Silicon-based negative electrode, binder of silicon-based negative electrode, silicon-based negative electrode material layer, preparation method of silicon-based negative electrode material layer and silicon-based battery

Abstract

The invention provides a silicon-based negative electrode, a binder of the silicon-based negative electrode, a silicon-based negative electrode material layer, a preparation method of the silicon-based negative electrode material layer and a silicon-based battery. The binder comprises polysiloxane imide and polydopamine. The bonding agent is prepared from polysiloxane imide and polydopamine; a rigid PI block in polysiloxane imide can provide high modulus to bear mechanical stress generated by a silicon-based negative electrode material, and a flexible Si-O-Si block is beneficial to reducing the mechanical stress and restoring deformation during lithiation and lithium removal; the polydopamine improves the adhesive property of the adhesive; the polysiloxane imide and the polydopamine are combined to form carboxyl-amino hydrogen bonds to form a dynamic network, so that instant binding power can be provided, volume expansion and shrinkage of the silicon-based negative electrode material are effectively inhibited, and the pulverization and falling risks of the silicon-based negative electrode material in the circulation process are effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a binder for a silicon-based negative electrode, in particular to a silicon-based negative electrode and its binder, a silicon-based negative electrode material layer and its preparation method, and a silicon-based battery. Background Art

[0002] With increasingly fierce competition in the power battery market, the energy density requirements for lithium-ion batteries continue to increase. Traditional graphite anode materials are no longer able to meet this demand. Silicon-based anode materials, with their ultra-high theoretical capacity of 4200 mA·h / g, have become a promising alternative to traditional graphite anodes. However, silicon as an anode material suffers from severe volume expansion during lithium insertion. Traditional binders are unable to adapt to the mechanical stress generated by this huge volume change, resulting in pulverization and shedding of the active material during cycling, leading to a rapid decrease in battery cycle life. Currently, silicon-based anode materials are being studied to improve battery performance by modifying the electrode binder and improving the stability of the electrode structure.

[0003] A common binder for silicon-based anodes is a combination of polyacrylic acid (PAA) and carboxymethyl cellulose (CMC). The carboxyl groups in PAA undergo dehydration condensation with the hydroxyl groups in CMC to form ester bonds, creating a cross-linked polyacrylic acid-carboxymethyl cellulose (c-PAA-CMC) binder. However, the c-PAA-CMC binder has a weak interaction with silicon-based materials, and its ability to inhibit the expansion of silicon-based anode materials remains limited.

[0004] CN117174826A discloses a negative electrode sheet and a lithium-ion battery including the negative electrode sheet. The negative electrode sheet comprises a functional current collector and a negative electrode material layer disposed on the functional current collector; the negative electrode material layer comprises a negative electrode main material and a composite adhesive; the functional current collector has a porous structure or a rough surface; the composite adhesive is a mixture of a first adhesive and a second adhesive; and the first adhesive is polydopamine. However, the adhesive in the negative electrode sheet has a limited effect on suppressing the expansion of the silicon-based negative electrode material and cannot meet the requirements of practical applications.

[0005] CN119662202A discloses a silicon-based negative electrode binder for lithium-ion batteries, a preparation method thereof, and a silicon-based negative electrode for lithium-ion batteries. The binder preparation method comprises: first preparing a PAA aqueous solution by mixing polyacrylic acid and deionized water; then physically mixing the PAA aqueous solution with a functional monomer at high temperature to obtain a polymer A; and finally cross-linking and polymerizing the obtained polymer A with a functional polymer to obtain a polymer B, which is the silicon-based negative electrode binder for lithium-ion batteries. Similarly, this silicon-based negative electrode binder for lithium-ion batteries still fails to effectively inhibit the expansion of silicon-based negative electrode materials.

[0006] The binders for silicon-based negative electrodes disclosed in the prior art all have certain defects. They cannot effectively inhibit the volume expansion of silicon-based negative electrode materials, causing pulverization and shedding of silicon-based negative electrode materials during the cycle, thereby resulting in the cycle performance of silicon-based batteries being unable to meet the requirements of practical applications. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the object of the present invention is to provide a silicon-based negative electrode and its binder, a silicon-based negative electrode material layer and its preparation method, and a silicon-based battery, wherein the binder includes polysiloxane imide and polydopamine; the rigid PI block in the polysiloxane imide can provide a high modulus to withstand the mechanical stress generated by the silicon-based negative electrode material, and the flexible Si-O-Si block helps to reduce the mechanical stress and recover the deformation during lithiation and delithiation; polydopamine improves the bonding performance of the binder; the combination of polysiloxane imide and polydopamine forms a dynamic network of carboxyl-amino hydrogen bonds, which can provide immediate bonding force and effectively inhibit the volume expansion and contraction of the silicon-based negative electrode material, thereby effectively reducing the risk of pulverization and shedding of the silicon-based negative electrode material during the cycle.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a binder for a silicon-based negative electrode, wherein the binder comprises polysiloxane imide and polydopamine.

[0010] The binder provided by the present invention includes polysiloxane imide, which is obtained by introducing a flexible siloxane-containing chain segment into a polyimide main chain. Therefore, the polysiloxane imide contains both a rigid polyimide (PI) block and a flexible siloxane (Si-O-Si) block. On the one hand, the rigid PI block in the polysiloxane imide can provide a high modulus to withstand the mechanical stress generated by the silicon-based negative electrode material. On the other hand, the flexible Si-O-Si block in the polysiloxane imide helps to reduce the mechanical stress through reversible shape deformation and recover the deformation during lithiation and delithiation, thereby better coping with the volume expansion of the silicon-based negative electrode material. On the other hand, the Si-O-Si block in the polysiloxane imide can also effectively enhance the compatibility of the polysiloxane imide with the electrolyte.

[0011] The binder provided by the present invention also includes polydopamine (PDA). Since PDA is rich in hydroxyl groups, PDA can form hydrogen bonds with oxygen atoms on the surface of the solid substrate, so that the binder containing PDA has good adhesion properties, thereby further improving the adhesion properties of the binder, thereby further reducing the risk of pulverization and shedding of silicon-based negative electrode materials during the cycle.

[0012] The binder provided by the present invention contains both polysiloxane imide and polydopamine. The combination of polysiloxane imide and polydopamine forms a dynamic network of carboxyl-amino hydrogen bonds, which can provide immediate bonding force and effectively inhibit the volume expansion and contraction of silicon-based negative electrode materials, thereby effectively reducing the risk of pulverization and shedding of silicon-based negative electrode materials during the cycle.

[0013] Preferably, the mass ratio of polysiloxane imide to polydopamine in the binder is (3-5):(15-25), typical but non-limiting combinations include 3:15, 3:20, 3:25, 4:15, 4:20, 4:25, 5:15, 5:20 or 5:25, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] In this application, by limiting the mass ratio of polysiloxane imide to polydopamine in the binder to (3-5): (15-25), it is ensured that the polysiloxane imide can provide sufficient rigid skeleton support and form moderate cross-linking with the amino / hydroxyl groups of polydopamine to relieve the volume expansion stress of silicon; it is also ensured that polydopamine can enhance adhesion and effectively inhibit the shedding of active substances.

[0015] Preferably, the adhesive further includes polyacrylic acid.

[0016] The binder provided by the present invention includes both polydopamine and polyacrylic acid. The esterification between the elastic polymer layer of polydopamine and polyacrylic acid forms a three-dimensional cross-linked structure, thereby further enhancing the stability of the negative electrode material layer containing the binder and improving the cycle stability of the silicon-based battery.

[0017] Preferably, based on the mass of the binder as 100%, the mass fraction of polysiloxane imide in the binder is 15-25wt%, the mass fraction of polydopamine is 30-50wt%, and the mass fraction of polyacrylic acid is 30-50wt%.

[0018] In the present invention, the mass fraction of the polysiloxane imide in the binder is 15 to 25 wt%, based on the mass of the binder as 100%, for example, it can be 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt% or 25 wt%, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0019] In the present invention, the mass fraction of the binder is 30 to 50 wt%, and the mass fraction of polydopamine in the binder is 30 to 50 wt%, for example, it can be 30 wt%, 32 wt%, 34 wt%, 36 wt%, 38 wt%, 40 wt%, 42 wt%, 44 wt%, 46 wt%, 48 wt% or 50 wt%, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] In the present invention, the mass fraction of the polyacrylic acid in the binder is 30 to 50 wt%, based on the mass of the binder as 100%, for example, it can be 30 wt%, 32 wt%, 34 wt%, 36 wt%, 38 wt%, 40 wt%, 42 wt%, 44 wt%, 46 wt%, 48 wt% or 50 wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] In the present invention, by limiting the mass fractions of polysiloxane imide, polydopamine and polyacrylic acid in the binder, it is ensured that the rigid skeleton of polysiloxane imide can fully combine with the dynamic hydrogen bond network of polydopamine, thereby inhibiting the volume expansion of silicon and repairing cracks, and it is also ensured that the carboxyl groups of polyacrylic acid can be fully esterified and cross-linked, thereby enhancing the deformation resistance of the binder and thus enhancing the structural stability of the negative electrode material layer.

[0022] In a second aspect, the present invention provides a silicon-based negative electrode material layer, wherein the silicon-based negative electrode material layer comprises a silicon negative electrode active material and the binder described in the first aspect.

[0023] The silicon negative electrode active material described in the present invention includes any one or a combination of at least two of nano-silicon particles, silicon oxide, silicon-carbon composite materials or silicon alloys. Typical but non-limiting combinations include a combination of nano-silicon particles and silicon oxide, a combination of silicon-carbon composite materials and silicon alloys, a combination of silicon oxide and silicon-carbon composite materials, or a combination of nano-silicon particles, silicon oxide and silicon-carbon composite materials, but is not limited to the listed materials. All materials used as silicon negative electrode active materials in the prior art can be applied in the present invention.

[0024] Preferably, the mass ratio of the silicon negative electrode active material to the binder in the silicon-based negative electrode material layer is (2 to 5):1, for example, it can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0025] The mass ratio of the silicon negative electrode active material to the binder in the silicon-based negative electrode material layer of the present invention is (2 to 5):1, which not only ensures that there is sufficient binder in the silicon-based negative electrode material layer, thereby effectively alleviating the volume expansion of the negative electrode material layer and inhibiting the pulverization and shedding of the silicon-based negative electrode material, thereby significantly improving the cycle stability, but also ensures that the silicon-based negative electrode material layer has sufficient silicon loading.

[0026] Preferably, the silicon-based negative electrode material layer also includes a conductive agent, and the mass ratio of the silicon negative electrode active material to the conductive agent in the silicon-based negative electrode material layer is (5 to 10):1, for example, it can be 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0027] Preferably, the conductive agent includes any one or a combination of at least two of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene or carbon fibers. Typical but non-limiting combinations include a combination of conductive carbon black and acetylene black, a combination of Ketjen black and carbon nanotubes, a combination of graphene and carbon fibers, or a combination of conductive carbon black, carbon nanotubes and graphene.

[0028] In a third aspect, the present invention provides a method for preparing the silicon-based negative electrode material layer according to the second aspect, the preparation method comprising:

[0029] The silicon negative electrode active material, the binder and the solvent are mixed and dried to obtain a silicon-based negative electrode material layer.

[0030] Preferably, the mixing also includes mixing in a conductive agent.

[0031] Preferably, the mixing comprises:

[0032] First, silicon negative electrode active material, conductive agent, polydopamine and polyacrylic acid are mixed to obtain a mixture; second, the obtained mixture is mixed with a solvent to obtain a mixed slurry; third, the obtained slurry is mixed with a polysiloxane imide solution to obtain a silicon-based negative electrode slurry.

[0033] Preferably, the first mixing method includes grinding.

[0034] Preferably, the second mixing method includes stirring for 5 to 20 hours, for example, it can be 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours or 20 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the solvent comprises any one or a combination of at least two of N-methylpyrrolidone, water, tetrahydrofuran, dimethylformamide or cyclohexanone. Typical but non-limiting combinations include a combination of N-methylpyrrolidone and water, a combination of tetrahydrofuran and dimethylformamide, a combination of water and cyclohexanone, or a combination of N-methylpyrrolidone, tetrahydrofuran and dimethylformamide.

[0036] Preferably, the solid-liquid ratio of the mixture obtained in the second mixing to the solvent is 1:(1.5-2.5), for example, it can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4 or 1:2.5, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable. The unit of solid-liquid ratio is g / mL.

[0037] Preferably, the third mixing method includes stirring for 1 to 10 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours or 10 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] Preferably, the mass fraction of polysiloxane imide in the polysiloxane imide solution in the third mixture is 5 to 20 wt%, for example, it can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt% or 20 wt%, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0039] Preferably, the method for preparing the polysiloxane imide solution is:

[0040] The amino-terminated dimethylsiloxane and pyromellitic dianhydride are subjected to a condensation reaction in a reaction solvent to obtain a polysiloxane imide solution.

[0041] The method for preparing the polysiloxane imide solution provided by the present invention has simple steps and only requires one step of copolymerization, thus simplifying the process.

[0042] Preferably, the reaction solvent comprises tetrahydrofuran and N-methylpyrrolidone, and the mass ratio of tetrahydrofuran to N-methylpyrrolidone in the reaction solvent is (5-10):3, for example, it can be 5:3, 5.5:3, 6:3, 6.5:3, 7:3, 7.5:3, 8:3, 8.5:3, 9:3, 9.5:3 or 10:3, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] The reaction solvent provided by the present invention includes tetrahydrofuran and N-methylpyrrolidone in a mass ratio of (5-10):3. The low-boiling point tetrahydrofuran is combined with the highly soluble N-methylpyrrolidone, which reduces solvent residue and improves the purity of the polysiloxane imide, thereby improving the electrochemical performance of the silicon-based negative electrode material layer.

[0044] Preferably, in the condensation reaction, the molar ratio of amino-terminated dimethylsiloxane to pyromellitic dianhydride is 1:(1-1.1), for example, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08 or 1:1.1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] In the method for preparing the polysiloxane imide solution provided by the present invention, the molar ratio of amino-terminated dimethylsiloxane and pyromellitic dianhydride is limited to 1:(1-1.1), thereby optimizing the ratio of siloxane to imide monomers, thereby preparing a polysiloxane imide with excellent mechanical properties and flexibility.

[0046] Preferably, the temperature of the condensation reaction is 20-30° C., and the condensation reaction is accompanied by stirring for 10-15 hours.

[0047] The temperature of the condensation reaction in the present invention is 20-30°C, for example, it can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C or 30°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] The condensation reaction of the present invention is accompanied by stirring for 10 to 15 hours, for example, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] Preferably, the drying temperature is 70-120° C. and the drying time is 8-16 hours.

[0050] The drying temperature in the present invention is 70-120°C, for example, it can be 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0051] The drying time in the present invention is 8 to 16 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours or 16 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] In a fourth aspect, the present invention provides a silicon-based negative electrode, comprising a current collector and the silicon-based negative electrode material layer according to the second aspect covering at least one surface of the current collector.

[0053] In a fifth aspect, the present invention provides a silicon-based battery, comprising the silicon-based negative electrode described in the fourth aspect.

[0054] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) The binder provided by the present invention includes polysiloxane imide, which is obtained by introducing a flexible siloxane-containing segment into a polyimide main chain, so the polysiloxane imide contains both a rigid polyimide (PI) block and a flexible siloxane (Si-O-Si) block; on the one hand, the rigid PI block in the polysiloxane imide can provide a high modulus to withstand the mechanical stress generated by the silicon-based negative electrode material; on the other hand, the flexible Si-O-Si block in the polysiloxane imide helps to reduce the mechanical stress through reversible shape deformation and recover the deformation during lithiation and delithiation, thereby better coping with the volume expansion of the silicon-based negative electrode material; on the other hand, the Si-O-Si block in the polysiloxane imide can also effectively enhance the compatibility of the polysiloxane imide with the electrolyte;

[0057] (2) The binder provided by the present invention also includes polydopamine (PDA). Since PDA is rich in hydroxyl groups, PDA can form hydrogen bonds with oxygen atoms on the surface of the solid substrate, so that the binder containing PDA has good adhesion properties, thereby further improving the adhesion properties of the binder, thereby further reducing the risk of pulverization and shedding of silicon-based negative electrode materials during the cycle process;

[0058] (3) The binder provided by the present invention contains both polysiloxane imide and polydopamine. The combination of polysiloxane imide and polydopamine forms a dynamic network of carboxyl-amino hydrogen bonds, which can provide immediate bonding force and effectively inhibit the volume expansion and contraction of the silicon-based negative electrode material, thereby effectively reducing the risk of pulverization and shedding of the silicon-based negative electrode material during the cycle.

[0059] (4) In this application, by limiting the mass ratio of polysiloxane imide to polydopamine in the binder to (3-5): (15-25), it is ensured that the polysiloxane imide can provide sufficient rigid skeleton support and form moderate cross-linking with the amino group / hydroxyl group of polydopamine to relieve the volume expansion stress of silicon; it is also ensured that polydopamine can enhance adhesion and effectively inhibit the shedding of active substances;

[0060] (5) The binder provided by the present invention includes both polydopamine and polyacrylic acid. The esterification between the elastic polymer layer of polydopamine and the polyacrylic acid forms a three-dimensional cross-linked structure, thereby further enhancing the stability of the negative electrode material layer containing the binder and improving the cycle stability of the silicon-based battery.

[0061] (6) In the present invention, by limiting the mass fractions of polysiloxane imide, polydopamine, and polyacrylic acid in the binder, it is ensured that the rigid skeleton of polysiloxane imide can fully combine with the dynamic hydrogen bond network of polydopamine, thereby inhibiting the volume expansion of silicon and repairing cracks, and it is also ensured that the carboxyl groups of polyacrylic acid can be fully esterified and cross-linked, thereby enhancing the deformation resistance of the binder and thus enhancing the structural stability of the negative electrode material layer;

[0062] (7) The mass ratio of the silicon negative electrode active material to the binder in the silicon-based negative electrode material layer of the present invention is (2-5):1, which not only ensures that there is sufficient binder in the silicon-based negative electrode material layer, thereby effectively alleviating the volume expansion of the negative electrode material layer and inhibiting the pulverization and shedding of the silicon-based negative electrode material, thereby significantly improving the cycle stability, but also ensures that the silicon-based negative electrode material layer has sufficient silicon loading;

[0063] (8) The method for preparing the polysiloxane imide solution provided by the present invention has simple steps and only requires one step of copolymerization, thus simplifying the process;

[0064] (9) The reaction solvent provided by the present invention includes tetrahydrofuran and N-methylpyrrolidone in a mass ratio of (5-10):3. The combination of low-boiling-point tetrahydrofuran and highly soluble N-methylpyrrolidone reduces solvent residue and improves the purity of polysiloxane imide, thereby improving the electrochemical performance of the silicon-based negative electrode material layer;

[0065] (10) In the method for preparing the polysiloxane imide solution provided by the present invention, the molar ratio of amino-terminated dimethylsiloxane and pyromellitic dianhydride is limited to 1: (1 to 1.1), thereby optimizing the ratio of siloxane to imide monomers, thereby preparing a polysiloxane imide with excellent mechanical properties and flexibility, which is beneficial to improving the expansion inhibition effect of the binder on the silicon-based negative electrode material. DETAILED DESCRIPTION

[0066] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0067] Example 1

[0068] This embodiment provides a binder for a silicon-based negative electrode, wherein the binder includes polysiloxane imide, polydopamine, and polyacrylic acid. Based on the mass of the binder as 100%, the mass fraction of polysiloxane imide in the binder is 20 wt %, the mass fraction of polydopamine is 40 wt %, and the mass fraction of polyacrylic acid is 40 wt %.

[0069] This embodiment further provides a silicon-based negative electrode material layer, wherein the silicon-based negative electrode material layer comprises nano-silicon particles with a D50 particle size of 120 nm and the binder described in this embodiment at a mass ratio of 3.5:1;

[0070] The silicon-based negative electrode material layer also includes conductive carbon black. The mass ratio of nano-silicon particles with a D50 particle size of 120 nm to the conductive carbon black in the silicon-based negative electrode material layer is 7:1.

[0071] This embodiment further provides a method for preparing the silicon-based negative electrode material layer of this embodiment, the preparation method comprising:

[0072] (1) Amino-terminated dimethylsiloxane and pyromellitic dianhydride in a molar ratio of 1:1.01 were added to a reaction solvent (composed of tetrahydrofuran and N-methylpyrrolidone in a mass ratio of 8:3), stirred at 25°C for 12 hours, and a condensation reaction was carried out to obtain a polysiloxane imide solution.

[0073] (2) mixing nano-silicon particles with a D50 particle size of 120 nm, conductive carbon black, polydopamine and polyacrylic acid by grinding to obtain a mixture; mixing the obtained mixture with a solvent by stirring for 12 hours to obtain a mixed slurry; mixing the obtained slurry with the polysiloxane imide solution obtained in step (1) by stirring for 4 hours, and then drying at 90° C. for 12 hours to obtain a silicon-based negative electrode slurry;

[0074] This embodiment further provides a silicon-based negative electrode, which includes a current collector and a silicon-based negative electrode material layer according to this embodiment covering at least one surface of the current collector.

[0075] Example 2

[0076] This embodiment provides a binder for a silicon-based negative electrode, wherein the binder includes polysiloxane imide, polydopamine, and polyacrylic acid. Based on the mass of the binder as 100%, the mass fraction of polysiloxane imide in the binder is 18 wt %, the mass fraction of polydopamine is 45 wt %, and the mass fraction of polyacrylic acid is 37 wt %.

[0077] This embodiment further provides a silicon-based negative electrode material layer, wherein the silicon-based negative electrode material layer comprises nano-silicon particles with a D50 particle size of 120 nm and the binder described in this embodiment at a mass ratio of 4:1;

[0078] The silicon-based negative electrode material layer further includes acetylene black, and the mass ratio of nano-silicon particles with a D50 particle size of 120 nm to acetylene black in the silicon-based negative electrode material layer is 6:1.

[0079] This embodiment further provides a method for preparing the silicon-based negative electrode material layer of this embodiment, the preparation method comprising:

[0080] (1) Amino-terminated dimethylsiloxane and pyromellitic dianhydride in a molar ratio of 1:1.03 were added to a reaction solvent (composed of tetrahydrofuran and N-methylpyrrolidone in a mass ratio of 9:3), stirred at 22°C for 14 hours, and a condensation reaction was carried out to obtain a polysiloxane imide solution.

[0081] (2) mixing nano-silicon particles with a D50 particle size of 120 nm, acetylene black, polydopamine and polyacrylic acid by grinding to obtain a mixture; mixing the obtained mixture with a solvent by stirring for 12 hours to obtain a mixed slurry; mixing the obtained slurry with the polysiloxane imide solution obtained in step (1) by stirring for 6 hours, and then drying at 90° C. for 12 hours to obtain a silicon-based negative electrode slurry;

[0082] This embodiment further provides a silicon-based negative electrode, which includes a current collector and a silicon-based negative electrode material layer according to this embodiment covering at least one surface of the current collector.

[0083] Example 3

[0084] This embodiment provides a binder for a silicon-based negative electrode, wherein the binder includes polysiloxane imide, polydopamine, and polyacrylic acid. Based on the mass of the binder as 100%, the mass fraction of polysiloxane imide in the binder is 23wt%, the mass fraction of polydopamine is 35wt%, and the mass fraction of polyacrylic acid is 45wt%.

[0085] This embodiment further provides a silicon-based negative electrode material layer, wherein the silicon-based negative electrode material layer comprises nano-silicon particles with a D50 particle size of 120 nm and the binder described in this embodiment at a mass ratio of 3:1;

[0086] The silicon-based negative electrode material layer further includes carbon nanotubes, and the mass ratio of nano-silicon particles with a D50 particle size of 120 nm to the carbon nanotubes in the silicon-based negative electrode material layer is 8.5:1.

[0087] This embodiment further provides a method for preparing the silicon-based negative electrode material layer of this embodiment, the preparation method comprising:

[0088] (1) Amino-terminated dimethylsiloxane and pyromellitic dianhydride in a molar ratio of 1:1.05 were added to a reaction solvent (composed of tetrahydrofuran and N-methylpyrrolidone in a mass ratio of 7:3), stirred at 28°C for 11 hours, and a condensation reaction was carried out to obtain a polysiloxane imide solution.

[0089] (2) mixing nano-silicon particles with a D50 particle size of 120 nm, carbon nanotubes, polydopamine and polyacrylic acid by grinding to obtain a mixture; mixing the obtained mixture with a solvent by stirring for 8 hours to obtain a mixed slurry; mixing the obtained slurry with the polysiloxane imide solution obtained in step (1) by stirring for 8 hours, and then drying at 100° C. for 10 hours to obtain a silicon-based negative electrode slurry;

[0090] This embodiment further provides a silicon-based negative electrode, which includes a current collector and a silicon-based negative electrode material layer according to this embodiment covering at least one surface of the current collector.

[0091] Example 4

[0092] This embodiment provides a binder for a silicon-based negative electrode, wherein the binder includes polysiloxane imide, polydopamine, and polyacrylic acid. Based on the mass of the binder as 100%, the mass fraction of polysiloxane imide in the binder is 15wt%, the mass fraction of polydopamine is 50wt%, and the mass fraction of polyacrylic acid is 35wt%.

[0093] This embodiment further provides a silicon-based negative electrode material layer, wherein the silicon-based negative electrode material layer comprises nano-silicon particles with a D50 particle size of 120 nm and the binder described in this embodiment at a mass ratio of 5:1;

[0094] The silicon-based negative electrode material layer also includes conductive carbon black, and the mass ratio of nano-silicon particles with a D50 particle size of 120 nm to the conductive carbon black in the silicon-based negative electrode material layer is 5:1.

[0095] This embodiment further provides a method for preparing the silicon-based negative electrode material layer of this embodiment, the preparation method comprising:

[0096] (1) Amino-terminated dimethylsiloxane and pyromellitic dianhydride in a molar ratio of 1:1 were added to a reaction solvent (composed of tetrahydrofuran and N-methylpyrrolidone in a mass ratio of 10:3), and stirred at 20°C for 15 hours to carry out a condensation reaction to obtain a polysiloxane imide solution.

[0097] (2) first mixing nano-silicon particles with a D50 particle size of 120 nm, conductive carbon black, polydopamine and polyacrylic acid by grinding to obtain a mixture; mixing the obtained mixture with a solvent by stirring for 16 hours to obtain a mixed slurry; mixing the obtained slurry with the polysiloxane imide solution obtained in step (1) by stirring for 3 hours, and then drying at 70° C. for 16 hours to obtain a silicon-based negative electrode slurry;

[0098] This embodiment further provides a silicon-based negative electrode, which includes a current collector and a silicon-based negative electrode material layer according to this embodiment covering at least one surface of the current collector.

[0099] Example 5

[0100] This embodiment provides a binder for a silicon-based negative electrode, wherein the binder includes polysiloxane imide, polydopamine, and polyacrylic acid. Based on the mass of the binder as 100%, the mass fraction of polysiloxane imide in the binder is 25wt%, the mass fraction of polydopamine is 30wt%, and the mass fraction of polyacrylic acid is 50wt%.

[0101] This embodiment further provides a silicon-based negative electrode material layer, wherein the silicon-based negative electrode material layer comprises nano-silicon particles with a D50 particle size of 120 nm and the binder described in this embodiment at a mass ratio of 2:1;

[0102] The silicon-based negative electrode material layer also includes conductive carbon black, and the mass ratio of nano-silicon particles with a D50 particle size of 120 nm to the conductive carbon black in the silicon-based negative electrode material layer is 10:1.

[0103] This embodiment further provides a method for preparing the silicon-based negative electrode material layer of this embodiment, the preparation method comprising:

[0104] (1) Amino-terminated dimethylsiloxane and pyromellitic dianhydride in a molar ratio of 1:1.1 were added to a reaction solvent (composed of tetrahydrofuran and N-methylpyrrolidone in a mass ratio of 5:3), stirred at 30°C for 10 hours, and a condensation reaction was carried out to obtain a polysiloxane imide solution.

[0105] (2) mixing nano-silicon particles with a D50 particle size of 120 nm, conductive carbon black, polydopamine and polyacrylic acid by grinding to obtain a mixture; mixing the obtained mixture with a solvent by stirring for 5 hours to obtain a mixed slurry; mixing the obtained slurry with the polysiloxane imide solution obtained in step (1) by stirring for 10 hours, and then drying at 120° C. for 8 hours to obtain a silicon-based negative electrode slurry;

[0106] This embodiment further provides a silicon-based negative electrode, which includes a current collector and a silicon-based negative electrode material layer according to this embodiment covering at least one surface of the current collector.

[0107] Example 6

[0108] This embodiment provides a binder for a silicon-based negative electrode, which is the same as that in Example 1 except that the mass fraction of polysiloxane imide in the binder is 5 wt % and the mass fraction of polydopamine is 55 wt %.

[0109] This embodiment further provides a silicon-based negative electrode material layer, which is the same as that of embodiment 1 except that the binder in the silicon-based negative electrode material layer is the binder described in this embodiment.

[0110] This embodiment further provides a silicon-based negative electrode, which is the same as that in embodiment 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this embodiment.

[0111] Example 7

[0112] This embodiment provides a binder for a silicon-based negative electrode, which is the same as that in Example 1 except that the mass fraction of polysiloxane imide in the binder is 40 wt % and the mass fraction of polydopamine is 20 wt %.

[0113] This embodiment further provides a silicon-based negative electrode material layer, which is the same as that of embodiment 1 except that the binder in the silicon-based negative electrode material layer is the binder described in this embodiment.

[0114] This embodiment further provides a silicon-based negative electrode, which is the same as that in embodiment 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this embodiment.

[0115] Example 8

[0116] This embodiment provides a binder for a silicon-based negative electrode, which is the same as that of Example 1 except that the polyacrylic acid in the binder is omitted.

[0117] This embodiment further provides a silicon-based negative electrode material layer, which is the same as that of embodiment 1 except that the binder in the silicon-based negative electrode material layer is the binder described in this embodiment.

[0118] This embodiment further provides a silicon-based negative electrode, which is the same as that in embodiment 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this embodiment.

[0119] Example 9

[0120] This embodiment provides a binder for a silicon-based negative electrode, which is the same as that in embodiment 1.

[0121] This embodiment provides a silicon-based negative electrode material layer, which is the same as that of embodiment 1 except that the mass ratio of nano-silicon particles with a D50 particle size of 120 nm to the binder in the silicon-based negative electrode material layer is 1:1.

[0122] This embodiment further provides a silicon-based negative electrode, which is the same as that in embodiment 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this embodiment.

[0123] Example 10

[0124] This embodiment provides a binder for a silicon-based negative electrode, which is the same as that in embodiment 1.

[0125] This embodiment provides a silicon-based negative electrode material layer, which is the same as that of Example 1 except that the mass ratio of nano-silicon particles with a D50 particle size of 120 nm to the binder in the silicon-based negative electrode material layer is 8:1.

[0126] This embodiment further provides a silicon-based negative electrode, which is the same as that in embodiment 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this embodiment.

[0127] Example 11

[0128] This embodiment provides a binder for a silicon-based negative electrode, which is the same as that in embodiment 1.

[0129] This embodiment provides a silicon-based negative electrode material layer, which is the same as that of Example 1 except that the mass ratio of tetrahydrofuran to N-methylpyrrolidone in the reaction solvent in the preparation method of the silicon-based negative electrode material layer is 2:3.

[0130] This embodiment further provides a silicon-based negative electrode, which is the same as that in embodiment 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this embodiment.

[0131] Example 12

[0132] This embodiment provides a binder for a silicon-based negative electrode, which is the same as that in embodiment 1.

[0133] This embodiment provides a silicon-based negative electrode material layer, which is the same as that of Example 1 except that the mass ratio of tetrahydrofuran to N-methylpyrrolidone in the reaction solvent in the preparation method of the silicon-based negative electrode material layer is 15:3.

[0134] This embodiment further provides a silicon-based negative electrode, which is the same as that in embodiment 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this embodiment.

[0135] Example 13

[0136] This embodiment provides a binder for a silicon-based negative electrode, which is the same as that in embodiment 1.

[0137] This embodiment provides a silicon-based negative electrode material layer, which is the same as that of Example 1 except that the molar ratio of amino-terminated dimethylsiloxane to pyromellitic dianhydride in the preparation method of the silicon-based negative electrode material layer is 1:0.9.

[0138] This embodiment further provides a silicon-based negative electrode, which is the same as that in embodiment 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this embodiment.

[0139] Example 14

[0140] This embodiment provides a binder for a silicon-based negative electrode, which is the same as that in embodiment 1.

[0141] This embodiment provides a silicon-based negative electrode material layer, which is the same as that of Example 1 except that the molar ratio of amino-terminated dimethylsiloxane to pyromellitic dianhydride in the preparation method of the silicon-based negative electrode material layer is 1:1.3.

[0142] This embodiment further provides a silicon-based negative electrode, which is the same as that in embodiment 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this embodiment.

[0143] Comparative Example 1

[0144] This comparative example provides a binder for a silicon-based negative electrode, which is the same as Example 1 except that the polysiloxane imide in the binder is omitted and the masses of polydopamine and polyacrylic acid in the binder are increased compared with the same period of time so that the total mass of the binder remains unchanged.

[0145] This comparative example also provides a silicon-based negative electrode material layer, which is the same as Example 1 except that the binder in the silicon-based negative electrode material layer is the binder described in this comparative example.

[0146] This comparative example also provides a silicon-based negative electrode, which is the same as Example 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this comparative example.

[0147] Comparative Example 2

[0148] This comparative example provides a binder for a silicon-based negative electrode, which is the same as Example 1 except that polydopamine is omitted from the binder and the masses of polysiloxane imide and polyacrylic acid in the binder are increased relatively to keep the total mass of the binder unchanged.

[0149] This comparative example also provides a silicon-based negative electrode material layer, which is the same as Example 1 except that the binder in the silicon-based negative electrode material layer is the binder described in this comparative example.

[0150] This comparative example also provides a silicon-based negative electrode, which is the same as Example 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this comparative example.

[0151] Comparative Example 3

[0152] This comparative example provides a binder for a silicon-based negative electrode, wherein the binder is composed of sodium carboxymethyl cellulose and polyacrylic acid in a mass ratio of 1:2.

[0153] This comparative example also provides a silicon-based negative electrode material layer, which is the same as Example 1 except that the binder in the silicon-based negative electrode material layer is the binder described in this comparative example.

[0154] This comparative example also provides a silicon-based negative electrode, which is the same as Example 1 except that the silicon-based negative electrode material layer of the silicon-based negative electrode is the silicon-based negative electrode material layer provided in this comparative example.

[0155] The silicon-based negative electrodes provided in the above embodiments and comparative examples were subjected to a peeling performance test. The peeling performance test was performed using a peeling force testing machine. The width and length of the electrode piece were fixed, and the peeling strength of the electrode piece was tested using a tensile testing machine. The peeling strength of the silicon-based negative electrode obtained by the test is shown in Table 1.

[0156] The silicon-based negative electrode provided in the above embodiment and comparative example is used to prepare a lithium-ion battery. The method for preparing the lithium-ion battery is as follows: 80g of LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black and polyvinylidene fluoride are fully ground in a mortar at a mass ratio of 8:1:1, and then the resulting mixture is dispersed in 150 ml of N-methylpyrrolidone and stirred for 12 hours to obtain a slurry; the resulting slurry is coated on an aluminum foil, and then dried under vacuum at 90°C for 12 hours to obtain a positive electrode sheet; a PE diaphragm is selected as the diaphragm; the positive electrode sheet, the diaphragm and the silicon-based negative electrode provided in the above embodiments and comparative examples are stacked in sequence, and a battery core is obtained through a lamination process. The battery core is placed in an outer packaging shell, dried, and injected with an electrolyte (a solution of 1.2 mol / L LiPF6 in a 3:7 mixture of ethylene carbonate and ethyl methyl carbonate) at an electrolyte injection coefficient of 3.6 g / Ah. After vacuum packaging, standing, formation and capacity separation processes, a lithium-ion battery is obtained.

[0157] The obtained lithium-ion battery was subjected to an initial full charge rebound rate test. The method for the initial full charge rebound rate test is as follows: using a standard charging method, constant current and constant voltage charging at a voltage of 4.25V and a current of 0.33C, with a cut-off current of 0.05C. After full charge, the battery was disassembled to measure the full charge thickness of the negative electrode, and the initial full charge rebound rate was obtained as shown in Table 1;

[0158] The obtained lithium-ion battery was subjected to a cycle performance test. The cycle performance test method was as follows: charge and discharge were performed at 25° C. in a voltage range of 2.5 to 4.25 V at a current of 1 C for 500 cycles. The capacity retention rate of the battery after 500 cycles was tested as shown in Table 1. The full charge rebound rate of the battery after 500 cycles was tested using the same method as the initial full charge rebound rate test. The full charge rebound rate after 500 cycles was shown in Table 1.

[0159] Table 1

[0160]

[0161]

[0162] From Table 1, we can get:

[0163] (1) The silicon-based negative electrode prepared using the binder provided in Examples 1 to 5 of the present invention exhibited a high peeling force in the peeling performance test, a small initial full-charge rebound rate, a high capacity retention rate, and a small full-charge rebound rate after 500 cycles;

[0164] (2) By comparing Example 1 with Examples 6 and 7, it can be seen that in this application, by limiting the mass ratio of polysiloxane imide to polydopamine in the binder to (3-5): (15-25), it is ensured that the polysiloxane imide can provide sufficient rigid skeleton support and form moderate cross-linking with the amino group / hydroxyl group of polydopamine to relieve the volume expansion stress of silicon; it is also ensured that polydopamine can enhance adhesion and effectively inhibit the shedding of active substances;

[0165] (3) By comparing Example 1 with Example 8, it can be seen that the binder provided by the present invention includes both polydopamine and polyacrylic acid. The esterification between the elastic polymer layer of polydopamine and polyacrylic acid forms a three-dimensional cross-linked structure, thereby further enhancing the stability of the negative electrode material layer containing the binder and improving the cycle stability of the silicon-based battery.

[0166] (4) By comparing Example 1 with Examples 9 and 10, it can be seen that the mass ratio of the silicon negative electrode active material to the binder in the silicon-based negative electrode material layer of the present invention is (2-5):1, which not only ensures that there is sufficient binder in the silicon-based negative electrode material layer, thereby effectively alleviating the volume expansion of the negative electrode material layer and inhibiting the pulverization and shedding of the silicon-based negative electrode material, thereby significantly improving the cycle stability, but also ensures that the silicon-based negative electrode material layer has sufficient silicon loading;

[0167] (5) By comparing Example 1 with Examples 11 and 12, it can be seen that the reaction solvent provided by the present invention includes tetrahydrofuran and N-methylpyrrolidone in a mass ratio of (5-10):3. The combination of low-boiling-point tetrahydrofuran and highly soluble N-methylpyrrolidone reduces solvent residue and improves the purity of polysiloxane imide, thereby improving the electrochemical performance of the silicon-based negative electrode material layer;

[0168] (6) By comparing Example 1 with Examples 13 and 14, it can be seen that in the method for preparing the polysiloxane imide solution provided by the present invention, by limiting the molar ratio of amino-terminated dimethylsiloxane and pyromellitic dianhydride to 1: (1 to 1.1), the ratio of siloxane to imide monomer is optimized, thereby preparing a polysiloxane imide with excellent mechanical properties and flexibility, which is beneficial to improving the expansion inhibition effect of the binder on the silicon-based negative electrode material;

[0169] (7) By comparing Example 1 with Comparative Examples 1 to 3, it can be seen that the binder provided by the present invention includes polysiloxane imide, which is obtained by introducing a flexible segment containing siloxane into the main chain of polyimide, so the polysiloxane imide contains both a rigid polyimide (PI) block and a flexible siloxane (Si-O-Si) block; on the one hand, the rigid PI block in the polysiloxane imide can provide a high modulus to withstand the mechanical stress generated by the silicon-based negative electrode material; on the other hand, the flexible Si-O-Si block in the polysiloxane imide helps to reduce the mechanical stress through reversible shape deformation and recover the deformation during lithiation and delithiation, thereby better coping with the volume expansion of the silicon-based negative electrode material; on the other hand, the Si-O-Si block in the polysiloxane imide can also effectively enhance the compatibility of the polysiloxane imide with the electrolyte;

[0170] The binder provided by the present invention also includes polydopamine (PDA). Since PDA is rich in hydroxyl groups, PDA can form hydrogen bonds with oxygen atoms on the surface of the solid substrate, so that the binder containing PDA has good adhesion properties, thereby further improving the bonding properties of the binder, thereby further reducing the risk of pulverization and shedding of silicon-based negative electrode materials during the cycle process;

[0171] The binder provided by the present invention contains both polysiloxane imide and polydopamine. The combination of polysiloxane imide and polydopamine forms a dynamic network of carboxyl-amino hydrogen bonds, which can provide immediate bonding force and effectively inhibit the volume expansion and contraction of silicon-based negative electrode materials, thereby effectively reducing the risk of pulverization and shedding of silicon-based negative electrode materials during the cycle.

[0172] 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 thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A binder for a silicon-based negative electrode, characterized in that: The adhesive includes polysiloxane imide and polydopamine.

2. The adhesive according to claim 1, characterized in that The mass ratio of polysiloxane imide to polydopamine in the binder is (3-5):(15-25).

3. The adhesive according to claim 1, characterized in that The binder also includes polyacrylic acid.

4. The adhesive according to claim 1, characterized in that Based on the mass of the binder as 100%, the mass fraction of polysiloxane imide in the binder is 15-25wt%, the mass fraction of polydopamine is 30-50wt%, and the mass fraction of polyacrylic acid is 30-50wt%.

5. A silicon-based negative electrode material layer, characterized in that: The silicon-based negative electrode material layer comprises a silicon negative electrode active material and the binder according to any one of claims 1 to 4.

6. The silicon-based negative electrode material layer according to claim 5, characterized in that: The mass ratio of the silicon negative electrode active material to the binder in the silicon-based negative electrode material layer is (2-5):1; Preferably, the silicon-based negative electrode material layer further includes a conductive agent, and the mass ratio of the silicon negative electrode active material to the conductive agent in the silicon-based negative electrode material layer is (5-10):

1.

7. A method for preparing the silicon-based negative electrode material layer according to claim 5 or 6, characterized in that: The preparation method comprises: The silicon negative electrode active material, the binder and the solvent are mixed and dried to obtain a silicon-based negative electrode material layer.

8. The preparation method according to claim 7, characterized in that The mixing also includes mixing in a conductive agent; Preferably, the mixing comprises: First, a silicon negative electrode active material, a conductive agent, polydopamine and polyacrylic acid are mixed to obtain a mixture; second, the obtained mixture is mixed with a solvent to obtain a mixed slurry; third, the obtained slurry is mixed with a polysiloxane imide solution to obtain a silicon-based negative electrode slurry; Preferably, the method for preparing the polysiloxane imide solution is: Carrying out a condensation reaction between amino-terminated dimethylsiloxane and pyromellitic dianhydride in a reaction solvent to obtain a polysiloxane imide solution; Preferably, the reaction solvent comprises tetrahydrofuran and N-methylpyrrolidone, and the mass ratio of tetrahydrofuran to N-methylpyrrolidone in the reaction solvent is (5-10):3; Preferably, in the condensation reaction, the molar ratio of amino-terminated dimethylsiloxane to pyromellitic dianhydride is 1:(1-1.1); Preferably, the temperature of the condensation reaction is 20-30° C., and the condensation reaction is accompanied by stirring for 10-15 hours.

9. A silicon-based negative electrode, characterized in that: The silicon-based negative electrode comprises a current collector and a silicon-based negative electrode material layer according to claim 5 or 6 covering at least one surface of the current collector.

10. A silicon-based battery, characterized in that: The silicon-based battery comprises the silicon-based negative electrode according to claim 9.

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