CN115472835A - Carbon quantum dot composite positive electrode conductive agent and preparation method thereof - Google Patents
Carbon quantum dot composite positive electrode conductive agent and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the technical field of preparation of carbon quantum dot materials, in particular to a carbon quantum dot composite anode conductive agent and a preparation method thereof. The carbon quantum dot composite positive electrode conductive agent comprises the following raw materials in parts by weight: 80-180 parts of carbon quantum dots and 1-5 parts of carbon fibers; the carbon quantum dot comprises the following preparation raw materials: 80-160 parts of organic carbon, 8-18 parts of strong acid, 0.1-3 parts of auxiliary agent, 370-470 parts of first solvent and 0.1-0.8 part of dispersing agent; the carbon fiber is prepared from the following raw materials: 5-15 parts of acrylonitrile, 0.01-0.5 part of comonomer, 0.01-0.5 part of initiator and 50-80 parts of second solvent. The cathode material and the lithium ion battery prepared by the carbon quantum dot composite cathode conductive agent can improve the conductivity of the cathode material and the electrochemical activity of the lithium ion battery, and can also keep good cycle stability.
Description
Technical Field
The invention relates to the technical field of carbon quantum dot material preparation, in particular to the field of IPC H01M4, and more particularly relates to a carbon quantum dot composite positive electrode conductive agent and a preparation method thereof.
Background
With the development of science and technology, people have higher and higher requirements on lithium ion batteries, and the performance of a positive electrode material as a part of the lithium ion battery directly influences the performance of the lithium ion battery. In order to improve the performance of the lithium ion battery cathode material, a conductive agent is added in the process of manufacturing the cathode material, although the conductive agent can be dispersed in the cathode material to improve the conductivity of the material, the traditional conductive agents such as conductive graphite, carbon black and the like have limited conductivity and are difficult to uniformly disperse in an electrode, and the conductive agent does not have electrochemical activity per se, and the performance of the electrode and the lithium ion battery can be influenced by adding excessive conductive agent.
The carbon quantum dots serving as a novel 0D-type spherical carbon nano material not only have the characteristics of the traditional semiconductor metal quantum dots, but also have the advantages of simplicity in preparation, easiness in functionalization and the like. The carbon quantum dot composite positive electrode conductive agent with excellent performance is prepared by compounding the carbon fibers and the carbon quantum dots, so that the specific surface area and the mechanical strength of the carbon fibers can be increased, binding sites of electroactive substances can be increased, the flowing and ion transmission of electrolyte are facilitated, and the electrochemical activity is high.
In the prior art, a patent application publication number of CN113471427A discloses a carbon quantum dot and graphene composite material, a preparation method and an application thereof, wherein the composite material is synthesized by taking anhydrous citric acid as organic carbon and ferric trichloride hexahydrate as a catalyst through a simple catalytic graphite method. The capacitor assembled by the composite material has good cycling stability, but has low specific capacity, and the application of the capacitor in the lithium ion battery is limited.
The patent application publication No. CN109244422A discloses a carbon quantum dot/CNTs composite positive conductive agent and a preparation method thereof, wherein the positive conductive agent is obtained by dispersing CNTs slurry, citric acid and ethylenediamine in water, and dialyzing after hydrothermal reaction. The lithium ion battery prepared by the positive electrode conductive agent has low capacity retention rate after 400 cycles, which shows that the lithium ion battery has poor cycle stability and limits the application of the lithium ion battery.
The applicant finds that the traditional conductive agent has limited conductivity, is difficult to uniformly disperse in the electrode, has no electrochemical activity, and can influence the performance of the electrode and the lithium ion battery when being added excessively. Therefore, a positive electrode conductive agent is needed, which is added into a positive electrode material in a small amount, so that the conductivity of the positive electrode material and the electrochemical activity of the lithium ion battery can be improved, and good cycle stability can be maintained.
Disclosure of Invention
In order to solve the above problems, in a first aspect of the present invention, a carbon quantum dot composite positive electrode conductive agent is provided, which is prepared from the following raw materials: carbon quantum dots, carbon fibers.
The carbon quantum dots comprise the following preparation raw materials in parts by weight: 80-160 parts of organic carbon, 8-18 parts of strong acid, 0.1-3 parts of auxiliary agent, 370-470 parts of first solvent and 0.1-0.8 part of dispersing agent; the carbon fiber comprises the following preparation raw materials in parts by weight: 5-15 parts of acrylonitrile, 0.01-0.5 part of comonomer, 0.01-0.5 part of initiator and 50-80 parts of second solvent.
Preferably, the carbon quantum dot composite positive electrode conductive agent comprises the following raw materials: carbon quantum dots, carbon fibers; the carbon quantum dot comprises the following raw materials in parts by weight: 80-120 parts of organic carbon, 8-14 parts of strong acid, 1-3 parts of auxiliary agent, 370-450 parts of first solvent and 0.1-0.5 part of dispersing agent; the carbon fiber comprises the following raw materials in parts by weight: 8-13 parts of acrylonitrile, 0.01-0.3 part of comonomer, 0.01-0.3 part of initiator and 50-70 parts of second solvent.
Preferably, the organic carbon is selected from one or more of citric acid and its ester, glucosamine, small molecular alcohol, oil and fat, urea, amino acid, caulis Sacchari sinensis (Saccharum OFFICINARUM L.) extract, and gluconate; further, it is an extract of sugar cane (Saccharum OFFICINARUM L.).
Preferably, the extract of sugar cane (Saccharum OFFICINARUM L.) is commercially available, such as the extract of sugar cane (Saccharum OFFICINARUM L.) produced by Sa' an Reli bioengineering Co., ltd, supplier 10-1.
Preferably, the strong acid is selected from one or more of concentrated sulfuric acid, concentrated nitric acid, perchloric acid, selenic acid, chloric acid, chlorous acid, concentrated perchloric acid, permanganic acid and xenon acid; further, concentrated sulfuric acid and concentrated nitric acid; further, the mass ratio of the concentrated sulfuric acid to the concentrated nitric acid is (2-5): 1; further, 3:1.
The concentrated sulfuric acid is a concentrated sulfuric acid aqueous solution with the content of 98 percent; the concentrated nitric acid is a concentrated nitric acid aqueous solution with the content of 68 percent.
Preferably, the auxiliary agent is selected from one or more of concentrated ammonia solution, sodium hydroxide, sodium bicarbonate and phosphate buffer solution; further, sodium hydroxide is used.
Preferably, the first solvent is selected from one or more of propanol, ethanol, isopropanol, acetone, methanol, isopropanol, propylene carbonate, methyl butanone and methyl isobutyl ketone; further, ethanol and isopropanol; further, the mass ratio of the ethanol to the isopropanol is (2-5): 1; further, the mass ratio of the ethanol to the isopropanol is 3:1.
the mass ratio of the organic carbon to the first solvent is 1: (1-5); preferably, it is 1:4.
preferably, the dispersant has a hydroxyl value of 70 to 120mgKOH/g and an average molecular weight of 600 to 3000.
Preferably, the dispersant is selected from one or more of polyethylene glycol, sodium polyphosphate and sodium hexametaphosphate; further, polyethylene glycol; further, PEG-1500.
Preferably, the PEG-1500 is commercially available, for example, PEG-1000 available from Sanyo corporation of Japan.
Preferably, the comonomer is selected from one or more of methyl acrylate, methyl methacrylate, methacrylic acid and itaconic acid; preferably, it is methyl acrylate.
Preferably, the initiator is selected from one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate, benzoyl peroxide, lauroyl peroxide, potassium persulfate, sodium persulfate and ammonium persulfate; preferably, it is dimethyl azodiisobutyrate.
Preferably, the second solvent is selected from one or more of sodium thiocyanate, dimethyl sulfoxide, nitric acid, acetone, N-dimethylformamide and deionized water; preferably, the mixed solution is a mixed solution of dimethyl sulfoxide, N, N-dimethylformamide and deionized water; further, the mass ratio of the dimethyl sulfoxide to the N, N-dimethylformamide to the deionized water is (1-10): 1: (1-4); further, the ratio of 3.
Preferably, the mass ratio of the acrylonitrile to the comonomer is (55-75) 1; preferably, it is 50.
Preferably, the mass ratio of the carbon quantum dots to the carbon fibers is (40-70): 1; preferably, it is 60.
The applicant unexpectedly finds that the mass ratio of (2-5): 1, ethanol and isopropanol are used as first solvents, when the mass ratio of organic carbon to the solvents is 1 (1-5), the prepared carbon quantum dots are uniform in particle size, and the average particle size is 1-2nm. This is because the mass ratio is (2-5): 1, the surface tension of the mixed solvent of the ethanol and the isopropanol is small, so that the agglomeration of particles can be reduced, and on the other hand, the ethanol and the isopropanol have synergistic effect, so that the solubility of organic carbon in a system can be well increased, and carbon quantum dots prepared by the method are uniformly distributed in the system. When the mass ratio of the organic carbon to the solvent is 1 (1-5), the prepared carbon quantum dots have good dispersibility, uniform size distribution and average particle size of 1-2nm. The carbon quantum dots with good dispersibility and uniform size distribution are attached to the surface of the carbon fiber, so that the specific surface area of the carbon quantum dot composite anode conductive agent is increased, the contact area of the carbon quantum dot composite anode conductive agent and the anode material is larger, the electrochemical performance of the anode material is improved, and the specific capacity of the lithium ion battery is further improved.
The second aspect of the invention provides a preparation method of the carbon quantum dot composite positive electrode conductive agent, which comprises the following steps:
s1, mixing organic carbon and strong acid in a flask, heating to 80-150 ℃ in an oil bath, and uniformly stirring;
s2, centrifuging the solution in the flask at 9000-12000r/min for 40-50min, taking supernatant, adding an auxiliary agent into the supernatant, and uniformly stirring;
s3, adding a first solvent into the solution obtained in the step (2), fully mixing and stirring, centrifuging at a speed of 9000-12000r/min for 40-50min, and removing supernatant to obtain the carbon quantum dots;
s4, placing acrylonitrile, a comonomer, an initiator and a second solvent in a nitrogen atmosphere, stirring, heating to 50-80 ℃ in an oil bath, and preserving heat for 5-7 hours to obtain a substance I;
s5, washing and filtering the substance with hot water, and drying and grinding in vacuum to obtain organic fibers;
s6, placing the organic fiber in an oxidizing atmosphere at 220-280 ℃ for 50-150min, and then placing in an inert atmosphere at 1200-1600 ℃ for 5-10min to obtain a substance II;
s7, placing the second substance into a sealing device filled with inert atmosphere, and keeping the temperature of 2500-2800 ℃ for 5-20s to obtain carbon fibers;
s8, ultrasonically dispersing carbon quantum dots and carbon fibers in water, wherein the ultrasonic power is 400-600W, and the ultrasonic time is 10-20min;
s9, transferring the solution in the step S8 to a hydrothermal reaction kettle for hydrothermal reaction, keeping the temperature of the hydrothermal reaction at 150-250 ℃ for 4-6h, and cooling to room temperature;
s10, taking out the solution obtained in the step S9, and dialyzing by adopting a dialysis bag, wherein the molecular weight cut-off of the dialysis bag is 1-3KD. The dialysis time is 24-48 h.
The applicant unexpectedly finds that after the carbon fiber raw material is placed in an oxidizing atmosphere at 220-280 ℃ for 50-150min, the prepared carbon fiber has high density and good conductivity, and the prepared lithium ion battery has high cycle stability. The carbon fiber raw material is placed in an oxidizing atmosphere at 220-280 ℃ to react for 50-150min, so that hydroxyl and carbonyl groups can be formed in carbon fiber molecules, hydrogen bonds can be formed between molecules and in molecules, the stability of the carbon fiber is improved, the density and compactness of the carbon fiber can be improved, a firm conductive network is formed, the carbon fiber is in closer contact with a positive electrode material and a positive electrode conductive agent prepared from carbon quantum dots, the probability of insufficient contact between the conductive agent and an active substance caused by volume expansion and contraction change of the positive electrode material in the charging and discharging process is reduced, and the resistance increase caused by insufficient contact between the positive electrode conductive agent and the active substance is inhibited,thereby improving the cycle performance of the lithium ion battery. If the reaction time is too long, the production cost is increased, and if the reaction time is too short, the reaction with oxygen is insufficient, hydroxyl and carbonyl cannot be formed in carbon fiber molecules, the carbon fiber has low stability and density, and cannot be in close contact with a positive electrode material, so that the cycle performance of the lithium ion battery cannot be improved. The density of the prepared carbon fiber is 1.8-2.2g/cm 3 The resistivity at 25 ℃ is 700 mu omega/cm, which shows that the carbon quantum dot positive electrode conductive agent has good conductivity and high density, and when the carbon quantum dot positive electrode conductive agent is applied to a lithium ion battery, the internal resistance of the prepared battery is low and is 27.5 mu omega, the battery is discharged for 1000 times at 3C rate, and the capacity of the battery still reaches more than 95 percent, which shows that the composite material has high electrochemical activity and reversibility and good stability.
The applicant unexpectedly finds that the mass ratio of the prepared carbon quantum dots to the carbon fibers is (40-70): the carbon quantum dot positive electrode conductive agent is prepared in 1 hour, so that the specific surface area and the mechanical strength of carbon fibers can be increased, binding sites of electroactive substances can be increased, and the prepared carbon quantum dot positive electrode conductive agent is applied to a positive electrode material and can load a large amount of active substances, so that the positive electrode material has high electrochemical activity and high cycle stability. This is because too much carbon fiber does not enhance the electron transport rate and has a limited effect of improving the detection rate and sensitivity, and too little carbon fiber increases the carbon quantum dot, which hinders the electron transport and reduces the electrochemical sensing efficiency of the positive electrode material. Therefore, the carbon quantum dots and the carbon fibers prepared according to the invention are prepared according to the mass ratio of (40-70): 1, the carbon quantum dots are uniformly loaded on the surface of the carbon fiber, so that the surface defects of the carbon fiber are improved, the specific surface area and the stability of the carbon fiber are improved, binding sites with a positive electrode material are increased, a good conductive network is easily formed in an electrode by adopting a line-point mode contact, better conductivity and stability are shown, the using amount of the conductive agent can be reduced, and the capacity of a battery is improved. When the introduction amount of the carbon quantum dot anode conductive agent is 0.1wt%, the prepared anode material has small charge transfer resistance, and the cathode and anode peak potential difference of the anode material is about 20mV at a scanning rate of 10mV/s, which indicates that the anode material prepared from the carbon quantum dot anode conductive agent has high electrochemical activity and reversibility. When the carbon quantum dot anode material is applied to a lithium ion battery, the specific capacity is 1400mAh/g at 25 ℃ when the current density is 100 mA/g; when the composite material is discharged for 1000 times at 3C rate, the capacity of the battery still reaches over 95 percent, which shows that the composite material has high electrochemical activity and reversibility and good stability.
The reaction temperature of the hydrothermal reaction of the carbon fiber and the carbon quantum dot mixed liquid is 150-250 ℃, and the heat preservation time is 4-6h, so that the prepared carbon quantum dot positive electrode conductive agent has high reversibility and stability. The reason is that when the temperature is too high, the carbon quantum dots are easy to react in series at high temperature, which affects the stability of the composite material, and when the temperature is too low, the carbon quantum dots cannot obtain enough energy, cannot be uniformly attached to the surface of the carbon fibers, and cannot obtain the carbon quantum dot positive electrode conductive agent. Therefore, the carbon quantum dot anode conductive agent obtained by the heat preservation reaction at the temperature of 150-250 ℃ for 4-6h has small charge transfer impedance of the prepared anode material, the easier the electrons diffuse in the anode material, and the carbon fibers and the carbon quantum dots are used as the anode conductive agent to form a good conductive network, thereby providing a convenient channel for the transportation of the electrons in the electrode, and further improving the specific capacity of the lithium ion battery.
Has the advantages that:
1. selecting the following components in percentage by mass (2-5): the ethanol and the isopropanol in the step 1 are used as first solvents, on one hand, the surface tension of the solvents is small, the agglomeration of particles can be reduced, and carbon quantum dots prepared by the solvents are uniformly distributed in a system, and on the other hand, the ethanol and the isopropanol have synergistic effect, so that the solubility of organic carbon in the system can be well increased. When the mass ratio of the organic carbon to the solvent is 1 (1-5), the prepared carbon quantum dots have good dispersibility in the solution, uniform size distribution and average particle size of 1-2nm. The carbon quantum dots with good dispersibility and uniform size distribution are attached to the surface of the carbon fiber, so that the specific surface area of the carbon quantum dot composite anode conductive agent is increased, the contact area of the carbon quantum dot composite anode conductive agent and the anode material is larger, the electrochemical performance of the anode material is improved, and the specific capacity of the lithium ion battery is further improved.
2. The carbon fiber raw material is placed in an oxidizing atmosphere at 220-280 ℃ to react for 50-150min, so that hydroxyl and carbonyl groups can be formed in carbon fiber molecules, hydrogen bonds can be formed between molecules and in molecules, the stability of the carbon fiber is improved, the density and compactness of the carbon fiber can be improved, and a firm conductive network is formed, so that the carbon fiber is in closer contact with a positive electrode material and a positive electrode conductive agent prepared from carbon quantum dots, the probability of insufficient contact between the conductive agent and an active substance caused by volume expansion and contraction change of the positive electrode material in the charging and discharging process is reduced, the resistance increase caused by insufficient contact between the positive electrode conductive agent and the active substance is inhibited, the conductivity of the positive electrode material is improved, and the electrochemical performance and the cycling stability of the lithium ion battery are improved.
3. Selecting the mass ratio of carbon quantum dots to carbon fibers as (40-70): the carbon quantum dot composite anode conductive agent is prepared by 1, the specific surface area and the mechanical strength of carbon fibers can be increased, binding sites of electroactive substances can be increased, the carbon quantum dots are uniformly loaded on the surfaces of the carbon fibers, the surface defects of the carbon fibers are improved, the specific surface area and the stability of the carbon fibers are improved, the binding sites of the carbon quantum dots and an anode material are increased, a good conductive network is easily formed in an electrode by adopting a 'line-point' mode contact, better conductivity and stability are shown, the using amount of the conductive agent can be reduced, and the electrochemical activity and the cycling stability of a battery are improved.
4. When the reaction temperature of the hydrothermal reaction of the carbon fiber and the carbon quantum dot mixed liquid is 150-250 ℃ and the heat preservation time is 4-6h, the prepared carbon quantum dot composite anode conductive agent has high reversibility and stability.
5. The carbon quantum dot composite anode conductive agent prepared by the invention is not only suitable for lithium ion batteries, but also can be applied to the fields of super capacitors, electrochemical sensors, dye-sensitized solar cells and the like.
Detailed Description
Examples
Example 1
Embodiment 1 provides a carbon quantum dot composite positive electrode conductive agent, which is prepared from the following raw materials: carbon quantum dots, carbon fibers.
The carbon quantum dots comprise the following preparation raw materials in parts by weight: 100 parts of organic carbon, 10 parts of strong acid, 2.5 parts of an auxiliary agent, 400 parts of a first solvent and 0.3 part of a dispersing agent; the carbon fiber comprises the following preparation raw materials in parts by weight: 10 parts of acrylonitrile, 0.2 part of comonomer, 0.15 part of initiator and 60 parts of second solvent.
The mass ratio of the carbon quantum dots to the carbon fibers is 60.
The organic carbon is selected from sugar cane (Saccharum OFFICINARUM L.).
The caulis Sacchari sinensis (Saccharum OFFICINARUM L.) extract is obtained from 10-1 of caulis Sacchari sinensis (Saccharum OFFICINARUM L.) extract produced by Sierra Ruili bioengineering Co.
The strong acid is selected from concentrated sulfuric acid and concentrated nitric acid; the mass ratio of the concentrated sulfuric acid to the concentrated nitric acid is 3:1.
the concentrated sulfuric acid is a concentrated sulfuric acid aqueous solution with the content of 98 percent; the concentrated nitric acid is a concentrated nitric acid aqueous solution with the content of 68 percent.
The auxiliary agent is selected from sodium bicarbonate.
The first solvent is selected from ethanol and isopropanol, and the mass ratio of the ethanol to the isopropanol is 3:1.
The hydroxyl value of the dispersant is 75-80mgKOH/g, and the average molecular weight is 1450-1550.
The dispersant is selected from polyethylene glycol, which is purchased from PEG-1500 manufactured by Sanyo corporation of Japan.
The comonomer is selected from methyl acrylate.
The initiator is selected from dimethyl azodiisobutyrate;
the second solvent is a mixed solution of dimethyl sulfoxide, N, N-dimethylformamide and deionized water.
The mass ratio of the dimethyl sulfoxide to the N, N-dimethylformamide to the deionized water is 3.
A preparation method of a carbon quantum dot composite positive electrode conductive agent comprises the following steps:
(1) Mixing caulis Sacchari sinensis (Saccharum OFFICINARUM L.) extract with concentrated sulfuric acid and concentrated nitric acid in flask, heating to 140 deg.C in oil bath, and stirring;
(2) Centrifuging the solution in the flask at 10000r/min for 48min, taking supernatant, and adding sodium bicarbonate into the supernatant;
(3) Adding ethanol, isopropanol and polyethylene glycol into the solution obtained in the step (2), fully mixing and stirring, centrifuging at the speed of 10000r/min for 48min, and removing supernatant to obtain carbon quantum dots;
(4) Placing acrylonitrile, a comonomer, an initiator and a second solvent in a nitrogen atmosphere, stirring, heating to 65 ℃ in an oil bath, and preserving heat for 6 hours to obtain a substance I;
(5) Washing the substance with hot water, filtering, and vacuum drying and grinding to obtain organic fiber;
(6) Placing the organic fiber in an oxidizing atmosphere at 270 ℃ for 120min, and then placing the organic fiber in an inert atmosphere at 1500 ℃ for 7min to obtain a substance II;
(7) Putting the substance II into a sealing device filled with inert atmosphere, and keeping the temperature of 2600 ℃ for 10s to obtain carbon fiber;
(8) Ultrasonically dispersing carbon quantum dots and carbon fibers in water, wherein the ultrasonic power is 450W, and the ultrasonic time is 15min;
(9) Then transferring the solution obtained in the step (8) to a hydrothermal reaction kettle for hydrothermal reaction, wherein the reaction temperature of the hydrothermal reaction is 180 ℃, keeping the temperature for reaction for 5 hours, and cooling to room temperature;
(10) And (4) taking out the solution in the step (9), and dialyzing by adopting a dialysis bag, wherein the molecular weight cut-off of the dialysis bag is 2KD. And (5) dialyzing for 30 hours to obtain the product.
Example 2
Embodiment 2 provides a carbon quantum dot composite positive electrode conductive agent, which is prepared from the following raw materials: carbon quantum dots, carbon fibers.
The carbon quantum dots comprise the following preparation raw materials in parts by weight: 100 parts of organic carbon, 10 parts of strong acid, 2.5 parts of an auxiliary agent, 400 parts of a first solvent and 0.3 part of a dispersing agent; the carbon fiber comprises the following preparation raw materials in parts by weight: 10 parts of acrylonitrile, 0.5 part of comonomer, 0.15 part of initiator and 60 parts of second solvent.
The mass ratio of the carbon quantum dots to the carbon fibers is 25:1.
the organic carbon is selected from sugar cane (Saccharum OFFICINARUM L.).
The caulis Sacchari sinensis (Saccharum OFFICINARUM L.) extract is obtained from 10-1 of caulis Sacchari sinensis (Saccharum OFFICINARUM L.) extract produced by Sierra Ruili bioengineering Co.
The strong acid is selected from concentrated sulfuric acid and concentrated nitric acid; the mass ratio of the concentrated sulfuric acid to the concentrated nitric acid is 3:1.
the concentrated sulfuric acid is a concentrated sulfuric acid aqueous solution with the content of 98 percent; the concentrated nitric acid is a concentrated nitric acid aqueous solution with the content of 68 percent.
The auxiliary agent is selected from sodium bicarbonate.
The first solvent is selected from methanol.
The hydroxyl value of the dispersant is 75-80mgKOH/g, and the average molecular weight is 1450-1550.
The dispersant is selected from polyethylene glycol, which is purchased from PEG-1500 manufactured by Sanyo corporation of Japan.
The comonomer is selected from methyl acrylate.
The initiator is selected from dimethyl azodiisobutyrate;
the second solvent is a mixed solution of dimethyl sulfoxide, N-dimethylformamide and deionized water.
The mass ratio of the dimethyl sulfoxide to the N, N-dimethylformamide to the deionized water is 3.
A preparation method of a carbon quantum dot composite positive electrode conductive agent comprises the following steps:
(1) Mixing caulis Sacchari sinensis (Saccharum OFFICINARUM L.) extract with concentrated sulfuric acid and concentrated nitric acid in flask, heating to 140 deg.C in oil bath, and stirring;
(2) Centrifuging the solution in the flask at 10000r/min for 48min, taking supernatant, and adding sodium bicarbonate into the supernatant;
(3) Adding ethanol, isopropanol and polyethylene glycol into the solution obtained in the step (2), fully mixing and stirring, centrifuging at the speed of 10000r/min for 48min, and removing supernatant to obtain carbon quantum dots;
(4) Placing acrylonitrile, a comonomer, an initiator and a second solvent in a nitrogen atmosphere, stirring, heating to 65 ℃ in an oil bath, and preserving heat for 6 hours to obtain a substance I;
(5) Washing and filtering the substance with hot water, and drying and grinding in vacuum to obtain organic fibers;
(6) Placing the organic fiber in an oxidizing atmosphere at 270 ℃ for 20min, and then placing the organic fiber in an inert atmosphere at 1500 ℃ for 7min to obtain a substance II;
(7) Putting the substance II into a sealing device filled with inert atmosphere, and keeping the temperature of 2600 ℃ for 10s to obtain carbon fiber;
(8) Ultrasonically dispersing carbon quantum dots and carbon fibers in water, wherein the ultrasonic power is 450W, and the ultrasonic time is 15min;
(9) Then transferring the solution obtained in the step (8) to a hydrothermal reaction kettle for hydrothermal reaction, wherein the reaction temperature of the hydrothermal reaction is 180 ℃, keeping the temperature for reaction for 5 hours, and cooling to room temperature;
(10) And (4) taking out the solution in the step (9), and dialyzing by adopting a dialysis bag, wherein the molecular weight cut-off of the dialysis bag is 2KD. And (5) dialyzing for 30 hours to obtain the product.
Performance test method
1. Particle size measurement
For example 1-2, 15 μm carbon quantum dots were repeatedly dropped on a copper mesh several times by using a micro-syringe, and then air-dried, and the dispersion and particle size of the carbon nanodots were observed by a transmission electron microscope, and the measured data are shown in Table 1.
2. Carbon fiber Density test
The density of the carbon fibers in example 1-2 was measured by GB/T30019-2013 "measurement of carbon fiber Density", and the measured data are shown in Table 1.
3. Carbon fiber resistivity testing
For example 1-2, the resistivity of the carbon fiber was measured by using GBT 32993-2016 "measurement of volume resistivity of carbon fiber", and the measured data are shown in Table 1.
4. Cyclic voltammetry test
For examples 1-2, each of these was reacted with LiCoO 2 Preparing an anode material into an electrode, measuring a cyclic voltammetry curve of the electrode in a three-electrode system, wherein a platinum sheet is used as a counter electrode, a silver wire is used as a reference electrode, the prepared electrode is used as a working electrode, 1mol/L LiTFSI solution is used as electrolyte, the scanning rate is 10mV/s, the potential difference between the cathode and Yang Fengzhi of the electrode is calculated from the cyclic voltammetry curve, and the measured data are recorded in Table 1.
5. Specific capacity and cycling stability
In order to evaluate the electrochemical performance and the cycling stability of the lithium ion battery applied in the embodiments 1-2, the battery tester is used to respectively test the specific capacity, the charge-discharge current density is 100mA/g, the potential range is 1.0-2.5V, the specific capacity after the first charge-discharge and 1000 times of charge-discharge is recorded, and the capacity retention rate is calculated. Cell assembly based on examples 1-2: the positive electrode material is made of LiCoO 2 And mixing the graphite powder with 0.1wt% of carbon quantum dot composite positive electrode conductive agent to obtain the composite negative electrode, wherein the negative electrode is graphite, and assembling the composite negative electrode into a battery in a glove box.
TABLE 1
Claims (10)
1. The carbon quantum dot composite positive electrode conductive agent is characterized by comprising the following raw materials: carbon quantum dots, carbon fibers; the carbon quantum dots comprise the following preparation raw materials in parts by weight: 80-160 parts of organic carbon, 8-18 parts of strong acid, 0.1-3 parts of auxiliary agent, 370-470 parts of first solvent and 0.1-0.8 part of dispersing agent; the carbon fiber is prepared from the following raw materials: 5-15 parts of acrylonitrile, 0.01-0.5 part of comonomer, 0.01-0.5 part of initiator and 50-80 parts of second solvent.
2. The carbon quantum dot composite cathode conductive agent according to claim 1, wherein the carbon quantum dot is prepared from the following raw materials in parts by weight: 80-120 parts of organic carbon, 8-14 parts of strong acid, 1-3 parts of auxiliary agent, 370-450 parts of first solvent and 0.1-0.5 part of dispersant; the carbon fiber comprises the following preparation raw materials in parts by weight: 8-13 parts of acrylonitrile, 0.01-0.3 part of comonomer, 0.01-0.3 part of initiator and 50-70 parts of second solvent.
3. The carbon quantum dot composite positive electrode conductive agent as claimed in claim 1 or 2, wherein the dispersant is one or more selected from polyethylene glycol, sodium polyphosphate and sodium hexametaphosphate.
4. The carbon quantum dot composite positive electrode conductive agent as claimed in claim 1 or 2, wherein the first solvent is one or more selected from propanol, ethanol, isopropanol, acetone, methanol, isopropanol, propylene carbonate, methyl butanone, and methyl isobutyl ketone.
5. The carbon quantum dot composite positive electrode conductive agent according to claim 1 or 2, wherein the mass ratio of the organic carbon to the first solvent is (1-5): 1.
6. The carbon quantum dot composite positive electrode conductive agent according to claim 1 or 2, wherein the mass ratio of the acrylonitrile to the comonomer is (55-75): 1.
7. The carbon quantum dot composite positive electrode conductive agent according to claim 1 or 2, wherein the mass ratio of the carbon quantum dots to the carbon fibers is (40-70): 1.
8. the preparation method of the carbon quantum dot composite positive electrode conductive agent according to any one of claims 1 to 7, characterized by comprising the steps of:
s1, mixing and stirring organic carbon and strong acid uniformly in a flask, centrifuging to obtain supernatant, adding a first solvent, an auxiliary agent and a dispersing agent, continuously stirring, centrifuging to remove the supernatant, and thus obtaining the carbon quantum dots;
s2, placing acrylonitrile, a comonomer, an initiator and a second solvent in a nitrogen atmosphere, stirring, heating to 50-80 ℃ in an oil bath, preserving heat for 5-7 hours, and then carrying out preoxidation, carbonization and graphitization to obtain carbon fibers;
and S3, adding the graphene solid into the carbon quantum dots, uniformly mixing by ultrasonic waves, filling the mixed liquid into a reaction kettle, placing the reaction kettle in a hydrothermal reaction kettle for keeping the temperature constant, cooling to room temperature, and dialyzing to obtain the carbon quantum dot composite positive electrode conductive agent.
9. The method for preparing the carbon quantum dot composite cathode conductive agent according to claim 8, wherein the pre-oxidation temperature in the step S2 is 220-280 ℃, and the carbon quantum dot composite cathode conductive agent is kept in an oxidation atmosphere for 50-150min.
10. The method for preparing the carbon quantum dot composite cathode conductive agent according to claim 8, wherein the reaction temperature in the hydrothermal reaction kettle in the step S3 is 150-250 ℃, and the heat preservation time is 4-6 hours.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116914123A (en) * | 2023-09-11 | 2023-10-20 | 浙江华宇钠电新能源科技有限公司 | High-stability layered positive electrode material of battery for vehicle and preparation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116914123A (en) * | 2023-09-11 | 2023-10-20 | 浙江华宇钠电新能源科技有限公司 | High-stability layered positive electrode material of battery for vehicle and preparation method thereof |
| CN116914123B (en) * | 2023-09-11 | 2023-12-15 | 浙江华宇钠电新能源科技有限公司 | High-stability layered positive electrode material of battery for vehicle and preparation method thereof |
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