Negative pole piece and preparation method thereof, secondary battery and electric equipment

Abstract

The embodiment of the invention provides a negative pole piece and a preparation method thereof, a secondary battery and electric equipment. The negative pole piece comprises a negative pole material layer arranged on the surface of a current collector, and a protective layer and a lithium supplementing layer which are sequentially stacked on the surface, deviating from the current collector, of the negative pole material layer, the protective layer comprises a protein derivative. The negative pole piece provided by the embodiment of the invention has relatively low requirements on a production environment, is relatively high in safety performance in a production process, and can be used for improving the energy density and the cycle performance of the battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode plate and a preparation method thereof, a secondary battery and an electrical device. Background Art

[0002] In order to improve the energy density and first coulomb efficiency of secondary batteries, the industry often chooses to replenish lithium at the negative electrode. One of the common methods of replenishing lithium at the negative electrode is to set a lithium metal replenishing layer on the surface of the negative electrode material layer, which will cause the negative electrode sheet to heat up severely during the winding process. The resulting heat accumulation will destroy the performance of the lithium replenishing layer material, increase the risk of spontaneous combustion of the lithium replenishing layer, and seriously threaten production safety. Summary of the invention

[0003] In view of this, the embodiments of the present application provide a negative electrode sheet and a preparation method thereof, a secondary battery and an electrical device. The negative electrode sheet provided in the embodiments of the present application has relatively loose requirements on the production environment, has high safety performance during the production process, and can be used to improve the energy density and cycle performance of the battery.

[0004] A first aspect of an embodiment of the present application provides a negative electrode plate, comprising a negative electrode material layer disposed on a current collector surface, a protective layer and a lithium supplement layer stacked in sequence on the negative electrode material layer away from the current collector surface; the protective layer comprises a protein derivative.

[0005] The protective layer is provided between the lithium replenishment layer and the negative electrode material layer; the protective layer can effectively suppress the heat generation of the negative electrode sheet during the winding process, thereby reducing the heat accumulation of the negative electrode sheet during the winding process, effectively reducing the risk of fire of the negative electrode sheet, and improving the production safety performance of the negative electrode sheet. In addition, the protein derivative in the protective layer has a film-forming polypeptide, which can further increase the flexibility of the protective layer and its adhesion to the negative electrode active material layer, which can not only better suppress the heat generation of the negative electrode sheet during the winding process, but also help to suppress the expansion of the negative electrode material layer during the charge and discharge cycle, thereby improving the cycle performance of the negative electrode sheet. Based on the inherent properties of the lithium replenishment layer, the negative electrode sheet can also improve the first coulomb efficiency of the battery.

[0006] A second aspect of the embodiment of the present application provides a method for preparing a negative electrode sheet, comprising:

[0007] Providing a current collector and a negative electrode material layer stacked in layers, forming a protective layer on the surface of the negative electrode material layer facing away from the current collector, wherein the protective layer includes a protein derivative;

[0008] A lithium supplement layer is formed on the surface of the protective layer away from the negative electrode material layer to obtain a negative electrode plate.

[0009] The preparation method has simple process, high production efficiency and is suitable for large-scale industrial production.

[0010] A third aspect of the embodiments of the present application provides a secondary battery, comprising the negative electrode plate provided in the first aspect of the embodiments of the present application, or comprising a negative electrode plate prepared by the preparation method of the negative electrode plate provided in the second aspect of the embodiments of the present application.

[0011] Due to the negative electrode plate provided in the embodiment of the present application, the secondary battery can have both higher energy density and better cycle performance.

[0012] The fourth aspect of the embodiment of the present application provides an electric device, including the negative electrode sheet provided in the first aspect of the embodiment of the present application, or including the negative electrode sheet prepared by the method for preparing the negative electrode sheet provided in the second aspect of the embodiment of the present application, or including the secondary battery provided in the third aspect of the embodiment of the present application. Since the secondary battery provided in the embodiment of the present application is used to power the electric device, the electric device has a strong endurance and a good market prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1A A schematic structural diagram of a cross section of a negative electrode sheet provided in one embodiment of the present application;

[0014] Figure 1B A schematic structural diagram of a cross section of a negative electrode sheet provided in another embodiment of the present application;

[0015] Figure 1C A schematic structural diagram of a cross section of a negative electrode sheet provided in yet another embodiment of the present application;

[0016] Figure 2 A schematic diagram of the arrangement of the positive electrode sheet and the negative electrode sheet in a secondary battery provided in one embodiment of the present application. DETAILED DESCRIPTION

[0017] See also Figures 1A to 1C The embodiment of the present application provides a negative electrode plate 1, comprising a negative electrode material layer 20 arranged on the surface of a current collector 10, a protective layer 30 and a lithium supplement layer 40 stacked in sequence on the surface of the negative electrode material layer 20 away from the current collector 10; the protective layer 30 comprises a protein derivative.

[0018] In the embodiments of this application, please refer to Figure 1A , the negative electrode material layer may be disposed on one surface of the current collector; or the negative electrode material layer may be disposed on both opposite surfaces of the current collector. Figure 1B When negative electrode material layers are disposed on both sides of the current collector, the surfaces of the negative electrode material layers on both sides may be sequentially stacked with a protective layer and a lithium supplement layer; see Figure 1C Alternatively, the surface of the negative electrode material layer on one side of the current collector may be stacked with the above-mentioned protective layer and lithium supplement layer.

[0019] In the negative electrode sheet provided in the embodiment of the present application, the above-mentioned protective layer is arranged between the lithium replenishment layer and the negative electrode material layer; the above-mentioned protective layer can effectively suppress the heat generation of the negative electrode sheet during the winding process, thereby reducing the heat accumulation of the negative electrode sheet during the winding process, effectively reducing the risk of fire of the negative electrode sheet, and improving the production safety performance of the negative electrode sheet. In addition, the protein derivative in the protective layer has a film-forming polypeptide, which can further increase the flexibility of the protective layer and its adhesion to the negative electrode active material layer, which can not only better suppress the heat generation of the negative electrode sheet during the winding process, but also help to suppress the expansion of the negative electrode material layer during the charge and discharge cycle, thereby improving the cycle performance of the negative electrode sheet. Based on the inherent properties of the lithium replenishment layer, the above-mentioned negative electrode sheet can also improve the first coulomb efficiency and energy density of the battery. Therefore, the negative electrode sheet can be used to provide a battery with both high energy density and better cycle performance.

[0020] In some embodiments of the present application, the lithium supplement layer includes metallic lithium. The material of the lithium supplement layer can be lithium alone or a lithium alloy, which is not limited in the present application. Of course, the lithium supplement layer can also be other lithium supplement materials.

[0021] In some embodiments of the present application, the lithium supplement layer includes metallic lithium, and the surface density of the lithium supplement layer is 1 g / m 2 -8 g / m 2 This helps optimize the electrochemical performance of the final battery. Specifically, the surface density of the lithium supplement layer can be, for example, 1 g / m 2 , 2g / m 2 , 3g / m 2 , 4g / m 2 , 5g / m 2 , 6g / m 2 , 7g / m 2 , 8g / m 2 In the embodiment of the present application, the surface density of the lithium supplementing layer = the mass of the lithium supplementing layer / the thickness of the lithium supplementing layer.

[0022] In some embodiments of the present application, the thickness of the lithium replenishment layer is 1μm-15μm. In this way, while taking into account a large amount of lithium replenishment, it is also beneficial to the volume energy density of the battery; at the same time, the lithium replenishment layer within this thickness range cooperates with the protective layer to generate less heat. Specifically, the thickness of the lithium replenishment layer can be, for example, 1μm, 2μm, 5μm, 8μm, 10μm, 12μm, 15μm, etc.

[0023] In some embodiments of the present application, the protective layer further includes nano-metal materials. Nano-metal particles have good thermal conductivity, which helps to accelerate the dissipation of heat, and thus can further improve the production safety performance of the negative electrode sheet.

[0024] In some embodiments of the present application, the material of the nanometal material includes, but is not limited to, one or more of gold, silver, magnesium, aluminum and zinc. The above nanometal material has excellent thermal conductivity and low lithium nucleation potential. When the above negative electrode sheet is applied to a lithium-ion battery, under the combined action of the above nanometal material and the protein derivative, it can also induce the uniform deposition of active lithium ions on the negative electrode, inhibit the growth of negative electrode lithium dendrites, and thus improve the battery's cycle performance and safety performance.

[0025] In some specific embodiments, the nano-metal material is dispersed in the protein derivative. In some specific embodiments, the nano-metal material is evenly dispersed in the protein derivative. In this way, the structural uniformity of the protective layer is better, which is more conducive to inducing the uniform deposition of active lithium ions in the negative electrode and more conducive to the performance of the battery. In some specific embodiments, the protective layer includes a composite of in-situ grown nano-metal material and protein derivative.

[0026] In the embodiments of the present application, the nanometal material may be nanometal particles or nanometal wires. In some embodiments of the present application, the size of the nanometal particles is 2nm-100nm. Controlling the size of the nanometal particles within the above range is conducive to the induction effect on active lithium ions, and can also effectively reduce the occurrence of adverse phenomena such as agglomeration, improve the uniformity of the protective layer, and reduce heat accumulation. It should be noted that when the nanometal material is nanometal particles, the above size is the particle size of the nanometal particles (D 50 ); When the nanometal material is a nanometal wire, the axial size and radial size of the nanometal wire are both in the range of 2nm-100nm. Further, the size of the nanometal wire is 80nm-100nm. The metal nanowires within this size range have better binding properties with protein derivatives and can form a more stable protective layer. Specifically, the size of the nanometal material can be, for example, 2nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm. In the embodiments of the present application, a scanning electron microscope can be used to characterize the size of the nanometal material.

[0027] In some embodiments of the present application, in the protective layer, the total mass of the nanometal material is 3%-130% of the total mass of the protein derivative. In this way, it is not only beneficial to improve the protective effect of the protective layer on the winding process of the negative electrode sheet, but also effectively inhibit the expansion of the negative electrode material layer during the charge and discharge cycle, and is also conducive to inducing the uniform deposition of active lithium ions, and the cost of the negative electrode sheet is low. Specifically, the total mass of the nanometal material can be, for example, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, 120%, 125%, 130% of the total mass of the protein derivative. In the embodiment of the present application, the mass ratio of the nanometal material and the protein derivative can be tested by inductively coupled plasma testing (ICP).

[0028] In some embodiments of the present application, the protective layer also includes a fast ion conductor material. The fast ion conductor material can effectively improve the ionic conductivity of the protective layer, which is beneficial to the rate performance of the final battery. In some specific embodiments, the fast ion conductor material is evenly dispersed in the protective layer. In the embodiment of the present application, the fast ion conductor material can be any fast ion conductor material suitable for secondary batteries. Specifically, when the above-mentioned negative electrode plate is applied to a lithium-ion battery, the above-mentioned fast ion conductor material can be, for example, zinc nitrate, lithium perchlorate, lithium nitrate, aluminum oxide, lithium aluminum titanium phosphate (LATP), lithium bis(trifluoromethanesulfonyl imide) (LiFSI), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), lithium lanthanum zirconate (LLZO), silicon dioxide, lithium sulfide, lithium hexafluorophosphate One or more.

[0029] In some embodiments of the present application, in the protective layer, the total mass of the fast ion conductor material accounts for 1%-30% of the total mass of the protein derivative. In this way, the protective layer can achieve better suppression of the thermal effect of the negative electrode sheet during the winding process and improve the safety performance of the negative electrode sheet, while also helping to improve the rate performance of the negative electrode sheet, and can effectively suppress the expansion of the negative electrode material layer during the charge and discharge cycle, thereby improving the battery cycle life. That is, the negative electrode sheet has both better safety performance, good rate performance and cycle life. Specifically, the mass of the fast ion conductor can be, for example, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, etc. of the mass of the protein derivative. In the embodiment of the present application, thermogravimetric analysis (TGA) combined with ICP can be used to test the mass ratio of the fast ion conductor material and the protein derivative.

[0030] In some embodiments of the present application, the protective layer includes protein derivatives and nanometal materials and fast ion conductor materials dispersed in the protective layer. In some specific embodiments, in the protective layer, the total mass of the fast ion conductor material accounts for 1%-30% of the total mass of the protein derivative, and the ratio of the sum of the mass of the fast ion conductor material and the protein derivative to the mass of the nanometal material is 1: (0.33-1). In this way, the comprehensive electrochemical performance of the negative electrode plate is better. Specifically, the ratio of the sum of the mass of the fast ion conductor material and the protein derivative to the mass of the nanometal material can be, for example, 1: 0.33, 1: 0.4, 1: 0.5, 1: 0.6, 1: 0.7, 1: 0.8, 1: 0.9, 1: 1.0, etc. In some embodiments, based on the mass of the protective layer, the mass of the nanometal material accounts for 25%-50%, the mass of the protein derivative accounts for 38%-75%, and the mass of the fast ion conductor accounts for 0.5%-17.3%. Specifically, based on the mass of the protective layer, the mass proportion of the nanometal material can be, for example, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%; the mass proportion of the protein derivative can be, for example, 38%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%; the mass proportion of the fast ion conductor can be, for example, 0.5%, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 17%, etc. In this way, it is more conducive to optimizing the comprehensive electrochemical performance of the negative electrode sheet.

[0031] In some embodiments of the present application, the protein derivative includes silk protein. Silk protein has strong viscosity, which can reduce or eliminate the need for a binder, and can also achieve adhesion between the protective layer and the negative electrode active material layer, and is also beneficial for inhibiting the expansion of the negative electrode material layer during the charge and discharge cycle; in addition, silk protein has good electronic conductivity, which is beneficial for the performance of the battery.

[0032] In some embodiments of the present application, the thickness of the protective layer is 1 μm-10 μm. Controlling the thickness of the protective layer within an appropriate range is beneficial to ensuring the high safety performance of the negative electrode plate, and is also beneficial to the rapid penetration of active ions, and can also take into account the energy density of the final battery. Specifically, the thickness of the protective layer can be, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. In the embodiment of the present application, a scanning electron microscope can be used to test the thickness of the protective layer.

[0033] In some embodiments of the present application, the above-mentioned negative electrode material layer can be any negative electrode material layer known in the field suitable for the corresponding secondary battery. For example, in some embodiments, the negative electrode material layer includes a negative electrode active material, a binder and a conductive agent. The above-mentioned negative electrode active material includes but is not limited to silicon-based negative electrode materials and carbon-based negative electrode materials, wherein silicon-based negative electrode materials include but are not limited to silicon element, silicon oxide, silicon-carbon composite materials; carbon-based negative electrode materials include but are not limited to graphite, hard carbon, etc. In some specific embodiments, the above-mentioned negative electrode material active material includes a silicon-based negative electrode material, and the mass proportion of the silicon-based negative electrode material in the negative electrode material layer is 5%-95%.

[0034] The present application also provides a method for preparing a negative electrode sheet, comprising:

[0035] S1. providing a current collector and a negative electrode material layer stacked in layers, and forming a protective layer on a surface of the negative electrode material layer facing away from the current collector, wherein the protective layer comprises a protein derivative;

[0036] S2, forming a lithium supplement layer on the surface of the protective layer away from the negative electrode material layer to obtain a negative electrode plate.

[0037] In the embodiment of the present application, the negative electrode material layer may be disposed on one side of the current collector, or on both sides of the current collector. When negative electrode material layers are disposed on both sides of the current collector, a protective layer and a lithium replenishing layer may be sequentially formed on one negative electrode material layer, or on both sides of the current collector.

[0038] The preparation method has simple process, high production efficiency and is suitable for large-scale industrial production.

[0039] In some embodiments of the present application, in step S1, forming a protective layer on the surface of the negative electrode material layer away from the current collector includes:

[0040] The mixture of the protein derivative and the nano-metal material is dispersed in a solvent to obtain a slurry, and the slurry is formed on the surface of the negative electrode material layer away from the current collector, and then dried.

[0041] Since the protein derivative itself has a certain viscosity, its slurry also has a certain bonding property. When the protective layer is prepared by the above preparation method, a small amount of slurry can penetrate into the negative electrode material layer. Since the protein derivative itself has excellent bonding properties, when preparing the negative electrode material layer, the amount of binder (such as styrene-butadiene rubber, etc.) added in the negative electrode material layer can be appropriately reduced.

[0042] In the embodiments of the present application, any process known in the art may be used to prepare the negative electrode material layer.

[0043] In some embodiments of the present application, the preparation of the negative electrode material layer includes: mixing the negative electrode active material and the conductive agent, the optional binder, etc. The above-mentioned negative electrode active material can be any negative electrode active material known in the art that is suitable for the corresponding type of secondary battery; in some specific embodiments, the negative electrode active material includes a silicon-based negative electrode material, and the mass proportion of the silicon-based negative electrode material in the negative electrode material layer is 5%-95%.

[0044] In some embodiments of the present application, in step S1, the above-mentioned solvent includes but is not limited to dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMF), N-methylpyrrolidone (NMP), ethylene glycol, propylene glycol, water, etc.

[0045] In some embodiments of the present application, in step S1, before dispersing the mixture of the protein derivative and the nano-metal material in the solvent, the step includes: preparing a mixture of the protein derivative and the nano-metal material.

[0046] In some embodiments, protein derivatives and nano-metal materials can be synthesized in situ. In some specific embodiments, a silk fibroin solution is mixed with a metal salt solution, reacted at 75°C-85°C, and the reaction time is 75min-240min, and a metal nanomaterial @ silk fibroin complex is formed in situ, and freeze-dried to obtain a metal nanomaterial @ silk fibroin powder. In some embodiments of the present application, the metal in the above-mentioned metal salt includes but is not limited to one or more of gold, silver, magnesium, aluminum and zinc. For example, the above-mentioned metal salt can be a mixture of metal salts of different metals.

[0047] In other embodiments, the metal nanomaterial and the protein derivative are mixed by a physical method, and the mixture is dispersed in a solvent; specifically, the protein derivative can be first dissolved in a solvent to obtain a uniform solution, and then the nanometal material is added to the solution, stirred, and a slurry is obtained. In some specific embodiments, the preparation method of the nanometal material includes: adding a metal salt to a boiling mixture of tannic acid and sodium citrate, heating and stirring, reacting, and centrifuging to purify to obtain the metal nanomaterial. The size of the nanometal material can be adjusted by adjusting the concentration of tannic acid. In some embodiments of the present application, the material of the above-mentioned metal nanomaterial includes but is not limited to one or more of gold, silver, magnesium, aluminum and zinc.

[0048] In some implementations of the present application, in step S1, the size of the nanometal material is 2nm-100nm.

[0049] In some embodiments of the present application, in step S1, the nanometal material and the protein derivative are mixed at a mass ratio of (3-130):100, or the protein derivative and the nanometal material are synthesized in situ at a target mass ratio of (3-130):100.

[0050] In some embodiments of the present application, in step S1, when the nano-metal material and the protein derivative are mixed, a fast ion conductor is also mixed, that is, the slurry also includes a fast ion conductor.

[0051] In some embodiments of the present application, in step S1, the fast ion conductor is added at 1%-30% of the mass of the protein derivative.

[0052] In some implementations of the present application, in step S1, the thickness of the protective layer finally obtained is controlled to be 1 μm-10 μm.

[0053] In some embodiments of the present application, in step S2, the preparation of the lithium supplement layer includes: forming lithium metal on the surface of the protective layer away from the negative electrode material layer. Specifically, the lithium metal powder can be formed on the surface of the protective layer by any process known in the art such as wet coating, dry rolling, 3D printing, etc., or the lithium foil can be formed on the surface of the protective layer by a rolling process.

[0054] In some embodiments of the present application, in step S2, the thickness of the lithium supplement layer finally obtained is controlled to be 1 μm-15 μm.

[0055] In the implementation manner of the present application, after step S2, the negative electrode sheet is also rolled up.

[0056] The embodiments of the present application also provide a secondary battery, including the negative electrode sheet provided in the embodiments of the present application, or including a negative electrode sheet prepared by the method for preparing the negative electrode sheet provided in the embodiments of the present application.

[0057] Due to the negative electrode plate provided in the embodiment of the present application, the secondary battery can have both higher energy density and better cycle performance.

[0058] The secondary battery provided in the embodiment of the present application may be a liquid battery using a liquid electrolyte, a solid-state battery using a solid-state electrolyte, or a semi-solid-state battery.

[0059] In some embodiments of the present application, the secondary battery is a lithium secondary battery.

[0060] In some implementations of this application, please see Figure 2 The secondary battery comprises a positive electrode sheet 2, the negative electrode sheet 1, and an electrolyte ( Figure 2 In the embodiment of the present application, the secondary battery includes a plurality of negative electrode sheets, and the plurality of negative electrode sheets may all be the negative electrode sheets provided in the embodiment of the present application, or only some of them may be the negative electrode sheets provided in the embodiment of the present application.

[0061] In the embodiment of the present application, the above-mentioned positive electrode plate can be any positive electrode plate known in the field of the corresponding secondary battery, and the present application does not limit this.

[0062] In the embodiments of the present application, the above-mentioned separator can be any known separator in the art suitable for corresponding secondary batteries, and the present application does not impose any limitation on this.

[0063] The present application also provides an electric device, including the secondary battery provided in the present application. In some embodiments of the present application, the electric device includes electronic components, and the secondary battery is used to power the electronic components. Since the secondary battery provided in the present application is used to power the electric device, the electric device has a strong endurance and a good market prospect.

[0064] In some implementations of the present application, the above-mentioned electrical equipment includes but is not limited to vehicles, mobile phones, laptops, tablet computers and other 3C electronic products, site energy backup systems, smart photovoltaic power stations, etc.

[0065] The technical solution of the present application is further illustrated by multiple embodiments below.

[0066] Example 1

[0067] (1) coating negative electrode slurry on opposite sides of a negative electrode current collector (specifically, a copper foil with a width of 160 mm and a thickness of 8 μm), drying at 393 K, and rolling to form a negative electrode material layer; wherein the negative electrode slurry comprises a negative electrode active material (specifically, silicon dioxide), polyacrylic acid, and conductive carbon in a mass ratio of 100:5:1;

[0068] (2) Dissolve silk fibroin in DMSO, and then add 20 wt% of a fast ion conductor (specifically aluminum oxide) based on the mass of the silk fibroin to obtain a slurry; apply the slurry on the surface of the negative electrode material layer, and dry it at 365 K to obtain a protective layer with a thickness of 2 μm; then roll a lithium foil with a thickness of 5 μm on the surface of the protective layer to form a lithium replenishing layer, and then roll up 50 m.

[0069] Embodiment 2-5

[0070] The difference from Example 1 is that the thickness of the protective layer is changed. The thickness of the protective layer in Examples 2-5 is 0.5 μm, 12 μm, 1 μm and 10 μm respectively.

[0071] Embodiment 6-9

[0072] The difference from Example 1 is that the content of the fast ion conductor is changed. The content of the fast ion conductor in Examples 6-9 is 40%, 0.5%, 1%, and 30% respectively.

[0073] Example 10

[0074] The difference from Example 1 is that in step (2), Ag nanoparticles @ silk fibroin are dissolved in DMSO, and then 20wt% of a fast ion conductor (specifically alumina) is added based on the mass of the silk fibroin to obtain a slurry; the slurry is coated on the surface of the negative electrode material layer, and dried at 365K to obtain a protective layer with a thickness of 2μm; in the protective layer, 33wt% of Ag nanoparticles are added based on the mass of the silk fibroin, wherein the size of the Ag nanoparticles is 37±3nm.

[0075] Then, a lithium foil with a thickness of 5 μm was rolled on the surface of the protective layer to form a lithium supplement layer, and the rolled foil was rolled up for 50 m.

[0076] Examples 11-13

[0077] The difference from Example 10 is that the content of nanoparticles is changed. The content of metal nanoparticles in Examples 11-13 is 140%, 3%, and 130%, respectively.

[0078] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that the negative electrode plate of Comparative Example 1 does not contain a protective layer.

[0081] Comparative Example 2

[0082] The difference from Example 1 is that the protective layer in the negative electrode plate of Comparative Example 2 is a polyacrylic acid binder layer.

[0083] Performance Testing

[0084] (1) The center temperature of the negative electrode coil after winding of each embodiment and comparative example was tested. The results are summarized in Table 1.

[0085] (2) Electrochemical performance test

[0086] Preparation of test battery: Cut the negative electrode coils provided in each embodiment 1-13 and comparative example 1-2, prepare the battery by Z-type stacking of the positive electrode sheet, the negative electrode sheet provided in each embodiment and comparative example and the separator to obtain a dry battery cell; the separator is located between the positive electrode sheet and the negative electrode sheet. Inject the electrolyte, let it stand at 45°C for 48 hours, and then pressurize, repackage, exhaust, and separate the capacity at 45°C to obtain each test battery. Among them, the positive electrode sheet includes a positive current collector (specifically aluminum foil), and a positive electrode material layer located on the opposite sides of the positive current collector. The positive electrode material layer includes a positive active material (specifically NCM622) with a mass ratio of 96:3:0.5:0.5, a binder (specifically polyvinylidene fluoride), and a conductive agent (acetylene black).

[0087] Electrochemical performance test:

[0088] Five test batteries prepared in each of Examples 1-13 and Comparative Examples 1-2 were taken and cycle tested at 0.2C at 25±1°C on a secondary battery performance testing device.

[0089] The steps are as follows: standby for 10 minutes; constant voltage charging to 4.2V / 0.05C cut-off; standby for 10 minutes; constant current discharge to 2.5V, which is one cycle. When the battery capacity is less than 80% of the initial discharge capacity during the cycle, the cycle is terminated, and the number of cycles is the cycle life of the battery, and the average value is taken for each group. The results are recorded in Table 1.

[0090] Table 1

[0091] Case Pole coil center temperature (℃) Cycle number (no.) Example 1 48 700 Example 2 105 450 Example 3 40 400 Example 4 60 650 Example 5 40 420 Example 6 55 430 Example 7 40 510 Example 8 42 600 Example 9 44 670 Example 10 40 850 Embodiment 11 38 440 Example 12 44 610 Embodiment 13 38 580 Comparative Example 1 Spontaneous combustion / Comparative Example 2 110 290

[0092] It can be seen from the data in Table 1 that the negative electrode sheet provided in the embodiment of the present application has a low risk of heat generation and ignition during the winding process, and has excellent production safety performance. In addition, the negative electrode sheet provided in the embodiment of the present application has excellent cycle performance; when the protective layer of the negative electrode sheet further contains nano-metal materials, its cycle life can be further improved.

[0093] The above is an exemplary embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made thereto without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A negative electrode plate, characterized in that: The invention comprises a negative electrode material layer arranged on the surface of a current collector, a protective layer and a lithium supplement layer stacked in sequence and arranged on the negative electrode material layer away from the surface of the current collector; the protective layer comprises a protein derivative.

2. The negative electrode sheet according to claim 1, characterized in that: The protective layer also includes nano-metal materials; the nano-metal materials are dispersed in the protein derivatives.

3. The negative electrode sheet according to claim 2, characterized in that: The material of the nano metal material includes one or more of gold, silver, magnesium, aluminum and zinc.

4. The negative electrode sheet according to claim 2 or 3, characterized in that: The size of the nano metal material is 2nm-100nm.

5. The negative electrode sheet according to any one of claims 2 to 4, characterized in that: The total mass of the nano-metal material is 3%-130% of the total mass of the protein derivative.

6. The negative electrode sheet according to any one of claims 2 to 5, characterized in that: The protective layer also includes a fast ion conductor material; the total mass of the fast ion conductor material accounts for 1%-30% of the total mass of the protein derivative.

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that: The protein derivatives include silk protein.

8. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The thickness of the protective layer is 1 μm-10 μm.

9. The negative electrode sheet according to any one of claims 1 to 8, characterized in that: The negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based negative electrode material. The mass proportion of the silicon-based negative electrode material in the negative electrode material layer is 5%-95%.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that: The thickness of the lithium supplement layer is 1 μm-15 μm.

11. A method for preparing a negative electrode sheet, characterized in that: include: Providing a current collector and a negative electrode material layer stacked in layers, forming a protective layer on the surface of the negative electrode material layer facing away from the current collector, wherein the protective layer includes a protein derivative; A lithium supplement layer is formed on the surface of the protective layer away from the negative electrode material layer to obtain a negative electrode plate.

12. The preparation method according to claim 11, characterized in that: The forming of a protective layer on the surface of the negative electrode material layer away from the current collector comprises: The mixture of the protein derivative and the nano-metal material is dispersed in a solvent to obtain a slurry, and the slurry is formed on the surface of the negative electrode material layer away from the current collector, and then dried.

13. A secondary battery, characterized in that: The invention comprises the negative electrode sheet as described in any one of claims 1 to 10, or comprises the negative electrode sheet prepared by the method for preparing the negative electrode sheet as described in claim 11 or 12.

14. An electrical device, characterized in that: It comprises the negative electrode sheet as described in any one of claims 1 to 10, or, it comprises the negative electrode sheet prepared by the method for preparing the negative electrode sheet as described in claim 11 or 12, or, it comprises the secondary battery as described in claim 13.

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