CN110165213A - A kind of preparation method of lithium ion battery graphene anode material - Google Patents

Abstract

The invention discloses a preparation method of a graphene positive electrode material for a lithium ion battery. The specific steps are as follows: prepare graphite oxide, disperse the graphite oxide in water to obtain a graphite oxide suspension, add concentrated sulfuric acid to the suspension, and ultrasonically disperse Prepare the mixed solution evenly, then put the mixed solution into the reaction kettle and react at 200-250°C for 15-20h, wash to obtain three-dimensional reduced graphene oxide; add lithium iron phosphate, carbon nanotubes, graphene and PVDF into the stirring tank , set the revolution speed to 15‑25r/min, the dispersion speed to 200‑400r/min, and dry mix for 20‑40min. The three-dimensional porous structure of the present invention constructs rich voids to provide channels for the rapid transmission of lithium ions, which is conducive to the transfer of lithium ions on the surface and reaching the reactive active sites, thereby improving the conductivity of lithium iron phosphate, so it has excellent conductivity, The rate performance, cycle performance and low temperature performance provide a lithium-ion battery cathode material with simple processing technology, low cost, high capacity and safety for the application of lithium-ion batteries.

Description

A kind of preparation method of graphene cathode material for lithium ion battery

technical field

The invention relates to the technical field of preparation of lithium-ion battery materials, in particular to a preparation method of graphene cathode materials for lithium-ion batteries.

Background technique

New energy sources, such as wind energy, solar energy, and geothermal energy, have attracted widespread attention due to their clean, efficient, and renewable advantages. However, the above-mentioned dispersed and discontinuous energy is difficult to be directly utilized, and energy storage systems are usually required for storage. Chemical power is one of the most common energy storage systems in today's society. Among them, lithium-ion batteries (LIBs) have become the main development trend of chemical power sources due to their advantages such as high specific energy, long cycle life, no memory effect, and environmental friendliness, and have been widely used in various portable electronic devices, electric vehicles, aerospace, etc. field. As the core component of the power lithium-ion battery, the cost and performance of the cathode material will directly affect the cost and performance of the battery as a whole. Transition metal phosphates have an open space for lithium storage and are new cathode materials for lithium batteries. For example, LiFePO ₄ has the advantages of high specific capacity of 170mAh/g, low cost and low toxicity. However, its electrical conductivity is low (10 ^-9 S/cm ² ), and lithium ion diffusion is poor (10 ^-14 ~ 10 ^-16 cm ² /s), resulting in rapid capacity decay during high rate charge and discharge. Studies have shown that the special structure of graphene with two-dimensional high specific surface area and its excellent electron transport ability can effectively improve the conductivity of positive electrode materials and improve the diffusion and transport ability of lithium ions. Therefore, the development of high-stability composite cathode materials with excellent performance and low price is the focus of lithium-ion battery research.

Graphene, as an advanced carbon material, is considered as an ideal component of composite electrode materials due to its superior electronic conductivity, large specific surface area, and special two-dimensional structure. Three-dimensional graphene is formed by stacking single atomic layers of carbon, and has the advantages of ultra-low density, high surface area, high thermal conductivity, high temperature resistance, corrosion resistance, ductility and flexibility. In recent years, with the in-depth research on graphene, it has been found that the good conductivity of graphene plays an important role in improving the performance of lithium-ion batteries. The three-dimensional graphene improves the conductivity and dispersion of the composite material, and the electrolyte and the active material of the electrode material can fully contact, thereby further improving the electrochemical performance of the three-dimensional graphene composite material.

LiFePO ₄ exists in the form of phospholithium in nature, belongs to the orthorhombic crystal system, and the space group is Pmnb. There are 4 lithium iron phosphate units in each unit cell, and its unit cell parameters are: a=0.6008nm, b=1.0324nm, c=0.4694nm. Lithium iron phosphate has a stable and ordered olivine structure, that is, the oxygen atoms in the crystal structure are arranged in a slightly twisted hexagonal close-packed manner, in which Fe and Li are respectively located in the center of the oxygen atom octahedron, forming FeO ₆ octahedron and LiO ₆ octahedra. P is in the center of the oxygen atom tetrahedron, forming a PO ₄ tetrahedron, forming a structurally stable three-dimensional space network structure connected by covalent bonds. Therefore, lithium iron phosphate has good thermal stability and safety as a positive electrode material. , especially suitable for large-scale applications. However, the poor rate performance limits its practical application, which is determined by its own slow lithium ion diffusion coefficient and low electronic conductivity. At present, methods such as surface conductive layer coating, ion doping, and morphology optimization are mostly used to solve this problem. Recent research work has shown that combining lithium-ion battery electrode materials with graphene can effectively improve the electronic conductivity of the material and improve the rate performance of the material. Therefore, constructing a lithium iron phosphate/graphene three-dimensional structure composite material and using the flexible network conductive structure of graphene to improve the conductivity of the electrode material can improve the rate performance of the material.

At present, most graphene composite materials are in the mixed state of graphene and lithium iron phosphate. Lithium iron phosphate is unevenly distributed on the surface and inside of graphene. During charging and discharging, lithium iron phosphate is easy to fall off on graphene, which reduces the conductivity. , ultimately affecting the performance of lithium-ion batteries.

Contents of the invention

The object of the present invention is to provide a kind of preparation method of graphene cathode material for lithium-ion batteries, to solve the problems raised in the above-mentioned background technology.

To achieve the above object, the present invention provides the following technical solutions:

A kind of preparation method of graphene cathode material for lithium ion battery, concrete steps are as follows:

(1) Weigh 6-10 parts of graphite and 2-4 parts of NaNO ₃ into a beaker, stir vigorously, slowly add 100-150mL of concentrated sulfuric acid, stir for 40-60min, then slowly add 15-25 parts of NaNO 3 KMnO ₄ , after adding 0.5h, continue to stir for 20 hours, stop stirring due to increased viscosity of the reactant, and obtain a paste-like purple-red substance; after standing for 6-10d, slowly add 450-550mL of deionized water and 25 -35mL of H ₂ O ₂ , the color of the solution becomes more obvious bright yellow at this time, after the solution is fully reacted, centrifuge and wash to obtain graphite oxide;

(2) Disperse graphite oxide in water to prepare graphite oxide suspension, add concentrated sulfuric acid to the suspension, and ultrasonically disperse evenly to obtain a mixed solution, then put the mixed solution in a reaction kettle and react at 200-250°C for 15 -20h, washing to obtain three-dimensional reduced graphene oxide;

(3) Add 80-100 parts of lithium iron phosphate, 1-2 parts of carbon nanotubes, 3-5 parts of graphene and 1-2 parts of PVDF into the mixing tank, set the revolution speed to 15-25r/min, and the dispersion speed 200-400r/min, dry mixing 20-40min;

(4) Add deionized water that is 6-8 times the mass of the mixture, and stir for 10-15 minutes at a revolution speed of 20-30r/min and a dispersion speed of 600-800r/min. The revolution speed is set to 25-35r/min, the dispersion speed is set to 800-1200r/min, and the dispersion is obtained by stirring for 30-50min;

(5) Stir the obtained dispersion at a temperature of 60-80°C to immerse the generated rheological body into the interlayer of three-dimensional reduced graphene oxide to form an intercalation complex, and then dry the intercalation complex to constant weight Composite precursors are prepared;

(6) Grind the composite precursor to obtain a powder, and then place the powder in an inert gas protective atmosphere furnace to pre-decompose to obtain an intermediate product. The pre-decomposition temperature is controlled at 250-300°C, and the pre-decomposition time is 3-5 hours;

(7) Calcining the intermediate product in a protective atmosphere furnace with reducing gas, and then cooling to room temperature to obtain a calcined product, wherein the calcining temperature is 500-600°C, and the calcining time is 8-10 hours;

(8) Pulverizing and sorting the calcined product in step (7) to obtain a graphene positive electrode material for lithium ion batteries.

As a further scheme of the present invention:

In the step (3), 90 parts of lithium iron phosphate, 1.5 parts of carbon nanotubes, 4 parts of graphene and 1.5 parts of PVDF are added to the stirring tank.

As a further scheme of the present invention:

The carbon nanotubes are multi-walled carbon nanotubes with a diameter of ≤6nm.

As a further scheme of the present invention:

The inert gas is selected from one or both of nitrogen and argon.

As a further solution of the present invention:

In the step (7), the calcination temperature is 550° C., and the calcination time is 9 hours.

Compared with prior art, the beneficial effect of the present invention is:

The three-dimensional porous structure of the present invention constructs rich voids to provide channels for the rapid transmission of lithium ions, which is conducive to the transfer of lithium ions on the surface and reaching the reactive active sites, thereby improving the conductivity of lithium iron phosphate, so it has excellent conductivity, The rate performance, cycle performance and low temperature performance provide a lithium-ion battery cathode material with simple processing technology, low cost, high capacity and safety for the application of lithium-ion batteries.

Detailed ways

The technical solution of this patent will be further described in detail below in conjunction with specific embodiments.

Example 1

A kind of preparation method of graphene cathode material for lithium ion battery, concrete steps are as follows:

(1) Weigh 6 parts of graphite and 2 parts of NaNO ₃ into a beaker, stir mechanically, slowly add 100mL of concentrated sulfuric acid, stir for 40min, then slowly add 15 parts of KMnO ₄ , after 0.5h, continue stirring After 20 hours, due to the increase in the viscosity of the reactant, the stirring was stopped, and a paste-like purple-red substance was obtained; after standing for 6 days, 450mL of deionized water and 25mL of H ₂ O ₂ were slowly added, and the color of the solution became more obvious at this time. After the solution is fully reacted, it is centrifuged and washed to obtain graphite oxide;

(2) Disperse graphite oxide in water to prepare graphite oxide suspension, add concentrated sulfuric acid to the suspension, and disperse uniformly by ultrasonic to obtain a mixed solution, then put the mixed solution in a reaction kettle for 15 hours at 200°C, wash Obtain three-dimensional reduced graphene oxide;

(3) Add 80 parts of lithium iron phosphate, 1 part of carbon nanotubes, 3 parts of graphene and 1 part of PVDF into the mixing tank, set the revolution speed to 15r/min, the dispersion speed to 200r/min, and dry mix for 20 minutes;

(4) Add deionized water that is 6 times the mass of the mixture, and at a revolution speed of 20r/min and a dispersion speed of 600r/min, after stirring for 10 minutes, stop the machine to scrape the wall, and then set the revolution speed to 25r/min. The dispersion speed is set to 800r/min, and the dispersion is obtained by stirring for 30 minutes;

(5) Stir the obtained dispersion at a temperature of 60°C to immerse the generated rheological body into the interlayer of three-dimensional reduced graphene oxide to form an intercalation complex, and then dry the intercalation complex to constant weight to obtain composite precursor;

(6) Grind the composite precursor to obtain a powder, and then place the powder in an inert gas protective atmosphere furnace to pre-decompose to obtain an intermediate product. The pre-decomposition temperature is controlled at 250°C, and the pre-decomposition time is 3 hours;

(7) The intermediate product is calcined in a protective atmosphere furnace with reducing gas, and then cooled to room temperature to obtain a calcined product, wherein the calcining temperature is 500°C, and the calcining time is 8 hours;

(8) Pulverizing and sorting the calcined product in step (7) to obtain a graphene positive electrode material for lithium ion batteries.

Example 2

A kind of preparation method of graphene cathode material for lithium ion battery, concrete steps are as follows:

(1) Weigh 7 parts of graphite and 2.5 parts of NaNO ₃ into a beaker, stir mechanically, slowly add 110mL of concentrated sulfuric acid, stir for 45min, then slowly add 18 parts of KMnO ₄ , after 0.5h, continue stirring After 20 hours, due to the increase in the viscosity of the reactant, the stirring was stopped, and a paste-like purple-red substance was obtained; after standing for 7 days, 480 mL of deionized water and 28 mL of H ₂ O ₂ were slowly added, and the color of the solution became more obvious at this time After the solution is fully reacted, it is centrifuged and washed to obtain graphite oxide;

(2) Disperse graphite oxide in water to prepare graphite oxide suspension, add concentrated sulfuric acid to the suspension, and ultrasonically disperse evenly to obtain a mixed solution, then put the mixed solution in a reaction kettle for 16 hours at 210°C, wash Obtain three-dimensional reduced graphene oxide;

(3) Add 85 parts of lithium iron phosphate, 1.2 parts of carbon nanotubes, 3.5 parts of graphene and 1.2 parts of PVDF into the mixing tank, set the revolution speed to 18r/min, the dispersion speed to 250r/min, and dry mix for 25 minutes;

(4) Add deionized water that is 6.5 times the mass of the mixture, and at a revolution speed of 22r/min and a dispersion speed of 650r/min, stop stirring for 11 minutes and then stop the scraper to scrape the wall, and then set the revolution speed to 28r/min. Set the dispersion speed to 900r/min, stir for 35min to obtain the dispersion;

(5) Stir the obtained dispersion at a temperature of 65°C to immerse the generated rheological body into the interlayer of three-dimensional reduced graphene oxide to form an intercalation complex, and then dry the intercalation complex to a constant weight to obtain composite precursor;

(6) Grind the composite precursor to obtain a powder, and then place the powder in an inert gas protective atmosphere furnace to pre-decompose to obtain an intermediate product. The pre-decomposition temperature is controlled at 260°C, and the pre-decomposition time is 3.5 hours;

(7) The intermediate product is calcined in a protective atmosphere furnace with reducing gas, and then cooled to room temperature to obtain a calcined product, wherein the calcining temperature is 520°C, and the calcining time is 8.5h;

(8) Pulverizing and sorting the calcined product in step (7) to obtain a graphene positive electrode material for lithium ion batteries.

Example 3

A kind of preparation method of graphene cathode material for lithium ion battery, concrete steps are as follows:

(1) Weigh 8 parts of graphite and 3 parts of NaNO ₃ into a beaker, stir mechanically, slowly add 120mL of concentrated sulfuric acid, stir for 50min, then slowly add 20 parts of KMnO ₄ , after 0.5h, continue stirring After 20 hours, due to the increase in the viscosity of the reactant, the stirring was stopped, and a paste-like purple-red substance was obtained; after standing for 8 days, 500 mL of deionized water and 30 mL of H ₂ O ₂ were slowly added, and the color of the solution became more obvious at this time. After the solution is fully reacted, it is centrifuged and washed to obtain graphite oxide;

(2) Disperse graphite oxide in water to prepare graphite oxide suspension, add concentrated sulfuric acid to the suspension, and ultrasonically disperse evenly to obtain a mixed solution, then put the mixed solution in a reaction kettle and react at 200-250°C for 15 -20h, washing to obtain three-dimensional reduced graphene oxide;

(3) Add 90 parts of lithium iron phosphate, 1.5 parts of carbon nanotubes, 4 parts of graphene and 1.5 parts of PVDF into the mixing tank, set the revolution speed to 20r/min, the dispersion speed to 300r/min, and dry mix for 30 minutes;

(4) Add deionized water that is 7 times the mass of the mixture, and when the revolution speed is 25r/min and the dispersion speed is 700r/min, after stirring for 12 minutes, stop the machine to scrape the wall, and then set the revolution speed to 30r/min. The dispersion speed is set to 1000r/min, and the dispersion is obtained by stirring for 40 minutes;

(5) Stir the obtained dispersion at a temperature of 70°C to immerse the generated rheological body into the interlayer of three-dimensional reduced graphene oxide to form an intercalation complex, and then dry the intercalation complex to a constant weight to obtain composite precursor;

(6) Grind the composite precursor to obtain a powder, and then place the powder in an inert gas protective atmosphere furnace to pre-decompose to obtain an intermediate product. The pre-decomposition temperature is controlled at 280°C, and the pre-decomposition time is 4 hours;

(7) The intermediate product is calcined in a protective atmosphere furnace with reducing gas, and then cooled to room temperature to obtain a calcined product, wherein the calcining temperature is 550°C, and the calcining time is 9 hours;

(8) Pulverizing and sorting the calcined product in step (7) to obtain a graphene positive electrode material for lithium ion batteries.

Example 4

A kind of preparation method of graphene cathode material for lithium ion battery, concrete steps are as follows:

(1) Weigh 9 parts of graphite and 3.5 parts of NaNO ₃ into a beaker, stir mechanically, slowly add 140mL of concentrated sulfuric acid, stir for 55min, then slowly add 22 parts of KMnO ₄ , after 0.5h, continue stirring After 20 hours, due to the increase in the viscosity of the reactant, the stirring was stopped, and a paste-like purple-red substance was obtained; after standing for 9 days, 520 mL of deionized water and 32 mL of H ₂ O ₂ were slowly added, and the color of the solution became more obvious at this time After the solution is fully reacted, it is centrifuged and washed to obtain graphite oxide;

(2) Disperse graphite oxide in water to prepare a suspension of graphite oxide, add concentrated sulfuric acid to the suspension, and disperse it uniformly by ultrasonic to obtain a mixed solution, then put the mixed solution in a reaction kettle for 19 hours at 240°C, wash Obtain three-dimensional reduced graphene oxide;

(3) Add 95 parts of lithium iron phosphate, 1.8 parts of carbon nanotubes, 4.5 parts of graphene and 1.8 parts of PVDF into the mixing tank, set the revolution speed to 22r/min, the dispersion speed to 350r/min, and dry mix for 35 minutes;

(4) Add deionized water 7.5 times the mass of the mixture, under the condition that the revolution speed is 28r/min and the dispersion speed is 750r/min, after stirring for 14min, stop the machine to scrape the wall, and then set the revolution speed to 32r/min, The dispersion speed is set to 1100r/min, and the dispersion is obtained by stirring for 45min;

(5) Stir the obtained dispersion at a temperature of 75°C to immerse the generated rheological body into the interlayer of three-dimensional reduced graphene oxide to form an intercalation complex, and then dry the intercalation complex to constant weight to obtain composite precursor;

(6) Grind the composite precursor to obtain a powder, and then place the powder in an inert gas protective atmosphere furnace for pre-decomposition to obtain an intermediate product. The pre-decomposition temperature is controlled at 290°C, and the pre-decomposition time is 4.5 hours;

(7) The intermediate product is calcined in a protective atmosphere furnace with reducing gas, and then cooled to room temperature to obtain a calcined product, wherein the calcining temperature is 580°C, and the calcining time is 9.5h;

(8) Pulverizing and sorting the calcined product in step (7) to obtain a graphene positive electrode material for lithium ion batteries.

Example 5

A kind of preparation method of graphene cathode material for lithium ion battery, concrete steps are as follows:

(1) Weigh 10 parts of graphite and 4 parts of NaNO ₃ into a beaker, stir mechanically, slowly add 150mL of concentrated sulfuric acid, stir for 60min, then slowly add 25 parts of KMnO ₄ , after 0.5h, continue stirring After 20 hours, due to the increase in the viscosity of the reactant, the stirring was stopped, and a paste-like purple-red substance was obtained; after standing for 10 days, 550 mL of deionized water and 35 mL of H ₂ O ₂ were slowly added, and the color of the solution became more obvious at this time After the solution is fully reacted, it is centrifuged and washed to obtain graphite oxide;

(2) Disperse graphite oxide in water to prepare graphite oxide suspension, add concentrated sulfuric acid to the suspension, and ultrasonically disperse evenly to obtain a mixed solution, then put the mixed solution in a reaction kettle for 20 hours at 250°C, wash Obtain three-dimensional reduced graphene oxide;

(3) Add 100 parts of lithium iron phosphate, 2 parts of carbon nanotubes, 5 parts of graphene and 2 parts of PVDF into the mixing tank, set the revolution speed to 25r/min, the dispersion speed to 400r/min, and dry mix for 40 minutes;

(4) Add deionized water that is 8 times the mass of the mixture, and when the revolution speed is 30r/min and the dispersion speed is 800r/min, after stirring for 15 minutes, stop the machine to scrape the wall, and then set the revolution speed to 35r/min. The dispersion speed is set to 1200r/min, and the dispersion is obtained by stirring for 50min;

(5) Stir the obtained dispersion at a temperature of 80°C to immerse the generated rheological body into the interlayer of three-dimensional reduced graphene oxide to form an intercalation complex, and then dry the intercalation complex to constant weight to obtain composite precursor;

(6) Grind the composite precursor to obtain a powder, and then place the powder in an inert gas protective atmosphere furnace for pre-decomposition to obtain an intermediate product. The pre-decomposition temperature is controlled at 300°C, and the pre-decomposition time is 5 hours;

(7) The intermediate product is calcined in a protective atmosphere furnace with reducing gas, and then cooled to room temperature to obtain a calcined product, wherein the calcining temperature is 600°C, and the calcining time is 10 hours;

(8) Pulverizing and sorting the calcined product in step (7) to obtain a graphene positive electrode material for lithium ion batteries.

The carbon nanotubes are multi-walled carbon nanotubes with a diameter of ≤6nm. The inert gas is selected from one or both of nitrogen and argon.

The three-dimensional porous structure of the present invention constructs rich voids to provide channels for the rapid transmission of lithium ions, which is conducive to the transfer of lithium ions on the surface and reaching the reactive active sites, thereby improving the conductivity of lithium iron phosphate, so it has excellent conductivity, The rate performance, cycle performance and low temperature performance provide a lithium-ion battery cathode material with simple processing technology, low cost, high capacity and safety for the application of lithium-ion batteries.

The preferred implementation of this patent has been described in detail above, but this patent is not limited to the above-mentioned implementation. Within the scope of knowledge of those of ordinary skill in the art, various implementations can be made without departing from the purpose of this patent. kind of change.

Claims (5)

1. a preparation method of graphene positive electrode material for lithium ion battery, is characterized in that, concrete steps are as follows: (1) Weigh 6-10 parts of graphite and 2-4 parts of NaNO ₃ into a beaker, stir vigorously, slowly add 100-150mL of concentrated sulfuric acid, stir for 40-60min, and then slowly add 15-25 parts of NaNO 3 KMnO ₄ , after adding 0.5h, continue to stir for 20 hours, stop stirring due to increased viscosity of the reactant, and obtain a paste-like purple-red substance; after standing for 6-10d, slowly add 450-550mL of deionized water and 25 -35mL of H ₂ O ₂ , the color of the solution becomes more obvious bright yellow at this time, after the solution is fully reacted, centrifuge and wash to obtain graphite oxide; (2) Disperse graphite oxide in water to prepare graphite oxide suspension, add concentrated sulfuric acid to the suspension, and ultrasonically disperse to obtain a mixed solution, then put the mixed solution in a reaction kettle and react at 200-250°C for 15 -20h, washing to obtain three-dimensional reduced graphene oxide; (3) Add 80-100 parts of lithium iron phosphate, 1-2 parts of carbon nanotubes, 3-5 parts of graphene and 1-2 parts of PVDF into the stirring tank, set the revolution speed to 15-25r/min, and the dispersion speed 200-400r/min, dry mixing 20-40min; (4) Add deionized water that is 6-8 times the mass of the mixture, under the condition that the revolution speed is 20-30r/min and the dispersion speed is 600-800r/min, after stirring for 10-15min, stop the scraper to scrape the wall, and then put The revolution speed is set to 25-35r/min, the dispersion speed is set to 800-1200r/min, and the dispersion is obtained by stirring for 30-50min; (5) Stir the obtained dispersion at a temperature of 60-80°C to immerse the generated rheological body into the interlayer of three-dimensional reduced graphene oxide to form an intercalation complex, and then dry the intercalation complex to constant weight Composite precursors are prepared; (6) Grinding the composite precursor to obtain a powder, and then pre-decomposing the powder in an inert gas protective atmosphere furnace to obtain an intermediate product, controlling the pre-decomposition temperature to 250-300°C, and the pre-decomposition time to 3-5h; (7) Calcining the intermediate product in a protective atmosphere furnace with reducing gas, and then cooling to room temperature to obtain a calcined product, wherein the calcining temperature is 500-600° C., and the calcining time is 8-10 h; (8) Pulverizing and sorting the calcined product in step (7) to obtain the graphene cathode material for lithium ion batteries. 2. the preparation method of graphene cathode material for lithium ion battery according to claim 1, is characterized in that, in described step (3), be the graphite of 90 parts of lithium iron phosphate, 1.5 parts of carbon nanotubes, 4 parts Alkene and 1.5 parts of PVDF were added to the stirred tank. 3. the preparation method of graphene cathode material for lithium ion battery according to claim 1, is characterized in that, described carbon nanotube is multi-walled carbon nanotube, diameter≤6nm. 4. the preparation method of graphene cathode material for lithium ion battery according to claim 1, is characterized in that, described inert gas is selected from one or both in nitrogen and argon. 5. The preparation method of graphene positive electrode material for lithium ion battery according to claim 1, characterized in that, in the step (7), the calcination temperature is 550°C, and the calcination time is 9h.