Electrochemical device and electric equipment

Abstract

The invention discloses an electrochemical device which comprises a cathode pole piece, an anode pole piece and a diaphragm, the diaphragm is arranged between the cathode pole piece and the anode pole piece, the anode pole piece comprises a silicon element, and the cathode pole piece comprises a first current collector and a first substance layer arranged on the first current collector; the first current collector comprises a first conductive layer, a polymer layer and a second conductive layer, and the polymer layer is arranged between the first conductive layer and the second conductive layer; the compaction density of the cathode plate is n, and n is more than or equal to 3.9 g / cm < 3 > and less than or equal to 4.3 g / cm < 3 >; the anode pole piece comprises a second current collector and a second substance layer, the second substance layer is arranged on at least one surface of the second current collector, and the second substance layer comprises a silicon element. According to the embodiment of the invention, the risk of brittle failure of the cathode pole piece during cold pressing and the risk of brittle failure of the cathode corner during winding can be reduced.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of energy storage, and particularly to an electrochemical device and an electrical equipment. 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 and other advantages. In the continuous development process of lithium-ion batteries, the requirements for the battery service life 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 and an electrical equipment, which are beneficial to improving the safety performance of the electrochemical device and extending the service life.

[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 a cathode electrode sheet, an anode electrode sheet and a separator. The cathode electrode sheet and the anode electrode sheet are alternately stacked, and the separator is disposed between adjacent cathode electrode sheets and anode electrode sheets. The cathode electrode sheet includes a first current collector and a first material layer, and the first material layer is disposed on at least one surface of the first current collector. The first current collector includes a first conductive layer, a polymer layer and a second conductive layer, and the polymer layer is disposed between the first conductive layer and the second conductive layer; the compaction density of the cathode electrode sheet is n, 3.9 g / cm 3 ≤n≤4.3 g / cm 3 ; the anode electrode sheet includes a second current collector and a second material layer, and the second material layer is disposed on at least one surface of the second current collector, and the second material layer includes silicon element. Wherein n = (the mass of the cathode electrode sheet per unit area - the mass of the first current collector per unit area) / (the total thickness of the cathode electrode sheet - the thickness of the first current collector). During the manufacturing process, when cold pressing the cathode electrode sheet, the polymer layer has high extensibility, and under high pressure, the polymer layer can deform, thereby reducing the risk of brittle fracture of the cathode electrode sheet, thereby reducing lithium plating of the electrochemical device, which is beneficial to extending the service life of the electrochemical device; furthermore, the pressure-bearing capacity of the cathode electrode sheet can be increased, and a greater pressure can be applied to the cathode electrode sheet during cold pressing, which is beneficial to increasing the compaction density of the cathode electrode sheet, thereby being beneficial to increasing the energy density of the electrochemical device. In addition, by making the cathode electrode sheet satisfy 3.9 g / cm 2 ≤n≤4.3 g / cm 2 , setting n≥3.9 g / cm 3 , the energy density of the battery cell can be improved; setting n≤4.3 g / cm 3, it can reduce the risk of cathode sheet fracture, improve the charging speed and reduce the capacity attenuation rate of the electrochemical device, thereby extending the service life of the electrochemical device.

[0005] In some embodiments, the first material layer includes a first material and a second material, the first material and the second material are mixed with each other, and the first material includes Li 5-x FeO 4-y , Li 6-x CoO 4-y , Li 2-z MnO2 or Li 1.2-r Ni 0.13 Fe 0.13 Mn 0.54 O2, where 4≤x≤5, 2≤y≤4, 1.6≤z≤2, 0.2≤r≤1.2. The first material can achieve lithium compensation for the cathode sheet, thereby improving the energy density of the electrochemical device.

[0006] In some embodiments, the compaction density n of the first material layer satisfies 4 g / cm 3 ≤n≤4.1 g / cm 3 , setting n≥4 g / cm 3 , can further improve the energy density of the battery cell; setting n≤4.1 g / cm 3 , can further improve the charging speed, and at the same time can further reduce the capacity attenuation rate of the electrochemical device, and further extend the service life of the electrochemical device.

[0007] In some embodiments, the elongation of the first current collector is b and satisfies: 10%≤b≤80%. By making the elongation b of the first current collector satisfy 10%≤b≤80%, the sheet resistance of the cathode sheet can be reduced, the charging time of the electrochemical device can be reduced, thereby improving the charging efficiency of the electrochemical device, and at the same time reducing the risk of cathode sheet fracture after the electrochemical device is cycled for charge and discharge, and slowing down the attenuation rate of the electrochemical device.

[0008] In some embodiments, the elongation b of the first current collector satisfies: 25%≤b≤45%. By making the elongation b of the first current collector further satisfy 25%≤b≤45%, the sheet resistance of the cathode sheet can be further reduced, the charging time of the electrochemical device can be further reduced, the charging efficiency can be improved, and at the same time the capacity attenuation rate of the electrochemical device can be further slowed down, and the service life can be extended.

[0009] In some embodiments, the elongation rate of the cathode current collector is c, and it satisfies: 8% ≤ c ≤ 60%. By making the elongation rate c of the cathode current collector satisfy 8% ≤ c ≤ 60%, the sheet resistance of the cathode current collector can be reduced, the charging time of the electrochemical device can be reduced, thereby improving the charging efficiency of the electrochemical device. At the same time, the risk of breakage of the cathode current collector after the electrochemical device is cycled for charging and discharging is reduced, and the attenuation rate of the electrochemical device is slowed down.

[0010] In some embodiments, the elongation rate c of the cathode current collector satisfies 20.5% ≤ c ≤ 39.6%. By making the elongation rate c of the cathode current collector further satisfy 20.5% ≤ c ≤ 39.6%, the sheet resistance of the cathode current collector can be further reduced, the charging time of the electrochemical device can be further reduced, the charging efficiency can be improved, and at the same time, the capacity attenuation rate of the electrochemical device can be further slowed down, and the service life can be extended.

[0011] In some embodiments, the thicknesses of the first conductive layer and the second conductive layer are both d, and it satisfies: 1 μm ≤ d ≤ 4 μm. By setting the thickness d of the first conductive layer and the second conductive layer to be d ≥ 1 μm, the sheet resistance of the cathode current collector can be reduced, the charging speed can be increased, and the capacity attenuation rate of the electrochemical device can be reduced; by setting d ≤ 4 μm, the energy density of the battery cell can be improved.

[0012] In some embodiments, the thickness d of the first conductive layer and the second conductive layer satisfies: 2 μm ≤ d ≤ 3 μm. By setting the thickness d of the first conductive layer and the second conductive layer to be d ≥ 2 μm, the sheet resistance of the cathode current collector can be further reduced, the charging speed can be further increased, and the capacity attenuation rate of the electrochemical device can be further reduced; by setting d ≤ 3 μm, the energy density of the battery cell can be further improved.

[0013] In some embodiments, the mass percentage of the first material in the first material layer is f, and it satisfies: 0.5% ≤ f ≤ 5%. By setting the proportion f of the first material to satisfy 0.5% ≤ f ≤ 5%, the charging efficiency of the electrochemical device can be improved, and the capacity attenuation rate of the electrochemical device can be slowed down, which is beneficial to extending the service life of the electrochemical device.

[0014] In some embodiments, the mass percentage f of the first material in the first material layer satisfies: 1% ≤ f ≤ 2%. By making the proportion f of the first material further satisfy 1% ≤ f ≤ 2%, the charging efficiency of the electrochemical device can be further improved, and the capacity attenuation rate of the electrochemical device can be further slowed down, thereby extending the service life of the electrochemical device.

[0015] In some embodiments, the mass percentage of the second material in the first material layer is g, and it satisfies: 92% ≤ g ≤ 96.5%. By setting the proportion g of the second material to satisfy 92% ≤ g ≤ 96.5%, the charging efficiency of the electrochemical device can be improved, and the capacity attenuation rate of the electrochemical device can be slowed down, which is beneficial to extending the service life of the electrochemical device.

[0016] In some embodiments, the mass percentage g of the second material in the first material layer satisfies: 95% ≤ g ≤ 96%. By setting the proportion g of the second material to further satisfy 95% ≤ g ≤ 96%, the charging efficiency of the electrochemical device can be further improved, and the rate of capacity decay of the electrochemical device can be further slowed down, thereby extending the service life of the electrochemical device.

[0017] In some embodiments, the charging gram capacity of the first material is greater than that of the second material, which is beneficial to improving the charging speed of the electrochemical device.

[0018] In some embodiments, the charging gram capacity w of the first material satisfies: 240 mAh / g ≤ w ≤ 900 mAh / g, thereby improving the charging speed of the electrochemical device.

[0019] In some embodiments, the second material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, or lithium manganese oxide.

[0020] In some embodiments, the mass percentage of silicon element in the second material layer is m, and satisfies: 5% ≤ m ≤ 50%. The increase in the content of silicon element can improve the energy density of the electrochemical device. However, 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% ≤ m ≤ 50%, it is possible to balance the improvement of the energy density of the electrochemical device and the reduction of volume expansion.

[0021] In some embodiments, the polymer layer includes at least one of polyethylene terephthalate, polyimide, polyamide, polyurethane, polyethylene, or polypropylene.

[0022] Some embodiments of the present application further provide an electrical device including the above-mentioned electrochemical device.

[0023] The beneficial effects of the embodiments of the present application are as follows: Different from the prior art, in the embodiments of the present application, the first current collector includes a first conductive layer, a polymer layer, and a second conductive layer, and the polymer layer is disposed between the first conductive layer and the second conductive layer; by mixing the first material and the second material to form the first material layer, the first material includes Li 5-x FeO 4-y 、Li 6- x CoO 4-y 、Li 2-z MnO2 or Li 1.2-r Ni 0.13 Fe 0.13 Mn 0.54At least one of O2 is used to dispose the first material layer on at least one surface of the first current collector; on the one hand, the first material can realize lithium supplementation for the cathode electrode sheet, thereby improving the charge and discharge efficiency of the electrochemical device; on the other hand, the polymer layer has high extensibility. During the manufacturing process, when cold pressing the cathode electrode sheet, under high pressure, the polymer layer can deform, thereby reducing the risk of brittle fracture of the cathode electrode sheet, thereby reducing lithium deposition in the electrochemical device. In addition, due to the high extensibility of the cathode, the cathode corner is not easily broken during winding, which is beneficial to extending the service life of the electrochemical device; furthermore, it can increase the pressure-bearing capacity of the cathode electrode sheet, and a greater pressure can be applied to the cathode electrode sheet during cold pressing, which is beneficial to increasing the compaction density of the cathode electrode sheet, thereby being beneficial to increasing the energy density of the electrochemical device. Additionally, by making it satisfy 3.9 g / cm 3 ≤n≤4.3 g / cm 3 , it is beneficial to improve the energy density of the electrochemical device, and balance the charge and discharge efficiency and delay the capacity attenuation rate of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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 to be used in 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 do not necessarily draw according to the actual scale.

[0025] Figure 1 is a schematic structural diagram of the electrochemical device provided in the embodiment of the present application;

[0026] Figure 2 is a schematic structural diagram of the battery cell provided in the embodiment of the present application.

[0027] LABEL DESCRIPTION

[0028] 100, Electrochemical device;

[0029] 1, Cathode electrode sheet; 11, First current collector; 111, First conductive layer; 112, Polymer layer; 113, Second conductive layer; 12, First material layer;

[0030] 2, Separator;

[0031] 3, Anode electrode sheet; 31, Second current collector; 32, Second material layer;

[0032] 4, Housing;

[0033] 5, Battery cell. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To facilitate the understanding of this application, the following provides a more detailed description of this application in conjunction with the accompanying drawings and specific embodiments. It should be noted that terms such as "first", "second", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0035] Unless otherwise defined, all 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 intended 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.

[0036] In addition, the technical features involved in different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0037] In an electrochemical device, silicon materials have a relatively high theoretical specific capacity, usually dozens of times that of graphite anode materials. Therefore, silicon-based batteries are becoming increasingly popular in the market.

[0038] However, a large amount of SEI (Solid Electrolyte Interface) film is generated during the first charging of silicon-based anode materials, consuming a large amount of active lithium, resulting in a low first Coulombic efficiency and a low energy density of the battery. In related technologies, it is often necessary to supplement an additional lithium source to the cathode electrode sheet to replace the consumption of active lithium in the cathode main material and improve the utilization rate of the cathode main material. The lithium supplement materials are usually Li5FeO4, Li6CoO4, etc. However, such lithium supplement materials have a small tap density themselves, and the lithium supplement materials contain residual alkali, resulting in a relatively large volume of the cathode electrode sheet per unit mass. At the same time, the processing environment of such materials is usually a drying room with a relatively low air humidity, which has little lubrication effect on the electrode sheet, resulting in a low tap density of the electrode sheet. In order to reduce the impact on the volume of the electrochemical device, a greater pressure needs to be applied during the cold pressing of the cathode electrode sheet to increase the tap density of the cathode electrode sheet and reduce the impact of the lithium supplement material on the volume of the cathode electrode sheet. However, the addition of the lithium supplement material will increase the brittleness of the cathode electrode sheet. During the cold pressing of the cathode electrode sheet, it is easy to cause the cathode electrode sheet to break brittlely, resulting in a loss of capacity of the electrochemical device; in addition, when the cathode electrode sheet is pierced, an ion channel is formed at the pierced position, which is prone to cause the phenomenon of lithium deposition. After lithium deposition, the service life of the electrochemical device will be greatly shortened, and the capacity will also decrease.

[0039] To solve at least some of the above problems, this application provides an electrochemical device and an electrical device, which can reduce the risk of brittle fracture of the cathode electrode sheet during cold pressing while increasing the tap density of the first material layer, thereby reducing the risk of lithium deposition in the electrochemical device and being beneficial to extending the service life of the electrochemical device.

[0040] The specific structure and functions of the present application will be described in detail below.

[0041] Please refer to Figure 1 and Figure 2 , the electrochemical device 100 includes an anode current collector 3, a separator 2, and a cathode current collector 1. The separator 2 is disposed between the anode current collector 3 and the cathode current collector 1. Among them, the anode current collector 3 contains silicon element.

[0042] In some embodiments, the electrochemical device 100 includes a housing 4. The above-mentioned anode current collector 3, separator 2, and cathode current collector 1 together form the battery core 5 of the electrochemical device 100. The battery core 5 is housed in the housing 4 so that the housing 4 can protect the battery core 5.

[0043] The electrical device includes the electrochemical device 100. In some embodiments, the electrical device can be a terminal product such as a mobile phone, a laptop computer, a tablet, etc.

[0044] In some embodiments, the anode current collector 3 includes a second current collector 31 and a second material layer 32. The second material layer 32 is disposed on the surface of the second current collector 31. Among them, the second material layer 32 contains silicon element.

[0045] It should be noted that the second material layer 32 contains silicon element. Here, "contains" means that the second material layer 32 contains silicon-containing materials such as pure silicon, silicon oxide, silicon carbide, etc. The silicon-containing materials serve as the main carriers for lithium ions to embed or extract.

[0046] In some embodiments, the second current collector 31 can be a copper foil.

[0047] 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 base material 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 base material layer 311. The second material layer 32 as described above can be disposed on the surface of the third conductive layer 312 facing away from the base material layer 311 and the surface of the fourth conductive layer 313 facing away from the base material layer 311.

[0048] In some embodiments, the mass percentage of silicon element in the second material layer 32 is m, and it satisfies: 5% ≤ m ≤ 50%. In some embodiments, m can be 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50% or the range composed of any two of these values or the 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 insertion or extraction of lithium ions, resulting in an increase in the volume of the electrochemical device. Therefore, by setting 5% ≤ m ≤ 50%, it is possible to balance the improvement of the energy density of the electrochemical device and the reduction of volume expansion.

[0049] 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.

[0050] The electrochemical device 100 can be arranged in a stacked form, that is, the anode electrode sheet 3 and the cathode electrode sheet 1 are alternately stacked, and the separator 2 is disposed between the adjacent 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.

[0051] In some embodiments, the number of the anode electrode sheet 3, the separator 2 and the cathode electrode sheet 1 can be multiple. The multiple anode electrode sheets 3 and the multiple cathode electrode sheets 1 are alternately stacked in sequence, and a separator 2 is disposed between an adjacent anode electrode sheet 3 and a cathode electrode sheet 1.

[0052] This application takes the stacked electrochemical device 100 as an example for illustration.

[0053] Please refer to Figure 2 , the cathode electrode sheet 1 includes a first current collector 11 and a first material layer 12. The first current collector 11 includes a first conductive layer 111, a polymer layer 112 and a second conductive layer 113. The polymer 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. The first material layer 12 includes a first material and a second material, and the first material and the second material are mixed with each other. The first material includes at least one of Li5-xFeO4-y, Li6-xCoO4-y, Li2-zMnO2 or Li1.2-rNi0.13Fe0.13Mn0.54O2, where 4 ≤ x ≤ 5, 2 ≤ y ≤ 4, 1.6 ≤ z ≤ 2, 0.2 ≤ r ≤ 1.2. 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.

[0054] In some embodiments, both the first conductive layer 111 and the second conductive layer 113 are metals. The metal material has good electrical conductivity, which is beneficial to improving the charge and discharge performance of the electrochemical device 100.

[0055] In some embodiments, the thicknesses of the first conductive layer 111 and the second conductive layer 113 are equal. When the thicknesses of the first conductive layer 111 and the second conductive layer 113 are inconsistent, it is likely to cause uneven current distribution inside the electrochemical device 100, thereby reducing the charge and discharge rate of the electrochemical device 100. By setting the thicknesses of the first conductive layer 111 and the second conductive layer 113 to be equal, it is beneficial to improve the uniformity of the current inside the electrochemical device 100 and is beneficial to improving the charge and discharge rate of the electrochemical device 100. It can be understood that, on the premise of not affecting the inventive purpose of this application, due to reasons such as production and processing accuracy, when the error between the thickness of the first conductive layer 111 and the thickness of the second conductive layer 113 does not exceed 10%, the thicknesses of the first conductive layer 111 and the second conductive layer 113 can also be considered equal.

[0056] 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.

[0057] The particle size of the second material is relatively large (usually greater than 5 μm), while the particle size of the first material is relatively small. By mixing the first material with the second material, when cold pressing the cathode electrode sheet 1, the first material can fill the gaps between the particles of the second material, which 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 through the first current collector 11, which is beneficial to reducing lithium deposition in the electrochemical device 100.

[0058] In some embodiments, the polymer layer 112 includes at least one of polyethylene terephthalate, polyimide, polyamide, polyurethane, polyethylene, and polypropylene. The polymer layer 112 has a high elongation rate, such that when the cathode electrode sheet 1 is subjected to pressure, it can extend, thereby reducing the risk of the first current collector 11 being pierced by large-sized particles (such as lithium cobalt oxide particles) in the second material. And because the polymer layer 112 has a high elongation rate, a greater pressure can be used for cold pressing the cathode electrode sheet 1, thereby increasing the tap density of the first material layer 12, enhancing the battery capacity and energy density of the electrochemical device 100. At the same time, combined with the first material in the present application, even when a greater pressure is used for cold pressing the cathode electrode sheet 1, the risk of the first current collector 11 being pierced can be reduced while increasing the tap density. Furthermore, in a silicon system, silicon has a large expansion rate after multiple charge and discharge cycles. By combining the first material and the polymer substrate into the electrochemical device 100 including silicon elements, by increasing the tap density of the first material layer 12, the total amount of active material is increased, thereby enhancing the energy density of the electrochemical device 100. Furthermore, on the premise of achieving the same energy density, the volume of the electrochemical device 100 can be reduced, thereby reducing the loss of energy density caused by silicon expansion.

[0059] 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 polymer layer 112; and / or, the first material layer 12 is disposed on the surface of the second conductive layer 113 facing away from the polymer layer 112.

[0060] Specifically, in some embodiments, the first material layer 12 is disposed on both opposite surfaces of the first current collector 11. Specifically, one first material layer 12 is disposed on the surface of the first conductive layer 111 facing away from the polymer layer 112, and another first material layer 12 is disposed on the surface of the second conductive layer 113 facing away from the polymer layer 112.

[0061] In some embodiments, the tap density of the first material layer 12 is n, and it satisfies 3.9 g / cm 3 ≤n≤4.3 g / cm 3 . In some embodiments, the value of n can be 3.9 g / cm 3 , 4.0 g / cm 3 , 4.1 g / cm 3 , 4.2 g / cm 3 , 4.3 g / cm 3 or a range formed by any two of these values or a value within the range formed by any two of these values. Setting n≥3.9 g / cm 3 can enhance the energy density of the battery cell 5; setting n≤4.3 g / cm 3, it is possible to reduce the risk of fracture of the cathode electrode sheet 1, improve the charging speed and reduce the capacity attenuation rate of the electrochemical device 100, thereby extending the service life of the electrochemical device 100.

[0062] Among them, n = (mass of the cathode electrode sheet 1 per unit area - mass of the first current collector 11 per unit area) / (total thickness of the cathode electrode sheet 1 - thickness of the first current collector 11).

[0063] Further, the compaction density n of the first material layer 12 satisfies 4 g / cm 3 ≤n≤4.2 g / cm 3 . Setting n≥4 g / cm 3 , the energy density of the battery cell 5 can be further improved; setting n≤4.2 g / cm 3 , the charging speed can be further improved, and at the same time, the capacity attenuation rate of the electrochemical device 100 can be further reduced, and the service life of the electrochemical device 100 can be further extended.

[0064] Further, the compaction density n of the first material layer 12 satisfies 4 g / cm 3 ≤n≤4.1 g / cm 3 , the charging speed can be further improved and the capacity attenuation rate of the electrochemical device 100 can be reduced, and the service life of the electrochemical device 100 can be further extended.

[0065] In some embodiments, the elongation of the first current collector 11 is b, and it satisfies: 5%≤b≤90%, preferably, 10%≤b≤80%. In some embodiments, the value of b can be 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% 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 elongation b of the first current collector 11 satisfy 10%≤b≤80%, the sheet resistance of the cathode electrode sheet 1 can be reduced, the charging time of the electrochemical device 100 can be reduced, thereby improving the charging efficiency of the electrochemical device 100, and the risk of fracture of the cathode electrode sheet 1 after cyclic charge and discharge of the electrochemical device 100 can also be reduced, while reducing the capacity attenuation rate of the electrochemical device 100.

[0066] Further, the elongation b of the first current collector 11 satisfies: 25%≤b≤45%. By making the elongation b of the first current collector 11 further satisfy 25%≤b≤45%, the sheet resistance of the cathode electrode sheet 1 can be further reduced, the charging time of the electrochemical device 100 can be further reduced, the charging efficiency can be improved, and the capacity attenuation rate of the electrochemical device 100 can be further slowed down, and the service life can be extended.

[0067] Further, the elongation b of the first current collector 11 is 35%. Setting the elongation b of the first current collector 11 to 35% can further reduce the sheet resistance of the cathode electrode sheet 1, improve the charging speed of the electrochemical device 100, and slow down the capacity attenuation rate of the electrochemical device 100. It can be understood that, without affecting the object of the present invention of this application, due to reasons such as production and processing precision, the elongation b of the first current collector 11 can be 35% ± 1%.

[0068] In some embodiments, the elongation of the cathode electrode sheet 1 is c, and it satisfies: 3.1% ≤ c ≤ 67.8%, preferably, 8% ≤ c ≤ 60%. In some embodiments, c can be 3.1%, 8%, 10%, 15%, 16%, 16.2%, 20%, 20.5%, 25%, 27.1%, 28%, 30%, 32%, 35%, 38%, 39.6%, 40%, 45%, 45.3%, 50%, 55%, 60%, 67.8% 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 making the elongation c of the cathode electrode sheet 1 satisfy 8% ≤ c ≤ 60%, the sheet resistance of the cathode electrode sheet 1 can be reduced, the charging time of the electrochemical device 100 can be reduced, thereby improving the charging efficiency of the electrochemical device 100, and the risk of breakage of the cathode electrode sheet 1 after cyclic charge and discharge of the electrochemical device 100 can also be reduced, while slowing down the capacity attenuation rate of the electrochemical device 100.

[0069] Further, the elongation c of the cathode electrode sheet 1 satisfies 20.5% ≤ c ≤ 39.6%. By making the elongation c of the cathode electrode sheet 1 further satisfy 20.5% ≤ c ≤ 39.6%, the sheet resistance of the cathode electrode sheet 1 can be further reduced, the charging time of the electrochemical device 100 can be further reduced, the charging efficiency can be improved, and the capacity attenuation rate of the electrochemical device 100 can be further slowed down, extending the service life.

[0070] Further, the elongation c of the cathode electrode sheet 1 is 27.1%. Setting the elongation c of the cathode electrode sheet 1 to 27.1% can further reduce the sheet resistance of the cathode electrode sheet 1, improve the charging speed of the electrochemical device 100, and slow down the capacity attenuation rate of the electrochemical device 100. It can be understood that, without affecting the object of the present invention of this application, due to reasons such as production and processing precision, the elongation of the cathode electrode sheet 1 can be 27.1% ± 1%.

[0071] In some embodiments, the thicknesses of the first conductive layer 111 and the second conductive layer 113 are both d, and satisfy: 0.5 μm ≤ d ≤ 5 μm. Preferably, 1 μm ≤ d ≤ 4 μm. In some embodiments, d can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 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. Setting the thickness d of the first conductive layer 111 and the second conductive layer 113 to be d ≥ 1 μm can reduce the sheet resistance of the cathode electrode 1, accelerate the charging speed, and reduce the capacity attenuation rate of the electrochemical device 100; setting d ≤ 4 μm can increase the energy density of the battery cell 5.

[0072] Furthermore, the thickness d of the first conductive layer 111 and the second conductive layer 113 satisfies: 2 μm ≤ d ≤ 3 μm. Setting the thickness d of the first conductive layer 111 and the second conductive layer 113 to be d ≥ 2 μm can further reduce the sheet resistance of the cathode electrode 1, further accelerate the charging speed, and further reduce the capacity attenuation rate of the electrochemical device 100; setting d ≤ 3 μm can further increase the energy density of the battery cell 5.

[0073] In some embodiments, the mass percentage of the first material in the first material layer 12 is f, and satisfies: 0.1% ≤ f ≤ 8%. Preferably, 0.5% ≤ f ≤ 5%. In some embodiments, f can be 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 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. Setting the proportion f of the first material to satisfy 0.5% ≤ f ≤ 5% can, while improving the charging efficiency of the electrochemical device 100, slow down the capacity attenuation rate of the electrochemical device 100, which is beneficial to extending the service life of the electrochemical device 100.

[0074] Furthermore, the mass percentage f of the first material in the first material layer 12 satisfies: 1% ≤ f ≤ 4%. Setting the proportion f of the first material to further satisfy 1% ≤ f ≤ 4% can further improve the charging efficiency of the electrochemical device 100, and further slow down the capacity attenuation rate of the electrochemical device 100, thereby extending the service life of the electrochemical device 100.

[0075] Furthermore, the mass percentage f of the first material in the first material layer 12 satisfies: 1% ≤ f ≤ 2%. Setting the proportion f of the first material to further satisfy 1% ≤ f ≤ 2% can further improve the charging efficiency of the electrochemical device 100, and further slow down the capacity attenuation rate of the electrochemical device 100, thereby extending the service life of the electrochemical device 100.

[0076] In some embodiments, the mass percentage of the second material in the first material layer 12 is g, and it satisfies: 89% ≤ g ≤ 96.9%. Preferably, 92% ≤ g ≤ 96.5%. In some embodiments, g can be 89%, 89.5%, 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 96.9% or a range formed by any two of these values or a value within the range formed by any two of these values. Setting the proportion g of the second material to satisfy 92% ≤ g ≤ 96.5% can improve the charging efficiency of the electrochemical device 100 and slow down the capacity attenuation rate of the electrochemical device 100, which is beneficial to extending the service life of the electrochemical device 100.

[0077] Furthermore, the mass percentage g of the second material in the first material layer 12 satisfies: 95% ≤ g ≤ 96%. Setting the proportion g of the second material to further satisfy 95% ≤ g ≤ 96% can further improve the charging efficiency of the electrochemical device 100 and further slow down the capacity attenuation rate of the electrochemical device 100, thereby extending the service life of the electrochemical device 100.

[0078] In some embodiments, the specific charge capacity of the first material is greater than that of the second material.

[0079] In some embodiments, the specific charge capacity w of the first material satisfies: 240 mAh / g ≤ w ≤ 900 mAh / g. In some embodiments, w can be 240 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 or a range formed by any two of these values or a value within the range formed by any two of these values.

[0080] In an embodiment of the present application, the first current collector 11 includes a first conductive layer 111, a polymer layer 112, and a second conductive layer 113. The polymer layer 112 is disposed between the first conductive layer 111 and the second conductive layer 113. The first material layer 12 is formed by mixing a first material and a second material. The first material includes at least one of Li5-xFeO4-y, Li6-xCoO4-y, Li2-zMnO2, or Li1.2-rNi0.13Fe0.13Mn0.54O2. The first material layer 12 is disposed on at least one surface of the first current collector 11. On the one hand, the first material can achieve lithium supplementation for the cathode electrode 1, thereby improving the charge-discharge efficiency of the electrochemical device 100. On the other hand, the polymer layer 112 has high extensibility. During the manufacturing process, when cold pressing the cathode electrode 1, under high pressure, the polymer layer 112 can deform, thereby reducing the risk of brittle fracture of the cathode electrode 1. At the same time, it can increase the pressure-bearing capacity of the cathode electrode 1, and a greater pressure can be applied to the cathode electrode 1 during cold pressing, which is beneficial to increasing the compaction density of the cathode electrode 1, and thus beneficial to increasing the energy density of the electrochemical device 100. In addition, by making 3.9 g / cm 3 ≤n≤4.3 g / cm 3 , it is possible to balance the improvement of the energy density and charge-discharge efficiency of the electrochemical device 100, and at the same time delay the capacity attenuation rate of the electrochemical device 100.

[0081] To enable readers to better understand the concept of the present application, experimental proofs are provided below.

[0082] The preparation of the electrochemical device in Example 1 is as follows:

[0083] <Preparation of the cathode electrode>

[0084] The cathode material (i.e., the second material) lithium cobaltate, the first material lithium ferrite as the first material supplementing lithium, the first binder polyvinylidene fluoride, and the first conductive agent conductive carbon black are mixed according to a mass ratio of 95:2:1.6:1.4, and N-methylpyrrolidone (NMP) is added as a solvent. The mixture is stirred evenly by a vacuum mixer to obtain a first material layer slurry with a solid content of 75 wt%. The first material layer slurry is evenly coated on the surfaces on both sides of the first current collector. Among them, the first current collector is a composite current collector, which includes a first conductive layer, a polymer layer, and a second conductive layer. The polymer layer is made of polyethylene terephthalate, and both the first conductive layer and the second conductive layer are made of copper alloy. After drying at 120 °C, a cathode electrode with a double-sided coated first material layer is obtained. The single-sided coating weight of the first material layer is 260 mg / 1540 mm 2At 25°C, use a pressure of 40 - 80t to compact the cathode sheet to reach the set thickness specification of 84μm. Then, after cutting and welding the tabs, the cathode sheet with a size of 74mm × 867mm is obtained for use.

[0085] <Preparation of Anode Sheet>

[0086] Mix the anode material artificial graphite, silicon carbide, the second binder styrene - butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in a mass ratio of 87.7∶10∶1∶1.3. Then add deionized water as a solvent to prepare a slurry with a solid content of 70wt%. After mixing evenly with a vacuum mixer, the slurry of the second material layer is obtained. Coat the slurry of the second material layer evenly on one surface of a copper foil with a thickness of 6μm (i.e., the second current collector), and dry it at 120°C to obtain a negative electrode with a single - sided coating of the second material layer. The single - sided coating weight of the second material layer is 95mg / 1540mm 2 。Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode with a double - sided coating of the second material layer. After drying at 120°C, cold - press it, and then cut and weld the tabs to obtain a negative electrode sheet with a size of 78mm × 875mm for use. Among them, the thickness of the double - sided second material layer is 93μm.

[0087] <Preparation of Electrolyte>

[0088] In an argon - atmosphere glove box with a water content of less than 10ppm, uniformly mix ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) in a mass ratio of 10∶30∶60 to obtain a basic solvent, and add lithium salt LiPF6 and stir 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.

[0089] <Separator>

[0090] Use a polyethylene porous polymer film with a thickness of 8μm (manufacturer: American Celgard Separator Co., Ltd.) as the separator.

[0091] <Preparation of Electrochemical Device>

[0092] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the cathode sheet and the anode sheet to play an isolation role, and wind them to obtain an electrode core. Put 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, forming, and shaping processes. Among them, the upper limit voltage of forming is 4.53V, the forming temperature is 85°C, and the forming time is 45min to 60min.

[0093] Different from Example 1, the cathode material in Comparative Example 1 does not include the first material lithium supplement agent, and the first current collector is aluminum foil.

[0094] Different from Example 1, the cathode material in Comparative Example 2 does not include the first material lithium supplement agent.

[0095] Different from Example 1, the first current collector in Comparative Example 3 is aluminum foil.

[0096] The differences between Comparative Example 4, Comparative Example 5, and Examples 1 to 5 lie in the compaction density of the first material layer. For specific parameters, see Table 1.

[0097] Different from Example 2, the elongation b of the first current collector and the elongation c of the cathode sheet in Examples 6 to 14 are different. For specific parameters, see Tables 1 and 2.

[0098] Different from Example 2, the thickness d of the first conductive layer and the second conductive layer and the elongation c of the cathode sheet in Examples 15 to 22 are different. For specific parameters, see Tables 1 and 3.

[0099] Different from Example 2, the proportion f of the first material, the proportion g of the second material, and the elongation c of the cathode sheet in Examples 23 to 30 are different. For specific parameters, see Tables 1 and 4.

[0100] Regarding the test method as follows:

[0101] Compaction density test:

[0102] At room temperature of 25°C, the electrochemical device is charged at a constant current of 2C to 4.53V, and then charged at a constant voltage until the current is less than or equal to 0.05C. Disassemble this electrochemical device, take out the cathode sheet, use a micrometer to measure the thickness of 16 different regions of the cathode sheet, and record the average value as the total thickness h1 of the cathode sheet, with the unit of cm. Use a micrometer to measure the thickness of 16 different regions of the cathode sheet with only the first current collector, and record the average value as the thickness h2 of the current collector of the cathode sheet, with the unit of cm. Weigh the mass of the cathode sheet per unit area, denoted as m1, with the unit of g / cm 2 ; weigh the mass of the cathode sheet with only the first current collector per unit area, denoted as m2. Then the compaction density n of the first material layer = (m1 - m2) / (h1 - h2), with the unit of g / cm 3 .

[0103] Elongation test of the first current collector:

[0104] Take the cathode current collector (i.e., the first current collector), cut it into a width of 20 mm and a length of 10 cm using a cutter, clamp the head and tail with a stretching machine, and set the stretching speed to 50 mm / min. Record the initial marked line distance G0 in mm. Start the stretching machine and stop the equipment until the current collector breaks, and record the final marked line distance G1 in mm. The elongation rate of the current collector = [(G1 - G0) / G0]×100%.

[0105] Testing the elongation rate of the cathode current collector:

[0106] Take the cathode current collector coated with the first material layer on both sides, cut it into a width of 20 mm and a length of 10 cm using a cutter, clamp the head and tail with a stretching machine, and set the stretching speed to 50 mm / min. Record the initial marked line distance T0 in mm. Start the stretching machine and stop the equipment until the cathode current collector breaks, and record the final marked line distance T1 in mm. The elongation rate of the current collector = [(T1 - T0) / T0]×100%.

[0107] Testing the sheet resistance:

[0108] Take the cathode current collector in the single-sided area (i.e., the cathode current collector with the first material layer on only one side), use a four-probe sheet resistance tester, gently insert the four tips of the probe into the surface of the conductive layer of the current collector in the single-sided area to be tested, keep it vertical, and ensure good contact. Read the resistance value displayed on the display screen when the measured value is stable, and record the measured value, which is the sheet resistance of the cathode current collector.

[0109] Testing the charging time:

[0110] At room temperature of 25°C, charge the electrochemical device at a constant current of 2C until 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 3V. Then charge the electrochemical device at a constant current of 2C until 4.53V, and then charge it at a constant voltage until the current is less than or equal to 0.05C. Record the total time from the second start of charging to the cut-off of the electrochemical device, which is the charging time of the battery cell.

[0111] Testing the energy density of the battery cell:

[0112] Place the electrochemical device in an incubator at 25°C and let it stand for 30 minutes to make the electrochemical device reach a constant temperature. Charge the constant-temperature 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 is 0.05C, and then discharge it at 0.5C until the voltage is 3.0V. Record the discharge energy. The energy density of the battery cell = discharge energy / (length × width × thickness of the electrochemical device), with the unit of Wh / L. Here, the length, width, and thickness refer to the length, width, and thickness of the packaged electrochemical device.

[0113] Testing the cycle performance:

[0114] At 25 °C, the electrochemical device is charged at a constant current of 2C to 4.53V, then charged at a constant voltage until the current is less than or equal to 0.05C, and then discharged at a constant current of 0.5C to 3V. This is one charge-discharge cycle, and the discharge capacity of the first cycle of the electrochemical device is recorded. The electrochemical device is charged and discharged in cycles according to the above method, and the discharge capacity of each cycle is recorded until the discharge capacity of the electrochemical device decays to 80% of the discharge capacity of the first cycle, and the number of charge-discharge cycles is recorded.

[0115] Cyclic cathode plate fracture test:

[0116] At 25 °C room temperature, the electrochemical device is charged at a constant current of 2C to 4.53V, then charged at a constant voltage until the current is less than or equal to 0.05C, and then discharged at a constant current of 0.5C to 3V. This is one charge-discharge cycle, and the discharge capacity of the first cycle of the electrochemical device is recorded. The electrochemical device is charged and discharged in cycles according to the above method, and the discharge capacity of each cycle is recorded until the discharge capacity of the electrochemical device decays to 80% of the discharge capacity of the first cycle. The cell with 80% of the discharge capacity after cyclic discharge is disassembled, the cathode plate is opened, and whether there are cracks is observed. If there are cracks greater than or equal to 1 cm, it is determined that the cyclic cathode plate of the cell is fractured; otherwise, it is not fractured.

[0117] Table 1

[0118]

[0119]

[0120] Among them, in Comparative Examples 1 to 5 and Examples 1 to 5, the mass percentage m of silicon element in the second material layer is 10% for all, the thickness d of the first conductive layer is 2 μm for all, the proportion f of the first material in the first material layer is 2% for all, and the proportion g of the second material in the first material layer is 95% for all.

[0121] Referring to Table 1, it can be seen from the comparison of Comparative Examples 1, 2, 3 and Examples 1 to 5 that:

[0122] Compared with Example 2, in Comparative Example 2, a cathode electrode sheet made of a conventional first material layer was tested, and the energy density of the battery cell was very low, the charging time was long, and the charging speed was slow. Compared with Example 2, in Comparative Example 1, aluminum foil was used as the current collector, and the cathode electrode sheet broke after cyclic charge and discharge; compared with Comparative Example 4, in Comparative Example 3, a cathode electrode sheet made of aluminum foil as the current collector and a first material layer including a first material was tested, and the cathode electrode sheet broke after cyclic charge and discharge. The breakage of the cathode electrode sheet easily leads to lithium plating, triggering various side reactions, resulting in the consumption of active materials, accelerating the continuous attenuation of the electrochemical device. In severe cases of breakage, there will be a sudden capacity attenuation. In addition, the breakage of the cathode electrode sheet will also increase the risk of short circuit of the electrochemical device. It should be noted that after cyclic charge and discharge refers to after the electrochemical device has undergone multiple cycles of charge and discharge and the discharge capacity has decayed to 80%. In Example 2, compared with Comparative Example 2, since the first material was added to the first material layer, the energy density of the battery cell was improved, the charging time was accelerated, and the cathode electrode sheet did not break after cyclic charge and discharge. That is to say, in the present application, in the silicon anode electrode sheet system, by using a composite current collector and combining the first material as a lithium supplement agent, the charging speed can be increased while improving the energy density of the battery cell, and the cathode electrode sheet does not break after cyclic charge and discharge.

[0123] Please continue to refer to Table 1. From the comparison of Comparative Example 4, Comparative Example 5, and Examples 1 to 5, it can be seen that when the compaction density n of the first material layer is less than 3.9 g / cm 3 ³, the energy density of the battery cell is relatively low. When the compaction density n is greater than 4.3 g / cm 3 ³, the charging time of the electrochemical device is long, the charging is slow, the cathode electrode sheet breaks after cyclic charge and discharge, and the number of cycles is small, indicating that the capacity attenuation speed of the electrochemical device is fast and the service life is short. Setting the compaction density n of the first material layer to be ≥ 3.9 g / cm 3 ³ can improve the energy density of the battery cell; setting n ≤ 4.3 g / cm 3 ³ can reduce the risk of breakage of the cathode electrode sheet, increase the charging speed, and reduce the capacity attenuation speed of the electrochemical device, thereby extending the service life of the electrochemical device.

[0124] From the comparison of Examples 1 to 5, it can be seen that when the compaction density n of the first material layer is less than 4 g / cm 3 ³, the decline speed of the energy density of the battery cell accelerates. When the compaction density n of the first material layer is greater than 4.2 g / cm 3 ³, the decline speed of the number of cycles accelerates, indicating that the attenuation speed of the electrochemical device accelerates, and the increase speed of the charging time accelerates, and the charging speed slows down. Therefore, setting n ≥ 4 g / cm 3 ³ can further improve the energy density of the battery cell; setting n ≤ 4.2 g / cm 3, it is possible to further reduce the capacity attenuation rate of the electrochemical device and further improve the charging speed.

[0125] Furthermore, when the compaction density n of the first material layer is greater than 4.1 g / cm 3 , the decline rate of the number of cycles of the electrochemical device accelerates. Therefore, by making the compaction density n of the first material layer further satisfy 4 g / cm 3 ≤n≤4.1 g / cm 3 , it is possible to further reduce the capacity attenuation rate of the electrochemical device.

[0126] Table 2

[0127]

[0128] Among them, the compaction density n of the cathode current collector in Comparative Example 6, Comparative Example 7, and Examples 21 to 27 is 4 g / cm 3 , the mass percentage m of silicon element in the second material layer is 10% for all, the thickness d of the first conductive layer is 2 μm for all, the proportion f of the first material in the first material layer is 2% for all, and the proportion g of the second material in the first material layer is 95% for all.

[0129] Please refer to Table 2. From the comparison between Examples 6 to 14, it can be seen that when the elongation rate b of the first current collector is less than 10%, the increase rate of the sheet resistance of the cathode current collector accelerates, the increase rate of the charging time accelerates, the cathode current collector breaks after cyclic charge and discharge, and the decrease rate of the number of cycles accelerates, resulting in an accelerated attenuation rate of the electrochemical device; when the elongation rate b of the first current collector is greater than 80%, the increase rate of the sheet resistance of the cathode current collector accelerates, the increase rate of the charging time accelerates, and at the same time, the decrease rate of the number of cycles of the electrochemical device accelerates. Therefore, in the present application, by making the elongation rate b of the first current collector satisfy 10%≤b≤80%, the sheet resistance of the cathode current collector can be reduced, the charging time of the electrochemical device can be reduced, thereby improving the charging efficiency of the electrochemical device, and the risk of the cathode current collector breaking after cyclic charge and discharge of the electrochemical device can also be reduced, while slowing down the attenuation rate of the electrochemical device.

[0130] Furthermore, when the elongation rate b of the first current collector is less than 25% or the elongation rate b of the first current collector is greater than 45%, the sheet resistance of the cathode current collector is relatively large, the charging time is relatively long, and the number of cycles is relatively small. Therefore, by making the elongation rate b of the first current collector further satisfy 25%≤b≤45%, the sheet resistance of the cathode current collector can be further reduced, the charging time of the electrochemical device can be further reduced, the charging efficiency can be improved, and the capacity attenuation rate of the electrochemical device can be further slowed down, extending the service life.

[0131] Furthermore, when the elongation rate b of the first current collector is less than 35%, as b decreases, the sheet resistance of the cathode electrode increases, the charging time of the electrochemical device increases, and the number of cycles of the electrochemical device decreases; when the elongation rate b of the first current collector is greater than 35%, as b increases, the sheet resistance of the cathode electrode increases, the charging time of the electrochemical device increases, and the number of cycles of the electrochemical device decreases. Therefore, in the present application, setting the elongation rate b of the first current collector to 35% can further reduce the sheet resistance of the cathode electrode, improve the charging speed of the electrochemical device, and slow down the capacity attenuation rate of the electrochemical device.

[0132] Please refer to Table 2. From the comparison between Examples 6 to 14, it can be seen that when the elongation rate c of the cathode electrode is less than 8%, the increase rate of the sheet resistance of the cathode electrode accelerates, the increase rate of the charging time accelerates, the cathode electrode breaks after cyclic charge and discharge, and the decrease rate of the number of cycles accelerates, resulting in an accelerated attenuation rate of the electrochemical device; when the elongation rate c of the cathode electrode is greater than 60%, the increase rate of the sheet resistance of the cathode electrode accelerates, the increase rate of the charging time accelerates, and at the same time, the decrease rate of the number of cycles of the electrochemical device accelerates. Therefore, in the present application, by making the elongation rate c of the cathode electrode satisfy 8% ≤ c ≤ 60%, the sheet resistance of the cathode electrode can be reduced, the charging time of the electrochemical device can be reduced, thereby improving the charging efficiency of the electrochemical device, and the risk of the cathode electrode breaking after cyclic charge and discharge of the electrochemical device can also be reduced, while slowing down the capacity attenuation rate of the electrochemical device.

[0133] Furthermore, when the elongation rate c of the cathode electrode is less than 20.5% or the elongation rate c of the cathode electrode is greater than 39.6%, the sheet resistance of the cathode electrode is relatively large, the charging time is relatively long, and the number of cycles is relatively small. Therefore, by making the elongation rate c of the cathode electrode further satisfy 20.5% ≤ c ≤ 39.6%, the sheet resistance of the cathode electrode can be further reduced, the charging time of the electrochemical device can be further reduced, the charging efficiency can be improved, and the capacity attenuation rate of the electrochemical device can be further slowed down, extending the service life.

[0134] Furthermore, when the elongation rate c of the cathode electrode is less than 27.1%, as c decreases, the sheet resistance of the cathode electrode increases, the charging time of the electrochemical device increases, and the number of cycles of the electrochemical device decreases; when the elongation rate c of the cathode electrode is greater than 27.1%, as c increases, the sheet resistance of the cathode electrode increases, the charging time of the electrochemical device increases, and the number of cycles of the electrochemical device decreases. Therefore, in the present application, setting the elongation rate c of the cathode electrode to 27.1% can further reduce the sheet resistance of the cathode electrode, improve the charging speed of the electrochemical device, and slow down the capacity attenuation rate of the electrochemical device.

[0135] Table 3

[0136]

[0137] Among them, the compaction density n of the cathode electrode sheets in Examples 15 to 22 is all 4 g / cm 3 , the mass percentage m of silicon element in the second material layer is all 10%, the elongation b of the first current collector is all 40%, the proportion f of the first material in the first material layer is all 2%, and the proportion g of the second material in the first material layer is all 95%.

[0138] Please refer to Table 3. From the comparison of Examples 15 to 22, it can be seen that as the thickness d of the first conductive layer and the second conductive layer increases, the energy density of the battery cell gradually decreases, the sheet resistance of the cathode electrode sheet gradually decreases, and the charging time gradually shortens. However, when the thickness d of the first conductive layer and the second conductive layer is less than 1 μm, the increase rate of the sheet resistance of the cathode electrode sheet speeds up, the extension rate of the charging time also speeds up, and the decrease rate of the number of cycles also speeds up; when the thickness d of the first conductive layer and the second conductive layer is greater than 4 μm, the energy density of the battery cell is low. Therefore, setting the thickness d of the first conductive layer and the second conductive layer to d≥1 μm can reduce the sheet resistance of the cathode electrode sheet 1, accelerate the charging speed, and reduce the capacity attenuation rate of the electrochemical device; setting d≤4 μm can improve the energy density of the battery cell.

[0139] Furthermore, when the thickness d of the first conductive layer and the second conductive layer is less than 2 μm, the increase rate of the sheet resistance of the cathode electrode sheet speeds up, and the decrease rate of the number of cycles of the electrochemical device speeds up; when the thickness d of the first conductive layer and the second conductive layer is greater than 3 μm, the decrease rate of the energy density of the battery cell speeds up. Therefore, setting the thickness d of the first conductive layer and the second conductive layer to d≥2 μm can further reduce the sheet resistance of the cathode electrode sheet, further accelerate the charging speed, and further reduce the capacity attenuation rate of the electrochemical device; setting d≤3 μm can further improve the energy density of the battery cell.

[0140] Table 4

[0141]

[0142]

[0143] Among them, in Examples 23 to 30, the proportion f of the first material represents the mass percentage of the first material in the first material layer, the proportion g of the second material represents the mass percentage of the second material in the first material layer. The compaction density n of the cathode electrode sheets in Comparative Example 10, Comparative Example 11, and Examples 41 to 46 is all 4 g / cm 3 , the mass percentage m of silicon element in the second material layer is all 10%, the elongation b of the first current collector is all 40%, and the thickness d of the first conductive layer and the second conductive layer is all 2 μm.

[0144] Please refer to Table 4. From the comparison between Example 23 and Example 30, it can be seen that when the proportion f of the first material is less than 0.5%, the charging time of the electrochemical device is longer and the number of cycles is lower; when the proportion f of the first material is greater than 5%, the charging time increases and the rate of decrease in the number of cycles accelerates. Therefore, in this application, setting the proportion f of the first material to satisfy 0.5% ≤ f ≤ 5% can improve the charging efficiency of the electrochemical device and slow down the rate of capacity decay of the electrochemical device, which is beneficial to extending the service life of the electrochemical device.

[0145] Furthermore, when the proportion f of the first material is less than 1%, the rate of increase in the charging time of the electrochemical device accelerates and the rate of decrease in the number of cycles accelerates; when the proportion f of the first material is greater than 4%, the rate of decrease in the number of cycles of the electrochemical device accelerates. Therefore, in this embodiment, setting the proportion f of the first material to further satisfy 1% ≤ f ≤ 4% can further improve the charging efficiency of the electrochemical device and further slow down the rate of capacity decay of the electrochemical device, thereby extending the service life of the electrochemical device.

[0146] Furthermore, when the proportion f of the first material is greater than 2%, as the proportion f of the first material increases, the charging time of the electrochemical device gradually increases and the number of cycles gradually decreases. Therefore, in this embodiment, setting the proportion f of the first material to further satisfy 1% ≤ f ≤ 2% can further improve the charging efficiency of the electrochemical device and further slow down the rate of capacity decay of the electrochemical device, thereby extending the service life of the electrochemical device.

[0147] Please continue to refer to Table 4. From the comparison between Example 23 and Example 30, it can be seen that when the proportion g of the second material is less than 92%, the charging time of the electrochemical device is longer and the number of cycles is lower; when the proportion g of the second material is greater than 96.5%, the charging time is longer and the rate of decrease in the number of cycles accelerates. Therefore, in this application, setting the proportion g of the second material to satisfy 92% ≤ g ≤ 96.5% can improve the charging efficiency of the electrochemical device and slow down the rate of capacity decay of the electrochemical device, which is beneficial to extending the service life of the electrochemical device.

[0148] Furthermore, when the proportion g of the second material is less than 95%, as the proportion g of the second material decreases, the charging time of the electrochemical device gradually increases and the number of cycles gradually decreases; when the proportion g of the second material is greater than 95%, as the proportion g of the second material increases, the charging time of the electrochemical device gradually increases and the number of cycles gradually decreases. Therefore, in this embodiment, setting the proportion g of the second material to further satisfy 95% ≤ g ≤ 96% can further improve the charging efficiency of the electrochemical device and further slow down the rate of capacity decay of the electrochemical device, thereby extending the service life of the electrochemical device.

[0149] The above are only 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 similarly included in the patent protection scope of the present application.

Claims

1. An electrochemical device, comprising a cathode electrode, an anode electrode and a separator, wherein the cathode electrode and the anode electrode are alternately laminated, the separator is disposed between adjacent cathode and anode electrodes, the cathode electrode includes a first current collector and a first material layer, and the first material layer is disposed on at least one surface of the first current collector, characterized in that, the first current collector includes a first conductive layer, a polymer layer and a second conductive layer, and the polymer layer is disposed between the first conductive layer and the second conductive layer; The compaction density of the cathode plate is n, 3.9 g / cm 3 ≤ n ≤ 4.3 g / cm 3 , the anode electrode includes a second current collector and a second material layer, the second material layer is disposed on at least one surface of the second current collector, and the second material layer contains silicon element.

2. The electrochemical device according to claim 1, wherein The first material layer includes a first material and a second material, and the first material includes Li 5-x FeO 4-y , Li 6-x CoO 4-y , Li 2-z MnO2 or Li 1.2-r Ni 0.13 Fe 0.13 Mn 0.54 O2, where at least one of 4≤x≤5, 2≤y≤4, 1.6≤z≤2, 0.2≤r≤1.2; the second material includes at least one of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate or lithium manganate.

3. The electrochemical device according to claim 1, characterized in that, The cathode electrode sheet satisfies: 4 g / cm 3 ≤n≤4.1 g / cm 3 .

4. The electrochemical device according to claim 1, characterized in that, the elongation of the first current collector is b, and satisfies: 10% ≤ b ≤ 80%.

5. The electrochemical device according to claim 4, characterized in that, the elongation b of the first current collector satisfies: 25% ≤ b ≤ 45%.

6. The electrochemical device according to claim 1, characterized in that, the elongation of the cathode electrode is c, and satisfies: 8% ≤ c ≤ 60%.

7. The electrochemical device according to claim 6, characterized in that, the elongation c of the cathode electrode satisfies: 20.5% ≤ c ≤ 39.6%.

8. The electrochemical device according to claim 7, characterized in that, the thicknesses of both the first conductive layer and the second conductive layer are d, and satisfy: 1 μm ≤ d ≤ 4 μm.

9. The electrochemical device according to claim 8, characterized in that, the thickness d of the first conductive layer and the second conductive layer satisfies: 2 μm ≤ d ≤ 3 μm.

10. The electrochemical device according to claim 2, characterized in that, the mass percentage of the first material in the first material layer is f, and satisfies: 0.5% ≤ f ≤ 5%.

11. The electrochemical device according to claim 10, characterized in that, the mass percentage f of the first material in the first material layer satisfies: 1% ≤ f ≤ 2%.

12. The electrochemical device according to claim 2, characterized in that, the mass percentage of the second material in the first material layer is g, and satisfies: 92% ≤ g ≤ 96.5%.

13. The electrochemical device according to claim 12, characterized in that, the mass percentage g of the second material in the first material layer satisfies: 95% ≤ g ≤ 96%.

14. The electrochemical device according to claim 2, characterized in that, the charge capacity per gram of the first material is greater than that of the second material.

15. The electrochemical device according to claim 14, characterized in that, the charge capacity per gram w of the first material satisfies: 240 mAh / g ≤ w ≤ 900 mAh / g.

16. The electrochemical device according to claim 1, characterized in that, the mass percentage of the silicon element in the second material layer is m, and satisfies: 5% ≤ m ≤ 50%.

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

18. An electrical device, characterized in that, Comprising the electrochemical device according to any one of claims 1-17.

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