CN115663122A - Bendable integrated negative electrode based on metal nanosheets and preparation method thereof - Google Patents
Bendable integrated negative electrode based on metal nanosheets and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the field of energy storage devices, and discloses a bendable integrated cathode based on metal nanosheets and a preparation method thereof. The invention directly obtains the cathode of the secondary battery by simple operation from a macroscopic aluminum foil material, and comprises the following steps: (1) Mixing graphene oxide, a carbon source and a solvent to prepare an isolation reagent; (2) spreading an isolation reagent on the surface of the aluminum foil; (3) folding the aluminum foil spread with the isolation reagent in half and rolling; (4) Repeating the steps (1) to (3) repeatedly until the thickness of the aluminum foil is reduced to a nanometer level; (5) And (5) reducing the material obtained in the step (4) to obtain the brick mud structure aluminum metal nanosheet/carbon/graphene integrated negative electrode, wherein microscopically, the negative electrode material has a nanoscale thickness, can effectively relieve/accommodate volume expansion, macroscopically, the constructed typical brick-mud structure configuration has excellent mechanical properties and good expansion resistance, and the structural integrity of the whole electrode is ensured to a certain degree.
Description
Technical Field
The invention belongs to the field of energy storage devices, and particularly relates to a bendable integrated cathode based on metal nanosheets and a preparation method thereof.
Background
The lithium ion battery has the advantages of high energy density, high energy efficiency, long cycle life, no memory effect, quick discharge and the like, so that the lithium ion battery has great market demands in the fields of consumer electronics products, electric vehicles, power grid peak shaving, energy storage power supplies, aerospace and the like. In order to meet the challenges of performance, cost, environment and the like of lithium ion batteries, the development of electrode materials with abundant reserves, low price, easy availability and excellent electrochemical performance is the current research and development direction.
The metal material is used as the battery cathode, the battery reaction is realized by utilizing the alloying/dealloying process of the metal cathode and lithium ions, and high specific capacity and high energy density can be obtained. Compared with the traditional commercial graphite negative electrode material (372 mAh/g), the metal negative electrode has very obvious advantages in the aspect of improving the battery capacity. Among various metal negative electrodes, aluminum metal has the advantages of high theoretical capacity, abundant raw materials and low price, so that the aluminum metal attracts wide attention of people. In addition, the aluminum also has excellent conductivity, can be used as a negative electrode active material and a current collector of the battery, and is favorable for further improving the energy density of the battery, reducing the quality of the battery and reducing the cost. In conclusion, the aluminum cathode has remarkable advantages, can reduce the comprehensive cost of the battery, and has great commercial prospect.
The development of the metal aluminum cathode can not only improve the cathode capacity but also solve the problem of limited lithium resource reserves; meanwhile, the aluminum cathode and the current collector are integrated, so that the energy density of the device can be further improved, and the safety of the lithium ion battery can be effectively improved. The novel efficient battery system battery has higher specific energy density and lower cost. However, when the aluminum foil is used as a negative electrode plate, the following problems exist, so that the cyclicity of the aluminum foil needs to be further improved: (1) The lithium ions undergo huge volume expansion during alloying with aluminum metal, causing electrode pulverization to cause capacity attenuation of the battery; (2) A solid electrolyte layer (SEI film) formed by the reaction of metal aluminum and electrolyte at an interface is thickened continuously along with time, the interface impedance is increased continuously, the coulombic efficiency is reduced, and the battery capacity is attenuated; (3) Because the volume of the aluminum metal cathode is constantly changed in the charging and discharging processes, an SEI film is unstable, and metal lithium and electrolyte are consumed due to continuous generation, cracking and regeneration in the lithium desorption process. In chinese patent publication No. cn201811561463.X, a metal nanosheet is prepared to solve the problem of volume expansion of metal. However, these metal nanoplates require the use of a binder and a current collector, and the active material is easily detached from the current collector during bending, resulting in capacity fade. Therefore, the development of integrated electrode materials becomes particularly important.
Disclosure of Invention
In order to overcome the defects and shortcomings of the prior art, the invention mainly aims to provide a preparation method of a bendable integrated negative electrode based on metal nanosheets. The invention aims to solve the problem of volume expansion and pulverization of an alloyed aluminum cathode in the charging and discharging processes and obtain an integrated bendable electrode material.
The invention also aims to provide a bendable integrated negative electrode based on the metal nanosheets prepared by the method.
The invention further aims to provide application of the bendable integrated negative electrode based on the metal nanosheets in a secondary battery. The invention starts from macroscopic metal foil, directly obtains the cathode of the secondary battery through simple operation, and can be directly used for assembling the battery.
The purpose of the invention is realized by the following scheme:
a preparation method of a bendable integrated negative electrode based on metal nano sheets comprises the following steps:
(1) Preparing an isolation reagent: uniformly mixing graphene oxide, a carbon source and a solvent to prepare an isolation reagent;
(2) Uniformly spreading a layer of isolating reagent on the surface of the metal foil;
(3) Folding and rolling the metal foil spread with the isolation reagent;
(4) Repeating the steps (1) to (3) repeatedly until the thickness of the metal foil is reduced to a nanometer level;
(5) And (4) carrying out high-temperature annealing treatment on the material obtained in the step (4) to obtain the required brick mud structure metal nanosheet/carbon/graphene integrated negative electrode.
The graphene oxide in the step (1) is obtained by intercalation oxidation of graphite, the size of a lamella of the graphene oxide is 10-50 mu m, and the thickness of the graphene oxide is 0.35-10nm (the number of layers of the corresponding graphene is 1-30);
the carbon source in the step (1) is one or more of Polyacrylonitrile (PAN), phenolic resin, polystyrene, polymethyl methacrylate, asphalt and other organic materials;
in the step (1), the solvent is one or more of N, N-Dimethylformamide (DMF), tetrahydrofuran, gasoline, cyclohexane, benzene and other organic solvents.
The mass and dosage ratio of the graphene oxide, the carbon source and the solvent in the step (1) is (0.5-15): (45-80): (15-45);
the thickness of the metal foil in the step (2) is 50-200 μm, and the thickness of the isolating reagent coated on the metal foil is 10-50 μm; the metal foil is preferably an aluminum foil;
the rolling in the step (3) is to be rolled to be half of the thickness of the metal foil after being folded in half;
the high-temperature annealing condition in the step (5) is that the temperature is 400-1000 ℃, the processing time is 20-120 minutes, the reducing atmosphere is hydrogen, and the inert gas is argon; the flow rate of the reducing gas is 10-200sccm, and the flow rate of the inert gas is 100-400sccm.
A bendable integrated negative electrode based on metal nano-sheets prepared by the above method;
the bendable integrated negative electrode based on the metal nanosheets is applied to a secondary battery;
the secondary battery comprises a positive current collector, a positive electrode, a brick mud structure metal nanosheet/carbon/graphene integrated negative electrode, electrolyte and a diaphragm;
the cathode material comprises a lithium ion embedded cathode compound material (such as lithium cobaltate, lithium iron phosphate, nickel cobalt manganese ternary material and the like), an anion insertion type layered cathode material (such as crystalline flake graphite, mesocarbon microbeads, molybdenum disulfide and the like), an organic cathode material (such as a metal and titanium blue complex and the like) which has an oxidation reduction reaction with anions and the like;
the electrolyte of the secondary battery comprises liquid electrolyte, gel electrolyte and solid electrolyte.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) The integrated negative electrode based on two-dimensional aluminum metal nanosheets, pyrolytic carbon and graphene for constructing the brick mud structure is prepared by the method. The structure has the following characteristics: microscopically: the active material metal nanosheet in the brick mud structure aluminum metal nanosheet/carbon/graphene integrated negative electrode has nanoscale thickness (typical thickness is less than 5 nm), and can effectively relieve/accommodate volume expansion. Meanwhile, the crimp structure in the plane direction can provide an external free space for volume expansion, and structural stress can be effectively relieved. Secondly, the graphene oxide has an ultra-large specific surface area and good film-forming property, and an amorphous carbon precursor and a metallic tin nanosheet can be bonded together in the rolling process to form a firm integrated structure; and reducing the graphene oxide into high-conductivity graphene through high-temperature carbonization, thereby obtaining the integrated negative electrode material with good conductivity. And thirdly, the amorphous carbon links the metal nano sheets and the graphene into a whole in the form of gravel, so that a good and firm brick mud structure is realized. On the other hand, macroscopically: the typical 'brick-mud' structural configuration constructed by the metal nanosheets and the carbon/graphene has excellent mechanical properties and good expansion resistance, so that the structural integrity of the whole electrode is kept to a certain degree.
(2) The integrated negative electrode prepared by the invention has the following characteristics: firstly, the integrated electrode has the advantages of simple process: directly obtaining a lithium ion battery cathode containing metal nano sheets from a macroscopic metal foil without mixing with a binder, a conductive agent and the like and coating the lithium ion battery cathode on a metal current collector; secondly, compounding uniformly: the metal nano sheet/carbon composite material is directly obtained from the macroscopic metal foil through rolling and pyrolysis carbonization, so that the oxidation of the metal nano sheet in the separation process is reduced, and the problem of uneven compounding caused by mixing of the metal nano sheet and a carbon source is avoided; thirdly, the performance is excellent: the synergistic effect of the aluminum metal with the nanometer thickness and the carbon generated in situ can combine the advantages of the aluminum metal and the carbon to structurally solve the problem of volume expansion and form a stable SEI film, so that the battery has good cycle stability; fourthly, the integrated electrode has the bending performance and can be used for manufacturing a bendable battery.
Drawings
Fig. 1 is a schematic structural diagram of an aluminum metal nanosheet/carbon/graphene integrated negative electrode with a brick mud structure: wherein (1) is a brick structure composed of aluminum metal nanosheets, and (2) is a mud structure composed of graphene and carbon.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The reagents used in the examples are commercially available without specific reference.
Example 1
Mixing graphene oxide, polyacrylonitrile and DMF in a ratio of 5:80:15 mixing to obtain an isolation reagent; uniformly spreading the isolation reagent on the surface of a metal foil, wherein the thickness of the aluminum foil is 50 microns, and the thickness of the isolation reagent coated on the aluminum foil is 20 microns; folding the aluminum foil spread with the isolation reagent in half and rolling the aluminum foil to half of the thickness of the folded aluminum foil; the spreading-folding-rolling steps were repeated 12 times; and reducing the material rolled for 12 times at 450 ℃ for 60 minutes to obtain an aluminum metal negative electrode foil/current collector, namely the required brick mud structure metal nanosheet/carbon/graphene integrated negative electrode.
Taking the aluminum metal negative electrode foil/current collector as a negative electrode and LiPF 6 DEC (4:6) (with 5wt.% FEC added) as an electrolyte and lithium iron phosphate as the positive electrode. The electrochemical properties are shown in tables 1 and 2.
Examples 2 to 6
The steps of the preparation process of the aluminum metal negative electrode foil/current collector surface modification in the embodiments 2-6 are the same as those of the embodiment 1, and the difference is that the polymer is selected.
Examples 7 to 10
The steps of the preparation process of the aluminum metal negative electrode foil/current collector surface modification in the embodiments 7-10 are the same as those of the preparation process of the aluminum metal negative electrode foil/current collector surface modification in the embodiment 1, except that the mixture ratio of the selected isolating layer is different.
Examples 11 to 14
Examples 11-14 were prepared using the same aluminum metal negative foil/current collector surface modification procedure as in example 1, except that the number of rolling passes was selected.
Example 15
The step of the aluminum metal negative electrode foil/current collector surface modification preparation process in the embodiment 15 is the same as that in the embodiment 1, except that the rolled aluminum metal negative electrode foil/current collector surface modification preparation process is not subjected to reduction treatment, but an aluminum metal nanosheet is stripped from the rolled material, and then the nanosheet, conductive carbon black and a PVDF binder are mixed and coated on a copper foil current collector in a ratio of 8.
Examples 2-6 the polymer used was different from that used in example 1. As can be seen from Table 1, the different cyclic properties and coulombic efficiencies of the selected polymers are greatly different.
Examples 7 to 10 are different in the compounding ratio of the selected separator from example 1, and it can be seen from the combination of examples 7 to 10 and example 1 that the separator material having a suitable compounding ratio exhibits more excellent cycle characteristics.
Examples 11-14 are different in the number of rolling passes, and in general, materials with suitable number of rolling passes exhibit more excellent cycle performance.
Example 15 in order to prepare an electrode using a general coating method and perform a turn test and a battery cycle performance test, the integrated electrode showed more excellent cycle performance as a whole.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. A preparation method of a bendable integrated cathode based on metal nano sheets is characterized by comprising the following steps:
(1) Preparing an isolation reagent: uniformly mixing graphene oxide, a carbon source and a solvent to prepare an isolation reagent;
(2) Uniformly spreading a layer of isolating reagent on the surface of the metal foil;
(3) Folding and rolling the metal foil spread with the isolation reagent;
(4) Repeating the steps (1) to (3) repeatedly until the thickness of the metal foil is reduced to a nanometer level;
(5) And (4) carrying out high-temperature annealing treatment on the material obtained in the step (4) to obtain the required brick mud structure metal nanosheet/carbon/graphene integrated negative electrode.
2. The method for preparing the bendable integrated anode based on the metal nano-sheets according to claim 1, is characterized in that: the graphene oxide in the step (1) is obtained by graphite intercalation oxidation, the size of a lamella of the graphene oxide is 10-50 mu m, the thickness of the graphene oxide is 0.35-10nm, and the number of corresponding graphene layers is 1-30.
3. The method for preparing the bendable integrated anode based on the metal nano-sheets according to claim 1, is characterized in that: the carbon source in the step (1) is one or more of polyacrylonitrile, phenolic resin, polystyrene, polymethyl methacrylate and asphalt;
in the step (1), the solvent is one or more of N, N-dimethylformamide, tetrahydrofuran, gasoline, cyclohexane and benzene.
4. The method for preparing the bendable integrated anode based on the metal nano-sheets according to claim 1, is characterized in that: the mass and dosage ratio of the graphene oxide, the carbon source and the solvent in the step (1) is (0.5-15): (45-80): (15-45).
5. The method for preparing the bendable integrated anode based on the metal nano-sheets according to claim 1, is characterized in that: the thickness of the metal foil in the step (2) is 50-200 μm, and the thickness of the isolation reagent coated on the metal foil is 10-50 μm; the metal foil is preferably an aluminum foil.
6. The method for preparing the bendable integrated anode based on the metal nano-sheets according to claim 1, is characterized in that: the rolling in the step (3) is to roll the metal foil to half the thickness of the metal foil after being folded in half.
7. The method for preparing the bendable integrated anode based on the metal nano-sheets according to claim 1, is characterized in that: the high-temperature annealing condition in the step (5) is that the temperature is 400-1000 ℃, the processing time is 20-120 minutes, the reducing atmosphere is hydrogen, and the inert gas is argon; the flow rate of the reducing gas is 10-200sccm, and the flow rate of the inert gas is 100-400sccm.
8. A bendable integrated anode based on metal nanoplates prepared according to the method of any one of claims 1 to 7.
9. Use of a bendable integrated anode based on metal nanoplates as described in claim 8 in a secondary battery.
10. Use of a bendable integrated anode based on metal nanoplates as described in claim 9 in a secondary battery, characterized in that: the secondary battery comprises a positive current collector, a positive electrode, a brick mud structure metal nanosheet/carbon/graphene integrated negative electrode, electrolyte and a diaphragm.
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