A method for preparing a tricellulose acetate-based binder and its application in sodium-ion batteries

Abstract

The application discloses a preparation method of a cellulose triacetate-based binder and application of the binder in a sodium ion battery, and the method comprises the following steps: firstly, cellulose triacetate is stirred and dissolved in N-methyl pyrrolidone to obtain a solution with a proper viscosity; and then, montmorillonite is added into the solution and stirred to be fully dispersed, so as to obtain the cellulose triacetate-based binder. The cellulose triacetate-based binder prepared by the method has wide sodium battery cathode protection compatibility, high ionic conductivity and excellent adhesion, and can be used for constructing a high-performance sodium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion battery cathode binder materials, and particularly relates to a preparation method of a cellulose triacetate-based binder and application thereof in sodium ion batteries. BACKGROUND

[0002] Sodium ion batteries have attracted considerable attention due to their natural abundance, low cost, and widespread availability of sodium resources, making them a promising alternative to lithium ion batteries. These advantages make sodium ion batteries a sustainable and cost-effective solution for large-scale energy storage, particularly in grid-scale systems. However, the development of high-performance sodium ion batteries faces major challenges, including limited ionic conductivity, poor cathode structural integrity, and low cycle stability under high voltage conditions. Among the various factors affecting the performance of sodium ion battery cathodes, the choice of binder plays a key role in maintaining electrode integrity, improving ionic conductivity, and promoting effective charge transport during charge and discharge cycles.

[0003] Traditional water-based and organic solvent-based binders have been widely used in lithium ion batteries. However, their application in sodium ion batteries is hindered by several limitations. Water-based adhesives are particularly limited by the humidity sensitivity of sodium ion battery cathodes. For example, some layered oxide cathodes undergo structural degradation when exposed to moisture. Similarly, some polyanion cathodes experience moisture-induced crystal structure degradation, resulting in increased internal resistance. These moisture-related drawbacks make water-based adhesives unsuitable as a universal solution for sodium ion battery cathodes. In addition, organic solvent-based adhesives also face major challenges, including low ionic conductivity and insufficient adhesion strength. Polyvinylidene fluoride (PVDF) is the most commonly used organic adhesive, which relies on weak van der Waals interactions with active materials and current collectors, resulting in poor structural stability during cycling. In addition, the low ionic conductivity of PVDF hinders the kinetics of cathode reactions, ultimately limiting the electrochemical performance of sodium ion batteries. Environmental issues and the non-renewability of organic solvent-based adhesives further emphasize the need to develop biologically sustainable alternatives. Biomass-based adhesives are a promising approach for energy storage applications due to their renewability, environmental friendliness, and intrinsic functional properties. However, simultaneously achieving the wide compatibility, high ionic conductivity, and excellent adhesion strength required for high-voltage sodium ion battery cathodes remains a major challenge. Therefore, developing a biomass-based adhesive that can meet these stringent requirements is a key research focus. SUMMARY

[0004] In view of the above problems existing in the cathode binder of sodium ion battery, the application provides a preparation method of a triacetyl cellulose-based binder, which realizes the balance of wide compatibility, high ionic conductivity and excellent bonding strength required by the cathode of high-voltage sodium ion battery through self-enrichment fast transmission mechanism, hydrogen bond crosslinking network and excellent film-forming property.

[0005] In order to achieve the above purposes, the application adopts the following technical solutions:

[0006] The preparation method of the triacetyl cellulose-based binder comprises the following steps:

[0007] Step 1: triacetyl cellulose (TAC) is stirred in N-methyl pyrrolidone until dissolved to obtain solution A;

[0008] Step 2: montmorillonite (MMT) is added into N-methyl pyrrolidone and stirred to obtain dispersion B;

[0009] Step 3: dispersion B is added into solution A, and the obtained mixture is stirred and ultrasonically dispersed to obtain the triacetyl cellulose-based binder.

[0010] Preferably, in the mixture, the concentration of triacetyl cellulose is 0.8 g / 15 mL, so as to ensure that the viscosity of the solution is suitable for use as a binder.

[0011] Preferably, in the mixture, the mass of montmorillonite accounts for 1% to 5% of the mass of triacetyl cellulose, so as to ensure that the obtained binder has high ionic conductivity. Most preferably, the mass of montmorillonite accounts for 3% of the mass of triacetyl cellulose.

[0012] Preferably, in step 1, the stirring time is 16 to 24 hours, and the stirring temperature is 50 to 70 DEG C, so as to ensure that triacetyl cellulose is fully dissolved and has no residue.

[0013] Preferably, in step 2, the stirring time is 16 to 24 hours, and the stirring temperature is room temperature, so as to ensure that montmorillonite is fully pre-dispersed and prevent montmorillonite from gathering.

[0014] Preferably, in step 3, the stirring time is 16 to 24 hours, and the stirring temperature is 50 to 70 DEG C, so as to ensure that triacetyl cellulose and montmorillonite are fully mixed, which is conducive to the dispersion of montmorillonite.

[0015] Preferably, in step 3, the ultrasonic time is 1 to 2 hours, so as to make montmorillonite fully and uniformly dispersed in triacetyl cellulose.

[0016] Preferably, the stirring speed in steps 1 to 3 is 400 to 600 rpm.

[0017] The cellulose triacetate-based binder prepared by the application can be used in sodium ion batteries.

[0018] Compared with the prior art, the beneficial effects of the application are embodied in:

[0019] The application prepares a cellulose triacetate-based binder (TAC-MMT) by interweaving natural montmorillonite (MMT) and cellulose triacetate (TAC). The binder provides wide compatibility, high ionic conductivity and excellent bonding strength for the cathode of a high-voltage sodium ion battery. Cellulose triacetate is an esterification product of cellulose, which can ensure excellent solubility and compatibility with the cathode of a sodium ion battery, and trace montmorillonite is a naturally abundant clay mineral with a negatively charged surface potential, which enhances the transport of sodium ions through a self-enrichment mechanism, thereby improving ionic conductivity. In addition, the hydrogen bond network between the proton acceptor (C=O) in cellulose triacetate and the proton donor (-OH) in montmorillonite significantly improves the bonding strength. These synergistic properties enable the sodium ion battery to operate efficiently under high-voltage conditions, ensuring long-term cycle stability. By combining environmentally friendly design principles with outstanding properties, this work provides a sustainable approach to advancing high-performance sodium ion battery technology. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The Fourier transform infrared spectrum of the TAC-MMT obtained in Example 1 of the application;

[0021] Figure 2 The scanning electron microscope image of the TAC-MMT film obtained in Example 1 of the application;

[0022] Figure 3 The X-ray diffraction pattern of the TAC-MMT obtained in Example 1 of the application;

[0023] Figure 4 The electrochemical impedance spectrogram of the TAC-MMT obtained in Example 1 of the application;

[0024] Figure 5 The stress-strain curve of the TAC-MMT obtained in Example 1 of the application after film formation;

[0025] Figure 6 The cycle performance test curve of the assembled half-cell when the TAC-MMT obtained in Example 1 of the application is used as the binder of the sodium vanadium oxyfluorophosphate cathode, the test rate is 1C, and the voltage interval is 2-4.3V.

[0026] Figure 7 The first cycle charge-discharge curve of the assembled half-cell when the TAC-MMT obtained in Example 1 of the application is used as the binder of the sodium vanadium oxyfluorophosphate cathode, the test rate is 0.1C, and the voltage interval is 2-4.3V.

[0027] Figure 8 SEM images of the electrode integrity of the TAC-MMT obtained in Example 1 as the binder for sodium fluorovanadate cathode, wherein (a) is before cycle test, and (b) is after 100 cycles of cycle test.

[0028] Figure 9 The ion conductivity test chart of the TAC film obtained in Example 2 with different MMT addition contents.

[0029] Figure 10 The Fourier transform infrared spectrum of the PVDF binder obtained in Comparative Example 1 of the present application.

[0030] Figure 11 The SEM image of the PVDF film obtained in Comparative Example 1 of the present application.

[0031] Figure 12 The X-ray diffraction spectrum of the PVDF binder obtained in Comparative Example 1 of the present application.

[0032] Figure 13 The electrochemical impedance spectrum of the PVDF binder obtained in Comparative Example 1 of the present application.

[0033] Figure 14 The stress-strain curve of the PVDF binder obtained in Comparative Example 1 of the present application after film formation.

[0034] Figure 15 The cycle performance test curve of the assembled half-cell when the PVDF binder obtained in Comparative Example 1 of the present application is used as the binder for sodium fluorovanadate cathode, the test rate is 1C, and the voltage interval is 2-4.3V.

[0035] Figure 16 The first cycle charge-discharge curve of the assembled half-cell when the PVDF binder obtained in Comparative Example 1 of the present application is used as the binder for sodium fluorovanadate cathode, the test rate is 0.1C, and the voltage interval is 2-4.3V.

[0036] Figure 17 The SEM images of the electrode integrity of the PVDF binder obtained in Comparative Example 1 of the present application as the binder for sodium fluorovanadate cathode, wherein (a) is before cycle test, and (b) is after 100 cycles of cycle test.

[0037] Figure 18 The electrochemical impedance spectrum of the TAC binder obtained in Comparative Example 2 of the present application.

[0038] Figure 19 The stress-strain curve of the TAC binder obtained in Comparative Example 2 of the present application after film formation.

[0039] Figure 20 The cycle performance test curve of the assembled half-cell when the TAC obtained in Invention Comparative Example 2 was used as the binder of the sodium vanadium fluorophosphate oxy-cathode, the test rate was 1C, and the voltage interval was 2-4.3V.

[0040] Figure 21 The first cycle charge-discharge curve of the assembled half-cell when the TAC obtained in Invention Comparative Example 2 was used as the binder of the sodium vanadium fluorophosphate oxy-cathode, the test rate was 0.1C, and the voltage interval was 2-4.3V. DETAILED DESCRIPTION

[0041] In order to further illustrate the present application, the preparation method and application of the triacetyl cellulose-based binder provided by the present application are described in detail below in combination with examples, and are described in combination with the drawings, but it should not be understood as limiting the scope of protection of the present application.

[0042] Example 1

[0043] The triacetyl cellulose-based binder was prepared according to the following steps:

[0044] Step 1: 0.8g of TAC was dissolved in 10ml of N-methyl pyrrolidone, and stirred and dissolved at 60°C for 24 hours to obtain solution A, and the color of the solution was colorless and transparent.

[0045] Step 2: 0.024g of MMT was added to 5ml of N-methyl pyrrolidone, and stirred at room temperature for 24 hours to pre-disperse the MMT, and obtain dispersion liquid B.

[0046] Step 3: Dispersion liquid B was added to solution A, and stirred at 60°C for 24 hours, and then ultrasonically treated for 2 hours to fully disperse the MMT without aggregation, and obtain the triacetyl cellulose-based binder, which is recorded as TAC-MMT.

[0047] Figure 1 The Fourier transform infrared spectrum of the TAC-MMT obtained in Example 1 showed that the acetyl ester group C=O occurred at 1740cm -1 , the peak value at 1366cm -1 corresponded to the vibration of the -CH3 group. The characteristic absorption peaks at 1035cm -1 and 1220cm -1 were attributed to the C-O-C bond in the TAC molecular framework. The disappearance of the MMT characteristic peak indicated that the particles were uniformly dispersed without aggregation.

[0048] In order to verify the film forming ability, a TAC-MMT film was manufactured by using a doctor blade method, and dried in a vacuum oven at 60°C for 24 hours. Figure 2 The scanning electron microscope image of the TAC-MMT film obtained in Example 1 showed that the flat morphology indicated excellent film forming property.

[0049] Figure 3 The X-ray diffraction pattern of the TAC-MMT obtained in Example 1 is mainly composed of TAC, and the disappearance of the MMT peak indicates uniform dispersion.

[0050] Figure 4 The electrochemical impedance spectrum of the TAC-MMT obtained in Example 1 is shown in the figure. As can be seen from the figure, the ionic conductivity of the TAC-MMT is 1.71 x 10 -4 S cm -1 .

[0051] Figure 5 The stress-strain curve of the TAC-MMT obtained in Example 1 after film formation is shown in the figure. As can be seen from the figure, the tensile strength of the TAC-MMT reaches 69.46 MPa.

[0052] A sodium fluorophosphate vanadate (Na3V2(PO4)2O2F) cathode was used as the active material, TAC-MMT was used as the binder, and Ketjen black was used as the conductive agent. An electrode slurry was prepared by uniformly mixing the materials in a mass ratio of 8:1:1, uniformly coated on an aluminum foil using a doctor blade method, dried in a vacuum oven at 80°C overnight, and then placed in a glove box for standby. A glass fiber GF / D was used as the battery separator, a 5% FEC solution in 1 mol L -1 of sodium perchlorate PC was used as the electrolyte, and a sodium foil was used as the counter electrode to assemble a CR2032 button cell for electrochemical testing.

[0053] Figure 6 When the TAC-MMT obtained in Example 1 was used as the binder of the sodium fluorophosphate vanadate cathode, the cycle performance test curve of the assembled half-cell was obtained. The test rate was 1C, and the voltage interval was 2-4.3V. After 100 cycles, the battery showed excellent cycle stability, with a capacity retention rate of 93.93%.

[0054] Figure 7 When the TAC-MMT obtained in Example 1 was used as the binder of the sodium fluorophosphate vanadate cathode, the first cycle charge-discharge curve of the assembled half-cell was obtained. The test rate was 0.1C, and the voltage interval was 2-4.3V. The first cycle coulombic efficiency was 90.21%, indicating that the TAC-MMT binder effectively inhibited the decomposition of the electrolyte at high voltage.

[0055] Figure 8 When the TAC-MMT obtained in Example 1 was used as the binder of the sodium fluorophosphate vanadate cathode, the adhesion between the electrode and the current collector was tested. After 100 cycles at a rate of 1C, the electrode still maintained the integrity with the current collector, indicating that the TAC-MMT had excellent adhesion and could meet the requirements of stable cycling of the cathode at high voltage.

[0056] Example 2

[0057] This embodiment is prepared by the same method as example 1, the only difference is that the amount of MMT added in step 2 is adjusted to 0.008g, 0.016g, 0.024g, 0.032g, 0.040g, respectively, so that the mass of MMT accounts for 1%, 2%, 3%, 4%, 5% of the mass of TAC, respectively.

[0058] Figure 9 The ion conductivity test diagram of the TAC film with different MMT addition contents obtained in example 2 is shown, and the ion conductivities of the samples obtained under the addition amounts of 1% to 5% are 0.78×10 -4 S cm -1 , 1.02×10 -4 S cm -1 , 1.71×10 -4 S cm -1 , 1.2×10 -4 S cm -1 , 0.89×10 -4 S cm -1 , respectively. It can be seen that the addition of 3% of MMT can effectively improve the transmission performance of ions, which is the best addition content.

[0059] Comparative Example 1

[0060] The PVDF material is prepared according to the following steps:

[0061] Step 1, first dissolve 0.08g of PVDF in 10ml of N-methyl pyrrolidone, stir at 60°C for 24 hours to make it fully dissolved, and obtain a PVDF binder.

[0062] Step 2, to verify the film forming ability, a doctor blade method is used to make a PVDF film, and dry it in a vacuum oven at 60°C for 24 hours.

[0063] Figure 10 The Fourier transform infrared spectrum of the PVDF binder obtained in comparative example 1.

[0064] Figure 11 The scanning electron microscope image of the PVDF binder film obtained in comparative example 1, the porous morphology shows that the film forming property is poor, and it is difficult to form a stable protection on the surface of the electrode.

[0065] Figure 12 The X-ray diffraction spectrum of the PVDF binder obtained in comparative example 1.

[0066] Figure 13 The electrochemical impedance spectrum of the PVDF binder obtained in comparative example 1, as shown in the figure, the ion conductivity of PVDF is 3.41×10 -6 S cm-1 , which is two orders of magnitude lower than TAC-MMT.

[0067] Figure 14 The stress-strain curve of the PVDF binder obtained in Comparative Example 1 is shown in the figure. As can be seen, the tensile strength of the PVDF is 27.38 MPa, and the bonding strength is weak, which is difficult to ensure the integrity of the electrode during the battery cycle.

[0068] Figure 15 The cycle performance test curve of the half battery assembled using the PVDF binder obtained in Comparative Example 1 as the binder of the sodium fluorophosphate vanadate cathode, the test rate is 1C, and the voltage interval is 2-4.3V. It can be seen that the battery capacity retention rate is low.

[0069] Figure 16 The first cycle charge-discharge curve of the half battery assembled using the PVDF binder obtained in Comparative Example 1 as the binder of the sodium fluorophosphate vanadate cathode, the test rate is 0.1C, and the voltage interval is 2-4.3V. The first cycle coulombic efficiency is only 78.11%, indicating that the PVDF binder is difficult to inhibit the continuous decomposition of the electrolyte at high voltage.

[0070] Figure 17 The adhesion test between the electrode and the current collector when the PVDF binder obtained in Comparative Example 1 is used as the binder of the sodium fluorophosphate vanadate cathode. After 100 cycles at a rate of 1C, there is a clear split between the electrode and the current collector of more than 5 microns, indicating that PVDF cannot meet the requirements of stable cycle of the cathode at high voltage.

[0071] Comparative Example 2

[0072] In this comparative example, the amount of MMT added in step 2 of Example 1 is adjusted to 0, and a TAC binder based on triacetate cellulose is prepared.

[0073] Figure 18 The electrochemical impedance spectrum of the TAC binder obtained in Comparative Example 2 is shown in the figure. As can be seen, the ionic conductivity of TAC is 0.41 x 10 -4 S cm -1 .

[0074] Figure 19 The stress-strain curve of the TAC binder obtained in Comparative Example 2 after film formation is shown in the figure. As can be seen, the tensile strength of TAC is 43.58 MPa.

[0075] Figure 20 The cycle performance test curve of the half battery assembled using the TAC binder obtained in Comparative Example 2 as the binder of the sodium fluorophosphate vanadate cathode, the test rate is 1C, and the voltage interval is 2-4.3V. After 100 cycles, the battery capacity retention rate is 85.64%.

[0076] Figure 21 When the TAC binder obtained in Comparative Example 2 was used as a binder for a sodium vanadium oxyfluorophosphate cathode, the first cycle charge-discharge curve of the assembled half battery was tested at a rate of 0.1 C and a voltage range of 2-4.3 V, and the first cycle coulombic efficiency was 82.06%.

[0077] The above merely illustrates the exemplary embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a cellulose triacetate-based adhesive, characterized in that, Includes the following steps: Step 1: Dissolve cellulose triacetate in N-methylpyrrolidone to obtain solution A; Step 2: Add montmorillonite to N-methylpyrrolidone and stir to obtain dispersion B; Step 3: Add dispersion B to solution A, stir the resulting mixture and sonicate until uniformly dispersed to obtain cellulose triacetate-based binder; in the mixture, the mass of montmorillonite accounts for 1% to 5% of the mass of cellulose triacetate.

2. The preparation method according to claim 1, characterized in that: In the mixture, the concentration of cellulose triacetate is 0.8 g / 15 mL.

3. The preparation method according to claim 1, characterized in that: In the mixture, montmorillonite accounts for 3% of the mass of cellulose triacetate.

4. The preparation method according to claim 1, characterized in that: In step 1, the stirring time is 16~24h and the stirring temperature is 50~70℃.

5. The preparation method according to claim 1, characterized in that: In step 2, the stirring time is 16-24 hours and the stirring temperature is room temperature.

6. The preparation method according to claim 1, characterized in that: In step 3, the stirring time is 16~24h and the stirring temperature is 50~70℃.

7. The preparation method according to claim 1, characterized in that: In step 3, the ultrasound duration is 1-2 hours.

8. The preparation method according to claim 1, characterized in that: The stirring speed in steps 1 to 3 is 400 to 600 rpm.

9. A cellulose triacetate-based binder prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the cellulose triacetate-based binder of claim 9 in a sodium-ion battery.

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