CN114267493B - Nitrogen-doped graphene-based aqueous conductive paste and preparation method and application thereof - Google Patents
Nitrogen-doped graphene-based aqueous conductive paste and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a preparation method of a nitrogen-doped graphene-based aqueous conductive paste, which comprises the following steps: preparing nano mesoporous spheres, preparing modified graphene fibers and preparing nitrogen-doped graphene-based aqueous conductive slurry. According to the invention, the nano mesoporous spheres, the Mxene, the nitrogen doped graphene and the CNTs are fixed on loose porous grid fibers together in a spinning fiber mode, so that an efficient conductive fiber net structure is prepared, and an electrode conductive frame is formed. After the conductive agent is coated on the electrode for forming, the grid fibers and the nano mesoporous spheres are of porous structures, so that the porous structure has a good buffering effect, stress caused by volume change can be effectively buffered, deformation, cracks and the like of the conductive agent or the electrode are prevented, lithium ions can be conveniently and rapidly passed, and the multiplying power performance and the cycling stability of the battery are improved. The invention also provides the water-based conductive paste based on the nitrogen doped graphene and application thereof.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a nitrogen-doped graphene-based aqueous conductive paste, and a preparation method and application thereof.
Background
Lithium ion batteries are widely used as main power sources for mobile phones, tablet computers, notebook computers and other portable electronic products due to the advantages of relatively high energy density, relatively long cycle life and the like, and are increasingly being used as power sources for hybrid electric vehicles, electric vehicles and electric non-motor vehicles. The lithium ion battery mainly comprises a positive electrode, a negative electrode, a diaphragm and electrolyte. When the battery is connected through an external circuit, chemical reactions are performed on the electrodes due to the difference of lithium chemical potentials of the positive electrode and the negative electrode, and electrons form current through the external circuit along with the transfer process of lithium ions inside the battery.
Because of the general poor conductivity of positive and negative electrode materials of lithium ion batteries, common solutions include adding a conductive agent to the electrode to enhance the electron transport efficiency of the electrode, thereby reducing the adverse effect of electrode polarization on the active material's effective capacity. Compared with common conductive agents such as conductive graphite, carbon black and the like, graphene has more excellent conductive performance and higher specific surface area, and a conductive effect which is difficult to reach by the conventional conductive agent can be achieved by a smaller amount of graphene, so that new materials with great potential of the graphene as the electrode conductive agent in the future are widely studied. However, the hydrophilicity of graphene is limited, the concentration of graphene in the aqueous conductive paste is easy to cause agglomeration, and the graphene is separated from an electrode due to the volume change of an active material in the charge-discharge process, so that the conductivity, the battery cycle stability and the like of the aqueous conductive paste are greatly reduced, and the expectation is difficult to achieve. In addition, the planar structure of the graphene can prevent the diffusion of lithium ions to a certain extent and prolong the diffusion path of the lithium ions, so that the graphene aqueous conductive paste can be coated on the electrode only in a thin layer form, the risk of falling off of the conductive agent is increased, and the preparation process of the electrode is increased.
Disclosure of Invention
In view of the above, the invention provides a preparation method of a nitrogen-doped graphene-based aqueous conductive paste, and also provides a nitrogen-doped graphene-based aqueous conductive paste prepared by the preparation method of the nitrogen-doped graphene-based aqueous conductive paste and application thereof, so as to solve the problems of poor stability, easy electrode falling off due to volume change in the charging and discharging process, and obstruction of lithium ions by a complex conductive network and the like of the existing conductive agent.
In a first aspect, the invention provides a preparation method of an aqueous conductive paste based on nitrogen doped graphene, which comprises the following steps:
preparing nano mesoporous spheres: providing a weak alkali aqueous solution with the mass fraction of 5-10%, a phenolic resin precursor, a silicon dioxide precursor and a guiding agent, wherein the volume of the phenolic resin precursor is not more than 10% of the volume of the weak alkali aqueous solution, firstly adding the silicon dioxide precursor and the guiding agent into the weak alkali aqueous solution, performing primary ultrasonic treatment for 5-30 s, then dripping the phenolic resin precursor into the weak alkali aqueous solution, continuing the primary ultrasonic treatment, removing silicon dioxide after reacting for 10-60 min at 30-60 ℃, centrifuging and collecting precipitate, and drying and carbonizing the precipitate to obtain the nano mesoporous spheres;
preparing modified graphene fibers: providing and uniformly mixing N-methyl pyrrolidone and nano mesoporous spheres, wherein the mass ratio of the N-methyl pyrrolidone to the nano mesoporous spheres is 100:2-10, sequentially adding Mxene, nitrogen-doped graphene and CNTs into the N-methyl pyrrolidone, wherein the mass ratio of the nano mesoporous spheres, the Mxene, the nitrogen-doped graphene and the CNTs is 100:1-5:5-20:5-20, carrying out secondary ultrasonic on the N-methyl pyrrolidone while adding the Mxene, the CNTs and the nitrogen-doped graphene, adding a fiber-forming polymer into the N-methyl pyrrolidone after the ultrasonic treatment is finished, transferring the fiber-forming polymer into an oil bath pot at 120-126 ℃, stirring uniformly, and then taking the mixed solution as spinning stock solution, and carrying out electrostatic spinning, collecting and shearing by using a spinning needle with the inner diameter being enlarged along the filament outlet direction to prepare the modified graphene fiber with the length of 0.2-10 mm;
preparing an aqueous conductive paste based on nitrogen doped graphene: providing modified graphene fibers, conductive graphite, a water-based dispersing agent and deionized water, uniformly mixing the modified graphene fibers, the conductive graphite and the water-based dispersing agent to form primary slurry, wherein the mass ratio of the modified graphene fibers to the conductive graphite to the water-based dispersing agent is 50-100:2-5:0.2-2, transferring the primary slurry to a ball mill, and ball milling for 5-20 min to obtain the water-based conductive slurry based on nitrogen-doped graphene;
the Mxene is Ti 3 C 2 Or Ti 2 C。
The preparation method of the nitrogen-doped graphene-based aqueous conductive paste comprises the following steps: a step of preparing nano mesoporous spheres, a step of preparing modified graphene fibers and a step of preparing nitrogen-doped graphene-based aqueous conductive paste. In the step of preparing the nano mesoporous spheres, firstly, a silicon dioxide precursor and a guiding agent are added into a weak base aqueous solution, and primary ultrasonic treatment is carried out, so that the silicon dioxide precursor undergoes hydrolysis polymerization reaction under the catalysis of the weak base aqueous solution to form silicon dioxide nano particles, and the generated silicon dioxide nano particles are prevented from agglomerating by means of primary ultrasonic treatment. After short primary ultrasonic treatment, rapidly dripping a phenolic resin precursor into a weak base aqueous solution, continuing the primary ultrasonic treatment, reacting for 10-60 min at 30-60 ℃, polymerizing the phenolic resin precursor under the catalysis of an alkaline solution to generate phenolic resin chains, and embedding the phenolic resin chains generated after the catalysis of the alkaline solution on the silica nanoparticles by taking the silica nanoparticles as a pore-forming agent by virtue of the action of a guiding agent, thereby preparing the silica/phenolic resin core-shell composite structure similar to a rambutan shape. After the reaction, collecting the precipitate by a centrifugal way, and then obtaining mesoporous resin nanospheres through a silicon dioxide removal step, wherein the mesoporous resin nanospheres are prepared into nano mesoporous spheres through a high-temperature carbonization process, the nano mesoporous spheres are made of carbon materials and have good conductivity, meanwhile, due to the step of removing silicon dioxide nanoparticle cores and the high-temperature carbonization process, the nano mesoporous spheres form a hollow structure and a large number of surface gaps, so that the subsequent embedding of Mxene, nitrogen-doped graphene and CNTs (carbon nanotubes) is facilitated, the effects of stabilizing the Mxene, the nitrogen-doped graphene and the CNTs are achieved, and meanwhile, the three-dimensional conductive framework is also facilitated to be constructed, and the overall conductivity is improved.
In the step of preparing the modified graphene fiber, the nano mesoporous spheres, mxene, nitrogen doped graphene and CNTs are added into N-methylpyrrolidone, and secondary ultrasound is performed on the mixed system. Mxene and nitrogen-doped graphene are firstly added into N-methylpyrrolidone, wherein Mxene is a two-dimensional material with excellent conductive performance, nitrogen-doped graphene is also a modified graphene material with quite hydrophilic property, and by means of the effect of ultrasonic dispersion, mxene and nitrogen-doped graphene are preferentially mixed with nano mesoporous spheres and are embedded into the nano mesoporous spheres, so that a conductive framework taking the nano mesoporous spheres as conductive units is constructed. Compared with graphene, the nitrogen-doped graphene has better hydrophilicity, the hydrophobic end of the nitrogen-doped graphene tends to be embedded into the nano mesoporous sphere, the hydrophilic end of the nitrogen-doped graphene tends to be exposed out of the nano mesoporous sphere, and the structure can also play a role in promoting stable dispersion of the nano mesoporous sphere. The Mxene is adsorbed on the surface of the nitrogen-doped graphene, and electrons can be rapidly transferred between the nitrogen-doped graphene and the Mxene two-dimensional materials by constructing a conductive network formed by mutually doping the Mxene and the nitrogen-doped graphene, so that the conductivity of the nitrogen-doped graphene is obviously improved, and the specific capacity of the battery under the high-rate discharge condition is improved. And then CNTs are added into the mixed system, the CNTs have smaller volume compared with the nitrogen-doped graphene, and the CNTs can be further embedded into the nano mesoporous spheres and the nitrogen-doped graphene by means of the effect of ultrasonic dispersion so as to enhance the conductivity of the nano mesoporous spheres serving as conductive units, and the nano mesoporous spheres play a role in maintaining the dispersion of the CNTs. Finally, the conductive structure is made by means of a spinning process: the nano mesoporous spheres, the Mxene, the nitrogen doped graphene and the CNTs are fixed on loose porous grid fibers together to prepare the efficient conductive fibers. The conductive components are distributed on the grid fibers, so that the grid fibers have a good fixing effect, and the conductive agent can be effectively prevented from falling off, so that the phenomenon that newly exposed conductive units (nano mesoporous spheres, nitrogen doped graphene and CNTs) react with electrolyte to consume reversible capacity is avoided. On the other hand, after the conductive agent is coated on the electrode for forming, the volume change is easy to cause in the electrode charging and discharging process, and the grid fibers and the nano mesoporous spheres are of porous structures, so that the porous structure has a good buffering effect, can effectively buffer the stress caused by the volume change, prevent the conductive agent from falling off or electrode deformation, cracks and the like, also facilitate quick passing of lithium ions, and improve the multiplying power performance and the cycling stability of the battery.
And (3) preparing the nitrogen-doped graphene-based aqueous conductive slurry, namely uniformly mixing the modified graphene fibers, the conductive graphite, the aqueous dispersing agent and deionized water to form primary slurry, and then transferring the primary slurry to a ball mill for ball milling, so that the uniform dispersion and uniform electrical conduction of the modified graphene fibers and the conductive graphite are further promoted, and the stability and durability of the overall conductive performance of the nitrogen-doped graphene-based aqueous conductive slurry are improved.
Preferably, in the step of preparing the nano mesoporous spheres, the weak alkali aqueous solution is ammonia water or sodium carbonate aqueous solution, the phenolic resin precursor comprises phenols and aldehydes, the phenols are phenol or aminophenol, the aldehydes are formaldehyde or acetaldehyde, the silica precursor is tetraethyl orthosilicate, tetramethyl orthosilicate or sodium silicate, and the guiding agent is ethylenediamine;
the mass ratio of the phenols, the aldehydes, the silicon dioxide precursor and the ethylenediamine is 500-1000:10-100:50-100:1-5. Therefore, the silica nanoparticles are generated by means of the silica precursor and used as pore-forming agents, the phenolic resin precursor is used for generating phenolic resin chains and embedding the silica nanoparticles, the guiding agent can promote the combination of the phenolic resin chains and the silica nanoparticles, the efficient embedding of the phenolic resin chains into the silica nanoparticles is ensured by proper mass ratio, and the prepared phenolic resin chains and the silica nanoparticles reach nanoscale dimensions and are uniformly dispersed, so that agglomeration is avoided.
Preferably, in the step of preparing the nano mesoporous spheres, the specific operation of removing the silicon dioxide is as follows: centrifugally collecting the precipitate, adding the precipitate into a strong alkali solution, stirring and uniformly mixing to promote dissolution of silicon dioxide, centrifugally collecting the precipitate, and repeating the dissolution and centrifugation processes for 1-3 times;
the strong alkali solution is sodium hydroxide or potassium hydroxide solution with the concentration of 1-5 mol/L, the centrifugal speed is 8000-12000 rpm, and the centrifugal time is 5-10 min. The silica nano particles are dissolved by the alkali solution, so that the phenolic resin is promoted to form hollow nano mesoporous spheres, and the nano mesoporous spheres are further separated by means of a centrifugal process.
Preferably, in the step of preparing the nano mesoporous spheres, the specific operation of carbonization is as follows: placing the precipitate in a tube furnace, heating to 1000-1200 ℃ under protective gas, and maintaining 1-3 h, wherein the protective gas is N 2 Or Ar. Under the high-temperature protective environment, the nano mesoporous spheres are fully carbonized to form mesoporous carbon microspheres, the carbonized mesoporous spheres can improve the conductivity, and simultaneously the carbonization process can promote the surface to form a void structure, thereby being beneficial to doping with nitrogen-doped graphene and CNTs in the later period.
Preferably, the sediment is carbonized and then transferred into a microwave digestion instrument for microwave digestion for 5-15 min, the temperature of microwave digestion is 65-70 ℃, and the power is 280-330W. The microwave digestion process can effectively promote the carbonized nano mesoporous spheres to be dispersed into micro powder, and simultaneously effectively maintain the microstructure of the mesoporous spheres to prevent pore canal collapse.
Preferably, in the step of preparing the modified graphene fiber, the content of N in the nitrogen-doped graphene is 10% -25%, and the thickness of the nitrogen-doped graphene is not more than 10 nm;
the fiber-forming polymer is PI powder or PAN powder, and the mass fraction of the fiber-forming polymer in the spinning solution is 5% -8%. The proper N content and thickness in the nitrogen-doped graphene can have the effect of improving the hydrophilicity, stability and ion trafficability, and then the conductive components (mesoporous spheres, nitrogen-doped graphene and CNTs) and the fiber-forming polymer with lower content are mixed and spun to form the porous fiber structure.
Preferably, in the step of preparing the modified graphene fiber, the nitrogen-doped graphene is pre-puffed at a high temperature, and the specific high-temperature puffing step is as follows: transferring the nitrogen-doped graphene to a tube furnace for high-temperature puffing for 30-90 s, filling inert gas into the tube furnace, wherein the temperature of the tube furnace is 600-800 ℃. The distance between the nitrogen-doped graphene layers can be effectively pulled through the high-temperature expansion process of the nitrogen-doped graphene, the surface area of the nitrogen-doped graphene is increased, the crenellated structure of the few-layer nitrogen-doped graphene layer is formed, and the subsequent penetration of CNTs into a conductive network and the passage of lithium ions are facilitated.
Preferably, the aqueous dispersing agent is any one of PVP (polyvinylpyrrolidone), SLS (sodium lignin sulfonate) or CMC (sodium carboxymethyl cellulose), and the mass fraction of the modified graphene fiber in the nitrogen-doped graphene-based aqueous conductive paste is 1% -5%. The aqueous dispersing agent can promote stable dispersion and electric conduction of the conductive carbon black and the modified graphene fiber.
Preferably, the primary ultrasound and the secondary ultrasound are both water bath ultrasound, and the ultrasound power is 200-300W. The primary ultrasonic and the secondary ultrasonic are both beneficial to the dispersion effect, prevent the agglomeration of the silicon dioxide nano particles and promote the combination of Mxene, CNTs and nitrogen doped graphene with the nano mesoporous spheres.
In a second aspect, the invention also provides a nitrogen-doped graphene-based aqueous conductive slurry, which comprises modified graphene fibers, conductive graphite, an aqueous dispersing agent and deionized water, wherein the mass ratio of the modified graphene fibers to the conductive graphite to the aqueous dispersing agent is 50-100:2-5:0.2-2, and the mass fraction of the modified graphene fibers in the nitrogen-doped graphene-based aqueous conductive slurry is 1-5%.
The nitrogen-doped graphene-based aqueous conductive slurry comprises modified graphene fibers, conductive graphite and an aqueous dispersing agent, wherein the modified graphene fibers are fibrous three-dimensional conductive frames and play a main role in conductivity. The modified graphene fiber adopts nano mesoporous spheres, nitrogen doped graphene, mxene and CNTs as main conductive components, and the nitrogen doped graphene has good hydrophilicity and can be uniformly dispersed in deionized water for a long time. By means of doping of the nitrogen doped graphene, CNTs and the nano mesoporous spheres, system dispersion and stability can be better promoted, stress generated by structural volume change can be effectively buffered, and efficient passing of lithium ions can be ensured. The modified graphene fibers can be connected automatically to realize electric conduction, the electric conduction effect between the modified graphene fibers can be further enhanced by means of the conductive graphite, the aqueous dispersing agent can promote uniform dispersion of the conductive graphite, and the overall stability of the conductive agent is enhanced.
In a third aspect, the invention also provides an application of the nitrogen-doped graphene-based aqueous conductive paste in a battery.
The aqueous conductive paste based on the nitrogen-doped graphene is applied to a battery, and can be coated on the electrode to enhance the conductivity of the electrode or mixed with an electrode active material to prepare the electrode, and the excellent conductivity and structural stability of the aqueous conductive paste based on the nitrogen-doped graphene can ensure the rate performance and the cycle stability of the battery.
Advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the embodiments of the invention.
Drawings
For a clearer description of the present invention, reference will be made to the following detailed description of embodiments taken in conjunction with the accompanying drawings.
FIG. 1 is a graph of results of a button cell cycle stability test;
FIG. 2 is a graph showing the results of a battery charge/discharge efficiency test;
fig. 3 is a graph showing the results of the rate performance test of the button cell.
Detailed Description
The following description is of the preferred embodiments of the present invention, and it should be noted that it will be apparent to those skilled in the art that modifications and variations can be made without departing from the principle of the invention, and these modifications and variations are also regarded as the scope of the invention.
The method for preparing the nitrogen-doped graphene-based aqueous conductive paste and the prepared nitrogen-doped graphene-based aqueous conductive paste are described in detail below through specific embodiments.
Preparing nitrogen doped graphene: a growth substrate monocrystalline copper foil is placed in a growth cavity of a CVD tube furnace, growth raw material aniline is placed in an upwind direction position of the growth cavity, the growth cavity is connected into a vacuum system, and a protective gas source (argon) is connected to the upwind direction and a vacuum pump is connected to the downwind direction. Vacuumizing the growth system, setting the growth temperature at 400-600 ℃, setting the argon flow at 200-400 sccm, and growing nitrogen-doped graphene on the surface of the monocrystalline copper foil. After the growth is finished, the temperature of the growth cavity is reduced to room temperature, the growth substrate is taken out, and the metal material with the large-area few-layer nitrogen-doped graphene laid on the surface is obtained, the growth substrate is etched, and the few-layer nitrogen-doped graphene with the nitrogen content of 10% -25% and the thickness of not more than 10 nm is collected and used for the subsequent procedures. The method can further carry out high-temperature puffing on the few-layer nitrogen-doped graphene based on experimental requirements, and comprises the following specific operations: transferring the few-layer nitrogen-doped graphene to a tube furnace for high-temperature puffing, vacuumizing the tube furnace, filling inert gas such as nitrogen or argon, setting the high-temperature puffing temperature of the tube furnace to 600-800 ℃, setting the high-temperature puffing time of the tube furnace to 30-90 s, and cooling to room temperature in the inert gas atmosphere to obtain the high-temperature puffed nitrogen-doped graphene.
Preparation of Mxene material: etching Al atoms in MAX parent metal (Ti 3AlC2 or Ti2 AlC) by hydrofluoric acidPreparation of Mxene (Ti) 3 C 2 Or Ti 2 C) Centrifuging and washing after etching is finished, and collecting Mxene material for the subsequent preparation process of the nitrogen-doped graphene-based aqueous conductive paste. In other embodiments, mxene materials are also commercially available.
The preparation of the nano mesoporous spheres comprises the following steps: providing 100 mL weak alkali aqueous solution, a phenolic resin precursor, a silicon dioxide precursor and ethylenediamine, wherein the phenolic resin precursor comprises two reaction monomers of phenols and aldehydes, the particle size distribution range of nano-silica is 50-100 nm, and the specific types and concentrations of weak alkali aqueous solution, the types and amounts of phenols and aldehydes, the types and amounts of the silicon dioxide precursor and the amount of ethylenediamine are shown in table 1. Silica precursor and directing agent were first added to 100 mL aqueous weak base solution, during which the aqueous weak base solution was subjected to water bath sonication, wherein the intensity and time of the sonication are shown in table 1. After the set ultrasonic time is over, the water bath ultrasonic process is not stopped, phenols and aldehydes are added into the weak alkali aqueous solution, and the weak alkali aqueous solution is heated or cooled to a set temperature to carry out phenolic resin polymerization reaction, wherein the reaction temperature and the reaction time are shown in table 1. After the reaction is finished, the reaction solution is centrifuged to collect the precipitate, the precipitate is added into a strong alkali solution to dissolve silicon dioxide, the precipitate is collected by centrifugation, and the dissolution and centrifugation processes are repeated for 1 time to prepare the phenolic resin mesoporous spheres. Wherein, the three centrifugation processes are the same, and the centrifugation speed, the centrifugation time and the types and the solubilities of the strong alkali solutions are shown in Table 1. Transferring the centrifugally collected phenolic resin mesoporous spheres into a tube furnace, and carbonizing at high temperature under the atmosphere of protective gas to obtain the nano mesoporous spheres. The specific protective gas types, carbonization temperatures and carbonization times are shown in table 1. In some embodiments, the high-temperature carbonized nano mesoporous spheres are also transferred to a microwave digestion instrument for microwave digestion, and specific microwave digestion time, microwave digestion temperature, microwave digestion power and the like are shown in table 1.
Table 1 process parameters in the step of preparing nano mesoporous spheres
(/ means that the example was not subjected to the process, in particular the microwave digestion process)
The preparation method comprises the following steps of: providing 100 mL of N-methylpyrrolidone, adding the nano mesoporous spheres prepared in the step of preparing nano mesoporous spheres into the N-methylpyrrolidone and uniformly mixing, wherein the mass of the nano mesoporous spheres is shown in table 2. And sequentially adding Mxene, nitrogen-doped graphene and CNTs into the N-methylpyrrolidone, wherein the mass of the Mxene, the nitrogen-doped graphene and the CNTs is shown in a table 2, and the nitrogen-doped graphene in the embodiment 3 and the embodiment 5 is high-temperature puffed nitrogen-doped graphene. In the process of specifically adding Mxene, nitrogen doped graphene and CNTs, water bath ultrasound is performed on N-methylpyrrolidone, and the ultrasound intensity and time are shown in table 2. After the completion of the ultrasound, a fiber forming polymer (PAN, polyacrylonitrile; PI, polyimide) was added to N-methylpyrrolidone and transferred to an oil bath PAN, and the mixture was heated in an oil bath with stirring, and the specific fiber forming polymer type and its mass fraction in the spinning dope, the oil bath temperature and the oil bath time are shown in Table 2. The mixture is stirred and mixed uniformly to be used as spinning solution, a spinning needle with the inner diameter increased along the filament outlet direction is used for electrostatic spinning, the inner diameter of the thin end of the spinning needle is 0.3 mm, the inner diameter of the thick end of the spinning needle is 0.36 mm, the electrostatic spinning voltage is 35 KV, and the receiving distance is 30 cm. And cutting the collected spinning fibers into short fibers with different lengths by using a fiber cutting machine, wherein the specific lengths are shown in Table 2, and thus the modified graphene fibers are obtained.
Table 2 process parameters of the step of preparing modified graphene fibers
Preparing an aqueous conductive paste based on nitrogen doped graphene: modified graphene fiber, conductive graphite, an aqueous dispersing agent and 1000 mL deionized water are provided and uniformly mixed to form primary slurry, wherein the dosage of the modified graphene fiber, the dosage of the conductive graphite, the type of the aqueous dispersing agent (PVP, polyvinylpyrrolidone; SLS, sodium lignin sulfonate; CMC, sodium carboxymethyl cellulose) and the dosage are shown in Table 3. And transferring the primary slurry to a ball mill for ball milling to obtain the nitrogen-doped graphene-based aqueous conductive slurry, wherein the specific ball milling rotating speed and time are shown in Table 3.
Table 3 process parameters in the step of preparing the nitrogen doped graphene based aqueous conductive paste
Effect example 1: cycle stability and charge-discharge efficiency test
The method comprises the steps of preparing a battery anode by taking SiOx-based materials as active materials, taking lithium sheets as counter electrodes, applying the nitrogen-doped graphene-based aqueous conductive slurry prepared in the previous examples 3-6 as a conductive agent, coating the anode, carrying out vacuum drying at 80 ℃ for 12 hours to obtain a corresponding anode, assembling a positive electrode, a negative electrode and the like into a corresponding button battery, and testing the cycle stability of the anode. The specific test method comprises the following steps: after constant current charge and discharge cycles were performed at a current density of 100 mA/g for 10 weeks, the current density was increased to 200 mA/g and cycled to 100 weeks.
As shown in fig. 1-2, the battery corresponding to example 3 had a specific capacity of 1340 mAh/g for the first time, a specific capacity of 1772.5 mAh/g for the discharge, a first charge/discharge efficiency of 75.6%, and a charge/discharge efficiency of 98.4% at 100 weeks. The battery corresponding to example 4 had a specific capacity of 1369.8 mAh/g for the first time, a specific capacity of 1788.2 mAh/g for the discharge, a charge-discharge efficiency of 76.6% for the first time and a charge-discharge efficiency of 99.5% at 100 weeks. The battery corresponding to example 5 had a specific capacity of 1356.2 mAh/g for the first time, a specific capacity of 1779.8 mAh/g for the discharge, a charge-discharge efficiency of 76.2% for the first time and a charge-discharge efficiency of 98.2% at 100 weeks. The battery corresponding to example 6 had a specific capacity of 1323.7 mAh/g for the first time, a specific capacity of 1762.6 mAh/g for the discharge, a charge-discharge efficiency of 98.6% for the first time and a charge-discharge efficiency of 98.6% at 100 weeks. Therefore, the use of the conductive agent can ensure that the battery has higher cycle stability and capacity retention rate, the charge and discharge efficiency after 100 weeks of charge and discharge cycle is kept above 98%, the charge and discharge efficiency is obviously higher than that of the battery prepared by the common conductive agent, the charge and discharge efficiency is possibly related to the relative stability of the conductive agent structure, and the SEI solidified film is not easy to fall off from the electrode in the charge and discharge process, so that the SEI solidified film is repeatedly formed and lithium ions are consumed.
Effect example 2: electrode rate capability test
The batteries prepared in effect example 1 using the nitrogen-doped graphene-based aqueous conductive slurries prepared in example 3 and example 4 were respectively subjected to charge and discharge tests under different current density conditions: the specific charge capacity was tested at a current density of 100 mA/g for 1-10 weeks, 200 mA/g for 11-20 weeks, 400 mA/g for 21-30 weeks, 800 mA/g for 31-40 weeks, 1000 mA/g for 41-50 weeks, and 100 mA/g for 51-60 weeks. As shown in FIG. 3, the batteries of example 3 had initial charge specific capacities of 1340.0 mAh/g, 1652.2 mA/g, 1566.7 mA/g, 1478.5 mA/g, 1383.1 mA/g and 1427.4 mA/g at current densities of 100 mA/g, 200 mA/g, 400 mA/g, 800 mA/g, 1000 mA/g and 100 mA/g, respectively; the specific charge capacities of the corresponding batteries of example 4 were 1369.8 mA/g, 1662.4 mA/g, 1591.2 mA/g, 1508.2 mA/g, 1414.5 mA/g and 1442.1 mA/g at current densities of 100 mA/g, 200 mA/g, 400 mA/g, 800 mA/g, 1000 mA/g and 100 mA/g, respectively. From this, the electrodes prepared in examples 3 and 4 have excellent rate performance, which is related to the porous structure of the modified graphene fiber mesh and the high-efficiency conductive network formed, and the porous modified graphene fiber mesh effectively improves the circulation effect and the electron conduction rate of lithium ions of the battery and the reversible capacity of the battery under the high-rate charge and discharge conditions.
The foregoing examples illustrate only a few embodiments of the invention and are described in detail herein without thereby limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.
Claims (10)
1. The preparation method of the nitrogen-doped graphene-based aqueous conductive paste is characterized by comprising the following steps of:
preparing nano mesoporous spheres: providing a weak alkali aqueous solution with the mass fraction of 5-10%, a phenolic resin precursor, a silicon dioxide precursor and a guiding agent, wherein the volume of the phenolic resin precursor is not more than 10% of the volume of the weak alkali aqueous solution, firstly adding the silicon dioxide precursor and the guiding agent into the weak alkali aqueous solution, performing primary ultrasonic treatment for 5-30 s, then dripping the phenolic resin precursor into the weak alkali aqueous solution, continuing the primary ultrasonic treatment, removing silicon dioxide after reacting for 10-60 min at 30-60 ℃, centrifuging and collecting precipitate, and drying and carbonizing the precipitate to obtain the nano mesoporous spheres;
preparing modified graphene fibers: providing and uniformly mixing N-methyl pyrrolidone and nano mesoporous spheres, wherein the mass ratio of the N-methyl pyrrolidone to the nano mesoporous spheres is 100:2-10, sequentially adding Mxene, nitrogen-doped graphene and CNTs into the N-methyl pyrrolidone, wherein the mass ratio of the nano mesoporous spheres, the Mxene, the nitrogen-doped graphene and the CNTs is 100:1-5:5-20:5-20, carrying out secondary ultrasonic on the N-methyl pyrrolidone while adding the Mxene, the CNTs and the nitrogen-doped graphene, adding a fiber-forming polymer into the N-methyl pyrrolidone after the ultrasonic treatment is finished, transferring the fiber-forming polymer into an oil bath pot at 120-126 ℃, stirring uniformly, and then taking the mixed solution as spinning stock solution, and carrying out electrostatic spinning, collecting and shearing by using a spinning needle with the inner diameter being enlarged along the filament outlet direction to prepare the modified graphene fiber with the length of 0.2-10 mm;
preparing an aqueous conductive paste based on nitrogen doped graphene: providing modified graphene fibers, conductive graphite, a water-based dispersing agent and deionized water, uniformly mixing the modified graphene fibers, the conductive graphite and the water-based dispersing agent to form primary slurry, wherein the mass ratio of the modified graphene fibers to the water-based dispersing agent is 50-100:2-5:0.2-2, and transferring the primary slurry to a ball mill for ball milling for 5-20 min to obtain the water-based conductive slurry;
the Mxene is Ti 3 C 2 Or Ti 2 C。
2. The method for preparing the nitrogen-doped graphene-based aqueous conductive paste according to claim 1, wherein in the step of preparing the nano mesoporous spheres, the weak base aqueous solution is ammonia water or sodium carbonate aqueous solution, the phenolic resin precursor comprises phenols and aldehydes, the phenols are phenol or aminophenol, the aldehydes are formaldehyde or acetaldehyde, the silica precursor is tetraethyl orthosilicate, tetramethyl orthosilicate or sodium silicate, and the guiding agent is ethylenediamine;
the mass ratio of the phenols, the aldehydes, the silicon dioxide precursor and the ethylenediamine is 500-1000:10-100:50-100:1-5.
3. The method for preparing the nitrogen-doped graphene-based aqueous conductive paste according to claim 1, wherein in the step of preparing the nano mesoporous spheres, the specific operation of removing the silicon dioxide is as follows: centrifugally collecting the precipitate, adding the precipitate into a strong alkali solution, stirring and uniformly mixing to promote dissolution of silicon dioxide, centrifugally collecting the precipitate, and repeating the dissolution and centrifugation processes for 1-3 times;
the strong alkali solution is sodium hydroxide or potassium hydroxide solution with the concentration of 1-5 mol/L, the centrifugal speed is 8000-12000 rpm, and the centrifugal time is 5-10 min.
4. The method for preparing the nitrogen-doped graphene-based aqueous conductive paste according to claim 1, wherein in the step of preparing the nano mesoporous spheres, the specific operation of carbonization is as follows: placing the precipitate in a tube furnace, heating to 1000-1200 ℃ under protective gas, and maintaining 1-3 h, wherein the protective gas is N 2 Or Ar.
5. The method for preparing the nitrogen-doped graphene-based aqueous conductive slurry according to claim 4, wherein the sediment is carbonized and then transferred into a microwave digestion instrument for microwave digestion for 5-15 min, the temperature of microwave digestion is 65-70 ℃, and the power is 280-330W.
6. The method for preparing the nitrogen-doped graphene-based aqueous conductive paste according to claim 1, wherein in the step of preparing the modified graphene fiber, the content of N in the nitrogen-doped graphene is 10% -25%, and the thickness of the nitrogen-doped graphene is not more than 10 nm;
the fiber-forming polymer is PI powder or PAN powder, and the mass fraction of the fiber-forming polymer in the spinning solution is 5% -8%.
7. The method for preparing the nitrogen-doped graphene-based aqueous conductive paste according to claim 1, wherein in the step of preparing the modified graphene fiber, the nitrogen-doped graphene is pre-puffed at a high temperature, and the specific high-temperature puffing step is as follows: transferring the nitrogen-doped graphene to a tube furnace for high-temperature puffing for 30-90 s, filling inert gas into the tube furnace, wherein the temperature of the tube furnace is 600-800 ℃.
8. The method for preparing the nitrogen-doped graphene-based aqueous conductive paste according to claim 1, wherein in the step of preparing the nitrogen-doped graphene-based aqueous conductive paste, the aqueous dispersant is any one of PVP, SLS or CMC, and the mass fraction of the modified graphene fibers in the nitrogen-doped graphene-based aqueous conductive paste is 1% -5%.
9. The nitrogen-doped graphene-based aqueous conductive paste prepared by the preparation method of the nitrogen-doped graphene-based aqueous conductive paste according to any one of claims 1 to 8, which is characterized by comprising modified graphene fibers, conductive graphite, an aqueous dispersing agent and deionized water, wherein the mass ratio of the modified graphene fibers to the conductive graphite to the aqueous dispersing agent is 50-100:2-5:0.2-2, and the mass fraction of the modified graphene fibers in the nitrogen-doped graphene-based aqueous conductive paste is 1% -5%.
10. The use of the aqueous conductive paste based on nitrogen-doped graphene according to claim 9 on a battery.
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