Negative electrode sheet and manufacturing method therefor, battery, and electric device

Abstract

A negative electrode sheet and a manufacturing method therefor, a battery, and an electric device. The negative electrode sheet comprises a current collector, a negative electrode active material layer, and a conductive layer; the negative electrode active material layer is provided on at least one side of the current collector; the conductive layer is provided on the side of the negative electrode active material layer distant from the current collector; the conductive layer comprises a lithium acrylate polymer; and the bonding force between the negative electrode active material layer and the current collector is negatively correlated with the surface density of the conductive layer. The negative electrode sheet achieves a high bonding force between the negative active material layer and the current collector, and a battery comprising the negative electrode sheet has excellent cycle performance and excellent fast charging performance.

Description

Negative electrode sheet and preparation method thereof, battery and electrical equipment

[0001] Priority information

[0002] This application claims priority and benefits of patent application 202311631966.0 filed with the State Intellectual Property Office of China on December 1, 2023, and the entire text of which is incorporated herein by reference. Technical Field

[0003] The present application belongs to the technical field of secondary batteries, and specifically relates to a negative electrode plate and a preparation method thereof, a battery, and an electrical device. Background Art

[0004] Secondary batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as in military equipment, aerospace and other fields.

[0005] The negative electrode plate of a battery generally includes a current collector and a negative electrode active material layer disposed on the current collector. However, the existing negative electrode active material layer is easily detached, and the battery's cycle performance and fast charging performance are poor.

[0006] Summary of the Invention

[0007] In view of the technical problems existing in the background technology, the present application provides a negative electrode plate, which aims to solve the problem that the negative electrode active material layer is easy to fall off and the cycle performance and fast charging performance of the battery containing it are poor.

[0008] In order to achieve the above-mentioned objectives, the first aspect of the present application provides a negative electrode plate, including a current collector, a negative electrode active material layer and a conductive layer, wherein the negative electrode active material layer is arranged on at least one side of the current collector; the conductive layer is arranged on the side of the negative electrode active material layer away from the current collector, and the conductive layer includes a lithium acrylate polymer; the bonding force between the negative electrode active material layer and the current collector is negatively correlated with the surface density of the conductive layer.

[0009] The present application includes at least the following beneficial effects: the lithium acrylate polymer is arranged on the side of the negative electrode active material layer away from the current collector, and the bonding force between the negative electrode active material layer and the current collector is negatively correlated with the surface density of the conductive layer, which can improve the fast charging capability and cycle performance of the battery, and can reduce the influence of the lithium acrylate polymer on the bonding force between the negative electrode active material layer and the current collector, so that the negative electrode active material layer is not easy to fall off from the current collector.

[0010] In some embodiments of the present application, the negative electrode active material layer has pores, into which at least a portion of the lithium acrylate polymer is embedded. This increases the contact area between the lithium acrylate polymer and the negative electrode active material layer, thereby improving the battery's fast charging capability and cycling performance without affecting the adhesion between the negative electrode active material layer and the current collector.

[0011] In some embodiments of the present application, at least one of the following conditions is met:

[0012] The bonding force between the negative electrode active material layer and the current collector is Z k Negative correlation, Z k is the reliable permeability of the lithium acrylate polymer in the negative electrode active material layer, the distance between the lithium acrylate polymer and the surface of the negative electrode active material layer away from the current collector in the pore is a mm, the thickness of the negative electrode sheet is D mm, the permeability = a / D×100%, and the permeability corresponding to the permeability distribution number reaching 90% is the reliable permeability;

[0013] The bonding force between the negative electrode active material layer and the current collector is negatively correlated with the thickness of the negative electrode sheet;

[0014] The bonding force between the negative electrode active material layer and the current collector is positively correlated with the tortuosity of the negative electrode active material layer;

[0015] The bonding strength between the negative electrode active material layer and the current collector is negatively correlated with the porosity of the negative electrode active material layer. This improves the cycle life and fast-charging performance of the secondary battery, reduces the effect of the lithium acrylate polymer on the bonding strength of the negative electrode active material layer, and ensures strong bonding between the negative electrode active material layer and the current collector, making it less likely to fall off.

[0016] In some embodiments of the present application, Z k =1%-60%, Z k The reliable permeability of the lithium acrylate polymer in the negative electrode active material layer is: The distance between the lithium acrylate polymer and the negative electrode active material layer surface facing away from the current collector in the pores is a mm, the thickness of the negative electrode sheet is D mm, and the permeability = a / D × 100%. The reliable permeability corresponds to the permeability distribution number reaching 90%. This can improve the cycle life and fast-charging performance of the secondary battery, and the adhesion between the negative electrode active material layer and the current collector is strong, preventing it from falling off.

[0017] In some embodiments of the present application, Z k=25%-45%. This can improve the cycle life and fast charging performance of the secondary battery, reduce the influence of the acrylic acid lithium polymer on the bonding force of the negative electrode active material layer, and strengthen the bonding force between the negative electrode active material layer and the current collector, making it difficult to fall off.

[0018] In some embodiments of the present application, a / D×100%=20%-50%. Thus, when a / D×100% is within the above range, the cycle life and fast charging performance of the secondary battery can be improved, and the bonding force between the negative electrode active material layer and the current collector is strong and not easy to fall off.

[0019] In some embodiments of the present application, a / D×100%=25%-40%. Thus, when a / D×100% is within the above range, the cycle life and fast charging performance of the secondary battery can be improved, and the bonding force between the negative electrode active material layer and the current collector is strong and not easy to fall off.

[0020] In some embodiments of the present application, the surface density of the conductive layer is 0.05g / 1540.25mm 2 -0.4g / 1540.25mm 2 Therefore, the surface density of the conductive layer is 0.05g / 1540.25mm 2 -0.4g / 1540.25mm 2 Within this range, the cycle life and fast charging performance of the secondary battery can be improved, and the bonding force between the negative electrode active material layer and the current collector is strong and not easy to fall off.

[0021] In some embodiments of the present application, the porosity of the negative electrode active material layer is 20%-40%. Therefore, when the porosity of the negative electrode active material layer is within the above range, the cycle life and fast charging performance of the secondary battery can be improved, and the bonding force between the negative electrode active material layer and the current collector is strong, which is not easy to fall off.

[0022] In some embodiments of the present application, the thickness of the negative electrode plate is 0.1 mm to 0.3 mm. Therefore, a thickness of the negative electrode plate within the range of 0.1 mm to 0.3 mm can improve the cycle life and fast charging performance of the secondary battery, and the bonding between the negative electrode active material layer and the current collector is strong, making it less likely to fall off.

[0023] In some embodiments of the present application, the tortuosity of the negative electrode active material layer is 0.5-7. Therefore, when the tortuosity of the negative electrode active material layer is within the above range, the cycle life and fast charging performance of the secondary battery can be improved, and the bonding force between the negative electrode active material layer and the current collector is strong and not easy to fall off.

[0024] In some embodiments of the present application, the bonding force between the negative electrode active material layer and the current collector is 5 N / m-20 N / m. Therefore, the bonding force between the negative electrode active material layer and the current collector is within the range of 5 N / m-20 N / m, which can improve the cycle life and fast charging performance of the secondary battery. The bonding force between the negative electrode active material layer and the current collector is strong and not easy to fall off.

[0025] In some embodiments of the present application, the lithium acrylate polymer includes at least one of lithium polyacrylate, lithium polymethacrylate, lithium polyethylacrylate, or lithium polypropylacrylate. Thus, the lithium acrylate polymer, using at least one of the above substances, can improve the cycle life and fast-charging performance of the secondary battery, and provide strong adhesion between the negative electrode active material layer and the current collector, preventing it from falling off.

[0026] In some embodiments of the present application, the mass fraction of lithium is 3% to 8.9% based on the total mass of the lithium acrylate polymer. Therefore, when the mass fraction of lithium in the lithium acrylate polymer is within the above range, the cycle life and fast charging performance of the secondary battery can be improved, and the bonding between the negative electrode active material layer and the current collector is strong, preventing it from falling off.

[0027] In some embodiments of the present application, the mass fraction of lithium is 5% to 7.5% based on the total mass of the lithium acrylate polymer. Therefore, when the mass fraction of lithium in the lithium acrylate polymer is within the above range, the cycle life and fast charging performance of the secondary battery can be improved, and the bonding between the negative electrode active material layer and the current collector is strong, preventing it from falling off.

[0028] In some embodiments of the present application, the number average molecular weight (Mn) of the lithium acrylate polymer is between 3,000 and 1,000,000. Therefore, a number average molecular weight (Mn) of the lithium acrylate polymer within this range can improve the cycle life and fast charging performance of the secondary battery, and strengthen the bonding between the negative electrode active material layer and the current collector, preventing it from falling off.

[0029] In some embodiments of the present application, the number average molecular weight (Mn) of the lithium acrylate polymer is between 100,000 and 500,000. Therefore, a number average molecular weight (Mn) of the lithium acrylate polymer within this range can improve the cycle life and fast charging performance of the secondary battery, and strengthen the bonding between the negative electrode active material layer and the current collector, preventing it from falling off.

[0030] A second aspect of the present application provides a method for preparing a negative electrode sheet, comprising:

[0031] forming a negative electrode active material layer on at least one side of the current collector;

[0032] forming a conductive layer on a side of the negative electrode active material layer away from the current collector, wherein the conductive layer comprises a lithium acrylic acid polymer;

[0033] The bonding force between the negative electrode active material layer and the current collector is negatively correlated with the surface density of the conductive layer.

[0034] Therefore, the negative electrode sheet prepared by the above method has a strong bonding force between the negative electrode active material layer and the current collector and is not easy to fall off. The secondary battery containing the negative electrode sheet has excellent cycle life and fast charging performance.

[0035] In some embodiments of the present application, a lithium acrylate polymer is sprayed onto the side of the negative electrode active material layer facing away from the current collector to form a conductive layer. At least a portion of the lithium acrylate polymer is embedded within the pores of the negative electrode active material layer. This creates a strong bond between the negative electrode active material layer and the current collector, preventing it from falling off. Secondary batteries containing this polymer exhibit excellent cycle life and fast-charging performance.

[0036] In some embodiments of the present application, the spray pressure is 0.1 kPa-100 kPa. As a result, the negative electrode active material layer has a strong bonding force with the current collector, is not easy to fall off, and the secondary battery containing the negative electrode active material layer has excellent cycle life and fast charging performance.

[0037] In some embodiments of the present application, the spraying temperature is 70° C.-150° C. Thus, the bonding force between the negative electrode active material layer and the current collector is strong and not easy to fall off, and the secondary battery containing the negative electrode active material layer has excellent cycle life and fast charging performance.

[0038] In some embodiments of the present application, a current collector containing a negative electrode active material layer is immersed in a lithium acrylate polymer solution to form a conductive layer on the side of the negative electrode active material layer away from the current collector, and at least a portion of the lithium acrylate polymer is embedded in the pores of the negative electrode active material layer. This creates a strong bond between the negative electrode active material layer and the current collector, making it less likely to fall off. Secondary batteries containing this solution have excellent cycle life and fast-charging performance.

[0039] In some embodiments of the present application, the mass proportion of the lithium acrylate polymer is 0.5% to 50% of the total mass of the lithium acrylate polymer solution. This provides a strong bond between the negative electrode active material layer and the current collector, preventing it from falling off, and resulting in a secondary battery containing the lithium acrylate polymer having excellent cycle life and fast charging performance.

[0040] In some embodiments of the present application, the mass of the lithium acrylate polymer accounts for 10%-20% of the total mass of the lithium acrylate polymer solution. This provides a strong bond between the negative electrode active material layer and the current collector, preventing it from falling off, and resulting in a secondary battery containing the lithium acrylate polymer having excellent cycle life and fast charging performance.

[0041] A third aspect of the present application provides a battery comprising the negative electrode sheet described in the first aspect of the present application or the negative electrode sheet prepared by the method described in the second aspect. As a result, the negative electrode active material layer has a strong bond with the current collector, is not easily detached, and the battery has excellent cycle life and fast charging performance.

[0042] A fourth aspect of the present application provides an electrical device comprising the battery described in the third aspect.

[0043] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to denote the same components. In the drawings:

[0045] FIG1 is a schematic structural diagram of a battery cell according to an embodiment of the present application;

[0046] FIG2 is a schematic structural diagram of a battery module according to an embodiment of the present application;

[0047] FIG3 is a schematic structural diagram of a battery pack according to an embodiment of the present application;

[0048] FIG4 is an exploded view of FIG3 ;

[0049] FIG5 is a schematic diagram of an embodiment of an electric device using a battery as a power source;

[0050] FIG6 is a scanning electron microscope image of the negative electrode active material layer of Example 1 of the present application.

[0051] Description of reference numerals:

[0052] 1: Battery pack; 2: Upper case; 3: Lower case; 4: Battery module; 5: Battery cell. DETAILED DESCRIPTION

[0053] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0054] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0055] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0057] With the technological advancements and increasing demand for electric vehicles and rechargeable mobile devices, secondary batteries, as a representative of the new energy sector, have seen rapid growth in research. Secondary batteries offer a wide range of applications due to their compact size and weight, making them easy to carry and use. Their high specific energy content allows for greater energy storage capacity, and lithium-ion batteries exhibit no memory effect, requiring no full discharge and recharge.

[0058] People are increasingly demanding the fast-charging performance of secondary batteries. When lithium acrylate polymers are added to the negative electrode, the Lewis acid small molecules in the electrolyte complex with the negatively charged carboxyl groups in the added lithium acrylate polymer, further increasing the electronegativity of the carboxyl groups, making it easier for lithium ions to dissociate and improving the battery's fast-charging performance. However, when lithium acrylate polymers are directly mixed with negative electrode active materials and applied to battery electrodes, because lithium acrylate polymers are linear binders, the binding force between the negative electrode active material particles and the current collector is weakened, resulting in a decrease in the bonding force between the negative electrode active material layer and the current collector, and the negative electrode active material layer is easily detached.

[0059] In the present application, the lithium acrylate polymer is arranged on the side of the negative electrode active material layer away from the current collector, which can improve the liquid absorption capacity and lithium ion conductivity of the negative electrode plate, reduce the concentration polarization of the negative electrode when lithium ions are charged and discharged at the negative electrode, and improve the fast charging capability and cycle performance of the battery; at the same time, the contact probability of the lithium acrylate polymer with the current collector is low, which can reduce the influence of the lithium acrylate polymer on the bonding force between the negative electrode active material layer and the current collector, making the negative electrode active material layer not easy to fall off.

[0060] The negative electrode sheet disclosed in the embodiment of the present application is suitable for a secondary battery, and the battery disclosed in the embodiment of the present application can be used in an electrical device that uses the battery as a power source or various energy storage systems that use the battery as an energy storage element. Electrical devices may include but are not limited to mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0061] In a first aspect, the present application provides a negative electrode sheet comprising a current collector, a negative electrode active material layer, and a conductive layer, wherein the negative electrode active material layer is disposed on at least one side of the current collector; the conductive layer is disposed on a side of the negative electrode active material layer away from the current collector, and the conductive layer comprises a lithium acrylic polymer;

[0062] The bonding force between the negative electrode active material layer and the current collector is negatively correlated with the surface density of the conductive layer.

[0063] It is understood that the lithium acrylate polymer refers to substituted or unsubstituted lithium polyacrylate, and lithium polyacrylate means that at least one hydrogen atom in polyacrylic acid is replaced by a lithium atom.

[0064] The present application includes at least the following beneficial effects: the lithium acrylate polymer is arranged on the side of the negative electrode active material layer away from the current collector. On the one hand, the small molecules of the electrolyte can be complexed with the carboxylate groups in the lithium acrylate polymer, which can improve the liquid absorption capacity of the negative electrode and the lithium ion conductivity of the negative electrode. When lithium ions are charged and discharged at the negative electrode, the concentration polarization of the negative electrode is reduced, which can improve the fast charging capacity and cycle performance of the battery. On the other hand, the contact probability between the lithium acrylate polymer and the current collector is low, which can reduce the effect of the lithium acrylate polymer on the bonding force between the negative electrode active material layer and the current collector, making the negative electrode active material layer not easy to fall off. In summary, the negative electrode plate proposed in the present application has a strong bonding force between the negative electrode active material layer and the current collector, and the battery containing the negative electrode plate has excellent cycle performance and fast charging performance.

[0065] By controlling the surface density of the conductive layer, the effect of the lithium acrylate polymer on the adhesion between the negative electrode active material layer and the current collector can be reduced, making the negative electrode active material layer less likely to fall off. The adhesion between the negative electrode active material layer and the current collector is strong, and batteries containing the negative electrode sheet have excellent cycling performance and fast charging performance.

[0066] The "area density of the conductive layer" refers to the mass of the conductive layer per unit area of ​​the current collector, which is a well-known concept in the art and can be measured using instruments and methods known in the art. For example, it can be obtained by the following method:

[0067] Step 1: Punch the current collector containing the negative electrode active material layer into a piece with an area of ​​1540.25 mm 2 The small disc is weighed and its mass is g1;

[0068] Step 2: After the conductive layer is applied on both sides, the pole piece is punched into an area of ​​1540.25mm 2 The small disc is weighed and its mass is g2;

[0069] Surface density = (g2-g1) / 1540.25, unit: g / 1540.25mm 2 .

[0070] In some embodiments of the present application, the negative electrode active material layer has pores, and at least a portion of the lithium acrylate polymer is embedded in the pores. This increases the contact area between the lithium acrylate polymer and the negative electrode active material, ensuring sufficient contact between the lithium acrylate polymer and the negative electrode active material, while also improving the battery's fast charging capability and cycling performance without affecting the adhesion between the negative electrode active material layer and the current collector.

[0071] It can be understood that the pores on the negative electrode active material layer refer to the gaps between the negative electrode active materials. The pores on the negative electrode active material layer can be seen on a scanning electron microscope image. The number of pores on the negative electrode active material layer can be expressed by porosity, which is described in detail below.

[0072] In some embodiments of the present application, the bonding force between the negative electrode active material layer and the current collector is Z k Negative correlation, Z k is the reliable permeability of the lithium acrylate polymer in the negative electrode active material layer, the distance between the lithium acrylate polymer and the surface of the negative electrode active material layer away from the current collector in the pore is a mm, the thickness of the negative electrode sheet is D mm, the permeability = a / D×100%, and the permeability corresponding to the permeability distribution number reaching 90% is the reliable permeability.

[0073] It can be understood that the physical meaning of permeability is the degree of penetration of the lithium acrylate polymer in the negative electrode active material layer. "The distance between the lithium acrylate polymer in the pore and the surface of the negative electrode active material layer away from the current collector" refers to the vertical distance between the lithium acrylate polymer and the surface of the negative electrode active material layer away from the current collector in the pore. On the surface of the negative electrode active material layer away from the current collector, the permeability is 0. When the lithium acrylate polymer is embedded in the interface between the current collector and the negative electrode active material layer, the permeability is 100%; that is, each position where the lithium acrylate polymer exists in the pore has a corresponding permeability value. Reliable permeability means that among the permeabilities of various positions in the negative electrode active material layer, the permeability greater than this permeability accounts for more than 90%. The reliable permeability of the lithium acrylate polymer in the negative electrode sheet can be determined by the following method:

[0074] Through in-situ Raman spectroscopy online testing, the main functional group -COO of lithium polyacrylate was identified in the thickness direction of the electrode, and the characteristic peak was 1460cm -1 -1300cm -1 The corresponding thickness / total thickness of the electrode is the permeability. When the permeability distribution number reaches 90%, the corresponding permeability is the reliable permeability.

[0075] The thickness D of the negative electrode sheet can be measured by the following method:

[0076] Use a micrometer to measure the thickness. Use the micrometer to take 10 points in the horizontal and vertical directions of the electrode, and take the average value as the electrode thickness.

[0077] The bonding force between the negative electrode active material layer and the current collector is well known in the art and can be measured using instruments and methods known in the art. For example, it can be obtained by the following method:

[0078] Refer to GB / T 2792-2014, "Test Method for Peel Strength of Adhesive Tapes." Specifically, take a 15-20 cm electrode sheet coated on both sides with negative electrode material; attach it to a steel plate with 3M double-sided tape. Test the electrode sheet using an INSTRON 3365 material testing machine to determine the relationship between force and distance; and calculate the electrode sheet adhesion value.

[0079] The bonding force between the negative electrode active material layer and the current collector is related to Z k Negative correlation means Z k The larger the Z is, the smaller the bonding force between the negative electrode active material layer and the current collector is. k, reducing the effect of the lithium acrylate polymer on the adhesion between the negative electrode active material layer and the current collector, making the negative electrode active material layer less likely to fall off. The adhesion between the negative electrode active material layer and the current collector is strong, and the battery containing the negative electrode sheet has excellent cycle performance and fast charging performance.

[0080] In some embodiments of the present application, the bonding strength between the negative electrode active material layer and the current collector is negatively correlated with the thickness of the negative electrode plate. Therefore, by controlling the thickness of the negative electrode plate, the effect of the lithium acrylate polymer on the bonding strength between the negative electrode active material layer and the current collector can be reduced, making the negative electrode active material layer less likely to fall off. The bonding strength between the negative electrode active material layer and the current collector is strong, and batteries containing the negative electrode plate exhibit excellent cycling performance and fast-charging performance.

[0081] The thickness of the negative electrode sheet includes at least the sum of the thickness of the current collector, the thickness of the negative electrode active material layer, and the thickness of the conductive layer. The thickness of the negative electrode sheet is well known in the art and can be measured using instruments and methods known in the art. For example, the thickness of the negative electrode sheet can be measured using a micrometer.

[0082] In some embodiments of the present application, the bonding force between the negative electrode active material layer and the current collector is positively correlated with the tortuosity of the negative electrode active material layer.

[0083] The bonding force between the negative electrode active material layer and the current collector is positively correlated with the tortuosity of the negative electrode active material layer. This means that the greater the tortuosity of the negative electrode active material layer, the greater the bonding force between the negative electrode active material layer and the current collector. Therefore, by controlling the tortuosity of the negative electrode active material layer, the effect of the lithium acrylate polymer on the bonding force between the negative electrode active material layer and the current collector can be reduced, making the negative electrode active material layer less likely to fall off. This strong bonding between the negative electrode active material layer and the current collector allows batteries containing the negative electrode sheet to exhibit excellent cycling performance and fast-charging performance.

[0084] Tortuosity is the degree of tortuosity. The electrolyte does not flow in a straight line in the negative electrode active material layer, but flows forward in a tortuous manner. Tortuosity reflects the degree of tortuosity. The tortuosity is equal to the ratio of the actual length of the electrolyte in the pore to the apparent length (macroscopic distance, i.e., the thickness of the negative electrode active material layer) passing through the negative electrode active material layer, that is, the actual length of the trajectory of the electrolyte particle in the pore when it passes through a unit distance of the negative electrode active material layer.

[0085] The tortuosity of the negative electrode active material layer is well known in the art and can be measured using instruments and methods known in the art. For example, it can be obtained by the following method:

[0086] 1. Two identical pole pieces and diaphragms are assembled into a symmetrical battery;

[0087] 2. Inject electrolyte and then soak;

[0088] 3. Perform electrochemical impedance spectroscopy (EIS) to obtain the electrode ion impedance Rion and calculate the lithium battery electrode tortuosity ε.

[0089] 4. The thickness of the electrode is L, the porosity is τ, and the area is A; the conductivity of the electrolyte is σ;

[0090] The thickness L of the electrode is measured using a micrometer. 10 points are taken in the horizontal and vertical directions of the electrode, and the average value is taken as the electrode thickness.

[0091] The porosity τ can be determined by referring to the national standard GB / T24586-2009 "Determination of apparent density, true density and porosity of iron ore". The specific test method is as follows: the electrode is immersed in ethyl methyl carbonate (EMC) for cleaning; based on the gas displacement method, the negative electrode is placed in a true density tester, the test system is sealed, helium is introduced according to the program, and the pressure of the gas in the sample chamber and expansion chamber is detected. Among them, the percentage of the pore volume in the electrode to the total volume of the electrode is the electrode porosity, which is calculated as: Porosity = (V-V0) / V×100%, where V0 is the true volume and V is the apparent volume.

[0092] The conductivity σ of the electrolyte can be measured using instruments and methods known in the art. For example, the industry standard HG / T4067-2015, "Lithium Hexafluorophosphate Electrolyte," can be used. The density meter's measurement temperature can be set to 20°C, and the sample can be injected into the instrument's measuring cell to perform the measurement and read the data.

[0093] 5. The formula for calculating tortuosity is: ε = (Rion·A·τ·σ) / L.

[0094] In some embodiments of the present application, the bonding strength between the negative electrode active material layer and the current collector is negatively correlated with the porosity of the negative electrode active material layer. Thus, by controlling the porosity of the negative electrode active material layer, the effect of the lithium acrylate polymer on the bonding strength between the negative electrode active material layer and the current collector can be reduced, making the negative electrode active material layer less likely to fall off. The bonding strength between the negative electrode active material layer and the current collector is strong, and batteries containing the negative electrode sheet exhibit excellent cycling performance and fast-charging performance.

[0095] The porosity of the negative electrode active material layer refers to the percentage of the pore volume in the negative electrode active material layer to the total volume of the negative electrode active material layer. The porosity of the negative electrode active material layer is well known in the art and can be measured using instruments and methods known in the art. For example, it can be obtained by the following method:

[0096] 1. Use tweezers to select >20 negative electrode pieces that do not contain a conductive layer. The pieces should be in good appearance and have no powder falling off the edges. Place them into the sample cup. Record the number of pieces and calculate the apparent volume V2. Apparent volume V2 = S × H × A, where

[0097] S-area, cm 2 ;

[0098] H-thickness, cm;

[0099] A-sample number, EA;

[0100] 2. Place the sample cup containing the sample in the true density tester, seal the test system, introduce helium according to the procedure, and test the gas pressure in the sample chamber and expansion chamber;

[0101] 3. Then calculate the real volume V1 according to Bohr's law (PV = nRT), and then obtain the porosity of the sample to be tested according to the following formula:

[0102] Porosity = (V2 - V1) / V2 x 100%.

[0103] In some embodiments of the present application, Z k =1%-60%. For example, Z k It can be 1%-59%, 5%-55%, 10%-50%, 15%-45%, 20%-40%, 25%-35%, etc. The reliable permeability of the lithium acrylate polymer in the negative electrode sheet is within the above range, which can improve the liquid absorption capacity and lithium ion conductivity of the negative electrode sheet, and improve the fast charging capacity and cycle performance of the battery; in addition, the contact probability between the lithium acrylate polymer and the current collector is low, which can reduce the effect of the lithium acrylate polymer on the bonding force between the negative electrode active material layer and the current collector, making the negative electrode active material layer not easy to fall off. The bonding force between the negative electrode active material layer and the current collector is strong, and the battery containing the negative electrode sheet has excellent cycle performance and fast charging performance. In other embodiments of the present application, Z k =25%-45%.

[0104] In some embodiments of the present application, a / D×100%=20%-50%. For example, a / D×100% can be 20%-49%, 22%-47%, 25%-45%, 28%-41%, 30%-40%, 32%-38%, 34%-35%, etc. Within the above a / D×100% range, the infiltration of the lithium acrylate polymer into the interface between the negative electrode active material layer and the current collector can be reduced, the bonding force between the negative electrode active material layer and the current collector is strong, and the battery containing the negative electrode sheet has excellent cycle performance and fast charging performance. In other embodiments of the present application, a / D×100%=25%-40%.

[0105] In some embodiments of the present application, the surface density of the conductive layer is 0.05g / 1540.25mm 2 -0.4g / 1540.25mm 2 For example, the surface density Q of the conductive layer can be 0.05g / 1540.25mm 2 -0.35g / 1540.25mm 2 , 0.1g / 1540.25mm 2 -0.3g / 1540.25mm 2 , 0.15g / 1540.25mm 2 -0.25g / 1540.25mm 2 , 0.15g / 1540.25mm 2 -0.2g / 1540.25mm 2 Specifically, the surface density of the conductive layer is 0.05g / 1540.25mm 2 -0.4g / 1540.25mm 2 In some other embodiments of the present invention, the surface density of the conductive layer is 0.1 g / 1540.25 mm 2 -0.2g / 1540.25mm 2 .

[0106] In some embodiments of the present application, the porosity of the negative electrode active material layer is 20%-40%. For example, the porosity τ of the negative electrode active material layer can be 20%-39%, 22%-37%, 25%-35%, 27%-34%, 30%-32%, etc. Specifically, when the porosity of the negative electrode active material layer is within the above range, the bonding force between the negative electrode active material layer and the current collector is strong, and the battery containing the negative electrode sheet has excellent cycle performance and fast charging performance. In other embodiments of the present application, the porosity of the negative electrode active material layer is 25%-35%.

[0107] In some embodiments of the present application, the thickness of the negative electrode plate is 0.1mm-0.3mm. For example, the thickness D of the negative electrode plate can be 0.1mm-0.29mm, 0.12mm-0.27mm, 0.15mm-0.25mm, 0.17mm-0.23mm, etc. Specifically, when the thickness of the negative electrode plate is within the range of 0.1mm-0.3mm, the bonding force between the negative electrode active material layer and the current collector is strong, and the battery containing the negative electrode plate has excellent cycle performance and fast charging performance. In other embodiments of the present application, the thickness of the negative electrode plate is 0.1mm-0.15mm.

[0108] In some embodiments of the present application, the tortuosity of the negative electrode active material layer is 0.5-7. For example, the tortuosity ε of the negative electrode active material layer can be 0.5-6.9, 1-6.5, 1.5-6, 2-5.5, 2.5-5, 3-4.5, 3.5-4, etc. The tortuosity of the negative electrode active material layer within the above range can reduce the intrusion of the lithium acrylate polymer into the interface between the negative electrode active material layer and the current collector, thereby strengthening the bonding force between the negative electrode active material layer and the current collector, and the battery containing the negative electrode sheet has excellent cycle performance and fast charging performance. In other embodiments of the present application, ε = 2-4.

[0109] In some embodiments of the present application, the bonding force between the negative electrode active material layer and the current collector is 5 N / m-20 N / m. For example, the bonding force F between the negative electrode active material layer and the current collector can be 5 N / m-19 N / m, 7 N / m-18 N / m, 10 N / m-15 N / m, 12 N / m-14 N / m, etc. The bonding force between the negative electrode active material layer and the current collector is within the range of 5 N / m-20 N / m. The bonding force between the negative electrode active material layer and the current collector is strong, and the battery containing the negative electrode sheet has excellent cycle performance and fast charging performance. In other embodiments of the present application, F = 7 N / m-15 N / m.

[0110] In some embodiments of the present application, the lithium acrylate polymer includes at least one of lithium polyacrylate, lithium polymethacrylate, lithium polyethylacrylate, or lithium polypropylacrylate. Specifically, the conductive layer comprising the aforementioned lithium acrylate polymer can enhance the negative electrode's liquid absorption capacity and lithium ion conductivity, improving the battery's fast charging capability and cycling performance, while also providing strong adhesion between the negative electrode active material layer and the current collector.

[0111] In some embodiments of the present application, the mass fraction of lithium is 3%-8.9% based on the total mass of the lithium acrylate polymer. For example, the mass fraction of lithium can be 3%-8.9%, 3.5%-8.5%, 4%-7%, 4%-6%, etc. Based on the total mass of the lithium acrylate polymer, the mass fraction of lithium = the mass of lithium / the mass of the lithium acrylate polymer. Within the above range, a portion of the lithium acrylate polymer penetrates into the pores of the negative electrode active material layer, which can improve the liquid absorption capacity of the negative electrode sheet and significantly improve the lithium ion conductivity. This can improve the electronic conductivity of the negative electrode sheet, reduce internal resistance, and increase the diffusion coefficient of lithium ions in the electrode material, thereby improving the fast charging capability and cycle performance of the battery. In addition, the bonding force between the negative electrode active material layer and the current collector is strong. In other embodiments of the present application, the mass fraction of lithium is 5%-7.5% based on the total mass of the lithium acrylate polymer.

[0112] Specifically, “the mass fraction of lithium based on the total mass of the lithium acrylate polymer” can be determined by the following method:

[0113] A lithium acrylate polymer sample of a certain mass M is measured using inductively coupled plasma emission spectroscopy (ICP) to determine the mass m1 of lithium in the polymer lithium salt. The average mass percentage of lithium in the polymer lithium salt is m1 / M × 100%. The sample to be tested is prepared as follows: 0.2 g of sample is weighed into a beaker, 10 mL of concentrated HNO3 solution is added, and the sample is digested on a 180°C hot plate for 30 minutes. After the sample digestion is complete, the sample is cooled to room temperature and the digested solution is transferred to a 50 mL volumetric flask via a funnel, bringing the volume to a constant level. Testing is performed according to USEPA-6010D-2018. A standard test solution is prepared: the National Nonferrous Metals Testing Center's ICP analysis multi-element standard solution, with curve concentration points of 0, 0.2, 0.5, 1.0, and 2.0 mg / L. A calibration curve for the standard solution is created using the instrument. The sample mass and volume are then input, and the digested solution is tested. Any solution outside the curve range needs to be diluted before testing. Finally, the element content (quantitative analysis) is determined based on the intensity of the spectral lines.

[0114] In some embodiments of the present application, the number average molecular weight (Mn) of the lithium acrylate polymer is 3,000-1,000,000. For example, the number average molecular weight (Mn) of the lithium acrylate polymer can be 3,000-990,000, 5,000-950,000, 10,000-900,000, 50,000-800,000, 100,000-700,000, 200,000-600,000, 300,000-500,000, 400,000-500,000, etc. Within the above-mentioned number average molecular weight (Mn) range, the lithium acrylate polymer is sufficient to improve the liquid absorption capacity and lithium ion conductivity of the negative electrode sheet, thereby improving the fast charging capability and cycle performance of the battery, and has little effect on the bonding force between the negative electrode active material layer and the current collector, thereby reducing the probability of the negative electrode active material layer falling off the current collector. In other embodiments of the present application, the number average molecular weight (Mn) of the lithium acrylate polymer is 100,000-500,000.

[0115] The "number average molecular weight Mn" of the lithium acrylate polymer is well known in the art and can be measured using instruments and methods known in the art. For example, it can be obtained by the following method:

[0116] Gel permeation chromatography was used in accordance with the national standard GB / T21863-2008 “Gel permeation chromatography (GPC) using tetrahydrofuran as eluent”.

[0117] For details, please refer to the following test steps: Use ultra-high performance polymer chromatograph: ACQUITY APC; detector: ACQUITY differential refractive index detector. The test steps are as follows: (1) Start preheating: Install the chromatographic column and pipeline, turn on the console in sequence, test the power supply, etc., and open the test software Empower; (2) Parameter setting, injection volume: 0μL to 50μL (depending on the sample concentration); pump flow rate: 0.2mL / min; mobile phase: 30mol / LLiBr in NMP solution; seal cleaning liquid: isopropanol; pre-column: PLgel10umMiniMIX-BGuard (size: 50mm×4.6mm×2); analytical phase: PLgel10umMiniMIX-B (size: 250mm×4.6mm); standard: polystyrene sleeve; run time: 30min; detector: ACQUITY differential refractive index (RI) detector; column oven temperature: 90℃; detector temperature: 55℃. (3) Sample testing: a. Standard sample and test sample preparation: Weigh 0.002g to 0.004g of standard sample / test sample respectively and add 2mL of mobile phase liquid to prepare a 0.1% to 0.5% mixed standard, and store in the refrigerator for >8h; b. Standard solution / sample testing: Edit the sample group to be tested, select the established sample group method, and after the baseline is stable, click the run queue to start testing the sample; (4) Data processing: Based on the relationship between retention time and molecular weight, use the chemical workstation to establish a calibration curve, integrate and quantify the sample spectrum, and the chemical workstation automatically generates the molecular weight and molecular weight distribution results.

[0118] In some embodiments of the present application, the current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments of the present application, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material can be a negative electrode active material for batteries that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0120] In some embodiments of the present application, the negative electrode active material comprises at least one of elemental lithium or a lithium alloy, wherein the lithium alloy comprises at least one of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, boron, carbon, and silicon. A lithium alloy refers to an alloy of lithium with other metals and / or non-metals, wherein the other metals and / or non-metals comprise at least one of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, boron, carbon, and silicon. Lithium's low operating voltage and high specific capacity significantly increase the battery's energy density.

[0121] In some embodiments of the present application, the negative electrode active material layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0122] In some embodiments of the present application, the negative electrode active material layer may further include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some embodiments of the present application, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0124] A second aspect of the present application provides a method for preparing a negative electrode sheet, comprising:

[0125] S100, forming a negative electrode active material layer on at least one side of the current collector

[0126] S200, forming a conductive layer on a side of the negative electrode active material layer away from the current collector, wherein the conductive layer includes a lithium acrylic acid polymer;

[0127] The bonding force between the negative electrode active material layer and the current collector is negatively correlated with the surface density of the conductive layer.

[0128] Thus, in the negative electrode sheet prepared using the above method, the lithium acrylate polymer is positioned on the side of the negative electrode active material layer away from the current collector. On the one hand, small molecules in the electrolyte can complex with the carboxylate groups in the lithium acrylate polymer, which can improve the negative electrode sheet's liquid absorption capacity and lithium ion conductivity. During lithium ion charging and discharging, the concentration polarization of the negative electrode is reduced, which can improve the battery's fast charging capability and cycle performance. On the other hand, the lithium acrylate polymer has a low contact probability with the current collector, which can reduce the lithium acrylate polymer's effect on the adhesion between the negative electrode active material layer and the current collector, making the negative electrode active material layer less likely to fall off. The strong adhesion between the negative electrode active material layer and the current collector makes it less likely to fall off, and the secondary battery containing the lithium acrylate polymer has excellent cycle life and fast charging performance.

[0129] In some embodiments of the present application, the negative electrode active material layer can be prepared by the following method: the components for preparing the negative electrode plate, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode active material layer can be obtained.

[0130] In some embodiments of the present application, a lithium acrylate polymer is sprayed onto the side of the negative electrode active material layer facing away from the current collector to form a conductive layer. At least a portion of the lithium acrylate polymer is embedded within the pores of the negative electrode active material layer. This ensures strong adhesion between the negative electrode active material layer and the current collector, making it less likely to fall off. Furthermore, the lithium acrylate polymer maintains sufficient contact with the negative electrode active material, resulting in a secondary battery containing the polymer exhibiting excellent cycle life and fast-charging performance.

[0131] The spray method involves spraying a slurry containing a lithium acrylate polymer onto the side of the negative electrode active material layer facing away from the current collector. The slurry forms mist-like droplets that adhere to the side of the negative electrode active material layer facing away from the current collector and enter the pores. After drying, they form a conductive layer. The conductive layer produced by this method is highly uniform and resists shedding from the negative electrode active material layer.

[0132] In some embodiments of the present application, a spray box is used, and the liquid inside the spray box is a slurry of a lithium acrylic polymer. The current collector containing the negative electrode active material layer passes through the spray box and is dried to complete the preparation of the conductive layer.

[0133] In some embodiments of the present application, the spray pressure is 0.1kPa-100kPa, and the spray pressure is the atomization pressure inside the spray box. For example, the spray pressure can be 0.1kPa-99kPa, 0.5kPa-98kPa, 1kPa-95kPa, 10kPa-90kPa, 20kPa-80kPa, 30kPa-70kPa, 40kPa-60kPa, 50kPa-60kPa, etc. Within the above spray pressure range, a uniform conductive layer can be formed, and the conductive layer is not easy to fall off from the negative electrode active material layer. The bonding force between the negative electrode active material layer and the current collector is strong and not easy to fall off, and the acrylic acid lithium polymer can fully contact the negative electrode active material, and the secondary battery containing it has excellent cycle life and fast charging performance.

[0134] In some embodiments of the present application, the spray temperature is 70°C-150°C. The spray temperature is the temperature inside the atomization box. For example, the spray temperature can be 70°C-149°C, 80°C-140°C, 90°C-130°C, 100°C-120°C, etc. Thus, within the above-mentioned spray temperature range, a uniform conductive layer can be formed, the conductive layer is not easy to fall off from the negative electrode active material layer, the bonding force between the negative electrode active material layer and the current collector is strong and not easy to fall off, and the lithium acrylate polymer can fully contact the negative electrode active material. The secondary battery containing the polymer has excellent cycle life and fast charging performance.

[0135] In some embodiments of the present application, when the current collector containing the negative electrode active material layer passes through the spray box, the speed of the current collector containing the negative electrode active material layer is 0.1m / s-10m / s. For example, the speed of the current collector containing the negative electrode active material layer can be 0.1m / s-9.9m / s, 0.5m / s-9.5m / s, 1m / s-9m / s, 2m / s-8m / s, 3m / s-7m / s, 4m / s-6m / s, etc., which can form a uniform conductive layer that is not easily detached from the negative electrode active material layer. In other embodiments of the present application, the speed of the current collector containing the negative electrode active material layer is 2m / s-5m / s.

[0136] In some embodiments of the present application, a current collector containing a negative electrode active material layer is immersed in a lithium acrylate polymer solution to form a conductive layer on the side of the negative electrode active material layer away from the current collector, and at least a portion of the lithium acrylate polymer is embedded in the pores of the negative electrode active material layer. The conductive layer prepared by this method has good uniformity and is not easily detached from the negative electrode active material layer. The negative electrode active material layer and the current collector have strong adhesion and are not easily detached. The lithium acrylate polymer is in full contact with the negative electrode active material, and secondary batteries containing this conductive layer have excellent cycle life and fast charging performance.

[0137] In some embodiments of the present application, the temperature of the slurry of the lithium acrylate polymer is 50°C-80°C. For example, the temperature of the slurry of the lithium acrylate polymer can be 50°C-79°C, 55°C-75°C, 60°C-70°C, etc.

[0138] In some embodiments of the present application, a current collector containing a negative electrode active material layer is passed through an immersion solution containing a lithium acrylate polymer at a speed of 1 m / min-50 m / min. For example, the speed at which the current collector containing a negative electrode active material layer passes through the immersion solution containing a lithium acrylate polymer can be 1 m / min-49 m / min, 5 m / min-45 m / min, 10 m / min-40 m / min, 20 m / min-30 m / min, etc., to form a uniform conductive layer that is not easily detached from the negative electrode active material layer. In other embodiments of the present application, a current collector containing a negative electrode active material layer is passed through an immersion solution containing a lithium acrylate polymer at a speed of 8 m / min-15 m / min.

[0139] In some embodiments of the present application, based on the total mass of the lithium acrylate polymer solution, the mass proportion of the lithium acrylate polymer is 0.5%-50%. For example, the mass proportion of the lithium acrylate polymer can be 0.5%-49%, 1%-45%, 5%-40%, 10%-30%, 15%-25%, etc. As a result, the bonding force between the negative electrode active material layer and the current collector is strong and not easy to fall off, and the lithium acrylate polymer can fully contact with the negative electrode active material, and the secondary battery containing it has excellent cycle life and fast charging performance. In other embodiments of the present application, based on the total mass of the lithium acrylate polymer solution, the mass proportion of the lithium acrylate polymer is 10%-20%.

[0140] In other embodiments of the present application, the conductive layer may be prepared by a dry process. Specifically, the lithium acrylate polymer powder is mixed with a conductive agent, etc., and then directly pressed onto the current collector by a dry process in a dry state.

[0141] A third aspect of the present application provides a battery comprising the negative electrode sheet described in the first aspect of the present application or the negative electrode sheet prepared by the method described in the second aspect. As a result, the negative electrode active material layer has a strong bond with the current collector, is not easily detached, and the battery has excellent cycle life and fast charging performance.

[0142] A battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0143] It can be understood that the battery proposed in this application is a lithium-ion battery.

[0144] Typically, a battery cell consists of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the battery's charge and discharge process, active metal ions (lithium ions) are inserted and removed between the positive and negative electrode sheets. The separator is placed between the positive and negative electrode sheets to isolate them. The electrolyte conducts the active metal ions between the positive and negative electrode sheets.

[0145] [Positive electrode]

[0146] In some embodiments of the present application, the positive electrode plate includes a positive electrode current collector, which can be a metal foil, a metal foam or a composite current collector. For example, as the metal foil, aluminum or stainless steel with a silver surface treatment, stainless steel, copper, aluminum, carbon electrode, carbon, nickel or titanium, etc. can be used. The composite current collector may include a polymer material base and a metal layer. The foam metal may be nickel foam, copper foam, aluminum foam, alloy foam, etc. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0147] In some embodiments of the present application, the positive electrode plate may further include a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. The specific type of the positive electrode active material is not limited, and active materials known in the art that can be used for battery positive electrodes can be used. Those skilled in the art can select according to actual needs.

[0148] The positive electrode active material may include, but is not limited to, at least one of a lithium transition metal oxide, an olivine-structured lithium-containing phosphate, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their modified compounds. These materials can all be obtained through commercial channels.

[0149] The battery's charge and discharge processes are accompanied by the intercalation and deintercalation of Li, and the Li content varies when the battery is discharged to different states. In the examples of this application, the Li content in the positive electrode materials listed is the initial state of the material, that is, the state before the material is added. When the positive electrode material is used in a battery system, the Li content will change after charge and discharge cycles.

[0150] In the examples of the present application regarding the positive electrode materials, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0151] The modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0152] The positive electrode active material layer may also optionally include a binder, a conductive agent, and other optional auxiliary agents.

[0153] As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers.

[0154] As an example, the adhesive may include at least one of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0155] [Electrolytes]

[0156] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0157] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0158] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0159] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0160] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0161] [Isolation film]

[0162] As the above-mentioned isolation membrane, the present application has no special restrictions and any known porous structure isolation membrane with electrochemical stability and mechanical stability can be selected according to actual needs. For example, it can include a single-layer or multi-layer film containing at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0163] The embodiment of the present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square or any other shape. FIG1 shows a battery cell 5 with a square structure as an example.

[0164] In some embodiments of the present application, the battery cell 5 may include an outer packaging for packaging the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[0165] In some embodiments of the present application, the outer packaging may include a housing and a cover. The housing may include a bottom plate and side plates connected to the bottom plate, with the bottom plate and side plates enclosing a receiving cavity. The housing may have an opening communicating with the receiving cavity, and the cover may be positioned over the opening to seal the receiving cavity.

[0166] The positive electrode sheet, negative electrode sheet, and separator can be wound or laminated to form an electrode assembly. The electrode assembly is encapsulated in the housing. The number of electrode assemblies contained in a battery cell can include one or more, which can be adjusted according to demand.

[0167] In some embodiments of the present application, the outer packaging of the battery cell may include a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0168] The outer packaging of the battery cell 5 may also include a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0169] In some embodiments of the present application, battery cells may be assembled into a battery module. The battery module may contain multiple batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0170] Figure 2 shows an example battery module 4. Referring to Figure 2 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0171] The battery module 4 may further include a housing having a housing space, wherein a plurality of battery cells 5 are housed in the housing space. In some embodiments of the present application, the battery modules may be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0172] Figures 3 and 4 illustrate an example battery pack 1. Referring to Figures 3 and 4 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0173] In a fourth aspect, the present application provides an electrical device comprising the battery described in the third aspect. Specifically, the battery can serve as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships, satellites, and energy storage systems.

[0174] FIG5 shows an example of an electric device, which includes a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0175] As another example, electric devices may include mobile phones, tablet computers, and laptop computers. These electric devices are generally required to be lightweight and thin, and may use batteries as power sources.

[0176] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0177] Example 1

[0178]

Positive electrode preparation

[0179] The positive electrode active material lithium iron phosphate (LFP), the conductive agent acetylene black, and the binder polyvinylidene fluoride were mixed in a mass ratio of 98:1:1, and the solvent N-methylpyrrolidone was added and stirred until the system became uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on both sides of the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying. The positive electrode sheet was then cut into 40mm×50mm rectangles. The positive electrode surface capacity was 3.5mAh / cm 2 .

[0180]

Negative electrode sheet preparation

[0181] (1) Preparation of negative electrode slurry: 96.5 wt.% of negative electrode active material graphite, 2.5 wt.% of styrene-butadiene rubber (SBR) binder, and 1 wt.% of SP conductive carbon black were uniformly dispersed in a deionized water solvent to prepare a negative electrode slurry.

[0182] (2) The negative electrode slurry is evenly coated on the current collector by a coating machine and dried to obtain a current collector containing a negative electrode active material layer.

[0183] (3) Preparation of lithium polyacrylate slurry: lithium polyacrylate is dispersed in deionized water to prepare a dispersion.

[0184] (4) The current collector containing the negative electrode active material layer is passed through a spray box containing lithium polyacrylate slurry at a speed of 5 m / s. The internal atomization pressure of the spray box is 25 kPa and the atomization temperature is 85°C. The box is then cooled until the lithium polyacrylate slurry is completely dried and solidified.

[0185] (5) The dried electrode sheets are rolled into a coil and rolled normally to obtain the negative electrode sheets.

[0186]

Isolation film

[0187] Polyethylene porous membrane is selected as the isolation membrane.

[0188]

Electrolyte preparation

[0189] The electrolyte was prepared by dissolving 1 M LiPF6 in a solution in which vinylene carbonate was added to a solvent in which ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:2.

[0190] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum packaging, standing, formation, and shaping processes, a secondary battery is obtained.

[0191] The secondary batteries containing negative electrode sheets of Example 2-51 and Comparative Example 1-2 are the same as Example 1 except for the different parameters (see Table 1).

[0192] The speeds of the current collector containing the negative electrode active material layer in Examples 3-5 passing through the spray box containing the lithium polyacrylate slurry are different. The speed of Example 3 is 2 m / s, and the speed of Z is 1 m / s. k =45%, the speed of Example 4 is 10m / s, Z k =1%, the speed of embodiment 5 is 0.5m / s, Z k =60%.

[0193] In Examples 20 and 21, except that the ratio of the negative electrode slurry is different from that in Example 1, the rest is the same as Example 1. The negative electrode slurry of Example 20 contains 98 wt.% of negative electrode active material graphite, 1 wt.% of styrene butadiene rubber (SBR) binder, and 1 wt.% of SP conductive carbon black. In Example 21, the negative electrode slurry contains 95.5 wt.% of negative electrode active material graphite, 3.5 wt.% of styrene butadiene rubber (SBR) binder, and 1 wt.% of SP conductive carbon black.

[0194] In Examples 45-49, except for [Negative Electrode Sheet Preparation] (5) (method for preparing the conductive layer) which is different from Example 1, the rest are the same as Example 1, and [Negative Electrode Sheet Preparation] (5) is replaced by: passing the current collector containing the negative electrode active material layer through an immersion box containing a lithium acrylate polymer solution at a speed of 10 m / min, and then passing through a cooling box until the lithium polyacrylate slurry is completely dried and solidified.

[0195] In Comparative Example 1, except that the lithium polyacrylate slurry in [Preparation of Negative Electrode Sheet] (5) (Preparation Method of Conductive Layer) was replaced with deionized water, the rest was the same as Example 1.

[0196] Comparative Example 2 was identical to Example 1 except that the negative electrode sheet preparation was different. The negative electrode sheet preparation was modified as follows: 95% wt of the negative electrode active material, graphite, 2.5% wt of styrene-butadiene rubber (SBR) binder, 1% wt of SP conductive carbon, and lithium polyacrylate were uniformly dispersed in deionized water to prepare a negative electrode slurry. The negative electrode slurry was evenly coated onto the current collector using a coater and dried to obtain a negative electrode sheet.

[0197] The parameters of the electrolytes of Examples 1-51 and Comparative Examples 1-2 of the present application are shown in Table 1.

[0198] Table 1

[0199] In Table 1, “ / ” indicates that no addition was made.

[0200] Parameter test:

[0201] 1. Reliable penetration:

[0202] Through in-situ Raman spectroscopy online testing, the main functional group -COO of lithium polyacrylate was identified in the thickness direction of the electrode, and the characteristic peak was 1460 -1 -1300cm -1 The corresponding thickness / negative electrode thickness is the permeability. When the permeability distribution number reaches 90%, the corresponding permeability is the reliable permeability.

[0203] 2. Negative electrode thickness

[0204] Use a micrometer to measure the thickness. Use the micrometer to take 10 points in the horizontal and vertical directions of the electrode, and take the average value as the electrode thickness.

[0205] 3. Adhesion between the negative electrode active material layer and the current collector:

[0206] Refer to GB / T 2792-2014, "Test Method for Peel Strength of Adhesive Tapes." Specifically, take a 15-20 cm electrode sheet coated on both sides with negative electrode material; attach the electrode sheet to a steel plate with 3M double-sided tape. Test the electrode sheet using an INSTRON 3365 material testing machine to determine the relationship between force and distance; and calculate the electrode sheet adhesion value.

[0207] 4. Surface density of conductive layer:

[0208] Step 1: Punch the current collector containing the negative electrode active material layer into a piece with an area of ​​1540.25 mm 2 The small disc is weighed and its mass is g1;

[0209] Step 2: After the conductive layer is applied on both sides, the pole piece is punched into an area of ​​1540.25mm 2 The small disc is weighed and its mass is g2;

[0210] Surface density = (g2-g1) / 1540.25, unit: g / 1540.25mm 2 .

[0211] 5. Tortuosity:

[0212] 1) Two identical pole pieces and diaphragms are assembled into a symmetrical battery.

[0213] 2) Inject electrolyte and soak,

[0214] 3) Perform electrochemical impedance spectroscopy (EIS) to obtain the electrode ionic impedance Rion and calculate the lithium battery electrode tortuosity ε.

[0215] 4) The thickness of the electrode is L, the porosity is τ, and the area is A; the conductivity of the electrolyte is σ;

[0216] The thickness L of the electrode is measured using a micrometer. 10 points are taken in the horizontal and vertical directions of the electrode, and the average value is taken as the electrode thickness.

[0217] The porosity τ can be determined by referring to the national standard GB / T24586-2009 "Determination of apparent density, true density and porosity of iron ore". The specific test method is as follows: the electrode is immersed in ethyl methyl carbonate (EMC) for cleaning; based on the gas displacement method, the negative electrode is placed in a true density tester, the test system is sealed, helium is introduced according to the program, and the pressure of the gas in the sample chamber and expansion chamber is detected. Among them, the percentage of the pore volume in the electrode to the total volume of the electrode is the electrode porosity, which is calculated as: Porosity = (V-V0) / V×100%, where V0 is the true volume and V is the apparent volume.

[0218] The conductivity σ of the electrolyte can be measured using instruments and methods known in the art. For example, the industry standard HG / T4067-2015, "Lithium Hexafluorophosphate Electrolyte," can be used. The density meter's measurement temperature can be set to 20°C, and the sample can be injected into the instrument's measuring cell to perform the measurement and read the data.

[0219] 5) The tortuosity is calculated using the formula: ε = (Rion·A·τ·σ) / L.

[0220] 6. Porosity of the negative electrode active material layer:

[0221] 1) Use tweezers to select >20 negative electrode pieces that do not contain a conductive layer. The pieces should be in good appearance and have no powder falling off the edges. Place them into the sample cup. Record the number of pieces and calculate the apparent volume V2. Apparent volume V2 = S × H × A, where

[0222] S-area, cm 2 ;

[0223] H-thickness, cm;

[0224] A-sample number, EA;

[0225] 2) Place the sample cup containing the sample in the true density tester, close the test system, introduce helium according to the procedure, and detect the pressure of the gas in the sample chamber and expansion chamber;

[0226] 3) Calculate the true volume V1 according to Bohr's law (PV = nRT), and then obtain the porosity of the sample to be tested according to the following formula:

[0227] Porosity = (V2 - V1) / V2 x 100%.

[0228] 7. Based on the total mass of lithium acrylate polymer, the mass fraction of lithium is:

[0229] A lithium acrylate polymer sample of a given mass, M, was measured using inductively coupled plasma emission spectroscopy (ICP) to determine the mass, m1, of lithium in the polymer lithium salt. The average mass percentage of lithium in the polymer lithium salt is m1 / M × 100%. The sample to be tested was prepared as follows: 0.2 g of sample was weighed into a beaker, 10 mL of concentrated HNO3 solution was added, and the sample was digested on a 180°C hot plate for 30 minutes. After the sample digested for 30 minutes, it was cooled to room temperature and the digested solution was transferred to a 50 mL volumetric flask via a funnel, bringing the volume to standard. Testing was performed according to USEPA-6010D-2018. A standard test solution was prepared: a multi-element standard solution from the National Nonferrous Metals Testing Center for ICP analysis, with concentrations at 0, 0.2, 0.5, 1.0, and 2.0 mg / L. A calibration curve for the standard solution was created using the instrument. The sample mass and volume were then input, and the digested solution was tested. Any solution outside the curve range needed to be diluted before testing. Finally, the element content was determined based on the intensity of the spectral lines.

[0230] 8. Number average molecular weight Mn of lithium acrylate polymer:

[0231] Gel permeation chromatography was used in accordance with the national standard GB / T21863-2008 “Gel permeation chromatography (GPC) using tetrahydrofuran as eluent”.

[0232] For details, please refer to the following test steps: Use ultra-high performance polymer chromatograph: ACQUITY APC; detector: ACQUITY differential refractive index detector. The test steps are as follows: (1) Start preheating: Install the chromatographic column and pipeline, turn on the console in sequence, test the power supply, etc., and open the test software Empower; (2) Parameter setting, injection volume: 0μL to 50μL (depending on the sample concentration); pump flow rate: 0.2mL / min; mobile phase: 30mol / LLiBr in NMP solution; seal cleaning liquid: isopropanol; pre-column: PLgel10umMiniMIX-BGuard (size: 50mm×4.6mm×2); analytical phase: PLgel10umMiniMIX-B (size: 250mm×4.6mm); standard: polystyrene sleeve; run time: 30min; detector: ACQUITY differential refractive index (RI) detector; column oven temperature: 90℃; detector temperature: 55℃. (3) Sample testing: a. Standard sample and test sample preparation: Weigh 0.002g to 0.004g of standard sample / test sample respectively and add 2mL of mobile phase liquid to prepare a 0.1% to 0.5% mixed standard, and store in the refrigerator for >8h; b. Standard solution / sample testing: Edit the sample group to be tested, select the established sample group method, and after the baseline is stable, click the run queue to start testing the sample; (4) Data processing: Based on the relationship between retention time and molecular weight, use the chemical workstation to establish a calibration curve, integrate and quantify the sample spectrum, and the chemical workstation automatically generates the molecular weight and molecular weight distribution results.

[0233] Performance testing:

[0234] 1. Battery cycle capacity retention rate test:

[0235] Taking Example 1 as an example, the ambient temperature of the secondary battery cycle is set to 25°C, and the charge and discharge cycle is performed using a rate of 0.5C (i.e., 70mA). The cut-off voltages for charge and discharge are set to 3.8V and 2.0V, respectively. After 1500 charge and discharge cycles, the discharge capacity at the 1500th cycle is recorded as the capacity of the battery after 1500 cycles. The ratio of the capacity of the battery after 1500 cycles to the initial capacity of the battery (the discharge capacity at the first cycle) is the cycle capacity retention rate. The cycle capacity retention rate test results of Examples 1-51 and Comparative Examples 1-2 are shown in Table 2.

[0236] 2. Battery charging time test:

[0237] (1) Taking Example 1 as an example, Cu wire is used as the three electrodes and charged at a charging rate of 5C until the negative electrode potential drops to 0mV. Then, the battery is switched to low-rate charging and charged at low rates of 4C, 3C, 2C, and 1C in sequence to obtain the maximum charging capacity Map of the battery.

[0238] (2) Starting from 0% SOC, step charging is performed using the battery's maximum capacity charging map until the battery cutoff voltage reaches 3.8V. The time required to charge from 0% SOC to 3.8V is recorded as the battery charging time.

[0239] The current collector containing the negative electrode active material layer obtained in the [Negative Electrode Sheet Preparation] step of Example 1 was subjected to a cross-section scanning electron microscope, and Figure 6 was obtained. It can be seen that the current collector of the embodiment of the present application is provided with a negative electrode active material layer, and the negative electrode active material layer has channels.

[0240] Table 2

[0241] As can be seen in Table 2, in Examples 1-51 of the present application, the lithium acrylate polymer is placed on the side of the negative electrode active material layer away from the current collector. This results in strong bonding between the negative electrode active material layer and the current collector, and the batteries containing the negative electrode plates exhibit excellent cycling and fast-charging performance. Comparative Example 1, in which no lithium acrylate polymer is added, and Comparative Example 2, in which the lithium acrylate polymer and negative electrode active material are uniformly mixed, exhibit inferior fast-charging and cycling performance compared to Examples 1-51.

[0242] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A negative electrode sheet, wherein: include: current collector; A negative electrode active material layer, the negative electrode active material layer is disposed on at least one side of the current collector; A conductive layer, the conductive layer is arranged on a side of the negative electrode active material layer away from the current collector, and the conductive layer comprises a lithium acrylic acid polymer; The bonding force between the negative electrode active material layer and the current collector is negatively correlated with the surface density of the conductive layer.

2. The negative electrode sheet according to claim 1, wherein: The negative electrode active material layer has pores, and at least a portion of the lithium acrylic acid polymer is embedded in the pores.

3. The negative electrode sheet according to claim 2, wherein: At least one of the following conditions is met: The bonding force between the negative electrode active material layer and the current collector is Z k Negative correlation, Z k is the reliable permeability of the acrylic lithium polymer in the negative electrode active material layer, the distance between the acrylic lithium polymer and the surface of the negative electrode active material layer away from the current collector in the pore is a mm, the thickness of the negative electrode sheet is D mm, the permeability = a / D×100%, and the permeability corresponding to the permeability distribution number reaching 90% is the reliable permeability; The bonding force between the negative electrode active material layer and the current collector is negatively correlated with the thickness of the negative electrode sheet; The bonding force between the negative electrode active material layer and the current collector is positively correlated with the tortuosity of the negative electrode active material layer; The bonding force between the negative electrode active material layer and the current collector is negatively correlated with the porosity of the negative electrode active material layer.

4. The negative electrode sheet according to claim 2, wherein: Z k =1%-60%, Z k is the reliable permeability of the lithium acrylate polymer in the negative electrode active material layer, the distance between the lithium acrylate polymer and the surface of the negative electrode active material layer away from the current collector in the pore is a mm, the thickness of the negative electrode plate is D mm, the permeability = a / D×100%, and the permeability corresponding to 90% of the permeability distribution number is the reliable permeability.

5. The negative electrode sheet according to claim 4, wherein: Z k ＝25％-45％。 6. The negative electrode sheet according to claim 4, wherein: a / D×100%=20%-50%.

7. The negative electrode sheet according to claim 4, wherein: a / D×100%=25%-40%.

8. The negative electrode sheet according to any one of claims 1 to 7, wherein: The surface density of the conductive layer is 0.05g / 1540.25mm 2 -0.4g / 1540.25mm 2 .

9. The negative electrode sheet according to any one of claims 1 to 7, wherein: The porosity of the negative electrode active material layer is 20%-40%.

10. The negative electrode sheet according to any one of claims 1 to 7, wherein: The thickness of the negative electrode plate is 0.1 mm-0.3 mm.

11. The negative electrode sheet according to any one of claims 1 to 7, wherein: The tortuosity of the negative electrode active material layer is 0.5-7.

12. The negative electrode sheet according to any one of claims 1 to 7, wherein: The bonding force between the negative electrode active material layer and the current collector is 5 N / m-20 N / m.

13. The negative electrode sheet according to any one of claims 1 to 7, wherein: The lithium acrylate polymer includes at least one of lithium polyacrylate, lithium polymethacrylate, lithium polyethylacrylate or lithium polypropylacrylate.

14. The negative electrode sheet according to any one of claims 1 to 7, wherein: Based on the total mass of the lithium acrylic acid polymer, the mass fraction of lithium is 3%-8.9%.

15. The negative electrode sheet according to any one of claims 1 to 7, wherein: Based on the total mass of the lithium acrylic acid polymer, the mass fraction of lithium is 5%-7.5%.

16. The negative electrode sheet according to any one of claims 1 to 7, wherein: The number average molecular weight Mn of the lithium acrylic acid polymer is 3,000-1,000,000.

17. The negative electrode sheet according to any one of claims 1 to 7, wherein: The number average molecular weight Mn of the lithium acrylic acid polymer is 100,000-500,000.

18. A method for preparing a negative electrode sheet, wherein: include: forming a negative electrode active material layer on at least one side of the current collector; A conductive layer is formed on the negative electrode active material layer at a side away from the current collector, wherein the conductive layer comprises a lithium acrylic polymer The bonding force between the negative electrode active material layer and the current collector is negatively correlated with the surface density of the conductive layer.

19. The method according to claim 18, wherein: The lithium acrylate polymer is sprayed on the side of the negative electrode active material layer away from the current collector by a spraying method to form a conductive layer, and at least part of the lithium acrylate polymer is embedded in the pores of the negative electrode active material layer.

20. The method according to claim 19, wherein: At least one of the following conditions is met: The spray pressure is 0.1kPa-100kPa; The spray temperature is 70°C-150°C.

21. The method according to claim 18, wherein: The current collector containing the negative electrode active material layer is immersed in a lithium acrylate polymer solution to form a conductive layer on the side of the negative electrode active material layer away from the current collector, and at least part of the lithium acrylate polymer is embedded in the pores of the negative electrode active material layer.

22. The method according to claim 21, wherein: Based on the total mass of the lithium acrylate polymer solution, the mass proportion of the lithium acrylate polymer is 0.5%-50%.

23. The method according to claim 21, wherein: Based on the total mass of the lithium acrylate polymer solution, the mass proportion of the lithium acrylate polymer is 10%-20%.

24. A battery, wherein: A negative electrode sheet comprising the negative electrode sheet described in any one of claims 1 to 17 or a negative electrode sheet prepared by the method described in any one of claims 18 to 23.

25. An electrical device, wherein: Comprising the battery of claim 24.

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