Reversible cross-linked polymer, preparation method thereof and application of reversible cross-linked polymer in battery

Abstract

The invention discloses a reversible cross-linked polymer, a preparation method thereof and an application of the reversible cross-linked polymer in a battery. The reversible cross-linked polymer contains a silane coupling group containing an imino group. The reversible cross-linked polymer provided by the invention has a self-healing capability, can reform a dynamic reversible bond at a crack interface when being damaged by external force, promotes the repair of the structural crack of the material, can repair the crack caused by expansion and shrinkage of a high-volume change negative electrode in the charging and discharging process, reduces the side reaction of the interface, and improves the performance of the battery. The stability of the high-energy-density lithium battery can be improved, the service life of the battery is prolonged, and the safety is improved. In addition, the cross-linked structure can improve the mechanical strength, and is also very beneficial to inhibition of non-uniform deposition of lithium and generation of lithium dendrites.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a reversible cross-linked polymer, a preparation method thereof, and an application thereof in a battery. Background Art

[0002] With the continuous development of the new energy industry, traditional lithium-ion batteries are difficult to meet the growing demands of people for high-power electric vehicles and other large-scale energy storage fields, which has promoted the research and development of new electrode active materials by scientific researchers. The theoretical specific capacity of a silicon negative electrode is as high as 4200 mAh / g, which is 10 times that of a traditional graphite negative electrode. It can effectively improve the energy density of a lithium-ion battery. Moreover, silicon is rich in reserves in the earth's crust, with low cost and environmental friendliness; the intercalation / deintercalation potential is moderate (~0.4V), and the safety performance is better. It is an ideal negative electrode material for lithium-ion batteries. However, silicon has a relatively large volume expansion during the charge and discharge process, and problems such as pulverization and exfoliation of the active material may occur during the cycling process. At the same time, the electrolyte is continuously consumed to generate a new interface film, which will cause rapid attenuation of the battery capacity and poor cycle stability. How to effectively suppress the volume expansion of the silicon negative electrode during the cycling process is the main problem that promotes its commercialization.

[0003] The binder in a lithium-ion battery plays an important role in maintaining the integrity of the electrode structure during the charge and discharge process. Selecting a suitable binder with good toughness and adhesion will be beneficial to suppressing the volume expansion effect of the silicon negative electrode, thereby ensuring effective contact between the silicon negative electrode and the conductive additive during the charge and discharge process and maintaining the integrity of the silicon negative electrode during the lithium intercalation / deintercalation process. Commonly used battery binders include polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), SBR, sodium alginate, guar gum, carrageenan, gum arabic, chitosan, PI, etc. Among them, polyvinylidene fluoride (PVDF) is prone to crystallization (crystallinity is about 50%), resulting in low conductivity of the electrode; binders such as styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA) do not play a good role in improving the suppression of volume expansion of the positive and negative electrodes.

[0004] Therefore, it is urgent to develop new materials to effectively suppress the volume expansion of the silicon negative electrode during the cycling process to meet the growing demands. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems existing in the prior art, such as easy expansion and cracking of the positive and negative electrodes of the battery, poor cycle stability, and short service life, and to provide a reversible cross-linked polymer, a preparation method thereof, and an application thereof in a battery negative electrode. This reversible cross-linked polymer has bonding performance and self-healing performance, plays a role in suppressing expansion during the cycling process, enhances the interaction force between the conductive agent and the silicon negative electrode, improves the cracking of the silicon negative electrode, and improves the cycle performance.

[0006] To achieve the above object, a first aspect of the present invention provides a reversible cross-linked polymer, and the reversible cross-linked polymer contains a silane coupling group containing an imino group.

[0007] A second aspect of the present invention provides a method for preparing a reversible cross-linked polymer, and the preparation method includes the following steps:

[0008] (1) Under polymerization reaction conditions, monomer A is polymerized with optional monomer B and optional monomer C to obtain a first polymer; wherein, the monomer A is a monomer with a thiolactone and a double bond; the monomer B is a monomer for increasing water solubility; the monomer C is a monomer containing a double bond; or, a compound E containing a thiolactone structure is subjected to a first reaction with a polymer F containing an acid anhydride or a carboxyl group to obtain a second polymer;

[0009] (2) The first polymer or the second polymer is subjected to a second reaction with an amine-containing compound to obtain a reversible cross-linked polymer.

[0010] A third aspect of the present invention provides a reversible cross-linked polymer obtained by the preparation method described in the second aspect above.

[0011] A fourth aspect of the present invention provides a negative electrode plate with a self-healing function, and the negative electrode plate includes the reversible cross-linked polymer described in any one of the first aspect or the third aspect above and a negative electrode active lithium storage material; wherein, there is a chemical bond interaction of ~Si-R-NH-C(=O)-~ between the reversible cross-linked polymer and the negative electrode active lithium storage material.

[0012] A fifth aspect of the present invention provides a battery, and the battery includes the negative electrode plate, a positive electrode plate, and a separator described in the fourth aspect above.

[0013] Through the above technical solutions, the beneficial technical effects obtained by the present invention are as follows:

[0014] (1) The reversible cross-linked polymer provided by the present invention has self-healing ability. When damaged by external forces, dynamic reversible bonds can be re-formed at the interface of the crack, promoting the repair of the structural crack of the material, being able to repair the cracks caused by the expansion and contraction of the high-volume-change negative electrode during charge and discharge, reducing interface side reactions, improving the stability of high-energy-density lithium batteries, extending the battery life, and enhancing safety. In addition, the chemical cross-linked structure can improve the mechanical strength, which is also very beneficial for suppressing the uneven deposition of lithium and the generation of lithium dendrites.

[0015] (2) The reversible cross-linked polymer of the present invention utilizes the dual self-healing functions of hydrogen bonds and disulfide bonds, and can form a dual binding force with the silicon negative electrode through chemical bonds and van der Waals forces, which can improve the cracking and swelling problems of the silicon negative electrode during cycling. In this system, an amine containing a disulfide bond can also be combined with a polymer containing a sulfur lactone for reaction. Through the additional introduced disulfide bonds and hydrogen bond interactions, the self-healing function is further enhanced, and the swelling of the silicon negative electrode during use is further inhibited.

[0016] (3) The method of the present invention introduces a material containing a sulfur lactone into the negative electrode by in-situ curing a monomer containing a sulfur lactone and other comonomers, and / or by combining a small molecule containing a sulfur lactone with a polymer. By adding a compound containing an amino group and an amino-containing silane coupling agent, the amino group undergoes a ring-opening reaction with the sulfur lactone, realizing the chemical bonding of the polymer with the active material in the silicon negative electrode while generating a mercapto compound. Subsequently, the mercapto groups will react with each other during the drying process of the electrode sheet to form disulfide bonds with self-healing ability.

[0017] (4) The reversible cross-linked polymer of the present invention helps to form sulfur-rich active bonds during charge and discharge, has a SEI with good thermal stability, can reduce the thickness of the SEI, reduce the battery impedance, and improve the cycling performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figures 1-3 is the infrared absorption spectrum of polymer A0 and polymer A1 prepared in the test example of the present invention;

[0019] Figure 4 is a photo of the self-healing of the resin sheet of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0021] "Optional" means that the monomer can be used or not used during the use process.

[0022] The first aspect of the present invention provides a reversible cross-linked polymer, and the reversible cross-linked polymer contains a silane coupling group containing an imino group.

[0023] In some embodiments of the present invention, the reversible cross-linked polymer further contains a structure formed by the ring-opening of a sulfur lactone.

[0024] In some embodiments of the present invention, the reversible cross-linked polymer contains amide bonds and disulfide bonds.

[0025] In the present invention, the reaction of thiolactone with an amino group to open the ring can generate amide bonds and mercapto groups, and the reaction between mercapto groups generates disulfide bonds.

[0026] In some embodiments of the present invention, the reversible cross-linked polymer contains the structure shown in Formula I:

[0027]

[0028] In Formula I, represents a polymer chain.

[0029] In some embodiments of the present invention, the reversible cross-linked polymer contains the structure shown in Formula II:

[0030]

[0031] In Formula II, R1 and R2 are each independently selected from the group consisting of an aliphatic alkylene group, an aromatic alkylene group, or a group composed of a divalent organic chain structure containing a heteroatom; represents a polymer chain; the -SH group can continue to react to form a disulfide bond.

[0032] In some embodiments of the present invention, R1 and R2 are each independently selected from the group consisting of methylene, ethylene, propylene, isopropylidene, p-phenylene, m-phenylene, o-phenylene, butyric acid group and groups that make up the group.

[0033] In the present invention, the reversible cross-linked polymer can have a chemical bond interaction with the negative electrode active material, which has a stronger interaction force than that between a conventional binder and the active material. At the same time, it is rich in polar groups such as amide bonds and amino groups inside, which can also enhance the interaction force between the binder and the current collector, providing good adhesion performance. Copolymerizing monomers with a low glass transition temperature will improve the brittleness of the reversible cross-linked polymer and provide good flexibility for the electrode sheet. At the same time, the hydrogen bond interaction between amide bonds, and the disulfide bond and hydrogen bond interaction endow the reversible cross-linked polymer with certain self-healing ability, and the chemical cross-linking of the whole system is beneficial to improving the mechanical strength.

[0034] The reversible cross-linked polymer of the present invention can help the negative electrode form a thinner and more stable SEI. At the same time, it has good adhesion and self-healing functions, and can improve the cycling performance of the silicon / silicon oxide negative electrode.

[0035] In some embodiments of the present invention, the molar ratio of the disulfide bond in the structure of Formula I to the disulfide bond in the structure of Formula II is 1:0 - 1; preferably 1:0.3 - 1.

[0036] In some embodiments of the present invention, the reversible cross-linked polymer further contains the structure shown in Formula III:

[0037]

[0038] In Formula III, R6 is an alkylene group; Si is coupled to the surface of the active material of the active substance.

[0039] In the present invention, the structure shown in Formula III is a product formed by the reaction of an amine-containing silane with the thiolactone functional group on the polymer, and the reaction of a silane coupling agent and the negative electrode active material.

[0040] In the present invention, the active material includes, but is not limited to, a negative electrode. For example, a silicon-containing negative electrode, a silicon-carbon negative electrode, a negative electrode containing silicon monoxide, a silicon negative electrode, which can be a composite of silicon monoxide and graphite, or a pure graphite negative electrode; preferably a negative electrode containing silicon or silicon monoxide.

[0041] In the present invention, the structure shown in Formula III can improve the adhesion performance of the reversible cross-linked polymer. For example, the interaction between the structure shown in Formula III and the negative electrode particles can better inhibit the expansion of the silicon negative electrode during use.

[0042] The reversible cross-linked polymer of the present invention utilizes the dual self-healing functions of hydrogen bonds and disulfide bonds, and can form a dual binding force with the silicon negative electrode through chemical bond binding and physical hydrogen bond binding, which can improve the cracking and expansion problems of the silicon negative electrode during cycling. In this system, an amine containing a disulfide bond can also be combined with a polymer containing a thiolactone to react, and through the additional disulfide bonds and hydrogen bond interactions, the self-healing function can be further enhanced, and the expansion of the silicon negative electrode during use can be further inhibited.

[0043] The second aspect of the present invention provides a method for preparing a reversible cross-linked polymer, and the preparation method includes the following steps:

[0044] (1) Under polymerization reaction conditions, polymerize monomer A, optional monomer B, and optional monomer C to obtain a first polymer; wherein, monomer A is a monomer with a thiolactone and a double bond; monomer B is a monomer for increasing water solubility; monomer C is a monomer containing a double bond; or, perform a first reaction on a compound E containing a thiolactone structure and a polymer F containing an anhydride or a carboxyl group to obtain a second polymer;

[0045] (2) Perform a second reaction on the first polymer or the second polymer with an amine-containing compound to obtain a reversible cross-linked polymer.

[0046] According to the present invention, "optional monomer B and optional monomer C" means that monomer B and monomer C can be added or not added during the reaction, can be added together, or can be added independently.

[0047] In some embodiments of the present invention, the monomer A has the structure shown in formula (1),

[0048]

[0049] In formula (1), R3 is a substituted group containing an unsaturated bond.

[0050] In some embodiments of the present invention, the monomer A is selected from at least one of the compounds having the structures shown in formulas A-1 to A-15;

[0051]

[0052]

[0053] wherein, R is a divalent hydrocarbon group with or without an alkyl side chain containing 1-9 carbon atoms; Z1 is hydrogen or methyl, and Z2 is a saturated alkylene group with or without an alkyl side chain containing 1-9 carbon atoms.

[0054] In some embodiments of the present invention, the monomer B is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, 2-(methacryloyloxy)ethyl succinate, maleic anhydride, carboxybetaine methacrylate, N-(3-aminopropyl)methacrylic acid, acrylamide, and N-(2-hydroxyethyl)acrylamide;

[0055] In the present invention, the monomer C is selected from monomers whose glass transition temperature of the polymer formed by self-polymerization is lower than 25 °C or comonomers that make the polymer in a rubber state at room temperature.

[0056] In some preferred embodiments of the present invention, the monomer C is selected from one or more of ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) methyl ether methacrylate, n-butyl methacrylate, isobutyl acrylate, lauryl acrylate, lauryl methacrylate, n-octyl acrylate, n-octyl methacrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate.

[0057] In some embodiments of the present invention, the compound E containing a thiolactone structure is cysteine thiolactone.

[0058] In some embodiments of the present invention, the polymer F containing an anhydride or a carboxyl group is selected from one or more of methyl vinyl ether-maleic anhydride copolymer, ethylene maleic anhydride copolymer, polyacrylic acid, and polyacrylic acid copolymer.

[0059] In the present invention, the molar ratio of the monomer A, monomer B and monomer C is 0.05 - 0.5:0.05 - 0.6:0 - 0.3.

[0060] In the present invention, monomer B is a monomer for improving flexibility. If monomer A itself has flexibility, monomer B may not be added; monomer C is a monomer for increasing water solubility. If monomer A itself has water solubility, monomer C may also not be added.

[0061] In the present invention, the molar ratio of the compound E containing a thiolactone structure to the polymer F containing an acid anhydride or a carboxyl group is 1:1 - 2, preferably 1:1.

[0062] In some embodiments of the present invention, the amine-containing compound is selected from at least one of the compound G containing both a disulfide bond and an amine group, the amine compound H, and an amine-containing silane coupling agent.

[0063] In some preferred embodiments of the present invention, the compound G containing both a disulfide bond and an amine group is selected from one or more of diaminodithiobenzene, 2,2'-dithiobis(diethylamine), 4,4'-dithiobis(2-aminobutyric acid), 3,3'-dithiobis(alanine), dithioformamidine, 2-(2-amino-5-methoxyphenyl)dithio-4-methoxyaniline, and the compound having the structure shown in formula G-1;

[0064]

[0065] In some preferred embodiments of the present invention, the amine compound H is selected from one or more of polyethyleneimine, ethylenediamine, propylenediamine, butylenediamine, 2,5-diaminopentanoic acid, and tris(2-aminoethyl)amine.

[0066] In the present invention, the amine group in the amine-containing silane coupling agent can be a primary amine group, a secondary amine group, or both a primary amine group and a secondary amine group.

[0067] In some embodiments of the present invention, the amine-containing silane coupling agent has the structure shown in formula (2):

[0068]

[0069] In formula (2), R4, R5 and R6 are each independently an alkoxy group or an alkyl group; R7 is a divalent alkylene group.

[0070] The reversible cross-linked polymer obtained by the method of the present invention has adhesion strength with the adherend; after adding a silane coupling agent containing an amino group, one end of the silane coupling agent is connected to the surface of the adherend (inorganic particles) through a chemical bond, and the other end is connected to the polymer through a chemical bond, so that the polymer and the adherend interact with each other through chemical bonds, further enhancing the adhesion strength between the polymer and the adherend.

[0071] In the present invention, the molar ratio of the first polymer based on thiolactone to the amino group in the amino group-containing compound is 1:0.5 - 1.

[0072] In some embodiments of the present invention, the molar ratio of the second polymer based on thiolactone to the amino group in the amino group-containing compound is 1:0.5 - 1.

[0073] In the present invention, the polymerization reaction is a radical polymerization. Preferably, the polymerization reaction conditions include: in the presence of an initiator, the temperature of the polymerization reaction is 45 - 80 °C; the time of the polymerization reaction is 1 - 24 h.

[0074] In the present invention, the initiator is selected from one or more of azobisisobutyronitrile, benzoyl peroxide, azobisisoheptonitrile, ammonium persulfate, and azobisisobutylimidazoline hydrochloride.

[0075] In the present invention, the first reaction is an amidation reaction, and the reaction conditions will vary depending on the type of catalyst. The common reaction conditions in the art can be used.

[0076] In some preferred embodiments, the conditions of the first reaction include: temperature 80 - 120 °C, time 3 - 20 h.

[0077] In the present invention, the second reaction is a cross-linking reaction, and the common reaction conditions in the art can be used.

[0078] In some preferred embodiments, the conditions of the second reaction include: temperature 80 - 140 °C, time 0.5 - 3 h.

[0079] The third aspect of the present invention provides a reversible cross-linked polymer prepared by the preparation method described in the second aspect above.

[0080] The reversible cross-linked polymer of the present invention can be used to prepare a negative electrode sheet, especially for preparing a silicon-containing negative electrode sheet.

[0081] The method of the present invention introduces a material containing thiolactone into the negative electrode by in-situ curing a monomer containing thiolactone and other comonomers, and / or by combining a small molecule containing thiolactone with a polymer. By adding a compound containing an amino group and an amino-functional silane coupling agent, the amino group reacts with the thiolactone to undergo a ring-opening reaction, achieving chemical bonding between the polymer and the active material in the silicon negative electrode while generating a mercapto compound. Subsequently, the mercapto groups react with each other during the drying process of the electrode sheet to form disulfide bonds with self-healing ability.

[0082] In the fourth aspect of the present invention, a negative electrode sheet with self-healing function is provided. The negative electrode sheet comprises the reversible cross-linked polymer described in any one of the foregoing first aspect or third aspect and a negative electrode active lithium storage material; wherein, there is a chemical bond interaction of ~Si-R-NH-C(=O)-~ between the reversible cross-linked polymer and the negative electrode active lithium storage material, and R is selected from divalent C1-C10 alkylene groups.

[0083] The reversible cross-linked polymer provided by the present invention has self-healing ability. When damaged by external force, dynamic reversible bonds can be re-formed at the interface of the crack, promoting the repair of the structural crack of the material, being able to repair the cracks caused by the expansion and contraction of the high volume change negative electrode during charge and discharge, reducing the interfacial side reactions, improving the stability of high energy density lithium batteries, extending the battery life, and enhancing the safety. In addition, the chemical cross-linking structure can improve the mechanical strength, which is also very beneficial for suppressing the uneven deposition of lithium and the generation of lithium dendrites.

[0084] The present invention provides a method for preparing a silicon negative electrode sheet, and the preparation method comprises the following steps:

[0085] S1. Under polymerization reaction conditions, polymerize monomer A with optional monomer B, optional monomer C, and optional monomer D to obtain a first polymer; wherein, monomer A is a monomer with a thiolactone and a double bond; monomer B is a monomer with a double bond and having a low Tg after polymerization; monomer C is a monomer for increasing water solubility; monomer D is a comonomer; or, carry out a first reaction on a compound E containing a thiolactone structure and a polymer F containing an anhydride or a carboxyl group to obtain a second polymer;

[0086] S2. Mix the first polymer or the second polymer, the negative electrode material, the conductive agent, and deionized water to obtain a mixture; then add a compound G containing a disulfide bond and an amino group or a compound H containing an amino group to the mixture to obtain an active material slurry;

[0087] S3. Coating the active material slurry on the negative electrode current collector, drying and carrying out a second reaction, and then through post-treatment to obtain the negative electrode sheet.

[0088] According to the present invention, "optional monomer B, optional monomer C, and optional monomer D" means that monomer B, monomer C, and monomer D can be added or not added during the reaction process, and can be added together or independently.

[0089] In step S1 of the present invention, the first reaction is an amidation reaction, and different types of catalysts will result in different reaction conditions.

[0090] In some embodiments of the present invention, the conditions of the first reaction include: temperature 80 - 120 °C, time 3 - 20 h.

[0091] In step S2 of the present invention, the negative electrode material includes but is not limited to: silicon-containing negative electrode, silicon-carbon negative electrode, silicon suboxide-containing, silicon negative electrode, which can be a composite of silicon suboxide and graphite, or a pure graphite negative electrode; preferably a negative electrode containing silicon or silicon suboxide.

[0092] In step S2 of the present invention, the conductive agent includes but is not limited to: conductive carbon black, carbon nanotubes, conductive graphite, graphene, etc.

[0093] In step S3 of the present invention, the second reaction is a crosslinking reaction that occurs during the drying process after coating, and the drying temperature is 60 - 140 °C, and the time is 0.5 - 3 h.

[0094] In the present invention, the negative electrode active material includes: small molecules with thiolactone and double bonds, negative electrode active material, conductive agent, and polymers or small molecules containing hydroxyl or amine groups; during the heating process, the double bonds polymerize to form a macromolecular binder, and the polymers or small molecules with amine groups react with the thiolactone on the polymer to obtain a crosslinked binder; among them, during the reaction process, the thiolactone ring opens to form a molecule containing a mercapto group, and the mercapto group is oxidized to form a disulfide bond during the process of baking to remove the solvent; the generated amide bond plays a role in hydrogen bond interaction.

[0095] In some embodiments of the present invention, the definitions of monomer A, monomer B, monomer C, monomer D, the compound E containing a thiolactone structure, the polymer F containing an acid anhydride or carboxyl group, the compound G containing a disulfide bond and an amine group, and the compound H containing an amine group are the same as those involved in the foregoing second aspect.

[0096] In some embodiments of the present invention, a silane coupling agent containing an amine group is further added to the mixture in step S2.

[0097] In some embodiments of the present invention, the silane coupling agent containing an amine group has a structure shown in formula (2):

[0098]

[0099] In formula (2), R4, R5, and R6 are each independently an alkoxy group or an alkyl group; R7 is a divalent alkylene group.

[0100] The reversible cross-linked polymer obtained by the method of the present invention has a bonding strength with the adherend; after adding a silane coupling agent containing an amino group, one end of the silane coupling agent is connected to the surface of the adherend (inorganic particles) through a chemical bond, and the other end is connected to the polymer through a chemical bond, so that the polymer and the adherend interact with each other through chemical bonds, further enhancing the bonding strength between the polymer and the adherend.

[0101] The fifth aspect of the present invention provides a battery, which includes the negative electrode sheet, the positive electrode sheet, and the separator described in the fourth aspect above.

[0102] In the present invention, the negative electrode sheet is preferably a silicon negative electrode sheet, and is preferably used for preparing a lithium ion battery.

[0103] The reversible cross-linked polymer of the present invention helps to form sulfur-rich active bonds during the charge and discharge process, has a SEI with good thermal stability, can reduce the thickness of the SEI, reduce the battery impedance, and improve the cycle performance of the battery.

[0104] The present invention uses small molecules or polymers containing sultone to modify hydroxyl groups or amino groups on the negative electrode surface to achieve chemical bonding between the binder and the negative electrode, improve the bonding force between the binder and the silicon negative electrode. At the same time, after the sultone ring is opened, disulfide bonds will be generated in the binder. Combining with the disulfide bonds in diamine / polyamine or alcohol as a cross-linking agent, and the hydrogen bond interaction between amide bonds, the disulfide bonds and hydrogen bond interactions endow the binder with certain self-healing ability, and the chemical cross-linking of the whole system is beneficial to improving the mechanical strength, improving the cracking and pulverization of the negative electrode, and improving the cycle life.

[0105] In the present invention, the negative electrode sheet is a three-dimensional network structure obtained by a chemical cross-linking reaction of a negative electrode binder, a silane coupling agent, and a negative electrode active material. The negative electrode sheet is preferably a silicon negative electrode sheet, and the silicon negative electrode sheet includes disulfide bonds and amide bonds; the negative electrode active material is selected from silicon negative electrodes and silicon-carbon negative electrode particles.

[0106] The present invention will be described in detail below through examples.

[0107] In the following examples and comparative examples, unless otherwise specified, various raw materials used are commercially available.

[0108] Test Example

[0109] Dissolve 9.2 g (0.06 mol) of DL-homocysteine thiolactone hydrochloride and 24 g (2.37 mol) of triethylamine in 900 mL of dichloromethane, stir and dissolve in an ice-water bath, slowly add dropwise 9.06 g (0.1 mol) of acryloyl chloride, control the temperature not to exceed 0 °C, and react for 5 h; wash the organic phase after the reaction 3 times with saturated brine, and dry it with anhydrous sodium sulfate. After filtration, concentrate the filtrate under reduced pressure. Dissolve the residue in 180 mL of ethyl acetate, filter it through a short column of silica gel, and recrystallize the filtrate with petroleum ether, then filter to obtain monomer A, named thiolactone acrylamide, and its structural formula is shown as formula A-7.

[0110] Preparation of polymer A0: Add 4 g of the above-obtained monomer A to 36 g of toluene to prepare a 10 wt% solution, add 40 mg of azobisisobutyronitrile, stir magnetically, and react at a constant temperature of 60 °C for 12 h; after polymerization, precipitate and wash 3 times with ethanol, and dry at 60 °C to obtain polymer A0.

[0111] Preparation of polymer A1: Take an appropriate amount of polymer A0 and dissolve it in tetrahydrofuran to prepare a 10 wt% solution, add n-hexylamine with a molar equivalent to the thiolactone. After complete dissolution, heat to 60 °C and stir for 6 h. Precipitate the product with methanol and dry it to obtain polymer A1.

[0112] Infrared characterization of the polymer: Take appropriate amounts of polymer A0 and polymer A1 powders, and use the ATR mode of Nicolet iS50 to test the infrared absorption spectrum, as Figures 1-3 shown. It can be seen from Figure 1 that after the reaction of polymer A0 with n-hexylamine, a mercapto group appears in polymer A1; it can be seen from Figure 2 that the absorption peak of the C=O double bond of polymer A1 undergoes a red shift compared to that of polymer A0. This is due to the stronger electron-donating ability of the N atom on -C(=O)-NH-, which proves that the amine group can effectively initiate the ring-opening reaction of the thiolactone. In addition, it can be seen from Figure 3 that the peak appearing at 2570 cm -1 in polymer A1 also proves the formation of disulfide bonds during the baking process.

[0113] Self-healing evaluation: Prepare a 20 wt% tetrahydrofuran solution of polymer A0, add an equimolar mass of 4,4'-dithiodianiline, mix well, pour it into a PTFE groove, slowly volatilize and dry to form a film. After the film is basically dry, transfer it and heat and cure it at 60 °C for 10 h to obtain a film, as Figure 4The thin films A and B shown in Figure 4 , where thin film B is a blue thin film obtained by adding a small amount of blue ink to the solution during the preparation of the thin film. Cut both of them from the middle position, splice the A and B samples, and heat them at 60 °C for 30 min under an external force of 10 g to obtain the self-healed thin film. The results are shown in

[0114] Example 1

[0115] Preparation of monomer A: Dissolve 9.2 g (0.06 mol) of DL-homocysteine thiolactone hydrochloride and 24 g (2.37 mol) of triethylamine in 900 mL of dichloromethane, stir and dissolve in an ice-water bath, slowly add dropwise 9.06 g (0.1 mol) of acryloyl chloride, control the temperature not to exceed 0 °C, and react for 5 h; Wash the organic phase after the reaction 3 times with saturated brine, dry it with anhydrous sodium sulfate, filter, concentrate the filtrate under reduced pressure, dissolve the residue in 180 mL of ethyl acetate, filter through a short silica column, and recrystallize the filtrate with petroleum ether, filter to obtain monomer A.

[0116] Preparation of polymer 1: Add 3 mmol of the monomer A obtained above, 4 mmol of 2-hydroxyethyl acrylate and 3 mmol of acrylic acid to 40 g of toluene, add 50 mg of azobisisobutyronitrile, stir magnetically, and react at a constant temperature of 60 °C for 12 h; After polymerization, precipitate and wash with ethanol 3 times to obtain polymer 1.

[0117] Preparation of the negative electrode sheet: Add silicon-carbon negative electrode, conductive agent conductive carbon black, and the polymer 1 obtained above to the mixing tank according to a mass ratio of 94:3:3, then add deionized water, stir for 6 h to mix evenly to obtain a slurry with a solid content of 40 - 45%; Add 3-aminopropyltriethoxysilane and 1,4-phenylenediamine disulfide, the molar ratio of the two is 1:2, and the total molar amount of amino groups of the two substances is equal to the molar amount of thiolactone in polymer 1. Continue to stir for 0.5 h, mix evenly to obtain the active material slurry; Coat with a coater, coat the active material slurry on the negative electrode current collector copper foil, then bake at 60 °C for 2 h, bake at 100 °C until dry, and then roll to obtain the negative electrode sheet S1.

[0118] Example 2

[0119] Prepare monomer A, polymer and negative electrode sheet according to the method of Example 1, the difference is only that the comonomer used in the polymer preparation process is adjusted to 3 mmol of monomer A, 4 mmol of 2-hydroxyethyl acrylate, 1.5 mmol of acrylic acid and 1.5 mmol of acrylamide, and polymer 2 and negative electrode sheet S2 are obtained respectively.

[0120] Example 3

[0121] The monomer A, polymer, and negative electrode sheet were prepared according to the method of Example 1, except that the comonomers used in the polymer preparation process were adjusted to 3 mmol of monomer A, 4 mmol of butyl acrylate, and 3 mmol of acrylic acid, and polymer 3 and negative electrode sheet S3 were obtained respectively.

[0122] Example 4

[0123] The monomer A, polymer 1, and negative electrode sheet were prepared according to the method of Example 1, except that in the process of preparing the negative electrode sheet, the crosslinking agent 4,4'-dithiodianiline was adjusted to a complex of 4,4'-dithiodianiline and propanediamine, and the molar ratio of the two was 7:3, and negative electrode sheet S4 was obtained.

[0124] Example 5

[0125] The monomer A, polymer 1, and negative electrode sheet were prepared according to the method of Example 1, except that in the process of preparing the negative electrode sheet, the crosslinking agent 4,4'-dithiodianiline was adjusted to a complex of 4,4'-dithiodianiline and propanediamine, and the molar ratio of the two was 5:5, and negative electrode sheet S5 was obtained.

[0126] Example 6

[0127] The monomer A, polymer 1, and negative electrode sheet were prepared according to the method of Example 1, except that in the process of preparing the negative electrode sheet, the crosslinking agent 4,4'-dithiodianiline was adjusted to a complex of 4,4'-dithiodianiline and propanediamine, and the molar ratio of the two was 3:7, and negative electrode sheet S6 was obtained.

[0128] Example 7

[0129] 1.44 g of methyl vinyl ether - maleic anhydride copolymer was dissolved in tetrahydrofuran. 1.5 g (0.01 mmol) of DL-homocysteine thiolactone hydrochloride and 2 g (0.2 mmol) of triethylamine were dissolved in 900 mL of tetrahydrofuran, stirred and dissolved in an ice-water bath, and 0.9 g (0.01 mmol) of acryloyl chloride was slowly added dropwise, controlling the temperature not to exceed 0 °C, and reacting for 5 h; the organic phase after the reaction was washed 3 times with saturated brine and dried with anhydrous sodium sulfate. After filtration, the filtrate was concentrated under reduced pressure, and the residue was precipitated in dichloromethane and dried to obtain polymer 7.

[0130] Preparation of the negative electrode sheet: The silicon-carbon negative electrode, the conductive agent conductive carbon black, and the polymer 7 obtained above were added to a stirring tank according to a mass ratio of 94:3:3, and then deionized water was added, and stirred for 6 h to be uniformly mixed to obtain a slurry with a solid content of 40-45%; 3-aminopropyltriethoxysilane and diaminodiphenyl disulfide were added, and the molar ratio of the two was 1:2, and the total molar amount of amino groups of the two substances was equal to the molar amount of thiolactone in polymer 1. Stir for another 0.5 h, and after mixing evenly, obtain the active material slurry; coat with a coater, coat the active material slurry on the negative electrode current collector copper foil, then bake at 60 °C for 2 h and bake to dry at 100 °C, and then obtain the negative electrode sheet S7 by rolling.

[0131] Comparative Example 1

[0132] The polymer and the negative electrode sheet were prepared according to the method of Example 1, except that:

[0133] Preparation of the polymer: The comonomers used in the preparation of the polymer were adjusted to 4 mmol of 2-hydroxyethyl acrylate and 3 mmol of acrylic acid to obtain polymer 8;

[0134] Preparation of the negative electrode sheet: The silicon-carbon negative electrode, the conductive agent conductive carbon black, and the polymer 8 obtained above were added to a stirring tank according to a mass ratio of 94:3:3, and then deionized water was added, and stirred for 6 h to be uniformly mixed to obtain an active material slurry with a solid content of 40-45%; coat with a coater, coat the active material slurry on the negative electrode current collector copper foil, then bake at 60 °C for 2 h and bake to dry at 100 °C, and then obtain the negative electrode sheet D1 by rolling.

[0135] Comparative Example 2

[0136] Monomer A, the polymer and the negative electrode sheet were prepared according to the method of Example 1, except that:

[0137] Preparation of the polymer: The monomer used in the preparation of the polymer was adjusted to 10 mmol of monomer A to obtain polymer 9;

[0138] Preparation of the negative electrode sheet: The silicon-carbon negative electrode, the conductive agent conductive carbon black, the polymer 9 obtained above and 3-aminopropyltriethoxysilane were added to a stirring tank according to a mass ratio of 94:3:3, and then deionized water was added, and stirred for 6 h to be uniformly mixed to obtain a slurry with a solid content of 40-45%; diaminodiphenyl disulfide was added, and the molar amount of amino groups was equal to the molar amount of thiolactone in polymer 9. Stir for another 0.5 h, and after mixing evenly, obtain the active material slurry; coat with a coater, coat the active material slurry on the negative electrode current collector copper foil, then bake at 60 °C for 2 h and bake to dry at 100 °C, and then obtain the negative electrode sheet D2 by rolling.

[0139] Comparative Example 3

[0140] The monomer A, polymer 1 and the negative electrode sheet were prepared according to the method of Example 1, except that:

[0141] During the preparation of the negative electrode sheet, 3-aminopropyltriethoxysilane was not added, and the others remained unchanged.

[0142] Comparative Example 4

[0143] Preparation of the negative electrode sheet: The silicon-carbon negative electrode, conductive agent conductive carbon black, styrene-butadiene latex SBR and polyacrylic acid (PAA) were added to a stirring tank according to a mass ratio of 94:3:1.5:1.5:, and then deionized water was added to prepare a negative electrode slurry. The ingredients were mixed and stirred to obtain a slurry with a solid content of 40-45%, and an active material slurry was obtained. It was coated with a coater, the active material slurry was coated on the negative current collector copper foil, and then the negative electrode sheet was dried at a temperature of 100°C and rolled to obtain the negative electrode sheet D4.

[0144] Comparative Example 5

[0145] Preparation of the negative electrode sheet: The silicon-carbon negative electrode, conductive agent conductive carbon black, styrene-butadiene latex SBR and sodium alginate were added to a stirring tank according to a mass ratio of 94:3:1.5:1.5:, and then deionized water was added to prepare a negative electrode slurry. The ingredients were mixed and stirred to obtain a slurry with a solid content of 40-45%, and an active material slurry was obtained. It was coated with a coater, the active material slurry was coated on the negative current collector copper foil, and then the negative electrode sheet was dried at a temperature of 100°C and rolled to obtain the negative electrode sheet D5.

[0146] Application Example

[0147] Preparation of the positive electrode sheet: Weigh 1.7 g of nickel 83, 0.15 g of Super-P and 0.15 g of PVDF, add 5 ml of N-methylpyrrolidone (NMP), stir at a rotation speed of 500 r / min for 12 h, and smear the uniformly mixed slurry on the aluminum foil with a spatula. The aluminum foil was placed in a vacuum oven at 100°C and dried for 12 h to obtain the positive electrode material.

[0148] Button cell assembly: The positive electrode sheet was punched into a 12 mm diameter circular sheet. The negative electrode sheets S1-S7 prepared in Examples 1-7 and the negative electrode sheets D1-D5 prepared in Comparative Examples 1-5 were respectively punched into 14 mm diameter circular sheets. A 16 mm polypropylene microporous membrane was selected as the separator. The positive and negative electrode sheets and the separator were assembled into a button cell in a glove box. The electrolyte was a mixed solvent of dimethyl carbonate, diethyl carbonate and ethylene carbonate, with a volume ratio of 1:1:1. Lithium hexafluorophosphate was used as the lithium salt, with a concentration of 1.2 M. 5% of fluoroethylene carbonate and 2% of vinylene carbonate were added as film-forming additives.

[0149] Battery performance evaluation: After leaving the prepared 2032 button battery encapsulated for 24 h, charge-discharge cycle tests were carried out at room temperature using a Blue Power battery test system in the voltage range of 2.75 V - 4.2 V, and the test results are shown in Table 1.

[0150] Table 1 Test Results

[0151]

[0152]

[0153] It can be seen from the results in Table 2 that the silicon-carbon negative electrode sheet prepared by the method of the present invention can extend the cycle performance of the battery.

[0154] It can be seen from the cell cycle performance data that, compared with Comparative Examples 1 - 5, the cells using the binder of the present invention have better capacity retention rate and can ensure good adhesion between the active material and the current collector. In Comparative Example 2, the crosslinking density of the system is too high and the brittleness is relatively large, which proves the necessity of introducing a tough copolymer unit. When the silane coupling agent is not introduced (Comparative Example 3), the cycle performance of the battery is inferior to that of the samples with the coupling agent (Examples 1 - 7), which shows the importance of the chemical bonding between the negative electrode active material and the polymer.

[0155] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A reversible crosslinked polymer, characterized in that, The reversible cross-linked polymer contains a silane coupling group containing an imino group.

2. The reversible crosslinked polymer according to claim 1, wherein, The reversible cross-linked polymer further contains a structure formed by ring-opening of thiolactone.

3. The reversible crosslinked polymer according to claim 1, wherein, The reversible cross-linked polymer contains amide bonds and disulfide bonds.

4. The reversible crosslinked polymer according to any one of claims 1-3, wherein, The reversible cross-linked polymer contains a structure shown in Formula I: In Formula I, represents a polymer chain.

5. The reversible crosslinked polymer according to claim 4, wherein, The reversible cross-linked polymer contains a structure shown in Formula II: In Formula II, R1 and R2 are each independently selected from the group consisting of an aliphatic alkylene group, an aromatic alkylene group, or a divalent organic chain structure containing a heteroatom; represents a polymer chain; the -SH group can continue to react to form a disulfide bond.

6. The reversible crosslinked polymer according to claim 5, wherein, R1 and R2 are each independently selected from the group consisting of methylene, ethylene, propylene, isopropylidene, p-phenylene, m-phenylene, o-phenylene, butyric acid group and groups of the composition group; Preferably, R1 and R2 are selected from the same group.

7. The reversible crosslinked polymer according to claim 5, wherein, The molar ratio of the disulfide bond in the structure of Formula I to the disulfide bond in the structure of Formula II is 1:0 - 1; preferably 1:0.3 - 1.

8. A method for preparing a reversible cross-linked polymer, characterized in that, The preparation method includes: (1) Under polymerization reaction conditions, polymerize monomer A, optional monomer B, and optional monomer C to obtain a first polymer; wherein, monomer A is a monomer with a thiolactone and a double bond; monomer B is a monomer for increasing water solubility; monomer C is a monomer containing a double bond; or, carry out a first reaction on a compound E containing a thiolactone structure and a polymer F containing an acid anhydride or a carboxyl group to obtain a second polymer; (2) Carry out a second reaction on the first polymer or the second polymer with an amine-containing compound to obtain a reversible cross-linked polymer.

9. The preparation method according to claim 8, wherein, Monomer A has a structure shown in Formula (1), In Formula (1), R3 is a substituted group containing an unsaturated bond.

10. The preparation method according to claim 9, wherein, Monomer A is selected from at least one of the compounds having structures shown in Formulae A-1 to A-15; wherein, R is a hydrocarbon group with or without an alkyl side chain containing 1 - 9 carbon atoms; Z1 is hydrogen or methyl, and Z2 is a saturated alkylene group with or without an alkyl side chain containing 1 - 9 carbon atoms.

11. According to the preparation method described in claim 8, wherein, Monomer B is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, 2-(methacryloyloxy)ethyl succinate monoester, maleic anhydride, carboxybetaine methyl methacrylate, N-(3-aminopropyl)methacrylic acid, acrylamide, and N-(2-hydroxyethyl)acrylamide; and / or, monomer C is selected from one or more of ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) methyl ether methacrylate, n-butyl methacrylate, isobutyl acrylate, lauryl acrylate, lauryl methacrylate, n-octyl acrylate, n-octyl methacrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate; and / or, the compound E containing a thiolactone structure is cysteine thiolactone; and / or, the polymer F containing an acid anhydride or a carboxyl group is selected from one or more of methyl vinyl ether - maleic anhydride copolymer, ethylene - maleic anhydride copolymer, polyacrylic acid, and polyacrylic acid copolymer; 12. The preparation method according to claim 8, wherein, The amine-containing compound is selected from at least one of a compound G containing both a disulfide bond and an amine group, an amine compound H, and an amine-containing silane coupling agent; Preferably, the compound G containing both a disulfide bond and an amino group is selected from one or more of diaminodithiobenzene, 2,2'-dithiobis(ethylamine), 4,4'-dithiobis(2-aminobutyric acid), 3,3'-dithiobis(alanine), dithioformamidine, 2-(2-amino-5-methoxyphenyl)dithio-4-methoxyaniline, and the compound having the structure shown in Formula G-1; Preferably, the amino compound H is selected from one or more of polyethyleneimine, ethylenediamine, propanediamine, butanediamine, 2,5-diaminopentanoic acid, and tris(2-aminoethyl)amine.

13. A reversibly crosslinked polymer prepared by the preparation method according to any one of claims 8-12.

14. A negative electrode tab having a self-healing function, characterized in that, The negative electrode sheet contains the reversibly crosslinked polymer according to any one of claims 1-7 and 13 and a negative electrode active lithium storage material; wherein, there is a chemical bond interaction of ~Si-R-NH-C(=O)-~ between the reversibly crosslinked polymer and the negative electrode active lithium storage material, and R is a divalent C1-C10 alkylene group.

15. A battery, characterized in that, The battery includes the negative electrode sheet, a positive electrode sheet, and a separator according to claim 14.

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