A kind of interpenetrating structure sodium ion solid-state electrolyte film and its preparation method

Abstract

This invention discloses an interpenetrating structure sodium-ion solid electrolyte film and its preparation method. The method involves mixing a metal-organic framework (MOF), polymer segments (PEO), and sodium salt to obtain a mixture. Acetonitrile solution is then added to the mixture, followed by ultrasonic treatment and stirring at room temperature to obtain a mixed solution. This solution is then poured into a mold and dried in a vacuum drying oven to obtain the sodium-ion solid electrolyte film. This preparation method utilizes the interpenetrating structure of the solid electrolyte formed by polymer segments passing through the pores of the MOF particles, which can further improve the ionic conductivity and ion transference number of the solid electrolyte. Furthermore, this interpenetrating structure sodium-ion solid electrolyte allows the battery to maintain a long cycle life of over 1000 cycles at high current rates, with a capacity retention rate (the ratio of battery capacity before and after cycling) as high as 95.6%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a sodium ion solid electrolyte thin film with a penetration structure and a preparation method thereof. BACKGROUND

[0002] In modern life, alkali metal batteries are widely used in the field of portable electronic products, but with the development of electronic consumer products and electric vehicles, traditional alkali metal batteries cannot meet people's demand for high energy density and safety, making energy problems a hot topic in the scientific community.

[0003] At the same time, the ultra-high theoretical capacity of lithium metal and sodium metal has also attracted widespread attention from researchers, but in the matching process of traditional liquid electrolyte and metal electrode, it will react with it, causing rapid capacity decay of the battery, and more likely to cause dendrite growth leading to battery short circuit, triggering thermal runaway. In addition, liquid lithium batteries have problems such as flammability, explosion and low battery energy density.

[0004] Solid electrolyte has high electrochemical window, good thermal stability and excellent mechanical properties, and is the best choice to replace liquid electrolyte. Solid electrolyte can be divided into inorganic solid electrolyte, organic solid electrolyte and composite solid electrolyte. Among them, organic solid electrolyte is easy to process and has good interface compatibility with the electrode, but it has problems such as low ionic conductivity; inorganic solid electrolyte has high ionic conductivity and high electrochemical window, but the solid-solid interface between inorganic solid electrolyte and electrode has a large impedance. Compared with the former two, the composite solid electrolyte has improved ionic conductivity, better flexibility and closer contact with the electrode, but the composite solid electrolyte still has defects such as low ion transference number and poor long cycle performance.

[0005] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0006] In view of the shortcomings of the prior art, the purpose of the present application is to provide a sodium ion solid electrolyte thin film with a penetration structure and a preparation method thereof, aiming to solve the problems of poor rate performance and poor long cycle performance at high rate of existing composite solid electrolyte.

[0007] The technical scheme of the present application is as follows:

[0008] A sodium ion solid electrolyte thin film with a penetration structure, comprising a metal organic framework with a hole structure and a polymer segment PEO penetrating inside the hole.

[0009] The sodium ion solid electrolyte thin film with a penetration structure, wherein the metal organic framework is selected from one of UIO-66, ZIF-8 and MOF-74.

[0010] The sodium ion solid-state electrolyte film of the interpenetrating structure, wherein the molecular weight of the polymer segment PEO is 500000-900000.

[0011] A preparation method of the sodium ion solid-state electrolyte film of the interpenetrating structure, comprising the steps of:

[0012] providing a metal organic framework, a polymer segment PEO and a sodium salt;

[0013] mixing the metal organic framework, the polymer segment PEO and the sodium salt to obtain a mixture, adding acetonitrile solution to the mixture and performing ultrasonic treatment, then performing normal temperature stirring to obtain a mixed solution;

[0014] pouring the mixed solution into a mold and performing drying treatment to obtain the sodium ion solid-state electrolyte film.

[0015] The preparation method of the sodium ion solid-state electrolyte film of the interpenetrating structure, wherein the mass of the metal organic framework accounts for 2%-5% of the sum of the mass of the metal organic framework and the mass of the polymer segment PEO.

[0016] The preparation method of the sodium ion solid-state electrolyte film of the interpenetrating structure, wherein the normal temperature stirring is stirring at a rotating speed of 840 rpm for 10 h.

[0017] The preparation method of the sodium ion solid-state electrolyte film of the interpenetrating structure, wherein the drying treatment is performed in a vacuum drying box, the pressure of the vacuum drying box is-2.5 MPa, and the temperature is 60℃.

[0018] The preparation method of the sodium ion solid-state electrolyte film of the interpenetrating structure, wherein the metal organic framework is UIO-66.

[0019] The preparation method of the sodium ion solid-state electrolyte film of the interpenetrating structure, wherein the preparation method of the UIO-66 comprises the steps of:

[0020] adding zirconium chloride and phthalic acid into a reaction kettle in a molar ratio of 1:1, and adding DMF, glacial acetic acid and concentrated hydrochloric acid, and preparing the UIO-66 through hydrothermal reaction.

[0021] The preparation method of the sodium ion solid-state electrolyte film of the interpenetrating structure, wherein the molar ratio of the glacial acetic acid to the DMF is 1:7, and the molar ratio of the concentrated hydrochloric acid to the DMF is 1:70.

[0022] Beneficial effects: the present application provides a kind of sodium ion solid electrolyte film of interpenetrating structure and preparation method thereof, by mixing metal organic framework, polymer chain segment PEO and sodium salt to obtain mixture, acetonitrile solution is added to the mixture and ultrasonic treatment is carried out, then normal temperature stirring is carried out, and mixed solution is obtained;Then the mixed solution is poured into mold, drying treatment is carried out in vacuum drying oven, and sodium ion solid electrolyte film is prepared.The preparation method utilizes the interpenetrating structure solid electrolyte formed by polymer chain segment passing through the pore structure of metal organic framework (MOF) particle, can further improve the ionic conductivity and ion transference number of solid electrolyte;And the interpenetrating structure sodium ion solid electrolyte makes battery at high rate of current, charge-discharge cycle can keep more than 1000 cycles, and capacity retention rate (the ratio of battery capacity before and after cycle) is as high as 95.6%. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Flow chart for the preparation method of the interpenetrating structure sodium ion solid electrolyte film of the present application;

[0024] Figure 2 Electrolyte ion conductivity image of different UIO-66 content in Example 1 of the present application;

[0025] Figure 3 SEM image of the interpenetrating structure sodium ion solid electrolyte film in Example 1 of the present application when the content of UIO-66 is 5%;

[0026] Figure 4 SEM image and optical photo of the interpenetrating structure sodium ion solid electrolyte film in Example 1 of the present application when the content of MOF is 10%;

[0027] Figure 5 DSC image of the interpenetrating structure sodium ion solid electrolyte film in Example 2 of the present application when the content of MOF is 50%-80%;

[0028] Figure 6 XRD image of the interpenetrating structure sodium ion solid electrolyte film in Example 2 of the present application when the content of MOF is 50%-80%;

[0029] Figure 7 Adsorption energy comparison chart of PEO-UIO-66-1 and PEO-UIO-66-2 models in Example 2 of the present application;

[0030] Figure 8 Ion transference number chart of the interpenetrating solid electrolyte of the present application;

[0031] Figure 9 4C rate long cycle chart of the battery assembled by using the solid electrolyte of the present application. DETAILED DESCRIPTION

[0032] The present application provides a kind of sodium ion solid electrolyte film of interpenetrating structure and preparation method thereof, to make the purpose, technical scheme and effect of the present application more clear, explicit, the following is further detailed in the present application.It should be understood that the specific embodiments described herein are merely intended to explain the present application and not to limit the present application.

[0033] In the embodiments and the patent application scope, unless the article has a special definition in the text, "a", "an", "said" and "the" can also include plural forms.If the description of "first", "second" and the like is involved in the embodiments of the present application, the description of "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features.Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features.

[0034] It should be further understood that the phrase "comprising" used in the specification of the present application means that the features, integers, steps, operations, elements and / or components exist, but does not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups.The phrase "and / or" used herein includes all or any unit and all combinations of the associated listed items.

[0035] Those skilled in the art can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as that generally understood by those skilled in the art to which the present application belongs.It should also be understood that terms such as those defined in general dictionaries should be understood as having meanings consistent with those in the prior art, and should not be interpreted with idealized or overly formal meanings unless specifically defined as such.

[0036] The present application provides a kind of sodium ion solid electrolyte film of interpenetrating structure, the sodium ion solid electrolyte film of interpenetrating structure includes metal organic framework with pore structure and polymer chain segment PEO interpenetrated in the inside of the pore.

[0037] Specifically, the polymer chain segment PEO interpenetrates into the metal organic framework makes PEO crystallization more difficult, increases the amorphous region of PEO, thereby improving the ionic conductivity;Secondly, the adsorption energy of metal organic framework to anion in electrolyte can be improved, further improving the ion transference number;Finally, high ionic conductivity and ion transference number can make the battery realize capacity retention rate of up to 95% or more after long cycle 1000 cycles under 4C high rate current condition.

[0038] In some embodiments, the metal organic framework is selected from one of UIO-66, ZIF-8, MOF-74; these metal organic frameworks have suitable pore sizes that allow the polymer segment PEO to pass through the pore structure of UIO-66, ZIF-8, MOF-74, forming an interpenetrated structure solid electrolyte.

[0039] In some embodiments, the molecular weight of the polymer segment PEO is 500000-900000, which can better pass through the pore structure of the metal organic framework, effectively prevent the crystallization of the polymer segment PEO by using the pore structure of the metal organic framework, thereby increasing the amorphous region, so that the ionic conductivity of the battery is improved. However, too high molecular weight will make it difficult to form such an interpenetrated structure, and too low molecular weight will result in an electrolyte film that cannot be formed. Therefore, by selecting a polymer segment PEO with a molecular weight of 500000-900000, the interpenetrated solid electrolyte structure prepared can have excellent ionic conductivity and ion transference number.

[0040] Reference is made to Figure 1 The present application also provides a preparation method of the interpenetrated structure sodium ion solid electrolyte film as described above, comprising the steps of:

[0041] Step S10: providing a metal organic framework, a polymer segment PEO, and a sodium salt;

[0042] Step S20: mixing the metal organic framework, the polymer segment PEO, and the sodium salt to obtain a mixture, adding acetonitrile solution to the mixture and performing ultrasonic treatment, then performing room temperature stirring to obtain a mixed solution;

[0043] Step S30: pouring the mixed solution into a mold and performing drying treatment to obtain a sodium ion solid electrolyte film.

[0044] In the present embodiment, after adding acetonitrile as a solvent, the PEO segment is dissolved therein, and the flowability of the solvent can cause the PEO segment to enter the MOF pore structure along with the solvent, thereby forming an interpenetrated structure solid electrolyte, which in turn improves a series of performances of the battery. The interpenetrated structure is mainly attributed to the pore radius of the selected MOF structure, and the interaction between the metal organic framework and the polymer segment PEO can greatly improve the performance of the battery, and the interpenetrated structure improves the ionic conductivity and ion transference number of the composite solid electrolyte, thereby solving the problems of poor rate performance and poor long cycle performance at high rate of the solid state battery.

[0045] Specifically, the present application uses metal organic framework to interpenetrate with PEO segment, and such interpenetration model plays many roles in the solid electrolyte of the battery. First, the polymer mainly achieves ion conduction due to the movement of its amorphous region, so the size of the amorphous region in the polymer is crucial, and the interpenetration type solid electrolyte formed by using PEO segment to pass through the pores of MOF can effectively prevent the polymer from crystallizing, and the increase of the amorphous region can improve the ion conductivity of the battery, thereby improving the battery performance. In addition, the design of the interpenetration type solid electrolyte makes it easier for the anions dissolved in the metal salt of the PEO segment to be fixed by the metal cluster of the MOF, thereby limiting the transfer of the anions, greatly improving the ion transference number of the electrolyte, and thereby ensuring the long cycle of the battery at high rate.

[0046] In a specific embodiment, the metal organic framework is UIO-66. By selecting UIO-66 as the metal organic framework, the ion conductivity and ion transference number of the solid electrolyte can be maximized, thereby ensuring the long cycle performance of the battery at high rate.

[0047] In a preferred embodiment, the molecular weight of the polymer segment PEO is 600000. When the polymer segment PEO with a molecular weight of 600000 is selected to interpenetrate the pore structure of the metal organic framework, the interpenetration effect is optimal.

[0048] In some embodiments, the mass of the metal organic framework accounts for 2% to 5% of the sum of the mass of the metal organic framework and the polymer segment PEO. When the mass of the metal organic framework accounts for less than 2% of the sum of the mass of the metal organic framework and the polymer segment PEO, the performance improvement of the solid electrolyte is limited, and when the content is greater than 5%, the metal organic framework will have a agglomeration effect, thereby affecting the performance of the electrolyte.

[0049] In a preferred embodiment, the mass of the metal organic framework accounts for 5% of the sum of the mass of the metal organic framework and the polymer segment PEO. When the content is 5%, the electrolyte film provides the highest ion conductivity and ion transference number.

[0050] In some embodiments, the sodium salt is NaClO4, and the molar ratio of the PEO to the sodium salt is 15:1. The addition of sodium salt can effectively improve the ion conductivity of the electrolyte.

[0051] In some embodiments, the room temperature stirring is stirring at a speed of 840 rpm for 10 h, so that the metal organic framework, the polymer segment PEO and the sodium salt are uniformly dispersed in the acetonitrile.

[0052] In some embodiments, the drying treatment is performed in a vacuum drying oven, the pressure of which is -2.5 MPa, and the temperature of which is 60°C.

[0053] In some embodiments, the mold in step S30 is a polytetrafluoroethylene mold, which has good demolding effect, so that the obtained electrolyte film is easy to fall off from the mold.

[0054] In some embodiments, the preparation method of the UIO-66 comprises the steps of: adding zirconium chloride and benzenedicarboxylic acid into a reaction kettle in a molar ratio of 1:1, and adding DMF (N,N-dimethylformamide), glacial acetic acid, and concentrated hydrochloric acid, to prepare the UIO-66 by hydrothermal reaction. In the step of preparing the UIO-66, the DMF is used as a solvent, the glacial acetic acid is used as an adjuster, and the concentrated hydrochloric acid is used as a catalyst.

[0055] In some embodiments, the molar ratio of the glacial acetic acid to the DMF is 1:7, and the molar ratio of the concentrated hydrochloric acid to the DMF is 1:70. Under this molar ratio, a monodisperse regular octahedral crystal UIO-66 with a diameter of 200 nm and a pore size of 1.1 nm is successfully prepared.

[0056] The following examples are further provided to illustrate the present application in detail. It should also be understood that the following examples are only used to further illustrate the present application, and cannot be understood as limiting the scope of protection of the present application. Any non-essential improvement and adjustment made by a person skilled in the art according to the above content of the present application shall fall within the protection scope of the present application.

[0057] Example 1

[0058] The interpenetrating structure sodium ion solid-state electrolyte films with the UIO-66 content (the mass of the UIO-66 accounts for the sum of the mass of the UIO-66 and the mass of the polymer segment PEO) of 0%, 2%, 5%, and 10% are respectively designed, the sum of the mass of PEO and the mass of UIO-66 is 0.5 g, and the content of sodium salt NaClO4 satisfies the molar ratio PEO:Na + = 15:1.

[0059] The specific steps are as follows:

[0060] According to the above design of the interpenetrating structure sodium ion solid-state electrolyte films with the UIO-66 content of 0%, 2%, 5%, and 10%, the components thereof are respectively:

[0061] MOF (0%): UIO-66 0 g, PEO 0.5 g, NaClO4 0.093 g;

[0062] MOF (2%): UIO-66 0.01 g, PEO 0.49 g, NaClO4 0.091 g;

[0063] MOF (5%): UIO-66 0.025 g, PEO 0.475 g, NaClO4 0.088 g;

[0064] MOF (10%): UIO-66 0.05 g, PEO 0.45 g, NaClO4 0.083 g;

[0065] The mixture of the above different contents was added into a conical flask, and 20 ml of acetonitrile was added as a solvent; the particles were first dispersed uniformly by ultrasonic for 15 min, and then stirred at room temperature (rotational speed 840 rpm) for 10 h to obtain a mixed solution. The obtained mixed solution was poured into a polytetrafluoroethylene mold, and the pressure and temperature in the vacuum drying box were kept at -2.5 MPa and 60°C, respectively, for 12 h to obtain an electrolyte film.

[0066] This example compares the electrolytes with 0%, 2%, 5%, and 10% different UIO-66 contents, as shown in Figure 2 , which proves that the electrolyte with a UIO-66 content of 5% has the best performance, Figure 3 , which proves that the electrolyte film with a UIO-66 content of 5% does not agglomerate, and therefore the test results show that the solid-state electrolyte with a content of 5% has the best performance.

[0067] When the MOF content is too low, it has limited performance improvement on the solid-state electrolyte, and when the content is too high, we find that the UIO-66 particles will agglomerate (as shown in Figure 4 ), thereby affecting the performance of the electrolyte.

[0068] Example 2

[0069] To verify the existence of the interpenetrating structure constructed in the present application, the following is specific:

[0070] In this example, UIO-66 particles are obtained by reacting ZrCl4 and terephthalic acid ligands in a high-pressure reaction kettle, and a MOF and PEO electrolyte film is formed by a hot solvent method. In order to prove the interpenetrating internal structure of this composite solid-state electrolyte, solid-state electrolyte films with MOF contents of 0%, 10%, 50%, 70%, and 80% are prepared, and DSC and XRD tests are performed; from the DSC images shown in Figure 5 , it can be seen that when the UIO-66 content increases from 50% to 80%, the PEO melting peak will gradually decrease until it disappears, and when the UIO-66 content increases to 70%, the PEO melting peak can be obviously found to decrease; from the XRD images shown inFigure 6 The characteristic peaks of PEO (23°, 18°) can be observed in the XRD images shown, which also disappear after the UIO-66 content increases to 80%, because the PEO chain segments are all limited inside the UIO-66 particles, and their characteristic peaks no longer appear; that is, because the PEO chain all passes through the MOF particles and cannot exhibit the corresponding characteristic peaks.

[0071] After confirming the feasibility of the interpenetrating solid-state electrolyte, the model is established by VETA software, and the characteristics and advantages of this interpenetrating structure are analyzed. First, the model of PEO chain segment penetrating through the UIO-66 MOF particle is established, which is denoted as PEO-UIO-66-1, and then the model of PEO chain segment without penetrating through the UIO-66 is established, which is denoted as PEO-UIO-66-2 for comparison, as shown in Figure 7 As shown, this interpenetrating structure can effectively adsorb anions in the electrolyte. When the PEO chain segment penetrates into the MOF particle material, the anions in the metal salt will be distributed around the PEO chain segment and distributed around it when the PEO penetrates into the MOF structure. This characteristic makes it more likely for the anions to be attracted and fixed by the metal clusters of the MOF, which will result in this interpenetrating solid-state electrolyte structure having a very high ion transference number, which is beneficial to the improvement of the battery concentration polarization, can make the battery cycle at high rate for a long time, and inhibit the generation of dendrites.

[0072] Further, in order to confirm this conclusion, the adsorption energy of anions by the two models is calculated and compared in this embodiment. Here, NaClO4 metal salt is selected to be added to the solid-state electrolyte, and DMol3 software is used for spin polarization calculation of density functional theory (DFT). The generalized gradient approximation (GGA) PBE functional and double numerical basis set plus polarization functional (DNP) and semi- nuclear pseudo potential function (DSPP) are adopted. The DFT-D correction in the form of Grimme is used to explain the dispersion interaction, and the self-consistent field convergence of each electronic energy is set to 1.0×10 -5 Ha, the geometric optimization convergence criterion is: energy is 1.0×10 -5 Ha, force is 0.0004 HaA -1 , displacement is 0.001 A, finally, the adsorption energy (Eads) is calculated as Eads = Ead / sub-Ead-Esub, where Ead / sub, Ead and Esub are the optimized adsorbate / substrate low system, the adsorbate in the structure and the pure substrate surface.

[0073] The conclusion is as shown in Figure 7As shown, the adsorption energy of metal cation sites on UIO-66 to anion ClO4 - of PEO-UIO-66-1 is much larger than that of PEO-UIO-66-2, which means that the former is more likely to adsorb anions to increase the ion transference number.

[0074] The interpenetrated solid-state electrolyte established by the present application has a strong ability to fix anions, so that the ion transference number is as high as 0.63, as shown in Figure 8 which also proves the excellent performance of the interpenetrated solid-state electrolyte.

[0075] The interpenetrated solid-state electrolyte is assembled into a 2016 button cell and a soft pack battery to test its long cycle capability at high rate, and the results show that the high ion transference number and high ion conductivity of the interpenetrated solid-state electrolyte allow it to perform long cycle of more than 1000 cycles at ultra-high current and the capacity retention rate is as high as 95.6%, as shown in Figure 9 and the battery capacity retention rate is as high as 97% after being assembled into a soft pack battery.

[0076] In summary, the present application provides an interpenetrated structure sodium ion solid-state electrolyte film and a preparation method thereof. A mixture is obtained by mixing a metal organic framework, a polymer chain segment PEO and a sodium salt, an acetonitrile solution is added to the mixture and ultrasonic treatment is performed, then normal temperature stirring is performed to obtain a mixed solution; then the mixed solution is poured into a mold and drying treatment is performed in a vacuum drying box to obtain a sodium ion solid-state electrolyte film. The preparation method utilizes an interpenetrated structure solid-state electrolyte formed by the polymer chain segment passing through the pore structure of the metal organic framework (MOF) particles, which can further improve the ion conductivity and ion transference number of the solid-state electrolyte; and the interpenetrated structure sodium ion solid-state electrolyte allows the battery to perform long cycle of more than 1000 cycles at high rate current, and the capacity retention rate (the ratio of the battery capacity before and after cycle) is as high as 95.6%.

[0077] It should be understood that the application of the present application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the present application.

Claims

1. An intercalation-type structure sodium-ion solid electrolyte thin film, characterized by, The interpenetrating structure sodium ion solid electrolyte film comprises a metal organic framework with a hole structure and a polymer segment PEO interpenetrated in the holes. The metal organic framework is selected from one of UIO-66, ZIF-8 and MOF-74; the molecular mass of the polymer segment PEO is 500000-900000; the mass of the metal organic framework accounts for 2%-5% of the sum of the mass of the metal organic framework and the mass of the polymer segment PEO; the interpenetrating structure sodium ion solid electrolyte film further comprises a sodium salt, and the molar ratio of the sodium salt to the polymer segment PEO is 1:

15.

2. The method of claim 1, wherein the method is characterized by: The method comprises the steps of: providing a metal organic framework, a polymer segment PEO and a sodium salt; mixing the metal organic framework, the polymer segment PEO and the sodium salt to obtain a mixture, adding an acetonitrile solution to the mixture and performing ultrasonic treatment, then performing normal temperature stirring to obtain a mixed solution; pouring the mixed solution into a mold and performing drying treatment to obtain a sodium ion solid electrolyte film.

3. The method of claim 2, wherein the method further comprises: The mass of the metal organic framework accounts for 2%-5% of the sum of the mass of the metal organic framework and the mass of the polymer segment PEO.

4. The method of claim 2, wherein the method further comprises: The normal temperature stirring is stirring at a rotation speed of 840 rpm for 10 h.

5. The method of claim 2, wherein the method further comprises: The drying treatment is performed in a vacuum drying box, the pressure of the vacuum drying box is -2.5 MPa, and the temperature is 60 DEG C.

6. The method of claim 2, wherein the method further comprises: The metal organic framework is UIO-66.

7. The method of claim 6, wherein the method further comprises: The preparation method of the UIO-66 comprises the steps of: adding zirconium chloride and phthalic acid into a reaction kettle at a molar ratio of 1:1, and adding DMF, glacial acetic acid and concentrated hydrochloric acid, and preparing the UIO-66 through hydrothermal reaction.

8. The method of claim 7, wherein the method further comprises: The molar ratio of the glacial acetic acid to the DMF is 1:7, and the molar ratio of the concentrated hydrochloric acid to the DMF is 1:70.

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