CN114759272A - Electrode assembly, electrochemical device comprising same and electronic device - Google Patents

Electrode assembly, electrochemical device comprising same and electronic device Download PDF

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Publication number
CN114759272A
CN114759272A CN202210536216.4A CN202210536216A CN114759272A CN 114759272 A CN114759272 A CN 114759272A CN 202210536216 A CN202210536216 A CN 202210536216A CN 114759272 A CN114759272 A CN 114759272A
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cathode
covering layer
electrode assembly
layer
corner
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闫宁
刘凯
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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • 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
    • H01M2004/027—Negative electrodes

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

Abstract

The application relates to the technical field of lithium batteries, and discloses an electrode assembly, an electrochemical device comprising the same and an electronic device comprising the same, wherein the electrode assembly comprises an anode piece, a cathode piece and an isolating membrane, the cathode piece comprises a cathode current collector, a first cathode covering layer arranged in a straight area of the cathode current collector and a second cathode covering layer arranged in a corner area of the cathode current collector, and the electric conductivity of the second cathode covering layer is lower than that of the first cathode covering layer; or the porosity of the corner region of the isolating membrane is smaller than that of the flat region of the isolating membrane. According to the electrode assembly, the corner region of the isolating membrane and/or the corner region of the cathode pole piece are optimized, and the situation of corner lithium precipitation is improved. Moreover, the corner is only optimized, and the overall performance of the battery cell is not greatly influenced.

Description

Electrode assembly, electrochemical device comprising same and electronic device
Technical Field
The present disclosure relates to lithium battery technologies, and more particularly, to an electrode assembly, and an electrochemical device and an electronic device including the same.
Background
In order to solve the severe problems of global energy crisis, environmental pollution, climate change, low-carbon economy and the like, research and development and application of power supplies in the fields of electric vehicles, large-scale power supplies and energy storage become inevitable, and rapid charging becomes one of the necessary requirements of users.
Can satisfy quick charge's electric core, the multiplying power that charges must be enough big. However, the larger the charge rate, the more likely interface problems of purpura and lithium deposition occur during use, which can lead to accelerated cell failure during cycling.
Therefore, improvements in the art are needed.
Disclosure of Invention
A primary object of the present application is to provide an electrode assembly.
A second invention of the present application is directed to an electrochemical device including the electrode assembly.
A third invention of the present application is directed to an electronic device including the electrochemical device.
The purpose of the application is achieved, and the technical scheme is as follows:
the application provides an electrode assembly, including anode plate, cathode plate and set up in the barrier film between anode plate and the cathode plate. The anode pole piece, the cathode pole piece and the isolating film are wound to form a winding structure, and the winding structure comprises a straight area and a corner area connected with the straight area. The cathode pole piece comprises a cathode current collector, and a first cathode covering layer and a second cathode covering layer which are arranged on the cathode current collector. The first cathode covering layer is located in a straight area of the cathode pole piece, the second cathode covering layer is located in a corner area of the cathode pole piece, and the electric conductivity of the second cathode covering layer is lower than that of the first cathode covering layer. In the technical scheme, the corner area of the cathode current collector is covered with the cathode covering layer with lower conductivity than the straight area, so that the lithium ion removal amount of the cathode in the corner area can be reduced, the accumulation of lithium ions at the anode in the corner area during charging is relieved, and the lithium precipitation risk is improved.
In some embodiments of the present application, the first cathode coating layer is a first cathode active material layer, and the second cathode coating layer is a second cathode active material layer having a lower electrical conductivity than the first cathode active material layer. In this embodiment, the resistivity of the active material layer can be adjusted by a conventional method such as adjusting the type and content of the conductive agent in the active material layer, the type of the active material, and adding a high-resistance material to the active material layer, so as to achieve the purpose that the conductivity of the second cathode active material layer is lower than that of the first cathode active material layer.
In some embodiments of the present application, the first cathode coating layer includes a first cathode active material, the second cathode coating layer includes a second cathode primary coating layer and a second cathode secondary coating layer, and the second cathode secondary coating layer is located on an inner side surface of the second cathode primary coating layer toward a winding center. The second cathode main covering layer is the first cathode active material layer, the second cathode auxiliary covering layer is a high-resistance material layer, and the resistance value of the high-resistance material layer is 0.1 omega to 5 omega. In the embodiment, the inner side of the corner area of the cathode pole piece is covered with one more high-resistance material layer, so that the conductivity of the inner side of the cathode pole piece is reduced, the extraction rate of cathode lithium ions is reduced, the total amount of lithium ions extracted in the unit charging and discharging circulation process is reduced, and the lithium extraction risk is improved.
In some embodiments of the present application, the thickness of the second cathode secondary coating layer is 0.02 to 0.1 times the thickness of the second cathode primary coating layer. In this embodiment, if the secondary cathode covering layer is too thin, for example, the thickness of the secondary cathode covering layer is less than 0.02 times of the thickness of the primary cathode covering layer, the inner resistance of the cathode plate cannot be effectively reduced, and the effect of reducing the lithium ion extraction rate is achieved; if the second cathode auxiliary coating layer is too thick, for example, the thickness is greater than 0.1 times the thickness of the second cathode main coating layer, the energy density is easily reduced.
In some embodiments of the present application, the high resistance material layer includes a ceramic material, preferably, the ceramic material is at least one of aluminum oxide, silicon nitride, silicon carbide, and boron nitride. The ceramic material not only provides high resistance to reduce the conductivity inside the corner regions of the cathode and improve the risk of lithium deposition, but also prevents short circuits during puncturing and improves battery safety.
In some embodiments of the present application, the first cathode capping layer has a thickness of between 50-100 um.
In some embodiments of the present application, the second cathode capping layer has an electrical conductivity of 50% to 95% of an electrical conductivity of the first cathode capping layer.
In some embodiments of the present application, the length of the second cathode covering layer is greater than the corner arc length of the cathode plate, and the difference between the two is less than or equal to 0.5mm, so as to ensure that the corner area is completely covered by the active material layer and/or the high resistance material layer, and ensure that no current collector is exposed at the joint of the straight area and the corner area, thereby effectively ensuring the improvement of lithium deposition at the corner.
The application also provides an electrode assembly, including anode piece, cathode piece and set up in barrier film between anode piece and the cathode piece, anode piece cathode piece with the barrier film is convoluteed and is set into the winding structure, the winding structure includes straight district and connection the turning district in straight district.
The porosity of the corner region of the separator is less than the porosity of the straight region of the separator. Through reducing the porosity of diaphragm in corner, reduced the percent of pass of lithium ion for the lithium ion quantity that imbeds the positive pole after educing in the corner through the barrier film reduces, and then has reduced and has educed the lithium risk.
In some embodiments of the present application, the porosity of the corner region of the separator is between 10-20%; the porosity of the flat region of the isolating membrane is between 25 and 35 percent. The porosity of the corner regions of the separator may be controlled by shrinking the voids by hot-pressing the corner regions of the separator.
In some embodiments of the present application, the isolation film includes a substrate and an isolation capping layer disposed on the substrate, and a thickness of the isolation capping layer is greater at a corner region of the isolation film than at a straight region of the isolation film. The isolation cover layer is a high-resistance material layer, and the resistance value of the high-resistance material layer is 0.1-5 omega.
In some embodiments, the high resistance material layer includes a ceramic material, preferably at least one of alumina, silicon nitride, silicon carbide, and boron nitride. The ceramic material can control the porosity of the straight area and the corner area of the isolating membrane, improve the risk of lithium precipitation, prevent short circuit during puncture, improve the safety of the battery, inhibit the shrinkage of the isolating membrane at high temperature and prevent the short circuit of a positive electrode and a negative electrode.
In some embodiments of the present application, the thickness of the isolation capping layer at the corner regions of the isolation film is 1.02 to 1.2 times its thickness at the flat regions of the isolation film. In this embodiment, if the isolation cover layer of the isolation film in the corner region is too thin, for example, the thickness of the isolation cover layer is less than 1.02 times of the thickness of the isolation cover layer in the straight region, the porosity of the isolation film cannot be effectively reduced, and lithium deposition is inhibited; if the isolation cover layer of the isolation film in the corner region is too thick, for example, the thickness is greater than 1.2 times of the thickness of the isolation cover layer in the flat region, the lithium ion passing rate in the corner region is seriously affected, which causes the decrease of the charge rate, and the energy density is also decreased due to too thick isolation film.
In some embodiments of the present application, the release coating has a thickness of between 1.5-2um at the flat region of the release film.
In some embodiments of the present application, the length of the isolation cover layer at the corner region of the isolation film is greater than the corner arc length of the isolation film, and the difference between the two is less than or equal to 0.5mm, so as to ensure that the corner region of the isolation film is covered by the isolation cover layer.
The present application also provides an electrochemical device comprising the electrode assembly as described in any one of the above.
The present application also provides an electronic device comprising an electrochemical device as described above.
Compared with the prior art, the electrode assembly, the electrochemical device comprising the electrode assembly and the electronic device comprising the electrode assembly have at least the following beneficial technical effects:
this application covers the cathode covering layer that the straight district of electric conductivity is lower in the corner district of the negative pole mass flow body, through reducing the volume of deviating from of the negative pole of corner district, lithium ion piles up in the positive pole department of corner district when alleviating to charge, and then has improved and has educed the lithium risk.
According to the cathode pole piece, the high-resistance material covering layer is coated on the inner side of the corner area of the cathode pole piece, so that the conductivity of the inner side of the cathode pole piece is reduced, the releasing rate of cathode lithium ions is reduced, the total amount of lithium ions separated out in the unit charging and discharging cycle process is reduced, and the risk of lithium separation is improved.
This application has reduced the porosity of corner through the thick mode of scribbling the thick liquid of scribbling of corner at the barrier film, has reduced the throughput rate of lithium ion for the lithium ion quantity that imbeds the positive pole after appearing in the corner through the barrier film reduces, and then has reduced and has appeared the lithium risk.
This application makes the structure in corner district change through the mode that carries out the hot pressing to the corner of barrier film or barrier film substrate, has reduced the porosity of corner, has reduced the percent of pass of lithium ion for the corner through the barrier film is appeared and is inserted anodal lithium ion quantity reduction after the lithium ion quantity reduces, and then has reduced and has analysed out the lithium risk.
This application only optimizes the corner, can not produce great influence to electric core wholeness ability, and various electric core structures all are suitable for the scheme of this application.
The technical scheme of the application is suitable for single-layer coating and multi-layer coating, and the problem of thinning cannot be caused by double-layer coating in the technical scheme of the application.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a first schematic view of an electrode assembly according to an embodiment of the present disclosure;
FIG. 2 is a second schematic structural view of an electrode assembly according to an embodiment of the present disclosure;
FIG. 3 is a schematic view of the coating position of the separator;
FIG. 4 is a schematic view of the corner region of the isolation film after being processed by hot pressing;
FIG. 5 is a partial structure diagram of a cover layer of the separator;
FIG. 6 is a schematic view of the coating position of the cathode plate;
FIG. 7 is a partial structural view of the cover layer of the cathode plate;
FIG. 8 is a partial structural view of a covering layer of a cathode plate in another embodiment;
in the figure, 1, an anode plate; 11. an anode current collector; 12. an anode capping layer; 2. a cathode plate; 21. a cathode current collector; 22. a cathode cover layer; 3. and (3) a barrier film.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments.
In the description of the present application, it is to be understood that the terms "first", "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless otherwise specified.
As shown in fig. 1 and 2, an embodiment of the present application relates to an electrode assembly, which includes an anode plate 1, a cathode plate 2, and a separator 3 disposed between the anode plate 1 and the cathode plate 2, wherein the anode plate 1, the cathode plate 2, and the separator 3 are wound to form a winding structure (flat cell), and the winding structure includes a flat region and a corner region connected to the flat region.
Wherein, anode plate 1 includes anode current collector 11 (can be the copper foil) and set up in anode overburden 12 on the anode current collector 11, cathode plate 2 includes cathode current collector 21 and set up in cathode overburden 22 on the cathode current collector 21 (can be the aluminium foil), barrier film 3 includes the substrate and set up in isolation overburden on the substrate. In fig. 1 and 2, X1 denotes a straight region of the cell, and X2 denotes a corner region of the cell. In the following description, the locations and lengths of the flat and corner regions of the various components are labeled with specific reference numbers in the associated figures.
As a modification of the electrode assembly of the present application, the cathode cover layer 22 includes a first cathode cover layer and a second cathode cover layer. The first cathode covering layer is located in a straight area of the cathode pole piece 2, the second cathode covering layer is located in a corner area of the cathode pole piece 2, and the electrical conductivity of the second cathode covering layer is lower than that of the first cathode covering layer. In the improvement scheme, the corner area of the cathode current collector 21 is coated with the active material covering layer with lower conductivity, and the lithium ion accumulation at the anode of the corner area during charging is relieved by reducing the lithium ion extraction amount of the cathode of the corner area, so that the lithium precipitation risk is improved.
As a modification of the electrode assembly of the present application, the first cathode covering layer is a first cathode active material layer a1, the second cathode covering layer is a second cathode active material layer a2, the electrical conductivity of the second cathode active material layer a2 is lower than that of the first cathode active material layer a1, and the covering layer structure is formed as shown in fig. 7.
As a modification of the electrode assembly of the present application, the first cathode covering layer includes a first cathode active material layer a1, the second cathode covering layer includes a second cathode main covering layer and a second cathode sub-covering layer, and the second cathode sub-covering layer is located on an inner side surface of the second cathode main covering layer toward the winding center. The second cathode main coating layer is the first cathode active material layer a1, the second cathode auxiliary coating layer is a high-resistance material layer A3, the resistance value of the high-resistance material layer A3 is 0.1 Ω to 5 Ω, the formed coating layer structure is shown in fig. 8, and the finally formed battery cell is shown in fig. 2. In the improved scheme, the high-resistance material layer A3 is additionally covered on the inner side of the corner area of the first cathode active material layer A1, so that the conductivity of the inner side of the cathode pole piece 2 is reduced, the extraction rate of cathode lithium ions is reduced, the total amount of the lithium ions precipitated in the unit charge-discharge cycle process is reduced, and the lithium precipitation risk is improved.
As a modification of the electrode assembly of the present application, the high-resistance material layer a3 may include a ceramic material, and preferably, the ceramic slurry is at least one of alumina, silicon nitride, silicon carbide, and boron nitride. The high-resistance material layer a3 may further include a binder, a dispersant, and a conductive agent, and the resistance value thereof may be adjusted by adjusting the ratio of the conductive agent.
As a modification of the electrode assembly of the present application, the first cathode cover layer has a thickness of 50-100 um.
As an improvement of the electrode assembly of the present application, the thickness of the second cathode secondary coating layer is 0.02 to 0.1 times the thickness of the second cathode primary coating layer. In the improvement, if the secondary cathode covering layer is too thin, for example, the thickness of the secondary cathode covering layer is less than 0.02 times of the thickness of the primary cathode covering layer, the internal resistance of the cathode plate cannot be effectively reduced, and the effect of reducing the lithium ion extraction rate is realized; if the second cathode auxiliary coating layer is too thick, for example, the thickness is greater than 0.1 times the thickness of the second cathode main coating layer, the energy density is easily reduced.
As an improvement of the electrode assembly of the present application, the thickness of the second cathode primary coating is consistent with the thickness of the first cathode coating, and is between 50-100um, and the thickness of the second cathode secondary coating is 0.02-0.1 times of the thickness of the second cathode primary coating.
As an improvement of the electrode assembly of the present application, the electrical conductivity of the second cathode cover layer is 50% to 95% (inclusive), preferably 70% to 90% (inclusive), of the electrical conductivity of the first cathode cover layer.
As an improvement of the electrode assembly of the present application, the length of the second cathode covering layer is greater than the corner arc length of the cathode plate 2, and the difference between the two is less than or equal to 0.5mm, so as to ensure that the corner area is completely covered by the second cathode active material layer A2 or the high resistance material layer A3, and ensure that no current collector is exposed at the joint of the straight area and the corner area, thereby effectively ensuring the improvement of lithium precipitation at the corner. The corner arc length of the cathode plate 2 can be calculated according to the following formula: the arc length C of the cathode corner is pi ═ D0+ (n-1) Δ T/2, wherein D0 is the diameter of the innermost corner of the anode plate 1 + the thickness of the isolating film 3 + the thickness of the double-sided anode plate 1, n is the number of cell layers, and Δ T is the thickness of the isolating film 3 + the thickness of the double-sided anode plate 1 + the thickness of the double-sided cathode plate 2.
In the above modification, the mass ratio of the components of the first cathode active material layer a1 may be: 92% -97% of a cathode main material; 1.5 to 4 percent of conductive agent; 1.5 to 4 percent of binder. The cathode main material can be at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, NCM ternary material, lithium nickel manganese oxide and lithium-rich manganese.
In the above modification, the mass ratio of the components of the second cathode active material layer a2 may be: 92% -97% of a cathode main material; 1.0 to 3 percent of conductive agent; 2.5 to 4 percent of binder. The cathode main material can be at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, NCM ternary material, lithium nickel manganese oxide and lithium-rich manganese.
In the above modification, the high-resistance material layer a3 may include a ceramic material. Taking the ceramic material as the alumina as an example, when the high-resistance material layer A3 is prepared, firstly, fine alumina powder is mixed with water, then, additives such as a dispersing agent, a binder, a conductive agent and the like are sequentially added, and the mixture is coated on the corresponding part of the pole piece after being stirred. Preferably, the mass ratio of each component of the high resistance material layer a3 may be: 85-95% of aluminum oxide; 2-5% of a dispersant; 2-6% of a binder; 2-10% of conductive agent. The ceramic material not only provides high resistance to reduce the conductivity inside the corner regions of the cathode and improve the risk of lithium deposition, but also prevents short circuits during puncturing and improves battery safety.
In the above modification, in order to realize that the electrical conductivity of the second cathode active material layer a2 is smaller than that of the first cathode active material layer a1, so that the electrical conductivity of the second cathode active material layer a2 is 50% to 95% of the electrical conductivity of the first cathode active material layer a1, the second cathode active material layer a2 may have at least the following two other modes when stirred:
first, the content of the conductive agent reduced by the second cathode active material layer a2 is 10% to 90%, preferably 50%, of the first cathode active material layer a1, and the remaining components are the same.
Second, doping can increase the cathodic resistance of additives, such as rare earth elements.
As an improvement of the electrode assembly of the present application, the porosity of the corner region of the separator 3 is smaller than the porosity of the flat region of the separator 3. In this improvement scheme, because the porosity of the corner of barrier film 3 is less, has reduced the percent of pass of lithium ion for the lithium ion quantity that imbeds the positive pole after educing in the corner through barrier film 3 reduces, and then has reduced and has educed the lithium risk.
In the present application, two preferred ways of achieving "the porosity of the corner regions of the separator 3 is less than the porosity of the flat regions thereof" are proposed, the first being by means of improved coating and the second being by means of a hot-pressing process.
In the above improvement, the porosity of the corner region of the separator 3 is 10 to 20%, and the porosity of the flat region of the separator is 25 to 35%.
As an improvement of the electrode assembly of the present application, it is known that the separator 3 includes a base material and a separator cover layer disposed on the base material, in the present modification, the thickness of the separator cover layer at the corner region of the separator 3 is greater than that at the flat region of the separator 3, the formed cover layer is as shown in fig. 3 and 5, the finally formed cell is as shown in fig. 1, the separator 3 at the corner region in fig. 1 is indicated by a thicker dotted line, and the separator 3 at the flat region is indicated by a common dotted line. The isolation cover layer is a high-resistance material layer B, and the resistance value of the high-resistance material layer B is 0.1-5 omega. In this improvement scheme, through the mode of scribbling high resistance thick liquids thickly in the corner of barrier film 3, reduced the porosity in corner, reduced lithium ion's percent of pass for the lithium ion quantity that imbeds the positive pole after the corner through barrier film 3 is separated out reduces, and then has reduced and has educed the lithium risk.
As an improvement of the electrode assembly of the present application, the high resistance material layer B may be a ceramic material, and preferably, the ceramic slurry is at least one of aluminum oxide, silicon nitride, silicon carbide, and boron nitride. The high-resistance material layer B can also comprise a binder, a dispersing agent and a conductive agent, and the resistance value of the high-resistance material layer B can be adjusted by adjusting the proportion of the conductive agent. Taking the ceramic material as aluminum oxide as an example, when the high-resistance material layer B is prepared, firstly, fine aluminum oxide powder is mixed with water, then, additives such as a dispersing agent, a binder, a conductive agent and the like are sequentially added, and after stirring, the high-resistance material layer B is coated on a corresponding position of the isolating membrane 3. Preferably, the mass ratio of each component of the high-resistance material layer B is: 85-95% of aluminum oxide; 2-5% of a dispersant; 2-6% of a binder; 2-10% of conductive agent. The ceramic material can control the porosity of the straight area and the corner area of the isolating membrane, improve the risk of lithium precipitation, prevent short circuit during puncture, improve the safety of the battery, inhibit the shrinkage of the isolating membrane at high temperature and prevent the short circuit of a positive electrode and a negative electrode.
As an improvement of the electrode assembly of the present application, the thickness of the separator cover layer at the corner regions of the separator 3 is 1.02 to 1.2 times its thickness at the flat regions of the separator 3, i.e., finally the total thickness of the cover layers at the corner regions of the separator 3 is 102 to 120% of the thickness of the cover layer at the flat regions. In the improvement, if the isolation covering layer of the isolation film 3 in the corner region is too thin, for example, the thickness is less than 1.02 times of the thickness of the isolation covering layer in the straight region, the porosity of the isolation film cannot be effectively reduced, and lithium precipitation is inhibited; if the isolation cover layer of the isolation film 3 in the corner region is too thick, for example, the thickness is greater than 1.2 times of the thickness of the isolation cover layer in the flat region, the lithium ion passing rate in the corner region is seriously affected, which causes the decrease of the charging rate, and the energy density is also decreased due to too thick isolation film.
As an improvement of the electrode assembly of the present application, the thickness of the isolation cover layer at the flat region of the isolation film 3 is between 1.5-2um, and the thickness of the cover layer at the corner region can be calculated according to the fact that the total thickness of the cover layer at the corner region of the isolation film 3 is at least 102% of the thickness of the cover layer at the flat region.
As an improvement of the electrode assembly of the present application, the length of the isolation cover layer at the corner region of the isolation film 3 is greater than the corner arc length of the isolation film 3, and the difference between the two is less than or equal to 0.5mm, so as to ensure that the corner region of the isolation film 3 is covered by the isolation cover layer. The corner arc length of the isolation film 3 can be calculated according to the following formula: the corner arc length C of the isolating film 3 is ═ D0+ (n-1) Δ T ]/2, wherein D0 is the innermost circle corner diameter of the anode plate 1 + the thickness of the double-sided anode plate 1, n is the number of cell layers, and Δ T is the thickness of the isolating film 3 + the thickness of the double-sided anode plate 1 + the thickness of the double-sided cathode plate 2.
As an improvement of the electrode assembly of the present application, when the hot pressing process is adopted for the treatment, the specific process steps at least include the following two types:
firstly, after the base material is manufactured, hot pressing is carried out on the corner area of the base material before the high-resistance material layer B is coated, and the subsequent coating and drying process steps of the high-resistance material layer B are normally carried out after the hot pressing is finished. Wherein the hot pressing temperature is 60 ℃ plus or minus 20 ℃, the time is 4s plus or minus 2s, the pressure is 0.2MPa plus or minus 0.05MPa, and the above is the preferable hot pressing condition, but the hot pressing condition is not limited to the above condition.
Secondly, after the substrate is manufactured, coating of the high-resistance material layer B is continuously finished, and after the coating is finished and dried, hot pressing is carried out on the corner area of the isolation film 3. Wherein the hot pressing temperature is 60 ℃ plus or minus 20 ℃, the time is 4s plus or minus 2s, and the pressure is 0.2MPa plus or minus 0.05MPa, which are the preferred hot pressing conditions, but not limited to the above conditions.
In the above-mentioned improvement scheme, the structure of the corner region is changed by performing hot-pressing treatment on the corner of the isolation film 3 or the isolation film substrate to shrink the gap thereof, as shown in fig. 3 and 4, the porosity at the corner is reduced, the passing rate of lithium ions is reduced, the number of lithium ions which are inserted into the anode after being separated out from the corner of the isolation film 3 is reduced, and the risk of lithium separation is reduced.
Preparation examples
Preparing the anode plate 1:
the anode active material includes an anode material capable of absorbing and releasing lithium (Li), and may include, but is not limited to: carbon materials, metal compounds, oxides, sulfides, lithium nitrides (e.g. LiN)3) Lithium metal, with lithiumAn alloying metal and polymer material anode active material. The preparation method comprises the steps of adopting graphite as an anode active substance, mixing the graphite, styrene butadiene rubber SBR serving as a binder and CMC (carboxymethyl cellulose) serving as a dispersant according to the weight ratio of 97% to 1% to 2%, diluting the mixture with a proper amount of distilled water, stirring the mixture in a vacuum stirrer to form uniform anode slurry, coating the anode slurry on a copper foil (an anode current collector 11) on one side to form an anode covering layer 12, and drying the coated single-side pole piece in a high-temperature oven at 85 ℃ to obtain the anode pole piece 1.
Preparation of the isolation film 3:
referring to fig. 3, fig. 3 is a schematic view of the coating position of the separator 3, wherein a represents the coating width, C1, C2 and C3 each represent a corner region, both sides of the corner region are flat regions, and b represents the coating length of the flat regions. The lengths of the corner regions C1, C2, and C3 of the isolation film 3 are increased by increasing the number of layers of the battery cells, so that the corner perimeter is increased. The length of the corner region of the separation film 3 is calculated as follows: c ═ D0+ (n-1) Δ T ]/2, D0 ═ the diameter of the innermost circle corner of the anode plate 1 + the thickness of the double-sided anode plate 1, n is the number of cell layers, and Δ T ═ the thickness of the isolating film 3 + the thickness of the double-sided anode plate 1 + the thickness of the double-sided cathode plate 2. The special instructions are as follows: c2 ═ pi ═ D0+ (n-1) Δ T'/2, Δ T ═ the thickness of the separator 3 + the thickness of the double-sided anode sheet 1.
Preparation of the high-resistance material layer B: mixing the fine aluminum oxide powder with water, sequentially adding a dispersant, a binder and a conductive agent additive, stirring to obtain the first slurry, and coating the first slurry on the corresponding position of the isolating membrane 3 to form a high-resistance material layer B. The mass ratio of each component of the first slurry is as follows: 91% of aluminum oxide; 3% of a dispersant; 3% of a binder; 3% of conductive initiator. In the production scheme of the separator 3 described below, the first slurry component used was the same. The first slurry may be applied in three ways, the first being applied to the inner side of the separator 3, the second being applied to the outer side of the separator 3, and the third being applied to both the inner side and the outer side. In the following production schemes of the separator 3, both the inner side and the outer side were selected for coating, and the coating method was kept uniform in all production schemes.
Isolation film 3-1: after the base material is manufactured, before the first slurry is coated, hot pressing is carried out on a corner area of the base material (namely the corner area of the isolation membrane 3), and after the hot pressing is finished, the subsequent first slurry coating step is normally carried out, so that the isolation membrane 3 is manufactured. Wherein the hot pressing temperature is 60 +/-20 ℃, the time is 4 +/-2 s, and the pressure is 0.2 +/-0.05 MPa.
3-2 of isolating film: and obtaining the isolating membrane 3 after the substrate is manufactured and the first slurry coating step is normally carried out. The corner regions of the separator 3 are hot pressed. Wherein the hot pressing temperature is 60 +/-20 ℃, the time is 4 +/-2 s, and the pressure is 0.2 +/-0.05 MPa.
3-3 of isolating film: and after the base material of the isolation film 3 is manufactured, spraying 2-4mg of the first slurry on the whole base material according to a conventional coating process. After the first slurry is completely dried, unfolding the isolation film 3, and spraying the corner area of the isolation film 3 by using the first slurry, wherein the spraying weight is 0.01-0.02mg, the coating width is consistent with that of the straight area, and the coating thickness is 5% of the first coating thickness, so that the isolation film 3 is prepared.
3-4 of isolating film: and after the base material of the isolation film 3 is manufactured, spraying 2-4mg of the first slurry on the whole base material according to a conventional coating process, wherein the coating thickness of the corner area is consistent with that of the straight area, and thus the isolation film 3 is manufactured.
Preparing the cathode plate 2:
referring to fig. 6, fig. 6 is a schematic view of the coating position of the cathode sheet 2, d represents the coating width, F1, F2 and F3 all represent corner regions, both sides of the corner regions are flat regions, and e represents the coating length of the flat regions. Wherein the lengths of the corner regions F1, F2 and F3 of the cathode plate 2 can be calculated according to the following formula: c ═ pi ═ D0+ (n-1) Δ T ]/2, wherein D0 ═ the diameter of the innermost circle corner of the anode plate 1 + the thickness of the separator 3 + the thickness of the double-sided anode plate 1, n is the number of cell layers, and Δ T ═ the thickness of the separator 3 + the thickness of the double-sided anode plate 1 + the thickness of the double-sided cathode plate 2.
Preparation of the first cathode active material layer a 1: the cathode active material is lithium cobaltate, a first cathode active material is prepared according to the composition of 95% of a cathode main material, 3% of conductive agent conductive carbon black and 78% of binder polyvinylidene fluoride (PVDF 2), and the first cathode active material layer A1 can be formed by coating the first cathode active material at the corresponding position. In the following production scheme of the cathode sheet 2, the first cathode active material layer a1 used has the same composition.
Preparation of the second cathode active material layer a 2: the cathode main material of the second cathode active material layer a2 and the first cathode active material layer a1 are both lithium cobaltate, the second cathode active material is prepared according to the composition of 95% of lithium cobaltate, 2% of conductive agent conductive carbon black and 3% of binder polyvinylidene fluoride, and the second cathode active material layer a2 can be formed by coating the corresponding positions with the second cathode active material. In the following production scheme of the cathode sheet 2, the second cathode active material layer a2 used has the same composition.
Preparation of the high-resistance material layer a 3: mixing the fine aluminum oxide powder with water, sequentially adding additives such as a dispersant, a binder, a conductive agent and the like, stirring to obtain third slurry, and coating the third slurry on a corresponding position to form the high-resistance material layer A3. The third slurry comprises the following components in percentage by mass: 91% of aluminum oxide; 3% of a dispersant; 3% of a binder; 3 percent of conductive agent. In the following preparation scheme of the cathode plate 2, the third slurry component is used in the same manner.
And 2-1, coating the first cathode active material on the flat area of the cathode current collector 21 during coating, and forming a corner area during coating. After the coating is dried, the corner area is sprayed with the second cathode active material. The thickness and width of the two coatings are the same, so that the conductivity of the corner region of the finally formed cathode plate 2 is 70% of that of the straight region.
2-2 of cathode pole piece: at the time of coating, the first cathode active material is uniformly coated on the entire cathode current collector 21. After the coating is dried, the third slurry is sprayed on the inner side surface of the corner area of the cathode current collector 21, so that the total thickness of the covering layer at the corner area is 101% -105% of the total thickness of the covering layer at the straight area, and the conductivity of the finally formed corner area of the cathode pole piece 2 is 78% of that of the straight area.
2-3 of cathode pole piece: the entire cathode current collector 21 is spray coated using the first cathode active material according to a conventional coating process, and the coating thickness is uniform in the corner regions and the straight regions.
Example 1
Preparing an electric core:
selecting the anode pole piece 1, the isolating film 3-1 and the cathode pole piece 2-3, welding tabs on the anode pole piece 1 and the cathode pole piece 2-3, and then sequentially laminating the anode pole piece 1, the isolating film 3-1 and the cathode pole piece 2-3 and winding the laminated anode pole piece 1, isolating film 3-1 and cathode pole piece 2-3 along the same direction to obtain the battery cell 1.
Preparing an electrolyte:
mixing Ethylene Carbonate (EC) and Ethyl Methyl Carbonate (EMC) according to a volume ratio of 3:7 to obtain an organic solvent, and then fully drying LiPF6Dissolved in the mixed organic solvent to prepare an electrolyte solution with the concentration of 1 mol/L.
Preparation of lithium ion secondary battery:
and (3) placing the battery core 1 in an aluminum plastic film packaging bag, leading out a tab, packaging, injecting the electrolyte, carrying out vacuum packaging, standing, forming, shaping and other processes to obtain the lithium ion secondary battery.
Example 2
And selecting the anode plate 1, the isolating membrane 3-2 and the cathode plate 2-3 to prepare the battery cell 2, wherein the rest of the working procedures are the same as those in the embodiment 1.
Example 3
And selecting the anode pole piece 1, the isolating membrane 3-3 and the cathode pole piece 2-3 to prepare the battery cell 3, wherein the rest procedures are the same as those in the embodiment 1.
Example 4
And selecting the anode plate 1, the isolating membrane 3-4 and the cathode plate 2-1 to prepare the battery cell 4, wherein the rest of the working procedures are the same as those in the embodiment 1.
Example 5
And selecting the anode pole piece 1, the isolating membrane 3-4 and the cathode pole piece 2-2 to prepare the battery cell 5, wherein the rest procedures are the same as those of the example 1.
Comparative example 1
And selecting the anode pole piece 1, the isolating membrane 3-4 and the cathode pole piece 2-3 to prepare the battery cell 6, wherein the rest of the procedures are the same as those in the embodiment 1. The cell 6 of this example is identical to a prior art cell prepared by a conventional coating process and can be used as a comparative example.
Examples of the experiments
10 battery cores are respectively selected from the battery cores 1-5 to carry out a lithium analysis test, wherein the circulation flow of the lithium analysis test is as follows: at normal temperature, the battery is subjected to constant current charging at a rate of 1C to a voltage of 4.48V, constant voltage charging to a current of 200mA, and then constant current discharging at a rate of 0.5C to 3.0V. Is a circulation flow, and the flow is circulated for 100 times. The battery is disassembled in a drying room with the humidity less than 5%, the state of the anode plate 1 is recorded by photographing, and the lithium analysis degree of the lithium ion battery is judged according to the following standards:
no lithium precipitation at corners: no lithium deposition is generated on the surface of the negative pole piece;
slight lithium precipitation at corners: the lithium deposition area on the surface of the negative pole piece is less than 10 percent;
severe lithium evolution: the lithium deposition area on the surface of the negative pole piece is more than 30 percent;
counting the number of cells in which lithium analysis occurs on the anode plate 1, wherein the result is shown in table 1 below:
scheme(s) Corner lithium deposition Cell number of corner lithium analysis
Battery cell 1 Slight lithium precipitation at corners 1
Battery cell 2 Slight segregation of lithium at corners 2
Battery cell 3 No lithium precipitation at corner 0
Battery cell 4 No lithium precipitation at corner 0
Battery cell 5 No lithium precipitation at corner 0
Battery cell 6 Severe lithium precipitation at corners 10
TABLE 1
In summary, as can be seen from table 1 above, compared with the battery cell 6 adopting the conventional coating process, the lithium battery of the present application achieves an improvement in corner lithium deposition by performing an optimization process on the corner region of the separator 3 and/or the corner region of the cathode plate 2. Moreover, the corner is only optimized, and the overall performance of the battery cell is not greatly influenced.
The present application also relates to an electrochemical device comprising an electrode assembly as described in any one of the above improvements.
The application also relates to an electronic device comprising an electrochemical device as described above. The foregoing is only a preferred embodiment of the present application, and it should be noted that, for those skilled in the art, several modifications and substitutions can be made without departing from the technical principle of the present application, and these modifications and substitutions should also be regarded as the protection scope of the present application.

Claims (19)

1. An electrode assembly, includes anode plate, cathode plate and set up in the barrier film between anode plate and the cathode plate, anode plate the cathode plate with the barrier film is rolled up and is set into winding structure, winding structure includes straight district and connection the turning district in straight district, its characterized in that:
the cathode pole piece comprises a cathode current collector, and a first cathode covering layer and a second cathode covering layer which are arranged on the cathode current collector;
the first cathode covering layer is located in a straight area of the cathode pole piece, the second cathode covering layer is located in a corner area of the cathode pole piece, and the electric conductivity of the second cathode covering layer is lower than that of the first cathode covering layer.
2. The electrode assembly of claim 1, wherein:
the first cathode covering layer is a first cathode active material layer, the second cathode covering layer is a second cathode active material layer, and the electrical conductivity of the second cathode active material layer is lower than that of the first cathode active material layer.
3. The electrode assembly of claim 1, wherein:
the first cathode covering layer is a first cathode active material layer, the second cathode covering layer comprises a second cathode main covering layer and a second cathode auxiliary covering layer, and the second cathode auxiliary covering layer is positioned on the inner side surface of the second cathode main covering layer facing to the winding center;
the second cathode main covering layer is the first cathode active material layer, the second cathode auxiliary covering layer is a high-resistance material layer, and the resistance value of the high-resistance material layer is 0.1 omega to 5 omega.
4. The electrode assembly of claim 3, wherein:
the thickness of the second cathode secondary covering layer is 0.02-0.1 times of that of the second cathode main covering layer.
5. The electrode assembly of claim 3, wherein:
the high resistance material layer includes a ceramic material.
6. The electrode assembly of claim 5, wherein:
the ceramic material is at least one of aluminum oxide, silicon nitride, silicon carbide and boron nitride.
7. The electrode assembly of any of claims 2-6, wherein:
the thickness of the first cathode covering layer is between 50 and 100 um.
8. The electrode assembly of any of claims 1-3, wherein:
the second cathode coating layer has an electrical conductivity of 50-95% of the electrical conductivity of the first cathode coating layer.
9. The electrode assembly of any of claims 1-3, wherein:
the length of the second cathode covering layer is larger than the corner arc length of the cathode pole piece, and the difference between the length of the second cathode covering layer and the corner arc length of the cathode pole piece is smaller than or equal to 0.5 mm.
10. An electrode assembly, includes anode plate, cathode plate and set up in the barrier film between anode plate and the cathode plate, anode plate the cathode plate with the barrier film is rolled up and is set into winding structure, winding structure includes straight district and connection the turning district in straight district, its characterized in that:
the porosity of the corner region of the separator is less than the porosity of the flat region of the separator.
11. The electrode assembly of claim 10, wherein:
the porosity of the corner region of the isolating membrane is between 10 and 20 percent; the porosity of the flat region of the isolating membrane is between 25 and 35 percent.
12. The electrode assembly of claim 10, wherein:
the isolation film comprises a substrate and an isolation covering layer arranged on the substrate, wherein the thickness of the isolation covering layer at the corner region of the isolation film is larger than that of the isolation covering layer at the straight region of the isolation film;
the isolation cover layer is a high-resistance material layer, and the resistance value of the high-resistance material layer is 0.1 omega to 5 omega.
13. The electrode assembly of claim 11, wherein:
the high resistance material layer includes a ceramic material.
14. The electrode assembly of claim 13, wherein:
the ceramic material is at least one of aluminum oxide, silicon nitride, silicon carbide and boron nitride.
15. The electrode assembly of claim 12, wherein:
the thickness of the isolation cover layer at the corner region of the isolation film is 1.02-1.2 times of the thickness of the isolation cover layer at the flat region of the isolation film.
16. The electrode assembly of claim 12 or 15, wherein:
the thickness of the isolation cover layer at the flat region of the isolation film is between 1.5-2 um.
17. The electrode assembly of claim 12, wherein:
the length of the isolation covering layer at the corner area of the isolation film is larger than the corner arc length of the isolation film, and the difference value of the two is smaller than or equal to 0.5 mm.
18. An electrochemical device comprising an electrode assembly according to any one of claims 1 to 17.
19. An electronic device, characterized in that it comprises the electrochemical device according to claim 18.
CN202210536216.4A 2022-05-17 2022-05-17 Electrode assembly, electrochemical device comprising same and electronic device Pending CN114759272A (en)

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