Electrode sheet, battery, battery pack and electric device

Abstract

Provided in the present application are an electrode sheet, a battery, a battery pack and an electric device. The electrode sheet comprises an electrode current collector and an electrode active layer located on the surface of at least one side of the electrode current collector. 0.8≤15830×Ra / G-1301 / G≤12, 3000 s≤G≤18000 s, and 0.5 μm≤Ra≤3 μm, wherein Ra is the surface roughness of the electrode active layer, with the unit of Ra being μm; and G is the air permeability value of the electrode active layer, with the unit of G being s.

Description

An electrode sheet, a battery, a battery pack, and an electrical device.

[0001] This application claims priority to Chinese Patent Application No. 202411555872.4, filed on October 31, 2024, entitled “An Electrode Sheet, Battery, Battery Pack and Electrical Device”, the entire contents of which are incorporated herein by reference.

[0002] This application claims priority to Chinese Patent Application No. 202411552090.5, filed on October 31, 2024, entitled “A negative electrode sheet, a battery, a battery pack and an electrical device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of electrochemical devices, specifically to an electrode sheet, a battery, a battery pack, and an electrical device. Background Technology

[0004] Rechargeable batteries are common electrochemical devices with wide applications. Improving their kinetic performance, rate performance, and fast-charging capabilities, as well as shortening charging time, is crucial for their practical application. Current technologies primarily improve rate performance by modifying electrode active materials and electrolytes; however, this approach has limited effectiveness and suffers from drawbacks such as high manufacturing costs, thus restricting their application. Therefore, improving battery rate performance remains a pressing technical challenge in this field. Summary of the Invention

[0005] This application provides an electrode sheet, a battery, a battery pack, and an electrical device to at least solve the problem of poor rate performance of batteries in the prior art.

[0006] This application provides an electrode sheet, including an electrode current collector and an electrode active layer located on at least one side surface of the electrode current collector; 0.8≤15830×Ra / G-1301 / G≤12; 3000s≤G≤18000s; 0.5μm≤Ra≤3μm; where Ra is the surface roughness of the electrode active layer, and the unit of Ra is μm; G is the air permeability value of the electrode active layer, and the unit of G is s; the air permeability value of the electrode active layer is measured according to the following process: a 20cm² area is selected from the electrode sheet. 2 ±5cm 2The test area is defined, and the electrode current collector of the test area is controlled such that one side of the surface has the electrode active layer and the other side is an empty foil area. The electrode current collector of the test area is distributed with pores of 30μm±3μm with a pore spacing of 100μm±5μm. Then, a membrane with a thickness of 14μm±2μm and a porosity of 40%±5% is respectively covered on both sides of the test area in the thickness direction. Then, the time it takes for 100mL±5mL of air to pass through the test area covered by the membrane under a pressure of 1.21KPa±0.1KPa is measured, which is the air permeability value of the electrode active layer.

[0007] According to one embodiment of this application, 1≤15830×Ra / G-1301 / G≤9.

[0008] According to one embodiment of this application, 3400s≤G≤15000s.

[0009] According to one embodiment of this application, 0.75μm≤Ra≤3μm.

[0010] According to one embodiment of this application, the areal density of the electrode active layer of the electrode sheet is 100 g / m². 2 ~500g / m 2 .

[0011] According to one embodiment of this application, the compaction density of the electrode active layer of the electrode sheet is 1.0 g / cc to 1.8 g / cc.

[0012] According to one embodiment of this application, the electrode sheet is a negative electrode sheet.

[0013] According to one embodiment of this application, an adhesive layer is provided between the electrode active layer and the electrode current collector, and the thickness of the adhesive layer is 0.2 μm to 2 μm.

[0014] In another aspect of this application, a battery is provided, including the aforementioned electrode sheet.

[0015] According to one embodiment of this application, the battery is a lithium-ion battery.

[0016] Another aspect of this application provides a battery pack including the aforementioned battery.

[0017] Another aspect of this application provides an electrical device including the aforementioned battery or battery pack.

[0018] The electrode sheet, battery, battery pack, and electrical equipment provided in this application, by synergistically regulating the air permeability G and surface roughness Ra of the electrode active layer of the electrode sheet, make it meet the following conditions: 0.8≤15830×Ra / G-1301 / G≤12, 3000s≤G≤18000s, 0.5μm≤Ra≤3μm, which can effectively improve the kinetic performance and electrochemical performance of the battery. Detailed Implementation

[0019] To enable those skilled in the art to better understand the solutions of this application, a further detailed description of this application is provided below. The specific embodiments listed below are merely descriptions of the principles and features of this application; the examples are only for explaining this application and are not intended to limit its scope. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0020] In related technologies, the rate performance of batteries is mainly improved by modifying materials such as electrode active materials and electrolytes. However, the improvement effect on battery rate performance is limited, and there are also drawbacks such as high battery manufacturing costs, which restricts applications. Therefore, how to improve the rate performance of batteries remains a technical problem that urgently needs to be solved in this field. Electrode sheets are an important component of batteries. Improving battery performance by adjusting the structure and other characteristics of electrode sheets can enhance battery kinetic performance without changing the electrode active materials and electrolytes. This has advantages such as reducing battery manufacturing costs, and therefore can be considered as a direction for improving battery kinetic performance, thereby improving battery rate performance.

[0021] According to the inventors' research, the preparation process of electrode sheets typically involves a rolling process. For example, in the wet electrode sheet preparation process, after the electrode slurry used to form the electrode sheet is coated onto the electrode current collector, it undergoes drying and rolling processes to form an electrode coating on the surface of the electrode current collector, thereby obtaining the electrode sheet. However, after rolling, the surface porosity of the electrode coating is relatively low, and the density of the electrode sheet surface is not conducive to the electrolyte wetting into the interior of the electrode sheet, affecting mass transfer and electrolyte retention. Furthermore, the porosity and tortuosity of the electrode sheet also have a significant impact on ion diffusion. Therefore, it is necessary to regulate the pore structure of the electrode surface to ensure that the electrolyte can fully wet the electrode, allowing solvated active ions in the electrolyte (such as solvated lithium ions in lithium-ion batteries) to be rapidly transported within the electrode. Simultaneously, the electrode interior also needs a suitable pore structure and tortuosity. For example, excessively small porosity or excessively high tortuosity will increase ion diffusion distance and resistance, hindering the embedding of solvated active ions in the electrolyte into the active material in the electrode coating (such as graphite in the negative electrode), resulting in poor battery rate performance. For instance, during high-rate charging, lithium dendrites are easily deposited on the negative electrode surface. Furthermore, although increasing the porosity of the electrode can improve the battery rate performance to some extent, the improvement is limited. This is because the ion diffusion capacity in the battery is affected not only by the porosity of the electrode but also by characteristics such as the tortuosity of the electrode. Additionally, excessively high porosity will increase the active surface area, leading to a decrease in battery initial efficiency and energy density.

[0022] In view of the above, in a first aspect, embodiments of this application provide an electrode sheet, including an electrode current collector and an electrode active layer located on at least one side surface of the electrode current collector; 0.8≤15830×Ra / G-1301 / G≤12; 3000s≤G≤18000s; 0.5μm≤Ra≤3μm; wherein, Ra is the surface roughness of the electrode active layer, and the unit of Ra is in μm; G is the air permeability value of the electrode active layer, and the unit of G is in seconds (s).

[0023] According to the inventors' research, by synergistically regulating the surface roughness Ra and permeability G of the electrode active layer to satisfy 0.8≤15830×Ra / G-1301 / G≤12, 3000s≤G≤18000s, and 0.5μm≤Ra≤3μm, the kinetic performance of the battery can be effectively improved, and the electrochemical performance such as the rate performance and fast charging performance can be enhanced. Specifically, the ratio of the battery's discharge capacity at 3C rate to its discharge capacity at 0.33C rate (or the 3C capacity retention rate) is greater than or equal to 82%, for example, greater than or equal to 83%, or greater than or equal to 84%.

[0024] The reason for this is that the surface roughness Ra of the electrode active layer is related to the surface pore state of the electrode active layer. The surface roughness of the electrode active layer affects the surface pore state, which in turn affects the wetting of the electrode active layer by the electrolyte and the ion transport capacity. At the same time, the surface roughness of the electrode active layer also affects the fit between the electrode sheet and the separator. If the surface roughness of the electrode active layer is too large, there is a risk that the electrode sheet will puncture the separator, which will also affect the battery performance. The air permeability value of the electrode active layer is related to the porosity and tortuosity of the electrode sheet. The air permeability value G represents the porous structure of the electrode sheet. The permeability of an electrode sheet is negatively correlated with the ease with which gas can pass through. Specifically, a higher permeability value indicates greater resistance to gas passage through the electrode sheet, which is detrimental to electrolyte wetting and reduces ion conductivity. During high-rate charging of the battery, lithium plating and other problems are more likely to occur, affecting the battery's kinetic performance. Conversely, a lower permeability value indicates less resistance to gas passage through the electrode sheet, which is beneficial for electrolyte wetting and can improve ion conductivity and battery kinetic performance. However, if the permeability value is too low, it can also damage the conductive network of the electrode active layer to some extent, affecting the battery's kinetic performance. In this embodiment, considering the combined effects of the surface roughness Ra and permeability G of the electrode active layer on the structure and performance of the negative electrode sheet, the surface roughness Ra and permeability G of the electrode active layer are synergistically controlled. By coordinating these two factors to meet the aforementioned range, the surface and internal pore structure of the electrode sheet can be controlled, enabling the electrode coating to possess both suitable surface pores and overall pore structure characteristics. This facilitates electrolyte wetting of the electrode sheet, improves the electrolyte retention capacity of the electrode sheet, enhances the mass transfer efficiency within the electrode sheet, and promotes ion transport, thereby improving the kinetic performance of the battery.

[0025] For example, 15830×Ra / G-1301 / G can be a range consisting of 0.8, 0.84, 0.87, 0.9, 0.93, 1, 1.05, 1.1, 1.3, 1.6, 2, 3, 4, 5, 6, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, or any two of them.

[0026] For example, G can be a range consisting of 3000s, 3100s, 3400s, 3500s, 3800s, 4000s, 5000s, 6000s, 7000s, 7600s, 8000s, 8400s, 9000s, 10000s, 12000s, 13000s, 14000s, 14500s, 15000s, 16000s, 17000s, 18000s, or any two of them.

[0027] For example, Ra can be a range of 0.5 μm, 0.6 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.82 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3 μm, or any combination thereof.

[0028] In some embodiments, 1≤15830×Ra / G-1301 / G≤9, which is beneficial for further improving the rate performance and other properties of the battery.

[0029] In some embodiments, 3400s≤G≤15000s is analyzed as follows: by further controlling G within this range, the negative electrode active layer can have a more suitable pore structure and conductive network, thereby improving ion conductivity and further improving the battery's rate performance and other performance characteristics.

[0030] In some embodiments, 0.75μm≤Ra≤3μm is beneficial for the electrode active layer to have a more suitable surface pore structure, which is more conducive to ion transport, thereby further improving the rate performance and other properties of the battery.

[0031] Specifically, the electrode active layer includes an electrode active material, and the mass percentage of the electrode active material in the electrode active layer can be 80% to 100%, for example (but not limited to) 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 100%, or any combination thereof.

[0032] Specifically, the aforementioned electrode sheet can be a negative electrode sheet, and correspondingly, the electrode active layer is a negative electrode active layer, the electrode active material is a negative electrode active material, and the electrode current collector is a negative electrode current collector. Specifically, the negative electrode active material can include a negative electrode active material capable of lithium intercalation / deintercalation, specifically including carbon-based active materials, silicon-based active materials, and Li4Ti5O4. 12 One or more of the following: tin alloy, tin, germanium, and indium. Specifically, carbon-based active materials may include one or more of the following: non-graphitized carbon, graphite, or carbon or pyrolytic carbon obtained by high-temperature oxidation of polyyne-based polymers, coke, sintered organic polymers, and activated carbon.

[0033] In some embodiments, the carbon-based active material includes one or more of graphite, graphene, mesophase microcarbon spheres, hard carbon, soft carbon, etc.

[0034] Specifically, silicon-based active materials may include silicon (Si), silicon alloys, and silicon-oxygen materials (SiO2). x Silicon-carbon materials (Si-C), silicon-oxygen-carbon materials (SiO) x One or more of -C).

[0035] In some embodiments, the negative electrode active material includes graphite. In addition to graphite, the negative electrode active material may also include or exclude other negative electrode active materials (such as silicon-based active materials and / or other carbon-based active materials other than graphite).

[0036] In some embodiments, the mass percentage of graphite in the negative electrode active layer (i.e., the mass ratio of graphite in the negative electrode active layer) can be 50% to 99%, for example (but not limited to) 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or any combination thereof.

[0037] In some specific embodiments, the negative electrode active material is graphite (in this case, the negative electrode sheet is a graphite negative electrode), and the mass percentage of graphite in the negative electrode active layer can be 80% to 100%, for example (but not limited to) 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 100%, or any combination thereof. This allows for a sufficient amount of negative electrode active material in the negative electrode active layer, which is beneficial for the performance of the negative electrode and also helps to improve the energy density of the battery.

[0038] In other specific embodiments, the negative electrode active material includes graphite, and in addition to graphite, it also includes one or more other negative electrode active materials such as silicon-based active materials, graphene, mesophase micro carbon spheres, hard carbon and soft carbon. The mass percentage of graphite in the negative electrode active layer can be 50% to 99%, for example (but not limited to) 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99% or any two of these ranges. The mass percentage of other negative electrode active materials in the negative electrode active layer besides graphite can be 1% to 50%, for example (but not limited to) 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any two of these ranges. This approach helps to balance the ion and electron diffusion rates of the negative electrode and the electrolyte's liquid retention capacity while maintaining a high energy density in the battery, thereby improving the battery's fast charging performance, rate performance, and cycle performance.

[0039] In some embodiments, the particle size D of the negative electrode active material 50 The particle size can be 5μm-25μm, such as 5μm, 8μm, 10μm, 13μm, 15μm, 18μm, 20μm, 23μm, 25μm, or any combination thereof. This range is beneficial for further improving the rate performance and fast charging performance of the battery. The reason for this is that by controlling the particle size D of the negative electrode active material... 50Within the aforementioned range, it is beneficial to achieve a larger compaction density of the negative electrode active material layer, while also controlling the deintercalation / intercalation path of active ions in the negative electrode sheet within a suitable length range, which is conducive to the transport of ions and electrons, thereby further improving the rate performance and fast charging performance of the negative electrode sheet.

[0040] In some specific embodiments, the particle size D of the graphite 50 It can be 5μm-25μm, for example, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm or any combination thereof.

[0041] In the embodiments of this application, graphite may include one or more of natural graphite, artificial graphite, and modified graphite; wherein, modified graphite includes, but is not limited to, oxidation-modified graphite and / or halogenated graphite, and halogenated graphite may include graphite modified by at least one element selected from fluorine, chlorine, bromine and iodine, such as fluorinated graphite (i.e., fluorine-modified graphite).

[0042] In general, to improve the structural stability and conductivity of the electrode active layer, the electrode active layer may also include a binder and a conductive agent.

[0043] In some embodiments, the mass percentage of the binder in the electrode active layer can be 1% to 5%, for example, 1%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or any combination thereof. By controlling the binder content in the electrode active layer within the above range, it is beneficial to improve the structural stability of the electrode sheet, while not crowding out the content of other components such as the electrode active material, thus facilitating the improvement of the overall performance of the electrode sheet.

[0044] In some embodiments, the mass percentage of the conductive agent in the electrode active layer can be 0.1% to 20%, for example, a range of 0.1%, 1%, 3%, 5%, 7%, 10%, 13%, 15%, 18%, 20%, or any combination thereof.

[0045] In some embodiments, the areal density of the electrode active layer of the electrode sheet can be 100 g / m². 2 ~500g / m 2 For example, 100g / m 2 150g / m 2 180g / m 2 200g / m 2 220g / m 2 250g / m 2 280g / m 2 300g / m 2320g / m 2 350g / m 2 380g / m 2 400g / m 2 420g / m 2 450g / m 2 500g / m 2 Or a range consisting of any two of them, such that the electrode sheet has a high areal density, which is beneficial to improving the energy density of the electrode sheet and the performance of the electrode, while also helping to maintain the high diffusion capacity of active ions in the electrode sheet and improve the kinetic performance of the electrode sheet.

[0046] In some embodiments, the compaction density of the electrode active layer of the electrode sheet can be 1.0 g / cc to 1.8 g / cc, for example, 1 g / cc, 1.2 g / cc, 1.4 g / cc, 1.5 g / cc, 1.6 g / cc, 1.8 g / cc or any combination thereof. In this way, the electrode sheet has a higher compaction density, which is beneficial to improving the energy density of the electrode sheet and to maximizing the electrode performance. At the same time, it is also beneficial to maintain a high diffusion capacity of active ions in the electrode sheet and improve the kinetic performance of the electrode sheet.

[0047] In some embodiments, an adhesive layer may be provided between the electrode active layer and the electrode current collector. The adhesive layer may include an adhesive and a conductive agent. The mass percentage of the conductive agent in the adhesive layer may be 90% to 99%, for example, 90%, 92%, 94%, 96%, 98%, 99%, or any combination thereof. The mass percentage of the adhesive in the adhesive layer may be 1% to 10%, for example, 1%, 2%, 4%, 6%, 8%, 10%, or any combination thereof. The conductive agent in the adhesive layer is a conventional conductive material in the art, such as carbon black.

[0048] In some embodiments, the thickness of the adhesive layer can be 0.2 μm to 2 μm, for example, a range of 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm or any two of these.

[0049] Specifically, the adhesive layer between the electrode active layer and the electrode current collector is mainly used to bond the electrode active layer and the electrode current collector, thereby improving the adhesion between them. The thickness of the adhesive layer is generally much smaller than the thickness of the electrode active layer, and it has virtually no impact on the OI value and air permeability of the electrode active layer. In practice, the air permeability G of the entire coating on either side of the negative electrode current collector can be directly measured, and the test result is the air permeability G of the negative electrode active layer.

[0050] In this embodiment, an electrode active layer can be provided on one side of the electrode current collector in the thickness direction, or an electrode active layer can be provided on both opposite sides of the electrode current collector in the thickness direction.

[0051] In the embodiments of this application, the binder in the electrode active layer can be any electrode-suitable binder known in the art. For example, when the electrode sheet is a negative electrode sheet, the binder in the negative electrode active layer can be any negative electrode-suitable binder known in the art. Specifically, the binder in the negative electrode active layer may include at least one of polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), tetrafluoroethylene and its copolymers, polyvinylidene fluoride and its copolymers, polyolefins and their copolymers (e.g., polyethylene-polyethylene glycol block copolymers), polyethers and their copolymers (e.g., polyethylene oxide), polyphenylene ethers and their copolymers, polysiloxanes and their copolymers (e.g., polydimethylsiloxane, poly(dimethylsiloxane-co-alkylmethylsiloxane)), polyesters and their copolymers (e.g., polyethylene ester, polyvinyl acetate, polyacrylate), carboxymethyl cellulose, styrene-butadiene latex, nitrile rubber, and polyacrylic acid (PAA). Specifically, polyolefins include one or more of polyethylene, polypropylene, ethylene / propylene copolymer, ethylene / vinylidene fluoride copolymer, and propylene / vinylidene fluoride copolymer; polytetrafluoroethylene and its copolymers may be at least one of tetrafluoroethylene / ethylene copolymer, tetrafluoroethylene / propylene copolymer, tetrafluoroethylene / vinylidene fluoride copolymer, tetrafluoroethylene / ether copolymer, tetrafluoroethylene / branched polyether copolymer, tetrafluoroethylene / vinyl ether copolymer, tetrafluoroethylene / branched polyether / vinyl ether copolymer, and tetrafluoroethylene / siloxane copolymer.

[0052] In the embodiments of this application, the conductive agent in the electrode active layer and the conductive agent in the adhesive layer can be conventional conductive materials in the art. For example, the conductive agent in the electrode active layer and the conductive agent in the adhesive layer can each independently include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0053] The embodiments of this application may employ conventional electrode current collectors in the art; for example, the negative electrode current collector may include copper foil.

[0054] For example, in a specific implementation, a negative electrode current collector (such as copper foil) with a base coat can be used, that is, the surface of the negative electrode current collector has a base coat. Then, the negative electrode film used to form the negative electrode active layer is pressed onto the negative electrode current collector. That is, the negative electrode film is bonded to the negative electrode current collector through the base coat to obtain the negative electrode sheet (the base coat forms the bonding layer of the negative electrode sheet).

[0055] In this embodiment, the electrode sheet can be prepared by a dry process (i.e., rolling the material used to form the negative electrode active layer into a film and then combining it with the negative electrode current collector to obtain the negative electrode sheet), or by a wet process (coating method) (i.e., coating the electrode slurry used to form the electrode active layer onto the surface of the electrode current collector, and after drying, rolling, and other processes, forming the electrode active layer on the surface of the electrode current collector to obtain the electrode sheet). The number of rolling cycles and the process parameters of the rolling process in the dry or wet process can be adjusted to form an electrode active layer with a preset air permeability value G and surface roughness Ra. These adjustment methods are conventional in the art and are not particularly limited, as long as the formed electrode active layer achieves the preset air permeability value G and surface roughness Ra. Relatively speaking, the dry process for preparing the electrode sheet eliminates the need for solvents and drying, offering advantages such as environmental friendliness and low cost.

[0056] In one specific embodiment of this application, the electrode sheet is prepared by a dry process, which may include the following steps: air-milling a mixture containing electrode active material and binder to obtain composite powder; calendering the composite powder into a film (roll forming film) to obtain a self-supporting film (electrode film); and pressing the self-supporting film with an electrode current collector to obtain the electrode sheet.

[0057] The conditions for air jet milling can be: pressure of 0.1MPa to 0.8MPa, for example 0.3MPa.

[0058] In practice, materials used to form the electrode active layer, such as electrode active materials, binders, and conductive agents, can be mixed (dry mixing) by grinding or other methods. Specifically, they can be added to conventional grinding equipment for dry mixing to ensure uniform mixing and dispersion, resulting in the aforementioned mixture. The mixture is then added to an air jet mill (or fiberization equipment, or high-speed pulverizer) for air jet milling. During the air jet milling process, further dispersion and fiberization of polymers such as binders are carried out, allowing the polymers to form a network to fix the electrode active material particles, resulting in a composite powder. Subsequently, the composite powder can be rolled at least once, for example, once (i.e., rolling the composite powder to obtain an electrode film) or multiple times (or multi-stage calendering treatment (such as the first calendering, second calendering, etc. below)) to calender it into a film, obtaining a self-supporting film. The self-supporting film is then bonded to an electrode current collector (specifically, an electrode current collector with a base coating on its surface) and hot-rolled using a roller press to composite the self-supporting film with the electrode current collector, thus obtaining an electrode sheet. In some embodiments, the process of calendering composite powder into a film includes: first calendering the composite powder to form an initial film; then subjecting the initial film to at least one subsequent calendering, for example, performing one subsequent calendering or performing two subsequent calenderings in sequence (i.e., performing a second calendering and a third calendering in sequence) to obtain a self-supporting film.

[0059] In the preparation of the self-supporting film, two rollers with a gap are used in each rolling process. The two rollers rotate in opposite directions (one roller rotates clockwise and the other counterclockwise). During the rolling process, the composite powder passes through the gap between the two rollers and is thus extruded into a film. For example, in the process of preparing a self-supporting film through a single rolling process, the composite powder passes through the gap between the two rollers and is extruded to form a self-supporting film with a preset compaction density and other characteristics. As another example, in the process of preparing a self-supporting film through multi-stage calendering, in the first calendering process, the composite powder passes through the gap between the two rollers and is extruded by the two rollers to form an initial film. In the second calendering process, the initial film passes through the gap between the two rollers and is extruded by the two rollers, thereby further controlling the areal density, compaction density, and other characteristics of the formed self-supporting film to form a self-supporting film with preset areal density, compaction density, and other characteristics.

[0060] In practice, the compaction density, air permeability G, surface roughness Ra, and other characteristics of the electrode coating in the produced electrode sheet can be controlled by adjusting the gap size (gap width) between the two rollers during the calendering process, the differential speed of the two rollers (the ratio of the rotational speed of one roller to the rotational speed of the other roller (i.e., speed ratio)), and the roller pressure (pressure of the two rollers). These control methods are all conventional operations in the field and are not particularly limited.

[0061] For example, in the preparation process of the self-supporting membrane, the roll gap width can be 80μm to 250μm, such as 80μm, 100μm, 120μm, 140μm, 160μm, 180μm, 200μm, 220μm, 240μm, 250μm or any combination thereof, and the differential speed (speed ratio) between the two rolls can be 1:(1.2 to 3.5), such as 1:1.2, 1:1.3, 1:1.4. The range is 1:1.6, 1:1.8, 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8, 1:3, 1:3.3, 1:3.5, or any two of these ranges. The rolling pressure can be 8 to 35 tons (t), for example, 8t, 10t, 12t, 14t, 16t, 18t, 20t, 22t, 24t, 26t, 28t, 30t, 33t, 35t, or any two of these ranges.

[0062] In another embodiment of this application, the electrode sheet is prepared by a wet process, and the preparation method may include the following steps: coating an electrode paste for forming the electrode active layer onto at least one side surface of the electrode current collector to form the electrode active layer, thereby obtaining the electrode sheet.

[0063] In practice, materials used to form the electrode active layer, such as electrode active material, conductive agent, and binder, can be placed in a solvent and dispersed evenly to obtain an electrode slurry. The electrode slurry is then coated onto the surface of the electrode current collector and dried using drying equipment such as an oven to remove the solvent, thus obtaining the electrode precursor. Then, conventional rolling equipment is used to roll the electrode precursor under certain pressure and roller gap conditions. Finally, the rolled electrode precursor is cut into sheets (i.e., cut to the preset size) to obtain the electrode sheet.

[0064] Generally, during the rolling process, two rollers are used for rolling, with a gap between them (roller gap). The two rollers rotate in opposite directions (one roller rotates clockwise and the other rotates counterclockwise). During the rolling process, the electrode precursor passes through the gap between the two rollers and is squeezed by them to achieve the rolling treatment of the electrode precursor.

[0065] In practice, the compaction density, air permeability G, surface roughness Ra, and other characteristics of the electrode active layer in the electrode sheet can be controlled by adjusting the number of rolling cycles, the gap size between the two rollers, and the differential speed of the two rollers (the ratio of the rotation speed of one roller to the rotation speed of the other roller). These control methods are all conventional operations in the field and are not particularly limited.

[0066] In the embodiments of this application, unless otherwise specified, the coating, drying, rolling and other processes involved are all conventional operations in the art, and the equipment used can be conventional equipment in the art, and there are no special restrictions on them.

[0067] Secondly, embodiments of this application provide a negative electrode sheet, including a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector; 0.8≤20352 / G-238×OI / G≤5.5; 3000s≤G≤18000s; OI≤60; wherein, OI=I (004) / I (110) I (004) I represents the intensity of the characteristic peak (004) in the X-ray diffraction pattern of the negative electrode active layer. (110) G is the intensity of the characteristic peak (110) in the X-ray diffraction pattern of the negative electrode active layer, and G is the air permeability value of the negative electrode active layer, with the unit of G being seconds. The air permeability value of the negative electrode active layer is measured according to the following process: a 20cm² area is selected from the negative electrode sheet. 2 ±5cm 2The test area is defined, and the negative electrode current collector of the test area is controlled such that one side of the surface has the negative electrode active layer and the other side is an empty foil area. The negative electrode current collector of the test area is distributed with pores of 30μm±3μm with a pore spacing of 100μm±5μm. Then, a membrane with a thickness of 14μm±2μm and a porosity of 40%±5% is respectively covered on both sides of the test area in the thickness direction. Then, the time it takes for 100mL±5mL of air to pass through the test area covered by the membrane under a pressure of 1.21KPa±0.1KPa is tested, which is the air permeability value of the negative electrode active layer.

[0068] By synergistically regulating the OI value and permeability G of the negative electrode active layer to satisfy 0.8≤20352 / G-238×OI / G≤5.5, 3000s≤G≤18000s, and OI≤60, the kinetic performance of the battery can be effectively improved, as well as its rate performance, fast charging performance, and other electrochemical properties.

[0069] According to the inventors' research, the permeability value G represents the ease with which gas can pass through the porous structure of the negative electrode sheet. The permeability value G is negatively correlated with the permeability of the negative electrode sheet. Specifically, the higher the permeability value, the greater the obstacle to gas passing through the negative electrode sheet, which is not conducive to electrolyte wetting and will reduce ion conductivity. During high-rate charging of the battery, problems such as lithium plating are more likely to occur, affecting the battery's dynamic performance. The lower the permeability value, the smaller the obstacle to gas passing through the negative electrode sheet, which is conducive to electrolyte wetting and can improve ion conductivity and battery dynamic performance. However, if the permeability value is too low, it will also damage the conductive network of the negative electrode active layer to a certain extent, affecting the battery's dynamic performance.

[0070] Furthermore, according to the inventors' research, the OI value of the negative electrode active layer is mainly related to the orientation degree of the negative electrode active material in the negative electrode active layer. The smaller the OI value of the negative electrode active layer, the more isotropic it tends to be. The higher the proportion of negative electrode active material with the layer structure perpendicular to the electrode sheet, the better it is to reduce the diffusion distance of ions from the separator side to the current collector side, and the better it is to facilitate the diffusion of lithium ions in the negative electrode active layer.

[0071] Therefore, by synergistically regulating the permeability values ​​G and OI of the negative electrode active layer to meet the above-mentioned range, the pore structure of the negative electrode active layer and the orientation (degree of orientation) of the negative electrode active material in the negative electrode active layer can be synergistically regulated, thereby improving the dynamic performance of the battery and enhancing its rate performance and fast charging performance. Specifically, this can be manifested in that the ratio of the battery's discharge capacity at a 3C rate to its discharge capacity at a 0.33C rate (or the 3C capacity retention rate) is greater than or equal to 82%, for example, greater than or equal to 83% or greater than or equal to 84%.

[0072] For example, 20352 / G-238×OI / G can be a range consisting of 0.8, 0.82, 0.83, 0.84, 0.87, 0.89, 0.92, 0.95, 0.98, 1, 1.4, 1.7, 2, 2.2, 2.5, 3, 3.5, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.7, 5, 5.2, 5.5, or any two of these values. For example, G can be a range of 3000s, 3100s, 3200s, 3300s, 3400s, 3500s, 3700s, 4000s, 4300s, 4500s, 5000s, 6000s, 6600s, 7000s, 7400s, 8000s, 9000s, 10000s, 12000s, 13000s, 14000s, 14500s, 15000s, 16000s, 17000s, 18000s, or any two of these values.

[0073] For example, the OI can be less than or equal to 60, or less than or equal to 50, or less than or equal to 40, or less than or equal to 35, or less than or equal to 30, or less than or equal to 25, or less than or equal to 20, or less than or equal to 15, or a range consisting of any two of the aforementioned values.

[0074] In some embodiments, 1≤20352 / G-238×OI / G≤4.2, which is beneficial for further improving the rate performance and other properties of the battery.

[0075] In some embodiments, 4500s≤G≤14500s is beneficial to further improve the rate performance and other properties of the battery. The reason for this is that by further controlling G within this range, the negative electrode active layer can have a more suitable pore structure and conductive network, thereby improving the ion conductivity and further enhancing the rate performance and other properties of the battery.

[0076] In some embodiments, 9≤OI≤35 is beneficial for the negative electrode active material in the negative electrode active layer to have more suitable orientation and other characteristics, thereby further improving the rate performance and other properties of the battery.

[0077] Specifically, the negative electrode active layer includes negative electrode active material. The OI value of the negative electrode active layer represents the orientation degree of the negative electrode active material in the negative electrode active layer. The OI value of the negative electrode active layer can also be called the OI value of the negative electrode active material in the negative electrode active layer.

[0078] Typically, the negative electrode active layer includes a negative electrode active material, wherein the particle size D of the negative electrode active material is... 50 The range is 5μm-25μm.

[0079] Generally, the mass percentage of the negative electrode active material in the negative electrode active layer can be 80% to 100%, for example (but not limited to) 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 100%, or any combination thereof.

[0080] Specifically, the negative electrode active material may include graphite. In addition, the negative electrode active material may include or exclude other lithium-intercalation / deintercalation-capable negative electrode active materials, specifically including other carbon-based active materials, silicon-based active materials, and Li4Ti5O. 12 One or more of the following: tin alloy, tin, germanium, and indium.

[0081] Specifically, other carbon-based active materials may include one or more of the following: non-graphitized carbon or carbon or pyrolytic carbon, coke, sintered organic polymers, activated carbon, etc., obtained by high-temperature oxidation of polyyne polymers.

[0082] In some embodiments, other carbon-based active materials besides graphite may include one or more of graphene, mesophase microcarbon spheres, hard carbon, soft carbon, etc.

[0083] Specifically, silicon-based active materials may include silicon (Si), silicon alloys, and silicon-oxygen materials (SiO2). x Silicon-carbon materials (Si-C), silicon-oxygen-carbon materials (SiO) x One or more of -C).

[0084] In some embodiments, the mass percentage of graphite in the negative electrode active layer (i.e., the mass ratio of graphite in the negative electrode active layer) can be 50% to 99%, for example (but not limited to) 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or any combination thereof.

[0085] In some specific embodiments, the negative electrode active material is graphite (in this case, the negative electrode sheet is a graphite negative electrode), and the mass percentage of graphite in the negative electrode active layer can be 80% to 100%, for example (but not limited to) 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 100%, or any combination thereof. This allows for a sufficient amount of negative electrode active material in the negative electrode active layer, which is beneficial for the performance of the negative electrode and also helps to improve the energy density of the battery.

[0086] In other specific embodiments, the negative electrode active material includes graphite, and in addition to graphite, it also includes one or more other negative electrode active materials such as silicon-based active materials, graphene, mesophase micro carbon spheres, hard carbon and soft carbon. The mass percentage of graphite in the negative electrode active layer can be 50% to 99%, for example (but not limited to) 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99% or any two of these ranges. The mass percentage of other negative electrode active materials in the negative electrode active layer besides graphite can be 1% to 50%, for example (but not limited to) 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any two of these ranges. This approach helps to balance the ion and electron diffusion rates of the negative electrode and the electrolyte's liquid retention capacity while maintaining a high energy density in the battery, thereby improving the battery's fast charging performance, rate performance, and cycle performance.

[0087] In some embodiments, the particle size D of the negative electrode active material 50 The particle size can be 5μm-25μm, such as 5μm, 8μm, 10μm, 13μm, 15μm, 18μm, 20μm, 23μm, 25μm, or any combination thereof. This range is beneficial for further improving the rate performance and fast charging performance of the battery. The reason for this is that by controlling the particle size D of the negative electrode active material... 50 Within the aforementioned range, it is beneficial to achieve a larger compaction density of the negative electrode active material layer, while also controlling the deintercalation / intercalation path of active ions in the negative electrode sheet within a suitable length range, which is conducive to the transport of ions and electrons, thereby further improving the rate performance and fast charging performance of the negative electrode sheet.

[0088] In some specific embodiments, the particle size D of the graphite 50 It can be 5μm-25μm, for example, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm or any combination thereof.

[0089] In the embodiments of this application, graphite may include one or more of natural graphite, artificial graphite, and modified graphite; wherein, modified graphite includes, but is not limited to, oxidation-modified graphite and / or halogenated graphite, and halogenated graphite may include graphite modified by at least one element selected from fluorine, chlorine, bromine and iodine, such as fluorinated graphite (i.e., fluorine-modified graphite).

[0090] In general, to improve the structural stability and conductivity of the negative electrode active layer, the negative electrode active layer may also include a binder and a conductive agent.

[0091] In some embodiments, the mass percentage of the binder in the negative electrode active layer can be 1% to 5%, for example, 1%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or any combination thereof. By controlling the binder content in the negative electrode active layer within the above range, it is beneficial to improve the structural stability of the negative electrode sheet, while not crowding out the content of other components such as the negative electrode active material, thus facilitating the improvement of the overall performance of the negative electrode sheet.

[0092] In some embodiments, the mass percentage of the conductive agent in the negative electrode active layer can be 0.1% to 20%, for example, a range of 0.1%, 1%, 3%, 5%, 7%, 10%, 13%, 15%, 18%, 20%, or any combination thereof.

[0093] In some embodiments, the areal density of the negative electrode active layer of the negative electrode sheet can be 100 g / m². 2 ~500g / m 2 For example, 100g / m 2 150g / m 2 180g / m 2 200g / m 2 220g / m 2 250g / m 2 280g / m 2 300g / m 2 320g / m 2 350g / m 2 380g / m 2 400g / m 2 420g / m 2 450g / m 2 500g / m 2 The range of either or both of these results in a negative electrode with a high areal density, which is beneficial for improving the energy density of the negative electrode and enhancing its performance. At the same time, it helps to maintain a high diffusion capacity of active ions in the negative electrode and improve its kinetic performance.

[0094] In some embodiments, the compaction density of the negative electrode active layer of the negative electrode sheet can be 1.0 g / cc to 1.8 g / cc, for example, 1 g / cc, 1.2 g / cc, 1.4 g / cc, 1.5 g / cc, 1.6 g / cc, 1.8 g / cc or any combination thereof. In this way, the negative electrode sheet has a high areal density, which is beneficial to improving the energy density of the negative electrode sheet and to maximizing the performance of the negative electrode. At the same time, it is also beneficial to maintain a high diffusion capacity of active ions in the negative electrode sheet and improve the kinetic performance of the negative electrode sheet.

[0095] In some embodiments, an adhesive layer may be provided between the negative electrode active layer and the negative electrode current collector. The adhesive layer may include an adhesive and a conductive agent. The mass percentage of the conductive agent in the adhesive layer may be 90% to 99%, for example, 90%, 92%, 94%, 96%, 98%, 99%, or any combination thereof. The mass percentage of the adhesive in the adhesive layer may be 1% to 10%, for example, 1%, 2%, 4%, 6%, 8%, 10%, or any combination thereof. The conductive agent in the adhesive layer may be a conventional conductive material in the art; for example, the conductive agent in the adhesive layer may include carbon black.

[0096] In some embodiments, the thickness of the adhesive layer can be 0.2 to 2 μm, for example, a range of 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm or any two of these.

[0097] Specifically, the adhesive layer between the negative electrode active layer and the negative electrode current collector is mainly used to bond the two layers together, thereby improving the adhesion between them. The thickness of the adhesive layer is generally much smaller than that of the negative electrode active layer, and it has virtually no impact on the OI value and air permeability of the negative electrode active layer. In practice, the air permeability G and OI of the entire coating on either side of the negative electrode current collector can be directly measured, and the test results are the air permeability G and OI of the negative electrode active layer.

[0098] In this embodiment, a negative electrode active layer can be provided on one side of the negative electrode current collector in the thickness direction, or a negative electrode active layer can be provided on both sides of the negative electrode current collector in the thickness direction.

[0099] In the embodiments of this application, the adhesive in the negative electrode coating and the adhesive in the adhesive layer can be any adhesive suitable for negative electrodes known in the art. For example, the adhesive in the negative electrode coating and the adhesive in the adhesive layer can each independently include at least one of polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), tetrafluoroethylene and its copolymers, polyvinylidene fluoride and its copolymers, polyolefins and their copolymers (e.g., polyethylene-polyethylene glycol block copolymers), polyethers and their copolymers (e.g., polyethylene oxide), polyphenylene ethers and their copolymers, polysiloxanes and their copolymers (e.g., polydimethylsiloxane, poly(dimethylsiloxane-co-alkylmethylsiloxane)), polyesters and their copolymers (e.g., polyethylene ester, polyvinyl acetate, polyacrylate), carboxymethyl cellulose, styrene-butadiene latex, nitrile rubber, and polyacrylic acid (PAA). Specifically, polyolefins include one or more of polyethylene, polypropylene, ethylene / propylene copolymer, ethylene / vinylidene fluoride copolymer, and propylene / vinylidene fluoride copolymer; polytetrafluoroethylene and its copolymers may be at least one of tetrafluoroethylene / ethylene copolymer, tetrafluoroethylene / propylene copolymer, tetrafluoroethylene / vinylidene fluoride copolymer, tetrafluoroethylene / ether copolymer, tetrafluoroethylene / branched polyether copolymer, tetrafluoroethylene / vinyl ether copolymer, tetrafluoroethylene / branched polyether / vinyl ether copolymer, and tetrafluoroethylene / siloxane copolymer.

[0100] In the embodiments of this application, the conductive agent in the negative electrode active layer and the conductive agent in the adhesive layer can be conventional conductive materials in the art. For example, the conductive agent in the negative electrode active layer and the conductive agent in the adhesive layer can each independently include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0101] The embodiments of this application may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors may include copper foil.

[0102] For example, in a specific implementation, a negative electrode current collector (such as copper foil) with a base coat can be used, that is, the surface of the negative electrode current collector has a base coat. Then, the negative electrode film used to form the negative electrode active layer is pressed onto the negative electrode current collector. That is, the negative electrode film is bonded to the negative electrode current collector through the base coat to obtain the negative electrode sheet (the base coat forms the bonding layer of the negative electrode sheet).

[0103] In the embodiments of this application, the negative electrode sheet can be prepared by a dry process (i.e., rolling the material used to form the negative electrode active layer into a film and then compounding it with the negative electrode current collector to obtain the negative electrode sheet), or by a wet process (coating method) (i.e., coating the negative electrode slurry used to form the negative electrode active layer onto the surface of the negative electrode current collector, and then drying, rolling, and other processes to form the negative electrode active layer on the surface of the negative electrode sheet to obtain the negative electrode sheet). The negative electrode active layer with a preset air permeability value G and OI can be formed by adjusting the number of rolling cycles and the process parameters of the rolling process in the dry or wet process. These adjustment methods are all conventional operations in the art and are not particularly limited, as long as the formed negative electrode active layer achieves the preset air permeability values ​​G and OI. Relatively speaking, the dry process for preparing electrode sheets does not require the use of solvents or drying treatment, and has advantages such as being more environmentally friendly and cost-effective.

[0104] In one specific embodiment of this application, the negative electrode sheet is prepared by a dry process, which may include the following steps: air-milling a mixture containing negative electrode active material and binder to obtain composite powder; calendering the composite powder into a film (roll pressing film) to obtain a self-supporting film (negative electrode film); and pressing the self-supporting film with a negative electrode current collector to obtain the negative electrode sheet.

[0105] The conditions for air jet milling can be: pressure of 0.1MPa to 0.8MPa, for example 0.3MPa.

[0106] In practice, the negative electrode active material, binder, and conductive agent, etc., used to form the negative electrode active layer, can be mixed by grinding (dry mixing). Specifically, they can be added to conventional grinding equipment for dry mixing to ensure uniform mixing and dispersion, thus obtaining the above mixture. Then, the mixture is added to an air jet mill (or fiberization equipment, or high-speed pulverizer) for air jet milling. During the air jet milling process, further dispersion and fiberization of the polymers such as binders are carried out, allowing the polymers such as binders to form a network to fix the negative electrode active material. Material particles are processed to obtain composite powder. Subsequently, the composite powder can be rolled at least once, for example, once (i.e., the composite powder is rolled to obtain a negative electrode film) or multiple times (or multi-stage calendering process (such as the first calendering, second calendering, etc. below)) to calender it into a film to obtain a self-supporting film. The self-supporting film is then bonded to a negative electrode current collector (specifically, a negative electrode current collector with a base coating on its surface) and hot rolled by a rolling mill to composite the self-supporting film with the negative electrode current collector, thereby obtaining a negative electrode sheet.

[0107] In some embodiments, the process of calendering composite powder into a film includes: first calendering the composite powder to form an initial film; then subjecting the initial film to at least one subsequent calendering, for example, performing one subsequent calendering or performing two subsequent calenderings in sequence (i.e., performing a second calendering and a third calendering in sequence) to obtain a self-supporting film.

[0108] In the preparation of the self-supporting film, two rollers with a gap are used in each rolling process. The two rollers rotate in opposite directions (one roller rotates clockwise and the other counterclockwise). During the rolling process, the composite powder passes through the gap between the two rollers and is thus extruded into a film. For example, in the process of preparing a self-supporting film through a single rolling process, the composite powder passes through the gap between the two rollers and is extruded to form a self-supporting film with a preset compaction density and other characteristics. As another example, in the process of preparing a self-supporting film through multi-stage calendering, in the first calendering process, the composite powder passes through the gap between the two rollers and is extruded by the two rollers to form an initial film. In the second calendering process, the initial film passes through the gap between the two rollers and is extruded by the two rollers, thereby further controlling the areal density, compaction density, and other characteristics of the formed self-supporting film to form a self-supporting film with preset areal density, compaction density, and other characteristics.

[0109] In practice, the compaction density, air permeability G, OI value, and other characteristics of the negative electrode coating in the produced negative electrode sheet can be controlled by adjusting the gap size (roll gap width) between the two rolls during the calendering process, the differential speed of the two rolls (the ratio of the rotational speed of one roll to the rotational speed of the other roll (i.e., speed ratio)), and the roll pressure (pressure of the two rolls). These control methods are all conventional operations in the field and are not particularly limited.

[0110] For example, in the preparation process of the self-supporting membrane, the roll gap width can be 80μm to 250μm, such as 80μm, 100μm, 120μm, 140μm, 160μm, 180μm, 200μm, 220μm, 240μm, 250μm or any combination thereof, and the differential speed (speed ratio) between the two rolls can be 1:(1.2 to 3.5), such as 1:1.2, 1:1.4, 1:1 The range is 6, 1:1.8, 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8, 1:3, 1:3.3, 1:3.5 or any two of them, and the rolling pressure can be 8 to 35 tons (t), for example, 8t, 10t, 12t, 14t, 16t, 18t, 20t, 22t, 24t, 26t, 28t, 30t, 33t, 35t or any two of them.

[0111] In another embodiment of this application, the negative electrode sheet is prepared by a wet process, and the preparation method may include the following steps: coating a negative electrode slurry for forming the negative electrode active layer onto at least one side surface of the negative electrode current collector to form the negative electrode active layer, thereby obtaining the negative electrode sheet.

[0112] In practice, materials used to form the negative electrode active layer, such as negative electrode active material, conductive agent, and binder, can be placed in a solvent and dispersed evenly to obtain a negative electrode slurry. The negative electrode slurry is then coated on the surface of the negative electrode current collector and dried using drying equipment such as an oven to remove the solvent, thus obtaining the electrode precursor. Then, conventional rolling equipment is used to roll the electrode precursor under certain pressure and roller gap conditions. Finally, the rolled electrode precursor is cut into sheets (i.e., cut to a preset size) to obtain the negative electrode sheet.

[0113] Generally, during the rolling process, two rollers are used for rolling, with a gap between them (roller gap). The two rollers rotate in opposite directions (one roller rotates clockwise and the other rotates counterclockwise). During the rolling process, the electrode precursor passes through the gap between the two rollers and is squeezed by them to achieve the rolling treatment of the electrode precursor.

[0114] In practice, the compaction density, air permeability G, and OI of the negative electrode active layer in the obtained negative electrode sheet can be controlled by adjusting the number of rolling cycles, the gap size between the two rollers, and the differential speed of the two rollers (the ratio of the rotation speed of one roller to the rotation speed of the other roller). These control methods are all conventional operations in the field and are not particularly limited.

[0115] In the embodiments of this application, unless otherwise specified, the coating, drying, rolling and other processes involved are all conventional operations in the art, and the equipment used can be conventional equipment in the art, and there are no special restrictions on them.

[0116] Thirdly, embodiments of this application also provide a battery, including the above-described electrode sheet or an electrode sheet prepared according to the above-described electrode sheet preparation method. This battery has advantages corresponding to the above-described electrode sheet, which will not be elaborated further.

[0117] Fourthly, embodiments of this application also provide a battery, including the negative electrode sheet provided in the second aspect above or a negative electrode sheet prepared according to the method for preparing the negative electrode sheet in the second aspect above. This battery has advantages corresponding to the negative electrode sheet provided in the second aspect above, which will not be elaborated further.

[0118] In some embodiments, the battery described above may be a lithium-ion battery.

[0119] Generally, a battery includes an electrolyte, a battery cell, and a casing that encapsulates the battery cell. The electrolyte is injected into the battery cell inside the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of stacked positive electrode, separator, and negative electrode, which are then wound together.

[0120] In some embodiments, the electrode sheet described above is a positive electrode sheet.

[0121] The positive electrode in the battery may include a positive current collector and a positive active layer located on at least one side surface of the positive current collector. Specifically, the positive active layer may be provided on one side surface of the positive current collector in the thickness direction, or positive active layers may be provided on both opposite sides surface of the positive current collector in the thickness direction.

[0122] Specifically, the positive electrode active layer may include a positive electrode active material, a conductive agent, and a binder. In the positive electrode active layer, the mass percentage of the positive electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof. The mass fraction of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof. The mass fraction of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0123] In some embodiments, the positive electrode active material may include LiCoO2, LiNiO2, or LiCo. x Ni 1-x O2 (0≤x≤1), LiCo x Ni 1-x-y Al y O2(0≤x≤1,0≤y≤1), LiMn2O4, LiFe x Mn y M z O4 (M is one or more of Al, Mg, Ga, Cr, Co, Ni, Cu, Zn or Mo, 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1), Li 1+x L 1－y－z M y N zO2 (L, M, N are one or more of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S, B, -0.1≤x≤0.2, 0≤y≤1, 0≤z≤1, 0≤y+z≤1), LiFePO4, Li3V2(PO4)3, Li3V3(PO4)3, LiVPO4F, Li2CuO2, Li5FeO4, and metal sulfides and oxides (such as TiS2, V2S3, FeS, FeS2, LiMS) x (M is at least one of the transition metal elements such as Ti, Fe, Ni, Cu, Mo, etc., 1≤x≤2.5), TiO2, Cr3O8, V2O5, MnO2, etc.

[0124] In the embodiments of this application, the conductive agent in the positive electrode active layer can be a conventional conductive material in the art. For example, the conductive agent in the positive electrode active layer may include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0125] In this embodiment, the binder in the positive electrode active layer can be a conventional adhesive material in the art. For example, the binder in the positive electrode active layer may include one or more of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0126] The embodiments of this application may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0127] In this embodiment, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, binder, and other components used to form the positive electrode active layer can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0128] The electrolyte in this application embodiment can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), diethyl carbonate (DEC) and propylene carbonate (PC). Additives include, for example, fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Electrolyte salts may include lithium salts, such as lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0129] In this embodiment, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. Conventional separators in the art can be used in this embodiment, and there are no special restrictions.

[0130] In this embodiment, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited to these.

[0131] The embodiments of this application can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked in an alternating manner to obtain a stacked cell (or wound into a wound cell); then the cell is placed in a casing (outer packaging) and after conventional processes such as electrolyte injection (i.e., injection of electrolyte) and encapsulation, a battery is obtained.

[0132] This application also provides a battery pack including the above-described battery, which has advantages corresponding to the above-described negative electrode sheet, and will not be described in detail here.

[0133] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0134] This application also provides an electrical device, including the battery or battery pack described above. This electrical device has advantages corresponding to the negative electrode sheet described above, which will not be elaborated further.

[0135] The electrical equipment used in the embodiments of this application can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no special limitations on this.

[0136] In this embodiment, the surface roughness Ra of the electrode coating can be measured according to GB / T 1031-2009, specifically using the stylus method. The specific testing process for the surface roughness Ra of the electrode coating is as follows: the electrode sample is fixed on a metal plate, and the surface of the active layer of the electrode to be tested is positioned away from the metal plate. The surface roughness of the negative electrode material layer is then tested according to GB / T 1031-2009. Specifically, surface roughness Ra refers to the arithmetic mean deviation of the profile, which is the arithmetic mean of the absolute values ​​of the profile deviations within the sample (electrode sample) length. Understandably, in practical applications, the electrode generally includes an electrode current collector and an active electrode layer disposed on the surface of the current collector. In this case, the electrolyte mainly enters and diffuses into the active electrode layer from the pore structure of the surface of the active electrode layer away from the current collector, achieving wetting and liquid retention effects. Therefore, when the electrode has an electrode current collector, the surface of the active electrode layer is the surface away from the current collector; the aforementioned Ra specifically refers to the surface roughness of the side of the active electrode layer away from the current collector.

[0137] In this embodiment, the air permeability value of the electrode active layer refers to the average permeability of 100mL±5mL of air per 20cm at a pressure of 1.21KPa±0.1KPa. 2 ±5cm 2 The time of electrode active layer, and the air permeability value of the electrode active layer were measured according to the following procedure: a 20cm² area was selected from the electrode sheet. 2 ±5cm 2 The test area is defined, and the electrode current collector in the test area is controlled such that one side of the surface has an electrode active layer and the other side is an empty foil area. The electrode current collector in the test area is distributed with pores of 30μm±3μm in diameter at a pore spacing of 100μm±5μm. Then, a membrane with a thickness of 14μm±2μm and a porosity of 40%±5% is respectively covered on both sides of the test area in the thickness direction. Then, the time it takes for 100mL±5mL of air to pass through the test area covered by the membrane under a pressure of 1.21KPa±0.1KPa is measured (the air passes through the membrane covering one side of the test area, the test area, and the membrane covering the other side of the test area in sequence along the thickness direction of the test area). This is the air permeability value G of the electrode active layer.

[0138] Specifically, the permeability of the electrode active layer in the electrode sheet can be measured by referring to the conventional test method of the permeability value of the diaphragm and other samples. The test process is as follows: (1) Sample preparation stage: Cut out an electrode sample with a size of 9.5cm*9.5cm from the electrode sheet, take a 4.5cm*4.5cm area in the center of the electrode sample as the test area, and prepare the test area into a single-sided sheet (i.e., one side of the electrode current collector has an electrode active layer and the other side is an empty foil area (i.e., no electrode active layer). When both the front and back surfaces of the electrode current collector in the electrode sheet have electrode active layers, the electrode active coating on one side of the test area is removed by scraping or other means to form an empty foil area and obtain a single-sided sheet). The local single-sided sheet can ensure the flatness of the electrode sheet. (2) Processing stage: Place the local single-sided sheet in the processing area (workbench), with the empty foil area of ​​the electrode current collector facing upwards. Turn on the vacuum device (vacuum degree -30 to -50) to ensure that the electrode sheet is flat and adsorbed on the workbench without excessive deformation. Use a 20W nanosecond ultraviolet laser to perform negative electrode drilling, ensuring that the laser intensity just penetrates the foil material (i.e., electrode current collector) without damaging the dressing area (i.e., electrode active layer). Adjust according to the current collector. After drilling, the area to be tested will have holes distributed. The hole diameter is 30μm±3μm and the hole spacing is 100μm±5μm. (3) Testing stage: Use Wang Yan's air permeability tester (EG01-55-1MR) to test the air permeability value G. To ensure that there is no material spillage and contamination of the equipment, the permeability value G is measured by sandwiching a perforated single-sided sheet of the current collector between two layers of diaphragm. The diaphragm used is a polypropylene diaphragm (PP diaphragm) with a thickness of about 14μm±2μm and a porosity of about 40%±5%.

[0139] In this embodiment, the surface roughness Ra and air permeability G of the electrode coating of the electrode sheet can be characteristics of the electrode sheet before battery cycling (e.g., the electrode sheet before it is assembled into a battery) or characteristics of the electrode sheet disassembled from the battery after cycling.

[0140] In this embodiment, the particle size D of the electrode active material is... 50 The average particle size D of the electrode active material 50 It refers to the particle size on the particle size distribution curve of the electrode active material, starting from the smallest particle size side and accounting for 50% of the total volume; that is, the particle size D of the electrode active material. 50 This refers to the particle size that accumulates to 50% of the total volume in the particle size distribution of the positive electrode active material, starting from the smallest particle size side. The particle size D of the electrode active material in the test electrode active layer... 50In this case, the electrode active layer can be scraped off from the electrode sheet, and then the solid particulate products can be separated by washing with a solvent (such as water). The particle size D of the electrode active material can then be measured using conventional particle size analyzers or other instruments in the field. 50 In this embodiment, the testing process for the areal density and compaction density of the electrode coating is as follows: Take an electrode sheet sample (specifically, a cutter can be used to cut the electrode sheet to obtain an electrode sheet sample of suitable size), test the total mass m1 of the electrode sheet sample, the total thickness T1 of the electrode sheet sample (T1 = total thickness of the electrode active layer + thickness of the electrode current collector; when the electrode active layer is provided on both the front and back surfaces of the electrode current collector, the total thickness of the electrode active layer = thickness of the electrode active layer on one side of the electrode current collector + thickness of the electrode active layer on the other side of the electrode current collector), and the surface area S of the electrode sheet sample; then scrape off the electrode active layer on the electrode sheet sample, test the mass m2 of the obtained electrode current collector, and the thickness T2 of the electrode current collector, then the total thickness of the electrode active layer = T1 - T2, the areal density of the electrode active layer = (m1 - m2) / S, and the compaction density of the electrode active layer = areal density of the electrode active layer / total thickness of the electrode active layer = (m1 - m2) / (S × (T1 - T2)).

[0141] For the second aspect of the negative electrode, the OI value of the negative electrode active layer in the negative electrode can be measured by X-ray diffraction (XRD). The specific testing process is as follows: The negative electrode is placed in an XRD tester, so that X-rays are incident from the surface of the negative electrode active layer to obtain the X-ray diffraction pattern (XRD pattern) of the negative electrode active layer. The OI value of the negative electrode active layer is obtained according to the characteristic peaks in the XRD pattern that characterize the orientation degree of the negative electrode active material. Specifically, the OI value is the ratio of the intensity of the (004) characteristic peak and the (110) characteristic peak in the X-ray diffraction pattern of the negative electrode active layer, which can be expressed as OI = I (004) / I (110) For anode sheets with graphite as the main negative electrode active material, the OI value reflects the orientation degree of graphite in the negative electrode active layer. Taking a copper target as an example of the X-ray source used in XRD testing, the 2θ of the (004) characteristic peak of graphite is in the range of 53°-56°, and the 2θ of the (110) characteristic peak of graphite is in the range of 76°-79°. If other X-ray sources are used, the 2θ range of the (004) and (110) characteristic peaks of graphite under the corresponding X-ray source can be obtained by substituting the wavelength of the X-ray source into the Bragg diffraction formula.

[0142] In practice, when testing the OI value of the negative electrode active layer using the above method, samples are taken from three different locations on a single negative electrode, and the average value of the OI value is taken.

[0143] In this embodiment, the air permeability value of the negative electrode active layer refers to the average permeability of 100mL±5mL of air per 20cm at a pressure of 1.21KPa±0.1KPa. 2 ±5cm 2 The time of the negative electrode active layer was measured, and the air permeability of the negative electrode active layer was obtained according to the following procedure: A 20cm² area was selected from the negative electrode sheet... 2 ±5cm 2 The test area is defined, and the negative electrode current collector in the test area is controlled to have an electrode active layer on one side and an empty foil area on the other side. The negative electrode current collector in the test area is distributed with pores of 30μm±3μm in diameter at a pore spacing of 100μm±5μm. Then, a membrane with a thickness of 14μm±2μm and a porosity of 40%±5% is respectively covered on both sides of the test area in the thickness direction. Then, the time it takes for 100mL±5mL of air to pass through the test area covered by the membrane under a pressure of 1.21KPa±0.1KPa is measured (the air passes through the membrane on one side of the test area, the test area, and the membrane on the other side of the test area in sequence along the thickness direction of the test area). This is the air permeability value G of the negative electrode active layer.

[0144] Specifically, the air permeability of the negative electrode active layer in the negative electrode sheet can be measured by referring to the conventional test method of the air permeability value of the diaphragm and other samples. The test process is as follows: (1) Sample preparation stage: Cut out an electrode sample with a size of 9.5cm*9.5cm from the negative electrode sheet. Take a 4.5cm*4.5cm area in the center of the electrode sample as the test area. Prepare the test area into a single-sided sheet (i.e., one side of the negative electrode current collector has a negative electrode active layer and the other side is an empty foil area (i.e., it does not have a negative electrode active layer). When both the positive and negative surfaces of the negative electrode current collector in the negative electrode sheet have negative electrode active layers, remove the negative electrode active coating on one side of the test area by scraping or other means to form an empty foil area and obtain a single-sided sheet). The partial single-sided sheet can ensure the flatness of the electrode sheet. The degree is conducive to the consistent focus height of laser drilling in the later stage, and enhances the consistency of electrode drilling; place the local single-sided sheet in the processing area (workbench), with the side of the empty foil area of ​​the electrode current collector facing upward, turn on the vacuum device (vacuum degree -30 to -50), ensure that the electrode is flat and adsorbed on the workbench, and will not be excessively deformed, use a 20W nanosecond ultraviolet laser to drill the negative electrode, and ensure that the laser intensity just penetrates the foil material (i.e., the negative electrode current collector) without damaging the dressing area (i.e., the negative electrode active layer). The specific adjustment can be made according to the current collector. After drilling, the area to be tested is distributed with holes. The hole diameter is 30μm±3μm and the hole spacing is 100μm±5μm; (3) Testing stage: use Wang Yan's air permeability tester (EG01-55-1MR) to test the air permeability value G. To ensure that there is no material spillage that contaminates the equipment, the permeable value G is measured by sandwiching a perforated single-sided sheet between two diaphragms. The diaphragm used is a polypropylene diaphragm (PP diaphragm) with a thickness of about 14μm±2μm and a porosity of about 40%±5%.

[0145] In this embodiment, the characteristics of the negative electrode sheet, such as the OI value and the air permeability value G, can be characteristics of the negative electrode sheet before battery cycling (e.g., the negative electrode sheet before it is assembled into a battery) or characteristics of the negative electrode sheet disassembled from the battery after cycling.

[0146] In this embodiment, the particle size D of the negative electrode active material is... 50 The average particle size D of the negative electrode active material 50 It refers to the particle size on the particle size distribution curve of the negative electrode active material, starting from the smallest particle size side and accounting for 50% of the total volume; that is, the particle size D of the negative electrode active material. 50 This refers to the particle size at which the volume of the positive electrode active material accumulates to 50% from the smallest particle size side in the particle size distribution. The particle size D of the negative electrode active material in the negative electrode active layer is also considered. 50 At this time, the negative electrode active layer can be scraped off from the negative electrode sheet, and then the solid particulate products can be separated by washing with a solvent (such as water). The particle size D of the negative electrode active material can then be measured using conventional particle size analyzers or other instruments in the field.50 .

[0147] In this embodiment, the testing process for the areal density and compaction density of the electrode coating is as follows: Take a negative electrode sample (specifically, a cutter can be used to cut the negative electrode to obtain a negative electrode sample of suitable size), and test the total mass m1 and total thickness T1 of the negative electrode sample (T1 = total thickness of the negative electrode active layer + thickness of the negative electrode current collector; when both the positive and negative surfaces of the negative electrode current collector are provided with negative electrode active layers, the total thickness of the negative electrode active layer = thickness of the negative electrode active layer on one side of the negative electrode current collector + thickness of the negative electrode active layer on the other side of the negative electrode current collector). The thickness of the negative electrode active layer on the other side of the current collector), the surface area S on one side of the negative electrode sample in the thickness direction; then scrape off the negative electrode active layer on the negative electrode sample, test the mass m2 of the negative electrode current collector, and the thickness T2 of the negative electrode current collector, then the total thickness of the negative electrode active layer = T1-T2, the areal density of the negative electrode active layer = (m1-m2) / S, the compaction density of the negative electrode active layer = areal density of the negative electrode active layer / total thickness of the negative electrode active layer = (m1-m2) / (S×(T1-T2)).

[0148] The present application will be further described below through specific embodiments.

[0149] Example 1

[0150] 1. Preparation of positive electrode sheet

[0151] Lithium iron phosphate, conductive carbon black, and PVDF were mixed in a mass ratio of 92:6:2, and NMP was added to prepare a positive electrode slurry.

[0152] The positive electrode slurry is coated on both sides of the aluminum foil, and after drying and rolling, the positive electrode sheet is obtained.

[0153] 2. Preparation of negative electrode sheet

[0154] Graphite, conductive carbon black, and PTFE were mixed in a mass ratio of 97:1:2. The resulting mixture was then fed into an air jet mill for air jet milling to obtain composite powder. The air jet milling conditions were: pressure 0.3 MPa and time 30 min.

[0155] The composite powder is rolled to obtain a self-supporting diaphragm; the conditions for rolling (roller gap width, speed difference (speed ratio) between the two rollers, and pressure of the two rollers) are shown in Table 1.

[0156] A self-supporting film is bonded to a negative electrode current collector (copper foil) with a primer coating, and then hot-rolled using a roller press to fuse the self-supporting film and the negative electrode current collector into a single unit, thus producing a negative electrode sheet. The negative electrode current collector has primer coatings on both its front and back surfaces, and a self-supporting film is bonded to each side (i.e., both sides of the negative electrode current collector have a negative electrode active layer). The primer coating (adhesive layer) is composed of conductive carbon black and PAA in a mass ratio of 94:6, and the thickness of the adhesive layer is approximately 1 μm. The areal density of the negative electrode active layer in the negative electrode sheet is 200 g / m³. 2 .

[0157] 3. Assembly of lithium-ion batteries

[0158] The positive electrode, separator (PP separator) and negative electrode are made into a stacked cell; the stacked cell is placed in an aluminum-plastic film and assembled into a lithium-ion battery through processes such as electrolyte injection and encapsulation; the electrolyte used is composed of LiPF6, EC, DEC and VC in a mass ratio of 12:26:60:2.

[0159] Examples 2-13 and Comparative Examples 1-5 differ from Example 1 in that the air permeability G of the negative electrode active layer, the surface roughness Ra of the negative electrode active layer, the value of 15830×Ra / G-1301 / G, and the gap width and differential speed of the two rollers during the rolling process in the preparation of the negative electrode sheet are different, as detailed in Table 1. Except for the differences shown in Table 1, the other conditions are the same. In all examples and comparative examples, the compaction density of the negative electrode active layer in the negative electrode sheet is 1.5 g / cc.

[0160] Example 14: The difference from Example 1 is that the negative electrode current collector used is copper foil without a primer coating, and the preparation process of the negative electrode sheet is different; all other conditions are the same as in Example 1. The preparation process of the negative electrode sheet in Example 14 is as follows:

[0161] Artificial graphite, conductive carbon black, SBR, and CMC were mixed in a mass ratio of 97:1:1.2:0.8, and deionized water was added to prepare a negative electrode slurry.

[0162] The negative electrode slurry is coated onto both sides of a copper foil and dried to obtain the electrode precursor. The electrode precursor is then subjected to two rolling processes to achieve a target compaction density of 1.5 g / cc, and then cut into negative electrode sheets of a predetermined size. The thickness difference between the two rolling processes (i.e., the difference between the thickness of the electrode precursor after the first rolling and the thickness after the second rolling) is approximately 8 μm. The roll gap width is 90 μm in both rolling processes, and the rolling pressure is 20 t in both processes. The areal density of the negative electrode active layer in the negative electrode sheet is 200 g / m³. 2 .

[0163] The rate performance of the batteries in each embodiment and comparative example was tested through the following process, and the results are shown in Table 1: At 25°C, the battery was fully charged at 0.33C and then discharged at 0.33C, and the discharge capacity Q1 was measured; then the battery was fully charged at 0.33C and then discharged at 3C, and the discharge capacity Q2 was measured. The ratio of the discharge capacity Q2 at 3C to the discharge capacity Q1 at 0.33C is the capacity retention rate at 3C (i.e., 3C capacity retention rate = Q2 / Q1). The cutoff voltage range during battery charging and discharging is 2V to 3.8V.

[0164] Table 1

[0165] As shown in Table 1, compared to Comparative Examples 1 to 5, Examples 1 to 14, by synergistically controlling the surface roughness Ra and permeability G of the negative electrode active layer to satisfy 0.8≤15830×Ra / G-1301 / G≤12, 3000s≤G≤18000s, and 0.5μm≤Ra≤3μm, can improve the rate performance of the battery (the 3C capacity retention rate of the battery is not less than 82.4%). In particular, Examples 4 to 9 and Example 13, by further controlling 1≤15830×Ra / G-1301 / G≤9, can more significantly improve the rate performance of the battery (the 3C capacity retention rate of the battery is not less than 83.6%).

[0166] The following example further illustrates the impact of the negative electrode sheet provided in the second aspect on the rate performance of the battery.

[0167] Exploration Example 1

[0168] 1. Preparation of positive electrode sheet

[0169] Lithium iron phosphate, conductive carbon black, and PVDF were mixed in a mass ratio of 92:6:2, and NMP was added to prepare a positive electrode slurry.

[0170] The positive electrode slurry is coated on both sides of the aluminum foil, and after drying and rolling, the positive electrode sheet is obtained.

[0171] 2. Preparation of negative electrode sheet

[0172] Graphite, conductive carbon black, and PTFE were mixed in a mass ratio of 97:1:2. The resulting mixture was then fed into an air jet mill for air jet milling to obtain composite powder. The air jet milling conditions were: pressure 0.3 MPa and time 30 min.

[0173] The composite powder is rolled to obtain a self-supporting diaphragm; the conditions for rolling (roller gap width, speed difference (speed ratio) between the two rollers, and pressure of the two rollers) are shown in Table 2.

[0174] A self-supporting film is bonded to a negative electrode current collector (copper foil) with a primer coating on its surface, and then hot-rolled using a roller press to fuse the self-supporting film and the negative electrode current collector into a single unit, thus producing a negative electrode sheet. The negative electrode current collector has primer coatings on both its front and back surfaces, and a self-supporting film is bonded to each side (i.e., both sides of the negative electrode current collector have a negative electrode active layer). The primer coating (adhesive layer) is composed of conductive carbon black and PAA in a mass ratio of 94:6, and the thickness of the adhesive layer is approximately 1 μm. The areal density of the negative electrode active layer in the negative electrode sheet is 200 g / m³. 2 .

[0175] 3. Assembly of lithium-ion batteries

[0176] The positive electrode, separator (PP separator) and negative electrode are made into a stacked cell; the stacked cell is placed in an aluminum-plastic film and assembled into a lithium-ion battery through processes such as electrolyte injection and encapsulation; the electrolyte used is composed of LiPF6, EC, DEC and VC in a mass ratio of 12:26:60:2.

[0177] Examples 2 through 12, and comparative examples 1 through 5, differ from Example 1 in that the air permeability (G) of the negative electrode active layer, the OI of the negative electrode active layer, the value of 20352 / G - 238×OI / G, and the gap width, differential speed, and pressure of the two rollers during the negative electrode sheet preparation process are all different, as detailed in Table 2. Except for the differences shown in Table 2, all other conditions are the same. In all examples and comparative examples, the compaction density of the negative electrode active layer in the negative electrode sheet is 1.5 g / cc.

[0178] Example 13 differs from Example 1 in that the negative electrode current collector used is copper foil without a base coating, and the preparation process of the negative electrode sheet is different; all other conditions are the same as in Example 1. The preparation process of the negative electrode sheet in Example 14 is as follows:

[0179] Artificial graphite, conductive carbon black, SBR, and CMC were mixed in a mass ratio of 97:1:1.2:0.8, and deionized water was added to prepare a negative electrode slurry.

[0180] The negative electrode slurry is coated onto both sides of a copper foil and dried to obtain the electrode precursor. The electrode precursor is then subjected to two rolling processes to achieve a target compaction density of 1.5 g / cc, and then cut into negative electrode sheets of a predetermined size. The thickness difference between the two rolling processes (i.e., the difference between the thickness of the electrode precursor after the first rolling and the thickness after the second rolling) is approximately 12 μm. The roll gap width is 80 μm in both rolling processes, and the rolling pressure is 15 t in both processes. The areal density of the negative electrode active layer in the negative electrode sheet is 200 g / m³. 2 .

[0181] The rate performance of the batteries in each experimental and comparative experimental case was tested through the following process, and the results are shown in Table 2: At 25℃, the battery was fully charged at 0.33C and then discharged at 0.33C, and the discharge capacity Q1 was measured; then the battery was fully charged at 0.33C and then discharged at 3C, and the discharge capacity Q2 was measured. The ratio of the discharge capacity Q2 at 3C to the discharge capacity Q1 at 0.33C is the capacity retention rate at 3C (i.e., 3C capacity retention rate = Q2 / Q1). The cutoff voltage range during battery charging and discharging was 2V-3.8V.

[0182] Table 2

[0183] As shown in Table 2, compared to Comparative Examples 1 to 5, in Examples 1 to 13, by synergistically controlling the OI value and permeability G of the negative electrode active layer to satisfy 0.8≤20352 / G-238×OI / G≤5.5, 3000s≤G≤18000s, and OI≤60, the rate performance of the battery can be improved (the 3C capacity retention rate of the battery is not less than 82.2%). In particular, in Examples 6 to 9, by further controlling 1≤20352 / G-238×OI / G≤4.2, the rate performance of the battery can be improved even more significantly (the 3C capacity retention rate of the battery is not less than 84%).

[0184] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An electrode sheet, characterized in that, It includes an electrode current collector and an electrode active layer located on at least one side surface of the electrode current collector; 0.8≤15830×Ra / G-1301 / G≤12; 3000s≤G≤18000s; 0.5μm≤Ra≤3μm; Wherein, Ra is the surface roughness of the electrode active layer, and the unit of Ra is μm; G is the air permeability value of the electrode active layer, and the unit of G is s. The air permeability of the electrode active layer was measured according to the following procedure: a 20cm² area was selected from the electrode sheet. 2 ±5cm 2 The test area is defined, and the electrode current collector of the test area is controlled such that one side of the surface has the electrode active layer and the other side is an empty foil area. The electrode current collector of the test area is distributed with pores of 30μm±3μm with a pore spacing of 100μm±5μm. Then, a membrane with a thickness of 14μm±2μm and a porosity of 40%±5% is respectively covered on both sides of the test area in the thickness direction. Then, the time it takes for 100mL±5mL of air to pass through the test area covered by the membrane under a pressure of 1.21KPa±0.1KPa is measured, which is the air permeability value of the electrode active layer.

2. The electrode sheet according to claim 1, characterized in that, 1≤15830×Ra / G-1301 / G≤9.

3. The electrode sheet according to claim 1, characterized in that, 3400s≤G≤15000s.

4. The electrode sheet according to claim 1, characterized in that, 0.75μm≤Ra≤3μm.

5. The electrode sheet according to claim 1, characterized in that, The areal density of the electrode active layer of the electrode sheet is 100 g / m². 2 ~500g / m 2 .

6. The electrode sheet according to any one of claims 1-5, characterized in that, The compaction density of the electrode active layer of the electrode sheet is 1.0 g / cc to 1.8 g / cc.

7. The electrode sheet according to any one of claims 1-6, characterized in that, The electrode sheet is a negative electrode sheet.

8. The electrode sheet according to any one of claims 1-7, characterized in that, An adhesive layer is provided between the electrode active layer and the electrode current collector, and the thickness of the adhesive layer is 0.2μm to 2μm.

9. A battery, characterized in that, Includes the electrode sheet as described in any one of claims 1-8.

10. The battery according to claim 9, characterized in that, The battery is a lithium-ion battery.

11. A battery pack, characterized in that, Includes the battery as described in claim 9 or 10.

12. An electrical appliance, characterized in that, Includes the battery as described in claim 9 or 10, or the battery pack as described in claim 11.

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