A silicon-based negative electrode binder, a negative electrode sheet, a lithium ion battery and a preparation method thereof

Abstract

The application discloses a silicon-based negative electrode binder, a negative electrode sheet, a lithium ion battery and a preparation method thereof. The binder is formed by graft copolymerization of a polycarboxylic acid compound and an amine-rich aqueous polymer, and the binder has a three-dimensional network structure. The polycarboxylic acid compound comprises at least two carboxyl groups. The amine-rich aqueous polymer comprises at least two amine groups. The at least two carboxyl groups on the same molecular chain of the polycarboxylic acid compound react with the at least two amine groups on the same molecular chain of the amine-rich aqueous polymer. The silicon-based negative electrode binder, the negative electrode sheet, the lithium ion battery and the preparation method thereof can solve the problems that a silicon-based material is easy to expand, easy to fall off from a current collector and poor in dispersibility.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery materials, in particular to a silicon-based negative electrode binder, a negative electrode sheet, a lithium ion battery and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have the advantages of high capacity, long service life, safety and environmental protection, and are widely used in portable electronic devices such as smart phones, notebook computers and new energy vehicles. At the same time, higher requirements are put forward for the energy density and safety of lithium ion batteries. The theoretical energy of traditional graphite negative electrode is low, and the high-rate charge-discharge performance is poor, which cannot further meet the development needs of high-energy high-density lithium ion batteries. Emerging silicon negative electrode materials have high energy density and higher safety performance, and are abundant in reserves, so silicon-based negative electrodes are one of the important ways to improve the energy density and safety of lithium ion batteries.

[0003] The silicon-based negative electrode binder is an important component of the lithium ion battery negative electrode. In the electrode, the binder is responsible for connecting the active material, conductive carbon black and current collector, ensuring the structural and electrochemical stability of the electrode during the charge and discharge process. However, in actual application, when silicon-based materials are used as negative electrodes, although the capacity of the battery is effectively improved, the silicon-based materials are prone to swelling, and the silicon-based active materials are easy to fall off from the current collector. During the charge and discharge process of the battery, the silicon-based negative electrode material swells seriously, causing the active material to powder and leading to battery failure. In addition, the dispersion performance of the silicon-based negative electrode binder is poor, causing the slurry to settle and leading to uneven distribution of the electrode material on the current collector, further causing local peeling of the electrode material or lithium precipitation, hindering lithium ion and electron transmission, and ultimately leading to damage to the capacity performance and rate performance of the battery.

[0004] In order to solve the above problems, the amount of silicon-based negative electrode binder is often increased in the prior art to improve its adhesion to inhibit the swelling of silicon-based negative electrode materials. This method improves the adhesion of the silicon-based negative electrode binder and alleviates the swelling of the silicon-based negative electrode material to some extent, but still far from meeting the requirements. Increasing the amount of silicon-based negative electrode binder will cause a decrease in the amount of active material in the system, leading to a decrease in the kinetic performance of the electrode sheet and a decrease in the energy density of the battery.

[0005] Therefore, there is an urgent need to provide a silicon-based negative electrode binder with strong adhesion, good dispersion and effective inhibition of the swelling of silicon-based negative electrode materials. SUMMARY

[0006] The present application provides a silicon-based negative electrode binder, a negative electrode sheet, a lithium ion battery and a preparation method thereof to solve the problems of poor adhesion and poor dispersion of the silicon-based negative electrode binder in the prior art.

[0007] To solve one or more of the above technical problems, the technical scheme adopted by the present application is:

[0008] In a first aspect, the present application provides a silicon-based negative electrode binder, which is formed by graft copolymerization of a polycarboxylic acid compound and an amine-rich aqueous polymer, and has a three-dimensional network structure.

[0009] The polycarboxylic acid compound comprises at least two carboxyl groups.

[0010] The amine-rich aqueous polymer comprises at least two amine groups.

[0011] The at least two carboxyl groups on the same molecular chain of the polycarboxylic acid compound react with the at least two amine groups on the same molecular chain of the amine-rich aqueous polymer.

[0012] Further, the binder has intramolecular hydrogen bonds, and the three-dimensional network structure of the binder has π-π stacking interactions and dipole-dipole interactions.

[0013] Further, the polycarboxylic acid compound comprises at least one of aliphatic dicarboxylic acids, aromatic dicarboxylic acids, alicyclic dicarboxylic acids, tricarboxylic acids, or tetracarboxylic acids.

[0014] Specifically, the polycarboxylic acid compound comprises at least one of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2-methyl succinic acid, 2-methyl adipic acid, 3-methyl adipic acid, 3-methyl glutaric acid, 2-methyl suberic acid, 3,8-dimethyl sebacic acid, 3,7-dimethyl sebacic acid, hydrogenated dimer acid, dimer acid, and other aliphatic dicarboxylic acids; phthalic acid, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and other aromatic dicarboxylic acids; cyclohexane dicarboxylic acid and other alicyclic dicarboxylic acids; trimellitic acid, trimesic acid, and other tricarboxylic acids; and pyromellitic acid and other tetracarboxylic acids.

[0015] Further, the polycarboxylic acid compound comprises an unsaturated polycarboxylic acid compound containing a C=C bond.

[0016] Further, the polycarboxylic acid compound comprises at least one of maleic acid and (E)-but-2-ene-1,2,4-tricarboxylic acid.

[0017] Further, the amine-rich aqueous polymer comprises polyethyleneimine.

[0018] In a second aspect, corresponding to the above-mentioned silicon-based negative electrode binder, the present application provides a preparation method of a silicon-based negative electrode binder, which comprises:

[0019] dissolving the amine-rich aqueous polymer in a solvent to obtain a first mixture;

[0020] adding a polycarboxylic acid compound to the first mixture to obtain a second mixture;

[0021] adding an amidation reagent to the second mixture and reacting at a preset temperature for a preset time to obtain a third mixture;

[0022] treating the third mixture by dialysis or co-precipitation to obtain the silicon-based negative electrode binder.

[0023] Further, the solvent includes water or alcohol. Specifically, the alcohol includes methanol, ethanol, etc.

[0024] Further, the amidation reagent includes at least one of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide.

[0025] Further, the preset temperature is 15-45°C, and the preset time is 8-10 hours.

[0026] In a third aspect, corresponding to the above-mentioned silicon-based negative electrode binder, the present application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, and the negative electrode active material layer includes the above-mentioned silicon-based negative electrode binder, negative electrode active material and negative electrode conductive agent.

[0027] Further, the negative electrode active material includes any one of elemental silicon, silicon alloy, silicon carbide compound or silicon oxide compound or a combination of at least two thereof.

[0028] Further, the negative electrode conductive agent includes one or several of acetylene black, ketjen black, carbon fiber, superconducting carbon black, carbon nanotube and graphene.

[0029] Further, the shape of the negative electrode current collector includes any one of foil shape, plate shape or grid shape.

[0030] Further, the negative electrode current collector includes any one of elemental aluminum, copper, nickel or zinc.

[0031] Optionally, the negative electrode current collector is elemental copper, such as copper foil, etc.

[0032] Further, the negative electrode current collector includes any one of aluminum, copper, nickel or zinc alloy.

[0033] In a fourth aspect, corresponding to the above-mentioned negative electrode sheet, the present application provides a lithium ion battery, which includes a positive electrode sheet, a separator, an electrolyte and the above-mentioned negative electrode sheet, and the separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0034] In a fifth aspect, corresponding to the above-mentioned lithium ion battery, the application provides a preparation method of a lithium ion battery, the preparation method comprising:

[0035] The silicon-based negative electrode binder, the negative electrode active material and the negative electrode conductive agent are mixed uniformly to obtain a negative electrode slurry, and the negative electrode slurry is coated on the surface of a negative electrode current collector and dried to obtain a negative electrode sheet.

[0036] The positive electrode binder, the positive electrode active material and the positive electrode conductive agent are mixed uniformly to obtain a positive electrode slurry, and the positive electrode slurry is coated on the surface of a positive electrode current collector and dried to obtain a positive electrode sheet.

[0037] The positive electrode sheet, the negative electrode sheet and a separator film are laminated, and the lithium ion battery is obtained through liquid injection and formation.

[0038] According to the specific embodiments provided in the application, the following technical effects are disclosed:

[0039] The application provides a silicon-based negative electrode binder, a negative electrode sheet, a lithium ion battery and a preparation method thereof. By adding a polycarboxylic compound to the amine-rich water-based polymer, the -OH groups introduced through grafting can increase more active sites, effectively enhancing the adhesion between the current collector and the silicon negative electrode, thereby improving the peeling strength of the negative electrode sheet and the rate performance and stability of the corresponding lithium ion battery.

[0040] Further, the polycarboxylic compound used in the application includes at least two carboxyl groups, the amine-rich water-based polymer includes at least two amine groups, and the reaction between the at least two carboxylic acids on the same molecular chain and the at least two amine groups on the same molecular chain can improve the cross-linking degree of the binder generated after the reaction, ensuring the stability of the electrode material slurry during the preparation process, effectively preventing the electrode slurry from settling, improving the uniformity of the electrode slurry, ensuring the uniform distribution of the binder in the electrode active material, uniform stress distribution on the electrode surface, and effectively improving the stability and cycle life of the electrode structure.

[0041] In addition, after the reaction of the polycarboxylic compound and the amine-rich water-based polymer, a polymer binder with a three-dimensional network structure is generated. Due to its special molecular structure, the three-dimensional polymer binder has π-π stacking interaction and dipole-dipole interaction within the molecule, and contains a large number of hydrogen bonds in the polymer, so that the binder has a self-repairing function.

[0042] Of course, implementing any product of the application does not necessarily require all the advantages described above. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0044] As described in the background, using silicon-based materials as the negative electrode can improve the capacity and safety of lithium ion batteries, but silicon-based materials are prone to swelling. During the charging and discharging process of the battery, the silicon-based negative electrode material system swells seriously, causing the active material to pulverize and leading to battery failure. In addition, the dispersion performance of the silicon-based negative electrode binder is poor, causing the slurry to settle and leading to uneven distribution of the electrode material on the current collector, further causing local peeling of the electrode material, hindering the transport of lithium ions and electrons, and ultimately leading to damage to the capacity performance and rate performance of the battery.

[0045] To solve one or more of the above problems, the present application creatively proposes a silicon-based negative electrode binder, a negative electrode sheet, a lithium ion battery and a preparation method thereof. The binder is formed by graft copolymerization of a polycarboxylic acid compound and an amine-rich water-based polymer, which can solve the problems of easy swelling, easy falling off from the current collector and poor dispersion of silicon-based materials.

[0046] The following is an optional technical solution of the present application, but is not a limitation on the technical solutions provided by the present application. Through the following optional technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0047] The silicon-based negative electrode binder is a high molecular compound used to adhere the negative electrode active material to the current collector. Its main function is to bind and maintain the negative electrode active material, enhance the contact between the negative electrode active material and the negative electrode conductive agent, and between the negative electrode active material and the negative electrode current collector, and better stabilize the structure of the negative electrode sheet. In the embodiments of the present application, the silicon-based negative electrode binder is formed by graft copolymerization of a polycarboxylic acid compound and an amine-rich water-based polymer. Through grafting reaction of carboxyl and amine groups, carboxyl groups are introduced into the amine-rich water-based polymer binder. The -OH structure in the carboxyl group can increase more active sites and can form more hydrogen bonds or covalent bonds with silicon particles, enhancing the adhesion between the current collector and the silicon negative electrode, effectively inhibiting the swelling of the silicon negative electrode material, and further improving the rate performance and stability of the lithium ion battery.

[0048] Further, the polycarboxylic acid compound used in the present application includes at least two carboxyl groups, the amine-rich water-based polymer includes at least two amine groups, and the at least two carboxyl groups on the same molecular chain of the polycarboxylic acid compound react with the at least two amine groups on the same molecular chain of the amine-rich water-based polymer. The polycarboxylic acid compound includes at least one of aliphatic dicarboxylic acids, aromatic dicarboxylic acids, alicyclic dicarboxylic acids, tricarboxylic acids or tetracarboxylic acids.

[0049] Specifically, the polycarboxylic acid compound includes at least one of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2-methylsuccinic acid, 2-methyladipic acid, 3-methyladipic acid, 3-methylglutaric acid, 2-methyloctanedioic acid, 3,8-dimethylsebacic acid, 3,7-dimethylsebacic acid, hydrogenated dimer acid, dimer acid, and other aliphatic dicarboxylic acids; phthalic acid, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and other aromatic dicarboxylic acids; cyclohexane dicarboxylic acid and other alicyclic dicarboxylic acids; trimellitic acid, trimesic acid, and other tricarboxylic acids; and pyromellitic acid and other tetracarboxylic acids.

[0050] Further, the polycarboxylic acid compound includes an unsaturated polycarboxylic acid compound containing a C=C bond. Specifically, the unsaturated polycarboxylic acid includes at least one of maleic acid and (E)-but-2-ene-1,2,4-tricarboxylic acid. The two groups of -C=C- and -C=O contained in the unsaturated polycarboxylic acid form strong dipole-dipole interactions with the electrode material, which can improve the dispersing ability of the binder, can be distributed in a larger range on the surface of the silicon material, can effectively inhibit the expansion and contraction of silicon, and thus can improve the cycle life of the silicon negative electrode.

[0051] The amine group-rich aqueous polymer is a water-soluble polymer having a certain binding ability and including a plurality of amine groups, and is preferably polyethyleneimine.

[0052] In the graft copolymerization process of the polycarboxylic acid compound and the amine group-rich aqueous polymer, at least two carboxylic acids on the same molecular chain react with at least two amine groups on the same molecular chain, which improves the cross-linking degree of the binder generated after the reaction. The improvement of the cross-linking degree of the binder can effectively prevent the electrode slurry from settling, improve the uniformity and stability of the electrode slurry, ensure the uniform distribution of the binder in the electrode active material, and thus effectively improve the stability and cycle life of the electrode structure. Further, the reaction of the polycarboxylic acid compound and the amine group-rich aqueous polymer can generate a binder having a three-dimensional network structure, the binder having a three-dimensional network structure contains a large number of hydrogen bonds, and the three-dimensional network structure of the binder has π-π stacking interactions and dipole-dipole interactions, so that the binder has a self-repairing function. This self-repairing process is realized through the interaction between dynamic bond interactions or the diffusion and entanglement of polymer chains. The silicon-based negative electrode binder in the embodiments of the present application can continuously self-repair the damage caused in the charging and discharging process, so that the lithium ion battery always maintains high specific capacity and stable cycle performance.

[0053] The present application also provides a preparation method of a silicon-based negative electrode binder, which comprises:

[0054] S11: dissolving the amine group-rich aqueous polymer in a solvent to obtain a first mixture.

[0055] Preferably, the amine group-rich aqueous polymer is dissolved in a solvent to obtain a first mixture. The solvent includes water or alcohol. Specifically, the alcohol includes methanol, ethanol, etc.

[0056] S12: adding a polycarboxylic acid compound to the first mixture to obtain a second mixture.

[0057] S13: adding an amidation reagent to the second mixture and reacting at a preset temperature for a preset time to obtain a third mixture.

[0058] Preferably, the third mixture is obtained after reacting at 15-45°C for 8-10 hours.

[0059] Further, the amidation reagent includes at least one of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide.

[0060] S14: treating the third mixture by a dialysis method or a co-precipitation method to obtain a silicon-based negative electrode binder.

[0061] Corresponding to the above silicon-based negative electrode binder, the present application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, the negative electrode active material layer including the above silicon-based negative electrode binder, a negative electrode active material and a negative electrode conductive agent.

[0062] Further, the negative electrode active material includes any one or a combination of at least two of elemental silicon, silicon alloy, silicon carbon compound or silicon oxide compound.

[0063] Further, the negative electrode conductive agent includes one or several of acetylene black, ketjen black, carbon fiber, superconducting carbon black, carbon nanotube and graphene.

[0064] In a specific embodiment, the mass fraction of the silicon-based negative electrode binder, the negative electrode active material and the negative electrode conductive agent is 0.1-10%, 80-99% and 0.1-10%, respectively.

[0065] Further, the mass fraction of the silicon-based negative electrode binder can be 0.1%, 0.5%, 1%, 3%, 5%, 7%, 9% or 10%, and specific point values between the above point values, preferably 1-5%. Limited by the length and for the sake of simplicity, the present application does not list the specific point values included in the range.

[0066] Further, the mass fraction of the negative active material can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%, and specific point values between the above point values, preferably 90-99%, and for the sake of brevity, the present application will not exhaustively list the specific point values included in the range.

[0067] Further, the mass fraction of the negative active material can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%, and specific point values between the above point values, preferably 90-99%, and for the sake of brevity, the present application will not exhaustively list the specific point values included in the range.

[0068] Further, the shape of the negative current collector includes, but is not limited to, a foil shape, a plate shape, or a mesh shape, etc. The negative current collector includes, but is not limited to, aluminum, copper, nickel, or zinc single element, etc. For example, the negative current collector can be a copper single element, such as a copper foil, etc. Further, the negative current collector includes, but is not limited to, an aluminum, copper, nickel, or zinc alloy, etc.

[0069] Corresponding to the above negative electrode sheet, the present application also provides a lithium ion battery, which includes a positive electrode sheet, a separator, an electrolyte, and the above negative electrode sheet, the separator is arranged between the positive electrode sheet and the negative electrode sheet. Among them, the related content of the negative electrode sheet can be referred to the above introduction, which will not be repeated here.

[0070] As a more preferred embodiment, the positive electrode includes a current collector and a positive active material layer formed on the current collector;

[0071] The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. Specifically, copper, stainless steel, aluminum, nickel, titanium, or a metal current collector with a surface treated with carbon or other substances can be used.

[0072] The positive electrode current collector can generally have a thickness of 3 μm to 500 μm.

[0073] The positive electrode current collector can have fine concave-convex formed on its surface to improve the adhesion of the positive active material. For example, various shapes of positive electrode current collectors such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabric bodies, etc. can be used.

[0074] The positive active material layer can include a positive active material.

[0075] The positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium, specifically, can include a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of nickel, cobalt, manganese, and aluminum; preferably, can be a lithium transition metal composite oxide containing lithium and nickel, cobalt, or manganese.

[0076] More specifically, the lithium transition metal composite oxide can be a lithium manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium cobalt-based oxide (e.g., LiCoO2, etc.), a lithium nickel-based oxide (e.g., LiNiO2, etc.), a lithium nickel-manganese-based oxide (e.g., LiNi1-yMnyO2 (where 0 < y < 1), LiMn 2-z Ni z O4 (where 0 < z < 2), etc.), a lithium nickel-cobalt-based oxide (e.g., LiNi 1-y1 Co y1 O2 (where 0 < y1 < 1), etc.), a lithium manganese-cobalt-based oxide (e.g., LiCo 1-y2 Mn y2 O2 (where 0 < y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < z1 < 2), etc.), a lithium nickel-manganese-cobalt-based oxide (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1), or a lithium nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 AS2)O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, p2, q2, r3, and s2 are each an atomic fraction of an independent element, and 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1), etc.), and can include any one or two or more compounds thereof. Among these, from the aspect of being able to increase the capacity and stability of the battery, the lithium transition metal composite oxide can be LiCoO2, LiMnO2, LiNiO2, a lithium nickel-manganese-cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, or LiNi 0.8 Mn 0.1 Co0.1 )02, or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )02, etc. When considering the significant improvement effect obtained by controlling the type and content ratio of constituent elements forming the lithium transition metal complex oxide, the lithium transition metal complex oxide can be Li(Ni 0.6 Mn 0.2 Co 0.2 )02, Li(Ni 0.5 Mn 0.3 Co 0.2 )02, Li(Ni 0.7 Mn 0.15 Co 0.15 )02, or Li(Ni 0.8 Mn 0.1 Co 0.1 )02, etc., and any one thereof or a mixture of two or more thereof can be used.

[0077] The amount of the positive electrode active material contained in the positive electrode active material layer can be 80 to 99 wt%, preferably 92 to 98.5 wt%.

[0078] In addition to containing the above-described positive electrode active material, the positive electrode active material layer can further contain a positive electrode binder and / or a positive electrode conductive material.

[0079] The positive electrode binder is used to bind together components such as active materials, conductive materials, and current collectors, and specifically, can contain at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluorine rubber, preferably polyvinylidene fluoride.

[0080] The amount of the positive electrode binder contained in the positive electrode active material layer can be 1 to 20 wt%, preferably 1.2 to 10 wt%.

[0081] The conductive material is mainly used to assist and improve the conductivity in the secondary battery, and is not particularly limited as long as it has conductivity without causing chemical changes. Specifically, the conductive material can include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon powders, aluminum powders, and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxides; and polyphenylene derivatives, and can be preferably include carbon black in terms of improving the conductivity.

[0082] The specific surface area of the cathode conductive material can be 80 m 2 / g to 200 m 2 / g, preferably 100 m 2 / g to 150 m 2 / g.

[0083] The amount of the cathode conductive material included in the cathode active material layer can be 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%.

[0084] The thickness of the cathode active material layer can be 30 μm to 400 μm, preferably 50 μm to 110 μm.

[0085] The cathode can be manufactured by coating a cathode slurry including a cathode active material and, optionally, a cathode binder, a cathode conductive material, and a solvent for forming a cathode slurry on a cathode current collector, and then drying and roll-pressing.

[0086] The solvent for forming a cathode slurry can include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and the amount can be such that a preferred viscosity is obtained when a cathode active material and, optionally, a cathode binder, a cathode conductive material, etc. are included. For example, the amount of the solvent for forming a cathode slurry included in the cathode slurry can be such that the concentration of solids including a cathode active material, and, optionally, a cathode binder and a cathode conductive material is 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

[0087] The kind of electrolyte is not particularly limited in the present application, and any known electrolyte material can be used in the present application without departing from the inventive concept of the present application. As illustrative examples, the electrolyte can be a liquid electrolyte, a solid electrolyte, or a mixture of a solid electrolyte and a liquid electrolyte.

[0088] When the electrolyte is a liquid electrolyte, a separator should also be provided in the battery system.

[0089] The main role of the separator is to separate the negative electrode and the positive electrode and to provide a path for the movement of lithium ions. Any separator can be used without particular limitation, as long as it is a separator commonly used in secondary batteries. In particular, a separator having excellent electrolyte wettability and low resistance to ion movement in the electrolyte is preferred. Specifically, a porous polymer film, for example, a porous polymer film manufactured using a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butylene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or having a laminated structure of two or more layers thereof, can be used. Also, a typical porous nonwoven fabric, for example, a nonwoven fabric formed of glass fibers having a high melting point, polyethylene terephthalate fibers, or the like, can be used. In addition, a coated separator including a ceramic component or a polymeric material can be used to ensure heat resistance or mechanical strength, and can be selectively used in a single layer or a multi-layer structure.

[0090] In addition, the electrolyte used in the present application can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten-type inorganic electrolyte, etc. that can be used in the manufacture of a secondary battery, but is not limited thereto.

[0091] Specifically, the electrolyte can include an organic solvent and a lithium salt.

[0092] Any organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; an ether-based solvent such as dibutyl ether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; an aromatic hydrocarbon-based solvent such as benzene and fluorobenzene; a carbonate-based solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); an alcohol-based solvent such as ethanol and isopropyl alcohol; a nitrile such as R-CN (wherein R is a linear, branched, or cyclic C2-C20 hydrocarbon group, and can include a double-bonded aromatic ring or an ether bond); an amide such as dimethylformamide; a dioxolane such as 1,3-dioxolane; or a sulfolane can be used. Among the above-mentioned solvents, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and a high dielectric constant and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) that can increase the charge / discharge performance of the battery is more preferred. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0093] Any compound can be used as the lithium salt without particular limitation, as long as it can provide lithium ions used in lithium secondary batteries. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, and the like can be used as the lithium salt. The use concentration of the lithium salt can range from 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent performance, and lithium ions can move effectively.

[0094] As an embodiment, the electrolyte can be a solid-state electrolyte, and the solid-state electrolyte particles can include one or more of a polymer component, an oxide solid-state electrolyte, a sulfide solid-state electrolyte, a halide solid-state electrolyte, a borate solid-state electrolyte, a nitride solid-state electrolyte, or a hydride solid-state electrolyte. When a polymer particle is used, a lithium salt should be reviewed for use. As an embodiment, the polymer-based component can include one or more polymer materials selected from a group including polyethylene glycol, polyethylene oxide (PEO), poly(p-phenylene oxide) (PPO), poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyvinyl chloride (PVC), and combinations thereof. It can be understood that a high ionic conductivity of the polymer material is advantageous for the performance of the overall solid-state electrolyte material, and preferably, the polymer material should have an ionic conductivity greater than or equal to 10-4S / cm.

[0095] As an embodiment, the oxide particles can include one or more of a garnet ceramic, a LISICON-type oxide, a NASICON-type oxide, and a perovskite ceramic. As an illustrative example, the garnet ceramic can be selected from a group including Li 6.5 La3Zr 1.75 Te 0.25 O 12 , Li7La3Zr2O 12 , Li 6.2 Ga 0.3 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 , Li6.25 Al 0.25 La3Zr2O 12 Li 6.75 La3Zr 1.75 Nb 0.25 O 12 Li 6.75 La3Zr 1.75 Nb 0.25 O 12 and combinations thereof. LISICON-type oxides may be selected from the group consisting of: Li 14 Zn(GeO4)4, Li 3+x (P 1-x Si x O4 (where 0 < x < 1), Li 3+x Ge x V 1-x O4 (where 0 < x < 1) and combinations thereof. NASICON-type oxides can be defined by LiMM′(PO4)3, where M and M′ are independently selected from Al, Ge, Ti, Sn, Hf, Zr, and La. Preferably, NASICON-type oxides can be selected from the group consisting of: Li 1+x Al x Ge 2-x (PO4)3(LAGP) (where 0 ≤ x ≤ 2), Li 1+x Al x Ti 2-x (PO4)3(LATP) (where 0 ≤ x ≤ 2), Li 1+x Y x Zr 2-x (PO4)3(LYZP) (where 0≤x≤2), Li 1.3 Al 0.3 Ti 1.7 (PO4)3, LiTi2(PO4)3, LiGeTi(PO4)3, LiGe2(PO4)3, LiHf2(PO4)3, and combinations thereof. One or more perovskite ceramics may be selected from the group consisting of: Li 3.3 La 0.53 TiO3, LiSr 1.65 Zr 1.3 Ta 1.7 O9、Li 2x-y Sr 1-x Ta y Zr 1-y O3 (where x = 0.75y and 0.60 < y < 0.75), Li 3 / 8 Sr 7 / 16 Nb 3 / 4Zr 1 / 4O3, Li 3x La(2 / 3-x)TiO3(where 0 < x < 0.25) and combinations thereof. Preferably, the one or more oxide-based materials can have an ionic conductivity greater than or equal to about 10"5S / cm to less than or equal to about 10"1S / cm.

[0096] The sulfide solid-state electrolyte is selected from one or more sulfide-based materials from the group comprising: Li2S-P2S5, Li2S-P2S5-MSx(where M is Si, Ge and Sn and 0 < x < 2), Li 3.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.3 , Li 9.6 P3S 12 , Li7P3S 11 , Li9P3S9O3, Li 10.35 Si 1.35 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(Si 0.5 Sn 0.5 )PsS 12 , Li 10 GeP2S 12 (LGPS), Li6PS5X(where X is CI, Br or I), Li7P2S8I, Li 10.35 Ge 1.35 P 1.65 S 12 , Li 3.25 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 C 10.3 , (1-x)P2S 5-xLi2S (wherein 0.5 < x < 0.7) and combinations thereof.

[0097] The halide solid-state electrolyte can include one or more halide-based materials selected from the group comprising Li2CdCl4, Li2MgCl4, Li2CdI4, Li2ZnI4, Li3OCl, LiI, Li5ZnI4, Li3OCl 1-x Br x (wherein 0 < x < 1) and combinations thereof.

[0098] The borate solid-state electrolyte can include one or more borate-based materials selected from the group comprising Li2B4O7, Li2O-(B2O3)-(P2O5) and combinations thereof.

[0099] The nitride solid-state electrolyte can include one or more nitride-based materials selected from the group comprising Li3N, Li7PN4, LiSi2N3, LiPON and combinations thereof.

[0100] The hydride solid-state electrolyte can include one or more hydride-based materials selected from the group comprising Li3AlH6, LiBH4, LiBH4-LiX (wherein X is one of Cl, Br and I), LiNH2, Li2NH, LiBH4-LiNH2 and combinations thereof.

[0101] As a particular embodiment, the solid-state electrolyte can be a quasi-solid electrolyte comprising a mixture of the non-aqueous liquid electrolyte solution and the solid-state electrolyte system detailed above, for example, including one or more ionic liquids and one or more metal oxide particles (such as aluminum oxide (Al2O3) and / or silicon dioxide (SiO2)).

[0102] For the above lithium ion battery, the application further provides a preparation method of a lithium ion battery, the method comprising:

[0103] S21: uniformly mixing the above-mentioned silicon-based negative electrode binder, negative electrode active material and negative electrode conductive agent to obtain a negative electrode slurry, coating the negative electrode slurry to the surface of a negative electrode current collector and drying to obtain a negative electrode sheet.

[0104] Preferably, 0.1-10 wt% of the negative electrode binder, 80-99 wt% of the negative electrode active material and 0.1-10 wt% of the negative electrode conductive agent are uniformly mixed to obtain a negative electrode slurry, the negative electrode slurry is coated to the surface of a negative electrode current collector and dried to obtain a negative electrode sheet, and the negative electrode binder at least comprises a castor oil modified aqueous polyurethane.

[0105] S22: mixing the positive electrode binder, the positive electrode active material and the positive electrode conductive agent uniformly to obtain a positive electrode slurry, coating the positive electrode slurry to the surface of the positive electrode current collector, and drying to obtain a positive electrode sheet.

[0106] Preferably, 0.1-20wt% of the positive electrode binder, 79-99wt% of the positive electrode active material and 0.1-20wt% of the positive electrode conductive agent are mixed uniformly to obtain a positive electrode slurry, the positive electrode slurry is coated to the surface of the positive electrode current collector, and dried to obtain a positive electrode sheet.

[0107] S23: laminating the positive electrode sheet, the negative electrode sheet and the separator film, and obtaining the lithium ion battery through liquid injection and formation.

[0108] Embodiments of the present application will be described in more detail below with reference to examples and comparative examples. However, embodiments of the present application are not limited only to these examples.

[0109] Example 1

[0110] (1) Preparation of a silicon-based negative electrode binder

[0111] Polyethyleneimine (Mw = 270000) was dissolved in deionized water, and a first mixture was obtained after uniform mixing. Maleic acid was added to the first mixture, and a second mixture was obtained after uniform mixing. 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC hydrochloride) and N-hydroxysuccinimide (NHS) were added to the second mixture, and a third mixture was obtained after reaction at 25°C for 9 hours. The third mixture was treated by dialysis to obtain a silicon-based negative electrode binder.

[0112] The obtained binder was subjected to Fourier infrared spectroscopy test, and the peak positions were IR (KBr) u: 3670 cm -1 (-OH), 3450 cm -1 (-NH), 2970, 2850 cm -1 (-CH2-), 1650 cm -1 (-C=O), 700, 990, 910 cm -1 (=C-H).

[0113] (2) Preparation of a negative electrode sheet

[0114] The negative electrode active material with a mass fraction of 97%, the silicon-based negative electrode binder prepared in step (1) with a mass fraction of 1.5%, and the negative electrode conductive agent with a mass fraction of 1.5% were weighed. The silicon-based negative electrode binder was added to the above-mentioned negative electrode active material and negative electrode conductive agent, and the mixture was stirred uniformly to obtain a negative electrode slurry.

[0115] The negative electrode slurry was uniformly coated on the surface of the copper foil, and a battery negative electrode sheet was obtained after drying. The peel strength of the battery negative electrode sheet was tested.

[0116] (3) Preparation of the positive electrode sheet

[0117] The positive active material with a mass fraction of 97%, the positive electrode binder with a mass fraction of 1.5%, and the positive electrode conductive agent with a mass fraction of 1.5% were weighed. The positive electrode binder was added to the positive active material and the positive electrode conductive agent, and stirred uniformly to obtain a positive electrode slurry.

[0118] The positive electrode slurry was uniformly coated on the surface of the aluminum foil, and then dried to obtain a positive electrode sheet of a battery.

[0119] (4) Preparation of the lithium ion battery

[0120] The positive electrode sheet, the negative electrode sheet, and the separator film obtained above were laminated, and then subjected to liquid injection and formation to obtain the lithium ion battery. The prepared lithium ion battery was subjected to battery performance testing.

[0121] Example 2

[0122] Compared with Example 1, the difference lies in that (1) the preparation of the silicon-based negative electrode binder uses (E)-but-2-ene-1,2,4-tricarboxylic acid to replace maleic acid, and the rest of the experimental conditions are the same.

[0123] Comparative Example 1

[0124] Compared with Example 1, the difference lies in that (1) the preparation method of the silicon-based negative electrode binder is as follows: polyethyleneimine (Mw = 270000) is dissolved in deionized water to obtain a first mixture; 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC hydrochloride) and N-hydroxysuccinimide (NHS) are added to the first mixture, and the mixture is reacted at 25°C for 9 hours to obtain a second mixture; the second mixture is treated by dialysis to obtain the silicon-based negative electrode binder, and the rest of the experimental conditions are the same.

[0125] Comparative Example 2

[0126] Compared with Example 1, the difference lies in that (1) the preparation of the silicon-based negative electrode binder uses lauric acid to replace maleic acid, and the rest of the experimental conditions are the same.

[0127] Comparative Example 3

[0128] Compared with Example 1, the difference lies in that (1) the preparation of the silicon-based negative electrode binder uses 3-butenoic acid to replace maleic acid, and the rest of the experimental conditions are the same.

[0129] Comparative Example 4

[0130] Compared with Example 1, the difference lies in that the binder used is a water-based binder SBR / CMC.

[0131] Comparative Example 5

[0132] The difference compared with Example 1 is that the binder used is oily binder PVDF.

[0133] Test methods and conditions

[0134] 1. Test method of peel strength:

[0135] ① The negative electrode sheet provided by Examples 1-2 and Comparative Examples 1-5 was cut into 170 x 20 mm;

[0136] ② The cut negative electrode sheet was pasted in the middle of a thin steel plate with double-sided tape, with the end surface flush, and the thin steel plate was previously wiped clean with a dust-free paper, leaving no stains and dust;

[0137] ③ A 2kg heavy roller was rolled back and forth on the surface of the sheet 3 times;

[0138] ④ The steel plate with the fixed sheet was inserted into the lower clamp of the tester and fixed vertically; the sheet without tape was inserted into the upper clamp and fixed, so that the sheet pasted on the tape and the sheet fixed by the upper clamp formed 180°. After the test sample was fixed, it was first calibrated and zeroed, the test width was set, the sheet peel-off length was 100mm, and the peel-off speed was 5cm / min, then the test was started, and the peel strength curve and average value were obtained.

[0139] 2. Test method of first charge-discharge efficiency:

[0140] The lithium ion batteries provided by Examples 1-2 and Comparative Examples 1-5 were tested for discharge performance, with a current density of 0.1C; wherein the first charge-discharge efficiency = (first discharge specific capacity / first charge specific capacity) x 100%.

[0141] 3. Test method of room temperature 3C rate discharge performance:

[0142] The lithium ion batteries provided by Examples 1-2 and Comparative Examples 1-5 were respectively tested at a current density of 0.1C, 0.3C, 0.5C, 1C, 3C, 1C, 0.5C, 0.3C, and 0.1C.

[0143] 4. Test method of capacity retention rate after 500 cycles at room temperature:

[0144] ① Charge at 1C or specified current to the terminal voltage at a temperature of 25℃±2℃, with a cutoff current of 0.05C, and stand for 30min;

[0145] ② Discharge at 1C to the discharge terminal voltage (2.75V), record the discharge capacity, and stand for 30min;

[0146] ③ Cycle ① ~ ②, test the capacity retention rate of lithium ion battery after 500 cycles.

[0147] The test results of the mechanical properties of the silicon-based negative electrode sheet prepared in Example 1-2 and Comparative Example 1-5 and the battery performance of the lithium ion battery are shown in Table 1.

[0148] Table 1

[0149]

[0150] From the test results of Table 1 above, it can be seen that:

[0151] 1. From the test results of Example 1 and Comparative Example 1, it can be seen that the addition of a polycarboxylic compound in the water-based binder polyethyleneimine can increase more active sites through grafting introduction of -OH groups, effectively improving the adhesion and dispersibility of the binder, thereby improving the peel strength of the negative electrode sheet and the performance of the corresponding lithium ion battery.

[0152] 2. From the test results of Example 1, Comparative Example 2 and Comparative Example 3, it can be seen that compared with lauric acid containing a single carboxyl group and 3-butenoic acid containing a double bond and a single carboxyl group, the use of maleic acid, a polycarboxylic polymer, in the present application can effectively improve the adhesion of the binder and the dispersibility in the electrode material. The multiple carboxylic acids on the molecular chain of the maleic acid polycarboxylic polymer react with the multiple amine groups on the molecular chain of the water-based polymer polyethyleneimine, increasing the crosslinking degree of the polymer binder generated after the reaction. By improving the crosslinking degree of the polymer binder, the expansion and crushing of the silicon-based material can be inhibited, effectively improving the peel strength of the negative electrode sheet and further improving the performance of the lithium ion battery with silicon-based material as the negative electrode. Further, the maleic acid in the present application is an unsaturated polycarboxylic acid containing a C=C double bond. The simultaneous presence of C=C double bond and carboxyl group gives the polymer binder self-repairing performance, which can effectively prevent the destruction of the binder caused by the expansion of the silicon-based negative electrode, thereby maintaining the adhesion of the binder to the silicon-based negative electrode, thereby further improving the peel strength of the negative electrode sheet and the performance of the corresponding lithium ion battery.

[0153] 3. From the test results of Example 1 and Example 2, it can be seen that as the number of carboxyl groups in the polycarboxylic compound increases, the number of carboxyl groups contained in the same molecular chain also increases, and the multiple carboxylic acids and multiple amine groups on the same molecular chain react, which can effectively improve the crosslinking degree of the generated polymer binder, and the adhesion of the polymer binder is greatly improved. The increase in the number of carboxyl groups in the polycarboxylic compound has a significant effect on the improvement of the performance of the silicon-based negative electrode and the performance of the lithium ion battery with silicon-based material as the negative electrode.

[0154] 4、From the test results of Example 1, Comparative Example 4 and Comparative Example 5, compared with the water-based binder SBR / CMC and the oily binder PVDF in the prior art, the binder formed by graft copolymerization of a polycarboxylic acid compound and an amine-rich water-based polymer in the application has better adhesion and dispersion performance. The application of this binder to the negative electrode can improve the peel strength of the negative electrode sheet and the performance of the corresponding lithium ion battery.

[0155] As can be seen from the above, the application provides a silicon-based negative electrode binder, a negative electrode sheet, a lithium ion battery and a preparation method thereof, which can effectively solve the problems of easy expansion of silicon-based materials, easy falling off from the current collector and poor dispersion.

[0156] The above provides a silicon-based negative electrode binder, a negative electrode sheet, a lithium ion battery and a preparation method thereof, which are described in detail. This paper applies specific examples to explain the principles and implementation methods of the application. The above examples are only used to help understand the method and its core idea; at the same time, for those skilled in the art, according to the idea of the application, the specific implementation and application range will be changed. In summary, the content of this specification should not be understood as a limitation of the application.

Claims

1. A silicon-based negative electrode binder, characterized in that, The adhesive is formed by graft copolymerization of polycarboxylic acid compounds and amine-rich aqueous polymers with the addition of amidation reagents, and the adhesive has a three-dimensional network structure. The polycarboxylic acid compound comprises at least two carboxyl groups; The amine-rich aqueous polymer comprises at least two amine groups; At least two carboxyl groups on the same molecular chain of the polycarboxylic acid compound react with at least two amine groups on the same molecular chain of the amine-rich aqueous polymer; The polycarboxylic acid compound includes an unsaturated polycarboxylic acid compound containing a C=C bond; The amine-rich aqueous polymer includes polyethyleneimine.

2. The silicon-based negative electrode binder according to claim 1, characterized in that, The adhesive contains hydrogen bonds within its molecules, and its three-dimensional network structure exhibits π-π stacking interactions and dipole-dipole interactions.

3. The silicon-based negative electrode binder according to claim 1, characterized in that, The polycarboxylic acid compound includes at least one of aliphatic dicarboxylic acids, aromatic dicarboxylic acids, alicyclic dicarboxylic acids, tricarboxylic acids, or tetracarboxylic acids.

4. The silicon-based negative electrode binder according to claim 1, characterized in that, The polycarboxylic acid compound includes at least one of maleic acid and (E)-but-2-ene-1,2,4-tricarboxylic acid.

5. A method for preparing the silicon-based negative electrode binder according to any one of claims 1-4, characterized in that, The preparation method of the silicon-based negative electrode binder includes: The amine-rich aqueous polymer is dissolved in a solvent to obtain the first mixture; A polycarboxylic acid compound is added to the first mixture to obtain a second mixture; An amidation agent is added to the second mixture, and the mixture is reacted at a preset temperature for a preset time to obtain a third mixture. The silicon-based anode binder is obtained by treating the third mixture using dialysis or co-precipitation.

6. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector, wherein the negative active material layer includes a silicon-based negative electrode binder, a negative active material and a negative conductive agent as described in any one of claims 1-4.

7. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode as described in claim 6, a separator, and an electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode.

8. A method for preparing a lithium-ion battery as described in claim 7, characterized in that, The preparation method includes: The silicon-based negative electrode binder, negative electrode active material and negative electrode conductive agent as described in any one of claims 1-4 are mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is coated onto the surface of the negative electrode current collector and dried to obtain a negative electrode sheet. A positive electrode slurry is obtained by uniformly mixing a positive electrode binder, a positive electrode active material, and a positive electrode conductive agent. The positive electrode slurry is then coated onto the surface of a positive electrode current collector and dried to obtain a positive electrode sheet. The positive electrode, the negative electrode, and the separator are stacked together, and then liquid injection and formation are performed to obtain the lithium-ion battery.

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