PEO-based solid electrolyte, battery and preparation method of PEO-based solid electrolyte

Abstract

The invention relates to a solid electrolyte and a preparation method thereof, in particular to a PEO-based solid electrolyte with relatively high ionic conductivity and relatively good circularity, a preparation method of the PEO-based solid electrolyte and a battery prepared from the PEO-based solid electrolyte. Zinc oxide with rich hydroxyl and quantum dot morphology on the surface is prepared firstly, the hydroxyl can serve as Lewis base to interact with Li < + >, dissociation of lithium salt is promoted, and the concentration of Li < + > in the solid electrolyte is increased; then dispersing ZnO quantum dots in ethanol to form ZnO quantum dot sol, adding a certain amount of acetonitrile, and doping the ZnO quantum dot sol with LiTFSI and PEO; compared with direct doping of zinc oxide powder, doping of the zinc oxide quantum dot sol is more beneficial to improvement of the dispersity of zinc oxide in PEO, and the electrochemical performance of the solid electrolyte is improved. And the prepared PEO-based solid electrolyte is non-toxic and environment-friendly. And a solid-state battery assembled by the PEO-based solid-state electrolyte is relatively good in cycling stability at 1C.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte and a preparation method thereof, in particular to a PEO-based solid electrolyte with high ion conductivity and good cyclability and a preparation method thereof, and a battery made from the PEO-based solid electrolyte. Background Art

[0002] The development of smart devices, electric vehicles and new energy sources has put forward an increasing demand for energy storage. Lithium-ion solid-state batteries with high energy density and good safety performance have become a current research hotspot. Polymer solid electrolytes have good flexibility and low production costs, but their ionic conductivity is low and their cycle performance is poor, which limits their application. Adding inorganic fillers to polymer solid electrolytes to form composite electrolytes has become one of the effective ways to solve these problems.

[0003] In 1982, Jeweston et al. first added α-Al2O3 nanoparticles to PEO solid electrolyte to study the effect of inert fillers on the electrolyte (Solid State Ionics 7 (1982) 75-79). Subsequently, various inorganic fillers were tried to be added to polymer solid electrolytes, such as Al2O3, TiO2, SiO2, ZrO2, MgO, CuO, ZnO, etc. The addition of inorganic fillers reduces the crystallinity of the polymer, thereby improving the ionic conductivity of the solid electrolyte. However, inorganic nanoparticles are easy to agglomerate and have poor dispersion in the polymer, which makes it difficult to form a uniform and continuous Li+ in the polymer electrolyte. + Fast transmission channel, which limits the further improvement of the electrochemical performance of composite solid electrolytes. In order to solve these problems, researchers have tried many methods. Xie Jing et al. (Energy Storage Materials 43 (2021) 258-265) in situ grew ZnO quantum dots into PEO by vapor phase infiltration (VPI), but this method is cumbersome to operate and costly. Samira Najjar et al. (The Journal of Physical Chemistry C 124 (2020) 27907-27915.) chemically treated ZnO and covalently grafted it into PEO, but the problem of nanoparticle agglomeration has not been completely solved.

[0004] The present invention prepares a ZnO quantum dot sol with a diameter of about 4nm and rich hydroxyl groups on the surface by a sol-gel method, and uniformly mixes it with PEO to obtain a PEO-based composite solid electrolyte by a sol casting method, thereby preparing a solid-state battery with excellent performance. ZnO quantum dots are dispersed in ethanol to form a ZnO sol. The electrostatic interaction between ZnO quantum dots and ethanol and LiTFSI promotes the uniform dispersion of ZnO quantum dots in PEO. Good dispersion can effectively reduce the crystallinity of PEO, increase the area of ​​the amorphous region of PEO, and promote the formation of uniform and continuous Li in the PEO solid electrolyte. + Fast transmission channel; at the same time, the hydroxyl groups on the surface of ZnO quantum dots can act as Lewis bases to react with Li + interaction, promoting the dissociation of lithium salts and increasing the Li + The synergistic effect of these two mechanisms is conducive to improving ionic conductivity. Furthermore, the outer surface of the solid electrolyte with good dispersion contains a large number of uniformly dispersed ZnO quantum dots, which makes the solid electrolyte more lithium-philic, which will help reduce the impedance at the interface between the solid electrolyte and lithium metal, inhibit the growth of lithium dendrites, and improve the cycle stability. In summary, by adding ZnO quantum dot sol to PEO, its dispersibility in PEO can be effectively improved, thereby reducing the crystallinity of the solid electrolyte and forming a more uniform and continuous Li + Fast transmission channel, improving ionic conductivity, and reducing the impedance at the interface between solid electrolyte and lithium metal, inhibiting the growth of lithium dendrites, and ultimately improving the cycle stability of solid-state batteries. Summary of the invention

[0005] One of the purposes of the present invention is to provide a method for preparing a PEO-based solid electrolyte, and to obtain zinc oxide with quantum dot morphology, which has a smaller size and a higher specific surface area, and is beneficial to reducing the crystallinity of PEO. Compared with direct doping with zinc oxide powder, zinc oxide quantum dot sol doping is more conducive to improving the dispersibility of zinc oxide in PEO and improving the electrochemical performance of the solid electrolyte.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for preparing a PEO-based solid electrolyte, comprising the following steps:

[0007] S1. Add Zn(Ac)2·2H2O to ethanol to obtain an ethanol solution of Zn(Ac)2·2H2O; add KOH to ethanol to obtain an ethanol solution of KOH; add the ethanol solution of KOH dropwise to the ethanol solution of Zn(Ac)2·2H2O, stir at room temperature to obtain a transparent solution;

[0008] S2, pouring excess n-hexane into the transparent solution, separating the precipitated ZnO quantum dots after standing for a period of time and dispersing them in ethanol to obtain ZnO quantum dot sol;

[0009] S3, adding acetonitrile to the ZnO quantum dot sol, stirring at room temperature to obtain an ethanol-acetonitrile dispersion of ZnO quantum dots, and sequentially adding LiTFSI and PEO, stirring to obtain a polymer solution;

[0010] S4. Transferring the polymer solution to the surface of the substrate, curing and drying the solution, and obtaining a PEO-based solid electrolyte in which ZnO quantum dots are uniformly dispersed, wherein the mass percentage of the ZnO quantum dots is 1%-9%.

[0011] As a further improvement of the preparation method of PEO-based solid electrolyte:

[0012] Preferably, in step S1, the concentration of Zn(Ac)2·2H2O in the ethanol solution of Zn(Ac)2·2H2O is 0.05-0.07 g / ml, the concentration of KOH in the ethanol solution of KOH is 0.04-0.05 g / ml, and the mass ratio of Zn(Ac)2·2H2O to KOH in the two solutions is (2-3):1.

[0013] Preferably, when preparing the ZnO quantum dot sol in step S2, the dispersion concentration of the ZnO quantum dots in ethanol is 0.03-0.05 g / ml.

[0014] Preferably, in step S3, the ZnO quantum dot sol and acetonitrile are mixed in a volume ratio of (0.2-3):10.

[0015] Preferably, in step S3, the amount of LiTFSI added to the ethanol-acetonitrile dispersion of ZnO quantum dots is 0.02-0.04 g / ml, and the amount of PEO added is 0.08-0.12 g / ml.

[0016] Preferably, in step S4, after the polymer solution is transferred to the substrate surface, it is cured at ambient temperature for 24 hours and then transferred to a vacuum drying oven at 50-80° C. for drying for 10-30 hours.

[0017] Preferably, in step S4, the thickness of the prepared PEO-based solid electrolyte is 200-300 μm.

[0018] A second object of the present invention is to provide a PEO-based solid electrolyte prepared by the preparation method of the PEO-based solid electrolyte described in any one of the above.

[0019] The third object of the present invention is to provide a battery made of the above-mentioned PEO-based solid electrolyte, wherein the PEO-based solid electrolyte is cut into discs with a diameter of 18 mm, and the positive electrode material, solid electrolyte, negative electrode, gasket, and spring are placed in the positive electrode shell in order, and finally covered with the negative electrode shell, and placed on a hydraulic press for pressure maintenance to obtain the battery.

[0020] As a further improvement of the battery made of the above PEO-based solid electrolyte:

[0021] Preferably, the positive electrode is a LiFePO4 positive electrode, and the specific preparation method is as follows: LiFePO4, Super P, PVDF and NMP are mixed in a mass ratio of 80:10:10:200 to form a uniform slurry, which is poured on a carbon-coated aluminum foil and dried to obtain the positive electrode.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) This embodiment provides a method for preparing a PEO-based solid electrolyte. First, a quantum dot-shaped zinc oxide is prepared. The size of the zinc oxide is small (only about 4 nm) and the specific surface area is high, which is beneficial to reducing the crystallinity of PEO and facilitating the formation of Li + Transport in solid electrolytes. The ZnO surface contains abundant hydroxyl groups, which can act as a Lewis base to react with Li + interaction, promoting the dissociation of lithium salts and increasing the Li + concentration. The present invention disperses ZnO quantum dots in ethanol to form a ZnO quantum dot sol, which is then doped with LiTFSI and PEO. Compared with direct doping with zinc oxide powder, doping with zinc oxide quantum dot sol is more conducive to improving the dispersibility of zinc oxide in PEO and improving the electrochemical performance of solid electrolytes. The presence of ethanol is beneficial to the stability of ZnO quantum dots, preventing them from aggregating and piling up, and acetonitrile can dissolve PEO. Since ethanol and acetonitrile are infinitely miscible, ethanol and acetonitrile are used together as solvents to uniformly disperse ZnO quantum dots in PEO. This design provides a solution to the problem of poor dispersibility of inorganic nanoparticles in polymers. The preparation method is simple to operate and has low cost.

[0024] 2) The ZnO quantum dots in the PEO-based solid electrolyte prepared by the present invention are evenly dispersed, the crystallinity of the solid electrolyte film is significantly reduced, and the ionic conductivity is improved. The prepared PEO-based solid electrolyte is non-toxic and environmentally friendly. The solid-state battery assembled with the PEO-based solid electrolyte has good cycle stability at 1C. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Graph showing the ionic conductivity of the solid electrolyte membrane at 60 degrees Celsius in Examples 1 to 5 of the present invention.

[0026] Figure 2 1 is the XRD diagram of the PZL solid electrolyte membrane in Comparative Example 1 and the H-PZL solid electrolyte membrane in Example 1 of the present invention.

[0027] Figure 3It is the ionic conductivity-temperature diagram of the PZL in Comparative Example 1 and the H-PZL solid electrolyte membrane in Example 1 of the present invention.

[0028] Figure 4 This is the cycle curve of the LiFePO4 / / Li solid-state battery assembled with H-PZL solid-state electrolyte in Example 1 at 1C rate. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0030] Comparative Example

[0031] This comparative example provides a method for preparing a solid electrolyte and a solid battery, which specifically comprises the following steps:

[0032] S1. Add 2.4 g of Zn(Ac)2·2H2O to 40 ml of ethanol to obtain an ethanol solution of Zn(Ac)2·2H2O; add 0.9 g of KOH to 20 ml of ethanol to obtain an ethanol solution of KOH; add the ethanol solution of KOH dropwise to the ethanol solution of Zn(Ac)2·2H2O, and stir at 750 rpm for about 3 min at room temperature to obtain a transparent solution;

[0033] S2, pouring excess n-hexane into the transparent solution, separating the precipitated ZnO quantum dots after standing for a period of time, and obtaining ZnO powder after drying;

[0034] S3, add 0.03 g of ZnO quantum dot powder into 10 ml of acetonitrile, stir at room temperature for 10 min, then add 0.362 g of LiTFSI and 1 g of PEO in sequence, and stir at 800 rpm for 24 h to obtain a polymer solution;

[0035] S4. The polymer solution was transferred to the surface of the polytetrafluoroethylene substrate, and after curing at ambient temperature for 24 hours, it was transferred to a vacuum drying oven at 60° C. and dried for 24 hours to obtain a PEO-based solid electrolyte (abbreviated as PZL).

[0036] Example 1

[0037] This embodiment provides a method for preparing a PEO-based solid electrolyte, which specifically includes the following steps:

[0038] S1. Add 2.4 g of Zn(Ac)2·2H2O to 40 ml of ethanol to obtain an ethanol solution of Zn(Ac)2·2H2O with a concentration of 0.06 g / ml; add 0.9 g of KOH to 20 ml of ethanol to obtain an ethanol solution of KOH with a concentration of 0.045 g / ml; the mass ratio of Zn(Ac)2·2H2O to KOH in the two solutions is 2.66:1; add the ethanol solution of KOH dropwise to the ethanol solution of Zn(Ac)2·2H2O, stir at 750 rpm for about 3 min at room temperature to obtain a transparent solution;

[0039] S2, pouring 200 ml of excess n-hexane into the transparent solution, separating the precipitated ZnO quantum dots after standing for a period of time, dispersing the ZnO quantum dots in ethanol at a dispersion concentration of 0.043 g / ml, and obtaining a ZnO quantum dot sol with good dispersion;

[0040] S3, take 696.6 microliters of the above ZnO quantum dot sol (ZnO content is 0.03g), and add 10ml of acetonitrile thereto, the mixing volume ratio of ZnO quantum dot sol and acetonitrile is 0.7:10, stir at room temperature for 10min, and obtain an ethanol acetonitrile dispersion of ZnO quantum dots; then add 0.362g of LiTFSI and 1g of PEO in sequence, the added concentrations are 0.0362g / ml and 0.1g / ml respectively, and stir at a speed of 800rpm for 24h to obtain a polymer solution;

[0041] S4. The polymer solution was transferred to the surface of the polytetrafluoroethylene substrate, and after curing at ambient temperature for 24 hours, it was transferred to a vacuum drying oven at 60°C and dried for 24 hours to obtain a PEO-based solid electrolyte with uniformly dispersed ZnO quantum dots (abbreviated as H-PZL), and the mass percentage of ZnO quantum dots was 3%.

[0042] Example 2

[0043] This embodiment provides a method for preparing a PEO-based solid electrolyte and a solid-state battery. The specific steps refer to Example 1, except that in the above step S3, 232.2 microliters of the above ZnO quantum dot sol (ZnO content is 0.01g) are taken. Finally, a PEO-based solid electrolyte (abbreviated as H-PZL) and a solid-state battery with uniformly dispersed ZnO quantum dots are obtained, and the mass percentage of ZnO quantum dots is 1%.

[0044] Example 3

[0045] This embodiment provides a method for preparing a PEO-based solid electrolyte and a solid-state battery. The specific steps are referred to in Example 1, except that, in the above step S3, 1161 microliters of the above ZnO quantum dot sol (ZnO content is 0.05g) are taken. Finally, a PEO-based solid electrolyte (abbreviated as H-PZL) and a solid-state battery with uniformly dispersed ZnO quantum dots are obtained, and the mass percentage of ZnO quantum dots is 5%.

[0046] Example 4

[0047] This embodiment provides a method for preparing a PEO-based solid electrolyte and a solid-state battery. The specific steps refer to Example 1. In the above step S3, 1625.4 microliters of the above ZnO quantum dot sol (ZnO content is 0.07g) are taken. Finally, a PEO-based solid electrolyte (abbreviated as H-PZL) and a solid-state battery with uniformly dispersed ZnO quantum dots are obtained, and the mass percentage of ZnO quantum dots is 7%.

[0048] Example 5

[0049] This embodiment provides a method for preparing a PEO-based solid electrolyte and a solid-state battery. The specific steps refer to Example 1. In the above step S3, 2089.8 microliters of the above ZnO quantum dot sol (ZnO content is 0.09g) are taken. Finally, a PEO-based solid electrolyte (abbreviated as H-PZL) and a solid-state battery with uniformly dispersed ZnO quantum dots are obtained, and the mass percentage of ZnO quantum dots is 9%.

[0050] Performance Test:

[0051] 1) The ionic conductivity of the solid electrolyte was tested by the alternating current impedance method. The solid electrolytes prepared in the comparative example and Example 1 were sandwiched between stainless steel sheets (SS) to assemble into SS / solid electrolyte / SS symmetrical cells. The EIS test was performed on an electrochemical workstation with a test frequency range of 10 5 Hz-10 -1 Hz.

[0052] Figure 1 1-5. The ionic conductivity variation curves of the SS / / SS solid-state battery assembled with the H-PZL solid-state electrolyte membrane in the comparative example and Examples 1-5 at 60°C.

[0053] from Figure 1 The comparison shows that the SS / / SS solid-state battery assembled with H-PZL solid electrolyte has a higher ionic conductivity at 60°C, and the highest ionic conductivity is 1.54×10 -3 S cm -1 .

[0054] Figure 2The XRD images are of the solid electrolyte membrane (abbreviated as PZL) in which ZnO powder is directly dispersed in PEO in the comparative example and the solid electrolyte membrane (abbreviated as H-PZL) in which ZnO quantum dot sol is uniformly dispersed in PEO in Example 1. PEO has relatively sharp crystallization peaks at 19.28° and 23.50°. It can be seen from the figure that the XRD spectrum of H-PZL prepared by doping with ZnO quantum dot sol in Example 1 has a significantly lower diffraction peak intensity at the same position than that of PZL in the comparative example, which indicates that H-PZL has a lower degree of crystallinity.

[0055] Figure 3 The ionic conductivity diagram of the SS / / SS solid-state battery assembled with PZL in the comparative example and the H-PZL solid-state electrolyte in Example 1 at different temperatures. It can be seen from the figure that the ionic conductivity of the SS / / SS solid-state battery assembled with the H-PZL solid-state electrolyte is higher than that of PZL at different temperatures.

[0056] 2) The PEO-based solid electrolytes prepared in the comparative example and embodiments 1-5 were cut into discs with a diameter of 18 mm for standby use; LiFePO4, SuperP, PVDF and NMP were mixed in a mass ratio of 80:10:10:200 to form a uniform slurry, which was poured on a carbon-coated aluminum foil to prepare a LiFePO4 positive electrode; the LiFePO4 positive electrode, solid electrolyte, negative electrode, gasket and shrapnel were placed in the positive electrode shell in order, and finally the negative electrode shell was covered, the battery was placed on a hydraulic press for pressure maintenance and then taken out, and placed in an oven at 60°C for 12 hours to assemble the LiFePO4 / solid electrolyte / Li button battery, and the battery cycle performance was tested in the Xinwei battery test system, and the voltage range was set to 2.8V~3.8V.

[0057] Figure 4 This is the cycle curve of the LiFePO4 / / Li solid-state battery assembled with the H-PZL solid electrolyte membrane in Example 1 at 1C rate. Figure 4 It can be seen that the solid-state battery assembled with H-PZL solid electrolyte can cycle for 1000 cycles without short circuit, and the cycle performance is relatively excellent.

[0058] Those skilled in the art should understand that the above are only some specific embodiments of the present invention, rather than all embodiments. It should be noted that for those of ordinary skill in the art, many modifications and improvements can be made, and all modifications or improvements that do not exceed the scope of protection of the present invention should be regarded as.

Claims

1. A method for preparing a PEO-based solid electrolyte, characterized in that: The steps include: S1. Add Zn(Ac)2·2H2O to ethanol to obtain an ethanol solution of Zn(Ac)2·2H2O; add KOH to ethanol to obtain an ethanol solution of KOH; add the ethanol solution of KOH dropwise to the ethanol solution of Zn(Ac)2·2H2O, stir at room temperature to obtain a transparent solution; S2, pouring excess n-hexane into the transparent solution, separating the precipitated ZnO quantum dots after standing for a period of time and dispersing them in ethanol to obtain ZnO quantum dot sol; S3, adding acetonitrile to the ZnO quantum dot sol, stirring at room temperature to obtain an ethanol-acetonitrile dispersion of ZnO quantum dots, and sequentially adding LiTFSI and PEO, stirring to obtain a polymer solution; S4. Transferring the polymer solution to the surface of the substrate, curing and drying the solution, and obtaining a PEO-based solid electrolyte in which ZnO quantum dots are uniformly dispersed, wherein the mass percentage of the ZnO quantum dots is 1%-10%.

2. The method for preparing a PEO-based solid electrolyte according to claim 1, characterized in that: In step S1, the concentration of Zn(Ac)2·2H2O in the ethanol solution of Zn(Ac)2·2H2O is 0.05-0.07 g / ml, the concentration of KOH in the ethanol solution of KOH is 0.04-0.05 g / ml, and the mass ratio of Zn(Ac)2·2H2O to KOH in the two solutions is (2-3):

1.

3. The method for preparing a PEO-based solid electrolyte according to claim 1, characterized in that: When preparing the ZnO quantum dot sol in step S2, the dispersion concentration of the ZnO quantum dots in ethanol is 0.03-0.05 g / ml.

4. The method for preparing a PEO-based solid electrolyte according to claim 1, characterized in that: In step S3, the ZnO quantum dot sol and acetonitrile are mixed in a volume ratio of (0.2-3):

10.

5. The method for preparing a PEO-based solid-state battery according to claim 1, characterized in that: In step S3, the amount of LiTFSI added to the ethanol-acetonitrile dispersion of ZnO quantum dots is 0.02-0.04 g / ml, and the amount of PEO added is 0.08-0.12 g / ml.

6. The method for preparing a PEO-based solid electrolyte according to claim 1, characterized in that: In step S4, after the polymer solution is transferred to the substrate surface, it is cured at ambient temperature for 24 hours and then transferred to a vacuum drying oven at 50-80° C. for drying for 10-30 hours.

7. The method for preparing a PEO-based solid electrolyte according to claim 1, characterized in that: In step S4, the thickness of the prepared PEO-based solid electrolyte is 200-300 μm.

8. A PEO-based solid electrolyte prepared by the preparation method according to any one of claims 1 to 7.

9. A solid-state battery made from the PEO-based solid electrolyte according to claim 8, characterized in that: The PEO-based solid electrolyte is cut into discs with a diameter of 18 mm, and the positive electrode material, solid electrolyte, negative electrode, gasket, and shrapnel are placed in the positive electrode shell in order, and finally the negative electrode shell is covered, and the shell is placed on a hydraulic press to maintain pressure.

10. The solid-state battery according to claim 9, characterized in that: The positive electrode is a LiFePO4 positive electrode, and the specific preparation method is as follows: LiFePO4, Super P, PVDF and NMP are mixed in a mass ratio of 80:10:10:200 to form a uniform slurry, poured on a carbon-coated aluminum foil, and dried to obtain the positive electrode.

Images