Silver-coated copper composite conductive particles and electrolyte-resistant hot melt adhesive containing the same

Abstract

The present application relates to a kind of silver-coated copper composite conductive particles and containing the electrolyte-resistant hot melt adhesive of particle, the particle size of composite conductive particle is 5-50 μm, and is prepared by the following method: S1.Copper powder is ball milled, S2.Copper powder antioxidant treatment, S3.Silver-coated copper treatment, S4.Surface treatment.The electrolyte-resistant hot melt adhesive of the present application includes 20-50% resin matrix and 50-80% conductive particle by weight percentage;The conductive particle is the silver-coated copper composite conductive particle described above.Composite conductive particle is cleaned after degreasing, phosphorization, silane coating, silver-coated and surface modification treatment, improves its oxidation resistance and conductivity;By the compounding of different particle sizes composite conductive particles, and composite conductive particle step-by-step addition resin matrix, make composite conductive particle have good dispersibility and compatibility in resin matrix, improve the conductivity and adhesion of hot melt adhesive, and make hot melt adhesive have excellent electrolyte resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal conductive particle coating treatment, and particularly relates to a silver-coated copper composite conductive particle, and further relates to an electrolyte-resistant hot melt adhesive for internal conductive bonding of a lithium battery and a preparation method thereof. BACKGROUND

[0002] With the booming development of electric vehicles and mobile phones and other industries, consumers have increasingly high requirements for the endurance and safety performance of batteries. As a lithium ion battery, how to improve the capacity while ensuring the safety of the battery has become the biggest problem in technological innovation. The biggest safety hazard of the battery is the welding slag and welding bead generated during the welding of the tab, adapter plate, top cover and other components. During the operation of the battery, these "impurities" may fall off, which poses a risk of piercing the separator and causing internal short circuit of the battery. In addition, the no-tab cylindrical battery developed to meet the fast charging requirements is prone to welding problems if the welding process is used, which may cause damage to the pole piece or the separator.

[0003] The current mainstream welding scheme is divided into laser welding and ultrasonic welding. Ultrasonic welding is a friction welding process, with a temperature not exceeding 100℃, and belongs to cold welding. The welding quality is stable, the joint has no microscopic porosity defects, no brittle intermetallic compounds, and no problems such as molten metal spatter. However, the disadvantage is that it requires a flat and clean surface, and is only suitable for small current connections. Laser welding can withstand higher currents (60A), and has no requirements for the flatness and cleanliness of the components. However, the disadvantage is that there is no gap between the connected components, so a clamping system is required. For batteries, both welding processes produce welding slag and welding beads. To solve the above problems, the present application provides a new solution - conductive hot melt adhesive, which replaces the tab welding pole piece process for mobile phone batteries, the adapter plate welding to the top cover process for square batteries, and the no-tab cylindrical battery pole piece welding to the end cover process.

[0004] Adding conductive particles into hot melt adhesive is an effective means to provide hot melt adhesive with conductivity, and the conductivity, dispersibility and stability of the conductive particles have great influence on the performance of the conductive hot melt adhesive. Patent CN106148926A discloses a silver-coated copper powder and a preparation method thereof, which adopts a method of first displacement and then reduction to form a uniform and dense silver coating layer on the surface of the copper powder, thereby improving the conductivity. The displacement reaction and the reduction reaction are common methods for producing silver-coated copper particles at present. However, the silver layer obtained by the displacement reaction is relatively loose and has low bonding strength, and the copper complex formed by the displacement reaction is enriched on the periphery of the particles, which will seriously hinder the subsequent displacement reaction if not cleaned in time. Therefore, the invention adopts the method of first displacement and then reduction, and the obtained silver layer has poor stability and the copper core has poor oxidation resistance, which makes it difficult to be applied in practice. Patent CN107498064A discloses a preparation method of ultra-fine copper-silver core-shell composite powder for medium-high temperature electronic paste, which includes manufacturing copper powder, phosphating treatment and preparing silver-coated copper powder in sequence. The silver on the surface of the obtained copper-silver core-shell composite powder is not easy to fall off, has strong oxidation resistance and stable conductivity. However, the invention only adopts phosphating treatment on the surface of the copper powder, which is difficult to make the copper core have sufficient oxidation resistance to meet the stability requirements in harsh environments such as electrolyte; and the surface of the composite powder is not treated in any way, which has poor compatibility and dispersibility in the matrix resin, and it is difficult to obtain a composite material with stable performance.

[0005] In terms of composite adhesive, patent CN107236485A discloses a dendritic thermosetting adhesive and a preparation method thereof. The dendritic thermosetting adhesive contains silver-coated copper particle powder, which is composed of first dendritic powder with a particle size of 3-5 microns, second dendritic powder with a particle size of 6-8 microns and third dendritic powder with a particle size of 10-12 microns. The silver content of the silver-coated copper particle powder is 10%, and 95% of the surface of the silver-coated copper particle powder is covered with silver. The dendritic thermosetting adhesive of the invention has closely arranged particle powder, which can effectively improve the conductivity and adhere to the copper-clad plate substrate and the reinforcing steel sheet, thereby increasing the peel strength. Although the invention uses a combination of silver-coated copper powders with different particle sizes, the preparation and treatment of the silver-coated copper particles are simple, the silver content is low, and the silver-coated copper particles are not properly modified, which makes the copper in the particles easy to be oxidized and lost, and the dispersibility and compatibility between the silver-coated copper particles and the resin matrix are poor, which easily causes agglomeration in the resin matrix and affects the conductivity of the material. Secondly, the particle size of the particles is generally small, the filling effect between the particles is not obvious, and the particles have no additional effect of reinforcing the matrix. In addition, the coating prepared by the invention has a relatively thick thickness, which will be limited in actual application.

[0006] Based on the idea of adding conductive particles, the commonly used method of conductive hot melt adhesive is to blend conductive particles and resin matrix to prepare conductive hot melt adhesive. Patent CN104479298A discloses a conductive resin composition, which comprises the following components by weight: 100 parts of solid-liquid mixed epoxy resin, 50-70 parts of elastomer, 0.1-1 part of imidazole, 150-240 parts of conductive particles, 0.1-1 part of heat stabilizer, and 360-840 parts of solvent; wherein the solid-liquid mixed epoxy resin comprises solid epoxy resin and liquid epoxy resin; the elastomer is obtained by mixing modified acrylic resin and nitrile rubber at a mass ratio of 1:(0.15-2). The invention also relates to a preparation method of the above conductive resin composition. The elastomer obtained by mixing modified acrylic resin and nitrile rubber can impart excellent film-forming property to the conductive resin composition, and improve the bonding strength, crack resistance, high and low temperature resistance, and aging resistance of the conductive resin composition; the conductive particles improve their dispersibility and stability in the conductive resin composition after pretreatment. However, the pretreatment method of the invention is relatively simple, and the improvement of the dispersibility of the conductive particles is still limited, and the preparation method of the invention is only simple blending, and the improvement of the conductivity and oxidation resistance is also limited.

[0007] Patent CN107760242A discloses a preparation method of antioxidant conductive adhesive. The invention obtains copper sulfate solution and reducing solution by self-preparation, blends the two to obtain reaction liquid, and obtains ultra-fine copper powder by treatment. The ultra-fine copper powder is dispersed in deionized water and mixed with silver amine solution for reaction, and silver-coated copper powder is obtained by treatment. The silver-coated copper powder and polyurethane particles are incorporated into diluted hot melt epoxy resin, and diethylene triamine and tributyl phosphate are continuously incorporated to obtain antioxidant conductive adhesive. The silver on the surface of the copper powder has high conductivity and chemical stability, and the potential difference between copper ions and silver can prevent the silver from being electrochemically corroded and falling off, thereby improving the oxidation resistance of the conductive adhesive. The introduction of polyurethane into the epoxy resin can well improve the brittleness of the conductive adhesive and prevent the silver-coated copper powder from precipitating under the action of gravity, thereby preventing the precipitation of conductive particles in the conductive adhesive from causing electromigration phenomenon. Although the invention increases the treatment of silver-coated copper powder, its main purpose is to increase the oxidation resistance, and the silver-coated copper powder is not further treated after being prepared, which makes it difficult to ensure the dispersibility and compatibility of the silver-coated copper powder with the matrix. Moreover, the invention only simply blends the silver-coated copper powder to prepare the conductive adhesive under the condition of high filling amount of the silver-coated copper powder, which cannot ensure the full dispersion of the silver-coated copper powder in the matrix, thereby affecting the overall conductive performance. The conductive adhesive prepared by the invention cannot meet the actual use requirements.

[0008] Therefore, how to improve the oxidation resistance and high conductivity of silver-coated copper particles, their dispersibility and compatibility in the matrix, and the comprehensive performance of the material, such as the conductive performance, has become a technical problem to be solved in the field. SUMMARY

[0009] In view of the defects in the prior art, the present application aims to provide a silver-coated copper composite conductive particle which is fully treated and modified, and a hot melt adhesive resistant to electrolyte and capable of being used for internal conductive bonding of lithium batteries, which is prepared by using a step-by-step blending method and comprises the composite conductive particle.

[0010] Specifically, the present application provides a silver-coated copper composite conductive particle, characterized in that the particle size of the conductive particle is 5-50 μm, and the conductive particle is prepared by the following method:

[0011] S1. Ball milling of copper powder:

[0012] The copper powder is ball milled into spherical and / or flaky ultrafine copper powder with oleic acid as a grinding aid;

[0013] S2. Anti-oxidation treatment of copper powder:

[0014] 2.1 The ultrafine copper powder is ultrasonically dispersed in an organic solvent to obtain a solid content of 0.1-0.5 g / mL; an acetic acid solution of a silane coupling agent with a mass fraction of 5-8% is slowly added under the conditions of 50-70 ℃ and nitrogen protection, the PH is 3-4, and the reaction time is 15-20 h; the mass ratio of the silane coupling agent to the copper powder is (2-3):1;

[0015] 2.2 Filtration and washing to obtain the anti-oxidation copper powder;

[0016] S3. Silver-coated copper treatment:

[0017] 3.1 Ethylenediaminetetraacetic acid disodium salt (EDTA-2Na), polyvinylpyrrolidone (PVP), potassium sodium tartrate, glucose and formaldehyde are taken to obtain a first solution by stirring and dissolving; silver nitrate and triethylenetetramine are taken to obtain a second solution by stirring and dissolving in deionized water;

[0018] 3.2 The anti-oxidation copper powder is added to the first solution, and stirred for 5-10 min to obtain a mixed solution;

[0019] 3.3 The second solution is dropped into the mixed solution, and reacted for 30-60 min, and then separated by standing;

[0020] 3.4 The silver-coated copper particles are obtained by washing with deionized water and anhydrous ethanol in sequence and vacuum drying, and the silver accounts for 18-22% of the total mass of the particles;

[0021] S4. Surface treatment: the silver-coated copper particles are surface treated with a coupling agent solution with a mass fraction of 1-3% to obtain the silver-coated copper composite conductive particle; the coupling agent is at least one of a silane coupling agent, a titanate coupling agent and an aluminate coupling agent.

[0022] The application obtains the ultra-fine copper powder with suitable particle size by ball milling the copper powder, and the oil acid is added in the ball milling process to passivate and protect the ball-milled copper powder, and the oil acid has the lubricating and anti-oxidation protection effects.

[0023] The silane coupling agent is used to form a silane coating layer, which can significantly improve the oxidation resistance and corrosion resistance of the copper powder, and make the particles and the subsequent coating material form a rapid and close joint, so that the composite conductive particle structure is dense and not easy to corrode and peel off. The specific type of silane coupling agent is at least one of chlorosilane coupling agent, aminosilane coupling agent, fluorosilane coupling agent, epoxy silane coupling agent, mercapto silane coupling agent, methoxysilane coupling agent, ethoxysilane coupling agent, methoxyethoxy composite silane coupling agent and acetoxy silane coupling agent.

[0024] The silver-coated copper processing method used in the application avoids the displacement reaction and preferentially performs the reduction reaction, so that a uniform and dense silver layer is continuously coated on the surface of the copper powder, and the silver coating layer can significantly reduce the resistance of the composite particles and improve the conductivity of the material due to the high conductivity of silver.

[0025] In order to fully exert the advantages of the reduction reaction, first, the first solution and the second solution are effectively distributed, and the addition sequence is controlled; second, the combination of the complexing agent and the reducing agent is used to effectively protect and efficiently reduce the silver ions, so as to avoid the displacement reaction and form a loose coating layer; at the same time, PVP is added as a dispersant during the silver-coated copper powder treatment, PVP is a water-soluble polymer, and the N and O atoms on the molecular ring have lone pair electrons, which can form chemical bonds and physical adsorption with the surface atoms of the particles. The PVP is adsorbed on the surface of the particles, and the chain-like molecular C-N of the PVP extends to the surrounding, forming a steric hindrance effect, increasing the potential barrier between the particles, reducing the probability of mutual contact between the particles, and hindering the agglomeration between the particles. The dispersant has a great influence on the particle size and dispersibility of the powder during the coating process. Under the premise of ensuring the oxidation resistance and conductivity, better dispersibility and suitable powder particle size are obtained, and the amount of PVP added in the application is 3-5% of the mass of the copper powder, preferably 4%.

[0026] Through the above preparation method, the silver-coated copper composite conductive particle of the application actually has at least the following structure from inside to outside: copper core, silane coating layer, silver shell layer, surface modification layer. The oxidation resistance and corrosion resistance of the copper core are effectively realized, excellent conductivity, and good compatibility and dispersibility with the matrix material.

[0027] Further, after the ball milling of the copper powder in step S1 and before the silver-coating copper treatment in step S2, the superfine copper powder is subjected to a degreasing cleaning treatment, comprising the following steps:

[0028] Step one: the superfine copper powder is cleaned with anhydrous ethanol for 5-10 min, and then cleaned with deionized water;

[0029] Step two: the superfine copper powder is stirred in a mixed degreasing solution of 40-60 g / L NaOH and 40-60 g / L Na2CO3 for 5-10 min, and then cleaned with deionized water;

[0030] Step three: the superfine copper powder is cleaned with 3-5% dilute sulfuric acid at room temperature to remove the surface oxides and activate the outermost atoms, and then the superfine copper powder is cleaned with deionized water until the solution is colorless.

[0031] The superfine copper powder is subjected to a comprehensive and sufficient pretreatment and activation of alcohol cleaning-water cleaning-oil removal degreasing-acid cleaning before the silver-coating copper treatment. Since the oil auxiliary is used during the ball milling of the copper powder and partial oxidation is inevitable, the superfine copper powder is subjected to a sufficient cleaning treatment to remove the oxides and organic matters on the surface of the copper powder before the subsequent treatment, which is beneficial to the more uniform and dense coating of silver on the surface of copper, and improves the oxidation resistance and dispersibility of the silver-coating copper conductive particles.

[0032] Preferably, in the copper powder oxidation resistance treatment after the degreasing cleaning treatment, the superfine copper powder is subjected to phosphating treatment before silane coupling agent coating, comprising the following steps:

[0033] Step one: zinc nitrate, zinc phosphate, zinc oxide, nitric acid and phosphoric acid are added to deionized water to prepare a phosphating solution; preferably, the molar ratio of zinc nitrate to zinc phosphate is 1: (1-1.2), and the molar ratio of nitric acid to zinc oxide is (1.8-2.2): 1;

[0034] Step two: the superfine copper powder is added to the phosphating solution for stirring reaction, and then separated and vacuum filtered; preferably, the reaction temperature is 40-55°C, and more preferably 50°C; preferably, the reaction time is 20-40 min, and more preferably 30 min;

[0035] Step three: the superfine copper powder is washed with deionized water and anhydrous ethanol in sequence, and then vacuum dried to obtain the phosphated copper powder.

[0036] The present application carries out surface conversion of copper powder before silver coating, i.e. phosphating, of the pretreated silver-coated copper powder. The phosphating of copper powder is to form a stable and insoluble inorganic compound film layer through chemical and electrochemical reactions. The surface of copper powder is formed with a uniform, continuous and relatively dense fibrous phosphating film through phosphating of the surface of copper powder, which can inhibit the formation of copper surface micro-battery and effectively improve the corrosion resistance and oxidation resistance of the surface of copper powder. In addition, the phosphating film is very thin, but it has certain porosity in addition to filling and modifying the surface of copper powder, which is more conducive to subsequent coating. Through the above preparation method, the silver-coated copper composite conductive particles have the following structure from inside to outside: copper core, phosphating film, silane coating layer, silver shell layer and surface modification layer. The interlayer adhesion and the oxidation resistance of the copper core are further improved.

[0037] On the other hand, the phosphating process faces increasingly severe environmental protection situation because it contains heavy metals and substances such as phosphorus, nitrogen, sodium nitrite, which are limited in emission, and the treatment of wastewater and waste residue is relatively complex. In the case of relatively mild application environment, the silane coating layer can be used to provide oxidation resistance for the copper core, and the above-mentioned double anti-oxidation layer strengthening protection method can be used if necessary.

[0038] Preferably, in step S4, the silver-coated copper particles are surface treated by using a silane coupling agent, including the following steps:

[0039] Step one: prepare an ethanol aqueous solution of a silane coupling agent with a mass fraction of 1-3%, wherein ethanol and pure water are mixed according to a mass ratio of 1: (7-10), and acetic acid is added to adjust the pH value to 3-4.5, and then hydrolysis is carried out at 45-75°C for standby;

[0040] Step two: add silver-coated copper particles to the pre-hydrolyzed silane coupling agent solution and mix for 2-4h;

[0041] Step three: vacuum filtration, the obtained solid is repeatedly washed with anhydrous ethanol, dried at 50-65°C, and then cooled to obtain silver-coated copper composite conductive particles modified by a silane coupling agent.

[0042] The above conductive particles are sieved, and particles with a particle size of 5-50μm are selected for standby. Preferably, the conductive particles are classified according to particle size for standby, for example, they are divided into small particle size conductive particles with a particle size of 5-10μm, preferably 5-8μm, medium particle size conductive particles with a particle size of 15-30μm, preferably 20-25μm, and large particle size conductive particles with a particle size of 35-50μm, preferably 40-45μm, so as to make compounded conductive particles as needed.

[0043] The application improves the oxidation resistance and affinity with organic polymer of the material by surface treatment of the silver-coated copper composite conductive particles with coupling agent, and improves the water resistance, corrosion resistance, dispersibility and mechanical properties of the material. In addition, the amount of the outer layer coupling agent has a great influence on the conductivity of the material. Through testing, it is found that if the amount of the coupling agent is too small, the surface modification of the composite conductive particles is not enough, the dispersibility of the silver-coated copper powder in the base material is poor, and the silver-coated copper powder is easy to agglomerate. If the amount of the coupling agent is too large, the coating of the conductive powder is excessive, which will increase the resistance of the material to a certain extent and have an adverse effect on the conductivity of the material. Therefore, the application uses an ethanol aqueous solution of silane coupling agent with a mass fraction of 1-3%, and preferably a silane coupling agent solution with a mass fraction of 2.5%. The use of the silane coupling agent solution can improve the dispersibility and compatibility of the silver-coated copper composite conductive particles in the base material, reduce the resistance of the material, and improve the conductivity of the material.

[0044] The application uses coupling agent twice. The first time, a silane coupling agent is used to form a silane coating layer on the surface of the copper powder. The main function is to provide a dense and uniform oxidation-resistant protective layer for the copper powder, and to provide an outward connecting activity. The second time, a low-concentration coupling agent is used to form a surface treatment layer outside the silver layer. The main function is to improve the compatibility and dispersibility of the composite conductive particles with the base material. Both have their own advantages and functions, which are important advantages of the application over the existing silver-coated copper composite particles.

[0045] On the other hand, in order to effectively use the silver-coated copper composite conductive particles, the application also provides a heat-melt adhesive for electrolyte-resistant internal conductive bonding of lithium batteries, which comprises 20-50% of a resin matrix and 50-80% of conductive particles by weight percentage.

[0046] The resin matrix comprises the following components by weight percentage:

[0047] Main resin 20-100%

[0048] Tackifying resin 0-60%

[0049] Viscosity adjusting resin 0-40%;

[0050] The conductive particles are the silver-coated copper composite conductive particles described above.

[0051] Further, the main resin is selected from at least one of the following: ethylene-vinyl acetate copolymer (EVA), polypropylene (PP), amorphous polyalphaolefin resin (APAO), polybutadiene rubber (PBR), polyisoprene rubber (PIR), ethylene-octene copolymer (POE), maleic anhydride modified polyolefin (MA-APAO, MA-POE), acrylic acid modified polyolefin (AA-APAO, AA-POE), styrene-ethylene-butadiene-styrene copolymer (SEBS), styrene-isoprene-styrene block copolymer (SIS), ethylene acrylic acid copolymer (EAA), and ethylene methacrylic acid copolymer (EMAA); wherein the molecular weight of the main resin is ≤1000000, more preferably 5000-1000000. Specifically, the main resin is as follows:

[0052] Ethylene-vinyl acetate copolymer (EVA):

[0053] (I),

[0054] wherein m in formula (I) is 50-20,000, and n is 5-5000;

[0055] Polypropylene (PP):

[0056] (II),

[0057] wherein m in formula (II) is 50-20,000;

[0058] Amorphous polyalphaolefin resin (APAO):

[0059] (III),

[0060] wherein m and n in formula (III) are both 50-20,000;

[0061] Polybutadiene rubber (PBR)

[0062] (IV)

[0063] wherein n in formula (IV) is 50-20,000;

[0064] Polyisoprene rubber (PIR)

[0065] (V)

[0066] wherein n in formula (V) is 50-20,000;

[0067] Ethylene and octene copolymer (POE)

[0068] (VI)

[0069] wherein, m and n in formula (VI) are 50-20,000;

[0070] Maleic anhydride modified polyolefin (MA-APAO or MA-POE)

[0071] (VII)

[0072] wherein, a and d in formula (VII) are 50-20,000, b and c are 0-400;

[0073] Acrylic modified polyolefin (AA-APAO or AA-POE)

[0074] (VIII)

[0075] wherein, a and d in formula (VIII) are 50-20,000, b and c are 0-400;

[0076] Styrene-ethylene-butadiene-styrene copolymer (SEBS)

[0077] (IX)

[0078] wherein, a, b, c, d in formula (IX) are 0-20,000;

[0079] Styrene-isoprene-styrene block copolymer (SIS)

[0080] (X)

[0081] wherein, a, b, c in formula (X) are 0-20,000;

[0082] Ethylene-acrylic acid copolymer (EAA)

[0083] (XI)

[0084] wherein, m / n = 4:1-19:1, m, n are 0-20,000 in formula (XI);

[0085] Ethylene-methacrylic acid copolymer (EMAA)

[0086] (XII)

[0087] wherein, m / n = 4:1-19:1, m, n are 0-20,000 in formula (XII).

[0088] Further, the tackifying resin is one or more of rosin, rosin derivative, terpene resin, petroleum resin; and the viscosity adjusting resin is at least one of mineral oil, hydrogenated polybutadiene (Poly BD), paraffin wax, microcrystalline wax, synthetic wax, polyethylene wax, polypropylene wax and Sasol wax.

[0089] The tackifying resin can improve the viscosity of the main resin, has a high softening point, and can improve the wetting performance and initial tack performance. The tackifying resin not only has good compatibility with the polyolefin main resin, but also can greatly improve the adhesion to the metal substrate. The tackifying resin in the present patent includes natural resin and synthetic resin, wherein the proportion of natural resin in the total tackifying resin is 0-20%. The natural resin only includes one or more of rosin, rosin derivative, terpene resin. The natural series resin can be single rosin or rosin derivative or terpene resin, or a mixture of rosin and rosin derivative, or a mixture of rosin and terpene resin, or a mixture of rosin derivative and terpene resin, or a mixture of rosin and rosin derivative and terpene resin. The synthetic resin only includes petroleum resin, which is named because it is derived from petroleum. It has the characteristics of low acid value, good miscibility, water resistance, ethanol resistance and chemical resistance, etc. It has chemical stability to acid and alkali, and has the characteristics of adjusting viscosity and good thermal stability. Petroleum resin is divided into aliphatic resin (C5), alicyclic resin (DCPD), aromatic resin (C9), aliphatic / aromatic copolymer resin (C5 / C9) and hydrogenated petroleum resin according to the different raw materials. Hydrogenated petroleum resin includes C5 hydrogenated petroleum resin and C9 hydrogenated petroleum resin.

[0090] The viscosity adjusting resin is mainly used to improve the flowability of the hot melt adhesive, which can be mineral oil, hydrogenated polybutadiene (Poly BD), paraffin wax, microcrystalline wax, synthetic wax, polyethylene wax, polypropylene wax and Sasol wax. The present application can add one or more of mineral oil and hydrogenated polybutadiene to reduce the viscosity and softening point of the hot melt adhesive, and improve the compatibility and low temperature resistance of each component. One or more of paraffin wax, microcrystalline wax, synthetic wax, polyethylene wax, polypropylene wax and Sasol wax can also be added to reduce the viscosity of the hot melt adhesive, improve the softening point of the system and the bulk strength.

[0091] In order to improve the filling rate and filling quality of the conductive particles, the silver-coated copper composite conductive particles of the present application are preferably compounded by small particle size conductive particles with a particle size of 5-10 μm, medium particle size conductive particles with a particle size of 15-30 μm and large particle size conductive particles with a particle size of 35-50 μm; and the weight ratio of the small particle size conductive particles: medium particle size conductive particles: large particle size conductive particles is (10-13):(60-70):(17-30).

[0092] The composite conductive particle of the present application is compounded by small particle size conductive particles, medium particle size conductive particles and large particle size conductive particles in different weight proportions. By using different particle sizes, the large particle size conductive particles and the medium particle size conductive particles form the basic conductive path in the resin matrix, and the small particle size conductive particles fully fill the gap between the conductive particles, so that the conductive particles form a more complete and dense conductive path in the resin matrix, thereby improving the conductivity of the material.

[0093] The hot melt adhesive provided by the present application has a dispensing temperature 20-40 DEG C higher than the softening point, which is the optimal temperature range. If the dispensing temperature is too low, the adhesive will be drawn; if the dispensing temperature is too high, the adhesive will flow seriously and overflow the dispensing area, affecting the performance of other components or processes. The adhesive provided by the present application is in a liquid state above the softening point, and the adhesive will infiltrate the surface of the substrate to quickly form adhesive strength; during the subsequent battery baking process, the molecular chain movement of the hot melt adhesive is activated, and the adhesive is secondarily infiltrated into the microgrooves on the metal surface to form a riveting effect, further improving the adhesive strength. Meanwhile, the dissolution rate of the hot melt adhesive in the electrolyte is less than or equal to 3%, and the swelling rate is less than or equal to 20%. The hot melt adhesive provided by the present application will not dissolve into the electrolyte at high temperature due to the high dissolution rate, and the solubility of the electrolyte to the substance is appropriate after cooling, so that the precipitate will not occur, avoiding the problem that the precipitate blocks the separator and affects the transmission of lithium ions, and finally causing lithium precipitation and capacity reduction. The swelling rate of the present application is low, and the volume of the conductive particles in the adhesive will not increase due to the high swelling rate, the resistivity will increase, and finally the hot melt adhesive bonding position will overheat.

[0094] In a third aspect, the present application correspondingly provides a preparation method of an electrolyte-resistant hot melt adhesive for internal conductive bonding of a lithium battery, comprising the following steps:

[0095] S1: adding all the main resins into a preheated kneader, and stirring and melting for 30-50 minutes under nitrogen protection; preferably, the stirring speed is 5-10 rpm;

[0096] S2: adding large particle size conductive particles with a particle size of 35-50 μm, and kneading for 20-40 minutes under nitrogen protection; preferably, the stirring speed is 5-10 rpm;

[0097] S3: adding 40-60% of the total amount of medium particle size conductive particles with a particle size of 15-30 μm, and kneading for 20-40 minutes under nitrogen protection; preferably, the stirring speed is 5-10 rpm;

[0098] S4: adding 30-40% of the total amount of tackifying resins, and stirring at a speed of 5-10 rpm under nitrogen protection for 10-20 minutes; increasing the speed to 15-20 rpm, and kneading for 20-30 minutes;

[0099] S5: adding the rest of the medium particle size conductive particles, kneading for 20-40 minutes under nitrogen protection; wherein the stirring speed is preferably 15-20 rpm;

[0100] S6: adding 30-40% of the total amount of tackifying resin, kneading for 20-40 minutes under nitrogen protection; wherein the stirring speed is preferably 20-30 rpm;

[0101] S7: adding small particle size conductive particles with a particle size of 5-10 μm, kneading for 20-40 minutes under nitrogen protection; wherein the stirring speed is preferably 15-20 rpm;

[0102] S8: adding the rest of the total tackifying resin, kneading for 20-40 minutes under nitrogen protection; wherein the stirring speed is preferably 20-30 rpm;

[0103] S9: adding the total viscosity adjusting resin, stirring at a speed of 20-30 rpm, kneading for 40-80 minutes, and vacuumizing; filtering the material; the filter screen is preferably a 200-300 mesh filter screen made of 316 stainless steel.

[0104] The preparation method of the hot melt adhesive of the present application adopts a step-by-step blending method, and in particular, the silver-coated copper composite conductive particles are added in a sequence from large to small. Compared with the simple blending of all raw materials commonly used in the prior art, the method adopted by the present application not only improves the filling rate of the conductive particles, but also fully improves the compatibility of the conductive particles and the resin matrix, promotes the dispersion of the conductive particles in the resin matrix, and at the same time improves the comprehensive performance of the hot melt adhesive, such as conductivity, heat resistance and mechanical properties. The hot melt adhesive prepared by the present application has a softening point of ≥ 130℃, preferably 145℃-180℃.

[0105] The present application has the following advantages:

[0106] 1) The silver-coated copper composite conductive particles of the present application have excellent conductivity and oxidation resistance, as well as good dispersibility and compatibility in the matrix:

[0107] Firstly, the copper powder is fully cleaned, phosphated and anti-oxidized before silver coating treatment, providing a prerequisite for uniform and dense silver coating;

[0108] Secondly, the unique silver salt solution system used in the silver coating process of the copper powder effectively protects and fully reduces silver ions, and PVP is added as a dispersant, so that a uniform and dense silver layer is continuously coated on the surface of the copper powder, significantly reducing the resistance of the composite conductive particles and improving the conductivity of the material;

[0109] In addition, the two coupling agent treatments each have effects: the silane coupling agent on the surface of the copper powder fully coats the copper powder, providing a stable and uniform oxidation-resistant anticorrosion layer for the copper powder and improving the binding of the copper powder to the outside; the low-concentration coupling agent surface treatment of the silver-coated copper powder improves the oxidation resistance and affinity of the material to organic polymers, and improves the water resistance, corrosion resistance, dispersibility, and mechanical properties of the material. More importantly, the reasonable amount of the outermost coupling agent does not reduce the conductivity of the material due to excessive coating, on the contrary, the appropriate amount of silane coupling agent can fully improve the dispersibility of the material and improve the compatibility of the silver-coated copper powder and the resin matrix, thereby reducing the resistance of the material and improving the conductivity of the material,

[0110] 2) The resin matrix of the present application uses a main resin, a tackifying resin, and a viscosity adjusting resin and a combination, wherein the tackifying resin can improve the tackiness of the material, has a high softening point, and can improve the wetting performance and initial tack performance, and the tackifying resin not only has good compatibility with the main resin, but also can greatly improve the adhesion with the composite conductive particles. The viscosity adjusting resin can improve the flowability of the hot melt adhesive, improve the compatibility of the components, and improve the low temperature resistance.

[0111] 3) The present application uses composite conductive particles of different particle sizes, so that the conductive particles form a more complete and dense conductive path in the resin matrix, improving the conductivity of the material. Correspondingly, using a segmented and gradual blending method, compared with the simple blending of all raw materials commonly used in the prior art, the method used in the present application can fully improve the compatibility of the conductive particles and the resin matrix, and promote the dispersion of the conductive particles in the resin matrix. BRIEF DESCRIPTION OF DRAWINGS

[0112] Figure 1 show the volume resistivity test process of the present application;

[0113] Figure 2 show the interface resistance test process of the present application. DETAILED DESCRIPTION

[0114] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with examples.

[0115] Specifically, the silver-coated copper composite conductive particles of the present application have a particle size of 5-50 μm and are prepared by the following method:

[0116] S1. Ball milling of copper powder:

[0117] The copper powder is ball milled into spherical and / or flaky ultrafine copper powder with oleic acid as a grinding aid. The ball milling can use a planetary ball mill.

[0118] S2. Degreasing and cleaning treatment of the ultrafine copper powder:

[0119] 2.1: The ultra-fine copper powder is ultrasonically cleaned with anhydrous ethanol for 5-10 min, and then washed with deionized water for 2-4 times;

[0120] 2.2: The ultra-fine copper powder is degreased by stirring in a mixed degreasing solution of 40-60 g / L NaOH and 40-60 g / L Na2CO3 for 5-10 min, and then washed with deionized water for 2-4 times;

[0121] 2.3: The surface oxide of the ultra-fine copper powder is removed and the outermost atoms are activated at room temperature by using 3-5% dilute sulfuric acid, and then the ultra-fine copper powder is washed with deionized water until the solution is colorless.

[0122] S3. Phosphating treatment of ultra-fine copper powder:

[0123] 3.1: Zinc nitrate, zinc phosphate, zinc oxide, nitric acid and phosphoric acid are added to deionized water to prepare a phosphating solution; wherein the molar ratio of zinc nitrate to zinc phosphate is 1: (1-1.2), and the molar ratio of nitric acid to zinc oxide is (1.8-2.2):1;

[0124] 3.2: The ultra-fine copper powder is added to the phosphating solution and stirred for reaction, and then separated and vacuum filtered;

[0125] 3.3: The copper powder is washed with deionized water and anhydrous ethanol for 2-4 times, and then vacuum dried to obtain the phosphated copper powder.

[0126] S4. Antioxidant treatment of copper powder:

[0127] 4.1: The ultra-fine copper powder is ultrasonically dispersed in an organic solvent with a solid content of 0.1-0.5 g / mL; under the conditions of 50-70°C and nitrogen protection, a mass fraction of 5-8% silane coupling agent acetic acid solution is slowly added, the PH is 3-4, and the reaction time is 15-20 h; the mass ratio of the silane coupling agent to the copper powder is (2-3):1;

[0128] 4.2: The antioxidant copper powder is obtained by filtering and washing;

[0129] S5. Silver-coated copper treatment:

[0130] 5.1: Take disodium ethylenediaminetetraacetate (EDTA-2Na), polyvinylpyrrolidone (PVP), potassium sodium tartrate, glucose and formaldehyde, stir and dissolve to obtain a first solution; take silver nitrate and triethylenetetramine, add to deionized water and stir to dissolve to obtain a second solution;

[0131] In the first solution, the amount of disodium ethylenediaminetetraacetate (EDTA-2Na) and sodium potassium tartrate is 4-6% of the mass of copper powder, preferably 5%; the amount of polyvinylpyrrolidone (PVP) is 3-5% of the mass of copper powder, preferably 4%; the amount of glucose is 2-4% of the mass of copper powder, preferably 3%; the volume concentration of formaldehyde in the first solution is 0.3-0.5%, preferably 0.4%;

[0132] In the second solution, the molar ratio of silver nitrate to the above-mentioned sodium potassium tartrate is (0.8-1.5):1, preferably 1:1;

[0133] 5.2: The ultra-fine copper powder is added to the first solution, stirred for 5-10 min, and a mixed solution is obtained;

[0134] 5.3: The second solution is added dropwise to the mixed solution, reacted for 30-60 min, and separated by standing;

[0135] 5.4: Washed with deionized water and anhydrous ethanol for 2-4 times, vacuum dried for 9-12 h, to obtain silver-coated copper particles, wherein the silver accounts for 18-22% of the total mass of the particles, and the particles are silver gray;

[0136] S6 Surface treatment:

[0137] 6.1: An aqueous solution of ethanol with a mass fraction of 1-3% silane coupling agent is prepared, wherein ethanol and pure water are mixed in a mass ratio of 1:(7-10), and acetic acid is added to adjust the pH value to 3-4.5, and then hydrolyzed at 45-75°C for standby;

[0138] 6.2: The silver-coated copper particles are added to the pre-hydrolyzed silane coupling agent solution, and mixed and reacted for 2-4 h;

[0139] 6.3: Vacuum filtration, the obtained solid is repeatedly washed with anhydrous ethanol, and dried at 50-65°C, to obtain silver-coated copper composite conductive particles modified by silane coupling agent after cooling.

[0140] The above-mentioned conductive particles are sieved, and particles with a particle size of 5-50 μm are selected for standby. Preferably, the conductive particles are classified according to particle size for standby, which are divided into small particle size conductive particles with a particle size of 5-10 μm, medium particle size conductive particles with a particle size of 15-30 μm, and large particle size conductive particles with a particle size of 35-50 μm.

[0141] The electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises 20-50% of a resin matrix and 50-80% of conductive particles by weight percentage;

[0142] The resin matrix comprises the following components by weight percentage:

[0143] Main resin 20-100%

[0144] tackifying resin 0-60%

[0145] viscosity regulating resin 0-40%;

[0146] The main body resin is selected from at least one of ethylene-vinyl acetate copolymer (EVA), polypropylene (PP), amorphous polyalphaolefin resin (APAO), polybutadiene rubber (PBR), polyisoprene rubber (PIR), ethylene-octene copolymer (POE), maleic anhydride modified polyolefin (MA-APAO, MA-POE), acrylic acid modified polyolefin (AA-APAO, AA-POE), styrene-ethylene-butadiene-styrene copolymer (SEBS), styrene-isoprene-styrene block copolymer (SIS), ethylene acrylic acid copolymer (EAA) and ethylene methacrylic acid copolymer (EMAA).

[0147] The tackifying resin is one or more of rosin, rosin derivative, terpene resin, petroleum resin; the weight percentage is preferably 5-30%, more preferably 5-20%.

[0148] The viscosity regulating resin is at least one of mineral oil, hydrogenated polybutadiene (Poly BD), paraffin wax, microcrystalline wax, synthetic wax, polyethylene wax, polypropylene wax and Sasol wax; the weight percentage is preferably 1-10%, more preferably 1-5%.

[0149] The silver-coated copper composite conductive particle is compounded from small particle size conductive particles with a particle size of 5-10 μm, medium particle size conductive particles with a particle size of 15-30 μm and large particle size conductive particles with a particle size of 35-50 μm; and the weight ratio of the small particle size conductive particles: medium particle size conductive particles: large particle size conductive particles is (10-13):(60-70):(17-30).

[0150] The preparation method of the electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises the following steps:

[0151] S1: adding all the main body resin into a preheated kneader, stirring at a speed of 5-10 rpm under nitrogen protection, and stirring and melting for 30-50 min;

[0152] S2: adding large particle size conductive particles with a particle size of 35-50 μm, and kneading under nitrogen protection for 20-40 min; wherein the stirring speed is 5-10 rpm;

[0153] S3: adding 40-60% of the total amount of medium particle size conductive particles with a particle size of 15-30 μm, and kneading under nitrogen protection for 20-40 min; wherein the stirring speed is 5-10 rpm;

[0154] S4: Add 30-40% of the total tackifying resin, under nitrogen protection, stirring speed 5-10 rpm, knead for 10-20 minutes; increase the speed to 15-20 rpm, knead for 20-30 minutes;

[0155] S5: Add the remaining medium particle size conductive particles, knead for 20-40 minutes under nitrogen protection; wherein the stirring speed is 15-20 rpm;

[0156] S6: Add 30-40% of the total tackifying resin, under nitrogen protection, knead for 20-40 minutes; wherein the stirring speed is 20-30 rpm;

[0157] S7: Add small particle size conductive particles with a particle size of 5-10 μm, knead for 20-40 minutes under nitrogen protection; wherein the stirring speed is 15-20 rpm;

[0158] S8: Add the remaining total tackifying resin, under nitrogen protection, knead for 20-40 minutes; wherein the stirring speed is 20-30 rpm;

[0159] S9: Add all the viscosity adjusting resin, stirring speed 20-30 rpm, knead for 40-80 minutes, vacuum; filter the material; use a 200-300 mesh filter screen made of 316 stainless steel.

[0160] Example 1

[0161] Silver-coated copper composite conductive particles were prepared by the following method:

[0162] S1. Ball milling of copper powder:

[0163] The copper powder was ball milled into spherical and / or flaky ultrafine copper powder using oleic acid as a grinding aid.

[0164] S2. Degreasing and cleaning treatment of ultrafine copper powder:

[0165] 2.1: The ultrafine copper powder was ultrasonically cleaned with absolute ethanol for 10 min, and then washed with deionized water for 3 times;

[0166] 2.2: The ultrafine copper powder was stirred in a mixed oil removal solution of 50 g / L NaOH and 50 g / L Na2CO3 for 10 min, and then washed with deionized water for 3 times;

[0167] 2.3: At room temperature, the surface oxides of the ultrafine copper powder were removed and the outermost layer of atoms was activated using 4.5% by volume of dilute sulfuric acid, and then the ultrafine copper powder was rinsed with deionized water until the solution was colorless.

[0168] S3. Phosphating treatment of ultrafine copper powder:

[0169] 3.1: zinc nitrate, zinc phosphate, zinc oxide, nitric acid, phosphoric acid are added into deionized water to prepare a phosphating solution; wherein the molar ratio of zinc nitrate to zinc phosphate is 1:1, and the molar ratio of nitric acid to zinc oxide is 2:1;

[0170] 3.2: the superfine copper powder is added into the phosphating solution to stir and react, and then is separated by standing and vacuum filtration;

[0171] 3.3: the copper powder is washed with deionized water and anhydrous ethanol for 2 times respectively, and is vacuum dried to obtain the phosphorized copper powder.

[0172] S4. Copper powder antioxidant treatment:

[0173] 4.1: the superfine copper powder is ultrasonically dispersed in an organic solvent to obtain a solid content of 0.35 g / mL; under the conditions of about 60°C and nitrogen protection, an acetic acid solution of 8% silane coupling agent by mass fraction is slowly added, the PH is about 3.5, and the reaction time is 18 h; the mass ratio of the silane coupling agent to the copper powder is 2.5:1;

[0174] 4.2: the antioxidant copper powder is obtained by filtration and washing;

[0175] S5. Silver-coated copper treatment:

[0176] 5.1: disodium ethylenediaminetetraacetate, polyvinylpyrrolidone, potassium sodium tartrate, glucose and formaldehyde are taken to obtain a first solution by stirring and dissolving; silver nitrate and triethylenetetramine are taken to obtain a second solution by stirring and dissolving in deionized water;

[0177] 5.2: the superfine copper powder is added into the first solution to stir for 10 min to obtain a mixed solution;

[0178] 5.3: the second solution is dropped into the mixed solution to react for 45 min and then is separated by standing;

[0179] 5.4: the silver-coated copper particles are obtained by washing with deionized water and anhydrous ethanol for 2 times respectively and vacuum drying for 10 h, wherein the silver accounts for 20% of the total mass of the particles;

[0180] S6 Surface treatment:

[0181] 6.1: an aqueous solution of 2.5% silane coupling agent by mass fraction in ethanol is prepared, wherein the ethanol and pure water are mixed according to a mass ratio of 1:8, and acetic acid is added to adjust the pH value to 4, and then is hydrolyzed at 60°C for standby;

[0182] 6.2: the silver-coated copper particles are added into the pre-hydrolyzed silane coupling agent solution to mix and react for 3 h;

[0183] 6.3: the obtained solid is repeatedly washed with anhydrous ethanol and is dried at 65°C, and then the silver-coated copper composite conductive particles modified by the silane coupling agent are obtained after cooling.

[0184] The conductive particles are classified by sieving into small-diameter conductive particles with a particle size of 5-8 μm, medium-diameter conductive particles with a particle size of 20-25 μm, and large-diameter conductive particles with a particle size of 40-45 μm.

[0185] The electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises, by weight percentage, 40% of a resin matrix and 60% of conductive particles.

[0186] The resin matrix comprises, by weight percentage, the following components:

[0187] EAA (Escor 6000) 9%

[0188] APAO (M1018P) 45%

[0189] DCPD resin (Ruison PRS-5140) 40%

[0190] Naphthenic mineral oil (Karamay KN4010) 6%;

[0191] The silver-coated copper composite conductive particles are compounded from the small-diameter conductive particles, the medium-diameter conductive particles, and the large-diameter conductive particles. The weight ratio of the small-diameter conductive particles to the medium-diameter conductive particles to the large-diameter conductive particles is 12:66:22.

[0192] The method for preparing the electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises the following steps:

[0193] S1: adding, by weight percentage, APAO and EAA to a preheated kneader, and stirring and melting under nitrogen protection for 40 min;

[0194] S2: adding the large-diameter conductive particles, and kneading under nitrogen protection for 30 min;

[0195] S3: adding 50% of the total mass of the medium-diameter conductive particles, and kneading under nitrogen protection for 30 min;

[0196] S4: adding 30% of the total amount of DCPD resin, stirring at a speed of 10 rpm under nitrogen protection for 15 min, and increasing the speed to 20 rpm and kneading for 20 min;

[0197] S5: adding the remaining medium-diameter conductive particles, and kneading under nitrogen protection for 30 min;

[0198] S6: adding 30% of the total amount of DCPD resin, and kneading under nitrogen protection for 30 min;

[0199] S7: adding the small-diameter conductive particles, and kneading under nitrogen protection for 30 min;

[0200] S8: Add the rest of the DCPD resin, knead for 20 minutes under nitrogen protection;

[0201] S9: Add all the naphthenic mineral oil, stir at a rate of 30 rpm, knead for 60 minutes, and vacuum; filter the material.

[0202] Example 2

[0203] The preparation method of the silver-coated copper composite conductive particles is the same as that of Example 1.

[0204] The electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises 30% of a resin matrix and 70% of conductive particles by weight.

[0205] The components and proportions included in the resin matrix, and the blending method of the resin matrix and the conductive particles are the same as those of Example 1.

[0206] Example 3

[0207] The preparation method of the silver-coated copper composite conductive particles is the same as that of Example 1.

[0208] The electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises 20% of a resin matrix and 80% of conductive particles by weight.

[0209] The components and proportions included in the resin matrix, and the blending method of the resin matrix and the conductive particles are the same as those of Example 1.

[0210] Example 4

[0211] The preparation method of the silver-coated copper composite conductive particles is the same as that of Example 1.

[0212] The electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises 30% of a resin matrix and 70% of conductive particles by weight.

[0213] The resin matrix comprises the following components:

[0214] APAO (VESTOPLAST 891) 20%

[0215] MA-APAO (QF551) 20%

[0216] C9 resin (Yuanli Industry YL-140) 50%

[0217] Mineral oil (Dagang Petroleum 32#) 10%;

[0218] The silver-coated copper composite conductive particles are prepared from small-diameter conductive particles with a particle size of 5-8 microns, medium-diameter conductive particles with a particle size of 20-25 microns, and large-diameter conductive particles with a particle size of 40-45 microns. The weight ratio of the small-diameter conductive particles, the medium-diameter conductive particles, and the large-diameter conductive particles is 12:66:22.

[0219] The preparation method of the electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises the following steps:

[0220] S1: according to the mass percentage, add APAO and MA-APAO to the preheated kneader, and stir and melt under nitrogen protection for 40 minutes;

[0221] S2: add large-diameter conductive particles, and knead under nitrogen protection for 30 minutes;

[0222] S3: add 50% of the total mass of medium-diameter conductive particles, and knead under nitrogen protection for 30 minutes;

[0223] S4: add 30% of the total amount of C9 resin, stir at a speed of 10 rpm under nitrogen protection, and knead for 15 minutes; increase the speed to 20 rpm, and knead for 20 minutes;

[0224] S5: add the remaining medium-diameter conductive particles, and knead under nitrogen protection for 30 minutes;

[0225] S6: add 30% of the total amount of C9 resin, and knead under nitrogen protection for 30 minutes;

[0226] S7: add small-diameter conductive particles, and knead under nitrogen protection for 30 minutes;

[0227] S8: add the remaining C9 resin, and knead under nitrogen protection for 20 minutes;

[0228] S9: add all the mineral oil, stir at a speed of 30 rpm, and knead for 60 minutes, then vacuumize; filter the material.

[0229] Comparative Example 1

[0230] The preparation method of the silver-coated copper composite conductive particles is the same as that of Example 1.

[0231] The electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises 15% of a resin matrix and 85% of conductive particles by weight.

[0232] The components and proportions included in the resin matrix, and the blending method of the resin matrix and the conductive particles are the same as those of Example 1.

[0233] Comparative Example 2

[0234] The silver-coated copper composite conductive particles are prepared by the following method:

[0235] S1. Ball milling copper powder:

[0236] The copper powder is ball milled into spherical and flaky ultrafine copper powder with oleic acid as a grinding aid.

[0237] S2. Degreasing and cleaning treatment of ultrafine copper powder:

[0238] 2.1: The ultrafine copper powder is ultrasonically cleaned with anhydrous ethanol for 10 min, and then washed with deionized water for 2 times;

[0239] 2.2: The ultrafine copper powder is stirred and degreased in a mixed oil removal liquid of 50 g / L NaOH and 50 g / L Na2CO3 for 10 min, and then washed with deionized water for 3 times;

[0240] 2.3: The surface oxide of the ultrafine copper powder is removed and the outermost layer of atoms is activated at room temperature with 4.5% by volume of dilute sulfuric acid, and then the ultrafine copper powder is rinsed with deionized water until the solution is colorless.

[0241] S3. Phosphating treatment of ultrafine copper powder:

[0242] 3.1: Zinc nitrate, zinc phosphate, zinc oxide, nitric acid and phosphoric acid are added to deionized water to prepare a phosphating liquid; wherein the molar ratio of zinc nitrate to zinc phosphate is 1:1, and the molar ratio of nitric acid to zinc oxide is 1.8:1;

[0243] 3.2: The ultrafine copper powder is added to the phosphating liquid and stirred to react, and then separated by standing and vacuum filtration;

[0244] 3.3: The phosphorized copper powder is obtained by washing with deionized water and anhydrous ethanol for 2 times in sequence and vacuum drying.

[0245] S4. Silver-coated copper treatment:

[0246] 4.1: Dipotassium ethylenediaminetetraacetate, polyvinylpyrrolidone, potassium sodium tartrate, glucose and formaldehyde are taken to prepare a first solution by stirring and dissolving; silver nitrate and triethylenetetramine are taken to prepare a second solution by stirring and dissolving in deionized water;

[0247] 4.2: The ultrafine copper powder is added to the first solution and stirred for 10 min to obtain a mixed solution;

[0248] 4.3: The second solution is added dropwise into the mixed solution, and the reaction is carried out for 45 min, and then separated by standing;

[0249] 4.4: The silver-coated copper particles are obtained by washing with deionized water and anhydrous ethanol for 2 times in sequence and vacuum drying for 10 h.

[0250] The silver-coated copper composite conductive particles obtained in the comparative example 2 are not coated with an antioxidant silane coupling agent, and the silver layer is not subjected to surface treatment with a coupling agent.

[0251] The composite conductive particles are sieved and graded to obtain small-diameter conductive particles with a particle size of 5-8 μm, medium-diameter conductive particles with a particle size of 20-25 μm, and large-diameter conductive particles with a particle size of 40-45 μm. The weight ratio of the small-diameter conductive particles: medium-diameter conductive particles: large-diameter conductive particles is 12:66:22.

[0252] The electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises, by weight percentage, 30% of a resin matrix and 70% of conductive particles.

[0253] The components and proportions included in the resin matrix, and the blending manner of the resin matrix and the conductive particles are the same as in Example 1.

[0254] Comparative Example 3

[0255] Silver-coated copper composite conductive particles are prepared by the following method:

[0256] S1. Ball milling of copper powder:

[0257] The copper powder is ball milled into spherical and flaky ultrafine copper powder with oleic acid as a grinding aid.

[0258] S2. Degreasing and cleaning treatment of the ultrafine copper powder:

[0259] 2.1: The ultrafine copper powder is ultrasonically cleaned with anhydrous ethanol for 10 min, and then washed with deionized water for 2 times;

[0260] 2.2: The ultrafine copper powder is degreased by stirring in a mixed oil removal liquid of 50 g / L NaOH and 50 g / L Na2CO3 for 10 min, and then washed with deionized water for 3 times;

[0261] 2.3: The surface oxides of the ultrafine copper powder are removed and the outermost layer of atoms is activated at room temperature with 4.5% by volume of dilute sulfuric acid, and then the ultrafine copper powder is rinsed with deionized water until the solution is colorless.

[0262] S3. Silver-coated copper treatment:

[0263] 3.1: Ethylenediaminetetraacetic acid disodium salt, polyvinylpyrrolidone, potassium sodium tartrate, glucose, and formaldehyde are taken, stirred and dissolved to obtain a first solution; silver nitrate and triethylenetetramine are added to deionized water, stirred and dissolved to obtain a second solution;

[0264] 3.2: The ultrafine copper powder is added to the first solution, stirred for 10 min to obtain a mixed solution;

[0265] 3.3: The second solution is added dropwise to the mixed solution, reacted for 45 min, and separated by standing;

[0266] 3.4: Wash with deionized water and anhydrous ethanol for 2 times, vacuum drying for 10h, to obtain silver-coated copper particles.

[0267] The silver-coated copper composite conductive particles obtained in Comparative Example 3 were not subjected to anti-oxidation phosphating treatment and silane coupling agent coating, and the silver layer was not subjected to coupling agent surface treatment.

[0268] The composite conductive particles were sieved and graded to obtain small-particle-size conductive particles with a particle size of 5-8μm, medium-particle-size conductive particles with a particle size of 20-25μm, and large-particle-size conductive particles with a particle size of 40-45μm. The weight ratio of small-particle-size conductive particles: medium-particle-size conductive particles: large-particle-size conductive particles was 12:66:22.

[0269] The electrolyte-resistant hot melt adhesive for internal conductive bonding of lithium batteries comprises 30% of a resin matrix and 70% of conductive particles by weight.

[0270] The components and proportions included in the resin matrix, and the blending mode of the resin matrix and the conductive particles are the same as in Example 1.

[0271] Comparative Example 4

[0272] TB3301F, a single-component thermosetting heat-conducting and conductive adhesive from Japan Sanjiao Company, whose main components are epoxy resin and silver powder.

[0273] The material compositions of Examples 1-4 and Comparative Examples 1-3 are shown in Table 1:

[0274] Table 1

[0275]

[0276] Performance test

[0277] 1. Dissolution rate test

[0278] 1.1 Prepare 1.4±0.1g of adhesive blocks, and record the mass as M1, and place them in a glass bottle;

[0279] 1.2 Add 7±0.1g of electrolyte (pure solvent formula EC / PC / DEC / EP=3:3:1:3) to the container and seal it;

[0280] 1.3 Place the sample in an 85℃ oven and age for 24 hours;

[0281] 1.4 Prepare an aluminum foil box, and record the weight as M2;

[0282] 1.5 Take out the sample bottle, and while hot, pour the sample bottle electrolyte into the aluminum foil box, and bake at 150℃ for 2h, and weigh M3

[0283] 1.6 Calculate the dissolution rate, (M3-M2) x 100% / M1.

[0284] 2. Swelling rate test

[0285] 2.1 Prepare 2±0.1g of the rubber block, and mark the mass as M1, and place it in a 100mL PP container;

[0286] 2.2 Add 30g of electrolyte (pure solvent formula EC / PC / DEC / EP=3:3:1:3) into the 100mL PP container, and seal it;

[0287] 2.3 Place the sample into a 60℃ oven, and age it for 7 days;

[0288] 2.4 Take out the rubber block, and use a piece of tissue paper to absorb the electrolyte on the surface of the rubber block, and weigh it as M2 within 5min;

[0289] 2.5 Calculate the swelling rate (M2-M1) x 100% / M1.

[0290] 3. Melting point test

[0291] 3.1 Turn on the equipment, water bath and nitrogen; set the DSC program, 20-250℃, heating rate 10℃ / min;

[0292] 3.2 Weigh 5-10mg of the sample into an aluminum crucible;

[0293] 3.3 Start the measurement and process the data.

[0294] 4. Volume resistivity test

[0295] 4.1 Paste adhesive tape on the surface of a self-made mold, control the distance between the adhesive tapes to be 2.54mm, and obtain a groove with a thickness of 50μm;

[0296] 4.2 Apply hot melt adhesive to the groove, quickly scrape it flat, and cool it for 1h;

[0297] 4.3 Invert the sample on a self-made mold with 4 probes;

[0298] 4.4 Press it down so that the probes are in close contact with the adhesive strip, and obtain the resistance value to calculate the volume resistivity.

[0299] 5. Interfacial resistance test

[0300] 5.1 Paste two layers of adhesive tape on the aluminum sheet, and hollow out a point gluing groove with a size of 20x2mm in the middle part;

[0301] 5.2 Apply glue to the hollowed part;

[0302] 5.3 Attach copper sheet and secure, cure in oven at 100°C for 2 hours;

[0303] 5.4 Mark probe test area on copper and aluminum sheet respectively to ensure test accuracy;

[0304] 5.5 Test resistance value of both ends of aluminum sheet;

[0305] 5.6 Test resistance value of copper sheet and aluminum sheet after lapping by glue, calculate contact resistance by difference.

[0306] 6. Shear test

[0307] 6.1 Place aluminum or copper sheet in shear sample mold, and place 0.02 inch Spacer at glue position;

[0308] 6.2 Glue at Spacer position, cover with another aluminum sheet; immediately clamp glue position with dovetail clamp;

[0309] 6.3 After 24 hours at room temperature, test shear using 50KN sensor at 10 mm / min.

[0310] 7. Shear test after soaking in electrolyte

[0311] 7.1 Place aluminum or copper sheet in shear sample mold, and place 0.02 inch Spacer at glue position;

[0312] 7.2 Glue at Spacer position, cover with another aluminum sheet; immediately clamp glue position with dovetail clamp;

[0313] 7.3 After 24 hours at room temperature, place entire shear sample in aluminum film, add electrolyte (pure solvent formula EC / PC / DEC / EP = 3:3:1:3) to aluminum film to ensure complete soaking of shear sample, then heat seal opening; place in oven, 85°C for 12 hours of aging;

[0314] 7.4 After removing sample, allow to air dry electrolyte for 2 hours at room temperature; test shear using 50KN sensor at 10 mm / min; if shear sample is soaked open by electrolyte, then directly determine NG.

[0315] The performance test results of Examples 1-4 and Comparative Examples 1-4 of the present application are shown in Table 2 below:

[0316] Table 2

[0317]

[0318] Test result analysis

[0319] According to the comparison of examples 1-4, it can be seen that:

[0320] 1) The dissolution rate and swelling rate of the hot melt adhesive are relatively low, and the bubble liquid shear force attenuation is low;

[0321] 2) The interfacial resistance of the hot melt adhesive is almost 0Ω, and the volume resistivity is 10 -2 to 10 -5 Ω·cm;

[0322] 3) The resin matrix content of the hot melt adhesive is high, and the resistance is high. The content of conductive particles is increased, and the resistance is obviously reduced. However, when the content of conductive particles is too high (for example, comparative example 1), although better conductivity can be obtained, the shear force and bubble liquid shear force are both low. In summary, when the content of the resin matrix part of the hot melt adhesive is 20-40wt% (or the content of conductive particles is 60-80wt%), the hot melt adhesive can basically meet the comprehensive performance requirements of conductivity, mechanical properties and the like; more preferably, the content of the resin matrix is 25-30wt% (or the content of conductive particles is 70-80wt%).

[0323] It can be seen from comparative examples 1-4 that:

[0324] 1) The volume resistivity of the sample of comparative example 4 is low, the shear force is high, but the swelling rate and dissolution rate are high, and the sample is expanded by the electrolyte after the bubble liquid, which proves that its electrolyte resistance is poor and cannot be applied in this scene;

[0325] 2) The content of metal ions in comparative example 1 is too much, and the content of resin is less (15wt%), so the shear force is low, and the shear force decreases a lot after the bubble liquid, which cannot be applied in this scene;

[0326] 3) The metal particles in comparative examples 2 and 3 are not pretreated enough, so their dispersion effect in the hot melt adhesive is poor, which leads to the increase of interfacial resistance and volume resistivity, and the conductivity is insufficient. In addition, due to the agglomeration of metal particles, the hot melt adhesive is not uniform in microstructure. When the bonding interface is subjected to external force, the stress cannot be uniformly transmitted, resulting in a decrease in shear strength; at the same time, the shear force after the bubble liquid decreases obviously.

[0327] The above describes the preferred embodiments of the present application, which aims to make the spirit of the present application more clear and convenient to understand, and is not intended to limit the present application. Any modification, replacement, improvement made within the spirit and principles of the present application shall be included in the protection scope of the appended claims of the present application.

Claims

1. A silver-coated copper composite conductive particle, characterized by, The conductive particles have a particle size of 5-50 μm and are prepared by the following method: S1. Ball milling copper powder: The copper powder is ball milled into spherical and / or flaky ultrafine copper powder with oleic acid as a grinding aid; S2. Anti-oxidation treatment of copper powder: 2.

1. Ultrasonic dispersion of the ultrafine copper powder in an organic solvent with a solid content of 0.1-0.5 g / mL; under the conditions of 50-70°C and nitrogen protection, slowly add a 5-8% mass fraction of silane coupling agent in acetic acid solution with a pH of 3-4, and the reaction time is 15-20 h; the mass ratio of the silane coupling agent to the copper powder is (2-3):1; 2.

2. Filtration and washing to obtain the anti-oxidation copper powder; S3. Silver-coated copper treatment: 3.

1. Dissolution of ethylenediaminetetraacetic acid disodium salt, polyvinylpyrrolidone, potassium sodium tartrate, glucose and formaldehyde to obtain a first solution; dissolution of silver nitrate and triethylenetetramine in deionized water to obtain a second solution; 3.

2. Adding the anti-oxidation copper powder to the first solution and stirring for 5-10 min to obtain a mixture; 3.

3. Dropping the second solution into the mixture and reacting for 30-60 min, and then separating by standing; 3.

4. Washing with deionized water and anhydrous ethanol in sequence, and vacuum drying to obtain silver-coated copper particles, wherein the silver accounts for 18-22% of the total mass of the particles; S4. Surface treatment: surface treatment of the silver-coated copper particles with a 1-3% mass fraction of a coupling agent solution to obtain silver-coated copper composite conductive particles; the coupling agent is at least one of a silane coupling agent, a titanate coupling agent and an aluminate coupling agent.

2. The composite conductive particle according to claim 1, wherein After the step S1 of ball milling the copper powder and before the step S2 of anti-oxidation treatment of the copper powder, the ultrafine copper powder is subjected to a degreasing and cleaning treatment, including the following steps: Step one: ultrasonic cleaning of the ultrafine copper powder with anhydrous ethanol for 5-10 min, and then cleaning with deionized water; Step two: degreasing of the ultrafine copper powder in a mixed oil removal liquid of 40-60 g / L NaOH and 40-60 g / L Na2CO3 for 5-10 min, and then cleaning with deionized water; Step three: removal of surface oxides and activation of the outermost layer of atoms of the ultrafine copper powder with 3-5% dilute sulfuric acid at room temperature, and then rinsing the ultrafine copper powder with deionized water until the solution is colorless.

3. The composite conductive particle according to claim 2, wherein In the step 2.1 of the S2 anti-oxidation treatment of the copper powder, the ultrafine copper powder is subjected to phosphating treatment before the step 2.1, including the following steps: Step one: preparation of a phosphating liquid by adding zinc nitrate, zinc phosphate, zinc oxide, nitric acid and phosphoric acid into deionized water; Step two: stirring and reaction of the ultrafine copper powder in the phosphating liquid, standing and separation, and vacuum filtration; Step three: washing with deionized water and anhydrous ethanol in sequence, and vacuum drying to obtain phosphated copper powder.

4. The composite conductive particle according to any one of claims 1 to 3, wherein In the step S4, the silver-coated copper particles are subjected to surface treatment with a silane coupling agent, including the following steps: Step one: preparation of a 1-3% mass fraction of a silane coupling agent in an ethanol aqueous solution, wherein ethanol and pure water are mixed in a mass ratio of 1:(7-10), and then acetic acid is added to adjust the pH value to 3-4.5, and hydrolysis is carried out at 45-75°C for standby use; Step two: add silver-coated copper particles into pre-hydrolyzed silane coupling agent solution, mix and react for 2-4 hours; Step three: vacuum filtration, the obtained solid is repeatedly washed with anhydrous ethanol, dried at 50-65°C, and the silver-coated copper composite conductive particles modified by silane coupling agent are obtained after cooling.

5. An electrolyte resistant hot melt adhesive for internal conductive bonding of lithium batteries, characterized in that, The resin matrix comprises 20-50% of resin matrix and 50-80% of conductive particles by weight percentage; The resin matrix comprises the following components by weight percentage: Main resin 20-100% Tackifying resin 0-60% Viscosity adjusting resin 0-40%; The conductive particles are the silver-coated copper composite conductive particles according to any one of claims 1-4.

6. The hot melt adhesive of claim 5, wherein, The main resin is selected from at least one of the following: ethylene-vinyl acetate copolymer, polypropylene, amorphous poly-alpha olefin resin, polybutadiene rubber, polyisoprene rubber, ethylene-octene copolymer, maleic anhydride modified polyolefin, acrylic acid modified polyolefin, styrene-ethylene-butadiene-styrene copolymer, styrene-isoprene-styrene block copolymer, ethylene acrylic acid copolymer and ethylene methacrylic acid copolymer; wherein the molecular weight of the main resin is ≤1,000,000.

7. The hot melt adhesive of claim 6 wherein, The tackifying resin is one or more of rosin, rosin derivative, terpene resin and petroleum resin; and the viscosity adjusting resin is at least one of mineral oil, hydrogenated polybutadiene, paraffin wax, microcrystalline wax, synthetic wax, polyethylene wax, polypropylene wax and Sasol wax.

8. Hot-melt adhesive as claimed in any of the claims 5-7, characterized in that The silver-coated copper composite conductive particles are compounded from small particle size conductive particles with a particle size of 5-10 μm, medium particle size conductive particles with a particle size of 15-30 μm and large particle size conductive particles with a particle size of 35-50 μm.

9. The hot melt adhesive of claim 8 wherein, The weight ratio of the small particle size conductive particles: medium particle size conductive particles: large particle size conductive particles is (10-13):(60-70):(17-30).

10. A process for the preparation of an electrolyte resistant hot melt adhesive for internal conductive bonding of lithium batteries as claimed in any one of claims 5 to 9, characterized in that, The method comprises the following steps: S1: add all the main resin into a preheated kneader, melt and stir for 30-50 minutes under nitrogen protection; S2: add large particle size conductive particles with a particle size of 35-50 μm, knead for 20-40 minutes under nitrogen protection; S3: add 40-60% of the total amount of medium particle size conductive particles with a particle size of 15-30 μm, knead for 20-40 minutes under nitrogen protection; S4: add 30-40% of the total amount of tackifying resin, knead for 10-20 minutes under nitrogen protection at a stirring speed of 5-10 rpm, and then increase the stirring speed to 15-20 rpm and knead for 20-30 minutes; S5: add the remaining medium particle size conductive particles, knead for 20-40 minutes under nitrogen protection; S6: add 30-40% of the total amount of tackifying resin, knead for 20-40 minutes under nitrogen protection; S7: add small particle size conductive particles with a particle size of 5-10 μm, knead for 20-40 minutes under nitrogen protection; S8: add the remaining all tackifying resin, knead for 20-40 minutes under nitrogen protection; S9: add all the viscosity adjusting resin, knead for 40-80 minutes at a stirring speed of 20-30 rpm, and then vacuum filtration.

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