An electrochemical device and an electronic device

Abstract

The application provides an electrochemical device and an electronic 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 the surface of the positive electrode current collector, and the positive electrode material layer being arranged on the surface of the first coating layer away from the positive electrode current collector, the first coating layer comprising a first main material and a first binder, the first main material comprising a solid-state electrolyte, the surface of the solid-state electrolyte being provided with a carbon material, the Dv50 of the first main material being 50 nm to 200 nm, and the thickness of the first coating layer being 0.5 μm to 2 μm. The electrochemical device provided by the application has good nail-penetration safety performance, and also has good cycle performance and low-temperature discharge performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and particularly relates to an electrochemical device and an electronic device. BACKGROUND

[0002] Electrochemical devices (such as lithium ion batteries) have been popularized in daily life with the development of science and technology. Lithium ion batteries have entered our daily life with the progress of science and technology and the improvement of environmental protection requirements. With the large-scale popularization of lithium ion batteries, the service life thereof is increasingly valued by users, and consumers, the after-sales end, battery manufacturers and lithium battery manufacturers all put forward new requirements for the safety performance of the batteries.

[0003] However, with the rapid popularization of lithium ion batteries, the technology of product safety is not mature. In the use process, the positive pole piece and the negative pole piece of the lithium ion battery often contact each other or are connected by a nail in the process of being pierced, thereby causing internal short circuit. With the increasing attention to the piercing safety performance of lithium ion batteries, the market urgently needs a lithium ion battery with good piercing safety performance. SUMMARY

[0004] The purpose of the present application is to provide an electrochemical device and an electronic device, which improve the piercing safety performance of the electrochemical device while taking into account the cycle performance and low-temperature discharge capacity of the electrochemical device.

[0005] It should be noted that the present application is explained by taking a lithium ion battery as an example of the electrochemical device in the summary of the present application, but the electrochemical device of the present application is not limited to the lithium ion battery. The specific technical solutions are as follows:

[0006] 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, 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 a first main material and a first binder, the first main material comprising a solid-state electrolyte, a surface of the solid-state electrolyte being provided with a carbon material, the Dv50 of the first main material being 50 nm to 200 nm, preferably the Dv50 being 100 nm to 150 nm. The thickness of the first coating layer is 0.5 μm to 2 μm, preferably the thickness of the first coating layer is 0.5 μm to 1 μm. Compared with the prior art in which a non-solid-state electrolyte is used as the first coating layer, the present application uses a carbon-coated solid-state electrolyte as the first main material in the first coating layer, which can make the first coating layer have a more uniform conductive network, so that the first coating layer has better conductivity. At the same time, by adjusting the type and thickness of the first coating layer and the Dv50 of the first main material within the range of the present application, a first coating layer with relatively high density, high mechanical strength and good conductivity can be formed on the surface of the positive electrode current collector, which improves the nail penetration safety performance of the electrochemical device while taking into account good low-temperature discharge performance and cycle performance.

[0007] In an embodiment of the present application, the ratio of the thickness of the positive electrode material layer to the thickness of the first coating layer is 35 to 180. By adjusting the ratio of the thickness of the positive electrode material layer to the thickness of the first coating layer within the range of the present application, the thickness of the positive electrode material layer and the first coating layer can be optimized to improve the nail penetration safety performance of the electrochemical device while taking into account good low-temperature discharge performance and cycle performance.

[0008] In an embodiment of the present application, the solid-state electrolyte comprises at least one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide or lithium aluminum titanium phosphate. The mass percentage content of the first main material is 80% to 90% based on the mass of the first coating layer. By adjusting the mass percentage content of the first main material and the type of the solid-state electrolyte within the range of the present application, the electronic conductivity of the first main material can be improved, and the transport capacity of lithium ions and electrons can be better improved, thereby improving the low-temperature discharge performance and cycle performance of the electrochemical device.

[0009] In an embodiment of the present application, the carbon material comprises at least one of amorphous carbon, carbon nanotubes, conductive graphite or carbon nanofibers. The mass percentage content of the carbon material is 3% to 5% based on the mass of the first main material. By adjusting the type and mass percentage content of the carbon material within the range of the present application, a suitable carbon material can be arranged on the surface of the solid-state electrolyte, and the lithium ion and electron transport capacity of the first coating layer can be further improved, thereby improving the low-temperature discharge performance and cycle performance of the electrochemical device.

[0010] In an embodiment of the present application, the powder resistivity of the first main material is 50 Ω·cm to 100 Ω·cm. By adjusting the powder resistivity of the first main material within the range of the present application, the first main material can have a suitable powder resistivity, and the lithium ion and electron transmission capacity of the first main material can be improved, thereby improving the low-temperature discharge performance and cycle performance of the electrochemical device.

[0011] In an embodiment of the present application, the first binder includes a water-soluble metal salt compound, and the mass percentage of the first binder based on the mass of the first coating layer is 10% to 20%. By adjusting the mass percentage of the first binder within the range of the present application, the first binder can have a better interaction with the positive electrode sheet, and the interface adhesion can be improved, thereby improving the nail penetration safety performance of the electrochemical device while taking into account the good low-temperature discharge performance and cycle performance.

[0012] In an embodiment of the present application, the first binder includes a water-soluble metal salt compound, and the water-soluble metal salt compound includes at least one of a polyacrylic acid alkali metal salt and / or a polyacrylic acid alkaline earth metal salt. The polyacrylic acid alkali metal salt includes at least one of sodium polyacrylate, lithium polyacrylate or potassium polyacrylate. The polyacrylic acid alkaline earth metal salt includes at least one of calcium polyacrylate or magnesium polyacrylate. By adjusting the type of the first binder within the range of the present application, the first binder can have better hydrophilicity, the lithium ion and electron transmission capacity of the first binder can be improved, and the first binder can have better tensile strength and a larger number of polar functional groups, thereby improving the interface adhesion and improving the nail penetration safety performance of the electrochemical device while taking into account the good low-temperature discharge performance and cycle performance.

[0013] In an embodiment of the present application, the infrared spectrum of the first coating layer has a characteristic peak between 3200 cm -1 and 3400 cm -1 . When the infrared spectrum of the first coating layer has the characteristic peak, the hydroxyl functional groups on the surface of the solid-state electrolyte can improve the affinity with the first binder, increase the cohesion of the first coating layer, and increase the adhesion between the first coating layer and the positive electrode current collector, thereby improving the nail penetration safety performance of the electrochemical device.

[0014] A second aspect of the present application provides an electronic device including the electrochemical device in any of the foregoing embodiments, and thus the electronic device provided by the present application can improve the nail penetration safety performance of the electrochemical device while taking into account the good low-temperature discharge performance and cycle performance.

[0015] Advantages of the present application:

[0016] The first aspect of the present application provides an electrochemical device, the electrochemical device comprising a positive electrode tab, the positive electrode tab 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, 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 a first main material and a first binder, the first main material comprising a solid-state electrolyte, a surface of the solid-state electrolyte being provided with a carbon material, the Dv50 of the first main material being 50 nm to 200 nm. The thickness of the first coating layer is 0.5 μm to 2 μm. By regulating the type and thickness of the first coating layer and the Dv50 of the first main material within the range of the present application, a first coating layer with relatively high density, high mechanical strength and good electrical conductivity can be formed on the surface of the positive electrode current collector, which improves the nail penetration safety performance of the electrochemical device while taking into account good low-temperature discharge performance and cycle performance.

[0017] Of course, implementing any product or method of the present application does not necessarily require all the advantages described above to be achieved at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0019] Figure 1 A schematic diagram of the positive electrode tab structure of an embodiment of the present application;

[0020] Figure 2 An infrared spectrum test diagram of the first coating layer of Example 1;

[0021] Figure 3 An infrared spectrum test diagram of the first coating layer of Example 22.

[0022] Reference signs:

[0023] 11 - positive electrode current collector; 12 - first coating layer; 13 - positive electrode material layer. DETAILED DESCRIPTION

[0024] The technical solutions in the present application will be described clearly and completely below in combination with the embodiments of the present application and the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. All other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0025] It should be noted that in the specific embodiments of the present application, lithium-ion batteries are used as examples of electrochemical devices to explain the present application, but the electrochemical devices of the present application are not limited to lithium-ion batteries.

[0026] 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 disposed on a surface of the positive electrode current collector, the positive electrode material layer being disposed on a surface of the first coating layer away from the positive electrode current collector, the first coating layer comprising a first main material and a first binder, the first main material comprising a solid-state electrolyte, a surface of the solid-state electrolyte being provided with a carbon material, the Dv50 of the first main material being 50 nm to 200 nm, preferably the Dv50 being 100 nm to 150 nm, exemplarily the value of the Dv50 can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm or a range composed of any two of the above values. The thickness of the first coating layer is 0.5 μm to 2 μm, preferably the thickness of the first coating layer is 0.5 μm to 1 μm, exemplarily the value of the thickness of the first coating layer can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm or a range composed of any two of the above values.

[0027] The inventors have found that the contact between the positive material layer and the positive current collector can be improved, the low-temperature discharge performance and the cycle performance can be improved by arranging a first coating layer between the positive current collector and the positive material layer. At the same time, the first coating layer also serves as a safety layer, which can improve the nail penetration safety performance of the electrochemical device. The first coating layer comprises a first main material and a first binder, and the first main material comprises a solid-state electrolyte, and the surface of the solid-state electrolyte is provided with a carbon material. The use of the solid-state electrolyte as the first main material can improve the transmission capacity of lithium ions and electrons between the positive material layer and the positive current collector, improve the low-temperature discharge performance of the electrochemical device, and the surface of the main material is provided with a carbon material, which can further improve the electron transmission capacity of the functional coating layer, increase the conductive channel of the electrochemical device during the cycle process, and thus improve the cycle performance of the electrochemical device. Reducing the particle size Dv50 of the first main material to the nanometer level can increase the bulk density between the first main materials, form a relatively dense first coating layer on the surface of the positive current collector, enhance the protection effect of the positive current collector during the nail penetration test, wrap the metal burrs that may be generated by the positive current collector during the nail penetration test, reduce the occurrence of short circuit in the electrochemical device, reduce the probability of thermal runaway caused by local overheating of the electrochemical device, and improve the nail penetration safety performance of the electrochemical device. When the Dv50 of the first main material is greater than 200 nm, the first main material particles with excessively large particle size are easy to pierce the positive current collector during the nail penetration test, and the protection effect on the positive current collector is poor; when the Dv50 of the first main material is less than 50 nm, the process is difficult and the production cost is high, and there are more side reactions between the positive electrode sheet and the electrolyte, which leads to the decline of the cycle performance of the electrochemical device. When the thickness of the first coating layer is within the range of the present application, the first coating layer has high mechanical strength, which can protect the positive current collector during the nail penetration test, reduce the occurrence of short circuit in the electrochemical device, reduce the probability of thermal runaway caused by local overheating of the electrochemical device, and improve the nail penetration safety performance of the electrochemical device. When the thickness of the first coating layer is less than 0.5 μm, the nail penetration safety performance of the electrochemical device is low, and when the thickness of the first coating layer is greater than 2 μm, the volume energy density of the electrochemical device is low, thereby leading to the decline of the cycle performance of the electrochemical device. By adjusting the type and thickness of the first coating layer and the Dv50 of the first main material within the range of the present application, a first coating layer with relatively high mechanical strength and good conductivity can be formed on the surface of the positive current collector, which can improve the nail penetration safety performance of the electrochemical device while ensuring good low-temperature discharge performance and cycle performance.

[0028] In the present application, the above-mentioned "the first coating layer is arranged on the surface of the positive current collector" means that the first coating layer can be arranged on one surface of the positive current collector along the thickness direction of the positive current collector, or can be arranged on both surfaces of the positive current collector along the thickness direction of the positive current collector. It should be noted that the "surface" here can be the entire region of the positive current collector, or can be part of the region of the positive current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. Specifically, as shown inFigure 1 As shown, the first coating layer 12 and the positive electrode material layer 13 are sequentially stacked on both surfaces of the positive electrode current collector 11. The above-mentioned "the positive electrode material layer is arranged on the surface of the first coating layer away from the positive electrode current collector" and the like are understood in this way.

[0029] In the present application, Dv50 represents the particle size reaching 50% of the volume accumulation from the small particle size side in the particle size distribution on a volume basis.

[0030] In an embodiment of the present application, the ratio of the thickness of the positive electrode material layer to the thickness of the first coating layer is 35 to 180. Exemplarily, the ratio of the thickness of the positive electrode material layer to the thickness of the first coating layer can be 35, 50, 70, 100, 150, 180, or a range consisting of any two of the above-mentioned values. By adjusting the ratio of the thickness of the positive electrode material layer to the thickness of the first coating layer within the range of the present application, the thicknesses of the positive electrode material layer and the first coating layer can be optimized, which improves the nail penetration safety performance of the electrochemical device while taking into account good low-temperature discharge performance and cycle performance.

[0031] In an embodiment of the present application, the thickness of the positive electrode material layer is 70 μm to 90 μm. Exemplarily, the thickness of the positive electrode material layer can be 70 μm, 80 μm, 90 μm, or a range consisting of any two of the above-mentioned values.

[0032] In an embodiment of the present application, the solid-state electrolyte includes at least one of lithium lanthanum zirconium oxide (Li7La3Zr2O12), lithium lanthanum titanium oxide (Li6.75La3Ti0.25O3), where 0 < x < 0.16, or lithium aluminum titanium phosphate. 12 3x 2 / 3-x TiO3, where 0 < x < 0.16, or lithium aluminum titanium phosphate. The lithium lanthanum titanium oxide can include but is not limited to Li6.75La3Ti0.25O3; the lithium aluminum titanium phosphate can include but is not limited to lithium aluminum titanium phosphate LiAl0.1Ti0.9(PO4)3. 0.33 0.56 1.3 0.3 1.7 Exemplarily, the mass percentage of the first main material can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or a range consisting of any two of the above-mentioned values. By adjusting the mass percentage of the first main material and the type of the solid-state electrolyte within the range of the present application, the electronic conductivity of the first main material can be improved, and the transport capacity of lithium ions and electrons can be better improved, thereby improving the low-temperature discharge performance and cycle performance of the electrochemical device.

[0033] ​​​​​​In an embodiment of the present application, the carbon material includes at least one of amorphous carbon, carbon nanotube, conductive graphite or carbon nanofiber. The carbon nanotube can include, but is not limited to, at least one of single-walled carbon nanotube or multi-walled carbon nanotube. The mass percentage of the carbon material is 3% to 5% based on the mass of the first main material. Exemplarily, the mass percentage of the carbon material can be 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.2%, 4.4%, 4.6%, 4.8%, 5.0% or a range between any two of the above values. By adjusting the type and mass percentage of the carbon material, it is possible to set a suitable carbon material on the surface of the solid-state electrolyte within the scope of the present application, further improve the lithium ion and electron transport capacity of the first coating, and thus improve the low-temperature discharge performance and cycle performance of the electrochemical device.

[0034] The preparation method of the solid-state electrolyte is not particularly limited in the present application, as long as the purpose of the present application can be achieved. Exemplarily, the preparation method of the solid-state electrolyte can include, but is not limited to, the following steps: dispersing lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide or lithium aluminum titanium phosphate powder in an ethanol solution containing a silane coupling agent to obtain a suspension, heating the suspension at 25°C to 100°C for 1 to 6 hours, then filtering the product, washing it with deionized water and ethanol several times, and then drying it in a drying oven at 70°C to 90°C for 10 to 12 hours to obtain a solid-state electrolyte containing a hydroxyl functional group on the surface. The silane coupling agent can include, but is not limited to, at least one of 3-aminopropyl triethoxysilane (APTES) or 3-glycidoxypropyl trimethoxysilane (GPTS); the mass ratio of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide or lithium aluminum titanium phosphate to the silane coupling agent is 99:1 to 90:10.

[0035] The preparation method of the first main material is not particularly limited in the present application, as long as the purpose of the present application can be achieved. Exemplarily, the preparation method of the first main material can include, but is not limited to, the following steps: mixing the solid-state electrolyte and the carbon source in a mass ratio of 85:2 to 85:4, then adding water, stirring and dispersing uniformly to obtain a mixed solution, evaporating and drying the mixed solution at 80°C to 120°C to remove the solvent, then heat treating it at 500°C to 700°C in a nitrogen atmosphere for 7h to 9h, cooling and then grinding to obtain the first main material. When the carbon material arranged on the surface of the solid-state electrolyte is any one of carbon nanotube, conductive graphite or carbon nanofiber, the above-mentioned carbon material can be directly added as the carbon source; when the carbon material arranged on the surface of the solid-state electrolyte is amorphous carbon, the above-mentioned carbon source can be conductive carbon black or an organic carbon compound. Exemplarily, the organic carbon compound can include, but is not limited to, at least one of citric acid, glucose, sucrose or polyacrylic acid, and the organic carbon compound is converted into amorphous carbon after the above-mentioned heat treatment.

[0036] The method for regulating the mass percentage of the carbon material based on the first main material is not particularly limited in the present application. For example, the mass percentage of the carbon material based on the first main material can be regulated by regulating the mass ratio of the solid-state electrolyte and the carbon material. When the mass ratio of the solid-state electrolyte and the carbon material decreases, the mass percentage of the carbon material based on the first main material increases; when the mass ratio of the solid-state electrolyte and the carbon material increases, the mass percentage of the carbon material based on the first main material decreases.

[0037] The method for regulating the Dv50 of the first main material is not particularly limited in the present application. For example, the Dv50 of the first main material can be regulated by regulating the grinding time. When the grinding time decreases, the Dv50 of the first main material increases; when the grinding time increases, the Dv50 of the first main material decreases.

[0038] The method for regulating the powder resistivity of the first main material is not particularly limited in the present application. For example, the powder resistivity of the first main material can be regulated by regulating the mass ratio of the solid-state electrolyte and the carbon material. When the mass ratio of the solid-state electrolyte and the carbon material decreases, the powder resistivity of the first main material increases; when the mass ratio of the solid-state electrolyte and the carbon material increases, the powder resistivity of the first main material decreases.

[0039] In an embodiment of the present application, the powder resistivity of the first main material is 50 Ω·cm to 100 Ω·cm. For example, the powder resistivity of the first main material can be 50 Ω·cm, 55 Ω·cm, 60 Ω·cm, 65 Ω·cm, 70 Ω·cm, 75 Ω·cm, 80 Ω·cm, 85 Ω·cm, 90 Ω·cm, 95 Ω·cm, 100 Ω·cm, or a range defined by any two of the above values. By regulating the powder resistivity of the first main material within the range of the present application, the first main material can have a suitable powder resistivity, and the lithium ion and electron transport capacity of the first main material can be improved, thereby improving the low-temperature discharge performance and cycle performance of the electrochemical device.

[0040] In an embodiment of the present application, the first binder includes a water-soluble metal salt compound, and the mass percentage of the first binder based on the mass of the first coating layer is 10% to 20%. For example, the mass percentage of the first binder can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range defined by any two of the above values. By regulating the mass percentage of the first binder within the range of the present application, the first binder can have a better interaction with the positive electrode sheet, and the interfacial adhesion can be improved, thereby improving the nail penetration safety performance of the electrochemical device while ensuring good low-temperature discharge performance and cycle performance.

[0041] In an embodiment of the present application, the first binder comprises a water-soluble metal salt compound, and the water-soluble metal salt compound comprises at least one of a polyacrylic alkali metal salt and / or a polyacrylic alkaline earth metal salt. The polyacrylic alkali metal salt comprises at least one of sodium polyacrylate, lithium polyacrylate or potassium polyacrylate. The polyacrylic alkaline earth metal salt comprises at least one of calcium polyacrylate or magnesium polyacrylate. It is within the scope of the present application to adjust the type of the first binder to have better hydrophilicity, to improve the lithium ion and electron transport capacity of the first binder, and to have better tensile strength and a larger number of polar functional groups, thereby improving the interfacial adhesion, so as to improve the nail penetration safety performance of the electrochemical device while taking into account good low-temperature discharge performance and cycle performance.

[0042] In an embodiment of the present application, the infrared spectrum of the first coating layer has a characteristic peak between 3200 cm -1 and 3400 cm -1 . When the infrared spectrum of the first coating layer has the characteristic peak, it indicates that the surface of the solid-state electrolyte has a hydroxyl functional group, which can form a hydrogen bond or a covalent bond with the carboxyl group in the first binder, thereby improving the affinity with the first binder, increasing the cohesion of the first coating layer, increasing the adhesion between the first coating layer and the positive current collector, and thereby improving the nail penetration safety performance of the electrochemical device.

[0043] The method for preparing the positive electrode sheet is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the method for preparing the positive electrode sheet can include, but is not limited to, the following steps: mixing the solid-state electrolyte and the first binder in a mass ratio of (80 to 90):(10 to 20), adding deionized water as a solvent, and stirring uniformly to obtain a first coating layer slurry with a solid content of 70 wt% to 80 wt%; then coating the first coating layer slurry on one surface of a 5 μm to 20 μm positive current collector, and baking at 90°C to 180°C for 1 h to 3 h to obtain a first coating layer with a thickness of 0.5 μm to 2 μm. Then, a positive material layer slurry is prepared, the positive material layer slurry is coated on the surface of the first coating layer, and dried to obtain a positive electrode sheet coated with the first coating layer and the positive material layer on one side. The above steps are repeated on the other surface of the positive current collector to obtain a positive electrode sheet coated with the first coating layer and the positive material layer on both sides.

[0044] In the preparation of the first coating, the first binder baked at 90-180°C can increase the cohesion of the first coating and the adhesion between the first coating and the positive current collector. The reason is that, on the one hand, under the action of high temperature, the carboxyl group in the first binder (e.g., sodium polyacrylate) and the hydroxyl group in the solid-state electrolyte (e.g., lithium aluminum titanium phosphate) will undergo a dehydration reaction, and the water molecules produced in the reaction process can promote the reaction between the first binder and the hydroxyl group on the surface of the solid-state electrolyte to form a stable chemical bond (e.g., an ester bond); on the other hand, the surface of the positive current collector usually has an oxide layer (e.g., an aluminum oxide layer for an aluminum foil), and under the action of high temperature, the first binder (e.g., sodium polyacrylate) can react with the above-mentioned oxide to form a more stable compound, thereby increasing the cohesion of the first coating and the adhesion between the first coating and the positive current collector.

[0045] The positive current collector is not particularly limited in the present application as long as it can achieve the purpose of the present application, for example, it can include an aluminum foil, an aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector), etc.

[0046] The positive material layer includes a positive active material, and the present application does not have a particular limitation on the positive active material as long as it can achieve the purpose of the present application, for example, the positive active material can include but is not limited to at least one of lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate, or lithium titanate.

[0047] The positive electrode material layer can further include a conductive agent and a second binder. The kind of the conductive agent and the second binder is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, a metal material, or a conductive polymer, and the conductive carbon black can include, but is not limited to, at least one of acetylene black or Ketjen black. The carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The carbon fibers can include, but are not limited to, vapor grown carbon fibers (VGCF) and / or nanocarbon fibers. The metal material can include, but is not limited to, metal powder and / or metal fibers, and specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The conductive polymer can include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the second binder can include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene butadiene rubber, or polyvinylidene fluoride. The mass ratio of the positive electrode active material, the conductive agent, and the second binder in the positive electrode material layer is not particularly limited in the present application, and a person skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0048] The thickness of the positive electrode current collector is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 10 μm.

[0049] In the present application, the electrochemical device further includes a negative electrode tab including a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "the negative electrode tab includes a negative electrode current collector and a negative electrode material layer 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 in the thickness direction of the negative electrode current collector, or can be disposed on both surfaces of the negative electrode current collector in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or can be part of the area of the surface of the negative electrode current collector, and the present application is not particularly limited, as long as the purpose of the present application can be achieved.

[0050] The negative electrode current collector is not particularly limited in the present application, as long as the purpose of the present application can be achieved, and for example, can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, or a composite current collector. Exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, or a titanium-copper composite current collector, etc.

[0051] The negative material layer includes a negative active material, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the negative active material can include, but is not limited to, at least one of natural graphite, artificial graphite, meso-carbon microbead, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure lithium titanate Li4Ti5O12, or Li-Al alloy. 12

[0052] In some embodiments of the present application, the negative material layer can further include a conductive agent and a second binder, for example, can be at least one of the above-mentioned conductive agent and the above-mentioned second binder. The mass ratio of the negative active material, the conductive agent, and the second binder in the negative material layer is not particularly limited in the present application, and a person skilled in the art can select according to the actual needs as long as the purpose of the present application can be achieved.

[0053] The thickness of the negative material layer and the thickness of the negative current collector are not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the negative material layer is 80 μm to 100 μm, and the thickness of the negative current collector is 4 μm to 15 μm.

[0054] Optionally, the negative electrode sheet can further include a conductive layer, which is located between the negative current collector and the negative material layer. The composition of the conductive layer is not particularly limited in the present application, and can be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent and a second binder. The conductive agent and the second binder in the conductive layer are not particularly limited in the present application, and for example, can be at least one of the above-mentioned conductive agent and the above-mentioned second binder.

[0055] In the present application, the electrochemical device further includes a separator film. The separator film is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the material of the separator film can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator film can include at least one of woven film, non-woven film, microporous film, composite film, calendered film, or spunlaced film.

[0056] In some embodiments of the present application, the separator film can include a substrate layer and a surface treatment layer. The substrate layer can be a non-woven fabric or a composite film having a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. ​

[0057] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, which can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0058] In some embodiments of the present application, the inorganic layer includes ceramic particles and a second binder. The ceramic particles are not particularly limited in the present application, and for example, the ceramic particles can include at least one of silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The second binder is not particularly limited in the present application, and for example, the second binder can be at least one of the above-described second binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0059] In the present application, the thickness of the separation film is not particularly limited as long as the object of the present application can be achieved, and for example, the thickness of the separation film can be 3 μm to 30 μm.

[0060] In the present application, the electrochemical device further includes an electrolyte including a lithium salt and a non-aqueous solvent.

[0061] The lithium salt is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the lithium salt can include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. The content of the lithium salt in the electrolyte is not particularly limited in the present application as long as the object of the present application can be achieved.

[0062] The non-aqueous solvent is not particularly limited in the present application as long as the object of the present application can be achieved, and for example, the non-aqueous solvent can include, but is not limited to, at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, or another organic solvent.

[0063] The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro-carbonate compound. The chain carbonate compound can include, but is 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 cyclic carbonate compound can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluoro-carbonate compound can include, but is not limited to, at least one of fluoro-ethylene carbonate (FEC), 1,2-difluoro-ethylene carbonate, 1,1-difluoro-ethylene carbonate, 1,1,2-trifluoro-ethylene carbonate, 1,1,2,2-tetrafluoro-ethylene carbonate, 1-fluoro-2-methyl-ethylene carbonate, 1-fluoro-1-methyl-ethylene carbonate, 1,2-difluoro-1-methyl-ethylene carbonate, 1,1,2-trifluoro-2-methyl-ethylene carbonate, or trifluoromethyl-ethylene carbonate. The carboxylic acid ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or caprolactone. The ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvent can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the non-aqueous solvent in the electrolyte is not particularly limited in the present application, as long as the object of the present application is achieved.

[0064] The electrochemical device further includes a case for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art of electrochemical devices, which are not limited in the present application. The case is not particularly limited in the present application, and can be a case known in the art, as long as the object of the present application is achieved. For example, the case can be a hard case or a flexible case. The material of the hard case can be a metal, and the type of the metal is not particularly limited in the present application, and a metal hard case known in the art can be used, as long as the object of the present application is achieved. The flexible case can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, or the like.

[0065] The preparation process of the electrochemical device of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, the preparation process of the electrochemical device can include but is not limited to the following steps: stacking the positive electrode sheet, the separator film and the negative electrode sheet in order, and winding, folding, etc. as needed to obtain a wound electrode assembly, placing the electrode assembly into the shell, injecting the electrolyte into the shell and sealing to obtain the electrochemical device. Alternatively, the positive electrode sheet, the separator film and the negative electrode sheet are stacked in order, and then the four corners of the entire stack structure are fixed with adhesive tape to obtain a stack structure electrode assembly, the electrode assembly is placed into the shell, the electrolyte is injected into the shell and sealed to obtain the electrochemical device. In addition, the overcurrent prevention element, guide plate, etc. can also be placed in the shell to prevent the pressure inside the electrochemical device from rising, overcharging and discharging.

[0066] The second aspect of the present application provides an electronic device, which comprises the electrochemical device of any one of the preceding embodiments, and thus the electronic device provided by the present application has good nail-penetration safety performance, low-temperature discharge performance and cycle performance.

[0067] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery and a lithium ion capacitor, etc.

[0068] Embodiments

[0069] Hereinafter, embodiments and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations were carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0070] Test methods and equipment:

[0071] First coating thickness test

[0072] The positive electrode sheet was longitudinally cut in the thickness direction by plasma, polished by argon ion polishing technology to obtain a smooth cross section, and then observed and measured the thickness of the first coating at three positions by scanning electron microscopy (OXFORD·EDS) at a magnification of 40000 times, and the average value was taken as the thickness of the first coating.

[0073] Particle size test

[0074] The particle size of the first main material was measured using a Malvern particle size tester (Model MasterSizer 2000). 0.02 g of the first main material was added to a 50 mL clean beaker, 20 mL of dispersant ethanol was added, and ultrasonic cleaning was performed in a 120 W ultrasonic cleaner for 30 min to completely disperse the first main material in ethanol to obtain a sample dispersion liquid. The above sample dispersion liquid was tested using the Malvern particle size tester to obtain the particle size Dv50 of the first main material.

[0075] Nail penetration test

[0076] Ten lithium ion batteries in the examples were taken, and the lithium ion batteries were charged at a current of 0.5 C to 4.5 V at 25±3°C, and charged at a constant voltage to a current of 0.05 C to cut off, to obtain the lithium ion batteries in a full charge state. Then a steel nail with a diameter of 4 mm, made of carbon steel, a taper of 16.5 mm, and a total length of 100 mm was used to perform a nail penetration test on the fully charged lithium ion batteries at 25±3°C, with a nail penetration speed of 30 mm / s and a nail penetration depth of the taper of the steel nail penetrating through the lithium ion battery. The state of the lithium ion battery during the test was observed, and the lithium ion battery was determined to pass the nail penetration test if it did not burn or explode, and the number of lithium ion batteries that passed the nail penetration test was recorded. The safety performance of the lithium ion battery was represented by the nail penetration test pass rate, and the higher the nail penetration test pass rate, the better the safety performance of the lithium ion battery. The nail penetration test pass rate = the number of lithium ion batteries that passed the nail penetration test / 10.

[0077] Cycle performance test

[0078] The lithium ion battery was placed at 45°C±3°C for 30 min, then charged at a current of 1.25 C to 4.25 V, then charged at a current of 1.5 C to 4.5 V, then charged at a constant voltage of 4.5 V to 0.05 C, and then placed for 30 min. Then, the initial capacity was obtained by discharging at a current of 0.7 C to 3.0 V. The above cycle was repeated, and the discharge capacity retention rate of each step was obtained by taking the ratio of the discharge capacity of each step to the initial capacity. The number of cycles of the lithium ion battery at 45°C±3°C until the discharge capacity retention rate was 80% was recorded. The cycle performance of the lithium ion battery was represented by the number of cycles at 45°C±3°C until the capacity retention rate was 80%. The higher the number of cycles of the lithium ion battery at 45°C±3°C until the capacity retention rate was 80%, the better the cycle performance of the lithium ion battery.

[0079] Low temperature discharge performance test

[0080] After the lithium ion battery is placed in an environment of 25℃±3℃ for 5 min, it is charged to 4.5V at a constant current of 1.5C, and charged at a constant voltage until the current is cut off at 0.02C; the furnace temperature is adjusted to-10℃; the lithium ion battery is placed for 60 min; and the battery is discharged to 3.0V at a constant current of 0.2C. The low-temperature discharge capacity to 3.0V is recorded. The higher the low-temperature discharge capacity retention of the lithium ion battery at-10℃, the better the low-temperature discharge performance of the lithium ion battery.

[0081] After the lithium ion battery is placed in an environment of 25℃±3℃ for 5 min, it is charged to 4.5V at a constant current of 1.5C, and charged at a constant voltage until the current is cut off at 0.02C; the furnace temperature is adjusted to-10℃; the lithium ion battery is placed for 60 min; and the battery is discharged to 3.0V at a constant current of 0.2C. The low-temperature discharge capacity to 3.0V is recorded. The higher the low-temperature discharge capacity retention of the lithium ion battery at-10℃, the better the low-temperature discharge performance of the lithium ion battery.

[0082] Low-temperature discharge capacity retention at-10℃=(low-temperature discharge capacity / initial discharge capacity)×100%.

[0083] Powder resistivity test

[0084] After the lithium ion battery is discharged to 3V at 0.2C, the positive electrode sheet is removed, the positive electrode material layer is scraped off, the first coating layer is scraped off from the positive electrode current collector, and the first coating powder is obtained. After the first coating powder is heated at 400℃ in air, the first main material is obtained. The powder resistivity of the first main material is tested by a powder resistivity tester in a dry room to obtain the powder resistivity p of the first main material.

[0085] Infrared spectrum test

[0086] The lithium ion battery is discharged to 3.0V at a constant current of 0.1C, and the positive electrode sheet is obtained by disassembling the lithium ion battery. The positive electrode sheet is cleaned with dimethyl carbonate (DMC) for 10 min, and then baked at 100℃ for 2h. The positive electrode material layer on the positive electrode sheet is scraped off to obtain a positive electrode current collector coated with a first coating layer.

[0087] An infrared spectrum of the positive electrode current collector coated with the first coating layer is tested by an infrared spectrum analyzer (model Nicolet iS50) using a potassium bromide (KBr) tablet pressing method. Among them, Figure 2 is the infrared spectrum test chart of the first coating layer of Example 1, Figure 3 is the infrared spectrum test chart of the first coating layer of Example 22.

[0088] Carbon material content test

[0089] The lithium ion battery was discharged at 0.2C constant current to 3V, and the positive electrode sheet was obtained by disassembling the lithium ion battery. The positive electrode material layer on the positive electrode sheet was scraped off to obtain a positive electrode current collector coated with a first coating. The above positive electrode current collector was cut into 10 samples of 48mmx60mm. After heating in air at 400℃, cleaning and drying, the content of carbon element in the 10 samples was tested by inductively coupled plasma analyzer (ICP, model AVIO-200), and the average value was taken to obtain the content of carbon material in the first main material.

[0090] Example 1

[0091] Preparation of solid electrolyte

[0092] The lithium aluminum titanium phosphate powder was dispersed in an ethanol solution containing 3-aminopropyl triethoxysilane, and the mass ratio of lithium aluminum titanium phosphate to 3-aminopropyl triethoxysilane was 95:5, to obtain a suspension. After heating treatment at 75℃ for 4 hours, the product was filtered, washed with deionized water and ethanol for several times, and then dried in a drying oven at 80℃ for 12 hours to obtain a solid electrolyte containing hydroxyl functional groups on the surface.

[0093] Preparation of first main material

[0094] The above prepared solid electrolyte and citric acid were mixed in a mass ratio of 85:3, and then water was added. After stirring and dispersing uniformly, a mixed solution was obtained. After evaporative drying of the mixed solution at 100℃ to remove the solvent, heat treatment was carried out at 600℃ in a nitrogen atmosphere for 8h. After cooling, grinding was carried out to obtain the first main material. Among them, the amorphous carbon was obtained by heat treatment of citric acid; the Dv50 of the first main material was 150nm, the powder resistivity p of the first main material was 50.02Ω·cm, and the mass percentage content W of the carbon material based on the first main material was 4%. C 4%.

[0095] Preparation of positive electrode sheet

[0096] The first main material and the first binder sodium polyacrylate prepared above were mixed in a mass ratio of 85:15, deionized water was added as a solvent, and stirring was performed to obtain a first coating slurry with a solid content of 75wt%, which was coated on one surface of a 10μm positive electrode current collector aluminum foil. After baking at 120°C for 2 hours, a first coating layer was obtained. The positive electrode active material lithium cobaltate, the second binder polyvinylidene fluoride, and the conductive agent conductive carbon black were mixed in a mass ratio of 97.3:1.6:1.1, and N-methyl pyrrolidone (NMP) was added as a solvent. Stirring was performed in a vacuum stirrer to obtain a positive electrode slurry with a solid content of 75wt%. The positive electrode slurry was uniformly coated on the surface of the first coating layer, and was dried at 120°C to obtain a positive electrode sheet coated with the first coating layer and the positive electrode material layer on one side. The coating weight of the positive electrode active layer was 267.8mg / 1540mm 2 . Then the above steps were repeated on the other surface of the aluminum foil, and after drying at 120°C, a positive electrode sheet coated with the first coating layer and the positive electrode material layer on both sides was obtained. Then, after cold pressing, cutting, and welding of the tabs, a positive electrode sheet with a size of 74mm×867mm was obtained for use. Among them, the mass percentage of the first main material W1 was 85% and the mass percentage of the first binder W2 was 15% based on the mass of the first coating layer; the thickness of the first coating layer D1 was 1μm, the thickness of the single positive electrode material layer D2 was 85μm, and the ratio of the thickness of the positive electrode material layer to the thickness of the first coating layer D2 / D1 was 85.

[0097] The structure of the positive electrode sheet prepared in Example 1 is shown in Figure 1 .

[0098] <Preparation of a negative electrode sheet>

[0099] The negative electrode active material artificial graphite, the second binder styrene butadiene rubber (SBR), and the second binder carboxymethyl cellulose (CMC) were mixed in a mass ratio of 97.7:1:1.3, and then deionized water was added as a solvent to prepare a slurry with a solid content of 70wt%. After stirring in a vacuum stirrer, a negative electrode slurry was obtained. The negative electrode slurry was uniformly coated on one surface of a 6μm negative electrode current collector copper foil, and was dried at 120°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. The coating weight of the negative electrode material layer was 142mg / 1540mm 2 . Then the above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. After drying at 120°C, the negative electrode sheet was cold pressed, and then cutting and tab welding were performed to obtain a negative electrode sheet with a size of 78mm×875mm for use. Among them, the thickness of the single negative electrode material layer was 80μm.

[0100] <Preparation of an electrolyte>

[0101] In an argon atmosphere glove box with water content less than 10 ppm, carbonate compounds ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC) were uniformly mixed in a mass ratio of 10:30:60 to obtain a base solvent, and a lithium salt LiPF6 was added and stirred uniformly to obtain an electrolyte. The mass percentage of the lithium salt LiPF6 in the electrolyte was 12.5% based on the total mass of the electrolyte, and the balance was the base solvent.

[0102] <Separator>

[0103] A polyethylene porous polymer film (manufacturer: Celgard Membrane Co., Ltd., USA) with a thickness of 8 μm was used as a separator.

[0104] <Preparation of a lithium ion battery>

[0105] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and were wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum plastic film packaging bag, and was dehydrated at 80°C. The prepared electrolyte was injected, and the lithium ion battery was obtained after vacuum packaging, standing, formation, and shaping processes.

[0106] The upper limit voltage of formation was 4.53 V, the formation temperature was 85°C, and the formation time was 50 min.

[0107] Example 2

[0108] Except that <Preparation of a solid electrolyte> was replaced by the following steps, the rest was the same as Example 1.

[0109] <Preparation of a solid electrolyte>

[0110] The lithium lanthanum zirconium oxide powder was dispersed in an ethanol solution containing 3-aminopropyl triethoxysilane to obtain a suspension. After heating treatment of the suspension at 75°C for 4 hours, the product was filtered, washed with deionized water and ethanol for several times, and then dried in a drying oven at 80°C for 12 hours to obtain a solid electrolyte with hydroxyl functional groups on the surface.

[0111] Example 3

[0112] Except that <Preparation of a solid electrolyte> was replaced by the following steps, the rest was the same as Example 1.

[0113] <Preparation of a solid electrolyte>

[0114] The lithium lanthanum titanium oxide Li 0.33 La 0.56The TiO3 powder was dispersed in an ethanol solution containing 3-aminopropyl triethoxysilane to obtain a suspension, the suspension was heated and treated at 75°C for 4 hours, then the product was filtered, washed with deionized water and ethanol for several times, and then dried in a drying oven at 80°C for 12 hours to obtain a solid-state electrolyte with hydroxyl functional groups on the surface.

[0115] Examples 4 to 7

[0116] The rest was the same as Example 1 except that in <Preparation of positive electrode sheet>, the mass ratio of the first main material and the first binder was adjusted so that the mass percentage content W1 of the first main material based on the first coating and the mass percentage content W2 of the first binder based on the first coating were as shown in Table 1.

[0117] Examples 8 to 10

[0118] The rest was the same as Example 1 except that in <Preparation of first main material>, the grinding time was adjusted so that the Dv50 of the first main material was as shown in Table 1.

[0119] Examples 11 to 13

[0120] The rest was the same as Example 1 except that the thickness D1 of the first coating was adjusted according to Table 1, the ratio D2 / D1 of the thickness of the positive material layer to the thickness of the first coating changed accordingly, and the thickness D2 of the positive material layer remained unchanged.

[0121] Examples 14 to 15

[0122] The rest was the same as Example 1 except that the type of carbon material was adjusted according to Table 1.

[0123] Examples 16 to 19

[0124] The rest was the same as Example 1 except that in <Preparation of first main material>, the mass ratio of the solid-state electrolyte and citric acid was adjusted so that the mass percentage content W C The rest was the same as Example 1 except that the powder resistivity of the first main material changed accordingly as shown in Table 1.

[0125] Examples 20 to 21

[0126] The rest was the same as Example 1 except that the type of first binder was adjusted according to Table 1.

[0127] Example 22

[0128] The rest was the same as Example 1 except that in <Preparation of first main material>, the untreated titanium aluminum lithium phosphate prepared in <Preparation of solid-state electrolyte> of Example 1 was directly used as the solid-state electrolyte.

[0129] Comparative Example 1

[0130] The rest is the same as Example 1 except that no first coating is provided on the surface of the positive current collector.

[0131] Comparative Example 2

[0132] The rest is the same as Example 1 except that no carbon material is provided on the surface of the solid-state electrolyte in the preparation of the first main material, and the solid-state electrolyte is directly used as the first main material.

[0133] Comparative Examples 3 to 6

[0134] The rest is the same as Example 1 except that the relevant preparation parameters are adjusted according to Table 1.

[0135] The preparation parameters and performance tests of each example and comparative example are shown in Table 1.

[0136] Table 1

[0137]

[0138] Note: " / " in Table 1 indicates that the corresponding preparation parameter or substance does not exist, W C represents the mass percentage content of the carbon material based on the first main material, W1 represents the mass percentage content of the first main material based on the first coating, W2 represents the mass percentage content of the first binder based on the first coating, D1 represents the thickness of the first coating, D2 represents the thickness of the single-sided positive material layer, p represents the powder resistivity of the first main material, and the characteristic peak refers to the characteristic peak of the infrared spectrum of the first coating between 3200 cm -1 and 3400 cm -1 .

[0139] From Examples 1 to 22 and Comparative Examples 1 to 6, it can be seen that when the solid-state electrolyte with a carbon material on the surface is used as the first main material of the first coating, the positive electrode sheet has the first coating structure of the present application, and the Dv50 of the first main material and the thickness of the first coating are within the scope of the present application, the -10℃ low-temperature discharge capacity retention rate of the lithium ion battery, the 80% capacity retention cycle number, and the nail penetration test passing rate are higher, thereby indicating that the lithium ion battery of the present application has a higher nail penetration safety performance while taking into account good low-temperature discharge performance and cycle performance.

[0140] The kind of solid electrolyte and the kind of first binder generally affect the nail penetration safety performance, low temperature discharge performance and cycle performance of the lithium ion battery. As can be seen from Example 1 to Example 3 and Example 20 to Example 21, when the kind of solid electrolyte and the kind of first binder are within the scope of the present application, the -10℃ low temperature discharge capacity retention rate, 80% capacity retention cycle number and nail penetration test pass rate of the lithium ion battery are higher, thereby indicating that the lithium ion battery of the present application has higher nail penetration safety performance while taking into account good low temperature discharge performance and cycle performance.

[0141] The first main material based on the mass percentage content W1 of the first coating and the first binder based on the mass percentage content W2 of the first coating generally affect the nail penetration safety performance, low temperature discharge performance and cycle performance of the lithium ion battery. As can be seen from Example 1 and Example 4 to Example 7, when W1 and W2 are within the scope of the present application, the -10℃ low temperature discharge capacity retention rate, 80% capacity retention cycle number and nail penetration test pass rate of the lithium ion battery are higher, thereby indicating that the lithium ion battery of the present application has higher nail penetration safety performance while taking into account good low temperature discharge performance and cycle performance.

[0142] The ratio D1 / D2 of the thickness of the positive electrode material layer to the thickness of the first coating generally affects the nail penetration safety performance, low temperature discharge performance and cycle performance of the lithium ion battery. As can be seen from Example 1 and Example 11 to Example 13, when D1 / D2 is within the scope of the present application, the -10℃ low temperature discharge capacity retention rate, 80% capacity retention cycle number and nail penetration test pass rate of the lithium ion battery are higher, thereby indicating that the lithium ion battery of the present application has higher nail penetration safety performance while taking into account good low temperature discharge performance and cycle performance.

[0143] The kind of carbon material, the mass percentage content W C of the carbon material based on the first main material and the powder resistivity of the first main material generally affect the nail penetration safety performance, low temperature discharge performance and cycle performance of the lithium ion battery. As can be seen from Example 1 and Example 14 to Example 19, when the kind of carbon material, W C of the carbon material based on the first main material and the powder resistivity of the first main material are within the scope of the present application, the -10℃ low temperature discharge capacity retention rate, 80% capacity retention cycle number and nail penetration test pass rate of the lithium ion battery are higher, thereby indicating that the lithium ion battery of the present application has higher nail penetration safety performance while taking into account good low temperature discharge performance and cycle performance.

[0144] The infrared spectrum of the first coating is within the range of 3200 cm -1 to 3400 cm -1The presence of characteristic peaks typically affects the safety performance of lithium-ion batteries, low-temperature discharge performance, and cycle performance. As can be seen from Examples 1 and 22, the infrared spectrum of the first coating in Example 1 is at 3200 cm⁻¹. -1 Up to 3400cm -1 Characteristic peaks exist between the two; the infrared spectrum of the first coating in Example 22 is at 3200 cm⁻¹. -1 Up to 3400cm -1 There are no characteristic peaks between them. Example 1 shows higher low-temperature discharge capacity retention at -10℃, 80% capacity retention cycles, and pass rate in the pin penetration test, specifically at 3200cm. -1 Up to 3400cm -1 The presence of characteristic peaks in lithium-ion batteries indicates that they exhibit better nail penetration safety, low-temperature discharge performance, and cycle performance. This demonstrates that the lithium-ion battery of this application combines high nail penetration safety with good low-temperature discharge performance and cycle performance.

[0145] Specifically, such as Figure 2 As shown, Figure 2 The infrared spectrum of the first coating in Example 1 is shown below. In the infrared spectrum, at 3200 cm⁻¹... -1 Up to 3400cm -1 The presence of characteristic peaks indicates that the surface of the solid electrolyte has hydroxyl functional groups; such as Figure 3 As shown, Figure 3 The infrared spectrum of the first coating in Example 22 is shown below. In the infrared spectrum, at 3200 cm⁻¹... -1 Up to 3400cm -1 The absence of characteristic peaks indicates that the surface of the solid electrolyte does not have hydroxyl functional groups.

[0146] 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.

[0147] 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.

[0148] The various embodiments described in this specification are presented by way of example, and each embodiment is not mutually exclusive of the others. Each embodiment highlights a different aspect of the application.

Claims

1. An electrochemical device, comprising a positive electrode tab, the positive electrode tab comprising a positive electrode current collector, a first coating layer, and a positive electrode material layer, the first coating layer being disposed on a surface of the positive electrode current collector, the positive electrode material layer being disposed on a surface of the first coating layer away from the positive electrode current collector, the first coating layer comprising a first main material and a first binder, the first main material comprising a solid-state electrolyte, a surface of the solid-state electrolyte being provided with a carbon material, the first main material having a Dv50 of 50 nm to 200 nm, the first coating layer having a thickness of 0.5 μm to 2 μm.

2. The electrochemical device of claim 1, wherein, The first main material has a Dv50 of 100 nm to 150 nm.

3. The electrochemical device of claim 1, wherein, The first coating layer has a thickness of 0.5 μm to 1 μm.

4. The electrochemical device of claim 1, wherein, The positive electrode material layer has a thickness to thickness ratio to the first coating layer of 35 to 180.

5. The electrochemical device of claim 1, wherein, The solid-state electrolyte comprises at least one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, or lithium aluminum titanium phosphate; the first main material has a mass percentage of 80% to 90% based on a mass of the first coating layer.

6. The electrochemical device of claim 1, wherein, The carbon material comprises at least one of amorphous carbon, carbon nanotube, conductive graphite, or carbon nanofiber; the carbon material has a mass percentage of 3% to 5% based on a mass of the first main material.

7. The electrochemical device of claim 1, wherein, The first main material has a powder resistivity of 50 Ω·cm to 100 Ω·cm.

8. The electrochemical device of claim 1, wherein, The first binder comprises a water-soluble metal salt compound; the first binder has a mass percentage of 10% to 20% based on a mass of the first coating layer.

9. The electrochemical device of claim 8, wherein, The water-soluble metal salt compound comprises an alkali metal polyacrylate and / or an alkaline earth metal polyacrylate; the alkali metal polyacrylate comprises at least one of sodium polyacrylate, lithium polyacrylate, or potassium polyacrylate; the alkaline earth metal polyacrylate comprises at least one of calcium polyacrylate or magnesium polyacrylate.

10. The electrochemical device of claim 1, wherein, The first coating has characteristic peaks in its infrared spectrum between 3200 cm -1 and 3400 cm -1 . 11.An electronic device, comprising the electrochemical device of any one of claims 1 to 10.

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