Water-based conductive binder and preparation method thereof, negative pole piece and electrochemical energy storage device

Abstract

The invention relates to a water-based conductive binder and a preparation method thereof, a negative pole piece and an electrochemical energy storage device. The water-based conductive binder comprises a water-based binding polymer, nano cellulose and a conductive material. The water-based conductive binder has good functions of enhancing conductivity and inhibiting expansion of electrode material particles, so that the capacity and the cycle life of a battery are improved, and the water-based conductive binder is particularly suitable for a silicon-containing negative electrode active material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a water-based conductive binder, a preparation method thereof, a negative electrode sheet and an electrochemical energy storage device. BACKGROUND

[0002] Silicon material is a negative electrode material with ultra-high specific capacity (theoretical capacity 4200 mAh / g), which is more than ten times the capacity of traditional carbon-based materials, and has a comparable discharge platform, so it is considered to have good prospects for use in secondary battery negative electrode materials. However, the pure silicon negative electrode has poor conductivity and large internal resistance. During the charging and discharging process of the battery, the lithium extraction reaction of silicon will be accompanied by a huge volume change (> 300%), which will continuously destroy the initially formed SEI film (solid electrolyte interface film), and the volume expansion will expose the fresh negative electrode surface, which will react with the electrolyte and lithium ions to form a new SEI, and this cycle will continue, which will easily lead to a continuous decrease in the capacity of the lithium ion battery. The expansion of the silicon negative electrode will also cause the separation between the electrode materials and the current collector, thereby losing electrical contact, deteriorating the cycle performance, and greatly shortening the effective service life of the battery.

[0003] The prior art CN116235311A discloses a negative electrode for a secondary battery, which has a negative electrode composite material layer having a negative electrode active material including a Si compound, a conductive material including single-layer carbon nanotubes with a fiber diameter of less than 4 nm, and a binding material including cellulose nanofibers with a fiber diameter of 9 nm or less, the content of the cellulose nanofibers being 0.005 mass% or more and less than 0.2 mass% with respect to the mass of the negative electrode active material. Both the single-layer carbon nanotubes with a fiber diameter of less than 4 nm and the cellulose nanofibers with a fiber diameter of 9 nm or less need to be satisfied to uniformly disperse the carbon nanotubes, form a conductive network of the negative electrode active material including the Si compound and the single-layer carbon nanotubes, and thereby play a role in limiting the expansion of the silicon negative electrode. Moreover, the SBR used in the technical solution cannot form a binding network with the carbon nanotubes to inhibit the cyclic expansion of the silicon negative electrode. SUMMARY

[0004] The purpose of the present application is to provide a water-based conductive binder, a preparation method thereof, a negative electrode sheet and an electrochemical energy storage device, which has the effects of improving conductivity and inhibiting the expansion of negative electrode active material particles, thereby being beneficial to improving the capacity and cycle life of the battery.

[0005] To this end, the first aspect of the present application provides a water-based conductive binder, which comprises a water-based binding polymer, nanocellulose and a conductive material.

[0006] The crosslinked network structure is formed by the water-based binding polymer, nanocellulose and conductive material. In terms of improving the conductive performance, the conductive material in the crosslinked structure provides the conductive performance, and the nanocellulose has excellent ion transmission performance, which can effectively improve the diffusion coefficient of lithium ions. In terms of inhibiting the expansion of the electrode material, the water-based conductive binder has greater cohesion than the binder with a non-crosslinked structure due to the crosslinked structure, and the strong cohesion can effectively inhibit the expansion effect of the electrode sheet. When it is used for a silicon-based negative electrode material, it also has a significant inhibiting expansion effect. Specifically, the nanocellulose is rich in -OH and is easy to form hydrogen bonds or covalent bonds with other materials, so as to not only effectively improve the interpolymer force, but also enhance the force between the binder and the surface of the electrode active material particles; in addition, under the assistance of the conductive material "electric bridge", it can be better wrapped on the surface of the electrode active material particles, effectively inhibiting the expansion of the silicon-based material, thereby reducing the damage of the SEI film, and being beneficial to improving the capacity and cycle life of the battery.

[0007] In any embodiment, the water-based binding polymer at least partially covers the surface of the nanocellulose and / or the conductive material.

[0008] In any embodiment, the water-based binding polymer is chemically bonded to the nanocellulose, and the chemical bond includes a hydrogen bond and / or a covalent bond.

[0009] In any embodiment, the water-based binding polymer is chemically bonded to the conductive material, and the chemical bond includes a hydrogen bond and / or a covalent bond.

[0010] In any embodiment, the nanocellulose is chemically bonded to the conductive material, and the chemical bond includes a hydrogen bond and / or a covalent bond.

[0011] In any embodiment, the water-based binding polymer, nanocellulose and conductive material are chemically bonded to each other, and the chemical bond includes a hydrogen bond and / or a covalent bond.

[0012] In any embodiment, the water-based binding polymer, nanocellulose and conductive material form a three-dimensional crosslinked network structure.

[0013] In any embodiment, the mass relationship of the nanocellulose, conductive material and water-based binding polymer satisfies: (nanocellulose + water-based binding polymer) / conductive material ≥ 2.5.

[0014] The synergistic effect of nanocellulose, conductive material and water-based adhesive polymer, using the above mass ratio, is conducive to further improving the strong peeling strength, improving the conductivity and inhibiting the expansion capacity of the electrode active material. Among them, the synergistic effect of nanocellulose and conductive material mainly affects the inhibition capacity of expansion force, and by controlling the amount of the two within a certain range, excellent inhibition capacity and conductivity can be obtained at the same time, and cost advantage is also obtained; the synergistic effect of nanocellulose and water-based adhesive polymer mainly affects the peeling strength and ion conductivity, and if it is too small, the peeling strength will be insufficient, and if it is too large, it may cause the viscosity to be too high, thereby affecting the processing performance.

[0015] In any embodiment, the mass ratio of nanocellulose to conductive material is (0.1-1):(0.1-1), and the water-based conductive agent within this dosage range has more excellent comprehensive performance.

[0016] In any embodiment, the water-based adhesive polymer includes at least one of the following group: polyacrylic acid-based copolymer, styrene butadiene rubber (SBR polymer), sodium alginate (CMC), carboxymethyl chitosan, polyacrylonitrile-based copolymer (PAN), polyvinyl alcohol (PVA).

[0017] In any embodiment, the water-based adhesive polymer contains -COOM, and M is Li or Na. Under the synergistic effect of the nanocellulose, the transmission capacity of lithium ions or sodium ions can be further improved.

[0018] In any embodiment, the polymerized monomers of the polyacrylic acid-based copolymer include acrylic monomers and functional monomers, and the functional monomers include any one of cyano monomers, sulfonic acid monomers, ether monomers, amide monomers, or a combination of two or more thereof.

[0019] By using the above functional monomers, the modification of functional groups is realized, and the function of the water-based conductive adhesive is further improved. Among them, the cyano group can produce a conjugation effect with the electron pair on the conductive material (such as carbon nanotubes), thereby forming a conductive network and a crosslinking network, which is conducive to increasing the peeling force of the conductive adhesive and the active material. The sulfonic acid group improves the ion conductivity, thereby enhancing the conductivity of the conductive adhesive. The ether group enhances the flexibility of the adhesive, thereby improving the cracking and powder dropping of the pole piece. On the basis of the above, when the cyano group is combined with the sulfonic acid group or the ether group, a synergistic effect can be achieved, which can better improve the related performance of the adhesive, thereby further improving the battery performance.

[0020] In any embodiment, the conductive material includes at least one of the following group: conductive graphite, carbon black, Ketjen black, Super P, carbon nanotubes, carbon nanofibers, graphene.

[0021] Furthermore, the carbon nanotubes include at least one of the following: single-walled carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes.

[0022] In any embodiment, the carbon nanotube is at least one of single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0023] In any embodiment, the carbon nanotube is a single-walled carbon nanotube.

[0024] Using single-walled carbon nanotubes (SUVs) further improves conductivity and the ability to suppress expansion. Compared to multi-walled carbon nanotubes, SUVs have a larger aspect ratio and stronger conductivity, resulting in superior electrical performance. When SUVs are bound to the surface of the negative electrode active material particles, they can bridge the two ends of the active particles. Furthermore, due to their high mechanical strength, SUVs can better suppress the expansion of the active material during charge and discharge, improving battery cycle life. In addition, using SUVs requires only a smaller amount to meet the needs of practical applications, demonstrating promising prospects for industrial applications.

[0025] In any embodiment, the diameter of the carbon nanotubes and carbon nanofibers is independently 1 to 50 nm, and examples include: 1 to 40 nm, 1 to 30 nm, 1 to 20 nm, 1 to 10 nm, or 1 to 5 nm.

[0026] In any embodiment, the length of the carbon nanotubes and carbon nanofibers is independently 0.1–80 μm; examples include: 0.1–60 μm, 0.1–50 μm, 0.1–40 μm, 0.1–30 μm, 0.1–20 μm, 0.1–10 μm, 0.5–60 μm, 0.5–50 μm, 0.5–40 μm, 0.5–30 μm, 0.5–20 μm, and 0.5–10 μm.

[0027] In any embodiment, the nanocellulose includes at least one of the following: nanocellulose crystals, nanocellulose fibers, and bacterial cellulose.

[0028] In any embodiment, the length of the nanocellulose is 0.1 to 10.0 μm; preferably 1 to 5 μm.

[0029] In any embodiment, the diameter of the nanocellulose is 1 to 50 nm.

[0030] Using nanocellulose of appropriate length and / or diameter helps to keep the viscosity of the water-based binder within a suitable range, allowing it to better coat the surface of the electrode active material particles; it also has the advantage of bridging the electrode active material particles and forming a conductive network.

[0031] In any embodiment, the nanocellulose contains -COOM, where M is Li or Na. This nanocellulose provides excellent ion-conducting properties, thereby effectively improving the transport of lithium or sodium ions.

[0032] A second aspect of this application provides a method for preparing the water-based conductive adhesive:

[0033] In any embodiment, the nanocellulose and conductive material are mixed and dispersed evenly to obtain a conductive-cellulose slurry; the conductive-cellulose slurry is then mixed evenly with the aqueous binder polymer and neutralized with alkali to obtain the aqueous conductive binder; or,

[0034] In any embodiment, the nanocellulose and conductive material are mixed and dispersed evenly to obtain a conductive-cellulose slurry; the conductive-cellulose slurry is mixed with the polymer monomers of the water-based adhesive polymer, an initiator is added for polymerization, and then an alkali is added for neutralization to obtain the water-based conductive adhesive.

[0035] Conductive materials, especially carbon nanotubes, are prone to agglomeration in systems containing other materials. According to the embodiments of this application, nanocellulose and conductive materials are first mixed and dispersed. Because nanocellulose has carboxyl groups, it facilitates the dispersion of conductive materials, especially carbon nanotubes. The functional groups on the surface of carbon nanotubes interact with the hydroxyl groups of nanocellulose through hydrogen bonds, resulting in a stable carbon nanotube-nanocellulose slurry. The aqueous conductive binder obtained by this preparation method exhibits good uniformity and stability.

[0036] In addition, in some embodiments, an aqueous binder polymer can be coated on the surface of nanocellulose and / or conductive materials by in-situ polymerization to act as a steric hindrance, so that the conductive materials and nanocellulose are better dispersed and evenly distributed, preventing agglomeration and making it easier to mix with the main material.

[0037] In any embodiment, the neutralization by adding alkali specifically refers to adding an inorganic alkali solution to neutralize to a pH of 6.5 to 8.0.

[0038] In any embodiment, the inorganic base includes at least one of the following: lithium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, and sodium bicarbonate.

[0039] In any embodiment, the inorganic base includes lithium hydroxide.

[0040] When lithium hydroxide is used, it not only adjusts the pH of water-based conductive adhesives, but also has the following effects: Li +It can act as a link between water-based binder polymers and conductive materials (especially carbon nanotubes) and nanocellulose, not only forming a highly conductive network but also more effectively suppressing the expansion of electrode active material particles. Through these effects, internal resistance can be significantly reduced, and battery capacity and charge-discharge cycle rate under high current charging and discharging can be improved.

[0041] A third aspect of this application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; the negative electrode material layer contains a negative electrode active material and the aqueous conductive binder described in this application.

[0042] In any embodiment, the negative electrode active material comprises silicon.

[0043] In any embodiment, the negative electrode active material includes at least one of the following: elemental silicon, silicon-carbon composite, silicon-nitrogen composite, silicon oxide, silicon alloy, and silicon oxide-carbon composite.

[0044] A fourth aspect of this application provides an electrochemical energy storage device comprising any one of the aqueous conductive binder described in the first aspect of this application, the aqueous conductive binder prepared by the second aspect, and the negative electrode sheet described in the third aspect.

[0045] Furthermore, the electrochemical energy storage device includes, but is not limited to, lithium-ion batteries, sodium-ion batteries, semi-solid-state batteries, or all-solid-state batteries.

[0046] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Detailed Implementation

[0047] Exemplary embodiments of this disclosure will now be described in more detail. It should be understood that this disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0048] 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 application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0049] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0050] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0051] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0052] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0053] As a promising anode active material for rechargeable batteries, silicon-containing materials suffer from the following problems: During battery charging and discharging, the lithium insertion / extraction reaction of silicon is accompanied by huge volume changes (>300%), which continuously damages the initially formed SEI film. Simultaneously, the volume expansion exposes fresh anode surfaces, which then react with the electrolyte and lithium ions to form a new SEI. This cycle repeats, easily leading to a continuous decrease in the capacity of lithium-ion batteries. The expansion of the silicon anode can also cause separation between electrode materials and between the electrode material and the current collector, resulting in loss of electrical contact, deterioration of cycle performance, and a significant reduction in battery life.

[0054] Therefore, this application provides an aqueous conductive binder with a cross-linked structure, which has good functions of enhancing conductivity and inhibiting expansion. It is especially suitable for silicon-containing negative electrode active materials and can improve the above-mentioned problems to a certain extent, thereby helping to improve the battery capacity and cycle life.

[0055] The solutions described in the embodiments of this application are applicable to aqueous conductive binders, negative electrode sheets containing the aqueous conductive binders, and secondary batteries containing the negative electrode sheets.

[0056] Aqueous conductive binder

[0057] In some embodiments, an aqueous conductive adhesive is provided, comprising an aqueous adhesive polymer, nanocellulose, and a conductive material.

[0058] This aqueous conductive binder comprises an aqueous binder polymer, nanocellulose, and conductive materials forming a cross-linked network structure. Regarding improved conductivity, the conductive materials in the cross-linked structure provide electron conduction, while nanocellulose exhibits excellent ion transport properties, effectively enhancing the lithium-ion diffusion coefficient. In suppressing electrode material expansion, the cross-linked structure of this aqueous conductive binder provides greater cohesion compared to non-cross-linked binders. This strong cohesion effectively suppresses electrode expansion, demonstrating a significant anti-expansion effect when used in silicon-based anode materials. Specifically, nanocellulose is rich in -OH groups, readily forming hydrogen or covalent bonds with other materials. This not only effectively enhances intermolecular forces but also strengthens the interaction between the binder and the surface of the electrode active material particles. Furthermore, with the support of carbon nanotube "electric bridges," it can better encapsulate the surface of the electrode active material particles, effectively suppressing silicon-based material expansion and reducing SEI film damage, thus contributing to improved battery capacity and cycle life.

[0059] In some embodiments, the aqueous binder polymer at least partially covers the surface of the nanocellulose and / or conductive material.

[0060] For example, in-situ polymerization can be used to coat the surface of nanocellulose and / or conductive materials with water-based binder polymers, which acts as a steric hindrance, allowing the conductive materials and nanocellulose to be better dispersed and evenly distributed, preventing agglomeration. This not only improves the stability of the binder but also facilitates the mixing of the binder with the main material in the later stages.

[0061] In some embodiments, the aqueous binder polymer is chemically bonded to the nanocellulose, wherein the chemical bonds include hydrogen bonds and / or covalent bonds.

[0062] In some embodiments, the aqueous binder polymer is chemically bonded to the conductive material, wherein the chemical bonds include hydrogen bonds and / or covalent bonds.

[0063] In some embodiments, the nanocellulose is chemically bonded to the conductive material, wherein the chemical bonds include hydrogen bonds and / or covalent bonds.

[0064] In some embodiments, the aqueous binder polymer, nanocellulose, and conductive material are chemically bonded to each other, wherein the chemical bonds include hydrogen bonds and / or covalent bonds.

[0065] In some embodiments, the aqueous binder polymer, nanocellulose, and conductive material form a three-dimensional cross-linked network structure.

[0066] In some embodiments, the mass relationship between the nanocellulose, the conductive material, and the aqueous binder polymer satisfies the following: (nanocellulose + aqueous binder polymer) / conductive material ≥ 2.5, for example: (nanocellulose + aqueous binder polymer) / conductive material ≥ 5, (nanocellulose + aqueous binder polymer) / conductive material ≥ 10, (nanocellulose + aqueous binder polymer) / conductive material ≥ 15, (nanocellulose + aqueous binder polymer) / conductive material ≥ 20, etc.

[0067] In some embodiments, the mass relationship between the nanocellulose, the conductive material, and the aqueous binder polymer satisfies the following: (nanocellulose + aqueous binder polymer) / conductive material is 2.5 to 1000. Examples include: 5 to 1000, 5 to 800, 5 to 700, 5 to 600, 5 to 500, 5 to 400, 5 to 380, 5 to 350, 5 to 320, 5 to 300, 5 to 280, 5 to 260, 5 to 250, 5 to 240, 5 to 230, 5 to 220, 5 to 210, 5 to 200, 5 to 180, 5 to 150, 5 to 100, 10 to 1000, 10 to 800, 10 to 700, 10 to 600, 10 to 500, and 10 to 400. 10~380, 10~350, 10~320, 10~300, 10~280, 10~260, 10~250, 10~240, 10~230, 10~220, 10~210, 10~200, 10~180, 10~150, 10~100, 20~1000, 20~800, 20~700 20~600, 20~500, 20~400, 20~380, 20~350, 20~320, 20~300, 20~280, 20~260, 20~250, 20~240, 20~230, 20~220, 20~210, 20~200, 20~180, 20~150, 20~100, etc.

[0068] In some embodiments, the mass ratio of nanocellulose to conductive material is (0.1 to 1):(0.1 to 1); specific examples include: 0.1:1, 0.1:0.9, 0.1:0.8, 0.1:0.7, 0.1:0.6, 0.1:0.5, 0.1:0.4, 0.1:0.3, 0.1:0.2, 0.1:0.1, 1:0.1, 1:0.9, 1:0.8, 1:0.7, 1:0.6, 1:0.5, 1:0.4, 1:0.3, 1:0.2, 1:0.1, etc.

[0069] The synergistic effect of the nanocellulose, conductive material, and water-based binder polymer, using the aforementioned mass ratio, is beneficial for further improving peel strength, conductivity, and the ability to suppress the expansion of the electrode active material. Specifically, the synergistic effect of nanocellulose and conductive material mainly affects the ability to suppress expansion force; controlling their amounts within a certain range can simultaneously achieve excellent expansion suppression and conductivity, while also offering cost advantages. The synergistic effect of nanocellulose and water-based binder polymer mainly affects peel strength and ion conduction ability; too little will result in insufficient peel strength, while too much may lead to excessively high viscosity, thus affecting processing performance.

[0070] In some embodiments, the aqueous adhesive polymer includes at least one of the following: polyacrylic acid copolymer, styrene-butadiene rubber (SBR polymer), sodium alginate (CMC), carboxymethyl chitosan, polyacrylonitrile copolymer (PAN), and polyvinyl alcohol (PVA).

[0071] In some embodiments, the aqueous binder polymer includes a -COOM group, wherein M is Li or Na.

[0072] When the aqueous binder polymer has a -COOM group, the transport capacity of lithium ions or sodium ions can be further improved under the synergistic effect of the nanocellulose.

[0073] In some embodiments, the polymeric monomers of the polyacrylic acid copolymer include acrylic monomers and functional monomers, wherein the functional monomers include any one or a combination of two or more of cyano monomers, sulfonic acid monomers, ether monomers, and amide monomers. As an example, the polyacrylic acid copolymer has the structure shown in (Formula I) or / and (Formula II).

[0074]

[0075] While retaining the carboxyl groups (or, in other words, the polyacrylic acid copolymer has carboxyl groups), the polyacrylic acid copolymer can be modified with the aforementioned functional groups based on polyacrylic acid. This modification of functional groups further improves the functionality of the water-based conductive binder. Specifically, the cyano group can generate a conjugated effect with electron pairs on conductive materials (e.g., carbon nanotubes), thereby forming a conductive network and a cross-linked network, which helps increase the peel force between the conductive binder and the active material. The sulfonic acid group enhances ion conduction capability, thereby enhancing the conductivity of the conductive binder. The ether group enhances the binder's flexibility, thereby improving electrode cracking and powder shedding. Based on the above, combining the cyano group with the sulfonic acid group or the ether group can achieve a synergistic effect, better improving the relevant properties of the binder and further improving battery performance.

[0076] Specifically, the polyacrylic acid copolymer is obtained by polymerizing acrylic monomers and functional monomers.

[0077] The mass of the polyacrylic acid copolymer is 100%, and the mass content of the acrylic monomer is 10% to 90%, preferably 20% to 70%.

[0078] The mass of the polyacrylic acid copolymer is 100%, and the mass content of the functional monomer is 10% to 90%, preferably 30% to 80%.

[0079] The acrylic monomers include at least one of acrylic acid and methacrylic acid.

[0080] The functional monomers include any one or a combination of two or more of the following: cyano monomers, sulfonic acid monomers, ether monomers, and amide monomers.

[0081] The cyano monomer includes α,β-olefinic unsaturated nitrile monomers selected from acrylonitrile, α-haloacrylonitrile, α-alkylacrylonitrile, or combinations thereof, preferably acrylonitrile or methacrylonitrile.

[0082] The sulfonic acid monomer is selected from methpropylene sulfonic acid, propylene sulfonic acid, vinyl sulfonic acid, methyl vinyl sulfonic acid, allyl vinyl sulfonic acid, styrene sulfonic acid, 2-sulfoethyl methacrylate, 2-methyl-2-propen-1-sulfonic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, 3-allyloxy-2-hydroxy-1-propane sulfonic acid, or combinations thereof.

[0083] The ether monomer is preferably a cyclic ether monomer capable of forming a cyclic ether monomer unit. Examples include monomers containing an epoxy group (epoxy ring) (epoxy monomer unit) and monomers containing an oxetyl group (oxetane ring) (oxetyl monomer unit). From the viewpoint of further improving the heat shrinkage resistance, electrolyte affinity, and adhesion of the functional layer, epoxy monomers are preferred.

[0084] As epoxy-containing monomers, further preferred varieties include allyl glycidyl ether, (meth)acrylate glycidyl ester, 3,4-epoxycyclohexyl methyl methacrylate, and 4-hydroxybutyl acrylate glycidyl ether.

[0085] The amide monomer is selected from acrylamide, methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-n-propylmethacrylamide, N-isopropylmethacrylamide, isopropylacrylamide, N-n-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N-hydroxymethylmethacrylamide, N-(methoxymethyl)methacrylamide, and N-(ethoxymethyl)methacrylamide. N-(propoxymethyl)methacrylamide, N-(butoxymethyl)methacrylamide, N,N-dimethylmethacrylamide, N,N-dimethylaminopropylmethacrylamide, N,N-dimethylaminoethylmethacrylamide, N,N-dihydroxymethylmethacrylamide, diacetone methacrylamide, diacetone acrylamide, methacryloylmorpholine, N-hydroxymethylacrylamide, N-methoxymethylacrylamide, N,N'-methylenebisacrylamide (MBA), N-hydroxymethylacrylamide, or combinations thereof.

[0086] In some embodiments, the carbon nanotubes are at least one of single-walled carbon nanotubes (SWCNT or SWNT), multi-walled carbon nanotubes, and oligo-walled carbon nanotubes.

[0087] In some embodiments, the carbon nanotubes are single-walled carbon nanotubes.

[0088] Using single-walled carbon nanotubes (SUVs) further improves conductivity and the ability to suppress expansion. Compared to other carbon nanotubes, SUVs have a larger aspect ratio and stronger conductivity, resulting in superior electrical performance. When SUVs are bound to the surface of the negative electrode active material particles, they can bridge the two ends of the active particles. Furthermore, due to their high mechanical strength, SUVs can better suppress the expansion of the active material during charge and discharge, improving battery cycle life. In addition, using SUVs requires only a smaller amount to meet the needs of practical applications, demonstrating promising prospects for industrial applications.

[0089] In some embodiments, the diameter of the carbon nanotubes and carbon nanofibers is independently 1.0 to 50.0 nm; for example, it can be selected from about 1.0 nm, 1.5 nm, 2.0 nm, 2.5 nm, 3.0 nm, 3.5 nm, 4.0 nm, 4.5 nm, 5.0 nm, 10.0 nm, 15.0 nm, 20.0 nm, 25.0 nm, 30.0 nm, 35.0 nm, 40.0 nm, 45.0 nm, 50.0 nm, etc.

[0090] In any embodiment, the length of the carbon nanotubes and carbon nanofibers is independently 0.1–80.0 μm; for example, it can be selected from 0.1–60.0 μm, 0.1–50.0 μm, 0.1–40.0 μm, 0.1–30.0 μm, 0.1–20.0 μm, 0.1–10.0 μm, 0.5–60.0 μm, 0.5–50.0 μm, 0.5–40.0 μm, 0.5–30.0 μm, 0.5–20.0 μm, 0.5–10.0 μm, etc.

[0091] In any embodiment, the nanocellulose includes at least one of the following: nanocellulose crystals (CNC), nanocellulose fibers (CNF), and bacterial cellulose (BC).

[0092] In any embodiment, the length of the nanocellulose is 0.1–10.0 μm; preferably 1.0–5.0 μm. For example, the length of the nanocellulose can be about 0.1 μm, 0.5 μm, 1.0 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, etc.

[0093] In any embodiment, the diameter of the nanocellulose is 1 to 50 nm; for example, it can be about 1.0 nm, 1.5 nm, 2.0 nm, 2.5 nm, 3.0 nm, 3.5 nm, 4.0 nm, 4.5 nm, 5.0 nm, 10.0 nm, 15.0 nm, 20.0 nm, 25.0 nm, 30.0 nm, 35.0 nm, 40.0 nm, 45.0 nm, 50.0 nm, etc.

[0094] Using nanocellulose of appropriate length and / or diameter helps to keep the viscosity of the water-based binder within a suitable range, allowing it to better coat the surface of the electrode active material particles; it also has the advantage of bridging the electrode active material particles and forming a conductive network.

[0095] In some embodiments, the nanocellulose contains -COOM, where M is Li or Na. This nanocellulose provides excellent ion-conducting properties, thereby effectively improving the transport of lithium or sodium ions.

[0096] In some embodiments, the pH value of the aqueous conductive adhesive is 6.5 to 8.0; for example, the pH value of the aqueous conductive adhesive is about 6.5, 6.8, 7.0, 7.1, 7.2, 7.5, 7.7, 7.8, 7.9, 8.0, etc.

[0097] By making the pH value of the water-based conductive adhesive approximately neutral, it is beneficial to improve the stability of the adhesive itself.

[0098] In some embodiments, pH adjustment can be achieved by including an inorganic alkali neutralization step in the preparation process of the aqueous conductive adhesive. The inorganic alkali includes at least one from the group consisting of lithium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, etc.

[0099] In some of these embodiments, the inorganic base includes lithium hydroxide.

[0100] When lithium hydroxide is used, it not only adjusts the pH of water-based conductive adhesives, but also has the following effects: Li + It can act as a link between polyacrylic acid copolymers, carbon nanotubes, and nanocellulose, forming a highly conductive network and more effectively suppressing the expansion of electrode active material particles. Through these effects, internal resistance can be significantly reduced, and battery capacity and charge-discharge cycle rate under high current can be improved. This is particularly suitable for lithium-ion secondary batteries.

[0101] In some embodiments, the aqueous conductive binder does not contain other binders and / or dispersants, yet it still exhibits excellent adhesion and good dispersibility, effectively meeting the needs of industrial applications and achieving the technical effect of suppressing the expansion of electrode active material particles. Therefore, for the sake of improving operability and reducing costs, it may be omitted from the list of binders and / or dispersants.

[0102] Process for preparing an aqueous conductive binder

[0103] In some embodiments, a method for preparing the aqueous conductive adhesive is provided, comprising:

[0104] The nanocellulose and conductive material are mixed and dispersed evenly to obtain a conductive-cellulose slurry; the conductive-cellulose slurry is then mixed evenly with the aqueous binder polymer, and neutralized with alkali to obtain the aqueous conductive binder; or...

[0105] The nanocellulose and conductive material are mixed and dispersed evenly to obtain a conductive-cellulose slurry; the conductive-cellulose slurry is mixed with the polymer monomers of the water-based adhesive polymer, an initiator is added for polymerization, and then an alkali is added for neutralization to obtain the water-based conductive adhesive.

[0106] Conductive materials, especially carbon nanotubes, are prone to agglomeration in systems containing other materials. According to embodiments of this application, nanocellulose and conductive materials are first mixed and dispersed. Because nanocellulose contains carboxyl groups, it facilitates the dispersion of conductive materials, especially carbon nanotubes. The functional groups on the surface of carbon nanotubes interact with the hydroxyl groups of nanocellulose through hydrogen bonds, resulting in a stable carbon nanotube-nanocellulose slurry. The aqueous conductive binder obtained by this preparation method exhibits good uniformity and stability. Furthermore, in some embodiments, an in-situ polymerization method can be used to coat the surfaces of nanocellulose and conductive materials with an aqueous binder polymer, acting as a steric hindrance, allowing for better and more uniform dispersion and distribution of the conductive material and nanocellulose, preventing agglomeration, and facilitating mixing with the main material.

[0107] In some implementations, equipment such as homogenizers, ball mills, three-roll mills, and ultrasonic cell pulverizers can be used to disperse and pulverize the conductive material and nanocellulose to the nanoscale.

[0108] In some embodiments, the neutralization with alkali specifically refers to adding an inorganic alkali solution to neutralize to a pH of 6.5 to 8.0.

[0109] In some embodiments, the alkali neutralization step includes the following conditions: the temperature is 40 to 80°C; for example, it can be about 40°C, 45°C, 50°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc.

[0110] Under these heating temperature conditions, compared to room temperature, it is more conducive to opening the self-bonding hydrogen bonds or other forces of water-based binder polymers, nanocellulose, and conductive materials, resulting in a decrease in solution viscosity and easier formation of new Li groups. + The chemical bonds link them together. This makes them easy to prepare and process, and easier to scale up for industrial production.

[0111] In some embodiments, the inorganic base includes at least one of the following: lithium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, and sodium bicarbonate.

[0112] In some embodiments, the inorganic base includes lithium hydroxide.

[0113] When lithium hydroxide is used, it not only adjusts the pH of water-based conductive adhesives, but also has the following effects: Li + It can act as a link between water-based binder polymers, conductive materials, and nanocellulose, not only forming a highly conductive network but also more effectively suppressing the expansion of electrode active material particles. Through these effects, internal resistance can be significantly reduced, and battery capacity and charge-discharge cycle rate under high current charging and discharging can be improved.

[0114] Negative electrode sheet

[0115] In some embodiments, a negative electrode sheet is provided, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; the negative electrode material layer contains a negative electrode active material and an aqueous conductive binder of any embodiment of the present application.

[0116] By applying the aqueous conductive binder of the present application to the negative electrode material layer, conductivity can be significantly improved and the expansion of negative electrode active material particles during charging and discharging can be suppressed, thereby reducing the damage to the SEI film and improving the battery capacity and cycle life.

[0117] In some embodiments, the negative electrode active material comprises silicon. For example, the negative electrode active material may include at least one of the following: elemental silicon, silicon-carbon composites, silicon-nitrogen composites, silicon oxides, silicon alloys, silicon oxide-carbon composites, etc.

[0118] When using a negative electrode active material containing silicon, it is prone to problems such as insufficient conductivity and easy expansion. However, the water-based conductive binder of the present application can also significantly improve conductivity and inhibit expansion for a negative electrode active material containing silicon.

[0119] In some embodiments, the negative electrode active material may further include other negative electrode active materials known in the art for use in batteries, for example, it may include at least one selected from the group consisting of: natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 Li-Al alloy.

[0120] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0121] In some embodiments, the negative electrode material layer may optionally include other binders and / or dispersants besides the aqueous conductive binder.

[0122] In some embodiments, the negative electrode material layer does not include any binders and / or dispersants other than the aqueous conductive binder. Because the aqueous conductive binder provided in this application has good bonding and dispersing properties, it eliminates the need for additional binders, dispersants, etc., and the slurry used to prepare the negative electrode material layer exhibits good processing performance, resulting in good adhesion between the prepared negative electrode material layer and the negative electrode current collector.

[0123] In some embodiments, the negative electrode material layer may optionally include a conductive agent. For example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In some embodiments, the negative electrode material layer does not include conductive agents other than the aqueous conductive binder. Since the aqueous conductive binder provided in this application has good conductivity, it is possible to achieve good conductivity in the negative electrode material layer and the negative electrode sheet without adding additional conductive agents.

[0125] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode material layer, such as the negative electrode active material, the aqueous conductive binder, and any other optional components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes.

[0126] Electrochemical energy storage device

[0127] In some embodiments of this application, an electrochemical energy storage device is provided, which includes an aqueous conductive binder or a negative electrode sheet provided in any embodiment of this application. The electrochemical energy storage device can be a battery, such as, but not limited to, lithium-ion batteries, sodium-ion batteries, semi-solid-state batteries, or all-solid-state batteries.

[0128] In some embodiments of this application, a battery is provided, which includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte; the negative electrode is the negative electrode provided in any embodiment of this application.

[0129] In some embodiments, the battery is a secondary battery, such as a lithium-ion secondary battery. As an example, the lithium-ion battery is any one of the following: lithium iron phosphate / graphite series, lithium cobalt oxide / graphite series, lithium manganese oxide / graphite series, or ternary material / graphite series batteries.

[0130] [Positive electrode plate]

[0131] The positive electrode sheet includes a positive current collector and a positive electrode material disposed on at least one surface of the positive current collector, wherein the positive electrode material includes a positive active material.

[0132] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0133] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present invention is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0134] In some embodiments, the positive electrode material may optionally include a binder. For example, the binder may include one or more combinations selected from the group consisting of: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0135] In some embodiments, the cathode material may optionally include a conductive agent. For example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0136] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned positive electrode material, such as positive electrode active material, conductive agent, binder and any other components in a solvent (e.g. N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0137] [Negative electrode plate]

[0138] The negative electrode sheet provided in any embodiment of this application is used.

[0139] [Isolation membrane]

[0140] As for the separator, this application does not have any particular limitations, and any known porous structure separator with electrochemical and mechanical stability can be selected according to actual needs. For example, the separator can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0141] [Electrolytes]

[0142] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0143] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0144] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0145] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0146] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0147] [Battery manufacturing]

[0148] A battery can be prepared by forming an electrode assembly from positive electrode sheets, negative electrode sheets, and separator through a winding or stacking process, and then by injecting electrolyte after outer packaging.

[0149] The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. It can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0150] This application does not impose any particular restrictions on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape.

[0151] Preparation Example 1

[0152] This embodiment provides an aqueous conductive adhesive Y1, the preparation method of which includes:

[0153] 1. Preparation of polyacrylic acid-based copolymers

[0154] A polyacrylic acid-based copolymer is used as the water-based adhesive polymer. The composition of the polyacrylic acid-based copolymer is: acrylic acid: 2-acrylamide-2-phenylethanesulfonic acid: acrylonitrile in a mass ratio of 60:8:32.

[0155] The preparation was carried out according to the method disclosed in CN111139002A, but neutralization was not performed. The specific method is as follows:

[0156] Add 350 parts of pure water to a reactor, stir at 11 rpm, and purge with nitrogen at a flow rate of 2000 L / H to remove water-soluble oxygen for 1.5 hours. Then add 60 parts of acrylic acid, 8 parts of 2-acrylamide-2-phenylethanesulfonic acid, and 32 parts of acrylonitrile, and continue purging with nitrogen while stirring for 3 hours to obtain a solution. Then continue purging with nitrogen and heat the solution to 55°C at a rate of 1°C / min. Add 0.5 parts by mass (10%) of initiator solution to oxidize benzoyl and initiate the polymerization for 10 hours to obtain the polymerization product. Then, at 60°C, reduce the vacuum level to below 0.1 MPa using a vacuum pump to remove residual monomers, thus preparing the polyacrylic acid-based copolymer.

[0157] 2. Preparation of water-based conductive adhesives

[0158] The raw materials were weighed according to the following mass ratio: cellulose nanofiber (2 μm in length, 40 nm in diameter), single-walled carbon nanotubes (2 nm in diameter), and polyacrylic acid copolymer: 1:0.5:19.5. First, the carbon nanotubes and cellulose nanofibers were mixed uniformly using a high-speed disperser at 800 rpm, and then pressure dispersed using a homogenizer for 10 h to obtain a black suspension N1 with a high solids content. N1 was then mixed uniformly with the polyacrylic acid copolymer and further mixed uniformly using a high-speed adhesive disperser at 1000 rpm to obtain a mixed solution. The mixed solution was poured into a glass reactor and heated at 60°C with stirring. A lithium hydroxide solution (10% concentration) was added dropwise under peristaltic pump pressure of 10 rpm to adjust the pH of the mixed solution to 7.5. Then, deionized water was added to adjust the solids content to 5%, and the reaction continued for 1 h. The material was then sieved through a 200-mesh sieve to obtain an aqueous conductive binder Y1.

[0159] Preparation Example 2

[0160] This embodiment provides an aqueous conductive adhesive Y2, the preparation method of which includes:

[0161] Weigh each raw material according to the following mass ratio, wherein the polyacrylic acid copolymer is weighed according to its polymeric monomers. The mass ratio of nanocellulose fiber, single-arm carbon nanotube, and polyacrylic acid copolymer is 1:0.5:19.5; the composition of the polymeric monomers of the polyacrylic acid copolymer, i.e., the mass ratio, is acrylic acid:2-acrylamide-2-phenylethanesulfonic acid:acrylonitrile = 60:8:32.

[0162] First, single-arm carbon nanotubes (2 nm in diameter) and nanocellulose fibers (2 μm in length and 40 nm in diameter) were mixed evenly using a high-speed disperser at 800 rpm, and then dispersed under pressure for 10 h to obtain a black suspension N1 with a high solid content. N1 was mixed with acrylic acid, 2-acrylamide-2-phenylethanesulfonic acid, and acrylonitrile, and then mixed evenly using a high-speed adhesive disperser at 1000 rpm. Ammonium persulfate initiator was added to obtain a mixed solution. The mixed solution was poured into a glass reactor, heated and stirred at 60 °C, and lithium hydroxide solution (10% concentration) was added dropwise under the condition of peristaltic pump at 10 rpm to adjust the pH of the mixed solution to 7.5. Then, deionized water was added to adjust the solid content to 5% and the reaction was continued for 1 h. The material was then sieved through a 200-mesh sieve to obtain water-based conductive binder Y2.

[0163] Example 1

[0164] This embodiment provides a secondary battery, the preparation method of which includes:

[0165] 1) Positive electrode plate

[0166] Lithium iron phosphate, used as the positive electrode active material, carbon black, used as a conductive agent, and polyvinylidene fluoride, used as a binder, are dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 96:3:3 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto a positive electrode current collector aluminum foil, and after drying, cold pressing, slitting, and cutting, a positive electrode sheet is obtained.

[0167] 2) Negative electrode plate

[0168] The negative electrode active material, silicon oxide-carbon composite (SiO / C), and the water-based conductive binder Y1 are dispersed in deionized water at a mass ratio of 97.5:2.5 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector copper foil. After drying, cold pressing, slitting, and cutting, a negative electrode sheet is obtained.

[0169] 3) Diaphragm

[0170] Polyethylene film is used as the diaphragm.

[0171] 4) Electrolyte

[0172] The basic electrolyte is prepared by mixing the organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) in a ratio of 3:6:1, and then adding lithium hexafluorophosphate to a final concentration of 1.0M.

[0173] 5) Preparation of lithium-ion batteries

[0174] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode. The stacked electrodes are then used to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, a lithium-ion battery cell is obtained.

[0175] The following tests were performed using the following methods, and the test results are shown in Table 1:

[0176] 1. Diaphragm resistance

[0177] The prepared negative electrode sheet was subjected to resistance testing using a resistance testing instrument, and the test results are shown in Table 1.

[0178] 2. Peeling force

[0179] The negative electrode sheet was cut into a 30×100mm rectangle and the adhesion was tested using a tensile testing machine. The tensile speed was 100mm / min, the width was 30mm, and the weight was 1gf.

[0180] 3. Cohesion

[0181] Cut the negative electrode sheet into strips of 32×180mm, roll them, and then cut them into shorter strips. Adhere the pressure-sensitive tape to the stainless steel plate, then adhere the electrode sheet to the pressure-sensitive tape, and then adhere another layer of green adhesive to the pressure-sensitive tape. Use a tensile testing machine to clamp the green adhesive and peel it off 180°.

[0182] 4. Battery charge / discharge cycle test

[0183] The battery's initial charge / discharge capacity was tested at a 0.2C rate, and its initial charge / discharge efficiency was calculated. Cycle performance was tested using a 0.5C charge / 3C discharge rate for 300 cycles. The battery's test charge / discharge cutoff voltage was 2.8-4.2V.

[0184] 5. 50% SOC discharge DCR

[0185] DC resistance (DCR) test: Charge the cell to the nominal voltage at 0.5C, then charge at a constant voltage until the current is ≤0.05C, and record the capacity as 100% SOC; let it rest for 5 minutes. Discharge the battery at a constant current rate of 1C to 50% SOC, and after adjustment, test the voltage of the lithium-ion battery and record it as V1; discharge continuously at a constant current rate of 4C (denoted as I) for 10 seconds, and after the discharge, test the voltage of the lithium-ion battery and record it as V2; calculate the DC resistance using the formula: DCR=(V1-V2) / I.

[0186] 6. Thickness change after 50 cycles

[0187] The battery is charged and discharged 50 times according to the procedure in section 4. Then the battery is disassembled and the electrode thickness H1 is tested. The original electrode thickness is H2. Then the thickness change rate is ((H1-H2) / H2).

[0188] Example 2

[0189] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0190] In the preparation of the water-based conductive adhesive, the mass ratio of nanocellulose, single-walled carbon nanotubes, and polyacrylic acid copolymer is 1:0.1:19.9.

[0191] Example 3

[0192] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0193] In the preparation of the water-based conductive adhesive, the mass ratio of nanocellulose, single-walled carbon nanotubes, and polyacrylic acid copolymer is 0.1:0.1:20.8.

[0194] Example 4

[0195] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0196] In the preparation of the water-based conductive adhesive, the mass ratio of nanocellulose, single-walled carbon nanotubes, and polyacrylic acid copolymer is 1:1:19.

[0197] Example 5

[0198] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0199] In the preparation of the water-based conductive adhesive, the mass ratio of nanocellulose, single-walled carbon nanotubes, and polyacrylic acid copolymer is 0.1:1:19.9.

[0200] Example 6

[0201] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0202] In the preparation of the water-based conductive adhesive, the mass ratio of nanocellulose, single-walled carbon nanotubes, and polyacrylic acid copolymer is 3.5:6.5:11.

[0203] Example 7

[0204] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0205] In the preparation of the water-based conductive adhesive, the mass ratio of nanocellulose, single-walled carbon nanotubes, and polyacrylic acid copolymer is 3:6:12.

[0206] Example 8

[0207] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0208] In the preparation of the water-based conductive adhesive, the mass ratio of nanocellulose, single-walled carbon nanotubes, and polyacrylic acid copolymer is 6:0.5:14.5.

[0209] Example 9

[0210] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0211] In the preparation of the water-based conductive adhesive, the mass ratio of nanocellulose, single-walled carbon nanotubes, and polyacrylic acid copolymer is 0.08:1:19.5.

[0212] Example 10

[0213] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0214] The length of the nanocellulose is 0.5 μm.

[0215] Example 11

[0216] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0217] The length of the nanocellulose is 10 μm.

[0218] Example 12

[0219] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0220] In the preparation of water-based conductive adhesives, lithium hydroxide is replaced with sodium hydroxide.

[0221] Example 13

[0222] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0223] The water-based conductive adhesive is Y2 obtained in Preparation Example 2.

[0224] Example 14

[0225] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 3, and related tests were performed:

[0226] The water-based conductive adhesive was prepared using the process described in Preparation Example 2.

[0227] Example 15

[0228] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 5, and related tests were performed:

[0229] The water-based conductive adhesive was prepared using the process described in Preparation Example 2.

[0230] Example 16

[0231] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0232] In the preparation of water-based conductive adhesives, carboxyl-neutralized polyacrylic acid copolymers are used to replace the original polyacrylic acid copolymers. The carboxyl-neutralized polyacrylic acid copolymers are prepared by the following method: after removing residual monomers, the preparation of the polyacrylic acid copolymers includes the following step: neutralizing with an aqueous lithium hydroxide solution at 50°C to a pH of 7.5, thus obtaining the carboxyl-neutralized polyacrylic acid copolymer.

[0233] Comparative Example 1

[0234] Except for the following differences, lithium-ion battery cells were prepared according to the same steps as in Example 1, and related tests were performed:

[0235] No nanocellulose is added in the preparation of the water-based conductive adhesive.

[0236] The test results of the lithium-ion battery cells prepared in the above embodiments and comparative examples are shown in Table 1:

[0237] Table 1

[0238]

[0239]

[0240] By comparing Example 1 and Comparative Example 1, it can be seen that when nanocellulose is lacking, the cycle retention rate of the battery decreases significantly, and the cycle expansion of Comparative Example 1 is slightly larger.

[0241] Comparing Examples 1-9 reveals that the mass ratio of nanocellulose, conductive material, and aqueous binder polymer in the aqueous conductive binder has a certain impact on the performance of the electrode and the battery. For example, in Examples 6 and 7, the ratio of (nanocellulose + aqueous binder polymer) to conductive material is relatively small, resulting in lower peel strength and cohesive strength of the electrode compared to Examples 1-5, and a decrease in the cycle retention rate of the battery. Furthermore, the increase in electrode thickness after cycling is more pronounced. As another example, in Examples 8 and 9, the mass ratio of nanocellulose to conductive material is either larger or smaller (12 in Example 8, 0.08 in Example 9), resulting in weaker peel strength and cohesive strength of the electrode compared to Examples 1-5.

[0242] A comparison of Examples 12 and 1 shows that using lithium hydroxide as the neutralizing alkali is more beneficial for improving the battery's initial efficiency and cycle performance compared to other alkalis. A comparison of Examples 13-15 with Examples 1, 3, and 5 shows that using the method of Preparation Example 1 is more beneficial for further reducing the battery's DC resistance and improving battery performance compared to the method of Preparation Example 2.

[0243] Comparing Examples 16 and 1, it is evident that mixing the aqueous binder polymer, conductive material, and nanocellulose before neutralization during the preparation process is more beneficial for improving the DC impedance and cycle performance of the battery. This is likely because, with pre-neutralization, the number of active groups such as carboxyl groups on the surface of the aqueous binder polymer is easily reduced; in the post-neutralization method, the aqueous binder polymer first reacts with the active groups between the conductive material and nanocellulose, resulting in a binder with a higher degree of cross-linking and stronger carbon nanotube dispersion stability, thus improving lithium-ion diffusion and inhibiting electrode expansion.

[0244] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An aqueous conductive binder, characterized by, The water-based conductive binder comprises a water-based binding polymer, nanocellulose and a conductive material.

2. The aqueous conductive binder of claim 1, wherein, At least one of the following features is included: The water-based binding polymer at least partially covers the surface of the nanocellulose and / or the conductive material; The water-based binding polymer is chemically bonded with the nanocellulose; The water-based binding polymer is chemically bonded with the conductive material; The nanocellulose is chemically bonded with the conductive material; The water-based binding polymer, nanocellulose and conductive material are chemically bonded with each other; The water-based binding polymer, nanocellulose and conductive material form a three-dimensional cross-linked network structure; The chemical bond includes a hydrogen bond and / or a covalent bond.

3. The aqueous conductive binder according to claim 1 or 2, wherein The mass relationship of the nanocellulose, conductive material and water-based binding polymer satisfies (nanocellulose + water-based binding polymer) / conductive material ≥ 2.5; Preferably, the mass ratio of the nanocellulose to the conductive material is (0.1-1.0) : (0.1-1.0).

4. The aqueous conductive binder according to any one of claims 1 to 3, wherein The water-based binding polymer includes at least one of a polyacrylic acid-based copolymer, a styrene-butadiene rubber, sodium alginate, carboxymethyl chitosan, a polyacrylonitrile-based copolymer and polyvinyl alcohol; Preferably, the water-based binding polymer contains -COOM, and M is Li or Na; Preferably, the polyacrylic acid-based copolymer includes acrylic monomers and functional monomers, and the functional monomers include at least one of a cyano monomer, a sulfonic acid monomer, an ether monomer and an amide monomer.

5. The aqueous conductive binder according to any one of claims 1 to 4, wherein The conductive material includes at least one of conductive graphite, carbon black, Ketjen black, Super P, carbon nanotubes and carbon nanofibers; Preferably, the carbon nanotubes include at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes and oligo-walled carbon nanotubes; Preferably, the diameter of the carbon nanotubes and carbon nanofibers is independently 1-50 nm; Preferably, the length of the carbon nanotubes and carbon nanofibers is independently 0.1-80.0 μm.

6. The aqueous conductive binder according to any one of claims 1 to 5, wherein The nanocellulose includes at least one of nanocellulose crystals, nanocellulose fibers and bacterial cellulose; Preferably, the length of the nanocellulose is 0.1-10.0 μm; Preferably, the diameter of the nanocellulose is 1-50 nm; Preferably, the nanocellulose contains -COOM, and M is Li or Na.

7. The method of producing an aqueous conductive binder as claimed in any one of claims 1 to 6, characterized by, The method comprises the following steps: Mixing and uniformly dispersing the nanocellulose and conductive material to obtain a conductive-cellulose slurry; Mixing the conductive-cellulose slurry and the water-based binding polymer, and neutralizing with alkali to obtain the water-based conductive binder; Alternatively, Mixing and uniformly dispersing the nanocellulose and conductive material to obtain a conductive-cellulose slurry; mixing the conductive-cellulose slurry and the polymerization monomers of the water-based binding polymer, adding an initiator for polymerization, and then neutralizing with alkali to obtain the water-based conductive binder.

8. A negative electrode sheet characterized by comprising: The negative electrode active material layer comprises a negative electrode active material and the water-based conductive binder according to any one of claims 1 to 6 or prepared by the preparation method of claim 7.

9. The negative electrode sheet according to claim 8, wherein The negative electrode active material comprises silicon element; Preferably, the negative electrode active material comprises at least one of the following: silicon element, silicon-carbon composite, silicon-nitrogen composite, silicon oxide, silicon alloy, and silicon oxide-carbon composite.

10. An electrochemical energy storage device, characterized by Any one of the water-based conductive binder according to any one of claims 1 to 6, the water-based conductive binder prepared by the preparation method of claim 7, or the negative electrode plate according to claim 8 or 9; Preferably, the electrochemical energy storage device is a lithium ion battery, a sodium ion battery, a semi-solid battery, or a full-solid battery.

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