A binder composition, a sodium-ion battery cathode slurry and a sodium-ion battery

Abstract

The application belongs to the technical field of sodium ion batteries, and particularly relates to a binder composition, a sodium ion battery positive electrode slurry and a sodium ion battery. The binder composition comprises 0.5-100% and 0-99.5% of a first binder and a second binder by mass percentage, the first binder is one or more of polyacrylic acid, polymethacrylic acid, poly-methyl-vinyl-ether-copoly-maleic acid, and the second binder is one or more of polyvinylidene fluoride, polyacrylonitrile-based binder, polyurethane-based binder and polyimide-based binder. A high-molecular polymer containing a carboxyl group (-COOH) is used as a binder composition component to prepare the sodium ion battery positive electrode slurry. The carboxyl group can be neutralized with alkaline substances in the positive active material of the sodium ion battery positive electrode slurry, so as to ensure the uniformity and fluidity of the positive electrode slurry, to obtain a uniform sodium ion battery positive electrode sheet, and to obtain a sodium ion battery with good electrochemical stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a binder composition, a sodium ion battery positive electrode slurry and a sodium ion battery. BACKGROUND

[0002] With the wide application of lithium ion batteries in various industries, the development bottleneck caused by the rising prices of raw materials and the limited reserves of lithium resources is becoming more and more obvious, which will limit the application and development of lithium ion batteries in the field of new energy storage in the future. As a low-cost energy storage battery, sodium ion battery has great application potential and prospect due to the same reaction mechanism as lithium ion battery.

[0003] Sodium ion battery is mainly composed of positive electrode, negative electrode, separator, electrolyte and positive and negative electrode shell. Sodium ions move back and forth between the positive and negative electrodes of the battery to realize the charging and discharging of the battery. Sodium ion battery has many advantages: first, sodium resources are abundant, the crust abundance of sodium element (2.6%) is much higher than that of lithium (0.0065%), and the price is lower; second, high safety, sodium ions are easy to be passivated and inactivated in the process of thermal runaway, and the thermal stability is much higher than the safety requirements of national standard; third, fast charging performance is good, the stokes diameter of sodium ion is smaller than that of lithium ion, the ionic conductivity of sodium salt electrolyte is higher than that of lithium salt electrolyte under the same concentration, the first ionization energy is smaller, and the charging capacity can reach more than 80% at room temperature; fourth, good low temperature performance, it also has more than 90% discharge retention rate in-20℃ low temperature environment. Therefore, it is very important to develop new type of sodium ion battery for energy storage technology field.

[0004] The preparation of positive electrode of sodium ion battery is an important link in the production and preparation process of sodium ion battery, mainly including stirring and coating of positive electrode slurry. The positive electrode slurry is mainly composed of active material, conductive agent, binder and dispersion solvent. After the binder is dissolved in the dispersion solvent, the active material and the conductive agent are combined together to form the slurry. The slurry is coated on the current collector foil, and the electrode is formed after drying.

[0005] Currently, polyvinylidene fluoride (PVDF) is commonly used as a binder and N-methyl pyrrolidone (NMP) is commonly used as a dispersion solvent in sodium-ion battery cathode slurry. When PVDF and alkaline sodium-ion battery cathode active material come into contact, PVDF will release hydrogen fluoride (HF) to form a double bond, and further form a gelled network structure, which makes the uniformity and flowability of the cathode slurry poor, and even forms a jelly-like state, which seriously affects the performance of the sodium-ion battery. The cathode active material exhibits alkalinity, on the one hand, because the sodium salt is added in excess during the preparation of the cathode active material; on the other hand, the active oxygen anions on the surface of the cathode material will react with carbon dioxide and water in the air to generate carbonate, and sodium ions will migrate from the bulk to the surface and form sodium carbonate on the surface of the material. During the preparation and storage of the cathode active material, it is difficult to completely remove the alkalinity, and the cathode slurry is prone to rapid gelation under the condition of 10-40% relative humidity, which increases the difficulty of coating and uniformity.

[0006] Chinese patent CN110459771A uses a boron-containing inorganic additive to neutralize the alkalinity of the slurry to improve the brittleness of the high-nickel ternary material during the preparation of the electrode sheet. Chinese patent CN111697207A uses an organic weak acid additive to neutralize the alkalinity of the slurry, which can improve the stability of the slurry, but the addition of additional substances will affect the electrochemical performance of the sodium-ion battery. SUMMARY

[0007] The purpose of the present application is to solve the above technical problems, and to provide a binder composition for preparing a sodium-ion battery cathode slurry, which can ensure good uniformity and flowability of the cathode slurry, and obtain a sodium-ion battery with high electrochemical stability.

[0008] The binder composition in the technical scheme of the present application comprises a first binder and a second binder in a mass percentage of 0.5-100% and 0-99.5%, respectively.

[0009] Further, the first binder is one or more of polyacrylic acid, polymethacrylic acid, and poly-methyl-vinyl-ether co-maleic acid.

[0010] The high-molecular polymer containing carboxyl groups (-COOH) is used as the first binder, which can bind the cathode active material and the conductive agent to form a cathode slurry. The carboxyl groups can react with the alkaline substances in the cathode active material to a certain extent to ensure the uniformity and flowability of the cathode slurry.

[0011] Further, the second binder is one or more of polyvinylidene fluoride, polyacrylonitrile binder, polyurethane binder, and polyimide binder.

[0012] Further, the binder composition comprises polyvinylidene fluoride, polymethacrylic acid and polymethyl vinyl ether copolymerized maleic acid.

[0013] Further, the mass percentages of polyvinylidene fluoride, polymethacrylic acid and polymethyl vinyl ether copolymerized maleic acid in the binder composition are 45-55%, 20-25% and 25-30%, respectively.

[0014] The polyvinylidene fluoride, polymethacrylic acid and polymethyl vinyl ether copolymerized maleic acid retain the binding effect of polyvinylidene fluoride after compounding, ensuring the capacity to be exerted, while the polymethacrylic acid and polymethyl vinyl ether copolymerized maleic acid prolong the gelation time of the slurry, which helps to improve the uniformity of the slurry coating, and the binding effect of the three is more firm after compounding, greatly improving the cycle stability of the sodium ion battery.

[0015] 80-96 parts of positive active material;

[0016] 1-10 parts of conductive agent;

[0017] 1-10 parts of the above binder composition;

[0018] 20-400 parts of dispersion solvent.

[0019] Further, the solid content of the sodium ion battery positive electrode slurry is 20-80%, and the viscosity is 1000-10000 mPa·s.

[0020] Further, the positive active material is any one of sodium transition metal oxide, sodium polyanion compound and sodium prussian blue analogue.

[0021] The sodium transition metal oxide in the present application is not limited, and any substance that can be used as sodium transition metal oxide in sodium ion battery can be used, and the sodium transition metal oxide is exemplified by any one of NaCoO2, NaFeO2, NaNiO2, NaNiFeMnO2, NaNi 0.5 Mn 0.5 O2.

[0022] The sodium polyanion compound in the present application is not limited, and any substance that can be used as sodium polyanion compound in sodium ion battery can be used, and the sodium polyanion compound is exemplified by any one of Na3V2(PO4)3, NaFePO4, Na2Fe2(SO4)3 and Na2Fe2P2O7.

[0023] The sodium Prussian blue analogues in the application are not limited, and any substance that can be used as sodium Prussian blue analogues in sodium ion batteries can be used, and the sodium Prussian blue analogues are listed as any one of NaFeFe(CN) 6, Na 2 CoFe(CN) 6, and Na 2 NiFe(CN) 6.

[0024] The conductive agent of the sodium ion battery positive electrode slurry in the application is not limited, and any substance that can be used as a conductive agent for a sodium ion battery can be used, and the conductive agent is listed as one or more of carbon black, acetylene black, flaky graphite, spherical graphite, carbon fiber, and carbon nanotube.

[0025] Further, the dispersion solvent is one or more of N-methylpyrrolidone (NMP), N, N-dimethylformamide (DMF), and acetone.

[0026] The application also provides a sodium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and a battery shell, wherein the positive electrode sheet is obtained by coating the above-mentioned sodium ion battery positive electrode slurry on a positive electrode current collector and drying.

[0027] Further, the thickness of the positive electrode sheet is 100-150 μm.

[0028] Further, the positive electrode current collector is any one of an aluminum sheet, a stainless steel sheet, a nickel sheet, a titanium sheet, and a carbon-coated sheet.

[0029] Further, the thickness of the positive electrode current collector is 10-15 μm.

[0030] The negative electrode sheet of the sodium ion battery comprises a negative electrode current collector, a negative electrode active material loaded on the current collector, a conductive agent, and a negative electrode binder, and the substances and amounts used are not limited, and any substance that can be used as a negative electrode current collector, a negative electrode active material, a conductive agent, and a negative electrode binder for a sodium ion battery can be used, and the negative electrode current collector is listed as any one of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, and stainless steel, and the negative electrode active material is listed as one or more of sodium, titanium, zinc, indium, tin, silicon, and carbon material.

[0031] The separator of the sodium ion battery is not limited, and any substance that can be used as a separator for a sodium ion battery can be used, and the separator is listed as any one of a polyolefin resin, a polyphenylene sulfide resin, a polyamide resin, a polyimide resin, and an inorganic fiber.

[0032] The electrolyte of the sodium ion battery is not limited, and any substance that can be used as an electrolyte for a sodium ion battery can be used, and the electrolyte is formed by dissolving a salt containing sodium ions and anions in an organic solvent.

[0033] The preparation method of the sodium ion battery comprises the following steps: separating a positive electrode sheet and a negative electrode sheet by a diaphragm, obtaining an electrode sheet group by winding or slicing, placing the electrode sheet group into a battery shell, injecting an electrolyte, and sealing the battery shell to obtain the sodium ion battery.

[0034] Further, the battery shell is any one of a button cell shell, a square aluminum shell, an aluminum plastic film, and a cylindrical shell.

[0035] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0036] (1) The sodium ion battery positive electrode slurry is prepared by using a high-molecular polymer containing a carboxyl group (-COOH) as a binder composition component, and a sodium ion battery with good electrochemical stability is obtained.

[0037] (2) The carboxyl group can react with alkaline substances in the sodium ion battery positive electrode slurry positive active material to ensure the uniformity and flowability of the positive electrode slurry, so that a uniform sodium ion battery positive electrode sheet is obtained.

[0038] (3) The sodium ion battery positive electrode slurry of the present application can be used in various models of sodium ion batteries, and has a large-scale commercial application prospect. DETAILED DESCRIPTION

[0039] The technical scheme of the present application will be further described and explained by specific examples below, and it should be understood that the specific examples described herein are only used to help understand the present application and are not used to limit the present application. If not otherwise specified, the raw materials used in the examples of the present application are all commonly used raw materials in the art, and the methods used in the examples are all conventional methods in the art.

[0040] In the above examples and comparative examples, NaNiFeMnO2 is used as the positive active material, hard carbon material is used as the negative active material, conductive carbon black Super-P is used as the conductive agent, the electrolyte is NaPF6 solution, the molecular weight of polyacrylic acid is 1.5 million, the molecular weight of polymethylacrylic acid is 1 million, and the molecular weight of polymethylvinyl ether copolymer maleic acid is 2 million.

[0041] Example 1

[0042] The preparation method of the sodium ion battery in this example comprises the following steps:

[0043] (1) Using polyacrylic acid as a binder, positive electrode active material, Super-P and polyacrylic acid are mixed in a mass ratio of 94:2:4, and N-methylpyrrolidone of equal mass to the three is added and stirred evenly to obtain a sodium-ion battery positive electrode slurry with a solid content of 50% and a viscosity of 3000 mPa·s. The slurry is coated on a 12 μm thick aluminum foil, dried thoroughly in an open environment to remove the NMP dispersion solvent, and pressed to obtain a sodium-ion battery positive electrode sheet with a thickness of 100 μm.

[0044] (2) Using carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as negative electrode binders, the negative electrode active material, Super-P, CMC and SBR are mixed in a mass ratio of 96:1.5:1.0:1.5, and an appropriate amount of water is added and stirred evenly. The mixture is coated on an aluminum foil with a thickness of 12μm, dried and dehydrated in an open environment, and pressed to obtain a sodium-ion battery negative electrode sheet with a thickness of 150μm.

[0045] (3) Separate the obtained sodium-ion battery positive electrode and sodium-ion battery negative electrode with a separator, and obtain an electrode assembly by winding. Place the electrode assembly into a button battery case, inject electrolyte, and seal the battery case to obtain a sodium-ion soft pack battery.

[0046] Example 2

[0047] The method for preparing the sodium-ion battery in this embodiment includes the following steps:

[0048] (1) Polymethyl methacrylate is used as a binder. The positive electrode active material, Super-P and polymethyl methacrylate are mixed in a mass ratio of 93:2:5. N-methylpyrrolidone with a mass of 1.5 times that of the three is added and stirred evenly to obtain a sodium-ion battery positive electrode slurry with a solid content of 40% and a viscosity of 2000 mPa·s. The slurry is coated on a 12 μm thick aluminum foil, dried fully in an open environment to remove the NMP dispersion solvent, and pressed to obtain a sodium-ion battery positive electrode sheet with a thickness of 100 μm.

[0049] (2) Using carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as negative electrode binders, the negative electrode active material, Super-P, CMC and SBR are mixed in a mass ratio of 96:1.5:1.5:1.5, and an appropriate amount of water is added and stirred evenly. The mixture is coated on an aluminum foil with a thickness of 12 μm, dried and dehydrated in an open environment, and pressed to obtain a sodium-ion battery negative electrode sheet with a thickness of 150 μm.

[0050] (3) Separate the obtained sodium-ion battery positive electrode and sodium-ion battery negative electrode with a separator, and obtain an electrode assembly by winding. Place the electrode assembly into a button battery case, inject electrolyte, and seal the battery case to obtain a sodium-ion soft pack battery.

[0051] Example 3

[0052] The only difference between this embodiment and Example 1 is that in step (1), 20% PVDF and 80% polyacrylic acid are used as the binder composition, the positive electrode active material, Super-P and the binder composition are mixed in a mass ratio of 94:2:4, and N-methylpyrrolidone of equal mass to the three is added and stirred evenly to obtain sodium-ion battery positive electrode slurry.

[0053] Example 4

[0054] The difference between this embodiment and Example 1 is that in step (1), 50% PVDF and 50% polymethyl vinyl ether copolymaleic acid by mass fraction are used as the binder composition. The positive electrode active material, Super-P and the binder composition are mixed in a mass ratio of 94:2:4, and N-methylpyrrolidone with an equal mass to the three is added and stirred evenly to obtain sodium-ion battery positive electrode slurry.

[0055] Example 5

[0056] The difference between this embodiment and Example 1 is that in step (1), 50% PVDF and 50% polymethyl methacrylate by mass fraction are used as the binder composition, the positive electrode active material, Super-P and the binder composition are mixed in a mass ratio of 94:2:4, and N-methylpyrrolidone of the same mass and amount as the three are added and stirred evenly to obtain sodium-ion battery positive electrode slurry.

[0057] Example 6

[0058] The difference between this embodiment and Example 1 is that in step (1), 50% polymethyl vinyl ether copolymer maleic acid and 50% polymethyl methacrylate are used as the binder composition. The positive electrode active material, Super-P and the binder composition are mixed in a mass ratio of 94:2:4, and N-methylpyrrolidone of equal mass to the three is added and stirred evenly to obtain sodium-ion battery positive electrode slurry.

[0059] Example 7

[0060] The difference between this embodiment and Example 1 is that in step (1), 50% PVDF, 25% polymethyl methacrylate and 25% polymethyl vinyl ether copolymaleic acid by mass fraction are used as the binder composition. The positive electrode active material, Super-P and the binder composition are mixed in a mass ratio of 94:2:4, and N-methylpyrrolidone with the same mass and amount as the three is added and stirred evenly to obtain sodium-ion battery positive electrode slurry.

[0061] Example 8

[0062] The difference between this embodiment and Example 1 is that in step (1), 50% PVDF, 25% polymethyl methacrylate and 25% polyacrylic acid by mass fraction are used as the binder composition, the positive electrode active material, Super-P and the binder composition are mixed in a mass ratio of 94:2:4, and N-methylpyrrolidone with the same mass and amount as the three is added and stirred evenly to obtain sodium-ion battery positive electrode slurry.

[0063] Comparative Example 1

[0064] The only difference between this comparative example and Example 1 is that in step (1), PVDF is used as a binder, and the positive electrode active material, Super-P and binder are mixed in a mass ratio of 94:2:4. N-methylpyrrolidone of equal mass to the three is added and stirred evenly to obtain a sodium-ion battery positive electrode slurry with a solid content of 50% and a viscosity of 3000 mPa·s.

[0065] Comparative Example 2

[0066] The only difference between this comparative example and Example 1 is that in step (1), polyacrylate is used as a binder, and the positive electrode active material, Super-P and binder are mixed in a mass ratio of 94:2:4. N-methylpyrrolidone of equal mass to the three is added and stirred evenly to obtain a sodium-ion battery positive electrode slurry with a solid content of 50% and a viscosity of 3000 mPa·s.

[0067] A small amount of the sodium-ion battery cathode slurry obtained in the above examples and comparative examples was placed in a 250 mL beaker and allowed to stand at room temperature with 20% relative humidity. The gelation time of the slurry was recorded. The electrochemical performance of the sodium-ion battery was tested in the voltage range of 2–4 V, and the test results are shown in Table 1 below.

[0068] Table 1 Electrochemical Performance Data of Sodium-ion Batteries

[0069]

[0070] As can be seen from the data in Table 1, the binder composition in the sodium-ion secondary battery positive electrode slurry obtained by the present invention uses a high molecular polymer containing carboxyl groups (-COOH), which effectively improves the uniformity and flowability of the positive electrode slurry. Compared with the traditional positive electrode slurry that only uses PVDF as a binder, the binder composition is more stable, has a longer gelation time, and ensures the battery capacity and cycle performance of the sodium-ion battery. Moreover, the compounding of polyvinylidene fluoride, polymethacrylic acid and polymethyl vinyl ether with maleic acid has even better effects.

[0071] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the spirit of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A sodium-ion battery positive electrode slurry, characterized in that, The components include the following parts by weight: 80-96 parts of positive electrode active material; Conductive agent 1-10 parts; 1-10 parts of adhesive composition; Dispersion solvent 20-400 parts; The adhesive composition comprises polyvinylidene fluoride, polymethacrylic acid and polymethyl vinyl ether copolymaleic acid; wherein the mass percentages of polyvinylidene fluoride, polymethacrylic acid and polymethyl vinyl ether copolymaleic acid are 50%, 25% and 25%, respectively.

2. The sodium-ion battery positive electrode slurry according to claim 1, characterized in that, The solid content of the sodium-ion battery cathode slurry is 20-80%, and the viscosity is 1000-10000 mPa·s.

3. A sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. The positive electrode is obtained by coating the sodium-ion battery positive electrode slurry of claim 1 onto the positive electrode current collector and then drying it.

4. The sodium-ion battery according to claim 3, characterized in that, The thickness of the positive electrode sheet is 100~150μm.

5. A method for preparing a sodium-ion battery as described in claim 3, characterized in that, The process involves separating the positive and negative electrode sheets with a separator, obtaining an electrode assembly by winding or slicing, placing the electrode assembly into a battery case, injecting electrolyte, and sealing the battery case to obtain a sodium-ion battery.

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