An electrochemical device and an electronic device

Abstract

The application provides an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector, a first coating layer and a positive electrode material layer, the first coating layer is arranged on the surface of the positive electrode current collector, and the positive electrode material layer is arranged on the surface of the first coating layer away from the positive electrode current collector. The first coating layer comprises a first main material, the first main material comprises a lithium-rich manganese-based material or a metal oxide, and the mass percentage of the first main material is 20% to 95% based on the mass of the first coating layer. The membrane sheet resistance of the positive electrode sheet is R1 Ω when the state of charge is greater than 80%, and the membrane sheet resistance is R2 Ω when the state of charge is 0% to 50%. 100%≤(R1-R2) / R2×100%≤500%. The electrochemical device provided by the application can improve the fast charging performance while ensuring good nail penetration safety.

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 nail safety performance of the batteries.

[0003] Due to abnormal conditions such as nail penetration and impact of lithium ion batteries, the aluminum foil as a commonly used positive electrode current collector is prone to short circuit, which seriously affects the safety of the battery. The short circuit can usually be reduced by adding a coating layer with high resistivity on the surface of the aluminum foil. However, these high-resistance coatings affect the battery performance to some extent, such as cycle life, internal resistance growth rate and fast charging ability. SUMMARY

[0004] The purpose of the present application is to provide an electrochemical device and an electronic device, which improve the fast charging performance of the electrochemical device while taking into account good nail safety performance.

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

[0006] In an embodiment of the present application, the electrochemical device comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector, a first coating layer and a positive electrode material layer, the first coating layer is arranged on the surface of the positive electrode current collector, and the positive electrode material layer is arranged on the surface of the first coating layer away from the positive electrode current collector. The first coating layer comprises a first main material, the first main material comprises a lithium-rich manganese-based material or a metal oxide, and the mass percentage of the first main material is 20% to 95% based on the mass of the first coating layer; the membrane resistance of the positive electrode sheet when the state of charge is greater than 80% is R1Ω, the membrane resistance of the positive electrode sheet when the state of charge is 0% to 50% is R2Ω, and 100%≤(R1-R2) / R2×100%≤500%, preferably 150%≤(R1-R2) / R2×100%≤480%. When the mass percentage of the first main material and the value of (R1-R2) / R2×100% are within the above ranges, the positive electrode sheet exhibits high membrane resistance at high state of charge and low membrane resistance at low state of charge, realizing self-adaptive adjustment of the membrane resistance of the positive electrode sheet with the state of charge, which can increase the charging speed of the electrochemical device, reduce the short-circuit power, and improve the fast-charging performance while taking into account good nail-penetration safety performance.

[0007] In an embodiment of the present application, 0.4≤R1≤80 and 0.2≤R2≤13. When the value of R1 is within the range of the present application, the membrane resistance of the positive electrode sheet when the state of charge is greater than 80% is relatively high, which can increase the short-circuit resistance and improve the nail-penetration safety performance of the electrochemical device. When the value of R2 is within the range of the present application, the positive electrode sheet has a relatively low membrane resistance when the state of charge is 0% to 50%, which can improve the charging speed of the electrochemical device at low state of charge and improve the fast-charging performance of the electrochemical device.

[0008] In an embodiment of the present application, the membrane resistance of the positive electrode sheet when the state of charge is 50% to 100% is R3Ω, and 0.3≤R3≤82. When the value of R3 is within the range of the present application, the membrane resistance of the positive electrode sheet when the state of charge is 50% to 100% is relatively high, which improves the nail-penetration safety performance of the electrochemical device.

[0009] In an embodiment of the present application, the lithium-rich manganese-based material comprises at least one of lithium nickel cobalt manganese oxide or lithium manganate. When the lithium-rich manganese-based material is selected from the materials within the above range, the positive electrode sheet has a suitable membrane resistance at different states of charge, which improves the fast-charging performance while taking into account good nail-penetration safety performance.

[0010] In an embodiment of the present application, the metal oxide comprises ZnO, and the metal oxide further comprises Al; the mass percentage of the Al is 0.6% to 4% based on the mass of the metal oxide. When the mass percentage of the Al is within the above range, the sheet resistance of the positive electrode plate has a wider adjustable range, and can be adjusted to a suitable sheet resistance at different states of charge, thereby improving the fast-charging performance while taking into account the good nail-penetration safety performance.

[0011] In an embodiment of the present application, the metal oxide comprises TiO2, and at least part of the surface of the TiO2 is provided with a first component, the first component comprises SnO2, and the first component further comprises Sb; the mass percentage of the first component is 44.44% to 55.25% based on the mass of the metal oxide, and the mass percentage of the Sb is 30.2% to 38.8% based on the mass of the first component. When the mass percentage of the first component based on the mass of the metal oxide and the mass percentage of the Sb based on the mass of the first component are within the above ranges, the sheet resistance of the positive electrode plate has a wider adjustable range, and can be adjusted to a suitable sheet resistance at different states of charge, thereby improving the fast-charging performance while taking into account the good nail-penetration safety performance.

[0012] In an embodiment of the present application, the first coating further comprises inorganic particles, and the inorganic particles comprise at least one of nanometer boehmite or aluminum trioxide; the mass percentage of the inorganic particles is 0% to 77% based on the mass of the first coating. When the mass percentage of the inorganic particles is within the above range, the fast-charging performance is improved while taking into account the good nail-penetration safety performance.

[0013] In an embodiment of the present application, the average particle size of the first main material is 160 nm to 400 nm, and preferably 200 nm to 320 nm. When the average particle size of the first main material is within the range of the present application, the protection of the positive electrode current collector during the nail-penetration test can be enhanced, the metal burrs possibly generated by the positive electrode current collector during the nail-penetration test can be wrapped, the occurrence of short circuit in the electrochemical device is reduced, the probability of thermal runaway caused by local overheating of the electrochemical device is reduced, and the nail-penetration safety performance of the electrochemical device is improved.

[0014] In an embodiment of the present application, the first coating further comprises a first binder, and the first binder comprises at least one of polyvinylidene fluoride, polyacrylic acid or polymethyl methacrylate; the mass percentage of the first binder is 3% to 15% based on the mass of the first coating. When the first binder is selected from the above materials and the mass percentage is within the range of the present application, the adhesion between the first coating and the positive electrode current collector can be improved, thereby improving the nail-penetration safety performance of the electrochemical device.

[0015] In an embodiment of the present application, the thickness of the first coating layer is 0.2-2 μm, preferably 1-1.5 μm. When the thickness of the first coating layer is within the range of the present application, the volume energy density and the nail penetration safety performance of the electrochemical device can be improved.

[0016] The second aspect of the present application provides an electronic device comprising the electrochemical device of any of the preceding embodiments. The electronic device of the present application has good nail penetration safety performance and fast charging performance.

[0017] Advantages of the present application:

[0018] The present application provides an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector, a first coating layer and a positive electrode material layer, the first coating layer is arranged on the surface of the positive electrode current collector, and the positive electrode material layer is arranged on the surface of the first coating layer away from the positive electrode current collector. The first coating layer comprises a first main material, the first main material comprises a lithium-rich manganese-based material or a metal oxide, and the mass percentage of the first main material is 20-95% based on the mass of the first coating layer. The membrane resistance of the positive electrode sheet when the state of charge is greater than 80% is R1 Ω, and the membrane resistance of the positive electrode sheet when the state of charge is 0-50% is R2 Ω, and 100%≤(R1-R2) / R2×100%≤500%. When the mass percentage of the first main material and the value of (R1-R2) / R2×100% are within the above ranges, the positive electrode sheet exhibits high membrane resistance at high state of charge and low membrane resistance at low state of charge, realizing self-adaptive adjustment of the membrane resistance of the positive electrode sheet with the state of charge, which can increase the charging speed of the electrochemical device, reduce the short-circuit power, and improve the fast charging performance while ensuring good nail penetration safety performance.

[0019] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0020] 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.

[0021] Figure 1 Structure schematic diagram of the positive electrode sheet in an embodiment of the present application;

[0022] Figure 2 Scatter plot of the membrane resistance of the positive electrode sheet in Example 1-1 of the present application varying with the state of charge;

[0023] Figure 3A scatter plot of the sheet resistance of the positive electrode sheet in Example 1 of the present application as a function of the state of charge;

[0024] Figure 4 A scatter plot of the sheet resistance of the positive electrode sheet in Example 1 of the present application as a function of the state of charge; DETAILED DESCRIPTION

[0025] 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, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0026] It should be noted that the specific embodiments of the present application explain the present application by taking lithium ion batteries as examples of electrochemical devices, but the electrochemical devices of the present application are not limited to lithium ion batteries.

[0027] In an embodiment of the present application, the electrochemical device comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector, a first coating layer and a positive electrode material layer, the first coating layer is arranged on the surface of the positive electrode current collector, and the positive electrode material layer is arranged on the surface of the first coating layer away from the positive electrode current collector. The first coating layer comprises a first main material, the first main material comprises a lithium-rich manganese-based material or a metal oxide, and the mass percentage of the first main material is 20% to 95% based on the mass of the first coating layer. The membrane sheet resistance of the positive electrode sheet at a state of charge greater than 80% is R1Ω, the membrane sheet resistance of the positive electrode sheet at a state of charge of 0% to 50% is R2Ω, and 100%≤(R1-R2) / R2×100%≤500%, preferably 150%≤(R1-R2) / R2×100%≤480%. For example, the mass percentage of the first main material can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or a range formed by any two of them; the value of (R1-R2) / R2×100% can be 100%, 150%, 200%, 300%, 400%, 480%, 500%, or a range formed by any two of them. When the mass percentage of the first main material and the value of (R1-R2) / R2×100% are within the above ranges, the positive electrode sheet exhibits high membrane sheet resistance at high state of charge and low membrane sheet resistance at low state of charge, achieving self-adaptive adjustment of the membrane sheet resistance of the positive electrode sheet with the state of charge, which can increase the charging speed of the electrochemical device, reduce the short-circuit power, and improve the fast-charging performance while ensuring good nail-penetration safety performance. When (R1-R2) / R2×100% is greater than 500%, the membrane sheet resistance of the positive electrode sheet from low state of charge to high state of charge increases at a higher rate, resulting in reduced fast-charging performance of the electrochemical device; when (R1-R2) / R2×100% is less than 100%, the membrane sheet resistance of the positive electrode sheet from low state of charge to high state of charge increases at a lower rate, and the short-circuit safety resistance at high state of charge is lower, resulting in reduced nail-penetration safety performance of the electrochemical device.

[0028] In an embodiment of the present application, 0.4≤R1≤80, 0.2≤R2≤13. For example, R1 can be 0.4, 1, 10, 20, 30, 40, 50, 60, 70, 80, or a range between any two of them; R2 can be 0.2, 1, 3, 5, 7, 9, 11, 13, or a range between any two of them. When the value of R1 is within the range of the present application, the upper limit of the membrane sheet resistance of the positive electrode tab when the state of charge is greater than 80% is higher, which can increase the short-circuit resistance, reduce the short-circuit power, reduce the dangerous short-circuit points between the positive current collector and the negative current collector during the nail penetration test, reduce the heat power generated by the short circuit, and improve the nail penetration safety performance of the electrochemical device. When the value of R2 is within the range of the present application, the positive electrode tab has a lower membrane sheet resistance when the state of charge is 0% to 50%, which can improve the charging speed of the electrochemical device at low state of charge, while improving the fast-charging performance and good nail penetration safety performance.

[0029] In an embodiment of the present application, the membrane sheet resistance of the positive electrode tab when the state of charge is 50% to 100% is R3Ω, and 0.3≤R3≤82. For example, R3 can be 0.3, 1, 10, 20, 30, 40, 50, 60, 70, 80, 82, or a range between any two of them. When the value of R3 is within the range of the present application, the membrane sheet resistance of the positive electrode tab when the state of charge is 50% to 100% is higher, which can increase the short-circuit resistance, reduce the short-circuit power, reduce the dangerous short-circuit points between the positive current collector and the negative current collector during the nail penetration test, reduce the heat power generated by the short circuit, and improve the nail penetration safety performance of the electrochemical device.

[0030] In the present application, the above-mentioned "the first coating is arranged on the surface of the positive current collector" means that the first coating 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 area of the positive current collector, or can be part of the area 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 in FIG. 1, the first coating 12 and the positive material layer 13 are sequentially arranged on both surfaces of the positive current collector 11. The above-mentioned "the positive material layer is arranged on the surface of the first coating away from the positive current collector" and the like are understood in the same way. Figure 1

[0031] In an embodiment of the present application, the lithium-rich manganese-based material includes at least one of lithium nickel cobalt manganese oxide or lithium manganate (LiMnO2). For example, the lithium nickel cobalt manganese oxide can include but is not limited to LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.2 ​Mn 0.3 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2or LiNi 0.9 Co 0.05 Mn 0.05 at least one of O2. When the lithium-rich manganese-based material is selected from the materials within the above range, the positive electrode tab has a suitable sheet resistance at different states of charge, improving the nail penetration safety performance and fast charging performance of the electrochemical device.

[0032] In an embodiment of the present application, the metal oxide comprises ZnO, and the metal oxide further comprises Al; the mass percentage of Al is 0.6% to 4% based on the mass of the metal oxide. For example, the mass percentage of Al can be 0.6%, 1%, 1.5%, 2%, 3%, 4%, or a range between any two of the values. When the mass percentage of Al is within the above range, the sheet resistance of the positive electrode tab has a wider adjustable range, and can be adjusted to a suitable sheet resistance at different states of charge, improving the fast charging performance while taking into account the good nail penetration safety performance.

[0033] In an embodiment of the present application, the metal oxide comprises TiO2, and at least part of the surface of TiO2is provided with a first component, the first component comprises SnO2, and the first component further comprises Sb; the mass percentage of the first component is 44.44% to 55.25% based on the mass of the metal oxide, and the mass percentage of Sb is 30.2% to 38.8% based on the mass of the first component. For example, the mass percentage of the first component can be 44.44%, 45%, 47%, 49%, 51%, 53%, 55%, 55.25% based on the mass of the metal oxide, or a range between any two of the values; the mass percentage of Sb can be 30.2%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 38.8% based on the mass of the first component, or a range between any two of the values. When the mass percentage of the first component based on the mass of the metal oxide and the mass percentage of Sb based on the mass of the first component are within the above ranges, the sheet resistance of the positive electrode tab has a wider adjustable range, and can be adjusted to a suitable sheet resistance at different states of charge, improving the fast charging performance while taking into account the good nail penetration safety performance.

[0034] In an embodiment of the present application, the first coating further comprises inorganic particles, the inorganic particles comprising at least one of nanobohmite or aluminum trioxide; the mass percentage of the inorganic particles is 0% to 77% based on the mass of the first coating. For example, the mass percentage of the inorganic particles can be 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 77%, or a range between any two of them. When the mass percentage of the inorganic particles is within the above range, the conductivity of the inorganic particles is low, and the introduction of the first coating can further improve the membrane resistance of the positive electrode sheet at high state of charge, realizing the self-adaptive adjustment of the membrane resistance of the positive electrode sheet with a wider adjustable range of state of charge, while improving the fast charging performance and taking into account the good nail safety performance.

[0035] In an embodiment of the present application, the average particle size of the first main material is 160 nm to 400 nm, preferably 200 nm to 320 nm. For example, the average particle size of the first main material can be 160 nm, 200 nm, 250 nm, 320 nm, 350 nm, 400 nm, or a range between any two of them. When the average particle size of the first main material is within the range of the present application, the first main material with a nano-scale particle size can increase the packing density between particles, form a more dense first coating on the surface of the positive current collector, increase the pressure collapse resistance of the first coating, enhance the protection of the positive current collector during the nail test, wrap the metal burrs that may be generated by the positive current collector during the nail 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 safety performance of the electrochemical device.

[0036] In an embodiment of the present application, the first coating further comprises a first binder, the first binder comprising at least one of polyvinylidene fluoride, polyacrylic acid, or polymethyl methacrylate; the mass percentage of the first binder is 3% to 15% based on the mass of the first coating. For example, the mass percentage of the first binder can be 3%, 5%, 7%, 9%, 11%, 15%, or a range between any two of them. When the first binder is selected from the above materials and the mass percentage is within the range of the present application, the adhesion of the first coating as a whole can be improved, and the adhesion between the first coating and the positive current collector can be improved, thereby improving the nail safety performance of the electrochemical device.

[0037] In an embodiment of the present application, the thickness of the first coating layer is 0.2 μm to 2 μm, preferably 1 μm to 1.5 μm. For example, the thickness of the first coating layer can be 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.25 μm, 1.5 μm, 2 μm, or a range defined by any two of the above values. 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. Meanwhile, the thin first coating layer can also improve the volumetric energy density of the electrochemical device.

[0038] The method for preparing the metal oxide 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 metal oxide can include, but is not limited to, the following steps:

[0039] (1) Take ZnO and an aluminum-containing compound in a mass ratio of 99:1 to 94:6, mix and grind, and then calcine at 500°C to 700°C for 2 to 3 hours to obtain an Al-doped ZnO powder. Or take ZnO and an aluminum-containing compound in a mass ratio of 99:1 to 94:6, dissolve them in water, and add ammonia as a precipitant, and stir to precipitate. Then, form an Al-doped ZnO powder by filtering, drying, and calcining at 500°C to 700°C.

[0040] (2) Take a tin-containing compound and an antimony-containing compound in a mass ratio of 62:38 to 48:52 to obtain a mixture, and then take the mixture and TiO2 in a mass ratio of 1:1 to 7:3. Dissolve the mixture in ethanol to obtain a sol precursor solution. Disperse TiO2 particles in the sol precursor solution using ultrasonic dispersion, adjust the pH of the solution by adding an appropriate amount of water or ammonia, and make the tin-containing compound and the antimony-containing compound hydrolyze on the surface of the TiO2 and gradually form a gel mixture. After drying treatment of the TiO2 particles containing the gel mixture on the surface, calcine at 400°C to 700°C to finally form a TiO2 material with antimony-doped SnO2 on the surface.

[0041] The above-mentioned aluminum-containing compound can include, but is not limited to, at least one of Al2O3 or Al(NO3)3; the above-mentioned antimony-containing compound can include, but is not limited to, at least one of Sb2O3 or SbCl3; and the above-mentioned tin-containing compound can include, but is not limited to, SnCl4.

[0042] The method for regulating the average particle size 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. For example, the average particle size of the first main material can be regulated by regulating the grinding time and the grinding speed. Illustratively, when other conditions remain unchanged, the average particle size of the first main material decreases as the grinding time is prolonged, and the average particle size of the first main material increases as the grinding time is shortened.

[0043] The method for regulating the mass percentage content of Al element based on metal oxide is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the mass percentage content of Al element based on metal oxide can be regulated by regulating the mass ratio of ZnO and the aluminum-containing compound. When the mass ratio of ZnO and the aluminum-containing compound increases, the mass percentage content of Al element based on metal oxide decreases; when the mass ratio of ZnO and the aluminum-containing compound decreases, the mass percentage content of Al element based on metal oxide increases.

[0044] The method for regulating the mass percentage content of the first component based on metal oxide is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the mass percentage content of the first component based on metal oxide can be regulated by the mass ratio of the sol precursor solution and TiO2. When the mass ratio of the sol precursor solution and TiO2 increases, the mass percentage content of the first component based on metal oxide increases; when the mass ratio of the sol precursor solution and TiO2 decreases, the mass percentage content of the first component based on metal oxide decreases.

[0045] The method for regulating the mass percentage content of Sb element based on the first component is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the mass percentage content of Sb element based on metal oxide can be regulated by regulating the mass ratio of the tin-containing compound and the antimony-containing compound. When the mass ratio of the tin-containing compound and the antimony-containing compound increases, the mass percentage content of Sb element based on metal oxide decreases; when the mass ratio of the tin-containing compound and the antimony-containing compound decreases, the mass percentage content of Sb element based on metal oxide increases.

[0046] The method for regulating the values of R1 and R2 is not particularly limited in the present application, as long as the purpose of the present application can be achieved. In the present application, the values of R1 and R2 will be affected by multiple preparation parameters in the preparation process of the positive electrode sheet, and will change with the changes of these preparation parameters, for example, the type and mass percentage content of the first main material, the type and mass percentage content of the first binder, the type and mass percentage content of the inorganic particles, the thickness of the first coating, the mass percentage content of Al element based on metal oxide, the mass percentage content of Sb element based on the first component, etc., as long as R1 and R2 satisfy 100%≤(R1-R2) / R2×100%≤500%.

[0047] The preparation method of the positive electrode tab is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the preparation method of the positive electrode tab can include, but is not limited to, the following steps: mixing the first main material, the inorganic particles and the first binder in a mass ratio of (20 to 95):(0 to 77):(3 to 15), adding deionized water as a solvent, and stirring uniformly to obtain a first coating slurry with a solid content of 70wt% to 80wt%. Then the first coating slurry is coated on one surface of the positive current collector with a thickness of 5μm to 20μm, and baked at 90℃ to 180℃ for 1h to 3h to obtain a first coating layer with a thickness of 0.2μm to 2μm. Then a positive material layer slurry is prepared, and the positive material layer slurry is coated on the surface of the first coating layer, and dried to obtain a positive electrode tab 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 tab coated with the first coating layer and the positive material layer on both sides.

[0048] The positive current collector is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, it can include aluminum foil, aluminum alloy foil or composite current collector (such as aluminum-carbon composite current collector) and the like.

[0049] The positive material layer includes a positive active material, and the positive active material is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, the positive active material can include, but is not limited to, at least one of nickel-cobalt-manganese lithium phosphate (such as NCM811, NCM622, NCM523, NCM111), nickel-cobalt-aluminum lithium phosphate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate or lithium titanate.

[0050] The positive electrode material layer can further include a conductive agent and a second binder, and 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 nano carbon 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, butadiene-styrene 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.

[0051] The thickness of the positive electrode current collector and the thickness of the positive electrode material layer 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 positive electrode material layer can be 70 μm to 90 μm, and the thickness of the positive electrode current collector can be 5 μm to 20 μm.

[0052] 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.

[0053] 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.

[0054] 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

[0055] 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.

[0056] 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.

[0057] 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 can be the above-mentioned conductive agent and the above-mentioned second binder.

[0058] 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.

[0059] 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. ​

[0060] 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.

[0061] 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).

[0062] 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.

[0063] In the present application, the electrochemical device further includes an electrolyte including a lithium salt and a non-aqueous solvent.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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 structure of the electrode assembly, placing the electrode assembly into the case, injecting the electrolyte into the case 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 an electrode assembly of the stack structure, the electrode assembly is placed into the case, the electrolyte is injected into the case and sealed to obtain the electrochemical device. In addition, the overcurrent prevention element, the guide plate, etc. can also be placed in the case as needed, thereby preventing the pressure rise inside the electrochemical device, overcharging and discharging.

[0069] The second aspect of the present application provides an electronic device, which includes the electrochemical device of any of the foregoing embodiments. The electronic device of the present application has good nail-penetration safety performance and fast-charging performance.

[0070] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the 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 flash, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0071] Embodiments

[0072] Hereinafter, embodiments and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0073] Test method and equipment:

[0074] First main material average particle size test

[0075] The lithium ion battery is disassembled to obtain a positive electrode sheet. The positive electrode sheet is longitudinally cut in a thickness direction by using plasma. The argon ion polishing technology is adopted for polishing to obtain a smooth cross section. Then, the scanning electron microscope (OXFORD·EDS) is used to observe the first main material particles under a magnification of 50,000 times. Then, 30 particles are randomly selected from the SEM photos by using the image analysis software. The areas of the particles are calculated. Then, the particles are assumed to be spherical. The particle diameter D (diameter) of each particle is calculated by the following formula: D = 2 x (S1 / π)1 / 2; wherein S1 is the area of the particle. The average particle diameter of the 30 particles is taken as the average particle diameter of the first main material.

[0076] First coating thickness test

[0077] The lithium ion battery is disassembled to obtain a positive electrode sheet. The positive electrode sheet is longitudinally cut in a thickness direction by using plasma. The argon ion polishing technology is adopted for polishing to obtain a smooth cross section. Then, the scanning electron microscope (OXFORD·EDS) is used to observe the first main material particles under a magnification of 50,000 times. Then, 30 particles are randomly selected from the SEM photos by using the image analysis software. The areas of the particles are calculated. Then, the particles are assumed to be spherical. The particle diameter D (diameter) of each particle is calculated by the following formula: D = 2 x (S1 / π)1 / 2; wherein S1 is the area of the particle. The average particle diameter of the 30 particles is taken as the average particle diameter of the first main material.

[0078] Nail penetration test

[0079] Ten lithium ion batteries in the examples or comparative examples are fully charged at 25±3°C. The specific steps are as follows: charging at a current of 0.5C to 4.5V, and then charging at a constant voltage of 4.5V to a current of 0.05C.

[0080] The nail penetration test is carried out on the lithium ion battery at 25±3°C. The steel nail has a diameter of 4mm, a material of carbon steel, a taper of 16.5mm, and a total length of 100mm. The nail penetration speed is set to 30mm / s. The nail penetration depth is determined by the taper of the steel nail penetrating through the lithium ion battery. The state of the lithium ion battery during the test is observed. The determination standard is that the lithium ion battery does not burn or explode. The nail penetration test pass rate = (the number of lithium ion batteries that do not burn or explode in the nail penetration test / 10) x 100%.

[0081] Fast charging performance test

[0082] The fast charging performance of the lithium ion battery is evaluated by the charging time of the lithium ion battery. The longer the charging time, the worse the fast charging performance. The shorter the charging time, the better the fast charging performance.

[0083] The test process is as follows: the lithium ion battery is discharged at 0.2C constant current to 3.0V, at which time the lithium ion battery is in a full discharge state, the full discharge lithium ion battery is placed in a 25℃ constant temperature box, and after standing for 30 minutes, the lithium ion battery is charged at 3C current constant current to 4.5V, and then charged at 4.5V constant voltage to 0.05C, at which time the lithium ion battery is in a full charge state, and the charging time t1 of the lithium ion battery from full discharge to full charge is recorded, in seconds.

[0084] Membrane resistance test

[0085] First, the lithium ion battery is rated voltage full charge: the specific steps are as follows: charged at 0.5C current constant current to 4.5V, and then charged at 4.5V constant voltage to 0.05C current cutoff. Then discharge at 0.1C rate for t hours to obtain a lithium ion battery with a target state of charge: t = [(100%-target SOC) / 10%]. After disassembling the lithium ion battery by discharging to different states of charge, the positive electrode sheet is obtained, after wiping off the surface electrolyte and attached substances, the part of the positive electrode current collector surface coated with a first coating and a positive electrode material layer is cut into a test sample with a size of 60mmx80mm, using a membrane resistance meter, the test pressure is 0.4T, the pressure holding time is 10s, and the test area is a circle with a diameter of 154mm 2 The membrane resistance of the positive electrode sheet at different states of charge in each example is obtained. The membrane resistance of the positive electrode sheet with a state of charge of 100% is denoted as R1, the membrane resistance of the positive electrode sheet with a state of charge of 0% is denoted as R2, and the membrane resistance of the positive electrode sheet with a state of charge of 50% is denoted as R3. The membrane resistance of the positive electrode sheet at different states of charge in each example is obtained. The lithium ion batteries prepared according to the lithium ion battery preparation methods of examples 1-1, comparative example 1 and comparative example 2 are disassembled at different states of charge, and the membrane resistance of the positive electrode sheet is measured to obtain Figure 2 、 Figure 3 and Figure 4 .

[0086] Mass percentage content test of Al element, Sb element and first component

[0087] (1) The lithium ion battery was discharged to 3V at 0.2C, and then the positive electrode sheet was removed. The positive electrode sheet was cut into 10 small round pieces with a diameter of 16 mm. The positive electrode material layer was scraped off with a knife, and the first coating layer was scraped off from the positive electrode current collector of the single small round piece to obtain the first coating layer powder. 0.2g of the first coating layer powder was digested with 10mL aqua regia, and diluted with deionized water to 100mL in a volumetric flask. The inductively coupled plasma analyzer (ICP, model AVIO-200) was used for testing, with the radio frequency generator (RF) frequency set at 40.68MHz, the argon secondary pressure at 0.6MPa, the radio frequency power at 1400W, and the pump speed at 1.0mL / min. The contents of Al, Zn, Sn, Sb and Ti elements in the first coating layer of the single small round piece were tested. The average of the contents of Al, Zn, Sn, Sb and Ti elements obtained from the above 10 small round pieces was taken as the mass percentage of Al, Zn, Sn, Sb and Ti elements in the first coating layer. The aqua regia was obtained by mixing concentrated nitric acid and concentrated hydrochloric acid in a volume ratio of 1:1.

[0088] (2) The mass percentage of Sn element in the first coating layer was converted to the mass percentage of SnO2, denoted as W1, the mass percentage of Sb element was denoted as W2, the mass percentage of Sb element was converted to the mass percentage of Sb2O5, denoted as W3, and the mass percentage of Ti element was converted to the mass percentage of TiO2, denoted as W4. The mass percentage of the first component based on metal oxides = (W1+W3) / (W1+W3+W4)×100%, and the mass percentage of Sb element based on the first component W Sb =W2 / (W1+W3)×100%.

[0089] (3) The mass percentage of Zn element in the first coating layer was converted to the mass percentage of ZnO, denoted as W5, the mass percentage of Al element was denoted as W6, and the mass percentage of Al element was converted to the mass percentage of Al2O3, denoted as W7. The mass percentage of Al element based on metal oxides W Al =W6 / (W5+W7)×100%.

[0090] Example 1-1

[0091] <Preparation of the first main material>

[0092] (1) Take tin-containing compound SnCl4 and antimony-containing compound SbCl3 with a mass ratio of 55:45 to obtain a mixture, then take the mixture and TiO2 with a mass ratio of 5:3, dissolve the mixture in ethanol to obtain a sol precursor solution. Disperse TiO2 particles in the sol precursor solution by ultrasonic dispersion, adjust the pH of the solution by adding ammonia water, and when the pH of the solution reaches 5, the tin-containing compound SnCl4 and the antimony-containing compound SbCl3 hydrolyze on the surface of TiO2 and gradually form a gel mixture. After drying treatment of the TiO2 particles containing the gel mixture on the surface, calcination is carried out at 500°C, and finally a TiO2 material with antimony-doped SnO2 on the surface is formed. Among them, the mass percentage content of the first component based on metal oxide is 50%, the mass percentage content of the Sb element based on the first component is 36%, and the average particle size of the first main material is 260 nm.

[0093] <Preparation of positive electrode sheet>

[0094] The first main material and the first binder polyacrylic acid prepared above are mixed in a mass ratio of 91:9, deionized water is added as a solvent, and stirring is uniformly carried out to obtain a first coating slurry with a solid content of 75wt%. The first coating slurry is coated on one surface of an 8μm positive current collector aluminum foil, and after drying at 120°C, a first coating layer with a thickness of 1.25μm is obtained. The positive active material lithium cobaltate, the conductive agent carbon nanotube (CNT), and the second binder polyvinylidene fluoride are mixed in a mass ratio of 97.3:1.1:1.6, and N-methyl pyrrolidone (NMP) is added as a solvent. The positive electrode slurry is uniformly stirred in a vacuum stirrer to obtain a positive electrode slurry with a solid content of 75wt%. The positive electrode slurry is uniformly coated on the surface of the first coating layer, and after drying at 120°C, a positive electrode sheet with a single-sided coating of the first coating layer and the positive material layer is obtained. The coating weight of the positive active layer is 267.8mg / 1540mm 2 . Then the above steps are repeated on the other surface of the aluminum foil, and after drying at 120°C, a positive electrode sheet with a double-sided coating of the first coating layer and the positive material layer is obtained. Then, after cold pressing, cutting, and welding the tab, a positive electrode sheet with a specification of 74mm×867mm is obtained for use. The thickness of the single-sided positive material layer is 90μm.

[0095] The structure of the positive electrode sheet prepared in Example 1-1 is shown in Figure 1 .

[0096] <Preparation of negative electrode sheet>

[0097] The negative active material artificial graphite, the second binder styrene-butadiene rubber (SBR), and the second binder carboxymethyl cellulose (CMC) are mixed in a mass ratio of 97.7:1:1.3, then deionized water is added as a solvent to prepare a slurry with a solid content of 70 wt%, and the slurry is stirred uniformly in a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and dried at 120°C to obtain a negative electrode sheet with a single-side coated negative electrode material layer, and the coated weight of the negative electrode material layer is 142 mg / 1540 mm 2 . Then the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-side coated negative electrode material layer. After drying at 120°C and cold pressing, the negative electrode sheet is cut and the tabs are welded to obtain a negative electrode sheet with a size of 78 mm x 875 mm for use. The thickness of the single-side negative electrode material layer is 85 μm.

[0098] <Preparation of electrolyte>

[0099] In an argon atmosphere glove box with a water content of less than 10 ppm, carbonate compounds ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are uniformly mixed in a mass ratio of 10:30:60 to obtain a base solvent, and a lithium salt LiPF6 is added and stirred uniformly to obtain an electrolyte. The mass percentage of the lithium salt LiPF6 in the electrolyte is 12.5% based on the total mass of the electrolyte, and the balance is the base solvent.

[0100] <Separator>

[0101] A polyethylene porous polymer film (manufacturer: Celgard Separator, Inc., USA) with a thickness of 8 μm is used as a separator.

[0102] <Preparation of lithium ion battery>

[0103] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and the electrode assembly is obtained by winding. The electrode assembly is placed in an aluminum plastic film packaging bag, and the water is removed at 80°C. The prepared electrolyte is injected, and the lithium ion battery is obtained after vacuum packaging, standing, formation, and shaping. The upper limit voltage of formation is 4.53 V, the formation temperature is 85°C, and the formation time is 50 min.

[0104] Examples 1-2 to 1-7

[0105] Except that aluminum oxide is added as an inorganic particle in the <Preparation of positive electrode sheet>, and the mass percentage of the first main material, the mass percentage of the inorganic particle, and the mass percentage of the first binder are adjusted according to Table 1, the rest is the same as Example 1-1.

[0106] Example 1-8 to Example 1-13

[0107] The rest was the same as Example 1-1 except that in <Preparation of positive electrode sheet>, the mass ratio of sol precursor solution and TiO2 and the mass ratio of tin-containing compound and antimony-containing compound were adjusted so that the mass percentage of the first component and the mass percentage of Sb element were as shown in Table 1.

[0108] Example 1-14 to Example 1-23

[0109] The rest was the same as Example 1-1 except that in <Preparation of positive electrode sheet>, the average particle diameter of the first main material and the thickness of the first coating layer were adjusted according to Table 1.

[0110] Example 1-24

[0111] The rest was the same as Example 1-1 except that in <Sheet resistance test>, the sheet resistance of the positive electrode sheet with a state of charge of 90% was recorded as R1, the sheet resistance of the positive electrode sheet with a state of charge of 20% was recorded as R2, and the sheet resistance of the positive electrode sheet with a state of charge of 60% was recorded as R3.

[0112] Example 1-25

[0113] The rest was the same as Example 1-1 except that in <Preparation of positive electrode sheet>, the type of the first binder was replaced with polyvinylidene fluoride.

[0114] Example 1-26

[0115] The rest was the same as Example 1-6 except that in <Preparation of positive electrode sheet>, the type of inorganic particles was replaced with nanometer boehmite.

[0116] Example 1-27

[0117] The rest was the same as Example 1-1 except that <Preparation of first main material> was replaced with the following preparation process.

[0118] <Preparation of first main material>

[0119] ZnO and aluminum-containing compound Al2O3 with a mass ratio of 94:6 were mixed and ground, and then calcined at 600°C for 3 hours to obtain Al element-doped ZnO powder.

[0120] Example 1-28 to Example 1-31

[0121] The rest was the same as Example 1-27 except that in <Preparation of positive electrode sheet>, the mass ratio of ZnO and aluminum-containing compound was adjusted so that the mass percentage of Al element was as shown in Table 1.

[0122] Example 2-1

[0123] Preparation of the positive electrode sheet

[0124] The first main material Li-rich manganese-based material LiMnO2, the first binder polyacrylic acid, and deionized water as a solvent were mixed in a mass ratio of 91:9, and stirred uniformly to obtain a first coating slurry with a solid content of 75wt%. The first coating slurry was coated on one surface of an 8μm positive current collector aluminum foil, and dried at 120°C to obtain a first coating layer with a thickness of 1.25μm. The positive electrode active material lithium cobaltate, the conductive agent carbon nanotube (CNT), and the second binder polyvinylidene fluoride were mixed in a mass ratio of 97.3:1.1:1.6, and N-methyl pyrrolidone (NMP) was added as a solvent. The mixture was stirred uniformly 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 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 dried at 120°C to obtain a positive electrode sheet coated with the first coating layer and the positive electrode material layer on both sides. Then the positive electrode sheet was cold-pressed, cut, and the tab was welded to obtain a positive electrode sheet with a size of 74mm×867mm. The average particle size of the first main material was 260nm, and the thickness of the single-sided positive electrode material layer was 90μm.

[0125] Preparation of the negative electrode sheet

[0126] 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%. The slurry was stirred uniformly in a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on one surface of a 6μm negative current collector copper foil, and 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. The negative electrode sheet was dried at 120°C, cold-pressed, cut, and the tab was welded to obtain a negative electrode sheet with a size of 78mm×875mm. The thickness of the single-sided negative electrode material layer was 85μm.

[0127] Preparation of the electrolyte

[0128] 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.

[0129] <Separator>

[0130] A polyethylene porous polymer film (manufacturer: Celgard Membrane Co., Ltd., USA) with a thickness of 8 μm was used as a separator.

[0131] <Preparation of lithium ion battery>

[0132] 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 the electrode assembly was obtained by winding. The electrode assembly was placed in an aluminum plastic film packaging bag, and the water was removed at 80°C. The prepared electrolyte was injected, and the lithium ion battery was obtained after vacuum packaging, standing, formation, and shaping. The upper limit voltage of formation was 4.53 V, the formation temperature was 85°C, and the formation time was 50 min.

[0133] Examples 2-2 to 2-4

[0134] Except that the mass percentage of the first main material, the mass percentage of the inorganic particles, and the mass percentage of the first binder were adjusted according to Table 2 in the <Preparation of positive electrode sheet>, the rest was the same as Example 2-1.

[0135] Examples 2-5 to 2-6

[0136] Except that the type of lithium-rich manganese-based material was adjusted according to Table 2 in the <Preparation of positive electrode sheet>, the rest was the same as Example 2-1.

[0137] Comparative Example 1

[0138] Except that no first coating layer was provided on the surface of the positive current collector, the rest was the same as Example 1-1.

[0139] Comparative Examples 2 to 6

[0140] Except that the relevant preparation parameters were adjusted according to Table 1, the rest was the same as Example 1-1.

[0141] Comparative Examples 7 to 8

[0142] Except that the relevant preparation parameters were adjusted according to Table 2, the rest was the same as Example 2-1.

[0143] The data for each embodiment and comparative example are shown in Table 1 and Table 2.

[0144] Table 1

[0145]

[0146] Note: In Table 1, " / " indicates that the corresponding preparation parameter or substance does not exist. Al The content of Al is expressed as a mass percentage of the metal oxide. Sb t1 represents the mass percentage of Sb element based on the first component, and t1 represents the charging time of the lithium-ion battery from full discharge to full charge.

[0147] From Examples 1-1 to 1-31, and Comparative Examples 1 to 6, it can be seen that when the positive electrode has the structure of the first coating of this application, and the mass percentage of the first main material, the values ​​of R1 and R2, the value of (R1-R2) / R2×100%, the mass percentage of inorganic particles, and the mass percentage of the first binder are within the range of this application, the resulting lithium-ion battery has a shorter charging time from full discharge to full charge and a higher pass rate in the nail penetration test. This demonstrates that the lithium-ion battery of this application improves fast charging performance while also ensuring good nail penetration safety performance. In Comparative Example 1, the positive electrode does not have the first coating structure of this application. In Comparative Examples 2 to 6, the mass percentage of the first main material and / or the value of (R1-R2) / R2×100% are not within the range of this application. The resulting lithium-ion battery has a longer charging time from full discharge to full charge and / or a lower pass rate in the nail penetration test, failing to achieve both good fast charging performance and nail penetration safety performance.

[0148] from Figure 2 It can be seen that when the positive electrode sheet of Example 1-1 has the structure of the first coating of this application and the mass percentage of the first main material, the value of (R1-R2) / R2×100%, the mass percentage of inorganic particles, and the mass percentage of the first binder are within the range of this application, the positive electrode sheet exhibits high film resistance in a high charged state and low film resistance in a low charged state, thus achieving adaptive adjustment of the film resistance of the positive electrode sheet with changes in the state of charge. Figure 3 and Figure 4 It can be seen that the positive electrode sheet of Comparative Example 1 does not have the first coating structure of this application. The mass percentage of the first main material, the value of (R1-R2) / R2×100%, the mass percentage of inorganic particles, and the mass percentage of the first binder in the positive electrode sheet of Comparative Example 3 are not within the scope of this application. The film resistance of the positive electrode sheet under different charging states does not show an obvious trend, and it is impossible to achieve adaptive adjustment of the film resistance of the positive electrode sheet with the change of charging state.

[0149] The mass percentage of the first component and the mass percentage of the element Sb generally affect the fast charging performance and the nail penetration safety performance of the lithium ion battery. As can be seen from Example 1-1 and Example 1-8 to Example 1-13, when the mass percentage of the first component and the mass percentage of the element Sb are within the range of the present application, the lithium ion battery obtained has a shorter charging time from full discharge to full charge and a higher pass rate in the nail penetration test, thereby indicating that the lithium ion battery of the present application improves the fast charging performance while taking into account good nail penetration safety performance.

[0150] The average particle size of the first main material and the thickness of the first coating generally affect the fast charging performance and the nail penetration safety performance of the lithium ion battery. As can be seen from Example 1-1 and Example 1-14 to Example 1-23, when the average particle size of the first main material and the thickness of the first coating are within the range of the present application, the lithium ion battery obtained has a shorter charging time from full discharge to full charge and a higher pass rate in the nail penetration test, thereby indicating that the lithium ion battery of the present application improves the fast charging performance while taking into account good nail penetration safety performance.

[0151] The type of inorganic particles and the type of first binder generally affect the fast charging performance and the nail penetration safety performance of the lithium ion battery. As can be seen from Example 1-1 and Example 1-25 to Example 1-26, when the type of inorganic particles and the type of first binder are within the range of the present application, the lithium ion battery obtained has a shorter charging time from full discharge to full charge and a higher pass rate in the nail penetration test, thereby indicating that the lithium ion battery of the present application improves the fast charging performance while taking into account good nail penetration safety performance.

[0152] The type of metal oxide and the mass percentage of the element Al generally affect the fast charging performance and the nail penetration safety performance of the lithium ion battery. As can be seen from Example 1-1 and Example 1-27 to Example 1-31, when the mass percentage of the element Al is within the range of the present application, the lithium ion battery obtained has a shorter charging time from full discharge to full charge and a higher pass rate in the nail penetration test, thereby indicating that the lithium ion battery of the present application improves the fast charging performance while taking into account good nail penetration safety performance.

[0153] Table 2

[0154]

[0155] Note: " / " in Table 2 indicates that the corresponding preparation parameter or substance does not exist, and t1 represents the charging time of the lithium ion battery from full discharge to full charge.

[0156] As can be seen from Example 2-1 to Example 2-6, Comparative Example 7 to Comparative Example 8, when the positive electrode plate has the structure of the first coating of the application and the mass percentage content of the first main material, the value of (R1-R2) / R2x100%, the mass percentage content of the inorganic particles and the mass percentage content of the first binder are within the range of the application, the charging time of the obtained lithium ion battery from full discharge to full charge is shorter, and the nail penetration test passing rate is higher, thereby indicating that the lithium ion battery of the application can improve the fast charging performance while taking into account the good nail penetration safety performance. The mass percentage content of the first main material in Comparative Example 7 to Comparative Example 8 is not within the range of the application, the charging time of the obtained lithium ion battery from full discharge to full charge is longer or the nail penetration test passing rate is lower, and the good fast charging performance and nail penetration safety performance cannot be taken into account.

[0157] The type of lithium-rich manganese-based material usually affects the fast charging performance and nail penetration safety performance of the lithium ion battery. As can be seen from Example 2-1 and Example 2-5 to Example 2-6, when the type of lithium-rich manganese-based material is within the range of the application, the charging time of the obtained lithium ion battery from full discharge to full charge is shorter, and the nail penetration test passing rate is higher, thereby indicating that the lithium ion battery of the application can improve the fast charging performance while taking into account the good nail penetration safety performance.

[0158] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

[0159] It should be noted that in this paper, relationship terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the term "includes", "contains" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method or article including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method or article.

[0160] Each embodiment in the specification is described in a related manner, and the same or similar parts between each embodiment can be referred to each other, and each embodiment mainly explains the difference from other embodiments.

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, and 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, the first main material comprising a lithium-rich manganese-based material or a metal oxide, the mass percentage of the first main material being 20% to 95% based on the mass of the first coating layer; the membrane sheet resistance of the positive electrode tab at a state of charge greater than 80% is R1Ω, the membrane sheet resistance of the positive electrode tab at a state of charge of 0% to 50% is R2Ω, and 100%≤(R1-R2) / R2×100%≤500%.

2. The electrochemical device of claim 1, wherein, 150%≤(R1-R2) / R2×100%≤480%.

3. The electrochemical device of claim 1, wherein, 0.4≤R1≤80, 0.2≤R2≤13.

4. The electrochemical device of claim 1, wherein, the membrane sheet resistance of the positive electrode tab at a state of charge of 50% to 100% is R3Ω, and 0.3≤R3≤82.

5. The electrochemical device of claim 1, wherein, the lithium-rich manganese-based material comprises at least one of lithium nickel cobalt manganese oxide or lithium manganate.

6. The electrochemical device of claim 1, wherein, the metal oxide comprises ZnO, and the metal oxide further comprises an Al element, the mass percentage of the Al element being 0.6% to 4% based on the mass of the metal oxide.

7. The electrochemical device of claim 1, wherein, the metal oxide comprises TiO2, at least part of the surface of the TiO2 being provided with a first component, the first component comprising SnO2, and the first component further comprising an Sb element, the mass percentage of the first component being 44.44% to 55.25% based on the mass of the metal oxide, and the mass percentage of the Sb element being 30.2% to 38.8% based on the mass of the first component.

8. The electrochemical device of claim 1, wherein, the first coating layer further comprises inorganic particles, the inorganic particles comprising at least one of nanometer boehmite or aluminum trioxide, and the mass percentage of the inorganic particles being 0% to 77% based on the mass of the first coating layer.

9. The electrochemical device of claim 1, wherein, the average particle size of the first main material is 160nm to 400nm.

10. The electrochemical device of claim 9, wherein, the average particle size of the first main material is 200nm to 320nm.

11. The electrochemical device of claim 1, wherein, the first coating layer further comprises a first binder, the first binder comprising at least one of polyvinylidene fluoride, polyacrylic acid or polymethyl methacrylate, and the mass percentage of the first binder being 3% to 15% based on the mass of the first coating layer.

12. The electrochemical device of claim 1, wherein, the thickness of the first coating layer is 0.2μm to 2μm.

13. The electrochemical device of claim 12, wherein, the thickness of the first coating layer is 1μm to 1.5μm. 14.An electronic device, comprising the electrochemical device according to any one of claims 1 to 13.

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