PEO composite solid electrolyte based on synergistic effect of montmorillonite intercalation and ethylene carbonate plastification as well as preparation method and application of PEO composite solid electrolyte

Abstract

The invention discloses a PEO composite solid electrolyte based on synergistic effect of montmorillonite intercalation and ethylene carbonate plastification as well as a preparation method and application of the PEO composite solid electrolyte, and belongs to the technical field of composite solid electrolyte materials. MMT and EC are added into PEO at the same time, EC molecules are embedded between MMT layers, the MMT interlayer spacing is expanded, an interlayer liquid fast channel is formed, a multi-path ion transmission network is constructed, and the ion conductivity and electrochemical cycle stability are improved. And the EC is additionally provided with a PEO chain segment, so that diffusion of ions in a PEO / EC amorphous region is accelerated synergistically, and the ionic conductivity is further improved. Meanwhile, MMT can also adsorb free EC molecules, reduce oxygenolysis of the free EC molecules under high voltage, promote formation of a compact SEI film rich in LiF / LiCOs on an electrode interface, and widen an electrochemical window. In addition, MMT serves as a rigid framework to provide mechanical support for PEO, EC plasticization reduces the acting force between PEO chains, dendritic crystal growth pressure can be borne, and battery short circuit is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite solid electrolytes; specifically, it relates to a PEO composite solid electrolyte based on the synergistic effect of montmorillonite intercalation and ethylene carbonate plasticization, and a preparation method and application thereof. Background Art

[0002] The main chain of polyethylene oxide (PEO) contains strong electron-donating groups. In the complex system composed of ether oxygen functional groups and alkali metals, PEO acts as an ion-conducting matrix and alkali metals act as charge carrier sources. Under the action of the ether oxygen atoms in the molecular chain, the metal salt dissociates into charge carriers, and with the help of the short-range segment motion of the polymer, the ions migrate in the polymer medium and exhibit ionic conductivity. PEO's good alkali metal ion conductivity is due to its combination of crystalline and amorphous structures. Therefore, as the amorphous region of PEO increases, the conductivity continues to increase. However, PEO is easy to crystallize, resulting in low conductivity, which greatly limits the application of PEO-based polymer electrolytes. Existing technology uses montmorillonite (MMT) to improve ionic conductivity and tensile strength in PEO. While montmorillonite enhances mechanical strength through physical crosslinking, its lamellar structure hinders the movement of PEO segments, limiting the improvement in ionic conductivity. Large amounts of MMT are required to improve PEO's ionic conductivity. However, excessive MMT can embrittle the electrolyte, resulting in an elongation at break of less than 50%, making it difficult to adapt to changes in electrode volume. Furthermore, the Lewis acid sites on the MMT surface can catalyze side reactions, leading to the decomposition of lithium salts. Summary of the Invention

[0003] In order to solve the above-mentioned problems existing in existing PEO-based solid electrolytes, the present invention provides a PEO composite solid electrolyte based on the synergistic effect of montmorillonite intercalation and ethylene carbonate plasticization, as well as its preparation method and application. The technical solution of the present invention is as follows: The present invention aims to provide a PEO composite solid electrolyte based on the synergistic effect of montmorillonite intercalation and ethylene carbonate plasticization, which is made of polyethylene oxide (PEO), alkali metal salt, montmorillonite (MMT) and ethylene carbonate (EC).

[0004] It is further defined that the molecular weight of the polyethylene oxide (PEO) is 600,000.

[0005] It is further defined that the alkali metal salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0006] It is further defined that the mass ratio of polyethylene oxide (PEO), alkali metal salt, MMT and EC is (40-60): (12-18): (4-6): (2-3), and preferably, the mass ratio of polyethylene oxide (PEO), alkali metal salt, MMT and EC is 40:13:4:2.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned PEO composite solid electrolyte based on the synergistic effect of montmorillonite intercalation and ethylene carbonate plasticization.

[0008] A method for preparing a PEO composite solid electrolyte based on the synergistic effect of montmorillonite intercalation and ethylene carbonate plasticization comprises the following steps: Step 1: Add polyethylene oxide (PEO) and alkali metal salt to a solvent and stir at room temperature until completely dissolved; Step 2: Then add montmorillonite and ethylene carbonate, continue stirring until completely dissolved, quickly pour into a mold at room temperature, flatten, and let stand to dry to obtain a PEO composite solid electrolyte.

[0009] It is further defined that in step 1, the purity of polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide, montmorillonite, and ethylene carbonate is analytical grade.

[0010] It is further defined that in step 1, the solvent is acetonitrile.

[0011] It is further defined that in step 1, stirring is performed using a magnetic stirrer at a stirring speed of 300 r / min to 500 r / min.

[0012] It is further defined that in step 1, the stirring time is about 6 h.

[0013] It is further defined that in step 2, a magnetic stirrer is used for stirring at a stirring speed of 300 r / min to 500 r / min.

[0014] It is further defined that in step 2, the stirring time is about 8 h.

[0015] It is further defined that in step 2, the drying time at room temperature is 24 h.

[0016] An all-solid-state alkali metal battery comprises any of the above-mentioned composite solid electrolytes or a composite solid electrolyte prepared by any of the above-mentioned methods.

[0017] A flexible electronic and micro device comprises any of the above-mentioned composite solid electrolytes or a composite solid electrolyte prepared by any of the above-mentioned methods.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention simultaneously adds MMT and EC to PEO, embeds EC molecules between MMT layers, expands the MMT interlayer spacing, and forms interlayer liquid fast channels. At the same time, it also constructs MMT-EC interface channel hopping transmission. By building a multi-path ion transport network, the ionic conductivity and lithium ion migration number are improved. The resulting composite solid electrolyte has a charge and discharge capacity of up to 162 mAh / g at high temperature. The present invention uses EC to plasticize PEO segments to achieve ion diffusion in the PEO / EC amorphous region, achieving synergistic acceleration and achieving an ionic conductivity of 3.9×10 -4 S / cm. At the same time, MMT can also adsorb free EC molecules, reduce their oxidative decomposition at high voltage, and promote the formation of a dense SEI film rich in LiF / Li2CO3 at the electrode interface, so that the electrochemical window can be widened to 4.7 V at high temperature. In addition, MMT provides mechanical support for PEO as a rigid skeleton. EC plasticization reduces the force between PEO chains, which can withstand the pressure of dendrite growth, avoid battery short circuit, and solve the problem that the strength and toughness of traditional solid electrolytes cannot be improved at the same time. The elongation at break can be increased to more than 800% and can withstand a tensile force of 3.2 MPa.

[0019] In order to further understand the features and technical contents of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings. However, the accompanying drawings are provided for reference and illustration only and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a SEM image of the pure PEO electrolyte prepared in Comparative Example 1; Figure 2 This is a SEM photo of the PEO composite solid electrolyte prepared in Example 1; Figure 3 The stress-strain curves of the PEO composite solid electrolyte prepared in Example 1, the pure PEO electrolyte prepared in Comparative Example 1, and the PEO-MMT electrolyte prepared in Comparative Example 2 are shown; Figure 4 The long cycle performance diagram of the all-solid-state lithium metal battery assembled with the PEO composite solid electrolyte prepared in Example 1, the pure PEO electrolyte prepared in Comparative Example 1, and the PEO-MMT electrolyte prepared in Comparative Example 2; Figure 5 LSV plots of the PEO composite solid electrolyte prepared in Example 1, the pure PEO electrolyte prepared in Comparative Example 1, and the PEO-MMT electrolyte prepared in Comparative Example 2; Figure 6 The AC impedance curves of the PEO composite solid electrolyte prepared in Example 1, the pure PEO electrolyte prepared in Comparative Example 1, and the PEO-MMT electrolyte prepared in Comparative Example 2 are shown. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0024] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are conventional in the art and can be obtained commercially by those skilled in the art unless otherwise specified.

[0025] Example 1: The preparation method of the PEO composite solid electrolyte based on the synergistic effect of montmorillonite intercalation and ethylene carbonate plasticization in this example is carried out according to the following steps: 1. Weigh the raw materials of the PEO+10%MMT+5%EC composite solid electrolyte of this embodiment as follows: Acetonitrile 10 g, polyethylene oxide (PEO) 0.5 g, montmorillonite (MMT) 0.05 g, ethylene carbonate (EC) 0.025 g, lithium bis(trifluoromethanesulfonyl)imide 0.163 g.

[0026] 2. The operation process of preparing the double cross-linked gel electrolyte of this embodiment is as follows: (1) First, 0.5 g of polyethylene oxide (PEO) and 0.163 g of lithium bis(trifluoromethanesulfonylimide) were dissolved in 10 g of acetonitrile and stirred at 300 r / min with a magnetic stirrer at room temperature of 25°C for 6 h. The polyethylene oxide and lithium bis(trifluoromethanesulfonylimide) solids were completely dissolved and set aside to obtain a mixed solution A.

[0027] (2) Add 0.05 g of montmorillonite (MMT) and 0.025 g of ethylene carbonate (EC) to the mixed solution A in (1) and stir at 300 r / min at room temperature for 8 h until all the solids of montmorillonite and ethylene carbonate are dissolved to obtain a mixed solution B.

[0028] (3) Pour the mixed solution B into the mold quickly at room temperature, spread it flat, and let it dry for 24 h.

[0029] (4) The dried film was peeled off from the mold to obtain a composite solid electrolyte, named PEO+10%MMT+5%EC.

[0030] Comparative Example 1: The difference between this comparative example and the embodiment is that: in (1), the amount of MMT used is 0 g, the amount of EC used is 0 g, and the obtained composite solid electrolyte is named PEO.

[0031] Comparative Example 2: The difference between this comparative example and the embodiment is that: in (1), the amount of MMT used is 0.05 g, the amount of EC used is 0 g, and the obtained composite solid electrolyte is named PEO+10%MMT.

[0032] The surface micromorphology of the composite solid electrolytes prepared in Comparative Example 1 and Example 1 was characterized, and the SEM photos were as follows: Figure 1 and Figure 2 As shown in the figure, it can be clearly observed that EC molecules are embedded in the interlayers of montmorillonite, expanding the interlayer spacing, and the expanded pores form "interlayer liquid fast channels".

[0033] The PEO+10%MMT+5%EC prepared in Example 1, the PEO prepared in Comparative Example 1, and the PEO+10%MMT prepared in Comparative Example 2 were subjected to tensile tests. Figure 3 As shown, it can be seen that the PEO+10%MMT+5%EC prepared in Example 1 is superior to the PEO prepared in Comparative Example 1 and the PEO+10%MMT prepared in Comparative Example 2 in terms of tensile strength and ductility, indicating that the flexible plasticizing effect of EC balances the rigidity of montmorillonite and realizes a "rigid and flexible" structure.

[0034] The PEO+10%MMT+5%EC prepared in Example 1, the PEO prepared in Comparative Example 1, and the PEO+10%MMT prepared in Comparative Example 2 were subjected to cyclic charge and discharge tests. Figure 4 As shown, it can be seen that the PEO+10%MMT+5%EC prepared in Example 1 is higher than the PEO prepared in Comparative Example 1 and the PEO+10%MMT prepared in Comparative Example 2 in terms of both discharge specific capacity and charge-discharge efficiency, indicating that EC is adsorbed on the surface of montmorillonite, suppressing side reactions through the dielectric shielding effect, and promoting the formation of a stable LiF / Li2CO3 composite SEI film, thereby improving the cycle life.

[0035] The PEO+10%MMT+5%EC prepared in Example 1, the PEO prepared in Comparative Example 1, and the PEO+10%MMT prepared in Comparative Example 2 were subjected to LSV tests at high temperature. Figure 5 As shown, it can be seen that the electrochemical window of PEO+10%MMT+5%EC prepared in Example 1 is wider and more stable than that of PEO prepared in Comparative Example 1 and PEO+10%MMT prepared in Comparative Example 2, indicating that montmorillonite reduces the direct contact between EC and the positive electrode by adsorbing EC molecules and anchoring anions, thereby improving the electrochemical window.

[0036] AC impedance test was performed on PEO+10%MMT+5%EC prepared in Example 1, PEO prepared in Comparative Example 1 and PEO+10%MMT prepared in Comparative Example 2 at high temperature. Figure 6 As shown by Figure 6 From the impedance curve calculation results, it can be seen that the conductivity of PEO+10%MMT+5%EC prepared in Example 1 is higher than that of PEO prepared in Comparative Example 1 and PEO+10%MMT prepared in Comparative Example 2, indicating that EC is inserted between PEO chains and montmorillonite layers as a plasticizer, significantly reducing the resistance to chain segment movement, while expanding the distance between montmorillonite layers to form an "interlayer liquid channel", thereby improving the ionic conductivity.

[0037] The above description is merely a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above. Some modifications and changes to the present invention should also fall within the scope of protection of the claims of the present invention.

Claims

1. A PEO composite solid electrolyte based on the synergistic effect of montmorillonite intercalation and ethylene carbonate plasticization, characterized in that: It is made of polyethylene oxide (PEO), alkali metal salt, montmorillonite (MMT) and ethylene carbonate (EC).

2. The composite solid electrolyte according to claim 1, characterized in that The molecular weight of PEO is 600,000.

3. The composite solid electrolyte according to claim 1, characterized in that The alkali metal salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

4. The composite solid electrolyte according to claim 1, characterized in that The mass ratio of PEO, alkali metal salt, MMT and EC is (40~60): (12~18): (4~6): (2~3).

5. The PEO-based composite solid electrolyte according to claim 4, characterized in that: The mass ratio of PEO, alkali metal salt, MMT and EC is 40:13:4:

2.

6. A method for preparing the composite solid electrolyte according to any one of claims 1 to 5, characterized in that: include: Step 1: Add PEO and alkali metal salt to acetonitrile and stir at room temperature until completely dissolved; Step 2: Then add montmorillonite and ethylene carbonate, continue stirring until completely dissolved, quickly pour into a mold at room temperature, flatten, and let stand to dry to obtain a PEO-based composite solid electrolyte.

7. The method according to claim 6, characterized in that In steps 1 and 2, the stirring speed is 300 r / min-500 r / min.

8. The method according to claim 6, characterized in that: In step 2, the static drying time is 24 h.

9. An all-solid-state alkali metal battery, characterized in that: The composite solid electrolyte comprises the composite solid electrolyte according to any one of claims 1 to 5 or the composite solid electrolyte prepared by the method according to any one of claims 6 to 8.

10. A flexible electronic and micro device, characterized in that: The invention comprises the PEO-based composite solid electrolyte according to any one of claims 1 to 5 or the composite solid electrolyte prepared by the method according to any one of claims 6 to 8.

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