Composite binder, electrode slurry, electrode plate and all-solid-state battery

Abstract

The present disclosure relates to a composite binder, an electrode slurry, an electrode pole piece and an all-solid-state battery, wherein the composite binder comprises a rigid binder and a flexible binder, wherein the rigid binder is a polysaccharide binder with an average degree of substitution of 1.5 or more, and the flexible binder is a rubber binder containing C-O bonds, and the molar content of the C-O bonds is 0.1-2% based on the total number of moles of C-H bonds on the flexible binder. The method introduces a rigid binder with a high degree of substitution and a flexible binder with a low oxygen-containing group for complementary use, thereby enhancing the solubility of the composite binder in a solvent, effectively improving the viscosity of the composite binder and the stability of the sulfide solid electrolyte, and enhancing the adhesion between inorganic particles in the slurry and between particles and current collectors, thereby effectively improving the stability of the slurry and the mechanical and electrochemical properties of the pole piece, and improving the first cycle efficiency of the battery.

Description

Technical Field

[0001] The present disclosure relates to the technical field of all-solid-state battery electrodes, and in particular, to a composite binder, an electrode slurry, an electrode pole piece and an all-solid-state battery. Background Art

[0002] All-solid-state batteries are considered to be the next generation of highly safe batteries because they use solid electrolytes to replace the electrolytes of traditional batteries and have non-flammable properties. Among them, sulfide solid electrolytes have high ionic conductivity (up to 10 - 2 S / cm) and low grain boundary impedance, which has attracted wide attention in the industry. In the preparation and coating process of sulfide solid-state battery electrode slurry, the use of highly polar and protic solvents (such as NMP and H2O commonly used in traditional battery systems) will react with the electrolyte, causing serious deterioration of electrolyte conductivity and failure of battery performance. Therefore, it is necessary to select non-polar and low-polarity solvents to inhibit the decomposition of sulfide solid-state electrolytes.

[0003] However, due to the weak polarity of non-polar and low-polar solvent molecules, the dispersion of highly polar inorganic particles (including active materials, solid electrolytes and conductive agents) is poor, which makes the inorganic particles easily agglomerated and settled. In addition, due to the density of electrolyte particles (2g / cm 3 about) and active material density (such as 5.1g / cm for LiCoO2 positive electrode material 2 ), which makes them more likely to be decomposed in low-polarity dispersion systems, resulting in uneven gradients in the composite electrode layer and affecting battery performance. Summary of the invention

[0004] The purpose of the present invention is to provide a composite binder, an electrode slurry, an electrode pole piece and an all-solid-state battery. The composite binder introduces a rigid binder with a high degree of substitution and a flexible binder with a low oxygen-containing group for complementary use, thereby effectively improving the viscosity of the composite binder and the stability of the sulfide solid electrolyte, improving the stability of the slurry and the mechanical and electrochemical properties of the pole piece.

[0005] The first aspect of the present disclosure provides a composite adhesive, which includes a rigid adhesive and a flexible adhesive, wherein the rigid adhesive is a polysaccharide adhesive with an average degree of substitution of 1.5 or more, and the flexible adhesive is a rubber adhesive containing CO bonds, and the molar content of the CO bonds is 0.1-2% based on the total molar number of CH bonds in the flexible adhesive.

[0006] The rigid binder can ensure the viscosity of the slurry and stabilize the inorganic particles; the average degree of substitution of the rigid binder is above 1.5, which can increase the solubility of the binder in the solvent on the one hand, and weaken the side reaction between the binder and the sulfide solid electrolyte on the other hand. The flexible binder has a flexible chain structure, which can improve the flexibility of the prepared electrode and prevent bending, cracking, and material loss. In addition, after hydroxylation, its adhesion can be enhanced, and the adhesion between solid particles and between particles and current collectors can be enhanced. The molar content of CO bonds is controlled at 0.1-2%, which can ensure the stability of the composite binder and the sulfide solid electrolyte.

[0007] The complementary effects of rigid binders and flexible binders can greatly improve the stability of sulfide solid-state battery electrode slurry and the mechanical and electrochemical properties of the electrode.

[0008] Optionally, the polysaccharide binder includes a polyhexasaccharide binder and / or a polypentasaccharide binder, the average degree of substitution of the polyhexasaccharide binder is greater than 2.0, and the average degree of substitution of the polypentasaccharide binder is greater than 1.5; the polyhexasaccharide binder is selected from one or more of a cellulose binder, a chitosan binder, a seaweed binder and a starch binder; the polypentasaccharide binder is selected from a polyribose binder, and the polyribose binder has the following structural fragments: Wherein, R1 to R4 are the same or different and are independently selected from hydroxyl, amine, and alkyl with 1 to 6 carbon atoms; and n is 500 to 10,000.

[0009] Optionally, the preparation method of the rubber adhesive containing CO bonds includes: using a plasma treatment system to perform plasma treatment on the rubber adhesive, the conditions of the plasma treatment include: using a mixture of CH4 and O2 as a gas source, the system output power is 10 to 500W, and the output frequency is 10kHz to 1GHz; the rubber adhesive is a non-polar rubber adhesive, and the non-polar rubber adhesive includes one or more of polybutadiene rubber adhesive, polyisoprene rubber adhesive, styrene-butadiene rubber adhesive, chloroprene rubber adhesive and polyethylene propylene rubber adhesive.

[0010] Optionally, the CO bond of the flexible binder includes one or more of a hydroxyl CO bond, an alkoxy CO bond and a carboxyl CO bond.

[0011] Optionally, based on the total mass of the composite binder, the content of the rigid binder is 5wt% to 95wt%, and the content of the flexible binder is 5wt% to 95wt%; preferably, the content of the rigid binder is 20wt% to 75wt%, and the content of the flexible binder is 25wt% to 80wt%; more preferably, the content of the rigid binder is 30wt% to 55wt%, and the content of the flexible binder is 45wt% to 70wt%.

[0012] Optionally, the mass ratio of the rigid binder to the flexible binder is (0.1-3):1, preferably (0.3-1.2):1.

[0013] Optionally, the weight average molecular weight of the rigid binder is 10 4 ~10 7 , preferably 10 5 ~10 6 The weight average molecular weight of the flexible binder is 10 4 ~10 7 , preferably 10 5 ~10 6 . .

[0014] A second aspect of the present disclosure provides an electrode slurry, which comprises an electrode active material, a sulfide solid electrolyte, a solvent and the composite binder described in the first aspect of the present disclosure.

[0015] Optionally, the solvent is selected from an organic solvent having a relative dielectric constant less than 6; preferably, the organic solvent is selected from at least one of an alkane solvent and an ether solvent; more preferably, the organic solvent is selected from one or more of methylcyclohexane, heptane, decane, anisole and cyclopentyl ether.

[0016] Optionally, based on the total weight of solids in the electrode slurry, the content of the electrode active material is 30wt% to 85wt%, and the content of the sulfide solid electrolyte is 10wt% to 60wt%; the electrode slurry also contains a conductive agent, and based on the total weight of solids in the electrode slurry, the content of the conductive agent is 0wt% to 15wt%; based on the total weight of the electrode slurry, the content of the solvent is 25wt% to 75wt%, and the content of the composite binder is 0.5wt% to 10wt%; the weight ratio of the composite binder to the solvent is 1:(20~60), and the weight ratio of the composite binder to the sulfide solid electrolyte is 1:(10~25).

[0017] Optionally, the viscosity of the electrode slurry at 25° C. is 2000-4000 mPa·s.

[0018] A third aspect of the present disclosure provides an electrode plate prepared using the electrode slurry described in the second aspect of the present disclosure.

[0019] A fourth aspect of the present disclosure provides an electrode plate, which includes a current collector and an electrode material layer covering the current collector, wherein the electrode material layer includes an electrode active material, a sulfide solid electrolyte and the composite binder provided in the first aspect of the present disclosure.

[0020] Optionally, based on the total weight of the electrode material layer, the content of the electrode active material is 30wt% to 85wt%, and the content of the sulfide solid electrolyte is 10wt% to 60wt%; the content of the composite binder is 0.1wt% to 10wt%, preferably 0.1wt% to 5wt%; preferably, the electrode material layer also contains a conductive agent, and based on the total weight of the electrode material layer, the content of the conductive agent is 0wt% to 15wt%.

[0021] Optionally, the weight ratio of the composite binder to the sulfide solid electrolyte is 1:(10-25).

[0022] A fifth aspect of the present disclosure provides an all-solid-state battery comprising the electrode plates described in the third and fourth aspects of the present disclosure.

[0023] Through the above technical scheme, the composite binder provided by the present invention introduces a rigid binder with a high degree of substitution and a flexible binder with a low oxygen-containing group for complementary use, thereby effectively improving the viscosity of the composite binder and the stability of the electrolyte, enhancing the solubility of the composite binder in the solvent, enhancing the adhesion between inorganic particles in the slurry and between the particles and the current collector, inhibiting the sedimentation and stratification caused by uneven solid content of the slurry, and playing a role in stabilizing the slurry, thereby effectively improving the stability of the slurry and the mechanical and electrochemical properties of the electrode, and improving the first-cycle efficiency of the battery.

[0024] Other features and advantages of the present disclosure will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0025] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0026] The first aspect of the present disclosure provides a composite adhesive, which includes a rigid adhesive and a flexible adhesive, wherein the rigid adhesive is a polysaccharide adhesive with an average degree of substitution of 1.5 or more, and the flexible adhesive is a rubber adhesive containing CO bonds, and the molar content of the CO bonds is 0.1-2% based on the total molar number of CH bonds on the flexible adhesive.

[0027] In the present disclosure, "degree of substitution" refers to the number of hydroxyl active hydrogen or amine active hydrogen on the sugar ring of the polysaccharide binder replaced by alkyl, and "average degree of substitution" refers to the average value of the degree of substitution on all sugar rings of the polysaccharide binder. The test method for the average degree of substitution can be nuclear magnetic resonance and gas chromatography, wherein the method of nuclear magnetic resonance testing is: dissolving a dried polysaccharide binder sample in a deuterated reagent, measuring the nuclear magnetic resonance spectrum and performing spectral attribution, and calculating the degree of substitution according to the displacement and intensity ratio of the characteristic spectral peak. For specific methods, see Sakuragi T, Nishimura T, Nasu Y, et al. Immobilization of radioactive iodine using AgI vitrification technique for the TRU wastes disposal: evaluation of leaching and surface properties [J]. MRS Online Proceedings Library Archive, 2008, 1107.; The gas chromatography test method is: use constant boiling hydroiodic acid to decompose the substituents on the polysaccharide binder molecules, analyze the amount of characteristic gases such as ethylene and ethyl iodide produced, and then calculate the result. For specific methods, see Jin-Feng Zhong, Xin-Sheng Chai, et al. Determination of degree of substitution in succinic anhydride modified cellulose by headspace gas chromatography [J]. Journal of Chromatography A, 2012, 1229, 16.

[0028] In the present disclosure, the CH bonds on the flexible binder refer to all CH bonds on the main chain and side chains of the flexible binder, wherein the molar content of CO bonds can be obtained by comparing the peak area of ​​the CO bond characteristic peak with the CH bond characteristic peak in the nuclear magnetic resonance characteristic spectrum of the flexible binder.

[0029] The composite binder provided by the present invention introduces a rigid binder with a high degree of substitution and a flexible binder with a low oxygen-containing group for complementary use, thereby enhancing the solubility of the composite binder in the solvent, effectively improving the viscosity of the composite binder and the stability of the sulfide solid electrolyte, enhancing the adhesion between inorganic particles in the slurry and between the particles and the current collector, inhibiting the sedimentation and stratification caused by uneven solid content of the slurry, and stabilizing the slurry, thereby effectively improving the stability of the slurry and the mechanical and electrochemical properties of the electrode, and improving the first-cycle efficiency of the battery.

[0030] In one embodiment of the present disclosure, the polysaccharide binder includes a polyhexasaccharide binder and / or a polypentasaccharide binder, the average degree of substitution of the polyhexasaccharide binder is greater than 2.0, and the average degree of substitution of the polypentasaccharide binder is greater than 1.5; in a preferred embodiment, the average degree of substitution of the polyhexasaccharide binder is 2.4-3.0, and the average degree of substitution of the polypentasaccharide binder is 1.7-2.0.

[0031] In one embodiment of the present disclosure, in the polysaccharide binder, the carbon number of the alkyl group replacing the hydroxyl active hydrogen or the amine active hydrogen can be less than 6, for example, the carbon number of the alkyl group can be 1, 2, 3, 4 or 5; the polyhexasaccharide binder is selected from one or more of cellulose binders, chitosan binders, seaweed binders and starch binders; for example, the polyhexasaccharide binder can be ethyl cellulose (CAS No. 9004-57-3), methyl cellulose (CAS No. 9004-67-5), methyl ethyl cellulose (CAS No. 9004-59-5). The polypentacarbose binder is selected from polyribose binders, and the polyribose binder has the following structural fragments: Wherein, R1 to R4 are the same or different, and are independently selected from hydroxyl, amine, and alkyl with 1 to 6 carbon atoms, and n is 500 to 10000; in the above embodiment, the number of hydroxyl active hydrogen or amine active hydrogen in R1 to R4 replaced by alkyl is 1.5 or more, and the number of carbon atoms of the alkyl can be 1, 2, 3, 4 or 5. In the above embodiment, by selecting a polysaccharide binder with a high degree of substitution of a five-membered ring or a six-membered ring as a rigid binder, the molecular rigidity and the viscosity of the slurry can be increased, and the solubility of the composite binder in the solvent can be increased. At the same time, the hydroxyl sites of the highly substituted polysaccharide binder are significantly reduced, which weakens the side reaction between the composite binder and the sulfide solid electrolyte, and plays a role in stabilizing the inorganic particles and preventing the slurry from settling and stratifying.

[0032] In one embodiment of the present disclosure, the preparation method of the rubber adhesive containing CO bonds includes: using a plasma treatment system to perform plasma treatment on the rubber adhesive, the conditions of the plasma treatment include: using a mixed gas of CH4 and O2 as a gas source, the output power of the system is 10 to 500W, and the output frequency is 10kHz to 1GHz; the rubber adhesive is a non-polar rubber adhesive, and the non-polar rubber adhesive includes one or more of polybutadiene rubber adhesive, polyisoprene rubber adhesive, styrene-butadiene rubber adhesive, chloroprene rubber adhesive and polyethylene propylene rubber adhesive. In the above embodiment, the plasma treatment method can be a low-pressure vacuum plasma treatment technology, a high-pressure jet plasma treatment technology, etc.; by selecting a preferred plasma treatment method, the surface of the rubber adhesive can be partially oxidized, a certain amount of oxygen-containing groups are introduced into the rubber molecules, and the stability of the composite adhesive and the adhesion of the composite adhesive to solid particles and between particles and current collectors are enhanced.

[0033] In one embodiment of the present disclosure, the CO bond of the flexible binder includes one or more of a hydroxyl CO bond, an alkoxy CO bond and a carboxyl CO bond. The hydroxyl CO bond refers to a bond between a hydroxyl group and a carbon atom connected to a carbon atom; the alkoxy CO bond refers to a bond between an alkoxy group and a carbon atom connected to a carbon atom; the carboxyl CO bond refers to a CO bond on a carboxyl group connected to a carbon atom.

[0034] In one embodiment of the present disclosure, based on the total mass of the composite binder, the content of the rigid binder is 5wt% to 95wt%, and the content of the flexible binder is 5wt% to 95wt%; in a preferred embodiment, the content of the rigid binder is 20wt% to 75wt%, and the content of the flexible binder is 25wt% to 80wt%; more preferably, the content of the rigid binder is 30wt% to 55wt%, and the content of the flexible binder is 45wt% to 70wt%.

[0035] In one embodiment of the present disclosure, the mass ratio of the rigid binder to the flexible binder is (0.1-3):1, preferably (0.3-1.2):1.

[0036] In the above embodiment, by selecting a preferred ratio of rigid binder and flexible binder, the solubility and stability of the composite binder in the solvent can be further increased, thereby improving the stability of the slurry and the mechanical and electrochemical properties of the electrode.

[0037] In one embodiment of the present disclosure, the weight average molecular weight of the rigid binder is 10 4 ~10 7 , preferably 105 ~10 6 The weight average molecular weight of the flexible binder is 10 4 ~10 7 , preferably 10 5 ~10 6 , the end distance of the rigid binder in the solvent is 150-300nm; wherein, the end distance refers to the maximum straight-line distance from one end of the rigid binder molecule to the other end; the solvent refers to the solvent in the electrode slurry, and the end distance is tested by the light scattering method, using a He-Ne laser particle size analyzer, model: Zetasizer Nano ZS, according to the difference in light scattering of particles of different extension scales to analyze the end distance of the rigid binder molecule in the solvent. In the above embodiment, by selecting the above-mentioned weight-average molecular weight rigid binder and flexible binder, the viscosity of the composite binder can be further improved and the viscosity of the slurry can be enhanced; wherein the flexible binder has a flexible chain structure, which can improve the flexibility of the prepared electrode, prevent bending, cracking, and material loss, etc., and the end distance of the rigid binder in the solvent is 150-300nm, which can complex more solvent small molecules, thereby inhibiting the agglomeration and flocculation of inorganic particles in the slurry, increasing the viscosity of the slurry, and increasing the viscosity of the slurry by 100-10,000 times.

[0038] A second aspect of the present disclosure provides an electrode slurry, which comprises an electrode active material, a sulfide solid electrolyte, a solvent and the composite binder described in the first aspect of the present disclosure.

[0039] In one embodiment of the present disclosure, the electrode active material includes a positive electrode active material or a negative electrode active material, and the positive electrode active material includes one or more of an olivine positive electrode material, a layered oxide positive electrode material, a spinel positive electrode material, a sulfur positive electrode material, and a sulfide positive electrode material; the negative electrode active material includes one or more of a graphite negative electrode material and a silicon-based negative electrode material; the silicon-based negative electrode material includes but is not limited to a silicon negative electrode material, a silicon alloy negative electrode material, a silicon-carbon negative electrode material, and a silicon-oxygen negative electrode material; in one embodiment of the present disclosure, the electrode active material includes a positive electrode active material, and the positive electrode active material includes LiFePO4, NCM, NCA, LiCoO2, LiMn2O4, Li4Ti5O 12 , S8, FeS2 and CuS.

[0040] In one embodiment of the present disclosure, the lithium ion conductivity of the sulfide solid electrolyte is higher than 10 -4S / cm; preferably, the sulfide solid electrolyte includes one or more of a fast ion conductor solid electrolyte, a argyrodite solid electrolyte, a glass ceramic system solid electrolyte and a thiophosphate system solid electrolyte; more preferably, the sulfide solid electrolyte includes Li3PS4, LGPS, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li6PS5Cl, LiI-(70Li2S-30P2S5), Li7P3S 11 , Li4PS4I and Li7P2S8I.

[0041] In one embodiment of the present disclosure, the electrode slurry further comprises a conductive agent, and the conductive agent is selected from one or more of carbon black conductive agents, carbon nanotubes and vapor grown carbon fibers (VGCF).

[0042] In one embodiment of the present disclosure, the solvent is selected from non-polar organic solvents and weakly polar organic solvents. In a preferred embodiment, the solvent is selected from organic solvents with a relative dielectric constant of less than 6, such as organic solvents with a relative dielectric constant of 1, 2, 3, 4, 5, or a numerical range between any two of them. The organic solvent does not react with the sulfide solid electrolyte in the slurry; the organic solvent is selected from alkane solvents and / or ether solvents; more preferably, the organic solvent is selected from one or more of methylcyclohexane, heptane, decane, anisole and cyclopentyl ether.

[0043] In one embodiment of the present disclosure, based on the total weight of solids in the electrode slurry, the content of the electrode active material is 30wt% to 85wt%, and the content of the sulfide solid electrolyte is 10wt% to 60wt%; the electrode slurry also contains a conductive agent, based on the total weight of solids in the electrode slurry, the content of the conductive agent is 0wt% to 15wt%; based on the total weight of the electrode slurry, the content of the solvent is 25wt% to 75wt%, and the content of the composite binder is 0.5wt% to 10wt%; the weight ratio of the composite binder to the solvent is 1: (20 to 60), and the weight ratio of the composite binder to the sulfide solid electrolyte is 1: (10 to 25). In the above embodiment, by selecting a slurry with a preferred composition, the agglomeration and flocculation of inorganic particles in the slurry can be further suppressed, the stability of the slurry can be improved, and the battery performance can be improved.

[0044] In one embodiment of the present disclosure, the viscosity of the electrode slurry at 25° C. is 2000-4000 mPa·s. In the above embodiment, by selecting a slurry with a preferred viscosity, the stability of the slurry can be further enhanced, and the mechanical and electrochemical properties of the electrode sheet can be improved.

[0045] A third aspect of the present disclosure provides an electrode plate prepared using the electrode slurry described in the second aspect of the present disclosure.

[0046] In one embodiment of the present disclosure, the method for preparing the electrode plate using the electrode slurry is as follows: the electrode slurry is uniformly coated on the current collector, dried and pressed; wherein the coating method can be spraying, scraping and extrusion coating; the drying conditions include: in a vacuum environment or an argon environment, the drying temperature is 60 to 150°C, and the time is 2 to 24 hours; the pressing conditions include: the pressure is 5 to 500 MPa, and the pressing method is flat plate pressing or isodiametric pressing; wherein the slurry making equipment can be a ball mill, a degassing machine, a liquid flow disperser or a screw extruder.

[0047] A fourth aspect of the present disclosure provides an electrode plate, which includes a current collector and an electrode material layer covering the current collector, wherein the electrode material layer includes an electrode active material, a sulfide solid electrolyte and the composite binder provided in the first aspect of the present disclosure.

[0048] In one embodiment of the present disclosure, based on the total weight of the electrode material layer, the content of the electrode active material is 30wt% to 85wt%, and the content of the sulfide solid electrolyte is 10wt% to 60wt%; the content of the composite binder is 0.1wt% to 10wt%, preferably 0.1wt% to 5wt%; preferably, the electrode material layer further comprises a conductive agent, and based on the total weight of the electrode material layer, the content of the conductive agent is 0wt% to 15wt%.

[0049] In one embodiment of the present disclosure, the weight ratio of the composite binder to the sulfide solid electrolyte is 1:(10-25). In the above embodiment, by selecting the composite binder and sulfide solid electrolyte with the preferred ratio, the stability and conductivity of the electrode plate can be enhanced, and the battery performance can be improved.

[0050] In one embodiment of the present disclosure, the electrode sheet has a peeling force of 9 to 20 N / m and a thickness of 10 to 100 μm.

[0051] A fifth aspect of the present disclosure provides an all-solid-state battery comprising the electrode plates described in the third and fourth aspects of the present disclosure.

[0052] Through the above technical scheme, the composite binder provided by the present invention introduces a rigid binder with a high degree of substitution and a flexible binder with a low oxygen-containing group for complementary use, thereby enhancing the solubility of the composite binder in the solvent, effectively improving the viscosity of the composite binder and the stability of the sulfide solid electrolyte, enhancing the adhesion between inorganic particles in the slurry and between the particles and the current collector, inhibiting the sedimentation and stratification caused by uneven solid content of the slurry, and playing a role in stabilizing the slurry, thereby effectively improving the stability of the slurry and the mechanical and electrochemical properties of the electrode, and improving the first-cycle efficiency of the battery.

[0053] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited thereby.

[0054] In the following examples, unless otherwise specified, the raw materials used are commercially available products.

[0055] The test method for the average degree of substitution is the nuclear magnetic resonance method, and the instrument model is GY-PNMR12-6HF;

[0056] The test method for the molar content of CO bonds in rubber adhesives is the nuclear magnetic resonance method, and the instrument model is GY-PNMR12-6HF;

[0057] The weight average molecular weight was tested by light scattering method, and the instrument model was Zetasizer Nano ZS;

[0058] The electrode stripping force is tested according to the method specified in GB 2792-1998;

[0059] The electrode thickness is tested by an inductive thickness meter, and the instrument model is Mahr C1202.

[0060] Example 1

[0061] (1) A vacuum plasma treatment system (model: CRF-VPO-8L-S) was used to perform plasma surface treatment on polybutadiene rubber, wherein a mixture of CH4 and O2 was selected as the gas source, the output power of the system was 45 W, the output frequency was 2 MHz, and the rubber was treated with plasma gas. The plasma treatment time was 15 s to prepare a flexible adhesive containing CO bonds. The flexible adhesive was tested and analyzed using a nuclear magnetic resonance spectrometer. Based on the total molar number of CH bonds in the flexible adhesive, the molar content of CO bonds contained in the flexible adhesive was 2%;

[0062] (2) LiNbO3@LiCoO2 was selected as the positive electrode active material (i.e., LiNbO3-coated LiCoO2, purchased from Xiamen Tungsten Industry), Li6PS5Cl was selected as the sulfide solid electrolyte, acetylene black was selected as the conductive agent, ethyl cellulose with an average degree of substitution of 2.5 was selected as the rigid binder (purchased from Dow Chemical, USA), polybutadiene rubber binder with a molar content of CO bonds of 2% was selected as the flexible binder, and anisole was selected as the solvent; the rigid binder and the flexible binder were fully dissolved in anisole at a mass ratio of 30:70 to prepare a composite binder solution with a composite binder mass concentration of 10%; LiNbO3@LiCoO2:Li6PS5Cl:acetylene black = 70:30:2 were weighed to prepare a mixed sample with a total mass of 55g, 11g of the above composite binder solution and 36g of anisole were added, wherein the weight average molecular weight of the rigid binder was 10 6 The end-to-end distance in the solvent is 200 nm, and the weight average molecular weight of the flexible binder is 10 6 ; A vortex mixer (AS ONE test tube shakers) was used to disperse the mixture at a rotation speed of 2000RPM for 10 minutes to obtain a positive electrode slurry 1, whose viscosity at 25°C was 3000mPa·s.

[0063] (3) Preparation of electrode sheet: The above-mentioned positive electrode slurry 1 is mixed and coated on the Al current collector. The coating thickness is controlled to be 30 μm, and then placed in a vacuum oven at 60°C for 5 hours to obtain an electrode sheet 1. The electrode sheet 1 contains 37.74g LiNbO3@LiCoO2 (positive electrode active material), 16.17g Li6PS5Cl (sulfide solid electrolyte), 1.078g acetylene black (conductive agent) and 1.1g composite binder.

[0064] Example 2

[0065] The same as Example 1, except that the ethyl cellulose with an average degree of substitution of 2.5 is replaced by ethyl chitosan with an average degree of substitution of 2.5 (purchased from Shanghai Sinopharm Group) of the same weight, to obtain a positive electrode slurry 2 and an electrode plate 2.

[0066] Example 3

[0067] The method is the same as Example 1, except that the polybutadiene rubber binder having a molar content of CO bonds of 2% is replaced with the polyisoprene rubber having a molar content of CO bonds of 2% by weight, to obtain a positive electrode slurry 3 and an electrode plate 3.

[0068] Example 4

[0069] The same as Example 1, the only difference is that the mass ratio of the rigid binder to the flexible binder is adjusted to 40:60, and the positive electrode slurry 4 and the electrode plate 4 are obtained.

[0070] Example 5

[0071] The same as Example 1, the only difference is that the positive electrode active material LiNbO3@LiCoO2 is replaced with the same weight of LiNbO3@NCM622 (i.e., LiNbO3-coated NCM622, purchased from Xiamen Tungsten Industry), to obtain a positive electrode slurry 5 and an electrode plate 5.

[0072] Example 6

[0073] Same as Example 1, except that the sulfide solid electrolyte Li6PS5Cl is replaced by the same weight of Li7P3S 11 , and obtain positive electrode slurry 6 and electrode sheet 6.

[0074] Example 7

[0075] The same as Example 1, the only difference is that the mass ratio of the rigid binder to the flexible binder is adjusted to 5:95, and the positive electrode slurry 7 and the electrode plate 7 are obtained.

[0076] Example 8

[0077] The method is the same as Example 1, except that the mass ratio of the rigid binder to the flexible binder is adjusted to 80:20, thereby obtaining a positive electrode slurry 8 and an electrode plate 8.

[0078] Example 9

[0079] Same as Example 1, except that the weight average molecular weight of the rigid binder is 10 4 , the weight average molecular weight of the flexible binder is 10 4 , and obtain positive electrode slurry 9 and electrode plate 9.

[0080] Example 10

[0081] The same as Example 1, the only difference is that: the positive electrode active material LiNbO3@LiCoO2 is 38.10g, the sulfide solid electrolyte Li6PS5Cl is 16.17g, the conductive agent acetylene black is 1.078g, the total mass of the solvent anisole is 45.9g, and the composite binder is 0.74g, to obtain a positive electrode slurry 10 and an electrode plate 10.

[0082] Embodiment 11

[0083] The same as Example 1, the only difference is that: the positive electrode active material LiNbO3@LiCoO2 is 36.82g, the sulfide solid electrolyte Li6PS5Cl is 16.17g, the conductive agent acetylene black is 1.078g, the total mass of the solvent anisole is 45.9g, and the composite binder is 2.02g, to obtain a positive electrode slurry 11 and an electrode plate 11.

[0084] Example 12

[0085] The same as Example 1, the only difference is that in the positive electrode slurry, the positive electrode active material LiNbO3@LiCoO2 is 35.79g, the sulfide solid electrolyte Li6PS5Cl is 16.17g, the conductive agent acetylene black is 1.078g, the total mass of the solvent anisole is 45.9g, and the composite binder is 3.05g, to obtain a positive electrode slurry 12 and an electrode plate 12.

[0086] Comparative Example 1

[0087] The same as Example 1, except that: no rigid binder is added, and the composite binder only contains a polybutadiene rubber binder with a molar content of CO bonds of 2%, to obtain a comparative slurry 1 and a comparative electrode 1.

[0088] Comparative Example 2

[0089] The same as Example 1, except that no flexible binder is added, and the composite binder only contains ethyl cellulose with an average degree of substitution of 2.5, to obtain a comparative slurry 2 and a comparative electrode 2.

[0090] Comparative Example 3

[0091] The same as Example 1, the only difference is that: no rigid binder is added, and the polybutadiene rubber binder with a molar content of CO bonds of 2% is replaced by a polybutadiene rubber binder with a molar content of CO bonds of 5% of the same weight, to obtain a comparative slurry 3 and a comparative electrode 3.

[0092] Comparative Example 4

[0093] The same as Example 1, except that no flexible binder is added, and ethyl cellulose with an average degree of substitution of 2.5 is replaced by ethyl cellulose with an average degree of substitution of 0.7 (commercially available from Dow Chemical, USA) of the same weight, to obtain comparative slurry 4 and comparative electrode 4.

[0094] Comparative Example 5

[0095] The same as Example 1, except that the ethyl cellulose with an average degree of substitution of 2.5 is replaced by ethyl cellulose with an average degree of substitution of 0.7 of the same weight, to obtain comparative slurry 5 and comparative electrode 5.

[0096] Comparative Example 6

[0097] The same as Example 1, except that the polybutadiene rubber binder having a molar content of CO bonds of 2% is replaced with the same weight of polybutadiene rubber without CO bonds, to obtain a comparative slurry 6 and a comparative electrode 6.

[0098] Comparative Example 7

[0099] The same as Example 1, except that the polybutadiene rubber binder with a molar content of CO bonds of 2% is replaced with the same weight of polybutadiene rubber with a molar content of CO bonds of 5%, to obtain a comparative slurry 7 and a comparative electrode 7.

[0100] Test Case

[0101] (1) Test of slurry solid content:

[0102] The positive electrode slurry and the reference slurry prepared in Examples 1 to 12 and Comparative Examples 1 to 7 were placed in a 100 mL beaker and allowed to stand for 1 h. 1 mL of slurry was taken from the area close to the slurry liquid surface (upper layer), the middle layer (middle layer) and the bottom of the beaker (lower layer) with a pipette, and the mass M was weighed. The slurry was then placed in a vacuum oven at 60°C for 5 h. After being fully dried, the mass m was weighed again. The solid content of the upper / middle / lower layers of slurry was calculated as m / M×100%, and the difference in solid content of the upper / middle / lower layers was compared; wherein, the upper layer of the slurry refers to 2 / 3 of the slurry height to the slurry liquid surface, the middle layer of the slurry refers to 1 / 3 to 2 / 3 of the slurry height, and the lower layer of the slurry refers to the bottom of the cup to 1 / 3 of the slurry height.

[0103] (2) Test of slurry viscosity: The slurry was placed in a 100 mL beaker and the slurry viscosity was tested at room temperature using a rotational viscometer (Brookfield). The rotor was a standard rotor No. 1 and the speed was determined according to the actual slurry conditions.

[0104] (3) Preparation of half-cell and electrochemical performance test:

[0105] The electrode plates, reference plates and lithium indium alloy plates prepared in Examples 1 to 12 and Comparative Examples 1 to 7 were cut into small discs of φ15 mm, respectively. 200 mg of Li6PS5Cl electrolyte powder was weighed in a glove box with an argon atmosphere, and pressed into an electrolyte plate at 120 MPa using a φ15 mm mold. The electrode plates or reference plates cut into discs were added to one side of the electrolyte plate as working electrodes, and a pressure of 380 MPa was applied to combine the working electrode plate with the electrolyte. Then, a lithium indium alloy plate was placed on the other side of the electrolyte as a counter electrode, and a pressure of 50 MPa was applied to fit the lithium indium alloy plate on the electrolyte plate, and finally assembled into a half-cell.

[0106] The half-cell assembled by the above method was subjected to constant current charge and discharge test using a Landian multi-channel charge and discharge test system (LAND CT2001A); the half-cell was charged to 3.7V at a constant current rate of 0.1C at room temperature, and then discharged to 2.0V at a constant current rate of 0.1C, and the first discharge capacity and first charge capacity of the battery were recorded. The first-cycle discharge capacity of the half-cell was obtained by dividing the recorded first discharge capacity by the mass of the positive electrode active material in the battery; the first-cycle efficiency (%) was calculated as (first charge capacity / first discharge capacity)×100%.

[0107] The test results are as follows:

[0108]

[0109] It can be seen from the above data that comparative examples 1 to 4 do not use rigid binders or flexible binders, the stability of the slurry is poor, the inorganic particles are easy to agglomerate and settle, resulting in poor peeling force of the prepared electrode pole sheet, and the active material is easy to fall off the current collector; among them, the molar content of CO bonds of the flexible binder used in comparative example 3 is greater than 2%, and the average substitution degree of the rigid binder used in comparative example 4 is less than 1.5, which makes the binder easy to react with the sulfide solid electrolyte, resulting in the ionic conductivity of the electrolyte and the first-cycle efficiency of the battery. Although comparative examples 5 to 7 use both rigid binders and flexible binders, the average substitution degree of the rigid binder used in comparative example 5 is less than 1.5, and the molar content of CO bonds of the flexible binder used in comparative example 7 is greater than 2%, which makes the composite binder easy to react with the sulfide solid electrolyte and the first-cycle efficiency of the battery is low. Comparative Example 6 uses a polybutadiene rubber binder without CO bonds as a flexible binder, which makes the composite binder have poor slurry stabilization ability and weak adhesion, and thus makes the electrode sheet peeling force poor and the first cycle efficiency of the battery low. Therefore, the composite binder provided by Examples 1 to 12 of the present disclosure has better performance than that provided by Comparative Examples 1 to 7.

[0110] Comparison of the data of Example 1 with Examples 7 to 8 shows that when Example 1 adopts the preferred rigid binder to flexible binder mass ratio (0.1 to 3): 1, the solid content distribution of the upper, middle and lower layers of the prepared electrode slurry is more uniform, the slurry dispersion is better, and the first cycle discharge capacity of the half-cell is higher; Comparison of the data of Example 1 with Example 9 shows that when Example 1 adopts the preferred rigid binder of the present disclosure with a number average molecular weight of 10 5 ~10 6 , the number average molecular weight of the flexible binder is 10 5 ~10 6When the implementation method is adopted, the solid content distribution of the upper, middle and lower layers of the prepared electrode slurry is more uniform, and the first-cycle efficiency is higher; among them, from the comparison of the data of Example 1 with Examples 10 to 12, it can be seen that when Example 1 adopts the implementation method of the preferred composite binder to solvent of the present disclosure of 1: (20 to 60) and the weight ratio of the composite binder to the sulfide solid electrolyte of 1: (10 to 25), the prepared electrode slurry has better dispersion, better mechanical properties of the pole piece, and higher first-cycle efficiency of the battery.

[0111] The preferred embodiments of the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0112] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0113] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A composite adhesive, characterized in that: The composite adhesive includes a rigid adhesive and a flexible adhesive, wherein the rigid adhesive is a polysaccharide adhesive, and the polysaccharide adhesive includes a polyhexasaccharide adhesive and / or a polypentasaccharide adhesive, wherein the average degree of substitution of the polyhexasaccharide adhesive is 2.4 to 3.0, and the average degree of substitution of the polypentasaccharide adhesive is 1.7 to 2.0, and the flexible adhesive is a rubber adhesive containing a CO bond, and the molar content of the CO bond is 0.1 to 2% based on the total molar number of CH bonds in the flexible adhesive.

2. The composite adhesive according to claim 1, characterized in that: The polyhexacarb binder is selected from one or more of cellulose binders, chitosan binders, seaweed binders and starch binders; the polypentacarb binder is selected from polyribose binders, and the polyribose binder has the following structural fragments: Wherein, R1 to R4 are the same or different and are independently selected from hydroxyl, amine, and alkyl having 1 to 6 carbon atoms, and n is 500 to 10,000.

3. The composite adhesive according to claim 1, characterized in that: The preparation method of the rubber adhesive containing CO bonds comprises: using a plasma treatment system to perform plasma treatment on the rubber adhesive, wherein the plasma treatment conditions include: using a mixed gas of CH4 and O2 as a gas source, the output power of the system is 10 to 500 W, and the output frequency is 10 kHz to 1 GHz; The rubber adhesive is a non-polar rubber adhesive, and the non-polar rubber adhesive includes one or more of polybutadiene rubber adhesive, polyisoprene rubber adhesive, styrene-butadiene rubber adhesive, chloroprene rubber adhesive and polyethylene propylene rubber adhesive.

4. The composite adhesive according to claim 1, characterized in that: The CO bonds of the flexible adhesive include one or more of hydroxyl CO bonds, alkoxy CO bonds and carboxyl CO bonds.

5. The composite adhesive according to claim 1, characterized in that: Based on the total mass of the composite binder, the content of the rigid binder is 5wt% to 95wt%, and the content of the flexible binder is 5wt% to 95wt%.

6. The composite adhesive according to claim 5, characterized in that: Based on the total mass of the composite binder, the content of the rigid binder is 20wt% to 75wt%, and the content of the flexible binder is 25wt% to 80wt%.

7. The composite adhesive according to claim 6, characterized in that: Based on the total mass of the composite binder, the content of the rigid binder is 30wt% to 55wt%, and the content of the flexible binder is 45wt% to 70wt%.

8. The composite adhesive according to claim 1, characterized in that: The mass ratio of the rigid binder to the flexible binder is (0.1-3):

1.

9. The composite adhesive according to claim 8, characterized in that: The mass ratio of the rigid binder to the flexible binder is (0.3-1.2):

1.

10. The composite adhesive according to claim 1, characterized in that: The weight average molecular weight of the rigid binder is 10 4 ~10 7 The weight average molecular weight of the flexible binder is 10 4 ~10 7 .

11. The composite adhesive according to claim 10, characterized in that: The weight average molecular weight of the rigid binder is 10 5 ~10 6 The weight average molecular weight of the flexible binder is 10 5 ~10 6 .

12. An electrode slurry, characterized in that: The electrode slurry comprises an electrode active material, a sulfide solid electrolyte, a solvent and the composite binder according to any one of claims 1 to 11.

13. The electrode slurry according to claim 12, characterized in that: The solvent is selected from organic solvents having a relative dielectric constant of less than 6.

14. The electrode slurry according to claim 13, characterized in that: The organic solvent is selected from at least one of an alkane solvent and an ether solvent.

15. The electrode slurry according to claim 14, characterized in that: The organic solvent is selected from one or more of methylcyclohexane, heptane, decane, anisole and cyclopentyl ether.

16. The electrode slurry according to claim 12, characterized in that: Based on the total weight of solids in the electrode slurry, the content of the electrode active material is 30wt% to 85wt%, and the content of the sulfide solid electrolyte is 10wt% to 60wt%; The electrode slurry further comprises a conductive agent, and the content of the conductive agent is 0wt% to 15wt% based on the total weight of the solids in the electrode slurry; Based on the total weight of the electrode slurry, the content of the solvent is 25wt% to 75wt%, and the content of the composite binder is 0.5wt% to 10wt%; The weight ratio of the composite binder to the solvent is 1:(20-60), and the weight ratio of the composite binder to the sulfide solid electrolyte is 1:(10-25).

17. The electrode slurry according to claim 12, characterized in that: The viscosity of the electrode slurry at 25° C. is 2000-4000 mPa·s.

18. An electrode sheet prepared using the electrode slurry according to any one of claims 12 to 17.

19. An electrode plate, characterized in that: The electrode plate comprises a current collector and an electrode material layer covering the current collector, wherein the electrode material layer comprises an electrode active material, a sulfide solid electrolyte and the composite binder according to any one of claims 1 to 11.

20. The electrode plate according to claim 19, characterized in that: Based on the total weight of the electrode material layer, the content of the electrode active material is 30wt% to 85wt%, the content of the sulfide solid electrolyte is 10wt% to 60wt%; and the content of the composite binder is 0.1wt% to 10wt%.

21. The electrode plate according to claim 20, characterized in that: Based on the total weight of the electrode material layer, the content of the composite binder is 0.1wt% to 5wt%.

22. The electrode plate according to claim 20, characterized in that: The electrode material layer further comprises a conductive agent, and the content of the conductive agent is 0 wt % to 15 wt % based on the total weight of the electrode material layer.

23. The electrode plate according to claim 19, characterized in that: The weight ratio of the composite binder to the sulfide solid electrolyte is 1:(10-25).

24. An all-solid-state battery comprising the electrode sheet according to any one of claims 18 to 23.

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