Negative current collector and preparation method thereof, pole piece and battery

Abstract

The invention relates to the field of new energy batteries, in particular to a negative electrode current collector and a preparation method thereof, a pole piece and a battery, and the preparation method comprises the following steps: preparing a carbon nanotube with a hydroxyl group on the surface; mixing a carbon nanotube with hydroxyl on the surface, an isocyanate raw material, diol, water and a second organic solvent, and carrying out heating reflux treatment to obtain a third product; mixing the third product, a polytetrahydrofuran raw material, a second organic solvent and a second ammonium salt, and carrying out a polymerization reaction to obtain a precipitate; carrying out drying treatment on the precipitate, so as to obtain foam polyurethane modified by the carbon nano tube; and taking the foam polyurethane modified by the carbon nano tube as a working electrode, carrying out deposition reaction on the working electrode to obtain a base material with a metal layer deposited on the surface, and washing and drying the base material with the metal layer deposited on the surface. The negative electrode current collector lithium metal battery provided by the invention has relatively large energy density, relatively small battery internal resistance, relatively strong cycle performance and relatively low safety risk.

Description

Technical Field

[0001] The present invention relates to the field of new energy batteries, and in particular to a negative electrode current collector and a preparation method thereof, a pole piece and a battery. Background Art

[0002] Lithium-ion batteries have been widely used due to their advantages such as high specific energy, long cycle life, zero memory, and low self-discharge rate. In the application of large-scale transportation vehicles such as electric vehicles and electric ships, there are high requirements for endurance, so lithium-ion batteries are required to have a higher energy density. Lithium metal batteries have attracted much attention due to their extremely high theoretical specific capacity (3860mAh / g) and lowest electrode potential (3.04V compared to the standard hydrogen electrode). However, during repeated electroplating / stripping cycles, the harmful growth of lithium dendrites hinders the practical application of lithium metal anodes. The formation of lithium dendrites consumes part of the electrolyte, and some lithium dendrites lose contact with the electrode after cycling and become dead lithium, reducing the initial coulombic efficiency and shortening the battery life.

[0003] Due to its lightweight and porous structure, copper foam offers significant advantages for improving the energy density and rate performance of lithium-ion batteries, making it a key area for future current collector development. However, its poor toughness can cause the formation of lithium metal dendrites on its surface, posing a safety hazard. Therefore, a lightweight, tough, porous anode current collector is urgently needed in the field. Summary of the Invention

[0004] In view of this, the present invention is dedicated to providing a negative electrode current collector and its preparation method, a pole piece and a battery, so as to solve the problems of insufficient energy density and large internal resistance of lithium-ion batteries in the prior art.

[0005] In order to solve the above-mentioned technical problems, the present invention is achieved as follows:

[0006] A first aspect of the present invention provides a method for preparing a negative electrode current collector, the method comprising the following steps:

[0007] S1, mixing carbon nanotubes, borohydride, a first ammonium salt, and a first organic solvent and performing a first heating reflux treatment to obtain a first product;

[0008] S2. Mixing the first product, water, hydroxide, and oxidant with the first organic solvent and performing an oxidation reaction to obtain a second product; filtering, washing, and performing a first drying process on the second product to obtain carbon nanotubes containing hydroxyl groups on the surface;

[0009] S3, mixing the carbon nanotubes having hydroxyl groups on the surface, an isocyanate raw material, a diol, water, and a second organic solvent and performing a second heating reflux treatment to obtain a third product;

[0010] S4, mixing the third product, the polytetrahydrofuran raw material, the second organic solvent, and the second ammonium salt and performing a polymerization reaction to obtain a precipitate; performing a second drying treatment on the precipitate to obtain a carbon nanotube-modified foamed polyurethane;

[0011] S5. Using the carbon nanotube-modified foam polyurethane as a working electrode, placing the working electrode, counter electrode and reference electrode in an electrolyte containing metal ions for a deposition reaction to obtain a substrate with a metal layer deposited on the surface, and performing a washing treatment and a third drying treatment on the substrate with the metal layer deposited on the surface.

[0012] Optionally, in step S1, the mass ratio of the carbon nanotubes, the borohydride and the first ammonium salt is (2-10): (0.5-4.5): (0.5-6.5); the amount of the first organic solvent is 25-125 mL per gram of the carbon nanotubes; the borohydride includes at least one of sodium borohydride, potassium borohydride, calcium borohydride, magnesium borohydride and lithium borohydride; the first ammonium salt includes at least one of ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium bisulfate, ammonium fluoride, ammonium carbonate and ammonium bicarbonate; the first organic solvent includes at least one of tetrahydrofuran, acetonitrile, formamide and acetone; optionally, in step S1, the conditions for the first heating reflux treatment include: a heating reflux temperature of 80-100°C and a heating reflux time of 8-16 hours.

[0013] Optionally, in step S2, the mass ratio of the first product and the hydroxide is (2 to 10): (1 to 9); the amount of the first organic solvent is 25 to 125 mL per gram of the first product; the amount of water is 25 to 125 mL per gram of the first product; the hydroxide includes at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide; the oxidant includes at least one of hydrogen peroxide, sodium hypochlorite and sodium peroxide; optionally, in step S2, the conditions of the oxidation reaction include: an oxidation temperature of 20 to 60°C, and an oxidation time of 6 to 10 hours; the washing liquid used in the filtration and washing treatment includes at least one of water, ethanol and acetone; the conditions of the first drying treatment include: a drying pressure of -0.09 to -0.08 MPa, a drying temperature of 40 to 80°C, and a drying time of 8 to 16 hours.

[0014] Optionally, in step S3, the mass ratio of the carbon nanotubes containing hydroxyl groups on the surface, the isocyanate raw material and the diol is (31~93):(2~10):(87~261); the amount of the second organic solvent is 4~20mL per gram of the carbon nanotubes containing hydroxyl groups on the surface; the amount of water is 1~5mL per gram of the carbon nanotubes containing hydroxyl groups on the surface; the isocyanate raw material includes at least one of toluene diisocyanate, diphenylmethane diisocyanate and naphthalene 1,5-diisocyanate; the diol includes at least one of ethylene glycol, propylene glycol and butanediol; the second organic solvent includes at least one of toluene, xylene and benzene; optionally, in step S3, the conditions for the second heating reflux treatment include: the heating reflux temperature is 100~120℃, and the heating reflux time is 4~10h.

[0015] Optionally, in step S4, the mass ratio of the third product and the polytetrahydrofuran raw material is (10-40): (0.5-5.5); the amount of the second organic solvent is 1-4 mL per gram of the third product; the polytetrahydrofuran raw material includes at least one of polytetrahydrofuran, poly-2-methyltetrahydrofuran and poly-2-ethyltetrahydrofuran; the second ammonium salt includes at least one of ammonium bicarbonate, ammonium chloride and ammonium carbonate; optionally, in step S4, the conditions of the polymerization reaction include: a polymerization temperature of 80-120°C and a polymerization time of 8-16 hours; the conditions of the second drying treatment include: a drying pressure of -0.09-0.08 MPa, a drying temperature of 40-80°C, and a drying time of 10-16 hours.

[0016] Optionally, in step S5, the counter electrode is a platinum sheet; the reference electrode is Ag / AgCl; in the electrolyte containing metal ions, the concentration of metal ions is 0.1 to 0.9 mol / L; optionally, the metal ions are copper ions; optionally, in step S5, the conditions of the deposition treatment include: a constant potential of -1.5 to -0.7 V, and a deposition time of 5 to 15 min; the washing liquid used in the washing treatment includes anhydrous ethanol; the conditions of the third drying treatment include: a drying pressure of -0.09 to -0.08 MPa, a drying temperature of 25 to 45°C, and a drying time of 8 to 16 h.

[0017] The second aspect of the present invention provides a negative electrode current collector, which is prepared according to the above method;

[0018] Wherein, the negative electrode current collector comprises a porous substrate and a metal layer, and the metal layer is arranged on the surface and in the pores of the porous substrate;

[0019] The materials of the substrate include carbon nanotubes with hydroxyl groups on the surface and foam polyurethane; the carbon nanotubes with hydroxyl groups on the surface and the foam polyurethane are connected through hydrogen bonds.

[0020] Optionally, in the substrate, the mass ratio of the carbon nanotubes containing hydroxyl groups on the surface and the foamed polyurethane is (0.02~0.1):1; the mass ratio of the substrate to the metal layer is 1:0.2~1; the thickness of the substrate is 0.004~0.12mm; the thickness of the metal layer is 0.5~10μm; optionally, the material of the metal layer includes copper.

[0021] A third aspect of the present invention provides a negative electrode plate, which includes the negative electrode current collector prepared according to the above preparation method, or the above negative electrode current collector.

[0022] A fourth aspect of the present invention provides a battery, comprising a negative electrode plate, wherein the negative electrode plate is the negative electrode plate described above.

[0023] Through the above technical solution, the beneficial technical effects of the present invention are:

[0024] (1) In the preparation method of the negative electrode current collector of the present invention, carbon nanotubes containing hydroxyl groups on the surface are first prepared, and then a foamed polyurethane modified with carbon nanotubes is prepared. Finally, the foamed polyurethane modified with carbon nanotubes is used as a working electrode. The working electrode, the counter electrode, and the reference electrode are placed in an electrolyte containing metal ions to undergo a deposition reaction, thereby obtaining a substrate having a metal layer deposited on the surface. The foamed polyurethane material contains a large number of pores. The addition of the second ammonium salt during the preparation process causes it to decompose into gas at high temperature. After the gas escapes, a large number of pore structures are formed in the material, thereby increasing the porosity. While reducing the internal resistance of the battery, the lithium has a larger deposition area, which can improve the battery cycle performance. More metal is deposited through the deposition reaction, and the carbon nanotube-modified polyurethane is used at the same time, so the internal resistance of the battery can be further reduced.

[0025] (2) The negative electrode current collector of the present invention is a porous and lightweight foam copper material, which can reduce the weight of the negative electrode plate, thereby improving the battery energy density; applying the negative electrode current collector of the present invention to the battery can reduce the internal resistance of the battery, enhance the cycle performance of the battery, and reduce the safety risk of the battery.

[0026] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention.

[0028] Figure 1 Shown is a schematic diagram of the negative electrode current collector of the present invention.

[0029] Description of Reference Numerals

[0030] 1: Metal layer;

[0031] 2: Porous substrate. DETAILED DESCRIPTION

[0032] The present invention discloses a negative electrode current collector and a method for preparing the same, a pole piece, and a battery. Those skilled in the art can refer to the contents of this document and appropriately improve the process parameters to achieve the desired results. It should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0033] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0034] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0035] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0036] Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, the terms "include" and "comprising" used in the present invention may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0038] In order to solve the problems of insufficient energy density and large internal resistance of lithium-ion batteries in the prior art, the present invention adopts the following technical solutions:

[0039] A first aspect of the present invention provides a method for preparing a negative electrode current collector, the method comprising the following steps:

[0040] S1, mixing carbon nanotubes, borohydride, a first ammonium salt, and a first organic solvent and performing a first heating reflux treatment to obtain a first product;

[0041] S2. Mixing the first product, water, hydroxide, and oxidant with the first organic solvent and performing an oxidation reaction to obtain a second product; filtering, washing, and performing a first drying process on the second product to obtain carbon nanotubes containing hydroxyl groups on the surface;

[0042] S3, mixing the carbon nanotubes having hydroxyl groups on the surface, an isocyanate raw material, a diol, water, and a second organic solvent and performing a second heating reflux treatment to obtain a third product;

[0043] S4, mixing the third product, the polytetrahydrofuran raw material, the second organic solvent, and the second ammonium salt and performing a polymerization reaction to obtain a precipitate; performing a second drying treatment on the precipitate to obtain a carbon nanotube-modified foamed polyurethane;

[0044] S5. Using the carbon nanotube-modified foam polyurethane as a working electrode, placing the working electrode, counter electrode and reference electrode in an electrolyte containing metal ions for a deposition reaction to obtain a substrate with a metal layer deposited on the surface, and performing a washing treatment and a third drying treatment on the substrate with the metal layer deposited on the surface.

[0045] In the preparation method of the negative electrode current collector of the present invention, carbon nanotubes containing hydroxyl groups on the surface are first prepared, and then a foamed polyurethane modified with the carbon nanotubes is prepared. Finally, the foamed polyurethane modified with the carbon nanotubes is used as a working electrode. The working electrode, the counter electrode, and the reference electrode are placed in an electrolyte containing metal ions to undergo a deposition reaction, thereby obtaining a substrate having a metal layer deposited on the surface. The foamed polyurethane material contains a large number of pores. The addition of a second ammonium salt during the preparation process causes it to decompose into gas at high temperature. After the gas escapes, a large number of pore structures are formed in the material, thereby increasing the porosity. While reducing the internal resistance of the battery, the lithium has a larger deposition area, which can improve the battery cycle performance. The deposition reaction deposits more metal, and the use of carbon nanotube-modified polyurethane can further reduce the internal resistance of the battery.

[0046] In the present invention, if the amount of carbon nanotubes used is too small, the conductivity of the foil may be insufficient; if the amount of carbon nanotubes used is too much, agglomeration may occur, thereby reducing the conductivity of the foil. As an embodiment of the present invention, in step S1, the mass ratio of the carbon nanotubes, the borohydride and the first ammonium salt can be (2-10): (0.5-4.5): (0.5-6.5). Exemplarily, the mass ratio of the carbon nanotubes, the borohydride and the first ammonium salt can be any of 1:0.25:0.25, 1:2.25:0.25, 1:0.25:3.25, 1:2.25:3.25, 1:0.05:0.05 and 1:0.45:0.65, or any value within the range of any two of the above values.

[0047] According to the present invention, if the amount of the first organic solvent is too large, the reaction rate may be slowed down; if the amount of the first organic solvent is too small, the carbon nanotubes may agglomerate, increasing the product resistance. In an embodiment of the present invention, the amount of the first organic solvent may be 25 to 125 mL per gram of the carbon nanotubes. For example, the amount of the first organic solvent may be any one of 25 mL, 50 mL, 75 mL, 100 mL, and 125 mL per gram of the carbon nanotubes, or any value within the range consisting of any two of the above values.

[0048] Illustratively, the borohydride may include at least one of sodium borohydride, potassium borohydride, calcium borohydride, magnesium borohydride, and lithium borohydride.

[0049] Illustratively, the first ammonium salt may include at least one of ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium bisulfate, ammonium fluoride, ammonium carbonate, and ammonium bicarbonate.

[0050] Illustratively, the first organic solvent may include at least one of tetrahydrofuran, acetonitrile, formamide, and acetone.

[0051] In some embodiments, the conditions of the first heating and reflowing treatment in step S1 may include: a heating and reflowing temperature of 80 to 100° C. and a heating and reflowing time of 8 to 16 hours. As an example, the temperature of the first heating and reflowing treatment may be 80° C., 85° C., 90° C., 95° C., 100° C., etc., and the time of the first heating and reflowing treatment may be 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, etc.

[0052] As an embodiment of the present invention, in step S2, if the amount of hydroxide is too large, the reaction rate may be slowed down; if the amount of hydroxide is too small, the reaction product may be affected (the surface -OH content is small). In some embodiments, the mass ratio of the first product and the hydroxide can be (2 to 10): (1 to 9). Exemplarily, the mass ratio of the first product and the hydroxide can be any of 2:1, 1:1, 1:2, 1:4.5 and 10:9 or any value within the range of any two of the above values.

[0053] According to the present invention, in step S2, if the amount of the first organic solvent is too large, the reaction rate may be slowed down; if the amount of the first organic solvent is too small, CNT-OH may be agglomerated. In some embodiments, the amount of the first organic solvent may be 25 to 125 mL per gram of the first product. For example, the amount of the first organic solvent may be any one of 25 mL, 50 mL, 75 mL, 100 mL, and 125 mL per gram of the first product, or any value within the range of any two of the above values.

[0054] According to the present invention, in step S2, if the amount of water used is too large, the polyurethane pores may be too large and too many, and the product strength may be insufficient; if the amount of water used is too small, the polyurethane pore structure may be reduced. In some embodiments, the amount of water used may be 25 to 125 mL per gram of the first product. For example, the amount of water used per gram of the first product may be any of 25 mL, 50 mL, 75 mL, 100 mL, and 125 mL, or any value within the range consisting of any two of the above values.

[0055] Illustratively, the hydroxide may include at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0056] Illustratively, the oxidant may include at least one of hydrogen peroxide, sodium hypochlorite, and sodium peroxide.

[0057] In some embodiments, the oxidation reaction conditions in step S2 may include: an oxidation temperature of 20 to 60° C. and an oxidation time of 6 to 10 hours. As an example, the oxidation reaction temperature may be 20° C., 30° C., 40° C., 50° C., 60° C., etc., and the oxidation reaction time may be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0058] Illustratively, the washing liquid used in the filter washing treatment may include at least one of water, ethanol and acetone.

[0059] In some embodiments, the conditions of the first drying process may include: a drying pressure of -0.09 to -0.08 MPa, a drying temperature of 40 to 80° C., and a drying time of 8 to 16 hours. As an example, the temperature of the first drying process may be 80° C., 85° C., 90° C., 95° C., 100° C., etc., and the first drying process time may be 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, etc.

[0060] As an embodiment of the present invention, in step S3, the mass ratio of the carbon nanotubes containing hydroxyl groups on the surface, the isocyanate raw material and the diol can be (31-93): (2-10): (87-261).

[0061] According to the present invention, the amount of the second organic solvent used can be 4 to 20 mL per gram of the carbon nanotubes containing hydroxyl groups on the surface. For example, the amount of the second organic solvent used can be any one of 4 mL, 5 mL, 10 mL, 15 mL, and 20 mL per gram of the carbon nanotubes containing hydroxyl groups on the surface, or any value within a range consisting of any two of the above values.

[0062] According to the present invention, the amount of water used can be 1 to 5 mL per gram of the carbon nanotubes containing hydroxyl groups on the surface.

[0063] Illustratively, the isocyanate raw material may include at least one of toluene diisocyanate, diphenylmethane diisocyanate, and naphthalene 1,5-diisocyanate.

[0064] Illustratively, the diol may include at least one of ethylene glycol, propylene glycol, and butylene glycol.

[0065] Illustratively, the second organic solvent may include at least one of toluene, xylene, and benzene.

[0066] In some embodiments, the conditions of the second heating and reflowing treatment in step S3 may include: a heating and reflowing temperature of 100 to 120° C. and a heating and reflowing time of 4 to 10 hours. As an example, the temperature of the second heating and reflowing treatment may be 100° C., 105° C., 110° C., 115° C., 120° C., etc., and the time of the second heating and reflowing treatment may be 4 hours, 6 hours, 8 hours, 10 hours, etc.

[0067] As an embodiment of the present invention, in step S4, if the amount of polytetrahydrofuran raw material used is too large, it may cause residues in the product, thereby increasing the resistance value and reducing the porosity of the substrate; if the amount of polytetrahydrofuran raw material used is too small, it may result in too little product. In some embodiments, the mass ratio of the third product and the polytetrahydrofuran raw material can be (10-40): (0.5-5.5). Exemplarily, the mass ratio of the third product and the polytetrahydrofuran raw material can be any of 10:0.5, 40:0.5, 10:5.5 and 40:5.5, or any value within the range of any two of the above values.

[0068] According to the present invention, the amount of the second organic solvent used per gram of the third product may be 1 to 4 mL. For example, the amount of the second organic solvent used per gram of the third product may be any one of 1 mL, 2 mL, 3 mL, and 4 mL, or any value within a range consisting of any two of the above values.

[0069] Illustratively, the polytetrahydrofuran raw material may include at least one of polytetrahydrofuran, poly-2-methyltetrahydrofuran, and poly-2-ethyltetrahydrofuran.

[0070] For example, the second ammonium salt may include at least one of ammonium bicarbonate, ammonium chloride, and ammonium carbonate. Ammonium bicarbonate is preferably used. Ammonium bicarbonate is easily decomposed into ammonia, carbon dioxide, and water when heated to 60°C. Therefore, in addition to the pores obtained by foaming, the thermal decomposition of ammonium bicarbonate can also form relatively abundant pores inside or on the surface of the polyurethane.

[0071] In some embodiments, the conditions of the polymerization reaction in step S4 may include: a polymerization temperature of 80 to 120°C, and a polymerization time of 8 to 16 hours; the conditions of the second drying treatment may include: a drying pressure of -0.09 to -0.08 MPa, a drying temperature of 40 to 80°C, and a drying time of 10 to 16 hours.

[0072] Illustratively, in step S5, the counter electrode may be a platinum sheet; and the reference electrode may be Ag / AgCl.

[0073] As an embodiment of the present invention, the concentration of the metal ions in the electrolyte containing metal ions may be 0.1 to 0.9 mol / L. For example, the concentration of the metal ions in the electrolyte containing metal ions may be any value among 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, and 0.9 mol / L, or any value within a range consisting of any two of the above values.

[0074] For example, the metal ions may be copper ions.

[0075] In the present invention, if the deposition treatment time is too short, the conductivity of the current collector may deteriorate; if the deposition treatment time is too long, the surface Cu layer may agglomerate, thereby affecting the conductivity of the current collector. In some embodiments, the conditions of the deposition treatment in step S5 may include: a constant potential of -1.5 to -0.7V, a deposition time of 5 to 15 minutes; illustratively, the washing liquid used in the washing treatment may include anhydrous ethanol. The conditions of the third drying treatment may include: a drying pressure of -0.09 to -0.08MPa, a drying temperature of 25 to 45°C, and a drying time of 8 to 16 hours. As an example, the temperature of the third drying treatment may be 100°C, 105°C, 110°C, 115°C, 120°C, etc., and the time of the third drying treatment may be 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, etc.

[0076] The second aspect of the present invention provides a negative electrode current collector, such as Figure 1 As shown, the negative electrode current collector is prepared according to the above method;

[0077] Wherein, the negative electrode current collector comprises a porous substrate and a metal layer, and the metal layer is arranged on the surface and in the pores of the porous substrate;

[0078] The materials of the substrate include carbon nanotubes with hydroxyl groups on the surface and foam polyurethane; the carbon nanotubes with hydroxyl groups on the surface and the foam polyurethane are connected through hydrogen bonds.

[0079] The negative electrode current collector of the present invention is a porous and lightweight foam copper material, which can reduce the weight of the negative electrode plate, thereby improving the battery energy density; applying the negative electrode current collector of the present invention to the battery can reduce the battery internal resistance, enhance the battery cycle performance, and reduce the battery safety risk.

[0080] In the present invention, a suitable mass ratio of carbon nanotubes containing hydroxyl groups on their surfaces to polyurethane foam has the technical effect of reducing the resistance of the foil. As one embodiment of the present invention, in the substrate, the mass ratio of the carbon nanotubes containing hydroxyl groups on their surfaces to the polyurethane foam can be (0.02-0.1):1.

[0081] In the present invention, a suitable substrate-to-metal layer mass ratio can reduce the resistance of the foil and increase the porosity of the substrate. In some embodiments, the substrate-to-metal layer mass ratio can be 1:0.2 to 1. For example, the substrate-to-metal layer mass ratio can be any of 1:0.2, 1:0.4, 1:0.6, 1:0.8, and 1:1, or any value within a range consisting of any two of these values.

[0082] In some embodiments, the thickness of the substrate may be 0.004 to 0.12 mm. For example, the thickness of the substrate may be any value among 0.004 mm, 0.01 mm, 0.03 mm, 0.06 mm, 0.09 mm, and 0.12 mm, or any value within a range consisting of any two of the above values.

[0083] In some embodiments, the thickness of the metal layer may be 0.5 to 10 μm. For example, the thickness of the metal layer may be any value among 0.5 μm, 1 μm, 3 μm, 5 μm, 8 μm and 10 μm, or any value within a range consisting of any two of the above values.

[0084] Exemplarily, the material of the metal layer includes copper.

[0085] A third aspect of the present invention provides a negative electrode plate, which includes the negative electrode current collector prepared according to the above preparation method, or the above negative electrode current collector.

[0086] A fourth aspect of the present invention provides a battery, comprising a negative electrode plate, wherein the negative electrode plate is the negative electrode plate described above.

[0087] The present invention is further described in detail below by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0088] Example 1

[0089] (1) Preparation of carbon nanotubes containing hydroxyl groups on the surface

[0090] 6g of carbon nanotubes were placed in a reaction vessel, followed by the addition of 2.5g of sodium borohydride and 3.5g of ammonium sulfate, followed by 250mL of tetrahydrofuran. The mixture was mixed in the reaction vessel and subjected to a first heating reflux at 90°C for 12h, followed by cooling to room temperature to obtain a first product. 6g of the first product was then mixed with 250mL of deionized water, 75mL of tetrahydrofuran, 15mL of hydrogen peroxide, and 5g of sodium hydroxide and subjected to an oxidation reaction at 40°C to obtain a second product. The second product was filtered, washed with hot water, then with ethanol and acetone, and dried in a vacuum oven at 60°C for 12h to obtain a dried substance, namely carbon nanotubes containing surface hydroxyl groups, designated as CNT-OH.

[0091] (2) Synthesis of polyurethane

[0092] 2 g of the CNT-OH obtained in step (1), 1 mol of ethylene glycol, 1 mol of toluene diisocyanate (TDI), 10 g of deionized water, and 40 mL of toluene were added to a reaction vessel, mixed, and subjected to a second heating reflux treatment, wherein the second heating reflux treatment conditions include: a temperature of 110° C. and a time of 6 hours in an oil bath, to obtain a third product. 25 g of the third product, 3 g of polytetrahydrofuran, 40 mL of toluene, and 4 g of ammonium bicarbonate powder were stirred uniformly and then subjected to a polymerization reaction for 12 hours to obtain a precipitate; the precipitate was dried in a vacuum oven at 60° C. for 12 hours to obtain a carbon nanotube-modified foam polyurethane, which can be recorded as CNT-PU.

[0093] (3) Copper plating on modified polyurethane surface (synthesis of foam copper)

[0094] The modified CNT-PU obtained in step (2) was used as a working electrode using the electrolytic cell principle, and a platinum sheet and an Ag / AgCl electrode were used as a counter electrode and a reference electrode, respectively. The electrodes were immersed in a 0.5 mol / L copper sulfate solution containing a sulfuric acid solution, and electroplated at a constant potential of -1.1 V (relative to the Ag / AgCl electrode) for 600 s to obtain a Cu layer on the surface of the PP film. The surface was then lightly rinsed with anhydrous ethanol and vacuum dried at 35°C for 12 h to obtain foam copper, which was recorded as Cu / CNT-PU-600.

[0095] (4) Preparation of positive electrode sheet

[0096] Lithium nickel cobalt manganate powder, conductive carbon and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 8:1:1 to obtain a mixed material, and the mixed material is thoroughly stirred in N-methylpyrrolidone (NMP) to obtain a positive electrode active slurry of the corresponding positive electrode sheet, and the positive electrode active slurry is coated on aluminum foil to obtain a first electrode sheet, wherein the mass fraction of the lithium nickel cobalt manganese oxide powder in the first electrode sheet is 80wt%, and after drying and pressing, a positive electrode sheet is obtained.

[0097] (5) Preparation of lithium-ion batteries

[0098] Ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed organic solvent, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0099] The foam copper obtained in step (3) is used as the negative electrode sheet, the positive electrode sheet obtained in step (4) and the PE separator are wound to obtain the corresponding winding core, and then dried, electrolyte injected, packaged, formed, and capacity divided to obtain a lithium-ion battery.

[0100] Example 2

[0101] The preparation method of the lithium-ion battery in this embodiment is generally the same as that in Example 1, except that: in step (3), the electrodeposition is carried out at a constant potential of -1.1 V (relative to the Ag / AgCl electrode) for 300 s, and the obtained foam copper material is recorded as Cu / CNT-PU-300.

[0102] Example 3

[0103] The preparation method of the lithium-ion battery in this embodiment is generally the same as that in Example 1, except that: in step (3), the electrodeposition is carried out at a constant potential of -1.1 V (relative to the Ag / AgCl electrode) for 900 s, and the obtained foam copper material is recorded as Cu / CNT-PU-900.

[0104] Example 4

[0105] The preparation method of the lithium-ion battery in this embodiment is generally the same as that in Example 1, except that in step (2), the amount of CNT-OH added is 0.5 g.

[0106] Example 5

[0107] The preparation method of the lithium-ion battery in this embodiment is generally the same as that in Example 1, except that in step (2), the amount of CNT-OH added is 3.5 g.

[0108] Example 6

[0109] The preparation method of the lithium ion battery in this embodiment is generally the same as that in Example 1, except that in step (2), the amount of deionized water added is 5 g.

[0110] Example 7

[0111] The preparation method of the lithium ion battery in this embodiment is generally the same as that in Example 1, except that in step (2), the amount of deionized water added is 15 g.

[0112] Comparative Example 1

[0113] From commercially available 4.5 μm copper foil.

[0114] Comparative Example 2

[0115] The preparation method of the lithium-ion battery in this comparative example is generally the same as that in Example 1, except that ordinary carbon nanotubes are used instead of CNT-OH in step (2).

[0116] Comparative Example 3

[0117] The preparation method of the lithium ion battery in this comparative example is generally the same as that in Example 1, except that ammonium bicarbonate is not added in step (2).

[0118] Test Example 1

[0119] The pole pieces prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to performance tests, and the test results are shown in Table 1.

[0120] Physical performance related tests of pole pieces:

[0121] (1) Liquid absorption test method: Take a 5×5 cm2 roller-pressed negative electrode from each group, weigh it and record it as a, and soak it in the electrolyte for 1 hour to allow it to fully absorb the electrolyte. After the absorption is complete, hang the electrode for 5 minutes to dry the electrolyte attached to the diaphragm surface, weigh it and record it as b. The electrode liquid absorption rate is (ba) / a×100%.

[0122] (2) Electrode diaphragm resistance test method: Place the electrode in the diaphragm resistance test to test and obtain the diaphragm resistance of the corresponding electrode.

[0123] Table 1

[0124] Group Liquid absorption rate% Diaphragm resistance / mΩ Example 1 139 0.18 Example 2 127 0.23 Example 3 122 0.25 Example 4 121 0.31 Example 5 117 0.34 Example 6 124 0.25 Example 7 121 0.27 Comparative Example 1 / 0.42 Comparative Example 2 109 0.36 Comparative Example 3 103 0.38

[0125] Test Example 2

[0126] The batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to performance tests. The test results are shown in Table 2.

[0127] Battery performance test:

[0128] (1) First coulombic efficiency: After the battery is manufactured, it is first charged to 3.75V at a constant current of 0.1C to obtain the formation capacity C0. The battery is then divided into different capacities and charged to 4.25V at a constant current of 0.33C. It is then charged to I≤0.05C at a constant voltage of 4.25V to obtain the capacity C1 of the divided battery. After standing for 5 minutes, the battery is discharged to 2.8V at a constant current of 1C to obtain the discharge capacity C2. It is then discharged to 2.8V at a constant current of 0.1C to obtain the discharge capacity C3. Finally, it is discharged to 2.8V at a constant current of 0.01C to obtain the discharge capacity C4. The first efficiency is calculated as (C2+C3+C4) / (C0+C1)*100%.

[0129] (2) Energy density: First, weigh each group of tested batteries and record the mass of the battery as m. Then, at 25°C, charge the battery at a constant current of 0.1C to 4.25V, then charge it at a constant voltage of 4.25V to a current ≤0.05C. After standing for 5 minutes, discharge it at a constant current of 0.1C to 2.8V to obtain the discharge energy Q. The battery energy density is calculated as Q / m.

[0130] (3) Cycle capacity retention rate: At 25°C, the battery is first charged to 4.25V at a constant current of 0.5C, then charged at a constant voltage of 4.25V to a current of I≤0.05C, and the 0.5C charging capacity of the battery is recorded as C0. After standing for 15 minutes, it is discharged to 2.8V at a constant current of 0.5C, and the discharge capacity of the cycle is recorded as C1. According to this cycle process, the discharge capacity of 100 cycles is recorded as C 100 , and obtain the battery capacity retention rate for 100 cycles.

[0131] Table 2

[0132]

[0133] It can be seen from Tables 1 and 2 that the electrode prepared in the embodiment of the present invention has a significantly improved liquid absorption rate and a significantly reduced membrane resistance compared with the comparative example; the battery prepared in the embodiment of the present invention has a significantly reduced internal resistance, significantly improved first efficiency, energy density and cycle performance compared with the comparative example. Specifically, Examples 1, 2, and 3 change the physical properties of the electrode by changing the time of electroplating copper. A suitable electroplating time is required. A shorter electroplating time results in insufficient content of the electroplated copper layer, insufficient conductivity, increased diaphragm resistance, and less pores after thermal decomposition of ammonium bicarbonate, resulting in a decrease in liquid absorption rate; too long a deposition time may cause the copper layer to agglomerate on the polyurethane, resulting in an increase in diaphragm resistance and a decrease in liquid absorption rate; Examples 4 and 5 change the CNT content. Too little CNT, as a porous three-dimensional material, may cause insufficient conductivity and a decrease in liquid absorption rate; too much may cause agglomeration, resulting in a decrease in conductivity and insufficient liquid absorption rate; Examples 6 and 7 change the pore structure inside the polyurethane by changing the water content. Too little water causes a decrease in porosity, less copper foil deposition, and increased resistance; too much water causes a larger porosity, resulting in uneven agglomeration of the copper layer, a decrease in porosity, and an increase in diaphragm resistance.

[0134] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a negative electrode current collector, characterized in that: The preparation method comprises the following steps: S1, mixing carbon nanotubes, borohydride, a first ammonium salt, and a first organic solvent and performing a first heating reflux treatment to obtain a first product; S2. Mixing the first product, water, hydroxide, and oxidant with the first organic solvent and performing an oxidation reaction to obtain a second product; filtering, washing, and performing a first drying process on the second product to obtain carbon nanotubes containing hydroxyl groups on the surface; S3, mixing the carbon nanotubes having hydroxyl groups on the surface, an isocyanate raw material, a diol, water, and a second organic solvent and performing a second heating reflux treatment to obtain a third product; S4, mixing the third product, the polytetrahydrofuran raw material, the second organic solvent, and the second ammonium salt and performing a polymerization reaction to obtain a precipitate; performing a second drying treatment on the precipitate to obtain a carbon nanotube-modified foamed polyurethane; S5. Using the carbon nanotube-modified foam polyurethane as a working electrode, placing the working electrode, counter electrode and reference electrode in an electrolyte containing metal ions for a deposition reaction to obtain a substrate with a metal layer deposited on the surface, and performing a washing treatment and a third drying treatment on the substrate with the metal layer deposited on the surface.

2. The preparation method according to claim 1, characterized in that In step S1, the carbon nanotubes, the borohydride, and the first ammonium salt are mixed in a mass ratio of (2-10):(0.5-4.5):(0.5-6.5); The amount of the first organic solvent is 25 to 125 mL per gram of the carbon nanotubes; The borohydride comprises at least one of sodium borohydride, potassium borohydride, calcium borohydride, magnesium borohydride and lithium borohydride; The first ammonium salt includes at least one of ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium bisulfate, ammonium fluoride, ammonium carbonate and ammonium bicarbonate; The first organic solvent comprises at least one of tetrahydrofuran, acetonitrile, formamide and acetone; Optionally, in step S1, the conditions for the first heating reflux treatment include: a heating reflux temperature of 80 to 100° C., and a heating reflux time of 8 to 16 hours.

3. The preparation method according to claim 1, characterized in that In step S2, the mass ratio of the first product and the hydroxide is (2-10): (1-9); The amount of the first organic solvent is 25 to 125 mL per gram of the first product; The amount of water used is 25 to 125 mL per gram of the first product; The hydroxide includes at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide; The oxidant comprises at least one of hydrogen peroxide, sodium hypochlorite and sodium peroxide; Optionally, in step S2, the conditions of the oxidation reaction include: an oxidation temperature of 20 to 60°C, and an oxidation time of 6 to 10 hours; the washing liquid used in the filtration and washing treatment includes at least one of water, ethanol and acetone; the conditions of the first drying treatment include: a drying pressure of -0.09 to -0.08 MPa, a drying temperature of 40 to 80°C, and a drying time of 8 to 16 hours.

4. The preparation method according to claim 1, characterized in that In step S3, the carbon nanotubes containing hydroxyl groups on the surface, the isocyanate raw material and the diol are mixed in a mass ratio of (31-93): (2-10): (87-261); The amount of the second organic solvent is 4 to 20 mL per gram of the carbon nanotubes containing hydroxyl groups on the surface; The amount of water used is 1 to 5 mL per gram of the carbon nanotubes containing hydroxyl groups on the surface; The isocyanate raw material includes at least one of toluene diisocyanate, diphenylmethane diisocyanate and naphthalene 1,5-diisocyanate; The diol includes at least one of ethylene glycol, propylene glycol and butanediol; The second organic solvent comprises at least one of toluene, xylene and benzene; Optionally, in step S3, the conditions for the second heating reflux treatment include: a heating reflux temperature of 100 to 120° C., and a heating reflux time of 4 to 10 hours.

5. The preparation method according to claim 1, characterized in that In step S4, the mass ratio of the third product and the polytetrahydrofuran raw material is (10-40): (0.5-5.5); The amount of the second organic solvent used is 1 to 4 mL per gram of the third product; The polytetrahydrofuran raw material includes at least one of polytetrahydrofuran, poly-2-methyltetrahydrofuran and poly-2-ethyltetrahydrofuran; The second ammonium salt includes at least one of ammonium bicarbonate, ammonium chloride and ammonium carbonate; Optionally, in step S4, the conditions of the polymerization reaction include: a polymerization temperature of 80 to 120° C., and a polymerization time of 8 to 16 hours; the conditions of the second drying treatment include: a drying pressure of -0.09 to -0.08 MPa, a drying temperature of 40 to 80° C., and a drying time of 10 to 16 hours.

6. The preparation method according to claim 1, characterized in that In step S5, The counter electrode is a platinum sheet; The reference electrode is Ag / AgCl; In the electrolyte containing metal ions, the concentration of metal ions is 0.1 to 0.9 mol / L; Optionally, the metal ion is a copper ion; Optionally, in step S5, the conditions of the deposition treatment include: a constant potential of -1.5 to -0.7 V, and a deposition time of 5 to 15 min; the washing liquid used in the washing treatment includes anhydrous ethanol; the conditions of the third drying treatment include: a drying pressure of -0.09 to -0.08 MPa, a drying temperature of 25 to 45°C, and a drying time of 8 to 16 h.

7. A negative electrode current collector, characterized in that: The negative electrode current collector is prepared by the method according to any one of claims 1 to 6; Wherein, the negative electrode current collector comprises a porous substrate and a metal layer, and the metal layer is arranged on the surface and in the pores of the porous substrate; The materials of the substrate include carbon nanotubes with hydroxyl groups on the surface and foam polyurethane; the carbon nanotubes with hydroxyl groups on the surface and the foam polyurethane are connected through hydrogen bonds.

8. The negative electrode current collector according to claim 7, characterized in that: In the substrate, the mass ratio of the carbon nanotubes containing hydroxyl groups on the surface to the foamed polyurethane is (0.02-0.1):1; The mass ratio of the substrate to the metal layer is 1:0.2-1; The thickness of the substrate is 0.004 to 0.12 mm; the thickness of the metal layer is 0.5 to 10 μm; Optionally, the material of the metal layer includes copper.

9. A negative electrode plate, characterized in that: The negative electrode sheet comprises the negative electrode current collector prepared by the preparation method according to any one of claims 1 to 6, or the negative electrode current collector according to claim 7 or 8.

10. A battery, characterized in that: The battery includes a negative electrode plate, wherein the negative electrode plate is the negative electrode plate according to claim 9.

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