Negative electrode sheet, method for manufacturing the same, secondary battery, and electric device

Abstract

The embodiment of the present application provides a negative pole piece, a preparation method thereof, a secondary battery and an electric device. The negative pole piece comprises a negative material layer arranged on the surface of a current collector, a protection layer and a lithium supplement layer which are arranged on the negative material layer in sequence and away from the surface of the current collector; and the protection layer comprises a protein derivative. The negative pole piece provided by the embodiment of the present application has a relatively relaxed requirement for a production environment, has a relatively high safety performance in a production process, and can be used for improving the energy density and cycle performance of a battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to negative electrode sheets and their preparation methods, secondary batteries, and electrical devices. Background Technology

[0002] To improve the energy density and initial coulombic efficiency of secondary batteries, the industry often chooses to perform lithium replenishment on the negative electrode. One common method for negative electrode lithium replenishment is to set a lithium metal replenishment layer on the surface of the negative electrode material layer. This causes the negative electrode sheet to generate severe heat during the winding process. The resulting heat accumulation can damage the performance of the replenishment layer material, increase the risk of spontaneous combustion of the replenishment layer, and seriously threaten production safety. Summary of the Invention

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

[0004] The first aspect of this application provides a negative electrode sheet, including a negative electrode material layer disposed on the surface of a current collector, a protective layer disposed on the negative electrode material layer away from the surface of the current collector, and a lithium replenishment layer; the protective layer includes a protein derivative.

[0005] A protective layer is disposed between the lithium replenishment layer and the negative electrode material layer. This protective layer can effectively suppress heat generation of the negative electrode sheet during the winding process, thereby reducing heat accumulation and the risk of fire, thus improving the production safety performance of the negative electrode sheet. Furthermore, the protein derivatives in the protective layer, which are film-forming peptides, can further increase the flexibility of the protective layer and its adhesion to the negative electrode active material layer. This not only better suppresses heat generation during the winding process but also helps to suppress the expansion of the negative electrode material layer during charge-discharge cycles, thereby improving the cycle performance of the negative electrode sheet. Based on the inherent properties of the lithium replenishment layer, the aforementioned negative electrode sheet can also improve the initial coulombic efficiency of the battery.

[0006] The second aspect of this application provides a method for preparing a negative electrode sheet, comprising:

[0007] A current collector and a negative electrode material layer are provided in a stacked manner, and a protective layer is formed on the surface of the negative electrode material layer opposite to the current collector, the protective layer comprising a protein derivative;

[0008] A lithium replenishment layer is formed on the surface of the protective layer opposite to the negative electrode material layer to obtain the negative electrode sheet.

[0009] The above preparation method is simple, efficient, and suitable for large-scale industrial production.

[0010] The third aspect of this application provides a secondary battery, including the negative electrode sheet provided in the first aspect of this application, or the negative electrode sheet prepared by the method of the negative electrode sheet preparation provided in the second aspect of this application.

[0011] Because it incorporates the negative electrode provided in the embodiments of this application, the secondary battery can have both high energy density and superior cycle performance.

[0012] A fourth aspect of this application provides an electrical device, including a negative electrode sheet provided in the first aspect of this application, or a negative electrode sheet prepared by the method described in the second aspect of this application, or a secondary battery provided in the third aspect of this application. Because the electrical device is powered by the secondary battery provided in this application, it has a longer battery life and a promising market prospect. Attached Figure Description

[0013] Figure 1A A simplified structural diagram of the cross-section of a negative electrode sheet provided in an embodiment of this application;

[0014] Figure 1B A simplified schematic diagram of the cross-section of the negative electrode sheet provided in another embodiment of this application;

[0015] Figure 1C A simplified schematic diagram of the cross-section of the negative electrode sheet provided in another embodiment of this application;

[0016] Figure 2 This is a simplified schematic diagram illustrating the arrangement of the positive and negative electrode plates in a secondary battery according to an embodiment of this application. Detailed Implementation

[0017] Please see Figures 1A to 1C This application provides a negative electrode 1, which includes a negative electrode material layer 20 disposed on the surface of a current collector 10, a protective layer 30 disposed on the negative electrode material layer 20 away from the surface of the current collector 10, and a lithium replenishment layer 40; the protective layer 30 includes a protein derivative.

[0018] In this embodiment of the application, please refer to Figure 1A The negative electrode material layer can be disposed on one side of the current collector surface; or the negative electrode material layer can be disposed on both opposite sides of the current collector surface. Please refer to [link / reference]. Figure 1B When negative electrode material layers are disposed on both opposite surfaces of the current collector, a protective layer and a lithium replenishment layer may be sequentially stacked on both opposite surfaces of the negative electrode material layers; please refer to Figure 1C Alternatively, the protective layer and lithium replenishment layer may be stacked on the surface of the negative electrode material layer on one side of the current collector.

[0019] In the negative electrode sheet provided in this application embodiment, a protective layer is disposed between the lithium replenishment layer and the negative electrode material layer. This protective layer can effectively suppress heat generation during the winding process of the negative electrode sheet, thereby reducing heat accumulation and the risk of fire, thus improving the production safety performance of the negative electrode sheet. Furthermore, the protein derivatives in the protective layer are film-forming peptides, which can further increase the flexibility of the protective layer and its adhesion to the negative electrode active material layer. This not only better suppresses heat generation during the winding process but also helps to suppress the expansion of the negative electrode material layer during charge-discharge cycles, 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 battery's initial coulombic efficiency and energy density. Therefore, this negative electrode sheet can be used to provide a battery with both high energy density and superior cycle performance.

[0020] In some embodiments of this application, the lithium replenishment layer includes metallic lithium. The material of the lithium replenishment layer can be elemental lithium or a lithium alloy; this application does not impose any limitations on this. Of course, the lithium replenishment layer can also be other lithium replenishment materials.

[0021] In some embodiments of this application, the lithium replenishment layer comprises metallic lithium, and the areal density of the lithium replenishment layer is 1 g / m³. 2 -8 g / m 2 This facilitates the optimization of the final battery's electrochemical performance. Specifically, the areal density of the lithium replenishment layer can, for example, be 1 g / m². 2 2g / m 2 3g / m 2 4g / m 2 5g / m 2 6g / m 2 7g / m 2 8g / m 2 In this embodiment, the areal density of the lithium replenishment layer = mass of the lithium replenishment layer / thickness of the lithium replenishment layer.

[0022] In some embodiments of this application, the thickness of the lithium replenishment layer is 1μm-15μm. This allows for a larger lithium replenishment capacity while also improving the battery's volumetric energy density; furthermore, the lithium replenishment layer within this thickness range, in conjunction with the protective layer, generates 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 this application, the protective layer also includes nanomaterials. Nanomaterials have superior thermal conductivity, which helps to accelerate heat dissipation, thus further improving the production safety performance of the negative electrode sheet.

[0024] In some embodiments of this application, the nanomaterials are made of one or more of gold, silver, magnesium, aluminum, and zinc. These nanomaterials have superior thermal conductivity and lower lithium nucleation potential. When the negative electrode is applied to a lithium-ion battery, the combined effect of the nanomaterials and protein derivatives can induce uniform deposition of active lithium ions on the negative electrode, inhibiting the growth of lithium dendrites and thus improving the battery's cycle performance and safety.

[0025] In some embodiments, the nanomaterial is dispersed within the protein derivative. In other embodiments, the nanomaterial is uniformly dispersed within the protein derivative. This results in better structural uniformity of the protective layer, which is more conducive to inducing uniform deposition of active lithium ions at the negative electrode and thus better maximizing battery performance. In some embodiments, the protective layer comprises a composite of in-situ grown nanomaterial and protein derivative.

[0026] In this application, the nanomaterial can be either nanomaterial particles or nanomaterial wires. In some embodiments of this application, the size of the nanomaterial particles is 2nm-100nm. Controlling the size of the nanomaterial particles within this range is beneficial for their inductive effect on active lithium ions, and can also effectively reduce the occurrence of undesirable phenomena such as agglomeration, thereby improving the uniformity of the protective layer and reducing heat accumulation. It should be noted that when the nanomaterial is nanomaterial particles, the above-mentioned size refers to the particle size (D) of the nanomaterial particles. 50 When the nanomaterial is a nanowire, both the axial and radial dimensions of the nanowire are in the range of 2nm-100nm. Further, the size of the nanowire is 80nm-100nm. Nanowires within this size range exhibit better binding to protein derivatives and can form a more stable protective layer. Specifically, the size of the nanomaterial can be, for example, 2nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, or 100nm. In the embodiments of this application, scanning electron microscopy can be used to characterize the size of the nanomaterial.

[0027] In some embodiments of this application, the total mass of the nanomaterial in the protective layer is 3%-130% of the total mass of the protein derivative. This not only improves the protective effect of the protective layer during the winding process of the negative electrode sheet, but also effectively suppresses the expansion of the negative electrode material layer during charge-discharge cycles, and facilitates the uniform deposition of active lithium ions, resulting in a lower cost for the negative electrode sheet. Specifically, the total mass of the nanomaterial 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%, or 130% of the total mass of the protein derivative. In the embodiments of this application, inductively coupled plasma (ICP) testing can be used to determine the mass ratio of the nanomaterial to the protein derivative.

[0028] In some embodiments of this 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 uniformly dispersed in the protective layer. In the embodiments of this application, the fast ion conductor material can be any fast ion conductor material suitable for secondary batteries. Specifically, when the above-mentioned negative electrode sheet is applied to a lithium-ion battery, the fast ion conductor material can be, for example, one or more of 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, and lithium hexafluorophosphate.

[0029] In some embodiments of this application, the total mass of the fast ion conductor material in the protective layer accounts for 1%-30% of the total mass of the protein derivative. Thus, the protective layer can achieve better suppression of the thermal effects of the negative electrode sheet during the winding process, improve the safety performance of the negative electrode sheet, and also improve the rate performance of the negative electrode sheet. Furthermore, it can effectively suppress the expansion of the negative electrode material layer during charge-discharge cycles, thereby improving the battery cycle life. That is, the negative electrode sheet possesses superior safety performance, good rate performance, and good 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% of the mass of the protein derivative. In the embodiments of this application, thermogravimetric analysis (TGA) combined with ICP can be used to test the mass ratio of the fast ion conductor material to the protein derivative.

[0030] In some embodiments of this application, the protective layer includes protein derivatives and nanomaterials and fast-ion conductors dispersed within the protective layer. In some specific embodiments, the total mass of the fast-ion conductors in the protective layer accounts for 1%-30% of the total mass of the protein derivatives, and the ratio of the sum of the mass of the fast-ion conductors and protein derivatives to the mass of the nanomaterials is 1:(0.33-1). This results in superior overall electrochemical performance of the negative electrode. Specifically, the ratio of the sum of the mass of the fast-ion conductors and protein derivatives to the mass of the nanomaterials 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 percentage of the nanomaterials is 25%-50%, the mass percentage of the protein derivatives is 38%-75%, and the mass percentage of the fast-ion conductors is 0.5%-17.3%. Specifically, based on the mass of the protective layer, the mass percentage of nanomaterials can be, for example, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, or 50%; the mass percentage of protein derivatives can be, for example, 38%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%; and the mass percentage of fast ion conductors can be, for example, 0.5%, 1%, 2%, 5%, 8%, 10%, 12%, 15%, or 17%. This is more conducive to optimizing the overall electrochemical performance of the negative electrode.

[0031] In some embodiments of this application, the protein derivative includes silk fibroin. Silk fibroin has strong adhesion, which can reduce or eliminate the need for binders, and can also achieve adhesion between the protective layer and the negative electrode active material layer. It also helps to suppress the expansion of the negative electrode material layer during charge-discharge cycles. In addition, silk fibroin has good electronic conductivity, which is beneficial to the performance of the battery.

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

[0033] In some embodiments of this application, the aforementioned negative electrode material layer can be any negative electrode material layer known in the art for use with 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 aforementioned negative electrode active material includes, but is not limited to, silicon-based negative electrode materials and carbon-based negative electrode materials. Silicon-based negative electrode materials include, but are not limited to, elemental silicon, silicon suboxide, and silicon-carbon composite materials; carbon-based negative electrode materials include, but are not limited to, graphite and hard carbon. In some specific embodiments, the aforementioned negative electrode active material includes a silicon-based negative electrode material, and the mass percentage of the silicon-based negative electrode material in the negative electrode material layer is 5%-95%.

[0034] This application also provides a method for preparing a negative electrode sheet, including:

[0035] S1. A current collector and a negative electrode material layer are stacked together, and a protective layer is formed on the surface of the negative electrode material layer away from the current collector, the protective layer comprising a protein derivative;

[0036] S2. A lithium replenishment layer is formed on the surface of the protective layer opposite to the negative electrode material layer to obtain a negative electrode sheet.

[0037] In this embodiment, a negative electrode material layer may be disposed on one side of the current collector, or a negative electrode material layer may be disposed on both opposite sides of the current collector. When a negative electrode material layer is disposed on both opposite sides of the current collector, a protective layer and a lithium replenishment layer may be sequentially formed on one negative electrode material layer, or a protective layer and a lithium replenishment layer may be sequentially formed on the surfaces of both negative electrode material layers.

[0038] The above preparation method is simple, efficient, and suitable for large-scale industrial production.

[0039] In some embodiments of this application, step S1, which involves 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 nanomaterial is dispersed in a solvent to obtain a slurry. The slurry is then formed on the surface of the negative electrode material layer away from the current collector and dried.

[0041] Since protein derivatives themselves have a certain degree of viscosity, their slurry also has a certain degree of adhesive properties. When the protective layer is prepared using the above preparation method, a small amount of slurry can penetrate into the negative electrode material layer. Since protein derivatives themselves have better adhesive properties, the amount of binder (such as styrene-butadiene rubber) added to the negative electrode material layer can be appropriately reduced when preparing the negative electrode material layer.

[0042] In this embodiment, the negative electrode material layer can be prepared using any process known in the art.

[0043] In some embodiments of this application, the preparation of the negative electrode material layer includes: mixing a negative electrode active material and a conductive agent, and optionally a binder. The aforementioned negative electrode active material can be any negative electrode active material known in the art and 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 percentage of the silicon-based negative electrode material in the negative electrode material layer is 5%-95%.

[0044] In some embodiments of this application, in step S1, the solvents mentioned above include, but are not limited to, dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMF), N-methylpyrrolidone (NMP), ethylene glycol, glycerol, water, etc.

[0045] In some embodiments of this application, step S1, before dispersing the mixture of the protein derivative and the nanomaterial in a solvent, includes: preparing the mixture of the protein derivative and the nanomaterial.

[0046] In some embodiments, protein derivatives and nanomaterials can be synthesized in situ. In some specific embodiments, a silk fibroin solution is mixed with a metal salt solution and reacted at 75°C-85°C for 75-240 minutes to form a metal nanomaterial@silk fibroin complex in situ. The complex is then freeze-dried to obtain metal nanomaterial@silk fibroin powder. In summary, the metals in the aforementioned metal salts include, but are not limited to, one or more of gold, silver, magnesium, aluminum, and zinc. For example, the aforementioned metal salts can be mixtures of metal salts of different metals.

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

[0048] In some embodiments of this application, in step S1, the size of the nanomaterial is 2nm-100nm.

[0049] In some embodiments of this application, in step S1, nanomaterials and protein derivatives are mixed in a mass ratio of (3-130):100, or protein derivatives and nanomaterials are synthesized in situ in a target mass ratio of (3-130):100.

[0050] In some embodiments of this application, step S1, when mixing the nanomaterials and protein derivatives, also includes mixing fast ion conductors. That is, the slurry also includes fast ion conductors.

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

[0052] In some embodiments of this application, in step S1, the thickness of the final protective layer is controlled to be 1μm-10μm.

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

[0054] In some embodiments of this application, in step S2, the thickness of the final lithium replenishment layer is controlled to be 1μm-15μm.

[0055] In this embodiment of the application, after step S2, the negative electrode sheet is further wound up.

[0056] This application also provides a secondary battery, including the negative electrode sheet provided in this application embodiment, or the negative electrode sheet prepared by the method provided in this application embodiment.

[0057] Because it incorporates the negative electrode provided in the embodiments of this application, the secondary battery can have both high energy density and superior cycle performance.

[0058] The secondary battery provided in this application embodiment can be a liquid battery using a liquid electrolyte, a solid battery using a solid electrolyte, or a semi-solid battery.

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

[0060] For some embodiments of this application, please refer to Figure 2 The aforementioned secondary battery includes a positive electrode 2, the aforementioned negative electrode 1, and an electrolyte located between the positive electrode 2 and the negative electrode 1. Figure 2 (Not shown in the image) and separator 3. In the embodiments of this application, the secondary battery includes multiple negative electrode plates. All of the multiple negative electrode plates can be the negative electrode plates provided in the embodiments of this application, or only some of them can be the negative electrode plates provided in the embodiments of this application.

[0061] In the embodiments of this application, the aforementioned positive electrode sheet can be any positive electrode sheet known in the art and applicable to the corresponding secondary battery. This application does not impose any limitations on this.

[0062] In the embodiments of this application, the aforementioned separator can be any known separator applicable to the corresponding secondary battery within the field, and this application does not impose any restrictions on it.

[0063] This application also provides an electrical device, including the secondary battery provided in this application embodiment. In some embodiments of this application, the electrical device includes electronic components, and the secondary battery is used to power the aforementioned electronic components. Because the electrical device is powered by the secondary battery provided in this application embodiment, the electrical device has a strong battery life and a promising market prospect.

[0064] In some embodiments of this application, the aforementioned electrical equipment includes, but is not limited to, vehicles, mobile phones, laptops, tablets and other 3C electronic products, site energy backup power systems, smart photovoltaic power stations, etc.

[0065] The technical solution of this application is further described below with reference to several embodiments.

[0066] Example 1

[0067] (1) A negative electrode slurry is coated on the opposite two sides of the negative electrode current collector (specifically, a copper foil with a width of 160 mm and a thickness of 8 μm), dried at 393 K, and rolled to form a negative electrode material layer; wherein, the negative electrode slurry includes a negative electrode active material (specifically, silicon suboxide), polyacrylic acid and conductive carbon in a mass ratio of 100:5:1.

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

[0069] Examples 2-5

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

[0071] Examples 6-9

[0072] The difference from Example 1 is that the fast ion conductor content is changed. In Examples 6-9, the fast ion conductor content 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 20wt% of fast ion conductor (specifically alumina) is added based on the mass of 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 silk fibroin, wherein the size of Ag nanoparticles is 37±3nm.

[0075] A 5μm thick lithium foil is then rolled onto the surface of the protective layer to form a lithium replenishment layer, and then wound up to 50m.

[0076] Examples 11-13

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

[0078] To highlight the beneficial effects of the embodiments of this application, the following comparative examples are provided.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that the negative electrode sheet 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 sheet of Comparative Example 2 is a polyacrylic acid adhesive layer.

[0083] Performance testing

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

[0085] (2) Electrochemical performance testing

[0086] Preparation of test batteries: The negative electrode rolls provided in Examples 1-13 and Comparative Examples 1-2 were cut, and the positive electrode sheet, the negative electrode sheet provided in each example and the comparative example, and the separator were stacked in a Z-shaped manner to prepare batteries, obtaining dry cells; the separator is located between the positive electrode sheet and the negative electrode sheet. Electrolyte was injected, and the cells were placed at 45°C for 48 hours, followed by pressure formation at 45°C, secondary encapsulation, degassing, and capacity testing to obtain the test batteries. The positive electrode sheet includes a positive current collector (specifically aluminum foil) and a positive electrode material layer located on opposite sides of the positive current collector. The positive electrode material layer includes a positive active material (specifically NCM622), a binder (specifically polyvinylidene fluoride), and a conductive agent (acetylene black) in a mass ratio of 96:3:0.5:0.5.

[0087] Electrochemical performance testing:

[0088] Five test batteries were taken from each of the examples 1-13 and comparative examples 1-2, and the batteries were subjected to a cyclic test at 0.2C at 25±1℃ on a secondary battery performance testing device.

[0089] The steps are as follows: rest for 10 minutes; charge at constant voltage to 4.2V / 0.05C (cut off); rest for 10 minutes; discharge at constant current to 2.5V, which constitutes one cycle. During the cycle, the cycle terminates when the battery capacity falls below 80% of the initial discharge capacity. The number of cycles is the battery's cycle life, and the average value for each group is taken. The results are recorded in Table 1.

[0090] Table 1

[0091] Case Temperature at the center of the electrode roll (°C) Number of loops (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 Example 11 38 440 Example 12 44 610 Example 13 38 580 Comparative Example 1 Spontaneous combustion / Comparative Example 2 110 290

[0092] As can be seen from the data in Table 1, the negative electrode sheet provided in this application embodiment has a low risk of heat generation and fire during the winding process, and has excellent production safety performance. In addition, the negative electrode sheet provided in this application embodiment has better 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 description is an exemplary embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A negative electrode sheet, characterized in that, The device includes a negative electrode material layer disposed on the surface of a current collector, a protective layer disposed on the negative electrode material layer away from the surface of the current collector, and a lithium replenishment layer; the protective layer includes a protein derivative and nano-metallic materials and fast ion conductor materials dispersed in the protective layer, wherein the total mass of the fast ion conductor materials accounts for 1%-30% of the total mass of the protein derivatives, and the protein derivatives include silk protein.

2. The negative electrode sheet according to claim 1, characterized in that, The nanomaterials are made of one or more of the following: gold, silver, magnesium, aluminum, and zinc.

3. The negative electrode sheet according to claim 1, characterized in that, The size of the nanomaterial is 2 nm-100 nm.

4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The total mass of the nanomaterials is 3%-130% of the total mass of the protein derivatives.

5. The negative electrode sheet according to any one of claims 1-3, characterized in that, The thickness of the protective layer is 1μm-10μm.

6. The negative electrode sheet according to any one of claims 1-3, characterized in that, The negative electrode material layer includes a negative electrode active material, which includes a silicon-based negative electrode material, and the silicon-based negative electrode material accounts for 5%-95% of the mass of the negative electrode material layer.

7. The negative electrode sheet according to any one of claims 1-3, characterized in that, The thickness of the lithium replenishment layer is 1μm-15μm.

8. A method for preparing a negative electrode sheet, characterized in that, include: A current collector and a negative electrode material layer are provided in a stacked manner. A protective layer is formed on the surface of the negative electrode material layer away from the current collector. The protective layer includes a protein derivative and nano-metallic materials and fast ion conductor materials dispersed 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. The protein derivative includes silk protein. A lithium replenishment layer is formed on the surface of the protective layer opposite to the negative electrode material layer to obtain the negative electrode sheet.

9. The preparation method according to claim 8, characterized in that, The formation of a protective layer on the surface of the negative electrode material layer opposite to the current collector includes: The mixture of the protein derivative, nanomaterial, and fast ion conductor material is dispersed in a solvent to obtain a slurry. The slurry is then formed on the surface of the negative electrode material layer away from the current collector and dried.

10. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-7, or includes the negative electrode sheet prepared by the preparation method as described in claim 8 or 9.

11. An electrical appliance, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-7, or includes the negative electrode sheet prepared by the preparation method as described in claim 8 or 9, or includes the secondary battery as described in claim 10.

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