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 and a first binder, the first main material comprises a lithium supplement material, and the lithium supplement material comprises at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium orthosilicate or lithium ferrite; the infrared spectrum of the first coating layer has a characteristic peak between 3200 cm ‑1 and 3400 cm ‑1 . The electrochemical device provided by the application can balance the nail penetration safety performance, capacity and volume energy density.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and in particular 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, their service life is increasingly valued by users, and consumers, after-sales, battery manufacturers and lithium battery manufacturers have put forward new requirements for the nail safety performance of the batteries.

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

[0004] The purpose of the present application is to provide an electrochemical device and an electronic device. The electrochemical device of the present application can balance the nail safety performance, capacity and volumetric energy density.

[0005] It should be noted that the present application is explained by taking a lithium ion battery as an example 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] The first aspect of the present application provides an electrochemical device, which comprises 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 comprises a first main material and a first binder, the first main material comprising a lithium supplementing material, and the lithium supplementing material comprising at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium orthosilicate or lithium ferrite. The infrared spectrum of the first coating layer has a characteristic peak between 3200 cm -1 and 3400 cm -1 . When the electrochemical device has the first coating layer of the present application, and the selected lithium supplementing material is within the above range, and the infrared spectrum of the first coating layer is within the range of 3200 cm -1 and 3400 cm -1When there is a characteristic peak between 0.5 V and 1.0 V, the lithium supplement material can supplement the lithium ions lost by the electrochemical device during the cycle process, improve the capacity and volumetric energy density of the electrochemical device, and the lithium supplement material can form strong hydrogen bond with the first binder to improve the cohesion and adhesion between the first coating and the positive electrode current collector, so that the first coating has high mechanical strength, can protect the positive electrode current collector during the nail penetration test, reduce the possibility of short circuit in the electrochemical device, reduce the short circuit joule heat, and reduce the probability of thermal runaway caused by local overheating of the electrochemical device, while improving the capacity and volumetric energy density of the electrochemical device, the nail penetration safety performance of the electrochemical device is also improved.

[0007] In an embodiment of the present application, at least part of the surface of the lithium supplement material is provided with a first component, the first component includes carbon element, nitrogen element and oxygen element, the mass percentage content of the carbon element is 63.5% to 73.8%, the mass percentage content of the nitrogen element is 7.6% to 17.9%, and the mass percentage content of the oxygen element is 12% to 24.5%, based on the mass of the first component; preferably, the mass percentage content of the carbon element is 66.25% to 70.1%, the mass percentage content of the nitrogen element is 7.8% to 17.5%, and the mass percentage content of the oxygen element is 12.4% to 22.3%, based on the mass of the first component. When the mass percentage content of the carbon element, the nitrogen element and the oxygen element in the first component is within the above range, the oxygen element provides a hydrogen bond donor to form a hydrogen bond between the bonding group in the binder and the main material, and the nitrogen element makes there are more polar sites on the surface of the lithium supplement material, which is beneficial to form a good bond with the binder, can improve the cohesion and adhesion between the first coating and the positive electrode current collector, and improve the nail penetration safety performance of the electrochemical device.

[0008] In an embodiment of the present application, the mass percentage content of the first component based on the mass of the first main material is 2% to 10%. When the mass percentage content of the first component based on the mass of the first main material is within the above range, the first main material has good electrical conductivity, further improves the lithium supplement capacity, and improves the volumetric energy density of the electrochemical device.

[0009] In an embodiment of the present application, the Dv50 of the first main material is 50 nm to 200 nm, preferably 100 nm to 150 nm. When the particle size of the first main material is within the above range, the nano-sized first main material can increase the packing density between particles, form a more dense first coating on the surface of the positive electrode current collector, improve the pressure collapse resistance of the first coating, and enhance the protection of the positive electrode current collector during the nail penetration test, so that the electrochemical device has high capacity and high volumetric energy density while having good nail penetration safety performance.

[0010] In an embodiment of the present application, the mass percentage of the first main material is 84.5% to 94.8% based on the mass of the first coating. When the mass percentage of the first component based on the mass of the first main material is within the above range, the first coating can have a high compaction density while having good overall adhesion, thereby improving the capacity, volumetric energy density, and nail penetration safety of the electrochemical device.

[0011] In an embodiment of the present application, the sphericity of the first main material is 0.705 to 0.874. When the sphericity of the first main material is within the above range, the first main material particles are in a close-packed interlocking bite, thereby improving the protection of the positive current collector, reducing short-circuit joule heat, and improving the nail penetration safety of the electrochemical device.

[0012] In an embodiment of the present application, the first binder includes a water-soluble polymer metal salt; the mass percentage of the first binder is 5.2% to 15.5% 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 tensile strength of the first coating can be improved, and the adhesion between the first coating and the positive current collector can be improved, thereby improving the nail penetration safety of the electrochemical device.

[0013] In an embodiment of the present application, the metal element in the water-soluble polymer metal salt includes at least one of lithium, sodium, potassium, rubidium, cesium, francium, beryllium, barium, strontium, calcium, or magnesium; and the polymer in the water-soluble polymer metal salt includes at least one of polyacrylic acid, carboxymethyl cellulose, polyacrylonitrile, or styrene butadiene. When the water-soluble metal salt is selected from the above materials, the tensile strength of the first coating can be improved, and the adhesion between the first coating and the positive current collector can be improved, thereby improving the nail penetration safety of the electrochemical device.

[0014] In an embodiment of the present application, the water-soluble polymer metal salt includes at least one of sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, calcium polyacrylate, magnesium polyacrylate, lithium carboxymethyl cellulose, or sodium carboxymethyl cellulose. When the water-soluble metal salt is selected from the above materials, the tensile strength of the first coating can be improved, and the adhesion between the first coating and the positive current collector can be improved, thereby improving the nail penetration safety of the electrochemical device.

[0015] In an embodiment of the present application, the first coating further includes a first conductive agent, and the first conductive agent includes at least one of conductive carbon black, activated carbon, carbon nanotubes, or carbon nanofibers; the mass percentage of the first conductive agent is 0.2% to 0.5% based on the mass of the first coating. When the first conductive agent is selected from the above materials and the mass percentage is within the range of the present application, the first coating has a high short-circuit resistance while having good electrical conductivity, thereby improving the cycle performance of the electrochemical device.

[0016] In an embodiment of the present application, the particle size of the secondary particles of the first conductive agent is < 50 nm. When the particle size of the secondary particles of the first conductive agent is within the above range, it indicates that the first conductive agent has good dispersibility in the first coating layer, which improves the conductivity of the first coating layer and the cycle performance of the electrochemical device.

[0017] In an embodiment of the present application, the thickness of the first coating layer is 0.2 μm to 2 μm, preferably 0.5 μm to 2 μm. When the thickness of the first coating layer is within the above range, the first coating layer has high mechanical strength, which improves the nail penetration safety performance of the electrochemical device.

[0018] In an embodiment of the present application, the adhesion between the first coating layer and the positive electrode current collector is F1, 500 N / m ≤ F1 ≤ 900 N / m. For example, F1 can be 500 N / m, 600 N / m, 700 N / m, 800 N / m, 900 N / m, or a range between any two of them. When the adhesion F1 between the first coating layer and the positive electrode current collector is within the above range, it indicates that the first coating layer has good adhesion with the positive electrode current collector, which improves the nail penetration safety performance and cycle performance of the electrochemical device.

[0019] In an embodiment of the present application, the cohesion of the first coating layer is F2, 1400 N / m ≤ F2 ≤ 2500 N / m. For example, F2 can be 1400 N / m, 1500 N / m, 2000 N / m, 2500 N / m, or a range between any two of them. When the cohesion F2 of the first coating layer is within the above range, the first coating layer as a whole has strong adhesion, which can improve the adhesion between the first coating layer and the positive electrode current collector, thereby improving the nail penetration safety performance of the electrochemical device.

[0020] In an embodiment of the present application, the sheet resistance of the positive electrode tab is 0.5 Ω to 5 Ω. For example, the sheet resistance of the positive electrode tab can be 0.5 Ω, 1 Ω, 2 Ω, 3 Ω, 4 Ω, 5 Ω, or a range between any two of them. When the sheet resistance of the positive electrode tab is within the above range, the positive electrode tab has good conductivity, which improves the cycle performance of the electrochemical device.

[0021] The second aspect of the present application provides an electronic device comprising the electrochemical device in any of the foregoing embodiments. The electronic device of the present application has good nail penetration safety performance and high capacity and volume energy density.

[0022] The beneficial effects of the present application are:

[0023] 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 and a first binder, the first main material comprises a lithium supplement material, and the lithium supplement material comprises at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium orthosilicate or lithium ferrite. The infrared spectrum of the first coating layer has a characteristic peak between 3200 cm -1 and 3400 cm -1 When the electrochemical device has the first coating layer of the application, and the selected lithium supplement material is within the above range, and the infrared spectrum of the first coating layer has a characteristic peak between 3200 cm -1 and 3400 cm -1 The lithium supplement material can supplement the lithium ions lost in the cycle process of the electrochemical device, improve the capacity and volume energy density of the electrochemical device, and at the same time, the lithium supplement material can form strong hydrogen bond with the first binder, improve the cohesion and adhesion between the first coating layer and the positive electrode current collector, so that the first coating layer has high mechanical strength, can protect the positive electrode current collector in the nail penetration test process, reduce the possibility of short circuit in the electrochemical device, reduce the short circuit joule heat, 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.

[0024] Of course, implementing any product or method of the application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0026] Figure 1 It is a schematic diagram of the positive electrode sheet structure of an embodiment of the application;

[0027] Figure 2 It is an infrared spectrum test diagram of the first coating layer of Example 1-1;

[0028] Figure 3 It is an infrared spectrum test diagram of the first coating layer of Comparative Example 2;

[0029] Figure 4 It is a scanning electron microscope diagram of the cross section of the positive electrode sheet of an embodiment of the application. DETAILED DESCRIPTION

[0030] The technical solutions in the present application will be clearly and completely described below with reference to the embodiments of the present application and drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. All other embodiments obtained by those skilled in the art based on the present application are within the scope of the present application.

[0031] It should be noted that in the specific embodiments of the present application, the present application is explained 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.

[0032] 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 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 comprises a first main material and a first binder, the first main material comprising a lithium supplementing material, the lithium supplementing material comprising at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium orthosilicate or lithium ferrite. The infrared spectrum of the first coating layer has a characteristic peak between 3200 cm -1 and 3400 cm -1 . When the electrochemical device has the first coating layer of the present application, and the selected lithium supplementing material is within the above range, and the infrared spectrum of the first coating layer has a characteristic peak between 3200 cm -1 and 3400 cm -1 , the lithium supplementing material can supplement the lithium ions lost in the cycle process of the electrochemical device, improve the capacity and volume energy density of the electrochemical device, and at the same time, the lithium supplementing material can form strong hydrogen bonds with the first binder, improve the cohesion and adhesion between the first coating layer and the positive electrode current collector, so that the first coating layer has high mechanical strength, can protect the positive electrode current collector in the nail penetration test process, reduce the possibility of short circuit in the electrochemical device, reduce the short circuit joule heat, 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.

[0033] In the present application, the above-mentioned "the first coating layer is disposed on the surface of the positive electrode current collector" means that the first coating layer can be disposed on one surface of the positive electrode current collector along the thickness direction of the positive electrode current collector, or can be disposed on both surfaces of the positive electrode current collector along the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of the positive electrode current collector, or can be part of the area of the positive electrode 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 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 disposed on the surface of the first coating layer away from the positive electrode current collector" is understood in the same way. Figure 1

[0034] ​In an embodiment of the present application, at least part of the surface of the lithium supplementing material is provided with a first component, the first component comprising carbon element, nitrogen element and oxygen element, the mass percentage content of the carbon element being 63.5% to 73.8%, the mass percentage content of the nitrogen element being 7.6% to 17.9%, and the mass percentage content of the oxygen element being 12% to 24.5%, based on the mass of the first component; preferably, the mass percentage content of the carbon element is 66.25% to 70.1%, the mass percentage content of the nitrogen element is 7.8% to 17.5%, and the mass percentage content of the oxygen element is 12.4% to 22.3%, based on the mass of the first component. For example, the mass percentage content of the carbon element based on the mass of the first component can be 63.5%, 65%, 66.25%, 67%, 69%, 70.1%, 71%, 73%, 73.8%, or a range formed by any two of the above values; the mass percentage content of the nitrogen element based on the mass of the first component can be 7.6%, 7.8%, 8%, 10%, 12%, 14%, 16%, 17.5%, 17.9%, or a range formed by any two of the above values; and the mass percentage content of the oxygen element based on the mass of the first component can be 12%, 12.4%, 13%, 14%, 15%, 16%, 17%, 18%, 18.6%, 20%, 22.3%, 24%, 24.5%, or a range formed by any two of the above values. When the mass percentage content of the carbon element, the nitrogen element and the oxygen element based on the mass of the first component is within the above range, the oxygen element provides a hydrogen bond donor to form a hydrogen bond between the binding groups in the binder and the host material, and the nitrogen element provides more polar sites on the surface of the lithium supplementing material, which is conducive to forming a good bond with the binder, improving the cohesion and adhesion between the first coating and the positive electrode current collector, protecting the positive electrode current collector during the nail penetration test, reducing the possibility of short circuit in the electrochemical device, reducing the short circuit joule heat, reducing the probability of thermal runaway caused by local overheating of the electrochemical device, and improving the nail penetration safety performance of the electrochemical device.

[0035] In an embodiment of the present application, the mass percentage content of the first component based on the mass of the first host material is 2% to 10%. For example, the mass percentage content of the first component based on the mass of the first host material can be 2%, 4%, 6%, 8%, 10%, or a range formed by any two of the above values. When the mass percentage content of the first component based on the mass of the first host material is within the above range, the first host material has good electrical conductivity, further improving the lithium supplementing capacity, and improving the capacity and volume energy density of the electrochemical device.

[0036] In an embodiment of the present application, the Dv50 of the first main material is 50 nm to 200 nm, preferably 100 nm to 150 nm. For example, the Dv50 of the first main material can be 50 nm, 100 nm, 150 nm, 200 nm, or a range between any two of these values. When the particle size of the first main material is within the above range, the first main material of nanoscale particle size can increase the packing density between particles, form a more dense first coating layer on the surface of the positive current collector, improve the pressure collapse resistance of the first coating layer, enhance the protection of the positive current collector during the nail penetration test, wrap the metal burrs that the positive current collector can generate during the nail penetration test, reduce the occurrence of short circuits in the electrochemical device, while the first coating layer has a high compaction density, reducing the loss of energy density, thereby enabling the electrochemical device to have high capacity and high volumetric energy density while having good nail penetration safety performance.

[0037] In the present application, Dv50 represents the particle size at which the volume accumulation is 50% from the small particle size side in the particle size distribution of the first main material on a volume basis.

[0038] In an embodiment of the present application, the mass percentage content of the first main material is 84.5% to 94.8% based on the mass of the first coating layer. For example, the mass percentage content of the first main material based on the mass of the first coating layer can be 84.5%, 85%, 90%, 94%, 94.8%, or a range between any two of these values. When the mass percentage content of the first component based on the mass of the first main material is within the above range, the first coating layer can have a high compaction density while also having good overall adhesion, improving the capacity, volumetric energy density, and nail penetration safety performance of the electrochemical device.

[0039] In an embodiment of the present application, the sphericity of the first main material is 0.705 to 0.874. For example, the sphericity of the first main material can be 0.705, 0.71, 0.75, 0.79, 0.83, 0.87, 0.874, or a range between any two of these values. When the sphericity of the first main material is within the above range, it is beneficial for the first main material particles to produce inlaid occlusion between particles, improving the packing density of the first main material, and during the nail penetration test, when the first coating layer is damaged by mechanical abuse, the first main material particles are less likely to produce relative slipping between particles, improving the protection of the positive current collector, reducing the short circuit joule heat, and improving the nail penetration safety performance of the electrochemical device.

[0040] In an embodiment of the present application, the first binder includes a water-soluble polymer metal salt; the mass percentage of the first binder based on the mass of the first coating layer is 5.2% to 15.5%. For example, the mass percentage of the first binder can be 5.2%, 7%, 9%, 11%, 15%, 15.5%, or a range defined by any two of the numbers. When the first binder is selected from the above-mentioned materials and the mass percentage is within the range of the present application, the adhesion of the first coating layer as a whole can be improved, the adhesion between the first coating layer and the positive current collector can be increased, and thus the nail penetration safety performance of the electrochemical device can be improved.

[0041] In an embodiment of the present application, the metal element in the water-soluble polymer metal salt includes at least one of lithium, sodium, potassium, rubidium, cesium, francium, beryllium, barium, strontium, calcium, or magnesium; and the polymer in the water-soluble polymer metal salt includes at least one of polyacrylic acid, carboxymethyl cellulose, polyacrylonitrile, or styrene butadiene. When the water-soluble metal salt is selected from the above-mentioned materials, the water-soluble metal salt compound has good hydrophilicity, which is conducive to the transmission of electrons and ions, and the electronic conductivity and ionic conductivity are better than those of non-water-soluble polymer polymers such as polyvinylidene fluoride and polyvinylidene chloride. Therefore, the first coating layer can improve the kinetic performance of the electrochemical device and improve the cycle performance of the electrochemical device. In addition, the specific surface area of the water-soluble metal salt compound is large, and it can be highly dispersed after being contacted with water. When applied as a binder in the first coating layer, the tensile strength of the first coating layer can be improved. In addition, the water-soluble metal salt compound has many polar functional groups, which can further improve the adhesion between the first coating layer and the positive current collector and improve the nail penetration safety performance of the electrochemical device.

[0042] In an embodiment of the present application, the water-soluble polymer metal salt includes at least one of sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, calcium polyacrylate, magnesium polyacrylate, lithium carboxymethyl cellulose, or sodium carboxymethyl cellulose. When the water-soluble metal salt is selected from the above-mentioned materials, the adhesion of the first coating layer as a whole can be improved, the adhesion between the first coating layer and the positive current collector can be increased, and thus the nail penetration safety performance of the electrochemical device can be improved.

[0043] In an embodiment of the present application, the first coating layer further includes a first conductive agent, and the first conductive agent includes at least one of conductive carbon black, activated carbon, carbon nanotubes, or carbon nanofibers; the mass percentage of the first conductive agent based on the mass of the first coating layer is 0.2% to 0.5%. For example, the mass percentage of the first conductive agent based on the mass of the first coating layer can be 0.2%, 0.3%, 0.4%, 0.5%, or a range defined by any two of the numbers. When the first conductive agent is selected from the above-mentioned materials and the mass percentage is within the range of the present application, the first coating layer has good conductivity while having a relatively high short-circuit resistance, and thus the cycle performance of the electrochemical device can be improved.

[0044] In an embodiment of the present application, the cross section of the first coating along the thickness direction in a scanning electron microscope image with a magnification of 30000 times in a range of 4 μm x 4 μm, the particle size of the secondary particles of the first conductive agent is < 50 nm. For example, the particle size of the secondary particles of the first conductive agent can be 1 nm, 10 nm, 20 nm, 30 nm, 40 nm, 49 nm or a range consisting of any two of them. In the preparation process of the first coating, the particle size of the first conductive agent particles is small, and it is easy to aggregate to form secondary particles of the first conductive agent. When the particle size of the secondary particles is < 50 nm, it cannot be observed in the scanning electron microscope image of the cross section of the first coating, indicating that the secondary particles are uniformly dispersed in the first coating without agglomeration to form secondary particles with larger particle size, improving the conductivity of the first coating and improving the cycle performance of the electrochemical device.

[0045] In an embodiment of the present application, the thickness of the first coating is 0.2 μm to 2 μm, preferably 0.5 μm to 2 μm. For example, the thickness of the first coating 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, 0.95 μm, 1 μm, 1.5 μm, 2 μm or a range consisting of any two of them. When the thickness of the first coating is in the above range, the first coating 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.

[0046] In an embodiment of the present application, the adhesion between the first coating and the positive current collector is F1, 500 N / m ≤ F1 ≤ 900 N / m. For example, F1 can be 500 N / m, 600 N / m, 700 N / m, 800 N / m, 900 N / m or a range consisting of any two of them. When the adhesion F1 between the first coating and the positive current collector is in the above range, it indicates that the first coating has good adhesion with the positive current collector. The first coating can wrap the metal burrs that may be generated in the positive current collector under abnormal conditions such as nail penetration and impact, to reduce the occurrence of short circuit in the electrochemical device, and at the same time, it can reduce the probability of thermal runaway or overheating combustion of the electrochemical device due to local overheating, and improve the nail penetration safety performance of the electrochemical device. On the other hand, since the positive material layer will expand during the cycle, the first coating with strong adhesion can relieve the deformation of the positive current collector during the cycle, reduce the contact between the positive current collector and the positive material layer, and improve the cycle performance of the electrochemical device.

[0047] In an embodiment of the present application, the first coating layer has a cohesion F2 of 1400 N / m to 2500 N / m. For example, F2 can be 1400 N / m, 1500 N / m, 2000 N / m, 2500 N / m, or a range defined by any two of the above values. When the cohesion F2 of the first coating layer is within the above range, the first coating layer as a whole has strong adhesion, which can improve the adhesion between the first coating layer and the positive current collector, thereby improving the nail penetration safety performance of the electrochemical device.

[0048] In an embodiment of the present application, the positive electrode tab has a sheet resistance of 0.5 Ω to 5 Ω. For example, the positive electrode tab can have a sheet resistance of 0.5 Ω, 1 Ω, 2 Ω, 3 Ω, 4 Ω, 5 Ω, or a range defined by any two of the above values. When the sheet resistance of the positive electrode tab is within the above range, the positive electrode tab has good electrical conductivity, which improves the cycle performance of the electrochemical device.

[0049] The method for preparing 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 method for preparing the first main material can include, but is not limited to, the following steps: taking a lithium supplement material and an organic compound precursor with a mass ratio of 70:30 to 90:10, calcining at 300°C to 400°C under a nitrogen atmosphere, and obtaining the first main material after ball milling.

[0050] The above-mentioned organic compound precursor can include, but is not limited to, at least one of phenol formaldehyde resin, polyacrylonitrile, polyethyleneimine, hexamethylenetetramine, or urea.

[0051] The method for regulating the mass percentage content of carbon 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, it can be regulated by regulating the mass ratio of the organic compound precursor and the lithium supplement material. Illustratively, as the mass ratio of the organic compound precursor and the lithium supplement material increases, the mass percentage content of carbon element based on the first component increases, and as the mass ratio of the organic compound precursor and the lithium supplement material decreases, the mass percentage content of carbon element based on the first component decreases. In addition, the mass percentage content of carbon element based on the first component can also be regulated by the type of the organic compound precursor.

[0052] The method for regulating the mass percentage content of nitrogen 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, it can be regulated by the calcination temperature. Illustratively, as the calcination temperature increases, the mass percentage content of nitrogen element based on the first component increases, and as the calcination temperature decreases, the mass percentage content of nitrogen element based on the first component decreases.

[0053] The method for regulating the mass percentage content of oxygen 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, it can be regulated by regulating the calcination temperature. Illustratively, the mass percentage content of oxygen element based on the first component decreases as the calcination temperature increases, and the mass percentage content of oxygen element based on the first component increases as the calcination temperature decreases.

[0054] The method for regulating the mass percentage content of the first component based on 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, it can be regulated by regulating the mass ratio of the organic compound precursor and the lithium supplement material. Illustratively, the mass percentage content of the first component based on the first main material increases as the mass ratio of the organic compound precursor and the lithium supplement material increases, and the mass percentage content of the first component based on the first main material decreases as the mass ratio of the organic compound precursor and the lithium supplement material decreases.

[0055] The method for regulating the Dv50 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, it can be regulated by regulating the time of ball milling treatment. Illustratively, the Dv50 of the first main material decreases as the time of ball milling treatment increases, and the Dv50 of the first main material increases as the time of ball milling treatment decreases.

[0056] The method for regulating the sphericity 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, it can be regulated by regulating the sphericity of the lithium supplement material. The lithium supplement material with different sphericity can be purchased in the present application, and the sphericity of the lithium supplement material can be tested by the “Sphericity Test” test method provided in the present application, and the lithium supplement material with the desired sphericity can be selected.

[0057] In an embodiment of the present application, the first coating layer comprises the first main material and the first binder, and the mass percentage content of the first main material is 84.5% to 94.8% and the mass percentage content of the first binder is 5.2% to 15.5% based on the mass of the first coating layer.

[0058] In an embodiment of the present application, the first coating layer comprises the first main material, the first binder and the first conductive agent, and the mass percentage content of the first main material is 84.5% to 94.8%, the mass percentage content of the first binder is 5% to 15%, and the mass percentage content of the first conductive agent is 0.2% to 0.5% based on the mass of the first coating layer.

[0059] 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 and the first binder in a mass ratio of (84.5 to 94.8):(5.2 to 15.5), adding deionized water as a solvent, and stirring uniformly to obtain a first coating slurry with a solid content of 70wt% to 80wt%; or mixing the first main material, the first binder, and the first conductive agent in a mass ratio of (84.5 to 94.8):(5 to 15):(0.2 to 0.5), 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 with a single-side coated first coating layer and a positive material layer. The above steps are repeated on the other surface of the positive current collector to obtain a positive electrode tab with a double-side coated first coating layer and a positive material layer.

[0060] 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), etc.

[0061] 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 iron manganese phosphate, or lithium titanate.

[0062] The positive electrode material layer can further include a second conductive agent and a second binder. The kind of the second 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 second 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. 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. 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 second conductive agent, and the second binder in the positive electrode material layer is not particularly limited in the present application, and can be selected by a person skilled in the art according to actual needs, as long as the purpose of the present application can be achieved.

[0063] 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 20 μm.

[0064] 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” herein 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. The present application is not particularly limited, as long as the purpose of the present application can be achieved.

[0065] 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. For example, the negative electrode current collector 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.

[0066] 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-type lithium titanate Li4Ti5O12, or Li-Al alloy. 12

[0067] In some embodiments of the present application, the negative material layer can further include a second conductive agent and a second binder, for example, can be at least one of the above-mentioned second conductive agent and the above-mentioned second binder. The mass ratio of the negative active material, the second 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 actual needs as long as the purpose of the present application can be achieved.

[0068] 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.

[0069] 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 second conductive agent and a second binder. The second 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 second conductive agent and the above-mentioned second binder.

[0070] 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.

[0071] 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. ​

[0072] 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.

[0073] 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).

[0074] 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.

[0075] In the present application, the electrochemical device further includes an electrolyte including a lithium salt and a non-aqueous solvent.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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, the guide plate, etc. can also be placed in the shell to prevent the pressure inside the electrochemical device from rising, overcharging and discharging.

[0081] 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 higher capacity and volume energy density.

[0082] 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 audio 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.

[0083] Embodiments

[0084] 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 on a mass basis.

[0085] Test method and equipment:

[0086] First main material Dv50 test

[0087] The lithium ion battery in each of the embodiments and comparative examples was disassembled to obtain a positive electrode sheet, and the disassembled positive electrode sheet was calcined at 400°C in air to obtain a powder, and then a particle size analyzer was used to test the particle size to obtain the Dv50 of the first main material.

[0088] Sphericity test

[0089] A certain number (more than 5000) of dispersed lithium supplement material particles or first main material particles are subjected to image capture and processing by a Malvern automatic image particle size analyzer, and then the microstructure and morphology of the particles are accurately analyzed by image-guided Raman spectroscopy (MDRS) to obtain the longest diameter and the shortest diameter of all the particles, and the ratio of the shortest diameter to the longest diameter of each particle is calculated to obtain the sphericity of each particle, and the average sphericity of all the particles is obtained. In this application, the sphericity of the lithium supplement material refers to the average sphericity of the lithium supplement material, and the sphericity of the first main material refers to the average sphericity of the first main material.

[0090] Scanning electron microscope test

[0091] The positive electrode sheet is longitudinally cut along the thickness direction by plasma, polished by argon ion polishing technology to obtain a smooth cross section, and then the cross section of the positive electrode sheet is observed by a scanning electron microscope (OXFORD·EDS) at a magnification of 30000 times and in a range of 4 μm x 4 μm. If the secondary particles of the first conductive agent cannot be observed, the particle size of the secondary particles of the first conductive agent is recorded as “< 50 nm”, and if the secondary particles of the first conductive agent can be observed, the particle size of the secondary particles of the first conductive agent is recorded as “≥ 50 nm”. The scanning electron microscope image of the cross section of the positive electrode sheet of Example 1-1 is shown in FIG. 1. Figure 4

[0092] Carbon element, nitrogen element and oxygen element content test

[0093] (1) The lithium ion battery is discharged to 3V at 0.2C, and the positive electrode sheet is removed. The positive electrode sheet is cut into 10 small circular pieces with a diameter of 16 mm, and the first coating layer is scraped off from the positive electrode current collector of each small circular piece to obtain first coating layer powder. The first coating layer powder is mixed with water and centrifuged at 3500 rpm to obtain the lower powder, which is the first main material. 0.2 g of the first main material is digested with 10 mL aqua regia, and diluted with deionized water to a 100 mL volumetric flask. The inductively coupled plasma analyzer (ICP, model AVIO-200) is used for testing, with the radio frequency generator (RF) frequency set at 40.68 MHz, the argon secondary pressure at 0.6 MPa, the radio frequency power at 1400 W, and the pump speed at 1.0 mL / min. The carbon element, nitrogen element and oxygen element contents in the first main material of a single small circular piece are tested. The carbon element, nitrogen element and oxygen element contents obtained from the above 10 small circular pieces are averaged to obtain the mass percentage contents of carbon element, nitrogen element and oxygen element in the first main material, W C , W N and W O . The aqua regia is obtained by mixing concentrated nitric acid and concentrated hydrochloric acid in a volume ratio of 1:1.

[0094] ​(2) the mass percentage content of carbon element in the first main material is denoted as W1, the mass percentage content of nitrogen element is denoted as W2, and the mass percentage content of oxygen element is denoted as W3, the mass percentage content of carbon element in the first component is W C =W1 / (W1+W2+W3), the mass percentage content of nitrogen element in the first component is W N =W2 / (W1+W2+W3), and the mass percentage content of oxygen element in the first component is W O =W3 / (W1+W2+W3).

[0095] Infrared spectrum test

[0096] The lithium ion battery was discharged at 0.1C constant current to 3.0V, and the positive electrode sheet was obtained by disassembling the lithium ion battery. The positive electrode sheet was washed with dimethyl carbonate (DMC) for 10 min, and then the positive electrode sheet was baked at 100°C for 2h for standby. 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 layer.

[0097] An infrared spectrum analyzer (model: Nicolet iS50) was used to test the infrared spectrum of the positive electrode current collector coated with the first coating layer by using potassium bromide (KBr) tabletting method. The infrared spectrum of the first coating layer of Example 1-1 is shown in Figure 2 , and the infrared spectrum of the first coating layer of Comparative Example 2 is shown in Figure 3 .

[0098] First coating layer thickness test

[0099] The positive electrode sheet was longitudinally cut along the thickness direction by plasma, polished by argon ion polishing technology to obtain a smooth cross section, and then a scanning electron microscope (OXFORD·EDS) was used to observe and measure the thickness of the first coating layer at three positions with a magnification of 40000 times. The average value was taken as the thickness of the first coating layer.

[0100] Nail penetration test

[0101] Ten lithium ion batteries in the examples or comparative examples were fully charged at 25±3°C, and the specific steps were as follows: charged at 0.5C current to 4.5V, and then charged at 4.5V constant voltage to 0.05C current cutoff.

[0102] The lithium ion battery is subjected to nail penetration test at 25±3°C, a steel nail with a diameter of 4 mm, a carbon steel material, a taper of 16.5 mm, and a total length of 100 mm is used, the nail penetration speed is set to 30 mm / s, and the nail penetration depth is determined by the taper of the steel nail penetrating the lithium ion battery. The state of the lithium ion battery during the test is observed, and the determination standard is that the lithium ion battery does not burn or explode, and the nail penetration test pass rate = the number of lithium ion batteries that do not burn or explode during the nail penetration test / 10 x 100%.

[0103] Cohesive force test

[0104] The part of the positive electrode sheet coated only with the first coating is punched with a mold to obtain a test strip with a length of 120 mm and a width of 30 mm. The surface of the steel plate is wiped clean with alcohol, and a double-sided tape (NITTO, NO5000NS) with a length of 100 mm and a width of 20 mm is attached to the steel plate. The test strip is centered and attached to the double-sided tape with the test surface facing down. Green tape (TODI paper, 100 mm long and 20 mm wide) is centered and attached to the test strip, a paper strip with a length of 100 mm and a width of 30 mm is taken, and the paper strip is inserted between the test strip and the green tape with an overlapping length of 15 mm. A rubber roller with a mass of 2 kg is pushed back and forth on the test strip 4 times to obtain a test sample. The test sample is tested using a tensile testing machine (SINTECH, Instron 3365). The test sample is fixed on the test table, then the paper strip is folded up 180° and fixed by a clamp, and then the tensile testing machine starts to slowly pull the paper strip at a speed of 10 mm / min until the test ends after the green tape separates from the first coating on the surface of the positive electrode sheet. The average tensile force in the stable region is recorded as the cohesive force F2 of the first coating, with units of N / m.

[0105] Adhesion force test

[0106] A positive electrode sheet coated with a first coating is taken and attached to a smooth steel plate with double-sided tape, the other side of the positive electrode sheet is attached with tape, and one end of the tape is fixed to the tensile testing machine. The speed is set to 10 mm / min, the tape is pulled straight up 180° by the tensile testing machine, and the adhesion force during the stretching of the tape is dynamically read by the sensor. The data is exported and averaged, and then divided by the width of the tape to obtain the adhesion force F1 between the first coating and the positive current collector.

[0107] Membrane resistance test

[0108] A test sample with a size of 60 mm x 80 mm is cut from the part of the positive current collector surface coated with the first coating and the positive material layer, and the membrane resistance of the positive electrode sheet is tested using a membrane resistance tester with a test pressure of 0.4T and a pressure holding time of 10s.

[0109] Discharge capacity test

[0110] The lithium ion battery was placed in an environment of 25°C, and was charged to 4.5V at a constant current of 1C, and was charged to 0.05C at a constant voltage of 4.5V; the lithium ion battery was allowed to stand for 10 min, and was discharged to a discharge cut-off voltage of 3.0V at a constant current of 0.2C, and the discharge capacity of the lithium ion battery was measured.

[0111] Volume energy density test

[0112] The lithium ion battery was charged to 4.5V at a constant current of 1C, and was charged to 0.05C at a constant voltage of 4.5V, and was discharged to 3.0V at 0.5C at 25°C, and the capacity at this time was recorded as D, the length, width and thickness of the lithium ion battery at this time were measured, and the volume V of the lithium ion battery was calculated, and the discharge voltage plateau P of the lithium ion battery was obtained, and the volume energy density VED of the lithium ion battery was D x P / V, and the unit was Wh / L.

[0113] Example 1-1

[0114] Preparation of the first main material

[0115] A lithium supplementing material LiFePO4 and an organic precursor phenolic resin with a mass ratio of 90:10 were calcined under a nitrogen atmosphere at 350°C, and the first main material was obtained after ball milling. The sphericity of the first main material was 0.71, and the particle size Dv50 of the first main material was 125 nm; the mass percentage content of the first component based on the mass of the first main material was 3%; the mass percentage content of carbon element based on the mass of the first component was W C 68.65%, the mass percentage content of nitrogen element based on the mass of the first component was W N 12.75%, and the mass percentage content of oxygen element based on the mass of the first component was W O 18.6%.

[0116] Preparation of the positive electrode sheet

[0117] The first main material and the first binder sodium polyacrylate prepared above were mixed in a mass ratio of 91:9, deionized water was added as a solvent, and stirring was performed 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 electrode current collector aluminum foil, and after drying at 120°C, a first coating layer with a thickness of 0.95μm was obtained. The positive electrode active material lithium cobaltate, the second 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 positive electrode slurry 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 after drying at 120°C, a positive electrode tab with a single-sided first coating layer and a positive electrode material layer was obtained. The coating weight of the positive electrode material 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 tab with a double-sided first coating layer and a positive electrode material layer was obtained. Then, after cold pressing, cutting, and welding of the tabs, a positive electrode tab with a size of 74mm x 867mm was obtained for use. The thickness of the single-sided positive electrode material layer was 90μm.

[0118] The structure of the positive electrode tab prepared in Example 1-1 is shown in Figure 1 .

[0119] <Preparation of a negative electrode tab>

[0120] 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 negative electrode 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 electrode current collector copper foil, and after drying at 120°C, a negative electrode tab with a single-sided negative electrode material layer was obtained. 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 tab with a double-sided negative electrode material layer. After drying at 120°C, the negative electrode tab was cold pressed, and then cutting and tab welding were performed to obtain a negative electrode tab with a size of 78mm x 875mm for use. The thickness of the single-sided negative electrode material layer was 85μm.

[0121] <Preparation of an electrolyte>

[0122] 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.

[0123] <Separator>

[0124] A polyethylene porous polymer film (manufacturer: Celgard Separator Company, USA) with a thickness of 8 μm was used as a separator.

[0125] <Preparation of a lithium ion battery>

[0126] 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 processes. The upper limit voltage of formation was 4.53 V, the formation temperature was 85°C, and the formation time was 50 min.

[0127] Examples 1-2 to 1-3

[0128] Except that the sphericity of the first main material was as shown in Table 1 by selecting different sphericity of the lithium supplement material in <Preparation of the first main material>, the rest was the same as Example 1-1.

[0129] Examples 1-4 to 1-9

[0130] Except that the Dv50 of the first main material was as shown in Table 1 by adjusting the time of ball milling in <Preparation of the first main material>, the rest was the same as Example 1-1.

[0131] Examples 1-10 to 1-14

[0132] Except that the mass percentage of the first component was as shown in Table 1 by adjusting the mass ratio of the lithium supplement material and the organic precursor in <Preparation of the first main material>, the rest was the same as Example 1-1.

[0133] Examples 1-15 to 1-23

[0134] The rest is the same as Example 1-1 except that the kind of organic compound precursor, the mass ratio of the lithium supplement material and the organic compound precursor, and the calcination temperature are adjusted so that the mass percentage of carbon element, the mass percentage of nitrogen element, and the mass percentage of oxygen element are as shown in Table 1 in the preparation of the first main material. Among them, polyurethane is used as the organic compound precursor in Example 1-17 to Example 1-18 and Example 1-21 to Example 1-22.

[0135] Example 1-24 to Example 1-29

[0136] The rest is the same as Example 1-1 except that the thickness of the first coating is adjusted according to Table 1.

[0137] Example 2-1 to Example 2-8

[0138] The rest is the same as Example 1-1 except that the first conductive agent conductive carbon black is added to the first coating slurry in the preparation of the positive electrode tab, and the mass percentage of the first conductive agent, the mass percentage of the first main material, and the mass percentage of the first binder are adjusted according to Table 2.

[0139] Example 2-9 to Example 2-12

[0140] The rest is the same as Example 1-1 except that the kind of lithium supplement material and the kind of first binder are adjusted according to Table 2.

[0141] Comparative Example 1

[0142] The rest is the same as Example 1-1 except that the first coating is not provided on the surface of the positive electrode current collector.

[0143] Comparative Example 2

[0144] The rest is the same as Example 1-1 except that polyurethane is used as the organic compound precursor in the preparation of the first main material, and the calcination temperature is adjusted so that the mass percentage of carbon element, the mass percentage of nitrogen element, and the mass percentage of oxygen element are as shown in Table 1 and Table 2, and the infrared spectrum of the first coating does not have a characteristic peak between 3200 cm -1 and 3400 cm -1 .

[0145] Comparative Example 3

[0146] The rest is the same as Example 1-1 except that the aluminum oxide with a particle size of 125 nm and a sphericity of 0.71 is directly used as the first main material in the preparation of the first main material, and the preparation parameters are adjusted according to Table 1 and Table 2.

[0147] Comparative Example 4

[0148] Except that boehmite with a particle size of 125 nm and a sphericity of 0.71 was directly used as the first main material in the preparation of the first main material, and the preparation parameters were adjusted according to Tables 1 and 2, the rest was the same as Example 1-1.

[0149] The preparation parameters and performance tests of each example and comparative example are shown in Tables 1 and 2.

[0150] Table 1

[0151]

[0152] Note: " / " in Table 1 means that the corresponding preparation parameter or substance does not exist, W C represents the mass percentage content of carbon element based on the first component, W N represents the mass percentage content of nitrogen element based on the first component, W O represents the mass percentage content of oxygen element based on the first component, F1 represents the adhesion between the first coating and the positive electrode current collector, F2 represents the cohesion of the first coating, and the infrared spectrum characteristic peak refers to the characteristic peak of the infrared spectrum of the first coating between 3200 cm -1 and 3400 cm -1 .

[0153] Table 2

[0154]

[0155] Note: " / " in Table 2 means that the corresponding preparation parameter or substance does not exist, W ZC represents the mass percentage content of the first main material, W DD represents the mass percentage content of the first conductive agent, W NJ represents the mass percentage content of the first binder, F1 represents the adhesion between the first coating and the positive electrode current collector, F2 represents the cohesion of the first coating, and the infrared spectrum characteristic peak refers to the characteristic peak of the infrared spectrum of the first coating between 3200 cm -1 and 3400 cm -1 .

[0156] As can be seen from Examples 1-1 to 1-29 and Comparative Examples 1 to 4, when the positive electrode sheet has the structure of the first coating of the present application and the infrared spectrum of the first coating is between 3200 cm -1 and 3400 cm -1characteristic peak, the adhesion between the first coating layer and the positive current collector is high, the capacity and the volumetric energy density of the obtained lithium ion battery are high, and the nail penetration test passing rate is high, thereby indicating that the lithium ion battery of the present application can balance the capacity, the volumetric energy density and the nail penetration safety performance. The positive electrode sheet in Comparative Example 1 does not have the first coating layer structure of the present application, the infrared spectrum of the first coating layer in Comparative Example 2 has no characteristic peak between 3200 cm -1 and 3400 cm -1 , the first main material of Comparative Example 3 uses aluminum oxide, the first main material of Comparative Example 4 uses boehmite, the surface of boehmite contains hydroxyl functional groups, and the first coating layer has a characteristic peak between 3200 cm -1 and 3400 cm -1 , the capacity and the volumetric energy density of the obtained lithium ion battery are low or the nail penetration test passing rate is low, and the nail penetration safety performance, the capacity and the volumetric energy density cannot be balanced.

[0157] Figure 2 , the infrared spectrum of the first coating layer of Example 1-1 has a characteristic peak between 3200 cm -1 and 3400 cm -1 . Figure 3 , the infrared spectrum of the first coating layer of Comparative Example 2 has no characteristic peak between 3200 cm -1 and 3400 cm -1 .

[0158] The sphericity of the first main material will generally affect the capacity, the volumetric energy density and the nail penetration safety performance of the lithium ion battery. As can be seen from Example 1-1 to Example 1-3, when the sphericity of the first main material is within the range of the present application, the cohesion of the first coating layer is high, the adhesion between the first coating layer and the positive current collector is high, the capacity and the volumetric energy density of the obtained lithium ion battery are high, and the nail penetration test passing rate is high, thereby indicating that the lithium ion battery of the present application can balance the capacity, the volumetric energy density and the nail penetration safety performance.

[0159] The Dv50 of the first main material will generally affect the capacity, the volumetric energy density and the nail penetration safety performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-4 to Example 1-9, when the Dv50 of the first main material is within the range of the present application, the cohesion of the first coating layer is high, the adhesion between the first coating layer and the positive current collector is high, the capacity and the volumetric energy density of the obtained lithium ion battery are high, and the nail penetration test passing rate is high, thereby indicating that the lithium ion battery of the present application can balance the capacity, the volumetric energy density and the nail penetration safety performance.

[0160] The mass percentage of the first component generally affects the capacity, volumetric energy density and nail penetration safety performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-10 to Example 1-14, when the mass percentage of the first component is within the range of the present application, the cohesion of the first coating is higher, the adhesion between the first coating and the positive current collector is higher, the capacity and volumetric energy density of the obtained lithium ion battery are higher, and the pass rate of the nail penetration test is higher, thereby indicating that the lithium ion battery of the present application can balance the capacity, volumetric energy density and nail penetration safety performance.

[0161] The mass percentage of carbon element, nitrogen element and oxygen element generally affects the capacity, volumetric energy density and nail penetration safety performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-15 to Example 1-23, when the mass percentage of carbon element, nitrogen element and oxygen element is within the range of the present application, the cohesion of the first coating is higher, the adhesion between the first coating and the positive current collector is higher, the capacity and volumetric energy density of the obtained lithium ion battery are higher, and the pass rate of the nail penetration test is higher, thereby indicating that the lithium ion battery of the present application can balance the capacity, volumetric energy density and nail penetration safety performance.

[0162] The thickness of the first coating generally affects the capacity, volumetric energy density and nail penetration safety performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-24 to Example 1-29, when the thickness of the first coating is within the range of the present application, the cohesion of the first coating is higher, the adhesion between the first coating and the positive current collector is higher, the capacity and volumetric energy density of the obtained lithium ion battery are higher, and the pass rate of the nail penetration test is higher, thereby indicating that the lithium ion battery of the present application can balance the capacity, volumetric energy density and nail penetration safety performance.

[0163] As can be seen from Example 1-1, Example 2-1 to 2-12, when the mass percentage of the first main material, the type of lithium supplementing material, the mass percentage of the first conductive agent, the type and mass percentage of the first binder, and the secondary particle size of the first conductive agent are within the range of the present application, the capacity and volumetric energy density of the obtained lithium ion battery are higher, and the pass rate of the nail penetration test is higher, thereby indicating that the capacity, volumetric energy density and nail penetration safety performance of the lithium ion battery of the present application are improved.

[0164] As can be seen from Figure 4 As can be seen from the scanning electron microscope image of the cross section of the positive electrode sheet, the secondary particles of the first conductive agent cannot be observed, indicating that the particle size of the secondary particles of the first conductive agent is less than 50 nm, and thereby the dispersibility of the first conductive agent in the first coating is better.

[0165] The preferred embodiments of the application are described above with the specific language, but it is understood that no limitation of the scope of the application is intended by the specification of the preferred embodiments. It is therefore understood that any modifications, changes, additions, or omissions are intended to fall within the scope of the application as defined in the appended claims.

[0166] It should be noted that, as used in this document, the terms "first", "second", etc. are used only to distinguish one entity or action from another, and do not necessarily require or imply any actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0167] The various embodiments in the specification are described in a related manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the difference from other embodiments.

Claims

1. An electrochemical device comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector, a first coating layer disposed on a surface of the positive electrode current collector, and a positive electrode material layer disposed on a surface of the first coating layer distal 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 lithium supplementing material, the lithium supplementing material comprising at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium orthosilicate, or lithium ferrite; the first coating layer having a characteristic peak in an infrared spectrum between 3200 cm -1 and 3400 cm -1 .

2. The electrochemical device of claim 1, wherein, At least part of a surface of the lithium supplementing material has a first component, the first component comprising carbon element, nitrogen element and oxygen element, a mass percentage content of the carbon element being 63.5% to 73.8%, a mass percentage content of the nitrogen element being 7.6% to 17.9%, and a mass percentage content of the oxygen element being 12% to 24.5%, based on a mass of the first component.

3. The electrochemical device of claim 2, wherein, The mass percentage content of the carbon element is 66.25% to 70.1%, the mass percentage content of the nitrogen element is 7.8% to 17.5%, and the mass percentage content of the oxygen element is 12.4% to 22.3%, based on the mass of the first component.

4. The electrochemical device of claim 2, wherein, A mass percentage content of the first component is 2% to 10%, based on a mass of the first main material.

5. The electrochemical device of claim 1, wherein, The Dv50 of the first main material is 50 nm to 200 nm.

6. The electrochemical device of claim 5, wherein, The Dv50 of the first main material is 100 nm to 150 nm.

7. The electrochemical device of claim 1, wherein, A mass percentage content of the first main material is 84.5% to 94.8%, based on a mass of the first coating.

8. The electrochemical device of claim 1, wherein, The sphericity of the first main material is 0.705 to 0.

874.

9. The electrochemical device of claim 1, wherein, The first binder comprises a water-soluble polymer metal salt; a mass percentage content of the first binder is 5.2% to 15.5%, based on the mass of the first coating.

10. The electrochemical device of claim 9, wherein, The metal element in the water-soluble polymer metal salt comprises at least one of lithium, sodium, potassium, rubidium, cesium, francium, beryllium, barium, strontium, calcium or magnesium; the polymer in the water-soluble polymer metal salt comprises at least one of polyacrylic acid, carboxymethyl cellulose, polyacrylonitrile or styrene butadiene.

11. The electrochemical device of claim 10, wherein, The water-soluble polymer metal salt comprises at least one of sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, calcium polyacrylate, magnesium polyacrylate, lithium carboxymethyl cellulose or sodium carboxymethyl cellulose.

12. The electrochemical device according to any one of claims 1 to 11, wherein The first coating further comprises a first conductive agent, the first conductive agent comprising at least one of conductive carbon black, activated carbon, carbon nanotube or carbon nanofiber; a mass percentage content of the first conductive agent is 0.2% to 0.5%, based on the mass of the first coating.

13. The electrochemical device of claim 12, wherein, The particle size of the secondary particles of the first conductive agent is less than 50 nm.

14. The electrochemical device according to any one of claims 1 to 11, wherein, The thickness of the first coating is 0.2 μm to 2 μm.

15. The electrochemical device according to any one of claims 1 to 11, wherein, The electrochemical device satisfies at least one of the following conditions: (1) the thickness of the first coating is 0.5 μm to 2 μm; (2) the adhesion between the first coating and the positive current collector is F1, 500 N / m ≤ F1 ≤ 900 N / m; (3) the cohesion of the first coating is F2, 1400 N / m ≤ F2 ≤ 2500 N / m; (4) the sheet resistance of the positive electrode tab is 0.5 Ω to 5 Ω.

16. An electronic device comprising the electrochemical device of any one of claims 1 to 15.

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