Fluoride-containing binder for sulfide all-solid-state battery, preparation method and application thereof

Abstract

The present invention relates to a fluorine-containing binder for sulfide all-solid-state batteries, and its preparation method and application. The binder is copolymerized by isoprene and lithium perfluorovinyl ether sulfonate. Specifically, lithium perfluorovinyl ether sulfonate, a chelating agent, an emulsifier, ferrous sulfate, a reducing agent, and an acid-base buffer are dissolved in water, cooled under an inert atmosphere, and isoprene, an initiator, and a molecular weight regulator are added. A polymerization reaction is performed to obtain the fluorine-containing binder. The isoprene of the present invention can enhance the solubility of the lithium perfluorovinyl ether sulfonate fragment in a non-polar solvent, thereby achieving solubility of the entire polymer in a non-polar solvent; the carbon-fluorine group of lithium perfluorovinyl ether sulfonate has a large spatial occupancy and can shield the hydrocarbon groups on the isoprene, thereby improving the stability of the entire polymer. The fluorine-containing binder prepared by the present invention is a binder with high elasticity, high ionic conductivity, and stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-solid-state lithium batteries, and specifically relates to a fluorine-containing binder for sulfide all-solid-state batteries, a preparation method and applications thereof, and in particular to a new fluorine-containing polymer binder suitable for sulfide electrolyte positive electrodes and a preparation method thereof. Background Art

[0002] Currently, wet coating of cathode materials remains the dominant method in battery production, requiring suitable solvents and binders. Cathode binders used in lithium-ion batteries, such as the fluoropolymer PVDF, rely on the highly polar solvent NMP for dissolution. However, these highly polar solvents react with the sulfide electrolyte, causing it to lose its lithium-ion conductivity. Other binders, such as nitrile rubber and butadiene rubber, can be dispersed in non-polar solvents, but their weak carbon-hydrogen bonds result in poor stability at high potentials. When applied to the cathode, they decompose, causing battery performance to decline. Furthermore, the inherent ionic insulation of rubber hinders lithium-ion transport, leading to increased polarization voltage and impacting battery charge and discharge performance. Summary of the Invention

[0003] The present invention addresses the problems existing in the prior art by providing a fluorinated binder for sulfide all-solid-state batteries, its preparation method, and its application. Specifically, the binder is used for wet-process preparation of sulfide all-solid-state battery cathodes. The binder exhibits high elasticity, high ionic conductivity, and stability. The binder exhibits excellent solubility in non-polar solvents and possesses ionic conductivity, significantly enhancing the electrochemical performance of all-solid-state batteries.

[0004] The purpose of the present invention can be achieved by the following solutions:

[0005] The present invention provides a fluorine-containing binder for sulfide all-solid-state batteries, the structural formula of which is shown below:

[0006] ;

[0007] Wherein a and b are the molar proportions of the respective monomers, a is 90-80%, and b is 10-20% (a+b=1).

[0008] The binder is copolymerized with isoprene and lithium perfluorovinyl ether sulfonate. The polymerization method of the binder is generally an emulsion polymerization method.

[0009] The present invention also provides a method for preparing the fluorine-containing binder, comprising the following steps:

[0010] Lithium perfluorovinyl ether sulfonate, a chelating agent, an emulsifier, ferrous sulfate, a reducing agent, and an acid-base buffer are dissolved in water, cooled under an inert atmosphere, and isoprene, an initiator, and a molecular weight regulator are added to carry out polymerization reaction to obtain a fluorine-containing binder.

[0011] As an embodiment of the present invention, the mass ratio of isoprene to lithium perfluorovinyl ether sulfonate is 70-80:42-52.

[0012] As an embodiment of the present invention, the mass ratio of lithium perfluorovinyl ether sulfonate to water is 42-52:400.

[0013] As one embodiment of the present invention, the mass ratio of lithium perfluorovinyl ether sulfonate, chelating agent, emulsifier, ferrous sulfate, reducing agent, acid-base buffer, initiator, and molecular weight regulator is 42-52: 0.04-0.09: 9-12: 0.01-0.033: 0.1-0.14: 0.1: 0.03-0.07: 0.9-1.5.

[0014] As an embodiment of the present invention, the chelating agent is disodium ethylenediaminetetraacetic acid. The chelating agent combines with iron ions to control the iron ion concentration.

[0015] As an embodiment of the present invention, the emulsifier is sodium lauryl sulfate and / or potassium oleate. During the emulsion polymerization process, the self-emulsification ability of lithium perfluorovinyl ether sulfonate can be used to reduce the amount of emulsifier.

[0016] As an embodiment of the present invention, the reducing agent is sodium formaldehyde sulfoxylate. The reducing agent plays a role in reducing iron ions.

[0017] As an embodiment of the present invention, the acid-base buffer is sodium pyrophosphate decahydrate.

[0018] In one embodiment of the present invention, the initiator is cumene hydroperoxide. Ferrous sulfate can lower the initiation temperature of the initiator. In the emulsion polymerization method, the initiator uses hydrogen peroxide and iron ions to form a low-temperature redox initiation system.

[0019] As an embodiment of the present invention, the molecular weight regulator is dodecyl mercaptan and / or tert-butyl dodecyl mercaptan.

[0020] As an embodiment of the present invention, the cooling is to 8-12°C, preferably 10°C.

[0021] As one embodiment of the present invention, the polymerization reaction time is 2-3 hours, preferably 2 hours.

[0022] As one embodiment of the present invention, after the polymerization reaction, the emulsion is broken with a saturated sodium chloride aqueous solution and then washed with water to obtain a fluorine-containing binder.

[0023] The present invention also provides a use of the fluorine-containing binder in preparing a sulfide all-solid-state battery positive electrode.

[0024] The present invention also provides a method for preparing a sulfide all-solid-state battery positive electrode, comprising the following steps:

[0025] The positive electrode material, the sulfide electrolyte, the conductive additive and the fluorine-containing binder are mixed and then ground, the obtained slurry is coated, warm dried and then vacuum dried to obtain the sulfide all-solid-state battery positive electrode.

[0026] As an embodiment of the present invention, the positive electrode material is lithium nickel cobalt manganese oxide.

[0027] As one embodiment of the present invention, the sulfide electrolyte is a lithium phosphorus sulfur chlorine electrolyte.

[0028] As one embodiment of the present invention, the conductive additive is conductive carbon.

[0029] As an embodiment of the present invention, the mass ratio of the positive electrode material, the sulfide electrolyte, the conductive additive, and the fluorine-containing binder is 0.7:0.2:0.05:0.05.

[0030] As one embodiment of the present invention, the grinding solvent is toluene.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) Isoprene can enhance the solubility of lithium perfluorovinyl ether sulfonate fragments in non-polar solvents, thereby achieving the solubility of the entire polymer in non-polar solvents; other dienes (such as butadiene) require the use of a high-pressure reactor for polymerization, and the reaction conditions are relatively high;

[0033] (2) The carbon-fluorine groups of lithium perfluorovinyl ether sulfonate occupy a large space, which can shield the hydrocarbon groups on isoprene, thereby improving the stability of the overall polymer;

[0034] (3) The strong electron-withdrawing effect of the carbon fluoride group also makes the lithium on the lithium sulfonate easy to dissociate, and the ionic conductivity is higher than that of non-fluorinated polymers such as lithium styrene sulfonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0036] Figure 1 is the infrared spectrum of P-1;

[0037] Figure 2 This is the P-1 long cycle charge and discharge capacity test diagram;

[0038] Figure 3 This is the D-2 long cycle charge and discharge capacity test diagram. DETAILED DESCRIPTION

[0039] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, provide detailed implementation methods and specific operating procedures, and will help those skilled in the art to further understand the present invention. It should be pointed out that the scope of protection of the present invention is not limited to the following embodiments, and a number of adjustments and improvements made under the premise of the concept of the present invention all fall within the scope of protection of the present invention.

[0040] Example 1

[0041] 0.09g of disodium ethylenediaminetetraacetic acid, 12g of sodium lauryl sulfate, 0.03g of ferrous sulfate, 0.1g of sodium formaldehyde sulfoxylate, 0.1g of sodium pyrophosphate decahydrate, and 52g of lithium perfluorovinyl ether sulfonate were weighed and fully dissolved in 400g of water. After adding them to the flask, the nitrogen was replaced three times. After the temperature was lowered to 10°C, 80g of isoprene, 0.07g of cumene hydroperoxide, and 1g of dodecyl mercaptan were weighed and injected into the flask to start the polymerization reaction. After 2 hours of polymerization, the emulsion was broken with a saturated sodium chloride aqueous solution, washed with water, and dried to obtain polymer P-1. The infrared spectrum of polymer P-1 is shown in FIG. Figure 1 As shown; the long cycle charge and discharge capacity test diagram is as follows Figure 2 shown.

[0042] Example 2

[0043] 0.04g of ethylenediaminetetraacetic acid disodium salt, 9g of sodium lauryl sulfate, 0.01g of ferrous sulfate, 0.12g of sodium formaldehyde sulfoxylate, 0.1g of sodium pyrophosphate decahydrate, and 42g of lithium perfluorovinyl ether sulfonate were weighed and dissolved in 400g of water. After adding these to a flask, the atmosphere was purged with nitrogen three times. After the temperature was lowered to 10°C, 70g of isoprene, 0.03g of cumene hydroperoxide, and 0.9g of dodecyl mercaptan were added and injected into the flask to initiate polymerization. After 2 hours of polymerization, the emulsion was broken with saturated sodium chloride solution, washed with water, and dried to obtain polymer P-2.

[0044] Example 3

[0045] 0.072g of ethylenediaminetetraacetic acid disodium salt, 9g of potassium oleate, 0.033g of ferrous sulfate, 0.13g of sodium formaldehyde sulfoxylate, 0.1g of sodium pyrophosphate decahydrate, and 49g of lithium perfluorovinyl ether sulfonate were weighed and dissolved in 400g of water. The mixture was then added to a flask, and the atmosphere was purged with nitrogen three times. After the temperature was lowered to 9°C, 72g of isoprene, 0.065g of cumene hydroperoxide, and 1.3g of dodecyl mercaptan were added and injected into the flask, and the polymerization reaction was initiated. After 2 hours of polymerization, the mixture was demulsified with saturated sodium chloride solution, washed with water, and dried to obtain polymer P-3.

[0046] Example 4

[0047] 0.09g of ethylenediaminetetraacetic acid disodium salt, 10g of sodium lauryl sulfate, 0.025g of ferrous sulfate, 0.14g of sodium formaldehyde sulfoxylate, 0.1g of sodium pyrophosphate decahydrate, and 50g of lithium perfluorovinyl ether sulfonate were weighed and dissolved in 400g of water. The mixture was then added to a flask, and the atmosphere was purged with nitrogen three times. After the temperature was lowered to 11°C, 76g of isoprene, 0.03g of tert-butyl hydroperoxide, and 1.5g of tert-butyl dodecyl mercaptan were added and injected into the flask to initiate polymerization. After 3 hours of polymerization, the mixture was demulsified with saturated sodium chloride solution, washed with water, and dried to obtain polymer P-4.

[0048] Comparative Example 1

[0049] The preparation steps of this comparative example are basically the same as those of Example 1, except that during the preparation of the polymer, lithium perfluorovinyl ether sulfonate is replaced with lithium p-styrene sulfonate to obtain sample D-1.

[0050] Comparative Example 2

[0051] The preparation steps of this comparative example are basically the same as those of Example 1, except that lithium perfluorovinyl ether sulfonate is not added during the preparation of the polymer, and sample D-2 is obtained. The long cycle charge and discharge capacity test graph of sample D-2 is shown in FIG. Figure 3 shown.

[0052] Performance testing:

[0053] The polymers prepared in the examples and comparative examples were subjected to ionic conductivity tests and long cycle tests, and the test methods were as follows:

[0054] (1) Polymer ionic conductivity test method

[0055] The ionic conductivity was determined using the AC impedance method. A 5wt% polymer solution was dissolved in toluene. The polymer solution was spread flat in a Teflon dish and dried at 50°C to form a membrane. The membrane was then placed in a pressure cell mold and pressurized to 0.3 MPa. The electrochemical workstation was set to an AC impedance test frequency range of 1 MHz to 1 Hz. After the test, the membrane thickness was measured and calculated using the following formula: σLi + =L / RS, where R is the AC impedance value, L is the membrane thickness, and S is the membrane area.

[0056] (2) Long cycle test method

[0057] A lithium nickel cobalt manganese oxide cathode, a lithium phosphorus sulfur chloride electrolyte, a conductive carbon, and a polymer binder were mixed in a mass ratio of 0.7:0.2:0.05:0.05. An appropriate amount of toluene was added, ground, and thoroughly mixed before being evenly coated on aluminum foil. After the solvent was essentially evaporated within the glove box, the mixture was transferred to a vacuum oven also within the glove box for drying at 60°C for 12 hours. A pressure battery mold was loaded with 100mg of the lithium phosphorus sulfur chloride electrolyte and compacted at 100mPa. The coated cathode and lithium indium negative electrodes were then added. The entire battery was then pressurized to 50mPa using a stainless steel rack. Charge and discharge tests were conducted at a 0.2C rate to examine the stability of different binders.

[0058] The changes in the electrical conductivity of the polymers obtained by polymerization at different ratios of the present invention are shown in Table 1.

[0059] Table 1

[0060]

[0061] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a fluorine-containing binder, characterized in that: The steps include: The fluorinated binder is obtained by dissolving lithium perfluorovinyl ether sulfonate, a chelating agent, an emulsifier, ferrous sulfate, a reducing agent, and an acid-base buffer in water, cooling the mixture under an inert atmosphere, adding isoprene, an initiator, and a molecular weight regulator, and performing a polymerization reaction. The mass ratio of isoprene to lithium perfluorovinyl ether sulfonate is 70-80:42-52.

2. The method for preparing a fluorine-containing binder according to claim 1, wherein: The mass ratio of lithium perfluorovinyl ether sulfonate and water is 42-52:400; And / or, the mass ratio of lithium perfluorovinyl ether sulfonate, chelating agent, emulsifier, ferrous sulfate, reducing agent, acid-base buffer, initiator, and molecular weight regulator is 42-52: 0.04-0.09: 9-12: 0.01-0.033: 0.1-0.14: 0.1: 0.03-0.07: 0.9-1.

5.

3. The method for preparing a fluorine-containing binder according to claim 1, wherein: The chelating agent is disodium ethylenediaminetetraacetic acid; and / or, the emulsifier is sodium lauryl sulfate and / or potassium oleate; and / or, the reducing agent is sodium formaldehyde sulfoxylate; and / or, the acid-base buffer is sodium pyrophosphate decahydrate; and / or, the initiator is cumene hydroperoxide; And / or, the molecular weight regulator is dodecyl mercaptan and / or tert-butyl dodecyl mercaptan.

4. The method for preparing a fluorine-containing binder according to claim 1, wherein: Cooling means lowering the temperature to 8-12℃; And / or, the polymerization reaction time is 2-3 hours.

5. The method for preparing a fluorine-containing binder according to claim 1, wherein: After the polymerization reaction, the emulsion is broken with a saturated sodium chloride aqueous solution and then washed with water to obtain a fluorine-containing binder.

6. Use of the fluorine-containing binder obtained by the preparation method according to claim 1 in preparing a sulfide all-solid-state battery positive electrode.

7. A method for preparing a sulfide all-solid-state battery positive electrode, characterized in that: The steps include: The positive electrode material, the sulfide electrolyte, the conductive additive, and the fluorine-containing binder obtained by the preparation method according to claim 1 are mixed and then ground, the obtained slurry is coated, dried, and then vacuum-dried to obtain the sulfide all-solid-state battery positive electrode.

8. The method for preparing a sulfide all-solid-state battery positive electrode according to claim 7, characterized in that: The positive electrode material is lithium nickel cobalt manganese oxide; and / or, the sulfide electrolyte is a lithium phosphorus sulfur chlorine electrolyte; and / or, the conductive additive is conductive carbon; And / or, the mass ratio of the positive electrode material, the sulfide electrolyte, the conductive additive, and the fluorine-containing binder is 0.7:0.2:0.05:0.05; And / or, the grinding solvent is toluene.

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