CN116783726A - Positive electrode, electrochemical device and electronic device using same - Google Patents

Positive electrode, electrochemical device and electronic device using same Download PDF

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Publication number
CN116783726A
CN116783726A CN202280010594.7A CN202280010594A CN116783726A CN 116783726 A CN116783726 A CN 116783726A CN 202280010594 A CN202280010594 A CN 202280010594A CN 116783726 A CN116783726 A CN 116783726A
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China
Prior art keywords
positive electrode
functional layer
active material
equal
binder
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陈梅锋
刘晓欠
韩冬冬
刘胜奇
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Publication of CN116783726A publication Critical patent/CN116783726A/en
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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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers

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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)

Abstract

An electrochemical device includes a positive electrode including: the positive electrode current collector and the film layer positioned on the surface of the positive electrode current collector; the film layer includes a positive electrode active material layer and a functional layer between the positive electrode current collector and the positive electrode active material layer. The binding force between the positive electrode active material layer and the functional layer is F1N/m, the binding force between the functional layer and the positive electrode current collector is F2N/m, and the safety performance of the electrochemical device can be remarkably improved by meeting the requirement that F1/F2 is more than or equal to 0.1 and less than or equal to 0.5.

Description

Positive electrode, electrochemical device and electronic device using same
Technical Field
The present application relates to the field of energy storage, and in particular, to a positive electrode, an electrochemical device using the positive electrode, and an electronic device.
Background
With the popularity of electronic products such as notebook computers, mobile phones, palm game players, tablet computers, etc., the safety requirements of electrochemical devices (e.g., lithium ion batteries) are becoming more stringent. The slitting process and the compacting process of the positive electrode or the negative electrode are inevitably involved in the production process of the lithium ion battery. The general current collector is copper foil, aluminum foil or metal foil such as stainless steel, and these metal foils receive intrinsic mechanical properties and the influence of cutting equipment state in the cutting process, can leave blemishes such as metal burr in cutting department. If the metal burrs are not treated, when the lithium ion battery is extruded from the outside, the metal burrs pierce through the isolating film, so that the internal short circuit of the anode and the cathode is caused, and serious consequences such as heating, smoking, ignition, explosion and the like of the battery are finally caused.
Disclosure of Invention
According to one aspect of the present application, the present application relates to an electrochemical device comprising a positive electrode including: the positive electrode current collector and the film layer positioned on the surface of the positive electrode current collector; the film layer comprises a positive electrode active material layer and a functional layer positioned between the positive electrode current collector and the positive electrode active material layer; the binding force between the positive electrode active material layer and the functional layer is F1N/m, and the binding force between the functional layer and the positive electrode current collector is F2N/m, so that F1/F2 is more than or equal to 0.1 and less than or equal to 0.5.
By arranging the functional layer between the positive electrode current collector and the positive electrode active material layer and enabling F1/F2 to be in the range, on one hand, F1/F2 is more than or equal to 0.1, the cohesiveness between the positive electrode active material layer and the functional layer is not much weaker than the cohesiveness between the functional layer and the current collector, when the positive electrode current collector is extruded from the outside, the risk of falling between the positive electrode active material layer and the functional layer can be reduced, and the occurrence of internal short circuit caused by falling of the positive electrode active material layer is prevented; on the other hand, F1/F2 is less than or equal to 0.5, and the functional layer can be ensured to be better extended along with the positive current collector when being extruded by the outside, so that the risk of internal short circuit caused by penetration of a isolating film by metal burrs is reduced, and the safety performance of the electrochemical device is improved.
In some embodiments, 10.ltoreq.F1.ltoreq.30. F1 in the above range can further ensure the adhesion between the positive electrode active material layer and the functional layer, reduce the risk of falling off between the positive electrode active material layer and the functional layer when externally pressed, and further improve the safety performance of the electrochemical device.
In some embodiments, 50.ltoreq.F2.ltoreq.300. F2 can further reduce the risk that functional layer and positive current collector drop in above-mentioned within range, improves the ductility of functional layer along with positive current collector, when receiving outside extrusion, reduces the risk that metal burr impaled the barrier film and lead to the internal short circuit.
In some embodiments, the functional layer has a thickness T1 μm and the positive electrode active material layer has a thickness T2 μm, satisfying 0.5.ltoreq.T1.ltoreq.10; T2/T1 is more than or equal to 5 and less than or equal to 20. In the range, the shielding effect of the functional layer on the metal burrs can be improved, so that the risk of internal short circuit caused by the penetration of the metal burrs through the isolating film when the isolating film is extruded by the outside is reduced; meanwhile, in the range, the thickness of the functional layer and the thickness of the positive electrode active material layer can be more matched, so that the electrochemical device has better energy density, and meanwhile, the safety performance is further improved, and the electrochemical device has better comprehensive performance.
In some embodiments, the membrane layer has a weight loss ratio of a% at 600 ℃ detected by thermogravimetric analysis under nitrogen atmosphere, the electrochemical device has a resistance of rΩ in a fully charged state, and at least one of the following conditions is satisfied: (I) R is more than or equal to 0.1A and less than or equal to 10A; (II) A is more than or equal to 1 and less than or equal to 20; (III) R is more than or equal to 10 and less than or equal to 50.
In some embodiments, the film has a differential thermogravimetric analysis curve with a first peak in the range of 300 ℃ to 400 ℃ and a second peak in the range of 410 ℃ to 600 ℃, the area ratio of the first peak to the second peak being X, satisfying 0.1 ∈x ∈0.5. At this time, the binder in the functional layer has high thermal stability, and can inhibit the falling-off of the functional layer and the positive electrode current collector at high temperature, thereby further improving the safety performance of the electrochemical device.
In some embodiments, the functional layer has a weight loss ratio of (100-A1)% at 600 ℃ and the positive electrode active material layer has a weight loss ratio of (100-A2)% at 600 ℃ as detected by thermogravimetric analysis under a nitrogen atmosphere, satisfying at least one of the following conditions: (i) A1 is 80-95; (ii) A2 is more than or equal to 95 and less than or equal to 99; (iii) A2/A1 is less than or equal to 1 and less than 1.3.
In some embodiments, the functional layer comprises first particles, a first conductive agent, a first binder.
In some embodiments, the first particles comprise a first metal element comprising at least one of Al, mg, ca, ti, ce, zn, Y, hf, zr, ba, sn or Ni, wherein the mass percent of the first particles is a%, based on the mass of the functional layer, satisfying 1.ltoreq.a.ltoreq.40.
In some embodiments, the first conductive agent comprises at least one of graphene, carbon nanotubes, carbon black, graphite fibers, or conductive carbon, wherein the mass percentage of the first conductive agent is b% based on the mass of the functional layer, satisfying 0.3.ltoreq.b.ltoreq.5.
In some embodiments, the functional layer further comprises third particles comprising lithium and a second metal element comprising at least one of Fe, mn, al, mg, co or Ni, wherein the mass percent of the third particles is c%, based on the mass of the functional layer, satisfying 40 c 94.5.
In some embodiments, the first binder comprises a polymer formed of at least one of acrylic acid, acrylamide, an acrylate, acrylonitrile, or an acrylate, wherein the mass percent of the first binder is d%, based on the mass of the functional layer, satisfying 3.ltoreq.d.ltoreq.15.
In some embodiments, the first binder is an aqueous binder.
In some embodiments, the functional layer further comprises a leveling agent comprising at least one of a siloxane-based compound, an oxy-olefin polymer, a carboxylate-based compound, an alcohol-based compound, an ether-based compound, or a fluorocarbon, the leveling agent being less than or equal to 1% by mass based on the mass of the functional layer.
In some embodiments, the first particles comprise at least one of alumina, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, diaspore, barium sulfate, calcium sulfate, or calcium silicate; the third particles comprise at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganate or lithium nickel cobalt manganate.
In some embodiments, the positive electrode active material layer includes a second binder having a composition different from that of the first binder, the first binder being W1% by mass based on the mass of the functional layer, the second binder being W2% by mass < W1% based on the mass of the positive electrode active material layer.
In some embodiments, the positive electrode active material layer includes an active material, a second conductive agent, and a second binder, wherein the mass percentage of the active material is 95% to 98.5%, the mass percentage of the second conductive agent is 0.5% to 2%, and the mass percentage of the second binder is 1% to 3%, based on the mass of the positive electrode active material layer.
In some embodiments, the second binder comprises at least one of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene-hexafluoropropylene, sodium polyacrylate, nitrile rubber, or polyacrylate.
According to another aspect of the application, the application relates to an electronic device comprising an electrochemical device according to any of the foregoing embodiments.
Detailed Description
Hereinafter, the present application will be described in detail. It should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present application on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Thus, the description shown in the embodiments described in the specification is merely a specific example for the purpose of illustration and is not intended to show all technical aspects of the application, and it is to be understood that various alternative equivalents and variants may be made thereto at the time of filing the present application.
In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means only a; only B; or A and B. In another example, if items A, B and C are listed, then the phrase "at least one of A, B and C" means only a; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.
Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.
1. Electrochemical device
The present application provides an electrochemical device comprising a positive electrode including: the positive electrode current collector and the film layer positioned on the surface of the positive electrode current collector; the film layer comprises a positive electrode active material layer and a functional layer positioned between the positive electrode current collector and the positive electrode active material layer; the binding force between the positive electrode active material layer and the functional layer is F1N/m, and the binding force between the functional layer and the positive electrode current collector is F2N/m, so that F1/F2 is more than or equal to 0.1 and less than or equal to 0.5.
By arranging the functional layer between the positive electrode current collector and the positive electrode active material layer and enabling F1/F2 to be in the range, on one hand, F1/F2 is more than or equal to 0.1, the cohesiveness between the positive electrode active material layer and the functional layer is not much weaker than the cohesiveness between the functional layer and the current collector, when the positive electrode current collector is extruded from the outside, the risk of falling between the positive electrode active material layer and the functional layer can be reduced, and the occurrence of internal short circuit caused by falling of the positive electrode active material layer is prevented; on the other hand, F1/F2 is less than or equal to 0.5, and the functional layer can be ensured to be better extended along with the positive current collector when being extruded by the outside, so that the risk of internal short circuit caused by penetration of a isolating film by metal burrs is reduced, and the safety performance of the electrochemical device is improved.
In some embodiments, 0.12.ltoreq.F1/F2.ltoreq.0.4. In some embodiments, 0.15.ltoreq.F1/F2.ltoreq.0.3. In some embodiments, F1/F2 may be 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a range between any two of the foregoing values.
In some embodiments, 10.ltoreq.F1.ltoreq.30. F1 in the above range can further ensure the adhesion between the positive electrode active material layer and the functional layer, reducing the risk of falling off between the positive electrode active material layer and the functional layer when externally pressed; meanwhile, the influence of the functional layer on the extension of the functional layer along with the positive electrode current collector can be reduced, and the safety performance of the electrochemical device is improved. In some embodiments, 15.ltoreq.F1.ltoreq.25. In some embodiments, F1 may be 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30 or a range between any two of the foregoing values.
In some embodiments, 50.ltoreq.F2.ltoreq.300. F2 can further reduce the risk that functional layer and positive current collector drop in above-mentioned within range, improves the ductility of functional layer along with positive current collector, when receiving outside extrusion, reduces the risk that metal burr impaled the barrier film and lead to the internal short circuit. In some embodiments, 100.ltoreq.F2.ltoreq.250. In some embodiments, F2 may be 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, or a range between any two of the foregoing.
In some embodiments, the functional layer has a thickness T1 μm and the positive electrode active material layer has a thickness T2 μm, satisfying 0.5.ltoreq.T1.ltoreq.10; T2/T1 is more than or equal to 5 and less than or equal to 20. In the range, the shielding effect of the functional layer on the metal burrs can be improved, so that the risk of internal short circuit caused by the penetration of the metal burrs through the isolating film when the isolating film is extruded by the outside is reduced; meanwhile, in the range, the thickness of the functional layer and the thickness of the positive electrode active material layer can be more matched, so that the electrochemical device has better energy density, and meanwhile, the safety performance is further improved, and the electrochemical device has better comprehensive performance. In some embodiments, 1.ltoreq.T1.ltoreq.8. In some embodiments, 1.5.ltoreq.T1.ltoreq.6. In some embodiments, 2.ltoreq.Tl.ltoreq.5. In some embodiments, T1 may be 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 5, 5.5, 6, 7, 8, 9, 10, or a range between any two of the foregoing values. In some embodiments, 7.ltoreq.T2/T1.ltoreq.19. In some embodiments, 10.ltoreq.T2/T1.ltoreq.18.
In some embodiments, the membrane layer has a weight loss ratio of a% at 600 ℃ detected by thermogravimetric analysis under nitrogen atmosphere, the electrochemical device has a resistance of rΩ in a fully charged state, and at least one of the following conditions is satisfied: (I) R is more than or equal to 0.1A and less than or equal to 10A; (II) A is more than or equal to 1 and less than or equal to 20; (III) R is more than or equal to 10 and less than or equal to 50.
In some embodiments, the film has a differential thermogravimetric analysis curve with a first peak in the range of 300 ℃ to 400 ℃ and a second peak in the range of 410 ℃ to 600 ℃, the area ratio of the first peak to the second peak being X, satisfying 0.1 ∈x ∈0.5.
In some embodiments, the functional layer has a weight loss ratio of (100-A1)% at 600 ℃ and the positive electrode active material layer has a weight loss ratio of (100-A2)% at 600 ℃ as detected by thermogravimetric analysis under a nitrogen atmosphere, satisfying at least one of the following conditions: (i) A1 is 80-95; (ii) A2 is more than or equal to 95 and less than or equal to 99; and (iii) 1.ltoreq.A2/A1 < 1.3. When the functional layer is at 600 ℃, organic compounds such as a binder in the functional layer are removed, the rest substances are inorganic particles, and the A1 can improve the rigidity of the functional layer in the range, so that the puncture resistance of the functional layer is improved, and the safety performance of the electrochemical device is improved. At 600 deg.c, the organic compound, such as a binder, in the positive electrode active material layer is removed, and the remaining material is positive electrode active material particles, A2 is in the above range, which enables the electrochemical device to have a higher energy density. Further, when A2/A1 is in the above range, the positive electrode active layer has a suitable rigidity, and can be better bonded with the functional layer upon cold pressing, further reducing the risk of the positive electrode active material layer falling off to cause internal short circuit upon external pressing.
In some embodiments, the functional layer comprises first particles, a first conductive agent, a first binder. When the functional layer contains the first particles, the first conductive agent and the first binder, the functional layer can have good safety performance, and meanwhile, the resistance of the functional layer is controlled, so that the electrochemical device has good rate performance, low-temperature performance and safety performance.
In some embodiments, the first particles comprise a first metal element comprising at least one of Al, mg, ca, ti, ce, zn, Y, hf, zr, ba, sn or Ni, wherein the mass percent of the first particles is a%, based on the mass of the functional layer, satisfying 1.ltoreq.a.ltoreq.40.
In some embodiments, the first conductive agent comprises at least one of graphene, carbon nanotubes, carbon black, graphite fibers, or conductive carbon, wherein the mass percentage of the first conductive agent is b% based on the mass of the functional layer, satisfying 0.3.ltoreq.b.ltoreq.5.
In some embodiments, the functional layer further comprises third particles comprising lithium and a second metal element comprising at least one of Fe, mn, al, mg, co or Ni, wherein the mass percent of the third particles is c%, based on the mass of the functional layer, satisfying 40 c 94.5.
In some embodiments, the first binder comprises a polymer formed of at least one of acrylic acid, acrylamide, an acrylate, acrylonitrile, or an acrylate, wherein the mass percent of the first binder is d%, based on the mass of the functional layer, satisfying 3.ltoreq.d.ltoreq.15.
In some embodiments, the first binder is an aqueous binder. The aqueous binder is favorable for improving the adhesion between the functional layer and the positive current collector, so that the functional layer can be better adhered to the surface of the current collector, and the safety performance of the electrochemical device can be better improved.
In some embodiments, the functional layer further comprises a leveling agent comprising at least one of a siloxane-based compound, an oxy-olefin polymer, a carboxylate-based compound, an alcohol-based compound, an ether-based compound, or a fluorocarbon, the leveling agent being less than or equal to 1% by mass based on the mass of the functional layer.
In some embodiments, wherein the first particles comprise at least one of alumina, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, diaspore, barium sulfate, calcium sulfate, or calcium silicate; the third particles comprise at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganate or lithium nickel cobalt manganate.
In some embodiments, wherein the positive electrode active material layer includes a second binder having a different composition than the first binder, the first binder is present in a mass percentage of W1% based on the mass of the functional layer, and the second binder is present in a mass percentage of W2%, W2 < W1, based on the mass of the positive electrode active material layer.
In some embodiments, the positive electrode active material layer includes an active material, a second conductive agent, and a second binder, wherein the mass percentage of the active material is 95% to 98.5%, the mass percentage of the second conductive agent is 0.5% to 2%, and the mass percentage of the binder is 1% to 3%, based on the mass of the positive electrode active material layer.
In some embodiments, the second binder comprises at least one of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene-hexafluoropropylene, sodium polyacrylate, nitrile rubber, or polyacrylate.
In some embodiments, the electrochemical device has a side squeeze through of greater than or equal to 80%. In some embodiments, the side extrusion pass rate of the electrochemical device is greater than or equal to 90%. In some embodiments, the side extrusion pass rate of the electrochemical device is greater than or equal to 94%. In some embodiments, the side squeeze-through rate of the electrochemical device is greater than or equal to 96%.
In some embodiments, the electrochemical device of the present application includes, but is not limited to: primary batteries and secondary batteries of all kinds. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, lithium secondary batteries include, but are not limited to: a lithium metal secondary battery, a lithium ion secondary battery, or a lithium ion polymer secondary battery.
The electrochemical device of the present application further includes a separator, an electrolyte, and a negative electrode.
2. Method for preparing the electrochemical device
The method of manufacturing the electrochemical device of the present application is described in detail below by taking a lithium ion battery as an example.
Preparation of the negative electrode: dispersing a negative electrode active substance (at least one of carbon material, silicon material or lithium titanate) and a negative electrode binder in a solvent system according to a certain mass ratio, fully stirring and uniformly mixing, coating the mixture on a negative electrode current collector, and drying and cold pressing the mixture to obtain the negative electrode.
Preparation of positive electrode:
(1) Adding the first particles and/or the third particles, the first conductive agent and the first binder, optionally the leveling agent, to a solvent and mixing them uniformly to obtain a slurry of the functional layer (hereinafter referred to as "first slurry");
(2) Coating the first slurry in the step (1) on a target area of the positive electrode current collector;
(3) Drying the positive current collector containing the first slurry obtained in the step (2) to remove the solvent, thereby obtaining a positive current collector coated with a functional layer;
(4) Dispersing a positive electrode active material (at least one of lithium cobaltate, lithium manganate or lithium iron phosphate), a second conductive agent and a second binder in a solvent system according to a certain mass ratio, and fully stirring and uniformly mixing to obtain a slurry (hereinafter referred to as a second slurry) of the positive electrode active material;
(5) Coating the second slurry on the target area of the positive electrode current collector coated with the functional layer, which is obtained in the step (3);
(6) And (3) drying the positive electrode current collector containing the second slurry in the step (5) to remove the solvent, thereby obtaining the required positive electrode.
In some embodiments, the second conductive agent is to improve conductivity of the positive electrode active material layer by providing a conductive path to the active material. The second conductive agent may include at least one of: acetylene black, ketjen black, natural graphite, carbon black, carbon fiber, metal powder, or metal fiber (e.g., copper, nickel, aluminum, or silver), but examples of the second conductive agent are not limited thereto. In some embodiments, the amount of the second conductive agent may be suitably adjusted. The amount of the second conductive agent ranges from 1 to 30 parts by weight based on 100 parts by weight of the total amount of the positive electrode active material, the second conductive agent, and the second binder.
In some embodiments, examples of the solvent include, but are not limited to, N-methylpyrrolidone, acetone, or water. In some embodiments, the amount of solvent may be appropriately adjusted.
In some embodiments, the second binder may aid in bonding between the active material and the second conductive agent, or between the active material and the current collector. Examples of the second binder include, but are not limited to, polyvinylidene fluoride, polyvinylidene chloride, carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polypropylene, polyethylene, and various polymers. The amount of the second binder ranges from 1 to 30 parts by weight based on 100 parts by weight of the total amount of the active material, the second conductive agent, and the second binder.
In some embodiments, the current collector has a thickness in the range of 3 micrometers to 20 micrometers, although the disclosure is not limited thereto. The current collector is electrically conductive and does not cause adverse chemical changes in the fabricated battery. Examples of the current collector include copper, stainless steel, aluminum, nickel, titanium, or an alloy (e.g., copper-nickel alloy), but the disclosure is not limited thereto. In some embodiments, fine irregularities (e.g., surface roughness) may be included on the surface of the current collector to enhance adhesion of the surface of the current collector to the active material. In some embodiments, the current collector may be used in a variety of forms, examples of which include a film, sheet, foil, mesh, porous structure, foam, or jeopardy, but the present disclosure is not limited thereto.
Isolation film: in some embodiments, a porous polymeric film of Polyethylene (PE) is used as the separator. In some embodiments, the material of the isolation film may include fiberglass, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof. In some embodiments, the pores in the separator have diameters in the range of 0.01 microns to 1 micron, and the thickness of the separator is in the range of 5 microns to 500 microns.
Electrolyte solution: in some embodiments, the electrolyte includes an organic solvent, a lithium salt, and an additive. In some embodiments, the organic solvent includes at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate. In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt comprises lithium hexafluorophosphate (LiPF 6 ) Lithium tetrafluoroborate (LiBF) 4 ) Lithium difluorophosphate (LiPO) 2 F 2 ) Lithium bis (trifluoromethanesulfonyl) imide LiN (CF) 3 SO 2 ) 2 (LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO) 2 F) 2 ) (LiLSI), lithium bisoxalato borate LiB (C) 2 O 4 ) 2 (LiBOB), lithium difluorooxalato borate LiBF 2 (C 2 O 4 ) At least one of (LiDFOB).
And stacking the positive electrode, the isolating film and the negative electrode in sequence, so that the isolating film is positioned in the middle of the positive electrode and the negative electrode to play a role in isolation, and winding to obtain the bare cell. And placing the wound bare cell in an outer package, injecting electrolyte, packaging, and performing technological processes such as formation, degassing, trimming and the like to obtain the lithium ion battery.
3. Electronic device
The present application provides an electronic device comprising an electrochemical device according to the foregoing.
According to some embodiments of the application, the electronic device includes, but is not limited to: notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copiers, portable printers, headsets, video recorders, liquid crystal televisions, hand-held cleaners, portable CD-players, mini-compact discs, transceivers, electronic notebooks, calculators, memory cards, portable audio recorders, radios, stand-by power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game machines, watches, electric tools, flash lamps, cameras, household large-sized batteries or lithium-ion capacitors, and the like.
3. Detailed description of the preferred embodiments
The present application will be described in further detail with reference to examples. However, it should be understood that the following embodiments are merely examples, and the embodiment modes of the present application are not limited thereto.
Examples 1 to 46 and comparative examples 1 to 4
Step (1): adding the first particles and/or the third particles, the first conductive agent, the first binder and optionally the leveling agent into deionized water, and uniformly mixing to obtain a slurry (hereinafter referred to as a "first slurry") of the functional layer;
step (2): coating the first slurry in the step (1) on a target area of the positive electrode current collector;
step (3): drying the positive current collector containing the first slurry in the step (2) to remove the solvent, thereby obtaining a positive current collector coated with a functional layer;
step (4): dispersing the positive electrode active material, the conductive material and the second binder in an N-methyl pyrrolidone solvent system, and fully stirring and uniformly mixing to obtain a slurry (hereinafter referred to as a second slurry) of the positive electrode active material;
step (5): coating the second slurry on the target area of the positive electrode current collector coated with the functional layer, which is obtained in the step (3);
step (6): and (3) drying the positive electrode current collector containing the second slurry in the step (5) to remove the solvent, thereby obtaining the required positive electrode.
In example 1, the second conductive agent in the positive electrode active material layer was Carbon Nanotube (CNT) and conductive carbon (SP), the second binder was polyvinylidene fluoride (PVDF), the positive electrode active material was Lithium Cobaltate (LCO), the content of CNT was 0.5%, the content of SP was 0.6%, the content of PVDF was 1.3%, the content of the positive electrode active material was 97.6%, and the thickness of the positive electrode active material layer was 50 μm based on the weight of the positive electrode active material layer. In the functional layer, the first particles are boehmite (B1), the first binder is a polymer obtained by polymerizing 45% of acrylonitrile, 45% of lithium acrylate, and 10% of acrylamide, the first conductive agent is conductive carbon (SP), and the content ratios of the first particles, the first binder, and the first conductive agent are shown in table 1, for example, based on the weight of the functional layer. The thickness of the functional layer was 3. Mu.m.
The following table 1 specifically shows the composition differences of the functional layers and the positive electrode active material layers in the positive electrodes in examples 1 to 46 and comparative examples 1 to 4.
TABLE 1
Except for the above differences, the negative electrodes, electrolytes, separators, and the like in examples 1 to 46 and comparative examples 1 to 4 were not different, and were prepared by the following processes.
And (3) a negative electrode: and (3) fully and uniformly stirring active substances of artificial graphite, a conductive agent of acetylene black, a binder of styrene-butadiene rubber (SBR) and a thickener of sodium methyl cellulose (CMC) in a deionized water solvent system according to the mass ratio of about 95:2:2:1, coating the mixture on a Cu foil, and drying and cold pressing the mixture to obtain the negative electrode.
Electrolyte solution: in an argon atmosphere glove box with water content less than 10ppm, uniformly mixing Ethylene Carbonate (EC), diethyl carbonate (DEC), propylene Carbonate (PC) according to the weight ratio of 2:6:2, and fully drying lithium salt LiPF 6 Dissolved in the solvent, liPF 6 1.5% 1, 3-propane sultone, 3% fluoroethylene carbonate, 2% adiponitrile were added. Wherein the content of each substance is based on the total weight of the electrolyte.
Isolation film: PE porous polymeric film is used as a isolating film.
The positive electrode, the isolating film and the negative electrode are sequentially stacked, the isolating film is positioned in the middle of the positive electrode and the negative electrode to play a role of isolation, and the battery is obtained by winding, placing the isolating film in an outer package, injecting the prepared electrolyte, packaging, and performing processes of formation, degassing, trimming and the like.
Performance test method
Cohesive force
1) Sampling: removing the positive electrode coated with the functional layer from the lithium ion battery in the environment of (25+/-3) DEG C, and wiping the electrolyte remained on the surface of the positive electrode by using dust-free paper;
2) Sample preparation: taking a pole piece to be tested, cutting off samples with the width of x (20 mm) and the length of y (190 mm) by using a blade, wherein the size can be selected according to the size of the practically removed pole piece;
3) The double-sided adhesive tape is stuck on a steel plate with the width of 30mm and the length of 200mm, and the width of the double-sided adhesive tape is 20mm and the length of y (190 mm);
4) Attaching the positive electrode active material layer of the pole piece sample intercepted in the step 2 to a double-sided adhesive tape with the test surface facing downwards;
5) Fixing the steel plate and the pole piece sample by using a clamp, and testing the adhesive force and the stretching speed by using a high-speed rail AI-3000 tensile machine: 50mm/min, the tensile displacement can be determined according to the length of the sample;
7) The cohesive force f1=f1/x (pole piece width) between the positive electrode active material layer and the functional layer is calculated according to the tensile force value F1 (N) when the curve is run, and the unit is: n/m.
8) Repeating the steps of the pole piece sample for stripping the positive electrode active material layer, attaching the functional layer on the double-sided adhesive tape, and calculating the binding force F2=f2/x (pole piece width) between the functional layer and the positive electrode current collector according to the tensile force value F2 (N) when the curve is running, wherein the units are as follows: n/m.
Functional layer/positive electrode active material layer thickness
1) And (3) removing the positive electrode coated with the functional layer from the lithium ion battery in the environment of (25+/-3). Wiping the electrolyte remained on the surface of the positive electrode by using dust-free paper;
2) Cutting the anode coated with the functional layer under plasma to obtain the cross section of the anode;
3) Observing the cross section of the positive electrode obtained in the step 2) under a Scanning Electron Microscope (SEM), measuring the thickness T mu m of the functional layer, measuring at least 15 different points at intervals of about 2mm to 3mm between adjacent test points, and recording the average value of all the measurement points as the thickness T1 mu m of the functional layer; the thickness T2 μm of the positive electrode active material layer was measured in the same manner.
Positive electrode resistance in full charge state
1) Constant-current charging is carried out at a multiplying power of 0.05C until the full charge design voltage reaches 4.45V, and then constant-voltage charging is carried out at a full charge design voltage until the current reaches 0.025C (cut-off current), so that the lithium ion battery reaches a full charge state;
2) Disassembling the lithium ion battery to obtain a positive electrode;
3) Placing the positive electrode obtained in 2) in an environment with a humidity of about 5% to about 15% for 30min, and then sealing and transferring to a resistance test site;
4) Testing the resistance of the positive electrode obtained in 3) by using a BER1200 type diaphragm resistance tester, wherein the intervals between adjacent test points are 2mm to 3mm, at least 15 different points are tested, the average value of the resistance of all the test points is recorded as the positive electrode resistance R in a full charge state, and the test parameters are as follows: area of ram 153.94mm 2 Pressure 3.5t, hold time 50s.
Screw extrusion test
1) The length and width of the battery face upwards and are placed in the two parallel plates;
2) Placing a screw (0 # screw) with the thread diameter of 2mm, the screw length of 4mm, the head diameter of 3.8mm and the head thickness of 1.3mm at the center of the surface of the battery;
3) Pressing in the direction perpendicular to the parallel plates, applying a pressing force of about 13+/-1 kN between the two parallel plates, stopping pressing once the pressing force reaches the maximum value, and keeping for 3min; the test was conducted by taking 10 batteries as the pass of the test without ignition or explosion of the batteries, and the screw extrusion pass rate=throughput/10 was conducted in parallel.
Rate capability (2C/0.2C) test
In the environment of (25±3) °c, the battery was charged constant-current with a current of 0.5C to a voltage of 4.45V, then charged constant-voltage to an off-current of 0.05C, and then full-discharged with constant currents of 0.2C and 2C to 3.0V, respectively, to obtain discharge capacities of 0.2C and 2C, respectively, with rate performance=2c discharge capacity/0.2c discharge capacity×100%.
Low temperature performance test
In the environment of (25+/-3) DEG C, the battery is charged to 4.45V by constant current at 0.5C, then is charged to 0.05C by constant voltage, and then is fully discharged to 3.0V by constant current at 0.2C, thus obtaining the normal temperature capacity at 0.2C; the battery is charged to 4.45V with 0.5C current in constant current, then is charged to 0.05C with constant voltage, the battery is kept under the environment of (-20+/-3) DEG C for 60min, and then is fully discharged to 3.0V with 0.2C constant current, so as to obtain 0.2C low-temperature capacity, wherein the low-temperature performance=0.2C low-temperature capacity/0.2C normal-temperature capacity multiplied by 100%
The thermogravimetric analysis method comprises the following steps:
1. taking a proper amount of sample and placing the sample into a crucible;
2. editing a test program, setting the heating rate to be 10 ℃/min, and setting the test temperature interval to be 25-600 ℃; the atmosphere is nitrogen atmosphere;
3. running a program, and obtaining a TG (gradient magnetic resonance) and DSC curve after the test is finished; and obtaining the corresponding weight loss rate and peak area ratio according to the TG and DSC curves.
The following table 2 shows the properties of examples 1 to 46 and comparative examples 1 to 4.
TABLE 2
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Note that: the peak area ratio in table 2 is the area ratio of the first peak in the 300 ℃ to 400 ℃ range to the second peak in the 410 ℃ to 600 ℃ range of the differential thermogravimetric analysis curve of the film layer.
1. To investigate the presence or absence of functional layers
As is apparent from the above tables 1 and 2, the screw press passing rate of the lithium ion batteries of examples 1 to 46 having a functional layer and comparative examples 2 to 4 having a functional layer was significantly superior to that of the lithium ion battery of comparative example 1 having no functional layer. Therefore, the functional layer is arranged between the positive electrode current collector and the positive electrode active material layer, so that the screw extrusion passing rate of the electrochemical device can be remarkably improved.
2. When the binding force F1 (N/m) between the positive electrode active material layer and the functional layer, and the binding force F2 (N/m) between the functional layer and the positive electrode current collector are examined, as shown in the above tables 1 and 2, the screw extrusion transmittance of the corresponding lithium ion battery is remarkably improved when the binding force F2 (N/m) between the functional layer and the positive electrode current collector satisfies 0.1.ltoreq.F1/F2.ltoreq.0.5. On the one hand, F1/F2 is more than or equal to 0.1, so that the cohesiveness between the positive electrode active material layer and the functional layer is not much weaker than the cohesiveness between the functional layer and the current collector, and the risk of falling off between the positive electrode active material layer and the functional layer can be reduced when the positive electrode active material layer is extruded from the outside, and the occurrence of internal short circuit caused by falling off of the positive electrode active material layer is prevented; on the other hand, F1/F2 is less than or equal to 0.5, and the functional layer can be ensured to be better extended along with the positive current collector when being extruded by the outside, so that the risk of internal short circuit caused by penetration of a isolating film by metal burrs is reduced, and the safety performance of the electrochemical device is improved.
3. Discussion of functional layer thickness
From examples 1-25 to 27-46 in tables 1 and 2 above, it is understood that the electrochemical device can have a higher screw press passage rate when the thickness T1 (in μm) of the functional layer and the thickness T2 (in μm) of the positive electrode active material layer satisfy 0.5.ltoreq.T1.ltoreq.10 and 5.ltoreq.T2/T1.ltoreq.20.
The present application has been studied to find that too large a thickness T1 of the functional layer (e.g., greater than 10 μm) may unreasonably reduce the energy density of the electrochemical device. Too thin a thickness T1 of the functional layer (e.g., less than 0.5 μm) may be prone to overcoating. In the range, the shielding effect of the functional layer on the metal burrs can be improved, so that the risk of internal short circuit caused by the penetration of the metal burrs through the isolating film when the isolating film is extruded by the outside is reduced; meanwhile, in the range, the thickness of the functional layer and the thickness of the positive electrode active material layer can be more matched, the risk that the positive electrode active material layer falls off when being extruded by the outside is reduced, and the safety performance of the electrochemical device is further improved. For example, the T2/T1 of example 26 was 50, and the screw crush pass rate of the lithium ion battery prepared therefrom was 6/10, which is significantly lower than that of the other examples.
4. First, second and third particles in the functional layer
The functional layer of the present application including the first particles (insulating particles), the first conductive agent (conductive particles), and the third particles (particles that can be used as a positive electrode active material) can further improve the screw extrusion passage rate of the electrochemical device. As can be seen from a combination of tables 1 and 2, the first particles of examples 1 to 46 were boehmite and alumina, the first conductive agent was conductive carbon super p, carbon Nanotube (CNT), and carbon fiber, and the third particles were LFP (lithium iron phosphate) and LMFP (lithium manganese iron phosphate), which all obtained the desired screw extrusion passage rate. In addition, the third particles contained in the functional layer may also serve as a positive electrode active material, thereby further increasing the energy density of the electrochemical device.
In addition, it is to be understood that the composition of the functional layer of the present application is not limited to the kind specifically exemplified in the examples, wherein the first particles may include at least one of aluminum oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, diaspore, barium sulfate, calcium sulfate, or calcium silicate, and the third particles may include at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganate, or lithium nickel cobalt manganate.
5. Adhesive agent
The first binder used for the functional layer in examples 1 to 46 of the present application was acrylonitrile, acrylate, and acrylamide polymer, and the second binder used for the positive electrode active material layer was PVDF, polyacrylic acid, nitrile rubber, polytetrafluoroethylene-hexafluoropropylene, and the mass percentage of the first binder was W1% based on the mass of the functional layer, and the mass percentage of the second binder was W2% based on the mass of the positive electrode active material layer, wherein W2 < W1. By designing the kinds and contents of the first binder and the second binder, a positive electrode satisfying the aforementioned binding force requirements can be produced.
In addition, it should be understood that the binders used in the present application are not limited to the types set forth in the specific examples. Those skilled in the art will appreciate the use of a variety of suitable binder combinations based on the inventive concepts of the present application.
6. Thermogravimetric analysis
The differential thermogravimetric analysis curve of the functional layer and the positive electrode active material layer of the present application has a first peak in the range of 300 ℃ to 400 ℃ and a second peak in the range of 410 ℃ to 600 ℃, wherein the area ratio of the first peak to the second peak is X, wherein X is 0.1.ltoreq.x.ltoreq.0.5. Wherein the first peak represents the first binder in the functional layer and the second peak represents the second binder in the positive electrode active material layer. Through the area ratio X in the range, the functional layers have good thermal stability, and the falling-off of the functional layers and the positive electrode current collector at high temperature can be inhibited, so that the safety performance of the electrochemical device is improved.
7. Leveling agent
The leveling agent used for the functional layers in examples 1 to 46 of the present application is a siloxane-based compound. It is understood that it may also be at least one of an oxygen-containing olefin polymer, a carboxylate compound, an alcohol compound, an ether compound, or a fluorocarbon compound, and the mass percentage of the leveling agent is 0.01% to 0.5% based on the mass of the functional layer. The addition of the leveling agent is beneficial to forming a uniform and smooth functional layer, increasing the contact area of the functional layer, the current collector and the active material layer, increasing the cohesiveness and further improving the safety performance of the electrochemical device.
In summary, the electrochemical device of the application has a high screw extrusion passing rate and maintains good electrochemical performance.
Reference throughout this specification to "some embodiments," "one embodiment," "another example," "an example," "a particular example," or "a partial example" means that at least one embodiment or example in the present application includes the particular feature, structure, material, or characteristic described in the embodiment or example. Thus, descriptions appearing throughout the specification, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "example," which do not necessarily reference the same embodiments or examples in the application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.
Although illustrative embodiments have been shown and described, it will be understood by those skilled in the art that the foregoing embodiments are not to be construed as limiting the application, and that changes, substitutions and alterations may be made herein without departing from the spirit, principles and scope of the application.

Claims (10)

1. An electrochemical device comprising a positive electrode comprising:
the positive electrode current collector and the film layer positioned on the surface of the positive electrode current collector;
the film layer comprises a positive electrode active material layer and a functional layer positioned between the positive electrode current collector and the positive electrode active material layer;
the binding force between the positive electrode active material layer and the functional layer is F1N/m, and the binding force between the functional layer and the positive electrode current collector is F2N/m, so that F1/F2 is more than or equal to 0.1 and less than or equal to 0.5.
2. The electrochemical device of claim 1, wherein the positive electrode satisfies at least one of the following conditions:
(a)10≤F1≤30；
(b)50≤F2≤300。
3. the electrochemical device according to claim 1, wherein the functional layer has a thickness of T1 μm and the positive electrode active material layer has a thickness of T2 μm, satisfying 0.5.ltoreq.t1.ltoreq.10; T2/T1 is more than or equal to 5 and less than or equal to 20.
4. The electrochemical device of claim 1, wherein the membrane layer has a weight loss ratio a at 600 ℃ as detected by thermogravimetric analysis under nitrogen atmosphere, and the electrochemical device has a resistance R Ω in a fully charged state, satisfying at least one of the following conditions: (I) R is more than or equal to 0.1A and less than or equal to 10A; (II) A is more than or equal to 1 and less than or equal to 20; (III) R is more than or equal to 10 and less than or equal to 50.
5. The electrochemical device of claim 1, wherein the membrane layer has a differential thermogravimetric analysis curve with a first peak in the range of 300 ℃ to 400 ℃ and a second peak in the range of 410 ℃ to 600 ℃, the area ratio of the first peak to the second peak being X, satisfying 0.1 ∈x ∈0.5.
6. The electrochemical device according to claim 1, wherein the functional layer has a weight loss ratio of (100-A1)% at 600 ℃ and the positive electrode active material layer has a weight loss ratio of (100-A2)% at 600 ℃ as detected by thermogravimetric analysis under a nitrogen atmosphere, satisfying at least one of the following conditions:
(i)80≤A1≤95；
(ii)95≤A2≤99；
(iii)1≤A2/A1<1.3。
7. the electrochemical device of claim 1, wherein the functional layer comprises first particles, a first conductive agent, a first binder, satisfying at least one of the following conditions:
(1) The first particles comprise a first metal element, and the first metal element comprises at least one of Al, mg, ca, ti, ce, zn, Y, hf, zr, ba, sn or Ni, wherein the mass percentage of the first particles is a% based on the mass of the functional layer, and the mass percentage of the first particles is more than or equal to 1 and less than or equal to 40;
(2) The first conductive agent comprises at least one of graphene, carbon nano tubes, carbon black, graphite fibers or conductive carbon, wherein the mass percentage of the first conductive agent is b% based on the mass of the functional layer, and the mass percentage of the first conductive agent is more than or equal to 0.3 and less than or equal to 5;
(3) The functional layer further comprises third particles, wherein the third particles comprise lithium and a second metal element, and the second metal element comprises at least one of Fe, mn, al, mg, co or Ni, and the mass percentage of the third particles is c percent, so that the mass percentage of the third particles is 40-94.5;
(4) The first binder comprises a polymer formed by at least one of acrylic acid, acrylamide, acrylic acid salt, acrylonitrile or acrylic acid ester, wherein the mass percentage of the first binder is d percent based on the mass of the functional layer, and the d is more than or equal to 3 and less than or equal to 15;
(5) The first binder is an aqueous binder;
(6) The functional layer further comprises a leveling agent, wherein the leveling agent comprises at least one of siloxane compounds, oxygen-containing olefin polymers, carboxylate compounds, carboxylic ester compounds, alcohol compounds, ether compounds or fluorocarbon compounds, and the mass percentage of the leveling agent is less than or equal to 1% based on the mass of the functional layer;
(7) The first particles comprise at least one of alumina, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, diaspore, barium sulfate, calcium sulfate, or calcium silicate; the third particles comprise at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganate or lithium nickel cobalt manganate.
8. The electrochemical device according to claim 7, wherein the positive electrode active material layer includes a second binder having a composition different from that of the first binder, the first binder being W1% by mass based on the mass of the functional layer, the second binder being W2% by mass < W1% by mass based on the mass of the positive electrode active material layer.
9. The electrochemical device of claim 1, wherein the positive electrode active material layer comprises an active material, a second conductive agent, and a second binder, satisfying at least one of the following conditions:
(7) Based on the mass of the positive electrode active material layer, the mass percentage of the active material is 95 to 98.5%, the mass percentage of the second conductive agent is 0.5 to 2%, and the mass percentage of the second binder is 1 to 3%;
(8) The second binder comprises at least one of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene-hexafluoropropylene, sodium polyacrylate, nitrile rubber or polyacrylate.
10. An electronic device comprising the electrochemical device according to any one of claims 1-9.
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