CN113174044B - Modified polyimide binder and preparation method and application thereof - Google Patents
Modified polyimide binder and preparation method and application thereof Download PDFInfo
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- C08G73/1067—Wholly aromatic polyimides, i.e. having both tetracarboxylic and diamino moieties aromatically bound
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- H01M10/00—Secondary cells; Manufacture thereof
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Abstract
The invention relates to a modified polyimide binder, a preparation method and application thereof, wherein the modified polyimide binder has the following structural general formula:
wherein, m is n=5:1-1:5; the polymerization degree m+n is an integer of 100 to 5000; the structural formula of R1 contains self-repairing functional groups, wherein the self-repairing functional groups are disulfide bond or polysulfide bond functional groups containing dynamic reversible covalent bonds; the structural formulas of R2 and R3 are conjugated structures, and the R2 and R3 respectively comprise any one of aromatic compounds, heterocyclic compounds, aromatic derivatives or heterocyclic derivatives.
Description
Technical Field
The invention relates to the technical field of materials, in particular to a modified polyimide binder and a preparation method and application thereof.
Background
The lithium ion battery has the excellent characteristics of high energy density, long cycle life, low self-discharge rate, no memory effect and the like, gradually replaces the traditional lead-acid storage battery and the cadmium-nickel battery, and is widely applied to portable electronic equipment. To further expand the commercial applications of lithium ion batteries, significant challenges are presented in terms of high power output performance and safety performance. Among them, many electrochemical properties of lithium ion batteries, such as stability, irreversible capacity loss, etc., are closely related to the properties of the binder.
Because the theoretical capacity of the traditional graphite cathode is 372mAh/g only, and the theoretical capacity of a silicon material can reach ten times as much, the silicon material has poor volume expansibility, is easy to pulverize in the charge and discharge process, and has short service life, poor performance stability and the like. In this case, the scientific researchers use the silicon-carbon composite material as the negative electrode material, and the performance of the battery is improved. In the use process of the silicon-carbon composite material, the binder is an important component of the anode and the cathode of the lithium ion battery, is a high polymer for adhering an electrode active material layer on a current collector, and has the main effects of tightly adhering all components in an electrode and stabilizing a pole piece structure so as to relieve the expansion and shrinkage of the pole piece in the charge and discharge process of the battery, reduce the resistance of the electrode and play a quite important role in improving the performance of the battery.
The polyimide material has the characteristics of structural diversity, stable chemical structure, excellent mechanical property and the like, and has important significance for the lithium ion battery with high development capacity, stable cycle performance and good safety performance when being used as a binder in the negative electrode of the lithium ion battery.
At present, polyimide adhesives are widely applied to lithium batteries, but most of the polyimide adhesives are from the standpoint of good mechanical property, thermal stability and adhesion of polyimide, and few researches are carried out on the aspects of lithium ion mobility, conductivity, self-repairing performance and the like of counter electrodes with different functional groups. The application of the existing polyimide binder still has defects in the aspects of the binding capacity of an electrode and lithium ions, the ion transfer capacity, the electrochemical stability, the thermal stability, the dissolving capacity in an organic solvent, the electrolyte absorption capacity of the electrode, the electrode impedance, the flexibility and the like, and the comprehensive performance is required to be improved.
Disclosure of Invention
The embodiment of the invention provides a modified polyimide binder, a preparation method and application thereof, which are used for improving the cycle stability and overcharge safety of a lithium ion battery and solving the problem of low conductivity of a polymer.
In a first aspect, an embodiment of the present invention provides a modified polyimide adhesive having a structural general formula:
wherein, m is n=5:1-1:5; the polymerization degree m+n is an integer of 100 to 5000;
the structural formula of R1 contains self-repairing functional groups, wherein the self-repairing functional groups are disulfide bond or polysulfide bond functional groups containing dynamic reversible covalent bonds;
the structural formulas of R2 and R3 are conjugated structures, and the R2 and R3 respectively comprise any one of aromatic compounds, heterocyclic compounds, aromatic derivatives or heterocyclic derivatives.
Preferably, the R1 is one or more of diaryl disulfide, dialkyl disulfide and bi-heterocyclic disulfide;
r2 is one or more of benzene, naphthalene, perylene, anthracene, pyrrole, thiophene and furan;
r3 is one or more of benzoquinone, naphthalene, perylene, anthracene, imidazole, thiazole and oxazole.
Preferably, the R1 is specifically
R2 is specifically->
R3 is specifically
In a second aspect, an embodiment of the present invention provides a method for preparing the modified polyimide binder according to the first aspect, where the method includes:
under the protection of nitrogen, dissolving diamine monomer in an organic solvent, and stirring and dissolving at room temperature to obtain a first solution;
adding dianhydride monomer into the first solution, and continuing stirring and reacting for 12-24 hours at room temperature to obtain polyamic acid solution;
precipitating the polyamic acid solution in a poor solvent, washing, suction filtering and drying to obtain polyamic acid solid powder;
dissolving polyamic acid solid powder in proper amount of N-methyl pyrrolidone solvent to obtain polyamic acid adhesive;
the polyamide acid binder is formed into a modified polyimide binder after pole piece coating, rolling and heat treatment.
Preferably, the organic solvent is one or a mixture of more than one of tetrahydrofuran, N-methylpyrrolidone, N-dimethylacetamide and N, N-dimethylformamide;
the ratio of the organic solvent to the diamine monomer is set according to the structural general formula of the finally obtained modified polyimide adhesive, wherein R1:R3=5:1-1:5;
the amount of the dianhydride monomer and the diamine monomer are the same;
the modified polyimide binder has the structural general formula:
Preferably, the polyamic acid solution has a solid content of 8 to 12wt%; the solid content of the polyamic acid binder is 1wt% to 20wt%.
Preferably, the poor solvent comprises one or more of deionized water, methanol, ethanol, isopropanol, ethylene glycol, 2-butanol, cyclopentanol, cyclohexanol or phenol.
Preferably, the drying temperature is not higher than 150 ℃.
In a third aspect, an embodiment of the present invention provides an electrode sheet, where the electrode sheet is a positive electrode sheet or a negative electrode sheet, and the electrode sheet includes the modified polyimide binder described in the first aspect.
In a fourth aspect, an embodiment of the present invention provides a lithium battery, including the electrode slice described in the third aspect.
The modified polyimide binder provided by the embodiment of the invention introduces self-repairing functional groups into the polyimide structure, improves the flexibility of the polymer, and combines good mechanical stability and thermal stability of polyimide; the polyimide structure obtains a self-healing effect by introducing a reversible covalent bond or a hydrogen bond of a self-healing functional group, can resist the expansion of active substances in the charge and discharge process, ensures the cycle stability and overcharge safety of the lithium ion battery, and solves the problem of low conductivity of the polymer; by utilizing the characteristic that the conjugated polymer is easy to be oxidized and reduced, the aromatic imide conjugated structure enables the lowest unoccupied molecular orbital (Lowest Unoccupied Molecular Orbital, LUMO) energy level of the polyimide to be low, n-type doping is easy to carry out, ions are embedded into the polymer, so that charges on a main chain are neutralized, the polyimide is quickly and reversibly changed from an insulating state into a conductive state, the electronic conductivity of a binder is improved, and the impedance is reduced; and the binder can also provide certain reversible capacity, which is helpful for improving the first coulombic efficiency and the circulation capacity of the battery.
Drawings
The technical scheme of the embodiment of the invention is further described in detail through the drawings and the embodiments.
FIG. 1 is a flow chart of a method of preparing a modified polyimide adhesive according to an embodiment of the present invention;
FIG. 2 is a nuclear magnetic resonance hydrogen spectrum of the modified polyimide according to example 1 of the present invention;
FIG. 3 is a hydrogen nuclear magnetic resonance spectrum of the polyamic acid according to example 1 of the present invention;
fig. 4 is a comparison of 100 cycle stability and capacity retention at 0.1C for a lithium battery using a modified polyimide binder provided in example 1 of the present invention and a conventional polyacrylate binder.
Detailed Description
The invention is further illustrated by the drawings and the specific examples, which are to be understood as being for the purpose of more detailed description only and are not to be construed as limiting the invention in any way, i.e. not intended to limit the scope of the invention.
The invention provides a modified polyimide binder which can be used as a binder of a lithium ion battery and used in a positive electrode or a negative electrode.
The structural general formula of the modified polyimide binder is as follows:
wherein, m is n=5:1-1:5; the polymerization degree m+n is an integer of 100 to 5000;
the structural formula of R1 contains self-repairing functional groups, wherein the self-repairing functional groups are disulfide bond or polysulfide bond functional groups containing dynamic reversible covalent bonds; specifically, R1 is one or more of diaryl disulfide, dialkyl disulfide and bi-heterocyclic disulfide.
The structural formulas of R2 and R3 are conjugated structures, and R2 and R3 respectively comprise any one of aromatic compounds, heterocyclic compounds, aromatic derivatives or heterocyclic derivatives. R2 can be one or more of benzene, naphthalene, perylene, anthracene, pyrrole, thiophene and furan; r3 can be one or more of benzoquinone, naphthalene, perylene, anthracene, imidazole, thiazole and oxazole.
In a preferred embodiment, R1 is in particular
R2 is specifically->
R3 is specifically->
The modified polyimide adhesive can be prepared by the following steps:
specifically, the organic solvent is one or a mixture of more than one of tetrahydrofuran, N-methylpyrrolidone, N-dimethylacetamide and N, N-dimethylformamide;
the ratio of the organic solvent to the diamine monomer is set according to the structural general formula of the finally obtained modified polyimide adhesive, wherein R1: R3 = 5:1-1:5.
specifically, the amount of the dianhydride monomer added is the same as the amount of the diamine monomer.
The solid content of the polyamic acid solution is 8 to 12 weight percent; more preferably 10wt%.
specifically, the poor solvent comprises one or more of deionized water, methanol, ethanol, isopropanol, ethylene glycol, 2-butanol, cyclopentanol, cyclohexanol or phenol.
In the precipitation treatment, the volume of the poor solvent used is 5 to 10 times that of the organic solvent used in step 110.
In the drying process, vacuum drying may be specifically used, or other drying methods may be used for the purpose of removing the solvent. The drying temperature should not be higher than 150℃because excessive temperature is liable to induce imidization reaction, which reduces the solubility of the product, and thus drying at 60℃to 80℃is preferable.
specifically, the solid content of the polyamic acid binder is 1wt% to 20wt%. More preferably 5wt% to 15wt%.
Specifically, mixing an electrode active material, a conductive agent and the polyamic acid binder obtained in the step 140, adding a solvent, stirring uniformly to obtain electrode slurry, regulating the electrode slurry to a proper viscosity, coating the electrode slurry on a current collector, and drying to obtain a pole piece to be treated;
and rolling and cutting the pole piece to be treated, putting the pole piece into a tube furnace, introducing inert gas, heating to 5 ℃/min, respectively maintaining the temperature at 100 ℃, 200 ℃ and 300 ℃ for 1 hour, imidizing polyamide acid into polyimide, and finally cooling to obtain the electrode pole piece containing the polyimide binder.
The electrode plate can be a positive plate or a negative plate;
when the modified polyimide binder is used for the positive plate, the positive active material can be specifically nickel cobalt lithium manganate, ferric phosphate lithium, lithium manganate, lithium cobaltate, nickel cobalt lithium aluminate, lithium-rich manganese-based positive material and the like.
When the modified polyimide binder is used for the negative electrode sheet, the negative electrode active material may specifically include one or more of nano silicon, micro silicon, silicon oxygen, and silicon carbon materials.
The conductive agent used may specifically include: one or a combination of a plurality of conductive carbon black, carbon fiber, conductive graphite and carbon nano tube.
In the electrode paste, the weight ratio of the electrode active material, the conductive agent and the modified polyimide binder is preferably 8:1:1.
the positive plate or the negative plate prepared by the method can be applied to lithium ion batteries.
The modified polyimide binder provided by the embodiment of the invention introduces self-repairing functional groups into the polyimide structure, improves the flexibility of the polymer, and combines good mechanical stability and thermal stability of polyimide; the polyimide structure obtains a self-healing effect by introducing a reversible covalent bond or a hydrogen bond of a self-healing functional group, can resist the expansion of active substances in the charge and discharge process, ensures the cycle stability and overcharge safety of the lithium ion battery, and solves the problem of low conductivity of the polymer; by utilizing the characteristic that the conjugated polymer is easy to be oxidized and reduced, the aromatic imide conjugated structure enables the lowest unoccupied molecular orbital (Lowest Unoccupied Molecular Orbital, LUMO) energy level of the polyimide to be low, n-type doping is easy to carry out, ions are embedded into the polymer, so that charges on a main chain are neutralized, the polyimide is quickly and reversibly changed from an insulating state into a conductive state, the electronic conductivity of a binder is improved, and the impedance is reduced; and the binder can also provide certain reversible capacity, which is helpful for improving the first coulombic efficiency and the circulation capacity of the battery.
In order to better understand the technical scheme provided by the invention, the following specific processes for preparing the modified polyimide binder by applying the method provided by the embodiment of the invention, and the method and the battery characteristics for applying the modified polyimide binder to the lithium ion battery are respectively described in a plurality of specific examples.
Example 1
The embodiment provides a lithium ion battery negative electrode binder which is a modified polyimide polymer and has the structural formula:
wherein, m is n=4:1.
The preparation method of the modified polyimide binder of the embodiment comprises the following steps: 8mmol of
And 2 mmol->
Dissolving diamine monomer in 40ml N-methyl pyrrolidone, continuously introducing nitrogen, stirring at room temperature to dissolve completely, adding 10.02mmol dianhydride monomer->
Stirring at room temperature for 12 hours to obtain a polymer solution. Adding 300ml deionized water into polymer solution after reaction, stirring and precipitating, washing and suction filtering the obtained precipitate, and vacuum drying at 60deg.C for 12 hr to obtain fibrous white and pale yellow polyamide acid solid powder with structural formula +.>
The polyamic acid solid powder was dissolved in N-methylpyrrolidone, and stirred sufficiently at 15℃to be completely dissolved, whereby a 10wt% polyamic acid binder solution was obtained.
The negative electrode material comprises the following components in terms of ZT-SC-600 silicon-carbon negative electrode material: conductive carbon black: the mass ratio of the polyamic acid binder is 80:10:10, adding N-methyl pyrrolidone, regulating to obtain slurry with viscosity of 10000 mPa.s, uniformly scraping the slurry on copper foil with thickness of 100 μm, and drying in an oven at 80deg.C to obtain the negative plate to be treated.
Finally rolling the negative electrode plate to be treated under the pressure of 20MPa, shearing off redundant copper foil, putting the negative electrode plate into a tube furnace, introducing inert gas, programming the temperature to be 5 ℃/min, respectively maintaining the temperature at 100 ℃, 200 ℃ and 300 ℃ for 1 hour, imidizing polyamide acid into polyimide, and finally cooling to obtain the negative electrode plate containing polyimide binder.
In the process, the polyimide contained in the polyamide acid solid powder and the final negative electrode plate in the process are tested for nuclear magnetic resonance hydrogen spectrum, the results are respectively shown in fig. 2 and 3, and the successful synthesis of the polyimide binder can be ensured through the verification of the nuclear magnetic resonance hydrogen spectrum.
For comparison, a traditional polyacrylate adhesive is adopted, and a preparation process is adopted to prepare the negative electrode plate for comparison. The composition of the negative electrode slurry in this comparative example was: ZT-SC-600 silicon carbon negative electrode material: conductive carbon black: the mass ratio of polyacrylate is 80:10:10, the solvent is water. After the slurry is uniformly stirred, the slurry is coated on a copper foil by a scraper with the thickness of 100 mu m, and is placed in an oven with the temperature of 80 ℃ for forced air drying for 2 hours, then is rapidly forced air dried for 1 hour at the temperature of 120 ℃, finally is deeply dried for 1.5 hours at the temperature of 110 ℃, and the negative plate for comparison is obtained after rolling.
The negative electrode plate containing the polyimide binder prepared above and the negative electrode plate for comparison prepared by the conventional polyacrylate binder are respectively subjected to stripping test and comparison, and the results are shown in table 1.
| Adhesive agent | Peel strength (kN/m) | Stripping force (N) |
| Polyimide binder | 0.0796 | 1.1954 |
| Traditional polyacrylate binders | 0.0175 | 0.2634 |
TABLE 1
It can be seen that the polyimide-containing adhesive provided by the invention has much better peel strength than conventional polyacrylate adhesives.
The negative electrode plate containing the polyimide binder and the negative electrode plate for comparison were tested by a four-probe method, and the measured resistivity was compared with that shown in table 2.
| Electrode binder | Resistivity (mΩ cm) |
| Polyimide binder | 82.2 |
| Traditional polyacrylate binders | 348.1 |
TABLE 2
It can be seen that the polyimide-containing adhesive provided by the invention greatly improves the electronic conductivity and effectively reduces the impedance.
The negative electrode plate containing the polyimide binder and the negative electrode plate containing the traditional polyacrylate binder are respectively manufactured into button cells for performance comparison. Adopts Celgard2300 model diaphragm, the metal is lithium cathode, 1MLiPF 6 @1:1 (EC) +dimethyl carbonate (DMC) is the electrolyte. The test results shown in fig. 4 were obtained by the test. As can be seen from fig. 4, the cycle stability and capacity retention rate of the negative electrode sheet prepared by using the polyimide binder of the present invention at 0.1C for 100 weeks are significantly better than those of the negative electrode sheet prepared by using the conventional polyacrylate binder.
Example 2
The embodiment provides a lithium ion battery negative electrode binder which is a modified polyimide polymer and has the structural formula:
wherein, m is n=3:1.
The preparation method of the modified polyimide binder of the embodiment comprises the following steps: will be 7.5mmol
And 2.5 mmol->
Dissolving diamine monomer in 40ml N-methyl pyrrolidone, continuously introducing nitrogen, stirring at room temperature to dissolve completely, adding 10.02mmol dianhydride monomer->
Stirring at room temperature for 12 hours to obtain a polymer solution. After the reaction is finished, 300ml of deionized water is added into a high polymer solution to be stirred and precipitated, and the obtained precipitate is washed and filtered, and is dried in vacuum for 12 hours at 60 ℃ to obtain fibrous white and pale yellow polyamide acid polymer solid powder。
The preparation method of the negative electrode sheet and the battery assembly process are the same as in example 1.
The negative electrode plate prepared by the polyimide binder disclosed by the invention circulates for 100 weeks at 0.1C, the circulation capacity retention rate and the first-week efficiency are obviously superior to those of the negative electrode plate prepared by the traditional polyacrylate binder, and the measured data are compared with each other as shown in Table 3.
| Electrode binder | Cycle capacity retention rate | First week efficiency |
| Polyimide binder | 92.4％ | 94.5％ |
| Traditional polyacrylate binders | 64.6％ | 86.5％ |
TABLE 3 Table 3
Example 3
The embodiment provides a lithium ion battery negative electrode binder which is a modified polyimide polymer and has the structural formula:
wherein, m is n=3:2.
The preparation method of the modified polyimide binder of the embodiment comprises the following steps: will be 6mmol
And 4 mmol->
Dissolving diamine monomer in 40ml N-methyl pyrrolidone, continuously introducing nitrogen, stirring at room temperature to dissolve completely, adding 10.02mmol dianhydride monomer->
Stirring at room temperature for 12 hours to obtain a polymer solution. After the reaction is completed, 300ml of deionized water is added into the high polymer solution to be stirred and precipitated, and the obtained precipitate is washed and filtered, and is dried in vacuum at 60 ℃ for 12 hours to obtain fibrous white and pale yellow polyamide acid polymer solid powder.
The preparation method of the negative electrode sheet and the battery assembly process are the same as in example 1.
The negative electrode plate prepared by the polyimide binder disclosed by the invention circulates for 100 weeks at 0.1C, the circulation capacity retention rate and the first-week efficiency are obviously superior to those of the negative electrode plate prepared by the traditional polyacrylate binder, and the measured data are compared with each other in Table 4.
| Electrode binder | Cycle capacity retention rate | First week efficiency |
| Polyimide binder | 90.6％ | 92.1％ |
| Traditional polyacrylate binders | 64.6％ | 86.5％ |
TABLE 4 Table 4
Example 4
The embodiment provides a negative electrode binder of a lithium ion battery, which is a modified polyimide polymer,
wherein m: n=1:1.
The preparation method of the modified polyimide binder of the embodiment comprises the following steps: will 5mmol
And 5 mmol->
Dissolving diamine monomer in 40ml N-methyl pyrrolidone, continuously introducing nitrogen, stirring at room temperature to dissolve completely, adding 10.02mmol dianhydride monomer->
Stirring at room temperature for 12 hours to obtain a polymer solution. After the reaction is completed, 300ml of deionized water is added into the high polymer solution to be stirred and precipitated, and the obtained precipitate is washed and filtered, and is dried in vacuum at 60 ℃ for 12 hours to obtain fibrous white and pale yellow polyamide acid polymer solid powder.
The preparation method of the negative electrode sheet and the battery assembly process are the same as in example 1.
The negative electrode plate prepared by the polyimide binder disclosed by the invention circulates for 100 weeks at 0.1C, the circulation capacity retention rate and the first-week efficiency are obviously superior to those of the negative electrode plate prepared by the traditional polyacrylate binder, and the measured data are compared with each other in Table 5.
| Electrode binder | Cycle capacity retention rate | First week efficiency |
| Polyimide binder | 95.8％ | 93.8％ |
| Traditional polyacrylate binders | 64.6％ | 86.5％ |
TABLE 5
Example 5
The embodiment provides a negative electrode binder of a lithium ion battery, which is a modified polyimide polymer,
wherein, m is n=2:3.
The preparation method of the modified polyimide binder of the embodiment comprises the following steps: will be 4mmol
And 6 mmol->
Dissolving diamine monomer in 40ml N-methyl pyrrolidone, continuously introducing nitrogen, stirring at room temperature to dissolve completely, adding 10.02mmol dianhydride monomer->
Stirring at room temperature for 12 hours to obtain highA molecular solution. After the reaction is completed, 300ml of deionized water is added into the high polymer solution to be stirred and precipitated, and the obtained precipitate is washed and filtered, and is dried in vacuum at 60 ℃ for 12 hours to obtain fibrous white and pale yellow polyamide acid polymer solid powder.
The preparation method of the negative electrode sheet and the battery assembly process are the same as in example 1.
The negative electrode plate prepared by the polyimide binder disclosed by the invention circulates for 100 weeks at 0.1C, the circulation capacity retention rate and the first-week efficiency are obviously superior to those of the negative electrode plate prepared by the traditional polyacrylate binder, and the measured data are compared with each other in Table 6.
| Electrode binder | Cycle capacity retention rate | First week efficiency |
| Polyimide binder | 96.1％ | 96.7％ |
| Traditional polyacrylate binders | 64.6％ | 86.5％ |
TABLE 6
Example 6
The embodiment provides a negative electrode binder of a lithium ion battery, which is a modified polyimide polymer,
wherein, m: n=1:3.
The preparation method of the modified polyimide binder of the embodiment comprises the following steps: will be 2.5mmol
And 7.5 mmol->
Dissolving diamine monomer in 40ml N-methyl pyrrolidone, continuously introducing nitrogen, stirring at room temperature to dissolve completely, adding 10.02mmol dianhydride monomer->
Stirring at room temperature for 12 hours to obtain a polymer solution. After the reaction is completed, 300ml of deionized water is added into the high polymer solution to be stirred and precipitated, and the obtained precipitate is washed and filtered, and is dried in vacuum at 60 ℃ for 12 hours to obtain fibrous white and pale yellow polyamide acid polymer solid powder.
The preparation method of the negative electrode sheet and the battery assembly process are the same as in example 1.
The negative electrode plate prepared by the polyimide binder disclosed by the invention circulates for 100 weeks at 0.1C, the circulation capacity retention rate and the first-week efficiency are obviously superior to those of the negative electrode plate prepared by the traditional polyacrylate binder, and the measured data are compared with table 7.
| Electrode binder | Cycle capacity retention rate | First week efficiency |
| Polyimide binder | 89.9％ | 98.2％ |
| Traditional polyacrylate binders | 64.6％ | 86.5％ |
TABLE 7
Example 7
The embodiment provides a negative electrode binder of a lithium ion battery, which is a modified polyimide polymer,
wherein, m is n=1:4.
The preparation method of the modified polyimide binder of the embodiment comprises the following steps: will be 2mmol
And 8 mmol->
Dissolving diamine monomer in 40 mLN-methyl pyrrolidone, continuously introducing nitrogen, stirring at room temperature to dissolve completely, adding 10.02mmol dianhydride monomer->
Stirring at room temperature for 12 hours to obtain a polymer solution. After the reaction is completed, 300ml of deionized water is added into the high polymer solution to be stirred and precipitated, and the obtained precipitate is washed and filtered, and is dried in vacuum at 60 ℃ for 12 hours to obtain fibrous white and pale yellow polyamide acid polymer solid powder.
The preparation method of the negative electrode sheet and the battery assembly process are the same as in example 1.
The negative electrode plate prepared by the polyimide binder disclosed by the invention circulates for 100 weeks at 0.1C, the circulation capacity retention rate and the first-week efficiency are obviously superior to those of the negative electrode plate prepared by the traditional polyacrylate binder, and the measured data are compared with table 8.
| Electrode binder | Cycle capacity retention rate | First week efficiency |
| Polyimide binder | 86.4％ | 95.4％ |
| Traditional polyacrylate binders | 64.6％ | 86.5％ |
TABLE 8
The modified polyimide binder provided by the invention can be applied to the anode material system and also can be applied to the cathode material system. Suitable positive electrode materials include nickel cobalt lithium manganate, lithium iron phosphate, lithium manganate, lithium cobaltate, nickel cobalt lithium aluminate, lithium-rich manganese-based and other positive electrode materials.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (9)
1. The modified polyimide adhesive is characterized by having a structural general formula as follows:
wherein, m is n=5:1-1:5; the polymerization degree m+n is an integer of 100 to 5000;
the structural formula of R1 contains self-repairing functional groups, wherein the self-repairing functional groups are disulfide bond or polysulfide bond functional groups containing dynamic reversible covalent bonds;
the structural formulas of R2 and R3 are conjugated structures, and monomers before the reaction of R2 and R3 respectively comprise any one of aromatic compounds, heterocyclic compounds, aromatic derivatives and heterocyclic derivatives;
the monomer before the reaction of R1 is one or more of diaryl disulfide, dialkyl disulfide and bi-heterocyclic disulfide;
the monomer before the R1 reaction is specifically
The monomer before the reaction of R2 is specifically +.>
The monomer before the reaction of R3 is specifically +.>
2. The modified polyimide binder according to claim 1, wherein the monomer before the reaction of R2 is one or more of benzene, naphthalene, perylene, anthracene, pyrrole, thiophene, and furan;
the monomer before the R3 reaction is one or more of benzoquinone, naphthalene, perylene, anthracene, imidazole, thiazole and oxazole.
3. A method for preparing the modified polyimide adhesive according to any one of claims 1 to 2, comprising:
under the protection of nitrogen, dissolving diamine monomer in an organic solvent, and stirring and dissolving at room temperature to obtain a first solution;
adding dianhydride monomer into the first solution, and continuing stirring and reacting for 12-24 hours at room temperature to obtain polyamic acid solution;
precipitating the polyamic acid solution in a poor solvent, washing, suction filtering and drying to obtain polyamic acid solid powder;
dissolving polyamic acid solid powder in proper amount of N-methyl pyrrolidone solvent to obtain polyamic acid adhesive;
the polyamide acid binder is formed into a modified polyimide binder after pole piece coating, rolling and heat treatment.
4. The method according to claim 3, wherein the organic solvent is one or a mixture of several of tetrahydrofuran, N-methylpyrrolidone, N-dimethylacetamide, N-dimethylformamide;
the ratio of the organic solvent to the diamine monomer is set according to the structural general formula of the finally obtained modified polyimide adhesive, wherein R1:R3=5:1-1:5;
the amount of the dianhydride monomer and the diamine monomer are the same;
the modified polyimide binder has the structural general formula:
5. The method according to claim 3, wherein the polyamic acid solution has a solid content of 8 to 12% by weight; the solid content of the polyamic acid binder is 1wt% to 20wt%.
6. The method according to claim 3, wherein the poor solvent comprises one or more of deionized water, methanol, ethanol, isopropanol, ethylene glycol, 2-butanol, cyclopentanol, cyclohexanol, and phenol.
7. A method of preparation according to claim 3, wherein the drying temperature is not higher than 150 ℃.
8. An electrode sheet characterized in that the electrode sheet is a positive electrode sheet or a negative electrode sheet, comprising the modified polyimide binder according to any one of the preceding claims 1-2.
9. A lithium ion battery comprising the electrode sheet of claim 8.
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