Preparation method of cellulose triacetate-based binder and application of cellulose triacetate-based binder in sodium-ion battery

Abstract

The invention discloses a preparation method of a cellulose triacetate-based binder and application of the cellulose triacetate-based binder in a sodium ion battery, and the method comprises the following steps: firstly, stirring and dissolving cellulose triacetate in N-methyl pyrrolidone to obtain a solution with proper viscosity, then adding montmorillonite into the solution, and stirring and fully dispersing to obtain the cellulose triacetate-based binder. The cellulose triacetate-based binder prepared by the invention has wide sodium-ion cathode protection compatibility, high ionic conductivity and excellent cohesiveness, and can be used for constructing a high-performance sodium-ion battery.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion battery cathode binder materials, and in particular to a preparation method of a triacetyl cellulose-based binder and application thereof in a sodium ion battery. Background Art

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

[0003] Conventional water-based and organic solvent-based binders have been widely used in lithium-ion batteries. However, their application in sodium-ion batteries is hampered by several limitations. Water-based binders are particularly limited by the moisture 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 disadvantages make water-based binders unsuitable as a universal solution for sodium-ion battery cathodes. In addition, organic solvent-based binders also face significant challenges, including low ionic conductivity and insufficient bonding strength. Polyvinylidene fluoride (PVDF), the most commonly used organic binder, 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 cathode reaction kinetics, ultimately limiting the electrochemical performance of sodium-ion batteries. Environmental concerns and the non-renewable nature of organic solvent-based binders further emphasize the need to develop biomass-based sustainable alternatives. Biomass-based binders are a promising avenue for energy storage applications due to their renewability, environmental friendliness, and intrinsic functional properties. However, simultaneously achieving the broad compatibility, high ionic conductivity, and excellent bonding strength required for high-voltage sodium-ion battery cathodes remains a major challenge. Therefore, developing a biomass-based binder that can meet these stringent requirements is a key research priority. Summary of the invention

[0004] In view of the above-mentioned problems currently existing in the cathode binder of sodium ion batteries, the present invention provides a method for preparing a triacetyl cellulose-based binder, which achieves a balance between the wide compatibility, high ionic conductivity and excellent bonding strength required for the cathode of high-voltage sodium ion batteries through a self-enrichment fast transport mechanism, a hydrogen bond cross-linking network and excellent film-forming properties.

[0005] In order to achieve the purpose, the present invention adopts the following technical scheme:

[0006] A method for preparing a triacetyl cellulose-based binder comprises the following steps:

[0007] Step 1, stirring triacetyl cellulose (TAC) in N-methylpyrrolidone until dissolved to obtain solution A;

[0008] Step 2, adding montmorillonite (MMT) into N-methylpyrrolidone and stirring to obtain dispersion B;

[0009] Step 3: Add dispersion B into solution A, stir the resulting mixture and perform ultrasound until the mixture is uniformly dispersed to obtain a triacetylcellulose-based binder.

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

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

[0012] Preferably, in step 1, the stirring time is 16 to 24 hours and the stirring temperature is 50 to 70° C. to ensure that the cellulose triacetate is fully dissolved without residue.

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

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

[0015] Preferably, in step 3, the ultrasonic treatment time is 1 to 2 hours so that the montmorillonite is fully and evenly dispersed in the cellulose triacetate.

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

[0017] The triacetylcellulose-based binder prepared by the present invention can be used in sodium ion batteries.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The present invention prepares a triacetate cellulose-based binder (TAC-MMT) by interweaving natural montmorillonite (MMT) with triacetate cellulose (TAC). This binder provides wide compatibility, high ionic conductivity and excellent bonding strength for high-voltage sodium-ion battery cathodes. Cellulose triacetate is an esterification product of cellulose, which ensures excellent solubility and compatibility with the cathode of sodium-ion batteries, while trace amounts of montmorillonite are 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 triacetate cellulose and the proton donor (-OH) in montmorillonite significantly improves the bonding strength. These synergistic properties enable sodium-ion batteries to operate efficiently under high-voltage conditions, ensuring long-term cycling stability. By combining environmentally friendly design principles with excellent properties, this work provides a sustainable approach to advance high-performance sodium-ion battery technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the Fourier transform infrared spectrum of TAC-MMT obtained in Example 1 of the present invention;

[0021] Figure 2 This is a scanning electron microscope image of the TAC-MMT film obtained in Example 1 of the present invention;

[0022] Figure 3 This is the X-ray diffraction pattern of TAC-MMT obtained in Example 1 of the present invention;

[0023] Figure 4 This is the electrochemical impedance spectrum of TAC-MMT obtained in Example 1 of the present invention;

[0024] Figure 5 This is the stress-strain curve of TAC-MMT film formed in Example 1 of the present invention;

[0025] Figure 6 When the TAC-MMT obtained in Example 1 of the present invention is used as a binder for the sodium vanadyl fluorophosphate cathode, the cycle performance test curve of the assembled half-cell has a test rate of 1C and a voltage range of 2 to 4.3V.

[0026] Figure 7 When the TAC-MMT obtained in Example 1 of the present invention is used as the binder for the sodium vanadyl fluorophosphate cathode, the first cycle charge and discharge curve of the assembled half-cell has a test rate of 0.1C and a voltage range of 2 to 4.3V.

[0027] Figure 8 Scanning electron microscope images of electrode integrity when TAC-MMT obtained in Example 1 of the present invention is used as a binder for a sodium vanadyl fluorophosphate cathode, wherein (a) is before the cycle test, and (b) is after 100 cycles of the cycle test.

[0028] Fig. 9 This is a test chart of the ionic conductivity of TAC films with different MMT addition contents obtained in Example 2.

[0029] Fig.10 This is the Fourier transform infrared spectrum of the PVDF binder obtained in Comparative Example 1 of the present invention.

[0030] Fig.11 This is a scanning electron microscope image of the PVDF film obtained in Comparative Example 1 of the present invention.

[0031] Fig.12 This is the X-ray diffraction pattern of the PVDF binder obtained in Comparative Example 1 of the present invention.

[0032] Fig.13 This is the electrochemical impedance spectrum of the PVDF binder obtained in Comparative Example 1 of the present invention.

[0033] Fig.14 This is the stress-strain curve of the PVDF adhesive obtained in Comparative Example 1 of the present invention after film formation.

[0034] Fig.15 When the PVDF binder obtained in Comparative Example 1 of the present invention is used as the binder of the sodium vanadyl fluorophosphate cathode, the cycle performance test curve of the assembled half-cell has a test rate of 1C and a voltage range of 2 to 4.3V.

[0035] Fig.16 When the PVDF binder obtained in Comparative Example 1 of the present invention is used as the binder of the sodium vanadyl fluorophosphate cathode, the first cycle charge and discharge curve of the assembled half-cell has a test rate of 0.1C and a voltage range of 2 to 4.3V.

[0036] Fig.17 Scanning electron microscope images of electrode integrity when the PVDF binder obtained in Comparative Example 1 of the present invention is used as a binder for the sodium vanadyl fluorophosphate cathode, wherein (a) is before the cycle test, and (b) is after 100 cycles of the cycle test.

[0037] Fig.18 This is the electrochemical impedance spectrum of the TAC binder obtained in Comparative Example 2 of the present invention.

[0038] Fig.19 This is the stress-strain curve of the TAC adhesive obtained in Comparative Example 2 of the present invention after film formation.

[0039] Fig. 20 When the TAC obtained in Comparative Example 2 of the present invention is used as a binder for the sodium vanadyl fluorophosphate cathode, the cycle performance test curve of the assembled half-cell has a test rate of 1C and a voltage range of 2 to 4.3V.

[0040] Fig.21 When the TAC obtained in Comparative Example 2 of the present invention is used as the binder for the sodium vanadyl fluorophosphate cathode, the first cycle charge and discharge curve of the assembled half-cell has a test rate of 0.1C and a voltage range of 2 to 4.3V. DETAILED DESCRIPTION

[0041] In order to further illustrate the present invention, the preparation method and application of a triacetyl cellulose-based binder provided by the present invention are described in detail below in conjunction with the embodiments and illustrated in conjunction with the accompanying drawings, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] In this embodiment, a triacetylcellulose-based binder is prepared according to the following steps:

[0044] Step 1: Dissolve 0.8 g of TAC in 10 mL of N-methylpyrrolidone and stir to dissolve at 60° C. for 24 hours to obtain solution A, which is colorless and transparent.

[0045] Step 2: Add 0.024 g of MMT into 5 mL of N-methylpyrrolidone and stir at room temperature for 24 hours to pre-disperse the MMT to obtain dispersion B.

[0046] Step 3: Add dispersion B into solution A, stir at 60° C. for 24 hours, and then ultrasonicate for 2 hours to fully disperse the MMT without agglomeration, thereby obtaining a triacetylcellulose-based binder, which is recorded as TAC-MMT.

[0047] Figure 1 This is the Fourier transform infrared spectrum of TAC-MMT obtained in Example 1, showing that the acetyl ester group C=O is at 1740 cm -1 Extension vibration occurs at 1366cm -1 The peak at 1035cm corresponds to the vibration of the -CH3 group. -1 and 1220cm -1 The characteristic absorption peak at is attributed to the COC bond within the TAC molecular framework. The disappearance of the MMT characteristic peak indicates that the particles are uniformly dispersed without aggregation.

[0048] To verify the film-forming ability, TAC-MMT films were fabricated by the doctor blade method and dried in a vacuum oven at 60 °C for 24 h. Figure 2 This is a scanning electron microscope image of the TAC-MMT film obtained in Example 1. The smooth morphology indicates excellent film-forming properties.

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

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

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

[0052] Sodium vanadium fluorophosphate (Na3V2(PO4)2O2F) cathode was used as active material, TAC-MMT as binder, and Ketjen black as conductive agent. The electrode slurry was prepared by mixing at a mass ratio of 8:1:1. The slurry was evenly coated on aluminum foil using a doctor blade method, dried overnight at 80°C in a vacuum oven, and then placed in a glove box for use. Glass fiber GF / D was used as the battery separator, and 1 molL of 5% FEC was added. -1 Sodium perchlorate PC solution was used as the electrolyte, sodium foil was used as the counter electrode, and CR2032 button cells were assembled for electrochemical testing.

[0053] Figure 6 When the TAC-MMT obtained in Example 1 is used as the binder of the sodium vanadyl fluorophosphate cathode, the cycle performance test curve of the assembled half-cell is 1C, and the voltage range is 2 to 4.3 V. After 100 cycles, the battery shows excellent cycle stability, and the capacity retention rate is 93.93%.

[0054] Figure 7 When the TAC-MMT obtained in Example 1 is used as the binder of the sodium vanadyl fluorophosphate cathode, the first cycle charge and discharge curve of the assembled half-cell has a test rate of 0.1C and a voltage range of 2 to 4.3 V. The first cycle coulombic efficiency is 90.21%, indicating that the TAC-MMT binder effectively inhibits the decomposition of the electrolyte under high voltage.

[0055] Figure 8 The adhesion test between the electrode and the current collector was performed when the TAC-MMT obtained in Example 1 was used as a binder for the sodium vanadyl fluorophosphate cathode. After 100 cycles at a 1C rate, the electrode still maintained integrity with the current collector, indicating that TAC-MMT has excellent adhesion and can meet the requirements for stable cathode cycling at high voltage.

[0056] Example 2

[0057] In this embodiment, a triacetyl cellulose-based binder was prepared in the same manner as in Example 1, except that the amount of MMT added in step 2 was adjusted to 0.008 g, 0.016 g, 0.024 g, 0.032 g, and 0.040 g, respectively, so that the mass of MMT accounted for 1%, 2%, 3%, 4%, and 5% of the mass of TAC, respectively.

[0058] Fig. 9 The ionic conductivity test diagram of TAC film with different MMT addition contents obtained in Example 2, the ionic conductivity of the samples obtained with 1% to 5% addition is 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 It can be seen that 3% MMT addition can effectively improve the ion transmission performance and is the optimal addition content.

[0059] Comparative Example 1

[0060] This comparative example prepares PVDF material according to the following steps:

[0061] Step 1: First, 0.08 g of PVDF was dissolved in 10 mL of N-methylpyrrolidone and stirred at 60° C. for 24 hours to fully dissolve it to obtain a PVDF binder.

[0062] Step 2: To verify the film-forming ability, a PVDF film was prepared by a doctor blade method and dried in a vacuum oven at 60°C for 24 hours.

[0063] Fig.10 This is the Fourier transform infrared spectrum of the PVDF binder obtained in Comparative Example 1.

[0064] Fig.11 This is a scanning electron microscope image of the PVDF binder film obtained in Comparative Example 1. The porous morphology indicates that the film-forming property is poor and it is difficult to form a stable protection on the electrode surface.

[0065] Fig.12 This is the X-ray diffraction pattern of the PVDF binder obtained in Comparative Example 1.

[0066] Fig.13 The electrochemical impedance spectrum of the PVDF binder obtained in Comparative Example 1 is shown in the figure. As can be seen from the figure, the ionic conductivity of PVDF is 3.41×10 -6 S cm-1 , which is two orders of magnitude lower than TAC-MMT.

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

[0068] Fig.15 When the PVDF binder obtained in Comparative Example 1 is used as the binder of the sodium vanadyl fluorophosphate cathode, the cycle performance test curve of the assembled half-cell has a test rate of 1C and a voltage range of 2 to 4.3 V. It can be seen that the battery capacity retention rate is low.

[0069] Fig.16 When the PVDF binder obtained in Comparative Example 1 is used as the binder of the sodium vanadium fluorophosphate cathode, the first cycle charge and discharge curve of the assembled half-cell has a test rate of 0.1C and a voltage range of 2 to 4.3 V. The first cycle coulomb efficiency is only 78.11%, indicating that the PVDF binder is difficult to inhibit the continuous decomposition of the electrolyte under high voltage.

[0070] Fig.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 vanadyl fluorophosphate cathode. After 100 cycles at a 1C rate, an obvious split of more than 5 microns appeared between the electrode and the current collector, indicating that PVDF cannot meet the requirements of stable cathode cycling under high voltage.

[0071] Comparative Example 2

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

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

[0074] Fig.19 This is the stress-strain curve of the TAC adhesive obtained in Comparative Example 2 after film formation. As can be seen from the figure, the tensile strength of TAC is 43.58 MPa.

[0075] Fig. 20 When the TAC binder obtained in Comparative Example 2 is used as the binder of the sodium vanadyl fluorophosphate cathode, the cycle performance test curve of the assembled half-cell has a test rate of 1C and a voltage range of 2 to 4.3 V. After 100 cycles, the battery capacity retention rate is 85.64%.

[0076] Fig.21 When the TAC binder obtained in Comparative Example 2 is used as the binder for the sodium vanadyl fluorophosphate cathode, the first cycle charge and discharge curve of the assembled half-cell has a test rate of 0.1C, a voltage range of 2 to 4.3V, and a first cycle coulombic efficiency of 82.06%.

[0077] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a triacetyl cellulose-based binder, characterized in that: The following steps are involved: Step 1, stirring cellulose triacetate in N-methylpyrrolidone until dissolved to obtain solution A; Step 2, adding montmorillonite into N-methylpyrrolidone and stirring to obtain dispersion B; Step 3: Add dispersion B into solution A, stir the resulting mixture and perform ultrasound until the mixture is uniformly dispersed to obtain a triacetylcellulose-based binder.

2. The preparation method according to claim 1, characterized in that: In the mixed solution, the concentration of cellulose triacetate is 0.8 g / 15 mL, and the mass of montmorillonite accounts for 1% to 5% of the mass of cellulose triacetate.

3. The preparation method according to claim 1, characterized in that: In the mixed solution, the mass of 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 to 24 hours, and the stirring temperature is 50 to 70°C.

5. The preparation method according to claim 1, characterized in that: In step 2, the stirring time is 16 to 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 to 24 hours, and the stirring temperature is 50 to 70°C.

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

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

9. A triacetylcellulose-based binder obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the triacetylcellulose-based binder according to claim 9 in a sodium ion battery.

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