Carbon fluoride battery positive electrode and preparation of lithium carbon fluoride battery

Abstract

The invention discloses preparation and application of a flexible package carbon fluoride battery aqueous mixed binder positive electrode, and belongs to energy material technologies and related fields. The aqueous mixed binder is a mixture of one or two of a polyacrylonitrile multipolymer, polyoxyethylene and polyvinyl alcohol. According to the invention, the aqueous mixed binder is adopted to prepare the carbon fluoride positive electrode; the problems that a pole piece only using an acrylonitrile multipolymer binder is prone to brittle rupture and a pole piece only using polyoxyethylene and polyvinyl alcohol binder is poor in cohesiveness can be solved, the respective defects in the process of preparing the pole piece through the binder are avoided, and therefore the processing performance of the pole piece is effectively improved. The pole piece prepared by the aqueous mixed binder has abundant pores, the porosity range reaches 50-60%, enough space is left for a product in the carbon fluoride discharge process, and the problems of battery barren liquor and the like caused by discharge volume expansion of a positive pole piece are greatly relieved. In addition, the water-based binder can prevent the organic solvent from polluting the environment.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fluoride batteries, and particularly to a special preparation process of a binder used in carbon fluoride batteries Technical Background

[0002] The carbon fluoride battery uses graphite fluoride as the positive electrode and metallic lithium or metallic lithium alloy as the negative electrode. The mass specific capacity of the carbon fluoride material reaches 860 mAh / g, and the theoretical specific energy reaches 2180 Wh / kg, which is the highest mass specific energy among all known systems. The carbon fluoride battery has the advantages of high mass specific energy, good safety, and good storage performance, and has attracted extensive attention in recent years

[0003] Due to the characteristics of the self-discharge reaction of the carbon fluoride battery, its discharge process is accompanied by heat generation, and at the same time, it will bring about a large volume expansion of the positive electrode. As the reaction progresses, the polarization in the later stage of discharge increases, and the battery capacity cannot be effectively utilized. Constraining its volume expansion will inevitably cause large stress inside the battery, thus bringing potential safety hazards

[0004] Therefore, based on the characteristics of the carbon fluoride battery, providing a process technology that can improve the specific capacity of the carbon fluoride material and inhibit the volume expansion during the discharge process has important practical significance for the practical application of the carbon fluoride battery Summary of the Invention

[0005] The purpose of the present invention is to provide the preparation and application of an aqueous mixed binder positive electrode for a carbon fluoride battery. The present invention uses a mixed aqueous binder on the existing battery preparation process to prepare a carbon fluoride battery positive electrode with a high porosity, slow down the volume expansion from the inside of the electrode sheet, solve the deficiencies existing in the prior art, and provide a preparation method for a soft-packaged primary carbon fluoride battery. This method has a simple process, and the prepared positive electrode sheet is soft, has a stable structure, and good uniform spreading property, thereby improving the electrochemical performance of the carbon fluoride soft-pack battery

[0006] To achieve the above purpose, the present invention adopts the following technical solutions

[0007] One of the purposes of the present invention is to provide a preparation method of an aqueous binder for a carbon fluoride battery positive electrode. The porosity of the carbon fluoride positive electrode is 50-60%

[0008] A high-performance carbon fluoride battery, the high-performance carbon fluoride battery includes: carbon fluoride active material, conductive agent, and mixed binder

[0009] The mixed aqueous binder of the high-performance carbon fluoride battery is one or two mixtures of acrylonitrile copolymer and polyethylene oxide and polyvinyl alcohol binder, and the percentage of the acrylonitrile copolymer binder in the total mass is: 40-70%

[0010] The positive electrode active material is carbon fluoride, and the mass percentage of carbon fluoride in the total powder is 80-95%; the total powder amount is all solid powder materials in the positive electrode, including active material, conductive agent, and mixed binder.

[0011] The conductive agent is one or more of AB, CNT, graphene, and Super-P, accounting for 2.5-10% of the total powder amount;

[0012] The electrolyte uses one or more of LiFSI, LITFSI, and LiPF6 with a lithium salt concentration of 0.5-2 mol / L, and the solvent uses two or more of DEC, EC, EMC, and PC.

[0013] The preparation of the high-performance carbon fluoride battery further includes one of a separator and a negative electrode metal lithium foil or a lithium alloy (one of a lithium-magnesium alloy, a lithium-aluminum alloy, or a lithium-boron alloy). The separator is a single-layer pp or a multi-layer pp / pe composite separator. The thickness of the negative electrode is 50-200 μm, and the thickness of the separator is 12-30 μm.

[0014] The present invention can also adopt the following technical solutions:

[0015] Step 1: Glue application

[0016] Mix acrylonitrile copolymer binder, polyethylene oxide, and polyvinyl alcohol with water, and disperse them by high-speed stirring for 5-10 h to obtain a mixed binder;

[0017] Step 2: Slurry homogenization

[0018] Mix the conductive agent and the active material carbon fluoride with the mixed binder solution in sequence, add isopropanol with a mass fraction of 1-5%, and disperse them by high-speed stirring for 2-6 h to obtain a positive electrode slurry;

[0019] Step 3: Coating

[0020] Apply the slurry obtained in Step 2 evenly on the carbon-coated aluminum foil, and dry the solvent water and isopropanol through a blast drying oven;

[0021] Step 4: Die cutting

[0022] Die cut the dried positive electrode into positive electrode sheets, and die cut the metal lithium foil into negative electrode sheets;

[0023] Step 5: Assembly

[0024] Assemble the obtained positive electrode sheets, negative electrode sheets, and separator into a soft-packaged carbon fluoride battery cell by winding or Z-fold lamination, and inject liquid and seal it under vacuum.

[0025] In the preparation method of the above high-performance carbon fluoride battery, the porosity of the positive electrode sheet is 50-60% The present invention uses an aqueous mixed binder to prepare a carbon fluoride positive electrode, which can solve problems such as the easy embrittlement of the electrode sheet when using acrylonitrile copolymer alone and the poor adhesiveness when using polyethylene oxide and polyvinyl alcohol alone, avoiding the respective disadvantages in the process of preparing the electrode sheet with the binder, thereby effectively improving the processing performance of the electrode sheet, improving the poor electrical performance of the carbon fluoride battery, and enabling batch production. The electrode sheet prepared with the aqueous mixed binder has abundant voids, and the porosity range reaches 50 - 60%, leaving enough space for the products during the discharge process of carbon fluoride, greatly alleviating problems such as the liquid deficiency of the battery caused by the discharge volume expansion of the positive electrode. In addition, the aqueous binder can avoid environmental pollution caused by organic solvents.

[0026] In summary, the present invention has the following advantages and positive effects:

[0027] 1. Since the aqueous mixed binder is used in the preparation process of the positive electrode in the present invention, when using the aqueous mixed binder to prepare the electrode sheet, the key cyano functional group of the acrylonitrile copolymer belongs to a highly polar group. The greater the polarity of the molecule, the stronger the adhesiveness, the stronger the intermolecular force, the greater the difficulty of molecular chain rotation, and the lower the twisting ability. Therefore, after film formation, the electrode sheet will have the disadvantages of being hard and easy to break. Polyethylene oxide is a thermoplastic resin with softness and high strength, and has a relatively high ion migration rate, which can improve the conductivity of the electrode sheet to a certain extent, but has relatively poor adhesiveness when used as a binder. Polyvinyl alcohol products are white solids, and their aqueous solutions have good adhesiveness and film-forming properties, but when used alone as a binder, there are also problems such as poor adhesiveness. Therefore, using two or three of them in combination can solve the problems of easy embrittlement of the electrode sheet prepared with acrylonitrile copolymer binder alone and poor adhesiveness of polyethylene oxide and polyvinyl alcohol binders alone, avoiding the respective disadvantages in the process of preparing the electrode sheet with the binder, thereby effectively improving the processing performance of the electrode sheet, improving the poor electrical performance of the carbon fluoride battery, and enabling batch production.

[0028] 2. The electrode sheet prepared with the aqueous mixed binder has abundant voids, and the porosity range reaches 50 - 60%, leaving enough space for the products during the discharge process of carbon fluoride, greatly alleviating problems such as the discharge volume expansion of the positive electrode sheet. In addition, the aqueous binder can avoid environmental pollution caused by organic solvents. Description of the Drawings

[0029] Figure 1 It is the discharge curve diagram of Example 1. Figure 2 It is the discharge curve diagram of the carbon fluoride battery obtained in Example 2 at a discharge rate of 0.1C. Detailed Embodiments

[0030] The following will be combined with Figure 1 to specifically illustrate the present invention.

[0031] Example 1:

[0032] The aqueous mixed binder in this embodiment is a mixed solution of acrylonitrile copolymer (which can be one or two of LA132 or LA133, here it is LA132 with a molecular weight of 230,000): polyethylene oxide (with a molecular weight of 8,000,000): polyvinyl alcohol (with a molecular weight of 270,000) = 70:20:10 (by mass); the slurry is based on the total mass content of carbon fluoride, mixed binder, conductive agent Super P, water, and isopropanol being 100%; In the carbon fluoride positive electrode, the mass content of the carbon fluoride active material is 88%, the mixed binder is 6%, and the conductive agent is 6%; In the aqueous positive electrode slurry, based on the total mass of isopropanol and water being 100%, the mass content of water is 95%, the mass content of isopropanol is 5%, and the solid content is 25%.

[0032] Preparation of the glue solution:

[0033] The binder used is a mixed solution of acrylonitrile copolymer: polyethylene oxide: polyvinyl alcohol = 70:20:10 (by mass), with a solid content of 18% in water. It is placed in a Shenzhen Kejing MSK - SFM - 9 - 2L - 2 double - dispersion axis vacuum planetary mixer, with the set revolution speed of the public rotation being 100 rpm, the dispersion revolution speed being 2000 rpm, and mixed and dispersed for 10 h.

[0034] Preparation of the slurry:

[0035] (1) The prepared glue solution and the conductive agent Super P are placed in a Shenzhen Kejing MSK - SFM - 9 - 2L - 2 double - dispersion axis vacuum planetary mixer, with the revolution speed of the public rotation being 100 rpm and the dispersion revolution speed being 2000 rpm, and mixed and dispersed for 30 min;

[0036] (2) The mixed solution obtained in step (1), carbon fluoride, isopropanol, and water are mixed, and are successively mixed at a revolution speed of 100 rpm and a dispersion revolution speed of 2000 rpm for 30 min, and then continue to be mixed and dispersed at 100 rpm and a dispersion revolution speed of 2000 rpm for 3.5 h;

[0037] A preparation method of a carbon fluoride battery:

[0038] (3) The aqueous positive electrode slurry is coated on a 17 - μm - thick carbon - coated aluminum foil (with a 1 - μm - thick single - side coating) with a doctor blade thickness of 500 μm, and after drying by blowing air, a positive electrode sheet with a dry film thickness of 200 μm is obtained, and the porosity of the electrode sheet is 50%; The dried electrode sheet is die - cut into a positive electrode sheet, and a metal lithium foil mold (100 - μm thick) is cut into a negative electrode sheet.

[0039] (4) Stack the positive electrode sheet, negative electrode (100μm metallic lithium foil), and celgard2316 pp and pe composite separator in a Z-shaped pattern, then assemble them into an aluminum-plastic film soft-packaged battery cell, and add electrolyte (1.2mol / L LTFSI, EC:DMC:EMC = 1:2:1, V / V / V), and seal it under vacuum.

[0040] Figure 1 Figure 4 shows the discharge curve of the carbon fluoride battery obtained in this example at a 0.1C rate, and the energy density reaches 935 Wh / kg. It can be seen from the figure that the carbon fluoride battery obtained by the method of the present invention has excellent electrical performance.

[0041] Example 2

[0042] The difference from Example 1 is that the binder is a mixed solution of acrylonitrile copolymer: polyethylene oxide: polyvinyl alcohol = 70:10:20 (mass ratio).

[0043] Figure 2 Figure 5 shows the discharge curve of the carbon fluoride battery obtained in this example at a 0.1C rate, and the energy density reaches 880 Wh / kg.

[0044] Comparative Example 1

[0045] The difference from Example 1 is that an oil-based PVDF formulation is used, isopropanol and water are replaced with an equal mass of NMP, and the aqueous binder is replaced with an equal mass of oil-based binder PVDF.

[0046] Figure 1 Figure 6 is a comparative diagram of the 0.1C discharge curves of the carbon fluoride batteries obtained in Example 1 and Comparative Example 1 of the present invention. It can be seen from the figure that for the positive electrode prepared by the aqueous method in Example 1 and the positive electrode prepared by the oil-based method in Comparative Example 1, there is no voltage hysteresis phenomenon at the initial stage of discharge. During the discharge stage, its plateau is significantly higher than that of the positive electrode prepared by the oil-based method. The main reason is that the conductivity and porosity of the electrode sheet with the oil-based binder are relatively low, resulting in a higher resistance of the positive electrode sheet and affecting the current output; while for the positive electrode sheet prepared by the aqueous method, the aqueous binder itself has a relatively high conductivity, and in addition, its electrode sheet has a high porosity. The combination of the two can, on the one hand, improve the electronic conductivity of the electrode sheet, and on the other hand, improve the ionic conductivity of the electrode sheet, thereby reducing the voltage hysteresis phenomenon at the initial stage of discharge and increasing the discharge plateau of the battery.

Claims

1. A positive electrode of a carbon fluoride battery, characterized in that, The positive electrode of the carbon fluoride battery uses a mixed aqueous binder, which includes an acrylonitrile copolymer and one or two mixtures of polyethylene oxide and polyvinyl alcohol. The acrylonitrile copolymer accounts for 40-70% by mass of the total binder, preferably 55-70%, and the optimal ratio is 65-70% by mass.

2. The positive electrode of a carbon fluoride battery according to claim 1, characterized in that: The carbon fluoride positive electrode includes an active material, a conductive agent, and a mixed binder; The active material is carbon fluoride; The conductive agent is one or more of AB, CNT, graphene, and Super-P, accounting for 2.5-10% of the total powder amount, preferably 3-7%, and more preferably 5-6%; The mixed aqueous binder is an acrylonitrile copolymer and one or two mixtures of polyethylene oxide and polyvinyl alcohol, accounting for 2.5-10% of the total powder amount, preferably 3-7%, and more preferably 5-6%.

3. The positive electrode of a lithium carbon fluoride battery according to claim 1 or 2, characterized in that: The carbon fluoride positive electrode prepared with the mixed aqueous binder has abundant pores, and the porosity range reaches 50-60%, leaving enough space for the products during the discharge process of carbon fluoride, and can also store a sufficient amount of electrolyte, thereby improving the ionic conductivity of the positive electrode and greatly alleviating problems such as electrolyte deficiency caused by the discharge volume expansion of the positive electrode sheet.

4. The positive electrode of a lithium carbon fluoride battery according to claim 1, characterized in that: The molecular weight ranges of the acrylonitrile copolymer, polyethylene oxide, and polyvinyl alcohol are respectively: the acrylonitrile copolymer is 200,000-300,000, the polyethylene oxide is 2,000,000-9,000,000, and the polyvinyl alcohol is 250,000-300,000.

5. A carbon fluoride battery, characterized in that, Using the carbon fluoride battery positive electrode according to any one of claims 1-4 as the battery positive electrode sheet.

6. The carbon fluoride battery according to claim 5, characterized in that, The carbon fluoride battery further includes a negative electrode, a separator, and an electrolyte. The negative electrode is one of a metal lithium foil and a lithium alloy (one of a lithium magnesium alloy, a lithium aluminum alloy, or a lithium boron alloy); the separator is one of a single-layer pp or a multi-layer pp and pe composite separator; the thickness of the negative electrode is 50-200 μm, and the thickness of the separator is 12-30 μm; the electrolyte uses one or more of LiFSI, LITFSI, and LiPF6 with a lithium salt concentration of 0.5-2 mol / L, and the solvent uses two or more of DEC, EC, EMC, and PC.

7. A method for preparing the carbon fluoride battery according to claim 5 or 6, characterized in that: Including the following steps: Step 1: Glue application Mix the mixed aqueous binder and water in a certain mass ratio. The mass content of water is 50-90%. Disperse and mix them by high-speed stirring. The stirring speed is 50-200 rpm, and the dispersion speed is 500-3000 rpm. Stir and disperse for 5-10 h to obtain a mixed binder; Step 2: Slurry homogenization Mix the conductive agent and the active material carbon fluoride with the mixed binder solution in sequence, add a certain amount of water and isopropyl alcohol. Water accounts for 50-85% of the total mass, and isopropyl alcohol accounts for 1-5% of the total mass fraction. Disperse and mix them by high-speed stirring. The stirring speed is 50-200 rpm, and the dispersion speed is 500-3000 rpm. Stir and disperse for 2-6 h to obtain a positive electrode slurry; Step 3: Coating Apply the positive electrode slurry obtained in step 2 evenly on the carbon-coated aluminum foil, and blow-dry the solvent water and isopropyl alcohol; Step 4: Die cutting Die cut the dried positive electrode into a positive electrode sheet, and die cut the metal lithium foil or lithium alloy into a negative electrode sheet; Step 5: Assembly The obtained positive electrode sheet, negative electrode sheet and separator are assembled into a soft-packaged carbon fluoride battery cell with an aluminum-plastic film by winding or Z-fold lamination, and then electrolyte is injected and vacuum sealed.

8. The method for preparing a high-performance carbon fluoride battery according to claim 7, characterized in that, The thickness of the single-sided carbon coating layer of the carbon-coated aluminum foil is 1-5 μm, and the thickness of the positive dry film is 20-500 μm.

9. The method for preparing a high-performance carbon fluoride battery according to claim 7, characterized by, The porosity range of the positive electrode sheet is 50-60%.

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