CN110739460B - Composite conductive agent, preparation method thereof and electrode material containing composite conductive agent - Google Patents
Composite conductive agent, preparation method thereof and electrode material containing composite conductive agent Download PDFInfo
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
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- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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Abstract
The invention relates to a composite conductive agent, a preparation method thereof and an electrode material containing the same. The composite conductive agent comprises graphene and carbon nanotubes, wherein the graphene and the carbon nanotubes are connected through chemical bonds. According to the invention, the graphene and the carbon nano tube are bridged through chemical bonds, so that the electron transfer between the two conductive agents is enhanced, the surface contact with an active material and the long-range conductive capacity of the conductive agent are considered, the steric hindrance effect of the graphene on lithium ions can be reduced, the dispersion capacity in an electrode material is improved, the conductivity of a pole piece containing the composite conductive agent is up to 0.5-1.1S/cm, and the internal resistance of a battery containing the composite conductive agent is as low as 20-65 omega. The preparation method is simple and easy to operate, not only realizes the chemical bond connection of the graphene and the carbon nano tube, but also dopes nitrogen atoms in the conductive agent through the treatment of NHS, so that the electron transfer rate in the electrode can be effectively improved after the conductive agent is added into the electrode, and the conductivity is further enhanced.
Description
Technical Field
The invention belongs to the field of lithium ion batteries, and particularly relates to a composite conductive agent, a preparation method thereof and an electrode material containing the composite conductive agent.
Background
The conductive agent material is an important component of the lithium ion battery and plays an important role in the electrochemical performance of the lithium ion battery. After a proper amount of conductive agent is added into the electrode, the electron transfer rate in the electrode can be effectively improved. An excellent conductive agent should have several characteristics: 1. the conductivity is higher, and the electron transfer rate is improved; 2. high specific surface area, easy to contact with active materials; 3. easy to disperse, and can be well mixed with anode and cathode materials in the slurry preparation process.
The graphene conductive agent is a novel conductive agent developed in the last two years, and can better form a conductive network under the condition of small addition amount, and the effect is far better than that of traditional conductive agents such as conductive carbon black and the like. But currently, there are still a lot of bottlenecks in the practical application process. On one hand, the planar structure of graphene in the electrode can generate a steric hindrance effect on ion transmission, and the effect is more obvious particularly under a larger current multiplying power. On the other hand, the graphene has the problem of difficult lamellar dispersion in the electrode preparation process. In order to solve the above problems, the main solution at present is to "punch" a graphene sheet and form a nano-sized hole in the preparation process to reduce the diffusion distance of ions.
CN106848312A discloses modified porous graphene, a modified porous graphene negative electrode plate and a preparation method thereof. The modified porous graphene negative electrode material has the advantages of high coulombic efficiency, high multiplying power and the like by controlling parameters such as the specific surface area, the particle size, the pore size distribution, the surface functional group content and the like of the porous graphene. However, on one hand, the cost needs to be increased for preparing the porous graphene, and on the other hand, the existence of the pores can affect the electronic conductivity of the graphene and degrade the conductive effect of the graphene material.
In addition, conductive graphite, carbon black, or metal oxide is generally added to improve the conductive efficiency. The metal oxide and the graphene or the conductive carbon black are compounded to have a synergistic effect, so that the conductivity of the material can be improved.
CN109119634A discloses a conductive agent comprising graphene, conductive carbon black or conductive graphite, polyvinylidene fluoride and metal oxide. Has excellent cycle performance, rate capability and high temperature and low temperature resistance. However, the above methods cannot simultaneously solve the problems of weakening the steric hindrance effect of lithium ions of graphene and improving the conductivity.
Therefore, the application of the graphene material to the high-performance conductive agent market still has a great promotion space. There is a need to develop a high-performance graphene-based conductive agent, which can overcome the steric hindrance problem in graphene application and simultaneously has good electron transfer performance.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide a composite conductive agent, a preparation method thereof and an electrode material containing the composite conductive agent. According to the invention, the graphene and the carbon nano tube are bridged through chemical bonds, so that the electron transfer between the two conductive agents is effectively enhanced, the synergistic effect of the two conductive agents is fully exerted, and the surface contact between the conductive agent and active material particles and the long-range conductive capability of the conductive agent are considered; meanwhile, the composite conductive agent of the graphene and the carbon nano tube is adopted, so that the required amount of the graphene is effectively reduced, and the steric hindrance effect of the graphene on lithium ions is virtually reduced; in addition, compared with single graphene, carbon nanotubes or a mixture of the graphene and the carbon nanotubes, the composite conductive agent connected by chemical bonds has stronger dispersing capacity in the electrode, so that the contact area between the conductive agent and an electrode active material is increased, the electron transmission capacity is further improved, and the conductivity is enhanced.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a composite conductive agent, which includes graphene and carbon nanotubes, wherein the graphene and the carbon nanotubes are connected by a chemical bond.
According to the composite conductive agent, the graphene and the carbon nano tube are connected through chemical bonds instead of simple physical mixing of Van der Waals force combination, the combination of the graphene and the carbon nano tube is more stable, the electron transfer between the two conductive agents is enhanced, the surface contact with an active material and the long-range conductive capacity of the conductive agent are both considered, meanwhile, the composite conductive agent of the graphene and the carbon nano tube is adopted, the required amount of the graphene is effectively reduced, and the steric hindrance effect of the graphene on lithium ions is invisibly reduced; in addition, compared with single graphene, carbon nanotubes or a mixture of the graphene and the carbon nanotubes, the composite conductive agent connected by chemical bonds has stronger dispersing capacity in the electrode, so that the contact area between the conductive agent and an electrode active material is increased, the electron transmission capacity is further improved, and the conductivity is enhanced.
Preferably, the graphene has a single-layer or few-layer sheet structure, and has a diameter of 0.05-1 μm, and may be, for example, 0.05 μm, 0.06 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1 μm.
The term "few layers" as used in the present invention means that graphene is composed of 3 to 10 layers of carbon atom stacks that are periodically closely packed in a hexagonal honeycomb structure.
The diameter of the graphene is preferably 0.05-1 mu m, the graphene with the smaller diameter is selected to further reduce the steric hindrance effect of the graphene sheet layer on lithium ions, so that the resistivity is reduced, the remote electronic conductivity is increased by compounding with the carbon nano tube, and finally the composite conductive agent has excellent conductivity.
Preferably, the carbon nanotubes are single-walled or multi-walled carbon nanotubes, the diameter of the carbon nanotubes is 50-500nm, and may be, for example, 50nm, 60nm, 70nm, 90nm, 100nm, 120nm, 150nm, 200nm, 250nm, 300nm, 350nm, 380nm, 400nm, 450nm or 500nm, etc.; the length is 0.5 to 5 μm, and may be, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm.
The term "multi-walled" as used herein means that the carbon nanotubes are assembled from at least two layers of single-walled carbon nanotubes of different diameters, with a distance between the layers of about 0.34 nm.
Preferably, the graphene is nitrogen-doped graphene, and the carbon nanotube is a nitrogen-doped carbon nanotube.
Preferably, the mass ratio of the graphene to the carbon nanotubes is (3-19):1, for example, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1 or 19:1, preferably (7-11):1, and more preferably 9: 1.
It should be noted that, because the difference between the molecular weights of the graphene and the graphene oxide is not great, the mass ratio of the graphene to the carbon nanotube in the present invention is approximately equal to the mass ratio of the graphene oxide to the carbon nanotube in the preparation method according to the second aspect.
According to the invention, the graphene and the carbon nano tube are preferably of nitrogen-doped structures, which is beneficial to further improvement of electron transfer performance in the conductive agent; in addition, the mass ratio of the graphene to the carbon nanotubes is preferably controlled within the above range, because when the content of one of the graphene or the carbon nanotubes is too large, the graphene and the carbon nanotubes cannot be sufficiently bridged, which may cause non-uniform dispersion and reduced conductivity, and particularly, when the content of the graphene is too large, steric hindrance to lithium ions is increased, resistivity is increased, and transmission efficiency of the lithium ions is reduced, thereby reducing conductivity.
In a second aspect, the present invention provides a method for producing the composite conductive agent according to the first aspect, the method comprising: and mixing the graphene oxide dispersion liquid and the carbon oxide nanotube dispersion liquid, performing crosslinking treatment, and reducing to obtain the composite conductive agent.
According to the preparation method, the graphene and the carbon nano tube are connected through a chemical bond by crosslinking.
Preferably, the solvent of the graphene oxide dispersion liquid is selected from any one or a combination of at least two of tetrahydrofuran, dichloromethane or N, N-dimethylformamide, and is preferably tetrahydrofuran.
Preferably, the mass fraction of graphene oxide in the graphene oxide dispersion liquid is 0.1 to 3%, and may be, for example, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 2%, 2.2%, 2.5%, 2.8%, or 3%, preferably 0.2 to 1%, and more preferably 0.5%.
Preferably, the method for preparing the oxidized carbon nanotube dispersion liquid comprises: adding the carbon nano tube into an acid solution, oxidizing, filtering, washing and re-dispersing to obtain the carbon nano tube dispersion liquid.
Preferably, the acid solution is selected from any one of concentrated nitric acid, concentrated sulfuric acid, hypochlorous acid, chloric acid, perchloric acid or permanganic acid or a combination of at least two of the same.
Preferably, the temperature of the oxidation is 60 to 90 ℃, for example, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃ or 90 ℃, etc., preferably 70 to 80 ℃, and more preferably 75 ℃.
The oxidation time is preferably 0.5 to 12 hours, and may be, for example, 0.5 hour, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours, preferably 2 to 6 hours, and more preferably 4 hours.
Preferably, the number of washes is at least two, preferably three.
Preferably, the method of crosslinking treatment comprises: and adding the mixed solution of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide into the mixed solution of the graphene oxide dispersion liquid and the carbon oxide nanotube dispersion liquid for crosslinking treatment.
According to the invention, the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride and the N-hydroxysuccinimide are used for activating the graphene oxide and the carbon oxide nanotube to enable the graphene oxide and the carbon oxide nanotube to generate an esterification reaction, so that the graphene oxide and the carbon oxide nanotube are connected through ester bonds instead of simple physical mixing of Van der Waals force combination, and the combination of the graphene oxide and the carbon oxide nanotube is firmer. In addition, a nitrogen-containing functional group is formed in the composite conductive agent after the N-hydroxysuccinimide (NHS) treatment, and a nitrogen-doped structure is formed after the nitrogen-containing functional group is reduced by a reducing agent, so that the electron transfer performance in the composite conductive agent is further improved.
Preferably, the mass ratio of the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride to the N-hydroxysuccinimide is (0.8-1.2):1, for example, 0.8:1, 0.85:1, 0.9:1, 0.94:1, 1:1, 1.1:1, 1.5:1, 1.8:1 or 2:1, preferably (0.9-1.1):1, and more preferably 1: 1.
Preferably, the temperature of the crosslinking treatment is 60 to 150 ℃. For example, the temperature may be 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃ or 150 ℃.
Preferably, the time of the crosslinking treatment is 0.5 to 5 hours, and may be, for example, 0.5 hour, 1 hour, 1.5 hours, 1.8 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours or the like.
Preferably, the reduction method is reduction by using a reducing agent.
Preferably, the reducing agent comprises any one of hydrazine hydrate, sodium borohydride or hydrogen peroxide or a combination of at least two of the foregoing.
Preferably, the ratio of the mass of the reducing agent to the total mass of the graphene oxide and the carbon nanotubes is (2-8):1, and may be, for example, 2:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or the like.
Preferably, the preparation method further comprises: after the reduction, the resulting reduction product was centrifuged and dried.
Preferably, the centrifugation time is 2-60min, for example, 2min, 3min, 5min, 8min, 10min, 12min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, or 60min, etc., preferably 5-30min, and more preferably 20 min.
Preferably, the centrifuge used for the centrifugation has a rotation speed of 600-10000rmp, for example, 600rmp, 700rmp, 800rmp, 1000rmp, 1500rmp, 2000rmp, 2600rmp, 3000rmp, 3600rmp, 4000rmp, 4500rmp, 5000rmp, 6000rmp, 7000rmp, 8000rmp, 9000rmp or 10000rmp, preferably 2000-4000rmp, and more preferably 3000 rmp.
Preferably, the drying temperature is 70-120 ℃, for example, 70 ℃, 75, 80 ℃, 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃ or 120 ℃, preferably 80-110 ℃, more preferably 95 ℃.
Preferably, the drying time is 2 to 12 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, etc., preferably 4 to 8 hours, and more preferably 6 hours.
In a third aspect, the present invention also provides an electrode material comprising the composite conductive agent according to the first aspect.
Preferably, the amount of the composite conductive agent added to the electrode material is 1 to 10 wt%, and may be, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or the like.
According to the composite conductive agent, the graphene and the carbon nano tube are connected through the chemical bond, so that the conductivity is improved, the consumption of the conductive agent is reduced on the premise of achieving the same conductivity, and the compaction density of the battery pole piece is obviously improved.
In a fourth aspect, the present invention also provides a lithium ion battery comprising the electrode material according to the third aspect.
Compared with the prior art, the invention has the following beneficial effects:
(1) according to the composite conductive agent, the graphene and the carbon nano tube are bridged through chemical bonds, so that the electron transfer between the two conductive agents is effectively enhanced, the synergistic effect of the graphene and the carbon nano tube is fully exerted, the surface contact between the conductive agent and active material particles and the long-range conductive capacity of the conductive agent are considered, meanwhile, the composite conductive agent of the graphene and the carbon nano tube is adopted, the required amount of the graphene is effectively reduced, and the steric hindrance effect of the graphene on lithium ions is invisibly reduced; in addition, compared with single graphene, carbon nanotubes or a mixture of the graphene and the carbon nanotubes, the composite conductive agent connected by chemical bonds has stronger dispersing capacity in an electrode, the contact area of the conductive agent and an electrode active material is increased, the electron transmission capacity is further improved, the conductivity is enhanced, the conductivity of a pole piece containing the composite conductive agent can reach up to 1.1S/cm, the internal resistance of a battery containing the composite conductive agent is as low as 20 omega, and the conductive capacity is obviously enhanced;
(2) the preparation method is simple and easy to operate, the graphene and the carbon nano tube are connected through chemical bonds by crosslinking, and meanwhile, the composite conductive agent is doped with nitrogen atoms by processing of NHS (polyethylene glycol succinate), so that the electron transfer rate in the electrode can be effectively improved after the composite conductive agent is added into the electrode, and the conductivity is further enhanced;
(3) compared with the composite conductive agent consisting of the carbon nano tube and the graphene which are not bridged by chemical bonds, the composite conductive agent has the same conductive capability by only adding a small amount of the composite conductive agent, namely the required amount of the conductive agent is reduced, and the compaction density of the battery pole piece is obviously improved.
Drawings
Fig. 1 is a fourier transform infrared spectrum of the composite conductive agent obtained in example 1.
FIG. 2 is an X-ray photoelectron spectrum of the composite conductive agent obtained in example 1.
Detailed Description
The present invention is described in further detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.
Example 1
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent in the embodiment is as follows:
(1) dispersing 9g of graphene oxide in 1.8kg of tetrahydrofuran to obtain a graphene oxide dispersion liquid, wherein the diameter of the graphene oxide is 0.05 μm.
(2) Adding 1g of carbon nano tube into 20mL of concentrated nitric acid, heating and refluxing for 4h at 75 ℃, cooling, filtering, washing twice with deionized water, centrifuging, drying for 6h at 80 ℃, and re-dispersing in tetrahydrofuran to obtain an oxidized carbon nano tube dispersion liquid, wherein the diameter of the carbon nano tube is 50nm, and the length of the carbon nano tube is 5 mu m.
(3) And (2) mixing the graphene oxide dispersion liquid obtained in the step (1) and the carbon oxide nanotube dispersion liquid obtained in the step (2), adding a mixed solution of 0.1g of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) and 0.1g of N-hydroxysuccinimide (NHS), reacting for 4 hours at the temperature of 75 ℃, and carrying out esterification reaction on graphene oxide and the carbon oxide nanotube. The reaction product was centrifuged, washed three times with ethanol and redispersed to form an ethanol dispersion. 40g of sodium borohydride was added to the dispersion and heated under reflux at 70 ℃ for 2 h. And then washing the mixture for 2 times by using water, filtering the mixture, and drying the mixture for 6 hours at 95 ℃ to obtain the composite conductive agent.
The molecular structure of the composite conductive agent obtained in example 1 was characterized by fourier transform-fourier infrared spectroscopy and X-ray photoelectron spectroscopy, and the spectra thereof are shown in fig. 1 and 2.
As can be seen from FIG. 1, 1170cm-1The infrared absorption peak of (1) is the absorption peak of a saturated ester bond, 1250cm-1The infrared absorption peak of (A) is C-N bond stretching vibration absorption peak, 1740cm-1The infrared absorption peak is C ═ N double bond stretching vibration absorption peak;
as can be seen from FIG. 2, the XPS spectrum has a distinct signal peak of nitrogen, and the nitrogen is divided into pyrrole nitrogen, pyrimidine nitrogen and graphite nitrogen.
As can be seen from fig. 1 and 2, graphene and carbon nanotubes in the composite conductive agent are bridged by ester bonds, and a C — N bond exists in the molecular structure of the composite conductive agent, that is, a nitrogen-doped structure is formed in the composite conductive agent, and nitrogen doping can improve the carrier concentration of graphene and is also beneficial to further improving the electron transfer property.
Example 2
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent in the embodiment is as follows:
(1) dispersing 5g of graphene oxide in 1.5kg of tetrahydrofuran to obtain a graphene oxide dispersion liquid, wherein the diameter of the graphene oxide is 0.5 mu m.
(2) Adding 1g of carbon nano tube into 20mL of concentrated nitric acid, heating and refluxing for 0.5h at 90 ℃, cooling, filtering, washing twice with deionized water, centrifuging, drying for 6h at 80 ℃, and re-dispersing in tetrahydrofuran to obtain the oxidized carbon nano tube dispersion liquid, wherein the diameter of the carbon nano tube is 500nm, and the length of the carbon nano tube is 0.5 mu m.
(3) And (2) mixing the graphene oxide dispersion liquid obtained in the step (1) and the carbon oxide nanotube dispersion liquid obtained in the step (2), adding a mixed solution of 0.1g of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) and 0.1g of N-hydroxysuccinimide (NHS), and reacting at the temperature of 60 ℃ for 5 hours to perform esterification reaction on the graphene oxide and the carbon oxide nanotube. The reaction product was centrifuged, washed three times with ethanol and redispersed to form an ethanol dispersion. 24g of sodium borohydride was added to the dispersion and heated under reflux at 70 ℃ for 3 hours. And then washing with water for 2 times, filtering, and drying at 120 ℃ for 2 hours to obtain the composite conductive agent.
Example 3
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent in the embodiment is as follows:
(1) dispersing 15g of graphene oxide in 2kg of tetrahydrofuran to obtain a graphene oxide dispersion liquid, wherein the diameter of the graphene oxide is 1 μm.
(2) Adding 1g of carbon nano tube into 20mL of concentrated nitric acid, heating and refluxing for 12h at 60 ℃, cooling, filtering, washing twice with deionized water, centrifuging, drying for 2h at 120 ℃, and re-dispersing in tetrahydrofuran to obtain an oxidized carbon nano tube dispersion liquid, wherein the diameter of the carbon nano tube is 100nm, and the length of the carbon nano tube is 1 mu m.
(3) And (2) mixing the graphene oxide dispersion liquid obtained in the step (1) and the carbon oxide nanotube dispersion liquid obtained in the step (2), adding a mixed solution of 0.1g of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) and 0.1g of N-hydroxysuccinimide (NHS), and reacting at the temperature of 150 ℃ for 0.5h to perform esterification reaction on the graphene oxide and the carbon oxide nanotube. The reaction product was centrifuged, washed three times with ethanol and redispersed to form an ethanol dispersion. 64g of sodium borohydride was added to the dispersion, and the mixture was heated under reflux at 70 ℃ for 3 hours. And then washing with water for 2 times, filtering, and drying at 120 ℃ for 2 hours to obtain the composite conductive agent.
Example 4
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent in the embodiment is as follows:
(1) dispersing 17g of graphene oxide in 2.3kg of tetrahydrofuran to obtain a graphene oxide dispersion liquid, wherein the diameter of the graphene oxide is 0.3 μm.
(2) Adding 1g of carbon nano tube into 20mL of concentrated nitric acid, heating and refluxing for 3h at 80 ℃, cooling, filtering, washing twice with deionized water, centrifuging, drying for 6h at 85 ℃, and re-dispersing in tetrahydrofuran to obtain an oxidized carbon nano tube dispersion liquid, wherein the diameter of the carbon nano tube is 200nm, and the length of the carbon nano tube is 1.5 mu m.
(3) And (2) mixing the graphene oxide dispersion liquid obtained in the step (1) and the carbon oxide nanotube dispersion liquid obtained in the step (2), adding a mixed solution of 0.1g of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) and 0.1g of N-hydroxysuccinimide (NHS), reacting for 3 hours at the temperature of 120 ℃, and carrying out esterification reaction on graphene oxide and the carbon oxide nanotube. The reaction product was centrifuged, washed three times with ethanol and redispersed to form an ethanol dispersion. 72g of sodium borohydride was added to the dispersion, and the mixture was heated under reflux at 70 ℃ for 3 hours. And then washing the mixture for 2 times by using water, filtering the mixture, and drying the mixture for 10 hours at the temperature of 75 ℃ to obtain the composite conductive agent.
Example 5
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the mass of graphene oxide was 9.5g, and the mass of carbon nanotubes was 0.5 g.
Example 6
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the mass of the graphene oxide was 7.5g, and the mass of the carbon nanotube was 2.5 g.
Example 7
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the mass ratio of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) to N-hydroxysuccinimide (NHS) was 1.2:1, and the total mass was 0.2 g.
Example 8
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from the embodiment only in that: the mass ratio of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) to N-hydroxysuccinimide (NHS) was 0.8:1, and the total mass was 0.2 g.
Example 9
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from the embodiment only in that: the mass ratio of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) to N-hydroxysuccinimide (NHS) was 1:1, and the total mass was 0.2 g.
Example 10
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the mass ratio of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) to N-hydroxysuccinimide (NHS) was 1:1, and the total mass was 1 g.
Example 11
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the mass ratio of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) to N-hydroxysuccinimide (NHS) was 1:1, and the total mass was 0.02 g.
Example 12
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the mass of graphene oxide was 9.6g, and the mass of carbon nanotubes was 0.4 g.
Example 13
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the mass of the graphene oxide was 6.7g, and the mass of the carbon nanotube was 3.3 g.
Example 14
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the diameter of the graphene oxide was 0.02 μm.
Example 15
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the diameter of the graphene oxide was 2 μm.
Example 16
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the carbon nanotubes have a diameter of 20nm and a length of 6 μm.
Example 17
The embodiment provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the embodiment is different from that of the embodiment 1 only in that: the carbon nanotubes had a diameter of 700nm and a length of 0.3. mu.m.
Comparative example 1
The comparative example provides a composite conductive agent and a preparation method thereof
The preparation method of the composite conductive agent of the present comparative example is different from that of example 1 only in that: replacing step (3) with step (3'), step (3') comprising: and (3) mixing the graphene oxide dispersion liquid obtained in the step (1) and the carbon oxide nanotube dispersion liquid obtained in the step (2), centrifugally separating the mixture, washing the mixture with ethanol for three times, and dispersing the mixture to form an ethanol dispersion liquid. 40g of sodium borohydride was added to the dispersion and heated under reflux at 70 ℃ for 2 h. And then washing the mixture for 2 times by using water, filtering the mixture, and drying the mixture for 6 hours at 95 ℃ to obtain the composite conductive agent.
Performance testing
(1) Preparing an electrode for testing:
mixing lithium iron phosphate, the composite conductive agent provided in the examples and the comparative examples and a PVDF adhesive according to the mass ratio of 0.9:0.5:0.5, adding N-methyl pyrrolidone (NMP), preparing slurry, and coating the slurry to form an electrode, wherein the mass surface density of the electrode is 2g/cm2And the coating thickness is 150um, the pole piece is rolled after being dried, and the thickness of the compressed pole piece is reduced to 60% of the thickness before compression. And (3) testing the conductivity of the pole piece, assembling the pole piece, a diaphragm (the diaphragm is 2320, the thickness is 20 microns, and the diaphragm is purchased from American celgard company) and a lithium piece into a simulation battery, and testing the internal resistance of the battery.
The electrical conductivity and the internal cell resistance of the obtained electrode sheet are shown in table 1.
TABLE 1
As can be seen from the examples and performance tests, the conductivity of the electrode plate made of the composite conductive agent prepared in the examples 1-9 of the invention can reach more than 0.7S/cm, and the internal resistance of the lithium ion battery made of the electrode plate can be as low as 20 omega. Therefore, compared with the electrode plates prepared by adopting the composite conductive agent provided by the comparative examples 1 and 2, the conductivity of the electrode plate added with the composite conductive agent is obviously improved, because the graphene and the carbon nano tubes in the composite conductive agent are bridged by chemical bonds, the electron transfer between the two conductive agents is effectively enhanced, the surface contact between the conductive agent and active material particles and the long-range conductive capacity of the conductive agent are considered, a stable conductive network structure is formed in the electrode plate, the conductivity is improved, and meanwhile, the composite conductive agent of the graphene and the carbon nano tubes is adopted, the required amount of the graphene is effectively reduced, so that the steric hindrance effect on lithium ions is reduced; in addition, compared with single graphene, carbon nanotubes or a mixture of the graphene and the carbon nanotubes, the composite conductive agent connected by chemical bonds has stronger dispersing capacity in the electrode, so that the contact area between the conductive agent and an electrode active material is increased, the electron transmission capacity is further improved, and the conductivity is enhanced.
Compared with example 1, the composite conductive agent of comparative example 1 has no EDC and NHS treatment, the conductivity of the electrode plate is only 0.4S/cm, which is far lower than that of the electrode plate containing the composite conductive agent which is subjected to EDC and NHS activation treatment, the conductivity is reduced, in addition, the resistivity of the battery containing the composite conductive agent of comparative example 1 is as high as 78 omega, the resistance is increased, the electron transmission efficiency is reduced, and the conductivity is deteriorated. This is because the graphene oxide and the carbon nanotube oxide are activated by EDC and NHS, and the graphene oxide and the carbon nanotube oxide are bridged by a chemical bond, thereby improving the conductivity thereof.
Compared with examples 12 to 13, in examples 1 and 5 to 6, when the mass ratio of the graphene oxide to the carbon nanotubes is controlled to be (3-19):1, the obtained composite conductive agent has obviously higher conductivity after being applied to an electrode pole piece. This is because when the content of the graphene oxide or the carbon nanotube is increased, the graphene and the carbon nanotube cannot be sufficiently bridged, which may cause non-uniform dispersion and reduced conductivity, and particularly when the content of the graphene is increased, steric hindrance to lithium ions is increased, resistivity is increased, transmission efficiency of the lithium ions is reduced, and conductivity is further reduced. .
Comparative examples 7 to 9 show that when the mass ratio of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) to N-hydroxysuccinimide (NHS) is 1:1, the conductivity of the composite conductive agent after activation treatment is the best, since the amount of activated functional groups formed on the surfaces of graphene and carbon nanotubes is matched, and complete bridging reaction can be performed.
Comparative examples 9 to 11 show that, when the mass ratio of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) to N-hydroxysuccinimide (NHS) is constant, the greater the total mass, the greater the activation treatment effect, because the more abundant the bridging between graphene and carbon nanotubes and the higher the conductivity between them, and when the both are excessive, the excessive functional groups are formed on the surfaces of graphene and carbon nanotubes, which adversely affects the intrinsic conductivity of graphene and carbon nanotubes.
Compared with example 1, in examples 14 and 15, when the diameter of graphene exceeds 0.05-1 μm, the conductivity of the electrode sheet comprising the composite conductive agent is significantly reduced. This is because when the diameter of graphene is too small, it may cause non-uniform dispersion in the electrode material, decrease the contact area with the active material, and decrease the conductivity, while when the diameter of graphene is too large, steric hindrance in lithium ion transport may increase, increase the resistivity, and decrease the conductivity.
Compared with example 1, in examples 16 and 17, when the diameter of the carbon nanotube exceeds 50-500nm and the length exceeds 0.5-5 μm, namely the aspect ratio of the carbon nanotube is too large or too small, the conductivity of the electrode sheet containing the composite conductive agent is obviously reduced. This is because when the aspect ratio of the carbon nanotube is too small, the long-range conductivity between the active material particles cannot be effectively increased, and when the aspect ratio of the carbon nanotube is too large, the contact area with the active material in the electrode is reduced, and the conductivity is lowered.
Therefore, the diameter of the graphene and the length-diameter ratio of the carbon nano tube are optimized, so that the composite conductive agent forms a developed conductive network in the electrode plate, the surface contact with the active material and the long-range conductive capacity of the conductive agent are considered, the conductivity of the electrode plate is obviously improved, and the internal resistance of the battery is reduced.
The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (44)
1. The composite conductive agent is characterized by comprising graphene and carbon nanotubes, wherein the graphene and the carbon nanotubes are connected by chemical bonds through cross-linking treatment;
the graphene is of a single-layer or few-layer sheet structure, and the diameter of the graphene is 0.05-1 mu m;
the carbon nano tube is a single-wall or multi-wall carbon nano tube, the diameter of the carbon nano tube is 50-500nm, and the length of the carbon nano tube is 0.5-5 mu m;
the mass ratio of the graphene to the carbon nano tubes is (3-19) to 1;
the cross-linking agent for cross-linking treatment is 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in a mass ratio of (0.8-1.2) to 1.
2. The composite conductive agent according to claim 1, wherein the graphene is nitrogen-doped graphene, and the carbon nanotubes are nitrogen-doped carbon nanotubes.
3. The composite conductive agent according to claim 1, wherein the mass ratio of graphene to carbon nanotubes is (7-11): 1.
4. The composite conductive agent according to claim 1, wherein the mass ratio of graphene to carbon nanotubes is 9: 1.
5. A method for producing the composite conductive agent according to any one of claims 1 to 4, characterized by comprising: and mixing the graphene oxide dispersion liquid and the carbon oxide nanotube dispersion liquid, performing crosslinking treatment, and reducing to obtain the composite conductive agent.
6. The method according to claim 5, wherein the solvent of the graphene oxide dispersion is selected from tetrahydrofuran, dichloromethane orN,N-dimethylformamide, either alone or in combination of at least two.
7. The production method according to claim 5, wherein the mass fraction of graphene oxide in the graphene oxide dispersion liquid is 0.1 to 3%.
8. The production method according to claim 5, wherein the mass fraction of graphene oxide in the graphene oxide dispersion liquid is 0.2 to 1%.
9. The production method according to claim 5, wherein the mass fraction of graphene oxide in the graphene oxide dispersion liquid is 0.5%.
10. The method according to claim 5, wherein the method for preparing the oxidized carbon nanotube dispersion liquid comprises: and adding the carbon nano tube into an acid solution, oxidizing, filtering, washing and re-dispersing to obtain the oxidized carbon nano tube dispersion liquid.
11. The method according to claim 10, wherein the acid solution is selected from any one of concentrated nitric acid, concentrated sulfuric acid, hypochlorous acid, chloric acid, perchloric acid, or permanganic acid, or a combination of at least two thereof.
12. The method of claim 10, wherein the temperature of the oxidation is 60 to 90 ℃.
13. The method of claim 10, wherein the temperature of the oxidation is 70 to 80 ℃.
14. The method of claim 10, wherein the temperature of the oxidation is 75 ℃.
15. The method according to claim 10, wherein the oxidation time is 0.5 to 12 hours.
16. The method of claim 10, wherein the oxidation time is 2-6 hours.
17. The method according to claim 10, wherein the oxidation time is 4 hours.
18. The production method according to claim 10, wherein the number of washing is at least two.
19. The production method according to claim 10, wherein the number of washing is three.
20. The production method according to claim 5, wherein the crosslinking treatment method comprises: 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride andNadding the mixed solution of the-hydroxysuccinimide into the mixed solution of the graphene oxide dispersion liquid and the carbon oxide nanotube dispersion liquid, and performing crosslinking treatment.
21. The method of claim 20, wherein the 1- (3-dimethylaminopropyl) -3-ethyl group is present in a liquid formCarbodiimide hydrochloride andNthe mass ratio of hydroxysuccinimide is (0.8-1.2): 1.
22. The method of claim 20, wherein the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride salt is selected from the group consisting ofNThe mass ratio of hydroxysuccinimide is (0.9-1.1): 1.
23. The method of claim 20, wherein the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride salt is selected from the group consisting ofNThe mass ratio of the-hydroxysuccinimide is 1: 1.
24. The production method according to claim 20, wherein the temperature of the crosslinking treatment is 60 to 150 ℃.
25. The method according to claim 20, wherein the time for the crosslinking treatment is 0.5 to 5 hours.
26. The method of claim 20, wherein the reduction is carried out with a reducing agent.
27. The method of claim 26, wherein the reducing agent comprises any one of hydrazine hydrate, sodium borohydride or hydrogen peroxide or a combination of at least two of the foregoing.
28. The method according to claim 26, wherein a ratio of a mass of the reducing agent to a total mass of the graphene oxide and the carbon nanotube is (2-8): 1.
29. The method of manufacturing according to claim 5, further comprising: after the reduction, the resulting reduction product was centrifuged and dried.
30. The method of claim 29, wherein the centrifugation time is 2-60 min.
31. The method of claim 29, wherein the centrifugation time is 5-30 min.
32. The method of claim 29, wherein the centrifugation time is 20 min.
33. The method as claimed in claim 29, wherein the centrifuge is operated at a rotation speed of 600-10000 rmp.
34. The method as claimed in claim 29, wherein the centrifuge is operated at 2000-4000 rmp.
35. The method of claim 29, wherein the centrifugation is performed at a centrifuge speed of 3000 rmp.
36. The method of claim 29, wherein the drying temperature is 70-120 ℃.
37. The method of claim 29, wherein the drying temperature is 80-110 ℃.
38. The method of claim 29, wherein the drying temperature is 95 ℃.
39. The method of claim 29, wherein the drying time is 2-12 hours.
40. The method of claim 29, wherein the drying time is 4-8 hours.
41. The method of claim 29, wherein the drying time is 6 hours.
42. An electrode material comprising the composite conductive agent according to any one of claims 1 to 4.
43. The electrode material as claimed in claim 42, wherein the composite conductive agent is added to the electrode material in an amount of 1 to 10 wt%.
44. A lithium-ion battery comprising the electrode material of claim 42.
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