Electrochemical device

Abstract

The embodiment of the invention relates to the technical field of energy storage, and discloses an electrochemical device which comprises an anode plate, a diaphragm and a cathode plate, the diaphragm is arranged between the anode plate and the cathode plate, the anode plate comprises a silicon element, and the cathode plate comprises a first current collector, a first substance layer and a second substance layer. The first current collector comprises a first conductive layer, a first base material layer and a second conductive layer, the first base material layer is arranged between the first conductive layer and the second conductive layer, the first substance layer is arranged between the second substance layer and the first current collector, the first substance layer comprises a first material, the first material comprises a lithium element, and the particle size of the first material is D1; the second substance layer comprises a second material, the particle size of the second material is D2, and D1 is smaller than D2. Through the mode, the risk that the first current collector is pressed through during cold pressing of the cathode pole piece can be reduced, and lithium precipitation of the electrochemical device can be reduced.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of energy storage, and in particular to an electrochemical device. Background Art

[0002] With the rapid development of modern technology, the demand for high-performance energy storage devices in fields such as portable electronic devices and electric vehicles is increasing day by day. As an efficient and environmentally friendly energy storage device, lithium-ion batteries have been widely used in many fields due to their high energy density, long cycle life, low self-discharge rate, etc. During the continuous development of lithium-ion batteries, the requirements for the service life of the batteries are also getting higher and higher. Summary of the Invention

[0003] The main technical problem to be solved by the embodiments of the present application is to provide an electrochemical device that can reduce the risk of the cathode electrode sheet being pierced and brittle broken, thereby reducing the risk of lithium plating in the electrochemical device, and is beneficial to extending the service life of the electrochemical device.

[0004] To solve the above technical problem, one technical solution adopted by the embodiments of the present application is: to provide an electrochemical device, including an anode electrode sheet, a separator, and a cathode electrode sheet. The separator is disposed between the anode electrode sheet and the cathode electrode sheet. The anode electrode sheet includes silicon element. The cathode electrode sheet includes a first current collector, a first material layer, and a second material layer. The first current collector includes a first conductive layer, a first substrate layer, and a second conductive layer. The first substrate layer is disposed between the first conductive layer and the second conductive layer; the first material layer is disposed on the surface of the first conductive layer facing away from the first substrate layer, and / or, the first material layer is disposed on the surface of the second conductive layer facing away from the first substrate layer; the second material layer is disposed on the surface of the first material layer facing away from the first current collector; the first material layer includes a first material, the first material includes lithium element, the particle size of the first material is D1, the second material layer includes a second material, the particle size of the second material is D2, wherein, D1 < D2.

[0005] In this embodiment, by disposing the first material between the second material and the first current collector, when cold pressing the cathode electrode sheet, the first material can make the pressure more uniform, thereby reducing the risk of large particle size particles (such as lithium cobaltate particles) in the second material piercing the first current collector, which is beneficial to reducing lithium plating in the electrochemical device and is beneficial to extending the service life.

[0006] In some embodiments, the first material layer includes a first material, and the first material includes Li5-xFeO 4-y 、Li6-xCoO 4-y 、Li2-zMnO2、Li 1.2-r Ni 0.13 Fe 0.13 Mn 0.54At least one of O2 or Li1-tFePO4, where 4 ≤ x ≤ 5, 2 ≤ y ≤ 4, 1.6 ≤ z ≤ 2, 0.2 ≤ r ≤ 1.2, 0.8 ≤ t ≤ 1. The first material can be used as a lithium supplement agent to supplement lithium ions in the cathode current collector, thereby increasing the battery capacity and energy density of the electrochemical device.

[0007] In some embodiments, the first substrate layer includes at least one of polyethylene terephthalate, polyimide, polyamide, polyurethane, polyethylene, and polypropylene, so that the first substrate layer has a high elongation rate, enabling the cathode current collector to extend when under pressure and reducing the risk of the current collector breaking.

[0008] In some embodiments, the particle size D1 of the first material satisfies: 0.05 μm ≤ D1 ≤ 2 μm. If the particle size of the first material is too small, the particles of the first material are prone to agglomeration, which is not conducive to coating the first material layer on the first current collector. At the same time, the large specific surface area of the first material leads to more side reactions with the electrolyte, which is not conducive to battery performance. If the particle size of the first material is too large, when cold pressing the cathode current collector, it is easy to cause the cathode current collector to be pierced. In this embodiment, setting 0.05 μm ≤ D1 ≤ 2 μm can reduce the risk of the first current collector being pierced during cold pressing of the cathode current collector, thereby reducing the risk of lithium plating in the electrochemical device, while meeting the processability of the current collector and battery performance.

[0009] In some embodiments, the particle size D1 of the first material satisfies: 0.05 μm ≤ D1 ≤ 1 μm. Setting 0.05 μm ≤ D1 ≤ 1 μm can further reduce the risk of brittle fracture of the cathode current collector.

[0010] In some embodiments, the charging specific capacity of the first material is W, and it satisfies 160 mAh / g ≤ W ≤ 1200 mAh / g, which can improve the energy density of the electrochemical device and the electrical performance of the battery.

[0011] In some embodiments, the thickness of the first material layer is T, and it satisfies: 0.5 μm ≤ T ≤ 2.5 μm. This can improve the energy density of the electrochemical device, reduce the risk of the first current collector being pierced during cold pressing of the cathode current collector, improve the low-temperature discharge capacity retention rate of the electrochemical device, and slow down the capacity decay rate of the electrochemical device, thereby extending the service life.

[0012] In some embodiments, the thickness T of the first material layer satisfies: 1 μm ≤ T ≤ 2 μm, which can further slow down the capacity decay rate of the electrochemical device to further extend the service life of the electrochemical device.

[0013] In some embodiments, the first material layer includes a binder, and the binder is mixed with the first material.

[0014] In some embodiments, the adhesion force of the first material is F, and 500 N / m ≤ F ≤ 1200 N / m is satisfied. By setting F ≥ 500 N / m, the ability of the electrode sheet to resist external forces is relatively strong, and the risk of the cathode electrode sheet being pierced can be reduced; by setting F ≤ 1200 N / m, the low-temperature discharge capacity retention rate of the electrochemical device can be improved, the capacity decay rate of the electrochemical device can be slowed down, and thus the service life can be extended.

[0015] In some embodiments, the adhesion force F of the first material satisfies: 800 N / m ≤ F ≤ 1200 N / m, which can further reduce the risk of brittle fracture of the cathode electrode sheet.

[0016] In some embodiments, the mass percentage of the first material in the first material layer is c, and 60% ≤ c ≤ 95% is satisfied. By setting c ≥ 60%, the energy density of the electrochemical device can be improved, the capacity decay rate of the electrochemical device can be reduced, and the capacity retention rate of low-temperature discharge can be improved; by setting c ≤ 95%, the content of the adhesive can be ensured, good adhesion can be maintained, and the risk of the cathode electrode sheet being demolded during cold pressing can be reduced.

[0017] In some embodiments, the mass percentage c of the first material in the first material layer satisfies: 80% ≤ c ≤ 95%, which can further improve the energy density of the electrochemical device, reduce the capacity decay rate of the electrochemical device, and improve the capacity retention rate of low-temperature discharge of the electrochemical device.

[0018] In some embodiments, the second material includes at least one of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, or lithium manganate.

[0019] In some embodiments, the anode electrode sheet includes a second current collector and a third material layer. The third material layer is disposed on the surface of the second current collector, and the third material layer includes silicon element.

[0020] In some embodiments, the mass percentage of the silicon element in the third material layer is b, and 5% ≤ b ≤ 50% is satisfied. The increase in the content of the silicon element can improve the energy density of the electrochemical device, but silicon is prone to expansion during the insertion or extraction of lithium ions, resulting in an increase in the volume of the electrochemical device. By setting 5% ≤ b ≤ 50%, both the improvement of the energy density of the electrochemical device and the reduction of volume expansion can be taken into account.

[0021] The beneficial effects of the embodiments of the present application are: Different from the prior art, in the embodiments of the present application, the cathode electrode sheet includes a first current collector, a first material layer, and a second material layer. The first current collector includes a first conductive layer, a first substrate layer, and a second conductive layer. The first substrate layer is disposed between the first conductive layer and the second conductive layer. By disposing the first material layer between the first current collector and the second material layer, and the first material layer includes a first material, the first material includes Li5-xFeO4-y 、Li6-xCoO 4-y 、Li2-zMnO2、Li 1.2-r Ni 0.13 Fe 0.13 Mn 0.54 O2 or at least one of Li1-tFePO4, where 4 ≤ x ≤ 5, 2 ≤ y ≤ 4, 1.6 ≤ z ≤ 2, 0.2 ≤ r ≤ 1.2, 0.8 ≤ t ≤ 1. On the one hand, the first material can provide additional lithium ions, thereby improving the capacity of the electrochemical device; on the other hand, due to the smaller particle size of the first material, the packing density of the material is higher, so that when cold pressing the cathode electrode, the cathode electrode can be more evenly stressed, which is beneficial to reducing the risk of the first current collector being pierced, and further reducing the risk of lithium plating in the electrochemical device, which is beneficial to extending the service life of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0023] Figure 1 is a schematic structural diagram of the electrochemical device provided in the embodiment of the present application;

[0024] Figure 2 is a schematic structural diagram of the battery cell provided in the embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To facilitate the understanding of the present application, the following will describe the present application in more detail with reference to the drawings and specific embodiments. It should be noted that the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0026] Unless otherwise defined, all the technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not used to limit this application. The term "and / or" used in this specification includes any and all combinations of one or more of the related listed items.

[0027] In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0028] In electrochemical devices, silicon materials have a higher theoretical specific capacity, usually dozens of times that of graphite negative electrode materials. Therefore, silicon-based batteries are becoming increasingly popular in the market.

[0029] However, as the charge and discharge process proceeds, the silicon negative electrode material tends to expand and generate greater stress, which can easily cause the cathode electrode to break. Therefore, a cathode composite current collector is usually used in battery devices with a high silicon content to increase the elongation of the cathode electrode. However, the cathode composite current collector itself has low strength. When the cathode electrode is cold-pressed, large-size particles in the cathode active material (such as lithium cobalt oxide particles) can easily press through the current collector, resulting in an increased risk of current collector breakage, thereby increasing the risk of lithium precipitation in the electrochemical device, thereby shortening the service life of the electrochemical device; in addition, during the first charging process of the electrochemical device, the organic electrolyte will be reduced and decomposed on the surface of the negative electrode to form a SEI (Solid Electrolyte Interface) film. This process will permanently consume a large amount of lithium ions from the positive electrode, resulting in a low coulombic efficiency (FCE) of the first cycle, which reduces the capacity and energy density of the electrochemical device.

[0030] In order to solve at least some of the above-mentioned problems, the present application provides an electrochemical device. Generally, the introduction of a first material will deteriorate the compaction density of the electrode and the transmittance of the electrode. By arranging the first material between the conductive layer of the first current collector and the second material, on the one hand, lithium can be supplemented, thereby increasing the capacity of the electrochemical device. On the other hand, the first material has a small particle size, high adhesion, and high stacking density. During cold pressing, the cathode electrode can be subjected to more uniform force and has a strong ability to resist external forces, thereby reducing the risk of the first current collector being crushed by large-size particles (such as lithium cobalt oxide particles), which is beneficial to reducing lithium precipitation in the electrochemical device.

[0031] The specific scheme of the present application is described in detail below.

[0032] See also Figure 1 and Figure 2 The electrochemical device 100 includes an anode electrode piece 3, a separator 2 and a cathode electrode piece 1, wherein the separator 2 is disposed between the anode electrode piece 3 and the cathode electrode piece 1, wherein the anode electrode piece 3 includes silicon element.

[0033] In some embodiments, the electrochemical device 100 includes a shell 4 , and the anode electrode sheet 3 , the separator 2 , and the cathode electrode sheet 1 together constitute a battery cell 5 of the electrochemical device 100 . The battery cell 5 is accommodated in the shell 4 so that the shell 4 can protect the battery cell 5 .

[0034] In some embodiments, the anode electrode 3 includes a second current collector 31 and a third material layer 32 , wherein the third material layer 32 is disposed on the surface of the second current collector 31 , wherein the third material layer 32 includes silicon.

[0035] It should be noted that the third material layer 32 includes silicon element. Here, "includes" means that the third material layer 32 includes silicon-containing materials, such as pure silicon, silicon carbide, silicon oxide, etc. That is, during the charge and discharge process of the electrochemical device 100, the silicon-containing material serves as the main carrier for lithium ions to intercalate or deintercalate, rather than existing in the third material layer 32 and the anode electrode sheet 3 in the form of impurities.

[0036] In some embodiments, the second current collector 31 is a copper foil.

[0037] It can be understood that the second current collector 31 can also be a composite current collector, that is, the second current collector 31 includes a second substrate layer 311, a third conductive layer 312, and a fourth conductive layer 313. The third conductive layer 312 and the fourth conductive layer 313 are respectively disposed on both sides of the second substrate layer 311. The third material layer 32 as described above can be disposed on the surface of the third conductive layer 312 facing away from the second substrate layer 311 and the surface of the fourth conductive layer 313 facing away from the second substrate layer 311.

[0038] In some embodiments, the mass percentage of silicon element in the third material layer 32 is b, and it satisfies: 5% ≤ b ≤ 50%. In some embodiments, b can be 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, or a range composed of any two of these values, or a value within the range composed of any two of these values. The increase in the content of silicon element can improve the energy density of the electrochemical device, but silicon is prone to expansion during the intercalation or deintercalation of lithium ions, resulting in an increase in the volume of the electrochemical device. By setting 5% ≤ b ≤ 50%, it is possible to balance the improvement of the energy density of the electrochemical device and the reduction of volume expansion.

[0039] The electrochemical device 100 can be arranged in a wound form, that is, after the separator 2 is disposed between the anode electrode sheet 3 and the cathode electrode sheet 1, the anode electrode sheet 3, the separator 2, and the cathode electrode sheet 1 are wound and formed.

[0040] The electrochemical device 100 can be arranged in a stacked form, that is, the anode electrode sheet 3, the separator 2, and the cathode electrode sheet 1 are stacked, and the separator 2 is disposed between the anode electrode sheet 3 and the cathode electrode sheet 1. The separator 2 is used to electrically isolate the first anode electrode sheet 3 and the cathode electrode sheet 1, reducing the risk of short circuit of the electrochemical device 100.

[0041] The number of the anode electrode sheet 3, the separator 2, and the cathode electrode sheet 1 can be multiple. Multiple anode electrode sheets 3, multiple separators 2, and multiple cathode electrode sheets 1 are alternately stacked in sequence, and a separator 2 is disposed between an anode electrode sheet 3 and a cathode electrode sheet 1.

[0042] This application will be described by taking the laminated electrochemical device 100 as an example.

[0043] Please refer to Figure 1 , the cathode electrode sheet 1 includes a first current collector 11, a first material layer 12 and a second material layer 13. The first current collector 11 includes a first conductive layer 111, a first base material layer 112 and a second conductive layer 113. The first base material layer 112 is disposed between the first conductive layer 111 and the second conductive layer 113. The first material layer 12 is disposed on at least one surface of the first current collector 11, and the second material layer 13 is disposed on the surface of the first material layer 12 facing away from the first current collector 11. The first material layer 12 includes a first material, and the particle size of the first material is D1. The second material layer 13 includes a second material, and the particle size of the second material is D2, where D1 < D2. The first material includes at least one of Li5-xFeO4-y, Li6-xCoO4-y, Li2-zMnO2, Li1.2-rNi0.13Fe0.13Mn0.54O2 or Li1-tFePO4, where 4 ≤ x ≤ 5, 2 ≤ y ≤ 4, 1.6 ≤ z ≤ 2, 0.2 ≤ r ≤ 1.2, 0.8 ≤ t ≤ 1. The first material can be used as a lithium supplement agent to supplement lithium ions in the cathode electrode sheet 1, thereby increasing the battery capacity and energy density of the electrochemical device 100. The second material includes at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate or lithium manganate.

[0044] The particle size of the second material is larger (usually greater than 5 μm), while the particle size of the first material is smaller. By disposing the first material between the second material and the first current collector 11, when the cathode electrode sheet 1 is cold-pressed, the first material can make the pressure more uniform, thereby reducing the risk that large particle size particles (such as lithium cobaltate particles) in the second material pierce through the first current collector 11, which is beneficial to reducing lithium deposition in the electrochemical device 100.

[0045] In some embodiments, the first base material layer 112 includes at least one of polyethylene terephthalate, polyimide, polyamide, polyurethane, polyethylene, and polypropylene. That is, the first base material layer 112 includes a polymer material, and the first base material layer 112 has a relatively high elongation rate, so that the cathode electrode sheet 1 can extend when subjected to pressure, thereby reducing the risk of brittle fracture of the cathode electrode sheet 1. And because the first base material layer 112 has a relatively high elongation rate, combined with the first material in this application, a larger pressure is used to cold-press the cathode electrode sheet 1, and the risk of the first current collector 11 being pierced through is reduced while improving the compaction density. Furthermore, in the silicon-containing anode electrode sheet 3, silicon is prone to expansion after multiple charge and discharge cycles. By incorporating the first material and the polymer base material into the electrochemical device 100, the energy density of the electrochemical device 100 can be improved, and the loss of energy density caused by silicon expansion can be reduced.

[0046] In some embodiments, the first material layer 12 is disposed on one surface of the first current collector 11. Specifically, the first material layer 12 is disposed on the surface of the first conductive layer 111 facing away from the first base layer 112, and the second material layer 13 is disposed on the surface of the first material layer 12 facing away from the first conductive layer 111, that is, the first material layer 12 is disposed between the first conductive layer 111 and the second material layer 13; or, the first material layer 12 is disposed on the surface of the second conductive layer 113 facing away from the first base layer 112, and the second material layer 13 is disposed on the surface of the first material layer 12 facing away from the second conductive layer 113, that is, the first material layer 12 is disposed between the second conductive layer 113 and the second material layer 13.

[0047] In some embodiments, the first material layer 12 and the second material layer 13 are disposed on both opposite surfaces of the first current collector 11. Specifically, a first material layer 12 is disposed on the surface of the first conductive layer 111 facing away from the first base layer 112, and a second material layer 13 is disposed on the surface of the first material layer 12 facing away from the first conductive layer 111. Another first material layer 12 is disposed on the surface of the second conductive layer 113 facing away from the first base layer 112, and another second material layer 13 is disposed on the surface of the first material layer 12 facing away from the second conductive layer 113.

[0048] In some embodiments, the particle size D1 of the first material satisfies: 0.01 μm ≤ D1 ≤ 2.5 μm. Preferably, 0.05 μm ≤ D1 ≤ 2 μm. In some embodiments, D1 can be 0.01 μm, 0.03 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.3 μm, 2.5 μm or a value within the range formed by any two of these values or a value within the range formed by any two of these values. If the particle size D1 of the first material is too small, the particles of the first material are prone to agglomeration, which is not conducive to coating the first material layer 12 on the first current collector 11. At the same time, the specific surface area of the first material is large, and there are many side reactions with the electrolyte, which is not conducive to the battery performance; if the particle size D1 of the first material is too large, when the cathode electrode sheet 1 is cold-pressed, the cathode electrode sheet 1 is easily pierced. The particle size of the first material also affects the capacity decay rate of the electrochemical device 100. Whether the particle size is too large or too small, it is easy to accelerate the capacity decay rate of the electrochemical device 100. In this embodiment, by setting the particle size D1 of the first material to satisfy 0.05 μm ≤ D1 ≤ 2 μm, it is beneficial to reduce the capacity decay rate of the electrochemical device 100, thereby reducing the capacity decay rate of the electrochemical device 100, and further prolonging the service life of the electrochemical device. It can also reduce the agglomeration between the particles of the first material, and further reduce the risk of the first current collector being pierced during the cold pressing of the cathode electrode sheet, thereby reducing the risk of lithium plating in the electrochemical device.

[0049] In some embodiments, the particle size D1 of the first material further satisfies: 0.05 μm ≤ D1 ≤ 1 μm, which can further reduce the risk of brittle fracture of the cathode electrode sheet.

[0050] In some embodiments, the particle size D1 of the first material further satisfies: 0.5 μm ≤ D1 ≤ 1 μm, which can further slow down the capacity attenuation rate of the electrochemical device and extend its service life.

[0051] In some embodiments, the specific charge capacity of the first material is W, and 160 mAh / g ≤ W ≤ 1200 mAh / g. In some embodiments, W can be 160 mAh / g, 180 mAh / g, 200 mAh / g, 250 mAh / g, 300 mAh / g, 350 mAh / g, 400 mAh / g, 450 mAh / g, 500 mAh / g, 550 mAh / g, 600 mAh / g, 650 mAh / g, 700 mAh / g, 750 mAh / g, 800 mAh / g, 850 mAh / g, 900 mAh / g, 950 mAh / g, 1000 mAh / g, 1050 mAh / g, 1100 mAh / g, 1150 mAh / g, 1200 mAh / g, or a value within the range formed by any two of these values or a value within the range formed by any two of these values. The higher the specific charge capacity of the first material, the higher the energy density of the electrochemical device 100. By making the specific charge capacity W of the first material satisfy 160 mAh / g ≤ W ≤ 1200 mAh / g, the energy density of the electrochemical device 100 can be improved while meeting the performance requirements of the electrochemical device.

[0052] In some embodiments, the thickness of the first material layer 12 is T, and it satisfies: 0.2 μm ≤ T ≤ 3 μm. Preferably, 0.5 μm ≤ T ≤ 2.5 μm. In some embodiments, T can be 0.1 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3 μm, or a range composed of any two of these values, or a value within the range composed of any two of these values. By making the thickness T of the first material layer 12 satisfy 0.5 μm ≤ T ≤ 2.5 μm, while improving the energy density of the electrochemical device 100, the risk of the first current collector 11 being pierced during cold pressing of the cathode electrode sheet 1 can be reduced, taking into account the low-temperature discharge capacity retention rate of the electrochemical device 100 and the number of cycles of the electrochemical device 100, slowing down the capacity attenuation rate of the electrochemical device, and extending the service life. In addition, if the thickness of the first material layer 12 is too thin, when cold pressing the cathode electrode sheet 1, the second material layer 13 is likely to pierce through the first material layer 12 and then pierce through the first current collector 11. By making the thickness T of the first material layer 12 satisfy 0.5 μm ≤ T ≤ 2.5 μm, the risk of the first current collector 11 being pierced can be reduced.

[0053] In some embodiments, the thickness T of the first material layer 12 further satisfies: 1 μm ≤ T ≤ 2 μm. By setting the thickness T of the first material layer 12 ≥ 1 μm, the energy density of the electrochemical device 100 can be further improved; by setting T ≤ 2 μm, the capacity attenuation rate of the electrochemical device 100 can be further reduced.

[0054] In some embodiments, the first material layer 12 includes a binder, and the binder is mixed with the first material. The binder is used to increase the adhesion force between the first material layer 12 and the second material layer 13, and between the first material layer 12 and the first current collector 11.

[0055] In some embodiments, the adhesion force of the first material is F, and it satisfies: 300 N / m ≤ F ≤ 1500 N / m. Preferably, 500 N / m ≤ F ≤ 1200 N / m. In some embodiments, F can be 300 N / m, 350 N / m, 400 N / m, 450 N / m, 500 N / m, 550 N / m, 600 N / m, 650 N / m, 700 N / m, 750 N / m, 800 N / m, 850 N / m, 900 N / m, 950 N / m, 1000 N / m, 1050 N / m, 1100 N / m, 1150 N / m, 1200 N / m, 1250 N / m, 1300 N / m, 1350 N / m, 1400 N / m, 1450 N / m, 1500 N / m or a value within the range formed by any two of these values or a value within the range formed by any two of these values. By setting the adhesion force F of the first material ≥ 500 N / m, the ability of the electrode sheet to resist external forces is relatively strong, and the risk of the cathode electrode sheet 1 being punctured can be reduced; by setting F ≤ 1200 N / m, the capacity attenuation rate of the electrochemical device 100 can be slowed down and the low-temperature discharge capacity retention rate of the electrochemical device 100 can be increased, which is beneficial to extending the service life of the electrochemical device 100.

[0056] In some embodiments, the adhesion force F of the first material further satisfies 800 N / m ≤ F ≤ 1200 N / m, so that the risk of brittle fracture of the cathode electrode sheet 1 can be further reduced, and further the risk of lithium plating in the electrochemical device can be reduced.

[0057] In some embodiments, the mass percentage of the first material in the first material layer 12 is c, and it satisfies: 50% ≤ c ≤ 95%. Preferably, 60% ≤ c ≤ 95%. For example, c can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or a value within the range formed by any two of these values or a value within the range formed by any two of these values. Define the mass percentage of the first material in the first material layer 12 as the content of the first material. The higher the content of the first material, the higher the energy density of the electrochemical device 100 and the higher the capacity retention rate of low-temperature discharge, but the cost is also higher. In addition, when the content of the first material is too high, the content of the binder is too low, which easily causes the first material layer 12 to be demolded. Therefore, in this embodiment, by making the mass percentage c of the first material in the first material layer 12 satisfy 60% ≤ c ≤ 95%, the energy density of the electrochemical device 100 can be increased, the capacity attenuation rate of the electrochemical device 100 can be reduced, the low-temperature discharge ability can be increased, and the risk of demolding of the first material layer 12 can be reduced.

[0058] In some embodiments, the mass percentage c of the first material in the first material layer 12 further satisfies 80% ≤ c ≤ 95%, which can further improve the energy density of the electrochemical device 100, reduce the capacity decay rate of the electrochemical device 100, and thus extend the service life of the electrochemical device 100.

[0059] In some embodiments, the mass percentage c of the first material in the first material layer 12 further satisfies 90% ≤ c ≤ 95%, so as to further improve the energy density of the electrochemical device 100, reduce the capacity decay rate of the electrochemical device 100, and improve the capacity retention rate of the electrochemical device 100 during low-temperature discharge.

[0060] In the embodiments of the present application, the cathode electrode sheet 1 includes a first current collector 11, a first material layer 12, and a second material layer 13. The first current collector 11 includes a first conductive layer 111, a first substrate layer 112, and a second conductive layer 113. The first substrate layer 112 is disposed between the first conductive layer 111 and the second conductive layer 113. By disposing the first material layer 12 between the first current collector 11 and the second material layer 13, and the first material layer 12 includes a first material, the first material includes lithium element, the particle size of the first material is D1, the second material layer 12 includes a second material, and the particle size of the second material is D2, wherein D1 < D2. Since the particle size of the first material is smaller, the packing density of the material is higher. Thus, when the cathode electrode sheet 1 is cold-pressed, the cathode electrode sheet 1 can be stressed more evenly, which is beneficial to reducing the risk of the first current collector 11 being pierced, and further beneficial to reducing the lithium deposition of the electrochemical device 100.

[0061] To enable readers to better understand the concept of the present application, the following experimental proofs are provided:

[0062] Example 2

[0063] Preparation of Cathode Electrode Sheet

[0064] Mix the first material lithium nickel iron manganese oxide, binder, and the first conductive agent carbon black in a mass ratio of 90:5:5, add N-methylpyrrolidone (NMP) as a solvent, and mix evenly under the action of a vacuum mixer to obtain a first coating slurry with a solid content of 75 wt%. Coat it evenly on the two surfaces of an 8-μm positive composite current collector (i.e., the first current collector), and after drying and cold pressing, first coatings (i.e., the first material layers) are respectively formed on the two surfaces of the positive composite current collector, and the thickness of the first coating is 2 μm.

[0065] Then, the cathode active material lithium cobaltate, the second binder polyvinylidene fluoride, and the second conductive agent conductive carbon black are mixed in a mass ratio of 97.3∶1.6∶1.1, and N-methylpyrrolidone (NMP) is added as a solvent. The mixture is stirred evenly by a vacuum mixer to obtain a cathode active material layer slurry with a solid content of 75 wt%. The cathode active material layer slurry is evenly coated on the surface of the first coating on both sides of the cathode composite current collector, and dried at 120 °C to obtain a cathode electrode sheet with a double-sided coating of the first coating and the cathode active material layer. The cathode active material layer is the second material layer, and the single-sided coating weight of the cathode active material layer is 260 mg / 1540 mm2. At 25 °C, a pressure of 40 - 80 t is used to compact the cathode electrode sheet to reach the set electrode sheet thickness specification of 84 μm. Then, it is cut into pieces and the tabs are welded to obtain a cathode electrode sheet with a specification of 74 mm × 867 mm for use. Among them, the particle size D2 of the second material is 10 μm.

[0066] Preparation of Anode Electrode Sheet

[0067] The anode active material artificial graphite, silicon carbide, the third binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 87.7∶10∶1∶1.3, and then deionized water is added as a solvent to prepare a slurry with a solid content of 70 wt%. After being stirred evenly by a vacuum mixer, the anode slurry is obtained. The anode slurry is evenly coated on one surface of a copper foil anode current collector with a thickness of 6 μm and dried at 120 °C to obtain an anode electrode sheet with a single-sided coating of the anode active material layer. The single-sided coating weight of the anode active material layer is 95 mg / 1540 mm2. Then, the above steps are repeated on the other surface of the copper foil to obtain an anode electrode sheet with a double-sided coating of the anode active material layer. After drying at 120 °C, it is cold-pressed, and then cut into pieces and the tabs are welded to obtain an anode electrode sheet with a specification of 78 mm × 875 mm for use. Among them, the thickness of the double-sided anode active material layer is 93 μm.

[0068] Preparation of Electrolyte

[0069] In a glove box filled with argon gas with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) in the carbonate compound are uniformly mixed in a mass ratio of 10∶30∶60 to obtain a basic solvent, and lithium salt LiPF6 is added and stirred evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage content of lithium salt LiPF6 is 12.5%, and the balance is the basic solvent.

[0070] Separator

[0071] A polyethylene porous polymer film with a thickness of 8 μm is used as the separator.

[0072] Preparation of Electrochemical Device

[0073] Stack the above-mentioned cathode electrode sheet, separator, and anode electrode sheet in sequence, with the separator in the middle of the cathode electrode sheet and the anode electrode sheet to play an isolation role, and wind them to obtain an electrode assembly. Pack the electrode assembly into an aluminum-plastic film packaging bag, remove moisture at 80°C, inject the prepared electrolyte, and obtain an electrochemical device through vacuum packaging, standing, formation, and shaping processes. Among them, the upper limit voltage of formation is 4.53V, the formation temperature is 85°C, and the formation time is 45min to 60min.

[0074] Different from Example 2, in Comparative Example 1, the first material layer is not included, that is, the slurry of the positive electrode material layer is directly and evenly coated on the two surfaces of the positive electrode composite current collector.

[0075] Different from Example 2, in Comparative Example 2 and Example 1, the particle size D1 of the first material and the thickness T of the first material layer are adjusted, and the differences between each comparative example and the example are listed in Table 1.

[0076] Different from Example 2, in Examples 3 to 8, the particle size D1 of the first material is adjusted, and the differences between each comparative example and the example are listed in Table 1.

[0077] Different from Example 4, in Examples 9 to 14, the thickness T of the first material layer is adjusted, and the differences between each example are listed in Table 1 and Table 2.

[0078] Different from Example 4, in Examples 15 to 21, the adhesion force F of the first material is adjusted, and the differences between each example are listed in Table 1 and Table 3.

[0079] Different from Example 4, in Examples 22 to 24, the content of the first material is adjusted, and the differences between each example are listed in Table 1 and Table 4.

[0080] Different from Example 4, in Comparative Example 3, the content of the first material is 100%, that is, Comparative Example 3 does not include the second material layer.

[0081] Adhesion force test

[0082] Discharge the electrochemical device at a constant current of 0.1C to 3.0V, and disassemble the electrochemical device to obtain the positive electrode sheet. After soaking the positive electrode sheet in dimethyl carbonate (DMC), bake it in an oven at 80°C for 30min for use. Peel off the positive electrode material layer with tape to obtain the positive electrode current collector provided with the first coating. Paste the side provided with the first coating on a smooth steel plate with double-sided tape, stick the other side with adhesive paper, fix one end of the adhesive paper on the tensile machine, set the speed to 10mm / min, pull the adhesive paper straight at 180° with the tensile machine, read the adhesion force when the adhesive paper is stretched, and divide the data by the width of the adhesive paper to obtain the adhesion force between the first coating and the positive electrode current collector, with the unit of N / m.

[0083] Cell energy density test:

[0084] Place the electrochemical device in an incubator at 25°C and let it stand for 30 minutes to reach a constant temperature. Charge the electrochemical device at a constant current of 0.5C until the voltage reaches 4.53V, then charge it at a constant voltage of 4.53V until the current reaches 0.05C, and then discharge it at 0.5C until the voltage reaches 3.0V. Record the discharge energy. The cell energy density = discharge energy / (length × width × thickness of the electrochemical device), and the unit is Wh / L. Here, the length, width, and thickness refer to the length, width, and thickness of the packaged electrochemical device.

[0085] Number of cycling tests:

[0086] At 25°C, charge the electrochemical device at a constant current of 2C until the voltage reaches 4.53V, then charge it at a constant voltage until the current is less than or equal to 0.05C, and then discharge it at a constant current of 0.5C until the voltage reaches 3V. This is one charge-discharge cycle. Record the discharge capacity of the first cycle of the electrochemical device. Charge and discharge the electrochemical device according to the above method, record the discharge capacity of each cycle until the discharge capacity of the electrochemical device decays to 80% of the discharge capacity of the first cycle, and record the number of charge-discharge cycles.

[0087] Transmittance test of the cathode electrode sheet:

[0088] At room temperature of 25°C, place the cathode electrode sheet after double-sided coating drying in a cold press, set the compaction pressure to 40t - 80t, and use the equipment to cold-press the electrode sheet to the set target value. This process can pass through different pressures or multiple cold presses, and finally reach the set target value of the electrode sheet. Randomly take three places on the cold-pressed double-sided electrode sheet, fold the electrode sheet 180° once, use a 5kg roller to naturally press the folded part, and then open it 180°, which is one fold; the next time, fold it 180° in the opposite direction, use a 5kg roller to naturally press the folded part, and then open it 180°, which is two folds. Each electrode sheet is folded four times repeatedly, and record the number of light-transmitting points n at the folded part of the electrode sheet after each fold. When n is 0, it is opaque; when n is 1 - 3, it is slightly transparent; when n is greater than or equal to 4, it is severely transparent.

[0089] Penetration test of the cathode electrode sheet:

[0090] At room temperature of 25°C, place the cathode electrode sheet after drying the double-sided coating film in a cold press, set the compaction pressure to 40t - 80t, and use the equipment to cold press the electrode sheet to the set target value. This process can go through different pressures or multiple cold presses, and finally reach the set target value of the electrode sheet. Randomly take three double-sided electrode sheets after cold pressing and place them on white paper. Drop red mercurochrome on the electrode sheets and let it stand for 4h. Then observe whether the white paper under the electrode sheets is stained red by the red mercurochrome. If at least one piece of white paper of the electrode sheet is dyed red, the cathode electrode sheet is punctured; otherwise, the cathode electrode sheet is not punctured.

[0091] Low-temperature discharge capacity retention rate test

[0092] After leaving the electrochemical device to stand in an environment of 25°C ± 3°C for 5 minutes, charge it at a constant current of 1.5C to 4.53V, and then charge it at a constant voltage of 4.53V until the current cuts off at 0.02C. The charging capacity obtained by this step is the initial capacity C0. Adjust the temperature of the constant temperature furnace to -10°C, place the electrochemical device in it for 60 minutes, and then discharge it at a constant current of 0.2C to 3.0V, and record the discharge capacity C1. Low-temperature discharge capacity retention rate (%) = C1 / C0 × 100%. Evaluate the low-temperature discharge ability of the electrochemical device through the low-temperature discharge capacity retention rate. The larger the low-temperature discharge capacity retention rate, the better the low-temperature discharge ability; the smaller the low-temperature discharge capacity retention rate, the worse the low-temperature discharge ability.

[0093] Table 1

[0094]

[0095]

[0096] Please refer to Table 1. From the comparison of Comparative Example 1, Comparative Example 2, and Examples 1 to 8, it can be seen that when the first material is not provided on the cathode electrode sheet, the energy density, number of cycle times, and low-temperature discharge retention rate of the battery cell are all lower than those of other examples, and the first current collector of the cathode electrode sheet is punctured after cold pressing. Therefore, in this example, by providing the first material layer including the first material, the energy density, number of cycle times, and low-temperature discharge capacity retention rate of the electrochemical device can be improved, the risk of the first current collector of the cathode electrode sheet being punctured during cold pressing can be reduced, and the risk of the cathode electrode sheet being broken can be reduced.

[0097] It should be noted that the number of cycle times is closely related to the capacity attenuation rate. The more the number of cycle times, the slower the capacity attenuation rate and the longer the service life; conversely, the faster the capacity attenuation rate, the shorter the service life.

[0098] It should also be noted that the higher the light transmittance of the electrode sheet, the greater the risk of brittle fracture of the electrode sheet; conversely, the smaller the risk of brittle fracture of the electrode sheet.

[0099] When the particle size D1 of the first material is 10 μm, D1 = D2, and the first current collector of the cathode electrode sheet after cold pressing is pierced, which easily leads to lithium deposition in the electrochemical device. Therefore, setting D1 < D2 can reduce the risk of the cathode electrode sheet being pierced and can also improve the low-temperature discharge capacity retention rate and the number of cycles of the electrochemical device.

[0100] When the particle size D1 of the first material is less than 0.05 μm, the decrease rate of the number of cycles increases. When the particle size D1 of the first material is greater than 2 μm, the first current collector of the cathode electrode sheet after cold pressing is pierced, which easily leads to lithium deposition in the electrochemical device. Therefore, setting the particle size D1 of the first material ≥ 0.05 μm can improve the capacity attenuation rate of the electrochemical device, and setting the particle size D1 of the first material ≤ 2 μm can reduce the risk of the cathode electrode sheet being pierced and can also improve the low-temperature discharge capacity retention rate of the electrochemical device.

[0101] Furthermore, when the particle size D1 of the first material is greater than 1 μm, the cathode electrode sheet shows slight light transmission after being folded four times. Therefore, setting the particle size D1 of the first material to further satisfy 0.05 μm ≤ D1 ≤ 1 μm can further reduce the risk of the cathode electrode sheet brittle fracture, which is beneficial to further extend the service life of the electrochemical device.

[0102] Furthermore, when the particle size D1 of the first material is less than 0.5 μm, the number of cycles of the electrochemical device is relatively low. Therefore, setting the particle size D1 of the first material to further satisfy 0.5 μm ≤ D1 ≤ 1 μm is beneficial to further improve the number of cycles of the electrochemical device, thereby further slowing down the capacity attenuation rate of the electrochemical device and extending the service life.

[0103] Table 2

[0104]

[0105] Please refer to Table 2 and combine it with Table 1. It can be seen from the comparison of Example 4 and Examples 9 to 14 that when the thickness T of the first material layer is less than 0.5 μm, the number of cycles of the electrochemical device is relatively low, the low-temperature discharge capacity retention rate is low, and the first current collector of the cathode electrode sheet is pierced after cold pressing, and the electrode sheet shows serious light transmission after being bent three times; when the thickness T of the first material layer is greater than 2.5 μm, the number of cycles of the electrochemical device is relatively low. Therefore, setting the thickness T of the first material layer to satisfy 0.5 μm ≤ T ≤ 2.5 μm can improve the number of cycles of the electrochemical device, improve the energy density, and can improve the low-temperature discharge capacity retention rate of the electrochemical device, and can reduce the risk of the cathode electrode sheet being pierced and brittle fractured.

[0106] Further, when the thickness T of the first material layer is less than 1 μm, the decline rate of the number of cycles increases, and the retention rate of the low-temperature discharge capacity decreases. After three bends, slight light transmission occurs. When the thickness of the first material layer is greater than 2 μm, the decline rate of the number of cycles increases. Therefore, setting the thickness T of the first material layer to T≥1 μm can further improve the energy density of the electrochemical device 100; setting T≤2 μm can further reduce the capacity attenuation rate of the electrochemical device 100.

[0107] Table 3

[0108]

[0109] Please refer to Table 3. From the comparison between Example 4 and Examples 15 to 21, it can be seen that when the adhesion force F of the first material is less than 500 N / m, the first current collector is punctured after the cathode electrode sheet is cold-pressed. When the adhesion force F of the first material is greater than 1200 N / m, the decline rate of the number of cycles of the electrochemical device increases, and the decline rate of the retention rate of the low-temperature discharge capacity also increases. Therefore, setting the adhesion force F of the first material to F≥500 N / m can reduce the risk of the cathode electrode sheet being punctured; setting F≤1200 N / m can slow down the capacity attenuation rate of the electrochemical device and improve the retention rate of the low-temperature discharge capacity of the electrochemical device, which is beneficial to extending the service life of the electrochemical device.

[0110] Further, when the adhesion force F of the first material is less than 800 N / m, slight light transmission occurs after the electrode sheet is bent four times, which poses a risk of brittle fracture of the electrode sheet. Therefore, setting the adhesion force F of the first material to satisfy 800 N / m≤F≤1200 N / m can further reduce the risk of brittle fracture of the cathode electrode sheet.

[0111] Table 4

[0112]

[0113] Please refer to Table 4. From the comparison of Example 4, Examples 22 to 26, and Comparative Example 3, it can be seen that as the content of the first material increases, the energy density of the battery cell, the number of cycling times, and the retention rate of the low-temperature discharge capacity can all be improved. However, when the content of the first material is too high, the content of the adhesive in the first material layer is too low, which easily leads to the demolding of the first material layer, and the cost of the first material is relatively high. Among them, when the mass percentage c of the first material in the first material layer is less than 60%, the energy density of the battery cell, the number of cycling times, and the retention rate of the low-temperature discharge capacity are all relatively low. When the mass percentage c of the first material in the first material layer is greater than 95%, the improvement benefit of the first material on the energy density of the battery cell weakens, and it easily leads to the demolding of the first material layer. Therefore, setting the mass percentage c of the first material in the first material layer to satisfy 60% ≤ c ≤ 95% can improve the energy density of the electrochemical device, increase the number of cycling times, improve the low-temperature discharge ability, reduce the capacity attenuation rate of the electrochemical device, and at the same time take into account reducing the risk of demolding of the first material layer.

[0114] Furthermore, when the mass percentage c of the first material in the first material layer is less than 80%, the energy density of the battery cell is relatively low and the number of cycling times is relatively few. Therefore, setting 80% ≤ c ≤ 95% can further improve the energy density of the electrochemical device, and can further increase the number of cycling times and further reduce the capacity attenuation rate of the electrochemical device.

[0115] Furthermore, when c is less than 90%, the energy density of the battery cell is relatively low and the number of cycling times is relatively few. Therefore, setting the mass percentage c of the first material in the first material layer to further satisfy 90% ≤ c ≤ 95% can further improve the energy density of the electrochemical device, and can further increase the number of cycling times and further reduce the capacity attenuation rate of the electrochemical device.

[0116] The above are only the embodiments of the present application, and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present application.

Claims

1. An electrochemical device, comprising an anode electrode sheet, a separator, and a cathode electrode sheet, the separator being disposed between the anode electrode sheet and the cathode electrode sheet, the anode electrode sheet comprising silicon element, characterized in that, the cathode electrode sheet comprises a first current collector, a first material layer, and a second material layer, the first current collector comprises a first conductive layer, a first substrate layer, and a second conductive layer, the first substrate layer being disposed between the first conductive layer and the second conductive layer; the first material layer is disposed on the surface of the first conductive layer facing away from the first substrate layer, and / or, the first material layer is disposed on the surface of the second conductive layer facing away from the first substrate layer; the second material layer is disposed on the surface of the first material layer facing away from the first current collector; the first material layer comprises a first material, the first material comprises lithium element, the particle size of the first material is D1, the second material layer comprises a second material, the particle size of the second material is D2, wherein, D1 < D2.

2. The electrochemical device according to claim 1, characterized in that, The first material includes at least one of Li5-xFeO 4-y , Li6-xCoO 4-y , Li2-zMnO2, Li 1.2-r Ni 0.13 Fe 0.13 Mn 0.54 O2 or Li1-tFePO4, where 4 ≤ x ≤ 5, 2 ≤ y ≤ 4, 1.6 ≤ z ≤ 2, 0.2 ≤ r ≤ 1.2, 0.8 ≤ t ≤ 1.

3. The electrochemical device according to claim 1, characterized in that, the first substrate layer comprises at least one of polyethylene terephthalate, polyimide, polyamide, polyurethane, polyethylene, and polypropylene.

4. The electrochemical device according to claim 1, characterized in that, the particle size D1 of the first material satisfies: 0.05μm ≤ D1 ≤ 2μm.

5. The electrochemical device according to claim 4, characterized in that, the particle size D1 of the first material satisfies: 0.05μm ≤ D1 ≤ 1μm.

6. The electrochemical device according to claim 1, characterized in that, the charge capacity per gram of the first material is W, and satisfies 160mAh / g ≤ W ≤ 1200mAh / g.

7. The electrochemical device according to claim 1, characterized in that, the thickness of the first material layer is T, and satisfies: 0.5μm ≤ T ≤ 2.5μm.

8. The electrochemical device according to claim 7, characterized in that, the thickness T of the first material layer satisfies: 1μm ≤ T ≤ 2μm.

9. The electrochemical device according to claim 1, characterized in that, the first material layer comprises an adhesive, and the adhesive is mixed with the first material.

10. The electrochemical device according to claim 9, characterized in that, the adhesion force of the first material is F, and satisfies 500N / m ≤ F ≤ 1200N / m.

11. The electrochemical device according to claim 10, characterized in that, the adhesion force F of the first material satisfies: 800N / m ≤ F ≤ 1200N / m.

12. The electrochemical device according to claim 9, characterized in that, the mass percentage of the first material in the first material layer is c, and satisfies: 60% ≤ c ≤ 95%.

13. The electrochemical device according to claim 12, characterized in that, the mass percentage c of the first material in the first material layer satisfies: 80% ≤ c ≤ 95%.

14. The electrochemical device according to claim 1, characterized in that, The second material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, or lithium manganate.

15. The electrochemical device according to claim 1, wherein the anode current collector includes a second current collector and a third material layer, the third material layer is disposed on the surface of the second current collector, and the third material layer includes silicon element.

16. The electrochemical device according to claim 15, wherein the mass percentage of the silicon element in the mass of the third material layer is b, and satisfies: 5% ≤ b ≤ 50%.

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