High-performance polymer electrolyte membrane for sodium ion battery

Abstract

As a sustainable energy storage technology, an all-solid-state sodium ion battery is regarded as a promising research field, wherein a solid electrolyte is a key component. Due to high energy and power density, low cost and abundant metal sodium reserve of the polymer solid electrolyte, the polymer solid electrolyte is widely researched. And the fundamental problem in the development of the polymer solid electrolyte is to improve the relatively low room-temperature conductivity of the polymer solid electrolyte and develop the high-performance polymer electrolyte of the sodium-ion battery. The solid electrolyte can be divided into three categories: an inorganic solid electrolyte (ISE), a solid polymer electrolyte (SPE) and a composite polymer electrolyte (CPE). Inorganic solid electrolyte generally has high ionic conductivity and good thermal stability and flame retardance, but the inorganic solid electrolyte is too brittle and too hard and cannot be used for practical application. In addition, the solid polymer electrolyte made from the polymer matrix and the sodium salt additive has low flammability and excellent flexibility. However, the low room temperature ionic conductivity of solid polymer electrolytes limits their application. According to the research, the advantages of an inorganic solid electrolyte and a solid polymer electrolyte are combined, and the composite polymer electrolyte with excellent performance is prepared.

Description

Technical Field

[0001] The present invention relates to the fields of new materials and sodium-ion batteries, and particularly to a high-performance polymer electrolyte membrane for sodium-ion batteries and a preparation method thereof. Background Art

[0002] Since the concept of "rocking chair battery" was proposed by Armand in the 1990s, lithium-ion batteries (LIBs) have developed rapidly in the past 30 years. Currently, LIBs using liquid organic electrolytes (LOEs) have dominated the markets of portable electronic devices, electric vehicles, and hybrid electric vehicles due to their high energy density and long cycle life. However, with the increasing demand for LIBs, the price of LIBs has been rising due to the scarcity and uneven distribution of lithium resources. Since sodium-ion batteries (SIBs) have a similar working principle, they are considered as alternatives to LIBs. In addition, sodium is one of the most evenly distributed and abundant elements in the earth's crust. Due to the lower cost, sodium-ion batteries are competitive in large-scale energy storage systems. Currently, the LOEs used in commercial LIBs and SIBs are highly flammable, volatile, and prone to leakage, and there are huge potential hazards such as thermal runaway, fire, and even explosion under extreme conditions. Therefore, replacing LOEs is considered as one of the effective ways to solve the above problems. The emergence of solid electrolytes meets the pursuit of improved battery safety.

[0003] The electrolyte of a sodium-ion battery is usually composed of an organic electrolyte solution and a sodium salt. The organic electrolyte solution is required to have properties such as a large dielectric constant, a low melting point (liquid at room temperature), and strong sodium-ion conductivity, and can be carbonate organic solvents such as dimethyl carbonate and ethylene carbonate. Sodium salts usually include sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), etc. The most ideal characteristic of the electrolyte is ionic conductivity, while its electronic conductivity should be low to prevent short circuits. For strong electrolytes with enhanced characteristics, they should have good compatibility with the interface of the electrode and electrochemical, thermal, and voltage stability. Electrolytes are mainly divided into two categories: solid electrolytes and liquid electrolytes. Solid electrolytes usually focus on excellent mechanical strength and safety characteristics, while liquid electrolytes, due to their free fluidity, have excellent ion transport capabilities during charge and discharge cycles and can shuttle ions quickly.

[0004] Solid electrolytes are mainly divided into three categories: inorganic solid electrolytes (ISEs), solid polymer electrolytes (SPEs), and composite polymer electrolytes (CPEs). ISEs usually have high ionic conductivity, good thermal stability, and flame retardancy, but they are too brittle and hard to be used in practical applications. In addition, SPEs made of a polymer matrix and sodium salt additives have non-flammability and excellent flexibility. However, the low room-temperature ionic conductivity of SPEs limits their applications. CPEs combine the advantages of ISEs and SPEs and exhibit excellent performance. Different from LOEs with high ionic conductivity that can easily immerse porous electrode materials to achieve excellent electrolyte-electrode contact, two main problems need to be solved for the practical application of CPEs. The first problem is the ionic conductivity of CPEs, and the second problem is the high interfacial resistance between the solid electrolyte and the electrode, resulting in poor interfacial charge transfer. Although the transition from liquid electrolytes to solid electrolytes is the trend for next-generation batteries, some liquid phase may still be needed to enhance ionic conduction in the solid electrolyte region and the electrolyte-electrode interface area. Summary of the Invention

[0005] For a conventional separator / electrolyte system, when charging under high-voltage conditions, the cathode will release gas, and the active material / electrolyte will decompose, thus causing safety problems in the battery. Therefore, it may be necessary to develop new electrolytes that are relatively stable at higher voltages to prevent these safety risks, or it may be necessary to charge the battery to a lower voltage, but this will have an impact on the performance of the battery and will greatly reduce the energy density, which is not a commercially viable solution. The all-solid-state sodium-ion battery is regarded as a promising research field as a sustainable energy storage technology, and the solid electrolyte is a key component. Due to the high energy and power density of polymer solid electrolytes, as well as the low cost and abundant metal sodium reserves, extensive research has been carried out on them. The fundamental problem in the development of polymer solid electrolytes is to improve their relatively low room-temperature conductivity and develop high-performance sodium-ion battery polymer electrolytes.

[0006] The purpose of the present invention is to overcome the deficiencies of polymer solid electrolytes and provide a method for preparing a high-performance polymer electrolyte membrane for sodium-ion batteries. The present invention uses the solution casting method to prepare a composite polymer electrolyte membrane, and this electrolyte membrane exhibits excellent ionic conductivity performance.

[0007] To achieve the above technical objectives, the present invention adopts the following technical means:

[0008] The present invention relates to a high-performance polymer electrolyte membrane for sodium-ion batteries, which contains a crystalline thermoplastic polyether PEO. PEO is formed by the multiphase catalytic ring-opening polymerization of ethylene oxide and has a linear and regular helical structure. At the same time, PEO has a high dielectric constant, which enables the PEO polymer matrix to rapidly dissociate sodium salts and generate mobile Na+. However, as a semi-crystalline polymer, PEO is prone to crystallization at room temperature (RT). The slow dynamics of polymer chains in the crystalline region result in low ionic conductivity. Only the amorphous phase above the glass transition temperature (Tg) of the activated chain segments is beneficial for ion transport. Therefore, based on the above description, the present invention has made a series of designs to inhibit the crystallization of PEO on this basis.

[0009] This technical means is based on three main research contents, which are described as follows:

[0010] 1. Adding low-molecular-weight polyethylene glycol (PEG) as a plasticizer to the PEO-based polymer solid electrolyte can reduce the crystallinity of PEO through plasticization, enhance the segmental motion, increase the transference number of ions in the electrolyte, and thus improve the ionic conductivity of the electrolyte.

[0011] 2. Adding inorganic fillers to the polymer to prepare a composite polymer solid electrolyte.

[0012] 3. Conducting experimental characterization on the synthesized materials to verify whether they meet the expected goals, and analyzing and studying their modification mechanisms, chemical properties, and electrochemical properties.

[0013] The present invention combines various research examples and designs an inventive method that can significantly improve the performance of the electrolyte membrane.

[0014] In some examples, due to the addition of the PEG plasticizer, the amorphous phase of the polymer increases and the glass transition temperature decreases, thereby increasing the flexibility of the polymer chains. The transference number of sodium ions increases from 0.23 in the pure PEO electrolyte to 0.42 in the PEO / NaPO3 electrolyte.

[0015] In some instances, the influence of inert fillers on the PEO matrix is mainly reflected in two aspects: (1) reducing the crystallinity of PEO, increasing the amorphous region, and enhancing its ionic conduction ability; (2) fixing the anions of sodium salts through Lewis acid-base interactions, thereby generating more free Na+ and increasing the ionic conductivity. Different from inert fillers, in addition to the above two effects, active fillers can provide Na+ for ion transport by themselves, and the ion transport channels formed by particles at the interface can promote ion transport. Some studies have prepared Na+-ion conductive composite polymer solid electrolytes by solution casting using inert fillers such as Al2O3. Due to the complexation between the polymer, salt, and filler, when the content of Al2O3 is 4% (mass fraction), the room-temperature ionic conductivity is increased from 10−7 S·cm−1 to 10−5 S·cm−1; there are also some studies using the active ceramic filler NaAl5O8 to prepare CPE. The addition of NaAl5O8 alleviates the reactivity between PEO and Na, and the ionic conductivity of CPE is 3.6×10−6 S·cm−1 at 70 °C; at the same time, some high-performance two-dimensional materials have also been used as nano-fillers in composite electrolytes for research.

[0016] In some instances, the solution casting method, hot pressing method, or electrospinning method is applied to the preparation of the electrolyte membrane. The solution casting method is to mix solid PEO and sodium salt in a certain proportion and dissolve them in an organic solvent. After stirring to form a solution, the solution is cast on a polytetrafluoroethylene (PTFE) mold, and after drying and demolding, a PEO-based polymer solid electrolyte is obtained. This method is the most commonly used preparation method for polymer solid electrolytes at present. The advantages of solution casting film formation are that the film structure is uniform and the film thickness is easy to control. The disadvantages are that it takes a long time and is easy to cause pollution. When organic solvents remain, the solvent will cause the decomposition of solvent molecules during the battery cycle and side reactions with the electrode at the interface, resulting in problems such as an increase in the electrode / electrolyte interface impedance, an increase in polarization, a short battery cycle life, and a low Coulomb efficiency. This method is adopted in the present invention.

[0017] Based on the PEO polymer, a series of modifications were made to the polymer electrolyte membrane of the sodium-ion battery by adding plasticizers and inorganic fillers using the solution casting method. The specific steps are as follows:

[0018] Step 1. First, calculate the mass of the experimental raw materials required for each formula, and use an electronic balance to weigh the experimental raw materials separately according to the calculated values: PEO, PEG, sodium difluorooxalate, and carbon nanotubes.

[0019] Step 2. Mix the weighed raw materials, use acetonitrile as the solvent, with an acetonitrile volume of 10 mL, and ultrasonically disperse the powder evenly for 5 min using an ultrasonic cell disruptor, and then stir for 24 h using a magnetic stirrer to make it a homogeneous solution.

[0020] Step 3. Pour the prepared homogeneous solution into a polytetrafluoroethylene mold, dry it at room temperature for 48 h, take it out, cool it to room temperature, and then use tweezers to peel off the electrolyte film.

[0021] Step 4. Assemble the prepared electrolyte membrane into the battery case and conduct a series of performance characterizations.

[0022] Specifically, in Step 1, the selected polymers are PEO (purity > 99%), sodium difluoro(oxalato)borate (purity 98%), PEG (analytical pure), carbon nanotubes (analytical pure), acetonitrile (analytical pure), and the ratio of PEO to sodium difluoro(oxalato)borate is 12:1, and the mass fraction of carbon nanotubes is 50%.

[0023] Specifically, in Step 2, when using a magnetic stirrer for stirring, the rotation speed is 500 r / min.

[0024] Specifically, in Step 3, the drying temperature is 30 °C, and a ventilation setting is added.

[0025] Specifically, the performance characterizations carried out in Step 4 mainly include X-ray diffraction analysis (XRD), ultra-depth-of-field microscope analysis, infrared spectroscopy analysis, and electrochemical impedance spectroscopy test (EIS).

[0026] The present invention has the following beneficial effects:

[0027] The present invention is a high-performance polymer electrolyte membrane for sodium-ion batteries, which has high ionic conductivity (> 10−4 S·cm−1 at room temperature), electronic insulation, high chemical / electrochemical stability, good electrode / electrolyte interface contact, high mechanical strength, good flexibility, and thermal stability. The composite solid electrolyte obtained by adding inorganic fillers to the polymer matrix can improve the mechanical properties and electrochemical properties, and realize the optimization of a single solid electrolyte system.

[0028] The present invention provides a novel battery electrolyte membrane, which helps to reduce the dependence on lithium resources and meets the requirements of sustainable development and environmental protection. Sodium-ion batteries have broad application potential in fields such as large-scale energy storage systems, electric vehicles, and portable electronic devices. Studying sodium-ion battery electrolyte membranes can provide battery solutions with better performance and lower costs for these fields. Description of the Drawings

[0029] Figure 1 XRD of the original carbon nanotube powder, pure PEO, PEO / PEG (1:0.5), and CPE (PEO / PEG = 1:0.5) in Example 1 of the present invention.

[0030] Figure 2 Scanning electron microscope analysis diagram of the target product in the example of the present invention.

[0031] Figure 3 SEM analysis diagram of the target product obtained in the examples of the present invention. Figures (a), (b), (c), (d), and (e) are SEM diagrams of the target products obtained in Examples 1, 2, 3, 4, and 5 respectively Detailed implementation manners

[0032] The technical solutions of the present invention are illustrated by the following specific examples. It should be understood that one or more steps mentioned in the present invention do not exclude the existence of other methods and steps before and after the combined steps, or other methods and steps can be inserted between these explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. Unless otherwise specified, the numbers of each method step are only for the purpose of identifying each method step, rather than restricting the arrangement order of each method or limiting the implementation scope of the present invention. The change or adjustment of their relative relationship can also be regarded as the scope in which the present invention can be implemented under the condition of no substantial change in technical content

[0033] The experimental steps described in the present invention include: preparing a high-performance polymer electrolyte membrane for a sodium-ion battery using the solution casting method. First, a certain amount of PEO is weighed and added to acetonitrile (10 ml), and a glass rod is used to stir to prevent the dissolved polymer from sticking to the beaker wall. Then, according to the mass ratio of PEO:Na + = 12:1, a certain mass of sodium difluoro(oxalato)borate is weighed and added to the above solution, and carbon nanotubes with a mass fraction of 50% are added. Subsequently, PEG is added to the solution (meeting five ratios of PEO:PEG = 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5). First, it is ultrasonicated for 5 min using an ultrasonic cell disruptor to uniformly disperse the powder, and then it is stirred for 24 h using a magnetic stirrer at a rotation speed of 500 r / min to make it a homogeneous solution. The prepared homogeneous solution is poured into a polytetrafluoroethylene mold and dried at room temperature (30 degrees) for 48 h. After taking it out and cooling to room temperature, the electrolyte film is peeled off with tweezers. The prepared electrolyte film is assembled into a battery case for a series of performance characterizations

[0034] Example 1

[0035] The specific steps for preparing a high-performance polymer electrolyte membrane for a sodium-ion battery provided in this example are as follows:

[0036] A) Prepare the chemical supplies required for preparing the electrolyte membrane and configure the solution according to a certain ratio. Among them, the mass of PEO is 0.478 g, the mass of sodium difluoro(oxalato)borate is about 0.04 g, the mass of carbon nanotubes is 0.239 g, the mass of PEG meets PEO:PEG = 1:0.5, and the mass is 0.239 g. 10 mL of acetonitrile solution is added, and a glass rod is used to stir to prevent the dissolved polymer from sticking to the beaker wall

[0037] B) Ultrasonicate for 5 min using an ultrasonic cell disruptor to uniformly disperse the powder, and then stir for 24 h using a magnetic stirrer at a rotation speed of 500 r / min.

[0038] C) Pour the prepared homogeneous solution into a polytetrafluoroethylene mold, dry at room temperature for 48 h, take it out and cool to room temperature, and then use tweezers to peel off the electrolyte film.

[0039] D) Assemble the electrolyte membrane into the positive and negative electrode cases with electrode sheets on both sides.

[0040] The XRD test results of the obtained target product are as Figure 1 shown. The XRD pattern of pure PEO shows two diffraction peaks at 2θ of 19.36 and 23.72, corresponding to the (120) and (112) planes respectively. However, with the addition of PEG, the intensities of these two peaks become weaker and the peaks become broader, indicating a decrease in the crystallinity of PEO. The surface and cross-sectional morphologies of the CPE with added PEG were analyzed using a field emission scanning electron microscope (FESEM, HITACHI S-4300).

[0041] The obtained target product was analyzed by scanning electron microscope as Figure 2 shown. The thickness of the prepared CPE is about 85 μm, and the top views of the electrolytes all show a uniform morphology ( Figure 2 (a)).

[0042] The obtained target product was subjected to electrochemical analysis as Figure 3 (a) shown. In the figure, an incomplete semicircle appears in the high-frequency region. The diameter of the semicircle represents the grain boundary resistance Rgb, and the value of the grain resistance Rg is shown as the intercept of the semicircle on the Z'-axis in the high-frequency region of the spectrum. Therefore, the value corresponding to the obvious turning point of the curve can be approximately regarded as the total resistance of the electrolyte membrane (R = Rg + Rgb). The thickness of the electrolyte membrane measured in this example is about 200 μm, and the ionic conductivity of the electrolyte membrane in this example was calculated to be 1.9×10 -4 S / cm.

[0043] Example 2

[0044] This example provides the specific steps for preparing a high-performance polymer electrolyte membrane for a sodium-ion battery as follows:

[0045] A) Prepare the chemical supplies required for preparing the electrolyte membrane and configure the solution according to a certain ratio. Among them, the mass of PEO is 0.478 g, the mass of sodium difluorooxalate borate is about 0.04 g, the mass of carbon nanotubes is 0.239 g, the mass of PEG satisfies PEO:PEG = 1:1, the mass is 0.478 g, add 10 mL of acetonitrile solution, and stir with a glass rod to prevent the dissolved polymer from sticking to the wall of the beaker.

[0046] B) Use an ultrasonic cell disruptor to ultrasonicate for 5 min to uniformly disperse the powder, and then use a magnetic stirrer to stir for 24 h at a rotation speed of 500 r / min.

[0047] C) Pour the prepared homogeneous solution into a polytetrafluoroethylene mold, dry it at room temperature for 48 h, take it out, cool it to room temperature, and then use tweezers to peel off the electrolyte film.

[0048] D) Assemble the electrolyte membrane into the positive and negative electrode cases with electrode sheets on both sides.

[0049] Perform scanning electron microscope analysis on the obtained target product as Figure 2 shown. The thickness of the prepared CPE is about 85 μm, and the top views of the electrolytes all show a uniform morphology ( Figure 2 (b)).

[0050] Perform electrochemical analysis on the obtained target product as Figure 3 (b) shown. In the figure, an incomplete semicircle appears in the high-frequency region. The diameter of the semicircle represents the grain boundary resistance Rgb, and the value of the grain resistance Rg is shown as the intercept of the semicircle on the Z'-axis in the high-frequency region on the spectrum. Therefore, the value corresponding to the obvious turning point of the curve can be approximately regarded as the total resistance of the electrolyte membrane (R = Rg + Rgb). The thickness of the electrolyte membrane measured in this example is about 204 μm. By calculation, the ionic conductivity of the electrolyte membrane in this example is 5.9×10 -5 S / cm.

[0051] Example 3

[0052] This example provides a method for preparing a high-performance polymer electrolyte membrane for a sodium-ion battery. The specific steps are as follows:

[0053] A) Prepare the chemical supplies required for preparing the electrolyte membrane and configure the solution according to a certain ratio. Among them, the mass of PEO is 0.478 g, the mass of sodium difluorooxalate borate is about 0.04 g, the mass of carbon nanotubes is 0.239 g, the mass of PEG satisfies PEO:PEG = 1:1.5, and the mass is 0.717 g. Add 10 mL of acetonitrile solution and stir with a glass rod to prevent the dissolved polymer from sticking to the inner wall of the beaker.

[0054] B) Use an ultrasonic cell disruptor to ultrasonicate for 5 min to uniformly disperse the powder, and then use a magnetic stirrer to stir for 24 h at a rotation speed of 500 r / min.

[0055] C) Pour the prepared homogeneous solution into a polytetrafluoroethylene mold, dry it at room temperature for 48 h, take it out, cool it to room temperature, and then use tweezers to peel off the electrolyte film.

[0056] D) Assemble the electrolyte membrane into the positive and negative electrode shells with electrode sheets on both sides.

[0057] The obtained target product was analyzed by scanning electron microscopy. Figure 2 As shown in Figure 2, the thickness of the prepared CPE is about 85 μm, and the top view of the electrolyte shows a uniform morphology ( Figure 2 (c))

[0058] The obtained target product was subjected to electrochemical analysis. Figure 3 As shown in (c), an incomplete semicircle appears in the high-frequency region. The diameter of the semicircle represents the grain boundary resistance Rgb. The value of the grain resistance Rg is shown in the spectrum as the intercept of the semicircle with the Z' axis in the high-frequency region. Therefore, the value corresponding to the obvious turning point of the curve can be approximately regarded as the total resistance of the electrolyte membrane (R = Rg + Rgb). The thickness of the electrolyte membrane measured in this example is about 268μm. The ionic conductivity of the electrolyte membrane in this example is calculated to be 2.3×10 -4 s / cm.

[0059] Example 4

[0060] This embodiment provides a preparation method of a high-performance polymer electrolyte membrane for sodium ion batteries, and the specific steps are as follows:

[0061] A) Prepare the chemicals needed to prepare the electrolyte membrane and prepare the solution in a certain proportion. Among them, the mass of PEO is 0.478g, the mass of sodium difluorooxalatoborate is about 0.04g, the mass of carbon nanotubes is 0.239g, and the mass of PEG satisfies PEO:PEG=1:2, with a mass of 0.956g. Add 10mL of acetonitrile solution and stir with a glass rod to prevent the dissolved polymer from sticking to the wall of the beaker.

[0062] B) Ultrasonic cell crusher was used for 5 min to make the powder uniformly dispersed, and then magnetic stirrer was used for 24 h at a speed of 500 r / min.

[0063] C) Pour the prepared uniform solution into a polytetrafluoroethylene mold, dry it at room temperature for 48 hours, take it out and cool it to room temperature, then use tweezers to peel off the electrolyte film.

[0064] D) Assemble the electrolyte membrane into the positive and negative electrode shells with electrode sheets on both sides.

[0065] The obtained target product was analyzed by scanning electron microscopy. Figure 2 As shown in Figure 2, the thickness of the prepared CPE is about 85 μm, and the top view of the electrolyte shows a uniform morphology ( Figure 2 (d))

[0066] The obtained target product was subjected to electrochemical analysis.Figure 3 (d) As shown, in the figure, an incomplete semicircle appears in the high-frequency region. The diameter of the semicircle represents the grain boundary resistance Rgb. The value of the grain resistance Rg is manifested as the intercept of the semicircle with the Z'-axis in the high-frequency region on the spectrum. Therefore, the value corresponding to the obvious turning point of the curve can be approximately regarded as the total resistance of the electrolyte membrane (R = Rg + Rgb). The thickness of the electrolyte membrane measured in this example is about 300 μm. Through calculation, the ionic conductivity of the electrolyte membrane in this example is 7.02×10 -5 s / cm.

[0067] Example 5

[0068] This example provides a method for preparing a high-performance polymer electrolyte membrane for a sodium-ion battery. The specific steps are as follows:

[0069] A) Prepare the chemical supplies required for preparing the electrolyte membrane and configure the solution according to a certain ratio. Among them, the mass of PEO is 0.478 g, the mass of sodium difluorooxalate borate is about 0.04 g, the mass of carbon nanotubes is 0.239 g, the mass of PEG satisfies PEO:PEG = 1:2.5, and the mass is 1.195 g. Add 10 mL of acetonitrile solution and stir with a glass rod to prevent the dissolved polymer from sticking to the wall of the beaker.

[0070] B) Use an ultrasonic cell disruptor to ultrasonically disperse for 5 min to make the powder evenly dispersed, and then use a magnetic stirrer to stir for 24 h at a rotation speed of 500 r / min.

[0071] C) Pour the prepared homogeneous solution into a polytetrafluoroethylene mold, dry at room temperature for 48 h, take it out and cool to room temperature, and then use tweezers to peel off the electrolyte film.

[0072] D) Assemble the electrolyte membrane into the positive and negative electrode cases with electrode plates on both sides.

[0073] Perform electrochemical analysis on the obtained target product as Figure 3 (e) As shown, in the figure, an incomplete semicircle appears in the high-frequency region. The diameter of the semicircle represents the grain boundary resistance Rgb. The value of the grain resistance Rg is manifested as the intercept of the semicircle with the Z'-axis in the high-frequency region on the spectrum. Therefore, the value corresponding to the obvious turning point of the curve can be approximately regarded as the total resistance of the electrolyte membrane (R = Rg + Rgb). The thickness of the electrolyte membrane measured in this example is about 250 μm. Through calculation, the ionic conductivity of the electrolyte membrane in this example is 1.6×10 -5 s / cm.

[0074] After testing, different PEG contents have different effects on the ionic conductivity performance of the sodium-ion battery electrolyte membrane. Among them, when PEO:PEG = 1:1.5, the ionic conductivity of the sodium-ion battery electrolyte membrane is the highest.

[0075] The above description of the specific exemplary embodiments of the present invention is for the purpose of illustration and exemplification. The present invention is not limited to the above embodiments. Without departing from the essence of the present invention, any obvious improvements, substitutions or variations that can be made by those skilled in the art fall within the protection scope of the present invention. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A high-performance electrolyte membrane for sodium ion batteries, characterized in that: Sodium ion polymer electrolyte membranes are usually composed of an organic polymer matrix and a sodium salt dissolved in the polymer matrix, or further contain inorganic functional fillers.

2. The sodium ion electrolyte polymer membrane according to claim 1, characterized in that The polymer matrix of these electrolytes inherently contains polar functional groups such as -O-, C=O, and C≡N. The solvation of salts is successfully achieved by utilizing the coordination effect between the lone pair electrons of these functional groups and cations.

3. The sodium ion polymer electrolyte membrane according to claim 2, characterized in that: Many polymers such as polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA) have become common choices for constructing electrolyte matrices.

4. The sodium ion polymer electrolyte membrane according to claim 3, characterized in that The material used in this study uses PEO as the organic polymer for synthesizing sodium ion polymer electrolyte membrane. PEO can coordinate with sodium ions to form a movable space. PEO is easy to form a film, has good flexibility, a wide electrochemical window, and reliable stability.

5. The sodium ion polymer electrolyte membrane according to claim 4, characterized in that: The material used in this study uses polyethylene glycol (PEG) to enhance ion conduction within the solid electrolyte region and the electrolyte-electrode interface area. PEG is in liquid phase, but the electrolyte remains solid at room temperature.

6. The sodium ion polymer electrolyte membrane according to claim 5, characterized in that Nanofillers, as a known system dispersed in polymer electrolytes, have a dual role in polymer electrolytes. On the one hand, they improve the conductivity by establishing a quantum size effect, and on the other hand, they improve the mechanical stability of the electrolyte membrane. This study used carbon nanotubes as inorganic fillers in the polymer body.

7. The sodium ion polymer electrolyte membrane according to claim 6, characterized in that In this study, polymer solid electrolytes composed of polyethylene oxide (PEO, Mv 600,000, Sigma Aldrich), sodium difluorooxalatoborate, and carbon nanotubes were prepared using acetonitrile (CAN) as solvent, to which different amounts of polyethylene glycol (PEG, average Mn 400, Sigma Aldrich) were added as a plasticizer.

8. The sodium ion polymer electrolyte membrane according to claim 7, characterized in that the step include: A) Prepare the chemicals needed to prepare the electrolyte membrane and prepare the solution in a certain proportion; B) Use ultrasonic cell pulverizer to disperse the powder evenly, and then use magnetic stirrer to stir; C) pouring the prepared uniform solution into a polytetrafluoroethylene mold, drying and cooling; D) Assemble the electrolyte membrane into the positive and negative electrode shells with electrode sheets on both sides.

9. The sodium ion polymer electrolyte membrane according to claim 8, characterized in that The obtained sodium ion polymer electrolyte membrane was obtained by solution casting method, using an electronic balance to weigh a certain mass of PEO, sodium salt (PEO: Na salt = 12:1), 50wt% carbon nanotubes, and PEG in different mass ratios, and add them into a certain volume of the existing solution; Then, the powder was evenly dispersed by ultrasonic cell pulverizer for 5 min, and then stirred with a magnetic stirrer for 24 h to make it a uniform solution; The prepared uniform solution was poured into a polytetrafluoroethylene mold and placed in a vacuum drying oven at 50°C for 48 h. After cooling to room temperature, the electrolyte film was peeled off with tweezers.

10. The sodium ion polymer electrolyte membrane according to claim 9, characterized in that: The prepared electrolyte membrane is installed into the positive and negative electrode shells equipped with electrode sheets to prepare a simple battery; its characteristic is that PEG liquid phase is used as a plasticizer for the electrolyte membrane. At the same time, the use of inorganic filler carbon nanotubes also greatly improves the conductivity of the sodium ion electrolyte membrane.

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