Lithium-ion battery negative electrode assembly and preparation method thereof

Abstract

The present application relates to a kind of lithium ion battery negative electrode assembly and its preparation method.A kind of lithium ion battery negative electrode assembly includes current collector and the active material layer being arranged on the surface of current collector, and the active material layer includes the main body area and the thinning area of different thickness, and the thickness of thinning area is less than the thickness of main body area;The surface of thinning area is provided with functional layer, functional layer completely covers thinning area, and functional layer is level with the thickness of main body area in thickness direction;From the direction of active material layer to current collector, functional layer includes water-based adhesive layer and electrolyte layer being sequentially stacked on the surface of thinning area.The lithium ion battery negative electrode assembly of the present application constructs gradient functional layer by water-based adhesive layer and electrolyte layer sequentially superimposed on the surface of thinning area, two layers are formed integrated stable structure by molecular interpenetration in the process of co-curing, so as to be able to give consideration to environmental protection, have stable ion conduction and long-acting interface stability.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a lithium-ion battery negative electrode component and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles and energy storage. The negative electrode sheet is often thinned to accommodate welding and winding processes. However, due to the abrupt changes in thickness and pore structure in the thinned area, insufficient electrolyte wetting and obstructed ion transport can easily occur, affecting battery performance and safety.

[0003] To improve the performance of the thinned region, a functional layer is typically coated there, often using solvent-based systems based on materials such as PVDF-HFP. These systems rely on organic solvents like NMP, leading to issues such as high emissions, high recycling costs, and significant production safety risks. Solvent residues weaken interfacial bonding, affecting structural stability and the continuity of ion transport during long-term cycling. While aqueous slurries are widely used in electrode bulk coating, there is still a lack of ion transport design tailored to the pore structure and wetting kinetics of the thinned region, making it difficult to achieve both strong interfacial adhesion and efficient conduction.

[0004] Therefore, there is an urgent need in this field to develop a structure that can take into account environmental protection, stable ion conduction and long-term interface stability, improve the performance of the negative electrode thinning region and extend the battery cycle life. Summary of the Invention

[0005] Therefore, it is necessary to provide a lithium-ion battery anode component and its preparation method that can take into account environmental protection, stable ion conduction and long-term interface stability.

[0006] A lithium-ion battery negative electrode assembly includes: a current collector and an active material layer disposed on the surface of the current collector, the active material layer including a main region and a thinned region of different thicknesses, the thickness of the thinned region being less than the thickness of the main region;

[0007] A functional layer is provided on the surface of the thinning area, the functional layer completely covers the thinning area, and the thickness of the functional layer is flush with the thickness of the main body area in the thickness direction;

[0008] In the direction from the current collector to the active material layer, the functional layer includes an aqueous adhesive layer and an electrolyte layer sequentially stacked on the surface of the thinned area.

[0009] The lithium-ion battery anode assembly of this invention features a gradient functional layer constructed on the surface of the thinned region, consisting of a water-based binder layer and an electrolyte layer stacked sequentially. This functional layer utilizes the water-based binder layer to achieve tight wetting and strong bonding to the surface of the active material, while the electrolyte layer constructs a continuous, stable, and rapid ion transport channel, optimizing the current distribution in the thinned region and compensating for insufficient ions. The two layers form an integrated and stable structure through molecular interpenetration during the co-curing process. Furthermore, both layers are entirely aqueous, completely eliminating the use of organic solvents and their associated hazards. Overall, this allows the lithium-ion battery anode assembly of this invention to be environmentally friendly, possess stable ion conduction, and exhibit long-term interface stability.

[0010] In some embodiments, the aqueous adhesive layer comprises an aqueous adhesive and a nano-reinforcing material dispersed in the aqueous adhesive, wherein the mass ratio of the aqueous adhesive to the nano-reinforcing material is (20~40):(2~10).

[0011] In some embodiments, the nano-reinforcing material includes one or more of nanocellulose, nanocrystalline cellulose, carbon nanotubes, nanosilica, and graphene oxide.

[0012] In some embodiments, the electrolyte layer comprises a polymer matrix, a lithium salt, and a plasticizer, wherein the mass ratio of the polymer matrix, the lithium salt, and the plasticizer is (15~25):(8~15):(3~10).

[0013] In some embodiments, the polymer matrix includes one or more of polyvinyl alcohol, polyethylene oxide and its derivatives, aqueous dispersions of fluoropolymers, polyacrylonitrile and its copolymers, natural polymers and their derivatives, and synthetic water-soluble polymers.

[0014] In some embodiments, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium tetrafluoroborate.

[0015] In some embodiments, the thickness of the functional layer is 5 μm to 60 μm; wherein the dry thickness ratio of the aqueous adhesive layer to the electrolyte layer is 1:2 to 1:4.

[0016] A method for manufacturing a lithium-ion battery negative electrode component as described above includes the following steps:

[0017] Provide a negative electrode substrate with a main region and a thinned region;

[0018] Prepare a first slurry for forming an aqueous binder layer and a second slurry for forming an electrolyte layer;

[0019] A first wet film is formed by coating the surface of the thinned area with the first slurry, and then a second wet film is formed by coating the surface of the first wet film with the second slurry; and

[0020] The electrode coated with the first wet film and the second wet film is heat-treated to remove the solvent and form a functional layer.

[0021] The method for preparing the lithium-ion battery anode component according to the present invention has simple process steps and is easy to implement on existing electrode production lines. The key "wet film superposition coating" process allows the two slurry layers to permeate each other at the interface before curing, and after co-curing, they form an integrated gradient structure without a clear interface, resulting in stronger bonding.

[0022] In some embodiments, the first slurry comprises, by mass fraction: 20% to 40% aqueous binder, 2% to 10% nano-reinforcing material, and 50% to 70% first aqueous solvent; the second slurry comprises: 15% to 25% polymer matrix, 8% to 15% lithium salt, 3% to 10% plasticizer, and 50% to 65% second aqueous solvent.

[0023] The first aqueous solvent and the second aqueous solvent independently include one or more of deionized water, distilled water, ultrapure water, and a mixture of water and a water-soluble organic solvent; when a mixture of water and a water-soluble organic solvent is selected, the mass percentage of water in the mixture is not less than 70%.

[0024] The water-soluble organic solvent includes one or more of ethanol, isopropanol, ethylene glycol, and propylene glycol.

[0025] In some embodiments, the heat treatment is performed by hot air circulation curing at 60°C to 80°C for 10 to 15 minutes. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a lithium-ion battery negative electrode assembly according to an embodiment of the present invention.

[0027] Figure 2 This is a flowchart of a method for preparing a lithium-ion battery negative electrode assembly according to an embodiment of the present invention.

[0028] The markings in the diagram are as follows: 100 - Lithium-ion battery negative electrode component, 110 - Current collector, 120 - Active material layer, 121 - Main body region, 122 - Thinned region, 130 - Functional layer, 131 - Aqueous binder layer, 132 - Electrolyte layer. Detailed Implementation

[0029] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] The "dry thickness" used in this invention refers to the final thickness of each layer after the slurry is coated and the solvent is removed by heat treatment.

[0032] Please see Figure 1 A lithium-ion battery negative electrode assembly 100 according to one embodiment of the present invention includes: a current collector 110 and an active material layer 120 disposed on the surface of the current collector 110. The current collector 110 is a conductive substrate known in the art for lithium-ion battery negative electrodes, such as copper foil, copper alloy foil, three-dimensional porous copper current collector, or copper composite current collector, etc., and the present invention does not limit it.

[0033] The active material layer 120 includes a main region 121 and a thinned region 122 with different thicknesses, wherein the thickness of the thinned region 122 is less than the thickness of the main region 121.

[0034] In some embodiments, the active material layer 120 includes a negative electrode active material, which includes one or more of graphite, soft carbon, hard carbon, silicon-based materials (such as elemental silicon, silicon oxide, silicon-carbon composites), tin-based materials, lithium titanate and their composites, and the present invention does not impose specific limitations on this.

[0035] In some embodiments, the active material layer 120 further includes a conductive agent and a binder. The conductive agent provides an electronic conduction network and may include, for example, one or more of conductive carbon black, carbon nanotubes, graphene, and carbon fibers. The binder adheres the active material and the conductive agent to the current collector 110 and may include an aqueous binder or a solvent-based binder. In this invention, the active material layers 120 of the main region 121 and the thinned region 122 may have the same or different compositions and ratios.

[0036] It should be noted that the thinning region 122 is a region of reduced thickness formed along the length of the electrode, on one or both edges of the electrode width. The thinning region 122 may exist only on one edge of the electrode, or it may exist simultaneously on both symmetrical edges of the electrode; this invention does not limit this. Furthermore, in specific embodiments of this invention, the cross-sectional shape of the thinning region 122 is not limited and may be straight, arc-shaped, or stepped, etc. The formation of the thinning region 122 can be achieved through processes known in the art, such as laser etching, die-cutting, and mask coating. The width and depth of the thinning region 122 can be designed according to requirements such as tab welding, internal space optimization of the battery, or uniform ion distribution; for example, its width may be from 2 mm to 20 mm. The shape shown in the accompanying drawings is only one example and is not intended to limit the invention.

[0037] It should be noted that the thinning zone 122 may be a complete removal of the active material layer in the zone to partially expose the current collector 110 below, or it may retain a thinned active material layer. The present invention does not limit this.

[0038] Furthermore, in this embodiment, a functional layer 130 is provided on the surface of the thinned region 122. The functional layer 130 completely covers the thinned region 122, and the thickness of the functional layer 130 is flush with the thickness of the main body region 121 in the thickness direction. The functional layer 130 fills the thinned region 122, eliminating physical steps, which is beneficial for electrode flattening and battery assembly.

[0039] Furthermore, in this embodiment, in the direction from the current collector 110 to the active material layer 120, the functional layer 130 includes an aqueous adhesive layer 131 and an electrolyte layer 132 sequentially stacked on the surface of the thinned region 122. The electrolyte layer 132 is a solid electrolyte layer.

[0040] The lithium-ion battery negative electrode assembly 100 of this embodiment has a gradient functional layer 130 formed by sequentially stacking an aqueous binder layer 131 and an electrolyte layer 132 on the surface of the thinned region 122. The bottom aqueous binder layer 131 works synergistically with the top layer's high ion conductivity to reduce contamination while using aqueous solvents, thus solving the problems of weak interfacial bonding and poor ion transport in the thinned region 122 and improving the battery's cycle performance.

[0041] In some embodiments, the aqueous adhesive layer 131 includes an aqueous binder and nano-reinforcing materials dispersed in the aqueous binder, wherein the mass ratio of the aqueous binder to the nano-reinforcing materials is (20~40):(2~10). The aqueous binder provides the slurry with basic adhesive strength, rheological properties, and good bonding with the surface of the active material. The nano-reinforcing materials achieve strong interfacial adhesion and structural reinforcement; exemplarily, the nano-reinforcing materials are selected from nanomaterials with high aspect ratios or high specific surface areas.

[0042] In some embodiments, the waterborne binder includes one or more of cellulose-based binders, rubber-based elastic binders, polyacrylic acid (PAA) and its salts, polyvinyl alcohol (PVA), sodium alginate (SA), polyurethane (PU) emulsions, and acrylate emulsions. Cellulose-based binders include one or more of sodium carboxymethyl cellulose (CMC), potassium carboxymethyl cellulose, hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC), methyl cellulose (MC), microcrystalline cellulose, and nanocellulose. Rubber-based elastic binders include one or more of styrene-butadiene rubber (SBR) emulsions, carboxylated styrene-butadiene rubber emulsions, acrylonitrile rubber (NBR) emulsions, acrylate rubber (ACM) emulsions, styrene-butadiene-styrene block copolymer (SBS) latex, natural latex, and their modifiers. Using these established waterborne binders provides reliable adhesion, good slurry rheology, and compatibility with active material surfaces. For example, the CMC / SBR composite system combines the advantages of rigid bonding and elastic buffering, better adapting to cyclic stress.

[0043] In some embodiments, the nanoreinforcing materials include one or more of nanocellulose (CNF), nanocrystalline cellulose (CNC), carbon nanotubes (CNT), nano-silica, and graphene oxide (GO). Introducing these nanomaterials with high aspect ratios or high specific surface areas can form a three-dimensional reinforcing network in the aqueous binder layer, significantly improving the coating's mechanical strength, modulus, and toughness.

[0044] In some embodiments, the nanoreinforcing material is nanocellulose (CNF). Compared to other nanomaterials, nanocellulose has an extremely high aspect ratio and abundant surface hydroxyl groups, enabling it to self-assemble into a three-dimensional nanofiber network in aqueous slurry via hydrogen bonding. This network permeates the bonding system, enhancing the mechanical strength, modulus, and toughness of the dried coating. During coating and curing, nanocellulose partially embeds itself into the micropores and gaps of the underlying porous active material layer, physically locking the electrolyte layer and the active material together, improving interfacial peel strength, and solving the problem of interfacial weakening caused by residual organic solvent systems.

[0045] In some embodiments, the electrolyte layer 132 comprises a polymer matrix, a lithium salt, and a plasticizer, wherein the mass ratio of the polymer matrix, lithium salt, and plasticizer is (15~25):(8~15):(3~10). The polymer matrix is ​​a polymeric material that can dissolve or disperse in an aqueous solvent and form a gel film. It simultaneously functions as a film-forming framework and a binder, building a three-dimensional network to fix and transport lithium ions, and bonding firmly with the underlying aqueous adhesive layer through intermolecular forces during curing. The lithium salt is a water-stable lithium salt that does not undergo significant hydrolysis in the aqueous slurry or during subsequent curing. The plasticizer is used to insert between the molecular chains of the polymer matrix, weakening its crystallinity or intermolecular forces, thereby improving the flexibility and ionic conductivity of the cured electrolyte layer.

[0046] In some embodiments, the polymer matrix includes one or more of polyvinyl alcohol (PVA), polyethylene oxide (PEO) and its derivatives, aqueous dispersions of fluorinated polymers (such as polyvinylidene fluoride-hexafluoropropylene copolymer, PVDF-HFP), polyacrylonitrile (PAN) and its copolymers, natural polymers and their derivatives, and synthetic water-soluble polymers. The natural polymers and their derivatives include one or more of chitosan (CS) and sodium alginate (SA). The synthetic water-soluble polymers include one or more of polyvinylpyrrolidone (PVP), polyacrylic acid (PAA) and its salts, polyacrylamide (PAM), and polyhydroxyethyl methacrylate (PHEMA). These polymers can form films in an aqueous environment, constructing a three-dimensional network to accommodate and transport lithium ions. Polyvinyl alcohol (PVA) is preferred, as it possesses excellent film-forming properties, hydrophilicity, good compatibility with lithium salts, and its hydroxyl groups on its molecular chains can form strong hydrogen bonds with the underlying aqueous binder layer, promoting interfacial fusion.

[0047] In some embodiments, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiDFOB), and lithium tetrafluoroborate (LiBF4). Selecting these water-stable lithium salts ensures the retention of active lithium components throughout the water-based processing system, preventing corrosion of equipment, damage to the polymer matrix, or harm to the electrode interface due to acidic substances generated by hydrolysis. It also ensures a high and stable effective lithium ion carrier concentration in the cured electrolyte layer, thereby achieving excellent and stable ionic conductivity. The scope of protection of this invention is not limited to the lithium salts listed above; any lithium salt that is water-stable and achieves the objectives of this invention falls within the scope of protection of this invention.

[0048] In some embodiments, the plasticizer is a water-soluble polyol, oligoether compound, or sugar alcohol. Exemplarily, the plasticizer includes one or more of glycerol, ethylene glycol, propylene glycol, polyethylene glycol, sorbitol, and xylitol. The addition of the plasticizer can insert into the polymer molecular chains, weakening interchain forces and crystallinity, increasing chain mobility, thereby significantly improving the flexibility and ionic conductivity of the cured electrolyte layer.

[0049] In some embodiments, the thickness h2 of the functional layer 130 is 5 μm to 60 μm, and the thickness h1 of the active material layer 120 of the main body region 121 can be 30 μm to 60 μm. It should be noted that, unless otherwise specified, the thicknesses h1 and h2 mentioned in this invention refer to the final dry thickness after the electrode preparation is completed. Further, the thickness h1 of the active material layer 120 of the main body region 121 can be, but is not limited to, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, or 60 μm, and any value therein; the thickness h2 of the functional layer 130 can be, but is not limited to, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, or 60 μm, and any value therein.

[0050] In some embodiments, the dry thickness ratio (h3:h4) of the aqueous binder layer 131 to the electrolyte layer 132 is 1:2 to 1:4. By controlling the thickness ratio of the aqueous binder layer 131 to the electrolyte layer 132 within the range of 1:2 to 1:4, sufficient interfacial anchoring depth is ensured while avoiding overall obstruction to ion transport. This synergistically achieves the goals of long-term interfacial stability and efficient ion conduction, and avoids the volatile organic compound emissions, production costs, and safety hazards associated with traditional organic solvent processes.

[0051] When the thickness ratio of the aqueous binder layer 131 to the electrolyte layer 132 is close to 1:2, the aqueous binder layer 131 can provide more sufficient interfacial anchoring material, ensuring a strong bond between the functional layer and the active material layer 120, resulting in excellent interfacial stability. This is more suitable for applications with high requirements for cycle life and safety.

[0052] When the thickness ratio of the aqueous binder layer 131 to the electrolyte layer 132 is close to 1:4, the ion conduction layer is thicker, providing a more abundant and low-resistance bulk transport path for lithium ions, optimizing ion transport efficiency and reducing interface impedance. This makes it more suitable for applications that require high-rate and fast-charging performance.

[0053] Deviations from the above preferred range may lead to performance imbalances. If the aqueous binder layer 131 is too thick and the electrolyte layer 132 is relatively insufficient (less than 1:2), the interface bonding is strong, but the ion conduction capacity may become a bottleneck, the overall battery impedance increases, and the rate performance is limited. If the aqueous binder layer 131 is too thin and the electrolyte layer 132 is too thick (greater than 1:4), the interface anchoring effect may be insufficient, and there is a risk of interface delamination under long-term cycling. At the same time, an excessively thick gel layer may affect mechanical stability due to increased internal stress.

[0054] In some embodiments, the dry thickness ratio of the aqueous adhesive layer 131 to the electrolyte layer 132 may be, but is not limited to, 1:2, 1:3, or 1:4, as well as specific values ​​between the aforementioned point values.

[0055] In some embodiments, both surfaces of the current collector 110 are provided with an active material layer 120, and both surfaces of the active material layer 120 include a thinning region 122, and both surfaces of the thinning region 122 are provided with a functional layer 130.

[0056] The lithium-ion battery anode module of this invention features a gradient functional layer constructed on the surface of the thinned region, consisting of a water-based binder layer and an electrolyte layer stacked sequentially, with the dry-state thickness ratio of the water-based binder layer to the electrolyte layer controlled between 1:2 and 1:4. This functional layer utilizes the water-based binder layer to achieve tight wetting and strong bonding to the surface of the active material; the introduction of nano-reinforcing materials forms a physical anchoring network, which, combined with the elasticity of the binder system, ensures the integrity of the interface under long-term cycling and mechanical stress. The electrolyte layer constructs a continuous, stable, and rapid ion transport channel, optimizing the current distribution in the thinned region and compensating for insufficient ions. The two layers form an integrated and stable structure through molecular interpenetration during the co-curing process. Furthermore, both layers are entirely aqueous systems, completely eliminating the use of organic solvents and their associated hazards. By optimizing the thickness ratio of the water-based binder layer to the electrolyte layer, this invention achieves a balance between interface anchoring strength and ion transport efficiency, providing a lithium-ion battery anode module that combines environmental friendliness, long-term interface stability, and high-efficiency ion conduction.

[0057] Please see Figure 2 A method for preparing a lithium-ion battery negative electrode assembly according to an embodiment of the present invention includes the following steps:

[0058] S10, Provide a negative electrode substrate with a main region and a thinning region.

[0059] This step aims to prepare a negative electrode substrate with specific structural characteristics. Specifically, it involves coating an active material layer on the current collector surface and forming a thinned region with a thickness less than the main body region at the electrode edge or designated area by means of laser etching, mechanical polishing, or printing.

[0060] Preferably, the surface of the thinned area is pretreated, for example by ultrasonic cleaning, before the functional layer is coated, to remove surface dust, improve wettability, and enhance interfacial bonding activity, providing a clean and activated substrate for the subsequent coating of the functional layer. Optionally, the pretreatment operation is as follows: ultrasonic cleaning for 15 to 25 seconds at a power of 200 to 400 W.

[0061] S20. Prepare a first slurry for forming an aqueous binder layer and a second slurry for forming an electrolyte layer.

[0062] This step involves the preparation of two types of functional slurries. The first slurry is composed of an aqueous binder, nano-reinforcing materials, and a first aqueous solvent mixed in a specific mass ratio, and dispersed at 2000-4000 rpm for 30-60 minutes to form a homogeneous and stable system, ensuring good coatability and interfacial penetration. The second slurry consists of a polymer matrix, lithium salt, plasticizer, and a second aqueous solvent, which is stirred and mixed to form a homogeneous solution or dispersion, aiming to construct a gel precursor with ion-conducting properties. Both types of slurries are entirely aqueous systems, environmentally friendly, and have good process compatibility.

[0063] In some embodiments, the first slurry comprises, by mass fraction: 20% to 40% aqueous binder, 2% to 10% nano-reinforcing material and 50% to 70% first aqueous solvent; the second slurry comprises: 15% to 25% polymer matrix, 8% to 15% lithium salt, 3% to 10% plasticizer and 50% to 65% second aqueous solvent.

[0064] The first aqueous solvent and the second aqueous solvent refer to solvent systems with water as the main component.

[0065] In some embodiments, the first aqueous solvent and the second aqueous solvent independently include one or more of deionized water, distilled water, ultrapure water, and a mixed solvent of water and a water-soluble organic solvent; when the mixed solvent includes water and a water-soluble organic solvent, the mass percentage of water in the mixed solvent is not less than 70%.

[0066] The water-soluble organic solvents include one or more of ethanol, isopropanol, ethylene glycol, and propylene glycol.

[0067] Preferably, the first aqueous solvent and the second aqueous solvent are the same, which can ensure the formation of a seamless, integrated gradient structure during the curing process.

[0068] S30. A first slurry is coated on the surface of the thinned area to form a first wet film, and then a second slurry is superimposed on the surface of the first wet film to form a second wet film.

[0069] This step employs a sequential overlay coating process. First, a first slurry is precisely coated onto the thinned area to form a uniform bottom wet film. Then, while the bottom wet film is still uncured, a second slurry is immediately overlaid to form an upper wet film. The coating method is selected from blade coating, slot coating, and spraying to ensure uniform coating thickness. This "sequential wet film overlay" coating method facilitates the mutual penetration and fusion of the two slurry layers at the interface, promoting the formation of an integrated gradient structure during subsequent co-curing, and enhancing interlayer bonding and structural continuity.

[0070] S40. The electrode coated with the first wet film and the second wet film is heat-treated to remove the solvent and form a functional layer.

[0071] This step involves a gentle heat treatment to co-cur the two wet films. Under set temperature and time conditions, moisture and other volatile components are gradually removed, while the polymer components undergo gelation or cross-linking. The nano-reinforcing materials interact with the bonding system, the polymer matrix, and the lithium salt, ultimately forming a stable two-layer composite functional layer on the surface of the thinned area, which combines strong adhesion and high ionic conductivity, with a total thickness equal to that of the main area.

[0072] In some embodiments, the heat treatment operation involves hot air circulation curing at 60°C to 80°C for 10 to 15 minutes. Further, the heat treatment temperature may be, but is not limited to, 60°C, 65°C, 70°C, 75°C, or 80°C, or specific values ​​between these values; the curing time may be, but is not limited to, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, or 15 minutes, or specific values ​​between these values.

[0073] After step S40, the process may further include cutting the cured electrode sheet.

[0074] This step involves slitting the continuous electrode sheet that has undergone functional layer coating and curing to obtain a single negative electrode module that meets the size requirements for battery assembly. Care must be taken during the cutting process to protect the functional layer area from damage and ensure the structural integrity of the thinned area and the functional layer, thereby guaranteeing the performance consistency of the negative electrode module in subsequent battery manufacturing and use.

[0075] The method for preparing the lithium-ion battery anode component according to the present invention has simple process steps and is easy to implement on existing electrode production lines. The key "wet film superposition coating" process allows the two slurry layers to permeate each other at the interface before curing, and after co-curing, they form an integrated gradient structure without a clear interface, resulting in stronger bonding.

[0076] One embodiment of the battery includes any of the lithium-ion battery negative electrode components described above.

[0077] Furthermore, the battery is a lithium-ion battery. Specifically, the lithium-ion battery typically also includes a positive electrode, a separator, an electrolyte, and a battery casing.

[0078] The battery incorporating the negative electrode component of this invention has excellent interface stability and ion transport efficiency in its thinned region, thereby significantly improving the overall cycle life, rate performance and safety of the battery, especially under harsh conditions such as high temperature and long cycle.

[0079] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0080] Preparation of negative electrode substrate:

[0081] Graphite + 3% silicon-carbon anode active material (96% by mass), conductive agent conductive carbon black SP (1%), and binder CMC (3%) were added to deionized water as solvent and stirred evenly to obtain anode slurry. The above anode slurry was coated on a 6μm copper foil and dried. The thickness of the dry active material layer was 45μm. Laser etching was performed on the edge of the copper foil in the width direction to form a 5mm wide thinning area. The thinning area was ultrasonically cleaned for 20 seconds at a power of 300W.

[0082] The above-described negative electrode substrate was used in both the examples and comparative examples.

[0083] Example 1

[0084] A first slurry for forming an aqueous adhesive layer and a second slurry for forming an electrolyte layer were prepared respectively.

[0085] First slurry: by mass percentage, it includes 30% water-based binder (25% sodium carboxymethyl cellulose + 5% styrene-butadiene rubber), 5% nanocellulose, and 65% deionized water. After mixing, it is dispersed at 3000 r / min for 20 min to obtain a uniform slurry.

[0086] The second slurry, by mass percentage, includes 20% polyvinyl alcohol, 12% lithium bis(trifluoromethanesulfonyl)imide, 5% glycerol, and 63% deionized water. After mixing, it is stirred at a low speed of 1000 r / min for 10 min to obtain a uniform slurry.

[0087] A first slurry is applied to the surface of the thinned area to form a first wet film; then a second slurry is applied over the first wet film to form a second wet film. By controlling the amount of the first and second slurries applied, the functional layer formed after drying completely covers and fills the thinned area, making its surface level with the thickness of the adjacent non-thinned area.

[0088] The coated electrode was placed in a 65°C hot air circulating oven for 12 minutes to cure, remove the solvent, and gel the components, forming an integrated functional layer consisting of an aqueous binder layer and an electrolyte layer on the surface of the thinned area. After curing, the thickness of the aqueous binder layer was 1.5 μm, the thickness of the electrolyte layer was 4.5 μm, and the thickness ratio of the two layers was 1:3.

[0089] Example 2

[0090] A first slurry for forming an aqueous adhesive layer and a second slurry for forming an electrolyte layer were prepared respectively.

[0091] First slurry: by mass percentage, it includes 30% water-based binder (25% sodium carboxymethyl cellulose + 5% styrene-butadiene rubber), 5% cellulose nanocrystals (CNC), and 65% deionized water. After mixing, it is dispersed at 3000 r / min for 20 min to obtain a uniform slurry.

[0092] The second slurry, by mass percentage, includes 20% polyvinyl alcohol, 12% lithium bis(trifluoromethanesulfonyl)imide, 5% glycerol, and 63% deionized water. After mixing, it is stirred at a low speed of 1000 r / min for 10 min to obtain a uniform slurry.

[0093] A first slurry is applied to the surface of the thinned area to form a first wet film; then a second slurry is applied over the first wet film to form a second wet film. By controlling the amount of the first and second slurries applied, the functional layer formed after drying completely covers and fills the thinned area, making its surface level with the thickness of the adjacent non-thinned area.

[0094] The coated electrode was placed in a 65°C hot air circulating oven for 12 minutes to cure, remove the solvent, and gel the components, forming an integrated functional layer consisting of an aqueous binder layer and an electrolyte layer on the surface of the thinned area. After curing, the thickness of the aqueous binder layer was 1.5 μm, the thickness of the electrolyte layer was 4.5 μm, and the thickness ratio of the two layers was 1:3.

[0095] Example 3

[0096] A first slurry for forming an aqueous adhesive layer and a second slurry for forming an electrolyte layer were prepared respectively.

[0097] First slurry: by mass percentage, it includes 30% water-based binder (25% sodium carboxymethyl cellulose + 5% styrene-butadiene rubber), 5% nanocellulose, and 62% deionized water. After mixing, it is dispersed at 3000 r / min for 20 min to obtain a uniform slurry.

[0098] The second slurry, by mass percentage, includes 20% polyethylene oxide (PEO), 12% lithium bis(trifluoromethanesulfonyl)imide, 5% glycerol, and 63% deionized water. After mixing, it is stirred at a low speed of 1000 r / min for 10 min to obtain a uniform slurry.

[0099] A first slurry is applied to the surface of the thinned area to form a first wet film; then a second slurry is applied over the first wet film to form a second wet film. By controlling the amount of the first and second slurries applied, the functional layer formed after drying completely covers and fills the thinned area, making its surface level with the thickness of the adjacent non-thinned area.

[0100] The coated electrode was placed in a 65°C hot air circulating oven for 12 minutes to cure, remove the solvent, and gel the components, forming an integrated functional layer consisting of an aqueous binder layer and an electrolyte layer on the surface of the thinned area. After curing, the thickness of the aqueous binder layer was 1.5 μm, the thickness of the electrolyte layer was 4.5 μm, and the thickness ratio of the two layers was 1:3.

[0101] Example 4

[0102] A first slurry for forming an aqueous adhesive layer and a second slurry for forming an electrolyte layer were prepared respectively.

[0103] First slurry: by mass percentage, it includes 30% water-based binder (25% sodium carboxymethyl cellulose + 5% styrene-butadiene rubber), 5% nanocellulose, and 65% deionized water. After mixing, it is dispersed at 3000 r / min for 20 min to obtain a uniform slurry.

[0104] The second slurry, by mass percentage, includes 20% polyvinyl alcohol, 12% lithium bis(trifluoromethanesulfonyl)imide, 5% glycerol, and 63% deionized water. After mixing, it is stirred at a low speed of 1000 r / min for 10 min to obtain a uniform slurry.

[0105] A first slurry is applied to the surface of the thinned area to form a first wet film; then a second slurry is applied over the first wet film to form a second wet film. By controlling the amount of the first and second slurries applied, the functional layer formed after drying completely covers and fills the thinned area, making its surface level with the thickness of the adjacent non-thinned area.

[0106] The coated electrode was placed in a 65°C hot air circulating oven for 12 minutes to cure, remove the solvent, and gel the components, forming an integrated functional layer consisting of an aqueous binder layer and an electrolyte layer on the surface of the thinned area. After curing, the thickness of the aqueous binder layer was 2 μm, the thickness of the electrolyte layer was 4 μm, and the thickness ratio of the two layers was 1:2.

[0107] Example 5

[0108] A first slurry for forming an aqueous adhesive layer and a second slurry for forming an electrolyte layer were prepared respectively.

[0109] First slurry: by mass percentage, it includes 30% water-based binder (25% sodium carboxymethyl cellulose + 5% styrene-butadiene rubber), 5% nanocellulose, and 65% deionized water. After mixing, it is dispersed at 3000 r / min for 20 min to obtain a uniform slurry.

[0110] The second slurry, by mass percentage, includes 20% polyvinyl alcohol, 12% lithium bis(trifluoromethanesulfonyl)imide, 5% glycerol, and 63% deionized water. After mixing, it is stirred at a low speed of 1000 r / min for 10 min to obtain a uniform slurry.

[0111] A first slurry is applied to the surface of the thinned area to form a first wet film; then a second slurry is applied over the first wet film to form a second wet film. By controlling the amount of the first and second slurries applied, the functional layer formed after drying completely covers and fills the thinned area, making its surface level with the thickness of the adjacent non-thinned area.

[0112] The coated electrode was placed in a 65°C hot air circulating oven for 12 minutes to cure, remove the solvent, and gel the components, forming an integrated functional layer consisting of an aqueous binder layer and an electrolyte layer on the surface of the thinned area. After curing, the thickness of the aqueous binder layer was 1.2 μm, the thickness of the electrolyte layer was 4.8 μm, and the thickness ratio of the two layers was 1:4.

[0113] Example 6

[0114] A first slurry for forming an aqueous adhesive layer and a second slurry for forming an electrolyte layer were prepared respectively.

[0115] First slurry: by mass percentage, it includes 30% water-based binder (25% sodium carboxymethyl cellulose + 5% styrene-butadiene rubber), 5% nanocellulose, and 65% deionized water. After mixing, it is dispersed at 3000 r / min for 20 min to obtain a uniform slurry.

[0116] The second slurry, by mass percentage, includes 20% polyvinyl alcohol, 12% lithium bis(trifluoromethanesulfonyl)imide, 5% glycerol, and 63% deionized water. After mixing, it is stirred at a low speed of 1000 r / min for 10 min to obtain a uniform slurry.

[0117] A first slurry is applied to the surface of the thinned area to form a first wet film; then a second slurry is applied over the first wet film to form a second wet film. By controlling the amount of the first and second slurries applied, the functional layer formed after drying completely covers and fills the thinned area, making its surface level with the thickness of the adjacent non-thinned area.

[0118] The coated electrode was placed in a 65°C hot air circulating oven for 12 minutes to cure, remove the solvent, and gel the components, forming an integrated functional layer consisting of an aqueous binder layer and an electrolyte layer on the surface of the thinned area. After curing, the thickness of the aqueous binder layer was 3 μm, the thickness of the electrolyte layer was 3 μm, and the thickness ratio of the two layers was 1:1.

[0119] Comparative Example 1

[0120] No functional layer is coated on the negative electrode thinning region.

[0121] Comparative Example 2

[0122] The thinned area is coated only with the water-based adhesive layer of the formulation in Example 1. After drying, the water-based adhesive layer completely covers and fills the thinned area, and its surface is level with the thickness of the adjacent main body area.

[0123] Comparative Example 3

[0124] The thinned area is coated only with the electrolyte layer of the formulation in Example 1. After drying, the water-based adhesive layer completely covers and fills the thinned area, and its surface is level with the thickness of the adjacent main area.

[0125] Comparative Example 4

[0126] 10 wt% PVDF-HFP and 10 wt% LiTFSI were added to 80 wt% NMP solvent, mixed, and dispersed at 3000 r / min for 20 min to obtain a uniform slurry. This slurry was then coated onto a thinned area of ​​the negative electrode substrate, with a dry thickness controlled at 6 μm. Subsequently, it was dried at 90 °C under vacuum for 12 hours to remove the solvent.

[0127] Battery manufacturing:

[0128] Preparation of the positive electrode: NCM622, conductive carbon black (SP), and binder PVDF are added to solvent NMP in a mass ratio of 97%:1.8%:1.2%. After mixing, the mixture is coated onto aluminum foil using a coating machine, dried, and rolled to obtain the positive electrode.

[0129] Diaphragm: PE diaphragm is selected.

[0130] The positive electrode, separator, and negative electrode sheets prepared in the above steps were wound together, sealed with electrolyte (1M LiPF6 in EC:DEC=1:1 v / v electrolyte), assembled into a battery, and tested.

[0131] Performance testing:

[0132] The batteries assembled from the negative electrode sheets of Examples 1-6 and Comparative Examples 1-4 were subjected to performance tests. The test methods are as follows, and the test results are shown in Table 1.

[0133] (1) Test method for peel strength

[0134] Cut the prepared negative electrode sheet (including the thinned area and functional layer) into strips 25.0 ± 0.2 mm wide and at least 150 mm long. Cut a 100 mm long piece of high-strength double-sided adhesive tape, peel off the protective film on one side, and smoothly paste it onto the center of a standard steel plate. Roll it unidirectionally three times with a pressure roller at a speed of approximately 300 mm / min to ensure there are no air bubbles between the tape and the steel plate and that it is firmly adhered. Peel off the protective film on the other side of the double-sided adhesive tape. With the active material layer (including the functional layer) of the negative electrode sheet sample facing down, precisely align and smoothly paste it onto the exposed surface of the double-sided adhesive tape. Ensure that the electrode sheet is in complete contact with the tape, and leave sufficient length (approximately 50 mm) at the current collector end for clamping. Roll it back and forth three times with a standard 2 kg roller to provide constant and sufficient pressure. The sample with the adhesive tape applied is vertically fixed to a rigid plate with the free end of the tape facing upwards, leaving the end to be peeled (approximately 20 mm) suspended in the air. The prepared sample plate is then fixed to the base of the testing machine. The free end of the tape is carefully clamped into the upper clamp of the testing machine, ensuring a secure and centered grip. The testing program is started, and the upper clamp moves upwards at a constant speed (300 mm / min), peeling the tape along with its adhered functional layer from the negative electrode substrate. Peeling continues for at least 100 mm, and the force (F) during the peeling process is recorded in real time. From the force-displacement curve, the initial and final 20 mm data are discarded, and the average peeling force F_avg (unit: N) of the stable peeling section (approximately 60 mm) is taken.

[0135] Calculate the peel strength (σ, unit: N / m):

[0136] σ = F_avg / w

[0137] Where: F_avg is the average peel force (N), and w is the sample width (0.025 m).

[0138] (2) Battery cycle test method:

[0139] Test temperature: 45℃±2℃

[0140] ① Charge at 1C to the termination voltage (4.4V), cut-off current 0.05C, and let stand for 30 minutes;

[0141] ② Discharge at 1C to the final discharge voltage (2.8V), and let stand for 30 minutes;

[0142] Repeat cycles ① to ②, record the discharge capacity from the 1st to the 5th cycle, and calculate the arithmetic mean as the initial discharge capacity;

[0143] Continue the cycle until the 500th cycle, and record the discharge capacity of the 500th cycle;

[0144] Battery capacity retention rate after 500 cycles = discharge capacity of the 500th cycle / initial discharge capacity * 100%.

[0145] (3) Battery cycle interface peel strength test:

[0146] After cycling, the battery was disassembled in a glove box (filled with argon gas, with a water and oxygen content <0.1 ppm). The negative electrode was carefully removed and immersed in a sufficient amount of anhydrous dimethyl carbonate (DMC) solvent, gently agitated for 30 seconds to remove residual electrolyte and soluble by-reaction products. The cleaned electrode was then allowed to air dry at room temperature in the glove box. Following the pre-cycle peel strength test method, strip samples with a width of 25.0 mm and a length of at least 150 mm were cut from the corresponding location of the thinned area of ​​the electrode for testing.

[0147] Table 1 Performance test results of the examples and comparative examples

[0148]

[0149] The experimental data in Table 1 show that:

[0150] (1) The cycling capacity retention of all embodiments (bilayer) was significantly higher than that of Comparative Example 2 (adhesive layer only) and Comparative Example 3 (electrolyte layer only). Comparative Example 3 had extremely poor interfacial bonding and Comparative Example 2 had insufficient ion conduction, demonstrating the indispensability of the bilayer synergistic design of the present invention.

[0151] (2) Example 1 is superior to Comparative Example 4 (organic solvent system) in terms of cycle retention rate and post-cycle interface strength, which verifies the core technical advantages of the all-water system in solving the interface residual weakening and achieving long-term stability.

[0152] (3) Examples 1, 4, and 5 (thickness ratios of 1:3, 1:2, and 1:4, respectively) all exhibited excellent overall performance. Although Example 6 (thickness ratio of 1:1) had the highest initial and post-cycle peel strength, its capacity retention rate decreased relatively. This indicates that when the aqueous adhesive layer is too thick, although the interfacial bonding is stronger, the relatively thin electrolyte layer limits the efficiency of ion transport, resulting in a decrease in long-term capacity retention. This demonstrates the importance of controlling the thickness ratio between 1:2 and 1:4 for balancing performance.

[0153] This invention eliminates the use of organic solvents through an all-aqueous system, avoiding the environmental, safety, and interfacial residue hazards they pose. A strong interface is achieved through an aqueous binder layer containing nano-reinforced materials, solving the problem of weak interfacial bonding in traditional systems. A continuous ion channel is constructed through an electrolyte layer, which, in synergy with the aqueous binder layer, compensates for insufficient ion transport caused by abrupt changes in thickness in the thinned region.

[0154] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0155] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A lithium-ion battery negative electrode assembly, characterized in that, include: A current collector and an active material layer disposed on the surface of the current collector, the active material layer comprising a main region and a thinned region of different thicknesses, wherein the thickness of the thinned region is less than the thickness of the main region; A functional layer is provided on the surface of the thinning area, the functional layer completely covers the thinning area, and the thickness of the functional layer is flush with the thickness of the main body area in the thickness direction; In the direction from the current collector to the active material layer, the functional layer includes an aqueous adhesive layer and an electrolyte layer sequentially stacked on the surface of the thinned area; The water-based adhesive layer includes a water-based adhesive and a nano-reinforcing material dispersed in the water-based adhesive, wherein the mass ratio of the water-based adhesive to the nano-reinforcing material is (20~40):(2~10). The nano-reinforcing material includes one or more of nanocellulose, carbon nanotubes, nanosilica, and graphene oxide; The electrolyte layer comprises a polymer matrix, a lithium salt, and a plasticizer, wherein the mass ratio of the polymer matrix, the lithium salt, and the plasticizer is (15~25):(8~15):(3~10). The polymer matrix includes one or more of polyvinyl alcohol, polyethylene oxide and its derivatives, aqueous dispersions of fluoropolymers, polyacrylonitrile and its copolymers, and natural polymers and their derivatives.

2. The lithium-ion battery negative electrode assembly according to claim 1, characterized in that, The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium tetrafluoroborate.

3. The lithium-ion battery negative electrode assembly according to claim 1, characterized in that, The thickness of the functional layer is 5μm~60μm; The dry thickness ratio of the aqueous adhesive layer to the electrolyte layer is 1:2 to 1:

4.

4. A method for manufacturing a lithium-ion battery negative electrode assembly as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Provide a negative electrode substrate with a main region and a thinned region; Prepare a first slurry for forming an aqueous binder layer and a second slurry for forming an electrolyte layer; The first slurry is coated onto the surface of the thinned area to form a first wet film, and then the second slurry is coated onto the surface of the first wet film to form a second wet film; as well as The electrode coated with the first wet film and the second wet film is heat-treated to remove the solvent and form a functional layer.

5. The method for manufacturing a lithium-ion battery negative electrode assembly according to claim 4, characterized in that, The first slurry comprises, by mass fraction: 20% to 40% aqueous binder, 2% to 10% nano-reinforcing material and 50% to 70% first aqueous solvent; the second slurry comprises: 15% to 25% polymer matrix, 8% to 15% lithium salt, 3% to 10% plasticizer and 50% to 65% second aqueous solvent. Wherein, the first aqueous solvent and the second aqueous solvent independently include one or more of the following: deionized water, distilled water, ultrapure water, and a mixture of water and a water-soluble organic solvent; when a mixture of water and a water-soluble organic solvent is selected, the mass percentage of water in the mixture is not less than 70%; The water-soluble organic solvent includes one or more of ethanol, isopropanol, ethylene glycol, and propylene glycol.

6. The method for manufacturing a lithium-ion battery negative electrode assembly according to claim 4, characterized in that, The heat treatment process involves hot air circulation curing at 60℃~80℃ for 10 to 15 minutes.

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