Conductive film and preparation method thereof

Abstract

The present invention relates to the technical field of lithium-ion batteries, and in particular to a conductive film and a preparation method thereof, wherein the conductive film comprises a metal layer, a first film layer, a high-temperature resistant sponge layer and a conductive film layer which are compounded in sequence, the high-temperature resistant sponge layer is filled with a flame retardant, a plurality of holes are opened on the conductive film layer, the holes are filled with a plugging agent for plugging the holes, and the softening point of the plugging agent is 50-100° C. The conductive film of the present invention has the function of preventing the battery temperature from rising and improving the battery safety.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a conductive film and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in various electronic devices due to their high energy density, high average output voltage, and low self-discharge. However, due to improper use by people, such as overcharging, these wrong behaviors can cause the battery to heat up and even cause an explosion. Summary of the invention

[0003] In order to overcome the shortcomings and deficiencies in the prior art, the first object of the present invention is to provide a conductive film that has the function of preventing the battery temperature from rising and improving the battery safety.

[0004] The second object of the present invention is to provide a method for preparing a conductive film, which is simple and efficient.

[0005] The first purpose of the present invention is achieved through the following technical scheme: a conductive film, comprising a conductive film layer, a first film layer, a high temperature resistant sponge layer and a conductive film layer compounded in sequence, the high temperature resistant sponge layer is filled with a flame retardant, and a plurality of holes are opened on the conductive film layer compounded on the high temperature resistant sponge layer, and the holes are filled with a plugging agent for plugging the holes, and the softening point of the plugging agent is 50-100°C.

[0006] The second object of the present invention is achieved by the following technical solutions:

[0007] A method for preparing a conductive film, comprising the following preparation steps;

[0008] Step 1, compounding the first film layer on the upper and lower surfaces of the film substrate respectively;

[0009] Step 2: Compounding high temperature resistant sponge layers on the two first film layers respectively to obtain a composite film;

[0010] Step 3, immersing the composite film in a flame retardant solution, wherein the flame retardant solution is mixed with a flame retardant;

[0011] Step 4, taking out the composite film soaked in the flame retardant solvent, drying it, and then rolling the composite film with a rolling device to make the composite film thinner;

[0012] Step 5: coating the upper and lower surfaces of the thinned composite film with conductive film layers respectively;

[0013] Step 6: etching a plurality of holes on the upper and lower conductive film layers respectively by an etching process, wherein the holes penetrate both sides of the conductive film layer in the thickness direction, and then filling the holes on the conductive film layer with a plugging agent by a dispensing process;

[0014] Step 7, peeling off the first film layer on both sides of the film substrate to obtain two sets of conductive base films composited with conductive film layers;

[0015] Step eight, compounding a conductive film layer on the side of the conductive base film that is not compounded with the conductive film layer to obtain a conductive film.

[0016] The flame retardant is at least one of chlorine flame retardant, bromine flame retardant, phosphorus flame retardant, nitrogen flame retardant and intumescent flame retardant. The solvent of the flame retardant solution is at least one of ethanol, methanol, tetrahydrofuran, acetone and acetonitrile. The weight ratio of the solvent to the flame retardant is 3-5:1.

[0017] Wherein, the drying temperature of step 4 is 50-100°C.

[0018] The conductive film layer includes a second film composited on the high temperature resistant sponge layer and a copper-nickel composite coating, a copper coating and a thickened metal coating sequentially coated on the high temperature resistant sponge layer.

[0019] Wherein, the plugging agent is paraffin.

[0020] Wherein, the paraffin wax is modified paraffin wax, and the modified paraffin wax comprises paraffin wax, lithium chloride, conductive graphite and n-dodecanoic acid.

[0021] Wherein, the diameter of the hole is 2-3um.

[0022] Wherein, the porosity of the high temperature resistant sponge layer is 60-80%.

[0023] Wherein, the pore diameter of the high temperature resistant sponge layer is 1-2um.

[0024] The beneficial effects of the present invention are:

[0025] The present invention provides a high-temperature resistant sponge layer filled with a flame retardant and a conductive film with holes. Since the holes are filled with a blocking agent and the blocking agent melts at high temperatures, when the lithium-ion battery causes internal thermal runaway due to improper use or the like and the temperature rises to the softening point of the blocking agent, the blocking agent softens and the holes in the conductive film layer are opened. After the holes are opened, the flame retardant in the high-temperature resistant sponge layer is released from the holes into the battery, thereby preventing the battery temperature from further increasing, preventing internal combustion of the battery, and improving the safety performance of the battery.

[0026] The method of the present invention can prepare two groups of conductive films at one time by simultaneously compounding the first film, the high temperature resistant sponge layer and the conductive film layer on the upper and lower surfaces of the film substrate, thereby greatly improving the production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0028] Figure 1 is a cross-sectional view of a conductive film product according to an embodiment of the present invention;

[0029] Figure 2 is a top view of a conductive film according to an embodiment of the present invention;

[0030] Figure 3 It is a cross-sectional view of the composite process of the conductive film layer and the substrate according to an embodiment of the present invention.

[0031] Explanation of the reference numerals: 1. first film layer; 2. high temperature resistant sponge layer; 31. second film; 32. metal coating layer; 33. copper coating layer; 34. copper-nickel composite coating layer; 35. thickened metal coating layer; 4. hole; 5. film substrate; 6. metal layer. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in combination with the embodiments and drawings, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by technicians in this field without creative work are all within the scope of protection of the present invention. In addition, all the connection / connection relationships involved in the patent do not refer to the direct connection of components, but refer to the formation of a better connection structure by adding or reducing connection accessories according to the specific implementation situation. The various technical features in the invention can be combined interchangeably without conflicting with each other.

[0033] Example 1

[0034] A conductive film, such as Figure 1 and 2 As shown, it includes a metal layer 6, a first film layer 1, a high temperature resistant sponge layer 2 and a conductive film layer which are compounded in sequence, the high temperature resistant sponge layer 2 is filled with a flame retardant (not shown in the figure), a plurality of holes 4 are opened on the conductive film layer, the holes 4 are filled with a plugging agent for plugging the holes 4, and the softening point of the plugging agent is 50-100°C.

[0035] The present invention provides a high-temperature resistant sponge layer 2 filled with a flame retardant and a conductive film with holes 4. Since the holes 4 are filled with a blocking agent and the blocking agent melts at high temperatures, when the lithium-ion battery causes internal thermal runaway due to improper use or other reasons and the temperature rises to the softening point of the blocking agent, the blocking agent softens and the holes 4 of the conductive film layer are opened. After the holes 4 are opened, the flame retardant in the high-temperature resistant sponge layer 2 is released from the holes 4 into the battery, thereby preventing the battery temperature from further increasing, preventing internal combustion of the battery, and improving the safety performance of the battery.

[0036] In order to ensure that the flame retardant can be smoothly released from the high temperature resistant sponge layer 2, the diameter of the hole 4 is 2.5 um. The control of the diameter of the hole 4 can also ensure that the conductive film has good conductive properties.

[0037] Wherein, the plugging agent is paraffin.

[0038] Preferably, in this embodiment, the paraffin is modified paraffin, and the main components of the modified paraffin are 6 parts by weight of paraffin, 1 part by weight of lithium chloride, 3 parts by weight of conductive graphite and 1 part by weight of n-dodecanoic acid. Paraffin generally starts to soften at 50-60 degrees. By adding the above ingredients, the softening point of the paraffin can be increased without affecting its conductive properties. On the other hand, the softened paraffin contains lithium ions, which can also play a role in supplementing lithium and improving the energy density of the battery.

[0039] The conductive film layer includes a second film 31 and a metal coating layer 32 which are sequentially compounded on the surface of the high temperature resistant sponge layer 2 away from the first film layer 1. Compared with the metal film formed by calendering of metal materials, the metal coating layer 32 is lighter, which is beneficial to improve the energy density of the battery.

[0040] In order to improve the conductivity of the conductive film layer, the metal plating layer 32 includes a copper plating layer 33 .

[0041] The metal plating layer 32 further includes a copper-nickel composite plating layer 34 disposed between the second film 31 and the copper plating layer 33. Since the copper-nickel composite plating layer 34 can be plated onto the second film 31 better, the bonding force between the copper-nickel plating layer and the second film 31 is better than that between the copper plating layer 33, which is more conducive to improving the conductive stability and conductivity of the conductive film.

[0042] In order to increase the thickness of the metal plating layer 32, the metal plating layer 32 further includes a thickened metal plating layer 35 disposed on the side of the copper plating layer 33 away from the second film 31. The thickened metal plating layer 35 is plated by a water plating device, which can be an acidic water plating device or an alkaline water plating device, which can be freely selected according to the thickness and properties of the metal layer to be achieved. Specifically, the thickened metal plating layer 35 is a copper layer.

[0043] Specifically, the structure of the metal layer 6 is the same as that of the metal coating layer 32. That is, the metal layer 6 includes a copper-nickel composite coating 34, a copper coating 33 and a copper layer arranged in sequence, and the copper-nickel composite coating 34 is coated on the side of the first film layer away from the high temperature resistant sponge layer 2.

[0044] In order to facilitate the filling of the flame retardant, the porosity of the high temperature resistant sponge layer 2 is 60-80%.

[0045] In order to further facilitate the filling of the flame retardant and the release of the flame retardant from the high temperature resistant sponge layer 2, the pore diameter of the high temperature resistant sponge layer 2 is 1 um.

[0046] Example 2

[0047] A method for preparing a conductive film, comprising the following preparation steps;

[0048] Step 1: Using a thin film laminating device to laminate the first thin film layer 1 on the upper and lower surfaces of the thin film substrate 5;

[0049] Step 2: Compounding the high temperature resistant sponge layer 2 on the two first film layers 1 respectively to obtain a composite film;

[0050] Specifically, the porosity of the high temperature resistant sponge layer 2 is 70% and the pore diameter is 1 um.

[0051] Step 3, immersing the composite film in a flame retardant solution for 4 hours, wherein the flame retardant solution is mixed with a flame retardant;

[0052] Specifically, the flame retardant is a chlorine-based flame retardant, specifically chlorinated polyethylene. The solvent of the flame retardant solution is ethanol. The weight ratio of the solvent to the flame retardant is 4:1.

[0053] Step 4, taking out the composite film soaked in the flame retardant solvent, drying it at a temperature of 75° C., and then rolling the composite film with a rolling device to make the composite film thinner;

[0054] Step 5: Coat the upper and lower surfaces of the thinned composite film with conductive film layers, such as Figure 3 As shown;

[0055] Specifically, the conductive film layer includes a second film 31 composited on the high temperature resistant sponge layer 2 and a copper-nickel composite coating 34 , a copper coating 33 and a thickened metal coating 35 sequentially coated on the high temperature resistant sponge layer 2 .

[0056] The specific operations are as follows:

[0057] First, a second film 31 is composited on one side of the thinned composite film, and then a vacuum coating device is used in a vacuum environment to perform vacuum coating on the surface of the second film 31, and a copper-nickel composite coating 34 and a copper coating 33 are sequentially coated. Subsequently, a water plating device is used to coat a thickened metal coating 35 on the surface of the copper coating 33. The purpose of thickening the metal coating 35 is to increase the thickness of the metal coating.

[0058] The vacuum coating device used is a magnetron sputtering coating device or a vacuum evaporation coating device, and the water coating device can be an acidic water coating device or an alkaline water coating device, which can be freely selected according to the thickness and properties of the metal layer to be achieved.

[0059] Step 6: Use an etching process to etch a plurality of circular holes 4 on the conductive film layer. The diameter of the hole 4 is 2.5 μm. The hole 4 penetrates both sides of the thickness direction of the conductive film layer, that is, the depth of the hole 4 directly reaches the surface of the high temperature resistant sponge layer 2. Then, the plugging agent is filled into the hole 4 on the conductive film layer by a dispensing process. The filled composite material is as follows: Figure 3 shown.

[0060] Wherein, the plugging agent is paraffin.

[0061] Preferably, the paraffin wax is modified paraffin wax, and the modified paraffin wax includes 6 parts by weight of paraffin wax, 1 part by weight of lithium chloride, 3 parts by weight of conductive graphite and 1 part by weight of n-dodecanoic acid.

[0062] Step 7: Peel off the first film layer on both sides of the film substrate to obtain two groups of conductive base films composited with conductive film layers.

[0063] Step 8: A metal layer is plated on the side of the conductive base film that is not composited with the conductive film layer to obtain a conductive film, such as Figure 1 and 2 shown.

[0064] The metal layer includes a copper-nickel composite plating layer 34, a copper plating layer 33 and a thickened metal plating layer 35 which are sequentially plated on the side of the first film layer away from the high temperature resistant sponge layer. The plating method of the metal layer is the same as that of the copper-nickel composite plating layer 34, the copper plating layer 33 and the thickened metal plating layer 35 of the conductive film layer.

[0065] By using the conductive film of the present invention, when the battery is in thermal runaway due to improper use or other reasons, the temperature rises to the softening point of the modified paraffin wax, the modified paraffin wax softens, and the flame retardant in the high temperature resistant sponge is released, thereby preventing the battery temperature from further increasing and improving the safety performance of the battery. On the other hand, the softened paraffin wax contains lithium ions, which can also play a role in replenishing lithium and improving the energy density of the battery.

[0066] Example 3

[0067] A method for preparing a conductive film, comprising the following preparation steps;

[0068] Step 1: Using a thin film laminating device to laminate the first thin film layer 1 on the upper and lower surfaces of the thin film substrate 5;

[0069] Step 2: Compounding the high temperature resistant sponge layer 2 on the two first film layers 1 respectively to obtain a composite film;

[0070] Specifically, the porosity of the high temperature resistant sponge layer 2 is 60% and the pore diameter is 2 um.

[0071] Step 3, immersing the composite film in a flame retardant solution for 3 hours, wherein the flame retardant solution is mixed with a flame retardant;

[0072] Specifically, the flame retardant is a bromine flame retardant, specifically dibromomethane. The solvent of the flame retardant solution is methanol. The weight ratio of the solvent to the flame retardant is 3:1.

[0073] Step 4, taking out the composite film soaked in the flame retardant solvent, drying it at a temperature of 50° C., and then rolling the composite film with a rolling device to make the composite film thinner;

[0074] Step 5: Compound conductive film layers on the upper and lower surfaces of the thinned composite film, such as Figure 3 As shown, the structure of the conductive film layer and the specific operations during compounding are the same as those in Example 2, and will not be described in detail here.

[0075] Step 6: Use an etching process to etch a plurality of circular holes 4 on the conductive film layer. The diameter of the hole 4 is 2um. The hole 4 penetrates both sides of the thickness direction of the conductive film layer, that is, the depth of the hole 4 directly reaches the surface of the high temperature resistant sponge layer 2. Then, the plugging agent is filled into the hole 4 on the conductive film layer by a dispensing process. The filled composite material is as follows: Figure 3 shown.

[0076] Wherein, the plugging agent is paraffin.

[0077] Preferably, the paraffin wax is modified paraffin wax, and the modified paraffin wax includes 6 parts by weight of paraffin wax, 1 part by weight of lithium chloride, 3 parts by weight of conductive graphite and 1 part by weight of n-dodecanoic acid.

[0078] Step 7: Peel off the first film layer on both sides of the film substrate to obtain two groups of conductive base films composited with conductive film layers.

[0079] Step 8: A metal layer is plated on the side of the conductive base film that is not composited with the conductive film layer to obtain a conductive film, such as Figure 1 and Figure 2 shown.

[0080] Example 4

[0081] A method for preparing a conductive film, comprising the following preparation steps;

[0082] Step 1: Using a thin film laminating device to laminate the first thin film layer 1 on the upper and lower surfaces of the thin film substrate 5;

[0083] Step 2: Compounding the high temperature resistant sponge layer 2 on the two first film layers 1 respectively to obtain a composite film;

[0084] Specifically, the porosity of the high temperature resistant sponge layer 2 is 80% and the pore diameter is 2 um.

[0085] Step 3, immersing the composite film in a flame retardant solution for 5 hours, wherein the flame retardant solution is mixed with a flame retardant;

[0086] Specifically, the flame retardant is a phosphorus-based flame retardant, specifically ditolyl phosphate. The solvent of the flame retardant solution is tetrahydrofuran. The weight ratio of the solvent to the flame retardant is 5:1.

[0087] Step 4: taking out the composite film soaked in the flame retardant solvent, drying it at a temperature of 100° C., and then rolling the composite film with a rolling device to make the composite film thinner;

[0088] Step 5: Compound conductive film layers on the upper and lower surfaces of the thinned composite film, such as Figure 3 As shown, the structure of the conductive film and the specific compounding steps are the same as those in Example 2, and are not described in detail here.

[0089] Step 6: Use an etching process to etch a plurality of circular holes 4 on the two conductive film layers. The diameter of the hole 4 is 3um. The hole 4 penetrates both sides of the thickness direction of the conductive film layer, that is, the depth of the hole 4 directly reaches the surface of the high temperature resistant sponge layer 2. Then, the plugging agent is filled into the hole 4 on the conductive film layer by a dispensing process. The filled composite material is as follows: Figure 3 shown.

[0090] Wherein, the plugging agent is paraffin.

[0091] Preferably, the paraffin wax is modified paraffin wax, and the modified paraffin wax includes 6 parts by weight of paraffin wax, 1 part by weight of lithium chloride, 3 parts by weight of conductive graphite and 1 part by weight of n-dodecanoic acid.

[0092] Step 7: Peel off the first film layer on both sides of the film substrate to obtain two sets of conductive base films with conductive film layers, such as Figure 1 and Figure 2 shown.

[0093] Step 8: A metal layer is plated on the side of the conductive base film that is not composited with the conductive film layer to obtain a conductive film, such as Figure 1 and Figure 2 shown.

[0094] Comparative Example

[0095] A conductive film, the difference between the conductive film of the comparative example and the conductive film of Example 1 is that no holes are arranged on the conductive film layer of the conductive film of the comparative example, and no flame retardant is filled in the high temperature resistant sponge layer.

[0096] Performance Testing

[0097] 1. Preparation of lithium-ion battery containing comparative conductive film:

[0098] Graphite, PVDF and n-butyl acetate are mixed in a ratio of 2:1:2 to prepare a negative electrode active slurry, which is coated on the conductive film of the comparative example to obtain a negative electrode plate;

[0099] Lithium iron phosphate, PVDF, and ethyl acetate are prepared into a positive electrode active material in a ratio of 5:2:3, and the positive electrode active material is coated on a film plated with metal aluminum. The difference between the film plated with metal aluminum and the conductive film provided by the present invention is that the outermost metal layer is all aluminum layer, the thickness of the aluminum layer is also the same, and there are no holes and sealed flame retardants.

[0100] The diaphragm is made of a polyethylene film with a porosity of 85% and a pore size of 50nm. The electrolyte is a 1.0M LiPF6 EC+DMC+EMC solution. The positive electrode, negative electrode and diaphragm are assembled into a lithium-ion battery. All assemblies are carried out in a glove box.

[0101] 2. Preparation of a lithium ion battery containing the conductive film of Example 1:

[0102] The same process and ingredients as those of the comparative example are used, the only difference being the different conductive films used.

[0103] 3. Safety performance test: Take two groups of batteries made of the conductive film of the comparative example as control group 1 and control group 2, and take two groups of batteries made of the conductive film of Example 1 as experimental group 1 and experimental group 2. Put the four groups of batteries in a temperature box, and heat the temperature from room temperature to 130℃±2℃ at a rate of 5℃ / min. Keep this temperature for 30 minutes and then stop heating. Observe for 1 hour. There is no explosion, fire or leakage.

[0104] sample result Control group 1 combustion Control group 2 combustion Experimental Group 1 No burning, leakage, etc. Experimental Group 2 No burning, leakage, etc.

[0105] 4. Acupuncture experiment:

[0106] At room temperature, first charge the battery to 4.2V with a constant current of 0.5C, then switch to constant voltage charging. After charging is terminated, reduce the circuit to 0.05C and leave it for 60 minutes. Use a Φ5mm~Φ6mm high-temperature resistant steel needle (the cone angle of the needle tip is 45°~60°, and the surface of the needle is smooth, free of rust, oxide layer and oil), and penetrate it from a direction perpendicular to the battery plate at a speed of (25±5)mm / s. The penetration position should be close to the geometric center of the pierced surface, and the steel needle should remain in the battery.

[0107] sample result Control group 1 smoke Control group 2 Fire Experimental Group 1 No fire, smoke, etc. Experimental Group 2 No fire, smoke, etc.

[0108] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A conductive film, characterized in that: It comprises a metal layer, a first film layer, a high temperature resistant sponge layer and a conductive film layer which are compounded in sequence, wherein the high temperature resistant sponge layer is filled with a flame retardant, the conductive film layer is provided with a plurality of holes, the holes are filled with a plugging agent for plugging the holes, and the softening point of the plugging agent is 50-100°C; The hole penetrates both sides of the conductive film layer in the thickness direction; The plugging agent is paraffin; The paraffin wax is modified paraffin wax, and the modified paraffin wax comprises paraffin wax, lithium chloride, conductive graphite and n-dodecanoic acid.

2. A method for preparing a conductive film, characterized in that: The method comprises the following preparation steps; Step 1, compounding the first film layer on the upper and lower surfaces of the film substrate respectively; Step 2: Compounding high temperature resistant sponge layers on the two first film layers respectively to obtain a composite film; Step 3, immersing the composite film in a flame retardant solution, wherein the flame retardant solution is mixed with a flame retardant; Step 4, taking out the composite film soaked in the flame retardant solvent, drying it, and then rolling the composite film with a rolling device to make the composite film thinner; Step 5: coating the upper and lower surfaces of the thinned composite film with a conductive film layer; Step 6: etching a plurality of holes on the conductive film layer by an etching process, wherein the holes penetrate both sides of the conductive film layer in a thickness direction, and then filling the holes on the conductive film layer with a plugging agent by a dispensing process; Step 7, peeling off the first film layer on both sides of the film substrate to obtain two sets of conductive base films composited with conductive film layers; Step eight, compounding a conductive film layer on the side of the conductive base film that is not compounded with the conductive film layer to obtain a conductive film; The softening point of the plugging agent is 50-100°C; The plugging agent is paraffin; The paraffin wax is modified paraffin wax, and the modified paraffin wax comprises paraffin wax, lithium chloride, conductive graphite and n-dodecanoic acid.

3. The method for preparing a conductive film according to claim 2, characterized in that: The flame retardant is at least one of a chlorine-based flame retardant, a bromine-based flame retardant, a phosphorus-based flame retardant, a nitrogen-based flame retardant, and an intumescent flame retardant.

4. The method for preparing a conductive film according to claim 2, characterized in that: The drying temperature in step 4 is 50-100°C.

5. The method for preparing a conductive film according to claim 2, characterized in that: The conductive film layer comprises a second film composited on the high temperature resistant sponge layer and a copper-nickel composite plating layer, a copper plating layer and a thickened metal plating layer which are sequentially plated on the second film.

6. The method for preparing a conductive film according to claim 2, characterized in that: The diameter of the hole is 2-3um.

7. The method for preparing a conductive film according to claim 2, characterized in that: The porosity of the high temperature resistant sponge layer is 60-80%.

8. The method for preparing a conductive film according to claim 2, characterized in that: The pore diameter of the high temperature resistant sponge layer is 1-2 um.

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