CN116581295A - Positive electrode slurry, preparation method thereof and stability evaluation method - Google Patents
Positive electrode slurry, preparation method thereof and stability evaluation method Download PDFInfo
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- 239000011267 electrode slurry Substances 0.000 title claims abstract description 85
- 238000002360 preparation method Methods 0.000 title abstract description 8
- 238000011156 evaluation Methods 0.000 title abstract description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 119
- 229910021389 graphene Inorganic materials 0.000 claims abstract description 92
- 239000002086 nanomaterial Substances 0.000 claims abstract description 58
- 239000002002 slurry Substances 0.000 claims abstract description 58
- 239000002131 composite material Substances 0.000 claims abstract description 42
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 31
- 239000007774 positive electrode material Substances 0.000 claims abstract description 31
- 239000002041 carbon nanotube Substances 0.000 claims abstract description 27
- 229910021393 carbon nanotube Inorganic materials 0.000 claims abstract description 27
- 239000002904 solvent Substances 0.000 claims abstract description 27
- 238000000034 method Methods 0.000 claims abstract description 25
- 239000011230 binding agent Substances 0.000 claims abstract description 22
- 239000000463 material Substances 0.000 claims abstract description 14
- 238000004519 manufacturing process Methods 0.000 claims abstract description 7
- 238000012360 testing method Methods 0.000 claims description 28
- 239000000843 powder Substances 0.000 claims description 22
- 230000008859 change Effects 0.000 claims description 14
- 239000011268 mixed slurry Substances 0.000 claims description 14
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical group CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 12
- 238000007580 dry-mixing Methods 0.000 claims description 11
- 238000005070 sampling Methods 0.000 claims description 11
- 238000003756 stirring Methods 0.000 claims description 9
- 238000005303 weighing Methods 0.000 claims description 9
- 238000002156 mixing Methods 0.000 claims description 8
- 238000005375 photometry Methods 0.000 claims description 8
- 239000002033 PVDF binder Substances 0.000 claims description 7
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims description 7
- 238000004898 kneading Methods 0.000 claims description 6
- 239000004576 sand Substances 0.000 claims description 6
- 238000001132 ultrasonic dispersion Methods 0.000 claims description 6
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 claims description 5
- 239000002003 electrode paste Substances 0.000 claims description 4
- 239000006182 cathode active material Substances 0.000 claims 1
- 238000004020 luminiscence type Methods 0.000 abstract description 7
- 239000002245 particle Substances 0.000 description 7
- 239000007787 solid Substances 0.000 description 7
- 238000009736 wetting Methods 0.000 description 6
- 239000003795 chemical substances by application Substances 0.000 description 4
- 238000010907 mechanical stirring Methods 0.000 description 4
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 4
- 239000004810 polytetrafluoroethylene Substances 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 238000004513 sizing Methods 0.000 description 4
- 239000006256 anode slurry Substances 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000010998 test method Methods 0.000 description 3
- HFCVPDYCRZVZDF-UHFFFAOYSA-N [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O Chemical compound [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O HFCVPDYCRZVZDF-UHFFFAOYSA-N 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 239000006258 conductive agent Substances 0.000 description 2
- 239000006260 foam Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- -1 polytetrafluoroethylene Polymers 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- BQCIDUSAKPWEOX-UHFFFAOYSA-N 1,1-Difluoroethene Chemical compound FC(F)=C BQCIDUSAKPWEOX-UHFFFAOYSA-N 0.000 description 1
- 229910000572 Lithium Nickel Cobalt Manganese Oxide (NCM) Inorganic materials 0.000 description 1
- FBDMTTNVIIVBKI-UHFFFAOYSA-N [O-2].[Mn+2].[Co+2].[Ni+2].[Li+] Chemical compound [O-2].[Mn+2].[Co+2].[Ni+2].[Li+] FBDMTTNVIIVBKI-UHFFFAOYSA-N 0.000 description 1
- 239000011149 active material Substances 0.000 description 1
- 239000013543 active substance Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 239000006257 cathode slurry Substances 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 238000009775 high-speed stirring Methods 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 239000003755 preservative agent Substances 0.000 description 1
- 230000002335 preservative effect Effects 0.000 description 1
- 238000013112 stability test Methods 0.000 description 1
- 239000003381 stabilizer Substances 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/64—Fluorescence; Phosphorescence
- G01N21/6428—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes"
- G01N21/643—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes" non-biological material
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0416—Methods of deposition of the material involving impregnation with a solution, dispersion, paste or dry powder
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Life Sciences & Earth Sciences (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Immunology (AREA)
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Molecular Biology (AREA)
- Manufacturing & Machinery (AREA)
- Dispersion Chemistry (AREA)
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- Analytical Chemistry (AREA)
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Abstract
The application provides positive electrode slurry, a preparation method thereof and a stability evaluation method, and particularly relates to the technical field of battery manufacturing. The positive electrode slurry comprises a solvent, a positive electrode active material, a binder and a composite conductive slurry, wherein the positive electrode active material, the binder and the composite conductive slurry are dispersed in the solvent; the composite conductive paste comprises conductive carbon black, carbon nanotubes, graphene and graphene fluorescent nanomaterial, wherein the graphene fluorescent nanomaterial accounts for 3% -5% of the total mass of the conductive carbon black, the carbon nanotubes, the graphene and the graphene fluorescent nanomaterial. According to the application, graphene fluorescent nano material is added into the positive electrode slurry, and the stability of the slurry is characterized by comparing the fluorescence luminosity of the slurry before and after standing by utilizing the luminescence characteristic of the material. The method is simple and can continuously observe the stability of the slurry.
Description
Technical Field
The application relates to the technical field of battery manufacturing, in particular to positive electrode slurry, a preparation method thereof and a stability evaluation method.
Background
With the development of new energy, the requirement on the battery performance is higher and higher, and the stability of the positive and negative electrode slurry of the battery is one of important factors for determining the battery performance. The positive and negative electrode slurry is a suspension dispersion system formed by dispersing active materials, conductive agents, binders, stabilizers and the like in a solvent through high-speed stirring, wherein the particle sizes of different substance particles in the slurry are greatly different, the affinities of surface groups of the slurry to the solvent are different, in addition, agglomeration can occur among the particles, so that the different substance particles are unevenly dispersed in the slurry, and the stability of the slurry is poor. The slurry with poor stability can be settled in the coating process, the slurry can be seriously layered, the coating amount of active substances on the current collector is unstable, the consistency of the manufactured battery core is poor, and the battery performance is seriously affected. The stability of the battery paste is thus critical to battery production.
The patent CN106124363B respectively tests the viscosity change when the rotating speed is changed from small to large and the viscosity change when the rotating speed is changed from large to small, and respectively draws two slurry viscosity change curves along with the rotating speed; and then analyzing the coincidence of the viscosity of the two slurries along with the change curve of the rotating speed, and judging the stability of the anode slurry and the cathode slurry. The method does not continuously observe the stability of the slurry for a long period of time and whether it settles. Patent CN108169059a tests qualitative by testing the average solids content in the slurry, which is cumbersome in procedure and time consuming. Therefore, it is very important to develop a test method that can simply and continuously observe the stability of slurry for battery fabrication.
Disclosure of Invention
In view of the above drawbacks of the prior art, the present application provides a positive electrode slurry, a preparation method thereof and a stability evaluation method thereof, so as to solve the problems that the current battery slurry stability test method is tedious and cannot be observed continuously.
To achieve the above and other related objects, the present application provides a positive electrode slurry comprising a solvent, a positive electrode active material, a binder, and a composite conductive slurry, the positive electrode active material, the binder, and the composite conductive slurry being dispersed in the solvent; the composite conductive paste comprises conductive carbon black, carbon nanotubes, graphene and graphene fluorescent nanomaterial, wherein the graphene fluorescent nanomaterial accounts for 3% -5% of the total mass of the conductive carbon black, the carbon nanotubes, the graphene and the graphene fluorescent nanomaterial.
In an example of the present application, the mass ratio of the positive electrode active material, the binder and the composite conductive paste is (95% -98%): (1.5% -2.5%): (0.5% -2.5%).
In one example of the present application, the graphene fluorescent nanomaterial is selected from graphene quantum dots.
In an example of the present application, the positive electrode active material is selected from a ternary material or a lithium iron phosphate material.
In one example of the application, the solvent is selected from the group consisting of N-methylpyrrolidone and the binder is selected from the group consisting of polyvinylidene fluoride.
In another aspect, the present application provides a method for preparing a positive electrode slurry, comprising the steps of: weighing conductive carbon black, carbon nanotubes, graphene and graphene fluorescent nanomaterial according to a proportion, and preparing composite conductive slurry; dry-mixing the positive electrode active material and a binder to prepare first mixed dry powder; adding a certain solvent into the first mixed dry powder, and kneading to prepare first mixed slurry; and adding the composite conductive paste into the first mixed paste, and uniformly mixing to obtain the positive electrode paste.
In one example of the present application, the step of configuring the composite conductive paste includes: weighing the conductive carbon black, the carbon nano tube, the graphene and the graphene fluorescent nano material, and adding the conductive carbon black, the carbon nano tube, the graphene and the graphene fluorescent nano material into a kneader for dry mixing to prepare second mixed dry powder; adding the second mixed dry powder into a stirring device containing a solvent, and performing ultrasonic dispersion for 1-2 h to prepare second mixed slurry; and sucking the second mixed slurry into a sand mill to continuously disperse for 1-1.5 h, so as to obtain the composite conductive slurry.
In an example of the present application, after the mixing of the composite conductive paste and the first mixed paste is completed, the method further includes viscosity adjustment and bubble removal, so that the positive electrode paste meets the use requirement.
The application also provides an evaluation method of the stability of the positive electrode slurry, which comprises the following steps: testing fluorescence luminosity of the positive electrode slurry before and after standing; and judging the stability of the positive electrode slurry according to the fluorescence luminosity change.
In an example of the present application, the method for evaluating the stability of the positive electrode slurry includes the steps of: sampling from the prepared positive electrode slurry, marking the sample as a sample S1, and performing a fluorescence photometry test on the sample S1; placing the prepared positive electrode slurry in a container for standing, taking samples at intervals t, respectively marking the samples as samples S2, S3, … … and Sn, and performing fluorescence photometry on the taken samples; comparing the fluorescence luminosity changes of the samples S1, S2, S3, … … and Sn, and if the fluorescence luminosity is stable and unchanged or fluctuates, the stability of the positive electrode slurry is better; if the fluorescence intensity is in a decreasing trend, the stability of the positive electrode slurry is poor.
According to the application, the graphene fluorescent nano material is added into the positive electrode slurry, the graphene fluorescent nano material can be adsorbed on the surface and the luminescence characteristic of the positive electrode active material particles, and the stability of the slurry is characterized by comparing the fluorescence luminosity of the slurry before and after standing. The method is simple and can continuously observe the stability of the slurry. Because graphene is used as a conductive agent, the addition of graphene fluorescent nanomaterial in the positive electrode slurry does not have adverse effect on the positive electrode slurry, and the stability of the slurry can be characterized by utilizing the luminescence characteristic of the graphene fluorescent nanomaterial.
Drawings
In order to more clearly illustrate the embodiments of the application or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic flow chart of a method for preparing a positive electrode slurry according to the present application;
FIG. 2 is a schematic flow chart of step S1 in the preparation method of the positive electrode slurry of the present application;
FIG. 3 is a flow chart of the method for evaluating the stability of the positive electrode slurry according to the present application;
fig. 4 is a schematic flow chart of step S100 in the method for evaluating the stability of the positive electrode slurry according to the present application;
FIG. 5 is a test result of stability of the positive electrode slurry of example 1 of the present application;
fig. 6 is a test result of the stability of the positive electrode slurry of example 2 of the present application.
Detailed Description
Other advantages and effects of the present application will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present application with reference to specific examples. The application may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present application. It should be noted that the following embodiments and features in the embodiments may be combined with each other without conflict. It is also to be understood that the terminology used in the examples of the application is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the application. The test methods in the following examples, in which specific conditions are not noted, are generally conducted under conventional conditions or under conditions recommended by the respective manufacturers.
It should be understood that the terms such as "upper," "lower," "left," "right," "middle," and "a" and the like are used in this specification for descriptive purposes only and not for purposes of limitation, and that the application may be practiced without materially departing from the novel teachings and without departing from the scope of the application.
The application provides a positive electrode slurry, a preparation method and a stability evaluation method thereof, wherein a graphene fluorescent nanomaterial is added into the positive electrode slurry, and the stability of the positive electrode slurry is evaluated by utilizing the luminescence characteristic of the graphene fluorescent nanomaterial.
The positive electrode slurry comprises a solvent, a positive electrode active material, a binder and a composite conductive slurry, wherein the positive electrode active material, the binder and the composite conductive slurry are uniformly dispersed in the solvent; wherein, the mass ratio of the positive electrode active material to the binder to the composite conductive paste is (95% -98%): (1.5% -2.5%): (0.5% -2.5%), for example, the mass ratio of the positive electrode active material, the binder and the composite conductive paste may be 95%:2.5%:2.5%; or 98%:1.5%:0.5%; or 97%:2%:1%; etc.; the solvent content can be added according to the viscosity, solid content and other requirements of the positive electrode slurry.
The composite conductive paste comprises conductive carbon black, carbon nanotubes, graphene and graphene fluorescent nanomaterial, wherein the graphene fluorescent nanomaterial accounts for 3% -5% of the total mass of the conductive carbon black, the carbon nanotubes, the graphene and the graphene fluorescent nanomaterial, for example, the graphene fluorescent nanomaterial is 3%, 4% or 5% and the like. As an example, the mass ratio of each powder in the composite conductive paste is conductive carbon black: carbon nanotubes: graphene: graphene fluorescent nanomaterial=1:6:2.5:0.5. The duty cycle of the graphene fluorescent nanomaterial can be adjusted from the duty cycle of graphene. The graphene fluorescent nanomaterial is selected from graphene quantum dots, and has both the conductive property and the fluorescent luminous property of graphene.
In some embodiments, the positive electrode active material in the positive electrode slurry may be selected from ternary materials, such as lithium nickel cobalt manganese oxide, and may also be selected from positive electrode materials commonly used in the art, such as lithium iron phosphate materials; the solvent may be an organic solvent commonly used in the art, such as N-methylpyrrolidone (NMP), and the binder may be a kind commonly used in the art, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc.
Referring to fig. 1, the preparation method of the positive electrode slurry of the present application includes the following steps:
s10, weighing conductive carbon black, carbon nanotubes, graphene and graphene fluorescent nanomaterial according to a proportion, and preparing composite conductive slurry;
s20, dry-mixing the positive electrode active material and a binder to prepare first mixed dry powder;
s30, adding a certain solvent into the first mixed dry powder, and kneading to obtain first mixed slurry;
and S40, adding the composite conductive paste into the first mixed paste, and uniformly mixing to obtain the positive electrode paste.
Referring to fig. 2, step S10 of configuring the composite conductive paste specifically includes:
s11, weighing the conductive carbon black, the carbon nano tube, the graphene and the graphene fluorescent nano material, and adding the conductive carbon black, the carbon nano tube, the graphene and the graphene fluorescent nano material into a kneader for dry mixing to prepare second mixed dry powder;
s12, adding the second mixed dry powder into a stirring device containing a solvent, and performing ultrasonic dispersion for 1-2 hours to prepare second mixed slurry;
s13, sucking the second mixed slurry into a sand mill, and continuing to disperse for 1-1.5 h to obtain the composite conductive slurry.
The conductive carbon black, carbon nanotubes, graphene and graphene fluorescent nanomaterial in step S11 can be obtained by general commercial means. The graphene fluorescent nanomaterial is preferably graphene quantum dots, which have both graphene characteristics and luminescence characteristics. Of course, other materials with the same characteristics can be selected from the graphene fluorescent nano materials.
The composite conductive paste generally comprises conductive carbon black, carbon nano tubes and graphene, and the graphene fluorescent nano material is added into the composite conductive paste according to the application, wherein the graphene fluorescent nano material accounts for the proportion of the graphene, namely the conductive carbon black, the carbon nano tubes and the graphene (graphene+graphene fluorescent nano material in the application) can be set according to the proportion of the conventional composite conductive paste. In some embodiments, the graphene fluorescent nanomaterial comprises 3% -5% of the total mass of the conductive carbon black, carbon nanotubes, graphene, and graphene fluorescent nanomaterial, as an example, the conductive carbon black in the conductive paste: carbon nanotubes: graphene: the mass ratio of the graphene fluorescent nano material is 1:6:2.5:0.5.
The step S11 specifically includes: firstly, respectively weighing conductive carbon black, carbon nano tubes, graphene and graphene fluorescent nano materials according to a set proportion, then adding the weighed conductive carbon black, carbon nano tubes, graphene and graphene fluorescent nano materials into a kneader for dry mixing, so that all the components are uniformly mixed, and obtaining conductive dry powder which is marked as second mixed dry powder.
The step S12 specifically includes: adding a solvent into a stirring device such as a mechanical stirring barrel, adding a dispersing agent under stirring, and turning on an ultrasonic disperser and a water cooling system of the stirring device; and (3) adding the conductive dry powder prepared in the step (S11) into a mechanical stirring barrel containing a solvent, fully wetting the dry powder, and continuously mechanically stirring and wetting for 1-2 h, such as 1.5h under ultrasonic dispersion to prepare a second mixed slurry. The solvent is N-methyl pyrrolidone.
The step S13 specifically includes: and (3) sucking the second mixed slurry prepared in the step (S12) into a sand mill by a pump for dispersing for 1-1.5 h, for example, 1.25h, so as to obtain the composite conductive slurry.
Referring to fig. 1, step S20 is to dry mix the positive electrode active material with a binder, wherein the positive electrode active material may be lithium iron phosphate, ternary materials, such as lithium nickel cobalt manganate, or other common positive electrode materials, which is not limited herein; the binder may be selected from vinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a combination of both in any ratio. The dry blending step can be performed according to the conventional process in the art, and only the powder is required to be uniformly mixed.
The step S30 specifically includes: after uniformly mixing the positive electrode active material and the binder, adding a certain amount of solvent for kneading to prepare mixed slurry of the positive electrode active material and the binder, and marking the mixed slurry as first mixed slurry. The solvent in this step may be the same as or different from the solvent in the step S10 of preparing the composite conductive paste, and preferably both of them are the same.
The step S40 specifically includes: adding the composite conductive paste prepared in the step S10 into the first mixed paste prepared in the step S30 for premixing; then adding solvent such as NMP for premixing, and dispersing at high speed to uniformly mix the composite conductive paste with the first mixed paste.
After the step S40 is finished, a viscosity adjusting and defoaming step is further performed to enable the slurry to meet the use requirement, and the specific steps of viscosity adjusting and defoaming are referred to the conventional process in the art and are not described herein.
After the steps are finished, the positive electrode slurry can be obtained, and the graphene fluorescent nanomaterial with the luminescence characteristic is contained in the positive electrode slurry, and can be adsorbed on the surface of a positive electrode active material, so that the stability of the positive electrode slurry can be represented by observing the fluorescence luminosity change of the positive electrode slurry.
Referring to fig. 3, the method for evaluating the stability of the positive electrode slurry of the present application includes the following steps:
s100, testing fluorescence luminosity of the positive electrode slurry before and after standing;
and S200, judging the stability of the positive electrode slurry according to the change of fluorescence luminosity.
Specifically, the positive electrode slurry in step 100 is the positive electrode slurry described above, and since the positive electrode slurry contains the graphene fluorescent nanomaterial, the graphene fluorescent nanomaterial can be adsorbed on the surface of the positive electrode active material particles, if the positive electrode slurry is unstable, that is, the positive electrode active material sinks, the graphene fluorescent nanomaterial will sink with the positive electrode active material, and the measured fluorescence intensity of the upper layer positive electrode slurry will be weakened; in contrast, the fluorescence intensity of the lower layer positive electrode slurry is increased, and the stability of the positive electrode slurry can be judged by observing the change of the fluorescence intensity of the positive electrode slurry.
Referring to fig. 4, step S100 specifically includes:
s101, sampling from the prepared positive electrode slurry, marking as a sample S1, and performing fluorescence photometry on the sample S1.
Sample S1 is sampled immediately after the positive electrode slurry is prepared, and the amount of sampling is required to meet the fluorescence photometry, for example, 5ml is put into a sample tube, and then the fluorescence photometer is used for carrying out the fluorescence photometry on sample S1.
And S102, placing the prepared positive electrode slurry in a container for standing, taking samples at intervals t, respectively marking the samples as samples S2, S3, … … and Sn, and performing a fluorescence photometry test on the taken samples.
The interval time t may be 0.5h, 1h, 2h, 4h or 6h, etc., the standing observation time of the positive electrode slurry may be 24h, 48h, 72h, etc., where the sampling interval time and the stability observation time are not limited, and may be set according to actual requirements. For the convenience of testing, the longer the observation time of the positive electrode slurry is, the longer the sampling interval time can be properly amplified, and the shorter the observation time is, the shorter the sampling interval time can be. The slurry is sealed by using a preservative film in the standing process to prevent the solvent from evaporating; to ensure the accuracy of the test, samples in the same area are selected for each sampling, for example, each sampling is selected from an upper layer area of the slurry, or each sampling is selected from a lower layer area of the slurry; and the fluorescent test is needed to be performed immediately after sampling, so that the sample is prevented from being changed in the placing process, and the test result is prevented from being influenced. The fluorescence test is carried out by adopting a fluorescence photometer according to a conventional fluorescence test method.
With continued reference to fig. 3, step S200 compares the fluorescence changes of the samples S1, S2, S3, … …, sn, and specifically includes: drawing a time-fluorescence intensity relation curve by taking time as an abscissa and fluorescence intensity as an ordinate, and if the fluorescence intensity is unchanged or fluctuates little (the whole maintains a horizontal state) along with the change of time, considering that the stability of the slurry is better; if the fluctuation of the fluorescence intensity is relatively large with time (for example, if the sample is taken from the upper region of the slurry, the fluorescence intensity tends to decrease, and if the sample is taken from the lower region of the slurry, the fluorescence intensity tends to increase), the stability of the slurry is considered to be poor. This is because: the graphene fluorescent nano material is added into the positive electrode slurry, the material can be adsorbed on the surface of positive electrode material particles, if the stability of the positive electrode slurry is poor, the material in the positive electrode slurry can be settled, namely the positive electrode active material can drive the graphene fluorescent material to be settled, so that the graphene fluorescent nano material in the upper layer area of the positive electrode slurry is reduced, and the fluorescent intensity of the upper layer slurry is weakened; the graphene fluorescent nano material in the lower layer area is increased, and the fluorescence intensity of the slurry in the lower layer area is enhanced; if the stability of the positive electrode slurry is good, the positive electrode active material and the graphene fluorescent nanomaterial are well dispersed in the positive electrode slurry, and the fluorescence intensity of the positive electrode active material and the graphene fluorescent nanomaterial is small in change or even stable and unchanged along with the change of time. Therefore, the stability of the slurry for a long time can be qualitatively judged by observing the change of fluorescence luminosity of the positive electrode slurry.
Preferably, we can also quantitatively test the stability of the positive electrode slurry by using the correspondence between fluorescence and solid content. Specifically, the solid content of the slurry with different fluorescence degrees is tested, the fixed quantity corresponding to the slurry with different fluorescence degrees is collected in large quantity, the corresponding relation between the fluorescence degrees and the fixed quantity of the slurry is fitted by utilizing big data, the solid content of the slurry can be perceived according to the fluorescence degrees of the slurry by utilizing the corresponding relation, the solid content of the slurry is quantitatively judged, the stability and the processability of the slurry are controlled more clearly in the production process, and the method has an important guiding effect on the optimization of the production process. Compared with the method for directly testing the solid content, the method is more convenient and quicker.
The following detailed description of the present application is made with reference to several specific examples, wherein the starting materials and reagents used in the examples are commercially available or may be prepared by methods conventional in the art, unless otherwise indicated.
Example 1
Weighing conductive carbon black, carbon nano tubes, graphene and graphene fluorescent nano materials according to the mass ratio of 1:6:2.5:0.5, and adding the materials into a kneader for dry mixing; adding the dry mixed dry powder into a mechanical stirring barrel containing NMP, and fully wetting the dry powder; and (3) continuously mechanically stirring and wetting for 1h under ultrasonic dispersion, sucking into a sand mill by a pump for dispersion, and dispersing for 1.5h to obtain the composite conductive paste.
Lithium iron phosphate (95% by mass, the same applies below) and PVDF (2.5%) were dry blended; adding a certain amount of NMP for kneading after dry mixing uniformly; then adding composite conductive paste (2.5%) for premixing; adding NMP, premixing, dispersing at high speed, regulating viscosity, and removing foam to obtain the anode slurry.
Placing the prepared positive electrode slurry in a container, taking 5ml of upper slurry in a test tube, and performing fluorescence test on the upper slurry; then taking the upper sizing agent every 6 hours, and immediately carrying out fluorescence test every time of taking the sample until the sizing agent stands for 48 hours.
After the test is finished, a time-fluorescence intensity relation curve is drawn according to the test result, as shown in fig. 5: the fluorescence intensity of the positive electrode slurry was fluctuated with the extension of the standing time, but the change was not large, and the positive electrode slurry was maintained in a substantially horizontal state, which indicates that the positive electrode slurry of the present example was excellent in stability.
Example 2
Weighing conductive carbon black, carbon nano tubes, graphene and graphene fluorescent nano materials according to the mass ratio of 1:6:2.5:0.5, and adding the materials into a kneader for dry mixing; adding the dry mixed dry powder into a mechanical stirring barrel containing NMP, and fully wetting the dry powder; and (3) continuously mechanically stirring and wetting for 1h under ultrasonic dispersion, sucking into a sand mill by a pump for dispersion, and dispersing for 1.5h to obtain the composite conductive paste.
Dry-blending nickel cobalt lithium manganate (98% by mass, the same applies below) and PVDF (1.5%); adding a certain amount of NMP for kneading after dry mixing uniformly; then adding the composite conductive paste (0.5%) for premixing; adding NMP, premixing, dispersing at high speed, regulating viscosity, and removing foam to obtain the anode slurry.
Placing the prepared positive electrode slurry in a container, taking 5ml of upper slurry in a test tube, and performing fluorescence test on the upper slurry; then taking the upper sizing agent every 6 hours, and immediately carrying out fluorescence test every time of taking the sample until the sizing agent stands for 48 hours.
After the test is finished, a time-fluorescence intensity relation curve is drawn according to the test result, as shown in fig. 6: the fluorescence intensity of the positive electrode slurry prepared in this example showed a decrease in the fluorescence intensity with an increase in the standing time, indicating that the stability of the positive electrode slurry prepared in this example was poor.
According to the application, the graphene fluorescent nanomaterial is added into the positive electrode slurry, and the stability of the slurry is characterized by comparing the fluorescence luminosity of the slurry before and after standing by utilizing the luminescence characteristic of the graphene fluorescent nanomaterial. The method is simple and can continuously observe the stability of the slurry. Therefore, the application effectively overcomes some practical problems in the prior art, thereby having high utilization value and use significance.
The above embodiments are merely illustrative of the principles of the present application and its effectiveness, and are not intended to limit the application. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the application. Accordingly, it is intended that all equivalent modifications and variations of the application be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.
Claims (10)
1. A positive electrode slurry, comprising:
the cathode active material, the binder and the composite conductive paste are dispersed in the solvent;
the composite conductive paste comprises conductive carbon black, carbon nanotubes, graphene and graphene fluorescent nanomaterial, wherein the graphene fluorescent nanomaterial accounts for 3% -5% of the total mass of the conductive carbon black, the carbon nanotubes, the graphene and the graphene fluorescent nanomaterial.
2. The positive electrode slurry according to claim 1, wherein the mass ratio of the positive electrode active material, the binder and the composite conductive slurry is (95% -98%): (1.5% -2.5%): (0.5% -2.5%).
3. The positive electrode slurry according to claim 1, wherein the graphene fluorescent nanomaterial is selected from graphene quantum dots.
4. The positive electrode slurry according to claim 1, wherein the positive electrode active material is selected from a ternary material or a lithium iron phosphate material.
5. The positive electrode slurry according to claim 1, wherein the solvent is selected from N-methylpyrrolidone and the binder is selected from polyvinylidene fluoride.
6. A method for producing the positive electrode slurry according to any one of claims 1 to 5, comprising the steps of:
weighing conductive carbon black, carbon nanotubes, graphene and graphene fluorescent nanomaterial according to a proportion, and preparing composite conductive slurry;
dry-mixing the positive electrode active material and a binder to prepare first mixed dry powder;
adding a certain solvent into the first mixed dry powder, and kneading to prepare first mixed slurry;
and adding the composite conductive paste into the first mixed paste, and uniformly mixing to obtain the positive electrode paste.
7. The method of preparing a composite conductive paste according to claim 6, wherein the step of configuring the composite conductive paste comprises:
weighing the conductive carbon black, the carbon nano tube, the graphene and the graphene fluorescent nano material, and adding the conductive carbon black, the carbon nano tube, the graphene and the graphene fluorescent nano material into a kneader for dry mixing to prepare second mixed dry powder;
adding the second mixed dry powder into a stirring device containing a solvent, and performing ultrasonic dispersion for 1-2 h to prepare second mixed slurry;
and sucking the second mixed slurry into a sand mill to continuously disperse for 1-1.5 h, so as to obtain the composite conductive slurry.
8. The method of claim 6, wherein the mixing of the composite conductive paste and the first mixed paste is completed, and further comprising viscosity adjustment and defoaming.
9. A method for evaluating the stability of the positive electrode slurry according to any one of claims 1 to 5, comprising:
testing fluorescence luminosity of the positive electrode slurry before and after standing;
and judging the stability of the positive electrode slurry according to the fluorescence luminosity change.
10. The method for evaluating the stability of a positive electrode slurry according to claim 9, comprising the steps of:
sampling from the prepared positive electrode slurry, marking the sample as a sample S1, and performing a fluorescence photometry test on the sample S1;
placing the prepared positive electrode slurry in a container for standing, taking samples at intervals t, respectively marking the samples as samples S2, S3, … … and Sn, and performing fluorescence photometry on the taken samples;
comparing the fluorescence luminosity changes of the samples S1, S2, S3, … … and Sn, and if the fluorescence luminosity is stable and unchanged or slightly fluctuates, the stability of the positive electrode slurry is better; otherwise, the stability of the positive electrode slurry is poor.
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| CN117092069A (en) * | 2023-10-20 | 2023-11-21 | 瑞浦兰钧能源股份有限公司 | Method for detecting floating of binder in lithium ion battery slurry |
| CN117092069B (en) * | 2023-10-20 | 2024-03-15 | 瑞浦兰钧能源股份有限公司 | Method for detecting floating of binder in lithium ion battery slurry |
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