Negative electrode slurry, preparation method thereof, negative electrode sheet, battery cell, battery, and electric device

Abstract

The application provides a negative electrode slurry and a preparation method thereof, a negative electrode sheet, a battery monomer, a battery and an electrical equipment, and relates to the field of batteries. The negative electrode slurry comprises a negative electrode active material, a dispersion stabilizer, a conductive agent, a binder and water. The conductive agent comprises a granular conductive agent and a linear conductive agent. At least part of the linear conductive agent is coated on the surface of the negative electrode active material and the granular conductive agent. The specific surface area of the granular conductive agent is 60 m 2 / g to 300 m 2 / g. The length of the linear conductive agent is 20 mu m to 120 mu m. The tube diameter of the linear conductive agent is not greater than 20 nm. The negative electrode slurry can improve the safety problem of existing batteries caused by cycle expansion during the cycle process, and can also improve the energy density of the battery.

Description

Technical Field

[0001] This application relates to the field of batteries, and more specifically, to a negative electrode slurry and its preparation method, a negative electrode sheet, a battery cell, a battery, and an electrical device. Background Technology

[0002] Lithium batteries are characterized by high operating voltage, high energy density, long service life, no memory effect, and low self-discharge, making them the preferred power source for advanced electronic devices.

[0003] Lithium batteries have safety issues due to cycle expansion during cycling. The cycle expansion of lithium batteries is mainly caused by the cycle rebound of the negative electrode. Usually, in order to improve the energy density of the battery, a higher compaction density is selected, but this not only greatly affects the capacity of the negative electrode active material, but also reduces the cycle life.

[0004] Therefore, the primary problem to be solved is how to increase the energy density of the battery while reducing the rebound of the negative electrode. Summary of the Invention

[0005] This application provides a negative electrode slurry and its preparation method, a negative electrode sheet, a battery cell, a battery, and an electrical device, which can improve the safety problems caused by cycle expansion during the cycle of existing batteries, and can also improve the energy density of the battery.

[0006] In a first aspect, embodiments of this application provide a negative electrode slurry, comprising a negative electrode active material, a dispersant and stabilizer, a conductive agent, a binder, and water. The conductive agent includes particulate conductive agents and linear conductive agents, with at least a portion of the linear conductive agents coating the surfaces of the negative electrode active material and the particulate conductive agents; wherein the specific surface area of ​​the particulate conductive agents is 60 m². 2 / g~300 m 2 / g, the length of the linear conductive agent is 20 μm to 120 μm, and the diameter of the linear conductive agent is no greater than 20 nm.

[0007] In the technical solution of this application embodiment, at least a portion of a one-dimensional linear conductive agent with excellent electrical and thermal conductivity and a high aspect ratio is coated onto the surface of the negative electrode active material and the particulate conductive agent to form an interactive network-like winding structure similar to ropes. On the one hand, the network-like winding structure formed by the linear conductive agent on the surface of the negative electrode active material has a good binding and winding effect on the negative electrode active material, which can effectively suppress the volume change and expansion of the negative electrode active material during cycling, enhance the stability of the lithium battery, reduce cycle rebound, and extend the service life of the lithium battery. On the other hand, the linear conductive agent winding on the surface of the negative electrode active material and the particulate conductive agent makes the surface of the negative electrode active material uneven. Through physical riveting, it is beneficial to improve the adhesion stability of the negative electrode active material and the particulate conductive agent to the binder, enhance the adhesion and cohesion of the negative electrode slurry, strengthen the binding force on the negative electrode active material, reduce cycle rebound, and also reduce the safety hazard risk of the negative electrode active material and the particulate conductive agent detaching from the negative electrode sheet due to breaking free of the binder, thereby increasing the safety performance of the battery and making it suitable for large-scale industrial applications. Secondly, linear conductive agents achieve long-range conductivity through their one-dimensional structure with a high aspect ratio, while particulate conductive agents fill the spaces between particles of the negative electrode active material, forming short-range conductivity. This combination of particulate and linear conductive agents balances both short-range and long-range electronic conductivity, forming a stable three-dimensional conductive network in the negative electrode sheet prepared from the negative electrode slurry. This effectively reduces electronic conductivity and ion diffusion resistance, significantly improves the kinetics of the battery cell, fully utilizes the capacity of the negative electrode active material, and increases the energy density of the battery.

[0008] In some embodiments, the diameter of the linear conductive agent is ≤10nm. Within this range, the linear conductive agent has a larger aspect ratio and superior long-range conductivity. This not only facilitates dispersion and reduces processing difficulty, but also helps to form a stable three-dimensional conductive network in the negative electrode sheet prepared from the negative electrode slurry, effectively reducing the rebound of the negative electrode sheet while improving the battery energy density.

[0009] In some embodiments, the mass ratio of particulate conductive agent to linear conductive agent is 0.25 to 4:1; optionally, the mass ratio of particulate conductive agent to linear conductive agent is 0.25 to 0.67:1. Under the above mass ratio conditions, the particulate conductive agent and linear conductive agent can not only form a stable three-dimensional conductive network with long-range and short-range conductivity, effectively reducing electronic conductivity and ion diffusion resistance, significantly improving the kinetics of the battery cell, and fully utilizing the capacity of the active material to increase the energy density of the battery cell, but also facilitate the formation of a stable entangled mesh structure bound to the surface of the negative electrode active material, effectively reducing the cycle rebound of the negative electrode sheet.

[0010] In some embodiments, the linear conductive agent is at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon fibers. Linear conductive agents are abundant and readily available, and carbon nanotubes, composed of hexagonally arranged carbon atoms, possess excellent electrical and thermal conductivity, and a high aspect ratio, which are beneficial for improving the energy density of the battery and reducing cycle rebound of the negative electrode.

[0011] In some embodiments, the dispersant stabilizer includes at least one of sodium carboxymethyl cellulose and sodium dodecyl sulfate. The above-mentioned dispersant stabilizer can uniformly disperse the negative electrode active material, improving the uniformity and stability of the slurry.

[0012] In some embodiments, at least one of carbon materials, silicon-based materials, tin-based materials, and lithium titanate is used. The above-mentioned negative electrode active materials are readily available and can all maintain the contact state between the negative electrode active material and the linear conductive agent to maintain the lithium-ion conduction path, thereby increasing battery capacity and reducing cycle rebound of the negative electrode sheet.

[0013] In some embodiments, based on the mass percentage of each substance in the negative electrode slurry being 100%, the mass ratio of the negative electrode active material, conductive agent, dispersant stabilizer, and binder is 94.5–97.6:0.4–1.5:1–2:1–2, respectively.

[0014] The above-mentioned range of proportions is reasonable, which enables the negative electrode sheet prepared from the obtained negative electrode slurry to have low cycle rebound and high battery capacity when applied to batteries.

[0015] Secondly, this application provides a method for preparing the negative electrode slurry in the above embodiments, which includes the following steps: premixing the negative electrode active material, a portion of the dispersing stabilizer and the particulate conductive agent to obtain a mixed powder; mixing the mixed powder with water to obtain a first slurry with a solid content of 60wt% to 70wt%; mixing the remaining dispersing stabilizer, the dispersion of the linear conductive agent and water to obtain a second slurry; mixing the binder with the second slurry and adding water to adjust the solid content to 45wt% to 55wt%, and performing vacuum stirring.

[0016] In the technical solution of this application embodiment, the negative electrode active material, a portion of the dispersing stabilizer, and the particulate conductive agent are first premixed and then mixed with water to uniformly disperse the negative electrode active material and the particulate conductive agent in the water, forming a uniformly dispersed first slurry. Then, the remaining dispersing stabilizer, the dispersion of the linear conductive agent, and water are mixed. This not only facilitates uniform dispersion but also helps the linear conductive agent to uniformly disperse and wrap around the surface of the negative electrode active material and the particulate conductive agent, forming a binding effect on the negative electrode active material. This effectively suppresses the volume deformation and expansion of the negative electrode active material during charging and discharging, and forms a stable three-dimensional network conductive structure with the particulate conductive agent. Then, the binder is mixed with the second slurry. The addition of the binder allows the conductive agent and the negative electrode active material to be stably connected together. Finally, a uniformly dispersed negative electrode slurry is obtained through vacuum stirring.

[0017] In some embodiments, the mass content of the partial dispersant stabilizer in the dispersant stabilizer is 20% to 50%. That is, the amount of the partial dispersant stabilizer premixed with the particulate conductive agent is not greater than the amount of the remaining dispersant stabilizer mixed with the dispersion of the linear conductive agent. The above arrangement is beneficial to ensure that the components in the final second slurry are uniformly dispersed.

[0018] In some embodiments, the premixing step includes: adding the negative electrode active material, a portion of the dispersing stabilizer, and the particulate conductive agent to a mixing tank, and then stirring for 10 to 30 minutes at a revolution speed of 20 to 30 rpm and a rotation speed of 500 to 900 rpm. Within the above range, the premixing effect is good, and a uniformly dispersed mixed powder can be obtained.

[0019] In some embodiments, the step of mixing the powder with water includes: stirring for 40 to 60 minutes at a revolution speed of 10 to 30 rpm and a rotation speed of 300 to 700 rpm in the mixing tank. Within the above parameter range, the powder can be uniformly dispersed in water to form a first slurry.

[0020] In some embodiments, the step of mixing the remaining dispersion stabilizer, the dispersion of the linear conductive agent, and water to obtain a second slurry includes: stirring for 60 to 80 minutes at an orbital speed of 20 to 30 rpm and a rotational speed of 1400 to 1800 rpm in a stirring tank. Within the above parameter range, a uniformly dispersed second slurry can be obtained, which is beneficial for the stable bonding of the negative electrode active material and the conductive agent.

[0021] In some embodiments, the step of mixing the binder with the second slurry includes: stirring for 20 to 40 minutes at a revolution speed of 20 to 30 rpm and a rotation speed of 800 to 1200 rpm in the mixing tank. Within the above parameter range, the binder and the second slurry can be mixed evenly, which is beneficial for the stable bonding of the negative electrode active material, conductive agent, and binder together.

[0022] In some embodiments, the vacuum stirring process includes stirring for 15 to 25 minutes under the conditions of a vacuum degree ≥ -50 kPa, a stirring tank revolution speed of 5 to 15 rpm, and a rotation speed of 0 rpm. Within the above range, gas in the slurry can be effectively removed, ultimately obtaining a negative electrode slurry with uniform dispersion and excellent performance.

[0023] Thirdly, this application provides a negative electrode sheet, which includes a current collector and a negative electrode active coating formed on the current collector. The negative electrode active coating comprises a negative electrode active material, a dispersant stabilizer, a conductive agent, and a binder. The conductive agent includes particulate conductive agents and linear conductive agents, with at least a portion of the linear conductive agents coating the surfaces of the negative electrode active material and the particulate conductive agents; wherein the specific surface area of ​​the particulate conductive agent is 60 m². 2 / g~300 m 2 / g, the length of the linear conductive agent is 20μm~120μm, and the diameter of the linear conductive agent is no greater than 20nm.

[0024] Fourthly, this application provides a battery cell that includes the negative electrode sheet in the above embodiments.

[0025] Fifthly, this application provides a battery that includes the battery cell described in the above embodiments.

[0026] Sixthly, this application provides an electrical device that includes the battery described in the above embodiments, the battery being used to provide electrical energy.

[0027] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0028] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0029] Figure 1 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0030] Figure 2 Exploded structural diagrams of batteries according to some embodiments of this application;

[0031] Figure 3 This is an exploded structural diagram of a battery cell according to some embodiments of this application;

[0032] Figure 4 This is a schematic diagram of the structure of the negative electrode sheet in some embodiments of this application.

[0033] The reference numerals in the detailed embodiments are as follows:

[0034] 1000 - Vehicles;

[0035] 100 - Battery; 200 - Controller; 300 - Motor;

[0036] 10-Box body; 11-First part; 12-Second part;

[0037] 20-Battery cell; 21-End cap; 21a-Electrode terminal; 22-Housing casing; 23-Electrode assembly; 23a-Taper;

[0038] 24 - Negative electrode sheet; 241 - Current collector; 243 - Negative electrode active coating. Detailed Implementation

[0039] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0041] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0042] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0043] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0044] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0045] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0046] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0047] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0048] The inventors have noticed that power batteries have safety issues caused by cyclic expansion during cycling. The cyclic expansion of power batteries is mainly caused by the cyclic rebound of the negative electrode sheet. Usually, in order to improve the energy density of the battery, a higher compaction density is selected, but this not only greatly affects the capacity of the negative electrode active material, but also reduces the cycle life.

[0049] The applicant's research found that by changing the composition of the negative electrode slurry and adjusting the corresponding preparation method, a negative electrode sheet with high energy density and low rebound can be obtained, thereby improving the above-mentioned problems.

[0050] To improve the safety issues caused by cycle expansion in existing batteries during cycling, and to simultaneously increase battery energy density, the inventors, after in-depth research, designed a negative electrode slurry comprising a negative electrode active material, a dispersing stabilizer, a conductive agent, a binder, and water. The conductive agent includes particulate and linear conductive agents, with at least a portion of the linear conductive agent coating the surface of the negative electrode active material and the particulate conductive agent; wherein the specific surface area of ​​the particulate conductive agent is 60 m². 2 / g~300 m 2 / g, the length of the linear conductive agent is 20μm~120μm, and the diameter of the linear conductive agent is no greater than 20nm.

[0051] By introducing particulate and linear conductive agents, at least some of the linear conductive agents are coated on the surface of the negative electrode active material and the particulate conductive agents, forming a stable three-dimensional conductive network structure. This suppresses the volume change and expansion of the negative electrode active material during cycling, reduces cycle rebound, and through physical bonding, improves the adhesion stability between the negative electrode active material, the particulate conductive agent, and the binder, further reducing cycle rebound. On the other hand, it balances short-range and long-range electronic conductivity, significantly improving the kinetics of the battery cell while fully utilizing the capacity of the negative electrode active material and increasing the energy density of the battery.

[0052] The battery cells disclosed in this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power system for such an electrical device can be constructed using battery cells and batteries disclosed in this application. This helps to mitigate safety issues caused by cycle expansion and improves battery energy density and battery life.

[0053] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0054] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0055] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0056] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0057] Please refer to Figure 2 , Figure 2This is an exploded view of a battery 100 provided in some embodiments of this application. The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, jointly defining a space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 jointly define the space; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0058] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0059] Each battery cell 20 can be a secondary battery or a primary battery; it can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited to these. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes.

[0060] Please refer to Figure 3 , Figure 3 This is an exploded structural diagram of a battery cell 20 provided in some embodiments of this application. The battery cell 20 refers to the smallest unit that makes up a battery. Figure 3 The battery cell 20 includes an end cap 21, a housing 22, an electrode assembly 23, and other functional components.

[0061] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, allowing battery cell 20 to have higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with electrode assembly 23 to output or input electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0062] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0063] Electrode assembly 23 is the component in the battery cell 20 where electrochemical reactions occur. The casing 22 may contain one or more electrode assemblies 23. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and typically a separator is provided between the positive and negative electrode sheets. The portions of the positive and negative electrode sheets containing active material constitute the main body of the electrode assembly, while the portions of the positive and negative electrode sheets without active material each constitute a tab 23a. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs 23a connect to the electrode terminals to form a current loop.

[0064] According to some embodiments of this application, an embodiment of this application provides a negative electrode slurry, which includes a negative electrode active material, a dispersing stabilizer, a conductive agent, a binder, and water. The conductive agent includes particulate conductive agents and linear conductive agents, with at least a portion of the linear conductive agents coating the surfaces of the negative electrode active material and the particulate conductive agents; wherein, the specific surface area of ​​the particulate conductive agents is 60 m². 2 / g~300 m 2 / g, the length of the linear conductive agent is 20μm~120μm, and the diameter of the linear conductive agent is no greater than 20nm.

[0065] In the technical solution of this application embodiment, at least a portion of a one-dimensional linear conductive agent with excellent electrical and thermal conductivity and a high aspect ratio is coated onto the surface of the negative electrode active material and the particulate conductive agent to form an interactive network-like winding structure similar to ropes. On the one hand, the network-like winding structure formed by the linear conductive agent on the surface of the negative electrode active material has a good binding and winding effect on the negative electrode active material, which can effectively suppress the volume change and expansion of the negative electrode active material during cycling, enhance the stability of the lithium battery, reduce cycle rebound, and extend the service life of the lithium battery. On the other hand, the linear conductive agent winding on the surface of the negative electrode active material and the particulate conductive agent makes the surface of the negative electrode active material uneven. Through physical riveting, it is beneficial to improve the adhesion stability of the negative electrode active material and the particulate conductive agent to the binder, enhance the adhesion and cohesion of the negative electrode slurry, strengthen the binding force on the negative electrode active material, reduce cycle rebound, and also reduce the safety hazard risk of the negative electrode active material and the particulate conductive agent detaching from the negative electrode sheet due to breaking free of the binder, thereby increasing the safety performance of the battery and making it suitable for large-scale industrial applications. Secondly, linear conductive agents achieve long-range conductivity through their one-dimensional structure with a high aspect ratio, while particulate conductive agents fill the spaces between particles of the negative electrode active material, forming short-range conductivity. This balances both short-range and long-range electronic conductivity, forming a stable three-dimensional conductive network in the negative electrode sheet prepared from the negative electrode slurry. This effectively reduces electronic conductivity and ion diffusion resistance, significantly improves the kinetics of the battery cell, fully utilizes the capacity of the negative electrode active material, and increases the energy density of the battery.

[0066] In other words, the technical solution of this application utilizes the high mechanical strength of the linear conductive agent and the interactive network winding structure to reduce internal resistance, improve the dynamics and energy density of the battery cell, and at the same time reduce cycle rebound by suppressing the volume expansion of the negative electrode active material during the cycling process, thereby improving the cycle performance of the battery cell.

[0067] For example, the specific surface area of ​​the particulate conductive agent is 60 m². 2 / g、80 m 2 / g、100 m 2 / g、120 m 2 / g, 150m 2 / g、170 m 2 / g、200 m 2 / g、230 m 2 / g、250 m 2 / g、270 m 2 / g、300 m 2 Any value in / g or between any two values.

[0068] For example, the length of the linear conductive agent is any value of 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm or between any two values.

[0069] It is understandable that the tube diameter of the linear conductive agent is no greater than 20nm, which means that 0 < the tube diameter of the linear conductive agent is ≤ 20nm.

[0070] The adhesive includes, but is not limited to, at least one of polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, and polyimide.

[0071] According to some embodiments of this application, optionally, the diameter of the linear conductive agent is ≤10nm.

[0072] The linear conductive agents in this range have a larger aspect ratio and better long-range conductivity. They are not only easier to disperse and reduce processing difficulty, but also conducive to forming a stable three-dimensional conductive network in the negative electrode sheet prepared from the negative electrode slurry. This effectively reduces the rebound of the negative electrode sheet while improving the energy density of the battery.

[0073] According to some embodiments of this application, optionally, the mass ratio of particulate conductive agent to linear conductive agent is 0.25 to 4:1.

[0074] Within the above-mentioned ratio range, it is beneficial for particulate and linear conductive agents to form a stable three-dimensional conductive network with long-range and short-range properties, effectively reducing electronic conductivity and ion diffusion resistance, significantly improving the kinetics of the battery cell, fully utilizing the capacity of the negative electrode active material, and increasing the energy density of the battery cell. Moreover, the linear conductive agent is also conducive to forming a stable and bound network structure, which has a more obvious binding effect on the expansion of the negative electrode active material during the delithiation and lithium insertion process, and can effectively form a bound network structure to ensure the coating effect. If the mass ratio of particulate conductive agent to linear conductive agent is greater than 4, on the one hand, due to the increase in linear conductive agent, its π-π conjugation effect makes it difficult to disperse in the slurry, forming agglomerates on the surface of the negative electrode active material. This results in some CNTs agglomerating and tangling locally, while others fail to form a bound and tangled network structure. On the other hand, due to the decrease in particulate conductive agent, it is difficult to form a long-range and short-range three-dimensional conductive network. Therefore, this uneven CNT dispersion, local tangling and knotting phenomenon, and unstable three-dimensional network structure lead to a decrease in cycle rebound effect, obstruction of Li+ transport, and a decrease in the kinetics of the battery cell. If the mass ratio of particulate conductive agent to linear conductive agent is less than 0.25, due to the reduction in the amount of linear conductive agent, the long-range conductivity of the negative electrode sheet decreases, making it difficult to form a comprehensive and stable bound and tangled network structure. This increases cycle rebound and decreases the kinetics of the battery cell.

[0075] For example, the mass ratio of the particulate conductive agent and the linear conductive agent is any one of 0.25:1, 0.30:1, 0.45:1, 0.50:1, 0.67, 0.80:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or between any two values.

[0076] Optionally, the mass ratio of particulate conductive agent to linear conductive agent is 0.25 to 0.67:1.

[0077] Under the aforementioned mass ratio conditions, particulate and linear conductive agents can not only form stable three-dimensional conductive networks with both long-range and short-range properties, effectively reducing electronic conductivity and ion diffusion resistance, significantly improving the kinetics of battery cells, and fully utilizing the capacity of active materials to increase the energy density of battery cells, but also facilitate the formation of a stable, entangled network structure bound to the surface of the negative electrode active material, effectively reducing the cycle rebound of the negative electrode sheet.

[0078] Optionally, the mass ratio of particulate conductive agent to linear conductive agent is 0.67:1.

[0079] According to some embodiments of this application, optionally, the linear conductive agent is at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon fibers.

[0080] Linear conductive agents are abundant and readily available, and carbon nanotubes, composed of hexagonally arranged carbon atoms, possess excellent electrical and thermal conductivity and a high aspect ratio, which are beneficial for improving the energy density of batteries and reducing the cycle rebound of negative electrode plates.

[0081] According to some embodiments of this application, optionally, the dispersion stabilizer includes at least one of sodium carboxymethyl cellulose and sodium dodecyl sulfate.

[0082] The above-mentioned dispersant stabilizer can uniformly disperse the negative electrode active material, improving the uniformity and stability of the slurry.

[0083] According to some embodiments of this application, optionally, the negative electrode active material is at least one of carbon materials, silicon-based materials, tin-based materials, and lithium titanate.

[0084] The aforementioned negative electrode active materials are readily available, and all of them can maintain the contact state between the negative electrode active material and the linear conductive agent to maintain the lithium ion conduction path, thereby increasing battery capacity and reducing the cycle rebound of the negative electrode sheet.

[0085] Carbon materials have a low expansion and contraction rate, which can reduce the expansion and contraction of the negative electrode active material caused by the insertion and removal of lithium ions. This helps to maintain the contact state between the negative electrode active material and the linear conductive agent to maintain the lithium ion conduction path, thereby increasing battery capacity and reducing the cycle rebound of the negative electrode sheet.

[0086] Optionally, the carbon material includes at least one of graphite, soft carbon, hard carbon, and mesophase carbon microspheres, and the graphite includes at least one of artificial graphite and natural graphite.

[0087] Silicon-based materials include at least one of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys.

[0088] Tin-based materials include at least one of elemental tin, tin oxides, and tin alloys.

[0089] According to some embodiments of this application, optionally, based on the mass of each substance in the negative electrode slurry being 100%, the mass ratio of the negative electrode active material, conductive agent, dispersant stabilizer, and binder is 94.5–97.6:0.4–1.5:1–2:1–2, respectively.

[0090] Assuming each substance accounts for 100% of the mass of the negative electrode slurry, that is, the total mass of the negative electrode active material, conductive agent, dispersant stabilizer, and binder is 100.

[0091] The above-mentioned range of proportions is reasonable, which enables the negative electrode sheet prepared from the obtained negative electrode slurry to have low cycle rebound and high battery capacity when applied to batteries.

[0092] According to some embodiments of this application, this application also provides a method for preparing the negative electrode slurry in the above embodiments, which includes the following steps: premixing the negative electrode active material, a portion of the dispersing stabilizer and the particulate conductive agent to obtain a mixed powder; mixing the mixed powder with water to obtain a first slurry with a solid content of 60wt% to 70wt%; mixing the remaining dispersing stabilizer, the dispersion of the linear conductive agent and water to obtain a second slurry; mixing the binder with the second slurry and adding water to adjust the solid content to 45wt% to 55wt%, and performing vacuum stirring.

[0093] In the technical solution of this application embodiment, the negative electrode active material, a portion of the dispersing stabilizer, and the particulate conductive agent are first premixed and then mixed with water to uniformly disperse the negative electrode active material and the particulate conductive agent in the water, forming a uniformly dispersed first slurry. Then, the remaining dispersing stabilizer, the dispersion of the linear conductive agent, and water are mixed. This not only facilitates uniform dispersion but also helps the linear conductive agent to uniformly disperse and wrap around the surface of the negative electrode active material and the particulate conductive agent, forming a binding effect on the negative electrode active material. This effectively suppresses the volume deformation and expansion of the negative electrode active material during charging and discharging, and forms a stable three-dimensional network conductive structure with the particulate conductive agent. Then, the binder is mixed with the second slurry. The addition of the binder allows the conductive agent and the negative electrode active material to be stably connected together. Finally, a uniformly dispersed negative electrode slurry is obtained through vacuum stirring.

[0094] According to some embodiments of this application, optionally, the mass content of a portion of the dispersion stabilizer in the dispersion stabilizer is 20% to 50%.

[0095] That is, the amount of dispersion stabilizer premixed with the particulate conductive agent is not greater than the amount of dispersion stabilizer mixed with the dispersion of the linear conductive agent. The above setting is conducive to the uniform dispersion of each component in the final second slurry.

[0096] For example, the mass content of the dispersion stabilizer in the dispersion stabilizer is any one of 20%, 25%, 30%, 35%, 40%, 45%, 50%, or between any two values.

[0097] According to some embodiments of this application, optionally, the premixing process includes: adding the negative electrode active material, a portion of the dispersing stabilizer and the particulate conductive agent to a mixing tank, and stirring for 10 min to 30 min under the conditions that the revolution speed of the mixing tank is 20 rpm to 30 rpm and the rotation speed is 500 rpm to 900 rpm.

[0098] Within the above range, the premixing effect is good, and a uniformly dispersed mixed powder can be obtained.

[0099] For example, in the premixing step, the revolution speed of the mixing tank is any one of 20 rpm, 22 rpm, 25 rpm, 27 rpm, 30 rpm or between any two values, the rotation speed is any one of 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm or between any two values, and the mixing time is any one of 10 min, 15 min, 20 min, 25 min, 30 min or between any two values.

[0100] According to some embodiments of this application, optionally, the step of mixing the powder with water includes: stirring for 40 min to 60 min under the condition that the revolution speed of the mixing tank is 10 rpm to 30 rpm and the rotation speed is 300 rpm to 700 rpm.

[0101] Within the above parameter range, the mixed powder can be evenly dispersed in water to form the first slurry.

[0102] For example, in the step of mixing the powder with water, the revolution speed of the mixing tank is any one of 10 rpm, 13 rpm, 15 rpm, 18 rpm, 20 rpm, 22 rpm, 25 rpm, 27 rpm, 30 rpm or between any two values, the rotation speed is any one of 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm or between any two values, and the mixing time is any one of 40 min, 45 min, 50 min, 55 min, 60 min or between any two values.

[0103] According to some embodiments of this application, optionally, the step of mixing the remaining dispersion stabilizer, the dispersion of the linear conductive agent, and water to obtain the second slurry includes: stirring for 60 min to 80 min under the condition that the revolution speed of the stirring tank is 20 rpm to 30 rpm and the rotation speed is 1400 rpm to 1800 rpm.

[0104] Within the above parameter range, a uniformly dispersed second slurry can be obtained, which is beneficial for the stable connection of the negative electrode active material and the conductive agent.

[0105] For example, in the step of mixing the remaining dispersion stabilizer, the dispersion of the linear conductive agent, and water to obtain the second slurry, the revolution speed of the stirring tank is any one of 20 rpm, 22 rpm, 25 rpm, 27 rpm, 30 rpm or between any two values, the rotation speed is any one of 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm or between any two values, and the stirring time is any one of 60 min, 65 min, 70 min, 75 min, 80 min or between any two values.

[0106] According to some embodiments of this application, optionally, the step of mixing the binder with the second slurry includes: stirring for 20 min to 40 min under the condition that the revolution speed of the mixing tank is 20 rpm to 30 rpm and the rotation speed is 800 rpm to 1200 rpm.

[0107] Within the above parameter range, the binder can be uniformly dispersed in the second slurry to stably connect the negative electrode active material, conductive agent, and binder together.

[0108] For example, in the step of mixing the binder with the second slurry, the revolution speed of the mixing tank is any one of 20 rpm, 22 rpm, 25 rpm, 27 rpm, 30 rpm or between any two values, the rotation speed is any one of 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm or between any two values, and the mixing time is any one of 20 min, 635 min, 40 min or between any two values.

[0109] According to some embodiments of this application, optionally, the vacuum stirring process includes: stirring for 15 min to 25 min under the conditions of vacuum degree ≥ -50 kPa, the revolution speed of the stirring tank is 5 rpm to 15 rpm, and the rotation speed is 0 rpm.

[0110] Within the above range, gas in the slurry can be effectively removed, ultimately resulting in a negative electrode slurry with uniform dispersion of each component and excellent performance.

[0111] For example, in the vacuum stirring process, the revolution speed of the stirring tank is any one of 5 rpm, 7 rpm, 10 rpm, 13 rpm, 15 rpm or between any two values, and the stirring time is any one of 15 min, 17 min, 20 min, 23 min, 25 min or between any two values.

[0112] Please see Figure 4 According to some embodiments of this application, this application also provides a negative electrode sheet 24, which includes a current collector 241 and a negative electrode active coating 243 formed on the current collector 241. The negative electrode active coating 243 includes a negative electrode active material, a dispersant stabilizer, a conductive agent, and a binder. The conductive agent includes particulate conductive agents and linear conductive agents, and at least a portion of the linear conductive agent is coated on the surface of the negative electrode active material and the particulate conductive agent; wherein the specific surface area of ​​the particulate conductive agent is 60 m². 2 / g~300 m 2 / g, the length of the linear conductive agent is 20μm to 120μm, and the diameter of the linear conductive agent is no greater than 20nm. That is, the negative electrode active coating 243 is obtained by coating the current collector 241 with the negative electrode slurry of any of the above schemes.

[0113] According to some embodiments of this application, this application also provides a battery cell including the negative electrode sheet of any of the above schemes.

[0114] According to some embodiments of this application, this application also provides a battery, including a battery cell of any of the above solutions.

[0115] According to some embodiments of this application, this application also provides an electrical device including a battery of any of the above-described schemes, and the battery is used to provide electrical energy to the electrical device.

[0116] The electrical device can be any of the aforementioned battery-powered devices or systems.

[0117] The following specific embodiments are provided to better illustrate this application.

[0118] Examples and Comparative Examples

[0119] S1. Dry mixing of powder materials: Add 3.0687 kg of graphite (negative electrode active material), 0.01272 kg of conductive carbon black (granular conductive agent), and 0.00636 kg of sodium carboxymethyl cellulose (stabilizer) to the mixing tank of the mixer and mix the dry powder for 15 minutes. The stirring speed of the mixing tank is 25 rpm and the stirring rotation speed is 700 rpm to obtain a uniform dry powder mixture.

[0120] S2. Stirring 1: Add 1.81346 kg of deionized water to the dry powder mixture and stir for 50 min at a stirring speed of 20 rpm and a rotation speed of 500 rpm in the stirring tank to obtain a first slurry with uniform dispersion and a solid content of 63 wt%.

[0121] S3. Stirring 2: Add 0.02544 kg sodium carboxymethyl cellulose, 0.34071 kg carbon nanotube dispersion (linear conductive agent with a solid content of 5.6%) and 0.63323 kg deionized water to the first slurry. Stir for 70 min at a stirring speed of 20 rpm and a stirring rotation speed of 1600 rpm to obtain a uniformly dispersed second slurry.

[0122] S4. Stirring 3: Add 0.09938 kg of SBR emulsion as a binder to the second slurry, and stir for 30 minutes under the condition that the revolution speed of the mixing tank is 25 rpm and the rotation speed is 1000 rpm to obtain a uniformly mixed third slurry.

[0123] S5. Add a small amount of deionized water to the third slurry to adjust the viscosity. The deionized water is added in small amounts multiple times. Stir for 20 minutes at a revolution speed of 10 rpm and a rotation speed of 900 rpm in the mixing tank to obtain a fourth slurry with a viscosity of 8000 mPa•s.

[0124] S6. Seal the mixer and turn on the vacuum degassing until the vacuum degree inside the mixer reaches -50KPa. Stir for 20 minutes with the revolution speed of the mixing tank at 10rpm and the rotation speed at 0rpm to finally obtain a negative electrode slurry with a solid content of 53wt%.

[0125] [Preparation of negative electrode slurry in Examples 2-12 and Comparative Examples 1-2 and 5-8] The only difference between them and Example 1 is that the parameters shown in Table 1 are different.

[0126]

Preparation of negative electrode slurry in Example 13

[0127] [Preparation of Negative Electrode Slurry in Example 14] The only difference between this example and Example 1 is that the rotation speed in step S3 is 1400 rpm. [Preparation of Negative Electrode Slurry in Comparative Example 3] The only difference between this example and Example 1 is that only particulate conductive agent is added, and the remaining parameters are shown in Table 1.

[0128] [Preparation of negative electrode slurry in Comparative Example 4] The only difference between Comparative Example 4 and Example 1 is that only linear conductive agent is added, and the other parameters are shown in Table 1.

[0129] [Preparation of negative electrode slurry for Comparative Example 9] The only difference between Comparative Example 9 and Example 1 is that in step S1, the amount of sodium carboxymethyl cellulose added is 0.00318 kg, and in step S3, the amount of sodium carboxymethyl cellulose added is 0.02862 kg.

[0130] [Preparation of negative electrode slurry for Comparative Example 10] The only difference between Comparative Example 10 and Example 1 is that in step S1, the amount of sodium carboxymethyl cellulose added is 0.01908 kg, and in step S3, the amount of sodium carboxymethyl cellulose added is 0.01272 kg.

[0131]

Preparation of negative electrode slurry in Comparative Example 11

[0132]

Preparation of negative electrode slurry for Comparative Example 12

[0133] The parameters of the slurries prepared in each embodiment and comparative example are shown in Table 1. All contents in Table 1 refer to mass percentage.

[0134] Table 1

[0135]

[0136] Preparation of the negative electrode sheet

[0137] The negative electrode slurry was uniformly coated onto the negative electrode current collector copper foil at a coating speed of 20 m / min, with a coating mass of 120 g / 1540.25 mm. 2 The oven temperature was set to 80℃; the negative electrode sheet was compacted to a certain density using a cold press, with the cold pressing pressure set to 30 tons and the cold pressing speed to 15m / min. The adhesion of the negative electrode sheet after cold pressing was then tested.

[0138] Preparation of the positive electrode sheet

[0139] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2 O 2、 Conductive agent Super-P and binder polyvinylidene fluoride are stirred and dispersed in N-methylpyrrolidone at a mass ratio of 96:2:2 to prepare a positive electrode slurry. The slurry is coated on the positive electrode current collector aluminum foil and then compacted by a cold press to obtain the positive electrode sheet.

[0140] Preparation of Electrolyte

[0141] Lithium salt LiPF6 was added to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 35:65 and mixed thoroughly to obtain an electrolyte, wherein the molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0142]

Isolation Film

[0143] A 12μm thick polyethylene porous membrane was selected.

[0144] [Preparation of Lithium-ion Batteries]

[0145] The negative electrode sheet, separator, and positive electrode sheet are stacked in sequence, with the separator placed between the positive and negative electrode sheets to provide isolation. The cells are then wound to obtain a bare cell, which is then inserted into the battery casing. After baking, liquid injection, settling, encapsulation, formation, and capacity testing, a lithium-ion battery is obtained.

[0146] [Testing of relevant parameters for negative electrode plates]

[0147] The negative electrode adhesion test process is as follows: the 180° bending peel strength test is carried out using the Zhongzhi Testing Tensile Tester to obtain the adhesion of the negative electrode. The cell cycle rebound rate test process is as follows: the thickness of the negative electrode before and after cycle disassembly is measured using a micrometer, and the cycle rebound rate is calculated using a formula.

[0148] The testing process for relevant parameters of the negative electrode sheet in this embodiment and comparative example is as follows:

[0149] 1. Negative electrode adhesion test process

[0150] Equipment Model: Zhongzhi Tensile Testing Machine (Model LXG2-LLCS-0009), Specific Testing Procedure:

[0151] ① Take the electrode to be tested, cut a sample with a width of 30mm and a length of 150mm using a blade, and attach double-sided tape to the steel plate with a tape width of 20mm and a length of 150mm.

[0152] ② Place the electrode sample cut in step 1 onto double-sided tape with the test side facing down, and roll it three times in the same direction with a pressure roller. Insert a paper strip with a width of 20mm and a length of 100mm under the electrode and fix it with wrinkle glue.

[0153] ③ Turn on the power of the tensile testing machine. The indicator light will illuminate. Adjust the limit block to the appropriate position. Secure the end of the steel plate without the electrode sheet attached using the lower clamp, ensuring that the steel plate is placed perpendicular to the horizontal plane of the base and that the bottom of the steel plate is flush with the base. Fold the paper tape upwards and secure it using the upper clamp. Use the "up" and "down" buttons on the manual controller provided with the tensile testing machine to adjust the position of the upper clamp.

[0154] ④ Open the tensile testing program, pre-tension about 5mm, then "zero" the "force" and "displacement" parameters. After these two parameters are zero, click the start button to begin the test. When the curve in the graph flattens out and the displacement is greater than 70mm, click the pause icon. The machine will stop rising, and the displacement will automatically return to zero. Read and record the average value of the flattened part of the curve in the graph. Then record the test results. Perform three parallel tests and calculate the average value N1. The final adhesive force = N1 * 50.

[0155] 2. Testing the cyclic rebound rate

[0156] 2.1 Negative electrode thickness test before cell cycling

[0157] ① Take the six negative electrode sheets after the stacking process and mark them as number 1-6. The corresponding assembled battery cells are also numbered 1-6.

[0158] ② Take the calibrated micrometer, zero it, and then take 10 points evenly along the length of each electrode to measure the thickness. Record the data and take the average value, which is recorded as C1-C6.

[0159] 2.2 Negative electrode thickness test after cell cycling

[0160] ① After cycling the cells numbered 1-6 for 500 cycles under the same conditions, disassemble the cells and remove the corresponding negative electrode plates for later use.

[0161] ② Use a micrometer used for testing the thickness of the negative electrode sheet before electrical cycling. After calibration, zero the micrometer and then take 10 points evenly along the length of each disassembled negative electrode sheet to measure the thickness. Record the data and take the average value, which is recorded as D1-D5.

[0162] 2.3 Calculation of Cyclic Rebound Rate:

[0163] Cycle rebound rate: The rate of change in thickness of the negative electrode sheet after cell cycling relative to before cycling is denoted as T, T=(DC) / C×100%. Based on the results of tests 2.1 and 2.2, T1-T6 can be obtained, and the average value is taken as the cycle rebound rate.

[0164] [Battery Performance Test]

[0165] 1. Battery cycle performance test

[0166] The battery capacity retention rate test process is as follows: At 25°C, the batteries corresponding to each embodiment and comparative example are charged to 4.3V at a constant current of 1 / 3C, then charged to a current of 0.05C at a constant voltage of 4.3V, rested for 5 minutes, and then discharged to 2.8V at 1 / 3C. The resulting capacity is recorded as the initial capacity C0. The above steps are repeated for the same battery, and the discharge capacity C1000 of the battery after the 1000th cycle is recorded. Then, the battery capacity retention rate after each cycle is P1000 = C1000 / C0*100%.

[0167] The data in Table 1 were obtained after the battery had undergone 1000 cycles under the above test conditions.

[0168] 2. Battery DC resistance:

[0169] The DC impedance testing process for the batteries in each embodiment and comparative example is as follows: At 25°C, the batteries corresponding to each embodiment and comparative example are charged to 4.3V at a constant current of 1 / 3C, and then charged to a current of 0.05C at a constant voltage of 4.3V. After resting for 5 minutes, the voltage V1 is recorded. Then, the batteries are discharged at 1 / 3C for 30 seconds, and the voltage V2 is recorded. The internal resistance DCR of the battery is obtained by dividing (V2-V1) / (1 / 3C).

[0170] The test results of each embodiment and comparative example are shown in Table 1.

[0171] It should be noted that in Comparative Example 9, the amount of sodium carboxymethyl cellulose added in the dry mixing step was too small, resulting in slurry agglomeration, poor dispersibility, and particle scratches after coating, failing to meet the slurry's usage requirements. Therefore, its related performance was not measured. In Comparative Example 10, the amount of sodium carboxymethyl cellulose added in the dry mixing step was too large, resulting in poor slurry stability, sedimentation, filter clogging, and poor coating weight consistency, failing to meet the negative electrode slurry's usage requirements. Therefore, its related performance was not measured. In Comparative Examples 11 and 12, the process had problems, causing the graphite, SP, and CNT dispersions in the final slurry to easily agglomerate, resulting in poor dispersibility and difficulty in filtration, failing to meet the slurry's usage requirements. Therefore, its related performance was not measured.

[0172] Table 2 Test Results

[0173]

[0174] According to Tables 1 and 2, it can be seen that the negative electrode slurry obtained by the preparation method provided in this application has better adhesion and lower cycle rebound than the comparative example. This can improve the safety problem caused by cycle expansion in existing batteries during cycling, and the capacity retention rate is high after 1000 cycles and the DC resistance is low, thereby improving the energy density of the battery.

[0175] Comparing Examples 1-4 and Comparative Examples 2-6, it can be seen that only when particulate and linear conductive agents work together can the volume expansion of the negative electrode active material during cycling be effectively suppressed, the cycle rebound of the negative electrode sheet be reduced, and the cycle performance of the battery cell be improved. Specifically, when the mass ratio of particulate to linear conductive agent is 0.25-4:1, it not only exhibits lower cycle rebound and lower DC resistance, but also better cycle performance and adhesion. Especially when the mass ratio of particulate to linear conductive agent is 0.25-0.67:1, it exhibits even better low rebound and low DC resistance under conditions of good cycle performance.

[0176] Comparing Examples 1, 5-6, and Comparative Examples 7-8, it can be seen that the amount of conductive agent added has a significant impact on the performance of the slurry. When the mass percentage of conductive agent in the slurry is between 0.4% and 1.5%, it can effectively suppress the volume expansion of the negative electrode active material during cycling, reduce the cycle rebound of the negative electrode sheet, reduce the DC impedance of the battery, and improve the cycle performance of the battery.

[0177] Comparing Examples 1, 7-8, and Comparative Example 2, it can be seen that the specific surface area of ​​the particulate conductive agent has a significant impact on the performance of the final product. When the specific surface area of ​​the particulate conductive agent is less than 60 m², the performance is significantly affected.2 At / g, the adhesion of the negative electrode sheet obtained by the slurry decreased significantly, the DC resistance (DCR) increased, and the capacity retention rate decreased after 1000 battery cycles.

[0178] Comparing Examples 1, 9-12 and Comparative Example 3, it can be seen that the diameter and length of the linear conductive agent have a significant impact on the performance of the final product. When the length of the linear conductive agent is 20μm to 120μm and the diameter of the linear conductive agent is no greater than 20nm, the obtained slurry not only has good adhesion, but the prepared battery cells also have lower cycle rebound and lower DC impedance under the condition of better cycle performance.

[0179] In summary, the negative electrode slurry and its preparation method, negative electrode sheet, battery cell, battery and electrical equipment provided in this application can improve the safety problems caused by cycle expansion during the existing battery cycle, and can also improve the energy density of the battery.

[0180] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not 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. These 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, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a negative electrode slurry, wherein, The negative electrode slurry comprises a negative electrode active material, a dispersant and stabilizer, a conductive agent, a binder, and water. The conductive agent includes particulate conductive agents and linear conductive agents. The preparation method includes the following steps: The negative electrode active material, a portion of the dispersant stabilizer, and the particulate conductive agent are premixed to obtain a mixed powder. The mixed powder is mixed with water to obtain a first slurry with a solid content of 60wt% to 70wt%. The remaining amount of the dispersion stabilizer, the dispersion of the linear conductive agent, and water are added to the first slurry for mixing to obtain the second slurry. The binder is mixed with the second slurry, and water is added to adjust the solid content to 45wt% to 55wt%. The mixture is then subjected to vacuum stirring to obtain the negative electrode slurry. The mass content of the dispersion stabilizer in the dispersion stabilizer is 20% to 50%; The negative electrode active material includes graphite; based on a total mass of 100 for the negative electrode active material, the conductive agent, the dispersing stabilizer, and the binder, the conductive agent has a mass percentage of 0.4% to 1.5%, and the mass ratio of the particulate conductive agent to the linear conductive agent is 0.25 to 4:1; the specific surface area of ​​the particulate conductive agent is 60 m². 2 / g~300m 2 / g, wherein the length of the linear conductive agent is 20μm to 120μm, and the diameter of the linear conductive agent is not greater than 20nm.

2. The preparation method according to claim 1, wherein, The premixing process includes: adding the negative electrode active material, a portion of the dispersion stabilizer, and the particulate conductive agent to a mixing tank, and stirring for 10 to 30 minutes under the condition that the revolution speed of the mixing tank is 20 rpm to 30 rpm and the rotation speed is 500 rpm to 900 rpm.

3. The preparation method according to claim 1, wherein, The step of mixing the powder with water includes: stirring for 40 min to 60 min under the conditions that the revolution speed of the mixing tank is 10 rpm to 30 rpm and the rotation speed is 300 rpm to 700 rpm.

4. The preparation method according to claim 1, wherein, The step of mixing the remaining dispersion stabilizer, the dispersion of the linear conductive agent, and water to obtain the second slurry includes: stirring for 60 min to 80 min under the conditions that the revolution speed of the stirring tank is 20 rpm to 30 rpm and the rotation speed is 1400 rpm to 1800 rpm.

5. The preparation method according to claim 1, wherein, The step of mixing the binder with the second slurry includes: stirring for 20 min to 40 min under the conditions that the revolution speed of the mixing tank is 20 rpm to 30 rpm and the rotation speed is 800 rpm to 1200 rpm.

6. The preparation method according to any one of claims 1 to 5, wherein, The vacuum stirring process includes stirring for 15 to 25 minutes under the conditions of a vacuum degree ≥ -50 kPa, a revolution speed of 5 rpm to 15 rpm and a rotation speed of 0 rpm in the stirring tank.

7. A negative electrode slurry, wherein, It is prepared by the preparation method according to any one of claims 1-6, wherein the negative electrode slurry includes a negative electrode active material, a dispersant stabilizer, a conductive agent, a binder and water, wherein the conductive agent includes particulate conductive agent and linear conductive agent, and at least a portion of the linear conductive agent is coated on the surface of the negative electrode active material and the particulate conductive agent; The specific surface area of ​​the particulate conductive agent is 60 m². 2 / g~300 m 2 / g, wherein the length of the linear conductive agent is 20μm to 120μm, and the diameter of the linear conductive agent is not greater than 20nm.

8. The negative electrode slurry according to claim 7, wherein, The diameter of the linear conductive agent is ≤10nm.

9. The negative electrode slurry according to claim 7, wherein, The mass ratio of the particulate conductive agent to the linear conductive agent is 0.25 to 0.67:

1.

10. The negative electrode slurry according to claim 7, wherein, The linear conductive agent is at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon fibers.

11. The negative electrode slurry according to claim 7, wherein, The dispersion stabilizer includes at least one of sodium carboxymethyl cellulose and sodium dodecyl sulfate.

12. The negative electrode slurry according to claim 7, wherein, Based on the mass percentage of each substance in the negative electrode slurry being 100%, the mass ratio of the negative electrode active material, the conductive agent, the dispersing stabilizer, and the binder is 94.5–97.6: 0.4–1.5: 1–2: 1–2, respectively.

13. A negative electrode plate, wherein, The negative electrode sheet includes a current collector and a negative electrode active coating formed on the current collector. The negative electrode active coating is formed from the negative electrode slurry according to any one of claims 7-12. The negative electrode active coating includes a negative electrode active material, a dispersant stabilizer, a conductive agent, and a binder. The conductive agent includes particulate conductive agents and linear conductive agents. At least a portion of the linear conductive agents are coated on the surface of the negative electrode active material and the particulate conductive agents. The specific surface area of ​​the particulate conductive agent is 60 m². 2 / g~300 m 2 / g, wherein the length of the linear conductive agent is 20μm to 120μm, and the diameter of the linear conductive agent is not greater than 20nm.

14. A battery cell, wherein, Including the negative electrode sheet as described in claim 13.

15. A battery, wherein, Includes the battery cell as described in claim 14.

16. An electrical appliance, wherein, Includes the battery as described in claim 15, the battery being used to provide electrical energy.

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