Dithiol-modified copolymers, methods of making and using the same

Abstract

The application provides a dithiol modified copolymer and a preparation method and application thereof, and particularly relates to the technical field of lithium batteries. In the dithiol modified copolymer, the copolymer is a branched diene-vinyl pyridine copolymer, which is mainly obtained by copolymerization of branched diene and vinyl pyridine. The dithiol modified copolymer provided by the application has a main chain composed of flexible branched diene units, which endows the copolymer with a good elastic skeleton structure; vinyl pyridine is introduced as a functional monomer, so that a pyridine group is formed on the side chain of the copolymer; a dithiol compound introduces a thiol group (-SH) to the copolymer, and finally, the dithiol modified copolymer has a flexible main chain structure, and the side chain simultaneously contains a pyridine group and a thiol group, and has good elasticity and functional characteristics.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a dithiol-modified copolymer, its preparation method, and its application. Background Technology

[0002] Sulfide solid electrolytes are characterized by their high ionic conductivity (>10). -3 With its excellent compatibility (S / cm) and good mechanical ductility, ternary cathode materials have become the core electrolyte material for all-solid-state lithium batteries. However, ternary cathode materials, when matched with the electrolyte, undergo significant volume expansion (cell expansion rate 6–10%) in a deeply delithiated state, while sulfide electrolytes are rigid inorganic particles. This difference in properties leads to dynamic interface mismatch during cycling: on the one hand, the repeated expansion / contraction of ternary cathode material particles pushes sulfide particles away, causing physical contact loss and forming "dead zones" of ionic / electronic insulation; on the other hand, local contact stress can trigger sulfide electrolyte decomposition, generating a high-resistivity interface layer and exacerbating interface side reactions. During long-term cycling, the effective reaction area at the interface decreases, the battery internal resistance continues to rise, leading to capacity decay.

[0003] Traditional binders (such as PVDF) rely solely on van der Waals forces to bond ternary cathode material particles, which cannot adapt to dynamic volume changes and require polar solvents for dissolution. However, polar solvents have poor compatibility with sulfide electrolytes.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a dithiol-modified copolymer, its preparation method, and its application, aiming to solve at least one of the above-mentioned technical problems in the prior art.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] A first aspect of the present invention provides a dithiol-modified copolymer, said copolymer being a branched diene-vinylpyridine copolymer, mainly obtained by copolymerization of branched diene and vinylpyridine.

[0008] Furthermore, the branched diene contains 5 to 10 carbon atoms.

[0009] Preferably, the branched diene includes isoprene, 3-methyl-1,3-pentadiene, 2-methyl-1,5-hexadiene, 3-methyl-1,5-hexadiene, 3-methyl-1,5-heptadiene, 4-methyl-1,5-heptadiene, or 3,7-dimethyl-1,5-octadiene.

[0010] Furthermore, the dithiol compounds include 1,2-ethanedithiol, 1,6-hexanedithiol, polyethylene glycol dithiol, and 1,4-butanedithiol.

[0011] Preferably, the vinylpyridine comprises 2-vinylpyridine or 4-vinylpyridine.

[0012] Furthermore, the molar ratio of the branched diene to the vinylpyridine is (2~6):1.

[0013] Preferably, the amount of the dithiol compound is 0.8 to 1.2 times the mass of the copolymer.

[0014] A second aspect of the present invention provides a method for preparing the aforementioned dithiol-modified copolymer, comprising the following steps:

[0015] A. After adding a redox initiating emulsion to the reaction vessel, a protective gas is introduced, followed by the addition of a branched diene, vinylpyridine, and cumene hydroperoxide to carry out a copolymerization reaction to obtain a copolymer.

[0016] B. Add the copolymer, dithiol compound, and initiator to toluene to carry out an addition reaction to obtain the dithiol-modified copolymer.

[0017] Furthermore, the redox-initiating emulsion includes disodium ethylenediaminetetraacetate, emulsifier, ferrous salt, reducing agent, dispersant, and water.

[0018] Preferably, the concentration of the disodium ethylenediaminetetraacetate is 0.01~0.05wt%.

[0019] Preferably, the concentration of the emulsifier is 2-4 wt%.

[0020] Preferably, the concentration of the ferrous salt is 0.001~0.01wt%.

[0021] Preferably, the concentration of the reducing agent is 0.01~0.05wt%.

[0022] Preferably, the concentration of the dispersant is 0.01~0.05wt%.

[0023] Furthermore, the emulsifier includes at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl xylene sulfonate, and disodium polyoxyethylene ether sulfosuccinate.

[0024] Preferably, the ferrous salt includes at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous carbonate, and ferrous oxalate.

[0025] Preferably, the reducing agent includes at least one of sodium formaldehyde sulfoxylate, sodium dithionite, ascorbic acid, and sodium bisulfite.

[0026] Preferably, the dispersant includes at least one of sodium pyrophosphate, sodium hexametaphosphate, and sodium tripolyphosphate.

[0027] Further, in step A, the molar ratio of the branched diene to the vinylpyridine is (2~6):1.

[0028] Preferably, the redox initiating emulsion is 5 to 5.5 times the mass of the branched diene.

[0029] Preferably, the amount of cumene hydroperoxide used is 0.05~0.09% of the mass of the branched diene.

[0030] Preferably, the copolymerization reaction is carried out at a temperature of 5-15°C for 16-32 hours.

[0031] Preferably, in step B, the amount of the dithiol compound added is 0.8 to 1.2 times the mass of the copolymer.

[0032] Preferably, in step B, the initiator comprises azobisisobutyronitrile.

[0033] Preferably, in step B, the amount of the initiator is 2-6% of the mass of the copolymer.

[0034] Preferably, in step B, the temperature of the addition reaction is 50~60℃.

[0035] The third aspect of this invention provides the application of the aforementioned dithiol-modified copolymer as a binder for the positive electrode of a lithium battery.

[0036] Furthermore, the lithium battery includes a sulfide all-solid-state lithium-ion battery.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects:

[0038] The dithiol-modified copolymer provided by this invention has a main chain composed of flexible branched diene units, which endows the copolymer with a good elastic backbone structure. Vinylpyridine is introduced as a functional monomer, so that pyridine groups are formed on the side chains of the copolymer. A dithiol compound introduces thiol groups (-SH) into the copolymer. The resulting dithiol-modified copolymer has a flexible main chain structure and the side chains contain both pyridine groups and thiol groups, thus possessing both good elasticity and functionalization properties.

[0039] The preparation method provided by this invention first uses branched dienes and vinylpyridine as monomers to obtain a copolymer containing double bonds through emulsion polymerization in a redox-initiated emulsion. Subsequently, the copolymer and a dithiol compound are introduced with carboxyl and thiol groups via a mercapto-olefin click reaction to obtain the target product. This preparation method has continuous process steps, is easy to control, and is suitable for large-scale industrial production.

[0040] This invention utilizes a dithiol-modified copolymer as a binder for the positive electrode of lithium batteries, leveraging its synergistic design of a "thiol-pyridine-flexible framework" to achieve interface strengthening and stress buffering: the thiol groups (-SH) and the S in the sulfide electrolyte... 2- Stable chemical bonds are formed through Lewis acid-base interactions, firmly anchoring electrolyte particles; pyridine nitrogen reacts with Ni on the ternary cathode surface. 2+ / Co 3+ Coordination enhances the bonding force between the binder and the cathode; the flexible framework dynamically adapts to changes in cathode volume and maintains interface integrity, thereby simultaneously completing electrolyte fixation, cathode coordination, and stress buffering, significantly improving the cycle stability of the composite electrode. Attached Figure Description

[0041] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0042] Figure 1 This is an in-situ optical test photograph of the all-solid-state lithium battery prepared in Example 3 after 400 charge-discharge cycles;

[0043] Figure 2 This is an in-situ optical test image of the all-solid-state lithium battery prepared in Comparative Example 4 after 400 charge-discharge cycles. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0045] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.

[0046] A first aspect of the present invention provides a dithiol-modified copolymer, said copolymer being a branched diene-vinylpyridine copolymer, mainly obtained by copolymerization of branched diene and vinylpyridine.

[0047] The dithiol-modified copolymer provided by this invention has a main chain composed of flexible branched diene units, which endows the copolymer with a good elastic backbone structure. Vinylpyridine is introduced as a functional monomer, so that pyridine groups are formed on the side chains of the copolymer. A dithiol compound introduces thiol groups (-SH) into the copolymer. The resulting dithiol-modified copolymer has a flexible main chain structure and the side chains contain both pyridine groups and thiol groups, thus possessing both good elasticity and functionalization properties.

[0048] Furthermore, the branched diene contains 5 to 10 carbon atoms.

[0049] And / or, the branched diene includes isoprene, 3-methyl-1,3-pentadiene, 2-methyl-1,5-hexadiene, 3-methyl-1,5-hexadiene, 3-methyl-1,5-heptadiene, 4-methyl-1,5-heptadiene, or 3,7-dimethyl-1,5-octadiene.

[0050] Furthermore, the dithiol compounds include 1,2-ethanedithiol, 1,6-hexanedithiol, polyethylene glycol dithiol, and 1,4-butanedithiol.

[0051] And / or, the vinylpyridine includes 2-vinylpyridine or 4-vinylpyridine.

[0052] Furthermore, the molar ratio of the branched diene to the vinylpyridine is (2~6):1.

[0053] Typical, but not limiting, molar ratios of branched dienes to vinylpyridine can be, for example, 2:1, 3:1, 4:1, 5:1, or 6:1, or any ratio within the range of (2 to 6):1.

[0054] And / or, the amount of the dithiol compound is 0.8 to 1.2 times the mass of the copolymer.

[0055] Typical, but not limiting, molar ratios of branched dienes to vinylpyridine can be, for example, 2:1, 3:1, 4:1, 5:1, or 6:1, or any ratio within the range of (2 to 6):1.

[0056] A second aspect of the present invention provides a method for preparing the aforementioned dithiol-modified copolymer, comprising the following steps:

[0057] A. After adding a redox initiating emulsion to the reaction vessel, a protective gas is introduced, followed by the addition of a branched diene, vinylpyridine, and cumene hydroperoxide to carry out a copolymerization reaction to obtain a copolymer.

[0058] B. Add the copolymer, dithiol compound, and initiator to toluene to carry out an addition reaction to obtain the dithiol-modified copolymer.

[0059] The preparation method provided by this invention first uses branched dienes and vinylpyridine as monomers to obtain a copolymer containing double bonds through emulsion polymerization in a redox-initiated emulsion. Subsequently, the copolymer and a dithiol compound are introduced with carboxyl and thiol groups via a mercapto-olefin click reaction to obtain the target product. This preparation method has continuous process steps, is easy to control, and is suitable for large-scale industrial production.

[0060] Furthermore, the redox-initiating emulsion includes disodium ethylenediaminetetraacetate, emulsifier, ferrous salt, reducing agent, dispersant, and water.

[0061] And / or, the concentration of the disodium ethylenediaminetetraacetate is 0.01~0.05wt%.

[0062] Typical, but not limiting, concentrations of disodium ethylenediaminetetraacetate can be, for example, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, or 0.05 wt%, or any value in the range of 0.01 to 0.05 wt%.

[0063] And / or, the concentration of the emulsifier is 2-4 wt%.

[0064] Typical, but not limiting, emulsifier concentrations can be, for example, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, or 4 wt%, or any value in the range of 2 to 4 wt%.

[0065] And / or, the concentration of the ferrous salt is 0.001~0.01wt%.

[0066] Typical, but not limiting, ferrous salt concentrations can be, for example, 0.001 wt%, 0.002 wt%, 0.004 wt%, 0.006 wt%, 0.008 wt%, or 0.01 wt%, or any value in the range of 0.001 to 0.01 wt%.

[0067] And / or, the concentration of the reducing agent is 0.01~0.05wt%.

[0068] Typical, but not limiting, the concentration of the reducing agent can be, for example, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, or 0.05 wt%, or any value in the range of 0.01 to 0.05 wt%.

[0069] And / or, the concentration of the dispersant is 0.01~0.05wt%.

[0070] Typical, but not limiting, dispersant concentrations can be, for example, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, or 0.05 wt%, or any value in the range of 0.01 to 0.05 wt%.

[0071] Furthermore, the emulsifier includes at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl xylene sulfonate, and disodium polyoxyethylene ether sulfosuccinate.

[0072] And / or, the ferrous salt includes at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous carbonate, and ferrous oxalate.

[0073] And / or, the reducing agent includes at least one of sodium formaldehyde sulfoxylate, sodium dithionite, ascorbic acid, and sodium bisulfite.

[0074] And / or, the dispersant includes at least one of sodium pyrophosphate, sodium hexametaphosphate, and sodium tripolyphosphate.

[0075] Further, in step A, the molar ratio of the branched diene to the vinylpyridine is (2~6):1.

[0076] Typically, but not limitingly, in step A, the molar ratio of the branched diene to vinylpyridine can be, for example, 2:1, 3:1, 4:1, 5:1 or 6:1, or any ratio in the range of (2 to 6):1.

[0077] And / or, the redox-initiating emulsion is 5 to 5.5 times the mass of the branched diene.

[0078] Typical, but not limiting, amounts of redox-initiated emulsions can be, for example, 5, 5.1, 5.2, 5.3, 5.4, or 5.5 times the mass of the branched diene, or any multiple within the range of 5 to 5.5 times.

[0079] And / or, the amount of cumene hydroperoxide used is 0.05 to 0.09% of the mass of the branched diene.

[0080] Typical, but not limiting, amounts of cumene hydroperoxide can be, for example, 0.05%, 0.06%, 0.07%, 0.08%, or 0.09% of the mass of the branched diene, or any value in the range of 0.05% to 0.09%.

[0081] And / or, the copolymerization reaction is carried out at a temperature of 5~15℃ for a time of 16~32h.

[0082] Typical, but not limiting, the temperature of the copolymerization reaction can be, for example, 5 °C, 7 °C, 9 °C, 11 °C, 13 °C or 15 °C, or any temperature in the range of 5 to 15 °C; the reaction time can be, for example, 16 h, 20 h, 24 h, 28 h or 32 h, or any duration in the range of 16 to 32 h.

[0083] And / or, step A further includes a process of demulsifying, washing with saturated sodium chloride aqueous solution, and drying after the copolymerization reaction is completed to obtain the copolymer.

[0084] And / or, in step B, the amount of the dithiol compound added is 0.8 to 1.2 times the mass of the copolymer.

[0085] Typically, but not limitingly, in step B, the amount of dithiol compound added can be, for example, 0.8, 0.9, 1.0, 1.1, or 1.2 times the mass of the copolymer, or any multiple in the range of 0.8 to 1.2 times.

[0086] And / or, in step B, the initiator includes azobisisobutyronitrile (AIBN).

[0087] And / or, in step B, the amount of the initiator is 2 to 6% of the mass of the copolymer.

[0088] Typically, but not limitingly, in step B, the amount of initiator can be, for example, 2%, 3%, 4%, 5% or 6% of the copolymer mass, or any value in the range of 2 to 6%.

[0089] And / or, in step B, the temperature of the addition reaction is 50~60°C.

[0090] Typically, but not limitingly, in step B, the temperature of the addition reaction can be, for example, 50 °C, 52 °C, 54 °C, 56 °C, 58 °C, or 60 °C, or any temperature in the range of 50 to 60 °C.

[0091] And / or, in step B, after the addition reaction is completed, the process further includes product separation and vacuum drying.

[0092] The vacuum drying temperature is 45°C.

[0093] The third aspect of this invention provides the application of the aforementioned dithiol-modified copolymer as a binder for the positive electrode of a lithium battery.

[0094] This invention utilizes a dithiol-modified copolymer as a binder for the positive electrode of lithium batteries, leveraging its synergistic design of a "thiol-pyridine-flexible framework" to achieve interface strengthening and stress buffering: the thiol groups (-SH) and the S in the sulfide electrolyte... 2- Stable chemical bonds are formed through Lewis acid-base interactions, firmly anchoring electrolyte particles; pyridine nitrogen reacts with Ni on the ternary cathode surface. 2+ / Co 3+ Coordination enhances the bonding force between the binder and the cathode; the flexible framework dynamically adapts to changes in cathode volume and maintains interface integrity, thereby simultaneously completing electrolyte fixation, cathode coordination, and stress buffering, significantly improving the cycle stability of the composite electrode.

[0095] Furthermore, the lithium battery includes a sulfide all-solid-state lithium-ion battery.

[0096] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0097] Example 1

[0098] This embodiment provides a dithiol-modified copolymer, the preparation process of which is as follows:

[0099] 1. Weigh 0.09g of disodium ethylenediaminetetraacetate, 12g of sodium dodecyl sulfate, 0.03g of ferrous sulfate, 0.1g of sodium formaldehyde sulfoxylate, and 0.1g of sodium pyrophosphate decahydrate, and dissolve them in 400g of water to obtain a redox-initiated emulsion.

[0100] 2. Add the redox initiation emulsion to the flask, replace the nitrogen gas three times, lower the temperature to 10℃, add 80g of isoprene, 40g of 4-vinylpyridine, and 0.07g of cumene hydroperoxide to start the polymerization reaction. After 20 hours, demulsify with saturated sodium chloride aqueous solution, wash with water, and dry to obtain the copolymer.

[0101] 3. Take 5g of copolymer, 0.2g of azobisisobutyronitrile and 5g of 1,2-ethanedithiol and dissolve them in 100g of toluene solvent. Heat to 55℃ to trigger the selective addition of mercapto groups to the isoprene double bond. Then, vacuum dry at 45℃ to obtain the dithiol modified copolymer.

[0102] Example 2

[0103] This embodiment provides a dithiol-modified copolymer, the preparation process of which is as follows:

[0104] 1. Weigh 0.09g of disodium ethylenediaminetetraacetate, 12g of sodium dodecyl sulfate, 0.02g of ferrous sulfate, 0.3g of sodium formaldehyde sulfoxylate, and 0.1g of sodium pyrophosphate decahydrate, and dissolve them in 400g of water to obtain a redox-initiated emulsion.

[0105] 2. Add the redox initiation emulsion to the flask, replace the nitrogen gas three times, lower the temperature to 10℃, add 90g of isoprene, 30g of 4-vinylpyridine, and 0.05g of cumene hydroperoxide to start the polymerization reaction. After 20 hours, demulsify with saturated sodium chloride aqueous solution, wash with water, and dry to obtain the copolymer.

[0106] 3. Take 5g of copolymer, 0.2g of azobisisobutyronitrile and 5g of 1,6-hexanedithiol and dissolve them in 100g of toluene solvent. Heat to 55℃ to trigger the selective addition of mercapto groups to the isoprene double bond. Then, vacuum dry at 45℃ to obtain the dithiol modified copolymer.

[0107] Example 3

[0108] This embodiment provides a dithiol-modified copolymer, the preparation process of which is as follows:

[0109] 1. Weigh 0.09g of disodium ethylenediaminetetraacetate, 12g of sodium dodecyl sulfate, 0.03g of ferrous sulfate, 0.1g of sodium formaldehyde sulfoxylate, and 0.1g of sodium pyrophosphate decahydrate, and dissolve them in 400g of water to obtain a redox-initiated emulsion.

[0110] 2. Add the redox initiation emulsion to the flask, replace the nitrogen gas three times, lower the temperature to 10℃, add 80g of isoprene, 40g of 4-vinylpyridine, and 0.07g of cumene hydroperoxide to start the polymerization reaction. After 20 hours, demulsify with saturated sodium chloride aqueous solution, wash with water, and dry to obtain the copolymer.

[0111] 3. Take 5g of copolymer, 0.2g of azobisisobutyronitrile and 5g of polyethylene glycol dithiol (average molecular weight 1,000) and dissolve them in 100g of toluene solvent. Heat to 55℃ to trigger the selective addition of mercapto groups to the isoprene double bond. Then, vacuum dry at 45℃ to obtain the dithiol modified copolymer.

[0112] Example 4

[0113] This embodiment provides a dithiol-modified copolymer, the preparation process of which is as follows:

[0114] 1. Weigh 0.09g of disodium ethylenediaminetetraacetate, 12g of sodium dodecyl sulfate, 0.03g of ferrous sulfate, 0.1g of sodium formaldehyde sulfoxylate, and 0.1g of sodium pyrophosphate decahydrate, and dissolve them in 400g of water to obtain a redox-initiated emulsion.

[0115] 2. Add the redox initiation emulsion to the flask, replace the nitrogen gas three times, lower the temperature to 10℃, add 80g of isoprene, 40g of 4-vinylpyridine, and 0.07g of cumene hydroperoxide to start the polymerization reaction. After 20 hours, demulsify with saturated sodium chloride aqueous solution, wash with water, and dry to obtain the copolymer.

[0116] 3. Take 5g of copolymer, 0.2g of azobisisobutyronitrile and 5g of 1,4-butanedithiol and dissolve them in 100g of toluene solvent. Heat to 55℃ to trigger the selective addition of mercapto to the isoprene double bond. Then, vacuum dry at 45℃ to obtain the dithiol modified copolymer.

[0117] Example 5

[0118] This embodiment provides a dithiol-modified copolymer, the preparation process of which is as follows:

[0119] 1. Same as step 3 in Example 3.

[0120] 2. Add the redox initiating emulsion to the flask, replace the nitrogen gas three times, lower the temperature to 10℃, add 96.45g of 3-methyl-1,3-pentadiene, 40g of 2-vinylpyridine, and 0.07g of cumene hydroperoxide to start the polymerization reaction. After 20 hours, demulsify with saturated sodium chloride aqueous solution, wash with water, and dry to obtain the copolymer.

[0121] 3. Same as step 3 in Example 3.

[0122] Example 6

[0123] This embodiment provides a dithiol-modified copolymer, the preparation process of which is as follows:

[0124] 1. Same as step 3 in Example 3.

[0125] 2. Add the redox initiating emulsion to the flask, replace the nitrogen gas three times, lower the temperature to 10℃, add 162.17g of 3,7-dimethyl-1,5-octadiene, 40g of 4-vinylpyridine, and 0.07g of cumene hydroperoxide to start the polymerization reaction. After 20 hours, demulsify with saturated sodium chloride aqueous solution, wash with water, and dry to obtain the copolymer.

[0126] 3. Take 5g of copolymer, 0.2g of azobisisobutyronitrile and 5g of polyethylene glycol dithiol (average molecular weight 1,000) and dissolve them in 100g of toluene solvent. Heat to 55℃ to trigger the selective addition of mercapto groups to the isoprene double bond. Then, vacuum dry at 45℃ to obtain the dithiol modified copolymer.

[0127] Example 7

[0128] This embodiment provides a dithiol-modified copolymer, the preparation process of which is as follows:

[0129] 1. Same as step 3 in Example 3.

[0130] 2. Same as step 3 in Example 3.

[0131] 3. Take 5g of copolymer, 0.2g of azobisisobutyronitrile and 4g of polyethylene glycol dithiol (average molecular weight 1,000) and dissolve them in 100g of toluene solvent. Heat to 55℃ to trigger the selective addition of mercapto groups to the isoprene double bond. Then, vacuum dry at 45℃ to obtain the dithiol modified copolymer.

[0132] Example 8

[0133] This embodiment provides a dithiol-modified copolymer, the preparation process of which is as follows:

[0134] 1. Same as step 3 in Example 3.

[0135] 2. Same as step 3 in Example 3.

[0136] 3. Take 5g of copolymer, 0.2g of azobisisobutyronitrile and 6g of polyethylene glycol dithiol (average molecular weight 1,000) and dissolve them in 100g of toluene solvent. Heat to 55℃ to trigger the selective addition of mercapto groups to the isoprene double bond. Then, vacuum dry at 45℃ to obtain the dithiol modified copolymer.

[0137] Example 9

[0138] This embodiment provides a dithiol-modified copolymer, the preparation process of which is as follows:

[0139] 1. Same as step 3 in Example 3.

[0140] 2. Same as step 3 in Example 3.

[0141] 3. Take 5g of copolymer, 0.2g of azobisisobutyronitrile and 7g of polyethylene glycol dithiol (average molecular weight 1,000) and dissolve them in 100g of toluene solvent. Heat to 55℃ to trigger the selective addition of mercapto groups to the isoprene double bond. Then, vacuum dry at 45℃ to obtain the dithiol modified copolymer.

[0142] Comparative Example 1

[0143] This comparative example provides a dithiol-modified polyisoprene, and the preparation process is as follows:

[0144] 1. Same as step 3 in Example 3.

[0145] 2. Add the redox initiation emulsion to the flask, replace the nitrogen gas three times, lower the temperature to 10℃, add 80g of isoprene and 0.07g of cumene hydroperoxide, and start the polymerization reaction. After 20 hours, demulsify with saturated sodium chloride aqueous solution, wash with water, and dry to obtain the copolymer.

[0146] 3. Same as step 3 in Example 3.

[0147] Comparative Example 2

[0148] This comparative example provides a copolymer that, unlike Example 3, does not perform step 3; the copolymer obtained in step 2 is the final product.

[0149] Comparative Example 3

[0150] This comparative example provides an adhesive made of styrene-butadiene rubber, which is commercially available.

[0151] Comparative Example 4

[0152] This comparative example provides an adhesive made of ethyl cellulose, which is commercially available.

[0153] Test Example 1

[0154] The substances obtained in the examples and comparative examples were used as adhesives for bonding ability testing. Peel strength was used to reflect the bonding ability.

[0155] Peel strength test method: Dissolve the adhesive in toluene, add lithium nickel cobalt manganese oxide, sulfide solid electrolyte, adhesive and conductive agent in a ratio of 70:24:5:1 to form a slurry, coat it with copper foil and vacuum dry it at 80℃ to form a strip sample with a length of 400mm and a width of 10mm. A strip of transparent tape of a certain width is horizontally attached to the bottom and end face of an ungraded steel ruler. Double-sided tape is then attached to the transparent tape with the same length as the width of the transparent tape and centered. Finally, the test sample is attached to the double-sided tape with the end face flush. The sample is rolled back and forth on the electrode surface with a pressure roller more than 3 times. The unattached end of the electrode of the test sample is folded 180 degrees and clamped on the upper clamp of a tensile testing machine. The electrode is peeled at a tensile speed of 100mm / min. The peel strength test results are read and recorded in Table 1.

[0156] Table 1

[0157]

[0158] Test Example 2

[0159] All-solid-state lithium batteries were prepared according to the following method:

[0160] (1) Positive electrode: Aluminum foil with a diameter of 10 mm and a thickness of 12 μm is used as the positive electrode current collector. The copolymer obtained in the examples and comparative examples (as the binder) is dissolved in toluene. The slurry is formed by using toluene as the solvent according to the ratio of ternary positive electrode: binder: LGPS electrolyte: conductive agent 78:2:1.9:0.1 and coated on the aluminum foil. It is then vacuum dried at 80°C to form the electrode.

[0161] (2) Negative electrode: A copper foil with a diameter of 10 mm and a thickness of 12 μm is used as the negative electrode current collector; PVDF (as a binder) is dissolved in toluene, and carbon, sulfide solid electrolyte, binder and conductive agent are added in a ratio of 50:40:5:5 to form a slurry, which is coated on the copper foil and then vacuum dried at 80°C to form the slurry.

[0162] (3) Electrolyte: Li6PS5Cl powder (D50=5μm, ionic conductivity 10.32mS / cm) and PVDF are mixed in toluene at a ratio of 98:2 to form a slurry, which is then directly coated onto the negative electrode and vacuum dried at 80℃ to form the slurry.

[0163] The negative electrode sheet coated with electrolyte and the positive electrode sheet are placed in a pressure battery mold with an inner diameter of 10 mm. The solid electrolyte powder is pressed for 2 minutes at 100 MPa on a tablet press to form a sheet, and then assembled to obtain an all-solid-state lithium battery.

[0164] The all-solid-state lithium battery prepared above was subjected to electrical performance testing at a stacking voltage of 20 mPa, specifically including charge and discharge capacity testing at a rate of 0.2C, and the data are recorded in Table 2.

[0165] Table 2

[0166]

[0167] As can be seen from Table 2, the capacity retention rate of the examples is generally better than that of the comparative examples, which proves that the synthesized bifunctional groups of the binder contribute to capacity retention.

[0168] Test Example 3

[0169] The all-solid-state lithium batteries obtained by assembling the binders of Example 3 and Comparative Example 4 were assembled according to the method in Test Example 2, using a visible light-transmitting quartz mold. After 400 charge-discharge cycles, the expansion of the in-situ optical test electrode was measured.

[0170] Figure 1 This is an in-situ optical test photograph of the all-solid-state lithium battery prepared in Example 3 after 400 charge-discharge cycles; Figure 2 This is an in-situ optical test image of the all-solid-state lithium battery prepared in Comparative Example 4 after 400 charge-discharge cycles. Figure 1 and Figure 2 In both cases, the electrodes are placed with the negative electrode on top and the positive electrode on the bottom. It can be clearly seen that the cracks caused by the expansion of the positive electrode in Comparative Example 4 are larger than those in Example 3, which is also the main reason for its capacity decay.

[0171] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A dithiol-modified copolymer, characterized in that, The copolymer is a branched diene-vinylpyridine copolymer, obtained by copolymerizing a branched diene and vinylpyridine; The copolymer was then reacted with a dithiol compound to introduce thiol groups, resulting in a dithiol-modified copolymer.

2. The dithiol-modified copolymer according to claim 1, characterized in that, The branched diene has 5 to 10 carbon atoms; And / or, the branched diene includes isoprene, 3-methyl-1,3-pentadiene, 2-methyl-1,5-hexadiene, 3-methyl-1,5-hexadiene, 3-methyl-1,5-heptadiene, 4-methyl-1,5-heptadiene, or 3,7-dimethyl-1,5-octadiene.

3. The dithiol-modified copolymer according to claim 1, characterized in that, Dithiol compounds include 1,2-ethanedithiol, 1,6-hexanedithiol, polyethylene glycol dithiol, and 1,4-butanedithiol; And / or, the vinylpyridine includes 2-vinylpyridine or 4-vinylpyridine.

4. The dithiol-modified copolymer according to any one of claims 1 to 3, characterized in that, The molar ratio of the branched diene to the vinylpyridine is (2~6):1; And / or, the amount of the dithiol compound is 0.8 to 1.2 times the mass of the copolymer.

5. A method for preparing the dithiol-modified copolymer according to any one of claims 1 to 4, characterized in that, Includes the following steps: A. After adding a redox initiating emulsion to the reaction vessel, a protective gas is introduced, followed by the addition of a branched diene, vinylpyridine, and cumene hydroperoxide to carry out a copolymerization reaction to obtain a copolymer. B. Add the copolymer, dithiol compound, and initiator to toluene to carry out an addition reaction to obtain the dithiol compound modified copolymer.

6. The preparation method according to claim 5, characterized in that, The redox-initiated emulsion includes disodium ethylenediaminetetraacetate, emulsifier, ferrous salt, reducing agent, dispersant and water; And / or, the concentration of the disodium ethylenediaminetetraacetate is 0.01~0.05 wt%; And / or, the concentration of the emulsifier is 2-4 wt%; And / or, the concentration of the ferrous salt is 0.001~0.01 wt%; And / or, the concentration of the reducing agent is 0.01~0.05 wt%; And / or, the concentration of the dispersant is 0.01~0.05wt%.

7. The preparation method according to claim 6, characterized in that, The emulsifier includes at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl xylene sulfonate, and disodium polyoxyethylene ether sulfosuccinate. And / or, the ferrous salt includes at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous carbonate, and ferrous oxalate; And / or, the reducing agent includes at least one of sodium formaldehyde sulfoxylate, sodium dithionite, ascorbic acid, and sodium bisulfite; And / or, the dispersant includes at least one of sodium pyrophosphate, sodium hexametaphosphate, and sodium tripolyphosphate.

8. The preparation method according to claim 5, characterized in that, In step A, the molar ratio of the branched diene to the vinylpyridine is (2~6):1; And / or, the redox-initiating emulsion is 5 to 5.5 times the mass of the branched diene; And / or, the amount of cumene hydroperoxide used is 0.05~0.09% of the mass of the branched diene; And / or, the copolymerization reaction is carried out at a temperature of 5~15℃ for a time of 16~32h; And / or, in step B, the amount of the dithiol compound added is 0.8 to 1.2 times the mass of the copolymer; And / or, in step B, the initiator includes azobisisobutyronitrile; And / or, in step B, the amount of the initiator is 2-6% of the mass of the copolymer; And / or, in step B, the temperature of the addition reaction is 50~60°C.

9. The application of the dithiol-modified copolymer according to any one of claims 1 to 4 as a binder for the positive electrode of a lithium battery.

10. The application according to claim 9, characterized in that, The lithium battery includes a sulfide all-solid-state lithium-ion battery.

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