WO2023184228A1

WO2023184228A1 - Electrochemical device and electronic device

Info

Publication number: WO2023184228A1
Application number: PCT/CN2022/084043
Authority: WO
Inventors: 陈梅锋; 韩冬冬; 刘晓欠
Original assignee: 宁德新能源科技有限公司
Priority date: 2022-03-30
Filing date: 2022-03-30
Publication date: 2023-10-05
Also published as: CN116830287A

Abstract

The present application relates to an electrochemical device, comprising a positive electrode. The positive electrode comprises: a positive electrode current collector; a function layer; and a positive electrode active material layer. The function layer is disposed between the positive electrode current collector and the positive electrode active material layer. The thickness of the function layer is T μm, the resistance of the positive electrode is R Ω when the electrochemical device is in a fully charged state, and 2≤T×R≤200 is satisfied, such that the electrochemical performance of the electrochemical device can be maintained at a high level while effectively improving the safety performance of the electrochemical device.

Description

An electrochemical device and an electronic device

Technical field

This application relates to the field of energy storage, and specifically to an electrochemical device and an electronic device.

Background technique

With the popularity of electronic products such as laptops, mobile phones, handheld game consoles, and tablet computers, safety requirements for electrochemical devices (such as lithium-ion batteries) are becoming more and more stringent. However, during use, lithium-ion batteries may be impacted by external forces or punctured by foreign objects, which may cause short circuits in the positive and negative electrodes, leading to serious consequences such as heating, smoke, or fire and explosion of the battery.

Contents of the invention

According to one aspect of the present application, the present application relates to an electrochemical device including 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 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, which satisfies 2≤T×R≤200. By controlling the thickness T of the functional layer and the resistance R of the positive electrode in the fully charged state to satisfy the above relationship, the electrochemical performance of the electrochemical device can be maintained at a high level while effectively improving the safety performance of nail penetration of the electrochemical device.

In some embodiments, 0.5≤T≤10; and/or 1≤R≤10. By controlling T and R within the above ranges, the energy density and nail penetration safety performance of the electrochemical device can be improved.

In some embodiments, the functional layer includes first particles and a first conductive agent, the first particles include metal elements, and the metal elements include Al, Mg, Ca, Ti, Ce, Zn, Y, Hf, At least one of Zr, Ba, Sn or Ni.

In some embodiments, the first particles comprise aluminum oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, boehmite , at least one of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, diaspore, barium sulfate, calcium sulfate or calcium silicate.

In some embodiments, the first conductive agent includes at least one of graphene, carbon nanotubes, carbon black, graphite fiber, or conductive carbon.

In some embodiments, the average particle diameter of the first particles is H1 μm, and the average particle diameter of the first conductive agent is H2 μm, satisfying 0.5≤H1/H2≤3. By controlling the relative sizes of the first particles and the first conductive agent, the positive electrode resistance R in the fully charged state can be effectively controlled. When the sizes of the first particles and the first conductive agent satisfy the aforementioned relationship, the failure of nail penetration can be effectively suppressed while ensuring that the electrochemical device has excellent electrochemical performance.

In some embodiments, the average particle diameter of the first particles is H1 μm, satisfying 0.8≤T/H1≤20. T/H1 within the above range can effectively reduce coating leakage and particle scratches, thereby ensuring the coverage effect of the functional layer. It can also improve the electrochemical performance of the electrochemical device and reduce the energy density loss of the electrochemical device.

In some embodiments, the average particle diameter of the first particles is H1 μm, satisfying H1≤0.6.

In some embodiments, the specific surface area BET of the first particle satisfies 5 m ² /g ≤ BET ≤ 40 ^{m 2} /g.

In some embodiments, the functional layer includes a binder and a leveling agent.

In some embodiments, the binder includes a polymer formed from at least one of acrylic acid, acrylamide, acrylate, acrylonitrile, or acrylate.

In some embodiments, the binder has a weight average molecular weight of 700,000 to 800,000.

In some embodiments, the binder is an aqueous binder.

In some embodiments, the mass percentage of the binder is 2% to 20% based on the mass of the functional layer.

In some embodiments, the leveling agent includes silicone compounds, oxygen-containing olefin polymers, carboxylate compounds, carboxylate ester compounds, alcohol compounds, ether compounds, or fluorocarbon compounds. of at least one.

In some embodiments, the mass percentage of the leveling agent is 0.01% to 0.5% based on the mass of the functional layer.

In some embodiments, the thickness of the cathode active material layer is T2 μm, satisfying T2/T≤30. By controlling the ratio of the thickness of the positive active material layer to the thickness of the functional layer within the above range, the contact between the puncture object and the positive active material layer during the nailing process can be effectively suppressed, thereby effectively improving the safety performance of the electrochemical device.

In some embodiments, the area of the positive electrode current collector is W1cm ² and the area of the functional layer is W2cm ² , satisfying 0.9≤W2/W1≤1.

In some embodiments, the orthographic projection of the functional layer on the surface of the positive current collector covers the orthographic projection of the positive active material layer on the surface of the positive current collector.

According to another aspect of the present application, the present application relates to an electronic device comprising an electrochemical device according to any of the preceding embodiments.

Detailed ways

Hereinafter, the present application is described in detail. It is to be understood that the terms used in the specification and appended claims should not be construed to be limited to their ordinary and dictionary meanings, but rather on the basis that the inventor is allowed to appropriately define the terms for the best interpretation based on the principles associated with this application. The corresponding meanings and concepts of the technical aspects are explained. Accordingly, the descriptions shown in the embodiments described in the specification are specific examples for illustrative purposes only and are not intended to demonstrate all technical aspects of the application, and it will be understood that they may be completed by the time this application is filed. Many optional equivalents and variants.

In the detailed description and claims, a list of items connected by the term "one of," "one of," "one of," or other similar terms may mean any of the listed items. One. For example, if items A and B are listed, the phrase "one of A and B" means only A or only B. In another example, if the items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

In the detailed description and claims, a list of items connected by the term "at least one of," "at least one of," "at least one of," or other similar terms may mean that the listed items any combination of. 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 the 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 all of A, B and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

Additionally, quantities, ratios, and other numerical values are sometimes presented herein in range format. It should be understood that such range formats are for convenience and brevity, and should be flexibly construed to include not only the values expressly designated as range limits, but also all individual values or subranges encompassed within the stated range, as if expressly Specify each value and subrange individually.

1. Electrochemical device

The present application provides an electrochemical device, which includes a positive electrode including: 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. Satisfies 2≤T×R≤200.

This application can suppress the fire failure of the electrochemical device during nail penetration by arranging a functional layer between the positive electrode current collector and the positive electrode active material layer. At the same time, this application has concluded through a series of studies that by controlling the thickness T (in μm) of the functional layer and the resistance R (in Ω) of the positive electrode in the fully charged state to satisfy the above relationship, the electrochemical device can effectively improve the nail penetration. While maintaining safety performance, the electrochemical performance of the electrochemical device is maintained at a high level. In some embodiments, 2≤T×R≤150. In some embodiments, 2≤T×R≤100. In some embodiments, 2≤T×R≤65. In some embodiments, 2≤T×R≤30. In some embodiments, the value of T 30, 40, 50, 60, 70, 80, 90, 100, 150, 200 or the range between any two of the aforementioned values.

In some embodiments, 0.5≤T≤10. In some embodiments, 0.5≤T≤8. In some embodiments, 0.8≤T≤6. In some embodiments, 1≤T≤5. In some embodiments, 1.5≤T≤4. In some embodiments, 2≤T≤3. In some embodiments, T can 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 the range between any two of the aforementioned values.

In some embodiments, 1≤R≤10. In some embodiments, 1.5≤R≤9. In some embodiments, 1.6≤R≤8. In some embodiments, 1.8≤R≤7. In some embodiments, 2.0≤R≤6. In some embodiments, 2.2≤R≤5. In some embodiments, R can 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 the range between any two of the aforementioned values.

The inventor of the present application realized that, on the one hand, if the thickness of the functional layer is too thick, the energy density of the electrochemical device will be reduced; if the thickness of the functional layer is too thin, coating leakage will occur, and the safety performance of nail penetration cannot be effectively improved. On the other hand, as a whole, the functional layer and the cathode active material layer are as a whole. If the resistance of the cathode in the fully charged state is too large, it will not form an effective electrochemical device. If the resistance is too small, it will easily lead to reduced safety during nail penetration. Therefore, by controlling T and R within the above range, the energy density and nail penetration safety performance of the electrochemical device can be improved.

In some embodiments, the first particles comprise aluminum oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, boehmite , at least one of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, diaspore, 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 includes at least one of graphene, carbon nanotubes, carbon black, graphite fiber, or conductive carbon. The addition of the first conductive agent can improve the conductivity of the functional layer, thereby improving the electrochemical performance of the electrochemical device.

In some embodiments, the average particle diameter of the first particles is H1 μm, and the average particle diameter of the first conductive agent is H2 μm, satisfying 0.5≤H1/H2≤3. In some embodiments, H1/H2 can be 0.5, 0.6, 0.8, 1, 1.5, 2.0, 2.5, 3 or a range between any two of the aforementioned values. For the measurement of the average particle size of particles, use a scanning electron microscope to take SEM photos of the functional layer sample. Then, use image analysis software to randomly select 30 particles from the SEM photos and calculate the areas of each of these particles. Then, assume The particles are spherical, and the respective particle size D (diameter) is calculated by the following formula: D=2×(S1/π) ^1/2 ; where S1 is the area of the particle; and the particle diameters of the 30 particles obtained are calculated. average to obtain the average particle size 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 fully charged state can be effectively controlled. When the sizes of the first particles and the first conductive agent satisfy the aforementioned relationship, the failure of nail penetration can be effectively suppressed while ensuring that the electrochemical device has excellent electrochemical performance.

In some embodiments, within the positive electrode range of 5 μm×5 μm, the ratio of the number of the first particles to the number of the first conductive agent is 1 to 200. In some embodiments, within the positive electrode range of 5 μm×5 μm, the ratio of the number of the first particles to the number of the first conductive agent is 20 to 150. By controlling the ratio of the number of particles of the first particles to the first conductive agent, the safety performance of the electrochemical device can be ensured while ensuring the electrochemical performance of the electrochemical device.

In some embodiments, the average particle diameter of the first particles is H1 μm, satisfying 0.8≤T/H1≤20. In some embodiments, 2≤T/H1≤10. T/H1 within the above range can effectively reduce coating leakage and particle scratches, thereby ensuring the coverage effect of the functional layer. It can also improve the electrochemical performance of the electrochemical device and reduce the energy density loss of the electrochemical device.

In some embodiments, the average particle diameter of the first particles is H1 μm, satisfying H1≤0.6. In some embodiments, 0<H1≤0.5. In some embodiments, 0<H1≤0.4 μm.

In some embodiments, the specific surface area BET of the first particle satisfies 5 m ² /g ≤ BET ≤ 40 ^{m 2} /g. In some embodiments, 10 m ² /g ≤ BET ≤ 30 m ² /g.

In some embodiments, the functional layer includes a binder, wherein the binder includes a polymer formed from at least one of acrylic acid, acrylamide, acrylate, acrylonitrile, or acrylate.

In some embodiments, the binder is an aqueous binder. The water-based binder helps to improve the adhesion between the functional layer and the cathode current collector, allowing the functional layer to better adhere to the surface of the current collector, which can better improve the safety performance of the electrochemical device.

In some embodiments, the functional layer includes a leveling agent, and the leveling agent includes silicone compounds, oxygen-containing olefin polymers, carboxylate compounds, carboxylate ester compounds, alcohol compounds, At least one of ether compounds or fluorocarbon compounds.

In some embodiments, the thickness of the cathode active material layer is T2 μm, satisfying T2/T≤30. In some embodiments, T2/T≤25. In some embodiments, T2/T≤20. In some embodiments, T2/T≤15. In some embodiments, T2/T≤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 active material layer to the thickness of the functional layer within the above range, the contact between the puncture object and the positive active material layer during the nailing process can be effectively suppressed, thereby effectively improving the safety performance of the electrochemical device.

In some embodiments, the area of the positive electrode current collector is W1cm ² and the area of the functional layer is W2cm ² , satisfying 0.9≤W2/W1≤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 aforementioned 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 current collector covers the orthographic projection of the positive active material layer on the surface of the positive current collector. At this time, there is a functional layer underneath the entire positive active material layer, which can further improve the safety performance of the electrochemical device.

In some embodiments, the electrochemical device has a central nail penetration rate of ≥90%. In some embodiments, the electrochemical device has a center penetration rate of ≥92%. In some embodiments, the electrochemical device has a center penetration rate of ≥94%. In some embodiments, the electrochemical device has a center penetration rate of ≥96%.

In some embodiments, electrochemical devices of the present application include, but are not limited to: all kinds of primary or secondary batteries. 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 also includes a separator, an electrolyte and a negative electrode.

2. A method of preparing the aforementioned electrochemical device

The preparation method of 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: Disperse the negative electrode active material (at least one of carbon material, silicon material or lithium titanate) and the negative electrode binder in the solvent system according to a certain mass ratio, stir and mix evenly, and then apply it on the negative electrode assembly. On the fluid, after drying and cold pressing, the negative electrode is obtained.

Preparation of positive electrode:

(1) Add the first particles, the first conductive agent and the binder, and the optional leveling agent to the solvent and mix them evenly to obtain the slurry of the functional layer (hereinafter referred to as the "first slurry");

(2) Apply the first slurry in step (1) to the target area of the positive electrode current collector;

(3) Drying the positive electrode current collector containing the first slurry obtained in step (2) to remove the solvent to obtain the positive electrode current collector coated with the functional layer;

(4) Disperse the positive electrode active material (at least one of lithium cobalt oxide, lithium manganate or lithium iron phosphate), the second conductive agent, and the positive electrode binder in the solvent system according to a certain mass ratio, and stir thoroughly to mix evenly. Obtain the slurry of the positive electrode active material (hereinafter referred to as "second slurry");

(5) Coating the second slurry on the target area of the positive electrode current collector coated with the functional layer obtained in step (3);

(6) Dry the positive electrode current collector containing the second slurry in step (5) to remove the solvent, thereby obtaining the desired positive electrode.

In some embodiments, the second conductive agent improves the conductivity of the cathode active material layer by providing a conductive path to the active material. The second conductive agent may include at least one of the following: acetylene black, Ketjen black, natural graphite, carbon black, carbon fiber, metal powder or metal fiber (such as copper, nickel, aluminum or silver), but the second conductive agent Examples of the second conductive agent are not limited to these. In some embodiments, the amount of the second conductive agent can be appropriately adjusted. Based on 100 parts by weight of the total amount of the cathode active material, the second conductive agent and the cathode binder, the amount of the second conductive agent ranges from 1 to 30 parts by weight.

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 can be adjusted appropriately.

In some embodiments, the positive electrode binder can assist in bonding between the active material and the second conductive agent, or assist in bonding between the active material and the current collector. Examples of the positive electrode binder include, but are not limited to, polyvinylidene fluoride, polyvinylidene chloride, carboxymethylcellulose, polyvinyl acetate, polyvinylpyrrolidone, 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 microns to 20 microns, although the disclosure is not limited thereto. The current collector is electrically conductive and does not cause adverse chemical changes in the manufactured battery. Examples of the current collector include copper, stainless steel, aluminum, nickel, titanium, or alloys (eg, copper-nickel alloys), but the disclosure is not limited thereto. In some embodiments, fine irregularities (eg, 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 can be used in various forms, and examples thereof include films, sheets, foils, meshes, porous structures, foams, or similar materials, but the disclosure is not limited thereto.

Isolation film: In some embodiments, a polyethylene (PE) porous polymer film is used as the isolation film. In some embodiments, the material of the isolation membrane may include fiberglass, polyester, polyethylene, polypropylene, polytetrafluoroethylene or combinations thereof. In some embodiments, the pores in the isolation film have a diameter in the range of 0.01 micron to 1 micron, and the thickness of the isolation film ranges from 5 micron to 100 micron.

Electrolyte: In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and additives. In some embodiments, the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate At least one of ester 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 includes lithium hexafluorophosphate (LiPF ₆ ), lithium bis(fluorosulfonyl)imide LiN(CF ₃ SO ₂ ) ₂ (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO ₂ F) ₂ ) (LiFSI), lithium bisoxalatoborate LiB(C ₂ O ₄ ) ₂ (LiBOB) or lithium difluoroxalatoborate LiBF ₂ (C ₂ O ₄ ) (LiDFOB).

In some embodiments, the lithium salt content is 5%-30% based on the quality of the electrolyte. In some embodiments, the content of the lithium salt is 6%-25% based on the quality of the electrolyte. In some embodiments, the content of the lithium salt is 8%-20% based on the quality of the electrolyte. In some embodiments, the content of the lithium salt is 6%-18% based on the quality of the electrolyte.

In some embodiments, the additives include fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, vinyl sulfate, adiponitrile, succinonitrile, glutaronitrile , at least one of 1,3,6-hexanetrinitrile, 1,2,6-hexanetrinitrile, succinic anhydride, lithium difluorophosphate, and lithium tetrafluoroborate.

Stack the positive electrode, isolation film, and negative electrode in order so that the isolation film is between the positive and negative electrodes for isolation, and wind them to obtain a bare cell. The bare battery core obtained by winding is placed in an outer package, electrolyte is injected and packaged, and a lithium-ion battery is obtained through processes such as formation, degassing, and trimming.

3. Electronic devices

The present application provides an electronic device comprising the electrochemical device according to the foregoing content.

According to some embodiments of the present application, the electronic devices include, but are not limited to: notebook computers, pen-input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted Stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles , bicycles, lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, etc.

3. Specific Examples

The present application will be described in further detail below with reference to examples. However, it should be understood that the following embodiments are only examples, and the embodiments of the present application are not limited thereto.

Examples 1 to 43 and Comparative Examples 1 to 3

Step (1): Add the first particles, the first conductive agent and the binder, and the optional leveling agent to deionized water and mix evenly to obtain the slurry of the functional layer (hereinafter referred to as "the first slurry"). ");

Step (2): Apply the first slurry in step (1) to the target area of the positive electrode current collector;

Step (3): Dry the positive electrode current collector containing the first slurry in step (2) to remove the solvent, and obtain the positive electrode current collector coated with the functional layer;

Step (4): Combine the positive electrode active material (lithium cobalt oxide, mass percentage 97.3%), the second conductive agent (mass percentage 0.6% Super P and mass percentage 0.5% carbon nanotube CNT), the positive electrode binder (mass percentage 1.6 %PVDF) is dispersed in the N-methylpyrrolidone solvent system and stirred thoroughly to obtain a slurry of the positive electrode active material (hereinafter referred to as the "second slurry");

Step (5): Coating the second slurry on the target area of the positive electrode current collector coated with the functional layer obtained in step (3);

Step (6): Dry the positive electrode current collector containing the second slurry in step (5) to remove the solvent, thereby obtaining the desired positive electrode.

Table 1 below specifically shows the differences in functional layers in the positive electrodes in Examples 1 to 43 and Comparative Examples 1 to 3.

Table 1

Except for the above differences, there are no differences in the negative electrodes, electrolytes, separators, etc. in Examples 1 to 43 and Comparative Examples 1 to 3, and they are all prepared using the following process.

Negative electrode: Mix the active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) in deionized water at a mass ratio of 95:2:2:1. After the solvent system is fully stirred and mixed evenly, it is coated on a Cu foil, dried, and cold-pressed to obtain a negative electrode.

Electrolyte: In an argon atmosphere glove box with a water content of <10ppm, mix ethylene carbonate (abbreviated as EC), diethyl carbonate (abbreviated as DEC), and propylene carbonate (abbreviated as PC) according to 2:6:2 _Mix evenly at the _weight ratio of 2% adiponitrile. The content of each substance is based on the total weight of the electrolyte.

Isolation film: PE porous polymer film is used as the isolation film.

Stack the positive electrode, isolation film, and negative electrode in order, so that the isolation film is between the positive and negative electrodes for isolation, roll it up, place it in the outer package, inject the prepared electrolyte and package it, and then form and degas , trimming and other processes to obtain lithium-ion batteries.

Performance testing methods

Functional layer/positive electrode active material layer thickness

1) Remove the positive electrode coated with the functional layer from the lithium-ion battery in an environment of (25±3)℃. Use dust-free paper to wipe away the remaining electrolyte on the surface of the positive electrode;

2) Cut the positive electrode coated with the functional layer under plasma to obtain its cross section;

3) Observe the cross-section of the positive electrode obtained in 2) under a scanning electron microscope (SEM), and measure the thickness Tμm of the functional layer. The intervals between adjacent test points are 2mm to 3mm. Measure at least 15 different points, and record the average of all measurement points. is the thickness Tμm of the functional layer; the thickness T2μm of the positive electrode active material layer is measured in the same way.

Positive resistance in fully charged state

1) Charge with a constant current at a rate of 0.05C to the full charge design voltage of 4.45V, and then charge with a constant voltage of the full charge design voltage of 4.45V until the current is 0.025C (cut-off current), so that the lithium-ion battery reaches the full charge state;

2) Disassemble the lithium-ion battery to obtain the positive electrode;

3) Place the positive electrode obtained in 2) in an environment with a humidity of 5% to 15% for 30 minutes, and then seal and transfer it to the resistance test location;

4) Use the BER1200 diaphragm resistance tester to test the resistance of the positive electrode obtained in 3). The distance between adjacent test points is 2mm to 3mm. Test at least 15 different points. The average resistance of all test points is recorded as the positive electrode resistance in the fully charged state. R, where the test parameters are: pressure head area 153.94mm ² , pressure 3.5t, holding time 50s.

Nail penetration test

1) Charge the lithium-ion battery with a constant current at a rate of 0.5C to the full charge design voltage of 4.45V, and then charge with a constant voltage of the full charge design voltage of 4.45V to a cut-off current of 0.05C;

2) Use a high-temperature resistant steel needle with a diameter of 3mm to penetrate the needle in a direction perpendicular to the length and width of the lithium-ion battery at a speed of 150mm/s. The puncture point is the geometric center of the length and width of the lithium-ion battery. After completion, the steel needle remains 1 Hour. Take 10 lithium-ion batteries as a group, observe the status of the lithium-ion batteries during the test, and use the non-burning or non-explosion of the lithium-ion batteries as the passing standard to confirm the number of passed lithium-ion batteries. Center nail pass rate = number of passes/10.

Rate capacity retention rate (1.5C/0.2C)

In the environment of (25±3)℃, the lithium-ion battery is charged with a constant current at a rate of 0.5C to the full charge design voltage of 4.45V, and then charged with a constant voltage of the full charge design voltage of 4.45V to a cut-off current of 0.05C, and then charged with The 0.2C and 1.5C currents are discharged to 3.0V, and the discharge capacities of 0.2C and 1.5C are obtained respectively. The rate capacity retention rate (1.5C/0.2C) = 1.5C discharge capacity/0.2C discharge capacity.

Table 2 below shows various properties of Examples 1 to 43 and Comparative Examples 1 to 3.

Table 2

1. Explore the effects of the presence or absence of the functional layer, the thickness T of the functional layer, and the positive electrode resistance R in the fully charged state on the performance of the electrochemical device.

It can be seen from the above Table 1 and Table 2 that the center nail penetration rate (throughput/total test amount) of the lithium-ion batteries of Examples 1 to 43 with functional layers and Comparative Examples 2 to 3 with functional layers is significantly better than that without Lithium-ion battery of Comparative Example 1 of functional layer. It can be seen that providing a functional layer between the cathode current collector and the cathode active material layer can significantly improve the central nail penetration rate of the electrochemical device.

Through research, this application found that when the thickness T of the functional layer (measured in μm) and the positive electrode resistance R (measured in Ω) in the fully charged state satisfy 2≤T×R≤200, the lithium-ion battery can maintain a high Center-piercing nail pass rate while maintaining high magnification performance. For example, in Example 1-43, the thickness T of the functional layer and the positive electrode resistance R in the fully charged state both satisfy 2≤T×R≤200, in Comparative Example 2, T×R is 253, and in Comparative Example 3, T×R is 1.6, the center nail penetration rate of the lithium ion batteries of Examples 1 to 43 is significantly better than that of Comparative Example 3, and the rate performance is basically equivalent to Comparative Example 3. The central nail penetration rate of Examples 1 to 43 is comparable to that of Comparative Example 2, but the rate performance is significantly better than that of Comparative Example 2.

This application found through research that if the thickness T of the functional layer is too large, it will unreasonably reduce the energy density of the electrochemical device. If the thickness T of the functional layer is too thin, coating leakage will occur and the safety performance of nail penetration cannot be effectively improved. When 0.5≤T≤10, the electrochemical device can obtain ideal center-piercing throughput and rate performance. On the other hand, as a whole, the functional layer and the cathode active material layer are as a whole. If the resistance of the cathode in the fully charged state is too large, it will not form an effective electrochemical device. If the resistance is too small, it will easily lead to reduced safety during nail penetration. When 1 ≤ R ≤ 10, the electrochemical device can obtain ideal center penetration rate and rate performance.

2. Explore the impact 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 this application contains first particles and a first conductive agent. Combining Table 1 and Table 2, it can be seen that the first particles of Examples 1 to 43 used boehmite and diaspore, and the first conductive agent used conductive carbon (Super P) and carbon nanotubes (CNT), which can all be obtained Ideal center penetration rate and magnification capacity retention rate. However, it should be understood that the composition of the functional layer of the present application is not limited to the types specifically listed in the embodiments, wherein the first particles may include aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, and ceria. , nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, diaspore, barium sulfate, calcium sulfate or calcium silicate At least one, and the first conductive agent may include at least one of graphene, carbon nanotubes, carbon black, graphite fiber or conductive carbon.

By adjusting the particle size of the first particles and the particle size of the first conductive agent, the resistance of the functional layer can be adjusted, thereby affecting the central nail penetration rate and electrochemical performance of the electrochemical device. For example, combining Table 1 and Table 2, it can be seen that the average particle diameter of the first particles in the embodiments of the present application is H1 μm, the thickness of the functional layer is T μm, and Embodiments 6 to 34 and 36 to 2 ≤ T/H1 ≤ 10 are satisfied. 37, 39 to 43, compared to Example 35 with a T/H1 of 0.8, a significantly improved central nail penetration rate, and compared to Example 38 with a T/H1 of 16.7, a significantly improved rate capacity retention rate. It can be seen that by satisfying 2≤T/H1≤10, the lithium-ion battery can have better comprehensive performance.

Furthermore, by adjusting the relationship between the particle sizes of the first particles and the first conductive agent, a good conductive network is formed in the functional layer, which can improve the electron transmission efficiency and reduce the resistance between the current collector and the active material layer, thereby improving the Rate performance of lithium-ion batteries. Combining Table 1 and Table 2, it can be seen that the average particle size of the first particle is H1 μm, and the average particle size of the second particle is H2 μm. When 0.5≤H1/H2≤3 is satisfied, the rate capacity retention rate of the obtained lithium-ion battery is both 80 %above.

In addition, by controlling the ratio between the thickness of the positive active material layer and the thickness of the functional layer within an appropriate range, the contact between the puncture object and the positive active material layer during the nailing process can be effectively suppressed, thereby effectively improving the nailing performance of the electrochemical device. Safety performance. For example, in Examples 8 to 34 in which the thickness of the positive active material layer T2 μm and the thickness of the functional layer T μm satisfy T2/T≤30, the central nail penetration rate of the lithium ion battery is compared to the embodiment in which T2/T is 36. 35, can be significantly improved.

2.2 Binders and leveling agents

The binders used in the functional layers in Examples 1 to 43 of this application are acrylonitrile, acrylate, and acrylamide polymers. However, it should be understood that the binder used in the functional layer of the present application is not limited to the types listed in the specific embodiments. It may include a polymer formed from at least one of acrylic acid, acrylamide, acrylate, acrylonitrile, or acrylate. . The weight average molecular weight of the binders in Examples 1 to 43 of the present application is 700,000 to 800,000, and their mass percentage is 2% to 20%. By adjusting the mass fraction of the binder in the functional layer, a better bonding force between the active material, the functional layer and the current collector can be ensured, and the loosening or even falling off of the active material layer under abnormal conditions can be reduced, thus improving the electrical conductivity. Nailing safety performance and electrochemical performance of chemical devices.

The leveling agent used in the functional layer in the embodiment of the present application is a silicone compound or an oxygen-containing olefin polymer. It should be understood that it can also be at least one of carboxylate compounds, carboxylic ester compounds, alcohol compounds, ether compounds, or fluorocarbon compounds, and based on the quality of the functional layer, the leveling The mass percentage of the agent is 0.01% to 0.5%. The addition of leveling agent is beneficial to forming a uniform and smooth functional layer, increasing the contact area between the functional layer and the current collector and active material layer, and improving safety performance. For example, compared to Examples 1 to 4 and 6 to 7 in which no leveling agent is added, Example 5 in which polydimethylsiloxane is added as a leveling agent has an improved center nail pass rate.

3. Functional layer coverage area

The area of the positive electrode current collector is W1cm ² and the area of the functional layer is W2cm ² . In this application, by setting 0.9≤W2/W1≤1, the role of the functional layer can be better exerted and the safety performance of the electrochemical device can be improved. .

To sum up, the electrochemical device of the present application has a high central nail penetration rate and maintains a high rate performance.

References throughout this specification to “some embodiments,” “partial embodiments,” “one embodiment,” “another example,” “example,” “specific example,” or “partial example” mean the following: At least one embodiment or example in this application includes a specific feature, structure, material or characteristic described in the embodiment or example. Accordingly, phrases such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," etc. may appear in various places throughout this specification. "in", "in a particular example" or "for example" do not necessarily refer to the same embodiment or example in this application. Furthermore, the specific features, structures, materials, or characteristics herein may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been shown and described, those skilled in the art will understand that the above-described embodiments are not to be construed as limitations of the present application, and that changes may be made in the embodiments without departing from the spirit, principles and scope of the present application. , substitutions and modifications.

Claims

An electrochemical device comprising a positive electrode, the positive electrode comprising:

Positive electrode current collector; functional layer; and positive electrode active material layer;

The functional layer is disposed between the cathode current collector and the cathode active material layer,

Wherein, the thickness of the functional layer is Tμm, and when the electrochemical device is fully charged, the resistance of the positive electrode is RΩ, satisfying 2≤T×R≤200.
The electrochemical device according to claim 1, wherein 0.5≤T≤10; and/or 1≤R≤10.
The electrochemical device according to claim 1, wherein the functional layer includes first particles and a first conductive agent, the first particles include a metal element, and the metal element includes Al, Mg, Ca, Ti, Ce , at least one of Zn, Y, Hf, Zr, Ba, Sn or Ni.
The electrochemical device according to claim 3, wherein

The first particles include aluminum oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, boehmite, aluminum hydroxide, hydrogen At least one of magnesium oxide, calcium hydroxide, diaspore, barium sulfate, calcium sulfate or calcium silicate; and/or,

The first conductive agent includes at least one of graphene, carbon nanotubes, carbon black, graphite fiber or conductive carbon.
The electrochemical device according to claim 3, wherein the average particle diameter of the first particles is H1 μm, the average particle diameter of the first conductive agent is H2 μm, and at least one of the following conditions is met:

(a)0.5≤H1/H2≤3;

(b)0.8≤T/H1≤20;

(c)H1≤0.6;

(d) The specific surface area BET of the first particle satisfies 5m 2 /g≤BET≤40m 2 /g.
The electrochemical device according to claim 1, wherein the functional layer includes a binder and a leveling agent, wherein the binder meets at least one of the following conditions:

(i) The binder includes a polymer formed from at least one of acrylic acid, acrylamide, acrylate, acrylonitrile, or acrylate;

(ii) The weight average molecular weight of the binder is 700,000 to 800,000;

(iii) The binder is a water-based binder;

(iv) Based on the mass of the functional layer, the mass percentage of the binder is 2% to 20%; wherein the leveling agent meets at least one of the following conditions:

(I) The leveling agent contains at least one of silicone compounds, oxygen-containing olefin polymers, carboxylate compounds, carboxylate compounds, alcohol compounds, ether compounds, or fluorocarbon compounds. kind;

(II) Based on the mass of the functional layer, the mass percentage of the leveling agent is 0.01% to 0.5%.
The electrochemical device according to claim 1, wherein the thickness of the positive active material layer is T2 μm, satisfying T2/T≤30.
The electrochemical device according to claim 1, wherein the area of the positive electrode current collector is W1cm 2 and the area of the functional layer is W2cm 2 , satisfying 0.9≤W2/W1≤1.
The electrochemical device according to claim 8, wherein an orthographic projection of the functional layer on the surface of the positive current collector covers an orthographic projection of the positive active material layer on the surface of the positive current collector.
An electronic device comprising the electrochemical device according to any one of claims 1-9.