Polymer-based solid electrolyte membrane based on lithium iodide and preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to a polymer-based solid electrolyte membrane based on lithium iodide as well as a preparation method and application of the polymer-based solid electrolyte membrane. The polymer-based solid electrolyte membrane based on lithium iodide comprises the following components: lithium titanium aluminum phosphate, polyvinylidene fluoride hexafluoropropylene and lithium iodide. Through the composite synergistic effect of polyvinylidene fluoride hexafluoropropylene and lithium iodide, performance improvement is realized from three dimensions of interface compatibility, ion transmission kinetics and structural stability.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a polymer-based solid electrolyte membrane based on lithium iodide, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Solid-state lithium metal batteries show great application potential in solving the energy density and safety limitations of current liquid batteries, and are expected to meet the requirements of next-generation energy storage technologies. As one of the key materials therein, solid electrolytes play a huge role.

[0004] Solid electrolyte systems mainly include inorganic (ceramic / glass) electrolytes, organic polymer electrolytes, and their composites. Among them, inorganic solid electrolytes usually have the highest ionic conductivity. Especially for sulfide superionic conductors, their conductivity even exceeds that of liquid electrolytes. However, their brittleness and traditional sintering processes make their thickness usually above 200 μm, seriously affecting the energy density of solid-state lithium metal batteries. In contrast, polymer-based solid electrolytes have the advantages of low density, simple manufacturing process, and easy adjustment, and can achieve a thinner thickness, thereby effectively reducing the proportion of non-active components in the battery, reducing the transfer resistance of lithium ions, and achieving a higher energy density. However, current polymer-based solid electrolytes have problems such as low ionic conductivity, poor electrochemical stability, poor heat and fire resistance, and low lithium ion transference number. Summary of the Invention

[0005] To overcome the above problems, the present invention provides a polymer-based solid electrolyte membrane based on lithium iodide, a preparation method thereof, and an application thereof. The polymer-based solid electrolyte membrane described in the present invention is composed of a mixture of an inorganic solid electrolyte lithium aluminum titanium phosphate, a polymer polyvinylidene fluoride hexafluoropropylene, and an additive lithium iodide, and is a mixed solid electrolyte with more excellent ionic conductivity, more stable electrochemical performance, better heat and fire resistance, and higher lithium ion transference number, and can be applied to quasi-solid-state and all-solid-state lithium batteries.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] In the first aspect of the present invention, there is provided a polymer-based solid electrolyte membrane based on lithium iodide, and the components of the polymer-based solid electrolyte membrane include: lithium aluminum titanium phosphate, polyvinylidene fluoride hexafluoropropylene, and lithium iodide.

[0008] In a second aspect of the present invention, there is provided a method for preparing a polymer-based solid electrolyte membrane based on lithium iodide as described in the first aspect, comprising the following steps:

[0009] Dissolve lithium titanium aluminum phosphate, polyvinylidene fluoride hexafluoropropylene, and lithium iodide in an organic solvent to obtain a precursor slurry;

[0010] Coat the precursor slurry on a substrate, and after drying, obtain a polymer-based solid electrolyte membrane based on lithium iodide.

[0011] In a third aspect of the present invention, there is provided a lithium-air or lithium-oxygen battery, comprising an air cathode, a polymer-based solid electrolyte membrane based on lithium iodide as described in the third aspect, and a metallic lithium anode.

[0012] The beneficial effects of the present invention are as follows:

[0013] (1) The polymer-based solid electrolyte membrane based on lithium iodide designed in the present invention realizes performance improvement from three dimensions: interfacial compatibility, ion transport kinetics, and structural stability through the composite synergistic effect of polyvinylidene fluoride hexafluoropropylene and lithium iodide. In terms of interface optimization, polyvinylidene fluoride hexafluoropropylene not only provides a three-dimensional stock price coating for lithium titanium aluminum phosphate (LATP), effectively blocking the chemical erosion of the lithium anode by Ti 4+ , while the introduction of lithium iodide increases the flexibility of the polymer chain segments by reducing the crystallinity of the system, significantly enhancing the physical adhesion between the electrolyte membrane and the electrode, and realizing synchronous reduction of the interfacial impedance. In terms of ion transport regulation, the dual role of lithium iodide is particularly prominent: on the one hand, it forms amorphous ion channels by destroying the polymer crystalline region, accelerating the migration of lithium ions; on the other hand, as a lithium ion supplement source, it directly increases the concentration of mobile Li + in the electrolyte. The two work together to increase the ionic conductivity by more than double (from 2.44×10 -4 to 5.35×10 -4 S·cm -1 ), and at the same time increase the lithium ion transference number from 0.359 to 0.597. In terms of stability enhancement, the high thermal decomposition temperature of polyvinylidene fluoride hexafluoropropylene (>400 °C) and the flame retardant characteristics of lithium iodide complement each other, enabling the composite electrolyte to maintain structural integrity at a high temperature of 200 °C.

[0014] (2) The preparation method of the present application is simple and the preparation conditions are mild. The raw materials are cheap and easy to obtain, which is conducive to promoting the industrialization and popularization of hybrid solid electrolytes in lithium-air or lithium-oxygen batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0016] Figure 1 Optical photograph taken of the lithium iodide-based polymer solid electrolyte membrane prepared in Example 1;

[0017] Figure 2 SEM photographs of the polymer solid electrolyte membranes prepared in Examples 1-3 and Comparative Example 1, where (a) is Comparative Example 1, (b) is Example 1, (c) is Example 2, and (d) is Example 3;

[0018] Figure 3 X-ray diffraction patterns of the polymer solid electrolyte membranes prepared in Examples 1-3 and Comparative Example 1; where Example 1 is HSE-1, Example 2 is HSE-2, Example 3 is HSE-3, and Comparative Example 1 is HSE-0; PDF#01-074-1974 is the standard card for the X-ray diffraction pattern of lithium aluminum titanium phosphate; PDF#35-0754 is the standard card for the X-ray diffraction pattern of lithium iodide;

[0019] Figure 4 Results of the fire test and thermal stability test of the solid electrolyte membranes in Examples 1-2 and Comparative Examples 1 and 3, where (a) is the fire test of Comparative Example 1; (b) is the fire test of Example 1; (c) is the fire test of Example 2; (d) is the thermal stability test of Comparative Example 3; (e) is the optical picture for measuring the thickness of Example 2; (f) is the thermal stability test experiment of Comparative Example 1, Example 1, Example 2, Comparative Example 3, and Comparative Example 2; where Comparative Example 1 is HSE-0, Example 1 is HSE-1, Example 2 is HSE-2, Comparative Example 2 is GMSS04, and Comparative Example 3 is Celgard2400;

[0020] Figure 5 Schematic diagram of the structural assembly of a lithium-oxygen battery assembled with the solid electrolyte membranes prepared in Examples 1-3 and Comparative Example 1 of the present invention;

[0021] Figure 6 Test results of the ion transference number of the solid electrolyte membranes prepared in Examples 1-3 and Comparative Example 1 of the invention. The inset shows the constant voltage polarization curve and the EIS results before and after constant voltage polarization. (a) is Comparative Example 1, (b) is Example 1, (c) is Example 2, and (d) is Example 3;

[0022] Figure 7 Test results of the conductivity of the hybrid solid electrolytes prepared in Examples 1-3 and Comparative Example 1 of the invention; where (a) is the EIS curve of the stainless steel symmetric battery of the solid electrolyte with different lithium iodide contents, and (b) is the ionic conductivity curve of the solid electrolyte with different lithium iodide contents; where Comparative Example 1 is HSE-0, Example 1 is HSE-1, Example 2 is HSE-2, and Example 3 is HSE-3. Detailed implementation manners

[0023] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0024] It should be noted that the terms used herein are only for describing the specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] The first typical implementation manner of the present invention provides a lithium iodide-based polymer solid electrolyte membrane. The components of the polymer solid electrolyte membrane include: lithium aluminum titanium phosphate, polyvinylidene fluoride hexafluoropropylene, and lithium iodide.

[0026] In one or more implementation manners, the mass ratio of lithium aluminum titanium phosphate to polyvinylidene fluoride hexafluoropropylene is (6.5 - 7.5):(3.5 - 2.5), preferably 7:3.

[0027] In one or more implementation manners, the mass ratio of lithium iodide to the sum of the masses of lithium aluminum titanium phosphate and polyvinylidene fluoride hexafluoropropylene is (0.1 - 2):2, preferably 0.23:2.

[0028] The second typical implementation manner of the present invention provides a preparation method for the lithium iodide-based polymer solid electrolyte membrane described in the first aspect, including the following steps:

[0029] Dissolve lithium aluminum titanium phosphate, polyvinylidene fluoride hexafluoropropylene, and lithium iodide in an organic solvent to obtain a precursor slurry;

[0030] Coat the precursor slurry on a substrate and obtain a lithium iodide-based polymer solid electrolyte membrane after drying.

[0031] In one or more implementation manners, the organic solvent is a mixed solution of N-N dimethylformamide and acetone.

[0032] Preferably, the mass ratio of N-N dimethylformamide to acetone is (11 - 13):(4.5 - 5.5), preferably 12:5.

[0033] In one or more embodiments, the height of the coating on the substrate is 280 - 320 μm, preferably 300 μm, and the thickness of the dried lithium iodide-based polymer solid electrolyte membrane is 80 - 110 μm.

[0034] In one or more embodiments, the particle size of the lithium titanium aluminum phosphate is 200 - 400 nm.

[0035] In one or more embodiments, the number average molecular weight of poly(vinylidene fluoride - hexafluoropropylene) is 300,000 - 500,000 g / mol, preferably 400,000 g / mol.

[0036] In one or more embodiments, the solubility (mass percentage) of lithium iodide in the organic solvent is 3% - 58.8%, preferably 6.8%.

[0037] In one or more embodiments, the drying method is as follows:

[0038] After drying at room temperature, heat treatment is carried out.

[0039] Preferably, the drying time at room temperature is 15 - 25 min, preferably 20 min;

[0040] The heat treatment temperature is 55 - 65 °C, preferably 60 °C; the heat treatment time is 9 - 12 h, preferably 10 h.

[0041] In one or more embodiments, the substrate is selected from glass slides.

[0042] The third typical embodiment of the present invention provides a lithium - air or lithium - oxygen battery, including an air cathode, the lithium iodide - based polymer solid electrolyte membrane described in the first aspect or the lithium iodide - based polymer solid electrolyte membrane prepared by the preparation method described in the second aspect, and a metallic lithium anode.

[0043] In one or more embodiments, the air cathode includes a cathode current collector, carbon paper, a conductive material, a binder, and a catalyst;

[0044] Preferably, the conductive material is selected from one or more of conductive carbon black, carbon nanotubes, acetylene black, and Ketjen black;

[0045] Preferably, the binder is poly(vinylidene fluoride) or polytetrafluoroethylene.

[0046] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0047] In the embodiments of the present invention, polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), lithium titanium phosphate (LATP), lithium iodide (LiI), N,N-dimethylformamide, and acetone are all commercially available products, where LiI is anhydrous and has a purity of 99%.

[0048] The number-average molecular weight of polyvinylidene fluoride hexafluoropropylene is 400,000 g / mol.

[0049] Example 1

[0050] Preparation of a polymer-based solid electrolyte membrane based on lithium iodide:

[0051] (1) Drying treatment of raw materials: Put PVDF-HFP and LATP into a vacuum drying oven, set the temperature at 60 °C and dry for 24 h to remove moisture, then put them into a glove box for standby. Among them, the number-average molecular weight of PVDF-HFP is 300,000, and the particle size of LATP is 300 nm.

[0052] (2) Preparation of the precursor slurry: Weigh 1.4 g of LATP and dissolve it in a mixed solution of N,N-dimethylformamide and acetone (2.4 g of N,N-dimethylformamide and 1 g of acetone), and ultrasonicate for 1 h to completely crush the massive LATP to obtain an LATP solution; weigh 0.6 g of PVDF-HFP and add it to the LATP solution to obtain a homogeneous slurry, and stir it at 500 rpm for 24 h; weigh 0.11 g of LiI and add it to the stirred homogeneous slurry to obtain the precursor slurry of HSE-1. After stirring the slurry at 500 rpm for 48 h, reduce the rotation speed to 250 rpm and stir for 24 h to remove bubbles.

[0053] (3) Coating and film formation of the slurry

[0054] The stirred slurry is coated on a thin glass sheet using an infrared drying type flat coater, where the coating thickness is 300 μm. Place the glass sheet in a vacuum drying oven and let it stand at room temperature for 20 min, then raise the temperature to 60 °C and dry for 10 h to remove the solvent, obtaining a polymer-based solid electrolyte membrane based on lithium iodide; gently remove the film with tweezers. Use a hydraulic slicer to cut it into circular pieces with a diameter of 16 mm and a thickness of 80 μm - 110 μm, and place them in a glove box with a water and oxygen content less than 0.1 ppm for standby.

[0055] The optical photograph of the prepared polymer-based solid electrolyte membrane based on lithium iodide is as Figure 1 shown. It can be seen that the surface is light yellow, which is mainly due to the color caused by the addition of LiI.

[0056] Example 2

[0057] Preparation of a polymer-based solid electrolyte membrane based on lithium iodide:

[0058] (1) Raw material drying treatment: Put PVDF-HFP and LATP into a vacuum drying oven, set the drying temperature at 60 °C for 24 h to remove moisture, and then put them into a glove box for standby. Among them, the number-average molecular weight of PVDF-HFP is 300,000, and the particle size of LATP is 300 nm.

[0059] (2) Preparation of precursor slurry: Weigh 1.4 g of LATP and dissolve it in a mixed solution of N,N-dimethylformamide and acetone (2.4 g of N,N-dimethylformamide and 1 g of acetone), and ultrasonicate for 1 h to completely crush the massive LATP to obtain an LATP solution; weigh 0.6 g of PVDF-HFP and add it to the LATP solution to obtain a homogenate, and stir it at 500 rpm for 24 h; weigh 0.23 g of LiI and add it to the stirred homogenate to obtain the precursor slurry of HSE-2. After stirring the slurry at 500 rpm for 48 h, reduce the rotation speed to 250 rpm and stir for 24 h to remove air bubbles.

[0060] (3) Coating and film formation of the slurry

[0061] Coat the stirred slurry on a thin glass sheet using an infrared drying type flat coater, with a coating thickness of 300 μm. Place the glass sheet in a vacuum drying oven and let it stand at room temperature for 20 min, then heat it to 60 °C and dry for 10 h to remove the solvent, obtaining a lithium iodide-based polymer solid electrolyte membrane; gently remove the film with tweezers. Use a hydraulic slicing machine to cut it into circular pieces with a diameter of 16 mm and a thickness of 80 μm to 110 μm, and put them into a glove box with a water and oxygen content less than 0.1 ppm for standby.

[0062] Example 3

[0063] Preparation of lithium iodide-based polymer solid electrolyte membrane:

[0064] (1) Raw material drying treatment: Put PVDF-HFP and LATP into a vacuum drying oven, set the drying temperature at 60 °C for 24 h to remove moisture, and then put them into a glove box for standby. Among them, the number-average molecular weight of PVDF-HFP is 300,000, and the particle size of LATP is 300 nm.

[0065] (2) Preparation of precursor slurry: Weigh 1.4 g of LATP and dissolve it in a mixed solution of N,N-dimethylformamide and acetone (2.4 g of N,N-dimethylformamide and 1 g of acetone), and ultrasonicate for 1 h to completely crush the blocky LATP to obtain a LATP solution; weigh 0.6 g of PVDF-HFP and add it to the LATP solution to obtain a homogenate, which is stirred at 500 rpm for 24 h; weigh 0.5 g of LiI and add it to the stirred homogenate to obtain a precursor slurry of HSE-1. After stirring the slurry at 500 rpm for 48 h, reduce the speed to 250 rpm and stir for 24 h to eliminate bubbles.

[0066] (3) Slurry coating and film formation

[0067] The stirred slurry was coated on a thin glass sheet using an infrared drying flat plate coating machine, where the coating thickness was 300 μm, and the glass sheet was placed in a vacuum drying oven at room temperature for 20 minutes, then heated to 60°C and dried for 10 hours to remove the solvent, to obtain a polymer-based solid electrolyte membrane based on lithium iodide; the film was gently removed with tweezers. It was cut into discs with a diameter of 16 mm and a thickness of 80 μm to 110 μm using a hydraulic slicer, and placed in a glove box with less than 0.1 ppm of water and oxygen for standby use.

[0068] Example 4

[0069] Preparation of polymer-based solid electrolyte membrane based on lithium iodide:

[0070] (1) Raw material drying treatment: PVDF-HFP and LATP were placed in a vacuum drying oven, set to 60°C and dried for 24 hours to remove moisture, and then placed in a glove box for later use. The number average molecular weight of PVDF-HFP is 300,000, and the particle size of LATP is 300 nm.

[0071] (2) Preparation of precursor slurry: Weigh 1.4 g of LATP and dissolve it in a mixed solution of N,N-dimethylformamide and acetone (2.4 g of N,N-dimethylformamide and 1 g of acetone), and ultrasonicate for 1 h to completely crush the blocky LATP to obtain a LATP solution; weigh 0.6 g of PVDF-HFP and add it to the LATP solution to obtain a homogenate, which is then stirred at 500 rpm for 24 h; weigh 1.3 g of LiI and add it to the stirred homogenate to obtain a precursor slurry of HSE-1. After stirring the slurry at 500 rpm for 48 h, reduce the speed to 250 rpm and stir for 24 h to eliminate bubbles.

[0072] (3) Slurry coating and film formation

[0073] The stirred slurry was coated on a thin glass sheet using an infrared drying type flat coater, with a coating thickness of 300 μm. The glass sheet was placed in a vacuum drying oven and left standing at room temperature for 20 min, and then heated to 60 °C and dried for 10 h to remove the solvent, obtaining a polymer-based solid electrolyte membrane based on lithium iodide; the film was gently removed with tweezers. It was cut into discs with a diameter of 16 mm and a thickness in the range of 80 μm to 110 μm using a hydraulic slicer and placed in a glove box with a water and oxygen content less than 0.1 ppm for standby.

[0074] Comparative Example 1

[0075] Compared with Example 1, LiI was not added in this comparative example, and the preparation process was as follows:

[0076] Preparation of the polymer-based solid electrolyte membrane:

[0077] (1) Raw material drying treatment: PVDF-HFP and LATP were placed in a vacuum drying oven, dried at 60 °C for 24 h to remove moisture, and then placed in a glove box for standby. Among them, the number average molecular weight of PVDF-HFP was 300,000, and the particle size of LATP was 300 nm.

[0078] (2) Preparation of the precursor slurry: Weigh 1.4 g of LATP and dissolve it in a mixed solution of N,N-dimethylformamide and acetone (2.4 g of N,N-dimethylformamide and 1 g of acetone), and ultrasonicate for 1 h to completely crush the bulk LATP to obtain an LATP solution; weigh 0.6 g of PVDF-HFP and add it to the LATP solution to obtain a homogeneous slurry, which was stirred at 500 rpm for 24 h to obtain the precursor slurry of HSE-0. After the slurry was stirred at 500 rpm for 48 h, the rotation speed was reduced to 250 rpm and stirred for 24 h to eliminate bubbles.

[0079] (3) Coating and film formation of the slurry

[0080] The stirred slurry was coated on a thin glass sheet using an infrared drying type flat coater, with a coating thickness of 300 μm. The glass sheet was placed in a vacuum drying oven and left standing at room temperature for 20 min, and then heated to 60 °C and dried for 10 h to remove the solvent, obtaining a polymer-based solid electrolyte membrane based on lithium iodide; the film was gently removed with tweezers. It was cut into discs with a diameter of 16 mm and a thickness in the range of 80 μm to 110 μm using a hydraulic slicer and placed in a glove box with a water and oxygen content less than 0.1 ppm for standby.

[0081] Comparative Example 2

[0082] Commercial GMSS04 separator.

[0083] Comparative Example 3

[0084] Commercial Celgard 2400 separator.

[0085] Example 5

[0086] In this example, the performance of the solid electrolyte membranes in Examples 1 to 4 and Comparative Example 3 was characterized.

[0087] (1) Scanning electron microscope:

[0088] The scanning electron microscope images of the electrolyte films prepared in Examples 1 to 3 of the present invention and Comparative Example 1 at a scale of 1 μm are as Figure 2 shown, where HSE-0, HSE-1, HSE-2, and HSE-3 correspond to Figure 2 a, b, c, and d in. With the increase in the LiI addition content on the surface of the solid electrolytes in Examples 1 to 3, wonderful changes occurred on the surface. More and more gaps were filled, and the surface was no longer uneven but uniform and flat. The flat surface of the solid electrolyte can reduce the contact impedance with the electrode and provide a high migration efficiency of lithium ions.

[0089] (2) X-ray diffraction:

[0090] The X-ray diffraction results of the solid electrolytes prepared in Examples 1 to 3 of the present invention and Comparative Example 1 are as Figure 3 shown. In the figure, HSE-0, HSE-1, HSE-2, and HSE-3 correspond to Comparative Example 1 and Examples 1 to 3 respectively. Among them, PDF#01-074-1974 is the LATP standard card, and PDF#35-0754 is the LiI standard card. From Figure 3 it can be found that there are no impurity peaks in the solid electrolytes in Examples 1 to 3. With the increase in the lithium iodide content, the crystallinity shows a downward trend. The HSE-2 sample may have a higher ion diffusion rate and a higher degree of amorphization. In the solid electrolyte system, the amorphous phase and the carrier concentration usually promote the improvement of the ion diffusion rate. For the HSE-3 sample, its crystallinity is greatly reduced. This phenomenon may be attributed to the decrease in the ion diffusion rate and ionic conductivity caused by salt aggregation. At this concentration, Li + does not effectively contribute to ion conduction, but interacts with the polymer backbone, resulting in a decrease in the ion transport efficiency.

[0091] (3) Fire resistance and thermal stability:

[0092] The fire resistance and thermal stability of the mixed solid electrolytes in Examples 1 to 3 and Comparative Examples 1 and 3 are as Figure 4As shown, where Figures a, b, c, and d respectively correspond to the fire performance test experiments of Comparative Example 1, Example 1, Example 2, and Comparative Example 3. Among them, Figure e is an optical picture for measuring the thickness of the solid electrolyte membrane in Example 2. Figure f is the thermal stability test at room temperature, at 100 °C for ten minutes, and at 200 °C for ten minutes. In Figure f, HSE-1, HSE-2, HSE-3, Celgard2400, and GMSS04 respectively correspond to Comparative Example 1, Example 1, Example 2, Comparative Example 3, and Comparative Example 2. From Figure 4 a, b, c, and d, it can be seen that Comparative Example 1, Example 2, and Example 3 are more stable than Comparative Example 3 overall under the combustion of the outer flame of the alcohol lamp, without any phenomenon of being ignited. This is because the main body of Comparative Example 3 is organic matter such as polyethylene and polypropylene, which is extremely flammable and not safe in extreme cases of the battery. From Figure 4 Figure f, it can be seen that for Comparative Example 1, Example 1, and Example 2, only color changes occurred on their surfaces as the temperature increased, and their surface morphologies remained unchanged. However, serious surface deformations occurred for Comparative Example 2 and Comparative Example 3 at high temperatures. Among them, Comparative Example 3 had melted when the temperature reached 200 °C.

[0093] (4) Assembly of the battery: The structural assembly schematic taking the application of the hybrid solid electrolyte (HSE) in a lithium-oxygen battery as an example is as Figure 5 shown. Its structure from top to bottom is the positive electrode shell, air cathode, solid electrolyte membrane, lithium sheet, steel sheet, spring gasket, and negative electrode shell.

[0094] Measurement of lithium ion transference number:

[0095] The ion transference numbers of the hybrid solid electrolytes prepared in Examples 1 to 3 and Comparative Example 1 were measured using the classical ion transference number test method. The test process is as follows:

[0096] ① Assemble a lithium sheet / solid electrolyte / lithium sheet symmetric battery, add 5 μL of electrolyte solution (1 M LiTFSI + TEGDME) to ensure good contact, and place it in the glove box and let it stand for 24 h;

[0097] ② Use an electrochemical workstation to conduct EIS tests. The test conditions are 100000 Hz - 1 Hz, and the scanning rate is 5 mV·s -1 , and record the impedance data;

[0098] ③ Use the electrochemical workstation to conduct constant voltage polarization on the above battery. The perturbation voltage is 10 mV, the perturbation time is set to 3600 s, and stop observing after the current balance;

[0099] ④ Conduct EIS tests again with the same parameters as in step ②, and calculate the ion transference number through formula (1).

[0100]

[0101] Among them, in the formula, I ss is the current after constant-voltage polarization; I0 is the current before constant-voltage polarization; ΔV is the polarization voltage; R ss is the impedance before constant-voltage polarization; R0 is the impedance after constant-voltage polarization.

[0102] The test results are as Figure 6 shown. It can be seen that as the content of lithium iodide increases, the lithium-ion transference number calculated according to formula (1) also increases. Among them, the lithium-ion transference number of Example 2 reaches the maximum, which is because the addition of lithium iodide increases the content of lithium ions and fills the gaps between lithium titanium aluminum phosphate and polyvinylidene fluoride hexafluoropropylene, thereby increasing the lithium-ion transport rate.

[0103] (5) Conductivity test:

[0104] Assemble a steel sheet / solid electrolyte / steel sheet symmetric cell, set the test frequency to 100000 Hz - 1 Hz, and the test rate to 5 mV / s. The bulk impedance (without fitting) is obtained through an electrochemical workstation. Substitute the thickness L of the electrolyte, the effective area S, and the measured bulk impedance R into the ionic conductivity calculation formula to calculate the ionic conductivity. The ionic conductivity calculation formula is as shown in formula (2);

[0105]

[0106] Among them, σ is the ionic conductivity; L is the thickness of the solid electrolyte; R is the impedance of the solid electrolyte; S is the effective area of the solid electrolyte in contact with the steel sheet.

[0107] The test results are as Figure 7 shown. It can be seen from the figure that as the content of lithium iodide increases, the ionic conductivity gradually increases, and the ionic conductivity of HSE-2 reaches the highest. This is precisely because the addition of lithium iodide reduces the crystallinity of the solid electrolyte, and the low crystallinity can increase the amorphous region and optimize the ion transport path, thereby improving the lithium-ion conductivity.

[0108] Table 1 summarizes the performance of the solid electrolytes of Examples 1 - 3 and Comparative Examples 1 - 3.

[0109] Table 1 Performance of Solid Electrolytes

[0110]

[0111] As shown in Table 1, for Example 2, both the ionic conductivity and the lithium-ion transference number are the highest.

[0112] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lithium iodide-based polymer solid electrolyte membrane, characterized in that, The raw materials of the polymer-based solid electrolyte membrane include: lithium titanium aluminum phosphate, polyvinylidene fluoride hexafluoropropylene, and lithium iodide.

2. The polymer-based solid electrolyte membrane according to claim 1, wherein The mass ratio of lithium titanium aluminum phosphate to polyvinylidene fluoride hexafluoropropylene is (6.5 - 7.5):(3.5 - 2.5), preferably 7:3; Or, the mass ratio of lithium iodide to the sum of the masses of lithium titanium aluminum phosphate and polyvinylidene fluoride hexafluoropropylene is (0.1 - 2):2, preferably 0.23:

2.

3. The preparation method of the polymer-based solid electrolyte membrane according to claim 1 or 2, characterized in that It includes the following steps: Dissolve lithium titanium aluminum phosphate, polyvinylidene fluoride hexafluoropropylene, and lithium iodide in an organic solvent to obtain a precursor slurry; Coat the precursor slurry on a substrate, and after drying, obtain a lithium iodide-based polymer-based solid electrolyte membrane.

4. The preparation method according to claim 3, characterized in that ,, The organic solvent is a mixed solution of N-N, dimethylformamide and acetone; Preferably, the mass ratio of N-N, dimethylformamide to acetone is (11 - 13):(4.5 - 5.5), preferably 12:

5.

5. The preparation method according to claim 3, characterized in that, The particle size of the lithium titanium aluminum phosphate is 200 - 400 nm.

6. The preparation method according to claim 3, wherein The number average molecular weight of polyvinylidene fluoride hexafluoropropylene is 300000 - 500000 g / mol, preferably 400000 g / mol.

7. The preparation method according to claim 3, characterized in that, The solubility (mass percentage) of lithium iodide in the organic solvent is 3% - 58.8%, preferably 6.8%; Or, the substrate is selected from glass slides.

8. The preparation method according to claim 3, characterized in that, The coating height on the substrate is 280 - 320 μm, preferably 300 μm; the thickness of the dried lithium iodide-based polymer-based solid electrolyte membrane is 80 - 110 μm.

9. The preparation method according to claim 3, characterized in that, The drying method is: Dry at room temperature and then perform heat treatment; Preferably, the drying time at room temperature is 15 - 25 min, preferably 20 min; The heat treatment temperature is 55 - 65 °C, preferably 60 °C; the heat treatment time is 9 - 12 h, preferably 10 h.

10. A lithium-air or lithium-oxygen battery, characterized in that, It includes an air cathode, the polymer-based solid electrolyte membrane described in Claim 1 or 2, or the polymer-based solid electrolyte membrane prepared by the preparation method described in any one of Claims 3 - 9, and a lithium metal anode.

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