Electrochemical device and electronic device

Abstract

The invention provides an electrochemical device and an electronic device, the electrochemical device comprises a positive pole piece, the positive pole piece comprises a positive current collector, a first coating and a positive material layer, the first coating is arranged on the surface of the positive current collector, and the positive material layer is arranged on the surface, away from the positive current collector, of the first coating; the first coating comprises inorganic particles, and the inorganic particles comprise at least one of nano boehmite, aluminum oxide, titanium dioxide, magnesium oxide, zirconium oxide or zinc oxide; the positive electrode material layer comprises a first conductive agent, and the first conductive agent comprises a first carbon nanotube; the length of the first carbon nanotube is 2-5 [mu] m, and the diameter of the first carbon nanotube is 2-100 nm; and the ion transference number of the positive electrode material layer is 0.4-0.47. The electrochemical device provided by the invention can consider the nail penetrating safety performance, the low-temperature cycle performance and the quick charging performance.

Description

[0001] This application is a divisional application of the Chinese Patent Application No. 202510033849.7, filed on January 9, 2025, with the title of "An Electrochemical Device and Electronic Device", with the State Intellectual Property Office of the People's Republic of China. TECHNICAL FIELD

[0002] The present application relates to the technical field of electrochemistry, in particular to an electrochemical device and electronic device. BACKGROUND

[0003] Electrochemical devices (such as lithium ion batteries) have been popularized in daily life with the development of technology. Lithium ion batteries have entered our daily life with the progress of technology and the improvement of environmental protection requirements. With the large-scale popularization of lithium ion batteries, their service life is increasingly valued by users, and consumers, after-sales, battery manufacturers and lithium battery manufacturers have put forward new requirements for the safety performance of batteries.

[0004] However, with the rapid popularization of lithium ion batteries, the technology of product safety is not mature. In the use process, the positive electrode sheet and the negative electrode sheet often contact each other or are connected by nails during the nail penetration process of lithium ion batteries, resulting in internal short circuit. With people's increasing attention to the safety performance of lithium ion batteries, the market urgently needs a lithium ion battery with good nail penetration safety performance. SUMMARY

[0005] The purpose of the present application is to provide an electrochemical device and electronic device to improve the nail penetration safety performance, low temperature cycle performance and fast charging performance of the electrochemical device.

[0006] It should be noted that in the summary of the present application, the lithium ion battery is taken as an example to explain the present application, but the electrochemical device of the present application is not limited to lithium ion batteries. The specific technical solutions are as follows:

[0007] The first aspect of the present application provides an electrochemical device, the electrochemical device comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector, a first coating layer and a positive electrode material layer, the first coating layer being arranged on a surface of the positive electrode current collector, and the positive electrode material layer being arranged on a surface of the first coating layer away from the positive electrode current collector; the first coating layer comprising inorganic particles, the inorganic particles comprising at least one of nanometer boehmite, aluminum trioxide, titanium dioxide, magnesium oxide, zirconium oxide or zinc oxide; the positive electrode material layer comprising a first conductive agent, the first conductive agent comprising first carbon nanotubes; the length of the first carbon nanotubes being 2-5 μm, and the tube diameter of the first carbon nanotubes being 2-100 nm; and the ion transference number of the positive electrode material layer being 0.4-0.47. The electrochemical device comprises the above structure and the first conductive agent of the positive electrode material layer satisfies the above characteristics, which is conducive to providing the positive electrode sheet with an electron and ion matched transmission channel, improving the ion transmission rate, further improving the charging rate, and improving the fast charging performance and low temperature cycle performance; at the same time, when the first coating layer satisfies the above characteristics, it has a relatively high membrane resistance, which is conducive to increasing the short circuit resistance, reducing the dangerous short circuit points between the positive electrode sheet and the negative electrode sheet during the nail penetration test, reducing the heat power generated by the short circuit, improving the nail penetration safety performance of the electrochemical device, and matching the conductivity of the positive electrode material layer, thereby improving the low temperature cycle performance and fast charging performance of the electrochemical device, so that the electrochemical device provided by the present application can balance the nail penetration safety performance, low temperature cycle performance and fast charging performance.

[0008] In an embodiment of the present application, the length of the first carbon nanotubes is 2-4 μm, and / or the tube diameter of the first carbon nanotubes is 20-80 nm. By adjusting the length of the first carbon nanotubes and / or the tube diameter of the first carbon nanotubes within the above range, the conductivity of the positive electrode material layer is adjusted to a suitable value, which improves the safety performance of the electrochemical device and further improves the low temperature cycle performance and fast charging performance of the electrochemical device.

[0009] In an embodiment of the present application, the mass percentage content of the first carbon nanotubes is 0.5%-2.5% based on the mass of the positive electrode material layer. The mass percentage content of the first carbon nanotubes within the above range is conducive to improving the electronic conductivity, and the conductivity of the first coating layer of the positive electrode sheet and the positive electrode material layer are matched with each other, which improves the safety performance of the electrochemical device and further improves the low temperature cycle performance and fast charging performance of the electrochemical device.

[0010] In an embodiment of the present application, the mass percentage content of the first conductive agent is 0.6%-3.1% based on the mass of the positive electrode material layer. By adjusting the mass percentage content of the first conductive agent within the above range, the conductivity of the positive electrode material layer is adjusted to a suitable value, the conductivity of the first coating layer of the positive electrode sheet and the positive electrode material layer are matched with each other, which improves the safety performance of the electrochemical device and further improves the low temperature cycle performance and fast charging performance of the electrochemical device.

[0011] In an embodiment of the present application, the positive electrode material layer further comprises a second conductive agent, the second conductive agent comprises at least one of conductive carbon black or activated carbon; the mass percentage of the second conductive agent is 1.4% to 2.8% based on the mass of the positive electrode material layer. The category and mass percentage of the second conductive agent are within the above range, the electronic conductivity and ionic conductivity of the positive electrode material layer are improved, the low-temperature cycle performance and fast-charging performance of the electrochemical device are further improved while the safety performance of the electrochemical device is improved.

[0012] In an embodiment of the present application, the first coating further comprises a first binder and a third conductive agent, the Dv90 of the inorganic particles is 200 nm to 1000 nm, preferably 400 nm to 600 nm. By adjusting the Dv90 of the inorganic particles within the above range, the inorganic particles form a dense coating on at least one surface of the positive electrode current collector, the first coating can wrap the metal burrs that the positive electrode current collector may generate in the nail penetration test under abnormal conditions such as nail penetration and impact, enhance the protection of the positive electrode current collector during the nail penetration test, reduce the probability of internal short circuit of the electrochemical device, reduce the probability of thermal runaway caused by local overheating of the electrochemical device, and further improve the nail penetration safety performance of the electrochemical device.

[0013] In an embodiment of the present application, the thickness of the first coating is 0.2 μm to 2 μm, preferably 0.5 μm to 1.25 μm. By adjusting the thickness of the first coating within the above range, the thickness of the first coating is relatively thick and has high mechanical strength, which is conducive to protecting the positive electrode current collector during the nail penetration test, reducing the probability of internal short circuit of the electrochemical device, reducing the probability of thermal runaway caused by local overheating of the electrochemical device, and further improving the nail penetration safety performance of the electrochemical device.

[0014] In an embodiment of the present application, the ratio of the thickness of the first coating to the thickness of the positive electrode material layer is 0.18% to 2.2%. By adjusting the ratio of the thickness of the first coating to the thickness of the positive electrode material layer within the above range, it is conducive to adjusting the appropriate ion transmission path and improving the ion transmission rate, and further improving the fast-charging performance of the electrochemical device.

[0015] In an embodiment of the present application, the mass percentage of the inorganic particles is 80% to 94.5% based on the mass of the first coating. The mass percentage of the inorganic particles is within the above range, the first coating has a relatively high sheet resistance, which is conducive to increasing the short-circuit resistance, reducing the dangerous short-circuit points between the positive electrode sheet and the negative electrode sheet during the nail penetration test, reducing the heat power generated by the short circuit, and further improving the nail penetration safety performance of the electrochemical device.

[0016] In one embodiment of this application, the first binder comprises a water-soluble polymer metal salt; based on the mass of the first coating, the mass percentage content of the first binder is 0.5% to 15%. By controlling the first binder to be selected from the above-mentioned materials and within the above-mentioned mass percentage range, the water-soluble polymer metal salt has good hydrophilicity, which is beneficial to the transport of electrons and ions, and is beneficial to improving kinetic performance and low-temperature cycling performance; the water-soluble polymer metal salt has a large specific surface area and can be highly dispersed after contact with water. When used as the first binder in the first coating layer, it can improve the tensile strength of the first coating. At the same time, the water-soluble polymer metal salt has many polar functional groups and functional groups that can form hydrogen bonds, which form strong hydrogen bonds with the oxide layer on the surface of the positive electrode current collector, which is beneficial to improving the adhesion between the first coating and the positive electrode current collector, and improving the pin-piercing safety performance of the electrochemical device; at the same time, it reduces the degree of peeling between the first coating and the positive electrode current collector during cycling, improves the interfacial contact impedance during cycling, and further improves the low-temperature cycling performance and cycle life of the electrochemical device.

[0017] In one embodiment of this application, the metal element in the water-soluble polymer metal salt includes at least one selected from lithium, sodium, potassium, rubidium, cesium, francium, beryllium, barium, strontium, calcium, or magnesium; the polymer in the water-soluble polymer metal salt includes at least one selected from polyacrylic acid, carboxymethyl cellulose, polyacrylonitrile, or styrene-butadiene. The metal element and polymer in the water-soluble polymer metal salt, within the scope of this application, are beneficial for improving electron and ion transport performance, resulting in electronic and ionic conductivity superior to that of insoluble polymers such as polyvinylidene fluoride and polyvinylidene chloride, thereby enhancing mass transfer kinetics and further improving the kinetic performance and low-temperature cycling performance of the electrochemical device.

[0018] In one embodiment of this application, the water-soluble polymeric metal salt includes at least one selected from sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, calcium polyacrylate, magnesium polyacrylate, rubidium polyacrylate, cesium polyacrylate, francium polyacrylate, barium polyacrylate, strontium polyacrylate, lithium carboxymethyl cellulose, beryllium carboxymethyl cellulose, or sodium carboxymethyl cellulose. The variety of water-soluble polymeric metal salts within the scope of this application further improves the pin-penetration safety performance, low-temperature cycling performance, and kinetic performance of the electrochemical device.

[0019] In one embodiment of this application, the third conductive agent includes at least one of conductive carbon black, activated carbon, carbon nanotubes, or carbon nanofibers; the mass percentage of the third conductive agent is 0.7% to 5% based on the mass of the first coating. When the type and mass percentage of the third conductive agent are within the above range, the first coating exhibits both high short-circuit resistance and good conductivity, further improving the low-temperature cycling performance of the electrochemical device.

[0020] In one embodiment of this application, within a 4μm × 4μm range in a scanning electron microscope image at 30,000x magnification, the particle size of the secondary particles of the third conductive agent in the first coating is <50nm. The fact that the particle size of the secondary particles of the third conductive agent is within this range indicates that the third conductive agent is uniformly distributed and well-dispersed in the first coating, which can improve the conductive network density and further enhance the cycling and fast-charging performance of the electrochemical device.

[0021] In one embodiment of this application, the adhesion between the first coating and the positive electrode current collector is 500 N / m to 900 N / m. The adhesion between the first coating and the positive electrode current collector being within this range indicates good adhesion between them. The first coating can effectively encapsulate any metal burrs that may be generated in the current collector under abnormal conditions such as nail penetration or impact, thereby reducing the occurrence of internal short circuits in the electrochemical device. Simultaneously, it reduces the probability of thermal runaway or overheating combustion caused by localized overheating in the electrochemical device, further improving the nail penetration safety performance of the electrochemical device.

[0022] In one embodiment of this application, the film resistance of the first coating is between 200Ω and 2500Ω. A film resistance within this range is advantageous for increasing short-circuit resistance, reducing Joule heating generated instantaneously during a short circuit, lowering the risk of dangerous short circuits, and improving the safety performance of the electrochemical device.

[0023] In one embodiment of this application, in the electrochemical impedance spectroscopy of the positive electrode, the characteristic frequency is at 10... 4 Hz to 10 6 An Rcont peak exists in the Hz range, with a characteristic frequency of 10. -1 An Rct peak exists in the frequency range of Hz to 10Hz. The ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak is 10. -5 Up to 0.01. The positive electrode meets the above characteristics, resulting in low resistance to electron transport in the conductive network, thus improving the cycle and fast-charging performance of the electrochemical device.

[0024] In one embodiment of this application, the film resistance of the positive electrode is 1Ω to 3Ω. The positive electrode meeting these characteristics is beneficial for increasing short-circuit resistance, reducing Joule heating generated during short-circuit processes, lowering the risk of dangerous short circuits, and improving the safety performance of the electrochemical device.

[0025] In one embodiment of this application, the resistivity of the positive electrode material layer is 1.125 × 10⁻⁶. -5 Ω·cm to 1.875×10 -5The positive electrode sheet meets the above characteristics. The resistance of the positive electrode material layer is low and the electronic conductivity is good, indicating that the electrochemical device including the positive electrode sheet of this application has good low-temperature cycle performance and fast-charging performance. At the same time, the resistance of the first coating layer is high, and the resistance difference between the two is large. This can improve the low-temperature cycle performance, fast-charging performance and safety performance of the electrochemical device including the positive electrode sheet of this application while maintaining the same overall resistance of the positive electrode sheet.

[0026] The second aspect of this application provides an electronic device, which includes the electrochemical device described in the first aspect of this application. The electronic device of this application has good pin-penetration safety performance, low-temperature cycling performance, and fast-charging performance.

[0027] The beneficial effects of this application are:

[0028] This application provides an electrochemical device comprising a positive electrode, which includes a positive current collector, a first coating, and a positive electrode material layer. The first coating is disposed on the surface of the positive current collector, and the positive electrode material layer is disposed on the surface of the first coating away from the positive current collector. The first coating includes inorganic particles, which include at least one of nano-boehmite, aluminum oxide, titanium dioxide, magnesium oxide, zirconium oxide, or zinc oxide. The positive electrode material layer includes a first conductive agent, which includes a first carbon nanotube. The length of the first carbon nanotube is 2 μm to 5 μm, and the diameter of the first carbon nanotube is 2 nm to 100 nm. The ion transference number of the positive electrode material layer is 0.4 to 0.47. The electrochemical device includes the above-described structure, and the first conductive agent of the positive electrode material layer satisfies the above-described characteristics. This is beneficial for providing an electron-ion matching transport channel for the positive electrode, improving the ion transport rate, further increasing the charging rate, and improving fast charging performance and low-temperature cycling performance. At the same time, when the first coating satisfies the above-described characteristics, it has a high film resistance, which is beneficial for increasing the short-circuit resistance. This reduces the dangerous short-circuit points between the positive and negative electrode plates during the pin-penetration test, reduces the heat power generated by the short circuit, and improves the pin-penetration safety performance. At the same time, it matches the conductivity of the positive electrode material layer, improving the low-temperature cycling performance and fast charging performance of the electrochemical device. Therefore, the electrochemical device provided by this application can take into account the pin-penetration safety performance, low-temperature cycling performance, and fast charging performance.

[0029] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0031] Figure 1 This is a schematic cross-sectional view of the positive electrode sheet along its thickness direction in one embodiment of this application;

[0032] Figure 2 This is a scanning electron microscope image of the surface morphology of the first coating prepared in Example 1-1 of this application;

[0033] Figure 3 This is a scanning electron microscope image of a cross-section along the thickness direction of the positive electrode sheet prepared in Examples 1-1 of this application;

[0034] Figure 4 The graph shows the change in the capacity retention rate of the lithium-ion batteries prepared in Examples 1-1, Comparative Examples 2 and 6 of this application at 45°C.

[0035] Figure 5 The diagram shows the AC internal resistance variation of the positive electrode sheets prepared in Examples 1-1, Comparative Examples 2 and 6 of this application;

[0036] Figure 6 The electrochemical impedance spectroscopy of the positive electrode sheets prepared in Examples 1-1, Comparative Example 1, and Comparative Example 6 of this application is shown. Detailed Implementation

[0037] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0038] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0039] The first aspect of this application provides an electrochemical device comprising a positive electrode, which includes a positive current collector, a first coating, and a positive electrode material layer. The first coating is disposed on the surface of the positive current collector, and the positive electrode material layer is disposed on the surface of the first coating away from the positive current collector. The first coating comprises inorganic particles, including at least one of nano-boehmite, alumina, titanium dioxide, magnesium oxide, zirconium oxide, or zinc oxide. The positive electrode material layer comprises a first conductive agent, which includes a first carbon nanotube. The length of the first carbon nanotube is 2 μm to 5 μm, preferably 2 μm to 4 μm. The diameter of the first carbon nanotube is 2 nm to 100 nm, preferably 20 nm to 80 nm. The ion transference number of the positive electrode material layer is 0.4 to 0.47. For example, the length of the first carbon nanotube can be 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, or any two of these values; the diameter of the first carbon nanotube can be 2nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or any two of these values; the ion transference number of the cathode material layer can be 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, or any two of these values. When the electrochemical device includes the above structure and the first conductive agent of the positive electrode material layer satisfies the above characteristics, it is beneficial to provide an electron-ion matching transport channel for the positive electrode, improve the ion transport rate, further improve the charging rate, and improve the fast charging performance and low-temperature cycling performance of the electrochemical device. At the same time, when the first coating satisfies the above characteristics, it has a high film resistance, which is beneficial to increase the short-circuit resistance, reduce the dangerous short-circuit point between the positive and negative electrode during the pin-penetration test, and reduce the heat power generated by the short circuit. While improving the pin-penetration safety performance of the electrochemical device, it matches the conductivity of the positive electrode material layer, improves the low-temperature cycling performance and fast charging performance of the electrochemical device. Thus, the electrochemical device provided by this application can take into account the pin-penetration safety performance, low-temperature cycling performance, and fast charging performance.

[0040] In one embodiment of this application, the mass percentage of the first carbon nanotube is between 0.5% and 2.5% based on the mass of the positive electrode material layer. For example, the mass percentage of the first carbon nanotube can be 0.5%, 1%, 1.5%, 2%, 2.5%, or a range consisting of any two of these values. A mass percentage of the first carbon nanotube within the above range is beneficial for improving electronic conductivity. The conductivity of the first coating of the positive electrode sheet is matched with that of the positive electrode material layer, thereby improving the safety performance of the electrochemical device while further enhancing its low-temperature cycling performance and fast-charging performance.

[0041] In some embodiments of this application, the first carbon nanotube includes at least one of a first single-walled carbon nanotube, a first multi-walled carbon nanotube, or a first carbon nanofiber. The first single-walled carbon nanotube includes single-walled carbon nanotubes (SWCNTs), the first multi-walled carbon nanotube includes multi-walled carbon nanotubes (MWCNTs), and the first carbon nanofiber includes carbon nanofibers. The first carbon nanotube is selected from the above materials, the first conductive agent has good electronic conductivity, and the conductivity of the first coating of the positive electrode sheet matches that of the positive electrode material layer. This improves the safety performance of the electrochemical device while further enhancing its low-temperature cycling performance and fast-charging performance.

[0042] In some embodiments of this application, the first conductive agent further includes a second carbon nanotube. The second carbon nanotube includes at least one of second SWCNTs, second MWCNTs, or second carbon nanofibers; the second SWCNTs include SWCNTs, and the second MWCNTs include MWCNTs; the length of the second carbon nanotube is 300 nm to 1 μm, and the diameter is 2 nm to 50 nm; the second carbon nanofiber includes carbon nanofibers. Based on the mass of the cathode material layer, the mass percentage of the second carbon nanotube is 0.1% to 2.6%. The first conductive agent is a composite system and satisfies the above characteristics, which can improve the charging rate and further improve the fast-charging performance and low-temperature cycling performance of the electrochemical device.

[0043] In one embodiment of this application, the mass percentage of the first conductive agent is between 0.6% and 3.1%, based on the mass of the positive electrode material layer. For example, the mass percentage of the first conductive agent can be 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 3%, 3.1%, or a range consisting of any two of these values. By controlling the mass percentage of the first conductive agent within the above range, the conductivity of the positive electrode material layer is adjusted to a suitable value, and the conductivity of the first coating of the positive electrode sheet matches that of the positive electrode material layer. This improves the safety performance of the electrochemical device while further enhancing its low-temperature cycling performance and fast-charging performance.

[0044] In one embodiment of this application, the positive electrode material layer further includes a second conductive agent, which includes at least one of conductive carbon black or activated carbon; based on the mass of the positive electrode material layer, the mass percentage content of the second conductive agent is 1.4% to 2.8%. For example, the mass percentage content of the second conductive agent can be 1.4%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, or a range consisting of any two of these values. When the type and mass percentage content of the second conductive agent are within the above range, the electronic conductivity and ionic conductivity of the positive electrode material layer are improved, thereby improving the safety performance of the electrochemical device while further enhancing its low-temperature cycling performance and fast-charging performance.

[0045] In this application, the phrase "the first coating is disposed on the surface of the positive electrode current collector" means that the first coating can be disposed on one surface of the positive electrode current collector along its own thickness direction, or on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector or only a portion thereof; this application has no particular limitation, as long as the purpose of this application is achieved. The phrase "the positive electrode material layer is disposed on the surface of the first coating away from the positive electrode current collector" can be understood similarly. Specifically, as... Figure 1 As shown, a first coating layer 12 and a positive electrode material layer 13 disposed on the first coating layer 12 away from the surface of the positive electrode current collector 11 are sequentially stacked on the two surfaces of the positive electrode current collector 11.

[0046] The positive electrode material layer also includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it achieves the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. This application does not impose any particular limitation on the mass percentage content of the positive electrode active material in the positive electrode material layer, as long as it achieves the purpose of this application. Exemplarily, the mass percentage content of the positive electrode active material in the positive electrode material layer can be from 94% to 98%. For example, the mass percentage content of the positive electrode active material can be 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, or a range consisting of any two of these values.

[0047] The positive electrode material layer also includes a positive electrode binder. This application does not impose any particular limitation on the positive electrode binder, as long as it achieves the purpose of this application. For example, the positive electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride. This application does not impose any particular limitation on the mass percentage content of the positive electrode binder in the positive electrode material layer, as long as it achieves the purpose of this application. Exemplarily, the mass percentage content of the positive electrode binder in the positive electrode material layer may be from 0.1% to 2%. For example, the mass percentage content of the positive electrode binder may be 0.1%, 0.5%, 1%, 1.5%, 2%, or a range consisting of any two of these values.

[0048] In this application, the thickness of the single-sided positive electrode material layer is 70 μm to 90 μm. For example, the thickness of the single-sided positive electrode material layer can be 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, or a range of any two of these values.

[0049] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0050] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be from 5 μm to 20 μm.

[0051] In one embodiment of this application, the first coating further includes a first binder and a third conductive agent, and the Dv90 of the inorganic particles is 200 nm to 1000 nm, preferably 400 nm to 600 nm. For example, the Dv90 of the inorganic particles can be 200 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, or a range consisting of any two of these values. By controlling the Dv90 of the inorganic particles within the above range, the inorganic particles form a dense coating on at least one surface of the positive electrode current collector. The first coating can, under abnormal conditions such as nail penetration and impact, encapsulate the metal burrs that may be generated by the positive electrode current collector during nail penetration testing, enhance the protection of the positive electrode current collector during nail penetration testing, reduce the possibility of internal short circuits in the electrochemical device, reduce the probability of thermal runaway caused by local overheating of the electrochemical device, and further improve the nail penetration safety performance of the electrochemical device.

[0052] In this application, Dv90 represents the particle size that, in the volumetric particle size distribution, reaches 90% of the total volumetric size, starting from the smallest particle size.

[0053] In this application, inorganic particles of different sizes can be purchased. The particle size can be tested by referring to the "Inorganic Particle Size Test" method provided in the "Test Methods and Equipment" section of this application, and inorganic particles of the desired size can be selected.

[0054] In one embodiment of this application, the thickness of the first coating is from 0.2 μm to 2 μm, preferably from 0.5 μm to 1.25 μm. For example, the thickness of the first coating can be 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.25 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, or a range consisting of any two of these values. By controlling the thickness of the first coating within the above range, a thicker first coating results in higher mechanical strength, which is beneficial for protecting the positive electrode current collector during pin penetration testing, reducing the probability of internal short circuits in the electrochemical device, and lowering the probability of thermal runaway caused by local overheating of the electrochemical device, thereby further improving the pin penetration safety performance of the electrochemical device.

[0055] In one embodiment of this application, the ratio of the thickness of the first coating to the thickness of the single-sided positive electrode material layer is 0.18% to 2.2%. For example, the ratio of the thickness of the first coating to the thickness of the single-sided positive electrode material layer can be 0.18%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, or a range consisting of any two of these ratios. By controlling the ratio of the thickness of the first coating to the thickness of the single-sided positive electrode material layer within the above range, it is beneficial to control a suitable ion transport path, improve the ion transport rate, and further improve the fast-charging performance of the electrochemical device.

[0056] In one embodiment of this application, the inorganic particle mass percentage is between 80% and 94.5% based on the mass of the first coating. For example, the inorganic particle mass percentage can be 80%, 81%, 82%, 3%, 4%, 5%, 6%, 87%, 8%, 89%, 90%, 91%, 92%, 93%, 94%, 94.5%, or a range consisting of any two of these values. When the inorganic particle mass percentage is within the above range, the first coating has a higher film resistance, which is beneficial for increasing short-circuit resistance, reducing dangerous short-circuit points between the positive and negative electrodes during pin-through testing, reducing the heat power generated by short circuits, and further improving the pin-through safety performance of the electrochemical device.

[0057] In one embodiment of this application, the first adhesive comprises a water-soluble polymeric metal salt; the mass percentage of the first adhesive is 0.5% to 15% based on the mass of the first coating. For example, the mass percentage of the first adhesive can be 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range of any two of these values. By controlling the selection of the first binder from the aforementioned materials and ensuring its mass percentage content falls within the aforementioned range, the water-soluble polymer metal salt exhibits good hydrophilicity, which is beneficial for electron and ion transport. Its electronic and ionic conductivity is superior to that of non-water-soluble polymers such as polyvinylidene fluoride and polyvinylidene chloride. Therefore, the first coating is beneficial for improving the kinetic performance of the electrochemical device and enhancing its low-temperature cycling performance. Furthermore, the water-soluble polymer metal salt has a large specific surface area and can be highly dispersed upon contact with water. When used as the first binder in the first coating layer, it can improve the tensile strength of the first coating. Simultaneously, the water-soluble polymer metal salt has numerous polar functional groups and hydrogen-bonding functional groups, forming strong hydrogen bonds with the oxide layer on the surface of the positive electrode current collector. This enhances the adhesion between the first coating and the positive electrode current collector, improving the safety performance of the electrochemical device. It also reduces the degree of peeling between the first coating and the positive electrode current collector during cycling, improving the interfacial contact resistance during cycling, thereby further enhancing the low-temperature cycling performance and cycle life of the electrochemical device.

[0058] In one embodiment of this application, the metal element in the water-soluble polymer metal salt includes at least one selected from lithium, sodium, potassium, rubidium, cesium, francium, beryllium, barium, strontium, calcium, or magnesium; the polymer in the water-soluble polymer metal salt includes at least one selected from polyacrylic acid, carboxymethyl cellulose, polyacrylonitrile, or styrene-butadiene. The metal element and polymer in the water-soluble polymer metal salt, within the scope of this application, are beneficial for improving electron and ion transport performance, resulting in electronic and ionic conductivity superior to that of insoluble polymers such as polyvinylidene fluoride and polyvinylidene chloride, thereby enhancing mass transfer kinetics and further improving the kinetic performance and low-temperature cycling performance of the electrochemical device.

[0059] In one embodiment of this application, the water-soluble polymeric metal salt includes at least one of sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, calcium polyacrylate, magnesium polyacrylate, rubidium polyacrylate, cesium polyacrylate, francium polyacrylate, barium polyacrylate, strontium polyacrylate, lithium carboxymethyl cellulose, beryllium carboxymethyl cellulose, or sodium carboxymethyl cellulose. Within the scope of this application, water-soluble polymer metal salts exhibit good hydrophilicity, which is beneficial for electron and ion transport. Their electronic and ionic conductivity is superior to that of non-water-soluble polymers such as polyvinylidene fluoride and polyvinylidene chloride. Therefore, the first coating is beneficial for improving the kinetic performance of the electrochemical device and enhancing its low-temperature cycling performance. Furthermore, water-soluble polymer metal salts have a large specific surface area and can be highly dispersed upon contact with water. When used as a first binder in the first coating layer, they can improve the tensile strength of the first coating. At the same time, water-soluble polymer metal salts have many polar functional groups and functional groups that can form hydrogen bonds, which form strong hydrogen bonds with the oxide layer on the surface of the positive electrode current collector, thus improving the adhesion between the first coating and the positive electrode current collector and further enhancing the safety performance of the electrochemical device.

[0060] In one embodiment of this application, the third conductive agent includes at least one of conductive carbon black, activated carbon, carbon nanotubes, or carbon nanofibers; the mass percentage of the third conductive agent is 0.7% to 5% based on the mass of the first coating. For example, the mass percentage of the third conductive agent can be 0.7%, 1%, 2%, 3%, 4%, 5%, or a range consisting of any two of these values. When the type and mass percentage of the third conductive agent are within the above ranges, the first coating exhibits both high short-circuit resistance and good conductivity, further improving the low-temperature cycling performance of the electrochemical device.

[0061] In one embodiment of this application, within a 4μm × 4μm range in a scanning electron microscope image at 30,000x magnification, the particle size of the secondary particles of the third conductive agent in the first coating is <50nm. For example, the particle size of the secondary particles of the third conductive agent can be 0.01nm, 1nm, 10nm, 20nm, 30nm, 40nm, 49nm, or a range consisting of any two of these values. The fact that the particle size of the secondary particles of the third conductive agent is within the above range indicates that the third conductive agent is uniformly distributed and well-dispersed in the first coating, which can improve the conductive network density and further enhance the cycling and fast-charging performance of the electrochemical device.

[0062] In this application, the secondary particles of the third conductive agent refer to the secondary particles that are formed by the aggregation of the primary particles of the third conductive agent during the preparation of the positive electrode sheet.

[0063] In this application, the particle size of the secondary particles of the third conductive agent can be adjusted by ball milling dispersion process.

[0064] In one embodiment of this application, the adhesion force between the first coating and the positive electrode current collector is between 500 N / m and 900 N / m. For example, the adhesion force between the first coating and the positive electrode current collector can be 500 N / m, 550 N / m, 600 N / m, 650 N / m, 700 N / m, 750 N / m, 800 N / m, 850 N / m, 900 N / m, or a range consisting of any two of these values. The adhesion force between the first coating and the positive electrode current collector being within the above range indicates that the first coating and the positive electrode current collector have good adhesion. The first coating can encapsulate any metal burrs that may be generated in the current collector under abnormal conditions such as nail penetration or impact, thereby reducing the occurrence of internal short circuits in the electrochemical device. Simultaneously, it reduces the probability of thermal runaway or overheating combustion caused by localized overheating in the electrochemical device, further improving the nail penetration safety performance of the electrochemical device.

[0065] In one embodiment of this application, the film resistance of the first coating is between 200Ω and 2500Ω. For example, the film resistance of the first coating can be 200Ω, 300Ω, 400Ω, 600Ω, 800Ω, 1000Ω, 1200Ω, 1400Ω, 600Ω, 1800Ω, 2000Ω, 2200Ω, 2500Ω, or a range of any two of these values. Having the film resistance of the first coating within the above range is beneficial for increasing short-circuit resistance, reducing the Joule heat generated instantaneously during a short circuit, reducing the risk of dangerous short circuits, and improving the safety performance of the electrochemical device.

[0066] In one embodiment of this application, in the electrochemical impedance spectroscopy of the positive electrode, the characteristic frequency is at 10... 4 Hz to 10 6 An Rcont peak exists in the Hz range, with a characteristic frequency of 10. -1 An Rct peak exists in the frequency range of Hz to 10Hz. The ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak is 10. -5 Up to 0.01. For example, the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak can be 10. -5 10 -4 10 -3 The ratio is 0.01 or any two of these ratios. A positive electrode that meets these characteristics exhibits low resistance to electron transport in the conductive network, improving the cycling and fast-charging performance of the electrochemical device.

[0067] In one embodiment of this application, the film resistance of the positive electrode is from 1Ω to 3Ω. For example, the film resistance of the positive electrode can be 1Ω, 1.5Ω, 2Ω, 2.5Ω, 3Ω, or a range of any two of these values. The positive electrode meeting these characteristics is beneficial for increasing short-circuit resistance, reducing Joule heating generated during short-circuit processes, reducing the risk of dangerous short circuits, and improving the safety performance of the electrochemical device.

[0068] In one embodiment of this application, the resistivity of the positive electrode material layer is 1.125 × 10⁻⁶. -5 Ω·cm to 1.875×10 -5 Ω·cm. For example, the resistivity of the positive electrode material layer can be 1.125 × 10⁻⁶ Ω·cm. -5 Ω·cm, 1.25×10 -5 Ω·cm, 1.375×10 -5 Ω·cm, 1.5×10 -5 Ω·cm, 1.625×10 -5 Ω·cm, 1.75×10 -5 Ω·cm, 1.875×10 -5 Ω·cm or a range consisting of any two of these values. The positive electrode sheet satisfies the above characteristics, with low resistance and good electronic conductivity in the positive electrode material layer, indicating that the electrochemical device including the positive electrode sheet of this application has good low-temperature cycle performance and fast-charging performance; at the same time, the first coating has high resistance, and the resistance difference between the two is large, which can improve the safety performance and low-temperature cycle performance of the electrochemical device including the positive electrode sheet of this application while maintaining the same overall resistance of the positive electrode sheet.

[0069] In this application, the first carbon nanotube can be a commercially available conventional material, and its source is not particularly restricted, as long as it can achieve the purpose of this application. First carbon nanotubes with different lengths and diameters can be obtained by purchase, and the length and diameter of the first carbon nanotube can be obtained by testing. The desired length and diameter of the first carbon nanotube can be selected. The specific testing method for the length and diameter of the first carbon nanotube can be found in the "Testing of the Length and Diameter of the First Carbon Nanotube Conductive Agent" section of the Testing Methods and Equipment section.

[0070] In this application, the ion mobility of the cathode material layer can be controlled by the content of the first conductive agent, and / or the length, diameter, content, and type of the first carbon nanotube, and / or the content and type of the second conductive agent. Specifically, when other parameters remain constant, increasing the content of the first conductive agent increases the ion mobility of the cathode material layer, and vice versa; when other parameters remain constant, increasing the length of the first carbon nanotube increases the ion mobility of the cathode material layer, and vice versa; when other parameters remain constant, increasing the diameter of the first carbon nanotube increases the ion mobility of the cathode material layer, and vice versa; when other parameters remain constant, increasing the content of the first carbon nanotube increases the ion mobility of the cathode material layer, and vice versa; when other parameters remain constant, increasing the content of the second conductive agent increases the ion mobility of the cathode material layer, and vice versa.

[0071] This application does not impose any particular limitation on the method of adjusting the ratio of the first coating thickness to the cathode material layer thickness, as long as the purpose of this application can be achieved. For example, the ratio of the first coating thickness to the cathode material layer thickness can be adjusted by adjusting the individual values ​​of the first coating thickness and the cathode material layer thickness. Specifically, the thickness of the first coating can be adjusted by the coating weight per unit area, and the thickness of the cathode material layer can be adjusted by the coating weight per unit area.

[0072] This application does not impose any particular limitation on the method of adjusting the film resistance of the first coating, as long as the purpose of this application can be achieved. For example, the film resistance of the first coating can be adjusted by the Dv90 and type of inorganic particles, and / or the coating thickness of the first coating. Specifically, when other parameters remain constant, an increase in the Dv90 of the inorganic particles will decrease the film resistance of the first coating, and vice versa; when other parameters remain constant, an increase in the thickness of the first coating will increase the film resistance of the first coating, and vice versa.

[0073] This application does not impose any particular limitation on the method of controlling the film resistance of the positive electrode, as long as the purpose of this application can be achieved. For example, the film resistance of the positive electrode can be controlled by the content of the first conductive agent, and / or the length, diameter, content, and type of the first carbon nanotube, and / or the content and type of the second conductive agent, and / or the Dv90 and type of the inorganic particles, and / or the coating thickness of the first coating, and / or the conductivity of the positive electrode active material. Specifically, when other parameters remain constant, an increase in the content of the first conductive agent decreases the film resistance of the positive electrode, and vice versa; when other parameters remain constant, an increase in the length of the first carbon nanotube decreases the film resistance of the positive electrode, and vice versa; when other parameters remain constant, an increase in the diameter of the first carbon nanotube decreases the film resistance of the positive electrode, and vice versa; when other parameters remain constant, an increase in the content of the first carbon nanotube decreases the film resistance of the positive electrode, and vice versa; when other parameters remain constant, an increase in the content of the second conductive agent decreases the film resistance of the positive electrode, and vice versa; when other parameters remain constant, an increase in the conductivity of the positive electrode active material decreases the film resistance of the positive electrode, and vice versa; specifically, when other parameters remain constant, an increase in the Dv90 of the inorganic particles decreases the film resistance of the positive electrode, and vice versa; when other parameters remain constant, an increase in the thickness of the first coating increases the film resistance of the positive electrode, and vice versa.

[0074] This application does not impose any particular limitation on the method of controlling the resistivity of the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the resistivity of the positive electrode material layer can be controlled by the content of the first conductive agent, and / or the length, diameter, content, and type of the first carbon nanotube, and / or the content and type of the second conductive agent, and / or the conductivity of the positive electrode active material. Specifically, when other parameters remain unchanged, increasing the content of the first conductive agent decreases the resistivity of the positive electrode material layer, and vice versa; when other parameters remain unchanged, increasing the length of the first carbon nanotube decreases the resistivity of the positive electrode material layer, and vice versa; when other parameters remain unchanged, increasing the diameter of the first carbon nanotube decreases the resistivity of the positive electrode material layer, and vice versa; when other parameters remain unchanged, increasing the content of the first carbon nanotube decreases the resistivity of the positive electrode material layer, and vice versa; when other parameters remain unchanged, increasing the content of the second conductive agent decreases the resistivity of the positive electrode material layer, and vice versa; when other parameters remain unchanged, increasing the conductivity of the positive electrode active material decreases the resistivity of the positive electrode material layer, and vice versa.

[0075] This application does not impose any particular restrictions on the method of controlling the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectroscopy of the positive electrode, as long as the purpose of this application can be achieved. For example, the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectroscopy of the positive electrode can be controlled by the content of the first conductive agent, and / or the length, diameter, content, and type of the first carbon nanotube, and / or the Dv90 of the inorganic particles, the coating thickness of the first coating, and / or the content and type of the second conductive agent. Specifically, when other parameters remain constant, an increase in the content of the first conductive agent leads to a decrease in its ratio, and vice versa; when other parameters remain constant, an increase in the length of the first carbon nanotube leads to a decrease in its ratio, and vice versa; when other parameters remain constant, an increase in the diameter of the first carbon nanotube leads to a decrease in its ratio, and vice versa; when other parameters remain constant, an increase in the content of the first carbon nanotube leads to a decrease in its ratio, and vice versa; when other parameters remain constant, an increase in the content of the second conductive agent leads to a decrease in its ratio, and vice versa; when other parameters remain constant, an increase in the Dv90 of the inorganic particles leads to a decrease in its ratio, and vice versa; when other parameters remain constant, an increase in the thickness of the first coating leads to an increase in its ratio, and vice versa.

[0076] This application does not impose any particular limitation on the method of controlling the adhesion between the first coating and the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the adhesion between the first coating and the positive electrode current collector can be controlled by the mass percentage of inorganic particles Dv90 and the first binder. Specifically, when other parameters remain unchanged, increasing the inorganic particle Dv90 decreases the adhesion between the first coating and the positive electrode current collector, and vice versa; when other parameters remain unchanged, increasing the mass percentage of the first binder increases the adhesion between the first coating and the positive electrode current collector, and vice versa.

[0077] This application does not impose any particular limitation on the preparation method of the positive electrode sheet, as long as it can achieve the purpose of this application. For example, the preparation method of the positive electrode sheet may include, but is not limited to, the following steps: mixing inorganic particles, a first binder and a third conductive agent in a mass ratio of (80 to 94.5):(0.5 to 15):(0.7 to 5), adding deionized water as a solvent, and stirring evenly to obtain a first coating slurry with a solid content of 70 wt% to 80 wt%; then coating the first coating slurry onto one surface of the positive current collector, and baking it at 90°C to 180°C for 1 h to 3 h to obtain the first coating. Then, a positive electrode material layer slurry is prepared: the positive electrode active material, the first conductive agent, and the positive electrode binder are mixed in a mass ratio of (95 to 98):(0.6 to 3):(0.1 to 2), and a solvent is added. After stirring evenly, a positive electrode material layer slurry is obtained; or the positive electrode active material, the first conductive agent, the second conductive agent, and the positive electrode binder are mixed in a mass ratio of (94 to 97):(0.6 to 3.1):(1.4 to 2.8):(0.1 to 2), and a solvent is added. After stirring evenly, a positive electrode material layer slurry is obtained. The positive electrode material layer slurry with a solid content of 70 wt% to 80 wt% is coated on the surface of the first coating layer and dried to obtain a positive electrode sheet with a single-sided coating of the first coating layer and the positive electrode material layer. The above steps are repeated on the other surface of the positive electrode current collector to obtain a positive electrode sheet with a double-sided coating of the first coating layer and the positive electrode material layer.

[0078] In this application, the electrochemical device also includes a separator membrane. This application does not impose any particular limitation on the separator membrane, as long as it achieves the purpose of this application. For example, the material of the separator membrane may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0079] In some embodiments of this application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0080] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0081] In some embodiments of this application, the inorganic layer includes inorganic particles and an inorganic layer binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application also does not particularly limit the inorganic layer binder; for example, the inorganic layer binder may be at least one of the above-mentioned positive electrode binders.

[0082] In some embodiments of this application, the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0083] In this application, there is no particular limitation on the thickness of the separator, as long as it can achieve the purpose of this application. For example, the thickness of the separator can be from 3 μm to 30 μm.

[0084] In this application, the electrochemical device further includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the negative electrode current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0085] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0086] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0087] In some embodiments of this application, the negative electrode material layer may further include a negative electrode conductive agent, a negative electrode binder, and a thickener. This application does not impose any particular limitation on the types of negative electrode conductive agents, negative electrode binders, and thickeners, as long as they achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. Conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF), and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powder, and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the negative electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode conductive agent, negative electrode binder, and thickener in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0088] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm.

[0089] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0090] Optionally, the negative electrode sheet may further include a negative electrode conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the negative electrode conductive layer, and it can be a conductive layer commonly used in the art. For example, the negative electrode conductive layer includes a negative electrode conductive agent and a negative electrode conductive layer binder. This application does not impose any particular limitation on the negative electrode conductive agent and the negative electrode conductive layer binder; for example, it can be at least one of the aforementioned negative electrode conductive agent and negative electrode binder.

[0091] In this application, the electrochemical device also includes an electrolyte, which includes lithium salts and non-aqueous solvents.

[0092] This application does not impose any particular limitation on lithium salts, as long as they achieve the purpose of this application. For example, lithium salts may include, but are not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylboron (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), tris(trifluoromethanesulfonyl)methyl lithium (LiC(SO2CF3)3), lithium hexafluorosilicate (LiSiF6), lithium bis(oxalateborate)borate (LiBOB), and lithium difluoroborate (LiF2OB). This application does not impose any particular limitation on the content of lithium salts in the electrolyte, as long as they achieve the purpose of this application.

[0093] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0094] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.

[0095] The electrochemical device also includes a housing for accommodating the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of electrochemical devices. This application does not limit the scope of these other components. This application does not impose any particular limitation on the housing; it can be a housing known in the art, as long as it achieves the purpose of this application. For example, the housing can be a rigid housing or a flexible housing. The material of the rigid housing can be metal; this application does not limit the type of metal and can use known metal rigid housings, as long as they achieve the purpose of this application. The flexible housing can be a metal-plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0096] The preparation process of the electrochemical device described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the preparation process of the electrochemical device may include, but is not limited to, the following steps: stacking the positive electrode, the separator, and the negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the electrochemical device. Alternatively, stacking the positive electrode, the separator, and the negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the electrochemical device. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device.

[0097] A second aspect of this application provides an electronic device comprising the electrochemical device described in the first aspect of this application. The electronic device of this application exhibits superior pin-penetration safety performance, low-temperature cycling performance, and fast-charging performance.

[0098] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In some embodiments of this application, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0099] Example

[0100] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0101] Test method and equipment:

[0102] First carbon nanotube length and diameter test:

[0103] The sample was placed directly into the sample chamber of an OXFORD EDS scanning electron microscope, and the length and diameter of the first carbon nanotube were measured by surface observation. Observations were made at different locations on the sample surface, with a magnification of 50,000, to measure the length and diameter of the first carbon nanotube.

[0104] Select three different locations and measure the length and diameter of all the first carbon nanotubes within the field of view. The average value is the length and diameter of the first carbon nanotube.

[0105] Ion transference number test of positive electrode material layer:

[0106] Ion mobility number measurements were performed using a CHI660E electrochemical workstation. Lithium-ion batteries prepared in the examples or comparative cases were connected to the test equipment, a constant voltage of 1V was applied, and measurements were taken by recording the current change over time. The formula was used based on the current-time curve. Calculate the ion transport number, where t is the ion transport number, and i t i0 is the initial current value, which is the stable current value.

[0107] Thickness testing of the first coating and the cathode material layer:

[0108] The positive electrode sheet was longitudinally cut along the thickness direction using plasma, and a flat cross-section was obtained by argon ion polishing technology. Then, it was observed using a scanning electron microscope (OXFORD·EDS) at a magnification of 3000x. The thickness of the first coating was measured at 9 locations at equal intervals along the length of the positive electrode sheet, and the average value of the thickness at the 9 different locations was recorded as the thickness of the first coating.

[0109] The positive electrode sheet is longitudinally cut along the thickness direction using plasma, and a flat cross-section is obtained by argon ion polishing technology. Then, the thickness of the positive electrode material layer at three locations is measured using a scanning electron microscope (OXFORD·EDS) at a magnification of 1000x, and the average value is taken as the thickness of the positive electrode material layer.

[0110] The ratio (%) of the thickness of the first coating to the thickness of the cathode material layer = the thickness of the first coating / the thickness of the cathode material layer × 100%.

[0111] Particle size test of secondary particles of the third conductive agent:

[0112] The positive electrode sheet was plasma-cut longitudinally along the thickness direction, and a flat cross-section was obtained by argon ion polishing. The secondary particles of the third conductive agent were observed and their particle size was measured within a 4μm×4μm range in the scanning electron microscope (OXFORD·EDS) at a magnification of 30,000. The average particle size was recorded as the particle size of the secondary particles of the third conductive agent.

[0113] In electron microscopy testing, when the secondary particles could not be observed at a magnification of 30,000, the particle size of the secondary particles was recorded as <50nm, which indicates that the third conductive agent has good dispersibility.

[0114] Inorganic particle size testing:

[0115] The positive electrode sheet prepared in the examples or comparative examples was treated with N-methylpyrrolidone (NMP) for five consecutive washes to expose the first coating. Conductive adhesive was applied to the sample stage, and the treated positive electrode sheet was laid flat on the adhesive with the first coating facing upwards. Unadhesive powder was blown away with a syringe, and gold was sprayed onto it. The surface of the first coating was photographed using a Philips XL-30 field emission scanning electron microscope at an accelerating voltage of 10 kV and an emission current of 10 mA, at a magnification of 30,000x. Five different locations on the surface of the first coating were photographed. From the SEM images of each location, 100 particles were randomly selected, and the area of ​​each particle was calculated. Then, assuming the particles were spherical, their diameter D was calculated using the following formula: D = 2 × (S1 / π). 1 / 2 Where S1 is the area of ​​the particle; the particle size distribution is statistically analyzed to obtain the inorganic particle Dv90.

[0116] Electrochemical impedance spectroscopy (EIS) testing:

[0117] EIS testing was performed using a Solartron 1260 electrochemical impedance spectroscopy (EIS) system. The lithium-ion batteries prepared in the examples or comparative examples were connected to the system, ensuring good electrode contact. A 5 mV AC voltage was applied to the samples at frequencies ranging from 0.1 Hz to 1 MHz, and the AC current response was recorded to obtain the impedance spectrum of the positive electrode.

[0118] By fitting the circuit model and performing a refined decomposition using time-domain Fourier transform (DFT), the contact resistance (Rcont) was extracted (peak position at 10). 4 ~10 6 Hz) and charge transfer resistance (Rct) (peak position at 10 Hz) -1 ~10 1 The peak signal intensity (Hz), the ratio of the above two peak signal intensities, that is, the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak.

[0119] Diaphragm resistance test:

[0120] Using a two-probe film resistance meter (BER2500), the test area of ​​the first coating or positive electrode was 154 mm². 2 The pressure is 0.4T.

[0121] After removing the surface insulation using DMC, the positive electrode is directly tested to obtain the film resistance of the positive electrode.

[0122] The positive electrode sheet was subjected to five consecutive NMP scrubbing processes to expose the surface of the first coating. The first coating was then tested to obtain the film resistance of the first coating.

[0123] Resistivity test of positive electrode material layer:

[0124] Arrange the tips of four probes at equal intervals in a straight line, and label them as probe 1, 2, 3, and 4. The radius of curvature of the probe tip is 25 μm, and the probe spacing is fixed at 1 mm. Apply 150 g of pressure between the probe and the positive electrode material layer, and insert the probe to a depth of 2 μm. Obtain the voltage V and current I using a voltmeter and an ammeter, and calculate the sheet resistance of the positive electrode material layer as (π / ln2) × (V / I), where π is the mathematical constant pi.

[0125] The resistivity of the positive electrode material layer = sheet resistance of the positive electrode material layer / penetration depth 2μm.

[0126] Adhesion test between the first coating and the positive electrode current collector:

[0127] Take a positive electrode sheet coated with the first coating, with a sample size of 15mm × 250mm. Attach the positive electrode sheet to a smooth steel plate using double-sided tape. Attach adhesive tape to the other side of the positive electrode sheet, and fix one end of the adhesive tape to a tensile testing machine (Instron 5982). Set the speed to 10mm / min and pull the adhesive tape 180° straight. Read the adhesive force when the adhesive tape is stretched. After exporting the data, divide it by the width of the adhesive tape (15mm) to obtain the adhesive force between the first coating and the positive current collector.

[0128] Piercing test pass rate:

[0129] Take 50 lithium-ion batteries prepared in the examples or comparative examples, and fully charge them at 25±3℃. The specific steps are as follows: charge at a constant current of 0.5C to 4.5V, and then charge at a constant voltage of 4.5V to 0.05C current cutoff.

[0130] A nail penetration test was conducted on lithium-ion batteries at 25±3℃ using carbon steel nails with a diameter of 4mm, a taper of 16.5mm, and a total length of 100mm. The penetration speed was set to 30mm / s, and the penetration depth was determined by the nail's taper penetrating the lithium-ion battery. The state of the lithium-ion battery was observed during the test, with the criterion being that the battery did not burn or explode. The nail penetration test pass rate (%) = number of nail penetration tests passed / 50 × 100%.

[0131] First charging time test:

[0132] The lithium-ion battery was charged to 4.5V at a constant current of 3C under conditions of 25±3℃, and then charged to 0.05C at a constant voltage of 4.5V. The duration from the start of charging to the end of charging was calculated and recorded as the duration of the first charge.

[0133] Low temperature cycling performance test

[0134] After being left to stand at 25℃±3℃ for 30 min, the lithium-ion battery was charged at a constant current of 1.25C to 4.2V, then charged at a constant current of 1.5C to 4.5V, then charged at a constant voltage of 4.5V to 0.05C, and finally discharged at a constant current of 0.2C to 3.0V. This was recorded as capacity 1. The above full-charge process was repeated, and the battery was then transferred to an environment of -20℃±3℃ and left to stand for 30 min. It was then discharged at a constant current of 0.2C to 3.0V, and this was recorded as capacity 2. The low-temperature cycle capacity retention rate (%) was obtained by comparing capacity 2 with capacity 1.

[0135] 45℃ Cyclic Performance Test:

[0136] The lithium-ion batteries of Examples 1-1, Comparative Examples 2 and 6 were left to stand at 45℃±3℃ for 30 minutes, then charged at a constant current of 1.25C to 4.25V, then charged at a constant current of 1.5C to 4.5V, then charged at a constant voltage of 4.5V to 0.05C, left to stand for 30 minutes, and then discharged at a constant current of 0.7C to 3.0V. The discharge capacity obtained by this step was taken as the initial capacity. The above cycle was repeated, and on the 50th cycle, the batteries were left to stand for 30 minutes and then discharged at a constant current of 0.2C to 3.0V.

[0137] Repeat the above cycle. After the 100th cycle, let it stand for 30 minutes, and then discharge it to 3.0V with a constant current of 0.2C.

[0138] Repeat the above cycle until the 150th cycle, then let it stand for 30 minutes, and then discharge it to 3.0V with a constant current of 0.2C.

[0139] Repeat the above cycle until the 200th cycle, then let it stand for 30 minutes, and then discharge it to 3.0V with a constant current of 0.2C.

[0140] Repeat the above cycle until the 250th cycle, then let it stand for 30 minutes, and then discharge it to 3.0V with a constant current of 0.2C.

[0141] Repeat the above cycle until the 300th cycle, then let it stand for 30 minutes, and then discharge it to 3.0V with a constant current of 0.2C.

[0142] Repeat the above cycle until the 350th cycle, then let it stand for 30 minutes, and then discharge it to 3.0V with a constant current of 0.2C.

[0143] Repeat the above cycle. After the 400th cycle, let it stand for 30 minutes, and then discharge it to 3.0V with a constant current of 0.2C.

[0144] The discharge capacity retention rate at each cycle (0, 50, 100, 150, 200, 250, 300, 350, and 400 cycles) was obtained by comparing the discharge capacity with the initial capacity. The cycle capacity retention rate of the lithium-ion battery at 45℃±3℃ was recorded.

[0145] 1s DC internal resistance test method:

[0146] 1) The test environment temperature is 25±3℃. The lithium-ion battery is charged to 4.5V at a constant current of 0.5C, and then charged to 0.05C at a constant voltage of 4.5V. Let it stand for 30 minutes.

[0147] 2) Discharge the lithium-ion battery at 1C for 1 second;

[0148] 3) Denote the voltage drop in process 2) as ΔU and the ammeter as I;

[0149] 4) The DC internal resistance of a lithium-ion battery during 1C discharge for 1s is ΔU / I.

[0150] Lithium-ion battery internal resistance test:

[0151] The lithium-ion batteries from Examples 1-1, Comparative Examples 2, and 6 were charged at a constant current of 0.5C to 4.5V, then charged at a constant voltage of 4.5V to a current of 0.05C. After resting for 30 minutes, they were charged again at a constant voltage of 4.5V to a current of 0.05C. The AC internal resistance of the lithium-ion batteries was tested using a Hiokki BT4560 battery impedance meter, with the measurement frequency set to 1kHz and the disturbance voltage set to 5mV. The measured value was recorded as the initial internal resistance, and the above cycle was repeated for 800 cycles.

[0152] The internal resistance of the lithium-ion battery after each cycle is obtained by using the internal resistance after 0, 1, 50, 100, 150, 200, 300, 400, 500, 600, 700, and 800 cycles.

[0153] Example 1-1

[0154] <Preparation of the positive electrode>

[0155] Inorganic nano-boehmite (Dv90 of 500 nm), sodium polyacrylate as the first binder, and Ketjen black as the third conductive agent were mixed in a mass ratio of 89:9:2. Deionized water was added as a solvent, and the mixture was stirred until homogeneous to obtain a first coating slurry with a solid content of 75 wt%. The slurry was then ball-milled 25 times and coated onto one surface of a 10 μm positive electrode current collector aluminum foil. After baking at 120°C for 2 hours, a positive electrode current collector with the first coating was obtained. The above steps were then repeated on the other surface of the positive electrode current collector aluminum foil.

[0156] Lithium cobalt oxide (CCO) as the positive electrode active material, a first conductive agent, a second conductive agent, and polyvinylidene fluoride (PVDF) as the positive electrode binder were mixed in a mass ratio of 94.6:1.6:2:1.8. The first conductive agent consisted of first and second SWCNTs (similar to SWCNTs in the original text). The second conductive agent was acetylene black. NMP was added as a solvent, and the mixture was stirred uniformly in a vacuum mixer to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto the surface of the first coating away from the positive electrode current collector and dried at 120°C to obtain a positive electrode sheet with a single-sided coating of the first coating and the positive electrode material layer. The coating weight of the positive electrode material layer was 267.8 mg / 1540 mm². 2 Then, the above steps are repeated on the other surface of the aluminum foil. After drying at 120℃, a positive electrode sheet with a double-sided coating of the first coating layer and the positive electrode material layer is obtained. This is then cold-pressed, cut, and have tabs welded to obtain a positive electrode sheet with dimensions of 74mm × 867mm for later use. The compacted density of the positive electrode sheet is 4.23 g / cm³. 3 .

[0157] The thickness of the first coating is 0.8 μm, the thickness of the single-sided positive electrode material layer is 90 μm, and the ratio of the thickness of the single-sided positive electrode material layer to the thickness of the first coating is 0.89%.

[0158] In the positive electrode material layer, the first conductive agent includes first SWCNTs and second SWCNTs, with a mass percentage content of 1.6%. Specifically, the first SWCNTs have a mass percentage content of 1%, a length of 3 μm, and a diameter of 50 nm; the second SWCNTs have a mass percentage content of 0.6%, a length of 500 nm, and a diameter of 20 nm. The second conductive agent in the positive electrode material layer has a mass percentage content of 2%.

[0159] <Preparation of Negative Electrode Sheets>

[0160] Artificial graphite (negative electrode active material), acetylene black (negative electrode conductive agent), and carboxymethyl cellulose (CMC) (negative electrode binder) were mixed at a mass ratio of 97.7:1:1.3. Deionized water was then added as a solvent to prepare a slurry with a solid content of 70 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector and dried at 120°C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The coating weight of the negative electrode material layer was 142 mg / 1540 mm². 2The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 120℃ and cold pressing, the sheet is cut and tabs are welded to obtain a negative electrode sheet with dimensions of 78mm × 875mm for later use. The thickness of the single-sided negative electrode material layer is 90.3μm, and the compaction density is 1.75g / cm³. 3 .

[0161] <Preparation of Electrolyte>

[0162] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed at a mass ratio of 10:30:60 to obtain a base solvent. Lithium salt LiPF6 was then added and stirred until homogeneous to obtain the electrolyte. The lithium salt LiPF6 comprised 12.5% ​​of the total electrolyte mass, with the remainder being the base solvent.

[0163] <Isolation membrane>

[0164] A porous polyethylene polymer film with a thickness of 8 μm (manufacturer: Celgard Diaphragm Company, USA) was used as the separator.

[0165] <Preparation of Lithium-ion Batteries>

[0166] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to form an electrode assembly, which is placed in an aluminum-plastic film housing and dehydrated at 80°C. A prepared electrolyte is then injected, followed by vacuum sealing, settling, formation, and shaping processes to obtain a lithium-ion battery. The formation upper limit voltage is 4.15V, the formation temperature is 70°C, and the formation settling time is 2 hours.

[0167] Examples 1-2 to Examples 1-16

[0168] Except for adjusting the corresponding preparation parameters according to Table 1, the rest is the same as in Examples 1-1. Specifically, when the mass percentage of the first conductive agent and / or the second conductive agent changes, the mass percentage of the positive electrode active material changes accordingly, while the mass percentage of the positive electrode binder remains unchanged, and the sum of the mass percentages of all substances in the positive electrode material layer is 100%.

[0169] Examples 2-1 to 2-16

[0170] Except for adjusting the corresponding preparation parameters according to Table 3, the rest is the same as in Examples 1-1. Among them, in the <Preparation of Positive Electrode Sheet> of Examples 2-16, ball milling and dispersion are not performed, so that the particle size of the secondary particles of the third conductive agent is as shown in Table 3.

[0171] Comparative Example 1

[0172] <Preparation of the positive electrode>

[0173] Inorganic particles of boehmite (Dv90 of 500 nm), sodium polyacrylate as the first binder, and Ketjen black as the third conductive agent were mixed in a mass ratio of 89:9:2. Deionized water was added as a solvent and the mixture was stirred evenly to obtain a first coating slurry with a solid content of 75 wt%. This slurry was coated on one surface of a 10 μm positive electrode current collector aluminum foil and baked at 120 °C for 2 hours to obtain a positive electrode current collector with the first coating on its surface.

[0174] Lithium cobalt oxide (the positive electrode active material), a second conductive agent, and polyvinylidene fluoride (PVDF) (the positive electrode binder) were mixed in a mass ratio of 96:2:2. Acetylene black was used as the second conductive agent, and NMP was added as a solvent. The mixture was stirred uniformly in a vacuum mixer to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto the surface of the first coating layer away from the positive electrode current collector and dried at 120°C to obtain a positive electrode sheet with a single-sided coating of the first coating layer and the positive electrode material layer. The coating weight of the positive electrode material layer was 267.8 mg / 1540 mm². 2 Then, the above steps are repeated on the other surface of the aluminum foil. After drying at 120℃, a positive electrode sheet with a double-sided coating of the first coating layer and the positive electrode material layer is obtained. This is then cold-pressed, cut, and have tabs welded to obtain a positive electrode sheet with dimensions of 74mm × 867mm for later use. The compacted density of the positive electrode sheet is 4.23 g / cm³. 3 .

[0175] The thickness of the first coating is 0.8 μm, the thickness of the single-sided positive electrode material layer is 90 μm, and the ratio of the thickness of the single-sided positive electrode material layer to the thickness of the first coating is 0.89%.

[0176] In the positive electrode material layer, the mass percentage of the second conductive agent is 2%.

[0177] Comparative Examples 2 to 5

[0178] Except for adjusting the corresponding preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0179] Comparative Example 6

[0180] Except for the omission of the first coating in the <Preparation of the Positive Electrode>, the rest is the same as in Example 1-1.

[0181] The preparation parameters and performance of each embodiment and comparative example are shown in Tables 1 to 4.

[0182] Table 1

[0183] Note: In Table 1, " / " indicates that there is no corresponding preparation parameter, substance, or performance parameter.

[0184] Table 2

[0185] The length and diameter of the first carbon nanotube in the cathode material layer, as well as the ion migration number of the cathode material layer, affect the puncture safety performance, low-temperature cycling performance, and fast-charging performance of the electrochemical device. As can be seen from Examples 1-1 to 1-16 and Comparative Examples 1 to 6, when the length and diameter of the first carbon nanotube and the ion migration number of the cathode material layer are within the ranges specified in this application, the prepared lithium-ion batteries exhibit higher puncture test pass rates, shorter initial charging times, lower 1s DC internal resistance, and higher low-temperature capacity retention. This indicates that the puncture safety performance, low-temperature cycling performance, and fast-charging performance of the lithium-ion batteries prepared in the embodiments of this application are improved.

[0186] The film resistance of the positive electrode, the resistivity of the positive electrode material layer, and the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectroscopy of the positive electrode are affected by the length, diameter, mass percentage, and type of the first carbon nanotube, and / or the mass percentage of the first conductive agent, and / or the mass percentage and type of the second conductive agent. As can be seen from Examples 1-1 to 1-16, the length, diameter, mass percentage, and type of the first carbon nanotube, and / or the mass percentage of the first conductive agent, and / or the mass percentage and type of the second conductive agent are within the scope of this application, and the film resistance of the positive electrode, the resistivity of the positive electrode material layer, and the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectroscopy of the positive electrode are within the scope of this application.

[0187] like Figure 2 The image shows the surface morphology of the first coating prepared in Example 1-1 of this application. The inorganic particles of the first coating form a dense coating on the surface of the positive electrode current collector and are uniformly dispersed.

[0188] like Figure 3 The image shown is a cross-sectional view along the thickness direction of the positive electrode sheet prepared in Example 1-1 of this application. Figure 3 The middle part is the positive current collector. Figure 3 Above and below are positive electrode material layers and positive electrode active material particles in the positive electrode material layers, and between the positive electrode material layer and the positive electrode current collector is the first coating layer.

[0189] like Figure 4As shown, the lithium-ion batteries prepared in Examples 1-1 and Comparative Example 6 exhibited higher cycle capacity retention at 45°C, while Comparative Example 2 showed lower cycle capacity retention at 45°C. Notably, Comparative Example 6, lacking a first coating, had a 0% pass rate in the puncture test, indicating poor puncture safety performance of the lithium-ion battery prepared in Comparative Example 6.

[0190] like Figure 5 As shown, the lithium-ion batteries prepared in Examples 1-1 and Comparative Example 6 have lower AC impedance, while Comparative Example 2 has higher AC impedance. Specifically, Comparative Example 6, lacking a first coating, had a 0% pass rate in the puncture test, indicating poor safety performance of the lithium-ion battery prepared in Comparative Example 6 when punctured.

[0191] like Figure 6 The image shows the EIS spectra of the positive electrode sheets prepared in Examples 1-1 and Comparative Examples 1 and 6 of this application. The ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the EIS spectrum of the positive electrode sheet in Example 1-1 is within the range of this application. At the same time, the film resistance and resistivity of the positive electrode material layer of Example 1-1 are also within the range of this application. The lithium-ion battery prepared in Example 1-1 has good safety performance, fast charging performance and cycle performance.

[0192] The mass percentage of the first carbon nanotube and the first conductive agent affects the puncture safety performance, low-temperature cycling performance, and fast-charging performance of the electrochemical device. Examples 1-1, 1-5 to 1-7 show that the mass percentage of the first carbon nanotube and the first conductive agent is within the range of this application. The film resistance of the positive electrode, the resistivity of the positive electrode material layer, and the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectrum of the positive electrode are all within the range of this application. The prepared lithium-ion battery exhibits a high puncture test pass rate, a short first charging time, a low 1s DC internal resistance, and a high low-temperature capacity retention rate, indicating that the lithium-ion battery prepared in the examples of this application has good puncture safety performance, low-temperature cycling performance, and fast-charging performance.

[0193] The material of the first carbon nanotube affects the puncture safety performance, low-temperature cycling performance, and fast-charging performance of the electrochemical device. As can be seen from Examples 1-1 and 1-12, the material of the first carbon nanotube is within the scope of this application. The film resistance of the positive electrode, the resistivity of the positive electrode material layer, and the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectrum of the positive electrode are all within the scope of this application. The prepared lithium-ion battery exhibits a high puncture test pass rate, a short first charging time, a low 1s DC internal resistance, and a high low-temperature capacity retention rate, indicating that the puncture safety performance, low-temperature cycling performance, and fast-charging performance of the lithium-ion battery prepared in the embodiments of this application are improved.

[0194] The mass percentage content and material of the second conductive agent affect the puncture safety performance, low-temperature cycle performance, and fast-charging performance of the electrochemical device. As can be seen from Examples 1-1, 1-13 to 1-16, the mass percentage content and material of the second conductive agent are within the scope of this application. The film resistance of the positive electrode, the resistivity of the positive electrode material layer, and the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectrum of the positive electrode are all within the scope of this application. The prepared lithium-ion battery exhibits a high puncture test pass rate, a short first charging time, a low 1s DC internal resistance, and a high low-temperature capacity retention rate, indicating that the puncture safety performance, low-temperature cycle performance, and fast-charging performance of the lithium-ion battery prepared in the examples of this application are improved.

[0195] Table 3

[0196] Table 4

[0197] The Dv90 of inorganic particles in the first coating affects the puncture safety performance, low-temperature cycle performance, and fast-charging performance of the electrochemical device. As can be seen from Examples 1-1, 2-1 to 2-5, the Dv90 of inorganic particles is within the scope of this application. The film resistance of the first coating, the film resistance of the positive electrode, the resistivity of the positive electrode material layer, and the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectrum of the positive electrode are all within the scope of this application. The prepared lithium-ion battery exhibits a high puncture test pass rate, a short first charging time, a low 1s DC internal resistance, and a high low-temperature capacity retention rate, indicating that the lithium-ion battery prepared in the embodiments of this application has good puncture safety performance, low-temperature cycle performance, and fast-charging performance.

[0198] The mass percentage and type of inorganic particles, first binder, and third conductive agent in the first coating affect the puncture safety performance, low-temperature cycle performance, and fast-charging performance of the electrochemical device. As can be seen from Examples 1-1, 2-6 to 2-11, the mass percentage and type of inorganic particles, first binder, and third conductive agent in the first coating are within the scope of this application. The film resistance of the first coating, the film resistance of the positive electrode, the resistivity of the positive electrode material layer, and the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectrum of the positive electrode are within the scope of this application. The prepared lithium-ion battery exhibits a high puncture test pass rate, a short first charging time, a low 1s DC internal resistance, and a high low-temperature capacity retention rate, indicating that the lithium-ion battery prepared in the embodiments of this application has good puncture safety performance, low-temperature cycle performance, and fast-charging performance.

[0199] The thickness of the first coating affects the puncture safety performance, low-temperature cycle performance, and fast-charging performance of the electrochemical device. As can be seen from Examples 1-1, 2-12 to 2-15, the thickness of the first coating is within the range of this application. The film resistance of the first coating, the film resistance of the positive electrode, the resistivity of the positive electrode material layer, and the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectrum of the positive electrode are all within the range of this application. The prepared lithium-ion battery exhibits a high puncture test pass rate, a short first charging time, a low 1s DC internal resistance, and a high low-temperature capacity retention rate, indicating that the lithium-ion battery prepared in the embodiments of this application has good puncture safety performance, low-temperature cycle performance, and fast-charging performance.

[0200] The particle size of the secondary particles of the third conductive agent affects the puncture safety performance, low-temperature cycle performance, and fast-charging performance of the electrochemical device. As can be seen from Examples 1-1 and 2-16, the particle size of the secondary particles of the third conductive agent is within the range of this application. The film resistance of the first coating, the film resistance of the positive electrode, the resistivity of the positive electrode material layer, and the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak in the electrochemical impedance spectrum of the positive electrode are all within the range of this application. The prepared lithium-ion battery exhibits a high puncture test pass rate, a short first charging time, a low 1s DC internal resistance, and a high low-temperature capacity retention rate, indicating that the lithium-ion battery prepared in the embodiments of this application has good puncture safety performance, low-temperature cycle performance, and fast-charging performance.

[0201] The ratio of the thickness of the first coating to the thickness of the positive electrode material layer affects the puncture safety performance, low-temperature cycle performance, and fast-charging performance of the electrochemical device. As can be seen from Examples 1-1, 2-12, and 2-15, the ratio of the thickness of the first coating to the thickness of the positive electrode material layer is within the range of this application. The film resistance of the first coating, the film resistance of the positive electrode, the resistivity of the positive electrode material layer, and the ratio of the contact impedance of the Rcont peak and the fitted impedance of the Rct peak in the electrochemical impedance spectrum of the positive electrode are all within the range of this application. The prepared lithium-ion battery exhibits a high puncture test pass rate, a short first charging time, a low 1s DC internal resistance, and a high low-temperature capacity retention rate, indicating that the lithium-ion battery prepared in the embodiments of this application has good puncture safety performance, low-temperature cycle performance, and fast-charging performance.

[0202] The adhesion between the first coating and the positive electrode current collector is affected by the mass percentage content of the inorganic particles Dv90 and the first binder. As can be seen from Examples 1-1, 2-1 to 2-8, the mass percentage content of the inorganic particles Dv90 and the first binder is within the range of this application, and the adhesion between the first coating and the positive electrode current collector is within the range of this application.

[0203] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0204] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0205] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electrochemical device, the electrochemical device comprising a positive electrode plate, the positive electrode plate comprising a positive current collector, a first coating and a positive electrode material layer, the first coating being disposed on the surface of the positive current collector, and the positive electrode material layer being disposed on the surface of the first coating away from the positive current collector; The first coating comprises inorganic particles, which include at least one of nano-boehmite, aluminum oxide, titanium dioxide, magnesium oxide, zirconium oxide, or zinc oxide. The positive electrode material layer includes a first conductive agent, which includes a first carbon nanotube; the length of the first carbon nanotube is 2 μm to 5 μm, and the diameter of the first carbon nanotube is 2 nm to 100 nm; the ion transference number of the positive electrode material layer is 0.4 to 0.47; and the thickness of the first coating is 0.2 μm to 2 μm.

2. The electrochemical device according to claim 1, wherein, The electrochemical device satisfies at least one of the following conditions: (1) The length of the first carbon nanotube is 2 μm to 4 μm; (2) The diameter of the first carbon nanotube is 20 nm to 80 nm.

3. The electrochemical device according to claim 1, wherein, Based on the mass of the cathode material layer, the mass percentage of the first carbon nanotube is between 0.5% and 2.5%.

4. The electrochemical device according to claim 1, wherein, Based on the mass of the positive electrode material layer, the mass percentage of the first conductive agent is 0.6% to 3.1%.

5. The electrochemical device according to claim 1, wherein, The positive electrode material layer further includes a second conductive agent, which includes at least one of conductive carbon black or activated carbon; based on the mass of the positive electrode material layer, the mass percentage of the second conductive agent is 1.4% to 2.8%.

6. The electrochemical device according to claim 1, wherein, The Dv90 of the inorganic particles is between 200 nm and 1000 nm.

7. The electrochemical device according to claim 1, wherein, The thickness of the first coating is 0.5 μm to 1.25 μm.

8. The electrochemical device according to claim 6, wherein, The Dv90 of the inorganic particles is 400nm to 600nm.

9. The electrochemical device according to claim 1, wherein, The ratio of the thickness of the first coating to the thickness of the positive electrode material layer is 0.18% to 2.2%.

10. The electrochemical device according to claim 1, wherein, Based on the quality of the first coating, the inorganic particles have a mass percentage content of 80% to 94.5%.

11. The electrochemical device according to claim 1, wherein, The first coating further includes a first binder and a third conductive agent, wherein the first binder comprises a water-soluble polymer metal salt; the mass percentage of the first binder is 0.5% to 15% based on the mass of the first coating.

12. The electrochemical device according to claim 11, wherein, The metal element in the water-soluble polymer metal salt includes at least one of lithium, sodium, potassium, rubidium, cesium, francium, beryllium, barium, strontium, calcium, or magnesium; the polymer in the water-soluble polymer metal salt includes at least one of polyacrylic acid, carboxymethyl cellulose, polyacrylonitrile, or styrene-butadiene.

13. The electrochemical device according to claim 11, wherein, The water-soluble polymer metal salt includes at least one of sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, calcium polyacrylate, magnesium polyacrylate, rubidium polyacrylate, cesium polyacrylate, francium polyacrylate, barium polyacrylate, strontium polyacrylate, lithium carboxymethyl cellulose, beryllium carboxymethyl cellulose, or sodium carboxymethyl cellulose.

14. The electrochemical device according to claim 1, wherein, The first coating further includes a first binder and a third conductive agent, wherein the third conductive agent includes at least one of conductive carbon black, activated carbon, carbon nanotubes, or carbon nanofibers; and the mass percentage of the third conductive agent is 0.7% to 5% based on the mass of the first coating.

15. The electrochemical device according to claim 1, wherein, The first coating further includes a first binder and a third conductive agent. In a scanning electron microscope image with a magnification of 30,000x, the particle size of the secondary particles of the third conductive agent is <50nm within a 4μm×4μm range.

16. The electrochemical device according to claim 1, wherein, The adhesion between the first coating and the positive current collector is 500 N / m to 900 N / m.

17. The electrochemical device according to claim 1, wherein, The electrochemical device satisfies at least one of the following conditions: (1) The film resistance of the first coating is 200Ω to 2500Ω; (2) In the electrochemical impedance spectroscopy of the positive electrode, the characteristic frequency is at 10. 4 Hz to 10 6 An Rcont peak exists in the Hz range, with a characteristic frequency of 10. -1 An Rct peak exists in the frequency range of Hz to 10Hz, and the ratio of the contact impedance of the Rcont peak to the fitted impedance of the Rct peak is 10. -5 Up to 0.01; (3) The film resistance of the positive electrode is 1Ω to 3Ω; (4) The resistivity of the positive electrode material layer is 1.125 × 10⁻⁶. -5 Ω·cm to 1.875×10 -5 Ω·cm.

18. An electronic device comprising the electrochemical device according to any one of claims 1 to 17.

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