Metal foil and preparation method thereof, pole piece and battery

Abstract

The invention relates to the field of new energy batteries, in particular to a metal foil and a preparation method thereof, a pole piece and a battery, the metal foil comprises a base material and a conductive layer arranged on the surface of the base material; the material of the base material comprises a metal foil of which the surface contains hydroxyl; and the material of the conductive layer comprises carboxyl modified carbon nanotubes. When the metal foil is applied to a battery pole piece, the internal resistance of a battery is reduced, and the cycle performance of the battery is enhanced.

Description

Technical Field

[0001] The present invention relates to the field of new energy batteries, and particularly to a metal foil, a preparation method thereof, a pole piece and a battery. Background Art

[0002] In the process of manufacturing lithium ions, copper and aluminum foils are usually used as current collectors and carriers for positive and negative electrode slurries, and then wound and laminated with diaphragms to obtain lithium ion batteries. Therefore, the relevant properties of the foil are particularly important for the manufacture of pole pieces. Currently, the required properties of the foil are as follows: high conductivity, strong hydrophilicity, and good compatibility with the slurry (i.e., the slurry can be coated on the surface of the foil). At present, battery manufacturers use the method of plasma to treat the surface of the foil. However, (1) the plasma treatment effect has the disadvantage of timeliness, and the material after plasma surface treatment needs to be used as soon as possible, and its storage time is short; (2) the fatal disadvantage of oxygen plasma surface treatment is that the treated device is prone to generate new oxides and become secondary pollution; (3) another disadvantage of using the plasma surface treatment method is that the treatment process is complex, and improper control will damage the material surface; (4) generally speaking, plasma surface treatment equipment is generally more expensive, which is also a relatively obvious disadvantage of plasma surface treatment. Summary of the Invention

[0003] In view of this, the present invention is committed to providing a metal foil, a preparation method thereof, a pole piece and a battery to solve the problems of low electrolyte absorption capacity of the battery current collector and easy cracking and peeling of the slurry coating on the surface of the pole piece in the prior art.

[0004] To solve the above technical problems, the present application is implemented as follows:

[0005] The first aspect of the present invention provides a metal foil, which comprises a base material and a conductive layer provided on the surface of the base material;

[0006] The material of the base material comprises a metal foil with hydroxyl groups on the surface;

[0007] The material of the conductive layer comprises carboxyl-modified carbon nanotubes.

[0008] Optionally, the metal foil is selected from copper foil and / or aluminum foil; the mass ratio of the base material to the conductive layer is 1:0.005 - 0.035; the thickness of the metal foil is 8 - 15 μm; the thickness of the conductive layer is 0.5 - 3.5 nm.

[0009] The second aspect of the present invention provides a preparation method of a metal foil, and the preparation method comprises the following steps:

[0010] S1. Mix the metal foil, borohydride, ammonium salt and the first organic solvent, and perform the first heating and refluxing treatment to obtain a first product;

[0011] S2. Mix the first product, water, the first oxidant, hydroxide and the first organic solvent, and perform an oxidation reaction to obtain a second product;

[0012] S3. Perform filtration, washing treatment and the first drying treatment on the second product to obtain a metal foil with hydroxyl groups on its surface;

[0013] S4. Mix the carbon nanotubes, inorganic acid solution and the second oxidant to obtain a mixed material; perform the first centrifugation treatment, the first washing treatment and the second drying treatment on the mixed material to obtain a third product;

[0014] S5. Perform a hydrothermal reaction and ultrasonic treatment on the third product to obtain a fourth product; perform the second centrifugation treatment, the second washing treatment and the third drying treatment on the fourth product to obtain carboxyl-modified carbon nanotubes;

[0015] S6. Prepare a slurry containing the carboxyl-modified carbon nanotubes, and coat the slurry on at least one surface in the thickness direction of the metal foil with hydroxyl groups on its surface.

[0016] Optionally, in step S1, the mass ratio of the metal foil, the borohydride and the ammonium salt in the mixture is (3 - 9):(2 - 6):(4 - 8); the dosage of the first organic solvent is 50 - 170 mL relative to each gram of the metal foil; optionally, the metal foil is selected from copper foil and / or aluminum foil; optionally, the borohydride is selected from at least one of sodium borohydride, potassium borohydride, calcium borohydride, magnesium borohydride and lithium borohydride; optionally, the ammonium salt is selected from at least one of ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium bisulfate, ammonium fluoride, ammonium carbonate and ammonium bicarbonate; optionally, the first organic solvent is selected from at least one of tetrahydrofuran, acetonitrile, formamide and acetone.

[0017] Optionally, in step S2, the mass ratio of the first product and the hydroxide in the mixture is (3 - 20):(5 - 15); the dosage of the first organic solvent is 25 - 160 mL relative to each gram of the first product; the dosage of water is 25 - 160 mL relative to each gram of the first product; the dosage of the first oxidant is 0.5 - 25 mL relative to each gram of the first product; optionally, the first oxidant is selected from at least one of hydrogen peroxide, sodium hypochlorite and sodium peroxide; optionally, the hydroxide is selected from at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide; optionally, the second organic solvent is selected from at least one of toluene, xylene and benzene.

[0018] Optionally, in step S4, the mass fraction of the inorganic acid in the inorganic acid solution is 98-99%; optionally, the inorganic acid solution is selected from one of concentrated sulfuric acid, concentrated hydrochloric acid, and concentrated nitric acid; optionally, relative to each gram of the carbon nanotubes, the dosage of the inorganic acid solution is 0.02-0.06 L; optionally, the second oxidant is selected from at least one of hydrogen peroxide, sodium hypochlorite, and sodium peroxide, preferably hydrogen peroxide; optionally, relative to each gram of the carbon nanotubes, the dosage of the second oxidant is 0.03-0.08 L.

[0019] Optionally, in step S1, the conditions of the first heating and reflux treatment include: the heating and reflux temperature is 80-100°C, and the heating and reflux time is 8-16 h; and / or, in step S2, the conditions of the oxidation reaction include: the oxidation temperature is 20-60°C, and the oxidation time is 6-10 h; and / or, in step S3, 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: the drying temperature is 40-80°C, and the drying time is 8-16 h; and / or, in step S4, the conditions of the first centrifugation treatment include: the rotation speed is 5000-10000 rpm, and the time is 0.2-1 h; the washing liquid for the first washing treatment is ethanol and / or water; the second drying treatment is vacuum drying, and the conditions of the second drying treatment include: the drying temperature is 40-80°C, and the drying time is 8-16 h; and / or, in step S5, the conditions of the hydrothermal reaction include: the hydrothermal temperature is 80-100°C, and the hydrothermal time is 8-16 h; the ultrasonic treatment is carried out in ultrapure water, and the conditions of the ultrasonic treatment include: the ultrasonic frequency is 20-120 KHz, and the ultrasonic time is 30-90 min; the conditions of the second centrifugation treatment include: the rotation speed is 5000-10000 rpm, and the time is 0.2-1 h; the washing liquid for the second washing treatment is methanol and / or water; the third drying treatment is vacuum drying, and the conditions of the third drying treatment include: the drying temperature is 40-80°C, and the drying time is 8-16 h.

[0020] Optionally, the slurry further contains a binder and a solvent; optionally, the mass ratio of the carboxyl-modified carbon nanotubes, the binder, and the solvent in the slurry is 1:(0.2-0.8):(50-100); optionally, the binder is selected from at least one of polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, and polytetrafluoroethylene; optionally, the solvent is selected from water and / or N-methylpyrrolidone.

[0021] The third aspect of the present invention provides a pole piece, which includes a current collector, wherein the current collector is the above-mentioned metal foil material and / or the metal foil material prepared according to the above-mentioned preparation method.

[0022] A fourth aspect of the present invention provides a battery, which includes a positive electrode plate and a negative electrode plate. The positive electrode plate is the above-mentioned electrode plate; and / or, the negative electrode plate is the above-mentioned electrode plate.

[0023] Through the above technical solutions, the beneficial technical effects of the present invention are as follows:

[0024] (1) The metal foil of the present invention includes a base material and a conductive layer provided on the surface of the base material. The material of the base material includes a metal foil with hydroxyl groups on its surface, and the material of the conductive layer includes carboxyl-modified carbon nanotubes. By modifying the surface of the metal foil, a large number of hydroxyl groups are generated on the surface of the metal foil. On the one hand, it can effectively improve the electrolyte absorption capacity of the foil, enhance the affinity with the slurry, and further improve the battery performance. On the other hand, it is beneficial for the slurry to be coated on the foil, reducing the risk of coating cracking and peeling; by using carboxyl-modified carbon nanotubes as the material of the conductive layer, the battery resistance can be effectively reduced, and the battery performance can be improved.

[0025] (2) The preparation method of the metal foil of the present invention first mixes the metal foil, borohydride, ammonium salt and a first organic solvent and performs a first heating reflux treatment to obtain a first product (a metal foil with dehydrogenated products on its surface); then mixes the first product, water, a first oxidant, a hydroxide and a first organic solvent and performs an oxidation reaction, and after filtration, washing and drying treatments, a metal foil with hydroxyl groups on its surface is obtained; then mixes the carbon nanotubes, an inorganic acid solution and a second oxidant, performs centrifugation, washing and drying treatments to obtain a third product, performs a hydrothermal reaction and ultrasonic treatment on the third product to obtain a fourth product, and after centrifugation, washing and drying treatments on the fourth product, carboxyl-modified carbon nanotubes are obtained; then a slurry containing carboxyl-modified carbon nanotubes is prepared, and the slurry is coated on the surface of the metal foil with hydroxyl groups on its surface to obtain the metal foil. The preparation method of the present invention can effectively avoid introducing surface functional groups by means of plasma, etc., can effectively reduce the costs related to foil modification, and reduce the production cost.

[0026] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation section. Description of the Drawings

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

[0028] Figure 1 The related reaction equations involved in the preparation process of the metal foil with hydroxyl groups on its surface (taking aluminum foil as an example) are shown. Specific Implementation

[0029] The present invention discloses a metal foil material, a preparation method thereof, an electrode sheet and a battery. Those skilled in the art can draw on the content of this article and appropriately improve process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the present invention. The methods and applications of the present invention have been described through preferred embodiments. Relevant personnel can obviously make changes or appropriate alterations and combinations to 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.

[0030] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, 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 may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0031] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range or individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0032] If there is no special instruction, all implementation manners and optional implementation manners of this application can be combined with each other to form a new technical solution.

[0033] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0034] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0035] In order to solve the problems of low electrolyte absorption capacity of the battery current collector and easy cracking and peeling of the slurry coating on the surface of the electrode sheet in the prior art, the present invention adopts the following technical solutions:

[0036] The first aspect of the present invention provides a metal foil, which comprises a substrate and a conductive layer disposed on the surface of the substrate;

[0037] The material of the substrate comprises a metal foil with hydroxyl groups on its surface;

[0038] The material of the conductive layer comprises carboxyl-modified carbon nanotubes.

[0039] The metal foil of the present invention comprises a substrate and a conductive layer disposed on the surface of the substrate. The material of the substrate comprises a metal foil with hydroxyl groups on its surface, and the material of the conductive layer comprises carboxyl-modified carbon nanotubes. Among them, the metal foil with hydroxyl groups on its surface is beneficial to enhancing the absorption of the electrolyte and improving the battery cycle performance; the carboxyl-modified carbon nanotubes are beneficial to reducing the internal resistance of the battery and improving the battery performance; the hydroxyl groups on the surface of the metal foil with hydroxyl groups on its surface and the carboxyl groups on the surface of the carboxyl-modified carbon nanotubes can form hydrogen bonds or ester linkages, making the carbon nanotubes not easily fall off on the surface of the foil, thereby being beneficial to enhancing the battery cycle performance.

[0040] Exemplarily, the metal foil can be selected from copper foil and / or aluminum foil.

[0041] According to the present invention, an appropriate mass ratio of the substrate material to the conductive layer material can have the effect of enhancing the conductivity of the foil. If the proportion of the conductive layer material is too high and the proportion of the substrate material is too low, the conductive material may agglomerate, which may cause the resistance value of the foil to increase, thereby affecting electron conduction; if the proportion of the conductive layer material is too low and the proportion of the substrate material is too high, the conductive performance of the foil may decrease. In the present invention, the mass ratio of the substrate to the conductive layer can be 1:0.005 to 0.035; exemplarily, the mass ratio of the substrate to the conductive layer can be any value among 1:0.005, 1:0.01, 1:0.015, 1:0.02, 1:0.025, 1:0.03, and 1:0.035 or any value within the range formed by any two of the above values.

[0042] According to the present invention, the thickness of the metal foil can be 8 to 15 μm; exemplarily, the thickness of the metal foil can be any value among 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, and 15 μm or any value within the range formed by any two of the above values.

[0043] According to the present invention, the thickness of the suitable conductive layer can have the effect of enhancing the conductivity of the foil. If the thickness of the conductive layer is too large, the conductive layer will agglomerate, which may lead to a large resistance value of the foil, thereby affecting electron conduction; if the thickness of the conductive layer is too small, the conductivity of the foil may be reduced. In the present invention, the thickness of the conductive layer can be 0.5 to 3.5 nm. Exemplarily, the thickness of the conductive layer can be any value among 0.5 nm, 1.0 nm, 1.5 nm, 2.0 nm, 2.5 nm, 3 nm and 3.5 nm or any value within the range value composed of any two of the above values.

[0044] The second aspect of the present invention provides a method for preparing a metal foil, and the preparation method includes the following steps:

[0045] S1. Mix a metal foil, a borohydride, an ammonium salt and a first organic solvent and perform a first heating reflux treatment to obtain a first product;

[0046] S2. Mix the first product, water, a first oxidant, a hydroxide and the first organic solvent and perform an oxidation reaction to obtain a second product;

[0047] S3. Perform a filtration and washing treatment and a first drying treatment on the second product to obtain a metal foil with hydroxyl groups on its surface;

[0048] S4. Mix carbon nanotubes, an inorganic acid solution and a second oxidant to obtain a mixed material; perform a first centrifugation treatment, a first washing treatment and a second drying treatment on the mixed material to obtain a third product;

[0049] S5. Perform a hydrothermal reaction and an ultrasonic treatment on the third product to obtain a fourth product; perform a second centrifugation treatment, a second washing treatment and a third drying treatment on the fourth product to obtain carboxyl-modified carbon nanotubes;

[0050] S6. Prepare a slurry containing the carboxyl-modified carbon nanotubes and coat the slurry on at least one surface in the thickness direction of the metal foil with hydroxyl groups on its surface.

[0051] The preparation method of the modified metal foil of the present invention first mixes a metal foil, a borohydride, an ammonium salt, and a first organic solvent and performs a first heating reflux treatment to obtain a first product (a metal foil with dehydrogenated products on its surface); then mixes the first product, water, an oxidant, a hydroxide, and the first organic solvent and performs an oxidation reaction, and after filtration, washing, and drying treatments, a metal foil with hydroxyl groups on its surface is obtained; then carbon nanotubes, an inorganic acid solution, and a second oxidant are mixed, centrifuged, washed, and dried to obtain a third product, the third product is subjected to a hydrothermal reaction and ultrasonic treatment to obtain a fourth product, and after the fourth product is centrifuged, washed, and dried, carboxyl-modified carbon nanotubes are obtained; then a slurry containing the carboxyl-modified carbon nanotubes is prepared, and the slurry is coated on the surface of the metal foil with hydroxyl groups on its surface to obtain the metal foil. The preparation method of the present invention can effectively avoid introducing surface functional groups by means of plasma, etc., can effectively reduce the costs related to foil modification, and reduce the production cost.

[0052] In an exemplary embodiment of the present invention, the relevant reaction equations involved in the preparation process of the metal foil with hydroxyl groups on its surface (taking an aluminum foil as an example) are as Figure 1 shown.

[0053] Exemplarily, in the preparation process of the Al foil with hydroxyl groups on its surface, the borohydride and the ammonium salt (such as NaBH 4 and (NH 4 ) 2 SO 4 ) react in the first organic solvent to generate BH 3 -NH 3 , and then reflux on the Al foil to obtain dehydrogenated BH-NH 2 , and finally hydroxyl groups are generated on the surface of the Al foil under the action of the hydroxide and the oxidant (NaOH and H 2 O 2 ) to obtain Al-OH.

[0054] According to the present invention, in step S1, the mass ratio of the metal foil, the borohydride, and the ammonium salt in the mixture can be (3-9):(2-6):(4-8).

[0055] In the present invention, the amount of the first organic solvent used can be 50-170 mL relative to each gram of the metal foil; exemplarily, the amount of the first organic solvent used can be any value among 50 mL, 70 mL, 90 mL, 110 mL, 130 mL, 150 mL, and 170 mL or any value within the range formed by any two of the above-mentioned values relative to each gram of the metal foil.

[0056] Exemplarily, the metal foil can be selected from copper foil and / or aluminum foil.

[0057] Exemplarily, the borohydride may be selected from at least one of sodium borohydride, potassium borohydride, calcium borohydride, magnesium borohydride, and lithium borohydride.

[0058] Exemplarily, the ammonium salt may be selected from at least one of ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium bisulfate, ammonium fluoride, ammonium carbonate, and ammonium bicarbonate.

[0059] Exemplarily, the first organic solvent may be selected from at least one of tetrahydrofuran, acetonitrile, formamide, and acetone.

[0060] According to the present invention, in step S2, the mass ratio of the mixture of the first product and the hydroxide may be (3 to 20):(5 to 15).

[0061] In the present invention, the amount of the first organic solvent used may be 25 to 160 mL per gram of the first product; exemplarily, the amount of the first organic solvent used may be any value among 25 mL, 50 mL, 70 mL, 90 mL, 110 mL, 130 mL, 150 mL, and 160 mL per gram of the first product, or any value within the range formed by any two of the above values.

[0062] In the present invention, the amount of water used may be 25 to 160 mL per gram of the first product; exemplarily, the amount of water used may be any value among 25 mL, 50 mL, 70 mL, 90 mL, 110 mL, 130 mL, 150 mL, and 160 mL per gram of the first product, or any value within the range formed by any two of the above values.

[0063] In the present invention, the amount of the first oxidant used may be 0.5 to 25 mL per gram of the first product; exemplarily, the amount of the first oxidant used may be any value among 0.5 mL, 1 mL, 5 mL, 10 mL, 15 mL, 20 mL, and 25 mL per gram of the first product, or any value within the range formed by any two of the above values.

[0064] Exemplarily, the first oxidant may be selected from at least one of hydrogen peroxide, sodium hypochlorite, and sodium peroxide.

[0065] Exemplarily, the hydroxide may be selected from at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0066] Exemplarily, the second organic solvent may be selected from at least one of toluene, xylene, and benzene.

[0067] According to the present invention, in step S4, the mass fraction of the inorganic acid in the inorganic acid solution can be 98-99%. Exemplarily, the inorganic acid solution can be selected from one of concentrated sulfuric acid, concentrated hydrochloric acid, and concentrated nitric acid. In the present invention, the dosage of the inorganic acid solution can be 0.02-0.06 L per gram of the carbon nanotubes. Exemplarily, the dosage of the inorganic acid solution per gram of the carbon nanotubes can be any value among 0.02 L, 0.03 L, 0.04 L, 0.05 L, and 0.06 L or any value within the range formed by any two of the above values.

[0068] According to the present invention, the second oxidant can be selected from at least one of hydrogen peroxide, sodium hypochlorite, and sodium peroxide, and preferably hydrogen peroxide. In the present invention, the dosage of the second oxidant is 0.03-0.08 L per gram of the carbon nanotubes. Exemplarily, the dosage of the second oxidant per gram of the carbon nanotubes can be any value among 0.03 L, 0.04 L, 0.05 L, 0.06 L, 0.07 L, and 0.08 L or any value within the range formed by any two of the above values.

[0069] According to the present invention, in step S1, the conditions for the first heating and refluxing treatment include: the heating and refluxing temperature is 80-100 °C, and the heating and refluxing time is 8-16 h. As an example, the temperature of the first heating and refluxing treatment can be 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, etc., and the time of the first heating and refluxing treatment can be 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, etc.

[0070] According to the present invention, in step S2, the conditions for the oxidation reaction include: the oxidation temperature is 20-60 °C, and the oxidation time is 6-10 h. As an example, the temperature of the oxidation reaction can be 20 °C, 30 °C, 40 °C, 50 °C, 60 °C, etc., and the time of the oxidation reaction can be 6 h, 7 h, 8 h, 9 h, 10 h, etc.

[0071] According to the present invention, in step S3, the washing liquid used for the filtration and washing treatment includes at least one of water, ethanol, and acetone; the conditions for the first drying treatment include: the drying temperature is 40-80 °C, and the drying time is 8-16 h. As an example, the temperature of the first drying treatment can be 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, etc., and the time of the first drying treatment can be 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, etc.

[0072] According to the present invention, in step S4, the conditions for the first centrifugation treatment include: a rotation speed of 5000 - 10000 rpm and a time of 0.2 - 1 h; the washing liquid for the first washing treatment is ethanol and / or water; the second drying treatment is vacuum drying, and the conditions for the second drying treatment include: a drying temperature of 40 - 80 °C and a drying time of 8 - 16 h. As an example, the rotation speed of the first centrifugation treatment can be 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, etc., and the time of the first centrifugation treatment can be 0.2 h, 0.4 h, 0.6 h, 0.8 h, 1 h, etc.; the temperature of the second drying treatment can be 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, etc., and the time of the second drying treatment can be 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, etc.

[0073] According to the present invention, in step S5, the conditions for the hydrothermal reaction include: a hydrothermal temperature of 80 - 100 °C and a hydrothermal time of 8 - 16 h; the ultrasonic treatment is carried out in ultrapure water, and the conditions for the ultrasonic treatment include: an ultrasonic frequency of 20 - 120 KHz and an ultrasonic time of 30 - 90 min; the conditions for the second centrifugation treatment include: a rotation speed of 5000 - 10000 rpm and a time of 0.2 - 1 h; the washing liquid for the second washing treatment is methanol and / or water; the third drying treatment is vacuum drying, and the conditions for the third drying treatment include: a drying temperature of 40 - 80 °C and a drying time of 8 - 16 h. As an example, the hydrothermal temperature can be 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, etc., and the hydrothermal time can be 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, etc.; the ultrasonic frequency is 20 KHz, 40 KHz, 60 KHz, 80 KHz, 100 KHz, 120 KHz, and the ultrasonic time is 30 min, 50 min, 70 min, 90 min; the rotation speed of the second centrifugation treatment can be 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, etc., and the time of the second centrifugation treatment can be 0.2 h, 0.4 h, 0.6 h, 0.8 h, 1 h, etc.; the temperature of the third drying treatment can be 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, etc., and the time of the third drying treatment can be 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, etc.

[0074] In an embodiment of the present invention, the slurry may further contain a binder and a solvent; optionally, the mass ratio of the carboxyl - modified carbon nanotubes, the binder, and the solvent in the slurry is 1:(0.2 - 0.8):(50 - 100).

[0075] Exemplarily, the binder may be selected from at least one of polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, and polytetrafluoroethylene.

[0076] Exemplarily, the solvent may be selected from water and / or N-methylpyrrolidone (NMP).

[0077] The third aspect of the present invention provides a current collector, wherein the current collector is the above-mentioned metal foil and / or the metal foil prepared according to the above preparation method.

[0078] The fourth aspect of the present invention provides a battery, which includes a positive electrode current collector and a negative electrode current collector. The positive electrode current collector is the above-mentioned current collector; and / or, the negative electrode current collector is the above-mentioned current collector.

[0079] The present invention will be further described in detail below through examples. All raw materials used in the examples can be obtained through commercial channels.

[0080] Example 1

[0081] (1) Preparation of Al-OH

[0082] Put 6 g of conventional aluminum foil into a reaction vessel, then add 4 g of sodium borohydride and 6 g of ammonium sulfate thereto, and then add 500 mL of tetrahydrofuran. After mixing, a mixture is obtained; the mixture is heated under reflux at 90 °C for 12 h and cooled to room temperature to obtain a dehydrogenated product on the aluminum foil; then 500 mL of deionized water is added, and in the mixture of tetrahydrofuran and water, an oxidation reaction is carried out with 35 mL of hydrogen peroxide and 10 g of sodium hydroxide, and the mixture is oxidized at about 40 °C; then, the obtained substance is filtered, washed with hot water, and then washed with ethanol and acetone. The product is dried in a vacuum oven at 60 °C for 12 h to obtain a dried substance, that is, an Al foil containing hydroxyl groups, which can be denoted as Al-OH.

[0083] (2) Preparation of aluminum foil with a conductive layer on the surface

[0084] First, weigh 300 mg of carbon nanotubes (CNTs) and dissolve them in 30 mL of 98% H 2 SO 4 and 9 mL of 30% H 2 O 2Modified CNTs were prepared in a mixed solution. The mixture was slowly stirred at 22 °C for 10 - 30 h. Then it was centrifuged and collected, thoroughly washed with water and ethanol until the pH value became neutral, and then dried overnight under vacuum. The obtained modified CNTs were further treated by a simple hydrothermal reaction. 15 mL of ultrapure water was added, and strong ultrasonic treatment was carried out for about 1 hour. Then it was transferred to a centrifuge tube, centrifuged repeatedly, washed with water and methanol, and then dried overnight under vacuum to obtain carboxyl-modified CNTs, denoted as CNT-COOH. Then CNT-COOH and PVDF were dissolved in NMP according to a mass ratio of 5:1 and stirred evenly to obtain the CNT-COOH slurry. The CNT-COOH slurry was coated onto the prepared Al-OH using a small coater to form a conductive layer with a thickness of 2 μm, and an aluminum foil with a conductive layer on its surface was obtained.

[0085] (3) Preparation of the positive electrode plate

[0086] The ternary 6-series (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ) powder of the positive electrode active material, conductive carbon, and polyvinylidene fluoride (PVDF) were mixed according to a mass ratio of 8:1:1 to obtain a mixed material. The mixed material was stirred evenly in N-methylpyrrolidone (NMP) to obtain the positive electrode active slurry of the corresponding positive electrode plate. The positive electrode active slurry was coated onto the aluminum foil with a conductive layer on its surface to obtain the first electrode plate, where the mass fraction of LiNi 0.6 Co 0.2 Mn 0.2 O 2 was 80 wt%, and after drying and pressing, the positive electrode plate was obtained.

[0087] (4) Preparation of the negative electrode plate

[0088] The graphite powder of the negative electrode active material, conductive carbon, and PVDF were mixed according to a mass ratio of 8:1:1 to obtain a mixed material. The mixed material was stirred evenly in deionized water to obtain the negative electrode active slurry of the corresponding negative electrode plate. The negative electrode active slurry was coated onto a conventional copper foil to obtain a negative electrode homogeneous coating with a main material graphite mass fraction of 80 wt% and a surface density of the negative electrode slurry of 1.21 mg / cm 2 , and after drying and pressing, the negative electrode plate was obtained.

[0089] (5) Preparation of the lithium-ion battery

[0090] Ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:2:1 to obtain a mixed organic solvent. Then, the fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte solution.

[0091] The prepared positive electrode plate, negative electrode plate, and PE separator were wound to obtain a corresponding wound core, and then the wound core was placed in a case for main liquid injection, formation, and grading to obtain a corresponding aluminum shell battery.

[0092] Example 2

[0093] In this example, the preparation method of Al-OH was the same as that in Example 1 as a whole, except that the addition amount of sodium borohydride was 2 g.

[0094] In this example, the preparation method of the aluminum foil with a conductive layer on the surface, the preparation method of the positive electrode plate, the preparation method of the negative electrode plate, and the preparation method of the lithium-ion battery were the same as those in Example 1.

[0095] Example 3

[0096] In this example, the preparation method of Al-OH was the same as that in Example 1 as a whole, except that the addition amount of sodium borohydride was 6 g.

[0097] In this example, the preparation method of the aluminum foil with a conductive layer on the surface, the preparation method of the positive electrode plate, the preparation method of the negative electrode plate, and the preparation method of the lithium-ion battery were the same as those in Example 1.

[0098] Example 4

[0099] In this example, the preparation method of Al-OH was the same as that in Example 1 as a whole, except that the addition amount of ammonium sulfate was 4 g.

[0100] In this example, the preparation method of the aluminum foil with a conductive layer on the surface, the preparation method of the positive electrode plate, the preparation method of the negative electrode plate, and the preparation method of the lithium-ion battery were the same as those in Example 1.

[0101] Example 5

[0102] In this example, the preparation method of Al-OH was the same as that in Example 1 as a whole, except that the addition amount of ammonium sulfate was 8 g.

[0103] In this example, the preparation method of the aluminum foil with a conductive layer on the surface, the preparation method of the positive electrode plate, the preparation method of the negative electrode plate, and the preparation method of the lithium-ion battery were the same as those in Example 1.

[0104] Example 6

[0105] In this example, the preparation method of Al-OH was the same as that in Example 1.

[0106] In this embodiment, the preparation method of the aluminum foil with a conductive layer on its surface is the same as that in Embodiment 1 as a whole, except that: CNT-COOH and PVDF are dissolved in NMP according to a mass ratio of 3:1 and stirred evenly to obtain a CNT-COOH slurry.

[0107] In this embodiment, the preparation methods of the positive electrode plate, the negative electrode plate and the lithium ion battery are the same as those in Embodiment 1.

[0108] Embodiment 7

[0109] In this embodiment, the preparation method of Al-OH is the same as that in Embodiment 1.

[0110] In this embodiment, the preparation method of the aluminum foil with a conductive layer on its surface is the same as that in Embodiment 1 as a whole, except that: CNT-COOH and PVDF are dissolved in NMP according to a mass ratio of 7:1 and stirred evenly to obtain a CNT-COOH slurry.

[0111] In this embodiment, the preparation methods of the positive electrode plate, the negative electrode plate and the lithium ion battery are the same as those in Embodiment 1.

[0112] Comparative Example 1

[0113] (1) Preparation of the positive electrode plate

[0114] Mix the positive electrode active material ternary system 6 (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ) powder, conductive carbon and polyvinylidene fluoride (PVDF) according to a mass ratio of 8:1:1 to obtain a mixed material. Stir the mixed material evenly in N-methylpyrrolidone (NMP) to obtain the positive electrode active slurry of the corresponding positive electrode plate. Coat the positive electrode active slurry on the preparation of a conventional aluminum foil to obtain a first electrode plate, where the mass fraction of LiNi 0.6 Co 0.2 Mn 0.2 O 2 is 80wt%. After drying and pressing, a positive electrode plate is obtained.

[0115] In this comparative example, the preparation methods of the negative electrode plate and the lithium ion battery are the same as those in Embodiment 1.

[0116] Comparative Example 2

[0117] (1) Preparation of the positive electrode plate

[0118] Mix the ternary 6 system (LiNi0.6Co0.2Mn0.2O2) powder of the positive electrode active material, conductive carbon, and polyvinylidene fluoride (PVDF) according to a mass ratio of 8:1:1 to obtain a mixed material. Stir the mixed material evenly in N-methylpyrrolidone (NMP) to obtain the positive electrode active slurry for the corresponding positive electrode sheet. Coat the positive electrode active slurry on the commercially available carbon-coated aluminum foil to obtain the first electrode sheet, where the mass fraction of LiNi 0.6 Co 0.2 Mn 0.2 O 2 in the first electrode sheet is 80 wt%. After drying and pressing, the positive electrode sheet is obtained.

[0119] In this comparative example, the preparation method of the negative electrode sheet and the preparation method of the lithium-ion battery are the same as those in Example 1.

[0120] Comparative Example 3

[0121] (1) Preparation of aluminum foil with a conductive layer on the surface

[0122] First, weigh 300 mg of carbon nanotubes (CNTs) and dissolve them in a mixed solution of 30 mL of 98% H 2 SO 4 and 9 mL of 30% H 2 O 2 to prepare modified CNTs. Stir the mixture slowly at 22 °C for 10 - 30 h. Then, centrifuge and collect, wash thoroughly with water and ethanol until the pH value becomes neutral, and then dry overnight under vacuum. Further process the obtained modified CNTs through a simple hydrothermal reaction, add 15 mL of ultrapure water, and perform strong ultrasonic treatment for about 1 hour. Transfer to a centrifuge tube, centrifuge repeatedly, wash with water and methanol, and then dry overnight under vacuum to obtain carboxyl-modified CNTs, denoted as CNT-COOH. Then, dissolve CNT-COOH and PVDF in NMP according to a mass ratio of 5:1 and stir evenly to obtain the CNT-COOH slurry. Coat the CNT-COOH slurry onto a conventional aluminum foil using a small coater to form a conductive layer with a thickness of 2 μm, obtaining the aluminum foil with a conductive layer on the surface in this comparative example.

[0123] (2) Preparation of the positive electrode sheet

[0124] Mix the ternary 6 system (LiNi 0.6 Co 0.2 Mn 0.2 O 2) The powder, conductive carbon, and polyvinylidene fluoride (PVDF) are mixed according to a mass ratio of 8:1:1 to obtain a mixed material. The mixed material is fully stirred in N-methylpyrrolidone (NMP) to obtain the positive electrode active slurry for the corresponding positive electrode sheet. The positive electrode active slurry is coated on the aluminum foil with a conductive layer prepared in this comparative example to obtain a positive electrode sheet containing LiNi 0.6 Co 0.2 Mn 0.2 O 2 with a mass fraction of 80 wt%. After drying and pressing, a positive electrode sheet is obtained.

[0125] In this comparative example, the preparation method of the negative electrode sheet and the preparation method of the lithium-ion battery are the same as those in Example 1.

[0126] Comparative Example 4

[0127] (1) Preparation of Al-OH

[0128] Put 6 g of conventional aluminum foil into a reaction vessel, then add 4 g of sodium borohydride and 6 g of ammonium sulfate to it, and then add 500 mL of tetrahydrofuran. After mixing, a mixture is obtained; the mixture is heated under reflux at 90 °C for 12 h and cooled to room temperature to obtain a dehydrogenated product on the aluminum foil; then add 500 mL of deionized water, and in the mixture of tetrahydrofuran and water, an oxidation reaction is carried out with 35 mL of hydrogen peroxide and 10 g of sodium hydroxide, and the mixture is oxidized at about 40 °C; then, the obtained substance is filtered, washed with hot water, and then washed with ethanol and acetone. The product is dried in a vacuum oven at 60 °C for 12 h to obtain a dried substance, that is, an Al foil containing hydroxyl groups, which can be denoted as Al-OH.

[0129] (2) Preparation of the positive electrode sheet

[0130] The ternary 6-series positive electrode active material (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ) powder, conductive carbon, and polyvinylidene fluoride (PVDF) are mixed according to a mass ratio of 8:1:1 to obtain a mixed material. The mixed material is fully stirred in N-methylpyrrolidone (NMP) to obtain the positive electrode active slurry for the corresponding positive electrode sheet. The positive electrode active slurry is coated on the Al foil containing hydroxyl groups prepared in this comparative example to obtain a positive electrode sheet containing LiNi 0.6 Co 0.2 Mn 0.2 O 2 with a mass fraction of 80 wt%. After drying and pressing, a positive electrode sheet is obtained.

[0131] The preparation method of the negative electrode sheet and the preparation method of the lithium ion battery in this comparative example are the same as those in Example 1.

[0132] Comparative Example 5

[0133] (1) Preparation of Al-OH

[0134] Put 6 g of conventional aluminum foil into a reaction vessel, then add 4 g of sodium borohydride and 6 g of ammonium sulfate to it, and then add 500 mL of tetrahydrofuran. After mixing, a mixture is obtained; the mixture is heated under reflux at 90 °C for 12 h and cooled to room temperature to obtain a dehydrogenated product on the aluminum foil; then add 500 mL of deionized water, and in the mixture of tetrahydrofuran and water, an oxidation reaction is carried out with 35 mL of hydrogen peroxide and 10 g of sodium hydroxide, and the mixture is oxidized at about 40 °C; then, the obtained substance is filtered, washed with hot water, and then washed with ethanol and acetone. The product is dried in a vacuum oven at 60 °C for 12 h to obtain a dried substance, that is, Al foil containing hydroxyl groups, which can be denoted as Al-OH.

[0135] (2) Preparation of aluminum foil with a conductive layer on the surface

[0136] Carbon nanotubes and PVDF are dissolved in NMP according to a mass ratio of 5:1 and stirred evenly to obtain a CNT slurry. The CNT slurry is coated on the prepared Al-OH by a small coater to form a conductive layer with a thickness of 2 μm, and the aluminum foil with a conductive layer on the surface of this comparative example is obtained.

[0137] (2) Preparation of the positive electrode sheet

[0138] The positive electrode active material ternary system 6 (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ) powder, conductive carbon and polyvinylidene fluoride (PVDF) are mixed according to a mass ratio of 8:1:1 to obtain a mixed material. The mixed material is stirred evenly in N-methylpyrrolidone (NMP) to obtain the positive electrode active slurry of the corresponding positive electrode sheet. The positive electrode active slurry is coated on the aluminum foil with a conductive layer on the surface prepared in this comparative example to obtain a positive electrode sheet with a LiNi content of 0.6 Co 0.2 Mn 0.2 O 2 with a mass fraction of 80 wt%. After drying and pressing, a positive electrode sheet is obtained.

[0139] The preparation method of the negative electrode sheet and the preparation method of the lithium ion battery in this comparative example are the same as those in Example 1.

[0140] Test Example 1

[0141] The lithium-ion batteries obtained in Examples 1-7 and Comparative Examples 1-5 were tested for initial Coulombic efficiency, battery resistance, and cyclic capacity retention rate. The test results are shown in Table 1.

[0142] (1) Test method for initial Coulombic efficiency (first efficiency): First, the battery was formed by constant current charging at 0.1C to 3.75V. This step is the formation stage of the battery SEI film, and the capacity C of the battery after formation was recorded. 1 . Secondly, the battery was fully charged by constant current charging at 1C to 4.4V and constant voltage charging at 4.4V until I≤0.05C, and the charging capacity C was recorded. 2 . Finally, the battery discharge capacity C was obtained by constant current discharging at 1C to 2.8V. 3 . The initial Coulombic efficiency was calculated according to the formula C 3 / (C 1 +C 2 ).

[0143] (2) Test method for battery internal resistance: The battery internal resistance was measured by a battery internal resistance measuring instrument.

[0144] (3) Test method for cyclic capacity retention rate: The test was carried out according to the steps: a. constant current discharging at 1C to 2.8V; b. standing for 30 min; c. constant current charging at 1C to 4.4V; d. standing for 30 min; e. constant current discharging at 1C to 2.8V; f. standing for 30 min. Steps c-f were repeated, and the battery capacity C after 300 cycles was recorded. 4 . The capacity retention rate was calculated using C 4 / C 3 .

[0145] Table 1

[0146] First effect % Internal resistance / mΩ Capacity retention rate after 200 cycles / % Example 1 92.8 5.42 93.5 Example 2 90.6 5.84 91.6 Example 3 90.4 5.78 91.3 Example 4 90.1 5.83 91.2 Example 5 90.8 5.76 91.4 Example 6 91.2 5.62 92.6 Example 7 91.6 5.61 92.4 Comparative example 1 88.6 9.79 89.5 Comparative example 2 89.2 6.85 90.5 Comparative example 3 89.4 6.42 90.6 Comparative example 4 88.9 8.65 89.8 Comparative example 5 89.0 7.82 90.2

[0147] It can be seen from the data of Examples 1-7 and Comparative Examples 1-5 that using the metal foil prepared by the method of the present invention as the positive current collector can effectively improve the first cycle efficiency of the battery, reduce the internal resistance of the battery, and enhance the capacity retention rate of the battery.

[0148] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A metal foil material, characterized in that: The metal foil material comprises a substrate and a conductive layer arranged on the surface of the substrate; The material of the substrate includes a metal foil having a hydroxyl group on the surface; The material of the conductive layer includes carboxyl-modified carbon nanotubes.

2. The metal foil material according to claim 1, characterized in that: The metal foil is selected from copper foil and / or aluminum foil; The mass ratio of the substrate to the conductive layer is 1:0.005-0.035; The thickness of the metal foil is 8 to 15 μm; The thickness of the conductive layer is 0.5-3.5 nm.

3. A method for preparing a metal foil, characterized in that: The preparation method comprises the following steps: S1, mixing a metal foil, a borohydride, an 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, a first oxidant, a hydroxide and the first organic solvent and performing an oxidation reaction to obtain a second product; S3, filtering, washing and first drying the second product to obtain a metal foil having a hydroxyl group on its surface; S4, mixing the carbon nanotubes, the inorganic acid solution and the second oxidant to obtain a mixed material; performing a first centrifugation treatment, a first washing treatment and a second drying treatment on the mixed material to obtain a third product; S5, subjecting the third product to a hydrothermal reaction and an ultrasonic treatment to obtain a fourth product; subjecting the fourth product to a second centrifugal treatment, a second washing treatment, and a third drying treatment to obtain carboxyl-modified carbon nanotubes; S6. Prepare a slurry containing the carboxyl-modified carbon nanotubes, and apply the slurry to at least one surface in the thickness direction of the metal foil having a hydroxyl group on its surface.

4. The preparation method according to claim 3, characterized in that: In step S1, the mass ratio of the metal foil, the borohydride and the ammonium salt is (3-9): (2-6): (4-8); The amount of the first organic solvent used is 50 to 170 mL per gram of the metal foil; Optionally, the metal foil is selected from copper foil and / or aluminum foil; Optionally, the borohydride is selected from at least one of sodium borohydride, potassium borohydride, calcium borohydride, magnesium borohydride and lithium borohydride; Optionally, the ammonium salt is selected from at least one of ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium bisulfate, ammonium fluoride, ammonium carbonate and ammonium bicarbonate; Optionally, the first organic solvent is selected from at least one of tetrahydrofuran, acetonitrile, formamide and acetone.

5. The preparation method according to claim 3, characterized in that: In step S2, the mass ratio of the first product and the hydroxide is (3-20): (5-15); The amount of the first organic solvent is 25 to 160 mL per gram of the first product; The amount of water used is 25 to 160 mL per gram of the first product; The amount of the first oxidant is 0.5 to 25 mL per gram of the first product; Optionally, the first oxidant is selected from at least one of hydrogen peroxide, sodium hypochlorite and sodium peroxide; Optionally, the hydroxide is selected from at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide; Optionally, the second organic solvent is selected from at least one of toluene, xylene and benzene.

6. The preparation method according to claim 3, characterized in that: In step S4, the mass fraction of the inorganic acid in the inorganic acid solution is 98-99%; Optionally, the inorganic acid solution is selected from one of concentrated sulfuric acid, concentrated hydrochloric acid and concentrated nitric acid; Optionally, the amount of the inorganic acid solution is 0.02 to 0.06 L per gram of the carbon nanotubes; Optionally, the second oxidant is selected from at least one of hydrogen peroxide, sodium hypochlorite and sodium peroxide, preferably hydrogen peroxide; Optionally, the usage amount of the second oxidant is 0.03-0.08 L per gram of the carbon nanotubes.

7. The preparation method according to claim 3, characterized in that: In step S1, the first heating reflux treatment conditions include: heating reflux temperature of 80-100° C., heating reflux time of 8-16 h; and / or, In step S2, the conditions of the oxidation reaction include: oxidation temperature of 20 to 60° C., oxidation time of 6 to 10 h; and / or, In step S3, the washing liquid used in the filter washing treatment includes at least one of water, ethanol and acetone; the conditions of the first drying treatment include: a drying temperature of 40 to 80° C. and a drying time of 8 to 16 hours; and / or, In step S4, the conditions of the first centrifugal treatment include: a rotation speed of 5000-10000 rpm and a time of 0.2-1 h; the washing liquid of the first washing treatment is ethanol and / or water; the second drying treatment is vacuum drying, and the conditions of the second drying treatment include: a drying temperature of 40-80° C. and a drying time of 8-16 h; and / or, In step S5, the conditions of the hydrothermal reaction include: the hydrothermal temperature is 80-100°C, and the hydrothermal time is 8-16h; the ultrasonic treatment is carried out in ultrapure water, and the conditions of the ultrasonic treatment include: the ultrasonic frequency is 20-120KHz, and the ultrasonic time is 30-90min; the conditions of the second centrifugal treatment include: the rotation speed is 5000-10000rpm, and the time is 0.2-1h; the washing liquid of the second washing treatment is methanol and / or water; the third drying treatment is vacuum drying, and the conditions of the third drying treatment include: the drying temperature is 40-80°C, and the drying time is 8-16h.

8. The preparation method according to claim 3, characterized in that: The slurry also contains a binder and a solvent; Optionally, the mass ratio of the carboxyl-modified carbon nanotubes, the binder and the solvent in the slurry is 1:(0.2-0.8):(50-100); Optionally, the binder is selected from at least one of polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate and polytetrafluoroethylene; Optionally, the solvent is selected from water and / or N-methylpyrrolidone.

9. A pole piece, characterized in that: The pole piece includes a current collector, wherein the current collector is the metal foil material according to claim 1 or 2 and / or the metal foil material prepared according to the preparation method according to any one of claims 3 to 8.

10. A battery, characterized in that: The battery comprises a positive electrode plate and a negative electrode plate, wherein the positive electrode plate is the plate described in claim 9; and / or the negative electrode plate is the plate described in claim 9.

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