A carbon-coated aluminum foil for improving cycle rate performance of lithium batteries and a preparation method thereof

Abstract

The present application relates to the technical field of battery materials, in particular to a carbon-coated aluminum foil for improving the cycle rate performance of lithium batteries and a preparation method thereof, wherein the surface of an aluminum foil substrate is sequentially provided with a bottom layer material, a middle layer material and a top layer material; the bottom layer material comprises conductive graphite; the middle layer material comprises nano-conductive carbon black, modified graphene, polyurethane elastomer and boron nitride micro powder; the top layer material comprises carboxylated carbon nanotubes; and the bottom layer material, the middle layer material and the top layer material further comprise a binder and a dispersant. The large-particle graphite in the bottom layer of the carbon coating layer constructs a stable conductive framework, providing a stable path for electron transmission; the nanoscale carbon black in the middle layer cooperates with the modified graphene, using the high specific surface area of the carbon black to capture electrons, and the modified graphene quickly conducts electrons by virtue of excellent electron migration characteristics; and the carboxylated carbon nanotubes in the top layer adjust the electrode interface environment and promote the uniform diffusion of lithium ions, thereby significantly improving the cycle rate performance of lithium batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a carbon-coated aluminum foil for improving the cycle rate performance of lithium batteries and a preparation method thereof. BACKGROUND

[0002] Lithium batteries are a class of batteries that use non-aqueous electrolyte solutions with lithium metal or lithium alloy as the positive / negative electrode material. According to the form of lithium in the battery, lithium batteries can be divided into two categories: lithium metal batteries and lithium ion batteries. Lithium metal batteries are usually not rechargeable and contain metallic lithium, while lithium ion batteries can be charged and do not contain metallic lithium. Lithium batteries have the advantages of being lightweight, durable, and relatively less polluting to the environment. The carbon-coated aluminum foil in lithium batteries is a composite material that coats conductive carbon material on an aluminum foil substrate, mainly used in battery manufacturing, especially widely used in lithium batteries and power batteries. Carbon-coated aluminum foil has many advantages, including reducing battery internal resistance, suppressing battery polarization, improving battery energy density, and prolonging battery cycle life.

[0003] Now that lithium batteries are widely used in electric vehicles, portable electronic devices, and many other fields, there are many problems with traditional aluminum foil as a current collector during high-rate charging and discharging. For example, the contact resistance between the electrode and the current collector is high, leading to poor electron transmission and severe battery heating, which in turn affects the cycle life and rate performance of the battery. In addition, lithium batteries perform poorly when charged and discharged in high and low temperature environments, which greatly limits the cycle rate performance of lithium batteries during charging and discharging. SUMMARY

[0004] To solve the problem of insufficient cycle rate performance of lithium batteries in the prior art, the present application provides a carbon-coated aluminum foil for improving the cycle rate performance of lithium batteries and a preparation method thereof.

[0005] The technical solution adopted by the present application is as follows: a carbon-coated aluminum foil for improving the cycle rate performance of lithium batteries, an aluminum foil substrate surface is sequentially provided with a bottom layer material, a middle layer material and a top layer material; the bottom layer material comprises conductive graphite, the middle layer material comprises nano-conductive carbon black, modified graphene, polyurethane elastomer and boron nitride micro powder, and the top layer material comprises carboxylated carbon nanotubes; the bottom layer material, the middle layer material and the top layer material further comprise a binder and a dispersant.

[0006] Further, in some embodiments, the mass ratio of conductive graphite, binder and dispersant in the bottom layer material is 70:2:10; the mass ratio of nano-conductive carbon black, modified graphene, polyurethane elastomer, boron nitride micro powder, binder and dispersant in the middle layer material is 35:25:15:10:10:5; and the mass ratio of carboxylated carbon nanotubes, binder and dispersant in the top layer material is 80:15:5.

[0007] Further, in some embodiments, the thickness of the bottom layer material is 1-2 μm, the thickness of the middle layer material is 0.8-1.5 μm, and the thickness of the top layer material is 0.2-0.4 μm.

[0008] Further, in some embodiments, the adhesive is a butadiene-styrene rubber emulsion, and the dispersant is polyethylene glycol.

[0009] Further, in some embodiments, the method for preparing the modified graphene is as follows:

[0010] A1, 100 g of natural graphite flakes is crushed, and 1000 mL of a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 is added thereto, and stirring is continuously carried out at a rotation speed of 300 r / min for 48 h at room temperature until the reaction is completed;

[0011] A2, a strong oxidizing agent composed of 30 g of potassium permanganate and 100 mL of concentrated sulfuric acid is added thereto, and oxidation reaction is continuously carried out at a rotation speed of 250 r / min for 5 h at 35℃, and then 50 mL of a mixed solution composed of ethylene glycol and acetic acid in a molar ratio of 1:1 is added thereto to make ethyl glycolate, wherein the substance amount concentration of ethylene glycol and acetic acid is 2 mol / L, and then heating is carried out to 90℃, and 25 portions of clean water are added dropwise to the solution at a speed of 5 mL / min during the heating process, and hydrolysis reaction is carried out for 3 h, and finally 50 mL of hydrogen peroxide with a mass fraction of 30% is added to terminate the reaction, and after centrifugation, washing and impurity removal, oxidized graphite is obtained;

[0012] A3, 20 g of the oxidized graphite is added to 1000 mL of deionized water, and ultrasonic dispersion is carried out under the condition of an ultrasonic power of 500 W for 2 h to form a uniform dispersion liquid, 5 g of a reducing agent is added to the dispersion liquid, and partial oxidized graphite is reduced for 4 h to reserve part of ethyl glycolate, and modified graphene is obtained.

[0013] Further, in some embodiments, the concentration of the concentrated sulfuric acid is 98% by mass fraction, the concentration of the concentrated nitric acid is 68% by mass fraction, the reducing agent is sodium borohydride, and the sodium borohydride is configured into a sodium borohydride aqueous solution with a mass fraction of 10% when added.

[0014] The application also provides a preparation method of the aluminum foil, comprising the following steps:

[0015] B1, the aluminum foil is cleaned;

[0016] B2, the conductive graphite and the nano conductive carbon black are vacuum dried for standby use;

[0017] B3, the carboxylated carbon nanotubes are added into an ultrasonic dispersion machine, and 25 parts of N-methyl pyrrolidone with a mass fraction of 99% are added to disperse the carboxylated carbon nanotubes;

[0018] B4, coating slurry preparation:

[0019] B401, bottom layer slurry: conductive graphite, binder and dispersant are put into an ultrasonic reaction kettle, and deionized water is added, ultrasonic stirring and heating are performed to obtain a bottom layer slurry;

[0020] B402, middle layer slurry: nano-conductive carbon black, modified graphene, polyurethane elastomer and boron nitride powder are mixed in an ultrasonic reaction kettle, and then binder, dispersant and deionized water are added, ultrasonic stirring and heating are performed to obtain a middle layer slurry;

[0021] B403, top layer slurry: carboxylated carbon nanotubes, binder, dispersant and deionized water are ultrasonically stirred and heated in an ultrasonic reaction kettle to obtain a top layer slurry;

[0022] B5, coating: first, the bottom layer slurry is coated on the surface of the aluminum foil, and is left to dry, forming a bottom layer material on the surface of the aluminum foil; then, the middle layer slurry is coated on the bottom layer slurry, and is left to dry, forming a middle layer material on the surface of the bottom layer material; then, the top layer slurry is coated on the middle layer slurry, forming a top layer material on the surface of the middle layer material; finally, the coated aluminum foil is placed in an oven for drying to obtain a carbon-coated aluminum foil.

[0023] Further, in some embodiments, the solid content of the bottom layer slurry, the middle layer slurry and the top layer slurry is 30% to 40%.

[0024] Further, in some embodiments, the ultrasonic stirring frequency in the ultrasonic reaction kettle in step B4 is 50 to 80 kHz, the stirring time is 1.5 to 3 h, and the heating temperature is 35 to 50℃.

[0025] Further, in some embodiments, the surface of the aluminum foil is coated by using a coating machine, when the bottom layer slurry is coated, the coating machine doctor blade gap is 0.7 to 1 mm, the coating speed is 2 to 3 m / min, and the coating thickness of the bottom layer slurry is 1 to 2 μm; when the middle layer slurry is coated, the coating machine doctor blade gap is 0.5 to 0.8 mm, the coating speed is 2 to 2.5 m / min, and the coating thickness of the middle layer slurry is 0.8 to 1.5 μm; when the top layer slurry is coated, the coating machine doctor blade gap is 0.3 to 0.6 mm, the coating speed is 1 to 2 m / min, and the coating thickness of the top layer slurry is 0.2 to 0.4 μm.

[0026] Beneficial effects: 1、The carbon-coated aluminum foil has a carbon-coated layer designed as a multi-layer composite structure, the bottom layer of large-particle graphite in the carbon-coated layer constructs a stable conductive framework, is closely attached to the aluminum foil, and provides a stable path for electron transmission, the middle layer of nanoscale carbon black cooperates with modified graphene, captures electrons by using the high specific surface area of the carbon black, and the modified graphene quickly conducts electrons by virtue of excellent electron migration characteristics, and the two synergistically greatly improve the electron transmission efficiency, and the top layer of carboxylated carbon nanotubes adjusts the electrode interface environment and promotes uniform diffusion of lithium ions, so that the transmission of ions and electrons is more smooth during high-rate charging and discharging of the battery, thereby significantly improving the cycle rate performance of the lithium battery.

[0027] 2、The boron nitride powder is added to the middle layer, and the boron nitride powder acts as a heat shielding protective layer to effectively prevent heat from being rapidly conducted to the aluminum foil substrate under the high-temperature environment of high-temperature charging and discharging of the lithium battery, reduces the negative effects of high temperature on the electrical conductivity and mechanical properties of the aluminum foil, ensures that the battery can still maintain stable performance output under high-temperature working conditions, and further improves the charging and discharging stability of the lithium battery under high-temperature environment.

[0028] 3、The polyurethane elastomer has the characteristics of self-adaptive buffering, so during the charging and discharging process of the lithium battery, with the volume expansion and contraction of the electrode material, the elastic particles can dynamically adjust their own morphology, fill the micro voids caused by the volume change, and always maintain close contact between the electrode and the current collector, effectively preventing the problem of rapid increase in resistance caused by poor contact, ensuring stable battery performance under high-rate cycling, and further improving the overall performance and service life of the battery. DETAILED DESCRIPTION

[0029] The application will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without making creative changes belong to the protection scope of the application.

[0030] Embodiment 1

[0031] Preparation of modified graphene:

[0032] A1、100g of natural graphite flakes is crushed, and 1000mL of a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1 is added, wherein the concentration of the concentrated sulfuric acid is 98% by mass fraction, and the concentration of the concentrated nitric acid is 68% by mass fraction, and the stirring is continuously carried out at a speed of 300r / min for 48h at room temperature until the reaction is completed;

[0033] A2, a strong oxidizing agent composed of 30 g of potassium permanganate and 100 mL of concentrated sulfuric acid is added thereto, and oxidation is performed at 35°C for 5 h with stirring at a rotation speed of 250 r / min, and then 50 mL of a mixed solution composed of ethylene glycol and acetic acid at a molar ratio of 1:1, each having a concentration of 2 mol / L, is added thereto to make ethyl glycolate, and then heating is performed to 90°C, 25 parts of clean water is added dropwise thereto at a rate of 5 mL / min during the heating, and hydrolysis is performed for 3 h, and finally 50 mL of 30% hydrogen peroxide is added to terminate the reaction, and after centrifugation, washing, and impurity removal, oxidized graphite is obtained;

[0034] A3, 20 g of the oxidized graphite is added to 1000 mL of deionized water, and ultrasonic dispersion is performed for 2 h under the condition of an ultrasonic power of 500 W to form a uniform dispersion liquid, 5 g of a reducing agent, sodium borohydride, is added to the dispersion liquid in the form of a 10% sodium borohydride aqueous solution, and partial oxidized graphite is reduced for 4 h, and a part of the ethyl glycolate is reserved to obtain modified graphene containing 15% unmodified graphene.

[0035] The preparation of the carbon-coated aluminum foil includes the following steps:

[0036] B1, an aluminum foil with a purity of 99.5% and a thickness of 15 μm is selected, and then the aluminum foil is immersed in anhydrous ethanol for 30 min, and then the impurities and dirt on the surface of the aluminum foil are washed with clean water, and then the aluminum foil is taken out and naturally dried in a dust-free environment to obtain a clean aluminum foil base layer;

[0037] B2, 35 parts (by weight, the same below) of conductive graphite (particle size 8 μm) is placed in a vacuum oven for drying treatment, the vacuum oven is started, and the drying temperature is set to 80°C, and the drying time is 2 hours, and the water is removed, and then 17.5 parts of nano-conductive carbon black (particle size 50 nm) is placed in the vacuum oven for drying under the same drying conditions, and then taken out for use after drying;

[0038] B3, 40 parts of the finished carboxylated carbon nanotube is selected, an ultrasonic dispersion machine is prepared, the carboxylated carbon nanotube is placed in the ultrasonic dispersion machine, and 25 parts of N-methyl pyrrolidone is added, and then the ultrasonic dispersion machine is started to disperse the carboxylated carbon nanotube to prevent it from agglomerating;

[0039] B4, then the slurry preparation of the carbon-coated aluminum foil is performed, which includes the following steps:

[0040] B401, bottom layer slurry: the dried conductive graphite was put into the ultrasonic reactor, then 1 part of binder and 5 parts of dispersant were added into the reactor, then deionized water was added, and then the ultrasonic reactor was started to perform ultrasonic stirring and heating, wherein the ultrasonic frequency was 50 kHz, the heating temperature was 35℃, the stirring time was 1.5 h, and the bottom layer slurry was obtained, and the solid content was 30%(mass fraction);

[0041] B402, middle layer slurry: the dried nano conductive carbon black 17.5 parts, modified graphene 12.5 parts, polyurethane elastomer 7.5 parts (produced by Covestro Bayer AG, Germany, specific model TPU polyurethane elastomer 5377 transparent raw material, same below), boron nitride powder 5 parts (particle size 0.5 μm, produced by Yingkou Liaobin Fine Chemical Co., Ltd., specific model boron nitride 10043-11-5 raw material, same below), were mixed, then 5 parts of binder and 2.5 parts of dispersant were added, put into the ultrasonic reactor and added with deionized water, then the ultrasonic reactor was started to perform ultrasonic stirring and heating, wherein the ultrasonic frequency was 50 kHz, the heating temperature was 35℃, the stirring time was 1.5 h, and the middle layer slurry was obtained, and the solid content was 35%(mass fraction);

[0042] B403, top layer slurry: the carboxylated carbon nanotube 40 parts was put into the ultrasonic reactor, and the binder 7.5 parts, dispersant 2.5 parts and deionized water were added, then the ultrasonic reactor was started to perform ultrasonic stirring and heating, wherein the ultrasonic frequency was 50 kHz, the heating temperature was 35℃, the stirring time was 1.5 h, and the top layer slurry was obtained, and the solid content was 40%(mass fraction);

[0043] B5, prepare the coating machine, install the aluminum foil base layer on the work station of the coating machine, then lay the aluminum foil base layer on the conveying belt of the coating machine for forward conveying, then uniformly coat the primer slurry on the surface of the aluminum foil, then wait for the primer slurry to be successfully coated, and then place the aluminum foil base layer coated with the primer slurry to dry, to form a primer material, then place the aluminum foil base layer coated with the primer slurry on the coating machine again for coating of the middle layer slurry, then repeat the drying and feeding process to form a middle layer material, and finally coat the top layer slurry on the middle layer material to form a top layer material, to complete the attachment of the carbon coating layer. The gap, speed and coating thickness of the coating doctor blade are in order: primer slurry: 0.8 mm, 2.5 m / min, 1 μm; middle layer slurry: 0.5 mm, 2 m / min, 0.8 μm; top layer slurry: 0.3 mm, 1.5 m / min, 0.4 μm. After the three layers of slurry are coated, the aluminum foil base layer and the material coated with the carbon coating layer are placed in an oven for drying, the drying temperature is 100°C, and the drying time is 2 h. Finally, the carbon-coated aluminum foil is obtained. Subsequently, low-temperature plasma treatment is performed. The carbon-coated aluminum foil is placed in a low-temperature device, then a mixed gas of argon and hydrogen is introduced, and the surface of the carbon-coated aluminum foil is cleaned. After cleaning, the carbon-coated aluminum foil is cut to produce corresponding lithium batteries.

[0044] Under standard charge and discharge conditions, after 500 cycles, the battery capacity retention rate reaches 90%, the 3C high-rate discharge capacity retention rate is 85%, after 200 cycles of 1C rate charge and discharge at high temperature 60°C, the capacity retention rate is 80%, the battery resistance grows slowly, the electrode and the current collector contact well, and the heating phenomenon is not obvious. The contact resistance is measured by a four-probe resistance tester, and the resistance is 0.75 mΩ / cm2. The adhesion is measured by a tensile testing machine, and reaches 2.45 N / cm. The coating and the electrode material are combined tightly, and no adverse phenomena such as peeling and delamination occur during the cycle process.

[0045] Example 2

[0046] The modified graphene is prepared by the method of Example 1.

[0047] The preparation of the carbon-coated aluminum foil includes the following steps:

[0048] B1, select an aluminum foil with a purity of 99.2% and a thickness of 18 μm, then immerse the aluminum foil in anhydrous ethanol for 60 min, then wash the impurities and dirt on the surface of the aluminum foil with water, then take out and dry naturally in a dust-free environment to obtain a clean aluminum foil base layer;

[0049] B2, 35 parts of conductive graphite (particle size 6 μm) were placed into a vacuum oven for drying treatment, the vacuum oven was started, the drying temperature was set to 100°C, the drying time was 3 hours, the water was removed, and after the conductive graphite was dried, 17.5 parts of nano conductive carbon black (particle size 60 nm) were placed into the vacuum oven for drying under the same drying conditions, and after drying, they were taken out for standby;

[0050] B3, 40 parts of finished carboxylated carbon nanotubes were selected, an ultrasonic dispersing machine was prepared, the carboxylated carbon nanotubes were put into the ultrasonic dispersing machine, 25 parts of N-methyl pyrrolidone were added, and then the ultrasonic dispersing machine was started to disperse the carboxylated carbon nanotubes to prevent them from agglomerating;

[0051] B4, then the slurry preparation of the carbon-coated aluminum foil was carried out, which included the following steps:

[0052] B401, bottom layer slurry: the dried conductive graphite was put into an ultrasonic reaction kettle, then the corresponding amount of binder 1 part and dispersant 5 parts were added to the reaction kettle, then deionized water was added, and then the ultrasonic reaction kettle was started for ultrasonic stirring and heating, wherein the ultrasonic frequency was 70 kHz, the heating temperature was 35°C, the stirring time was 2h, and the bottom layer slurry with a solid content of 35% (mass fraction) was obtained;

[0053] B402, middle layer slurry: 17.5 parts of dried nano conductive carbon black, 12.5 parts of modified graphene, 7.5 parts of polyurethane elastomer and 5 parts of boron nitride powder (particle size 0.8 μm) were mixed, 5 parts of binder and 2.5 parts of dispersant were added, put into an ultrasonic reaction kettle and add deionized water, then start the ultrasonic reaction kettle for ultrasonic stirring and heating, wherein the ultrasonic frequency is 70 kHz, the heating temperature is 45°C, the stirring time is 3h, and the middle layer slurry with a solid content of 40% (mass fraction) is obtained;

[0054] B403, top layer slurry: 40 parts of carboxylated carbon nanotubes were put into an ultrasonic reaction kettle, and binder 7.5 parts, dispersant 2.5 parts and deionized water were added, then the ultrasonic reaction kettle was started for ultrasonic stirring and heating; wherein the ultrasonic frequency is 70 kHz, the heating temperature is 45°C, the stirring time is 2h, and the middle layer slurry with a solid content of 30% (mass fraction) is obtained;

[0055] B5, prepare a coating machine, install the aluminum foil base layer on the work station of the coating machine, then lay the aluminum foil base layer on the conveying belt of the coating machine for forward conveying, then uniformly coat the primer slurry on the surface of the aluminum foil, then wait for the primer slurry coating to be successful, then place the aluminum foil base layer coated with the primer slurry to dry, then place the aluminum foil base layer coated with the primer slurry on the coating machine again for coating of the middle layer slurry, then repeat the drying and feeding process, finally coat the top layer slurry on the middle layer slurry to complete the attachment of the carbon coating layer, the coating doctor blade gap, speed and coating thickness are sequentially the primer slurry: 1 mm, 2 m / min, 2 μm; the middle layer slurry: 0.6 mm, 2.5 m / min, 1 μm; the top layer slurry: 0.4 mm, 2 m / min, 0.3 μm, after the three layers of slurry are coated, the aluminum foil base layer and the material coated with the carbon coating layer are placed in an oven for drying, the drying temperature is 90°C, the drying time is 2.5 h, and finally the carbon-coated aluminum foil is obtained, and then the carbon-coated aluminum foil is placed in a low-temperature equipment, argon and hydrogen mixed gas is introduced, the surface of the carbon-coated aluminum foil is cleaned, and the carbon-coated aluminum foil is cut after cleaning to produce corresponding lithium batteries.

[0056] After 500 cycles under standard conditions, the battery capacity retention rate is 88%, the 3C high-rate discharge capacity retention rate is 82%, after 200 cycles of 1C rate charge and discharge at high temperature 60°C, the capacity retention rate is 78%, the battery resistance is stable, the electrode and the current collector contact is stable, the heat is controllable, the test resistance is 0.84 mΩ / cm2, the adhesion measurement value is 1.95 N / cm, and the coating stability is good, meeting the requirements of lithium batteries.

[0057] Example 3

[0058] The modified graphene is prepared by the method of Example 1.

[0059] The preparation of the carbon-coated aluminum foil includes the following steps:

[0060] B1, select an aluminum foil with a purity of 99.8% and a thickness of 12 μm, then immerse the aluminum foil in anhydrous ethanol for 50 min, then wash the impurities and dirt on the surface of the aluminum foil with water, then take out and dry naturally in a dust-free environment to obtain a clean aluminum foil base layer;

[0061] B2, put 35 parts of conductive graphite (particle size 9 μm) into a vacuum oven for drying treatment, start the vacuum oven, set the drying temperature to 90°C, and dry for 2.5 hours to remove water, then put 17.5 parts of nano conductive carbon black (particle size 40 nm) into the vacuum oven for drying under the same drying conditions, and take out after drying;

[0062] B3, select 40 parts of finished carboxylated carbon nanotubes, prepare an ultrasonic dispersing machine, put the carboxylated carbon nanotubes into the ultrasonic dispersing machine, and add 25 parts of N-methyl pyrrolidone, then start the ultrasonic dispersing machine to disperse the carboxylated carbon nanotubes to prevent them from agglomerating;

[0063] B4, then prepare the slurry for coating the carbon aluminum foil, which includes the following steps:

[0064] B401, bottom layer slurry: put the dried conductive graphite into the ultrasonic reaction kettle, then add the corresponding amount of binder 1 part and dispersant 5 parts into the reaction kettle, then add the corresponding amount of deionized water, then start the ultrasonic reaction kettle for ultrasonic stirring and heating; the ultrasonic frequency is 80 kHz, the heating temperature is 50℃, the stirring time is 3h, and the solid content of the bottom layer slurry is 40%(mass fraction)

[0065] B402, middle layer slurry: mix 17.5 parts of dried nano-conductive carbon black, 12.5 parts of modified graphene, 7.5 parts of polyurethane elastomer, and 5 parts of boron nitride powder (particle size is 0.3μm), then add 5 parts of binder and 2.5 parts of dispersant, put them into the ultrasonic reaction kettle and add deionized water, then start the ultrasonic reaction kettle for ultrasonic stirring and heating; the ultrasonic frequency is 80 kHz, the heating temperature is 50℃, the stirring time is 3h, and the solid content of the middle layer slurry is 30%(mass fraction);

[0066] B403, top layer slurry: put 40 parts of carboxylated carbon nanotubes into the ultrasonic reaction kettle, and add 7.5 parts of binder, 2.5 parts of dispersant and deionized water, then start the ultrasonic reaction kettle for ultrasonic stirring and heating; the ultrasonic frequency is 80 kHz, the heating temperature is 35℃, the stirring time is 1.5h, and the solid content of the top layer slurry is 35%(mass fraction);

[0067] B5, prepare the coating machine, install the aluminum foil base layer on the work station of the coating machine, then lay the aluminum foil base layer on the conveying belt of the coating machine for forward conveying, then uniformly coat the base layer slurry on the surface of the aluminum foil, then wait for the base layer slurry to be successfully coated, then place the aluminum foil base layer coated with the base layer slurry to dry, then place the aluminum foil base layer coated with the base layer slurry on the coating machine for coating of the middle layer slurry, then repeat the drying and feeding processes, finally coat the top layer slurry on the middle layer slurry to complete the attachment of the carbon coating layer, the coating doctor blade gap, speed and coating thickness are sequentially the base layer slurry: 0.7 mm, 3 m / min, 1.5 μm; the middle layer slurry: 0.8 mm, 2.5 m / min, 1.5 μm; the top layer slurry: 0.6 mm, 1 m / min, 0.2 μm, after the three layers of slurry are coated, the aluminum foil base layer and the material coated with the carbon coating layer are placed in an oven for drying, the drying temperature is 110°C, the drying time is 1.5 h, finally the carbon-coated aluminum foil is obtained, and then the carbon-coated aluminum foil is placed in a low-temperature equipment, argon and hydrogen mixed gas are introduced, the surface of the carbon-coated aluminum foil is cleaned, and the carbon-coated aluminum foil is cut to produce corresponding lithium batteries.

[0068] After 500 cycles under standard conditions, the battery capacity retention rate is 92%, the 3C high-rate discharge capacity retention rate is 88%, after 200 cycles of 1C rate charge and discharge under high temperature 60°C environment, the capacity retention rate is 82%, the battery resistance changes little, the electrode and the current collector always maintain close contact, the heat dissipation is good, the test resistance is 0.56 mΩ / cm2, the adhesion reaches 2.94 N / cm, and the carbon-coated aluminum foil and the electrode material work cooperatively under high-rate charge and discharge and high-temperature environment.

[0069] Comparative Example 1

[0070] The traditional pure aluminum foil is used as the lithium battery current collector without any carbon coating treatment, the commercially available aluminum foil with a purity of 99.5% and a thickness of 15 μm is directly selected, cut to a suitable size, and used for lithium battery assembly.

[0071] Comparative Example 2

[0072] The traditional pure aluminum foil is used and a single layer of carbon black is coated on the surface, the carbon black particle size is 50 nm, a binder is used for coating and bonding, and no other functional materials are added, and other conditions are the same as in Example 1.

[0073] Comparative Example 3

[0074] The traditional pure aluminum foil is used and a double layer is coated on the surface, the bottom layer is large particle conductive graphite (particle size is 8 μm), and the top layer is ordinary conductive carbon black (particle size is 50 nm), and no other materials in Examples 1-3 are added, and other conditions are the same as in Example 1.

[0075] Table 1 is a performance table of the contact resistance, adhesion and heat generation phenomenon of the carbon-coated aluminum foil:

[0076] Group / Item Contact resistance (mΩ / cm2) Adhesion (N / cm) Heat generation phenomenon Comparative Example 1 2.4 - Severe heat generation Comparative Example 2 1.56 1.45 Severe heat generation Comparative Example 3 1.08 1.75 Controllable heat generation Example 1 0.75 2.45 No obvious heat generation Example 2 0.84 1.95 Controllable heat generation Example 3 0.56 2.94 Low heat generation

[0077] As can be seen from Table 1, the performance of the contact resistance, adhesion and heat generation phenomenon of Examples 1-3 is significantly improved compared with Comparative Examples 1-3, and the performance of Example 3 is significantly improved compared with Examples 1-2.

[0078] Table 2 is the battery capacity retention rate data of the lithium battery after charging and discharging under different rate conditions:

[0079] Group / Item Standard charge-discharge retention rate (%) High-rate charge-discharge retention rate (%) High-temperature charge-discharge retention rate (%) Comparative Example 1 79 73 70 Comparative Example 2 82 79 76 Comparative Example 3 85 80 78 Example 1 90 85 80 Example 2 88 82 78 Example 3 92 88 82

[0080] Among them, the standard charge-discharge retention rate is the battery capacity retention rate after 500 cycles of standard power charger under standard environmental conditions, the high-rate charge-discharge retention rate is the battery capacity retention rate after 200 cycles of charge-discharge under standard environmental conditions using a high-rate charger of 3C, and the high-temperature charge-discharge retention rate is the battery capacity retention rate after 200 cycles of charge-discharge under high-temperature 60℃ environmental conditions using a 1C rate charger.

[0081] As can be seen from Table 2, the battery capacity retention rate of Examples 1-3 after charging and discharging under different standard conditions is significantly improved compared with Comparative Examples 1-3, and the performance of Example 3 is significantly improved compared with Examples 1-2.

[0082] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited to this. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present application.

Claims

1. A carbon-coated aluminum foil for improving cycle rate performance of a lithium battery, characterized by, The aluminum foil substrate surface is sequentially provided with a bottom layer material, a middle layer material and a top layer material; the bottom layer material comprises conductive graphite, the middle layer material comprises nano-conductive carbon black, modified graphene, polyurethane elastomer and boron nitride powder, and the top layer material comprises carboxylated carbon nanotubes; the bottom layer material, the middle layer material and the top layer material further comprise a binder and a dispersant; The mass ratio of the conductive graphite, the binder and the dispersant in the bottom layer material is 70:2:10; the mass ratio of the nano-conductive carbon black, the modified graphene, the polyurethane elastomer, the boron nitride powder, the binder and the dispersant in the middle layer material is 35:25:15:10:10:5; and the mass ratio of the carboxylated carbon nanotubes, the binder and the dispersant in the top layer material is 80:15:5; The thickness of the bottom layer material is 1-2 microns, the thickness of the middle layer material is 0.8-1.5 microns, and the thickness of the top layer material is 0.2-0.4 microns; The preparation method of the modified graphene is as follows: A1, 100g of natural graphite flakes is crushed, and 1000mL of a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1 is added, and stirred at a speed of 300r / min for 48h at room temperature until the reaction is completed; A2, a strong oxidizing agent composed of 30g of potassium permanganate and 100mL of concentrated sulfuric acid is added, and the oxidation reaction is carried out at a speed of 250r / min for 5h at 35℃, then 50mL of a mixed solution composed of ethylene glycol and acetic acid with a molar ratio of 1:1 is added to prepare ethyl glycolate, wherein the molar concentration of ethylene glycol and acetic acid is 2mol / L, then heated to 90℃, and 25 portions of water are added dropwise at a speed of 5mL / min during the heating process, and the hydrolysis reaction is carried out for 3h, finally 50mL of hydrogen peroxide with a mass fraction of 30% is added to terminate the reaction, and after centrifugation, washing and impurity removal, the oxidized graphite is obtained; A3, 20g of oxidized graphite is added to 1000mL of deionized water under the condition of ultrasonic power of 500W for 2h to form a uniform dispersion liquid, 5g of a reducing agent is added to the dispersion liquid to reduce part of the oxidized graphite for 4h, and part of the ethyl glycolate is reserved to obtain modified graphene.

2. The carbon-coated aluminum foil for improving cycle rate performance of lithium battery according to claim 1, wherein The binder is a butadiene-styrene rubber emulsion, and the dispersant is polyethylene glycol.

3. The carbon-coated aluminum foil for improving cycle rate performance of lithium battery according to claim 1, wherein The concentration of the concentrated sulfuric acid is 98% by mass fraction, the concentration of the concentrated nitric acid is 68% by mass fraction, and the reducing agent is sodium borohydride, which is configured as a 10% by mass fraction sodium borohydride aqueous solution when added.

4. The method of claim 1 to 3, wherein the method is characterized by, The method comprises the following steps: B1, the aluminum foil is cleaned; B2, the conductive graphite and the nano-conductive carbon black are vacuum dried for standby; B3, 40 parts by mass of carboxylated carbon nanotubes are added to an ultrasonic dispersion machine, and 25 parts by mass of N-methyl pyrrolidone with a mass fraction of 99% are added to disperse the carboxylated carbon nanotubes; B4, coating slurry preparation: B401, bottom layer slurry: conductive graphite, a binder and a dispersant are put into an ultrasonic reactor, deionized water is added, ultrasonic stirring and heating are carried out, and a bottom layer slurry is obtained; B402, middle layer slurry: the nanometer conductive carbon black, modified graphene, polyurethane elastomer and boron nitride micro powder are mixed in an ultrasonic reactor, then the binder and dispersant and deionized water are added, ultrasonic stirring and heating are carried out, and the middle layer slurry is obtained; B403, top layer slurry: the carboxylated carbon nanotube, binder, dispersant and deionized water are ultrasonic stirred and heated in an ultrasonic reactor to obtain the top layer slurry; B5, coating: first, the bottom layer slurry is coated on the surface of the aluminum foil, and the bottom layer material is formed on the surface of the aluminum foil after standing and drying; then the middle layer slurry is coated on the bottom layer slurry, and the middle layer material is formed on the surface of the bottom layer material after standing and drying; then the top layer slurry is coated on the middle layer slurry, and the top layer material is formed on the surface of the middle layer material; finally, the coated aluminum foil is placed in an oven for drying to obtain a carbon-coated aluminum foil.

5. The preparation method according to claim 4, characterized in that, The solid content of the bottom layer slurry, the middle layer slurry and the top layer slurry is 30% to 40%.

6. The preparation method according to claim 4, characterized in that, The ultrasonic stirring frequency in the ultrasonic reactor in step B4 is 50 to 80 kHz, the stirring time is 1.5 to 3 hours, and the heating temperature is 35 to 50℃.

7. The preparation method according to claim 4, characterized in that, The surface of the aluminum foil is coated by using a coating machine. When the bottom layer slurry is coated, the coating machine knife gap is 0.7 to 1 mm, the coating speed is 2 to 3 m / min, and the coating thickness of the bottom layer slurry is 1 to 2 μm; when the middle layer slurry is coated, the coating machine knife gap is 0.5 to 0.8 mm, the coating speed is 2 to 2.5 m / min, and the coating thickness of the middle layer slurry is 0.8 to 1.5 μm; when the top layer slurry is coated, the coating machine knife gap is 0.3 to 0.6 mm, the coating speed is 1 to 2 m / min, and the coating thickness of the top layer slurry is 0.2 to 0.4 μm.