WO2023184232A1

WO2023184232A1 - Electrochemical device and electronic device

Info

Publication number: WO2023184232A1
Application number: PCT/CN2022/084048
Authority: WO
Inventors: 刘晓欠; 韩冬冬; 王可飞
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: CN116783725A

Abstract

The present application relates to an electrochemical device. The electrochemical device comprises: a positive electrode which comprises a positive electrode current collector, a protective layer and a positive electrode active material layer. The protective layer is arranged between the positive electrode current collector and the positive electrode active material layer, wherein the protective layer comprises a first insulating material, the first insulating material comprises an element A, and the element A comprises at least one of Al, Si, Mg, Ca, Ti, Ce, Zn, Y, Hf, Zr, Ba or Sn. The electrochemical device can have improved safety characteristics.

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. At present, during the use of lithium-ion batteries, safety accidents still occur due to external impact or puncture. Among them, short circuit between the positive electrode current collector and the negative electrode active material layer is the most likely to cause accidents. Therefore, a technical means that can improve the safety performance of lithium-ion batteries is urgently needed.

Contents of the invention

According to one aspect of the present application, the present application provides an electrochemical device, which includes: a positive electrode, the positive electrode includes a positive electrode current collector, a protective layer and a positive electrode active material layer, the protective layer is disposed between the positive electrode current collector and the positive electrode active material layer between the positive active material layers; wherein the protective layer includes a first insulating material, the first insulating material includes A element, and the A element includes Al, Si, Mg, Ca, Ti, Ce, Zn, Y , Hf, Zr, Ba, or Sn at least one. By providing a protective layer between the positive electrode current collector and the positive electrode active material layer, the risk of a short circuit between the positive electrode current collector and the negative electrode active material layer can be reduced when the electrochemical device is impacted or punctured by external forces, thereby improving the performance of the electrochemical device. Safety performance.

In some embodiments, the protective layer further includes a first active material, the first active material includes Li element and M element, and the M element includes at least one of Mn or Fe.

In some embodiments, based on the mass of the protective layer, the mass percentage of the A element is a%, and the mass percentage of the M element is m%, satisfying: 0.3≤m/a≤170. By satisfying the above relationship, the electrochemical device can have excellent impedance characteristics while having excellent safety performance.

In some embodiments, the electrochemical device has an internal resistance of 20 mΩ to 55 mΩ at a 50% state of charge.

In some embodiments, the infrared spectrum of the protective layer has a characteristic peak in the range of 1400 cm-1 to 1700 cm-1 or 2100 cm-1 to 2300 cm-1.

In some embodiments, the protective layer includes a first adhesive that includes a polymer formed from at least one of acrylic acid, acrylate, acrylate, or acrylonitrile.

In some embodiments, the mass percentage of the first binder is 1% to 20% based on the mass of the protective layer.

In some embodiments, the first adhesive is an aqueous adhesive.

In some embodiments, the first insulating material includes aluminum oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, boehmite, hydrogen At least one of aluminum oxide, magnesium hydroxide, calcium hydroxide, calcium silicate, diaspore, barium sulfate, calcium sulfate or calcium silicate.

In some embodiments, based on the mass of the protective layer, the mass percentage of the first insulating material is 0.5% to 99%.

In some embodiments, the first active material includes at least one of lithium iron phosphate, lithium iron manganese phosphate, or lithium manganate.

In some embodiments, the protective layer further includes a leveling agent.

In some embodiments, the leveling agent includes at least one of a silicone compound, a silicone derivative, an oxygen-containing olefin polymer, an acrylate polymer, an acrylate polymer, or a fluorocarbon compound. kind.

In some embodiments, the mass percentage of the leveling agent is 0.001% to 6% based on the mass of the protective layer.

In some embodiments, the thickness of the protective layer is H1 μm, 0.5≤H1≤10.

In some embodiments, the thickness of the cathode active material layer is H2 μm, 20≤H2≤90.

In some embodiments, H2/H1≤30.

In some embodiments, the protective layer further includes a first conductive agent.

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

In some embodiments, based on the mass of the protective layer, the mass percentage of the first conductive agent is 0.1% to 20%.

In some embodiments, the positive active material layer includes a second active material, a second binder, and a second conductive agent. In some embodiments, the mass percentage of the second active material is 95% to 98% based on the mass of the cathode active material layer. In some embodiments, the second adhesive includes at least one of polyvinylidene fluoride, nitrile rubber, or polyacrylate. In some embodiments, the mass percentage of the second binder is 1.0% to 3.0% based on the mass of the cathode active material layer. In some embodiments, the second conductive agent includes at least one of graphene, graphite fiber, carbon nanotube, Ketjen black or conductive carbon. In some embodiments, the mass percentage of the second conductive agent is 1.0% to 2.0% based on the mass of the cathode active material layer.

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 "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. Project A can contain a single component or multiple components. Project B can contain a single component or multiple components. Project 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 protective layer and a positive active material layer. The protective layer is disposed between the cathode current collector and the cathode active material layer. Wherein, the protective layer includes a first insulating material, the first insulating material includes A element, and the A element includes Al, Si, Mg, Ca, Ti, Ce, Zn, Y, Hf, Zr, Ba, or At least one of Sn.

By providing a protective layer between the positive electrode current collector and the positive electrode active material layer, the risk of a short circuit between the positive electrode current collector and the negative electrode active material layer can be reduced when the electrochemical device is impacted or punctured by external forces, thereby improving the performance of the electrochemical device. Safety performance.

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

In some embodiments, the protective layer further includes a first active material, the first active material includes Li element and M element, and the M element includes at least one of Mn or Fe. In some embodiments, the first active material includes at least one of lithium iron phosphate, lithium iron manganese phosphate, or lithium manganate. In some embodiments, Mn is derived from at least one of lithium iron manganese phosphate (LFMP) or lithium manganate (LMO). In some embodiments, Fe is derived from at least one of lithium iron phosphate (LFP) or lithium iron manganese phosphate (LFMP).

By further including the first active material in the protective layer, on the one hand, the first active material has a greater resistance after being fully charged, thereby further improving the safety performance of the electrochemical device. On the other hand, it has electrochemical activity itself, which not only improves the safety performance of the electrochemical device, but also improves the internal resistance of the electrochemical device, allowing the electrochemical device to have better rate performance.

In some embodiments, based on the total mass of the protective layer, the mass percentage of the A element is a%, and the mass percentage of the M element is m%, where 0≤m/a≤170 is satisfied. In some embodiments, 0.3≤m/a≤170. In some embodiments, 0.3≤m/a≤15. By satisfying the above relationship, the electrochemical device can have excellent impedance characteristics while having excellent safety performance.

In some embodiments, 0.26%≤a≤52.5%, and/or m≤34.5%.

In some embodiments, the electrochemical device has an internal resistance of 20 mΩ to 55 mΩ at a 50% state of charge. In some embodiments, the internal resistance of the electrochemical device at 50% state of charge is 20mΩ, 22mΩ, 25mΩ, 30mΩ, 40mΩ, 50mΩ, or a range between any two of the aforementioned values.

In some embodiments, the mass percentage of the first insulating material is 9% to 98% based on the mass of the protective layer. In some embodiments, the mass percentage of the first insulating material is 9%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72% , 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 95%, 98% or the range between any two of the aforementioned values.

In some embodiments, based on the mass of the protective layer, the mass percentage of the first active material is 1% to 95%. In some embodiments, based on the mass of the protective layer, the mass percentage of the first active material is 20% to 70%. In some embodiments, the mass percentage of the first active material is 0.8%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or the range between any two of the aforementioned values.

In some embodiments, the protective layer includes a first adhesive. In some embodiments, the infrared spectrum of the protective layer has a characteristic peak in the range of 1400 cm-1 to 1700 cm-1 or 2100 cm-1 to 2300 cm-1. At this time, the first binder in the protective layer contains polar groups such as carboxyl or cyano groups, which can improve the bonding effect between the protective layer and the positive electrode current collector and reduce the risk of the electrochemical device being impacted or irritated by external forces. The risk of falling off during wear is thereby suppressed from the occurrence of short circuit between the positive electrode current collector and the negative electrode active material layer, and the safety performance of the electrochemical device is improved.

In some embodiments, the first binder is a water-based binder, which can improve the bonding effect between the safety layer and the positive electrode current collector and the positive electrode active material layer, thereby improving the safety performance of the electrochemical device.

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

In some embodiments, the first binder includes an acrylate and a polymer formed from at least one of acrylic acid, acrylonitrile, and acrylate. At this time, the first binder can have good stability while ensuring high bonding effect, thereby reducing the occurrence of side reactions and inhibiting the occurrence of flatulence in the electrochemical device.

In some embodiments, the mass percentage of the first binder is 1% to 20% based on the mass of the protective layer. In some embodiments, the mass percentage of the first binder is 1%, 2%, 3%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8% , 8.5%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or the range between any two of the aforementioned values. By adjusting the mass percentage of the first binder in the protective layer, a better bonding force between the positive active material layer, the protective layer and the current collector can be ensured, and the failure of the positive active material layer and the protective layer under abnormal conditions can be reduced. loose or even fall off, thereby improving the safety performance and electrochemical performance of the electrochemical device.

In some embodiments, the protective layer further includes a first conductive agent. In some embodiments, the first conductive agent includes at least one of graphene, graphite fiber, carbon nanotube, Ketjen black or conductive carbon.

In some embodiments, the mass percentage of the first conductive agent is 0.1% to 20% based on the mass of the protective layer. In some embodiments, the mass percentage of the first conductive agent is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.2% , 3.4%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.6%, 4.8%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 10%, 12 %, 14%, 16%, 18%, 20% or the range between any two of the aforementioned values.

In some embodiments, the protective layer further includes a leveling agent. In some embodiments, the leveling agent includes at least one of a silicone compound, a silicone derivative, an oxygen-containing olefin polymer, an acrylate polymer, an acrylate polymer, or a fluorocarbon compound. For example: polysiloxane, ethoxypropylene-propoxypropylene polymer, etc. In some embodiments, the mass percentage of the leveling agent is 0.001% to 6% based on the mass of the protective layer. In some embodiments, the mass percentage of the leveling agent is 0.001%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2 %, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6% or the range between any two of the aforementioned values. The addition of leveling agent is conducive to forming a uniform and smooth protective layer, increasing the contact area between the protective layer and the current collector and the positive active material layer, thereby improving the safety of the electrochemical device.

The protective layer may have a thickness of H1 μm, and the positive active material layer may have a thickness of H2 μm. In some embodiments, H2/H1≤30. In some embodiments, the value of H2/H1 is or ranges between any two values mentioned above. When H2/H1 is within the above range, it can suppress the risk of the positive active material layer falling off when the electrochemical device is hit or punctured by external forces, further improving the safety performance of the electrochemical device.

In some embodiments, 0.5≤H1≤10. In some embodiments, H1 is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or any of the foregoing The range between two values. H1 is within the above range. On the one hand, it can improve the shielding effect of the safety layer on the positive electrode current collector, thereby reducing the risk of short circuit between the positive electrode current collector and the negative electrode active material layer when the electrochemical device is impacted or squeezed by external force. On the other hand, it is possible to prevent the safety layer from being too thick, which would lead to a reduction in the energy density of the electrochemical device.

In some embodiments, 20≤H2≤90. In some embodiments, H2 is 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 or a range between any two of the aforementioned values.

In some embodiments, the positive active material layer includes a second active material, a second binder, and a second conductive agent.

In some embodiments, the second active material includes lithium cobalt oxide (abbreviated as LCO). In some embodiments, the mass percentage of the second active material is 94% to 99% based on the mass of the cathode active material layer. In some embodiments, based on the mass of the cathode active material layer, the mass percentage of the second active material is 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5 %, 99% or the range between any two of the aforementioned values.

In some embodiments, the second adhesive includes at least one of polyvinylidene fluoride (abbreviated as PVDF), nitrile rubber, or polyacrylate. In some embodiments, the mass percentage of the second binder is 0.5% to 2.5% based on the mass of the cathode active material layer. In some embodiments, based on the mass of the cathode active material layer, the mass percentage of the second binder is 0.5%, 1%, 1.5%, 2%, 2.5% or a range between any two of the aforementioned values.

In some embodiments, the second conductive agent includes at least one of graphene, graphite fibers, carbon nanotubes, Ketjen black, or conductive carbon. In some embodiments, the mass percentage of the second conductive agent is 0.5% to 3.5% based on the mass of the cathode active material layer. In some embodiments, based on the mass of the cathode active material layer, the mass percentage of the second conductive agent is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or between any two of the aforementioned values. scope.

By arranging a protective layer between the positive current collector and the positive active material layer of the electrochemical device, the present application can reduce the risk of short circuit between the positive current collector and the negative active material layer when the electrochemical device is impacted or punctured by external force, thus Improve the safety performance of electrochemical devices. At the same time, the present application recognizes that by controlling the material composition in the protective layer to include a first insulating material and a first active material, the protective layer can improve the safety performance of the electrochemical device while also improving the internal performance of the electrochemical device. block.

The electrochemical device of the present application also includes a separator, an electrolyte and a negative electrode.

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.

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 negative electrode binder, as well as optional conductive material, into the solvent system according to a certain mass ratio and stir thoroughly. After uniformity, it is coated on the negative electrode current collector, dried and cold pressed to obtain the negative electrode.

Preparation of positive electrode:

(1) Add the first insulating material, the first adhesive, the first conductive agent, and the optional first active material and leveling agent to the solvent and mix evenly to obtain a protective layer slurry (hereinafter referred to as "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 a positive electrode current collector coated with a protective layer;

(4) Disperse the second active material, the second conductive agent, and the second binder in the solvent system according to a certain mass ratio, stir and mix thoroughly to obtain a slurry of the positive electrode active material (hereinafter referred to as "second slurry"). material");

(5) Coating the second slurry on the target area of the positive electrode current collector coated with the protective 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.

The types of the first insulating material, the first conductive agent, the first binder, the first active material, the second active material, the second conductive agent and the second binder are as described above.

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 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 not particularly limited as long as the current collector is conductive without causing adverse chemical changes in the manufactured battery. Examples of the current collector include copper, stainless steel, aluminum, nickel, titanium, or alloys such as 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 (abbreviated as 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 microns to 500 microns.

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

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 or lithium-ion capacitors, etc.

4. 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 38 and Comparative Examples 1 to 3

Production of positive electrode

Step (1): Add the first insulating material, the first conductive agent, the first binder, and the optional first active material and/or leveling agent to deionized water and mix evenly to obtain a protective layer slurry. (hereinafter referred to as "first slurry");

Step (2) Coating the first slurry in step (1) on the target area of the positive electrode current collector;

Step (3) drying the positive electrode current collector containing the first slurry obtained in step (2) to remove the solvent to obtain a positive electrode current collector coated with a protective layer;

Step (4) Combine the second active material (lithium cobalt oxide, 97.3% by mass), the second conductive agent (0.6% by mass of conductive carbon (trade name: Super P)) and 0.5% by mass of carbon nanotubes (abbreviated as CNT)), the second binder (polyvinylidene fluoride (abbreviated as PVDF) with a mass percentage of 1.6%) are dispersed in the N-methylpyrrolidone solvent system and stirred thoroughly to obtain a slurry of the positive electrode active material (which will be called "second slurry");

Step (5) applying the second slurry to the target area of the positive electrode current collector coated with the protective layer obtained in step (3);

Step (6) Drying 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 protective layers in the positive electrodes in Examples 1 to 38 and Comparative Examples 1 to 3.

Table 1

Except for the above differences, there are no differences in the positive active material layer, positive current collector, etc. of the positive electrodes in Examples 1 to 38 and Comparative Examples 1 to 3, and they are all prepared using the aforementioned process.

Fabrication of electrochemical devices

The positive electrode of the electrochemical device was fabricated as described above.

Negative electrode: Combine the active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (abbreviated as SBR), and thickener sodium carboxymethylcellulose (abbreviated as CMC) in a mass ratio of approximately 95:2:2: 1. After fully stirring and mixing in the deionized water solvent system, apply it on Cu foil, dry it, and cold-press it to obtain the negative electrode.

Electrolyte: In an argon atmosphere glove box with a water content of <10 ppm, mix ethylene carbonate (abbreviated as EC), diethyl carbonate (abbreviated as DEC), and propylene carbonate (abbreviated as PC) according to 2:6: Mix evenly at a weight ratio of 2, and then dissolve the fully dried lithium salt LiPF ₆ in the above solvent. The content of LiPF ₆ is 12.5%. Add 1.5% 1,3-propane sultone and 3% fluoroethylene carbonate. , 2% adiponitrile. The content of each substance is based on the total weight of the electrolyte.

Isolation film: Polyethylene (abbreviated as 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 the battery.

Performance testing methods

Lithium-ion battery internal resistance growth rate

Storage conditions (placed at 85°C for 6 hours):

In an environment of 25±3°C, charge the lithium-ion battery at a constant current of 0.5C to the full charge design voltage of 4.45V, and then charge at a constant voltage of 4.45V to the full charge voltage to 0.025C. The initial internal resistance of the tested lithium-ion battery is recorded as imp0. Put the lithium-ion battery into a high-temperature furnace at 85±3℃ for 6h (hours) and then take it out. After the temperature of the lithium-ion battery drops to 25±3℃, test its internal resistance and record it as "IMP6h". The internal resistance growth rate after being placed at 85°C for 6 hours = (IMP6h-IMP0)/IMP0×100%.

Cycling conditions (25℃/45℃ cycle):

Complete the following tests in an environment of 25℃/45℃ (±3℃):

Charge the lithium-ion battery to a constant current of 0.5C to the full charge design voltage of 4.45V, then charge to a constant voltage of 4.45V to a full charge voltage of 0.02C. The initial internal resistance of the tested lithium-ion battery is recorded as IMP1. Then discharge to 3V with a constant current of 0.2C. After 500 cycles, at the 500th full charge, the internal resistance of the tested lithium-ion battery is recorded as IMP500. Internal resistance growth rate=(IMP500-IMP1)/IMP1×100%.

Center nail pass rate

The lithium-ion battery to be tested is charged with a constant current at a rate of 0.05C 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 until the current is 0.025C (cut-off current), so that the lithium-ion battery reaches full charge. Charging status, record the appearance of the lithium-ion battery before testing. Conduct a nail penetration test on the battery in an environment of 25±3°C. The diameter of the steel nail is 4mm, the extrusion speed is 30mm/s, and the nail penetration position is located at the geometric center of the lithium-ion battery. The test lasts for 3.5 minutes or stops after the battery surface temperature drops to 50°C. For the test, 20 lithium-ion batteries are used as a group, and the status of the lithium-ion batteries during the test is observed. The passing criterion is that the lithium-ion batteries do not burn or explode. Remember the center nail pass rate = number of passes/00.

Lithium-ion battery internal resistance

When the lithium-ion battery is charged to 50% of the design capacity, use a resistance meter to test the AC internal resistance of the lithium-ion battery using sinusoidal and 1000Hz frequency waves.

Protective layer/positive electrode active material layer thickness

1) Remove the positive electrode coated with protective 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 a protective layer under plasma to obtain its cross section;

3) Observe the cross section of the positive electrode obtained in 2) under SEM, and test the thickness of the protective layer H1μm. The interval between adjacent test points is about 2mm to 3mm. Test at least 15 different points. The average value of all test points is recorded as the protective layer. The thickness is H1μm. The thickness H2 μm of the positive electrode active material layer is measured in the same way.

Table 2 below shows various properties of Examples 1 to 38 and Comparative Examples 1 to 3.

1. Explore the impact of the presence or absence of a protective layer and the thickness of the protective layer on the performance of the electrochemical device

It can be seen from the aforementioned Table 1 and Table 2 that the center penetration rate of the lithium-ion batteries of Examples 1 to 38 with a protective layer and Comparative Examples 2 and 3 with a protective layer is significantly better than that of the lithium battery of Comparative Example 1 without a protective layer. ion battery. It can be seen that the protective layer added between the positive electrode current collector and the positive electrode active material layer can significantly improve the safety performance of the electrochemical device.

It can be seen from the comparison between Examples 2 to 14 and Example 15 in the aforementioned Table 1 and Table 2 that when the thickness of the protective layer is H1 μm and the thickness of the positive active material layer is H2 μm, H2/H1≤30 is satisfied. , Lithium-ion batteries can have a better center nail penetration rate. This is because H2/H1 is within the above range, which can suppress the risk of the positive active material layer falling off when the electrochemical device is impacted or punctured by external force, thus Further improve the safety performance of electrochemical devices.

2. Explore the impact of the composition of the protective layer on the performance of the electrochemical device

2.1 Insulating materials

The insulating material used in the protective layer in Embodiments 1 to 38 of the present application includes at least one of boehmite, alumina, barium sulfate, calcium sulfate or calcium silicate. However, it should be understood that the insulating material used in the protective layer of the present application is not limited to the types listed in the specific embodiments, and may include its analogs.

From the comparison of Examples 1 to 38 and Comparative Example 2 in the aforementioned Table 1 and Table 2, it can be found that when the protective layer contains an insulating material (such as boehmite), it can be improved compared to the case where the protective layer does not contain an insulating material. Center penetration rate of electrochemical devices.

2.2 First binder

The first binder used for the protective layer in Examples 1 to 38 of the present application may include acrylonitrile, acrylate, acrylamide polymer, polyacrylic acid, sodium carboxymethylcellulose, sodium polyacrylate, polyacrylate, polypropylene At least one of nitrile or nitrile rubber. However, it should be understood that the first adhesive used in the protective 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. things.

From the comparison between Examples 1 to 38 and Comparative Example 3 in Table 1 and Table 2, it can be found that when the first binder contained in the protective layer is a water-based binder, it can significantly improve the lithium content compared to PVDF. High-temperature storage internal resistance growth rate of ion batteries.

2.3 First active substance

The first active material used in the protective layer in Embodiments 1 to 38 of the present application may include at least one of lithium iron phosphate, lithium iron manganese phosphate, or lithium manganate. However, it should be understood that the first active material used in the protective layer of the present application is not limited to the types listed in the specific embodiments, and may include analogs thereof.

It can be seen from the comparison of Examples 1 to 7, Examples 8 to 9 and Comparative Example 2 in Table 1 and Table 2 that by adding the first active material, the examples in which m/a is in the range of 0.3 to 15 can Combining a high central nail penetration rate and low battery internal resistance, lithium-ion batteries can have good rate performance while having good safety performance.

In summary, the electrochemical device of the present application can have a higher center penetration rate and can have an improved high-temperature storage internal resistance growth rate.

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, which includes: a positive electrode, the positive electrode includes a positive electrode current collector, a protective layer and a positive electrode active material layer, the protective layer is disposed between the positive electrode current collector and the positive electrode active material layer; wherein, The protective layer includes a first insulating material, the first insulating material includes A element, and the A element includes Al, Si, Mg, Ca, Ti, Ce, Zn, Y, Hf, Zr, Ba or Sn. At least one.
The electrochemical device according to claim 1, wherein the protective layer further includes a first active material, the first active material includes Li element and M element, and the M element includes at least one of Mn or Fe. .
The electrochemical device according to claim 2, wherein based on the quality of the protective layer, the mass percentage of the A element is a%, and the mass percentage of the M element is m%, satisfying: 0.3≤m/a ≤170.
The electrochemical device according to claim 1, wherein the internal resistance of the electrochemical device at a 50% state of charge is 20 mΩ to 55 mΩ.
The electrochemical device of claim 1, wherein the protective layer includes a first binder that satisfies at least one of the following conditions:

(a) The infrared spectrum of the protective layer has characteristic peaks in the range of 1400cm -1 to 1700cm -1 or 2100cm -1 to 2300cm -1 ;

(b) the first binder includes a polymer formed from at least one of acrylic acid, acrylate, acrylate or acrylonitrile;

(c) Based on the mass of the protective layer, the mass percentage of the first adhesive is 1% to 20%;

(d) the first adhesive is a water-based adhesive;

(e) The first insulating material includes aluminum oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, boehmite, aluminum hydroxide, At least one of magnesium hydroxide, calcium hydroxide, calcium silicate, diaspore, barium sulfate, calcium sulfate or calcium silicate;

(f) Based on the mass of the protective layer, the mass percentage of the first insulating material is 0.5% to 99%.
The electrochemical device of claim 2, wherein the first active material includes at least one of lithium iron phosphate, lithium iron manganese phosphate, or lithium manganate.
The electrochemical device according to claim 1, wherein the protective layer further includes a leveling agent that satisfies at least one of the following conditions:

(1) The leveling agent contains at least one of silicone compounds, silicone derivatives, oxygen-containing olefin polymers, acrylate polymers, acrylate polymers or fluorocarbon compounds;

(2) Based on the mass of the protective layer, the mass percentage of the leveling agent is 0.001% to 6%.
The electrochemical device according to claim 1, wherein the thickness of the protective layer is H1 μm, the thickness of the positive active material layer is H2 μm, and at least one of the following conditions is met:

(I)0.5≤H1≤10;

(II)20≤H2≤90;

(III)H2/H1≤30.
The electrochemical device according to claim 1, wherein the protective layer further includes a first conductive agent that meets at least one of the following conditions:

(1) The first conductive agent contains at least one of graphene, graphite fiber, carbon nanotubes, Ketjen black or conductive carbon;

(2) Based on the mass of the protective layer, the mass percentage of the first conductive agent is 0.1% to 20%.
An electronic device comprising the electrochemical device according to any one of claims 1-9.