Silicon-containing negative electrode sheet, method for manufacturing the same, and battery

Abstract

The application provides a silicon-containing negative electrode sheet, a preparation method thereof and a battery, and the silicon-containing negative electrode sheet comprises a current collector and an active material layer on at least one side surface of the current collector, wherein the active material layer comprises a silicon-containing negative electrode material, a composite conductive additive, a binder and a conductive agent; the composite conductive additive comprises modified carbon nanotubes and doped polyaniline, and the doped polyaniline comprises a porous carbon substrate and polyaniline. The silicon-containing negative electrode sheet provided by the application introduces the doped polyaniline compounded with the modified carbon nanotubes as the composite conductive additive, so that an elastic network can be formed in the silicon-containing negative electrode sheet, a continuous conductive framework can also be formed, a buffer space is provided for the lithium intercalation expansion of silicon, fast ion and electron transmission is realized, the contact resistance between particles is reduced, the interface stability of the electrode sheet is improved, the electrode sheet resistance is reduced, and therefore the cycle performance and the rate performance of the battery are improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a silicon-containing negative electrode sheet, its preparation method, and a battery. Background Technology

[0002] Traditional graphite anodes, with a theoretical specific capacity of only 372 mAh / g, are no longer sufficient to support the performance upgrades of next-generation lithium-ion batteries. Silicon-based materials, with their ultra-high theoretical specific capacity of 4200 mAh / g, have become the most promising alternatives to graphite anodes. However, existing silicon anode systems still face key technological bottlenecks: silicon particles undergo volume expansion during charging and discharging; silicon's semiconductor properties result in poor electronic conductivity; the low surface polarity of lithium-silicon alloys leads to unstable physical contact; and repeated expansion and contraction cause continuous reorganization of the interface film, consuming lithium and electrolyte, leading to irreversible capacity decay, thus affecting the battery's cycle performance and rate performance.

[0003] In existing technologies, problems with silicon anode systems are addressed by improving anode binders, anode conductive agents, and silicon-carbon composite anode materials. For example, CN114068926A discloses a composite conductive agent slurry for silicon-carbon anode systems and its preparation method. By preparing a composite conductive agent slurry with specific components and applying it to silicon-carbon anodes, the anode conductive network is optimized, and the electrode electronic conduction efficiency is improved. However, this composite conductive agent slurry only optimizes electronic conduction performance and cannot effectively buffer the 170%-300% volume change of silicon particles during charging and discharging. Furthermore, it does not involve SEI film stability control, making it difficult to solve key defects such as electrode structure pulverization, interface failure, and continuous lithium source consumption during cycling.

[0004] For example, CN114614010A discloses a silicon-containing anode slurry for lithium-ion batteries, its preparation method, and its application. The silicon-containing anode slurry for lithium-ion batteries includes a silicon-containing anode material, a conductive agent, a binder, a modifying additive, and a dispersant. The modifying additive is nanocellulose modified with sodium alginate grafted with silane coupling agent. This silicon-containing anode slurry has insufficient buffering capacity against the volume expansion of silicon particles, and lacks a systematic solution in strengthening interfacial bonding, improving SEI film stability, and reducing irreversible capacity loss, thus having limited improvement on the cycle life and rate performance of the battery.

[0005] For example, CN119264841A discloses an adhesive for improving the first efficiency and cycle life of silicon anode cells and a battery using the adhesive. The adhesive is polymerized from acrylic acid, acrylic acid-like monomers and hydroxyethyl acrylate monomers. By improving the adhesive, the bonding strength of the adhesive is increased to adapt to the volume expansion of the silicon anode. However, this method lacks synergistic design in suppressing silicon volume expansion, improving conductivity and stabilizing the SEI film. A single modification strategy is difficult to meet the industrialization requirements of high capacity, long cycle life and low cost. In particular, the performance degradation is obvious under high rate charge and discharge conditions.

[0006] Based on the above research, the existing improvement methods cannot simultaneously and synergistically improve the multiple problems faced by the silicon anode system. There is a need to provide a silicon-containing anode sheet that can simultaneously solve the problems of silicon lithium intercalation expansion, poor electronic conductivity, and repeated SEI film recombination. Summary of the Invention

[0007] The purpose of this invention is to provide a silicon-containing negative electrode sheet, its preparation method, and a battery. The silicon-containing negative electrode sheet introduces modified carbon nanotube composite doped polyaniline as a composite conductive additive, which not only forms an elastic network in the silicon-containing negative electrode sheet, but also forms a continuous conductive framework, providing a buffer space for the lithium intercalation expansion of silicon, realizing rapid ion and electron transport, reducing the contact resistance between particles, improving the stability of the electrode interface, reducing the electrode resistance, thereby improving the battery cycle performance and rate performance.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a silicon-containing negative electrode sheet, the silicon-containing negative electrode sheet comprising a current collector and an active material layer on at least one side surface of the current collector, the active material layer comprising a silicon-containing negative electrode material, a composite conductive additive, a binder and a conductive agent;

[0010] The composite conductive additive includes modified carbon nanotubes and doped polyaniline, wherein the doped polyaniline comprises a porous carbon substrate and polyaniline.

[0011] This invention introduces a composite conductive additive into the active material layer of a silicon-containing anode electrode. The composite conductive additive includes modified carbon nanotubes and doped polyaniline. The modified carbon nanotubes and doped polyaniline are tightly bonded by intermolecular hydrogen bonds. The modified carbon nanotubes provide a fast electron transport channel, while the porous carbon substrate in the doped polyaniline has high conductivity and a rigid structure, which can act as a conductive framework to encapsulate silicon particles, preventing the conductive network from breaking after silicon pulverization. As a conjugated conductive polymer, polyaniline has reversible doping / dedoping characteristics, which can further expand the electron transport path and improve the overall conductivity of the electrode. This solves the core problem of poor conductivity of silicon itself. As a result, the composite conductive additive can not only form an elastic network in the silicon-containing anode electrode but also form a continuous conductive framework, providing a buffer space for the lithium intercalation expansion of silicon, enabling fast ion and electron transport, reducing the contact resistance between particles, improving the stability of the electrode interface, and reducing the electrode resistance, thereby improving the battery cycle performance and rate performance.

[0012] Preferably, in the composite conductive additive (based on a total mass of 100wt% of modified carbon nanotubes and doped polyaniline), the content of modified carbon nanotubes is 1wt% to 30wt%, for example, it can be 1wt%, 10wt%, 15wt%, 20wt%, 25wt% or 30wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 5wt% to 15wt%.

[0013] Preferably, in the composite conductive additive (based on a total mass of 100wt% of modified carbon nanotubes and doped polyaniline), the content of doped polyaniline is 70wt% to 99wt%, for example, it can be 70wt%, 75wt%, 80wt%, 85wt%, 90wt% or 99wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 85wt% to 95wt%.

[0014] In the composite conductive additive of the present invention, the modified carbon nanotubes and doped polyaniline are preferably within a specific content range. If the modified carbon nanotubes are relatively too few and the doped polyaniline is relatively too many, the modified carbon nanotubes cannot form a continuous conductive network well, resulting in a decrease in the conductivity of the composite conductive additive and a deterioration in the rate performance of the electrode. If the modified carbon nanotubes are relatively too many and the doped polyaniline is relatively too few, the carbon nanotubes in the composite conductive additive will become entangled and agglomerated, resulting in poor dispersion performance. They cannot be effectively dispersed and separated by the doped polyaniline, and the conductive network is uneven, which will reduce the conductivity of the composite conductive additive. Too little doped polyaniline will also make the adhesion of the composite conductive additive worse and reduce the stability of the three-dimensional conductive skeleton formed.

[0015] Preferably, in the doped polyaniline (based on a total mass of porous carbon and polyaniline of 100wt%), the content of porous carbon is 0.1wt% to 1wt%, for example, it can be 0.1wt%, 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt% or 1wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] Preferably, the content of polyaniline in the doped polyaniline (based on a total mass of porous carbon and polyaniline of 100wt%) is 99wt% to 99.9wt%, for example, it can be 99wt%, 99.1wt%, 99.3wt%, 99.5wt%, 99.7wt% or 99.9wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, the modified carbon nanotubes are carbon nanotubes modified with oxygen-containing functional groups.

[0018] Preferably, the oxygen-containing functional group includes a carboxyl group and / or a hydroxyl group.

[0019] The modified carbon nanotubes of this invention contain carboxyl and / or hydroxyl functional groups, which can form intermolecular hydrogen bonds with the N atoms on the polyaniline chain, thereby enabling the modified carbon nanotubes and doped polyaniline to be tightly bonded together.

[0020] Preferably, the active material layer further includes an auxiliary binder.

[0021] This invention further enhances the bonding strength of the active material layer and suppresses powder shedding by adding an auxiliary binder that works synergistically with the binder and composite conductive additive. In particular, when sodium alginate is selected as the auxiliary binder, its carboxyl groups can form strong hydrogen bonds / coordinate bonds with the hydroxyl groups on the silicon surface and the amino groups on the surface of the composite conductive additive. At the same time, it can interact with the oxygen-containing groups on the surface of the current collector (copper foil) to build a strong bonding interface between silicon particles, composite conductive additive and current collector, replacing the weak physical bonding of traditional binders and effectively suppressing the shedding of silicon particles during cycling.

[0022] Preferably, the content of the auxiliary binder in the active material layer is 0wt% to 1wt%, but not including 0wt%. For example, it can be 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, or 1wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the auxiliary binder comprises any one or a combination of at least two of the following: sodium carboxymethyl cellulose-styrene-butadiene rubber composite, styrene-butadiene rubber, polyacrylic acid, sodium alginate, or polyvinyl alcohol.

[0024] Preferably, the active material layer further includes a dispersant.

[0025] The active material layer of this invention also contains a dispersant to improve the dispersion uniformity of silicon-containing anode materials and composite conductive additives, and to prevent solid particles from agglomerating.

[0026] Preferably, the content of the dispersant in the active material layer is 0wt% to 0.5wt%, but not including 0wt%. For example, it can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, or 0.5wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the dispersant comprises any one or a combination of at least two of polyethylene glycol, polyethylene glycol monomethyl ether, polyvinylpyrrolidone, sodium polyacrylate, or sodium dodecylbenzenesulfonate.

[0028] Preferably, the content of silicon-containing anode material in the active material layer is 85wt%~90wt%, for example, it can be 85wt%, 86wt%, 87wt%, 88wt%, 89wt% or 90wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the silicon-containing anode material includes silicon-carbon material, wherein the silicon content is 10wt% to 40wt%, for example, it can be 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt% or 40wt%, and preferably the silicon-containing anode material is produced by carbon coating, CVD technology and nano-silicon technology.

[0030] Preferably, the content of the composite conductive additive in the active material layer is 4wt% to 8wt%, for example, it can be 4wt%, 5wt%, 6wt%, 7wt% or 8wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] The content of the composite conductive additive in the active material layer of the present invention will affect its function and thus affect the overall performance of the silicon-containing anode electrode. If the content of the composite conductive additive is too low, the improvement effect on the silicon-containing anode electrode will decrease. The core function of the composite conductive additive is to use the deformable space of its flexible conjugated polymer chain to form a uniform, thin and conductive elastic coating layer on the surface of the silicon-containing anode material particles, bridging the dispersed conductive agent, silicon-containing anode material, etc. together, filling the gaps between particles, eliminating contact resistance, and forming a through-type three-dimensional conductive network. Meanwhile, doped polyaniline contains a large number of polar groups such as -NH- and =N-, which can form hydrogen bonds, π-π conjugation, and electrostatic adsorption with hydroxyl / carboxyl groups on the surface of silicon carbon and carbon nanotubes. If too much composite conductive additive is added, the carbon nanotubes will first become entangled. Doped polyaniline itself contains polar polymer chains, and in excessive amounts, it will agglomerate, blocking the electron pathway. This will lead to an increase in the viscosity of the negative electrode slurry, a deterioration in the slurry processing performance, and uneven distribution of active materials on the electrode surface. In addition, the composite conductive additive has many active sites on its surface. When added in large quantities, it will consume a large amount of active lithium during cell formation, resulting in a decrease in the initial coulombic efficiency. Therefore, excessive content of composite conductive additive will have a negative impact on the rate performance, consistency, and cycle performance of silicon-containing negative electrode sheets.

[0032] Preferably, the content of the binder in the active material layer is 1wt% to 5wt%, for example, it can be 1wt%, 2wt%, 3wt%, 4wt% or 5wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the content of the conductive agent in the active material layer is 0wt% to 1wt%, but does not include 0wt%. For example, it can be 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, or 1wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the adhesive comprises any one or a combination of at least two of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium alginate, or polyvinyl alcohol.

[0035] In this invention, the adhesive and auxiliary adhesive are selected from different types of compounds.

[0036] Preferably, the conductive agent includes any one or a combination of at least two of Super-P Li, acetylene black, Ketjen black, carbon nanotubes, or graphene.

[0037] Preferably, the current collector comprises a copper foil, and the thickness of the current collector is 6μm to 9μm, for example, it can be 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm or 9μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the preparation method of the composite conductive additive includes the following steps:

[0039] (i) Mixing reducing sugar and aniline to obtain a mixture, and mixing the mixture with an acid solution to obtain an acidified mixture;

[0040] Concentrated sulfuric acid is first added to the acidified mixture to carry out a carbonization reaction, and then an initiator is added to carry out a polymerization reaction. After the polymerization reaction is completed, solid-liquid separation, washing and drying are carried out to obtain doped polyaniline.

[0041] (ii) The carbon nanotubes are mixed with an oxidant solution, and then solid-liquid separation and drying are performed to obtain modified carbon nanotubes;

[0042] (iii) The doped polyaniline described in step (i), the modified carbon nanotubes described in step (ii), and the additives are mixed and then heat-treated to obtain the composite conductive additive;

[0043] Steps (i) and (ii) are not in any particular order.

[0044] This invention employs a specific method to prepare doped polyaniline and modified carbon nanotubes. First, reducing sugar and aniline are mixed, dispersing the reducing sugar between aniline molecules. An acid solution is then added for acidification, activating the π-conjugated backbone of aniline and subsequently forming conductive polyaniline (the un-acidified intrinsic polyaniline is an insulator). Then, concentrated sulfuric acid is used to carbonize the reducing sugar, forming porous carbon. Aniline is then polymerized, achieving in-situ doping of porous carbon during polyaniline preparation, thus improving the structural stability and ion transport capacity of polyaniline. This invention also uses an oxidant to modify the carbon nanotubes, introducing oxygen-containing functional groups into the carbon nanotubes, enhancing their bonding strength with the doped polyaniline. Finally, heat treatment with an additive achieves a tight composite of the modified carbon nanotubes and the doped polyaniline, yielding the composite conductive additive.

[0045] Specifically, the role of in-situ generation of porous carbon in the preparation of polyaniline in this invention is as follows: Porous carbon provides growth sites for aniline, enabling aniline to polymerize inside and on the surface of the porous carbon, allowing it to grow thinly and uniformly in situ. It also reduces the entanglement of polyaniline molecular chains, preventing the formation of large, dense polyaniline aggregates. Simultaneously, the porous structure of the porous carbon provides stress release space, preventing the collapse of the conductive framework support structure and further limiting the volume expansion of silicon carbon. Furthermore, the continuous open-pore structure of the porous carbon is a natural ion transport channel, shortening the Li... + The diffusion distance improves wettability and rate performance.

[0046] Preferably, the reducing sugar in step (i) includes any one or a combination of at least two of glucose, fructose, galactose, lactose or maltose.

[0047] Preferably, the acid solution in step (i) includes a hydrochloric acid solution with a mass concentration of 5% to 10%, for example, it can be 5%, 6%, 7%, 8%, 9% or 10%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the amount of acid added in step (i) is 5wt% to 30wt% of the mass of the acidified mixture, for example, it can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt% or 30wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the temperature of the carbonization reaction in step (i) is 2°C to 8°C, for example, it can be 2°C, 3°C, 4°C, 5°C, 6°C, 7°C or 8°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, the amount of concentrated sulfuric acid added in step (i) is within 2 wt% of the mass of the acidified mixture, for example, it can be 0.5 wt%, 1 wt%, 1.5 wt% or 2 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] Preferably, the mass concentration of the concentrated sulfuric acid in step (i) is 80% to 98%, for example, it can be 80%, 84%, 88%, 92%, 96% or 98%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] Preferably, the initiator in step (i) comprises an ammonium persulfate solution with a mass concentration of 1% to 4%, for example, it may be 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or 4%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] The present invention uses ammonium persulfate solution for aniline polymerization, which acts as a strong oxidant to oxidize aniline into aniline cationic free radicals. The free radicals then couple to increase the chain length and form long polyaniline chains.

[0054] Preferably, the amount of initiator added in step (i) is 50wt% to 70wt% of the mass of the acidified mixture, for example, it can be 50wt%, 55wt%, 60wt%, 65wt% or 70wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 55wt% to 65wt%.

[0055] Preferably, the oxidant solution in step (ii) comprises a hydrogen peroxide solution with a mass concentration of 25% to 35%, for example, 25%, 27%, 29%, 31%, 33% or 35%, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0056] Preferably, the temperature at which the carbon nanotubes and the oxidant solution are mixed in step (ii) is 35°C to 55°C, for example, 35°C, 40°C, 45°C, 50°C or 55°C, and the time is 30 min to 120 min, for example, 30 min, 40 min, 60 min, 80 min, 100 min or 120 min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0057] Preferably, the carbon nanotubes in step (ii) account for 30wt% to 40wt% of the total mass of the carbon nanotubes and oxidant solution. For example, it can be 30wt%, 35wt% or 40wt%, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] Preferably, the adjuvant in step (iii) includes any one or a combination of at least two of organic acids, organic acid salts, or amide compounds; for example, it may be any one or a combination of at least two of sodium benzoate, sodium salicylate, p-aminobenzoic acid, urea, nicotinamide, or acetamide.

[0059] Preferably, the additive in step (iii) is 0.01wt% to 1wt% of the total mass of the doped polyaniline in step (i), the modified carbon nanotubes in step (ii), and the additive. For example, it can be 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, or 1wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0060] Preferably, the temperature of the heat treatment in step (iii) is 50℃~250℃, for example, 50℃, 100℃, 150℃, 200℃ or 250℃, and the time is 60min~240min, for example, 60min, 120min, 180min, 200min or 240min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] In a second aspect, the present invention provides a method for preparing a silicon-containing negative electrode sheet as described in the first aspect, the method comprising the following steps:

[0062] (1) The adhesive and deionized water are mixed for the first time to obtain the first adhesive solution;

[0063] (2) The composite conductive additive is mixed with the first adhesive solution in step (1) to obtain a second adhesive solution;

[0064] (3) The conductive agent is mixed with the second adhesive solution from step (2) to obtain a third adhesive solution;

[0065] (4) Mix the silicon-containing anode material, deionized water and the third adhesive solution described in step (3) in a fourth mixing process to obtain the anode slurry;

[0066] (5) The negative electrode slurry described in step (4) is coated on at least one side of the current collector and dried to obtain the silicon-containing negative electrode sheet.

[0067] Preferably, the amount of deionized water added in step (1) is 93.5wt% to 97.5wt% of the mass of the first adhesive solution. For example, it can be 93.5wt%, 94.5wt%, 95.5wt%, 96.5wt% or 97.5wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] Preferably, an auxiliary binder is added during the first mixing in step (1).

[0069] Preferably, step (2) is performed after the first adhesive solution has been left to stand for more than 12 hours in step (1). For example, it can be 12 hours, 14 hours, 16 hours, 18 hours or 20 hours, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] In this invention, the prepared first adhesive solution is allowed to stand for more than 12 hours to further dissolve the internal adhesive and auxiliary adhesive.

[0071] Preferably, the viscosity of the first adhesive in step (1) is 1000 mPa·s to 6000 mPa·s, for example, it can be 1000 mPa·s, 2000 mPa·s, 3000 mPa·s, 4000 mPa·s, 5000 mPa·s or 6000 mPa·s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] Preferably, before the composite conductive additive in step (2) is mixed with the first adhesive solution in step (1) for the second time, the composite conductive additive in step (2) is pretreated. The pretreatment includes mixing and dispersing the composite conductive additive with an organic solvent to obtain a composite conductive additive dispersion, and then mixing the composite conductive additive dispersion with the first adhesive solution in step (1) for the second time.

[0073] The present invention first pre-treats the composite conductive additive described in step (2), which can promote the formation of the three-dimensional elastic conductive network skeleton of the composite conductive additive.

[0074] Preferably, the power of the mixing and dispersion is 400W~1000W, for example, 400W, 500W, 600W, 700W, 800W, 900W or 1000W; the temperature is 20℃~30℃, for example, 20℃, 22℃, 24℃, 26℃, 28℃ or 30℃; and the time is 30min~60min, for example, 30min, 35min, 40min, 45min, 50min, 55min or 60min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0075] Preferably, the mass ratio of the composite conductive additive to the organic solvent is 1:(3-8), for example, it can be 1:3, 1:4, 1:5, 1:6, 1:7 or 1:8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0076] Preferably, a dispersant is also added during the third mixing in step (3).

[0077] Preferably, the rotation speeds of the first mixing in step (1), the second mixing in step (2), and the third mixing in step (3) are each independently 500 rpm to 1000 rpm, for example, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, or 1000 rpm, and the time is each independently 30 min to 60 min, for example, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0078] Preferably, the rotation speed of the fourth mixing in step (4) is 600 rpm to 1000 rpm, for example, 600 rpm, 700 rpm, 800 rpm, 900 rpm or 1000 rpm, and the time is 60 min to 90 min, for example, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min or 90 min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0079] Preferably, the silicon-containing anode material is placed in an oven before use and baked at a temperature of 100℃ to 150℃, for example, 100℃, 110℃, 120℃, 130℃, 140℃ or 150℃, with a vacuum degree of -90Kpa to -0.1MPa, for example, -90Kpa, -100Kpa, -0.05MPa or -0.1MPa, for 6h to 12h, for example, 6h, 8h, 9h, 10h or 12h, to prevent the powder from agglomerating.

[0080] Preferably, the viscosity of the negative electrode slurry in step (4) is 1000 mPa·s-6000 mPa·s, for example, it can be 1000 mPa·s, 2000 mPa·s, 3000 mPa·s, 4000 mPa·s, 5000 mPa·s or 6000 mPa·s, and the solid content is 30wt%-70wt%, for example, it can be 30wt%, 40wt%, 50wt%, 60wt% or 70wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0081] Preferably, the coating speed in step (5) is 600m / s to 800m / s, for example, it can be 600m / s, 650m / s, 700m / s, 750m / s or 800m / s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0082] Preferably, the drying in step (5) includes first drying at a temperature of 60℃-70℃, for example, 60℃, 62℃, 64℃, 66℃, 68℃ or 70℃, then drying at a temperature of 80℃-90℃, for example, 80℃, 82℃, 84℃, 86℃, 88℃ or 90℃, and finally drying at a temperature of 90℃-110℃, for example, 90℃, 95℃, 100℃, 105℃ or 110℃, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0083] Thirdly, the present invention provides a battery comprising a silicon-containing negative electrode sheet as described in the first aspect.

[0084] Compared with the prior art, the present invention has the following beneficial effects:

[0085] This invention introduces a composite conductive additive into the active material layer of a silicon-containing anode electrode. The composite conductive additive includes modified carbon nanotubes and doped polyaniline. The modified carbon nanotubes and doped polyaniline are tightly bonded by intermolecular hydrogen bonds. The modified carbon nanotubes provide a fast electron transport channel, while the porous carbon substrate in the doped polyaniline has high conductivity and a rigid structure, which can act as a conductive framework to encapsulate silicon particles, preventing the conductive network from breaking after silicon pulverization. As a conjugated conductive polymer, polyaniline has reversible doping / dedoping characteristics, which can further expand the electron transport path and improve the overall conductivity of the electrode. This solves the core problem of poor conductivity of silicon itself. As a result, the composite conductive additive can not only form an elastic network in the silicon-containing anode electrode but also form a continuous conductive framework, providing a buffer space for the lithium intercalation expansion of silicon, enabling fast ion and electron transport, reducing the contact resistance between particles, improving the stability of the electrode interface, and reducing the electrode resistance, thereby improving the battery cycle performance and rate performance. Attached Figure Description

[0086] Figure 1 This is a schematic diagram of the silicon-containing negative electrode sheet described in Embodiment 1 of the present invention;

[0087] Wherein, 1-current collector, 2-active material layer. Detailed Implementation

[0088] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0089] Example 1

[0090] This embodiment provides a silicon-containing negative electrode sheet (structural schematic diagram shown below). Figure 1 As shown, the silicon-containing negative electrode includes a current collector 1 and an active material layer 2. The silicon-containing negative electrode includes a current collector (specifically, a copper foil with a thickness of 7 μm) and an active material layer on one side of the current collector. The active material layer includes 90.5 wt% silicon-containing negative electrode material (specifically, silicon-carbon material with a silicon content of 10 wt%), 5 wt% composite conductive additive, 2 wt% binder (specifically sodium carboxymethyl cellulose), 1 wt% auxiliary binder (specifically sodium alginate), 0.5 wt% dispersant (specifically polyethylene glycol), and 1 wt% conductive agent (specifically conductive carbon black).

[0091] The composite conductive additive comprises 10 wt% modified carbon nanotubes and 90 wt% doped polyaniline. The modified carbon nanotubes are carboxyl and hydroxyl modified carbon nanotubes, and the doped polyaniline comprises 0.5 wt% porous carbon substrate and 99.5 wt% polyaniline.

[0092] The preparation method of the composite conductive additive includes the following steps:

[0093] (i) According to the formula, put the reducing sugar (specifically glucose) into a beaker, add aniline to it in several batches, stir it initially with a glass rod to form a mixture, add a small amount of 8% hydrochloric acid solution (the hydrochloric acid solution accounts for 15% of the total mass of the acidified mixture) to the mixture in several batches, and stir continuously to acidify the mixture to obtain an acidified mixture.

[0094] Transfer the beaker containing the acidified mixture to a constant temperature water bath and maintain the temperature at 5°C. After the temperature stabilizes, add 90% concentrated sulfuric acid (1 wt% of the mass of the acidified mixture) and stir continuously to completely carbonize the reducing sugars inside the mixture, forming porous carbon. After the reaction is complete, add 2% ammonium persulfate solution (60 wt% of the mass of the acidified mixture) to the beaker and stir continuously until the aniline polymerization reaction is complete. Once the polyaniline solution is obtained, filter the solution and rinse it repeatedly with ultrapure water. Transfer the filter paper and the filtered material to an oven for baking to obtain doped polyaniline.

[0095] (ii) Place single-walled carbon nanotube powder in a beaker, place the beaker in a water bath at 40°C, add a 30% hydrogen peroxide solution to form a suspension, stir continuously for 80 minutes, filter the suspension, and transfer it to an oven for drying to obtain modified carbon nanotubes; wherein, single-walled carbon nanotubes account for 35 wt% of the total mass of the suspension;

[0096] (iii) The prepared doped polyaniline and modified carbon nanotubes are weighed according to the formula and placed in a mortar. At the same time, an auxiliary agent (specifically sodium benzoate) is added and preliminarily mixed to obtain a mixture. The auxiliary agent accounts for 0.5 wt% of the total mass of the mixture. The mixture is transferred to a quartz crucible and heat-treated in a muffle furnace. The heat treatment temperature is controlled at 150°C and the time is controlled at 150 min. Finally, the heat-treated material is pulverized in an ultracentrifuge to obtain the composite conductive additive.

[0097] The method for preparing the silicon-containing negative electrode sheet includes the following steps:

[0098] Weigh 135.75g of silicon-carbon anode material (silicon content 10%) as silicon-containing anode material, weigh 7.5g of composite conductive additive, weigh 3g of sodium carboxymethyl cellulose as binder, weigh 1.5g of sodium alginate as auxiliary binder, weigh 0.75g of polyethylene glycol as dispersant, weigh 1.5g of conductive carbon black (SP) as conductive agent, weigh 203g of deionized water and weigh 23g of N-methylpyrrolidone for the following steps;

[0099] Among them, the silicon-containing anode material is placed in an oven and vacuum-baked at a baking temperature of 120℃ for 8 hours before use to prevent the powder from clumping.

[0100] (1) First, add the adhesive, auxiliary adhesive and some deionized water (the amount added is 95wt% of the mass of the first adhesive solution) into a beaker, and mix it for 45 minutes at 800 rpm using a disperser. Then let it stand for 12 hours to obtain the first adhesive solution.

[0101] (2) The composite conductive additive was mixed with N-methylpyrrolidone to achieve pretreatment, and then ultrasonically dispersed using an ultrasonic disperser at a power of 700W. During the dispersion process, the temperature was controlled at 25℃ and the ultrasonic time was controlled at 45min to obtain a composite conductive additive solution.

[0102] The first adhesive solution and the composite conductive additive solution from step (1) are transferred to a dispersion tank and mixed for 40 minutes at a speed of 750 rpm to obtain the second adhesive solution.

[0103] (3) Mix the second adhesive solution, conductive agent and dispersant at 650 rpm for 40 min to obtain the third adhesive solution;

[0104] (4) The silicon-containing anode material, another portion of deionized water, and the third adhesive solution from step (3) are mixed for a fourth time at 800 rpm for 80 min to obtain an anode slurry with a solid content of 40 wt%.

[0105] (5) The negative electrode slurry described in step (4) is coated on both sides of the current collector, and then baked using a stepped baking strategy, wherein the first stage baking temperature is 65°C, the second stage baking temperature is 85°C, and the third stage baking temperature is 100°C. The negative electrode roll that has been coated and baked is cut and baked a second time to obtain the silicon-containing negative electrode.

[0106] Example 2

[0107] This embodiment provides a silicon-containing negative electrode sheet, which includes a current collector (specifically a copper foil with a thickness of 9 μm) and active material layers on both sides of the current collector. The active material layers include 88.9 wt% silicon-containing negative electrode material (specifically a silicon-carbon material with a silicon content of 40 wt%), 8 wt% composite conductive additive, 1 wt% binder (specifically sodium carboxymethyl cellulose), 1 wt% auxiliary binder (specifically sodium alginate), 0.1 wt% dispersant (specifically polyethylene glycol), and 1 wt% conductive agent (specifically conductive carbon black).

[0108] The composite conductive additive comprises 5 wt% modified carbon nanotubes and 95 wt% doped polyaniline. The modified carbon nanotubes are carboxyl and hydroxyl modified carbon nanotubes, and the doped polyaniline comprises 0.1 wt% porous carbon substrate and 99.9 wt% polyaniline.

[0109] The preparation method of the composite conductive additive includes the following steps:

[0110] (i) According to the formula, put the reducing sugar (specifically glucose) into a beaker, add aniline to it in several batches, stir it initially with a glass rod to form a mixture, add a small amount of 10% hydrochloric acid solution (5% of the total mass of the acidified mixture) to the mixture in several batches, and stir continuously to acidify the mixture to obtain an acidified mixture.

[0111] The beaker containing the acidified mixture was transferred to a constant temperature water bath and the temperature was maintained at 8°C. After the temperature stabilized, 80% concentrated sulfuric acid (2 wt% of the mass of the acidified mixture) was added and stirred continuously to completely carbonize the reducing sugars inside the mixture and form porous carbon. After the reaction was completed, 4% ammonium persulfate solution (55 wt% of the mass of the acidified mixture) was added to the beaker and stirred continuously until the aniline polymerization reaction was completed. After obtaining the polyaniline solution, the solution was filtered and repeatedly rinsed with ultrapure water. The filter paper and the filtered material were then transferred to an oven for baking to obtain doped polyaniline.

[0112] (ii) Place single-walled carbon nanotube powder in a beaker, place the beaker in a water bath at 55°C, add a 25% hydrogen peroxide solution to form a suspension, stir continuously for 120 min, filter the suspension, and transfer it to an oven for drying to obtain modified carbon nanotubes; wherein, single-walled carbon nanotubes account for 30 wt% of the total mass of the suspension;

[0113] (iii) The prepared doped polyaniline and modified carbon nanotubes are weighed according to the formula and placed in a mortar. At the same time, an auxiliary agent (specifically sodium benzoate) is added and preliminarily mixed to obtain a mixture. The auxiliary agent accounts for 1 wt% of the total mass of the mixture. The mixture is transferred to a quartz crucible and heat-treated in a muffle furnace. The heat treatment temperature is controlled at 50°C and the time is controlled at 240 min. Finally, the heat-treated material is pulverized in an ultracentrifuge to obtain the composite conductive additive.

[0114] The method for preparing the silicon-containing negative electrode sheet includes the following steps:

[0115] Weigh 133.35g of silicon-carbon anode material as silicon-containing anode material, weigh 12.0g of composite conductive additive, weigh 1.5g of sodium carboxymethyl cellulose as binder, weigh 1.5g of sodium alginate as auxiliary binder, weigh 0.15g of polyethylene glycol as dispersant, weigh 1.5g of conductive carbon black (SP) as conductive agent, weigh 203g of deionized water and weigh 23g of N-methylpyrrolidone for the following steps;

[0116] Among them, the silicon-containing anode material is placed in an oven and vacuum-baked at a baking temperature of 150℃ for 6 hours before use to prevent the powder from clumping.

[0117] (1) First, add the adhesive, auxiliary adhesive and some deionized water (the amount added is 93.5 wt% of the mass of the first adhesive solution) into a beaker, and mix them for 30 min at 1000 rpm using a disperser. Then let it stand for 15 h to obtain the first adhesive solution.

[0118] (2) The composite conductive additive was mixed with N-methylpyrrolidone to achieve pretreatment, and then ultrasonically dispersed using an ultrasonic disperser at a power of 400W. During the dispersion process, the temperature was controlled at 30℃ and the ultrasonic time was controlled at 60min to obtain a composite conductive additive solution.

[0119] The first adhesive solution and the composite conductive additive solution from step (1) are transferred to a dispersion tank and mixed for 30 minutes at a speed of 1000 rpm to obtain the second adhesive solution.

[0120] (3) Mix the second adhesive solution, conductive agent and dispersant at 500 rpm for 60 min to obtain the third adhesive solution;

[0121] (4) The silicon-containing anode material, another portion of deionized water, and the third adhesive solution from step (3) are mixed for a fourth time at 1000 rpm for 60 min to obtain an anode slurry with a solid content of 40 wt%.

[0122] (5) The negative electrode slurry described in step (4) is coated on both sides of the current collector, and then baked using a stepped baking strategy. The baking temperature in the first stage is 70°C, the baking temperature in the second stage is 90°C, and the baking temperature in the third stage is 110°C. The negative electrode roll that has been coated and baked is cut and baked a second time to obtain the silicon-containing negative electrode.

[0123] Example 3

[0124] This embodiment provides a silicon-containing negative electrode sheet, which includes a current collector (specifically a copper foil with a thickness of 6 μm) and active material layers on both sides of the current collector. The active material layers include 90 wt% silicon-containing negative electrode material (specifically a silicon-carbon material with a silicon content of 25 wt%), 4 wt% composite conductive additive, 5 wt% binder (specifically sodium carboxymethyl cellulose), 0.1 wt% auxiliary binder (specifically sodium alginate), 0.5 wt% dispersant (specifically polyethylene glycol), and 0.4 wt% conductive agent (specifically conductive carbon black).

[0125] The composite conductive additive comprises 15 wt% modified carbon nanotubes and 85 wt% doped polyaniline. The modified carbon nanotubes are carboxyl and hydroxyl modified carbon nanotubes, and the doped polyaniline comprises 1 wt% porous carbon substrate and 99 wt% polyaniline.

[0126] The preparation method of the composite conductive additive includes the following steps:

[0127] (i) According to the formula, put the reducing sugar (specifically glucose) into a beaker, add aniline to it in several batches, stir it initially with a glass rod to form a mixture, add a small amount of 5% hydrochloric acid solution (the hydrochloric acid solution accounts for 30% of the total mass of the acidified mixture) to the mixture in several batches, and stir continuously to acidify the mixture to obtain an acidified mixture.

[0128] Transfer the beaker containing the acidified mixture to a constant temperature water bath and maintain the temperature at 2°C. After the temperature stabilizes, add 98% concentrated sulfuric acid (1 wt% of the mass of the acidified mixture) and stir continuously to completely carbonize the reducing sugars inside the mixture, forming porous carbon. After the reaction is complete, add 1% ammonium persulfate solution (65 wt% of the mass of the acidified mixture) to the beaker and stir continuously until the aniline polymerization reaction is complete. Once the polyaniline solution is obtained, filter the solution and rinse it repeatedly with ultrapure water. Transfer the filter paper and the filtered material to an oven for baking to obtain doped polyaniline.

[0129] (ii) Place single-walled carbon nanotube powder in a beaker, place the beaker in a water bath at 35°C, add a 35% hydrogen peroxide solution to form a suspension, stir continuously for 30 minutes, filter the suspension, and transfer it to an oven for drying to obtain modified carbon nanotubes; wherein, single-walled carbon nanotubes account for 40 wt% of the total mass of the suspension;

[0130] (iii) The prepared doped polyaniline and modified carbon nanotubes are weighed according to the formula and placed in a mortar. At the same time, an auxiliary agent (specifically sodium benzoate) is added and preliminarily mixed to obtain a mixture. The auxiliary agent accounts for 0.01 wt% of the total mass of the mixture. The mixture is transferred to a quartz crucible and heat-treated in a muffle furnace. The heat treatment temperature is controlled at 250°C and the time is controlled at 60 min. Finally, the heat-treated material is pulverized in an ultracentrifuge to obtain the composite conductive additive.

[0131] The method for preparing the silicon-containing negative electrode sheet includes the following steps:

[0132] Weigh 135g of silicon-carbon anode material as silicon-containing anode material, weigh 6g of composite conductive additive, weigh 7.5g of sodium carboxymethyl cellulose as binder, weigh 0.15g of sodium alginate as auxiliary binder, weigh 0.75g of polyethylene glycol as dispersant, weigh 0.6g of conductive carbon black (SP) as conductive agent, weigh 203g of deionized water and weigh 23g of N-methylpyrrolidone for the following steps;

[0133] Among them, the silicon-containing anode material is placed in an oven and vacuum-baked at a baking temperature of 100℃ for 12 hours before use to prevent the powder from clumping.

[0134] (1) First, add the adhesive, auxiliary adhesive and some deionized water (the amount added is 97.5 wt% of the mass of the first adhesive solution) into a beaker, and mix it for 60 min at 500 rpm using a disperser. Then let it stand for 12 h to obtain the first adhesive solution.

[0135] (2) The composite conductive additive was mixed with N-methylpyrrolidone to achieve pretreatment, and then ultrasonically dispersed using an ultrasonic disperser at a power of 1000W. During the dispersion process, the temperature was controlled at 20℃ and the ultrasonic time was controlled at 30min to obtain a composite conductive additive solution.

[0136] The first adhesive solution and the composite conductive additive solution from step (1) are transferred to a dispersion tank and mixed for 60 minutes at a speed of 500 rpm to obtain the second adhesive solution.

[0137] (3) Mix the second adhesive solution, conductive agent and dispersant at 1000 rpm for 30 min to obtain the third adhesive solution;

[0138] (4) The silicon-containing anode material, another portion of deionized water, and the third adhesive solution from step (3) are mixed for 90 minutes at 600 rpm to obtain an anode slurry with a solid content of 40 wt%.

[0139] (5) The negative electrode slurry described in step (4) is coated on both sides of the current collector, and then baked using a stepped baking strategy, wherein the first stage baking temperature is 60°C, the second stage baking temperature is 80°C, and the third stage baking temperature is 90°C. The coated and baked negative electrode roll is then cut and baked a second time to obtain the silicon-containing negative electrode.

[0140] Example 4

[0141] This embodiment provides a silicon-containing negative electrode sheet. Except for step (2) of its preparation method, in which the composite conductive additive solution is not pretreated and is prepared, but the composite conductive additive is prepared together with the binder, auxiliary binder and part of deionized water to prepare the first adhesive solution, the rest is the same as in Example 1.

[0142] Example 5

[0143] This embodiment provides a silicon-containing negative electrode sheet. Except for step (2) of its preparation method, in which the composite conductive additive solution is not pretreated and is prepared, but the composite conductive additive is mixed with the first adhesive solution in a second step, the silicon-containing negative electrode sheet is the same as that in Example 1.

[0144] Example 6

[0145] This embodiment provides a silicon-containing negative electrode sheet, which is the same as in Example 1 except that sodium alginate and other materials are replaced with polyacrylic acid.

[0146] The preparation method of the silicon-containing negative electrode sheet is the same as in Example 1, except that sodium alginate and other materials are replaced with polyacrylic acid to adapt to the change.

[0147] Example 7

[0148] This embodiment provides a silicon-containing negative electrode sheet. Except for the active material layer, in which the content of composite conductive additive is 2wt%, the content of binder is 4wt%, and the content of conductive agent is 2wt%, the silicon-containing negative electrode sheet is the same as that in Embodiment 1.

[0149] Except for the adaptive changes in the amount of raw materials added, the preparation method of the silicon-containing negative electrode sheet is the same as in Example 1.

[0150] Example 8

[0151] This embodiment provides a silicon-containing negative electrode sheet. Except for the active material layer, which contains 10 wt% composite conductive additive, 86 wt% silicon-containing negative electrode material, and 1.5 wt% binder, the silicon-containing negative electrode sheet is the same as that in Embodiment 1.

[0152] Except for the adaptive changes in the amount of raw materials added, the preparation method of the silicon-containing negative electrode sheet is the same as in Example 1.

[0153] Comparative Example 1

[0154] This comparative example provides a silicon-containing negative electrode sheet, which includes a current collector (specifically a copper foil with a thickness of 7 μm) and an active material layer on both sides of the current collector. The active material layer includes 90.3 wt% silicon-containing negative electrode material (specifically a silicon-carbon material with a silicon content of 10 wt%), 2 wt% sodium carboxymethyl cellulose, 4 wt% polyacrylic acid, 2 wt% conductive carbon black and 1.70 wt% carbon nanotubes.

[0155] The preparation method of the silicon-containing negative electrode sheet is the same as that in Example 1, except that the preparation process of the negative electrode slurry is different.

[0156] The preparation process of the negative electrode slurry in this comparative example includes the following steps:

[0157] According to the formula, sodium carboxymethyl cellulose, polyacrylic acid and deionized water are first mixed at 800 rpm for 45 min. Then, conductive carbon black and carbon nanotubes are added and mixed at 750 rpm for 40 min. Finally, silicon-containing anode material is added and mixed at 800 rpm for 50 min to obtain the anode slurry.

[0158] Comparative Example 2

[0159] This comparative example provides a silicon-containing negative electrode sheet, which includes a current collector (specifically a copper foil with a thickness of 7 μm) and an active material layer on both sides of the current collector. The active material layer includes 92.68 wt% silicon-containing negative electrode material (specifically a silicon-carbon material with a silicon content of 10 wt%), 0.98 wt% sodium carboxymethyl cellulose, 3.9 wt% sodium alginate, 0.98 wt% gelatin, and 1.46 wt% acetylene black.

[0160] The preparation method of the silicon-containing negative electrode sheet is the same as that in Example 1, except that the preparation process of the negative electrode slurry is different.

[0161] The preparation process of the negative electrode slurry in this comparative example includes the following steps:

[0162] According to the formula, sodium carboxymethyl cellulose, sodium alginate, gelatin and deionized water are first mixed at 800 rpm for 45 minutes. Then, acetylene black is added and mixed at 750 rpm for 40 minutes. Finally, silicon-containing anode material is added and mixed at 800 rpm for 50 minutes to obtain the anode slurry.

[0163] Comparative Example 3

[0164] This comparative example provides a silicon-containing negative electrode sheet, which includes a current collector (specifically a copper foil with a thickness of 7 μm) and an active material layer on both sides of the current collector. The active material layer includes 89.78 wt% silicon-containing negative electrode material (specifically a silicon-carbon material with a silicon content of 10 wt%), 3.12 wt% styrene-butadiene rubber, 4.73 wt% sodium alginate, 0.95 wt% gelatin, and 1.42 wt% acetylene black.

[0165] The preparation method of the silicon-containing negative electrode sheet is the same as that in Example 1, except that the preparation process of the negative electrode slurry is different.

[0166] The preparation process of the negative electrode slurry in this comparative example includes the following steps:

[0167] According to the formula, styrene-butadiene rubber, sodium alginate, gelatin and deionized water are first mixed at 800 rpm for 45 minutes. Then, acetylene black is added and mixed at 750 rpm for 40 minutes. Finally, silicon-containing anode material is added and mixed at 800 rpm for 50 minutes to obtain the anode slurry.

[0168] Comparative Example 4

[0169] This comparative example provides a silicon-containing negative electrode sheet. Except for the fact that the carbon nanotubes in the composite conductive additive are not modified, the doped polyaniline does not contain a porous carbon substrate, and the composite conductive additive preparation process is adapted to change, the silicon-containing negative electrode sheet is the same as that in Example 1.

[0170] Comparative Example 5

[0171] This comparative example provides a silicon-containing negative electrode sheet. Except for the fact that the composite conductive additive does not contain modified carbon nanotubes but only doped polyaniline, and the preparation process of the composite conductive additive is adapted to change, the silicon-containing negative electrode sheet is the same as that in Example 1.

[0172] Comparative Example 6

[0173] This comparative example provides a silicon-containing negative electrode sheet, which is the same as in Example 1 except that the composite conductive additive does not contain doped polyaniline, but is only modified carbon nanotubes, and the preparation process of the composite conductive additive is adapted to change.

[0174] The silicon-containing negative electrode, positive electrode, and separator obtained in the above embodiments and comparative examples are used to prepare lithium-ion batteries. In this process, lithium cobalt oxide, conductive carbon black, carbon nanotubes, and polyvinylidene fluoride are used to prepare a positive electrode slurry, which is coated on aluminum foil. After baking, slitting, and rolling, a positive electrode is obtained. The prepared positive and negative electrode sheets are then welded with tabs. The positive and negative electrode sheets with the tabs are then folded together with the separator to obtain a bare cell. An aluminum-plastic film is used as the outer shell to encapsulate the bare cell. After liquid injection, formation, capacity testing, and sealing, a lithium-ion battery is obtained.

[0175] The electrochemical performance of lithium-ion batteries is tested using the following methods:

[0176] Resistance test of silicon-containing negative electrode sheet: The test was conducted using the Yuaneng Technology BER2300 instrument. The silicon-containing negative electrode sheet was cut into a 5cm×10cm rectangle after it was manufactured, and placed on the test fixture. The test parameters were selected as follows: pressure 10MPa, pressure holding test for 10 seconds, sampling points 6-10 per sheet, and average value calculated.

[0177] Lithium-ion battery capacity testing: The Wuhan Landian CT3002A model was used for charging and discharging tests with a range of 5V 6A. The test format was 3-4.55V, 0.1C charge / discharge, cutoff current of 0.025C, and ambient temperature of 25℃ ± 0.5℃. The 0.1C discharge specific capacity was recorded.

[0178] Cycle retention rate test: The Wuhan Landian CT3002A model, with a charge / discharge range of 5V 6A, was used for testing. The test format was: 3-4.55V, 1C charge / discharge, cutoff current of 0.025C, and ambient temperature of 45℃±0.5℃. The cycle retention rate was recorded after 100 cycles.

[0179] Rate performance testing: A Wuhan Landian CT2001B charge / discharge tester with a range of 5V 20A was used for testing. The test format was 3-4.55V, with a cutoff current of 0.025C. The test rates were 1C, 2C, 3C, and 5C, and the ambient temperature was 25℃ ± 0.5℃. The ratio of the discharge specific capacity at 5C to the discharge specific capacity at 1C was recorded.

[0180] The test results are shown in Table 1 below:

[0181] Table 1

[0182]

[0183] As can be seen from Table 1 above:

[0184] As shown in Example 1 and Comparative Examples 1-3, the composite conductive additive, auxiliary binder, and dispersant in this invention work synergistically to construct a strong bonding interface. Compared to the weak physical bonding of traditional binders, this effectively inhibits the shedding of silicon particles during cycling, improves ion and electron transport, and reduces electrode resistance, thereby effectively improving the cycle performance and rate performance of the battery. As shown in Example 1 and Comparative Examples 4-6, this invention modifies carbon nanotubes and uses doped polyaniline, i.e., uses doped polyaniline composited with modified carbon nanotubes as a composite conductive additive, which can further enhance the stability and conductivity of the silicon-containing negative electrode, thereby further improving the stability of the electrode interface. The present invention improves the battery's cycle performance and rate performance by reducing electrode resistance. As shown in Examples 1 and 4-5, the present invention preferably pre-treats the composite conductive additive before use, which is beneficial for forming an elastic conductive network skeleton, thereby further promoting its performance. As shown in Examples 1 and 6, the present invention preferably uses sodium alginate as an auxiliary binder, which can play a synergistic role when used in combination with the composite conductive additive, which is beneficial for further improving the battery's performance. As shown in Examples 1 and 7-8, the present invention preferably uses the amount of composite conductive additive within a preferred range, which can further improve the overall electrochemical performance of the battery while ensuring its function.

[0185] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A silicon-containing negative electrode sheet, characterized in that, The silicon-containing negative electrode sheet includes a current collector and an active material layer on at least one side surface of the current collector, wherein the active material layer includes a silicon-containing negative electrode material, a composite conductive additive, a binder, and a conductive agent. The composite conductive additive includes modified carbon nanotubes and doped polyaniline, wherein the doped polyaniline comprises a porous carbon substrate and polyaniline.

2. The silicon-containing negative electrode sheet according to claim 1, characterized in that, The modified carbon nanotubes in the composite conductive additive are 1wt% to 30wt%, preferably 5wt% to 15wt%. Preferably, the content of doped polyaniline in the composite conductive additive is 70wt%~99wt%, more preferably 85wt%~95wt%. Preferably, the porous carbon content in the doped polyaniline is 0.1 wt% to 1 wt%. Preferably, the content of polyaniline in the doped polyaniline is 99 wt% to 99.9 wt%. Preferably, the modified carbon nanotubes are carbon nanotubes modified with oxygen-containing functional groups; Preferably, the oxygen-containing functional group includes a carboxyl group and / or a hydroxyl group.

3. The silicon-containing negative electrode sheet according to claim 1 or 2, characterized in that, The active material layer also includes an auxiliary binder; Preferably, the content of the auxiliary binder in the active material layer is 0wt%~1wt%, but does not include 0wt%; Preferably, the auxiliary binder comprises any one or a combination of at least two of the following: sodium carboxymethyl cellulose-styrene-butadiene rubber composite, styrene-butadiene rubber, polyacrylic acid, sodium alginate, or polyvinyl alcohol; Preferably, the active material layer further includes a dispersant; Preferably, the content of the dispersant in the active material layer is 0 wt% to 0.5 wt%, but excluding 0 wt%; Preferably, the dispersant comprises any one or a combination of at least two of polyethylene glycol, polyethylene glycol monomethyl ether, polyvinylpyrrolidone, sodium polyacrylate, or sodium dodecylbenzenesulfonate.

4. The silicon-containing negative electrode sheet according to claim 1 or 2, characterized in that, The active material layer contains 85wt%~90wt% silicon anode material. Preferably, the silicon-containing anode material includes silicon-carbon material; Preferably, the content of the composite conductive additive in the active material layer is 4wt%~8wt%; Preferably, the binder content in the active material layer is 1wt%~5wt%; Preferably, the conductive agent content in the active material layer is 0 wt% to 1 wt%, but excluding 0 wt%; Preferably, the adhesive comprises any one or a combination of at least two of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium alginate, or polyvinyl alcohol; Preferably, the conductive agent includes any one or a combination of at least two of Super-P Li, acetylene black, Ketjen black, carbon nanotubes, or graphene.

5. The silicon-containing negative electrode sheet according to claim 1 or 2, characterized in that, The preparation method of the composite conductive additive includes the following steps: (i) Mixing reducing sugar and aniline to obtain a mixture, and mixing the mixture with an acid solution to obtain an acidified mixture; Concentrated sulfuric acid is first added to the acidified mixture to carry out a carbonization reaction, and then an initiator is added to carry out a polymerization reaction. After the polymerization reaction is completed, solid-liquid separation, washing and drying are carried out to obtain doped polyaniline. (ii) The carbon nanotubes are mixed with an oxidant solution, and then solid-liquid separation and drying are performed to obtain modified carbon nanotubes; (iii) The doped polyaniline described in step (i), the modified carbon nanotubes described in step (ii), and the additives are mixed and then heat-treated to obtain the composite conductive additive; Steps (i) and (ii) are not in any particular order.

6. The silicon-containing negative electrode sheet according to claim 5, characterized in that, The reducing sugar in step (i) includes any one or a combination of at least two of glucose, fructose, galactose, lactose or maltose; Preferably, the acid solution in step (i) comprises a hydrochloric acid solution with a mass concentration of 5% to 10%; Preferably, the amount of acid added in step (i) is 5wt% to 30wt% of the mass of the acidified mixture; Preferably, the carbonization reaction in step (i) is carried out at a temperature of 2°C to 8°C; Preferably, the amount of concentrated sulfuric acid added in step (i) is within 2 wt% of the mass of the acidified mixture; Preferably, the initiator in step (i) comprises an ammonium persulfate solution with a mass concentration of 1% to 4%; Preferably, the amount of initiator added in step (i) is 50wt% to 70wt% of the mass of the acidified mixture, and more preferably 55wt% to 65wt%. Preferably, the oxidant solution in step (ii) comprises a hydrogen peroxide solution with a mass concentration of 25% to 35%; Preferably, in step (ii), the temperature for mixing the carbon nanotubes with the oxidant solution is 35°C to 55°C, and the time is 30 min to 120 min. Preferably, the carbon nanotubes in step (ii) account for 30wt%~40wt% of the total mass of the carbon nanotubes and the oxidant solution; Preferably, the adjuvant in step (iii) comprises any one or a combination of at least two of organic acids, organic acid salts, or amide compounds; Preferably, the additive in step (iii) is 0.01 wt% to 1 wt% of the total mass of the doped polyaniline in step (i), the modified carbon nanotubes in step (ii), and the additive; Preferably, the heat treatment in step (iii) is performed at a temperature of 50°C to 250°C for a time of 60 min to 240 min.

7. A method for preparing a silicon-containing negative electrode sheet as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: (1) The adhesive and deionized water are mixed for the first time to obtain the first adhesive solution; (2) The composite conductive additive is mixed with the first adhesive solution in step (1) to obtain a second adhesive solution; (3) The conductive agent is mixed with the second adhesive solution from step (2) to obtain a third adhesive solution; (4) Mix the silicon-containing anode material, deionized water and the third adhesive solution described in step (3) in a fourth mixing process to obtain the anode slurry; (5) The negative electrode slurry described in step (4) is coated on at least one side of the current collector and dried to obtain the silicon-containing negative electrode sheet.

8. The preparation method according to claim 7, characterized in that, The amount of deionized water added in step (1) is 93.5 wt% to 97.5 wt% of the mass of the first adhesive solution; Preferably, an auxiliary binder is also added during the first mixing in step (1); Preferably, step (2) is performed after the first adhesive solution has been left to stand for more than 12 hours in step (1).

9. The preparation method according to claim 7, characterized in that, Before the composite conductive additive in step (2) is mixed with the first adhesive solution in step (1) for the second time, the composite conductive additive in step (2) is pretreated. The pretreatment includes mixing and dispersing the composite conductive additive with an organic solvent to obtain a composite conductive additive dispersion, and then mixing the composite conductive additive dispersion with the first adhesive solution in step (1) for the second time. Preferably, a dispersant is also added during the third mixing in step (3); Preferably, the rotation speeds of the first mixing in step (1), the second mixing in step (2), and the third mixing in step (3) are each independently 500 rpm to 1000 rpm, and the time is each independently 30 min to 60 min; Preferably, the rotation speed of the fourth mixing in step (4) is 600 rpm to 1000 rpm, and the time is 60 min to 90 min; Preferably, the solid content of the negative electrode slurry in step (4) is 30wt%-70wt%.

10. A battery, characterized in that, The battery includes a silicon-containing negative electrode as described in any one of claims 1-6.

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