Adhesive, pole piece slurry, pole piece, and battery

Abstract

The present application relates to the technical field of lithium ion batteries, and provides a kind of binder, pole piece slurry, pole piece and battery.The binder includes polymer binder and coupling agent, and the coupling agent contains first group of organic affinity and second group of inorganic affinity.The binder of the present application is applied to positive electrode slurry, which can improve the dispersion effect of positive electrode active material and conductive ceramic particles in the positive electrode slurry, enhance the bonding performance of the positive electrode, and improve the ion transmission speed inside the positive electrode.The battery containing the positive electrode piece has the advantages of high rate capability and long cycle life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, and in particular to a binder, a pole piece slurry, and a pole piece and a battery prepared using the binder. BACKGROUND

[0002] Lithium ion batteries are widely used in mobile phones, notebook computers and new energy vehicles due to their high energy density, long cycle life and environmental friendliness. In recent years, with the increasing prominence of energy problems and environmental problems, new energy vehicles have become the mainstream direction of automobile development. Among them, the power battery as an important component of new energy vehicles is a key factor determining its service life and mileage. Therefore, the research of high energy density power battery has become an important link in the field of new energy vehicles. In the power battery, the performance of the positive electrode has an important influence on the capacity and energy density of the battery.

[0003] In the formulation process of the positive electrode of the lithium ion battery, a binder needs to be added to the positive electrode slurry to bond the active material particles (inorganic particles), enhance the contact between the active material particles and the conductive agent, and the current collector, and at the same time, can inhibit the volume expansion of the active material particles and improve the structural stability. At the same time, in the internal structure of the positive electrode, it is also necessary to maintain the continuity and smoothness of the ion channel, so as to be beneficial to the capacity of the active material at the bottom of the positive electrode, and also to affect the rate performance of the positive electrode. However, in the positive electrode slurry, smaller particle size inorganic particles (especially nanoparticles) tend to agglomerate in the organic slurry to form larger secondary particles. This not only makes the inorganic particles in the slurry disperse unevenly, prolongs the conduction path of electrons and lithium ions, but also reduces the uniformity of the positive electrode coating and the bonding effect of the binder, limits the capacity of the positive electrode and the rate performance, and aggravates the problems of volume expansion, pole piece powder falling and capacity attenuation of the positive electrode.

[0004] Therefore, it is of great significance to develop a positive electrode with good bonding performance, uniform dispersion of inorganic particles and good ion transmission performance of the positive electrode. SUMMARY

[0005] The present application aims to overcome the above-mentioned problems existing in the prior art, and provides a binder, in particular a positive electrode binder, a positive electrode slurry containing the positive electrode binder, and a positive electrode piece and a battery prepared using the positive electrode slurry. The positive electrode binder of the present application can improve the dispersion effect of the positive electrode active material and the conductive ceramic particles, enhance the bonding performance of the positive electrode, and improve the ion transmission speed in the positive electrode. The battery containing the positive electrode piece has the advantages of high rate performance and long cycle life.

[0006] The inventors of the present application find that when the binder is contained in the positive electrode slurry, through the synergistic effect of the positive electrode active material, the polymer binder, the coupling agent and the conductive ceramic nanoparticles, on the one hand, the cohesion of the positive electrode coating paste can be enhanced, and the bonding strength between the positive electrode active material and the conductive ceramic particles and the interface of the positive electrode coating paste / positive electrode current collector can be improved, so as to avoid the positive electrode powder falling or peeling. On the other hand, the uniform dispersion of each component in the positive electrode slurry can be promoted, the stability of the internal structure and morphology of the positive electrode is ensured, and the smooth transmission of the positive electrode electron and lithium ion in the battery cycle process is ensured, so as to prolong the cycle life of the lithium ion battery.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a binder, which comprises a polymer binder and a coupling agent, wherein the coupling agent contains a first group of organic affinity and a second group of inorganic affinity.

[0008] The second aspect of the present application provides a pole piece slurry, which comprises the binder of the first aspect of the present application.

[0009] The third aspect of the present application provides a pole piece, which comprises a current collector and a positive electrode active material layer coated on at least one side surface of the current collector, wherein the positive electrode active material layer comprises the binder of the first aspect of the present application and / or the pole piece slurry of the second aspect of the present application.

[0010] The fourth aspect of the present application provides a battery, which comprises at least one of the binder of the first aspect of the present application, the pole piece slurry of the second aspect of the present application and the pole piece of the third aspect of the present application.

[0011] The present application has the following beneficial effects by adopting the above technical solutions:

[0012] (1) The binder provided by the present application applied to the positive electrode can enhance the bonding strength between each component of the positive electrode, reduce the positive electrode powder falling and volume expansion, so as to improve the structure and morphology stability of the positive electrode pole piece;

[0013] (2) The binder provided by the present application applied to the positive electrode can improve the interface compatibility between the positive electrode active material particles in the positive electrode piece and the organic matter in the positive electrode slurry, inhibit the agglomeration of the positive electrode active material particles, promote the uniform dispersion of each component in the positive electrode slurry, ensure the efficient and smooth transmission of the positive electrode electron and lithium ion, and finally prolong the cycle life of the lithium ion battery;

[0014] (3) The pole piece slurry provided by the present application, especially the positive electrode slurry, can improve the dispersion effect of the conductive ceramic nanoparticles in the positive electrode (especially in the high surface loading positive electrode), optimize the lithium ion transmission path, improve the lithium ion transmission performance, and further improve the capacity performance, rate performance and cycle life of the positive electrode active material;

[0015] (4) The slurry of the electrode plate, especially the positive electrode slurry, can improve the bonding strength of the positive electrode paste / current collector interface, avoid the peeling of the paste from the current collector during the processing, and improve the processing performance of the electrode plate.

[0016] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are understood to be approximate values. The exact values and ranges included between any stated values or endpoints are also contemplated. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. For values which are greater than one, one unit is considered to be 1, 10, 100, 1,000 or 10,000 as appropriate. These are only examples of what is specifically DETAILED DESCRIPTION

[0017] The specific embodiments of the present application will now be described in detail below. It should be appreciated that the detailed description of specifically described embodiments is intended for purposes of illustration only and is not intended to limit the present application.

[0018] Unless otherwise defined, all scientific and technical terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0019] The first aspect of the present application provides a binder comprising a polymer binder and a coupling agent, the coupling agent containing a first group that is organophilic and a second group that is inorganophilic.

[0020] In the present application, the "first group that is organophilic" refers to a chemical functional group that can react with a chemical group of an organic substance (e.g., a polymer binder) to form a chemical bond.

[0021] The "second group that is inorganophilic" refers to a chemical functional group that can react with a chemical group (e.g., a hydroxyl group) on the surface of an inorganic substance (e.g., a positive active material and a conductive ceramic particle) to form a chemical bond.

[0022] In an example, the first group is selected from at least one of an isocyanate group (-N=C=O), an amino group (-NH2), an epoxy group (-CH(O)CH-), a mercapto group (-SH), a vinyl group (-CH=CH2), and a methacryloyloxy group an isostearoyl group (-OC 18 H 37 ).

[0023] In a preferred example, the first group is an isocyanate group and / or a methacryloyloxy group, and more preferably the first group is an isocyanate group.

[0024] In one example, the second group is an alkoxy group. The alcohol group after hydrolysis of the alkoxy group can dehydrate and condense with the hydroxyl groups on the surface of the positive active material and the conductive ceramic particles to form chemical bonds.

[0025] Illustratively, the second group is selected from at least one of a methoxy group (-OCH3), an ethoxy group (-OCH2CH3), a propoxy group (-OCH2CH2CH3), and an isopropoxy group (-OCH2CH2C(CH3)2).

[0026] In one example, the coupling agent has a first group at one end and a second group at the other end. The first group is an isocyanate group. The second group is an alkoxy group.

[0027] In one example, the coupling agent is selected from at least one of a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, a bimetal coupling agent, a phosphate coupling agent, a borate coupling agent, and a chromium complex.

[0028] Illustratively, the silane coupling agent is selected from at least one of 3-isocyanatopropyl triethoxysilane, 3-isocyanatopropyl trimethoxysilane, and 3-isocyanatopropyl triisopropoxysilane.

[0029] Illustratively, the titanate coupling agent is selected from isopropyl triisocyanato titanate and / or isopropyl triisostearyl titanate.

[0030] Illustratively, the aluminate coupling agent is selected from at least one of isopropyl diisocyanato aluminate and isopropyl di-stearyl aluminate.

[0031] In one preferred example, the coupling agent is selected from at least one of 3-isocyanatopropyl triethoxysilane (IPTS), 3-isocyanatopropyl trimethoxysilane, isopropyl triisocyanato titanate, and isopropyl diisocyanato aluminate.

[0032] In one example, the polymeric binder includes at least one of a homopolymer or a copolymer of an olefinic monomer, a halogen-substituted olefinic monomer, and an acrylic monomer.

[0033] Illustratively, the olefinic monomer includes, but is not limited to, butadiene, ethylene, propylene, and acrylonitrile.

[0034] Illustratively, the halogen-substituted olefinic monomer includes, but is not limited to, vinylidene fluoride, hexafluoropropylene, difluoroethylene, tetrafluoroethylene, and trichloroethylene.

[0035] Exemplarily, the acrylic monomer includes methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl acrylate, acrylamide, ethyl acrylate, butyl acrylate, methacrylic acid, acrylic acid, vinyl acetate, and propyl acrylate.

[0036] In an example, the polymer binder includes at least one of polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyhexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, and polytetrafluoroethylene (PTFE).

[0037] In a preferred example, the binder is a cathode binder.

[0038] The second aspect of the present application provides a cathode slurry including the binder of the first aspect of the present application.

[0039] In a preferred example, the cathode slurry is a cathode slurry including a cathode active material and conductive ceramic particles.

[0040] The inventors of the present application have found that, in the cathode slurry, the first group of the organophilic group in the coupling agent can react with the polymer binder to form a new chemical bond, and the second group of the inorganophilic group can react with and bond to the hydroxyl groups on the surfaces of the cathode active material particles and the conductive ceramic particles. Ultimately, through the coupling reaction, the coupling agent can form a "molecular bridge" between the polymer binder and the inorganic particles (the cathode active material particles and the conductive ceramic particles), converting the weak physical interaction between the two into a strong chemical bond, significantly improving the adhesion strength of the polymer binder to the cathode active material and the conductive ceramic particles, and inhibiting the agglomeration of the cathode active material and the conductive ceramic particles, promoting the uniform dispersion of the particles.

[0041] The inventors of the present application have also found that the conductive ceramic nanoparticles can be dispersed around the cathode active material particles, forming a continuous and unobstructed lithium ion transmission path, thereby improving the lithium ion transmission, rate performance, and cycle performance of the cathode (especially at high surface loadings).

[0042] To better improve the performance of the cathode of the battery, one or more of the technical features can be further preferred.

[0043] In an example, the content of the coupling agent is 0.05-2 wt% of the total mass of the cathode active material and the conductive ceramic particles.

[0044] In one example, the content of the coupling agent is 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.12 wt%, 0.14 wt%, 0.15 wt%, 0.18 wt%, 2 wt% of the total mass of the positive active material and the conductive ceramic particles.

[0045] Preferably, the content of the coupling agent is 0.1-1 wt%, more preferably 0.3-0.8 wt% of the total mass of the positive active material and the conductive ceramic particles.

[0046] In one example, the conductive ceramic particles are selected from at least one of a garnet type, a NASICON type, a perovskite type and a thio-LISICON type conductive ceramic particle.

[0047] Illustratively, the garnet type conductive ceramic particle includes Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO), Li7La3Zr2O 12 (LLZO(LLZO), Li5La3R2O 12 , Li6ALa2R2O 12 , Li 5.5 La3R 1.75 D 0.25 O 12 and Li7La3Zr2O 12 , wherein R is one of Nb or T.

[0048] Illustratively, the NASICON structure type solid state electrolyte includes Li 1.3 Al 0.3 Ti 1.7 (PO4)3(LATP), Li 1+x Al x Ge 2-x (PO4)3(LAGP), LiTi2(PO4)3, LiGe2(PO4)3and LiHf2(PO4)3, 0 < x < 2.

[0049] Illustratively, the perovskite structure type solid state electrolyte includes Li x La 2 / 3-x / 3 TiO3(LLTO), 0 < x < 3.

[0050] Illustratively, the thio-LISICON structure type solid state electrolyte includes Li 10 GeP2S 12 and Li 10 SnP2S 12 at least one of.

[0051] In a preferred example, the conductive ceramic particles are at least one of LLZTO, LLZO, LATP, LAGP and LLTO.

[0052] In an example, the conductive ceramic particles have a particle size of 300 nm to 500 nm.

[0053] In the present application, the term "particle size" refers to the geometric spherical diameter of a single particle and not the average value, and when a range is given, it means that the particle sizes of the particles in the same material all fall within the range; meanwhile, the present application allows a certain error, i.e. when less than 5% of the total number of particles have particle sizes not within the required range, it is also considered to meet the requirements. In the present application, the particle size of the conductive ceramic particles is measured by transmission electron microscopy.

[0054] In an example, the content of the conductive ceramic particles is 0.01-8 wt% based on the total weight of solids of the positive electrode slurry.

[0055] In the present application, the "total weight of solids of the positive electrode slurry" refers to the total weight of the solid components excluding the solvent. For example, the solid components can consist of positive electrode active material, polymer binder, coupling agent, conductive ceramic particles and conductive agent, and the total weight of solids is the total weight of the above five components.

[0056] Illustratively, the content of the conductive ceramic particles is 0.01 wt%, 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% and 8 wt% based on the total weight of solids of the positive electrode slurry.

[0057] In a preferred example, the content of the conductive ceramic particles is 0.1-5 wt% based on the total weight of solids of the positive electrode slurry.

[0058] In an example, the content of the polymer binder is 0.01-8 wt% based on the total weight of solids of the positive electrode slurry.

[0059] Illustratively, the content of the polymer binder is 0.01 wt%, 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% and 8 wt% based on the total weight of solids of the positive electrode slurry.

[0060] In a preferred example, the content of the polymer binder is 0.1-5 wt% based on the total weight of solids of the positive electrode slurry.

[0061] In an example, the principle of the synergistic effect of the components in the positive electrode slurry is explained by taking the silane coupling agent 3-isocyanate propyl triethoxysilane (IPTS) and the PVDF polymer binder as an example. In the IPTS, the central atom is silicon, one side of the IPTS is an isocyanate group, which is a Lewis base, and at 60°C, the isocyanate group can react with the PVDF polymer segment which is a Lewis acid, and the reaction will make the polymer segment react with the isocyanate group to form an amide bond. At the same time, the other side of the IPTS is three ethoxyl groups, which can react with and bond to the hydroxyl groups on the surface of the positive active material particles and the conductive ceramic particles. Finally, through the coupling reaction, the IPTS can form a "molecular bridge" between the polymer binder and the inorganic particles, converting the weak physical interaction between the two into a strong chemical bond, significantly improving the adhesion strength of the polymer binder to the positive active material particles, inhibiting the agglomeration of the particles, and promoting the uniform dispersion of the particles. In addition, with the assistance of the IPTS, the conductive ceramic particles can be uniformly dispersed around the positive active material particles, forming a continuous and unobstructed lithium ion transmission path, thereby improving the lithium ion transmission, rate performance and cycle performance of the positive electrode (especially at high surface load).

[0062] Through a large number of experimental tests, the inventors of the present application found that when the polymer binder is PVDF, the coupling agent is isopropyl triisocyanate titanate, and the conductive ceramic particles are LLZTO, the synergistic effect of the components in the positive electrode slurry is the best, and the performance of the positive electrode sheet prepared from the positive electrode slurry is the best.

[0063] In an example, the positive active material is a lithium-containing transition metal oxide.

[0064] Illustratively, the lithium-containing transition metal oxide is selected from at least one of NCM ternary material, LiFePO4, LiMn 0.75 Fe 0.25 PO4, LiCoO2, LiMn2O4, LiNi 0.5 Mn 1.5 O4, and lithium-rich manganese-based materials.

[0065] In an example, the content of the positive active material is 85-99 wt% based on the total weight of the solids in the positive electrode slurry.

[0066] In an example, the positive electrode slurry further comprises a conductive agent.

[0067] The type of conductive agent is not specifically limited, and a conductive agent suitable for a positive electrode in the art can be selected, for example, it can be conductive carbon black (SP), Ketjen black, acetylene black, graphite conductive agent (KS-6, KS-15, S-O, SEG-6), carbon fiber (VGCG), carbon nanotube (CNT), and graphene.

[0068] In one example, the content of the conductive agent is 0.01-8wt%, preferably 0.1-5wt%, based on the total weight of the solid of the positive electrode slurry.

[0069] The second aspect of the present application claims a positive electrode slurry, wherein each component can be stored separately, or several components can be mixed and stored together. It can be understood that the solvent can not be included for the convenience of storage, transportation and sale. The solvent can be added by the purchaser when preparing the positive electrode slurry.

[0070] The present application also provides a positive electrode slurry, which comprises the positive electrode slurry of the second aspect of the present application, and an organic solvent.

[0071] In one example, the organic solvent comprises at least one of N-methyl pyrrolidone (NMP), N-dimethylamide (DMF) and dimethyl sulfoxide (DMSO).

[0072] The third aspect of the present application provides a pole piece, which comprises a current collector, and an active material layer coated on at least one side surface of the current collector, wherein the active material layer comprises the binder of the first aspect of the present application and / or the positive electrode slurry of the second aspect of the present application.

[0073] In one example, the pole piece is a positive electrode piece.

[0074] In one example, the positive electrode piece comprises a current collector, and a positive electrode active layer coated on two opposite maximum surfaces of the current collector, wherein the positive electrode active layer is prepared from the positive electrode slurry of the first aspect of the present application.

[0075] The present application also provides a method for preparing the positive electrode piece, which comprises the following steps:

[0076] (1) adding the polymer binder into the organic solvent, and preparing a uniform solution I by high-speed stirring for 40-60min, wherein the organic solvent needs to be strictly dehydrated before use, so as to avoid the hydrolysis reaction of the coupling agent after meeting water;

[0077] (2) adding the coupling agent into the organic solvent, and preparing a uniform solution II by high-speed stirring for 40-60min, wherein the organic solvent needs to be strictly dehydrated before use;

[0078] (3) mixing the solution I and the solution II, and placing them in a stirring tank to prepare a mixed glue solution by high-speed stirring for 40-60min;

[0079] (4) mixing the positive electrode active material, the conductive ceramic particles and the conductive agent, and obtaining a uniformly dispersed solid mixture after high-speed stirring for 60min.

[0080] (5) adding the solid mixture into the glue solution, stirring at high speed for 60 min, then increasing the temperature of the slurry and continuously stirring to promote the reaction, and finally obtaining a positive electrode slurry which is uniformly dispersed and stable;

[0081] (6) uniformly coating the positive electrode slurry obtained in step (5) on both sides of the positive electrode current collector aluminum foil, and drying to obtain a positive electrode sheet.

[0082] The order of the above steps (1), (2), (3), etc. is not fixed and can be adjusted according to actual needs.

[0083] In an example, the solid content of the positive electrode slurry obtained in the above step (5) is 60-80 wt%, preferably 65-75 wt%.

[0084] In an example, in the above step (5), the temperature of the slurry is increased to 40-80°C, and continuously stirred for 2-12 h.

[0085] The fourth aspect of the present application provides a battery, which comprises at least one of the binder of the first aspect of the present application, the electrode sheet slurry of the second aspect of the present application, and the electrode sheet of the third aspect of the present application.

[0086] In the present application, the battery is a lithium ion battery. The lithium ion battery is a wound type or a stacked type lithium ion battery.

[0087] Preferably, the lithium ion battery contains the positive electrode sheet of the third aspect of the present application, and a negative electrode sheet, an electrolyte, and a separator.

[0088] The components of the battery other than the positive electrode sheet (such as the negative electrode sheet, the separator, the electrolyte, etc.) and the assembly method can be performed in a conventional manner in the art, and will not be described here.

[0089] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part 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 without creative labor fall within the scope of the present application.

[0090] The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0091] The present application will be described in detail below in conjunction with specific examples, which are used for understanding rather than limiting the present application.

[0092] The following Group I examples are used to illustrate the positive electrode slurry composition of the present application.

[0093] Example I1

[0094] A positive electrode slurry composition, the specific components and contents are as follows:

[0095] Positive electrode active material: LCO, 92wt%;

[0096] Polymer binder: PVDF, 2wt%;

[0097] Coupling agent: silane coupling agent IPTS, 0.48wt%;

[0098] Conductive ceramic particles: LLZTO nanoparticles, 3wt%, particle size about 400nm;

[0099] Conductive agent: conductive carbon black SP, 3wt%.

[0100] Example I2

[0101] A positive electrode slurry composition, the specific components and contents are as follows:

[0102] Positive electrode active material: lithium iron phosphate (LiFePO4), 92wt%;

[0103] Polymer binder: HFP, 3wt%;

[0104] Coupling agent: silane coupling agent IPTS, 0.3wt%;

[0105] Conductive ceramic particles: LLZTO nanoparticles, 2wt%, particle size about 300nm;

[0106] Conductive agent: conductive carbon black SP, 2wt%.

[0107] Example I3

[0108] A positive electrode slurry composition, the specific components and contents are as follows:

[0109] Positive electrode active material: NCM ternary material (lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O2), 92wt%;

[0110] Polymer binder: PVDF-HFP, 4wt%;

[0111] Coupling agent: silane coupling agent IPTS, 0.76wt%;

[0112] Conductive ceramic particles: LLZTO nanoparticles, 4wt%, particle size about 500nm;

[0113] Conductive agent: conductive carbon black SP, 4wt%.

[0114] Example Group I4

[0115] This group of examples is used to illustrate the effect of varying the amount of coupling agent in the positive electrode slurry composition.

[0116] Example I4a: Performed as for Example I1 except that the amount of coupling agent was 0.19 wt%;

[0117] Example I4b: Performed as for Example I1 except that the amount of coupling agent was 0.95 wt%.

[0118] Example Group I5

[0119] This group of examples is used to illustrate the effect of varying the coupling agent in the positive electrode slurry composition.

[0120] Example I5a: Performed as for Example I1 except that the coupling agent was 3-isocyanatopropyltrimethoxysilane;

[0121] Example I5b: Performed as for Example I1 except that the coupling agent was 3-isocyanatopropyltriisopropoxysilane;

[0122] Example I5c: Performed as for Example I1 except that the coupling agent was isopropyl diisocyanatoaluminate.

[0123] Example I6

[0124] A positive electrode slurry composition, the specific components and amounts being as follows:

[0125] Positive electrode active material: LCO, 92 wt%;

[0126] Polymeric binder: PVDF, 2 wt%;

[0127] Coupling agent: isopropyl triisocyanato titanate, 0.5 wt%;

[0128] Conductive ceramic particles: LLZTO nanoparticles, 3 wt%;

[0129] Conductive agent: conductive carbon black SP, 3 wt%.

[0130] Example Group I7

[0131] This group of examples is used to illustrate the effect of varying the coupling agent in the positive electrode slurry composition.

[0132] Example I7a: Performed as for Example I6 except that the conductive ceramic particles were LLTO;

[0133] Example I7b: Refer to Example I6, except that the conductive ceramic particles are LGPS.

[0134] Comparative Example D1

[0135] Refer to Example I1, except that the silane coupling agent is not included.

[0136] Comparative Example D2

[0137] Refer to Example I1, except that the conductive ceramic particles are not included.

[0138] Comparative Example D3

[0139] Refer to Example I1, except that the coupling agent is tetraethoxysilane.

[0140] Comparative Example D4

[0141] Refer to Example I1, except that the coupling agent is tetraisocyanatosilane.

[0142] Example Group II

[0143] Example Group II uses the positive electrode slurry composition of Example Group I to prepare a positive electrode sheet, and assembles a battery.

[0144] Examples II1-II14

[0145] 1. Preparation of a positive electrode sheet

[0146] (1) The polymer binder is added to NMP, and a uniform solution I is prepared by high-speed stirring for 40-60 min;

[0147] (2) The coupling agent is added to NMP, and a uniform solution II is prepared by high-speed stirring for 40-60 min. The organic solvent needs to be strictly water-free before use;

[0148] (3) The solution I and the solution II are mixed and placed in a stirring tank for high-speed stirring for 40-60 min to obtain a uniformly mixed glue solution;

[0149] (4) The positive electrode active material, conductive ceramic, and conductive agent are mixed, and a uniformly dispersed solid mixture is obtained after high-speed stirring for 60 min;

[0150] (5) The solid mixture is added to the above glue solution, and after high-speed stirring for 60 min, the temperature is raised to 60°C and continues to stir for 12 h, and finally a uniformly dispersed and stable positive electrode slurry is obtained, with a solid content of 70 wt%;

[0151] (6) The positive electrode slurry obtained in step (5) is uniformly coated on both sides of the positive electrode current collector aluminum foil, and after drying and rolling, a positive electrode sheet is obtained;

[0152] 2. Preparation of negative electrode sheet

[0153] A mixture containing a negative electrode active material was prepared by mixing artificial graphite as an active material, SBR-based binder, thickener sodium carboxymethyl cellulose, and conductive agent conductive carbon black, and uniformly dispersing the mixture by high-speed stirring. In the mixture, the solid content included 95 wt% artificial graphite, 1.5 wt% sodium carboxymethyl cellulose, 1.5 wt% conductive carbon black Super-P, and 2 wt% binder. A negative electrode active material slurry was prepared using deionized water as a solvent, and the solid content of the slurry was 50 wt%. The slurry was uniformly coated on both sides of a copper foil, and was dried and compacted by a roll press to obtain a negative electrode sheet.

[0154] 3. Assembly of battery

[0155] After the negative electrode sheet and the positive electrode sheet were punched, a bare battery was formed using Z-type stacking, and aluminum tabs and copper-nickel-plated tabs were respectively punched out. The bare battery was clamped using a glass clamp at a force of 100 MPa / m2, and was vacuum baked at 85°C for 24 hours, and was then packaged using an aluminum plastic film. An electrolyte was a 1M lithium hexafluorophosphate-containing electrolyte, and a solvent was a mixed solvent of ethylene carbonate / dimethyl carbonate / 1,2-propylene carbonate-1:1:1 (volume ratio). After packaging, the battery was formed and aged to obtain a square soft-pack battery having a length of 60 mm, a width of 40 mm, and a thickness of 5 mm, and the design capacity of the battery cell was 4000 mAh.

[0156] In Examples II1-II14, the positive electrode slurry compositions of Examples I1-I7 and Comparative Examples D1-D4 were used to prepare batteries, which were denoted as C1-C15, respectively.

[0157] Test Example

[0158] (1) Peeling force test: The positive electrode sheets of all the above examples and comparative examples were cut to the same size, and a peeling force test was performed according to the following method. The cut positive electrode sheet was coated with a peeling tape using a sheet peeling device, and the peeling force was directly measured. The battery cells of the above examples and comparative examples were 100% DOD charged and discharged 20 times, and the battery cells were disassembled after being fully discharged after 20 cycles. The adhesion of the electrode sheet to the separator was observed during disassembly of the battery cell. The positive electrode sheet was dried to remove the electrolyte, and was cut to the same size as in the above peeling force test. The peeling force of the electrode sheet after 20 cycles was measured according to the above method. At the same time, the occurrence of powdering of the negative electrode sheet was observed during cutting.

[0159] (2) Positive electrode capacity release: The ratio of the capacity (mAh) at the first 0.33C discharge of the battery cell to the mass (g) of the positive electrode active material.

[0160] Initial efficiency: The ratio of the first discharge capacity to the first charge capacity of the battery cell.

[0161] 45℃ cycle number for 80% capacity retention: at 45℃, 1C / 1C charge-discharge cycles were carried out on the lithium cobalt oxide cathode in the charge-discharge window of 4.45V to 3.0V, on the lithium iron phosphate cathode in the charge-discharge window of 3.65V to 2.2V, and on the 8-series ternary cathode in the charge-discharge window of 4.2V to 3V. The test process was as follows: first, 1C constant current charging to 4.2V, then constant voltage charging, cutoff current 0.05C, and finally 1C constant current discharging to 2.5V, and so on. The number of times when the ratio of discharge capacity to initial discharge capacity (capacity retention rate) reached 80% was recorded and placed in Table 1. At the same time, the ratio of the thickness of the full battery at the end of the cycle to the thickness of the initial discharge battery was recorded, which was the battery cycle expansion rate.

[0162] Table 1

[0163]

[0164]

[0165] As can be seen from the results in Table 1, the silane coupling agent in the cathode must have both a functional group that can react with the polymer binder and a functional group that can react with the inorganic particles, in order to promote the uniform dispersion of the active cathode material and the conductive ceramic particles, and inhibit particle agglomeration. At the same time, the coupling agent can also play a role in strengthening the cohesion of the cathode paste, avoiding the problem of cathode paste powder falling off, thereby ensuring the stability of the cathode structure. Moreover, inhibiting particle agglomeration also makes the lithium ion channel and electron channel inside the cathode always remain unblocked, which can fully develop the capacity of the cathode active material, reduce polarization, improve the initial efficiency of the battery (≥70%), and increase the cathode gram capacity. For 45℃ cycles, the batteries prepared in the examples of the present application all have a cycle number of more than 800 times when the capacity retention rate reaches 80%, and the cycle expansion is controlled within 12%, and the cycle performance and cycle expansion have been greatly improved.

[0166] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A pole piece, characterized in that, The pole piece comprises a current collector and an active material layer coated on at least one side surface of the current collector, the active material layer comprising a pole piece slurry; the pole piece slurry comprises a binder, the binder comprising a polymer binder and a coupling agent, the coupling agent being isopropyl triisocyanate titanate; The pole piece slurry is a positive electrode slurry, the positive electrode slurry comprising a positive electrode active material and conductive ceramic particles; the conductive ceramic particles are LLZTO; the particle size of the conductive ceramic particles is 300 nm-500 nm; the positive electrode active material is lithium cobaltate; the content of the conductive ceramic particles is 0.01-8 wt% based on the total solid weight of the positive electrode slurry; The content of the coupling agent is 0.3-0.8 wt% of the total mass of the positive electrode active material and the conductive ceramic particles.

2. The pole piece of claim 1, wherein, The pole piece slurry further comprises a conductive agent, the content of the conductive agent being 0.01-8 wt% based on the total solid weight of the pole piece slurry.

3. A battery, characterized by The battery comprises the pole piece according to any one of claims 1 or 2.

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