WO2024031510A1

WO2024031510A1 - Conductive adhesive connecting tab and pole, and battery containing same

Info

Publication number: WO2024031510A1
Application number: PCT/CN2022/111686
Authority: WO
Inventors: 赵利亚; 刘会会; 王龙
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-08-11
Filing date: 2022-08-11
Publication date: 2024-02-15

Abstract

The present application relates to a conductive adhesive, containing, on the basis of the total weight of the conductive adhesive, 14-78 wt% of a thermoplastic organic resin, 20-85 wt% of a conductive filler, 0.3-5 wt% of a curing agent and optionally 0-20 wt% of a diluent, the conductive filler being a mixture of Ag and at least two conductive substances selected from Cu, Al, Fe, Zn, Ni, carbon black and graphite. The present application also relates to a battery cell containing tabs and poles connected by the conductive adhesive, a battery pack containing the battery cell, and an electric device.

Description

Conductive adhesive connecting pole lugs and poles and batteries containing the same

Technical field

The present application relates to a conductive adhesive, which contains a thermoplastic resin, a conductive filler, a curing agent and optionally a diluent, wherein the conductive filler is a mixture of silver and at least two selected from specific conductive substances. The present application also relates to a battery unit including tabs and poles connected by the conductive glue, a battery pack including the battery unit, and an electrical device.

Background technique

In recent years, as traditional energy sources such as petroleum and coal become less and less available, lithium-ion batteries have attracted much attention due to their green, environmentally friendly, high-energy, low-carbon and other characteristics. The proportion of electric vehicles equipped with lithium-ion batteries is increasing. The lithium-ion batteries used in these vehicles are called power batteries. The tabs are an important part of the battery and are used to connect the battery poles to the poles outside the battery. In the existing technology, the connection methods between the pole lug and the shell include: ultrasonic welding, laser welding, resistance hot melt welding, riveting, bolt connection, etc. Among them, ultrasonic welding, laser welding, and resistance hot melt welding can fuse the terminal lug and the terminal metal of the casing (also called "pole post"). However, for batteries with multi-pole lug, the wrinkles between the terminal lug are narrow. The problem cannot be solved. At the same time, there are still battery failures caused by false welding, safety risks caused by over-welding, and battery safety risks caused by metal particles present in welding. There are also other problems in riveting and bolted connections, including poor contact caused by metal stress, inclusion of electrolyte between pole lugs, local heating, etc., resulting in reduced battery life. Moreover, in the event of short circuit or thermal runaway, it cannot disconnect the points and prevent thermal runaway. It can be said that the connection between the tabs and the casing is a key link of the power battery, which affects the reliability and safety of the power battery, and ultimately plays an important role in the market prospects of the power battery and the promotion of new energy vehicles.

Therefore, there is currently a need to provide an effective method for connecting the tabs and poles of a power battery, which can provide a good electrical connection between the tabs and poles of the battery, and can also improve the safety of the connection.

Contents of the invention

This application was made in view of the above issues, and its purpose is to provide a conductive adhesive for connecting the tabs and poles of the battery, so as to solve the problem of insufficient electrical performance and increased safety risks caused by the connection of the tabs and poles of the battery. technical problem.

In order to achieve the above objectives, the first aspect of this application provides a conductive adhesive, which includes:

14-78% by weight thermoplastic resin;

20-85% by weight conductive filler;

0.3-5% by weight curing agent, and

optionally 0-20% by weight of diluent, based on the total weight of the conductive adhesive,

The conductive filler is a mixture of Ag and at least two conductive substances selected from Cu, Al, Fe, Zn, Ni, carbon black and graphite.

The conductive adhesive of the present application contains a specific composition, especially a mixture of Ag and at least two other conductive substances as a conductive filler, and can be used to bond the tabs and poles of battery cells while ensuring sufficient bonding force. At the same time, the amount of Ag is greatly reduced, and the volume resistance of the resulting battery cell can be reduced, and/or the electrolyte resistance of the conductive adhesive can be improved.

In any embodiment, the conductive filler is a mixture of Ag, Ni and Cu. Further, the conductive filler is a mixture obtained by mixing Ag, Ni and Cu powders in a weight ratio of 20-60:20-40:20-40; optionally, the weight ratio is 40-60:20- 30:20-30. By adjusting the relative content of each conductive substance in the mixture, the volume resistance of the resulting battery cell can be further reduced.

In any embodiment, the thermoplastic organic resin is selected from one or more of epoxy resin, acrylic resin, phenolic resin, polyurethane, silicone, optionally epoxy resin. The weight average molecular weight of the epoxy resin may be 10,0000-100,0000g/mol, optionally 20,0000-60,0000g/mol. By selecting a suitable thermoplastic organic resin as the matrix, the electrolyte resistance of the conductive adhesive can be significantly improved.

In any embodiment, the curing agent is selected from the group consisting of dicyandiamide, triethanolamine, triethylamine, methylhexahydrophthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyl At least one of hexahydrophthalic anhydride and dodecylmaleic anhydride, optionally dicyandiamide. In some embodiments, the diluent is selected from at least one of acetone, ethyl acetate, 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, optionally ethyl acetate .

In any embodiment, the conductive adhesive further contains 0.1-1% by weight of initiator. The initiator may be selected from azobisisobutyronitrile or azobisisoheptanitrile. In some embodiments, the conductive adhesive further contains 0.1-0.5 wt% antioxidant. The antioxidant may be selected from carbodiimides and/or hindered phenols.

In any embodiment, the viscosity of the conductive adhesive before curing is 5000-20000 mPa.s, optionally 8000-16000 mPa.s. In some embodiments, the conductive adhesive has a curing temperature of 50-120°C, optionally 60-80°C.

A second aspect of the present application provides a battery cell, which includes:

The battery core includes a cylindrical structure formed by winding a positive electrode piece, a negative electrode piece, and a separator. The positive electrode piece is provided with a positive electrode tab, and the negative electrode piece is provided with a negative electrode tab;

The housing includes a hollow cylindrical structure with openings at both ends. The battery core is inserted into the housing. Positive poles and negative poles are respectively provided at both ends of the housing. The positive tabs and the The negative electrode tabs are respectively bonded to the positive electrode post and the negative electrode post through the conductive adhesive described in the first aspect of the application.

In any embodiment, the positive electrode tab and the negative electrode tab of the battery cell are full tabs. In some embodiments, the material of the positive electrode current collector and the positive electrode tab is aluminum foil, and the material of the negative electrode piece and the negative electrode tab is copper foil.

A third aspect of the present application provides a battery pack including a battery cell selected from the second aspect of the present application.

A fourth aspect of the present application provides an electrical device, which includes a battery cell selected from the second aspect of the present application or a battery pack of the third aspect of the present application.

Description of drawings

In order to explain the technical solution of the present application more clearly, the drawings required to be used in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on the drawings without exerting creative efforts.

Figure 1 is a schematic diagram of using conductive glue to bond pole tabs and pole posts in one embodiment of the present application.

Detailed ways

For the sake of simplicity, this application specifically discloses certain numerical ranges. However, any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range. Furthermore, each individually disclosed point or single value may itself serve as a lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.

In current cylindrical battery cells, the basic structure is the cell and the casing. The battery core includes a positive electrode piece, a separator, and a cylinder formed by winding the negative electrode piece. The positive electrode piece is provided with a positive electrode tab, and the negative electrode piece is provided with a negative electrode tab. The casing includes a hollow cylindrical structure with openings at both ends. The battery core is inserted into the casing. The two ends of the casing are respectively provided with positive poles and negative poles. The positive poles and the negative poles are The pole tabs are respectively connected to the positive pole and the negative pole. Usually, the connection is achieved by ultrasonic welding, laser welding, resistance heat welding, riveting, bolt connection, etc. However, these traditional connection methods can easily lead to safety risks such as poor contact, local thermal runaway, and battery failure, and they cannot solve the problem of wrinkles and narrow gaps between tabs, especially for systems with multi-pole tabs. There are currently some technical solutions that use conductive glue to connect the tabs and poles of battery cells, but the specific composition of the conductive glue has not been disclosed.

Therefore, there is a need in the art to provide a conductive adhesive that can be used to connect the tabs and poles of battery cells, so that an efficient electrical connection is produced between the tabs and poles, and the safety of the connection can also be improved.

Specifically, the first aspect of this application provides a conductive adhesive, which includes:

14-78% by weight thermoplastic organic resin;

20-85% by weight conductive filler;

0.3-5% by weight curing agent, and

The inventor found that when applying conductive glue to connect the tabs and poles of battery cells, the conductive glue with a specific composition can significantly reduce the usage of precious metals such as silver powder while achieving effective bonding performance, and/ Or significantly reduce the volume resistance of the connection, and/or improve the electrolyte resistance of the conductive adhesive. Specifically, the conductive adhesive of the present application contains a specific proportion of components, especially a mixture of Ag and at least two conductive substances selected from Cu, Al, Fe, Zn, Ni, carbon black and graphite as a conductive filler. Compared with the same quality of Ag powder as a conductive agent, a similar bonding effect can be achieved (reflected in good adhesion to copper or aluminum tabs), while also showing significantly reduced volume resistance, and/or Significantly inhibits the tendency of swelling or even dissolution in the electrolyte.

In some embodiments, in the conductive filler of the conductive adhesive, the weight proportion of Ag can be as low as 60% by weight or less, or even less than 50% by weight; optionally 20-60% by weight, further optionally 40% - 60% by weight, based on the total weight of the conductive filler.

In some embodiments, the conductive filler is a mixture of Ag, Ni, and Cu. Further, the conductive filler is a mixture obtained by mixing Ag, Ni and Cu powders in a weight ratio of 20-60:20-40:20-40; optionally, the weight ratio is 40-60:20- 30:20-30; specifically, the weight ratio is 50:25:25. The inventor found that selecting the powders of the above three metals and forming a mixture in a certain ratio can significantly reduce the volume resistance of the resulting battery cell. Under certain circumstances, the volume resistance can even be reduced by an order of magnitude compared to pure Ag powder, while the swelling and dissolution of the resulting conductive adhesive in the electrolyte is greatly reduced, indicating that its compatibility with the electrolyte has been significantly improved. The particle size of the metal powder can be 10-100 μm, optionally 10-40 μm, or can be outside the above range, which has no obvious impact on the conductive adhesive of the present application.

In some embodiments, the thermoplastic organic resin is selected from one or more of epoxy resin, acrylic resin, phenolic resin, polyurethane, and silicone, optionally epoxy resin. As the epoxy resin, you can choose any commercially available epoxy resin, such as bisphenol A-type epoxy resin or bisphenol F-type epoxy resin. The weight average molecular weight Mw of the epoxy resin may be 10,0000-100,0000g/mol, optionally 20,0000-60,0000g/mol. The inventor found that compared with other organic resins, choosing epoxy resin as the resin base material of the conductive adhesive of the present application can significantly improve the adhesive force of the conductive adhesive to the tab and the compatibility with the electrolyte. The thermoplastic organic resin can vary within a wide range, optionally 15-40% by weight, further optionally 18-30% by weight, based on the total weight of the conductive adhesive.

The conductive adhesive of the present application contains 0.3-5% by weight of curing agent, optionally 0.5-1% by weight, based on the total weight of the conductive adhesive. In some embodiments, the curing agent is selected from the group consisting of triethanolamine, triethylamine, methylhexahydrophthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, and decahydrophthalic anhydride. At least one of dialkyl maleic anhydrides, optionally triethanolamine. The curing agent is intended to cure the thermoplastic organic resin in the conductive adhesive after application. Generally, the type of curing agent can be selected so that the organic resin does not solidify at room temperature, but only undergoes a substantial curing reaction at a higher temperature when heated. After preparation, the conductive adhesive can also be stored in a low-temperature container, taken out when used, and allowed to solidify at room temperature or higher. In some embodiments, the conductive adhesive has a curing temperature of 40-90°C, optionally 60-80°C. By selecting the types of organic resin and curing agent, the curing temperature of the conductive adhesive can be within the above range. In this case, the resulting conductive adhesive can be stored at room temperature. However, in the case of long-term storage, it is more appropriate to store it in a low-temperature container, for example, below 0°C, or as low as -20°C. Depending on the type of curing agent, the conductive adhesive may be in a single-component or two-component form. However, for ease of use, conductive adhesives are often formulated as one-component forms.

The conductive adhesive of the present application contains 0-20% by weight of diluent, optionally 1-10% by weight, based on the total weight of the conductive adhesive. In some embodiments, the diluent is selected from at least one of acetone, ethyl acetate, 1,4-butanediol diglycidyl ether, and ethylene glycol diglycidyl ether, optionally acetone. In some embodiments, the conductive glue includes any diluent. The diluent is an inert organic solvent that is the active ingredient in the conductive adhesive to reduce the viscosity of the conductive adhesive and make it easier to apply to the bonding site. In some embodiments, the viscosity of the conductive glue before curing may be 5000-20000 mPa.s, optionally 8000-16000 mPa.s. By selecting an appropriate viscosity before curing, the conductive adhesive of the present application can be applied more conveniently. If the viscosity is too high, it will be difficult to cover the areas that need to be bonded with the conductive adhesive; if the viscosity is too low, the conductive adhesive will easily spread to other areas during application, affecting other structures of the battery.

In some embodiments, the conductive adhesive further contains 0.1-1% by weight of initiator. The initiator may be selected from azobisisobutyronitrile (AIBN) or azobisisoheptanitrile (ABVN). In some embodiments, the conductive adhesive further contains 0.1-0.5 wt% antioxidant. The antioxidant may be selected from carbodiimides and/or hindered phenols. The conductive adhesive may also include a curing accelerator, such as 2-ethyl-4-methylimidazole.

The conductive adhesive described in the first aspect of the present application has good electrical conductivity and can form a good electrical connection between the tabs and poles bonded by it, showing sufficient adhesive force and low volume resistance. . In addition, the thermal expansion characteristics of the organic resin in the conductive adhesive are used to cut off the connection path between the tab and the pole when the internal temperature of the battery cell is too high, thereby increasing the safety of the battery.

In some embodiments, both the positive electrode tab and the negative electrode tab of the battery cell are full tabs. By setting the positive electrode tab and the negative electrode tab as full tabs, each positive electrode tab can be conductively bonded to the corresponding positive electrode post, or each negative electrode tab can be conductively bonded to the corresponding negative electrode post. , making the conductivity between each tab and pole more uniform, thereby reducing the volume resistance. In some embodiments, the material of the positive electrode piece and the positive electrode tab is aluminum, and the material of the negative electrode piece and the negative electrode tab is copper. The way in which the positive electrode tab and the positive electrode post, and the negative electrode tab and the negative electrode post in the battery cell are connected through conductive glue can be referred to the description in Figure 6 of this application, which shows that in the cylindrical battery cell, the positive electrode tab Both the lug and the negative electrode lug adopt the full-pole lug method and are electrically connected to the corresponding poles through conductive glue.

The materials of each component of the battery cell of the present application can be selected within a wide range. In some embodiments, the battery cell is specifically a lithium ion secondary battery. The battery cells of the lithium ion secondary battery will be described in detail below.

Typically, a lithium-ion secondary battery includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte. During the charging and discharging process of the battery, active ions are inserted and detached back and forth between the positive and negative electrodes. The isolation film is arranged between the positive electrode piece and the negative electrode piece to play the role of isolation. The electrolyte plays a role in conducting ions between the positive and negative electrodes.

[Electrolyte]

The electrolyte plays a role in conducting ions between the positive and negative electrodes. The electrolyte includes organic solvents, lithium salts and additives.

In this application, the electrolyte salt can be a commonly used electrolyte salt in lithium ion secondary batteries, such as lithium salt, including the above-mentioned lithium salt as a high thermal stability salt, a lithium salt as a low resistance additive, or lithium that inhibits aluminum foil corrosion. Salt. As an example, the electrolyte salt may be selected from lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium bisfluorosulfonyl imide (LiFSI), bistrifluoromethanesulfonyl Lithium imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium difluorodioxalate phosphate (LiDFOP), fluorosulfonic acid Lithium (LiSO ₃ F), difluorodioxalate (NDFOP), Li ₂ F(SO ₂ N) ₂ SO ₂ F, KFSI, CsFSI, Ba(FSI) ₂ and LiFSO ₂ NSO ₂ CH ₂ CH ₂ CF ₃ More than one of them.

The type of solvent is not particularly limited and can be selected according to actual needs. In some embodiments, the solvent is a non-aqueous solvent. Alternatively, the solvent may include one or more of chain carbonate, cyclic carbonate, and carboxylic acid ester. In some embodiments, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate Ester (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) , one of ethyl butyrate (EB), 1,4-butyrolactone (GBL), tetrahydrofuran, sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) above.

In some embodiments, other additives are optionally included in the electrolyte. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and battery low-temperature performance. additives, etc. As an example, the additive is selected from the group consisting of unsaturated bond-containing cyclic carbonate compounds, halogen-substituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sultone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds At least one of a compound, an isocyanate compound, a phosphazene compound, a cyclic acid anhydride compound, a phosphite compound, a phosphate compound, a borate compound, and a carboxylate compound.

[Positive pole piece]

The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and a conductive agent.

As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In the lithium ion secondary battery of the present application, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials (such as aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalene). Formed on substrates such as ethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

The positive active material layer disposed on the surface of the positive current collector includes a positive active material. The positive active material used in the present application may have any conventional positive active material used in secondary batteries. In some embodiments, the cathode active material may include one or more selected from the group consisting of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide One or more of lithium nickel cobalt aluminum oxide and its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate, composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium iron manganese phosphate, lithium iron manganese phosphate One or more of the composite materials with carbon and its modified compounds. These materials are commercially available. The positive active material may be coated with carbon on its surface.

The positive active material layer optionally includes a conductive agent. However, there is no specific restriction on the type of conductive agent, and those skilled in the art can select according to actual needs. As an example, the conductive agent used for the cathode material may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

The positive active material layer also includes a water-based binder. The water-based adhesive may be selected from one or more types of soluble polysaccharides and their derivatives and water-soluble or water-dispersible polymers. As examples, the water-based binder may be methylcellulose and its salts, xanthan gum and its salts, chitosan and its salts, alginic acid and its salts; and polyethyleneimine and its salts , polyacrylamide, acrylic acid copolymers and their derivatives. In particular, the water-based adhesive is a compound of xanthan gum and acrylic acid copolymer, and the weight ratio of the compound is 2:1-0.2:2.8.

In this application, the positive electrode piece can be prepared according to methods known in the art. As an example, the carbon-coated cathode active material, conductive agent and aqueous binder can be dispersed in a solvent (such as water) to form a uniform cathode slurry; the cathode slurry is coated on the cathode current collector and dried. After drying, cold pressing and other processes, the positive electrode piece is obtained.

[Negative pole piece]

The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, where the negative electrode material layer includes a negative electrode active material.

As an example, the negative electrode current collector has two surfaces opposite in its own thickness direction, and the negative electrode material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In the lithium ion secondary battery of the present application, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming metal materials (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalene). Formed on substrates such as ethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In the lithium ion secondary battery of the present application, the negative electrode material layer usually contains a negative electrode active material and an optional binder, an optional conductive agent and other optional auxiliaries, and is usually formed by coating and drying the negative electrode slurry. . Negative electrode slurry coating is usually formed by dispersing the negative electrode active material and optional conductive agent and binder in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

The specific type of negative electrode active material is not limited. Active materials known in the art that can be used in the negative electrode of lithium ion secondary batteries can be used, and those skilled in the art can select according to actual needs. As an example, the negative active material may be selected from one or more of graphite, soft carbon, hard carbon, mesocarbon microspheres, carbon fibers, carbon nanotubes, elemental silicon, silicon oxide compounds, silicon carbon composites, and lithium titanate. kind.

As an example, the conductive agent may be selected from one or more types of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

As an example, the binder may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), One or more of polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

Other optional auxiliaries are, for example, thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[Isolation film]

Lithium-ion secondary batteries using an electrolyte also include a separator. The isolation film is arranged between the positive electrode piece and the negative electrode piece to play the role of isolation. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used. In some embodiments, the material of the isolation membrane can be selected from at least one type selected from the group consisting of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

In some embodiments, the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic. Examples of plastics include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

Figure 1 is a schematic diagram of using conductive glue to bond pole tabs and pole posts in one embodiment of the present application. The conductive glue is applied to all the tabs at the end of the cylindrical battery core in a cross shape, and is bonded to the poles on the casing. Thereby realizing the electrical connection between the tab and the pole.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially. Unless otherwise indicated, all content ratios are weight ratios, and all experiments are conducted at normal temperature (25°C) and normal pressure.

Example 1

(1) Preparation of conductive adhesive

Weigh 20g of epoxy resin (molecular weight: 300,000, from Guangzhou Huayu Chemical Industry) and 10g of acetone, place them in a reaction kettle at room temperature, and vacuum and stir at a rotation speed of 300 rpm for 10 to 30 minutes. Then add 80g Ag powder and continue stirring for 5 minutes. Finally, add 1g triethanolamine and 0.05g azobisisobutyronitrile (AIBN) to the mixture, and continue stirring at room temperature for 30 minutes to mix the components evenly to obtain a conductive adhesive. Finally, fill and discharge, and place Store in a storage container at -10°C until use.

(2) Preparation of battery cells

Preparation of positive electrode plates

The positive active material lithium iron phosphate, the conductive agent conductive carbon black and the binder are mixed in a weight ratio of 96:1:3, in which the binder is modified polyvinylidene fluoride. Stir the resulting mixture thoroughly to form a slurry. By adjusting the amount of solvent N-methylpyrrolidone added, the solid content of the obtained slurry was 57%.

Finally, the positive electrode sheet composition (slurry) is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut to obtain a positive electrode with a single-sided positive electrode sheet film layer weight of 350 mg/1540.25 mm ² piece.

Preparation of negative electrode plates

Dissolve the active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) in the solvent deionized water in a weight ratio of 97:0.4:1.5:1.1 , mix evenly and prepare negative electrode slurry; apply the negative electrode slurry one or more times evenly on the negative electrode current collector copper foil, and then dry, cold press, and cut to obtain negative electrode sheets.

Preparation of electrolyte

In an argon atmosphere glove box (H ₂ O <0.1ppm, O ₂ <0.1ppm), mix the organic solvent ethylene carbonate (EC)/ethyl methyl carbonate (EMC) evenly according to the volume ratio of 3/7, add 12.5 %LiPF ₆ lithium salt is dissolved in the organic solvent and stirred evenly to obtain an electrolyte.

Isolation film

An 8μm PE porous film is used as the base, and a 2μm ceramic coating is coated on both sides as an isolation membrane.

The positive electrode sheet, isolation film, and negative electrode sheet prepared as above are stacked in order so that the isolation film is between the positive and negative electrode sheets to play an isolation role, and then rolled to obtain a cylindrical bare cell. Solder the tabs to the bare battery core. Each positive electrode piece is provided with an aluminum positive electrode tab, and each negative electrode piece is provided with a copper negative electrode tab, and all the tabs are in the form of full tabs. The bare battery core is installed into an aluminum casing, which is provided with a positive pole and a negative pole. All positive electrode tabs are bonded to the positive electrode post through the conductive adhesive prepared above, and all negative electrode tabs are bonded to the negative electrode post through the conductive adhesive prepared above. The bonding was performed at a temperature of 25°C, resulting in a cross-shaped bond. The obtained battery cells are baked at 80 to 100°C to remove water, tested for helium, and then electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then sequentially subjected to processes such as standing, hot and cold pressing, formation, shaping, capacity testing, and high-temperature aging to obtain the lithium-ion battery product of Example 1.

Example 2-4

Except using the conductive filler composition shown in Table 1, other steps are the same as Example 1.

The conductive adhesive and battery cells obtained in Examples 1-4 were subjected to performance tests as described below, and the test results are summarized in Table 2.

1. Shear strength test

Shear strength is measured according to the national standard GB 7124-1986.

2. Electrolyte resistance performance test

Swelling: ① Take a 50*50*2mm glass plate and place the prepared conductive glue on the glass plate. The dispensing mass is 1 to 5g, preferably 1 to 3g. ②Put the glass plate into a sealed glass beaker, cover it, and place it in an oven at 80°C to 100°C to cure for 2 to 4 hours. ③ Take out the glass plate, remove the cured micelle, weigh the mass of the micelle with an electronic balance, and record the data. ④Put the weighed micelle into a beaker containing electrolyte, seal it and place it in an oven at 70°C. Take it out every 24 hours, wipe the liquid on the surface of the micelle with dust-free paper, and let it stand at room temperature for 10 to 30 minutes. Then weigh the micelle and record the data for 10 consecutive days. Calculate the dissolution rate of the micelles.

Dissolution: ① Take out the micelle soaked in the electrolyte for 10 days, dry the liquid on the surface of the micelle with dust-free paper, and let it sit at room temperature for 10 to 30 minutes. ②Then soak the micelles in dimethyl carbonate solvent and place them in an oven at 70°C to 90°C for 48 hours. ③ Take out the micelle, wipe the liquid on the surface of the micelle with dust-free paper, and finally place the micelle in a dry glass beaker and bake it at 70°C to 90°C for 1 to 3 hours. After taking it out, weigh it and calculate the dissolution. rate, at least 10 samples per group.

3. Volume resistance test

① Take a 50*50*2mm glass plate and put tape on the glass plate. Control the distance between the tapes to be 2.54mm and the thickness of the tape to be 50μm. ② Apply the configured conductive adhesive to the groove between the tapes. ③Put the glass plate into a sealed glass beaker, cover it, and place it in an oven at 80°C to 100°C to cure for 2 to 4 hours. ④ Take out the glass plate, test the resistance value with an insulation resistance tester, and calculate the volume resistance.

Table 1: Main components of the conductive adhesive of Examples 1-4 (in grams)

实施例Example	环氧树脂Epoxy resin	AgAg	NiNi	CuCu
11	2020	8080
22	2020	6060	2020
33	2020	4040	2020	2020
44	2020	2020	3030	3030

Table 2: Performance test results of conductive adhesives and batteries in Examples 1-4

It can be seen from the results of Examples 1-4 that compared with Ag powder alone, the mixture of conductive substances formed from the powders of Ag, Ni and Cu exhibits significantly improved resistance to electrolytes, specifically manifested as swelling. and decreased dissolution. In addition, at a specific weight ratio, a mixture of powders containing Ag, Ni and Cu as a conductive filler can reduce the volume resistance by one order of magnitude (Example 3). In fact, the mixture can significantly reduce the amount of Ag powder, which significantly reduces the manufacturing cost of conductive adhesive.

Example 5-7

Except that the resin types shown in Table 3 are used, other steps are the same as in Example 4.

The conductive adhesive and battery cells obtained in Examples 5-7 were subjected to the performance test described below, and the test results are summarized in Table 4 together with the results of Example 4.

Table 3: Main components of the conductive adhesive of Examples 4-7 (in grams)

实施例Example	树脂基体(20g)Resin matrix (20g)	AgAg	NiNi	CuCu
44	环氧树脂Epoxy resin	2020	3030	3030
55	丙烯酸树脂Acrylic	2020	3030	3030
66	聚氨酯树脂Polyurethane resin	2020	3030	3030
77	有机硅树脂Silicone resin	2020	3030	3030

Table 4: Performance test results of the conductive adhesive and battery of Examples 4-7

It can be seen from the results of Examples 4-7 that, while keeping the composition of the conductive filler unchanged, the type of organic resin mainly affects the adhesive force and electrolyte resistance of the obtained conductive adhesive, but has no obvious effect on the volume resistance. . It can be seen from the comparison that choosing epoxy resin as the thermoplastic organic resin matrix of the conductive adhesive results in the highest bonding strength and the lowest swelling and dissolution.

Although the present application has been described with reference to the embodiments, various modifications may be made and equivalents may be substituted for components thereof without departing from the scope of the application. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any way. The application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

A conductive adhesive containing:

14-78% by weight thermoplastic organic resin;

20-85% by weight conductive filler;

0.3-5% by weight curing agent, and

optionally 0-20% by weight of diluent, based on the total weight of the conductive adhesive,

The conductive filler is a mixture of Ag and at least two conductive substances selected from Cu, Al, Fe, Zn, Ni, carbon black and graphite.
The conductive adhesive according to claim 1, wherein the conductive filler is a mixture of Ag, Ni and Cu.
The conductive adhesive according to claim 1 or 2, wherein the conductive filler is a mixture obtained by mixing Ag, Ni and Cu powders in a weight ratio of 20-60:20-40:20-40; optionally, the The weight ratio is 40-60:20-30:20-30.
The conductive adhesive according to any one of claims 1 to 3, wherein the thermoplastic organic resin is selected from one or more of epoxy resin, acrylic resin, phenolic resin, polyurethane, and silicone, optionally Epoxy resin.
The conductive adhesive according to claim 4, wherein the weight average molecular weight of the epoxy resin is 10,0000-100,0000g/mol, optionally 20,0000-60,0000g/mol.
The conductive adhesive according to any one of claims 1 to 5, wherein the curing agent is selected from triethanolamine, triethylamine, methylhexahydrophthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, At least one of hexahydrophthalic anhydride, methylhexahydrophthalic anhydride and dodecylmaleic anhydride, optionally triethanolamine.
The conductive adhesive according to any one of claims 1 to 6, wherein the diluent is selected from the group consisting of acetone, ethyl acetate, 1,4-butanediol diglycidyl ether, and ethylene glycol diglycidyl ether. At least one, optionally acetone.
The conductive adhesive according to any one of claims 1 to 7, further comprising 0.1-1% by weight of an initiator; optionally, the initiator is selected from azobisisobutyronitrile or azobisisoheptan Nitrile.
The conductive adhesive according to any one of claims 1 to 8, further comprising 0.1-0.5% by weight of antioxidant; optionally, the antioxidant is selected from carbodiimide and/or hindered phenol.
The conductive adhesive according to any one of claims 1 to 9, whose viscosity before curing is 5000-20000 mPa.s, optionally 8000-16000 mPa.s.
The conductive adhesive according to any one of claims 1 to 10, its curing temperature is 40-90°C, optionally 60-80°C.
A battery cell including:

The battery core includes a cylindrical structure formed by winding a positive electrode piece, a negative electrode piece, and a separator. The positive electrode piece is provided with a positive electrode tab, and the negative electrode piece is provided with a negative electrode tab;

The housing includes a hollow cylindrical structure with openings at both ends. The battery core is inserted into the housing. Positive poles and negative poles are respectively provided at both ends of the housing. The positive tabs and the The negative electrode tabs are respectively bonded to the positive electrode post and the negative electrode post through the conductive adhesive according to any one of claims 1 to 11.
The battery cell according to claim 12, wherein both the positive electrode tab and the negative electrode tab are full tabs.
The battery cell according to claim 12 or 13, wherein the material of the positive electrode piece and the positive electrode tab is aluminum, and the material of the negative electrode piece and the negative electrode tab is copper.
A battery pack including the battery cell according to any one of claims 12 to 14.
An electrical device comprising the battery cell according to any one of claims 12 to 14 or the battery pack according to claim 15.