Composite silicon-based negative electrode, method of preparation, and secondary battery

Abstract

The present application relates to a kind of composite silicon-based negative electrode, preparation method and secondary battery.The composite silicon-based negative electrode of the present application includes the conductive mesh layer arranged sequentially from inside to outside at least one surface of negative electrode current collector, several gel porous membrane layers, and the active layer of negative electrode material covered in the gel porous membrane layer;The surface of the gel porous membrane in the gel porous membrane layer adheres negative active coating.By designing conductive mesh layer, gel porous membrane, the interaction strength and electrical conductivity of negative electrode structure are improved, and the cycle stability is improved.

Description

Technical Field

[0001] This invention relates to the field of silicon-based battery technology, and in particular to a composite silicon-based negative electrode, its preparation method, and a secondary battery. Background Technology

[0002] Si / SiO-based anode materials are considered the most competitive candidates for next-generation anodes in lithium-ion batteries (LiBs) due to their high specific energy density, natural abundance, and attractive operating voltage. However, Si / SiO-based anode materials typically undergo significant volume changes and structural collapse during cycling, leading to a severe reduction in battery life. To address this issue and improve the specific capacity of graphite anode materials by introducing Si / SiO-based anode materials, thus enabling their practical application in lithium-ion batteries, numerous designs have been proposed. These include selecting suitable electrolytes and additives to modify the SEI and CEI interfaces, constructing various shell-like nanostructures in Si / SiO-based anode materials, reserving a certain pore volume to accommodate volume changes, adding binders that form hydrogen and ester bonds, and using binder-rich branched structures to provide more bonding sites.

[0003] However, in actual use, Si / SiO-based anode materials have large volume changes. As the battery is charged and discharged, due to the poor mechanical tensile properties of the binder material and the relatively weak interaction between Si / SiO particles and the current collector, the anode is very prone to breakage and separation from the Si / SiO-based anode material during cycling, resulting in a sudden decrease in battery capacity and a severely shortened lifespan. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a composite silicon-based negative electrode, its preparation method, and a secondary battery. By providing a composite silicon-based negative electrode, its preparation method, and a secondary battery, this invention improves the interaction strength and conductivity of the negative electrode structure and enhances cycle stability through the design of a conductive mesh layer and a gel porous membrane.

[0005] This invention is achieved through the following technical solution:

[0006] The first objective of this invention is to provide a composite silicon-based negative electrode, comprising a conductive mesh layer, a plurality of gel porous membrane layers, and a negative electrode material active layer covering the gel porous membrane layers, which are sequentially disposed from the inside out on at least one surface of the negative electrode current collector; wherein a negative electrode active coating is adhered to the surface of the gel porous membrane layers.

[0007] In one embodiment of the present invention, at least one or more of the following conditions are satisfied:

[0008] The thickness of the negative electrode current collector is 3–18 μm;

[0009] The thickness of the conductive mesh layer is 0.1–12 μm; preferably 0.3–6 μm.

[0010] The thickness of the gel porous membrane layer is 1–12 μm; preferably 3–30 μm.

[0011] The thickness of the active layer of the negative electrode material is 30–260 μm; preferably 30–80 μm.

[0012] The second objective of this invention is to provide a method for preparing a composite silicon-based negative electrode, comprising the following steps:

[0013] A network of carbon containing a polymer is loaded onto at least one surface of the negative electrode current collector, and then heated to obtain a conductive network layer.

[0014] A negative electrode coating is prepared by mixing negative electrode material, conductive material and binder in a solvent;

[0015] A gel porous membrane is provided. The negative electrode coating is filtered by vacuum filtration using the gel porous membrane as a filter membrane, so that the negative electrode coating flows through the gel porous membrane to obtain a gel porous membrane with the negative electrode coating adhering to it.

[0016] A gel porous membrane with a negative electrode coating is coated on the conductive mesh layer to obtain a gel porous membrane layer.

[0017] The negative electrode coating is applied to the surface of the porous gel membrane to form the active layer of the negative electrode material. The coating is then cold-pressed, dried, and rolled to obtain the composite silicon-based negative electrode.

[0018] In one embodiment of the present invention, at least one of the following conditions is satisfied:

[0019] 1) The length of the network carbon is 0.02-2 μm;

[0020] 2) Heating conditions: Heating temperature is 200-500℃, and time is 10-60 min;

[0021] 3) The content of polymer in the polymer-containing network carbon is 1-8 wt%.

[0022] In one embodiment of the present invention, the network carbon is selected from one or more of carbon nanofibers, carbon microfibers, conductive carbon nanotubes, graphite carbon micro / nanowires, and graphite carbon micro / nanotubes.

[0023] In one embodiment of the present invention, the negative electrode current collector is selected from one or more of copper foil, red copper foil, and nickel-plated copper foil; the polymer is one or more of polytetrafluoroethylene, polypyrrole, polythiophene, polyethylene, polypropylene, polystyrene, polyacrylamide, and ethylene-propylene-diene copolymer resin.

[0024] In one embodiment of the present invention, the gel porous membrane is prepared by the following method:

[0025] (1) Adjust the polyacrylic acid solution to acidity, add thiourea, heat to dehydrate and condense, and separate to obtain polyacrylic acid-thiourea copolymer precipitate; add to gelling agent solution to obtain gel;

[0026] (2) Add inorganic ceramic particles to the gel in step (1), mix and stir to obtain a homogenous mixture, remove water by hot pressing, and remove air bubbles by standing to obtain a porous gel membrane.

[0027] The gelling agent in the gelling solution is selected from one or more of sodium citrate, sodium oxalate, and oxalic acid.

[0028] In one embodiment of the present invention, the mass ratio of the negative electrode material, the conductive material and the binder is 85-99:0.2-8:0.2-10;

[0029] The negative electrode material includes silicon-based negative electrode material and graphite negative electrode material;

[0030] The graphite anode material has a content of 35wt% to 98wt% in the anode material.

[0031] In one embodiment of the present invention, the areal density of the negative electrode coating of the negative electrode material active layer is 40-350 g / m³. 2 .

[0032] A third objective of the present invention is to provide a secondary battery comprising the composite silicon-based negative electrode provided in the first objective and the composite silicon-based negative electrode obtained by the preparation method described in the second objective.

[0033] The fourth objective of this invention is to provide a method for preparing a secondary battery, comprising the following steps:

[0034] (1) The positive electrode active material, conductive agent and binder are mixed in a mass ratio of 80-98:0.3-6:0.3-6 to make a negative electrode slurry, which is coated on copper foil and dried, rolled, cut into pieces and slits. The slits are then used to make a positive electrode.

[0035] (2) The bare cell is obtained by stacking and winding the silicon-based negative electrode, separator, positive electrode, separator, and silicon-based negative electrode in sequence. The tabs are welded, and the bare cell is placed in the battery aluminum shell / soft-pack aluminum-plastic film, top-sealed, side-sealed, dried to remove moisture, electrolyte is injected into the battery shell, top-sealed, formed, and determined to a certain capacity to obtain a secondary battery.

[0036] The technical solution of the present invention has the following advantages over the prior art:

[0037] This invention utilizes thiourea groups as the polymerization link to crosslink polyacrylic acid (lithium polyacrylate / sodium polyacrylate / polyacrylate), resulting in a polymer-type gel porous membrane with high mechanical strength and strain resistance. When embedded in a composite silicon-based negative electrode, this membrane reduces coating cracking and internal particle contact failure due to volume changes, thereby improving the interaction between Si / SiO particles in the negative electrode coating and the current collector. This makes it suitable for suppressing the reaction of Li... + The large volume change experienced by the composite silicon-based negative electrode during insertion and extraction results in a longer lifespan for the secondary battery.

[0038] Thiourea materials can not only crosslink polyacrylic acid (lithium polyacrylate / sodium polyacrylate / polyacrylate) polymers, but also enhance the interfacial forces between the coating binder and the gel porous membrane due to their dense hydrogen-bonded functional groups, allowing them to firmly "grasp" the active material particles. The overall structure enhances the "mechanical interlocking" effect of the binder. The addition of inorganic ceramic materials helps to reduce the shortcomings of insufficient conductivity of the gel porous membrane and improve the conductive connection of the composite silicon-based negative electrode structure. Attached Figure Description

[0039] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0040] Figure 1 This is a schematic diagram of the composite silicon-based negative electrode of the present invention.

[0041] Explanation of reference numerals in the accompanying drawings: 1. Negative electrode current collector; 2. Conductive mesh layer; 3. At least one layer of gel porous membrane; 4. Negative electrode coating on the gel porous membrane; 5. Coating layer of negative electrode coating. Detailed Implementation

[0042] To address the technical problems in existing technologies, such as the large volume change of Si / SiO-based anode materials, the poor mechanical tensile properties of the binder material, and the relatively weak interaction between Si / SiO particles and the current collector, which easily lead to the breakage of the anode and separation of the Si / SiO-based anode material from the electrode during cycling, resulting in sudden capacity decay and severely shortened battery life, the present invention proposes a technical solution.

[0043] The first objective of this invention is to provide a composite silicon-based negative electrode, comprising a conductive mesh layer, a plurality of gel porous membrane layers, and a negative electrode material active layer covering the gel porous membrane layers, which are sequentially disposed from the inside out on at least one surface of the negative electrode current collector; wherein a negative electrode active coating is adhered to the surface of the gel porous membrane layers.

[0044] Furthermore, several layers of gel porous membrane, preferably one or two layers.

[0045] The conductive mesh layer is covered by a negative electrode active coating under a gel porous membrane layer;

[0046] The gel porous membrane is covered by a negative electrode coating on both the top and bottom surfaces, and the top surface of the gel porous membrane is completely covered by the negative electrode coating.

[0047] In a specific embodiment, at least one or more of the following conditions are met:

[0048] The thickness of the negative electrode current collector is 3–18 μm;

[0049] The thickness of the conductive mesh layer is 0.1–12 μm; preferably 0.3–6 μm.

[0050] The thickness of the gel porous membrane layer is 1–12 μm; more preferably, it is 3–30 μm.

[0051] The thickness of the active layer of the negative electrode material is 30–260 μm, and more preferably 30–80 μm.

[0052] The second objective of this invention is to provide a method for preparing a composite silicon-based negative electrode, comprising the following steps:

[0053] A network of carbon containing a polymer is loaded onto at least one surface of the negative electrode current collector, and then heated to obtain a conductive network layer.

[0054] A negative electrode coating is prepared by mixing negative electrode material, conductive material and binder in a solvent;

[0055] A gel porous membrane is provided. The negative electrode coating is filtered by vacuum filtration using the gel porous membrane as a filter membrane, so that the negative electrode coating flows through the gel porous membrane to obtain a gel porous membrane with the negative electrode coating adhering to it.

[0056] A gel porous membrane with a negative electrode coating is coated on the conductive mesh layer to obtain a gel porous membrane layer.

[0057] The negative electrode coating is applied to the surface of the porous gel membrane to form the active layer of the negative electrode material. The coating is then cold-pressed, dried, and rolled to obtain the composite silicon-based negative electrode.

[0058] In this specific embodiment, at least one of the following conditions is satisfied:

[0059] 1) The length of the network carbon is 0.02-2 μm;

[0060] 2) Heating conditions: Heating temperature is 200-500℃, and time is 10-60 min;

[0061] 3) The content of polymer in the polymer-containing network carbon is 1-8 wt%.

[0062] In a specific embodiment, the network carbon is selected from one or more of carbon nanofibers, carbon microfibers, conductive carbon nanotubes, graphite carbon micro / nanowires, and graphite carbon micro / nanotubes.

[0063] In a specific embodiment, the negative electrode current collector is selected from one or more of copper foil, red copper foil, and nickel-plated copper foil; the polymer is one or more of polytetrafluoroethylene, polypyrrole, polythiophene, polyethylene, polypropylene, polystyrene, polyacrylamide, and ethylene-propylene-diene copolymer resin.

[0064] In a specific embodiment, the gel porous membrane is prepared by the following method:

[0065] (1) Adjust the polyacrylic acid compound solution to acidity, add thiourea, heat to dehydrate and condense, and separate to obtain polyacrylic acid-thiourea copolymer precipitate; add 2-45 wt% gelling agent solution to obtain gel;

[0066] (2) Add inorganic ceramic particles to the gel in step (1), mix and stir to obtain a homogenous mixture, hot press the mixture to remove water, let it stand to remove air bubbles, and obtain a porous gel membrane.

[0067] Furthermore, in step (1), the polyacrylic acid in the polyacrylic acid solution is selected from one or more of polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and polyacrylate.

[0068] Furthermore, in step (1), the acidic pH value is 1-6, and the acidic regulator for adjusting the acidity of the solution is a conventional acid in the art, preferably sulfuric acid.

[0069] Furthermore, in step (1), the temperature of the dehydration condensation is 30 to 110°C.

[0070] Furthermore, in step (1), the mass ratio of the solvent water to the polyacrylic acid compound and thiourea in the polyacrylic acid compound solution is 100:10 to 60:3-25. The dehydration condensation reaction principle: The carboxyl groups on the polyacrylic acid undergo dehydration condensation with the amino groups on the thiourea to obtain an amide.

[0071] Furthermore, in step (2), the inorganic ceramic particles are selected from at least one of alumina, boehmite, titanium dioxide, zirconium oxide, barium titanate, yttrium-doped zirconium oxide, gadolinium-doped cerium oxide, montmorillonite, and aluminosilicates.

[0072] Furthermore, in step (2), the citric acid content in the mixed slurry is 1-8 wt%, the content of polyacrylic acid-thiourea copolymer precipitate is 10-40 wt%, and the content of inorganic ceramic particles is 0.2-3 wt%.

[0073] Furthermore, in step (2), the temperature of the hot pressing dehydration is 90 to 150°C.

[0074] Furthermore, in step (2), the thickness of the gel porous membrane is 1 to 20 μm and the pore size is 1 to 30 μm.

[0075] In a specific embodiment, the mass ratio of the negative electrode material, the conductive material, and the binder is 85-99:0.2-8:0.2-10;

[0076] The negative electrode material includes silicon-based negative electrode material and graphite negative electrode material;

[0077] The graphite anode material has a content of 35wt% to 98wt% in the anode material.

[0078] Furthermore, the silicon-based anode material is in the form of a block, sheet, sphere, tube, or multilayer.

[0079] Furthermore, the silicon-based anode material is a nano-silicon-carbon material, a micro-silicon-carbon material, a nano-silicon-oxygen material, a micro-silicon-oxygen material, a lithium-containing nano-silicon-oxygen material, a lithium-containing micro-silicon-oxygen material, a magnesium-containing nano-silicon-oxygen material, or a magnesium-containing micro-silicon-oxygen material.

[0080] Furthermore, the graphite anode material is block, sheet, spherical, tubular, or multilayer artificial graphite.

[0081] Furthermore, the graphite anode material is modified natural graphite that has been oxidized, doped, halogenated, or coated.

[0082] In a specific embodiment, the conductive material is one or more of the following: conductive carbon fiber, oligowalled carbon nanotubes, single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, carbon black, conductive graphite, and graphene.

[0083] In a specific embodiment, the adhesive is one or more of the following: polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyacrylate, styrene-butadiene rubber, sodium alginate, chitosan, polyethylene glycol, polyamide, polyimide, polyacrylic acid, sodium polyacrylate, and lithium polyacrylate.

[0084] In a specific embodiment, the surface density of the negative electrode coating in the active layer of the negative electrode material is 40–350 g / m³. 2 .

[0085] A third objective of the present invention is to provide a secondary battery comprising the composite silicon-based negative electrode provided in the first objective and the composite silicon-based negative electrode obtained by the preparation method described in the second objective.

[0086] The fourth objective of this invention is to provide a method for preparing a secondary battery, comprising the following steps:

[0087] (1) The positive electrode active material, conductive agent and binder are mixed in a mass ratio of 80-98:0.3-6:0.3-6 to make a negative electrode slurry, which is coated on copper foil and dried, rolled, cut into pieces and slits. The slits are then used to make a positive electrode.

[0088] (2) The bare cell is obtained by stacking and winding the silicon-based negative electrode, separator, positive electrode, separator, and silicon-based negative electrode in sequence. The tabs are welded, and the bare cell is placed in the battery aluminum shell / soft-pack aluminum-plastic film, top-sealed, side-sealed, dried to remove moisture, electrolyte is injected into the battery shell, top-sealed, formed, and determined to a certain capacity to obtain a secondary battery.

[0089] Furthermore, in step (1), the positive electrode active material is at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, lithium iron manganese phosphate, and lithium iron phosphate.

[0090] Furthermore, in step (2), the diaphragm is a polymer diaphragm of at least one of polyethylene, polypropylene, polysulfonyl, polyacrylonitrile, polyvinyl alcohol, polyarylethersulfone, polyvinylidene fluoride, and polymalonic acid.

[0091] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0092] Example 1:

[0093] This embodiment provides a composite silicon-based negative electrode, its preparation method, and its application, as detailed below:

[0094] 1. Preparation method of composite silicon-based negative electrode:

[0095] (1) Conductive mesh layer: Carbon nanofibers with a particle size of 0.4μm to 1.9μm are sprayed onto the copper foil of the negative electrode current collector. The mesh carbon contains 3.5wt% of high molecular polymer, so that the mesh carbon adheres to the negative electrode current collector. After high temperature curing at 350℃ for 1h, a conductive mesh layer with a thickness of 0.3μm to 6μm is obtained.

[0096] (2) A mixture of silicon-based anode material (bulk lithium-containing micron silicon oxide material, content of 10wt%) and graphite anode material (sheet artificial graphite, content of 90wt%), conductive material (5wt% CNT carbon nanotubes and 95wt% carbon black), and binder (20wt% sodium carboxymethyl cellulose, 20wt% styrene-butadiene rubber and 60wt% polyacrylate) is mixed and stirred in a mass ratio of 96.5:1.5:2. Deionized water is added and stirred to adjust the viscosity to 3630 mPa·s to obtain anode coating. The anode coating is slowly injected into the funnel beaker above the vacuum filter. The vacuum filter is turned on to extract the air in the filter bottle. The anode coating in the funnel beaker flows through the pores on the gel porous membrane. Part of the anode coating adheres to the surface of the gel porous membrane. The gel porous membrane is then covered on the anode current collector with a conductive mesh layer on one side in step (1).

[0097] (3) Apply the negative electrode coating onto the gel porous membrane, then cold press and cut to obtain a single-sided composite silicon-based negative electrode. Cover the other side with the gel porous membrane as in (2), then apply the negative electrode coating onto the gel porous membrane, then dry, roll, trim, cut into pieces and slit to obtain a double-sided composite silicon-based negative electrode.

[0098] The gel porous membrane was prepared by the following method: ① First, polyacrylic acid was dissolved in deionized water, and then a small amount of 11M concentrated sulfuric acid was added until the pH of the solution was adjusted to 2.4. Then, thiourea was added to the above solution and stirred, and dehydration condensation was carried out at 60°C (100 parts by mass of deionized water, 20 parts by mass of polyacrylic acid, and 4 parts by mass of thiourea). ② Finally, the polyacrylic acid-thiourea copolymer precipitate was separated and added to a 4.5wt% citric acid solution to obtain a gel. Inorganic ceramic particles (zirconia) were then added and mixed and stirred to obtain a homogenized slurry (the content of citric acid in the homogenate was 1.6wt%, the content of polyacrylic acid-thiourea copolymer precipitate was 24.8wt%, and the content of inorganic ceramic particles was 0.5wt%). The slurry was hot-pressed at 120°C to remove water, and the bubbles were removed by standing to obtain a gel porous membrane with a thickness of 11μm and a pore size of 1μm to 8μm.

[0099] 2. Secondary battery:

[0100] (1) The positive electrode active material (lithium nickel cobalt manganese oxide, LiNi) 0.81 Co 0.09 Mn 0.10 O2), conductive agent (5wt% CNT carbon nanotubes and 95wt% carbon black), and binder (polyvinylidene fluoride) are mixed in a mass ratio of 97.5:1.5:1 to make a negative electrode slurry. The slurry is coated on copper foil, dried, rolled, cut into sheets, and slit. The slits are then used to make a positive electrode.

[0101] (2) The bare cell is obtained by stacking and winding the silicon-based negative electrode, polypropylene separator, positive electrode, separator, and silicon-based negative electrode in sequence. The tabs are welded, and the bare cell is placed in the battery aluminum shell / soft-pack aluminum-plastic film, top-sealed, side-sealed, dried to remove moisture, electrolyte injected into the battery shell, top-sealed, formed, and determined to a certain capacity, thus obtaining a secondary battery.

[0102] Example 2

[0103] This embodiment provides a composite silicon-based negative electrode, its preparation method, and its application, as detailed below:

[0104] 1. Preparation method of composite silicon-based negative electrode:

[0105] (1) Conductive mesh layer: Carbon nanofibers with a particle size of 0.3μm to 1.7μm are sprayed onto the copper foil of the current collector through the negative electrode. The mesh carbon contains 3.5wt% of high molecular polymer, so that the mesh carbon adheres to the current collector of the negative electrode. After high temperature curing at 350℃ for 1h, a conductive mesh layer of 0.3μm to 6μm is obtained.

[0106] (2) A mixture of silicon-based anode material (bulk lithium-containing micron silicon oxide material, content of 10wt%) and graphite anode material (sheet artificial graphite, content of 90wt%), conductive material (5wt% CNT carbon nanotubes and 95wt% carbon black), and binder (20wt% sodium carboxymethyl cellulose, 20wt% styrene-butadiene rubber and 60wt% polyacrylate) in a mass ratio of 96.5:1.5:2 is mixed and stirred. Deionized water is added and stirred to adjust the viscosity to 2960 mPa·s to obtain anode coating. The anode coating is slowly injected into the funnel beaker above the vacuum filter. The vacuum filter is turned on to extract the air in the filter bottle. The anode coating in the funnel beaker flows through the pores on the gel porous membrane. Part of the anode coating adheres to the top and bottom of the gel porous membrane. Then the gel porous membrane is covered on the negative electrode current collector with a conductive mesh layer on one side in step (1).

[0107] (3) Apply the negative electrode coating onto the gel porous membrane, then cold press and cut to obtain a single-sided composite silicon-based negative electrode. Cover the other side with the gel porous membrane as in (2), then apply the negative electrode coating onto the gel porous membrane, then dry, roll, trim, cut into pieces and slit to obtain a double-sided composite silicon-based negative electrode.

[0108] The gel porous membrane was prepared by the following method: ① First, polyacrylic acid was dissolved in deionized water, and then a small amount of 11M concentrated sulfuric acid was added until the pH of the solution was adjusted to between 2.7. Then, thiourea was added to the above solution and stirred, and dehydration condensation was carried out at 60°C (100 parts by mass of deionized water, 20 parts by mass of polyacrylic acid, and 4 parts by mass of thiourea) (reaction principle: the carboxyl groups on polyacrylic acid and the amino groups on thiourea undergo dehydration condensation to obtain amides). ② Finally, the polyacrylic acid-thiourea copolymer precipitate was separated and added to a 4.5 wt% citric acid solution to obtain a gel. Inorganic ceramic particles (alumina) were then added and mixed and stirred to obtain a homogenized slurry (the content of citric acid in the homogenized slurry was 1.3 wt%, the content of polyacrylic acid-thiourea copolymer precipitate was 22.9 wt%, and the content of inorganic ceramic particles was 0.8 wt%). The slurry was then hot-pressed at 120℃ to remove moisture and allowed to stand to remove air bubbles, resulting in a gel porous membrane with a thickness of 11 μm and a pore size of 1 μm to 8 μm.

[0109] 2. Secondary battery:

[0110] (1) The positive electrode active material (lithium nickel cobalt manganese oxide, LiNi) 0.81 Co 0.09 Mn 0.10 The negative electrode slurry is prepared by mixing O2, conductive agent (5% CNT carbon nanotubes and 95% carbon black), and binder (polyvinylidene fluoride) in a mass ratio of 97.5:1.5:1. It is then coated on copper foil, dried, rolled, cut into sheets, and slit to form the positive electrode.

[0111] (2) The bare cell is obtained by stacking and winding the silicon-based negative electrode, polypropylene separator, positive electrode, separator, and silicon-based negative electrode in sequence. The tabs are welded, and the bare cell is placed in the battery aluminum shell / soft-pack aluminum-plastic film, top-sealed, side-sealed, dried to remove moisture, electrolyte injected into the battery shell, top-sealed, formed, and determined to a certain capacity, thus obtaining a secondary battery.

[0112] Example 3

[0113] This embodiment provides a composite silicon-based negative electrode, its preparation method, and its application, as detailed below:

[0114] 1. Preparation method of composite silicon-based negative electrode:

[0115] (1) Conductive mesh layer: Carbon nanofibers with a particle size of 0.4μm to 1.9μm are sprayed onto the copper foil of the current collector through the negative electrode. The mesh carbon contains 3.5wt% of high molecular polymer, so that the mesh carbon adheres to the current collector of the negative electrode. After high temperature curing at 350℃ for 1h, a conductive mesh layer of 0.3μm to 6μm is obtained.

[0116] (2) A mixture of silicon-based anode material (bulk lithium-containing micron silicon oxide material, content of 15wt%) and graphite anode material (sheet artificial graphite, content of 85wt%), conductive material (5wt% CNT carbon nanotubes and 95wt% carbon black), and binder (20wt% sodium carboxymethyl cellulose, 20wt% styrene-butadiene rubber and 60wt% polyacrylic acid) in a mass ratio of 96.5:1.5:2 is mixed and stirred. Deionized water is added and stirred to adjust the viscosity to 2630 mPa·s to obtain anode coating. The anode coating is slowly injected into the funnel beaker above the vacuum filter. The vacuum filter is turned on to extract the air in the filter bottle. The anode coating in the funnel beaker flows through the pores on the gel porous membrane. Part of the anode coating adheres to the top and bottom of the gel porous membrane. The gel porous membrane is then covered on the anode current collector with a conductive mesh layer on one side in step (1).

[0117] (3) Apply the negative electrode coating onto the gel porous membrane, then cold press and cut to obtain a single-sided composite silicon-based negative electrode. Cover the other side with the gel porous membrane as in (2), then apply the negative electrode coating onto the gel porous membrane, then dry, roll, trim, cut into pieces and slit to obtain a double-sided composite silicon-based negative electrode.

[0118] The gel porous membrane was prepared by the following method: ① First, polyacrylic acid was dissolved in deionized water, and then a small amount of 11M concentrated sulfuric acid was added until the pH of the solution was adjusted to 2.7. Then, thiourea was added to the above solution and stirred, and dehydration condensation was carried out at 60°C (100 parts by mass of deionized water, 20 parts by mass of polyacrylic acid, and 4 parts by mass of thiourea) (reaction principle: the carboxyl group on polyacrylic acid and the amino group on thiourea undergo dehydration condensation to obtain an amide). ② Finally, the polyacrylic acid-thiourea copolymer precipitate was separated and added to a 4.5 wt% citric acid solution to obtain a gel. Then, inorganic ceramic particles (barium titanate) were added and mixed and stirred to obtain a homogenized slurry (the content of citric acid in the homogenized slurry was 1.7 wt%, the content of polyacrylic acid-thiourea copolymer precipitate was 35.1 wt%, and the content of inorganic ceramic particles was 1.2 wt%). The water was removed by hot pressing at 120℃, and the bubbles were removed by standing to obtain a gel porous membrane with a thickness of 12 μm and a pore size of 1 μm to 9 μm.

[0119] 2. Secondary battery:

[0120] (1) The positive electrode active material (lithium nickel cobalt manganese oxide, LiNi) 0.83 Co 0.11 Mn 0.06 The negative electrode slurry is prepared by mixing O2, conductive agent (5wt% CNT carbon nanotubes and 95wt% carbon black), and binder (polyvinylidene fluoride) in a mass ratio of 96:2:2. The slurry is coated on copper foil, dried, rolled, cut into sheets, and slit. The slits are then used to make the positive electrode.

[0121] (2) The bare cell is obtained by stacking and winding the silicon-based negative electrode, polypropylene separator, positive electrode, separator, and silicon-based negative electrode in sequence. The tabs are welded, and the bare cell is placed in the battery aluminum shell / soft-pack aluminum-plastic film, top-sealed, side-sealed, dried to remove moisture, electrolyte injected into the battery shell, top-sealed, formed, and determined to a certain capacity, thus obtaining a secondary battery.

[0122] Example 4

[0123] This embodiment provides a composite silicon-based negative electrode, its preparation method, and its application, as detailed below:

[0124] 1. Preparation method of composite silicon-based negative electrode:

[0125] (1) Conductive mesh layer: Carbon nanofibers with a particle size of 0.3μm to 1.7μm are sprayed onto the copper foil of the negative electrode current collector. The mesh carbon contains 6.0wt% of high molecular polymer, so that the mesh carbon adheres to the negative electrode current collector. After high temperature curing at 350℃ for 1h, a conductive mesh layer of 0.3μm to 6μm is obtained.

[0126] (2) The silicon-based negative electrode material (bulk micron silicon carbon material, content of 28wt%), graphite negative electrode material (sheet artificial graphite, content of 72wt%), conductive material (5wt% CNT carbon nanotubes and 95wt% conductive graphite), and binder (20wt% sodium carboxymethyl cellulose, 10wt% styrene-butadiene rubber and 70wt% polyacrylic acid) are mixed and stirred in a mass ratio of 93:3:4. Deionized water is added and stirred to adjust the viscosity to 2630mPa·s to obtain a negative electrode coating. The negative electrode coating is slowly injected into the funnel beaker above the vacuum filter. The vacuum filter is turned on to extract the air in the filter bottle. The negative electrode coating in the funnel beaker flows through the pores on the gel porous membrane. Part of the negative electrode coating adheres to the top and bottom of the gel porous membrane. Then the gel porous membrane is covered on the negative electrode current collector with a conductive mesh layer on one side in step (1).

[0127] (3) Apply the negative electrode coating onto the gel porous membrane, then cold press and cut to obtain a single-sided composite silicon-based negative electrode. Cover the other side with the gel porous membrane as in (2), then apply the negative electrode coating onto the gel porous membrane, then dry, roll, trim, cut into pieces and slit to obtain a double-sided composite silicon-based negative electrode.

[0128] The gel porous membrane was prepared by the following method: ① First, lithium polyacrylate was dissolved in deionized water, and then a small amount of 11M concentrated sulfuric acid was added until the pH of the solution was adjusted to 3.1. Then, thiourea was added to the above solution and stirred, and dehydration condensation was carried out at 85°C (100 parts by mass of deionized water, 50 parts by mass of polyacrylate, and 10 parts by mass of thiourea) (reaction principle: the carboxyl group on polyacrylate and the amino group on thiourea undergo dehydration condensation to obtain an amide). ② Finally, the polyacrylic acid-thiourea copolymer precipitate was separated and added to a 12wt% citric acid solution to obtain a gel. Then, inorganic ceramic particles (titanium dioxide) were added and mixed and stirred to obtain a homogenized slurry (the homogenized slurry contained 4.6wt% citric acid, 36.8wt% polyacrylic acid-thiourea copolymer precipitate, and 2.2wt% inorganic ceramic particles). The slurry was then hot-pressed at 135℃ to remove moisture and allowed to stand to remove air bubbles, resulting in a gel porous membrane with a thickness of 9μm and a pore size of 1μm to 7μm.

[0129] 2. Secondary battery:

[0130] (1) The positive electrode active material (lithium nickel cobalt manganese oxide, LiNi) 0.83 Co 0.11 Mn 0.06 The negative electrode slurry is prepared by mixing O2, conductive agent (5wt% CNT carbon nanotubes and 95wt% carbon black), and binder (polyvinylidene fluoride) in a mass ratio of 96:2:2. The slurry is coated on copper foil, dried, rolled, cut into sheets, and slit. The slits are then used to make the positive electrode.

[0131] (2) The bare cell is obtained by stacking and winding the silicon-based negative electrode, polypropylene separator, positive electrode, separator, and silicon-based negative electrode in sequence. The tabs are welded, and the bare cell is placed in the battery aluminum shell / soft-pack aluminum-plastic film, top-sealed, side-sealed, dried to remove moisture, electrolyte injected into the battery shell, top-sealed, formed, and determined to a certain capacity, thus obtaining a secondary battery.

[0132] Example 5:

[0133] This embodiment provides a composite silicon-based negative electrode, its preparation method, and its application, as detailed below:

[0134] 1. Preparation method of composite silicon-based negative electrode:

[0135] (1) Conductive mesh layer: Carbon nanofibers with a particle size of 0.3μm to 1.7μm are sprayed onto the copper foil of the negative electrode current collector. The mesh carbon contains 6.0wt% of high molecular polymer, so that the mesh carbon adheres to the negative electrode current collector. After high temperature curing at 350℃ for 1h, a conductive mesh layer of 0.3μm to 6μm is obtained.

[0136] (2) A mixture of silicon-based anode material (sheet-like and block-like micron-sized silicon-carbon material, content of 28wt%) and graphite anode material (sheet-like artificial graphite, content of 72wt%), conductive material (5wt% CNT carbon nanotubes and 95wt% conductive graphite), and binder (20wt% sodium carboxymethyl cellulose, 10wt% styrene-butadiene rubber and 70wt% polyacrylic acid) in a mass ratio of 93:3:4 is mixed and stirred. Deionized water is added and stirred to adjust the viscosity to 3100 mPa·s to obtain anode coating. The anode coating is slowly injected into the funnel beaker above the vacuum filter. The vacuum filter is turned on to extract the air in the filter bottle. The anode coating in the funnel beaker flows through the pores on the gel porous membrane. Part of the anode coating adheres to the top and bottom of the gel porous membrane. The gel porous membrane is then covered on the anode current collector with a conductive mesh layer on one side in step (1).

[0137] (3) Apply the negative electrode coating onto the gel porous membrane, then cold press and cut to obtain a single-sided composite silicon-based negative electrode. Cover the other side with the gel porous membrane as in (2), then apply the negative electrode coating onto the gel porous membrane, then dry, roll, trim, cut into pieces and slit to obtain a double-sided composite silicon-based negative electrode.

[0138] The gel porous membrane was prepared by the following method: ① First, lithium polyacrylate was dissolved in deionized water, and then a small amount of 11M concentrated sulfuric acid was added until the pH of the solution was adjusted to 3.1. Then, thiourea was added to the above solution and stirred, and dehydration condensation was carried out at 85°C (100 parts by mass of deionized water, 50 parts by mass of polyacrylate, and 10 parts by mass of thiourea). ② Finally, the polyacrylate-thiourea copolymer precipitate was separated and added to a 12wt% citric acid solution to obtain a gel. Inorganic ceramic particles (monaxyl oxide) were then added and mixed and stirred to obtain a homogenate (the homogenate contained 5.8wt% citric acid, 35.7wt% polyacrylate-thiourea copolymer precipitate, and 2.5wt% inorganic ceramic particles). The precipitate was hot-pressed at 135°C to remove water, and the bubbles were removed by standing to obtain a gel porous membrane with a thickness of 12μm and a pore size of 1μm to 9μm.

[0139] 2. Secondary battery:

[0140] (1) The positive electrode active material (lithium nickel cobalt manganese oxide, LiNi) 0.83 Co 0.11 Mn 0.06 O2, conductive agent (5wt% CNT carbon nanotubes and 95wt% carbon black), and binder (polyvinylidene fluoride) are mixed in a mass ratio of 96:2:2 to form a negative electrode slurry. This slurry is then coated onto copper foil, dried, rolled, cut into sheets, and slit to form a positive electrode.

[0141] (2) The bare cell is obtained by stacking and winding the silicon-based negative electrode, polypropylene separator, positive electrode, separator, and silicon-based negative electrode in sequence. The tabs are welded, and the bare cell is placed in the battery aluminum shell / soft-pack aluminum-plastic film, top-sealed, side-sealed, dried to remove moisture, electrolyte injected into the battery shell, top-sealed, formed, and determined to a certain capacity, thus obtaining a secondary battery.

[0142] Comparative Example 1:

[0143] The difference from Example 1 is that carbon nanofibers were not sprayed on the copper foil of the negative electrode current collector, and a conductive mesh layer was not designed.

[0144] Comparative Example 2:

[0145] The difference from Example 1 is that no gel porous membrane is set on the modified negative electrode current collector; only the negative electrode coating is coated on the copper foil of the negative electrode current collector.

[0146] Comparative Example 3:

[0147] The difference from Example 1 is that urea-sulfur was not added in the preparation of the gel porous membrane.

[0148] Example and comparative tests:

[0149] 1. Electrode resistance, electrode peeling force, and electrode surface condition:

[0150] The resistance of the negative electrode in each of Examples 1 to 5 and Comparative Examples 1 to 2 was measured using a resistance meter. The positive and negative terminals of the resistance meter were in contact with the negative electrodes of each of Examples 1 to 5 and Comparative Examples 1 to 2, and the resistance of the negative electrode was recorded.

[0151] The peel force of the negative electrodes of Examples 1-5 and Comparative Examples 1-2 was measured by a peel tester, and the peel force of the negative electrode coating on the negative electrode was measured at 180°C by double-sided adhesive.

[0152] Surface condition: The surface cracking of the secondary batteries in the examples and comparative examples was observed using scanning electron microscopy after 800 cycles on the negative electrode. The experimental results are shown in Table 1.

[0153] 2. Capacity retention during charge-discharge cycles of the secondary battery:

[0154] Using a charge-discharge testing system, the secondary battery was charged at a starting voltage of 2.8V and a cutoff voltage of 4.25V. It was then charged at 0.33C to the cutoff voltage, followed by constant voltage charging until the current was less than 0.05C. The battery was then discharged at 0.33C to the starting voltage, and then charged again at 0.33C to 4.25V. This process was repeated until the current was less than 0.05C. The capacity retention rate of the secondary battery during the 10th, 400th, and 800th charge-discharge cycles was calculated. The experimental results are shown in Table 2.

[0155] Table 1. Negative electrode details

[0156]

[0157] Table 2 Battery Capacity Retention Rate

[0158]

[0159]

[0160] As shown in Tables 1 and 2, the differences between Comparative Examples 1 and 3 and Example 1 are that Comparative Examples 1 and 3 did not have a conductive mesh layer with sprayed carbon nanofibers, a gel porous membrane, or urea-sulfur in the preparation of the gel porous membrane, respectively. This resulted in a significant increase in the internal resistance of the electrode sheets in each comparative example, and a decrease in the peel strength of the electrode sheets (Comparative Example 3 had even lower peel strength). The electrode sheets also showed more microcracks and more breakages. The capacity retention rate of the battery after 800 cycles also decreased more significantly. This indicates that the setting of a conductive mesh layer with sprayed carbon nanofibers, the setting of a gel porous membrane, and the addition of urea-sulfur in the preparation of the gel porous membrane in the present invention can improve the internal resistance and peel strength of the electrode sheets, reduce the cracking of the electrode sheets, and also improve the capacity retention rate and cycle stability of the battery.

[0161] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 did not use a gel porous membrane, resulting in increased internal resistance and decreased peel strength of the electrode sheet, particularly with numerous cracks and breakages. This demonstrates that the present invention, by incorporating a gel porous membrane, significantly improves the cracking of the electrode sheet, enhances the stability of the composite silicon anode structure, maintains a high capacity retention rate, and improves the cycle stability of the battery.

[0162] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A composite silicon-based negative electrode, characterized in that, It includes a conductive mesh layer, a plurality of gel porous membrane layers, and a negative electrode material active layer covering the gel porous membrane layers, which are sequentially disposed on at least one surface of the negative electrode current collector from the inside out; the surface of the gel porous membrane layer is coated with a negative electrode active coating; the gel porous membrane is a polymer-based gel porous membrane, comprising a polymer obtained by crosslinking polyacrylic acid with thiourea material.

2. The composite silicon-based negative electrode according to claim 1, characterized in that, At least one or more of the following conditions must be met: The thickness of the negative electrode current collector is 3–18 μm; The thickness of the conductive mesh layer is 0.1–12 μm; The thickness of the porous gel membrane is 1–12 μm; The thickness of the active layer of the negative electrode material is 30–260 μm.

3. A method for preparing a composite silicon-based negative electrode, characterized in that, Includes the following steps: A network of carbon containing a polymer is loaded onto at least one surface of the negative electrode current collector, and then heated to obtain a conductive network layer. A negative electrode coating is prepared by mixing negative electrode material, conductive material and binder in a solvent; A gel porous membrane is provided. A negative electrode coating is filtered by vacuum filtration using the gel porous membrane as a filter membrane, so that the negative electrode coating flows through the gel porous membrane to obtain a gel porous membrane with the negative electrode coating adhering to it. The gel porous membrane is a polymer-based gel porous membrane, comprising a polymer obtained by crosslinking polyacrylic acid with a thiourea material. A gel porous membrane with a negative electrode coating is coated on the conductive mesh layer to obtain a gel porous membrane layer. The negative electrode coating is applied to the surface of the porous gel membrane to form the active layer of the negative electrode material. The coating is then cold-pressed, dried, and rolled to obtain the composite silicon-based negative electrode.

4. The preparation method according to claim 3, characterized in that, At least one of the following conditions must be met: 1) The length of the network carbon is 0.02-2 μm; 2) Heating conditions: Heating temperature is 200-500℃, and time is 10-60 min; 3) The content of polymer in the polymer-containing network carbon is 1-8 wt%.

5. The preparation method according to claim 3, characterized in that, The network carbon is selected from one or more of carbon nanofibers, carbon microfibers, conductive carbon nanotubes, and graphite carbon micro / nanowires.

6. The preparation method according to claim 3, characterized in that, The negative electrode current collector is copper foil; the polymer is one or more of polytetrafluoroethylene, polypyrrole, polythiophene, polyethylene, polypropylene, polystyrene, polyacrylamide, and ethylene-propylene-diene copolymer resin.

7. The preparation method according to claim 3, characterized in that, The gel porous membrane was prepared by the following method: (1) Adjust the polyacrylic acid solution to acidity, add thiourea, heat to dehydrate and condense, and separate to obtain polyacrylic acid-thiourea copolymer precipitate; add to gelling agent solution to obtain gel; (2) Add inorganic ceramic particles to the gel in step (1), mix and stir to obtain a homogenous mixture, remove water by hot pressing, and remove air bubbles by standing to obtain a porous gel membrane.

8. The preparation method according to claim 3, characterized in that, The mass ratio of the negative electrode material, conductive material and binder is 85-99:0.2-8:0.2-10; The negative electrode material includes silicon-based negative electrode material and graphite negative electrode material; The graphite anode material has a content of 35wt% to 98wt% in the anode material.

9. The preparation method according to claim 3, characterized in that, The areal density of the negative electrode coating in the active layer of the negative electrode material is 40–350 g / m³. 2 .

10. A secondary battery, characterized in that, Includes the composite silicon-based negative electrode as described in claim 1 or 2, or the composite silicon-based negative electrode obtained by any one of claims 3-8.

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