Dry-method negative plate, preparation method thereof and lithium ion battery

Abstract

The invention provides a dry-method negative plate, a preparation method thereof and a lithium ion battery, and belongs to the technical field of secondary batteries. The dry-method negative plate comprises a negative current collector and a negative active layer arranged on at least one side surface of the negative current collector, the negative active layer comprises the following components by 100% of the total mass of the negative active layer: 95-98.5% of a negative active material, 0.5-1.5% of a binder, 0.5-2.5% of an additive and 0.5-1% of a conductive agent, the binder comprises polytetrafluoroethylene, and the conductive agent comprises polytetrafluoroethylene. The additive is polyvinyl pyridine alkyl ketone. According to the dry-method negative plate, polyvinyl pyridine alkyl ketone is added into the negative active layer, and the substance and polytetrafluoroethylene in the binder form a binary binder system, so that the first efficiency, the energy density and the cycle life of the battery can be improved, and the dynamic performance of the battery can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and particularly relates to a dry-type negative electrode sheet, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] In recent years, lithium-ion batteries have attracted much attention in the fields of electric vehicles, energy storage, etc. due to their excellent performance and wide application scenarios. At present, the mainstream production technology of lithium-ion batteries is the wet coating technology, which has problems such as energy waste, environmental pollution, electrode delamination, and is not applicable to sulfide all-solid-state batteries.

[0003] However, the dry electrode does not add any solvent during the manufacturing process, and has the advantages of cost reduction, environmental friendliness, delamination inhibition, and compatibility with sulfide solid electrolytes. During the dry mixing process of the dry electrode, due to the shear and friction between the mixer and the particles, different components of the electrode material can be evenly distributed, and since there is no slurry during the dry mixing process, there is no longer an electrode delamination problem caused by solvent evaporation. The dry electrode technology avoids the use of organic / polar solvents and only requires a very small amount of binder during the film forming process, and is particularly suitable for the preparation of sulfide all-solid-state batteries. Since solvents that react with sulfide solid electrolytes are not used, the dry electrode technology helps to better prepare sulfide solid electrolyte films and maintain their high ionic conductivity.

[0004] The dry electrode process in the prior art generally uses polytetrafluoroethylene (PTFE) binder to form a film by fibrillation to manufacture the electrode sheet, but polytetrafluoroethylene will have a side reaction with lithium at a lower potential (about 0.7 - 1.0V vs Li + / Li), consuming battery active materials and reducing the initial efficiency, energy density, and service life of the battery. In addition, the negative electrode active material in the lithium-ion battery in the prior art generally contains graphite, and the PTFE binder will also have a side reaction with graphite, causing irreversible decomposition of polytetrafluoroethylene and reducing the cycle life of the battery. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this reason, an embodiment of the present invention provides a dry-type negative electrode sheet, a preparation method thereof, and a lithium-ion battery.

[0006] In a first aspect, an embodiment of the present invention provides a dry-type negative electrode sheet, which includes a negative electrode current collector and a negative electrode active layer provided on at least one surface of the negative electrode current collector. Based on the total mass of the negative electrode active layer being 100%, the negative electrode active layer includes the following components: 95 - 98.5% of negative electrode active material, 0.5 - 1.5% of binder, 0.5 - 2.5% of additive, and 0.5 - 1% of conductive agent. The binder includes polytetrafluoroethylene, and the additive is polyvinylpyrrolidone.

[0007] The advantages and technical effects brought by the dry-type negative electrode sheet of the embodiments of the present invention are as follows:

[0008] In the dry-type negative electrode sheet of the embodiments of the present invention, polyvinylpyrrolidone is added to the negative electrode active layer, and this substance and polytetrafluoroethylene in the binder form a binary binder system. On the one hand, the presence of polyvinylpyrrolidone can prevent polytetrafluoroethylene from reacting with lithium at a lower potential (about 0.7 - 1.0V vs Li + / Li) to consume the negative electrode active material, thereby improving the initial efficiency, energy density and cycle life of the battery; on the other hand, polyvinylpyrrolidone can also induce the formation of a strong SEI rich in Li3N, thereby achieving fast lithium ion kinetics and excellent interfacial stability.

[0009] In some embodiments, based on the total mass of the negative electrode active layer being 100%, the content of polyvinylpyrrolidone is 1.25 - 2.5%.

[0010] In some embodiments, the negative electrode active material includes natural graphite and / or artificial graphite.

[0011] In some embodiments, the negative electrode active material further includes silicon oxide.

[0012] In some embodiments, the conductive agent is selected from at least one of conductive carbon black, graphene, carbon fiber, superconducting carbon, acetylene black, Ketjen black, carbon dots and carbon nanotubes.

[0013] In a second aspect, the embodiments of the present invention provide a method for preparing a dry-type negative electrode sheet, including the following steps:

[0014] S1. Mix the negative electrode active material with the additive to obtain a first mixture, and then grind the first mixture to obtain a first powder material;

[0015] S2. Mix the first powder material with the binder and the conductive agent to obtain a second mixture, and then first perform low-speed stirring on the second mixture, and then perform high-speed shear stirring to obtain a negative electrode powder material;

[0016] S3. Perform calendering treatment on the negative electrode powder material to obtain a negative electrode film, and then calender the negative electrode film on the negative electrode current collector to form the negative electrode active layer, obtaining a semi-finished negative electrode sheet.

[0017] S4. Perform hot roll pressing on the semi-finished negative electrode sheet to obtain the negative electrode sheet.

[0018] The advantages and technical effects brought by the preparation method of the embodiments of the present invention are as follows:

[0019] (1) During the preparation of the dry-process anode, by adding polyvinylpyrrolidone, this substance and polytetrafluoroethylene form a binary binder system. On the one hand, the presence of polyvinylpyrrolidone can prevent polytetrafluoroethylene from reacting with lithium at a lower potential (about 0.7 - 1.0 V vs Li + / Li) and consuming the anode active material, thereby improving the initial efficiency, energy density, and cycle life of the battery; on the other hand, polyvinylpyrrolidone can also induce the formation of a strong SEI rich in Li3N, thus achieving fast lithium-ion kinetics and excellent interfacial stability.

[0020] (2) The embodiments of the present invention provide an improved method for dry-process anode sheets. The required materials are common, the process is simple, and it has high practical value. It can improve the initial efficiency of the battery, reduce the internal resistance of the battery, is beneficial to the improvement of the cycle life, and makes the dry-process electrode comparable to the liquid battery in terms of performance.

[0021] In some embodiments, the grinding treatment is ball milling, the rotation speed of the ball milling is 180 - 220 rpm, and the time of the ball milling is 1 - 1.5 h.

[0022] In some embodiments, the rotation speed of the low-speed stirring is 200 - 500 rpm, and the time of the low-speed stirring is 1 - 2 min; and / or, the rotation speed of the high-speed shear stirring is 2000 - 3000 rpm, and the time of the high-speed shear stirring is 1 - 3 min.

[0023] In some embodiments, the thickness of the anode film is 40 - 50 μm, and / or, the thickness of the anode sheet is 85 - 100 μm.

[0024] In some embodiments, the temperature of the hot roll pressing is 100 - 160 °C.

[0025] In the third aspect, the embodiments of the present invention provide a lithium-ion battery, including the anode sheet described in the first aspect, or including the anode sheet obtained by the preparation method described in the second aspect.

[0026] The advantages and technical effects brought by the lithium-ion battery of the embodiments of the present invention are as follows:

[0027] Due to the use of the anode sheet described in the first aspect, or the anode sheet obtained by the preparation method described in the second aspect, the lithium-ion battery of the embodiments of the present invention has a high initial efficiency, a long cycle life, and high kinetic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Cyclic voltammograms of the coin cells assembled with the dry-process anode sheets of Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] Embodiments of the present invention will be described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0030] In a first aspect, an embodiment of the present invention provides a dry-type negative electrode sheet, which includes a negative electrode current collector and a negative electrode active layer provided on at least one surface of the negative electrode current collector. Based on the total mass of the negative electrode active layer being 100%, the negative electrode active layer includes the following components: 95-98.5% of negative electrode active material, 0.5-1.5% of binder, 0.5-2.5% of additive, and 0.5-1% of conductive agent. The binder includes polytetrafluoroethylene (PTFE), and the additive is polyvinylpyrrolidone (PVP).

[0031] In the dry-type negative electrode sheet of the embodiment of the present invention, by adding polyvinylpyrrolidone to the negative electrode active layer, this substance and polytetrafluoroethylene in the binder form a binary binder system. On the one hand, the presence of polyvinylpyrrolidone can prevent polytetrafluoroethylene from reacting with lithium at a lower potential (about 0.7-1.0V vs Li + / Li) and consuming the negative electrode active material, thereby improving the initial efficiency, energy density and cycle life of the battery; on the other hand, polyvinylpyrrolidone can also induce the formation of a strong SEI rich in Li3N, thereby achieving fast lithium ion kinetics and excellent interfacial stability.

[0032] There is no particular limitation on the type of the negative electrode active material in the dry-type negative electrode sheet of the embodiment of the present invention. The negative electrode active material can adopt the negative electrode active materials known in the art for lithium ion batteries. As an example, the negative electrode active material can 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, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for lithium ion batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0033] In some embodiments, the negative electrode active material includes natural graphite and / or artificial graphite. At this time, polyvinylpyrrolidone can also prevent direct contact between graphite and polytetrafluoroethylene, thereby slowing down the irreversible decomposition of polytetrafluoroethylene, preventing the negative electrode active layer from falling off, and improving the cycle life of the lithium ion battery.

[0034] In some embodiments, the negative electrode active material further includes silicon oxide. Silicon oxide has certain advantages over graphite in terms of theoretical specific capacity, safety, resource abundance, cost performance, etc. Therefore, selecting a composite of silicon oxide and graphite as the negative electrode active material can improve the specific capacity, safety, etc. of the lithium-ion battery.

[0035] In addition to polytetrafluoroethylene, the binder in the embodiments of the present invention may also contain other types, such as 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).

[0036] In some embodiments, based on the total mass of the negative electrode active layer being 100%, the content of polyvinylpyrrolidone is 1.25 - 2.5%, such as 1.25%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, etc. When the content of polyvinylpyrrolidone is too low, it is not conducive to inhibiting the side reaction between polytetrafluoroethylene and lithium at a lower potential, nor is it conducive to forming a strong SEI rich in Li3N.

[0037] For the dry-process negative electrode sheet in the embodiments of the present invention, there is no particular limitation on the type of conductive agent in the negative electrode active layer, and the conductive agent can be a conductive agent known in the art for lithium-ion batteries. As an example, the conductive agent can be selected from at least one of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon fibers.

[0038] There is no particular limitation on the type of negative electrode current collector for the dry-process negative electrode sheet in the embodiments of the present invention, and the negative electrode current collector can be a negative electrode current collector known in the art for lithium-ion batteries. The negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0039] In a second aspect, the embodiments of the present invention provide a method for preparing a dry-process negative electrode sheet, including the following steps:

[0040] S1. Mix the negative electrode active material with the additive to obtain a first mixture, and then grind the first mixture to obtain a first powder material;

[0041] S2. Mix the first powder material with the binder and the conductive agent to obtain a second mixture, and then first perform low-speed stirring on the second mixture and then perform high-speed shear stirring to obtain a negative electrode powder material;

[0042] S3. Perform calendering treatment on the negative electrode powder material to obtain a negative electrode film, and then calender the negative electrode film on the negative electrode current collector to form the negative electrode active layer, thereby obtaining a semi-finished negative electrode sheet.

[0043] S4. Perform hot roll pressing on the semi-finished negative electrode sheet to obtain the negative electrode sheet.

[0044] During the preparation process of the dry-process negative electrode, by adding polyvinylpyrrolidone, this substance and polytetrafluoroethylene form a binary binder system. On the one hand, the presence of polyvinylpyrrolidone can prevent polytetrafluoroethylene from reacting with lithium at a lower potential (about 0.7 - 1.0V vs Li + / Li) and consuming the negative electrode active material, thereby improving the initial efficiency, energy density and cycle life of the battery; on the other hand, polyvinylpyrrolidone can also induce the formation of a strong SEI rich in Li3N, thereby achieving fast lithium-ion kinetics and excellent interfacial stability.

[0045] The embodiment of the present invention provides an improved method for dry-process negative electrode sheets. The required materials are common and the process is simple, with high practical value. It can improve the initial efficiency of the battery, reduce the internal resistance of the battery, is beneficial to the improvement of the cycle life, and makes the dry-process electrode comparable to the liquid battery in terms of performance.

[0046] In the preparation method of the dry-process negative electrode sheet, first mixing the negative electrode active material with polyvinylpyrrolidone and then grinding is to mix polyvinylpyrrolidone and the negative electrode active material evenly, so that polyvinylpyrrolidone can better protect the negative electrode active material, and then mixing the first powder material with the binder and the conductive agent to carry out the subsequent negative electrode sheet preparation steps. If all the raw materials are mixed together, it is not conducive to the uniform dispersion of polyvinylpyrrolidone in the powder material and is not conducive to giving full play to the role of polyvinylpyrrolidone.

[0047] In some embodiments, the grinding treatment is ball milling. The rotation speed of the ball milling is 180 - 220 rpm, such as 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, etc., and the time of the ball milling is 1 - 1.5 h, such as 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, etc. The above ball milling can make the negative electrode active material and polyvinylpyrrolidone mix evenly.

[0048] In some embodiments, the rotation speed of the low-speed stirring is 200-500 rpm, such as 200 rpm, 300 rpm, 400 rpm, 500 rpm, etc., and the time of the low-speed stirring is 1-2 min, such as 1 min, 1.5 min, 2 min, etc. The above low-speed stirring is to uniformly mix the first powder material with the binder and the conductive agent.

[0049] In some embodiments, the rotation speed of the high-speed shear stirring is 2000-3000 rpm, such as 2000 rpm, 2200 rpm, 2400 rpm, 2600 rpm, 2800 rpm, 3000 rpm, etc., and the time of the high-speed shear stirring is 1-3 min, such as 1 min, 2 min, 3 min, etc. The above high-speed shear stirring is to fibrillate polytetrafluoroethylene.

[0050] In some embodiments, the thickness of the negative electrode film is 40-50 μm, such as 40 μm, 42 μm, 44 μm, 46 μm, 48 μm, 50 μm, etc. The above thickness of the negative electrode film is beneficial to obtaining a negative electrode active layer with a target thickness, and ensuring the energy density, safety and cycle life of the lithium-ion battery.

[0051] In some embodiments, the temperature of the hot roll pressing is 100-160 °C, such as 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, etc. The hot roll pressing within the above temperature range can obtain a negative electrode active layer with a target thickness, and ensure the energy density, safety and cycle life of the lithium-ion battery.

[0052] In some embodiments, the thickness of the negative electrode sheet is 85-100 μm, such as 85 μm, 90 μm, 95 μm, 100 μm, etc. The above thickness of the negative electrode sheet is to ensure the energy density, safety and cycle life of the lithium-ion battery.

[0053] In a third aspect, an embodiment of the present invention provides a lithium-ion battery, including the negative electrode sheet described in the first aspect, or including the negative electrode sheet obtained by the preparation method described in the second aspect.

[0054] Due to the adoption of the negative electrode sheet described in the first aspect, or the negative electrode sheet obtained by the preparation method described in the second aspect, the lithium-ion battery of the embodiment of the present invention has a high initial efficiency, a long cycle life and high kinetic performance.

[0055] The present invention will be described in detail below with reference to the embodiments and the drawings.

[0056] Example 1

[0057] Negative electrode preparation:

[0058] 1. Grind 77.6 g of artificial graphite, 19.4 g of silicon oxide compound, and 1.25 g of polyvinylpyrrolidone (PVP) for 1 h at 200 rpm in a ball mill.

[0059] 2. Add 1 g of polytetrafluoroethylene (PTFE) and 0.75 g of conductive carbon black (SP), stir at low speed for 1 min at 300 rpm to mix evenly, and then stir at high speed with high shear for 2 min at 3000 rpm to fibrillate the PTFE.

[0060] 3. Roll the negative electrode powder to obtain a negative electrode film with a thickness of 40 μm, and then roll the negative electrode film onto a carbon-coated copper foil with a thickness of 8 μm to form a negative electrode active layer.

[0061] 4. Then heat-roll the electrode sheet at 160 °C to obtain a negative electrode sheet with a thickness of 85 μm.

[0062] Positive electrode preparation:

[0063] Mix NCM811, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 97:1.5:1.5, add N-methylpyrrolidone (NMP) to adjust the viscosity, and complete the production of the electrode sheet through processes such as coating, rolling (3.5 g / cm 3 ), and cutting to obtain a positive electrode sheet.

[0064] Battery assembly:

[0065] Stack the positive electrode sheet, PE separator, and negative electrode sheet in sequence, place the electrode assembly in an outer packaging aluminum-plastic film, and obtain a 3 Ah soft-pack battery through processes such as vacuum packaging, standing, and formation.

[0066] Example 2

[0067] Negative electrode preparation:

[0068] 1. Grind 77.6 g of artificial graphite, 19.4 g of silicon oxide compound, and 2.5 g of polyvinylpyrrolidone (PVP) for 1 h at 200 rpm in a ball mill.

[0069] 2. Add 1.5 g of polytetrafluoroethylene (PTFE) and 1 g of conductive carbon black (SP), stir at low speed for 1 min at 300 rpm to mix evenly, and then stir at high speed with high shear for 2 min at 3000 rpm to fibrillate the PTFE.

[0070] 3. Roll the negative electrode powder to obtain a negative electrode film with a thickness of 40 μm, and then roll the negative electrode film onto a carbon-coated copper foil with a thickness of 8 μm to form a negative electrode active layer.

[0071] 4. Then heat-roll the electrode sheet at 160 °C to obtain a negative electrode sheet with a thickness of 85 μm.

[0072] Example 3

[0073] Preparation of the negative electrode:

[0074] 1. Mix 78.8 g of artificial graphite, 19.7 g of silicon oxide compound, and 0.5 g of polyvinylpyrrolidone (PVP) and ball-mill them at 200 rpm for 1 h.

[0075] 2. Add 0.5 g of polytetrafluoroethylene (PTFE) and 0.5 g of conductive carbon black (SP), stir slowly at 300 rpm for 1 min to mix evenly, and then stir at high speed of 3000 rpm for 2 min to fibrillate the PTFE.

[0076] 3. Roll the negative electrode powder to obtain a negative electrode film with a thickness of 40 μm, and then roll the negative electrode film on a carbon-coated copper foil with a thickness of 8 μm to form a negative electrode active layer.

[0077] 4. Then hot roll the electrode sheet at 160 °C to obtain a negative electrode sheet with a thickness of 85 μm.

[0078] Comparative Example 1

[0079] Preparation of the negative electrode:

[0080] 1. Mix 78.6 g of artificial graphite and 19.65 g of silicon oxide compound and ball-mill them at 200 rpm for 1 h.

[0081] 2. Add 1 g of polytetrafluoroethylene (PTFE) and 0.75 g of conductive carbon black (SP), stir slowly at 300 rpm for 1 min to mix evenly, and then stir at high speed of 3000 rpm for 2 min to fibrillate the polytetrafluoroethylene.

[0082] 3. Roll the negative electrode powder to obtain a negative electrode film with a thickness of 40 μm, and then roll the negative electrode film on a carbon-coated copper foil with a thickness of 8 μm to form a negative electrode active layer.

[0083] 4. Then hot roll the electrode sheet at 160 °C to obtain a negative electrode sheet with a thickness of 85 μm.

[0084] The preparation process of the positive electrode and the battery assembly are the same as those in Example 1.

[0085] Comparative Example 2

[0086] Preparation of the negative electrode:

[0087] Mix artificial graphite, silicon oxide compound, conductive carbon black (SP), and sodium carboxymethyl cellulose (CMC) in a mass ratio of 78.6:19.65:0.75:0.67, add deionized water to adjust the viscosity, and add styrene-butadiene rubber (SBR) when the viscosity is appropriate. The mass ratio of CMC to SBR is 0.67:0.33. Stir slowly, and then complete the production of the electrode sheet through processes such as coating, rolling (1.60 g / cm 3 ), and cutting.

[0088] The preparation of the positive electrode and the battery assembly process are the same as those in Example 1.

[0089] Table 1. Component contents of the negative electrode active layer in each example and comparative example

[0090]

[0091] The battery performance test method is as follows:

[0092] 1. Initial efficiency: The initial discharge capacity and the initial charge capacity are tested. The initial efficiency is equal to the percentage of the initial discharge capacity to the initial charge capacity. The results of the first test are shown in Table 2.

[0093] 2. Cycle life: At 25 °C, it is charged at a constant current and constant voltage of 0.5C to 4.2V, and then discharged at 1C to 2.5V. This cycle is repeated, and the capacity retention rate at different cycle numbers is calculated. The capacity retention rate after 500 cycles at room temperature is shown in Table 2.

[0094] 3. Cyclic voltammetry: The negative electrode sheets obtained in each example and comparative example are respectively assembled into coin cells for cyclic voltammetry testing. The scanning speed is 0.1 mV / s, and the scanning voltage range is from 0V to 1.5V. The test results are as Figure 1 shown.

[0095] Table 2. Initial efficiency of the batteries in each example and comparative example and capacity retention rate after 500 cycles at room temperature

[0096] First effect (%) Capacity retention rate after 500 cycles at room temperature (%) Example 1 86.4 95.1 Example 2 85.8 94.8 Example 3 84.5 93.2 Comparative example 1 80.5 84.2 Comparative example 2 88.6 96.4

[0097] Figure 1 It is the cyclic voltammetry curve (CV diagram) of the coin cell assembled with the dry-process negative electrode sheet of Example 1 and Comparative Example 1. It can be seen from this CV diagram that after adding PVP in Example 1, no obvious reduction peak appears in the voltage range of 0.7 - 1V. It further verifies that the addition of PVP can inhibit the reaction between PTFE and lithium.

[0098] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0099] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A dry negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active layer provided on at least one surface of the negative electrode current collector. Based on the total mass of the negative electrode active layer being 100%, the negative electrode active layer includes the following components: 95 - 98.5% of negative electrode active material, 0.5 - 1.5% of binder, 0.5 - 2.5% of additive, and 0.5 - 1% of conductive agent. The binder includes polytetrafluoroethylene, and the additive is polyvinylpyrrolidone.

2. The dry negative electrode sheet according to claim 1, characterized in that, Based on the total mass of the negative electrode active layer being 100%, the content of polyvinylpyrrolidone is 1.25 - 2.5%.

3. The dry negative electrode sheet according to claim 1 or 2, characterized in that, The negative electrode active material includes natural graphite and / or negative electrode graphite; Optionally, the negative electrode active material further includes silicon oxide compound.

4. The dry-type negative electrode sheet according to claim 1 or 2, characterized in that, The conductive agent is selected from at least one of conductive carbon black, graphene, carbon fiber, superconducting carbon, acetylene black, Ketjen black, carbon dots, and carbon nanotubes.

5. The preparation method of the dry-type negative electrode sheet according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1. Mix the negative electrode active material with the additive to obtain a first mixture, and then grind the first mixture to obtain a first powder. S2. Mix the first powder with the binder and the conductive agent to obtain a second mixture, and then first perform low-speed stirring on the second mixture and then high-speed shear stirring to obtain a negative electrode powder. S3. Perform calendering treatment on the negative electrode powder to obtain a negative electrode film, and then calender the negative electrode film on the negative electrode current collector to form the negative electrode active layer, obtaining a semi-finished negative electrode sheet. S4. Perform hot roll pressing on the semi-finished negative electrode sheet to obtain the negative electrode sheet.

6. The preparation method of the dry-type negative electrode sheet according to claim 5, characterized in that, The grinding treatment is ball milling, the rotation speed of the ball milling is 180 - 220 rpm, and the time of the ball milling is 1 - 1.5 h.

7. The preparation method of the dry-type negative electrode sheet according to claim 5, characterized in that, The rotation speed of the low-speed stirring is 200 - 500 rpm, and the time of the low-speed stirring is 1 - 2 min; and / or, the rotation speed of the high-speed shear stirring is 2000 - 3000 rpm, and the time of the high-speed shear stirring is 1 - 3 min.

8. The preparation method of the dry-type negative electrode sheet according to claim 5, characterized in that The thickness of the negative electrode film is 40 - 50 μm, and / or, the thickness of the negative electrode sheet is 85 - 100 μm.

9. The preparation method of the dry-type negative electrode sheet according to claim 5, characterized in that, The temperature of the hot roll pressing is 100 - 160 °C.

10. A lithium-ion battery, characterized in that, It includes the negative electrode sheet according to any one of claims 1 - 4, or the negative electrode sheet obtained by the preparation method according to any one of claims 5 - 9.

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