Negative pole piece and battery

Abstract

The invention discloses a negative pole piece and a battery. The negative pole piece comprises a first active layer, a second active layer and a functional layer, wherein the first active layer comprises a first silicon active material; the second active layer includes a second silicon active material. The functional layer is arranged between the first active layer and the second active layer and comprises a silane coupling agent and an additive A; the additive A comprises biomass polyphenol and / or a polymer A; the polymer A comprises at least one of polyacrylic acid, polymethyl methacrylate, polyacrylamide and polyurethane. According to the negative pole piece disclosed by the invention, the silane coupling agent in the functional layer can provide a firm framework and resist stripping. The silane coupling agent and the additive A can form a dynamic hydrogen bond network suitable for providing excellent toughness and energy dissipation capacity, so that the cooperation of the rigid framework and the energy dissipation unit is realized, the shear stress between the first active layer and the second active layer is favorably eliminated, and the circulation capacity and the use safety of the negative electrode plate are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode sheet and a battery. Background Technology

[0002] In related technologies, to mitigate volume expansion during battery cell cycling, a gradient distribution of silicon content is often achieved in at least two active material layers on the negative electrode. For example, when the negative electrode comprises two active material layers, the active material layer adjacent to the current collector uses a lower silicon content, while the active material layer farther from the current collector uses a higher silicon content. However, in this double-coated negative electrode, the different silicon content of adjacent active material layers makes them prone to shear stress between layers during cycling due to different expansion rates. This results in poor interlayer contact and a tendency for delamination between adjacent active material layers, potentially leading to safety issues. Summary of the Invention

[0003] This invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one object of this invention is to provide a negative electrode sheet that effectively eliminates the shear stress between the first and second active layers, thereby improving the cycle life of the negative electrode sheet and also enhancing its safety in use.

[0004] According to a first aspect of the present invention, a negative electrode sheet includes: a first active layer; a second active layer; and a functional layer; wherein the first active layer includes a first silicon active material; the second active layer includes a second silicon active material; the functional layer is disposed between the first active layer and the second active layer, wherein the functional layer includes a silane coupling agent and an additive A; the additive A includes a biomass polyphenol and / or a polymer A; the polymer A includes at least one selected from polyacrylic acid, polymethyl methacrylate, polyacrylamide, and polyurethane.

[0005] According to embodiments of the present invention, a functional layer is disposed between a first active layer and a second active layer in the negative electrode sheet. The covalent bonds of the silane coupling agent in the functional layer provide a robust framework to resist peeling. Both the silane coupling agent and additive A can act as hydrogen bond network builders to form a dynamic hydrogen bond network, providing excellent toughness and energy dissipation capacity. By fully leveraging the advantages of both, a synergy between the "rigid framework" and the "energy dissipation unit" is achieved, which can effectively eliminate the shear stress between the first and second active layers, helping to improve the cycle life of the negative electrode sheet and also enhancing its safety in use.

[0006] According to some embodiments of the present invention, the silane coupling agent in the functional layer accounts for 40% to 85% by mass; and / or, the additive A in the functional layer accounts for 15% to 60% by mass.

[0007] According to some embodiments of the present invention, the areal density of one side of the functional layer is 15 mg / m². 2 ~80mg / m 2 .

[0008] According to some embodiments of the present invention, the silane coupling agent includes at least one selected from γ-aminopropyltriethoxysilane, γ-ureopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-aminopropyltrimethoxysilane, phenyltriethoxysilane, and benzyltriethoxysilane.

[0009] According to some embodiments of the present invention, the biomass polyphenols include at least one of tannic acid and phytic acid.

[0010] According to some embodiments of the present invention, the negative electrode sheet includes a current collector, and the first active layer is disposed on the surface of the current collector; the first active layer includes a first binder; the mass percentage of the first binder in the first active layer is 3% to 10%; wherein the first binder includes at least one of polyacrylic acid, lithium-ionized polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, sodium alginate, polyvinylamine, and polyacrylamide.

[0011] According to some embodiments of the present invention, the second active layer includes a second adhesive; the mass percentage of the second adhesive in the second active layer is 7% to 15%; wherein the second adhesive includes at least one of polyacrylic acid, lithium-ionized polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, sodium alginate, polyvinylamine, and polyacrylamide.

[0012] According to some embodiments of the present invention, the mass percentage of the first silicon active material in the first active layer is 15% to 40%; the first silicon active material includes at least one of silicon-carbon material, silicon-oxygen material and elemental silicon.

[0013] According to some embodiments of the present invention, the mass percentage of the second silicon active material in the second active layer is 60% to 80%; the second silicon active material includes at least one of silicon-carbon materials, silicon-oxygen materials, and elemental silicon.

[0014] A battery according to a second aspect of the present invention includes: a negative electrode sheet according to the first aspect of the present invention described above.

[0015] The negative electrode 100 of this application has the following technical effects:

[0016] (1) This application introduces a functional layer between the first and second active layers. Through strong chemical bonds (e.g., Si-O-Si bonds formed between the silane coupling agent and Si) and dynamic reversible hydrogen bonds (e.g., hydrogen bonds formed between tannic acid and the organic end of the silane coupling agent, the carboxyl group of PAA, and itself, or hydrogen bonds formed between the silane coupling agent and tannic acid), interlayer stress is converted into chemical bond energy dissipation, thereby achieving stress elimination and ensuring the cycle performance of the silicon-based negative electrode. Furthermore, the above-mentioned method for preparing the negative electrode is easy to operate and suitable for industrial production.

[0017] (2) In the negative electrode sheet of this application, the covalent bond network formed by the silane coupling agent has high strength, plays the role of rigid skeleton and strong anchoring, and can effectively resist deformation and reduce the risk of interface failure.

[0018] (3) In the negative electrode of this application, the dynamic hydrogen bond network formed by the silane coupling agent and additive A plays the role of energy dissipation. When the stress is transferred to the functional layer, the hydrogen bond network undergoes reversible breakage, converting mechanical energy into chemical energy, thereby dissipating most of the stress and avoiding stress concentration.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0021] Figure 1 This is a schematic diagram of the negative electrode sheet according to an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the force exerted on the negative electrode sheet according to an embodiment of the present invention.

[0023] Figure label:

[0024] 100: Negative electrode plate;

[0025] 1: Current collector; 2: First active layer; 3: Second active layer; 4: Functional layer. Detailed Implementation

[0026] The following is for reference. Figures 1-2 A negative electrode 100 according to a first aspect embodiment of the present invention is described.

[0027] like Figures 1-2 As shown, the negative electrode 100 according to a first aspect embodiment of the present invention includes a first active layer 2, a second active layer 3 and a functional layer 4.

[0028] Specifically, functional layer 4 is disposed between the first active layer 2 and the second active layer 3, wherein functional layer 4 includes a silane coupling agent and additive A. Additive A includes biomass polyphenols and / or polymer A. Polymer A includes at least one of polyacrylic acid (PAM), polymethyl methacrylate (PMMA), polyacrylamide (PAA), and polyurethane (PU).

[0029] For example, in Figure 1 and Figure 2 In the example, functional layer 4 is a bonding bridging layer to connect the first active layer 2 and the second active layer 3. The negative electrode 100 of this application converts the stress between the first active layer 2 and the second active layer 3 into chemical bond energy dissipation through the strong chemical bonds and dynamic reversible bonds of functional layer 4, thereby realizing stress elimination between the first active layer 2 and the second active layer 3, which helps to improve the cycle performance of the negative electrode 100 and improve the safety of the use of the negative electrode 100.

[0030] Among them, the covalent bond network formed by the silane coupling agent in functional layer 4 (e.g., the Si-O-Si bond formed by the silane coupling agent and Si) has high strength, acting as a rigid framework and strong anchoring, effectively resisting deformation and preventing instantaneous interface failure. Biomass polyphenols, polyacrylic acid, polymethyl methacrylate, polyacrylamide, and polyurethane all contain polar groups such as hydroxyl (-OH) and carbonyl (C=O) groups in their molecular structures, which can form intramolecular hydrogen bonds, or intermolecular hydrogen bonds with polar groups such as the amino (-NH2) groups of the silane coupling agent and the carboxyl (-COOH) groups of the first or second binder, forming a stable three-dimensional network structure through hydrogen bonding. For example, the benzene ring backbone of biomass polyphenols is rich in hydrogen bond donors and acceptors. Simultaneously, the hydrogen bond energy of biomass polyphenols lies between covalent bonds and van der Waals forces, allowing them to break and reform under external stimuli (such as temperature). This dynamic nature gives the hydrogen bond network both processability and self-healing capabilities. Polymers can form hydrogen bond networks through ordered connections of intramolecular or intermolecular hydrogen bonds. For example, hydrogen bond donors and acceptors on polymer molecular chains form ordered or semi-ordered cross-linked structures through intramolecular (within the same chain segment) or intermolecular (between different chain segments / molecules) hydrogen bonding interactions.

[0031] Therefore, both the silane coupling agent and additive A in functional layer 4 can serve as dynamic hydrogen bond networks formed by hydrogen bond network construction, playing a role in energy dissipation. When stress is transferred to functional layer 4, the hydrogen bond network can undergo reversible breakage, converting mechanical energy into chemical energy, thereby dissipating most of the stress and effectively reducing stress concentration. Thus, functional layer 4 fully utilizes the advantages of silane coupling agent and additive A, achieving synergy between the "rigid framework" and the "energy dissipation unit," effectively eliminating the shear stress between the first active layer 2 and the second active layer 3, improving the cycle capacity of the negative electrode 100, and also contributing to improving the safety of the negative electrode 100 in use.

[0032] According to an embodiment of the present invention, a functional layer 4 is disposed between the first active layer 2 and the second active layer 3 in the negative electrode 100. The covalent bonds of the silane coupling agent in the functional layer 4 provide a robust framework to resist peeling. Both the silane coupling agent and additive A can act as hydrogen bond network builders to form a dynamic hydrogen bond network, providing excellent toughness and energy dissipation capacity. By fully leveraging the advantages of both, the synergy between the "rigid framework" and the "energy dissipation unit" is achieved, which can effectively eliminate the shear stress between the first active layer 2 and the second active layer 3, helping to improve the cycle life of the negative electrode 100 and also improving the safety of the negative electrode 100 in use.

[0033] According to some embodiments of the present invention, the mass percentage of the silane coupling agent in functional layer 4 is 40% to 85%. Exemplarily, the mass percentage of the silane coupling agent in functional layer 4 can be any value from 40%, 50%, 60%, 70%, 75%, and 85%, or a range of any combination thereof. The above-mentioned mass percentage of the silane coupling agent in functional layer 4 is reasonable, which helps to meet the requirements of a robust framework for functional layer 4, resist peeling, and participate in the formation of a hydrogen bond network, while reducing the amount of silane coupling agent used, thus reducing costs.

[0034] The mass percentage of additive A in functional layer 4 is 15% to 60%. For example, the mass percentage of additive A in functional layer 4 can be any value from 15%, 20%, 30%, 40%, 50%, and 60%, or a range of any combination of both. The aforementioned mass percentage of additive A in functional layer 4 is reasonable, facilitating the functional layer 4's function as an energy dissipation unit through additive A, effectively eliminating shear stress between the first active layer 2 and the second active layer 3, and improving the cycle life of the negative electrode 100. Simultaneously, reducing the amount of additive A used effectively lowers the cost of the negative electrode 100.

[0035] According to other embodiments of the present invention, the areal density of one side of functional layer 4 is 15 mg / m³. 2 ~80mg / m 2 For example, the areal density of one side of functional layer 4 can be 15 mg / m².2 20mg / m 2 40mg / m 2 50mg / m 2 70mg / m 2 80mg / m 2 The areal density is any value or a range of both. The essence of areal density is the mass carried per unit area. The areal density of one side of functional layer 4 is the mass per unit area of ​​functional layer 4 on one of the two sides along the thickness direction of the current collector 1 of the negative electrode 100. The above-mentioned areal density of one side of functional layer 4 is relatively reasonable, resulting in a more complete layer structure and higher functional precision. This is suitable for ensuring the structural stability of at least one side of the negative electrode 100, and helps to reasonably control the burden and cost of the first active layer 2.

[0036] According to some embodiments of the present invention, the silane coupling agent includes at least one of γ-aminopropyltriethoxysilane, γ-ureopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-aminopropyltrimethoxysilane, phenyltriethoxysilane, and benzyltriethoxysilane. At least one of the above-mentioned silane coupling agents is suitable for reacting with the chemical bonds of the first active layer 2 and / or the second active layer 3 to form stable covalent bonds, acting as a rigid framework and strong anchoring, effectively resisting deformation and preventing instantaneous interface failure. Simultaneously, at least one of the above-mentioned silane coupling agents can form a reversible hydrogen bond network to dissipate energy, reduce stress concentration, effectively eliminate shear stress between the first active layer 2 and the second active layer 3, improve the cycle life of the negative electrode 100, and also improve the safety of the negative electrode 100 in use.

[0037] Furthermore, biomass polyphenols include at least one of tannic acid and phytic acid. Both tannic acid and phytic acid can participate in the formation of hydrogen bond networks. By using at least one of tannic acid and phytic acid, hydrogen bond networks can be formed more quickly, realizing the function of functional layer 4. Mechanical energy can be converted into chemical energy more quickly through the hydrogen bond network, thereby dissipating most of the stress and effectively reducing stress concentration.

[0038] According to some further embodiments of the present invention, the negative electrode 100 includes a current collector 1, and a first active layer 2 is disposed on the surface of the current collector 1. Thus, the current collector 1 can be used to fix and support the first active layer 2 and facilitate electron transport. The current collector 1 and the first active layer 2 work together to ensure the stability of the negative electrode 100 during battery charging and discharging.

[0039] The first active layer 2 includes a first binder. The first binder in the first active layer 2 is a structural stabilizer and interface bonding agent for the negative electrode sheet 100, which helps to maintain the structural integrity of the first active layer 2 and ensure electron / ion transport during charge and discharge cycles.

[0040] The mass percentage of the first binder in the first active layer 2 is 3% to 10%. For example, the mass percentage of the first binder in the first active layer 2 can be any value from 3%, 4%, 6%, 7%, 8%, and 10%, or a range of any combination of both. The aforementioned mass of the first binder is reasonable, which helps to fully utilize its adhesive properties, improves the structural stability of the negative electrode 100, reduces the amount of first binder used, lowers costs, and facilitates the miniaturization design of the negative electrode 100.

[0041] The first binder includes at least one of polyacrylic acid, lithium-ionized polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, sodium alginate, polyethyleneamine, and polyacrylamide. All of the above-mentioned first binders are suitable for achieving adhesion to enhance the structural strength of the first active layer 2, and the first binders have good compatibility with the remaining components in the negative electrode 100 (e.g., silane coupling agent and additive A), which is beneficial for improving the structural and performance stability and reliability of the negative electrode 100.

[0042] According to some embodiments of the present invention, the second active layer 3 includes a second binder. The second binder in the second active layer 3 is a structural stabilizer and interface bonding agent of the negative electrode sheet 100, which helps to maintain the structural integrity of the second active layer 3 and ensure electron / ion transport during charge-discharge cycles.

[0043] The mass percentage of the second binder in the second active layer 3 is 7% to 15%. For example, the mass percentage of the second binder in the second active layer 3 can be any value from 7%, 8%, 10%, 12%, 14%, and 15%, or a range of any combination of both. The aforementioned mass of the second binder is reasonable, which helps to fully utilize its adhesive properties, improves the structural stability of the negative electrode 100, reduces the amount of second binder used, lowers costs, and facilitates the miniaturization design of the negative electrode 100.

[0044] The second binder includes at least one of polyacrylic acid, lithium-ionized polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, sodium alginate, polyethyleneamine, and polyacrylamide. All of the above-mentioned second binders are suitable for achieving adhesion to enhance the structural strength of the second active layer 3, and the above-mentioned second binders have good compatibility with the other components in the negative electrode 100 (e.g., silane coupling agent and additive A), which is beneficial for improving the structural and performance stability and reliability of the negative electrode 100.

[0045] According to other embodiments of the present invention, the mass percentage of the first silicon active material in the first active layer 2 is 15% to 40%. For example, the mass percentage of the first silicon active material in the first active layer 2 can be any value from 15%, 20%, 25%, 30%, 35%, and 40%, or a range of any combination thereof. The aforementioned content of the first silicon active material is reasonable, which is beneficial for fully utilizing the function of the first silicon active material, helps to increase the battery capacity using the aforementioned negative electrode 100, and at the same time, helps to reduce the volume expansion of the first active layer 2, thereby ensuring the reliability of the connection between the first active layer 2 and the current collector 1.

[0046] The first silicon active material includes at least one of silicon-carbon materials, silicon-oxygen materials, and elemental silicon. The core advantages of silicon-carbon materials, silicon-oxygen materials, and elemental silicon as active materials lie in their high energy density and adaptability to high capacity requirements. Furthermore, silicon-carbon materials, silicon-oxygen materials, and elemental silicon have low expansion rates and good cycle stability.

[0047] According to further embodiments of the present invention, the mass percentage of the second silicon active material in the second active layer 3 is 60% to 80%. Exemplarily, the mass percentage of the second silicon active material in the second active layer 3 can be any value from 60%, 63%, 68%, 70%, 75%, and 80%, or a range of any combination thereof. By displacing the second active layer 3 away from the current collector 1 and controlling the content of the second silicon active material within the aforementioned range, the battery capacity using the aforementioned negative electrode 100 can be sufficiently improved.

[0048] The second silicon-active material includes at least one of silicon-carbon materials, silicon-oxygen materials, and elemental silicon.

[0049] In addition, along the direction away from the current collector 1, a first active layer 2 and a second active layer 3 are sequentially arranged. The first active layer 2 has a smaller content of the first silicon active material, while the second active layer 3 has a larger content of the second silicon active material, forming a gradient arrangement of silicon active materials. This helps to reduce the expansion of the negative electrode 100. At the same time, combined with the functional layer 4, it further reduces the expansion of the negative electrode 100, which helps to improve the cycle capacity of the negative electrode 100 and also helps to improve the safety of the negative electrode 100 in use.

[0050] The first active layer 2 and the second active layer 3 may include other silicon-based materials with low expansion coefficients.

[0051] The areal density ratio of the first active layer 2 to the second active layer 3 is (0.8~1.2):1, preferably 1:1. The above-mentioned areal density ratio of the first active layer 2 to the second active layer 3 is reasonable. Within this range, it helps to improve the expansion of the negative electrode 100, thereby helping to improve the cycle stability of the negative electrode 100 and extend the cycle life of the negative electrode 100.

[0052] The method for preparing the negative electrode sheet 100 according to a second aspect embodiment of the present invention includes the following steps:

[0053] Preparation of the first active layer 2: The raw material of the first active layer 2 is placed on the surface of the current collector 1 to obtain the first active layer 2;

[0054] Preparation of functional layer 4: The raw material of functional layer 4 is placed on the surface of the first active layer 2 away from the current collector 1 to obtain functional layer 4;

[0055] Preparation of the second active layer 3: The raw material of the second active layer 3 is placed on the surface of the functional layer 4 away from the first active layer 2 to obtain the second active layer 3.

[0056] According to the preparation method of the present invention, the above preparation method is relatively simple and easy to operate, and is suitable for industrial production of negative electrode sheet 100. Therefore, it is beneficial to sequentially form a first active layer 2, a functional layer 4 and a second active layer 3 on the surface of current collector 1. The functional layer 4 is conducive to being stably anchored in the first active layer 2 and the second active layer 3, so as to improve the structural strength of negative electrode sheet 100 and extend the cycle life of negative electrode sheet 100.

[0057] According to some embodiments of the present invention, the step of preparing the functional layer 4 includes the preparation of a functional layer solution. The preparation step of the functional layer solution includes: mixing a silane coupling agent and additive A in a solvent to form a functional layer solution, wherein the solid content of the functional layer solution is 1.5 wt% to 4 wt%. Exemplarily, the solid content of the functional layer solution can be any value from 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 3 wt%, and 4 wt%, or a range of any combination thereof. Mixing the silane coupling agent and additive A to form a relatively uniform functional layer solution is beneficial for forming a relatively uniform functional layer 4 on the surface of the first active layer 2. Simultaneously, the relatively reasonable solid content of the functional layer solution helps ensure the fluidity of the functional layer solution, facilitating uniform placement on the surface of the first active layer 2. It also helps reduce the internal stress of the formed functional layer 4, thus reducing the risk of cracking of the prepared negative electrode 100. Furthermore, it helps maintain the viscosity of the functional layer solution, reducing the number of operations required to form the desired functional layer 4, while also reducing solvent usage, which helps reduce environmental and safety costs.

[0058] According to other embodiments of the present invention, the raw material of the second active layer 3 is disposed on the surface of the functional layer 4 away from the first active layer 2 and cured to obtain the second active layer 3. The curing of the raw material of the second active layer 3 after being disposed helps to strengthen the adhesion between the first active layer 2 and the functional layer 4, as well as the adhesion between the second active layer 3 and the functional layer 4, thereby preventing the negative electrode sheet 100 from peeling off.

[0059] Simultaneously, the first active layer 2 and functional layer 4 can be pre-cured after being applied. Pre-curing prevents the first active layer 2 and functional layer 4 from dissolving adjacent layer structures due to their high fluidity. It also helps retain some porosity in the first active layer 2 and functional layer 4, facilitating the penetration of film-forming substances into the subsequently applied functional layer 4 and second active layer 3, forming an anchoring effect and further enhancing interlayer bonding. Furthermore, pre-curing allows for the release of some solvent from the first active layer 2, functional layer 4, and second active layer 3, helping to reduce solvent residue during the complete curing stage. This reduces defects in the first active layer 2, functional layer 4, and second active layer 3, improving the density of the negative electrode 100, and consequently enhancing its mechanical strength and extending its cycle life.

[0060] The pre-curing process involves heat treatment at a temperature of 70℃ to 100℃ for 1 to 2 minutes. This heat treatment, through controlled heating, accelerates solvent evaporation and initial anchoring within the first active layer 2 and functional layer 4. For example, the heat treatment temperature can be any value from 70℃, 75℃, 80℃, 85℃, 90℃, and 100℃, or a range combining any two. The aforementioned heat treatment temperature is reasonable, which helps optimize the solvent evaporation efficiency in the first active layer 2 and functional layer 4, and improves the anchoring efficiency between functional layer 4 and the first active layer 2 and the second active layer 3.

[0061] For example, the heat treatment time can be any value or a range of any combination of 1 min, 1.3 min, 1.5 min, 1.6 min, 1.7 min, 1.8 min, and 2 min. The above heat treatment time is reasonable and helps to ensure the completion of pre-curing, so that the interlayer bonding force between the first active layer 2, the functional layer 4, and the second active layer 3 meets the requirements, while avoiding over-curing.

[0062] Specifically, the specific preparation method of the negative electrode 100 can be as follows:

[0063] S1, First active layer slurry: The first silicon active material, carbon, conductive agent and first binder required for preparation are thoroughly mixed, deionized water is added, and the mixture is stirred, dispersed and defoamed to prepare the first active layer slurry;

[0064] S2, First active layer 2: The first active layer slurry is coated onto the current collector 1 and dried to form the first active layer 2;

[0065] S3. Preparation of functional layer solution: Add silane coupling reagent and tannic acid to a mixed solvent of ethanol / water (v / v = 7:3);

[0066] S4, Functional Layer 4: Using a precision spraying system, the functional layer solution is uniformly sprayed onto the surface of the first active layer 2 away from the current collector 1, followed by heat treatment for pre-curing.

[0067] S5. Second active layer slurry: The required second silicon active material, carbon, conductive agent and second binder are thoroughly mixed, deionized water is added, and the mixture is stirred, dispersed and defoamed to prepare the second active layer slurry.

[0068] S6, Second active layer 3: The second active layer slurry is coated onto the surface of the functional layer 4 away from the current collector 1, dried to form the second active layer 3, and rolled to obtain the negative electrode sheet 100.

[0069] Furthermore, the carbon is one or more of graphite, soft carbon, and hard carbon; and / or,

[0070] Furthermore, the conductive agent is one or more of the following: conductive carbon black, acetylene black, carbon nanotubes, carbon fibers, graphene, etc.; and / or,

[0071] Further, the mass ratio of the first silicon active material, carbon, conductive agent, and first binder in the first active layer slurry is: (15%–40%): (45%–65%): (3%–10%): (3%–10%); and / or,

[0072] Furthermore, the mass ratio of the second silicon active material, carbon, conductive agent, and second binder in the second active layer slurry is: (60%–80%): (10%–20%): (3%–7%): (7%–15%); and / or,

[0073] Furthermore, the solid content of the first and second active layer slurries is 52% ± 3%; and / or,

[0074] Further, the viscosity of the first active layer slurry is 3000 mPa·s to 15000 mPa·s; and / or, the viscosity of the second active layer slurry is 3000 mPa·s to 15000 mPa·s; and / or,

[0075] Furthermore, the mass percentage of tannic acid in functional layer 4 is 15%–60%; and / or,

[0076] Furthermore, the volume ratio of the ethanol / water mixed solvent is 7:3.

[0077] A battery according to a second aspect of the present invention includes: a negative electrode 100 according to the first aspect of the present invention described above.

[0078] For example, a lithium sheet is used as the counter electrode, a polyethylene film is used as the separator (the separator thickness is 11 μm), and the electrolyte contains 1 mol·L⁻¹ -1A solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) of LiPF6 (EC to DMC volume ratio of 1:1) and containing 5 wt% fluoroethylene carbonate (FEC) additive was encapsulated in a high-purity argon glove box as a lithium-ion half-cell (CR2032 type).

[0079] According to the battery of the present invention, by employing the above-described negative electrode 100, the cycle stability of the battery is improved and the cycle life of the battery is extended, thereby enhancing the market competitiveness of the battery.

[0080] In some optional embodiments, the battery pack may include the negative electrode 100 of the first aspect embodiment of the present invention, or the negative electrode 100 prepared by the preparation method of the second aspect embodiment of the present invention, or the battery of the third aspect embodiment of the present invention. By using the above-mentioned negative electrode 100 or battery, the battery pack improves the safety of the battery pack, provides more uniform heat generation during battery charging and discharging, and enhances the structural stability during cycling.

[0081] In some optional embodiments, the electrical device may include the negative electrode 100 of the first aspect embodiment of the present invention, or the negative electrode 100 prepared by the preparation method of the second aspect embodiment of the present invention, or the battery of the third aspect embodiment of the present invention, or the battery pack described above. This results in higher power supply stability for the electrical device, which is beneficial for improving the user experience and thus enhancing the market competitiveness of the electrical device.

[0082] Among them, electrical equipment can be vehicles, aircraft, ferries, computers or energy storage cabinets, etc., without specific limitations.

[0083] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0084] Example 1

[0085] A negative electrode 100 includes a current collector 1, a first active layer 2, a bridging layer, and a second active layer 3.

[0086] First active layer slurry: Si / C, graphite and SuperP in a mass ratio of 30%:55%:8% are dry-mixed for 30 minutes to disperse them evenly. Then, deionized water is added and mixed for 60 minutes. After that, 7% of the first binder PAA is added and stirred for another 120 minutes to disperse the first active layer slurry evenly. The amount of deionized water is adjusted so that the final viscosity of the first active layer slurry is maintained at 3000 mPa.s to 15000 mPa.s and the solid content of the first active layer slurry is 52% ± 3%.

[0087] Preparation of the first active layer 2: The obtained first active layer slurry was coated on both sides of a 6µm copper foil, and the surface density of the first active layer 2 coating on one side was 3.8 mg / cm². 2 The first active layer 2 is obtained by drying.

[0088] Preparation of functional layer solution: First, add γ-aminopropyltriethoxysilane to ethanol / water (v / v = 7:3) solvent and stir until dissolved. Then add tannic acid and continue stirring until completely dissolved. The mass ratio of γ-aminopropyltriethoxysilane to tannic acid is 70%:30%, and the solid content is 2.6wt%.

[0089] Preparation of functional layer 4: The amount of the functional layer solution sprayed is controlled using a precision spraying system and uniformly sprayed onto the surface of the first active layer 2. The surface density of functional layer 4 is 30 mg / m². 2 Then heat-treated at 90℃ for 1 min;

[0090] Second active layer slurry: Dry mix elemental silicon, soft carbon, and SuperP in a mass ratio of 70%:15%:5% for 30 minutes to disperse them evenly. Then add deionized water and mix for 60 minutes. After that, add 10% of the second binder PAA and mix for another 90 minutes to disperse the slurry evenly. Adjust the amount of deionized water to keep the final viscosity of the obtained active material layer slurry between 3000 mPa.s and 15000 mPa.s and the solid content of the slurry between 52% and 3%.

[0091] Preparation of the second active layer 3: The obtained second active layer slurry is coated onto the surface of the functional layer 4, and the surface density of the second active layer 3 coating on one side is 3.8 mg / cm³. 2 The second active layer 3 is obtained by baking and then rolling to obtain the negative electrode sheet 100. After rolling, the thickness of the first active layer 2 is 36 μm and the thickness of the second active layer 3 is 36 μm.

[0092] The lithium sheet was used as the counter electrode, and a polyethylene film was used as the separator (the separator thickness was 11 μm). The electrolyte contained 1 mol·L⁻¹ - 1A solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) of LiPF6 (EC to DMC volume ratio of 1:1) and containing 5 wt% fluoroethylene carbonate (FEC) additive was encapsulated in a high-purity argon glove box as a lithium-ion half-cell (CR2032 type).

[0093] Example 2

[0094] The difference between this embodiment and Example 1 is that the mass ratio of γ-aminopropyltriethoxysilane to tannic acid is 40%:60%, while the other steps and parameters are the same as in Example 1.

[0095] Example 3

[0096] The difference between this embodiment and Example 1 is that the mass ratio of γ-aminopropyltriethoxysilane to tannic acid is 85%:15%, while the other steps and parameters are the same as in Example 1.

[0097] Example 4

[0098] The difference between this embodiment and Example 1 is that the mass ratio of γ-aminopropyltriethoxysilane to tannic acid is 90%:10%, while the other steps and parameters are the same as in Example 1.

[0099] Example 5

[0100] The difference between this embodiment and Example 1 is that the mass ratio of γ-aminopropyltriethoxysilane to tannic acid is 20%:80%, while the other steps and parameters are the same as in Example 1.

[0101] Example 6

[0102] The difference between this embodiment and Embodiment 1 is that the areal density of functional layer 4 is 15 mg / m³. 2 (dry weight), other steps and parameters are the same as in Example 1.

[0103] Example 7

[0104] The difference between this embodiment and Embodiment 1 is that the areal density of functional layer 4 is 80 mg / m³. 2 (dry weight), other steps and parameters are the same as in Example 1.

[0105] Example 8

[0106] The difference between this embodiment and Embodiment 1 is that the areal density of functional layer 4 is 5 mg / m³. 2 (dry weight), other steps and parameters are the same as in Example 1.

[0107] Example 9

[0108] The difference between this embodiment and Embodiment 1 is that the areal density of functional layer 4 is 90 mg / m³.2 (dry weight), other steps and parameters are the same as in Example 1.

[0109] Example 10

[0110] The difference between this embodiment and Example 1 is that γ-aminopropyltriethoxysilane is replaced with γ-methacryloxypropyltrimethoxysilane, while the other steps and parameters are the same as in Example 1.

[0111] Example 11

[0112] The difference between this embodiment and Example 1 is that γ-aminopropyltriethoxysilane is replaced with γ-(2,3-epoxypropoxy)propyltrimethoxysilane, while the other steps and parameters are the same as in Example 1.

[0113] Example 12

[0114] The difference between this embodiment and Embodiment 1 is that tannic acid is replaced with phytic acid, while the other steps and parameters are the same as in Embodiment 1.

[0115] Example 13

[0116] The difference between this embodiment and Embodiment 1 is that tannic acid is replaced with polyacrylamide (PAM), while the other steps and parameters are the same as in Embodiment 1.

[0117] Comparative Example 1

[0118] In this comparative example, the second active layer 3 was directly coated onto the surface of the first active layer 2 away from the current collector 1, without spraying the functional layer 4 in between. All other steps and parameters were the same as in Example 1.

[0119] Comparative Example 2

[0120] In this comparative example, γ-aminopropyltriethoxysilane was sprayed onto the surface of the first active layer 2 away from the current collector 1, without adding tannic acid. All other steps and parameters were the same as in Example 1.

[0121] Comparative Example 3

[0122] In this comparative example, tannic acid was sprayed onto the surface of the first active layer 2 away from the current collector 1, and γ-aminopropyltriethoxysilane was not added. All other steps and parameters were the same as in Example 1.

[0123] Performance testing

[0124] The performance of the silicon-based negative electrode 100 or battery prepared in each embodiment and comparative example is tested below:

[0125] (1) Adhesion test

[0126] Cut a spline with a width of 20 mm and a length of 120 mm (i.e., part of the negative electrode tab 100). After baking the spline in an environment of 100 °C for 10 min, paste it on the spline with 3M tape, roll it five times with a roller, and then peel off the tape. If no active material is carried on the tape, it is judged as qualified; otherwise, it is unqualified. In addition, it can also be judged whether the first active layer 2 and the second active layer 3 are peeled off simultaneously or only the second active layer 3 is peeled off by observing the peeling situation.

[0127] (2) Cycling performance test of the negative electrode tab 100

[0128] At room temperature of 25 °C, in the test voltage range of 0.01 V (discharge cut-off voltage) to 1.5 V (charge cut-off voltage), first activate for 3 cycles at a current density of 0.05 A / g; then perform charge-discharge cycling at a current density of 0.5 A / g, and test the capacity retention rate after 500 cycles.

[0129] (3) Rate performance test: At room temperature of 25 °C, in the test voltage range of 0.01 V (discharge cut-off voltage) to 1.5 V (charge cut-off voltage), first activate for 3 cycles at a current density of 0.05 A / g; then perform 1 cycle of charge-discharge test on the coin-type half-cell at current rates of 0.5 A / g and 5 A / g respectively, and measure the capacity retention rate of the negative electrode tab 100 under the condition of a current rate of 5 A / g.

[0130] Table 1 Performance test results of examples and comparative examples

[0131]

[0132]

[0133] Analysis of test results

[0134] It can be seen from the data in Table 1 that:

[0135] The negative electrode tab 100 prepared by the embodiment of the present invention has excellent performance. Specifically: the initial adhesion result is qualified, the capacity retention rate after 500 cycles ≥ 80.0%, the adhesion result after 500 cycles is qualified, and the capacity retention rate at 5 A / g ≥ 50.0%. Among them, meeting two or more items is regarded as an example, and meeting four items is regarded as a preferred example.

[0136] Combined with Examples 1-11 and Comparative Example 1, it can be found that by introducing the functional layer 4 between the first active layer 2 and the second active layer 3 in the present application, the cycling performance and rate performance of the negative electrode tab 100 and the battery using the above negative electrode tab 100 are effectively improved. And the preparation method of the above negative electrode tab 100 is easy to operate, suitable for industrial production, and has high industrial value.

[0137] Examples 1-5 show that the mass ratio of silane coupling agent and tannic acid affects the performance of the silicon-based negative electrode 100. Within the scope defined in this application, the negative electrode 100 exhibits a high cycle retention rate. If the content of the silane coupling agent is low (corresponding to a high tannic acid content), the negative electrode 100 is prone to stratification after cycling, affecting the cycle retention rate. If the content of the silane coupling agent is high (corresponding to a low tannic acid content), the kinetics deteriorate, leading to insufficient kinetics during cycling and negatively impacting the cycle retention rate.

[0138] Through Examples 1 and 6-9, it can be found that the areal density of functional layer 4 affects the performance of negative electrode 100. When the areal density of functional layer 4 is 15 mg / m³, the performance of negative electrode 100 is affected. 2 ~80mg / m 2 Within the battery, the cycle retention rate is relatively good, and the stability of the negative electrode 100 is also good. If the amount of functional layer solution sprayed is too low, the improvement on the negative electrode 100 is limited; if the amount of functional layer solution sprayed is too high, the functional layer 4 will be too thick, thus affecting the battery's kinetic performance and cycle performance.

[0139] Through Examples 1 and Comparative Examples 2-3, it can be found that spraying silane coupling agent alone or spraying tannic acid alone has limited effect on improving the negative electrode 100. If silane coupling agent is lacking, there is no effective connection between the first active layer 2 and the second active layer 3, resulting in delamination after cycling. If tannic acid is lacking, it is equivalent to lacking an energy dissipation unit. Relying solely on material deformation to resist stress will also eventually lead to delamination, resulting in poor improvement on the cycling performance of the negative electrode 100. Only by combining the strong framework of silane coupling agent with the strong energy dissipation capability of tannic acid can the contradiction of the interface being both "strongly bonded" and "capable of dissipation" be perfectly resolved, achieving a "1+1>2" effect.

[0140] Examples 1 and 10-13 show that changing the type of silane coupling reagent or additive A significantly improves the negative electrode 100.

[0141] Other configurations and operations of the negative electrode 100, battery, battery pack, and electrical equipment according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0142] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0143] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A negative electrode sheet, characterized in that, include: First active layer; Second active layer; Functional layer; The first active layer includes a first silicon active material; The second active layer includes a second silicon active material; The functional layer is disposed between the first active layer and the second active layer, wherein the functional layer includes a silane coupling agent and additive A; The additive A includes biomass polyphenols and / or polymer A; The polymer A includes at least one of polyacrylic acid, polymethyl methacrylate, polyacrylamide, and polyurethane.

2. The negative electrode sheet according to claim 1, characterized in that, The silane coupling agent in the functional layer comprises 40% to 85% by mass; and / or, The mass percentage of additive A in the functional layer is 15% to 60%.

3. The negative electrode sheet according to claim 1, characterized in that, The areal density of one side of the functional layer is 15 mg / m³. 2 ~80mg / m 2 .

4. The negative electrode sheet according to claim 1, characterized in that, The silane coupling agent includes at least one of γ-aminopropyltriethoxysilane, γ-ureopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-aminopropyltrimethoxysilane, phenyltriethoxysilane, and benzyltriethoxysilane.

5. The negative electrode sheet according to claim 1, characterized in that, The biomass polyphenols include at least one of tannic acid and phytic acid.

6. The negative electrode sheet according to claim 1, characterized in that, The negative electrode sheet includes a current collector, and the first active layer is disposed on the surface of the current collector; The first active layer includes a first adhesive; The mass percentage of the first adhesive in the first active layer is 3% to 10%. The first adhesive includes at least one of polyacrylic acid, lithium-ionized polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, sodium alginate, polyethyleneamine, and polyacrylamide.

7. The negative electrode sheet according to claim 1, characterized in that, The second active layer includes a second adhesive; The second adhesive in the second active layer accounts for 7% to 15% of the total mass. The second adhesive includes at least one of polyacrylic acid, lithium-ionized polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, sodium alginate, polyethyleneamine, and polyacrylamide.

8. The negative electrode sheet according to claim 1, characterized in that, The mass percentage of the first silicon active material in the first active layer is 15% to 40%. The first silicon-active material includes at least one of silicon-carbon materials, silicon-oxygen materials, and elemental silicon.

9. The negative electrode sheet according to claim 1, characterized in that, The mass percentage of the second silicon active material in the second active layer is 60% to 80%. The second silicon-active material includes at least one of silicon-carbon materials, silicon-oxygen materials, and elemental silicon.

10. A battery, characterized in that, include: The negative electrode sheet according to any one of claims 1-9.

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