Carbon dioxide-based crosslinking adhesive

Abstract

A carbon dioxide-based crosslinking adhesive belongs to the field of adhesive materials technology. It comprises a polycarbonate adhesive and a free radical initiator. The comonomer of the polycarbonate adhesive includes an epoxy compound, carbon dioxide, and a cyclic anhydride containing double bonds. The epoxy compound is at least one of ethylene oxide and propylene oxide, or any double-bonded epoxy compound. This invention utilizes carbon dioxide as the primary carbon source, significantly reducing the carbon footprint of the material and realizing the resource utilization of industrial waste gas. The synergistic effect of the double-bonded monomers (epoxide compound + anhydride) allows for crosslinking via free radical initiation during hot pressing, forming a three-dimensional network structure, enabling the electrode film to achieve high bonding strength at low temperatures of 100℃~130℃.

Description

Technical Field

[0001] This invention belongs to the field of adhesive materials technology, and specifically relates to a carbon dioxide-based crosslinking adhesive. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, high-energy-density and high-safety lithium-ion battery technology has become a research focus. Solid-state lithium batteries, due to the inherent non-flammable properties of solid electrolytes, exhibit significant advantages in thermal runaway protection and are considered a core direction for next-generation battery technology. However, the electrode manufacturing of solid-state batteries still faces significant challenges. The NMP solvent used in traditional wet electrode processes tends to remain in porous electrodes, hindering ion transport paths and posing compatibility risks with the solid electrolyte interface. This contradiction has spurred the rise of dry electrode processes, which directly construct an integrated electrode-electrolyte structure through hot pressing, effectively avoiding solvent residue problems, but simultaneously placing higher demands on the binder system.

[0003] Currently, mainstream polyvinylidene fluoride (PVDF) adhesives exhibit significant limitations in dry processes: their high glass transition temperature necessitates temperatures above 150°C for effective bonding, but this high-temperature treatment can lead to uncontrolled volume expansion of silicon-based anode materials and structural damage to thermosensitive solid electrolyte layers (such as sulfide electrolytes). Furthermore, the linear molecular chain structure of PVDF makes it difficult to form a three-dimensional cross-linked network in solvent-free conditions, resulting in insufficient mechanical strength of the electrode film and susceptibility to active material stripping during battery cycling. More importantly, existing adhesives generally lack universal interfacial bonding capabilities with different substrates (such as oxide electrolytes and lithium metal anodes), leading to persistently high electrode-electrolyte interface contact resistance.

[0004] In terms of environmental friendliness, traditional fluoropolymer adhesives suffer from a high carbon footprint throughout their entire life cycle. Their synthesis process relies on petroleum-based raw materials, and they are difficult to degrade after disposal. Although some studies have attempted to use bio-based adhesives such as starch and cellulose, the inherent hydrophilicity of these materials can cause electrode moisture absorption and failure, and they are prone to thermal decomposition during high-temperature hot pressing, leading to a sharp drop in adhesive strength. On the other hand, while carbon dioxide copolymer-based adhesives have the advantage of biodegradability, conventional polycarbonate materials suffer from insufficient molecular chain flexibility, making it difficult to balance high adhesive strength with electrode film ductility, thus limiting their application in dry processes. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a carbon dioxide-based crosslinking adhesive with excellent low-temperature processing performance and multi-interface compatibility.

[0006] The technical solution adopted by the present invention to solve its technical problem is: a carbon dioxide-based crosslinking adhesive, comprising a polycarbonate adhesive and a free radical initiator, wherein the comonomer of the polycarbonate adhesive comprises an epoxy compound, carbon dioxide and a cyclic anhydride, wherein the epoxy compound is at least one of ethylene oxide and propylene oxide, as well as any cyclohexane oxide and any double-bonded epoxy compound, and the cyclic anhydride comprises a double-bonded cyclic anhydride and any aromatic ovoid dicarboxylic anhydride.

[0007] This invention utilizes carbon dioxide as the main carbon source, significantly reducing the carbon footprint of materials and realizing the resource utilization of industrial waste gas; the synergistic effect of double bond monomers (epoxide + acid anhydride) can initiate cross-linking through free radicals during hot pressing to form a three-dimensional network structure, enabling the electrode film to obtain high bonding strength at low temperatures of 100℃~130℃, avoiding the problems of high-temperature expansion of silicon-based negative electrodes and thermal decomposition of sulfide electrolytes.

[0008] Preferably, in the above-mentioned carbon dioxide-based crosslinking adhesive, the total amount of the double-bonded cyclic anhydride and the double-bonded epoxy compound accounts for 1% to 20% of the molar percentage of the comonomer. This invention, by precisely controlling the density of crosslinking sites, provides sufficient double-bonded crosslinking sites while ensuring the flexibility of the main chain, achieving a balance between low-temperature, high-efficiency curing and mechanical strength, and improving the tensile strength and elongation at break of the electrode film.

[0009] The aromatic phthalic anhydride is phthalic anhydride or 1,8-naphthalene anhydride.

[0010] Preferably, in the above-mentioned carbon dioxide-based crosslinked adhesive, the structural formula of the carbon dioxide copolymer is:

[0011] ;

[0012] Where R is H, methyl or olefin, and at least one of R1 and R2 is an olefin; 180≤a≤400, 15≤b≤100, 0≤c≤100.

[0013] Long-chain carbonate units (segment a) form continuous ion transport channels through alternating ether and ester bonds, increasing the ionic conductivity of the electrode membrane to 10. -5 The spatial distribution of the b-segment double bond anhydride unit and the c-segment polyether unit regulates the crosslinking network density, ensuring uniform coating of the active material. At the same time, the unreacted epoxy groups form chemical bonds with the current collector oxide layer (Al2O3 / CuO), greatly reducing the interfacial contact resistance.

[0014] Preferably, in the above-mentioned carbon dioxide-based crosslinking adhesive, the double-bonded cyclic anhydride is at least one selected from maleic anhydride, citraconic anhydride, norbornene anhydride, halomaleic anhydride, dimethylmaleic anhydride, dodecenylsuccinic anhydride, itaconic anhydride, cis-1,2,3,6-tetrahydrophthalic anhydride, and methyltetrahydrophthalic anhydride.

[0015] More preferably, the double-bonded cyclic anhydride is a compound anhydride of maleic anhydride and norbornene anhydride in a molar ratio of 10:1 to 4.

[0016] Preferably, in the above-mentioned carbon dioxide-based crosslinking adhesive, the double-bonded epoxy compound is allyl glycidyl ether or 1,2-epoxy-4-vinylcyclohexane.

[0017] More preferably, the double-bonded epoxy compound is allyl glycidyl ether.

[0018] The high reactivity of maleic anhydride and the rigid ring structure of norbornene olefinic anhydride synergistically enhance the thermal stability of the cross-linked network. At the same time, the long-chain ether segment of allyl glycidyl ether improves the flexibility of the molecular chain, enabling the electrode film to form a micron-scale porous structure after hot pressing, which takes into account both ion transport and mechanical support.

[0019] A method for preparing the above-mentioned carbon dioxide-based crosslinked adhesive includes the following steps:

[0020] (1) Add the comonomer, copolymer catalyst and ring-opening initiator into the reactor, purge carbon dioxide to 0.5MPa~3.5MPa, and react at 40℃~100℃ for 2h~8h; after terminating the reaction, wash the copolymer to obtain polycarbonate adhesive;

[0021] (2) The polycarbonate binder and free radical initiator are mixed at a mass ratio of 1000:0.5~5 at 5℃~20℃ and then dried under low temperature vacuum.

[0022] Compared to traditional PVDF synthesis, this preparation method offers milder reaction conditions and reduced energy consumption. High-pressure dissolution with carbon dioxide promotes ring-opening of the epoxy compound, achieving a monomer conversion rate >90%. The product requires no solvent purification, reducing waste emissions. The free radical initiator and polycarbonate binder are packaged and stored separately to avoid pre-crosslinking during storage, ensuring binder stability. During hot pressing, the initiator rapidly decomposes to generate active free radicals, triggering double bond crosslinking and forming an interpenetrating network structure, guaranteeing electrode peel strength.

[0023] Preferably, in the above preparation method, the copolymerization catalyst is a metal catalyst or an organoborane catalyst. Organoborane catalysts can precisely control the molecular weight distribution of the copolymer and reduce side reactions. The organoborane catalyst is trimethylborane or triethylborane.

[0024] Preferably, in the above preparation method, the ring-opening initiator is an onium salt of an aliphatic or aromatic unsaturated organic acid.

[0025] Preferably, in the above preparation method, the ring-opening initiator includes tetra-n-butylammonium acetate, , and At least one of them.

[0026] The free radical initiator is a peroxide-based free radical initiator.

[0027] An application of the above-mentioned carbon dioxide-based crosslinking adhesive for the preparation of electrodes for lithium-ion batteries or solid-state batteries.

[0028] Specifically, the process includes the following steps: mixing the adhesive with the electrode active material and the conductive agent at a mass ratio of 80~95:2~10:3~10, forming an electrode film through a dry process, coating it onto the surface of the current collector, and forming an electrode after hot pressing (temperature 100℃~130℃, while simultaneously evaporating some unreacted monomers).

[0029] The polar hydroxyl / carboxyl groups of the polycarbonate segments of the adhesive of this invention strengthen the bonding force with the active material (such as NCM811, silicon-carbon anode) through hydrogen bonding, resulting in an electrode capacity retention rate (>90% after 1000 cycles). The crosslinked network and the sulfide electrolyte (such as Li6PS5Cl) undergo a sulfur-olefin click reaction during hot pressing to form an integrated interface with an interface impedance <10Ω·cm², resulting in an all-solid-state battery energy density >400Wh / kg.

[0030] The polycarbonate backbone contains hydrolyzable ester bonds and is biodegradable after disposal.

[0031] Positive electrode: The active material of the electrode is at least one of lithium cobalt oxide, ternary material (NCM / NCA), lithium iron phosphate, and lithium-rich manganese-based material, and the current collector is aluminum foil;

[0032] Negative electrode: The active material of the electrode is at least one of graphite, silicon-based material, lithium titanate, and lithium metal, and the current collector is copper foil or lithium metal substrate;

[0033] Solid-state battery applications: The electrode film and the solid electrolyte layer (such as polymer-based, sulfide-based or oxide-based electrolyte) are composited by hot pressing to form an integrated electrode-electrolyte structure.

[0034] The adhesive of this invention avoids the excessive introduction of hydrophilic groups in its molecular design, resulting in an electrode film water absorption rate of <0.5% and no delamination failure after damp heat cycling (85℃ / 85% RH).

[0035] Compared with existing technologies, this invention has the following advantages: It provides a novel adhesive system that combines low-temperature processability, multi-interface compatibility, and environmental friendliness. It can form a stable three-dimensional cross-linked network under mild hot-pressing conditions of 100℃~130℃, while simultaneously establishing chemical bonds with different electrode active materials, current collectors, and solid electrolyte layers. Furthermore, it achieves a balance between mechanical properties and ion transport efficiency through molecular structure design. In addition, this invention utilizes carbon dioxide as the main synthetic raw material, which not only reduces material costs but also aligns with strategic needs, making it of significant value in promoting the industrialization of solid-state batteries. Detailed Implementation

[0036] The present invention will now be described in detail through examples. Unless otherwise stated, all raw materials used are commercially available.

[0037] Example 1

[0038] (1) Ethylene oxide, allyl glycidyl ether, cyclic anhydride containing double bonds, triethylboron and The copolymer was added to the reactor in a molar ratio of 45:5:10:0.002:0.004, wherein the double-bonded cyclic anhydride was a compound anhydride of maleic anhydride and norbornene anhydride in a molar ratio of 10:2; carbon dioxide was introduced to 3.0 MPa and the reaction was carried out at 45°C for 4 hours; after the reaction was terminated, the copolymer was washed to obtain polycarbonate adhesive.

[0039] (2) The polycarbonate binder and diisopropyl peroxide dicarbonate are mixed at a mass ratio of 1000:2 at 15°C and then dried under low temperature vacuum.

[0040] Example 2

[0041] (1) Ethylene oxide, cyclic anhydride containing double bonds, triethylboron and The copolymer was added to the reactor in a molar ratio of 50:10:0.002:0.004, wherein the double-bonded cyclic anhydride was a compound anhydride of maleic anhydride and norbornene anhydride in a molar ratio of 10:2; carbon dioxide was introduced to 3.0 MPa and the reaction was carried out at 45°C for 4 hours; after the reaction was terminated, the copolymer was washed to obtain polycarbonate adhesive.

[0042] (2) The polycarbonate binder and diisopropyl peroxide dicarbonate are mixed at a mass ratio of 1000:2 at 15°C and then dried under low temperature vacuum.

[0043] Example 3

[0044] (1) Ethylene oxide, allyl glycidyl ether, maleic anhydride, triethylboron and The copolymer was added to a reactor in a molar ratio of 45:5:10:0.002:0.004; carbon dioxide was introduced to 3.0 MPa, and the reaction was carried out at 45°C for 4 hours; after the reaction was terminated, the copolymer was washed to obtain polycarbonate adhesive.

[0045] (2) The polycarbonate binder and diisopropyl peroxide dicarbonate are mixed at a mass ratio of 1000:2 at 15°C and then dried under low temperature vacuum.

[0046] Example 4

[0047] (1) Ethylene oxide, allyl glycidyl ether, norbornene adiene anhydride, triethylboron and The copolymer was added to a reactor in a molar ratio of 45:5:10:0.002:0.004; carbon dioxide was introduced to 3.0 MPa, and the reaction was carried out at 45°C for 4 hours; after the reaction was terminated, the copolymer was washed to obtain polycarbonate adhesive.

[0048] (2) The polycarbonate binder and diisopropyl peroxide dicarbonate are mixed at a mass ratio of 1000:2 at 15°C and then dried under low temperature vacuum.

[0049] Example 5

[0050] (1) Ethylene oxide, allyl glycidyl ether, citrate anhydride, triethylboron and The copolymer was added to a reactor in a molar ratio of 45:5:10:0.002:0.004; carbon dioxide was introduced to 3.0 MPa, and the reaction was carried out at 45°C for 4 hours; after the reaction was terminated, the copolymer was washed to obtain polycarbonate adhesive.

[0051] (2) The polycarbonate binder and diisopropyl peroxide dicarbonate are mixed at a mass ratio of 1000:2 at 15°C and then dried under low temperature vacuum.

[0052] Example 6

[0053] (1) Ethylene oxide, phthalic anhydride, norbornene anhydride, triethylboron and tetrabutylammonium acetate in a molar ratio of 50:5:1:0.003:0.005 were added to a reactor; carbon dioxide was introduced to 3.5 MPa and the reaction was carried out at 40°C for 2 h; after the reaction was terminated, the copolymer was washed to obtain polycarbonate adhesive.

[0054] (2) The polycarbonate binder and di-tert-butyl peroxide are mixed at a mass ratio of 1000:0.5 at 5°C and then dried under low temperature vacuum.

[0055] Example 7

[0056] (1) propylene oxide, cyclohexane oxide, cyclic anhydrides containing double bonds, trimethylboron and The copolymer was added to the reactor in a molar ratio of 40:5:20:0.001:0.002, wherein the double-bonded cyclic anhydride was a compound anhydride of maleic anhydride and norbornene anhydride in a molar ratio of 10:1; carbon dioxide was introduced to 0.5 MPa and the reaction was carried out at 100°C for 8 hours; after the reaction was terminated, the copolymer was washed to obtain polycarbonate adhesive.

[0057] (2) The polycarbonate binder and diisopropyl peroxide dicarbonate are mixed at a mass ratio of 1000:5 at 20°C and then dried under low temperature vacuum.

[0058] Electrode films were prepared using the adhesives obtained in each embodiment. The specific process is as follows: The ambient humidity was controlled at approximately 20%. The active material (NCM811 cathode material), conductive agent (carbon black), and adhesive components from each embodiment were dry-mixed at a mass ratio of 90:6:4 and uniformly dispersed by ball milling. The mixed powder was pre-formed by roller pressing and then coated onto the surface of a pre-treated current collector (copper foil). Subsequently, it was hot-pressed at 120°C and 20 MPa for 3 minutes to trigger the decomposition of the free radical initiator, causing double bonds to crosslink and forming a three-dimensional network structure that simultaneously chemically bonds with the current collector oxide layer (Al2O3 / CuO). After hot pressing, the electrode samples were shaped by cold pressing, cut, and packaged.

[0059] The above-described electrode film preparation process is only for the purpose of comparing the performance of the resulting adhesives, and the same process is used for preparation. However, in actual applications, the process needs to be adjusted according to different embodiments. For example, in Example 1, which contains maleic anhydride / norbornene compound anhydride, it is preferred to perform rapid crosslinking at a low temperature of 110°C; in Example 7, which uses an epoxy propylene backbone, it is preferred to perform hot pressing at 130°C to impart excellent flexibility to the electrode.

[0060] The properties of the adhesives and prepared electrode films in each embodiment were tested, and the results are shown in Table 1. The crosslinking efficiency was determined by rheological analysis at 130°C, based on the gelation time. Tensile strength and elongation at break were measured using the ASTM D638 tensile test. The current collector adhesion was measured by the ASTM D903 peel test at 180°. Ionic conductivity was measured and calculated using electrode film impedance testing at room temperature.

[0061] Table 1 Test Results

[0062] .

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A carbon dioxide-based crosslinking adhesive, characterized in that, The invention includes a polycarbonate adhesive and a free radical initiator. The comonomer of the polycarbonate adhesive includes an epoxy compound, carbon dioxide, and a cyclic anhydride. The epoxy compound is at least one of ethylene oxide and propylene oxide, as well as an epoxy compound containing a double bond and any cyclohexane oxide. The cyclic anhydride includes a cyclic anhydride containing a double bond and any aromatic ovoid dicarboxylic anhydride. The total amount of the double-bonded cyclic anhydride and the double-bonded epoxy compound in the comonomer is 1% to 20% in molar percentage. The double-bonded cyclic anhydride is a compound anhydride of maleic anhydride and norbornene enediic anhydride in a molar ratio of 10:1~4; the double-bonded epoxy compound is allyl glycidyl ether. The preparation method of the carbon dioxide-based crosslinked adhesive includes the following steps: (1) Add the comonomer, copolymer catalyst and ring-opening initiator into the reactor, purge carbon dioxide to 0.5MPa~3.5MPa, and react at 40℃~100℃ for 2h~8h; after terminating the reaction, wash the copolymer to obtain polycarbonate adhesive; (2) The polycarbonate binder and free radical initiator are mixed at a mass ratio of 1000:0.5~5 at 5℃~20℃ and then dried under low temperature vacuum to obtain the product; The ring-opening initiator includes tetra-n-butylammonium acetate, , and At least one of them.

2. The carbon dioxide-based crosslinking adhesive according to claim 1, characterized in that, The copolymerization catalyst is a metal catalyst or an organoborane catalyst.

3. The application of the carbon dioxide-based crosslinking adhesive of claim 1, characterized in that, Electrode fabrication for lithium-ion batteries or solid-state batteries.