Composite membrane and lithium ion battery containing the same

Abstract

The present invention provides a composite membrane, comprising a polymer layer, a surface treatment layer, a metal layer, and micropores; the polymer layer is the innermost layer, the surface treatment layer is arranged on both sides of the polymer layer, the metal layer is plated on the outer surface of the surface treatment layer, and the micropores penetrate the polymer layer, the surface treatment layer, and the metal layer. The polymer layer is composited by organic polymer materials and inorganic materials; the inorganic materials include conductive agents and solid electrolyte materials; the polymer layer has a thickness of 2-30 μm. The composite membrane provided by the present invention can increase the energy density and safety performance of the battery core on the basis of improving electrical performance.

Description

Technical Field

[0001] The invention relates to the field of lithium ion batteries, and in particular to a composite membrane and a lithium ion battery containing the composite membrane. Background Art

[0002] Lithium-ion secondary batteries have become the most widely used secondary batteries due to their advantages such as high voltage, high energy density, and long cycle life. However, lithium-ion batteries are prone to fire and explosion under some special conditions, such as mechanical damage such as extrusion, heavy impact or puncture, which leads to serious safety hazards. Therefore, their application development is greatly limited in some fields.

[0003] A large number of research results show that the biggest cause of these safety hazards is the internal short circuit of the battery. When an internal short circuit occurs, the lithium-ion battery will release a large amount of heat in a very short time, which can lead to fire and explosion. There are many modes of internal short circuit in the battery, among which the short circuit between the positive electrode collector and the negative electrode is the fastest and most dangerous mode of heat transfer.

[0004] To solve the above problems, many composite current collectors with high molecular polymers as base films have been widely developed, but these polymers are not conductive and the surface is relatively smooth, which is not conducive to direct evaporation of the current collector metal. Generally, a transition layer or adhesive layer needs to be added, but these added layers will affect the overall energy density of the battery. There are also patents that propose to improve the conductivity of high molecular polymer films by adding conductive agents. The conductivity is increased, but the ion conduction efficiency is reduced. Therefore, there is an urgent need for a polymer composite film that has both certain electronic conductivity and ionic conductivity and is easy for the current collector metal to adhere. Summary of the invention

[0005] The purpose of the present invention is to provide a composite membrane and a lithium ion battery containing the membrane in order to solve the above problems, which can improve the safety and electrochemical performance of the lithium ion battery while taking into account the ease of process implementation and the premise of improving the energy density.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A composite membrane comprises a polymer layer, a surface treatment layer, a metal layer and micropores; the polymer layer is the innermost layer, the surface treatment layer is arranged on both sides of the polymer layer, the metal layer is plated on the outer surface of the surface treatment layer, and the micropores penetrate the polymer layer, the surface treatment layer and the metal layer.

[0008] To optimize the above technical solutions, the specific measures taken also include:

[0009] Furthermore, the polymer layer is composed of an organic polymer material and an inorganic material; the inorganic material includes a conductive agent and a solid electrolyte material; the polymer layer has a thickness of 2-30 μm, preferably 4-16 μm, and a resistivity of 1×10 -9 ~1×10 -6 Ω·m.

[0010] Furthermore, the polymer material is selected from at least one of polypropylene, polyethylene, polyethylene terephthalate, polyimide, polyvinylidene fluoride, polymethyl methacrylate, polystyrene, polyurethane, epoxy resin or modified materials of the above materials.

[0011] Furthermore, the conductive agent is selected from at least one of carbon black, acetylene black, carbon nanotubes, carbon fibers, graphite, nanographite, graphene, fullerene, conductive metals and oxides thereof.

[0012] Furthermore, the solid electrolyte material is selected from perovskite type, antiperovskite type, NASICON type, LISICON type, Garnet type crystalline oxide, LiPON type glass oxide, crystalline Li 4-x A 1-x B x S4 (A = Ge, Si, B = P, Al, Zn), glassy Li2S-P2S5, crystalline Li x M y PS z (wherein, M is one or more of Si, Ge, Sn, P, Al, Zn, x+4y+5=2z, 0≤y≤1), sulfides or halides of glass-ceramic state Li2S-P2S5, Li6PS5X (X=Cl, Br, I) and at least one of the modified materials of the above materials.

[0013] Furthermore, the mass percentage of the organic polymer material is 55%-90%, the mass percentage of the conductive agent is 5%-25%, and the mass percentage of the solid electrolyte is 5%-20%.

[0014] Furthermore, the treatment method of the surface treatment layer is selected from one or more of corona treatment, electric spark treatment, plasma treatment, nickel plating, ALO plating, chemical treatment coating, and NaOH immersion; the thickness of the surface treatment layer is 0.005-0.05um.

[0015] Furthermore, the material of the metal layer is selected from at least one of copper, aluminum, nickel, zinc, titanium, silver and stainless steel; preferably copper and aluminum, the thickness of the aluminum layer is 0.5-3 μm, and the thickness of the copper layer is 0.5-2 μm.

[0016] Furthermore, the diameter of the micropores is 0.5-30 μm, and the spacing is 0.5-10 mm.

[0017] Furthermore, the present invention provides a lithium ion battery comprising the composite membrane.

[0018] The beneficial effects of the present invention are:

[0019] (1) The polymer layer in the composite film provided by the present invention has the following functions: a) increasing the conductivity of the current collector and improving the charge and discharge rate performance of the lithium-ion battery; b) solving the bonding problem between the traditional composite current collector substrate and the metal layer without the need to add a new adhesive or adhesion layer; c) increasing the tensile strength and elongation of the current collector, making it less likely to break due to crushing; d) increasing the ion conductivity of the foil by adding a solid electrolyte, reducing electrode polarization, and improving the electrochemical performance of the battery, while reducing the heat generated by the lithium battery, reducing the probability of fire, and improving the safety of the battery.

[0020] (2) The metal layer in the composite film provided by the present invention mainly plays the role of electron conduction.

[0021] (3) The micropores in the composite membrane provided by the present invention have the following functions: a) further reducing the surface density of the current collector and directly improving the weight energy density; b) increasing the adhesion between the positive and negative electrode active materials and the current collector and improving the qualified rate of the electrode sheet; c) improving the wettability of the slurry, electrolyte and foil; d) after the foil is through-hole, the diffusion path of lithium ions can be converted into three-dimensional all-round penetration, and the contact area between the positive and negative electrode materials and the foil can be entered into the gap, thereby reducing the migration radius of lithium ions, improving the conductivity efficiency, effectively reducing the internal resistance of the lithium-ion battery, reducing polarization, improving the rate performance and gram capacity, and thus improving the electrical performance of the battery cell. DETAILED DESCRIPTION

[0022] Example 1 A composite membrane and a lithium ion battery comprising the composite membrane

[0023] A composite membrane, comprising a polymer layer, a surface treatment layer, a metal layer, and micropores; the polymer layer is the innermost layer, the surface treatment layer is arranged on both sides of the polymer layer, the metal layer is plated on the outer surface of the surface treatment layer, and the micropores penetrate the polymer layer, the surface treatment layer, and the metal layer. The polymer layer is composed of an organic polymer material and an inorganic material; the inorganic material includes a conductive agent and a solid electrolyte material; the polymer layer has a thickness of 6 μm and a resistivity of 1×10 -9 ~1×10 -6 The polymer material is polyimide, the conductive agent is Super P carbon black (SP) and carbon nanotubes (CNT), and the solid electrolyte material is lithium aluminum titanium phosphate Li 1.3 Al0.3 Ti 1.7 P3O 12 (LATP), Li 10 GeP2S 12 (LGPS) and lithium lanthanum zirconium oxide Li7La3Zr2O 12 (LLZO). The mass percentage of the organic polymer material is preferably 55%-90% (the sample preparation and test range is 0%-95%), the mass percentage of the conductive agent is preferably 5%-25% (the sample preparation and test range is 0%-30%), and the mass percentage of the solid electrolyte is preferably 5%-20% (the sample preparation and test range is 0%-25%). The surface treatment layer is treated by corona treatment, and the thickness of the surface treatment layer is 0.01um. The materials of the metal layer are copper and aluminum, the thickness of the aluminum layer is 1μm, and the thickness of the copper layer is 1μm. The diameter of the micropores is 10μm and the spacing is 2mm.

[0024] A lithium ion battery, wherein the battery pole piece comprises the composite film.

[0025] Example 2 Preparation method of lithium ion battery containing composite membrane

[0026] 1) Preparation of a positive electrode sheet comprising a composite film:

[0027] The polymer material, conductive agent and solid electrolyte are uniformly mixed, heated, melted and stirred evenly, and then stretched to form a polymer layer with a thickness of 6μm by tape casting; the polymer layer is then wound on a roller, placed in a vacuum environment after corona treatment, and placed in a double-sided reciprocating evaporation coating machine vacuum chamber for evaporation to form a conductive metal aluminum layer with a thickness of 1μm on both sides to obtain a composite film. Then, a high-energy laser is used to punch holes on the surface of the composite film to obtain a microporous composite aluminum film, which is used as the positive electrode current collector of lithium-ion batteries.

[0028] 96% LCO, 2% SP and 2% PVDF are used with NMP as solvent, stirred evenly and then coated on the above-mentioned microporous composite aluminum film current collector, dried at 90°C and then rolled and cut, and then dried at 110°C under vacuum conditions for 4 hours, and the pole ears are welded to make the positive electrode sheet of the lithium-ion secondary battery.

[0029] Conventional positive electrode sheet: Use conventional aluminum foil as the current collector, and the remaining steps are the same as the above preparation method.

[0030] 2) Preparation of negative electrode sheet containing composite film:

[0031] The polymer material, conductive agent and solid electrolyte are uniformly mixed, heated, melted and stirred evenly, and then stretched to form a composite polymer layer with a thickness of 6um by tape casting; the composite polymer layer is then wound on a drum, placed in a vacuum environment after corona treatment, and placed in a double-sided reciprocating evaporation coating machine vacuum chamber for evaporation to form a conductive metal copper layer with a thickness of 1um on both sides to obtain a composite film. Then, a high-energy laser is used to punch holes on the surface of the composite film to obtain a microporous composite copper film, which is used as the negative electrode current collector of lithium-ion batteries.

[0032] Graphite, conductive agent SP, thickener CMC and adhesive SBR were added to deionized water in a mass ratio of 96.8:1:1:1.2 and mixed evenly to form negative electrode slurry, and then the negative electrode slurry was coated on the microporous composite copper film, dried at 85°C, rolled and cut. Then it was dried at 130°C under vacuum conditions for 6 hours, and the tabs were welded to form the negative electrode sheet of the lithium-ion battery.

[0033] Conventional negative electrode sheet: Use conventional copper foil as the current collector, and the remaining steps are the same as the above preparation method.

[0034] 3) Prepare electrolyte:

[0035] In a glove box filled with argon, ethylene carbonate, propylene carbonate and propyl propionate were mixed in a mass ratio of 2:1:3, and then lithium hexafluorophosphate with a concentration of 1 mol / L was slowly added to the mixed solution and stirred evenly to obtain a lithium-ion battery electrolyte.

[0036] 4) Assembling lithium-ion batteries:

[0037] The positive electrode sheet, negative electrode sheet and polyethylene separator with a thickness of 12 μm prepared by the above method are stacked and wound into a square core in sequence, and the core is loaded into a polymer soft-pack battery shell (made of aluminum-plastic film), and then vacuum-baked and injected with electrolyte. After packaging, the polymer soft-pack lithium-ion battery is obtained after standing, formation, degassing, aging and capacity separation.

[0038] Example 3 Testing method of lithium ion battery

[0039] 1) 0.7C cycle performance test: At 25°C, the formed lithium-ion battery is charged to 4.45V at 0.7C constant current and constant voltage, with a cut-off current of 0.02C. After being left for 10 minutes, it is discharged to 3.0V at 0.7C constant current. The charge and discharge cycle is continued until the capacity decays to less than 80% of the initial discharge capacity, and the test is stopped.

[0040] 2) Needle penetration test: At 25℃, discharge the divided lithium-ion battery at 0.2C to 3.0V, leave it for 10 minutes, then charge it at 0.5C constant current and constant voltage to 4.45V, and cut off at 0.02C. A high-temperature resistant steel needle is inserted into the battery at a speed of 25±5mm / s from a direction perpendicular to the battery plate. The penetration position should be close to the geometric center of the pierced surface. The steel needle stays in the battery to observe whether the battery catches fire or explodes.

[0041] 3) Heavy object impact test: At 25℃, discharge the divided lithium-ion battery at 0.2C to 3.0V, leave it for 10 minutes, and then charge it at 0.5C constant current and constant voltage to 4.45V, with a cut-off of 0.02C. Place the battery on the platform surface, place a metal rod with a diameter of 15.8±0.2mm horizontally on the upper surface of the geometric center of the battery, and use a weight of 9.1kg±0.1kg to hit the battery surface with the metal rod in a free fall state from a height of 610mm±25mm, and observe for 6 hours to see if there is any fire or explosion.

[0042] 4) Rate discharge performance test: At 25°C, the divided lithium-ion battery was first discharged at 0.2C to 3.0V, left for 10 minutes, and then charged at 0.5C constant current and constant voltage to 4.45V, with a cut-off of 0.02C. Then, it was discharged at different rates of 0.2C / 0.5C / 1C / 1.5C / 2C to 3.0V.

[0043] 5) High and low temperature discharge performance: At 25℃, the divided lithium-ion battery was first discharged at 0.2C to 3.0V, left for 10 minutes, and then charged at 0.5C constant current and constant voltage to 4.45V, and then cut off at 0.02C. Then, it was discharged at 0.2C to 3.0V at different temperatures of 25℃ / 55℃ / 0℃ / -10℃ / -20℃.

[0044] Example 4 Test Results

[0045] Table 1-1 lists the specific amounts of materials used for the composite film. The corresponding positive electrode sheets, negative electrode sheets, and electrolytes were prepared according to the preparation method provided in Example 2 and assembled into lithium-ion batteries, and then tested according to the test method provided in Example 3. To ensure the accuracy of the data, 5 batteries of each type were prepared (10 batteries for needle puncture and heavy object impact were prepared) and tested independently, and the final test results were averaged. The test results are shown in Tables 1-2, 1-3, 1-4, and 1-5.

[0046] Table 1-1 Current Collector Components

[0047]

[0048] Table 1-2 Current collector parameters

[0049]

[0050]

[0051] Comparing the positive electrode film 1# with 2# / 3# / 4# / 5# / 6#, and the negative electrode film 1# with 2# / 3# / 4# / 5# / 6#, we can see that: with the increase of the total amount of inorganic materials, the resistivity of the film decreases, the tensile strength increases, and the elongation decreases. Comparing the positive electrode film 3# with 7# and 8#, with the same total amount of inorganic materials, different solid electrolytes have little difference in the performance of the film. In general, the tensile strength and elongation of the composite film are greater than those of the pure metal current collector.

[0052] Table 1-3 lists the performance test results of lithium-ion batteries of battery samples 1-6 and 9 to verify the influence of different solid electrolyte contents in the positive electrode film. Comparing sample 1 with samples 2-6, it can be seen that: with the increase of solid electrolyte content, the electrical performance has a certain increase, but the safety performance will decrease. Comparing sample 9 with samples 1-6, it can be seen that: the composite film has a certain improvement on the safety performance of the battery cell. Properly increasing the content of solid electrolyte and conductive agent can achieve slightly better electrical performance than pure metal current collector while taking into account safety performance.

[0053] Table 1-3 Lithium-ion battery performance test results of samples 1-6 and 9

[0054]

[0055] Table 1-4 lists the performance test results of lithium-ion batteries of battery samples 1 and 10-14 to verify the influence of different solid electrolyte contents in the negative electrode film. Comparing battery samples 1 and 10-14, it can be seen that: with the increase of solid electrolyte content, the electrical performance has a certain increase, but the safety performance will decrease. Comparing sample 17 with sample 10-14, it can be seen that: the composite film has a certain improvement on the safety performance of the battery cell. Appropriately increasing the content of solid electrolyte and conductive agent can achieve slightly better electrical performance than pure metal current collector while taking into account safety performance.

[0056] Table 1-4 Lithium-ion battery performance test results of samples 1, 10-14, and 17

[0057]

[0058] Tables 1-5 list the performance test results of lithium-ion batteries of samples 3, 7, 8, 11, 15, and 16 to verify the influence of different polymer substrates in the positive and negative electrode films. Comparing samples 3, 7, 8 and 11, 15, and 16, it can be seen that: under the same solid electrolyte content, adding different solid electrolyte composite conductive positive and negative electrode films has slightly different effects on the performance of the battery cell, which may be related to the ion conductivity of the solid electrolyte and its stability relative to lithium metal. LLZO is selected to have the best performance on the battery cell.

[0059] Table 1-5 Lithium-ion battery performance test results of samples 3, 7, 8, 11, 15, and 16

[0060]

[0061] In summary, on the basis of improving electrical performance, the present invention preferably selects a composite conductive polyimide film that increases the energy density and safety performance of the battery core, and preferably selects the content range of polyimide, solid electrolyte and conductive agent: the mass percentage of polyimide in the polymer layer is 55%-90%, the mass percentage of the conductive agent is 5%-25%, and the mass percentage of the solid electrolyte is 5%-20%.

[0062] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A composite film, It is characterized in that It comprises a polymer layer, a surface treatment layer, a metal layer and micropores; the polymer layer is the innermost layer, the surface treatment layer is arranged on both sides of the polymer layer, the metal layer is plated on the outer surface of the surface treatment layer, and the micropores penetrate the polymer layer, the surface treatment layer and the metal layer; the polymer layer is composited by organic polymer materials and inorganic materials; the inorganic materials include conductive agents and solid electrolyte materials; the polymer layer has a thickness of 2-30 μm; the mass percentage of the organic polymer material is 55%-90%, the mass percentage of the conductive agent is 5%-25%, and the mass percentage of the solid electrolyte is 5%-20%; The polymer material is selected from at least one of polypropylene, polyethylene, polyethylene terephthalate, polyimide, polyvinylidene fluoride, polymethyl methacrylate, polystyrene, polyurethane, epoxy resin or modified materials of the above materials; the conductive agent is selected from at least one of carbon black, acetylene black, carbon nanotubes, carbon fibers, graphite, nanographite, graphene, fullerene, conductive metals and their oxides; the solid electrolyte material is selected from perovskite, antiperovskite, NASICON, LISICON, Garnet type crystalline oxides, LiPON type glass oxides, crystalline Li 4 -xA 1 -xBxS 4 , glassy Li 2 SP 2 S 5 , crystalline LixMyPSz, glass ceramic Li 2 SP 2 S 5 , Li 6 PS 5 At least one of the sulfide or halide of X and modified materials of the above materials; The treatment method of the surface treatment layer is selected from one or more of corona treatment, electric spark treatment, plasma treatment, nickel plating, ALO plating, chemical treatment coating, and NaOH immersion; the thickness of the surface treatment layer is 0.005-0.05um; The diameter of the micropores is 0.5-30 μm, and the spacing is 0.5-10 mm.

2. A composite membrane according to claim 1, It is characterized in that The material of the metal layer is selected from at least one of copper, aluminum, nickel, zinc, titanium, silver and stainless steel.

3. A lithium-ion battery, It is characterized in that Contains the composite film according to any one of claims 1 and 2.

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