Boron-nitrogen substituted one-dimensional carbon structure embedded with metal nanocrystals for lithium ion battery

Abstract

The invention discloses a boron-nitrogen substituted one-dimensional carbon structure embedded with metal nanocrystals for a lithium ion battery. Impurity atom substitution and structural modification are two important strategies for improving lithium storage of the carbon material, and lithium storage active sites are increased by adding impurity atoms; the modification of the metal nanocrystals can promote the transmission capability of electrons. The preparation method comprises the following steps: 1, preparation of a source material before pyrolysis: taking ultrapure water as a solvent, bonding urea and boric acid through hydrogen bonds, uniformly dispersing metal ions in a hydrated network system, heating and stirring the obtained uniform mixture until the mixture is solidified, and grinding to obtain a powder source material; and 2, one-step pyrolysis: in an inert atmosphere, heating the powder source material to a pyrolysis temperature by adopting a one-step pyrolysis method, keeping the temperature for several hours, and naturally cooling to room temperature to obtain the material. The one-dimensional carbon material prepared by the invention shows good lithium storage performance and long cycle life under the modification of impurity atom substitution and nanocrystalline.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of new energy materials, and relates to a one-dimensional carbon structure with boron and nitrogen substitution and embedded metal nanocrystals for lithium-ion batteries. Background Art

[0002] Carbon-based materials have been widely studied as electrode materials for lithium-ion batteries due to their excellent chemical stability and unique porosity. Graphite, as the current commercial anode material, occupies a large market share and has a good lithium intercalation voltage platform (0.2V vs Li / Li + ). However, after being assembled into a battery, graphite also has some problems. Co-intercalation of solvents leads to its instability during long-term charge and discharge processes, and it is easy to fall off, seriously affecting the cycle performance and service life of the battery. High-rate charge and discharge will cause large polarization, resulting in the loss of the electrochemical platform, reducing the potential, causing lithium metal deposition to form dendrites, leading to short circuits and even explosions. It is crucial to study other possible anode materials. One-dimensional carbon materials have been intensively studied because of their excellent physical and chemical properties, and it has been found through calculations that lithium ions can be adsorbed inside and outside carbon nanotubes. However, the conductivity of carbon nanotubes is related to their aspect ratio, and pure carbon nanotubes have a low capacity.

[0003] In recent years, in order to continuously improve their capacity, people have tried to prepare doped carbon nanotubes, including nitrogen-doped carbon nanotubes, boron-doped carbon nanotubes, and sulfur-doped carbon nanotubes. They show good electrochemical performance in supercapacitors and lithium-ion batteries. The unique tubular structure of carbon nanotubes can effectively buffer the mechanical stress caused by volume changes during charging and discharging. In previous studies, carbon materials with excellent properties can be prepared by introducing doping atoms (N, O, P, S, or B). The radius of heteroatoms is different from that of carbon atoms. Heteroatoms can increase the spacing between graphite layers, disrupt the original ordered structure of carbon materials, and promote the intercalation of lithium ions; the introduction of impurity atoms will cause uneven local charge distribution in space, increasing active sites; heteroatom doping has different physical and chemical properties from carbon atoms, which can enhance the adsorption ability and electron conduction ability of carbon materials for lithium ions. The addition of nano-metals can improve the electron transport ability of the material. In short, the modification of the structure by doping atoms and nanocrystals in the carbon structure can reduce the obstacles during lithium storage and improve the lithium storage capacity. Summary of the Invention

[0004] The purpose of the present invention is to form a source material based on high-temperature solidification of urea, boric acid, metal salt and polyethylene glycol, and to form a boron nitrogen carbon flake by in-situ substitutional pyrolysis at high temperature in an inert atmosphere. Nanocrystals formed by high-temperature decomposition of the metal salt catalyst are evenly dispersed on the boron nitrogen carbon flakes. Under continuous high temperature conditions, the local stress of the boron nitrogen carbon flakes will be inconsistent, so that the boron nitrogen carbon flakes will curl up to form a one-dimensional tubular structure, and finally the crystalline nanocrystals will be coated with carbon. When applied to lithium ion negative electrode materials, the nanocrystals have good cycle stability and cycle life.

[0005] To achieve this goal, the following technical solutions are applied:

[0006] The prepared one-dimensional carbon structure material with boron-nitrogen substitution and embedded metal nanocrystals was made into electrode sheets, assembled into button batteries, and placed on the blue power test system. 100 and 2000 m Ag -1 Current density is used to test lithium storage performance. The specific process is as follows:

[0007] 1. Preparation of boron, nitrogen and carbon sources: (1) Add urea, polyethylene glycol, boric acid and metal salts (nickel salt, tin salt, cobalt salt, manganese salt, iron salt), taking nickel nitrate as an example, to 20 ml of ultrapure water, with the mass ratio of urea to ultrapure water being 1:100-1:10, and stir evenly with a magnetic stirrer at room temperature; (2) Dissolve polyethylene glycol in a mixed solution of urea and ultrapure water (the mass ratio of polyethylene glycol to urea is 1:20 - 1:2); (3) Add metal salt to the above mixed solution (the mass ratio of metal salt to urea is 1:30-1:10), stir thoroughly, transfer the solution to a constant temperature heating table, stir at a constant temperature of 80-100°C for 6-40 hours to obtain a block; (4) Transfer the obtained block to an agate mortar and grind for 5-10 minutes to obtain a boron, nitrogen and carbon source.

[0008] 2. Preparation of one-dimensional carbon structure materials with boron nitrogen substitution and embedded metal nanocrystals: (1) Pour the boron nitrogen carbon source obtained above into a crucible; (2) Transfer the crucible to the central constant temperature zone of a tube furnace at room temperature; (3) In an argon atmosphere, heat the temperature from room temperature to 800-900°C at a rate of 1-10°C / min and maintain for 0.4-4 hours. Cool naturally to room temperature to obtain a one-dimensional carbon material with boron nitrogen substitution and embedded metal nanocrystals.

[0009] 3. Preparation of one-dimensional carbon material slurry with BN substitution and embedded metal nanocrystals: (1) Grind the active material, conductive agent and binder at a mass ratio of 8:1:1 for 20 minutes; (2) Add an appropriate amount of organic solvent to the evenly ground mixture and continue grinding for 2 hours at room temperature to obtain slurry. Coat it on copper foil and transfer it to a vacuum oven at a drying temperature of 60-80°C for 6-24 hours to obtain the pole piece, assemble it into a battery, and use it for lithium storage performance testing.

[0010] The beneficial effects of the present invention are as follows:

[0011] The one-dimensional carbon structure with boron and nitrogen substitution and embedded metal nanocrystals is used as the anode material for lithium-ion batteries. Boron and nitrogen, as impurity atoms, substitute for carbon atoms, change the local potential, and increase the lithium storage active sites. During the high-current charge and discharge process, the one-dimensional tubular structure of the carbon material can effectively buffer the volume change. Using boric acid as the B source and urea as the N source and C source, a boron-nitrogen-carbon source is first prepared, realizing the double substitution of B and N at the same time. By adjusting the amount of urea, the morphology and nitrogen content of the one-dimensional carbon can be controllably adjusted. The decomposition of metal salts to form crystalline nanocrystals embedded in the one-dimensional carbon material helps to improve the conductivity of the material and still maintain good capacity at high current. Description of the Drawings

[0012] Figure 1 Schematic diagram of the one-dimensional carbon structure with boron and nitrogen substitution and embedded metal nanocrystals.

[0013] Figure 2 Scanning electron microscope images of the one-dimensional carbon structure with boron and nitrogen substitution and embedded metal nanocrystals (a), and scanning electron microscope images of before (b) and after (c) cycling of the assembled battery.

[0014] Figure 3 Charge and discharge diagram of the battery assembled with the active material of the one-dimensional carbon structure with boron and nitrogen substitution and embedded metal nanocrystals at a small current of 100 mAg -1 during cycling.

[0015] Figure 4 Charge and discharge diagrams of the battery assembled with the active material of the one-dimensional carbon structure with boron and nitrogen substitution and embedded metal nanocrystals at different currents.

[0016] Figure 5 Charge and discharge diagram of the battery assembled with the active material of the one-dimensional carbon structure with boron and nitrogen substitution and embedded metal nanocrystals at a high current of 2000 mAg -1 during cycling. Detailed Embodiments

[0017] The following specific examples are used to further illustrate the present invention. It should be understood that the purpose of the given examples is to further elaborate on the content of the present invention and cannot be construed in any sense as a limitation on the protection scope of the present invention.

[0018] Example 1

[0019] Step 1: Preparation of boron, nitrogen, and carbon source: (1) Add 1 g of urea to 20 mL of ultrapure water and stir magnetically at room temperature until evenly mixed; (2) Dissolve 0.5 g of polyethylene glycol in the mixed solution of urea and ultrapure water; (3) Add 65 mg of nickel nitrate to the above mixed solution, transfer the fully stirred solution to a thermostatic magnetic stirrer, stir at 80 °C for 4 hours, and then naturally cool to room temperature; (4) Transfer the obtained boron, nitrogen, and carbon source to an agate mortar and grind for 5 minutes.

[0020] Step 2: Preparation of boron-substituted carbon and metal-embedded nanocrystalline material: (1) Pour the previously obtained boron, nitrogen, and carbon source into a crucible; (2) At room temperature, transfer the crucible to the central constant temperature zone of a tube furnace; (3) Under an argon atmosphere, heat from room temperature to 900 °C at a heating rate of 5 °C / min and hold for 4 hours. Naturally cool to room temperature to obtain the boron-substituted and metal-embedded nanocrystalline material.

[0021] Example 2

[0022] Step 1: Preparation of boron, nitrogen, and carbon source: (1) Add 2 g of urea to 20 mL of ultrapure water and stir magnetically at room temperature until evenly mixed; (2) Dissolve 0.5 g of polyethylene glycol in the mixed solution of urea and ultrapure water; (3) Add 65 mg of nickel nitrate to the above mixed solution, transfer the fully stirred solution to a thermostatic magnetic stirrer, stir at 80 °C for 4 hours, and then naturally cool to room temperature; (4) Transfer the obtained boron, nitrogen, and carbon source to an agate mortar and grind for 5 minutes.

[0023] Step 2: Preparation of boron-substituted and metal-embedded nanocrystalline material: (1) Pour the previously obtained boron, nitrogen, and carbon source into a crucible; (2) At room temperature, transfer the crucible to the central constant temperature zone of a tube furnace; (3) Under an argon atmosphere, heat from room temperature to 900 °C at a heating rate of 5 °C per minute and hold for 4 hours. Naturally cool to room temperature to obtain the boron-substituted and nanocrystalline material. dui

[0024] The above examples are only used to explain and illustrate the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the protection scope of this application. It should be noted that for those of ordinary skill in the art, any modifications and changes made to the present invention without departing from the technical concept of this application fall within the protection scope of this application.

Claims

1. A one-dimensional carbon structure with boron-nitrogen substitution and metal-embedded nanocrystals for lithium-ion batteries, characterized in that, It has the following preparation steps: (1) Using boron- and nitrogen-containing compounds as the boron-nitrogen source, dissolve urea, boric acid, metal salts, and polyethylene glycol in ultrapure water. They are bonded by hydrogen bonds, and metal ions are distributed in this system. After high-temperature curing to obtain a block, grind it in a mortar for 15 minutes to obtain a powder material.

2. (2) Place the powder material in an alumina crucible and directly perform pyrolysis treatment under a protective atmosphere to obtain a carbon material.

3. The one-dimensional carbon structure with boron and nitrogen substitution and metal-embedded nanocrystals for a lithium-ion battery according to claim 1, wherein: In step (1), the mass of urea is 1 - 10 g. The mass of boric acid is 10 mg - 600 mg. The metal salt can be nickel salt, iron salt, cobalt salt, manganese salt, and tin salt, and its mass is 30 mg - 300 mg. The mass of polyethylene glycol is 100 mg - 1000 mg.

4. The one-dimensional carbon structure with boron and nitrogen substitution and metal-embedded nanocrystals for a lithium-ion battery according to claim 1, characterized in that: In step (2), the pyrolysis treatment temperature is 800 - 900 °C, the heating rate is 1 - 10 °C / min; the holding time is 0.5 - 4 hours, and the protective atmosphere is argon or nitrogen.

5. A one-dimensional carbon structure material with boron-nitrogen substitution and embedded metal nanocrystals prepared as described in claim 1, which is used in a lithium-ion battery, has good stability, and has excellent lithium storage performance.

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