Electrode and lithium ion battery

Abstract

The invention relates to the technical field of batteries, in particular to an electrode and a lithium ion battery. The electrode comprises an electrode active material layer, the electrode active material layer comprises an electrode active material, a first binder, a second binder and a plasticizer, the first binder comprises polyamide-imide, and the second binder comprises at least one of sodium carboxymethyl cellulose, sodium alginate, polyacrylic acid, polyvinyl alcohol and chitosan; a dispersion medium of the electrode active material layer comprises water; based on the total weight of the electrode active material layer, the content of the first binder is 0.2%-20%, and the content of the second binder is 0.1%-10%; the lithium ion secondary battery includes the electrode of the present invention. The lithium ion battery provided by the invention has good discharge power characteristic, long service life and cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrode and a lithium ion battery. Background Art

[0002] In order to meet the development of miniaturization and lightweight of portable electronic devices, lithium-ion batteries have been widely studied due to their advantages of high discharge voltage, high energy density and long cycle life, and are constantly developing towards high energy density. However, in the negative electrode using materials that form alloying reactions with lithium as the main active material, the volume of the active material changes greatly during the absorption and release of lithium, so there are problems such as micronization of the active material, separation from the current collector, and reduced current collection in the electrode, which makes the charge and discharge cycle characteristics worse; commonly used binders such as polyimide binders, although they have high bonding strength and high tensile strength, their dispersion medium is usually an organic solvent, which is not only costly, but also pollutes the environment. Therefore, it is of great significance to develop a new electrode with good bonding between the electrode active material and the electrode current collector. Summary of the invention

[0003] The purpose of the present invention is to optimize the composition of the electrode active material layer in the electrode, use polyamideimide as the first binder, and the polyamideimide is obtained by solidifying a polyamide-amic acid compound as a precursor, realize water-based ingredient slurrying, and match it with a second binder and a plasticizer to reduce the battery resistance, solve the problem of electrode active material detaching from the current collector and reduced current collection in the electrode, and improve the charging and discharging power characteristics, low temperature performance and cycle performance of lithium-ion batteries.

[0004] In the prior art, polyimide is mainly composed of insoluble or poorly soluble substances. Its precursor polyamic acid is usually synthesized in an organic solvent such as N-methylpyrrolidone (NMP), dimethylacetamide, dimethylformamide or dimethyl sulfoxide solution, and is used in the form of an organic solvent solution of polyamic acid. Finally, the polyamic acid is dehydrated and cyclized under high temperature conditions to form a polyimide solid. The polyamic acid solution has poor stability, is easy to precipitate and precipitate, and is difficult to store. The use of polyimide binders has the problems of inconvenience in use, high cost of organic solvents, high energy consumption for evaporation and recovery of organic solvents, and harm to the environment. On the other hand, binders such as polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) have poor bonding performance with current collectors. Due to the high expansion / contraction characteristics of alloyed negative electrode materials during lithium insertion / detachment, it is easy to cause the conductive channel between the electrode active materials to fail and the electrode active materials to detach from the current collector, thereby causing the battery's cycle performance and capacity to deteriorate.

[0005] In order to solve the above problems, the inventors of the present invention use polyamideimide as the first binder, which not only has excellent adhesion, mechanical strength and stability, but also its precursor is water-soluble, and can realize water-based pulping ingredients. However, using only polyamideimide as a binder will cause the low-temperature performance of the battery to deteriorate. After experimental research, the inventors further introduced a second binder. The second binder has low impedance, can promote the electronic conduction and lithium ion migration of the electrode, and improve the battery's charge and discharge power characteristics, cycle performance and service life; the first binder and the second binder complement each other, which not only solves the problem of the first binder's large interface impedance and affecting the low-temperature performance of the battery, but also makes up for the mechanical strength and high-temperature characteristics that the second binder does not have.

[0006] When there is good adhesion between the electrode active material layer and the current collector, how to further reduce the internal resistance of the battery and overcome the resistance to lithium ion transmission is an effective way to further optimize the electrochemical performance of the battery. The inventors added water-soluble small molecule plasticizers to the electrode active material layer to increase the free space between the molecular chains of the binder polymer, thereby improving the internal resistance of the battery, and improving the cycle performance and low-temperature performance.

[0007] Based on this, the inventor of the present invention proposes the following technical solution:

[0008] On the one hand, the present invention provides an electrode, which includes an electrode active material layer, the electrode active material layer includes an electrode active substance, a first binder, a second binder and a plasticizer, the first binder includes polyamideimide, and the second binder includes at least one of sodium carboxymethyl cellulose, sodium alginate, polyacrylic acid, polyvinyl alcohol and chitosan; the dispersion medium of the electrode active material layer is water; based on the total weight of the electrode active material layer, the content of the first binder is 0.2%-20%, and the content of the second binder is 0.1%-10%.

[0009] A second aspect of the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the electrode provided by the first aspect of the present invention.

[0010] Through the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0011] (1) In the present invention, polyamideimide has a large number of imide groups, exhibits high adhesion, improves the adhesion between the electrode active material layer and the current collector, and inhibits the shedding of the electrode active material; and the second binder with low impedance characteristics matches the polyamideimide, improves the electronic conduction and lithium ion migration of the battery, and improves the mechanical strength of the electrode and the cycle performance of the battery.

[0012] (2) In the present invention, the preparation of the electrode active material layer realizes the slurrying of water-based ingredients, avoiding the use of high-boiling point and highly toxic organic solvents, and reducing environmental pollution.

[0013] (3) In the present invention, the use of small molecule water-soluble plasticizer can reduce the migration impedance of lithium ions on the surface of the electrode active material, reduce the internal resistance of the battery, and improve the low temperature performance of the battery.

[0014] (4) The lithium-ion battery provided by the present invention has good charge and discharge power characteristics, cycle performance and service life.

[0015] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. DETAILED DESCRIPTION

[0016] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0017] A first aspect of the present invention provides an electrode, comprising an electrode active material layer, wherein the electrode active material layer comprises an electrode active substance, a first binder, a second binder and a plasticizer, wherein the first binder comprises polyamideimide, and the second binder comprises at least one of sodium carboxymethyl cellulose, sodium alginate, polyacrylic acid, polyvinyl alcohol and chitosan; and the dispersion medium of the electrode active material layer comprises water.

[0018] In the present invention, based on the total weight of the electrode active material layer, the content of the first binder is 0.2%-20%, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18% or 20%; the content of the second binder is 0.1%-10%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.6%, 0.8%, 1%, 2%, 3%, 4%, 6%, 8%, 9% or 10%.

[0019] In one embodiment, the second binder includes at least one of sodium carboxymethyl cellulose and polyacrylic acid.

[0020] In the present invention, the first binder includes polyamideimide. Since there are a large number of imide groups in the molecular structure of polyamideimide, it has high bonding properties. When the first binder with high bonding properties is used for the electrode active material layer, it can inhibit the failure of the conductive channel between the electrode active materials and the separation of the electrolytic active materials from the current collector during the electrode charging and discharging process, improve the current collection and charge and discharge cycle characteristics in the electrode, and the processing performance of the electrode is improved compared with the use of polyimide binder; however, when the first binder is used alone, the migration resistance of lithium ions becomes larger, and the low-temperature characteristics of the battery deteriorate.

[0021] Furthermore, in order to solve the above problems, the inventors introduced a second binder into the electrode active material layer, and the second binder has low impedance characteristics. The second binder has a large number of carboxyl functional groups in its molecular structure, which can combine with the electrode active material before polyamideimide, hindering the coverage of the electrode active material by polyamideimide, thereby improving the electronic conduction and lithium ion migration of the electrode. It not only overcomes the increase in electrode interface impedance and degradation of battery low-temperature characteristics caused by the use of the first binder alone, but also makes up for the mechanical strength and high temperature resistance that the second binder does not have, thereby improving the cycle performance of the battery.

[0022] In the present invention, polyamideimide exists in the electrode slurry prepared by the electrode active material layer in the form of its precursor polyamide-amic acid compound. The electrode slurry uses water as a solvent. The polyamide-amic acid compound can be completely dissolved or mostly dissolved in water, thereby realizing water-based ingredient slurrying, avoiding the use of high-boiling point toxic organic solvents, and avoiding environmental pollution.

[0023] In the present invention, the electrode active material layer further includes a plasticizer, and the plasticizer includes at least one of ethylene glycol, propylene glycol, glycerol and citric acid.

[0024] In the present invention, based on the total weight of the electrode active material layer, the content of the plasticizer is 0.05%-2%, for example, 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.4%, 0.6%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 1.9%, 1.95%, 1.98% or 2%.

[0025] In the present invention, adding a plasticizer to the electrode active material layer can further reduce the battery impedance, alleviate the lithium ion transmission resistance, and increase the transmission rate. When the small molecule water-soluble plasticizer penetrates into the molecular chain network of the high molecular polymer, it can increase the free space between the molecular chains, optimize the interchain space structure between the molecules of the first binder and / or the second binder in the electrode active material layer, reduce the crystallinity of the first binder and / or the second binder, thereby reducing the migration impedance of lithium ions on the surface of the electrode active material, reducing the internal resistance of the battery, and improving the electrochemical performance of the battery.

[0026] In the present invention, the weight average molecular weight of the first binder is 1000 g / mol-100000 g / mol, for example, 1000 g / mol, 2000 g / mol, 3000 g / mol, 4000 g / mol, 6000 g / mol, 8000 g / mol, 9000 g / mol, 10000 g / mol, 20000 g / mol, 30000 g / mol, 40000 g / mol, 50000 g / mol, 60000 g / mol, 70000 g / mol, 80000 g / mol, 90000 g / mol or 100000 g / mol.

[0027] In the present invention, the polyamide-imide comprises a structural formula The first repeating unit of the present invention is characterized in that R comprises a divalent aromatic group.

[0028] In the present invention, the polyamide-imide comprises a structural formula The second repeating unit of the present invention is characterized in that R comprises a divalent aromatic group.

[0029] In the present invention, the R comprises In one of the following, A includes one of the following divalent groups: -SO 2 —,—CO—,—C(CH 3 ) 2 —, —O—, —S— and the space key.

[0030] In the present invention, when the A is a null bond, it means that A does not exist, that is, the benzene ring on one side is directly connected to the benzene ring on the other side.

[0031] In the present invention, the second repeating unit (Formula I-2) includes two characteristic structures of 1,3 and 1,4 polyamide-amic acid, in which two amide groups are linked to an aromatic ring.

[0032] In the present invention, the polyamideimide comprises a first repeating unit of an amide-imide structure as shown in Formula I-1 and a second repeating unit of an amide-amic acid structure as shown in Formula I-2.

[0033] In the present invention, based on the sum of the molar contents of the first repeating unit and the second repeating unit, the content of the first repeating unit is greater than 80%, for example, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, 99.5% or 100%.

[0034] In one embodiment, based on the sum of the molar contents of the first repeating unit and the second repeating unit, the content of the first repeating unit is greater than 90%, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5% or 100%.

[0035] In one embodiment, based on the sum of the molar contents of the first repeating unit and the second repeating unit, the content of the first repeating unit is greater than 95%, for example, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.2%, 99.4%, 99.6%, 99.8% or 100%.

[0036] In the present invention, the electrode active material is a positive electrode active material and / or a negative electrode active material.

[0037] In the present invention, the positive electrode active material includes at least one of lithium titanate, lithium metal oxide of metal M, lithium metal phosphate of metal M and lithium metal silicate of metal M, and the metal M includes at least one of nickel, iron, vanadium, cobalt and manganese.

[0038] In one embodiment, the positive electrode active material includes LiCoO 2 、LiNiO 2 、LiMnO 2 、LiMn 2 O 4 、Nickel cobalt aluminum oxide (NCA), nickel cobalt manganese oxide (NMC), Li 3 V 2 (PO 4 ) 3 、LiVPO 4 F. LiMnPO 4 and LiFePO 4 / C.

[0039] In one embodiment, the positive electrode active material includes LiCoO 2 , NMC and LiFePO 4 / C.

[0040] In the present invention, the negative electrode active material includes at least one of natural graphite, artificial graphite, mesophase carbon microbeads, hard carbon, tin, tin alloy, tin oxide, silicon, silicon alloy, silicon-oxygen material and silicon-carbon composite material.

[0041] In one embodiment, the negative electrode active material includes at least one of tin, tin alloy, tin oxide, silicon, silicon alloy, silicon-oxygen material and silicon-carbon composite material.

[0042] In the present invention, based on the total weight of the electrode active material layer, the content of the electrode active substance is 68%-99.65%, for example, 68%, 69%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, 99.5% or 99.65%.

[0043] In the present invention, the precursor for forming the polyamideimide includes a polyamide-amic acid compound.

[0044] In the present invention, the polyamide-amic acid compound includes a structural formula The third repeating unit of (Formula I-3), R comprises a divalent aromatic group, R 1 It includes an organic basic compound or an inorganic basic compound and a carboxyl group to form a neutralization reaction part.

[0045] In one embodiment, the organic basic compound includes an amine compound.

[0046] In one embodiment, the organic basic compound includes a tertiary amine compound.

[0047] In one embodiment, the organic basic compound includes triethylamine.

[0048] In the present invention, the polyamide-amic acid compound is selected from R 1 It is a compound with low boiling point and volatile groups, making -CO-R 1 —It is easy to decompose and volatilize during heating, which is beneficial to the cyclization and curing of polyamide-amic acid compounds.

[0049] In the present invention, the R comprises In one of the following, A includes one of the following divalent groups: -SO 2 —,—CO—,—C(CH 3 ) 2 —, —O—, —S— and the space key.

[0050] In the present invention, when the A is a null bond, it means that A does not exist, that is, the benzene ring on one side is directly connected to the benzene ring on the other side.

[0051] In the present invention, an electrode active material, a polyamide-amic acid compound, a second binder and a plasticizer are mixed with a dispersion medium to obtain an electrode slurry.

[0052] In the present invention, the polyamide-amic acid compound can be composed of a second repeating unit (Formula I-2) and a third repeating unit (Formula I-3), with the third repeating unit (Formula I-3) being the main component, and the first repeating unit (Formula I-1) is inevitably generated during the synthesis of the polyamide-amic acid compound.

[0053] In the present invention, in the electrode slurry, based on the sum of the molar contents of the first repeating unit, the second repeating unit and the third repeating unit, the content of the third repeating unit is greater than 60%, for example, 61%, 62%, 65%, 67%, 70%, 72%, 75%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, 99.5% or 100%.

[0054] In one embodiment, in the electrode slurry, based on the sum of the molar contents of the first repeating unit, the second repeating unit and the third repeating unit, the content of the third repeating unit is greater than 80%, for example, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, 99.5% or 100%.

[0055] In one embodiment, in the electrode slurry, based on the sum of the molar contents of the first repeating unit, the second repeating unit and the third repeating unit, the content of the third repeating unit is greater than 90%, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5% or 100%.

[0056] In the present invention, by regulating the content of the third repeating unit, when the electrode slurry is prepared using the electrode active material layer, the solubility of the polyamide-amic acid compound in the electrode slurry can be increased, so that the polyamide-amic acid compound is completely dissolved or mostly dissolved in the electrode slurry.

[0057] In the present invention, the polyamideimide is obtained by curing the polyamide-amic acid compound, and the curing temperature is 150°C-450°C, for example, 150°C, 155°C, 160°C, 170°C, 180°C, 190°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 340°C, 380°C, 400°C, 410°C, 420°C, 430°C, 435°C or 440°C.

[0058] In one embodiment, the curing temperature is 200°C-350°C, for example, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C or 350°C.

[0059] In one embodiment, the curing temperature is 250°C-300°C, for example, 250°C, 255°C, 260°C, 265°C, 270°C, 275°C, 280°C, 285°C, 290°C, 295°C or 300°C;

[0060] In the present invention, the curing time is 0.5h-12h, for example, 0.5h, 1h, 1.5h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 10.5h, 11h, 11.5h or 12h.

[0061] In the present invention, when preparing the electrode slurry, the polyamide-amic acid compound can be added in the form of an aqueous solution of the polyamide-amic acid compound or in the form of a polyamic acid solid, and then acid-base neutralization is performed in the electrode slurry to dissolve and disperse it.

[0062] In the present invention, the polyamide-amic acid compound aqueous solution includes one of Torlon AI-30 and Torlon AI-50 of Solvay Advanced Polymers, LLC.

[0063] In the present invention, when preparing the electrode slurry, there is no limitation on the order of adding the first binder, the second binder and the plasticizer.

[0064] In one embodiment, when preparing the electrode slurry, the second binder is first added and dispersed before adding the first binder.

[0065] In the present invention, when preparing the electrode slurry, the second binder is not limited in form, and can be a powder or an aqueous solution.

[0066] In the present invention, the second binder can be a conventional choice in the art, such as one of SUNROSE MAC series sodium carboxymethyl cellulose powder and Macklin P832271 polyacrylic acid viscous liquid (solid content 50%, average molecular weight MW 5000).

[0067] In the present invention, when preparing the electrode slurry, the dispersion medium of the electrode active material layer may further include an organic solvent or alcohol miscible with water, such as N-methylpyrrolidone or ethanol.

[0068] In the present invention, the electrode active material layer further includes a conductive agent, and the conductive agent is a positive electrode conductive agent and / or a negative electrode conductive agent.

[0069] In the present invention, the weight ratio of the positive electrode conductive agent to the electrode active material is 1%-15%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0070] In one embodiment, the weight ratio of the positive electrode conductive agent to the electrode active material is 2%-10%, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%.

[0071] In the present invention, the weight ratio of the negative electrode conductive agent to the electrode active material is less than 15%, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0072] In one embodiment, the weight ratio of the negative electrode conductive agent to the electrode active material is less than 10%, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%.

[0073] In one embodiment, the weight ratio of the negative electrode conductive agent to the electrode active material is less than 8%, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5% or 8%.

[0074] In the present invention, the positive electrode conductive agent includes at least one of natural graphite, artificial graphite, graphene, acetylene black, Ketjen black, carbon fiber, carbon nanotubes and conductive carbon black.

[0075] In the present invention, the negative electrode conductive agent includes at least one of natural graphite, artificial graphite, graphene, acetylene black, Ketjen black, carbon fiber, carbon nanotubes and conductive carbon black.

[0076] In the present invention, the addition of the conductive agent can improve the electronic conduction between the electrode active materials and between the electrode active materials and the current collector; by adjusting the weight ratio of the positive electrode conductive agent and / or the negative electrode conductive agent to the electrode active material layer, when the weight ratio of the positive electrode conductive agent and / or the negative electrode conductive agent to the electrode active material layer is too small, the conductive agent in the electrode active material layer is insufficient, and the transmission path and conductive network formed inside the electrode are too few, which makes it difficult to improve the transmission efficiency of lithium ions and is not conducive to improving the battery efficiency; when the weight ratio of the positive electrode conductive agent and / or the negative electrode conductive agent to the electrode active material layer is too large, the conductive agent in the electrode active material layer is excessive, which will cause the internal resistance of the battery to increase, affecting the charge and discharge efficiency of the battery.

[0077] In the present invention, the electrode active material layer is a positive electrode active material and / or a negative electrode active material.

[0078] In the present invention, the negative electrode active material may further include a third binder, and the content of the third binder is less than 8% based on the total weight of the negative electrode active material, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5% or 8%.

[0079] In one embodiment, the content of the third binder is less than 5%.

[0080] In the present invention, the third binder includes at least one of hydroxypropylene cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, acrylonitrile polymer, styrene-butadiene rubber (SBR) and nitrile rubber.

[0081] A second aspect of the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the electrode according to the first aspect of the present invention.

[0082] In the present invention, the lithium-ion battery includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet includes a positive electrode collector, and the positive electrode collector can be a conventional choice in the art, for example, including one of aluminum foil, nickel mesh and nickel foam; the negative electrode sheet includes a negative electrode collector, and the negative electrode collector can be a conventional choice in the art, for example, including one of copper foil, nickel-copper alloy foil, stainless steel foil, nickel mesh and nickel foam.

[0083] In one embodiment, the negative electrode current collector comprises copper foil.

[0084] In the present invention, the battery further comprises other binders, and all of them are conventionally selected by those skilled in the art. For example, the other binder comprises styrene-butadiene rubber (SBR).

[0085] In the present invention, the lithium ion battery further includes an electrolyte.

[0086] In the present invention, the electrolyte includes a non-aqueous electrolyte, and the non-aqueous electrolyte includes one of a non-aqueous electrolyte solution and a solid electrolyte.

[0087] In the present invention, the non-aqueous electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0088] In the present invention, the non-aqueous organic solvent includes one or more of carbonate solvents, carboxylate solvents, ether solvents, ketone solvents, alcohol solvents and aprotic solvents.

[0089] In the present invention, the carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate and fluorocarbonate.

[0090] In the present invention, the carboxylic acid ester solvent includes at least one of methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate and butyrolactone.

[0091] In the present invention, the ether solvent includes at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran and tetrahydrofuran.

[0092] In the present invention, the ketone solvent includes cyclohexanone.

[0093] In the present invention, the alcohol solvent includes at least one of ethanol and isopropanol.

[0094] In the present invention, the aprotic solvent includes at least one of a nitrile compound (for example, X-CN, wherein X is a C2 to C20 straight chain, branched or cyclic hydrocarbon group and aromatic group), an amide compound (for example, dimethylformamide), a dioxolane compound (for example, 1,3-dioxolane) and sulfolane.

[0095] In the present invention, the non-aqueous organic solvent may be a single solvent or a mixture of solvents.

[0096] In the present invention, when the non-aqueous organic solvent is a mixture of solvents, the mixture of solvents may include a mixture of cyclic and chain carbonate solvents, and the cyclic and chain carbonate solvents in the carbonate solvents are mixed according to a volume ratio of 1:1-1:9, for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8 or 1:9.

[0097] In the present invention, the non-aqueous electrolyte may further include an additive, and the additive includes at least one of carbon dioxide, vinylene carbonate, fluoroethylene carbonate, sultone, biphenyl and cyclohexylbenzene.

[0098] In the present invention, additives are used to improve battery performance and safety in use.

[0099] In the present invention, the non-aqueous electrolyte further comprises a lithium salt, wherein the lithium salt comprises LiPF 6 , LiBF 4 、LiCF 3 SO 3 、LiN(SO 2 C 2 F 5 ) 2 、LiN(CF 3 SO 2 ) 2 、LiN(CF 3 SO 2 )(C 4 F 9 SO 2 )、LiC(CF 3 SO 2 ) 3 、LiC(C 2 F 5 SO 2 ) 3 、LiClO 4 , at least one of LiCl, LiI, LiBOB, LiDFOB and LiTFOP.

[0100] In the present invention, dissolving the lithium salt in the non-aqueous organic solvent is beneficial to the transmission of lithium ions between the positive electrode and the negative electrode.

[0101] In the present invention, based on the total weight of the electrolyte, the molar concentration of the lithium salt is 0.1M-2M, for example, 0.1M, 0.2M, 0.3M, 0.4M, 0.6M, 0.8M, 1M, 1.2M, 1.4M, 1.6M, 1.8M or 2M.

[0102] In the present invention, the solid electrolyte includes at least one of a gel polymer electrolyte and an inorganic solid electrolyte.

[0103] In the present invention, the gel polymer includes at least one of a polyethylene oxide or polyacrylonitrile polymer electrolyte impregnated with an electrolyte.

[0104] In the present invention, the inorganic solid electrolyte comprises LiI and Li 3 At least one of N.

[0105] In the present invention, the lithium-ion battery further comprises a separator, and the separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride and polyimide.

[0106] In the present invention, the lithium-ion battery includes one of a steel-shell cylindrical battery, a steel-shell square battery, an aluminum-shell square battery and a bag-shaped aluminum-plastic film soft-pack battery.

[0107] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usages, and do not represent the difference in order.

[0108] The present invention will be described in detail below by way of examples. The examples described in the present invention are only a part of the examples of the present invention, rather than all of the examples. Based on the examples in the present invention, all other examples obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0109] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0110] The following examples are used to illustrate the lithium ion secondary battery of the present invention.

[0111] Preparation of positive electrode:

[0112] Preparation Example 1-1:

[0113] The precursor of the first binder is a polyamide-amic acid compound aqueous solution Torlon AI-30, with a solid content of 35wt%, and the second binder is Macklin P832271 polyacrylic acid (PAA) viscous liquid (solid content 50%, average molecular weight MW ~ 5000); the plasticizer is glycerol. 4 / C powder, acetylene black, Torlon AI-30, Macklin P832271 and propylene glycol in a weight ratio of 100:6:11.4:4:0.3 were prepared into a positive electrode slurry with deionized water, coated on both sides of an aluminum foil current collector with a thickness of 12 μm, dried at 80°C, heated and cured at 250°C for 3 hours, and rolled and cut to produce a positive electrode sheet A1 with a size of 480 mm × 44 mm.

[0114] Comparative Preparation Example 1-2:

[0115] LiFePO 4 / C powder, acetylene black and polyvinylidene fluoride are prepared into positive electrode slurry with NMP in a weight ratio of 100:6:6, coated on both sides of an aluminum foil current collector with a thickness of 12μm, dried at 120℃, and rolled and cut to make a positive electrode sheet AC1 with a size of 480mm×44mm.

[0116] Comparative Preparation Examples 1-3:

[0117] The precursor of the first binder is a polyamide-amic acid compound aqueous solution Torlon AI-30, with a solid content of 35wt%, and the second binder is Macklin P832271 polyacrylic acid viscous liquid (solid content 50%, average molecular weight MW 5000). 4 / C powder, acetylene black, Torlon AI-30 and Macklin P832271 were mixed with deionized water in a ratio of 100:6:11.4:4 to form a positive electrode slurry, which was coated on both sides of a 12μm thick aluminum foil current collector, dried at 80°C, and cured at 250°C for 3 hours. The electrode pieces were cut by roller pressing to produce a positive electrode AC2 with a size of 480mm×44mm.

[0118] Preparation of negative electrode:

[0119] Preparation Example 2-1:

[0120] The precursor of the first binder is a polyamide-amic acid compound aqueous solution Torlon AI-30, with a solid content of 35wt%; the second binder is Macklin P832271 polyacrylic acid viscous liquid (solid content 50%, average molecular weight MW ~ 5000); the plasticizer is propylene glycol. Artificial graphite, acetylene black, Torlon AI-30, Macklin P832271, and propylene glycol are mixed with deionized water in a ratio of 100:3:8.5:2:0.2 to form a negative electrode slurry, which is coated on both sides of a copper foil current collector with a thickness of 8μm, dried at 80℃, and heated and cured at 250℃ for 3 hours. Roll-press and cut the electrode sheets to make a negative electrode sheet B1 with a size of 483mm×46mm.

[0121] Preparation Example 2-2:

[0122] The precursor of the first binder is a polyamide-amic acid compound aqueous solution Torlon AI-30 with a solid content of 35wt%; the second binder is Macklin P832271 polyacrylic acid viscous liquid (solid content 50%, average molecular weight MW ~ 5000); the plasticizer is propylene glycol. Silicone material (Berryt BS0-2), carbon fiber, Torlon AI-30, Macklin P832271 and propylene glycol are prepared into a negative electrode slurry with a ratio of 100:8:17.1:6:0.5 with deionized water, and coated on both sides of a copper foil current collector with a thickness of 8μm. After drying at 80℃, heat and cure at 250℃ for 3 hours, roll-press and cut the pole pieces to make a negative electrode B2 with a size of 483mm×46mm.

[0123] Comparative Preparation Example 2-3:

[0124] The precursor of the first binder is a polyamide-amic acid compound aqueous solution Torlon AI-30 with a solid content of 35wt%; the second binder is Macklin P832271 polyacrylic acid viscous liquid (solid content 50%, average molecular weight MW ~ 5000). Artificial graphite, acetylene black, Torlon AI-30 and Macklin P832271 are mixed with deionized water in a ratio of 100:3:8.5:2 to form a negative electrode slurry, which is coated on both sides of a copper foil current collector with a thickness of 8μm. After drying at 80℃, heat and cure at 250℃ for 3 hours, roll and cut the pole pieces to make a negative electrode BC1 with a size of 483mm×46mm.

[0125] Comparative Preparation Example 2-4:

[0126] Artificial graphite, acetylene black, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are mixed with deionized water in a ratio of 100:3:1.5:2.5 to form a negative electrode slurry, which is then coated on both sides of a copper foil current collector with a thickness of 8 μm. After drying at 120°C, the electrodes are rolled and cut into pieces to form a negative electrode BC2 with a size of 483 mm × 46 mm.

[0127] Comparative Preparation Example 2-5:

[0128] The precursor of the first binder is the polyamide-amic acid compound aqueous solution Torlon AI-30. The silicon oxide material (Barrett BS0-2), carbon fiber, and Torlon AI-30 are mixed with deionized water at a ratio of 100:8:22.8 to form a negative electrode slurry, which is then coated on both sides of a copper foil current collector with a thickness of 8 μm. After drying at 80°C, it is heated and cured at 250°C for 3 hours, and the pole pieces are rolled and cut to make a negative electrode BC3 with a size of 483 mm × 46 mm.

[0129] Lithium-ion battery assembly :

[0130] Diaphragm: 12μm thick PE film is used.

[0131] Non-aqueous electrolyte: electrolyte lithium salt is 1 mol / L LiPF 6 , the solvent system is EC+DEC+FEC (weight ratio is 3:6:1).

[0132] A 053450 lithium-ion battery was prepared by conventional methods using the positive electrode sheet, negative electrode sheet, separator and electrolyte.

[0133] The embodiments and comparative examples are set as shown in Table 1:

[0134] Positive electrode Negative plate Example 1 A1 B1 Example 2 A1 BC2 Example 3 AC1 B1 Example 4 A1 B2 Example 5 AC1 B2 Comparative Example 1 AC1 BC2 Comparative Example 2 AC1 BC1 Comparative Example 3 AC2 BC2 Comparative Example 4 AC2 BC1 Comparative Example 5 AC2 BC3

[0135] Test example:

[0136] (1) Peel strength:

[0137] The obtained electrode was cut into a rectangle of 100 mm long and 25 mm wide as a test piece, and the electrode active material layer was fixed upward. After affixing a transparent tape to the surface of the active material layer of the test piece, the 180° peeling stress was measured at a speed of 50 mm / min from one end of the test piece. The test was performed 5 times, and the average value was taken as the peeling strength. The greater the peeling strength, the better the bonding state between the electrode active material layer and the current collector.

[0138] The peel strength test results are recorded in Table 2.

[0139] (2) Initial capacity at room temperature:

[0140] At a temperature of 25°C, the obtained lithium ion secondary battery was charged to 3.8V at a constant current of 0.5C, and then charged at a constant voltage of 3.8V with a cut-off current of 0.05C; left for 10 minutes; and then discharged to 2.0V at a constant current of 0.2C, and the obtained discharge capacity was the initial capacity of the battery at room temperature.

[0141] (3) Discharge internal resistance:

[0142] At a temperature of 25°C, the obtained lithium ion secondary battery was charged to 3.8V at a constant current of 0.5C, and then charged at a constant voltage of 3.8V with a cut-off current of 0.05C; discharged at a constant current of 0.2C for 2.5h; after standing for 2h, the open circuit voltage V0 was recorded; then discharged at a constant current of 1C for 10s, and the discharge cut-off voltage V1 was recorded. The discharge internal resistance R = (V0-V1) / I1, where I1 is the current size of the 1C discharge current.

[0143] (4) Rate discharge characteristics:

[0144] At a temperature of 25°C, the obtained lithium ion secondary battery was charged to 3.8 V at a constant current of 0.5C, then charged at a constant voltage of 3.8 V with a cut-off current of 0.05C, and discharged to 2.0 V at a constant current of 2C. The ratio of the 2C discharge capacity to the 0.2C discharge capacity was expressed as a percentage as the rate discharge characteristic.

[0145] (5) Normal temperature cycle characteristics:

[0146] At a temperature of 25°C, the obtained lithium ion secondary battery was charged to 3.8V at a constant current of 0.5C, and then charged at a constant voltage of 3.8V with a cut-off current of 0.05C; the battery was discharged at a constant current of 0.5C for 100 cycles, and the ratio of the discharge capacity of the 100th cycle to the 1st cycle was expressed as a percentage as the normal temperature cycle characteristic.

[0147] (6) Low temperature capacity retention rate:

[0148] For the low-temperature characteristics of the battery, the battery with tested initial capacity at room temperature is charged and discharged in a constant temperature environment of -20°C using the same charging and discharging test method. The ratio of the initial capacity at -20°C to the initial capacity at room temperature of 25°C is taken as the low-temperature capacity retention rate.

[0149] When the negative electrode uses negative electrode powder containing silicon oxide, the test results of the battery performance are recorded in Table 3; when the negative electrode uses artificial graphite, the test results of the battery performance are recorded in Table 4.

[0150] Table 2:

[0151] electrode Active substances Binder Slurry system Peel strength (N / m) Preparation Example 1-1 A1 <![CDATA[LiFePO 4 / C]]> PAI+PAA+propylene glycol water 23 Preparation Example 1-2 AC1 <![CDATA[LiFePO 4 / C]]> PVDF NMP 9 Preparation Example 1-3 AC2 <![CDATA[LiFePO 4 / C]]> PAI+PAA water 25 Preparation Example 2-1 B1 Artificial graphite PAI+PAA+propylene glycol water 17 Preparation Example 2-2 B2 Silicon oxygen material PAI+PAA+propylene glycol water 24 Preparation Example 2-3 BC1 Artificial graphite PAI+PAA water 18 Preparation Example 2-4 BC2 Artificial graphite SBR+CMC water 7 Preparation Example 2-5 BC3 Silicon oxygen material PAI water 28

[0152] Table 3:

[0153]

[0154] Table 4:

[0155]

[0156] It can be seen from Table 3 and Table 4 that the lithium ion battery prepared by the present invention has good charge and discharge power characteristics, low temperature performance and cycle performance compared with the comparative example.

[0157] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. An electrode, characterized in that: The electrode includes an electrode active material layer, which includes an electrode active substance, a first binder, a second binder and a plasticizer, wherein the first binder includes polyamideimide, and the second binder includes at least one of sodium carboxymethyl cellulose, sodium alginate, polyacrylic acid, polyvinyl alcohol and chitosan; the dispersion medium of the electrode active material layer includes water; based on the total weight of the electrode active material layer, the content of the first binder is 0.2%-20%, and the content of the second binder is 0.1%-10%.

2. The electrode according to claim 1, wherein The plasticizer includes at least one of ethylene glycol, propylene glycol, glycerol and citric acid; And / or, based on the total weight of the electrode active material layer, the content of the plasticizer is 0.05%-2%.

3. The electrode according to claim 1, wherein The weight average molecular weight of the first binder is 1000 g / mol-100000 g / mol.

4. The electrode according to claim 1, wherein The polyamideimide comprises a structural formula of A first repeating unit, wherein R comprises a divalent aromatic group; And / or, the polyamide-imide comprises a structural formula of The second repeating unit of the present invention is characterized in that R comprises a divalent aromatic group.

5. The electrode according to claim 4, wherein Based on the sum of the molar contents of the first repeating unit and the second repeating unit, the content of the first repeating unit is greater than 80%, preferably greater than 90%, and more preferably greater than 95%.

6. The electrode according to claim 1, wherein The electrode active material is a positive electrode active material and / or a negative electrode active material; And / or, the positive electrode active material includes at least one of lithium titanate, lithium metal oxide of metal M, lithium metal phosphate of metal M and lithium metal silicate of metal M, and the metal M includes at least one of nickel, iron, vanadium, cobalt and manganese; And / or, the negative electrode active material includes at least one of natural graphite, artificial graphite, mesophase carbon microbeads, hard carbon, tin, tin alloy, tin oxide, silicon, silicon alloy, silicon-oxygen material and silicon-carbon composite material; And / or, based on the total weight of the electrode active material layer, the content of the electrode active substance is 68%-99.65%.

7. The electrode according to claim 1, wherein The precursor for forming the polyamideimide includes a polyamide-amic acid compound.

8. The electrode according to claim 7, wherein The polyamide-amic acid compound includes a structural formula of The third repeating unit of R comprises a divalent aromatic group, and R1 comprises a part formed by a neutralization reaction of an organic basic compound or an inorganic basic compound and a carboxyl group; More preferably, the organic basic compound comprises a tertiary amine compound; More preferably, the organic basic compound comprises triethylamine.

9. The electrode according to claim 7, wherein The polyamideimide is obtained by curing the polyamide-amic acid compound, and the curing temperature is 150°C-450°C; preferably 200°C-350°C; more preferably 250°C-300°C; And / or, the curing time is 0.5h-12h.

10. A lithium ion battery, characterized in that: The electrode comprises the electrode described in any one of claims 1 to 9.

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