
taking 10 lithium ion batteries in the embodiment, fully charging the batteries at 25 +/-3 ℃ (charging the batteries to 4.45V at a constant current of 0.5C and stopping charging the batteries at a constant voltage of 0.05C), extruding the batteries for 3h (extruding the wide surface of an electrode assembly) at normal temperature, setting the extrusion pressure to be 10kN, and setting the standard that the surface temperature does not exceed 150 ℃ and the batteries are not disintegrated, cracked or ignited within 3 hours of the test.
And (3) drop test:
taking 10 lithium ion batteries in the embodiment, fully charging the batteries at 25 +/-3 ℃ (constant current charging is carried out to 4.45V at 0.5C, constant voltage charging is carried out to 0.05C, and current is cut off), and freely dropping the batteries from a position with the height of 1.5 m to the surface of the smooth marble in a dropping sequence: front-back-lower-upper-left-right-upper-lower-right, each face/corner continuously falls for 1 time into one round (the bar code face is the back face), 5 rounds of tests are carried out to check whether the appearance is damaged or not and liquid leakage occurs, and the voltage internal resistance is tested, and the pass standard is that the appearance is not damaged or liquid leakage does not occur, and the voltage drop is less than 30 mV.
Table 1 shows the respective parameters and evaluation results of examples 1 to 13 and comparative examples 1 to 6, respectively. In examples 2 to 9, the lithium iron phosphate in the protective coating slurry was replaced with other active materials or material combinations, and the total amount of the first active material and other parameters were consistent with those in example 1. Examples 10 to 13 were only to replace the lithium cobaltate in the positive electrode active material layer slurry with other active materials or material combinations, and the total amount of the second active material and other parameters were kept in agreement with those in example 1.
Group of protective coating pastes in comparative example 1 and comparative examples 3 to 6To 90.0 wt% Al2O310.0% by weight of polyvinylidene fluoride (PVDF), the other parameters being the same as in example 1. The second active material in the positive electrode active material layers in comparative examples 3 to 6 is different from example 1. Comparative example 2 was not coated with a protective coating.
TABLE 1
Figure BDA0003484663870000131
Figure BDA0003484663870000141
As can be seen from comparing examples 1 to 9 and comparative example 2, the volume energy density of the formed lithium ion battery is improved by providing the protective coating layer, and the crush pass rate and the drop pass rate of the lithium ion battery are significantly improved, relative to the positive electrode without the protective coating layer.
As can be seen by comparing examples 1 to 9 and comparative example 1, the volumetric energy density of the lithium ion battery is significantly increased by employing an active material in the protective coating layer, relative to a protective coating layer that does not contain an active material. The same results can be obtained by comparing examples 10 to 13 and comparative examples 3 to 6.
As can be seen from comparative examples 1 to 9, the first active materials of the protective coating layer, such as lithium iron phosphate and lithium manganese phosphate, all have the effect of improving the volume energy density, the extrusion throughput rate, and the drop throughput rate of the lithium ion battery. As can be seen from comparison of examples 10 to 13, the use of different active materials in the positive electrode active material layer has a large influence on the volumetric energy density of the lithium ion battery.
Table 2 and table 3 show the respective parameters and evaluation results of examples 1 and 14 to 60, respectively.
Among them, in examples 14 to 21, the width of the protective coating layer and the ratio of the width of the protective coating layer to the width of the positive electrode active material layer were different from those of example 1.
In examples 22 to 25, the thickness of the protective coating layer was different from that of example 1.
In examples 26 to 37, the contents of the respective components of the protective coating layer were different from those of example 1; in example 38, the binder composition used was different from that of example 1.
In examples 39 to 43, Dv99 of the first active material was different from example 1.
In examples 44 to 53, the conductive agent and binder components in the protective coating layer were different from those in example 1.
In examples 54 to 56, the relative positions of the outer edge of the protective coating and the outer edge of the anode active material layer were different from those of example 1.
In examples 57 to 60, the distance d between the outer edge of the positive electrode active material layer and the outer edge of the negative electrode active material layer at the corresponding side was different from that of example 1.
Figure BDA0003484663870000151
Figure BDA0003484663870000161
Figure BDA0003484663870000171
TABLE 3
Figure BDA0003484663870000181
Figure BDA0003484663870000191
As can be seen from comparative examples 14 to 18, when the ratio of the width of the protective coating layer to the width of the positive electrode active material layer is too small, the damage of the protective coating layer by dropping is too large, resulting in a decrease in the drop passage rate; when the ratio of the width of the protective coating layer to the width of the positive electrode active material layer is too large, for example, 7%, the area of the positive electrode active material layer is occupied relative to the case of 5%, and the energy density is rather lowered.
As can be seen from comparing examples 14 to 16 and examples 19 to 21, when the width of the protective coating is too small, the protection against the extrusion test decreases, resulting in a decrease in the extrusion pass rate; when the width of the protective coating layer is too large, the area of the positive electrode active material layer is occupied, and the energy density is decreased.
As can be seen from comparing examples 1, 22 to 25, when the thickness of the protective coating is less than 10 μm, both the squeeze pass rate and the drop pass rate are reduced, since when the protective coating is too thin, burrs out of specification may cause short circuits. When the thickness H of the protective coating is greater than (H-5), the resistance of the protective coating in a full charge state is increased, and the adhesive force between the protective coating and the positive current collector is also reduced. In addition, when the protective coating is excessively thick, a gap exists between the positive electrode active material layer and the separator, resulting in increased polarization, a slight decrease in energy density, and head deformation in the appearance of the electrochemical device. In addition, as the thickness of the protective coating increases, the volumetric energy density of the electrochemical device increases first and then decreases.
It can be seen from comparative examples 26 to 37 that the conductive agent of the protective coating is too small, the electronic resistance is too large, and the gram volume performance of the protective coating is low; the protective coating has too much conductive agent and too low resistance, resulting in a decrease in extrusion throughput and drop throughput. In addition, the adhesive of the protective coating is excessive, the ionic resistance is too large, and the gram capacity exertion of the protective coating is low; the protective coating has too little binder and too low binding power, so that the protective coating falls off in the extrusion and falling processes, and the protective effect is lost.
As can be seen from comparing example 1 with example 38, the adhesion between the protective coating and the positive electrode current collector was significantly increased using the adhesive having high adhesion property.
As can be seen from comparative examples 39 to 43, when 1.2Dv99 is greater than the thickness h of the protective coating layer, scratches are easily generated, resulting in a decrease in the extrusion throughput and the drop throughput, and in addition, the adhesive force between the protective coating layer and the positive electrode current collector is decreased.
It can be seen from comparison of examples 44 to 53 that various types of conductive agents and binders are used in the protective coating layer, and that a good protective effect can be achieved.
As can be seen from comparative examples 54 to 56, when the outer edge of the protective coating is flush with or outside (i.e., partially falls on) the outer edge of the anode active material layer, a better protective effect can be obtained. When the outer edge of the protective coating is inside the outer edge of the negative electrode active material layer, the orthographic projection of the part of the positive electrode current collector partially overlaps with the negative electrode active material layer, short circuits easily occur, and the extrusion throughput and the drop throughput are reduced.
As can be seen from comparative examples 57 to 60, the distance d between the outer edge of the positive electrode active material layer and the outer edge of the negative electrode active material layer at the corresponding side was excessively large, decreasing the energy density of the electrochemical device; when the distance d is too small, the anode is easy to damage in the falling process, aluminum burrs occur, short circuit is caused, lithium precipitation of the cathode is easy to cause due to the too small distance d, and the extrusion passing rate is also reduced after the lithium precipitation.
The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the disclosure herein is not limited to the particular combination of features described above, but also encompasses other combinations of features described above or equivalents thereof. For example, the above features and the technical features having similar functions disclosed in the present application are mutually replaced to form the technical solution.

Claims (14)

1. An electrochemical device comprising a positive electrode comprising a positive current collector, a protective coating, and a positive active material layer disposed on at least one surface of said positive current collector, said protective coating disposed along a side of said positive current collector proximate to an ear portion;
the protective coating comprises a first active material, and the first active material comprises at least one of lithium iron phosphate or lithium manganese iron phosphate.
2. The electrochemical device according to claim 1, wherein the positive electrode active material layer includes a second active material including at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium nickel manganese oxide, or lithium cobalt manganese oxide.
3. The electrochemical device according to claim 1, wherein a ratio of the width of the protective coating layer to the width of the positive electrode active material layer is 1% to 5%.
4. The electrochemical device of claim 1 or 3, wherein the protective coating has a width of 0.5mm to 5 mm.
5. The electrochemical device according to claim 1, wherein a thickness H of the protective coating layer and a thickness H of the positive electrode active material layer satisfy: h is more than or equal to 10 mu m and less than or equal to (H-5) mu m.
6. The electrochemical device of claim 1 or 5, wherein the thickness h of the protective coating and the Dv99 of the first active material satisfy: 1.2Dv99 is less than or equal to h.
7. The electrochemical device according to claim 1, wherein the protective coating further comprises a conductive agent and a binder, and the mass ratio of the first active material, the conductive agent, and the binder is (78-98.5%): (0.5-10%): (1% to 12%).
8. The electrochemical device of claim 7, wherein the conductive agent comprises at least one of conductive carbon black, conductive graphite, carbon fiber, multi-walled carbon nanotubes, single-walled carbon nanotubes, hard carbon, soft carbon, ketjen black, or graphene, and the binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethylcellulose, lithium sodium carboxymethylcellulose, polyacrylic acid, polyacrylate, modified polyvinylidene fluoride, modified styrene-butadiene rubber, or polyurethane.
9. The electrochemical device of claim 1, wherein the protective coating has an electrical resistance greater than or equal to 30 Ω in a fully charged state.
10. The electrochemical device according to claim 1, wherein an adhesive force between the protective coating layer and the positive electrode current collector is 5N/m to 200N/m.
11. The electrochemical device according to claim 1, wherein the protective coating layer partially overlaps the positive electrode active material layer.
12. The electrochemical device according to claim 1, further comprising a negative electrode including a negative electrode current collector and a negative electrode active material layer on at least a portion of a surface of the negative electrode current collector, wherein an orthographic projection of the protective coating partially falls on the negative electrode active material layer or an outer edge of the protective coating is aligned with an outer edge of the negative electrode active material layer.
13. The electrochemical device according to claim 1, wherein an orthographic projection of an outer edge of the positive electrode active material layer on a side away from the tab portion falls on the negative electrode active material layer, and a distance between the outer edge of the positive electrode active material layer and an outer edge of the negative electrode active material layer at the corresponding side is between 2mm and 4 mm.
14. An electronic device comprising the electrochemical device according to any one of claims 1 to 13.
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