CN116830287A - An electrochemical device and an electronic device - Google Patents
An electrochemical device and an electronic device Download PDFInfo
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- CN116830287A CN116830287A CN202280010582.4A CN202280010582A CN116830287A CN 116830287 A CN116830287 A CN 116830287A CN 202280010582 A CN202280010582 A CN 202280010582A CN 116830287 A CN116830287 A CN 116830287A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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Abstract
本申请涉及一种电化学装置，其包含正极，所述正极包括：正极集流体；功能层；和正极活性材料层。所述功能层设置于所述正极集流体与所述正极活性材料层之间。所述功能层的厚度为Tμm，所述电化学装置在满充状态下，所述正极的电阻为RΩ，通过满足2≤T×R≤200，可以在有效提高电化学装置安全性能的同时，将电化学装置的电化学性能维持在较高水平。The present application relates to an electrochemical device including a positive electrode, which includes: a positive current collector; a functional layer; and a positive active material layer. The functional layer is disposed between the cathode current collector and the cathode active material layer. The thickness of the functional layer is Tμm. When the electrochemical device is fully charged, the resistance of the positive electrode is RΩ. By satisfying 2≤T×R≤200, the safety performance of the electrochemical device can be effectively improved. Maintain the electrochemical performance of the electrochemical device at a high level.
Description
Technical Field
The present application relates to the field of energy storage, and in particular, to an electrochemical device 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. However, during the use process of the lithium ion battery, the lithium ion battery may be impacted by external force or pierced by foreign matters, so that the internal short circuit of the positive electrode and the negative electrode is caused, and serious consequences such as smoke generation or fire explosion of the battery are 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: a positive electrode current collector; a functional layer; and a positive electrode active material layer. The functional layer is disposed between the positive electrode current collector and the positive electrode active material layer. The thickness of the functional layer is T mu m, and the resistance of the positive electrode is RΩ under the full charge state of the electrochemical device, so that the T multiplied by R is more than or equal to 2 and less than or equal to 200. By controlling the thickness T of the functional layer and the resistance R of the positive electrode in the full charge state to meet the above relation, the electrochemical performance of the electrochemical device can be maintained at a higher level while the nailing safety performance of the electrochemical device is effectively improved.
In some embodiments, 0.5.ltoreq.T.ltoreq.10; and/or 1.ltoreq.R.ltoreq.10. By controlling T and R within the above ranges, the energy density and the piercing safety performance of the electrochemical device can be improved.
In some embodiments, the functional layer comprises first particles comprising a metallic element comprising at least one of Al, mg, ca, ti, ce, zn, Y, hf, zr, ba, sn or Ni and a first conductive agent.
In some embodiments, the first particles comprise 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, boehmite, barium sulfate, calcium sulfate, or calcium silicate.
In some embodiments, the first conductive agent comprises at least one of graphene, carbon nanotubes, carbon black, graphite fibers, or conductive carbon.
In some embodiments, the first particles have an average particle size of H1 μm and the first conductive agent has an average particle size of H2 μm, satisfying 0.5.ltoreq.H2.ltoreq.3. By controlling the relative sizes of the first particles and the first conductive agent, the positive electrode resistance R in the full charge state can be effectively controlled. When the sizes of the first particles and the first conductive agent satisfy the aforementioned relationship, it is possible to ensure that the electrochemical device has excellent electrochemical performance while effectively suppressing the nail penetration failure.
In some embodiments, the first particles have an average particle size of H1 μm, satisfying 0.8.ltoreq.T/H1.ltoreq.20. T/H1 in the above range can effectively reduce the missing coating and the particle scratch, thereby ensuring the covering effect of the functional layer, improving the electrochemical performance of the electrochemical device and reducing the energy density loss of the electrochemical device.
In some embodiments, the first particles have an average particle size of H1 μm, satisfying H1.ltoreq.0.6.
In some embodiments, the specific surface area BET of the first particles satisfies 5m 2 /g≤BET≤40m 2 /g。
In some embodiments, the functional layer comprises a binder and a leveling agent.
In some embodiments, the binder comprises a polymer formed from at least one of acrylic acid, acrylamide, an acrylate, acrylonitrile, or an acrylate.
In some embodiments, the weight average molecular weight of the binder is 70 to 80 tens of thousands.
In some embodiments, the binder is an aqueous binder.
In some embodiments, the binder is 2% to 20% by mass based on the mass of the functional layer.
In some embodiments, the leveling agent comprises at least one compound selected from the group consisting of a siloxane-based compound, an oxyalkylene-containing polymer, a carboxylate-based compound, an alcohol-based compound, an ether-based compound, and a fluorocarbon.
In some embodiments, the leveling agent is 0.01% to 0.5% by mass based on the mass of the functional layer.
In some embodiments, the thickness of the positive electrode active material layer is T2 μm, satisfying T2/T.ltoreq.30. By controlling the ratio of the thickness of the positive electrode active material layer to the thickness of the functional layer within the above range, contact between the puncture material and the positive electrode active material layer during the nailing process can be effectively suppressed, and thus the safety performance of the electrochemical device can be effectively improved.
In some embodiments, the positive electrode current collector has an area of W1cm 2 The area of the functional layer is W2cm 2 Satisfies 0.9.ltoreq.W2/W1.ltoreq.1.
In some embodiments, the orthographic projection of the functional layer on the surface of the positive electrode current collector covers the orthographic projection of the positive electrode active material layer on the surface of the positive electrode current collector.
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 "one of," "one of," or other similar terms may mean any of the listed items. For example, if items a and B are listed, the phrase "one of a and B" means either only a or only B. In another example, if items A, B and C are listed, one of the phrases "A, B and C" means only a; only B; or only 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.
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: a positive electrode current collector; a functional layer; and a positive electrode active material layer. The functional layer is disposed between the positive electrode current collector and the positive electrode active material layer. The thickness of the functional layer is T mu m, and the resistance of the positive electrode is RΩ in the full charge state of the electrochemical device. Satisfies the condition that T multiplied by R is less than or equal to 2 and less than or equal to 200.
According to the application, the functional layer is arranged between the positive electrode current collector and the positive electrode active material layer, so that the fire failure of the electrochemical device during nailing can be inhibited. Meanwhile, the application is obtained through a series of researches: by controlling the thickness T (in μm) of the functional layer and the resistance R (in Ω) of the positive electrode in the full charge state to satisfy the above-described relationship, the electrochemical performance of the electrochemical device can be maintained at a high level while effectively improving the nail penetration safety performance of the electrochemical device. In some embodiments, 2.ltoreq.TxR.ltoreq.150. In some embodiments, 2.ltoreq.T.ltoreq.R.ltoreq.100. In some embodiments, 2.ltoreq.T.ltoreq.R.ltoreq.65. In some embodiments, 2.ltoreq.TxR.ltoreq.30. In some embodiments, the value of t×r is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, or a range between any two of the foregoing values.
In some embodiments, 0.5.ltoreq.T.ltoreq.10. In some embodiments, 0.5.ltoreq.T.ltoreq.8. In some embodiments, 0.8.ltoreq.T.ltoreq.6. In some embodiments, 1.ltoreq.T.ltoreq.5. In some embodiments, 1.5.ltoreq.T.ltoreq.4. In some embodiments, 2.ltoreq.T.ltoreq.3. In some embodiments, T may be 0.3, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.5, 2.6, 2.8, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8, 8.5, 9, 9.5, 10, or a range between any two of the foregoing values.
In some embodiments, 1.ltoreq.R.ltoreq.10. In some embodiments, 1.5.ltoreq.R.ltoreq.9. In some embodiments, 1.6.ltoreq.R.ltoreq.8. In some embodiments, 1.8.ltoreq.R.ltoreq.7. In some embodiments, 2.0.ltoreq.R.ltoreq.6. In some embodiments, 2.2.ltoreq.R.ltoreq.5. In some embodiments, R may be 1.0, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8, 8.5, 9, 9.5, 10, or a range between any two of the foregoing values.
The inventors of the present application have recognized that, on the one hand, too thick a functional layer reduces the energy density of the electrochemical device, and too thin a functional layer causes missing coating, which is not effective in improving the safety performance of the nail. On the other hand, the functional layer and the positive electrode active material layer as a whole, too large positive electrode resistance in the full charge state cannot form an effective electrochemical device, and too small resistance tends to cause a decrease in safety in the case of nailing. Therefore, by controlling T and R within the above-described ranges, the energy density and the piercing safety performance of the electrochemical device can be improved.
In some embodiments, the functional layer comprises first particles comprising a metallic element comprising at least one of Al, mg, ca, ti, ce, zn, Y, hf, zr, ba, sn or Ni and a first conductive agent.
In some embodiments, the first particles comprise 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, boehmite, barium sulfate, calcium sulfate, or calcium silicate. The addition of the first particles can increase the resistance of the functional layer, thereby improving the nail penetration safety performance of the electrochemical device.
In some embodiments, the first conductive agent comprises at least one of graphene, carbon nanotubes, carbon black, graphite fibers, or conductive carbon. The addition of the first conductive agent can increase the conductivity of the functional layer, thereby improving the electrochemical performance of the electrochemical device.
In some embodiments, the first particles have an average particle size of H1 μm and the first conductive agent has an average particle size of H2 μm, satisfying 0.5.ltoreq.H2.ltoreq.3. In some embodiments, H1/H2 may be 0.5, 0.6, 0.8, 1, 1.5, 2.0, 2.5, 3, or a range between any two of the foregoing values. For measurement of the average particle diameter of the particles, SEM photographs of the functional layer samples were taken with a scanning electron microscope, then 30 particles were randomly selected from the SEM photographs using image analysis software, and the respective areas of the particles were determined, and then, assuming that the particles were spherical, the respective particle diameters D (diameters) were determined by the following formula: d=2× (S1/pi) 1/2 The method comprises the steps of carrying out a first treatment on the surface of the Wherein S1 is the area of the particles; and the particle diameters of the obtained 30 particles were arithmetically averaged to obtain an average particle diameter H of the particles. By controlling the relative sizes of the first particles and the first conductive agent, the resistance R of the positive electrode in the full charge state can be effectively controlled. When the sizes of the first particles and the first conductive agent satisfy the aforementioned relationship, it is possible to ensure that the electrochemical device has excellent electrochemical performance while effectively suppressing the nail penetration failure.
In some embodiments, the ratio of the number of the first particles to the number of the first conductive agent is 1 to 200 in the positive electrode range of 5 μm×5 μm. In some embodiments, the ratio of the number of the first particles to the number of the first conductive agent is 20 to 150 in the positive electrode range of 5 μm×5 μm. By controlling the ratio of the first particles to the number of particles of the first conductive agent, the safety performance of the electrochemical device can be ensured while the electrochemical performance of the electrochemical device is ensured.
In some embodiments, the first particles have an average particle size of H1 μm, satisfying 0.8.ltoreq.T/H1.ltoreq.20. In some embodiments, 2.ltoreq.T/H1.ltoreq.10. T/H1 in the above range can effectively reduce the missing coating and the particle scratch, thereby ensuring the covering effect of the functional layer, improving the electrochemical performance of the electrochemical device and reducing the energy density loss of the electrochemical device.
In some embodiments, the first particles have an average particle size of H1 μm, satisfying H1.ltoreq.0.6. In some embodiments, 0 < H1.ltoreq.0.5. In some embodiments, 0 < H1.ltoreq.0.4 μm.
In some embodiments, the specific surface area BET of the first particles satisfies 5m 2 /g≤BET≤40m 2 And/g. In some embodiments, 10m 2 /g≤BET≤30m 2 /g。
In some embodiments, the functional layer comprises a binder, wherein the binder comprises a polymer formed of at least one of acrylic acid, acrylamide, an acrylate, acrylonitrile, or an acrylate.
In some embodiments, the weight average molecular weight of the binder is 70 to 80 tens of thousands.
In some embodiments, the 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 binder is 2% to 20% by mass based on the mass of the functional layer.
In some embodiments, the functional layer 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.
In some embodiments, the leveling agent is 0.01% to 0.5% by mass based on the mass of the functional layer.
In some embodiments, the thickness of the positive electrode active material layer is T2 μm, satisfying T2/T.ltoreq.30. In some embodiments, T2/T.ltoreq.25. In some embodiments, T2/T.ltoreq.20. In some embodiments, T2/T.ltoreq.15. In some embodiments, T2/T.ltoreq.10. In some embodiments, T2/T may be 8, 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30, etc. By controlling the ratio of the thickness of the positive electrode active material layer to the thickness of the functional layer within the above range, contact between the puncture material and the positive electrode active material layer during the nailing process can be effectively suppressed, and thus the safety performance of the electrochemical device can be effectively improved.
In some embodiments, the positive electrode current collector has an area of W1cm 2 The area of the functional layer is W2cm 2 Satisfies 0.9.ltoreq.W2/W1.ltoreq.1. In some embodiments, W2/W1 may be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or a range between any two of the foregoing values. By controlling the coverage area of the functional layer within the above range, the safety performance of the electrochemical device can be further improved.
In some embodiments, the orthographic projection of the functional layer on the surface of the positive electrode current collector covers the orthographic projection of the positive electrode active material layer on the surface of the positive electrode current collector. At this time, a functional layer is provided under the entire positive electrode active material layer, so that the safety performance of the electrochemical device can be further improved.
In some embodiments, the central penetration rate of the electrochemical device is greater than or equal to 90%. In some embodiments, the center pin passing rate of the electrochemical device is greater than or equal to 92%. In some embodiments, the center pin passing rate of the electrochemical device is greater than or equal to 94%. In some embodiments, the center pin passing 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 or 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: lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries.
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, the first conductive agent and the binder, and 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 positive electrode 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 part by weight 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 positive electrode 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 positive electrode binder may aid in adhesion between the active material and the second conductive agent, or between the active material and the current collector. Examples of the positive electrode binder include, but are not limited to, polyvinylidene fluoride, polyvinylidene chloride, carboxymethyl cellulose, polyvinyl acetate, polyvinyl pyrrolidone, polypropylene, polyethylene, and various polymers. The amount of the positive electrode 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 positive electrode 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 100 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 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) or lithium difluorooxalato borate LiBF 2 (C 2 O 4 ) At least one of (LiDFOB).
In some embodiments, the lithium salt content is 5% -30% based on the mass of the electrolyte. In some embodiments, the lithium salt is present in an amount of 6% to 25% based on the mass of the electrolyte. In some embodiments, the lithium salt is present in an amount of 8% to 20% based on the mass of the electrolyte. In some embodiments, the lithium salt is present in an amount of 6% to 18% based on the mass of the electrolyte.
In some embodiments, the additive comprises at least one of fluoroethylene carbonate, ethylene carbonate, vinyl ethylene carbonate, 1, 3-propane sultone, vinyl sulfate, adiponitrile, succinonitrile, glutaronitrile, 1,3, 6-hexanetrinitrile, 1,2, 6-hexanetrinitrile, succinic anhydride, lithium difluorophosphate, lithium tetrafluoroborate.
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, home-use large-sized storage batteries, 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 43 and comparative examples 1 to 3
Step (1): adding the first particles, the first conductive agent and the binder, and optionally the leveling agent, into deionized water, and uniformly mixing to obtain a slurry of the functional layer (hereinafter referred to as "first slurry");
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 a positive electrode active material (lithium cobaltate, 97.3 mass percent), a second conductive agent (super P, 0.6 mass percent and carbon nano tube CNT, 0.5 mass percent) and a positive electrode binder (PVDF, 1.6 mass percent) in an N-methylpyrrolidone 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.
The following table 1 specifically shows the functional layer differences in the positive electrodes in examples 1 to 43 and comparative examples 1 to 3.
TABLE 1
Except for the above differences, the negative electrodes, electrolytes, separators, and the like in examples 1 to 43 and comparative examples 1 to 3 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 carboxymethyl cellulose (CMC) in a deionized water solvent system according to the mass ratio of 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) and Propylene Carbonate (PC) according to the weight ratio of 2:6:2, and then 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 contents of the substances are based on the total weight of the electrolyteAnd (5) counting.
Isolation film: PE porous polymeric film is used as a isolating film.
And stacking the anode, the isolating film and the cathode in sequence, enabling the isolating film to be positioned in the middle of the anode and the cathode to play a role of isolation, winding, placing in an outer package, injecting the prepared electrolyte, packaging, and carrying out processes such as formation, degassing, trimming and the like to obtain the lithium ion battery.
Performance test method
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 anode obtained in the step 2) under a Scanning Electron Microscope (SEM), measuring the thickness T mu m of the functional layer, and measuring at least 15 different points at intervals of 2mm to 3mm between adjacent test points, wherein the average value of all the measurement points is recorded as the thickness T 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 to 4.45V of full charge design voltage at a multiplying power of 0.05C, and then constant-voltage charging is carried out to 0.025C (cut-off current) at the full charge design voltage of 4.45V, 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 the step 2) in an environment with the humidity of 5-15% 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.
Penetration test
1) Constant-current charging is carried out on the lithium ion battery to 4.45V of full charge design voltage at the rate of 0.5C, and then constant-voltage charging is carried out on the lithium ion battery to 0.05C at the rate of 4.45V of full charge design voltage;
2) The high temperature resistant steel needle with the diameter of 3mm penetrates from the direction perpendicular to the long and wide plane of the lithium ion battery at the speed of 150mm/s, the penetrating point is the geometric center of the long and wide plane of the lithium ion battery, and the steel nail is reserved for 1 hour after the penetrating point is finished. And 10 lithium ion batteries are taken as a group, the states of the lithium ion batteries in the test process are observed, and the passing number of the lithium ion batteries is confirmed by taking the non-burning and non-explosion of the lithium ion batteries as passing standards. Central pass = number of passes/10.
Rate capacity retention (1.5C/0.2C)
In an environment of (25±3) °c, the lithium ion battery was charged constant-current to a full charge design voltage of 4.45V at a rate of 0.5C, then charged constant-voltage to an off-current of 0.05C at a full charge design voltage of 4.45V, and then discharged to 3.0V with 0.2C and 1.5C currents, respectively, to obtain discharge capacities of 0.2C and 1.5C, respectively, and a rate capacity retention ratio (1.5C/0.2C) =1.5C discharge capacity/0.2C discharge capacity.
The following table 2 shows the properties of examples 1 to 43 and comparative examples 1 to 3.
TABLE 2
1. To investigate the influence of the presence or absence of the functional layer, the thickness T of the functional layer, and the positive electrode resistance R in the full charge state on the performance of the electrochemical device
As can be seen from the above tables 1 and 2, the center through-pin passing rate (throughput/total test) of the lithium ion batteries of examples 1 to 43 having a functional layer and comparative examples 2 to 3 having a functional layer was significantly better than 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 central penetrating nail passing rate of the electrochemical device can be remarkably improved.
According to the application, through researches, when the thickness T (in terms of mum) of the functional layer and the positive electrode resistance R (in terms of omega) in a full charge state are satisfied with 2-T multiplied by R-200, the lithium ion battery can keep higher central through nail passing rate and higher multiplying power performance. For example, the thickness T of the functional layers in examples 1 to 43 and the positive electrode resistance R in the full charge state satisfy 2.ltoreq.TxR.ltoreq.200, the TxR in comparative example 2 is 253, the TxR in comparative example 3 is 1.6, the center pin passing rate of the lithium ion batteries of examples 1 to 43 is significantly superior to that of comparative example 3, and the rate performance is substantially equivalent to that of comparative example 3. The center pass rates of examples 1 to 43 were comparable to comparative example 2, but the rate performance was significantly better than comparative example 2.
According to the application, the research shows that too large thickness T of the functional layer can unreasonably reduce the energy density of the electrochemical device, and too thin thickness T of the functional layer can cause missing coating, so that the safety performance of the penetrating nail can not be effectively improved. When T is more than or equal to 0.5 and less than or equal to 10, the electrochemical device can obtain ideal central through-nail passing rate and multiplying power performance. On the other hand, the functional layer and the positive electrode active material layer as a whole, too large positive electrode resistance in the full charge state cannot form an effective electrochemical device, and too small resistance tends to cause a decrease in safety in the case of nailing. When R is more than or equal to 1 and less than or equal to 10, the electrochemical device can obtain ideal central piercing rivet passing rate and multiplying power performance.
2. Discussion of the Effect of the composition of the functional layer on the Performance of the electrochemical device
2.1 first particles and first conductive agent
The functional layer of the present application comprises first particles and a first conductive agent. As can be seen from a combination of tables 1 and 2, the first particles of examples 1 to 43 used boehmite and diaspore, and the first conductive agent used conductive carbon (Super P) and Carbon Nanotube (CNT), which can obtain the desired center-through passage rate and rate capacity retention rate. However, 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 alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, diaspore, barium sulfate, calcium sulfate, or calcium silicate, and the first conductive agent may include at least one of graphene, carbon nanotube, carbon black, graphite fiber, or conductive carbon.
The resistance of the functional layer can be adjusted by adjusting the particle size of the first particles and the particle size of the first conductive agent, thereby affecting the central piercing rate and electrochemical performance of the electrochemical device. For example, as is clear from the combination of tables 1 and 2, the first particles in the examples of the present application have an average particle diameter of H1 μm, a thickness of the functional layer of T μm, examples 6 to 34, 36 to 37, 39 to 43 satisfying 2.ltoreq.T/H1.ltoreq.10, have a significantly improved center-through passage ratio relative to example 35 where T/H1 is 0.8, and have a significantly improved rate capacity retention ratio relative to example 38 where T/H1 is 16.7. Therefore, the lithium ion battery has better comprehensive performance by meeting the requirement that T/H1 is less than or equal to 2 and less than or equal to 10.
Further, by adjusting the relation between the first particles and the particle size of the first conductive agent, a good conductive network is formed in the functional layer, so that the electron transmission efficiency can be improved, the resistance between the current collector and the active material layer can be reduced, and the rate performance of the lithium ion battery can be improved. As can be seen from the results of Table 1 and Table 2, the average particle diameter H1 μm of the first particles and the average particle diameter H2 μm of the second particles were such that the retention rate of the rate capacity of the obtained lithium ion battery was 80% or more when 0.5.ltoreq.H2.ltoreq.3 was satisfied.
In addition, by controlling the ratio of the thickness of the positive electrode active material layer to the thickness of the functional layer within a proper range, contact between the puncture object and the positive electrode active material layer in the nailing process can be effectively inhibited, and thus the nailing safety performance of the electrochemical device can be effectively improved. For example, examples 8 to 34, in which the thickness T2 μm of the positive electrode active material layer and the thickness T μm of the functional layer were satisfied with T2/T.ltoreq.30, were able to be significantly improved by example 35, in which the center pin passing rate of the lithium ion battery was 36 with respect to T2/T.
2.2 binders, leveling Agents
The binders used for the functional layers in examples 1 to 43 of the present application are acrylonitrile, acrylate, acrylamide polymers. However, it should be understood that the binder used in the functional layer of the present application is not limited to the kind exemplified in the specific examples, and may include a polymer formed of at least one of acrylic acid, acrylamide, acrylate, acrylonitrile, or acrylate. The weight average molecular weight of the binders of examples 1 to 43 of the present application is 70 to 80 tens of thousands, and the mass percentage thereof is 2 to 20%. By adjusting the mass fraction of the binder in the functional layer, the better binding force among the active material, the functional layer and the current collector can be ensured, and the loosening and even falling-off of the active material layer under abnormal conditions can be reduced, so that the nailing safety performance and the electrochemical performance of the electrochemical device can be improved.
The leveling agent used for the functional layer in the embodiment of the application is a siloxane compound or an oxygen-containing olefin polymer. It is understood that it may also be at least one of 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 and improving the safety performance. For example, example 5, with the corresponding addition of the leveling agent polydimethylsiloxane, had improved center pin passage relative to examples 1-4, 6-7, with no leveling agent added.
3. Functional layer coverage area
The area of the positive electrode current collector is W1cm 2 The area of the functional layer is W2cm 2 According to the application, through setting W2/W1 to be more than or equal to 0.9 and less than or equal to 1, the function of the functional layer can be better played, and the nailing safety performance of the electrochemical device is improved.
In summary, the electrochemical device of the application has a higher central piercing rate and maintains a higher rate capability.
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)
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