CN112993206A - Electrode slice and electrochemical energy storage device - Google Patents
Electrode slice and electrochemical energy storage device Download PDFInfo
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- CN112993206A CN112993206A CN202110161687.7A CN202110161687A CN112993206A CN 112993206 A CN112993206 A CN 112993206A CN 202110161687 A CN202110161687 A CN 202110161687A CN 112993206 A CN112993206 A CN 112993206A
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- thermal expansion
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Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
- Secondary Cells (AREA)
Abstract
The invention provides an electrode plate and an electrochemical energy storage device. The electrode plate provided by the invention comprises a thermal expansion coating, wherein the thermal expansion coating comprises a thermal expansion polymer. According to the invention, the thermal expansion coating comprising the thermal expansion polymer is arranged in the electrode plate, so that the conductive network in the electrode plate can be damaged, the internal resistance of the electrode plate can be increased, the temperature rise of the electrode plate can be slowed down, and the safety performance of the electrode plate in thermal abuse can be improved when the electrochemical device is subjected to thermal abuse and the temperature of the electrode plate rises. The electrochemical energy storage device provided by the invention has excellent safety performance due to the electrode slice with better safety performance.
Description
Technical Field
The invention relates to an electrode slice and an electrochemical energy storage device, and belongs to the field of electrochemical energy storage.
Background
The electrochemical energy storage device can realize the high-efficiency conversion of electric energy and chemical energy, and along with the development of scientific technology, the electrochemical energy storage device is more and more common in daily production and life of people and is more and more widely applied. In particular, electrochemical energy storage devices are more and more widely applied to wearable electronic products, electric vehicles and other products closely related to the daily life of people, and therefore, the safety of the electrochemical energy storage devices is more and more concerned by people.
In the use process of the electrochemical energy storage device, due to factors such as excessive charging and discharging, external impact and the like, heat abuse is easy to occur, the thermal safety problems such as ignition, explosion and the like of the electrochemical energy storage device are generated, and the serious threat is generated to the safe use of the electrochemical energy storage device by people. How to improve the safety of the electrochemical energy storage device when thermal abuse occurs is a technical problem to be solved urgently in the field of electrochemical energy storage.
In the prior art, when an electrochemical energy storage device is prepared, a plurality of active layers are formed on a current collector, and an active material with higher thermal stability is used in an underlying active layer arranged on the surface of the current collector to improve the safety of the electrochemical energy storage device during thermal abuse, however, the improvement degree of the safety of the electrochemical energy storage device during thermal abuse is limited in such a way.
Disclosure of Invention
The present invention provides an electrode sheet, which improves the safety of the electrode sheet during hot abuse by providing a thermal expansion coating layer comprising a thermal expansion polymer in the electrode sheet.
The invention also provides an electrochemical energy storage device, which comprises the electrode plate, so that the electrochemical energy storage device has excellent safety performance when thermal abuse occurs.
In one aspect, the invention provides an electrode sheet comprising a thermally-expandable coating; wherein the thermally expansive coating comprises a thermally expansive polymer.
The electrode sheet as described above, wherein the thermal expansion polymer comprises an expandable core and a thermoplastic shell covering at least a part of the outer surface of the expandable core;
the expandable core has a boiling point no higher than the softening temperature of the thermoplastic shell.
The electrode sheet as described above, wherein the swelling core is a liquid hydrocarbon compound.
The electrode sheet as described above, wherein the hydrocarbon compound is at least one of propylene, butane, isobutane, n-pentane, cyclopentane, isopentane, neopentane, n-hexane, cyclohexane, isooctane, and n-octane.
The electrode sheet as described above, wherein the thermoplastic casing is formed by polymerizing one or more of butylene succinate, styrene, acrylonitrile, methacrylate, ethyl acetate, acrylate, and vinylidene chloride.
The electrode sheet as described above, wherein the thermal expansion polymer further comprises a conductive layer, and the conductive layer is coated on at least a part of the outer surface of the thermoplastic housing.
The electrode sheet as described above, wherein the thickness of the thermal expansion coating layer is 1 to 5 μm.
The electrode sheet as described above, wherein the thermal expansion coating further comprises a conductive agent, a binder, and an active material;
wherein, the thermal expansion coating comprises 1-10% of conductive agent, 1-10% of adhesive, 5-30% of thermal expansion polymer and 60-89% of active substance by mass percent.
The electrode sheet as described above, wherein the electrode sheet further comprises a current collector and an active layer;
wherein the thermal expansion coating is disposed on at least one functional surface of the current collector, and the active layer is disposed on a surface of the thermal expansion coating remote from the current collector.
The invention also provides an electrochemical energy storage device which comprises the electrode plate.
The electrode plate is provided with the thermal expansion coating comprising the thermal expansion polymer, when the electrochemical energy storage device is subjected to thermal abuse, the temperature of the electrode plate rises, and the thermal expansion polymer in the thermal expansion coating is heated to expand in volume. On one hand, the volume increase of the thermal expansion polymer can destroy an original electron conduction network in the electrode plate, reduce electron transmission in the electrode plate, reduce further heat generation of the electrode plate, relieve heat accumulation and reduce safety risks such as fire and explosion caused by overheating; on the other hand, the volume expansion resistance of the thermal expansion polymer is increased due to heating, so that the internal resistance of the electrode plate is increased, the conductivity of the electrode plate is reduced, the heat generation of the electrode plate is reduced, the safety of the electrode plate in thermal abuse is improved, and the safety risk of an electrochemical energy storage device using the electrode plate in thermal abuse is reduced.
It is worth mentioning that when the electrochemical energy storage device is not in a heat abuse state, the volume of the thermal expansion polymer in the thermal expansion coating can be reduced after the temperature is reduced, and the thermal expansion polymer can be increased again when the next heat abuse occurs, so that the thermal expansion polymer can automatically respond according to the temperature, the safety performance of the electrode plate and the electrochemical energy storage device is improved, and the service life of the electrochemical energy storage device is prolonged. Moreover, the electrode plate can purposefully design the content of the thermal expansion polymer in the thermal expansion coating and the physical properties of the thermal expansion polymer according to the requirements of different electrochemical energy storage devices, so that the design of the volume expansion temperature, the volume expansion degree and the like of the thermal expansion polymer in the electrode plate can be realized according to different safety requirements of different electrochemical energy storage devices, and the safety performance of the electrochemical energy storage devices in thermal abuse is improved in a targeted manner.
In addition, the thermal expansion coating is arranged in the electrode plate, so that the operation is simple, large-scale instruments and equipment do not need to be purchased additionally, the production process flow of the conventional electrode plate is compatible, the safety risk of the electrode plate and an electrochemical energy storage device using the electrode plate during thermal abuse can be remarkably improved at lower cost, and the large-scale application in industrial production is facilitated.
The electrochemical energy storage device has good safety performance when thermal abuse occurs due to the electrode plate with excellent safety performance when thermal abuse occurs, meets the safety requirements of the electrochemical energy storage device at present, and has extremely high popularization value and application prospect.
Drawings
FIG. 1 is a schematic structural diagram of a thermal expansion coating according to an embodiment of the present invention;
FIG. 2 is a schematic structural view of a thermally expandable polymer 2 according to an embodiment of the present invention;
FIG. 3 is a schematic structural view of a thermally expandable polymer 2 according to another embodiment of the present invention; a
FIG. 4 is a schematic structural diagram of an electrode sheet according to an embodiment of the present disclosure;
FIG. 5 is a schematic structural diagram of an electrode sheet according to another embodiment of the present invention;
FIG. 6 is a schematic structural diagram of an electrode sheet according to yet another embodiment of the present invention;
fig. 7 is a schematic diagram of a lithium ion battery needling test in the test example of the present invention.
Reference numerals:
1. a thermally expansive coating;
2. a thermally expandable polymer;
3. an expandable inner core;
4. a thermoplastic shell;
5. a conductive layer;
6. a current collector;
7. an active layer;
8. a diaphragm.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
One aspect of the present invention provides an electrode sheet. Fig. 1 is a schematic structural diagram of a thermal expansion coating according to an embodiment of the present invention.
As shown in fig. 1, the electrode sheet of the present invention includes a thermal expansion coating layer 1; wherein the thermally expandable coating 1 comprises a thermally expandable polymer 2.
The electrode sheet is not strictly limited, and for example, the electrode sheet may be a positive electrode sheet or a negative electrode sheet.
The thermal expansion polymer 2 referred to in the present invention is a polymer whose volume begins to gradually increase and expand to several times or more as it increases to a certain temperature, and whose volume can gradually decrease as the temperature decreases.
The electrode plate is provided with the thermal expansion coating 1 comprising the thermal expansion polymer 2, when the electrochemical energy storage device is subjected to thermal abuse, the temperature of the electrode plate rises, and the thermal expansion polymer 2 contained in the thermal expansion coating 1 is heated to expand in volume. The thermal expansion polymer 2 expands when heated, so that on one hand, the interval between particles and other substances in the thermal expansion coating 1 is enlarged, the conduction of electrons in the thermal expansion coating 1 is hindered, the conductive network of the thermal expansion coating 1 is damaged, and the heat generation of the thermal expansion coating 1 is reduced. On the other hand, the volume of the thermal expansion polymer 2 is increased, so that the thermal expansion coating 1 expands in volume, and the contact between other substances in the electrode plate, which are used as bridges to realize electronic conduction through the thermal expansion coating 1, is also affected, the contact area between each substance and the thermal expansion coating 1 is reduced, the electronic conduction path is increased, the conductive network of the whole electrode plate is damaged, the electronic transmission between the substances in the electrode plate can be blocked, and the heat generation of the whole electrode plate is reduced.
In addition, the volume of the thermal expansion polymer 2 increases, which increases the resistance, increases the internal resistance of the electrode sheet, and further reduces the heat generation of the electrode sheet during heat abuse.
According to the invention, the thermal expansion coating 1 comprising the thermal expansion polymer 2 is arranged, so that when the electrode plate is subjected to thermal abuse, the electronic transmission in the electrode plate can be blocked, and the internal resistance of the electrode plate is increased, so that the heat generation of the electrode plate during thermal abuse is reduced, the further temperature rise speed of the electrode plate is slowed down, the safety performance of the electrode plate is improved, the safety risks of ignition, explosion and the like of an electrochemical energy storage device comprising the electrode plate are reduced, and the safety performance of the electrochemical energy storage device is improved.
In some embodiments of the present invention, the thermo-expandable polymer 2 comprises an expandable core 3, and a thermoplastic shell 4 covering at least a portion of an outer surface of the expandable core 3;
wherein the boiling point of the expandable core 3 is not higher than the softening temperature of the thermoplastic shell 4.
Fig. 2 is a schematic structural view of a thermal expansion polymer 2 according to an embodiment of the present invention. In the present invention, the thermoplastic shell 4 covers at least a part of the outer surface of the expandable inner layer 3, including, as shown in fig. 2, the thermoplastic shell 4 covers the entire outer surface of the expandable inner core 3; and the thermoplastic shell 4 covers only a portion of the outer surface of the expandable core 3. In a specific implementation, the coating of the expandable inner core 3 by the thermal expansion plastic shell 4 may be selected according to the properties of the expandable inner core 3.
The present invention is not limited strictly to the specific shape of the thermally expandable polymer 2; for example, the thermal expansion polymer 2 may be spherical as shown in fig. 2, and in this case, when the radius of the thermal expansion polymer 2 is increased by one time, the volume can be increased by eight times, and the volume increasing effect is very significant. Of course, the shape of the thermally expandable polymer 2 may also be an ellipsoid shape, or a flake shape; or any mixture of spherical, ellipsoidal and flake forms, and can be selected as required in the specific implementation process.
The softening temperature referred to herein is the temperature at which the thermoplastic shell 4 begins to soften rapidly, and in a particular implementation, the softening temperature may be obtained according to the B50 test method specified in GB1633-2000 (using a force of 50N, at a heating rate of 50 ℃/h).
In some embodiments of the invention, the swelling core 3 is a liquid hydrocarbon compound.
The process of the substance changing from the liquid state to the gas state is an endothermic process, and in the embodiment, the process of the liquid hydrocarbon compound changing from the liquid state to the gas state can absorb a part of heat, so that when heat abuse occurs, the thermal expansion polymer 2 can also absorb a part of heat, the temperature rise speed of the electrode plate is reduced, and the safety performance of the electrode plate is improved.
Exemplary liquid hydrocarbon compounds are at least one of n-butane, isobutane, n-pentane, cyclopentane, isopentane, neopentane, n-hexane, cyclohexane, isooctane, n-octane.
It can be understood that different liquid hydrocarbon compounds have different boiling points, and in the specific implementation process, the composition of the liquid hydrocarbon compounds can be selected according to the requirements of different electrode plates, so as to regulate and control the temperature of the volume expansion of the thermal expansion polymer 2.
The composition of the thermoplastic shell 4 is not critical to the present invention, and in some embodiments of the present invention, the thermoplastic shell 4 is polymerized from one or more of butylene succinate, styrene, acrylonitrile, methacrylate, ethyl acetate, acrylate, and vinylidene chloride.
Fig. 3 is a schematic structural diagram of a thermal expansion polymer 2 according to another embodiment of the present invention, as shown in fig. 3, in this embodiment, the thermal expansion polymer 2 further includes a conductive layer 5, and the conductive layer 5 covers at least a part of an outer surface of the thermoplastic housing 4.
It should be emphasized here that the conductive layer 5 covering at least a part of the outer surface of the thermoplastic shell 4 includes the conductive layer 5 covering only a part of the outer surface of the thermoplastic shell 4, and also includes the conductive layer 5 completely covering the outer surface of the thermoplastic shell 4, and the area of the conductive layer 5 covering the thermoplastic shell 4, the thickness of the conductive layer 5, and the like can be designed according to the need of the thermal expansion polymer 2 for conductivity during the specific operation process.
It can be understood that, in the electrode sheet, when the electrochemical energy storage device is normally charged and discharged without heat abuse, the internal resistance of the electrode sheet should be reduced. The conductive layer 5 is used for improving the conductivity of the thermal expansion polymer 2 during normal charge and discharge of the electrochemical energy storage device, and reducing the resistance of the thermal expansion polymer 2, so that the internal resistance of the electrode plate during normal charge and discharge is reduced.
The composition of the conductive layer 5 is not strictly limited by the present invention, and for example, in some embodiments of the present invention, the conductive layer 5 may be a carbon black-based conductive substance.
It can be understood that the thickness of the thermal expansion coating 2 has some effect on the performance of the electrode sheet. In some embodiments of the invention, the thickness of the thermal expansion coating 2 is 1-5 μm.
It is understood that the thermally-expansible polymer 2 in the thermally-expansible coating layer 1 does not substantially contribute to the capacity of the electrode sheet, and may reduce the volume and mass energy density of the electrode sheet. Therefore, in order to improve the conductivity of the electrode sheet in the thermal expansion coating 1 in the normal charge and discharge process, the binding capacity of the electrode sheet to each substance in the thermal expansion coating 1 is improved, and the influence of the thermal expansion coating 1 on the volume and mass energy density of the electrode sheet is reduced. In some embodiments of the present invention, the thermal expansion coating 1 further comprises a conductive agent, a binder, and an active material;
wherein, the thermal expansion coating 1 comprises 1 to 10 percent of conductive agent, 1 to 10 percent of adhesive, 5 to 30 percent of thermal expansion polymer 2 and 60 to 89 percent of active substance according to the mass percentage.
The specific composition of the conductive agent is not limited in the present invention, and the conductive agent may be a carbon-based conductive agent, for example, at least one of superconducting carbon black, ketjen black, acetylene black, carbon nanotubes, graphene, and fullerene.
The specific composition of the adhesive is not limited in the present invention, and for example, the adhesive may be at least one of polyvinylidene fluoride, polyacrylate, high density polyethylene, low density polyethylene, polysulfone, polyamide, polypropylene, polystyrene, polyanhydride, polycarbonate, polymethyl methacrylate, and epoxy resin.
The active substance in the invention is a substance which generates electrochemical reaction in the charging and discharging processes of the electrode plate and determines the charging and discharging performance of the electrode plate and the performance of an electrochemical energy storage device using the electrode plate. The specific composition of the active substance is not strictly limited, and an appropriate active substance can be selected according to the application of the electrode plate in the specific implementation process.
The present invention is not limited to a strict manner of forming the thermal expansion coating 1, and in some embodiments of the present invention, the thermal expansion polymer 2, the active material, the binder, and the conductive agent are dissolved in the solvent according to a certain mass ratio, and after being uniformly stirred by the stirrer, the thermal expansion coating 1 is formed by coating and drying.
The present invention is not limited to the above-mentioned solvent, and the solvent may be one of N-methylpyrrolidone, hydrofluoroether, acetone, tetrahydrofuran, dichloromethane, and pyridine, for example, as long as it can uniformly disperse the thermal expansion polymer 2, the conductive agent, and the adhesive.
The present invention does not impose a strict restriction on the position of the thermal expansion coating 1 in the electrode sheet, which in some embodiments of the present invention further comprises a current collector 6 and an active layer 7;
wherein the thermal expansion coating 1 is arranged on at least one functional surface of the current collector 6, and the active layer 7 is arranged on the surface of the thermal expansion coating 1 far away from the current collector 6.
Fig. 4 is a schematic structural diagram of an electrode sheet according to an embodiment of the present invention, and as shown in fig. 4, the electrode sheet according to the embodiment includes a thermal expansion coating 1, a current collector 6, and an active layer 7, where the thermal expansion coating 1 is disposed on one functional surface of the current collector 6, and the active layer 7 is disposed on one surface of the thermal expansion coating 1 away from the current collector 6.
The current collector 6 is mainly used for loading active substances in the electrode sheet and outputting current generated by the active substances to the outside. Generally, the current collector 6 is in the form of a sheet, and the functional surface of the current collector 6 means a large surface of the current collector 6, thereby enabling effective loading of an active material. The invention does not strictly limit the way of forming the thermal expansion coating 1 on the functional surface of the current collector 6, and in the specific operation process, a gravure coater can be adopted to coat and then dry the functional surface of the current collector 6, and the thermal expansion coating 1 is formed on the functional surface of the current collector 6.
It can be understood that the current collector is generally in the form of a sheet, and has two functional surfaces, and the thermal expansion coating 1 is disposed on at least one functional surface of the current collector 6, including the thermal expansion coating 1 disposed on one functional surface of the current collector 6 as shown in fig. 4, and in this case, the other functional surface of the current collector 6 may not be provided with the thermal expansion layer 1. Fig. 5 is a schematic structural diagram of an electrode sheet according to another embodiment of the present invention, and as shown in fig. 5, thermal expansion coatings 1 may also be disposed on two functional surfaces of a current collector 6, so as to further improve the safety performance of the electrode sheet.
The current collector 6 is not limited strictly, for example, the current collector 6 may be one of an aluminum foil and a copper foil, and may be selected according to the use of the electrode sheet in the specific implementation process.
It can be understood that the active layer 7 functions to further reduce the influence of the thermal expansion coating 1 on the capacity of the electrode sheet and increase the energy density of the electrode sheet during normal charge and discharge of the electrode sheet. The active layer 7 in the present invention includes an active material, and illustratively, the mass percentage of the active material in the active layer 7 is higher than that of the active material in the thermal expansion coating layer 1, and the thickness of the active layer 7 is generally larger than that of the thermal expansion coating layer 1, and the active layer 7 is a composition mainly generating energy in the electrode sheet.
The composition of the active layer 7 is not strictly limited in the present invention, for example, in some embodiments of the present invention, the electrode sheet is a negative electrode sheet, and the active layer 7 may be one of a metal lithium sheet, a metal lithium alloy, a graphite negative electrode, a silicon negative electrode, and a silicon carbon negative electrode.
In other embodiments of the present invention, the electrode sheet is a positive electrode sheet, and the active layer includes an active material, a conductive agent, and a binder. The active material, conductive agent and adhesive in the active layer 7 may be the same as or different from those in the thermal expansion coating layer 1, and may be selected according to the use and structure of the electrode sheet in a specific process.
Illustratively, the active material in the active layer 7 may be LiCoO2、LiFePO4、LiNi0.3Co0.3Mn0.3O2、LiNi0.5Co0.3Mn0.2O2、LiNi0.6Co0.2Mn0.2O2、LiNi0.8Co0.1Mn0.1O2、LiNi0.8Co0.15Al0.05O2、LiNi0.5Mn1.5O4At least one of (1); the conductive agent in the active layer 7 may be at least one of acetylene black, conductive carbon black, ketjen black, carbon nanotubes, and graphene; the binder in the active layer 7 can be polyvinylidene fluoride and carboxymethyl celluloseAt least one of sodium cellulose and sodium alginate.
The mode of forming the active layer 7 is not particularly limited in the present invention, and the active layer 7 may be formed by coating using a transfer coater or an extrusion coater, for example.
The thermal expansion coating 1 is disposed between the current collector 6 and the active layer 7 to act as a conductive bridge between the active layer 7 and the current collector 1. When the electrochemical energy storage device is subjected to thermal abuse, the thermal expansion polymer 2 in the thermal expansion coating 1 expands, an electron transmission path between an active material in the active layer 7 and the current collector 6 is enlarged, the electron transmission rate between the active material in the active layer 7 and the current collector 6 is reduced, electron transfer between the active material in the active layer 7 and the current collector is blocked, a conductive network in the electrode plate is damaged, further temperature rise of the electrochemical energy storage device during thermal abuse can be relieved, and the safety performance of the electrochemical energy storage device is improved. Because the active material in the active layer 7 is the part of the electrode plate mainly generating energy, the effect of blocking the electron transmission between the active material in the active layer 7 and the current collector 6 to reduce the temperature rise and improve the safety performance of the electrode plate during heat abuse is most obvious.
Fig. 6 is a schematic structural view of an electrode sheet according to still another embodiment of the present invention, as shown in fig. 6, the active layer 7 is disposed on the functional surface of the current collector 6, and the thermal expansion coating 1 is disposed on the surface of the active layer 7 away from the current collector 6. It can be understood that, in the present embodiment, the side of the thermal expansion coating layer 1 remote from the functional surface of the current collector 6 is provided with the separator 8. When the electrochemical energy storage device is subjected to thermal abuse, the temperature of the electrode plate rises, the thermal expansion polymer 2 in the thermal expansion coating 1 expands, the distance between the active layer 7 and the diaphragm 8 is increased, ion transmission is blocked, and the safety performance of the electrode plate is improved.
Another aspect of the present invention provides an electrochemical energy storage device, which includes the electrode sheet described above.
The electrochemical energy storage device is not strictly limited, for example, the electrochemical energy storage device can be a lithium ion battery, in the specific implementation process, on the basis of the electrode plate, another electrode plate and a diaphragm matched with the electrode plate are selected, a lithium ion battery cell is prepared by adopting methods such as lamination or winding, and then the lithium ion battery is obtained after baking, liquid injection, formation and packaging.
The present invention does not strictly limit the configuration of another electrode sheet that matches the above-described electrode sheet, and the other electrode sheet may be an electrode sheet that includes the thermal expansion coating 1 and is configured according to the technical solution of the present invention, or an electrode sheet that does not include the thermal expansion coating 1 and is configured according to the prior art.
The electrode sheet and the electrochemical energy storage device of the present invention will be described in detail below with reference to specific examples.
Manufacturing an electrode plate:
example 1
The manufacturing method of the electrode plate comprises the following steps:
1. thermally expanding a polymer, lithium iron phosphate, carbon black and polyvinylidene fluoride according to a mass ratio of 10.5: 79: 4: 6.5 sequentially adding the mixture into N-methyl pyrrolidone and uniformly stirring the mixture by a stirrer to prepare first slurry;
wherein the mass of the lithium iron phosphate is 10 kg; the heat-expandable polymer is obtained by coating polyethylene with n-pentane;
2. coating the first slurry on the functional surface of an aluminum foil through a gravure coater, wherein the coating speed of the gravure coater is 5m/s, the baking temperature of the aluminum foil is 125 ℃, and two thermal expansion coatings are formed on the two functional surfaces of the aluminum foil;
wherein the thickness of the thermal expansion coating is 2 μm;
2. lithium cobaltate, carbon black and polyvinylidene fluoride are mixed according to the mass ratio of 95: 3: 2, sequentially adding N-methyl pyrrolidone and uniformly stirring by using a stirrer to prepare a second slurry;
3. coating the second slurry on the surface of the thermal expansion coating layer, which is far away from the aluminum foil, by using an extrusion coating machine, wherein the baking temperature of the aluminum foil is 125 ℃, and forming two active layers on the two surfaces of the two thermal expansion coating layers, which are far away from the aluminum foil; the positive electrode sheet was obtained and designated as P1.
Example 2
The electrode sheet of this example was produced in substantially the same manner as in example 1, except that the thickness of the thermally expandable coating in step 2 of this example was 3 μm, to give a positive electrode sheet, which was designated as P2.
Example 3
The electrode sheet of this example was produced in substantially the same manner as in example 1, except that the thickness of the thermally expandable coating layer in step 2 of this example was 4 μm, to give a positive electrode sheet, which was designated as P3.
Example 4
The electrode sheet of this embodiment is basically the same as that of embodiment 1 in the manufacturing process, and the only difference is that, in step 1 of this embodiment, the thermal expansion polymer, the lithium iron phosphate, the carbon black, and the polyvinylidene fluoride are mixed in a mass ratio of 20: 69: 5: 6, sequentially adding the raw materials into N-methyl pyrrolidone;
the thickness of the thermally expandable coating in step 2 of this example was 3 μm, giving a positive plate, noted P4.
Example 5
The electrode sheet of this embodiment is basically the same as that of embodiment 1 in the manufacturing process, and the only difference is that, in step 1 of this embodiment, the thermal expansion polymer, the lithium iron phosphate, the carbon black, and the polyvinylidene fluoride are mixed in a mass ratio of 20: 60: 5: 15 are added into N-methyl pyrrolidone in sequence;
the thickness of the thermally expandable coating in step 2 of this example was 3 μm, giving a positive plate, noted P5.
Example 6
The electrode sheet of this embodiment is basically the same as that of embodiment 1 in the manufacturing process, and the only difference is that, in step 1 of this embodiment, the thermal expansion polymer, the lithium iron phosphate, the carbon black, and the polyvinylidene fluoride are mixed in a mass ratio of 20: 60: 8: 12 are sequentially added into N-methyl pyrrolidone;
the thickness of the thermally expandable coating in step 2 of this example was 3 μm, giving a positive plate, noted P6.
Example 7
The electrode sheet of this embodiment is basically the same as that of embodiment 1 in the manufacturing process, and the only difference is that, in step 1 of this embodiment, the thermal expansion polymer, the lithium iron phosphate, the carbon black, and the polyvinylidene fluoride are mixed in a mass ratio of 30: 59.5: 4: 6.5 adding into N-methyl pyrrolidone in turn;
the thickness of the thermally expandable coating in step 2 of this example was 3 μm, giving a positive plate, noted P7.
Example 8
The electrode sheet of this embodiment is basically the same as that of embodiment 1 in the manufacturing process, and the only difference is that, in step 1 of this embodiment, the thermal expansion polymer, the lithium iron phosphate, the carbon black, and the polyvinylidene fluoride are mixed in a mass ratio of 30: 59.5: 4: 6.5 adding into N-methyl pyrrolidone in turn;
the thickness of the thermally expandable coating in step 2 of this example was 4 μm, giving a positive plate, noted P8.
Table 1 tabulates the compositions of the electrode sheets of examples 1-8.
TABLE 1
LiFePO4: lithium iron phosphate;
PVDF: polyvinylidene fluoride.
Comparative example 1
The preparation of the electrode plate of the comparative example comprises the following steps:
1. lithium cobaltate, carbon black and polyvinylidene fluoride are mixed according to the mass ratio of 95: 3: 2, sequentially adding N-methyl pyrrolidone and uniformly stirring by using a stirrer to prepare slurry;
2. coating the slurry on the functional surface of an aluminum foil by using an extrusion coating machine, wherein the baking temperature of the aluminum foil is 125 ℃, and forming an active layer on the surface of the thermal expansion coating layer away from the aluminum foil; the positive electrode sheet was obtained and designated as D1.
Comparative example 2
The preparation of the electrode plate of the comparative example comprises the following steps:
1. lithium iron phosphate, carbon black and polyvinylidene fluoride are mixed according to the mass ratio of 79.5: 4: 16.5 sequentially adding the mixture into N-methyl pyrrolidone and uniformly stirring the mixture by a stirrer to prepare first slurry;
wherein the mass of the lithium iron phosphate is 10 kg;
2. coating the first slurry on the functional surface of the aluminum foil through a gravure coater, wherein the coating speed of the gravure coater is 5 m/s; after coating, baking the aluminum foil at 125 ℃ to form two bottom coatings on two functional surfaces of the aluminum foil;
wherein the thickness of the primer layer is 2 μm;
2. lithium cobaltate, carbon black and polyvinylidene fluoride are mixed according to the mass ratio of 95: 3: 2, sequentially adding the mixture into N-methyl pyrrolidone and uniformly stirring the mixture by a stirrer to prepare second slurry;
3. coating the second slurry on the surfaces of the two bottom coatings far away from the aluminum foil by using an extrusion coater, and then baking the aluminum foil at 125 ℃ to form two active layers on the two surfaces of the two bottom coatings far away from the aluminum foil; the positive electrode sheet was obtained and designated as D2.
Preparation of lithium ion battery
Winding the positive plate P1, the positive plate P2, the positive plate P3, the positive plate P4, the positive plate P5, the positive plate P6, the positive plate P7, the positive plate P8, the positive plate D1 and the positive plate D2 respectively matched with a negative plate and a diaphragm commonly used in the field, and then packaging, baking, injecting electrolyte, forming and packaging to obtain the lithium ion battery, wherein the obtained lithium ion battery is respectively marked as CP1, CP2, CP3, CP4, CP5, CP6, CP7, CP8, CD1 and CD 2;
the active layer of the common negative plate in the field is prepared from artificial graphite (active substance), superconducting carbon black (conductive agent), styrene-butadiene latex (adhesive) and sodium carboxymethylcellulose (thickening agent) according to a mass ratio of 96.5: 1: 1.5: 1, forming; the electrolyte is prepared from ethylene carbonate, ethyl propionate, lithium hexafluorophosphate, ethylene sulfite and 1, 3-propane sultone according to the mass ratio of 35.9: 47: 12: 0.15: 4.95.
Test examples
The lithium ion batteries CP1-CP8, CD1 and CD2 obtained in the above examples 1 to 8 and comparative examples 1 to 2 were subjected to the tests of the needling performance, the overcharge performance, the extrusion performance, the oven temperature performance and the weight impact performance, and the test results are shown in table 2.
1. Needling performance:
and (3) carrying out 5 times of charge-discharge cycles on the lithium ion battery under the conditions of 0.7C-rate constant-current constant-voltage charging and 0.7C-rate constant-current discharging, finishing the acupuncture test within 2 days after the completion of the cycles, and enabling the lithium ion battery to be in a fully charged state during the acupuncture test. Fig. 7 is a schematic diagram of a lithium ion battery needling test in an experimental example of the present invention, as shown in fig. 7, an iron nail with a diameter of 3mm is used to penetrate through the center of the maximum surface of the lithium ion battery in a manner of being perpendicular to the maximum surface of the lithium ion battery, the needling speed is 35mm/s, the iron nail is left in the lithium ion battery, the lithium ion battery is not ignited and not exploded, and is recorded as passing, 20 samples are tested for each lithium ion battery, and the passing rate is a ratio of the number of the passed samples to the total number of the samples 20.
2. Overcharge performance:
the lithium ion battery was charged to 4.8V at 0.7C. Monitoring the temperature change of the lithium ion battery in the charging process, and terminating the test when one of the following two conditions occurs: a) the lithium ion battery continues to charge for a longer time than 7 hours or the greater of the manufacturer defined charge times; b) the temperature of the lithium ion battery is reduced to be 20% lower than the peak value; the lithium ion batteries are not ignited and not exploded and are recorded as passing, 20 samples are tested in each lithium ion battery, and the passing rate is the ratio of the number of the passed samples to the total number of the samples of 20.
3. Extrusion performance:
the lithium ion battery is placed in two extrusion planes, the maximum plane of the lithium ion battery is parallel to the extrusion planes, the extrusion is carried out in the direction perpendicular to the maximum plane of the lithium ion battery, 15.0kN +/-0.78 kN extrusion force is applied between the two extrusion planes, 1 sample is subjected to an extrusion test only once, the lithium ion battery is not ignited and not exploded and is recorded as passing, 20 samples are tested for each lithium ion battery, the extrusion performance test is carried out for each sample only once, and the passing rate is the ratio of the number of the passed samples to the total number of the samples of 20.
4. Furnace temperature performance:
and (2) putting the lithium ion batteries into a test box, heating the test box at a temperature rise rate of (5 +/-2) ° C/min, keeping the temperature of 150 +/-2 ℃ for 10min after the temperature in the box reaches 150 +/-2 ℃, recording that the lithium ion batteries do not catch fire or explode and pass, testing 20 samples for each lithium ion battery, wherein the pass rate is the ratio of the number of the samples passing the test to the total number of the samples 20.
5. Impact properties of weights:
placing a lithium ion battery on the surface of a platform, enabling the larger surface of the lithium ion battery to be parallel to the surface of the platform, transversely placing a metal rod with the diameter of 16.8mm +/-0.2 mm on the upper surface of the geometric center of the lithium ion battery, impacting the surface of the lithium ion battery with the metal rod from a high position of 610mm +/-25 mm in a free falling state by adopting a weight of 9.1kg +/-0.1 kg, observing for 6 hours, recording that the lithium ion battery is not ignited and not exploded as passing, testing 20 samples for each lithium ion battery, and enabling the passing rate to be the ratio of the number of the tested samples to the total number of the samples to be 20.
TABLE 2
As can be seen from Table 2:
1. compared with the comparative example 1 and the comparative example 2, the lithium ion battery prepared by the positive plate obtained in the examples 1 to 8 has improved needling performance, overcharge performance, extrusion performance, furnace temperature performance and weight impact performance passing rate, and the safety performance of the lithium ion battery is obviously improved. It is demonstrated that the use of the thermally-expansible coating comprising a thermally-expansible polymer provided by the present invention can improve the safety performance of an electrochemical energy-storage device in thermal abuse.
2. Compared with the example 1, the lithium ion batteries prepared from the positive plates obtained in the examples 2 and 3 have increased needling performance, overcharge performance, extrusion performance, furnace temperature performance and weight impact performance pass rate, which shows that the safety performance of the lithium ion batteries can be optimized by adjusting the thickness of the thermal expansion coating under the condition that the compositions of the thermal expansion coating are consistent.
3. Compared with example 4, the lithium ion batteries prepared from the positive electrode sheets obtained in examples 5, 6, 7 and 8 have increased needling performance, overcharge performance, extrusion performance, furnace temperature performance and weight impact performance passing rate, which indicates that the safety performance of the lithium ion batteries can be improved by adjusting the contents of active substances, adhesives and conductive agents in the thermal expansion coating.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. An electrode sheet, comprising a thermally expansive coating;
wherein the thermally expansive coating comprises a thermally expansive polymer.
2. The electrode sheet of claim 1, wherein the thermally expandable polymer comprises an expandable core, and a thermoplastic outer shell coating at least a portion of an outer surface of the expandable core;
wherein the expandable core has a boiling point not higher than the softening temperature of the thermoplastic shell.
3. The electrode sheet of claim 2, wherein the swelling core is a liquid hydrocarbon compound.
4. The electrode sheet according to claim 3, wherein the liquid hydrocarbon compound is at least one of n-butane, isobutane, n-pentane, cyclopentane, isopentane, neopentane, n-hexane, cyclohexane, isooctane, and n-octane.
5. The electrode sheet of any one of claims 2-4, wherein the thermoplastic casing is polymerized from one or more of butylene succinate, polyvinyl chloride, styrene, acrylonitrile, methacrylate, ethyl acetate, acrylate, and vinylidene chloride.
6. The electrode sheet of claim 2, wherein the thermally expansive polymer further comprises an electrically conductive layer coated on at least a portion of an outer surface of the thermoplastic casing.
7. Electrode sheet according to any one of claims 1 to 6, characterized in that the thickness of the thermally expandable coating is 1-5 μm.
8. An electrode sheet as claimed in any one of claims 1 to 7, wherein the thermally expansive coating further comprises a conductive agent, a binder and an active substance;
wherein, the thermal expansion coating comprises 1-10% of conductive agent, 1-10% of adhesive, 5-30% of thermal expansion polymer and 60-89% of active substance by mass percent.
9. An electrode sheet as claimed in any one of claims 1 to 8, wherein the electrode sheet further comprises a current collector and an active layer;
wherein the thermal expansion coating is disposed on at least one functional surface of the current collector, and the active layer is disposed on a surface of the thermal expansion coating remote from the current collector.
10. An electrochemical energy storage device comprising the electrode sheet according to any one of claims 1 to 9.
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