Negative electrode and method for manufacturing the same, and electric device

Abstract

The embodiment of the application discloses a negative electrode and a preparation method thereof and an electric device. The negative electrode comprises a current collector and an active material layer arranged on at least one side of the current collector. The active material layer comprises a main body area and a thinned area at an end. The negative electrode further comprises a composite structure layer covering and adhering to the surface of the thinned area. The composite structure layer comprises a conductive enhancement layer and a gradient electrolyte layer which are sequentially combined along the thickness direction of the active material layer and gradually away from the current collector. The gradient electrolyte layer comprises lithium salt. The concentration of the lithium salt in the gradient electrolyte layer linearly increases away from the conductive enhancement layer. The conductive enhancement layer and the gradient electrolyte layer along the thickness direction of the active material layer and gradually away from the current collector are covered and adhered to the thinned area. The charge transport kinetics of the region is optimized, a continuous ion driving force is formed during large-current charging, the ion flux and the electron flux are matched, lithium precipitation is effectively inhibited, the fast-charging capacity retention rate of the battery is improved, and the cost is reduced.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a negative electrode and its preparation method, and an electrical device thereof. Background Technology

[0002] With the increasing market demand for fast charging technology, battery charging performance faces challenges. In actual production, to meet battery packaging and safety requirements, the edge of the negative electrode is usually designed with a thinned region, where the areal density of active material is lower than that of the non-thinned region. During high-current charging, the ion flux in the thinned region is insufficient, and lithium ions cannot be inserted in time, leading to lithium deposition on the negative electrode surface and impairing the battery's cycle life.

[0003] Currently, existing technologies improve battery fast-charging performance by optimizing the electrolyte; however, these methods do not address the specific thinned region. Furthermore, using high-concentration lithium salts across the entire electrode increases material costs and triggers other interfacial side reactions. In addition, traditional conductive additives such as graphene exhibit solvent agglomeration in localized areas, leading to uneven ion and electron conduction and failing to address the performance degradation problem in the thinned region at high rates.

[0004] Therefore, it is necessary to develop a composite electrolyte solution that can adapt to the thinned negative electrode region to solve the problems of lithium plating and performance degradation of batteries under fast charging conditions. Summary of the Invention

[0005] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a negative electrode and its preparation method, as well as an electrical device, to realize a composite electrolyte scheme that can adapt to the thinned region of the negative electrode, and solve the problems of lithium plating and performance degradation of batteries under fast charging conditions.

[0006] In a first aspect, this application provides a negative electrode, comprising: a current collector and an active material layer disposed on at least one side of the current collector, the active material layer comprising a main region and a thinned region located at an end;

[0007] The negative electrode also includes a composite structure layer covering and adhering to the surface of the thinned area. The composite structure layer includes a conductive enhancement layer and a gradient electrolyte layer that are sequentially composited along the thickness direction of the active material layer and gradually move away from the current collector.

[0008] The gradient electrolyte layer includes a lithium salt, the concentration of which increases linearly with distance from the conductive enhancement layer.

[0009] In some embodiments, the conductive reinforcement layer includes an adhesive, a conductive material, and nano-quantum dots, wherein the mass ratio of the adhesive, the conductive material, and the nano-quantum dots is (65-75):(20-30):(3-5).

[0010] The adhesive includes a water-based adhesive;

[0011] The conductive material includes one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon nanofibers, and conductive carbon black.

[0012] The nano-quantum dots include one or more of graphene quantum dots, carbon quantum dots, nitrogen-doped graphene quantum dots, and molybdenum sulfide quantum dots.

[0013] In some embodiments, the conductive reinforcement layer includes a conductive framework constructed from the conductive material, wherein the nano-quantum dots are filled and dispersed in the conductive framework, and the nano-quantum dots have a particle size of 5nm-20nm.

[0014] In some embodiments, the gradient electrolyte layer is horizontally aligned with the main region and is composed of multiple sublayers of the same thickness;

[0015] The concentration of lithium salt in each of the sublayers is 1 mol / L-1.9 mol / L, and the concentration difference of lithium salt between the highest concentration sublayer and the lowest concentration sublayer is 0.4 mol / L-0.9 mol / L.

[0016] In some embodiments, the gradient electrolyte layer further includes a polymer matrix and a toughening agent, wherein the mass ratio of the polymer matrix to the lithium salt and the toughening agent is (15-30):(10-25):(3-6).

[0017] In some embodiments, the thickness of the conductive enhancement layer is 1 μm-3 μm, the thickness of the gradient electrolyte layer is 3 μm-5 μm, and the thickness ratio of the conductive enhancement layer to the gradient electrolyte layer is 1:(2-3).

[0018] In a second aspect, this application provides a method for preparing a negative electrode, used to prepare a negative electrode as described in any one of the first aspects, the method comprising:

[0019] A negative electrode substrate having a main body region and a thinned region located at its ends is provided;

[0020] A first slurry for forming a conductive reinforcement layer and a second slurry with at least three different lithium salt concentrations for forming a gradient electrolyte layer are prepared respectively.

[0021] The conductive reinforcement layer is formed by coating the surface of the thinned area with the first slurry and then performing a first curing process.

[0022] The at least three lithium salt concentrations of the second slurry are coated on the surface of the conductive reinforcement layer in order of increasing concentration gradient, and the gradient electrolyte layer is formed by a second curing treatment.

[0023] In some embodiments, the preparation of the first slurry for forming the conductive reinforcement layer and the second slurry for forming the gradient electrolyte layer with at least three different lithium salt concentrations includes:

[0024] A binder, conductive material, and nano-quantum dots are added to a first solvent, and the mixture is dispersed to obtain a first slurry.

[0025] At least three second slurries with different lithium salt concentrations were prepared. The preparation of each second slurry included: adding a polymer matrix and a toughening agent to a diluting solvent to obtain a matrix solution; adding a pre-calculated target amount of lithium salt to the matrix solution in portions, and then adding a second solvent for homogeneous dispersion to obtain a second slurry with a target lithium salt concentration.

[0026] The interval between the multiple additions is 5 min to 20 min, and the addition temperature is 45℃ to 65℃.

[0027] In some embodiments, the solid content in the first slurry is 15%-20%, and the first solvent includes one or more of deionized water and alcohol solvents;

[0028] In the second slurry: the mass percentage of the second solvent is 10%-20%, and the mass percentage of the diluent solvent is 20%-60%;

[0029] The diluting solvent includes one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide, and N,N-dimethylacetamide.

[0030] Thirdly, this application also provides an electrical device including the negative electrode as described in any one of the first aspects.

[0031] The above-described one or more embodiments of this application have at least one or more of the following beneficial effects:

[0032] This application provides a negative electrode and its preparation method, as well as an electrical device. A composite structure layer is laminated over a thinned region at the end of the active material layer of the negative electrode. The composite structure layer includes a conductive reinforcement layer and a gradient electrolyte layer stacked along the thickness direction of the active material layer and gradually moving away from the current collector layer. This synergistically optimizes the charge transport dynamics in this region. The conductive reinforcement layer can rapidly transport electrons, and the lithium salt concentration in the gradient electrolyte layer increases linearly with distance from the conductive reinforcement layer. This forms a continuous ion driving force during high-current charging, ensuring that the ion flux matches the electron flux, thereby effectively suppressing lithium plating and improving the fast-charging capacity retention rate of the battery. At the same time, this localized functional design avoids the use of expensive materials in the entire electrode sheet, reducing costs.

[0033] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0034] The disclosure of this application will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this application. Furthermore, similar numbers in the drawings are used to denote similar components, wherein:

[0035] Figure 1 This is a schematic diagram of the negative electrode structure provided in one embodiment of this application;

[0036] Figure 2 This is a schematic diagram of the negative electrode substrate provided in one embodiment of this application.

[0037] Among them: 1. Current collector; 2. Active material layer; 21. Main body region; 22. Thinning region; 3. Composite structure layer; 31. Conductivity enhancement layer; 32. Gradient electrolyte layer. Detailed Implementation

[0038] Some embodiments of this application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of this application and are not intended to limit the scope of protection of this application.

[0039] As described in the background section, in actual production, to meet battery packaging and safety requirements, a thinned area is typically designed at the edge of the negative electrode sheet. The areal density of the active material in this area is lower than that in the non-thinned area. During high-current charging, the ion flux in the thinned area is insufficient, preventing timely lithium ion insertion. At high-rate charging, the ion conductivity is poor, leading to lithium plating. Furthermore, the interface between the composite electrolyte layer and the negative electrode active material has high interfacial impedance, hindering efficient lithium ion transport. Current methods for optimizing the electrolyte to improve the battery's fast-charging performance cannot solve the performance degradation problem of the thinned area at high rates.

[0040] To address the aforementioned issues, this application creatively proposes a negative electrode, its preparation method, and an electrical device. A composite structure layer is bonded to the thinned region at the end of the negative electrode active material layer, forming a continuous ion driving force during high-current charging. This ensures that the ion flux matches the electron flux, thereby effectively suppressing lithium plating and improving the battery's fast-charging capacity retention rate. Simultaneously, this locally functionalized design avoids the use of expensive materials across the entire electrode, reducing costs.

[0041] The present application will be described in detail below through specific embodiments.

[0042] Specifically, this application provides a negative electrode, referring to... Figure 1 As shown, it includes: a current collector 1 and an active material layer 2 disposed on at least one side of the current collector 1. The active material layer 2 includes a main body region 21 and a thinned region 22 located at the end. It should be noted that... Figure 1 The thinning region 22 is schematically shown as a sloping area with gradually decreasing thickness, but the thinning region 22 described in this application is not limited to this. The thinning region 22 refers to a region in the active material layer 2 with a thickness less than the main body region 21, and its specific shape can be a contour with a gradual or abrupt change in thickness known in the art. For ease of understanding and description, the region in the active material layer 2 with uniform thickness other than the thinning region 22 is named the main body region 21 in this application.

[0043] The negative electrode also includes a composite structure layer 3 covering and adhering to the surface of the thinned region 22. The composite structure layer 3 includes a conductive enhancement layer 31 and a gradient electrolyte layer 32 that are sequentially composited along the thickness direction of the active material layer 2 and gradually move away from the current collector 1. The gradient electrolyte layer 32 includes a lithium salt, and the concentration of the lithium salt in the gradient electrolyte layer 32 increases linearly with the distance from the conductive enhancement layer 31. That is, the concentration of the lithium salt in the gradient electrolyte layer 32 increases in a fixed proportion with the increase of the distance from the conductive enhancement layer 31.

[0044] In this application, the conductive enhancement layer 31 and the gradient electrolyte layer 32 are flush with the outer edges of the active material layer 2 in the length and width directions in the vertical direction.

[0045] In some embodiments, the conductive reinforcement layer 31 includes an adhesive, a conductive material, and nano-quantum dots, wherein the mass ratio of the adhesive, conductive material, and nano-quantum dots is (65-75):(20-30):(3-5). Optionally, the mass ratio of the adhesive, conductive material, and nano-quantum dots can be 65:20:3, 65:20:5, 65:23:4, 70:25:4.5, 75:20:3, 75:30:3, 65:30:5, 75:30:5, or any ratio within the above range.

[0046] The binder includes an aqueous binder, which contains polar groups such as hydroxyl groups, which can encapsulate conductive materials such as carbon nanotubes and graphene quantum dots through hydrogen bonds and ion-dipole interactions, effectively inhibiting their aggregation.

[0047] In some examples, the water-based binder includes one or more of polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), sodium alginate (SA), and a compound system of CMC and PAA.

[0048] The conductive material includes one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon nanofibers, and conductive carbon black. The nano-quantum dots include one or more of graphene quantum dots, carbon quantum dots, nitrogen-doped graphene quantum dots, and molybdenum sulfide quantum dots.

[0049] In some embodiments, the conductive enhancement layer 31 includes a conductive framework constructed from the conductive material, with the nano-quantum dots filling and dispersed within the conductive framework. The nano-quantum dots have a particle size of 5nm-20nm. Optionally, the particle size of the nano-quantum dots can be 5nm, 8nm, 10nm, 13nm, 15nm, 19nm, 20nm, or any value within the aforementioned particle size range. The conductive material constructs the conductive framework, and the nano-quantum dots fill and disperse within the conductive framework network, together forming a three-dimensional continuous electronic conductive network. This allows electrons to be transported seamlessly within the three-dimensional space of the conductive enhancement layer 31, adapting to the electron transport requirements of high-rate charging and avoiding problems such as electron accumulation due to local network discontinuities and lithium plating caused by electron transport lag during high-rate charging.

[0050] In some embodiments, the gradient electrolyte layer 32 is horizontally aligned with the main body region 21, that is, the composite structure layer 3 completely covers the thinned region 22 and its total thickness matches that of the main body region 21. If the composite structure layer 3 is too thin, the gradient electrolyte layer 32 is recessed relative to the main body region 21 in the horizontal direction, resulting in insufficient ion conduction; if the composite structure layer 3 is too thick, the gradient electrolyte layer 32 protrudes from the main body region 21 in the horizontal direction, resulting in increased interfacial impedance.

[0051] The gradient electrolyte layer 32 has a uniform thickness and is composed of multiple sublayers of the same thickness. In the gradient electrolyte layer 32, the concentration of the lithium salt increases linearly in each sublayer, that is, it increases linearly from the side closer to the conductive reinforcement layer 31 to the side farther from the conductive reinforcement layer 31 (i.e., towards the battery separator), and the concentration difference between adjacent sublayers remains constant. The concentration of the lithium salt in each sublayer is 1 mol / L-1.9 mol / L, and the concentration difference between the highest and lowest concentration sublayers is 0.4 mol / L-0.9 mol / L. Optionally, it can be 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or any value within the above range. Preferably, the linearly increasing gradient difference of the lithium salt concentration is 0.6 mol / L. Correspondingly, the concentration range of the lithium salt can be 1.0 mol / L-1.6 mol / L, 1.1-1.7 mol / L, 1.3-1.9 mol / L, etc. It should be noted that: regardless of any point value within the above gradient difference range selected for the linearly increasing gradient difference of the lithium salt concentration, the concentration of the lithium salt is not less than 1.0 mol / L and is less than the saturation concentration of the lithium salt in the solvent.

[0052] In a preferred embodiment, the concentration of the lithium salt in the gradient electrolyte layer 32 increases linearly from 1.2 mol / L to 1.8 mol / L, with a concentration difference of 0.6 mol / L.

[0053] In some embodiments, the gradient electrolyte layer 32 further includes a polymer matrix and a toughening agent, wherein the mass ratio of the polymer matrix to the lithium salt and the toughening agent is (15-30):(10-25):(3-6). Optionally, the mass ratio of the polymer matrix to the lithium salt and the toughening agent can be 15:10:3, 15:20:5, 15:25:4, 15:10:3, 18:17:3.5, 23:19:4, 30:10:3, 30:20:4, 30:25:5, 30:25:6, or any ratio within the above range.

[0054] The lithium salt comprises one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, and a mixture of lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate; the polymer matrix comprises one or more of polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polymethyl methacrylate, polyvinylidene fluoride, polypropylene carbonate, and a blend of polyvinylidene fluoride and polymethyl methacrylate; the toughening agent comprises one or more of polyvinylidene fluoride-hexafluoropropylene copolymer, thermoplastic polyurethane, ethylene-vinyl acetate copolymer, polycaprolactone, and polyether block amide.

[0055] In some embodiments, the thickness of the conductive reinforcement layer 31 is 1μm-3μm. Optionally, the thickness of the conductive reinforcement layer 31 can be 1μm, 1.3μm, 1.5μm, 2μm, 2.5μm, 2.8μm, 3μm, or any value within the above thickness range. The thickness of the gradient electrolyte layer 32 is 3μm-5μm. Optionally, the thickness of the gradient electrolyte layer 32 can be 3μm, 3.3μm, 3.5μm, 3.8μm, 4μm, 4.2μm, 4.5μm, 5μm, or any value within the above thickness range. The thickness ratio of the conductive reinforcement layer 31 to the gradient electrolyte layer 32 is 1:(2-3). Optionally, the thickness ratio of the conductive reinforcement layer 31 to the gradient electrolyte layer 32 can be 1:2, 1:2.3, 1:2.5, 1:2.7, 1:3, or any ratio within the above range.

[0056] Preferably, the dry-state thickness ratio of the conductive enhancement layer 31 to the gradient electrolyte layer 32 is 1:2. When the dry-state thickness ratio of the conductive enhancement layer 31 to the gradient electrolyte layer 32 is 1:2, the electron conduction and ion transport efficiency is optimal, the interface impedance is lowest, and the risk of lithium plating at high rates is minimized. If the thickness ratio is too large, such as 1:4, the conductive enhancement layer is too thin, the electron conduction network is discontinuous, electron transport is hindered at high rates, and the risk of lithium plating increases. If the thickness ratio is too small, such as 1:1.5, the ion conduction channels are slightly thin, the ion flux is insufficient at high rates (above 5C), and the capacity retention decreases.

[0057] In some embodiments, the current collector 1 may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0058] In some embodiments, the active material layer 2 includes a negative electrode active material and a negative electrode binder.

[0059] The negative electrode active material in this application embodiment is not particularly limited, as long as it is a substance that can electrochemically adsorb and release s-region metal ions such as lithium ions, sodium ions, potassium ions, and magnesium ions, such as carbonaceous materials, metal compound materials, or their oxides, carbides, nitrides, silicides, sulfides, phosphides, etc. These substances can be used alone, or two or more can be used in combination.

[0060] In some embodiments, carbon materials can be selected as the negative electrode active material. Specifically, one or more of the following can be selected: graphite, needle coke, amorphous carbon, carbon-containing mesophase, carbon fiber, and carbon materials with low graphitization. Graphite can include natural graphite, artificial graphite, etc. Alternatively, materials obtained by coating these materials with carbon materials, such as amorphous carbon or graphitides, can also be used. Amorphous carbon includes, but is not limited to, particles obtained by sintering a monolithic mesophase, and particles obtained by sintering a carbon precursor after infusible treatment. Furthermore, non-metallic materials that can be used as negative electrode active materials include elemental silicon and its compounds, such as Si and SiO. x (0≤x<2), because silicon-containing materials are prone to expansion and easy to fall off from the negative electrode current collector, and have poor conductivity, they are often used in combination with carbon materials, such as core-shell structures containing carbon coating layers.

[0061] In some embodiments, elemental metals and metal compounds can also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0062] In some embodiments, the mass percentage of the negative electrode active material contained in the active material layer 2 can be 80wt%-99wt%, for example, 80wt%, 85wt%, 90wt%, 95wt%, 97wt%, 99wt%, etc.

[0063] When the negative electrode active material is a non-metallic material such as carbon material, the negative electrode binder can be a water-based binder, such as sodium carboxymethyl cellulose, styrene-butadiene latex, polyacrylic acid, acrylic copolymers, cyclodextrin, or one or more of these.

[0064] In some embodiments, the active material layer 2 further includes a negative electrode conductive agent. The negative electrode conductive agent is used to improve the electronic conductivity within the active material layer 2 and reduce electrode polarization. The negative electrode conductive agent can be selected from any conductive material known in the art, such as including but not limited to: carbon black materials (e.g., acetylene black, Ketjen black, conductive carbon black), carbon nanotubes (single-walled carbon nanotubes, multi-walled carbon nanotubes), carbon nanofibers, graphene, reduced graphene oxide, and combinations thereof.

[0065] In some embodiments, the mass percentage of the negative electrode conductive agent in the active material layer 2 can be 0.5wt%-5wt%, for example 0.5wt%, 1wt%, 1.5wt%, 2wt%, 3wt%, 4wt%, 5wt%, etc.

[0066] The active material layer 2 can be obtained by coating the negative electrode current collector 1 with a negative electrode slurry and then performing operations such as drying. The negative electrode slurry includes at least a negative electrode active material and a negative electrode binder.

[0067] This application also provides a method for preparing a negative electrode, used to prepare a negative electrode as described in any of the above embodiments, the method comprising:

[0068] S110, providing a negative electrode substrate having a main body region and a thinned region located at its ends.

[0069] Specifically, the negative electrode substrate includes a current collector 1 and an active material layer 2 disposed on at least one side of the current collector 1. The active material layer 2 includes a main body region 21 and a thinned region 22 located at the end of the main body region 21.

[0070] In some embodiments, laser etching can be used to partially remove the edge of the negative electrode active material film to form a thinned region. The laser wavelength is 355nm-365nm; the laser power is 5W-15W; the number of etching cycles is 1-3; and the etching depth is 5μm-20μm.

[0071] S120. Prepare a first slurry for forming a conductive reinforcement layer and a second slurry with at least three different lithium salt concentrations for forming a gradient electrolyte layer.

[0072] S130. After coating the surface of the thinned area with the first slurry, the conductive reinforcement layer is formed by a first curing treatment.

[0073] S140. The at least three lithium salt concentrations of the second slurry are coated on the surface of the conductive reinforcement layer in order of increasing concentration gradient, and the gradient electrolyte layer is formed by the second curing treatment.

[0074] In some embodiments, after step S110, the method further includes: roughening the surface of the thinned area to increase the adhesion between the thinned area and the conductive reinforcement layer 31.

[0075] By way of example only: the surface roughening treatment may be plasma treatment.

[0076] In some embodiments, the preparation of the first slurry for forming the conductive reinforcement layer in step S120 includes:

[0077] A binder, conductive material, and nano-quantum dots are added to a first solvent, and the mixture is dispersed to obtain a first slurry.

[0078] Specifically, after adding a binder, conductive material and nano-quantum dots to the first solvent, the mixture is stirred at 2500r / min-5000r / min for 20min-40min to obtain the first slurry.

[0079] In some embodiments, the solid content in the first slurry is 15%-20%, and the first solvent includes one or more of deionized water and alcohol solvents, which are compatible with the aqueous binder in the conductive reinforcement layer. The alcohol solvent includes, but is not limited to, ethanol and ethylene glycol, and can be miscible with deionized water in any proportion to adjust the polarity and evaporation rate of the first slurry.

[0080] Optionally, the solid content in the first slurry can be 15%, 17%, 18%, 19%, 20%, or any value within the above-mentioned range. In some embodiments, the preparation of at least three second slurries with different lithium salt concentrations for forming a gradient electrolyte layer in step S120 includes:

[0081] At least three second slurries with different lithium salt concentrations were prepared. The preparation of each second slurry included: adding a polymer matrix and a toughening agent to a diluent to obtain a matrix solution; adding a pre-calculated target amount of lithium salt to the matrix solution in portions, and then adding a second solvent for homogeneous dispersion to obtain a second slurry with a target lithium salt concentration.

[0082] The interval between the multiple additions is 5 min to 20 min, and the addition temperature is 45℃ to 65℃.

[0083] Specifically, the polymer matrix and toughening agent are added to a diluent and stirred at 50-75°C and 200-450 rpm for 1-4 hours until the polymer and toughening agent dissolve to form a matrix solution. The diluent includes, but is not limited to, solvents with good flowability such as NMP. The target amount of lithium salt, calculated in advance according to the target concentration, is added to the matrix solution at least twice, with an interval of 5-20 minutes between each addition. During the addition process, the mixture is stirred at 45-65°C and 200-450 rpm to avoid excessively high local concentrations that could lead to crystallization.

[0084] In the second slurry: the mass percentage of the second solvent is 10%-20%, and the mass percentage of the diluent solvent is 20%-60%. Optionally, the mass percentage of the second solvent in the second slurry can be 10%, 12%, 15%, 17%, 18%, 20%, or any value within the above range. The mass percentage of the diluent solvent in the second slurry can be 20%, 25%, 30%, 33%, 37%, 40%, 42%, 46%, 50%, 55%, 60%, or any value within the above range.

[0085] The diluting solvent includes one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide, and N,N-dimethylacetamide.

[0086] In some examples, the second solvent includes an organic solvent, which includes, but is not limited to, at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, and propylene carbonate.

[0087] After adding the target amount of lithium salt in portions, add the organic solvent, cool to 25℃-40℃, and continue stirring for 0.5h-2h. Homogenize and disperse at 6000r / min-15000r / min for 10min-30min; after filtration, obtain the second slurry with the corresponding target concentration.

[0088] In some embodiments, the first curing process is pre-baking at 70°C-90°C for 2-6 minutes.

[0089] In some embodiments, step S140 includes:

[0090] A composite wet film is obtained by sequentially coating the surface of the conductive reinforcement layer with the second slurry of different lithium salt concentrations, and the composite wet film is subjected to a second curing treatment to form a gradient electrolyte layer with a lithium salt concentration gradient.

[0091] In some examples, the second curing process is drying under vacuum at 110°C-130°C for 10-25 minutes.

[0092] This application also provides an electrical device, including the negative electrode as described in any of the above embodiments.

[0093] In some embodiments, the electrical device further includes a positive electrode.

[0094] In some embodiments, the positive electrode includes a positive current collector and a positive electrode layer disposed on the positive current collector.

[0095] In some embodiments, the positive electrode layer includes a positive electrode active material, which includes a compound that can reversibly insert and deintercalate lithium ions.

[0096] In some embodiments, the positive electrode active material comprises one or more transition metal cations, including but not limited to manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof.

[0097] In some embodiments, the positive electrode active material is one of layered oxides, spinel oxides, and polyanionic compounds.

[0098] In some embodiments, the layered oxides (e.g., rock salt layered oxides) include LiCoO2 (LCO) and LiNi. x Mn y Co 1-x-yO2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi 1-x-y Co x Al y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi x Mn 1-x O2 (where 0≤x≤1) and xLi2MnO3·(1-x)LiTMO2 (where M is one of Mn, Ni, and Co; 0≤x≤1).

[0099] In some embodiments, the spinel oxide includes LiMn2O4 (LMO) and LiNi. 0.5 Mn 1.5 O4.

[0100] In some embodiments, the polyanionic compound includes a phosphate, such as LiFePO4, LiMnPO4, Li3V2(PO4)3, or LiMn. x Fe 1-x At least one of PO4 (0 < x < 1) and its doped derivatives.

[0101] In some embodiments, the polyanionic compound includes a silicate, which includes Li2FeSiO4.

[0102] In some implementations, the mass of the positive electrode active material accounts for 60% to 95% of the mass of the positive electrode layer.

[0103] In some embodiments, the positive electrode layer also includes a binder. The binder can improve the bonding between the positive electrode active material particles and also improve the bonding between the positive electrode layer and the positive electrode current collector.

[0104] In some embodiments, non-limiting examples of adhesives include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0105] It is understood that when the positive electrode layer is prepared using a dry method, the binder should include at least a fibrous binder, including but not limited to one or more of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyvinylidene fluoride hexafluoropropylene, polypropylene, polyethylene, and polyimide.

[0106] In some embodiments, the binder accounts for 0.1% to 20% of the mass of the positive electrode layer.

[0107] In some embodiments, the positive electrode layer also includes a conductive agent to impart conductivity to the electrode. The conductive agent can include any conductive material, as long as it does not cause a chemical change.

[0108] In some embodiments, the conductive agent includes carbon-based materials, metals and their derivatives, conductive polymers, and MXenes, etc.

[0109] Among them, carbon-based materials include, but are not limited to, natural graphite, artificial graphite, graphene, carbon black, acetylene black, Ketjen black, superconducting carbon black, carbon nanotubes, carbon fibers, etc.

[0110] Metals and their derivatives include, but are not limited to, metal powders, metal fibers, metal nanowires, etc., and metals include, but are not limited to, copper, nickel, aluminum, silver, etc.

[0111] Conductive polymers include, but are not limited to, polypyrrole, PEDOT:PSS, and polyaniline.

[0112] In some embodiments, the conductive agent accounts for 0.1% to 20% of the mass of the positive electrode layer.

[0113] In some embodiments, the positive electrode layer also includes a fast ion conductor to improve the ionic conductivity of the positive electrode layer. This application does not limit the type of fast ion conductor; it can be an oxide solid electrolyte, a sulfide solid electrolyte, a halide solid electrolyte, a lithium salt, etc.

[0114] In some embodiments, the mass of the fast ion conductor accounts for 1% to 20% of the mass of the positive electrode layer; preferably 5% to 20%.

[0115] In some embodiments, the positive electrode includes a positive current collector, which includes a metallic material capable of conducting electrons, including but not limited to at least one of aluminum, nickel, tin, copper, and stainless steel.

[0116] In some embodiments, the positive current collector includes at least one of aluminum foil, carbon-coated aluminum foil, stainless steel foil, nickel foam, and porous metal.

[0117] In some embodiments, the battery of this application has a separator between the positive and negative electrodes to prevent short circuits. The material and shape of the separator used in the battery of this application are not particularly limited, and can be any technology disclosed in the prior art.

[0118] In some embodiments, the diaphragm comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0119] In some embodiments, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide.

[0120] In some implementations, the battery also includes an electrolyte.

[0121] In some implementations, the electrolyte includes a lithium salt and a solvent.

[0122] In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0123] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0124] In some embodiments, the electrolyte also includes additives. These additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance characteristics, such as additives that improve battery overcharge performance, high-temperature performance, and low-temperature performance.

[0125] In some embodiments, the aforementioned additives include 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, vinyl sulfate, and 4... At least one of the following: methyl vinyl sulfate, propylene sulfate, saturated phosphate compounds and unsaturated phosphate compounds, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(triethylsilane) borate, succinic acid nitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebaconitrile.

[0126] In some implementations, the battery includes a solid electrolyte layer.

[0127] In some embodiments, the solid electrolyte layer includes one of an organic solid electrolyte and an inorganic solid electrolyte; the organic solid electrolyte includes a polymer electrolyte, which includes one of a polyoxyethylene electrolyte, a polyvinylidene fluoride electrolyte, a polyacrylonitrile-based electrolyte, and a polymethyl methacrylate (PMMA)-based electrolyte.

[0128] Inorganic solid electrolytes include one or more of the following: oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, hydride solid electrolytes, boride solid electrolytes, and nitride solid electrolytes.

[0129] In some embodiments, the oxide solid electrolyte is composed of oxide solid electrolyte particles, including garnet ceramics, LISICON type oxides, NASICON type oxides, and perovskite type ceramics.

[0130] Garnet ceramics include, but are not limited to, Li 6.5 La 24 Zr 1.75 Te 0.25 O 12 、Li7La 24 Zr2O 12 Li 6.2 Ga 0.24 La 2.95 Rb 0.05 Zr2O 12 Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 Li 6.25 Al 0.25 La 24 Zr2O 12 Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12 Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12 And their combinations.

[0131] LISICON type oxides include, but are not limited to, Li 14 Zn(GeO4)4, Li 24+x (P 1-x Si x O4 (where 0 < x < 1), Li 24+x Ge x V1-x O4 (where 0 < x < 1) and their combinations.

[0132] NASICON-type oxides can be produced from LiMM′(PO4). 24 Defined where M and M′ are independently selected from Al, Ge, Ti, Sn, Hf, Zr, and La. NASICON-type oxides include, but are not limited to, Li. 1+x Al x Ge 2-x (PO4) 24 (LAGP) (where 0 ≤ x ≤ 2), Li 1+ x Al x Ti 2-x (PO4) 24 (LATP) (where 0 ≤ x ≤ 2), Li 1+x Y x Zr 2-x (PO4) 24 (LYZP) (where 0≤x≤2), Li 1.24 Al 0.24 Ti 1.7 (PO4) 24 LiTi2(PO4) 24 LiGeTi(PO4) 24 LiGe2(PO4) 24 LiHf2(PO4) 24 And their combinations.

[0133] Perovskite ceramics include, but are not limited to, Li 24.24 La 0.524 TiO 24 LiSr 1.65 Zr 1.24 Ta 1.7 O9、Li 2x-y Sr 1- x Ta y Zr 1-y O 24 (where x = 0.75y and 0.60 < y < 0.75), Li 24 / 8 Sr 7 / 16 Nb 24 / 4 Zr 1 / 4 O 24 Li 24x La (2 / 24-x) TiO 24 (where 0 < x < 0.25) and their combinations.

[0134] In some embodiments, the ionic conductivity of the oxide solid electrolyte is 10.-5 S / cm~10 -1 S / cm.

[0135] In some embodiments, the sulfide solid electrolyte is composed of sulfide solid electrolyte particles, including but not limited to Li2S-P2S5 and Li2S-P2S5-MS. x (where M is Si, Ge, and Sn and 0 ≤ x ≤ 2), Li 24.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.24 Li 9.6 P 24 S 12 Li7P 24 S 11 Li9P 24 S9O 24 Li 10.245 Si 1.245 P 1.65 S 12 Li 9.81 Sn 0.81 P 2.19 S 12 Li 10 (Si 0.5 Ge 0.5 P2S 12 Li (Ge 0.5 Sn 0.5 P2S 12 Li 10 GeP2S 12 (LGPS), Li6PS5X (where X is Cl, Br, or I), Li7P2S8I, Li 10.245 Ge 1.245 P 1.65 S 12 Li 24.25 Ge 0.25 P 0.75 S4, Li 10 SnP2S 12 Li 10 SiP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.24 , (1-x)P2S5-xLi2S (where 0.5≤x≤0.7) and their combinations.

[0136] In some embodiments, the ionic conductivity of the sulfide solid electrolyte is 10.-7 S / cm ~ 1S / cm.

[0137] In some embodiments, the halide solid electrolyte layer includes halide solid electrolyte particles, and the halide solid electrolyte particles include Li a M b X c N d M includes one or more of the basic metal elements, such as Zr, Hf, In, Sc, Y, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. M also includes doped metal elements, used in conjunction with the aforementioned basic metal elements, such as one or more of Nb, Ta, Al, La, Mg, Ca, Ba, and Ag. X includes one or more of F, Cl, Br, and I. N includes one or more of O and S, and satisfies a+mb=c+nd, where m and n are the weighted valences of M and N, respectively, 1≤a≤4, b>0, c>0, and d≥0.

[0138] For example, the halide solid electrolyte particles can be Li₂ZrCl₆, Li₂ZrCl₅F, or Li₂ZrCl₆. 5.5 O 0.25 At least one of Li3InCl6, Li3YCl6, Li2HfCl6, LiInBr4, Li3InBr6, Li3LaI6, Li3LuCl6, and Li3ErCl6.

[0139] In some embodiments, the ionic conductivity of the halide solid electrolyte is 10. -8 S / cm~10 -1 S / cm.

[0140] In some embodiments, the hydride solid electrolyte is composed of hydride solid electrolyte particles, including but not limited to Li 24 AlH6, LiBH4, LiBH4-LiX (where X is one of Cl, Br and I), LiNH2, Li2NH, LiBH4-LiNH2 and combinations thereof.

[0141] In some embodiments, the ionic conductivity of the hydride solid electrolyte is 10. -7 S / cm~10 -2 S / cm.

[0142] In some embodiments, the boride solid electrolyte is composed of borate solid electrolyte particles, including but not limited to Li₂B₄O₇ and Li₂O-(B₂O₃)₂O₃. 24 )-(P2O5) and their combinations.

[0143] In some embodiments, the ionic conductivity of the boride solid electrolyte is 10. -7 S / cm~10 -2 S / cm.

[0144] In some embodiments, the nitride solid electrolyte comprises nitride solid electrolyte particles, including Li 24 N, Li7PN4, LiSi2N 24 LiPON and their combinations.

[0145] In some embodiments, the ionic conductivity of the nitride solid electrolyte is 10. -9 S / cm ~ 1S / cm.

[0146] The present application will be further described in detail below with reference to embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection claimed in this application.

[0147] Example 1: (1) Preparation of negative electrode substrate: Graphite + 5% silicon-carbon negative electrode active material, conductive agent conductive carbon black SP, and binder CMC were added to deionized water in a mass ratio of 95:1:3 and stirred evenly to obtain a negative electrode slurry; the above negative electrode slurry was coated on a 6μm copper foil and dried. At the edge of the copper foil in the width direction, laser etching was performed to form a 6mm wide thinning area, so that the thickness of the active material layer in the thinning area was less than the thickness of the active material layer in the main area. The thinning area was subjected to plasma treatment for 20 seconds to obtain the following: Figure 2 The negative electrode substrate shown.

[0148] (2) Preparation of the first slurry for forming the conductive reinforcement layer: Weigh the following raw materials by mass percentage: sodium carboxymethyl cellulose (CMC) 12.6%, multi-walled carbon nanotubes (MWCNTs) 4.5%, graphene quantum dots (GQDs) 0.9%, and 82% deionized water. After mixing the above raw materials, first perform ultrasonic dispersion for 20 minutes, and then perform high-speed mechanical stirring at 5000 r / min for 30 minutes to obtain a conductive reinforcement layer slurry with a solid content of 18%.

[0149] (3) Prepare a second slurry for the gradient electrolyte layer, and formulate three second slurries with different lithium salt concentrations:

[0150] A second slurry with a lithium salt concentration of 1.2 mol / L was prepared, and its composition by mass percentage is as follows:

[0151] The composition comprises 17.91% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), 3.98% thermoplastic polyurethane (TPU), 14.93% lithium hexafluorophosphate (LiPF6), 52.23% diluent solvent N-methylpyrrolidone (NMP), and a second solvent composed of ethylene carbonate (EC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC), totaling 10.95%. These percentages are calculated based on the feed amounts and processes described in the examples, where NMP includes both the initial addition and the amount added after volume adjustment. The specific preparation steps are as follows:

[0152] Weigh 18.0 g of PVDF-HFP and 4.0 g of TPU, add 50 g of NMP as a diluent, and stir at 60 °C and 300 r / min for 2 hours until dissolved to form a matrix solution. Weigh 15.0 g of LiPF6 and add it to the matrix solution in three equal portions, 15 minutes apart, while maintaining stirring at 60 °C and 300 r / min. Then add 11.0 g of a mixed organic solvent consisting of EC, FEC, and EMC in a volume ratio of 3:4:3, cool to 40 °C, and continue stirring for 1 hour. Transfer the mixed slurry to a volumetric flask, dilute with NMP, and bring the volume to the 83 mL mark. Then pour out the slurry, homogenize it at 10000 r / min for 20 minutes, and filter it through a filter membrane to obtain a second slurry with a concentration of 1.2 mol / L.

[0153] A second slurry with a lithium salt concentration of 1.5 mol / L was prepared, and its composition by mass percentage is as follows:

[0154] The composition comprises 17.71% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), 3.94% thermoplastic polyurethane (TPU), 18.44% lithium hexafluorophosphate (LiPF6), 49.08% diluent solvent N-methylpyrrolidone (NMP), and 10.83% a mixed solvent consisting of ethylene carbonate (EC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC). These percentages are calculated based on the feed amounts and processes described in the examples, where NMP includes both the initial addition and the amount added after volume adjustment. The specific preparation steps are as follows:

[0155] Weigh 18.0 g of PVDF-HFP and 4.0 g of TPU, add 45 g of NMP as a diluent, and stir at 60 °C and 300 r / min for 2 hours until dissolved to form a matrix solution. Weigh 18.92 g of LiPF6 and add it to the matrix solution in three equal portions, 15 minutes apart, while maintaining stirring at 60 °C and 300 r / min. Then add 11.0 g of a mixed organic solvent consisting of EC, FEC, and EMC in a volume ratio of 3:4:3, cool to 40 °C, and continue stirring for 1 hour. Transfer the mixture to a volumetric flask, dilute with NMP, and bring the volume to the 83 mL mark. Pour out the mixture, homogenize at 10000 r / min for 20 minutes, and filter through a filter membrane to obtain an electrolyte slurry with a concentration of 1.5 mol / L.

[0156] A second slurry with a lithium salt concentration of 1.8 mol / L was prepared, and its composition by mass percentage is as follows:

[0157] The composition comprises 17.53% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), 3.90% thermoplastic polyurethane (TPU), 21.92% lithium hexafluorophosphate (LiPF6), 43.17% diluent solvent N-methylpyrrolidone (NMP), and 10.48% mixed solvent composed of ethylene carbonate (EC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC). These percentages are calculated based on the feed amounts and processes described in the examples, where NMP includes both the initial addition and the replenishment amount at constant volume. The specific preparation steps are as follows:

[0158] Weigh 18.0 g of PVDF-HFP and 4.0 g of TPU, add 40 g of NMP as a diluent, and stir at 60 °C and 300 r / min for 2.5 hours until dissolved to form a matrix solution. Weigh 22.70 g of LiPF6 and add it to the matrix solution in three equal portions, 15 minutes apart, while maintaining stirring at 60 °C and 300 r / min. Then add 11.0 g of a mixed organic solvent composed of EC, FEC, and EMC in a volume ratio of 3:4:3, cool to 40 °C, and continue stirring for 1 hour. Transfer the mixed slurry to a volumetric flask, dilute with NMP, and bring the volume to the 83 mL mark. Then pour out the slurry, homogenize it at 12000 r / min for 20 minutes, and filter it through a filter membrane to obtain a second slurry with a concentration of 1.8 mol / L.

[0159] (4) A conductive reinforcement layer slurry is uniformly coated onto the surface of the pretreated thinned area and pre-baked at 80°C for 3 minutes to form a conductive reinforcement layer with a dry thickness of 2 μm. Using a gradient coating device with an independent slurry tank, electrolyte slurries with lithium salt concentrations of 1.2 mol / L, 1.5 mol / L, and 1.8 mol / L are sequentially coated onto the surface of the conductive reinforcement layer. The electrode coated with the composite wet film is placed in a vacuum drying oven and cured at 120°C for 15 minutes to allow the solvent to evaporate, forming a gradient electrolyte layer with a dry thickness of 4 μm. The lithium salt concentration in this electrolyte layer exhibits a gradient distribution that increases linearly from the side near the conductive reinforcement layer to the surface.

[0160] The resulting negative electrode sheet has its thinned area filled with a composite structure layer consisting of a conductive reinforcement layer and a gradient electrolyte layer, making the total thickness of the thinned area the same as that of the main body area.

[0161] (5) Battery fabrication:

[0162] 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.

[0163] PP diaphragm is selected.

[0164] The positive electrode, separator, and negative electrode sheet prepared in the above steps are wound up, sealed with electrolyte (1M LiPF6 in EC:DEC=1:1v / v electrolyte), and then assembled into a battery.

[0165] Example 2: The difference between this example and Example 1 is that the lithium salt is replaced with a compound system of LiTFSI and LiDFOB, with a mass ratio of LiTFSI to LiDFOB of 1:1, and the polymer matrix is ​​replaced with a blend of PVDF and PMMA, with a mass ratio of PVDF to PMMA of 7:3.

[0166] Example 3: The difference between this example and Example 1 is that the conductive material in the first slurry is replaced with conductive carbon black (SP).

[0167] Example 4: The difference between this example and Example 1 is that the dry state thickness of the conductive reinforcement layer is 1.5 μm and the dry state thickness of the gradient electrolyte layer is 4.5 μm.

[0168] Example 5: The difference between this example and Example 1 is that the dry state thickness of the conductive reinforcement layer is 4 μm and the dry state thickness of the gradient electrolyte layer is 2 μm.

[0169] Comparative Example 1: The difference between this comparative example and Example 1 is that the negative electrode thinning area is not coated with any layer.

[0170] Comparative Example 2: The difference between this comparative example and Example 1 is that the thinned area is coated only with a conductive reinforcement layer of the same thickness as the formulation in Example 1.

[0171] Comparative Example 3: The difference between this comparative example and Example 1 is that the thinned area is coated only with a gradient electrolyte layer of the same thickness as the formulation in Example 1.

[0172] Comparative Example 4: The difference between this comparative example and Example 1 is that the gradient electrolyte layer is replaced with a single lithium salt concentration of 1.5 mol / L electrolyte layer of the same thickness. The composition and preparation steps of this slurry are exactly the same as those of the 1.5 mol / L slurry described in Example 1. The same conductive reinforcement layer slurry is first coated on the surface of the pretreated thinned area and pre-baked at 80°C for 3 minutes to form a conductive reinforcement layer with a dry thickness of 2 μm. This step is completely consistent with Example 1. Subsequently, the above-mentioned 1.5 mol / L electrolyte slurry is coated onto the surface of the conductive reinforcement layer in one go using a single slurry tank. The electrode is placed in a vacuum drying oven and the solvent is evaporated under the same conditions (cured at 120°C for 15 minutes) to form a single-concentration electrolyte layer with a total dry thickness of 4 μm.

[0173] The batteries prepared in the above embodiments and comparative examples were subjected to battery cycle tests, and the test methods are as follows:

[0174] Magnification 1: Test temperature: 45℃±2℃.

[0175] ① Charge at 0.5C to the termination voltage (4.2V), cut-off current 0.05C, and let stand for 30 minutes.

[0176] ② Discharge at 1C to the final discharge voltage (2.5V), and let stand for 30 minutes;

[0177] Repeat ①-②, and record the average discharge capacity of the first to third cycles as the initial discharge capacity;

[0178] Battery capacity retention after 500 cycles = Discharge capacity on the 500th cycle / Initial discharge capacity 100%.

[0179] Multiplier 2: Test temperature: 45℃±2℃.

[0180] ③ Charge at 1C to the termination voltage (4.2V), cut-off current 0.05C, and let stand for 30 minutes.

[0181] ④ Discharge at 1C until the final discharge voltage (2.5V), then let stand for 30 minutes.

[0182] Repeat cycles ③-④, and record the average discharge capacity of the first to third cycles as the initial discharge capacity.

[0183] Battery capacity retention after 500 cycles = Discharge capacity on the 500th cycle / Initial discharge capacity 100%.

[0184] Magnification 3: Test temperature: 45℃±2℃.

[0185] ⑤ Charge at 3C to the termination voltage (4.2V), cut-off current 0.05C, and let stand for 30 minutes.

[0186] ⑥ Discharge at 1C to the final discharge voltage (2.5V), and let stand for 30 minutes.

[0187] Repeat steps ⑤-⑥, and record the average discharge capacity of the first to third cycles as the initial discharge capacity.

[0188] Battery capacity retention after 500 cycles = Discharge capacity on the 500th cycle / Initial discharge capacity 100%.

[0189] The test results are shown in the table below:

[0190]

[0191] As shown in the table above: the battery cycle capacity retention rate of Examples 1-4 is significantly better than that of Comparative Examples 1-4; Example 5, due to the unreasonable ratio of the thickness of the conductive reinforcement layer and the gradient electrolyte layer, although it is a double-layer structure, has poor performance and is even lower than some of the comparative examples.

[0192] Example 1 exhibits the best performance because its thickness ratio and lithium salt gradient difference are both optimal parameters, and the raw materials are well-matched, achieving a match between electron and ion fluxes and effectively suppressing lithium plating. Examples 2-4 show slightly lower performance than Example 1 but still demonstrate excellent results. The substitution of raw materials or minor adjustments to the thickness ratio did not disrupt the core synergistic effect, proving that the technical solution has good flexibility and applicability.

[0193] Comparative Example 1, with no coating on the thinned region, exhibited the worst 3C performance, verifying that without a composite structure layer in the thinned region, severe high-rate lithium plating led to rapid capacity decay. Comparative Examples 2 and 3, with only a conductive reinforcement layer coated on the thinned region and only a gradient electrolyte layer coated on the thinned region, showed better performance than Comparative Example 1 but were still far inferior to the Example, because a single coating could not form a synergistic effect, resulting in a mismatch between electron and ion flux. Comparative Example 4, with only a single concentration lithium salt coated on the thinned region, performed worse than the Example, due to the lack of a lithium salt concentration gradient, insufficient ion driving force, and poor lithium plating suppression.

[0194] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0195] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0196] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A negative electrode, characterized in that, include: A current collector and an active material layer disposed on at least one side of the current collector, the active material layer comprising a main region and a thinned region located at an end; The negative electrode also includes a composite structure layer covering and adhering to the surface of the thinned area. The composite structure layer includes a conductive reinforcement layer and a gradient electrolyte layer that are sequentially composited along the thickness direction of the active material layer and gradually move away from the current collector. The conductive reinforcement layer includes a binder, a conductive material, and nano-quantum dots, and the mass ratio of the binder, conductive material, and nano-quantum dots is (65-75):(20-30):(3-5). The binder includes an aqueous binder; the conductive material includes one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon nanofibers, and conductive carbon black; the nano-quantum dots include one or more of graphene quantum dots, carbon quantum dots, nitrogen-doped graphene quantum dots, and molybdenum sulfide quantum dots; the conductive reinforcement layer includes a conductive framework constructed from the conductive material, wherein the nano-quantum dots are filled and dispersed in the conductive framework, and the particle size of the nano-quantum dots is 5nm-20nm; The gradient electrolyte layer includes a lithium salt, and the concentration of the lithium salt in the gradient electrolyte layer increases linearly with distance from the conductive enhancement layer. The gradient electrolyte layer is horizontally overlapped with the main region and is composed of multiple sublayers of the same thickness; the concentration of lithium salt in each sublayer is 1 mol / L-1.9 mol / L, and the concentration difference of lithium salt between the highest concentration sublayer and the lowest concentration sublayer is 0.4 mol / L-0.9 mol / L.

2. The negative electrode according to claim 1, characterized in that, The gradient electrolyte layer further includes a polymer matrix and a toughening agent, wherein the mass ratio of the polymer matrix to the lithium salt and the toughening agent is (15-30):(10-25):(3-6).

3. The negative electrode according to claim 1 or 2, characterized in that, The thickness of the conductive enhancement layer is 1μm-3μm, the thickness of the gradient electrolyte layer is 3μm-5μm, and the thickness ratio of the conductive enhancement layer to the gradient electrolyte layer is 1:(2-3).

4. A method for preparing a negative electrode, characterized in that, The method for preparing the negative electrode as described in any one of claims 1-3 comprises: A negative electrode substrate having a main body region and a thinned region located at its ends is provided; The preparation of a first slurry for forming a conductive reinforcement layer and a second slurry with at least three different lithium salt concentrations for forming a gradient electrolyte layer includes: adding a binder, a conductive material and nano-quantum dots to a first solvent, and dispersing them to obtain the first slurry; Prepare at least three second slurries with different lithium salt concentrations; The conductive reinforcement layer is formed by coating the surface of the thinned area with the first slurry and then performing a first curing process. The at least three lithium salt concentrations of the second slurry are coated on the surface of the conductive reinforcement layer in order of increasing concentration gradient, and the gradient electrolyte layer is formed by a second curing treatment.

5. The method for preparing the negative electrode according to claim 4, characterized in that, The preparation of each of the second slurries includes: adding a polymer matrix and a toughening agent to a diluting solvent to obtain a matrix solution; adding a pre-calculated target amount of lithium salt to the matrix solution in portions, then adding a second solvent for homogeneous dispersion to obtain a second slurry with a target lithium salt concentration; The interval between the multiple additions is 5 min to 20 min, and the addition temperature is 45℃ to 65℃.

6. The method for preparing the negative electrode according to claim 5, characterized in that, The solid content in the first slurry is 15%-20%, and the first solvent includes one or more of deionized water and alcohol solvents; In the second slurry: the mass percentage of the second solvent is 10%-20%, and the mass percentage of the diluent solvent is 20%-60%; The diluting solvent includes one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide, and N,N-dimethylacetamide.

7. An electrical device, characterized in that, Includes the negative electrode as described in any one of claims 1-3.

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