Modified solid electrolyte as well as preparation method and application thereof

Abstract

The invention provides a modified solid electrolyte and a preparation method and application thereof. The modified solid electrolyte comprises a first solid electrolyte layer and a second solid electrolyte layer, the first solid electrolyte layer comprises a first polymer, a first oxide and a first lithium salt, and the second solid electrolyte layer comprises a second polymer, a second oxide and a second lithium salt; the first oxide is obtained by calcining and decomposing a first MOF material, and the first MOF material is at least one of Ni, Co and Mn; the second oxide is obtained by calcining and decomposing a second MOF material, and the second MOF material is an MOF material of Li. The provided modified solid electrolyte is beneficial to formation of a lithium-rich SEI film on the surface of lithium metal and uniform deposition of lithium ions, reduction of growth of lithium dendrites, reduction of dissolution of a positive electrode material, improvement of interface contact between the solid electrolyte and an electrode, improvement of ionic conductivity and cycling stability, and improvement of energy storage performance and service life of a solid lithium ion battery.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery solid electrolytes, and in particular relates to modified solid electrolytes and a preparation method and application thereof. Background Art

[0002] The revolution of energy technology is inseparable from the development of energy storage devices. Starting from lead-acid batteries, the scientific research community has been committed to improving the energy density of devices. Lithium-ion batteries, which began to be commercialized at the end of the last century, have attracted widespread attention due to their high energy density. They are currently widely used in transportation, portable electronic devices and low-altitude economy. However, the organic electrolyte of conventional commercial lithium-ion batteries is volatile and flammable. In the thermal runaway reaction of the battery, a large amount of heat energy will be released, causing the electrolyte to burn, thereby causing the entire battery to catch fire and explode. Therefore, how to improve the safety of lithium-ion batteries is a problem that researchers have always faced.

[0003] Using solid electrolytes instead of liquid electrolytes is currently the most direct means to solve safety problems. Among them, all-solid electrolytes composed of organic long-chain polymers are favored by the business community because of their simple processing, low cost and relatively softness. However, the current problems of poor interface contact and low ion conductivity of organic solid electrolytes seriously restrict their development. The current modification direction is to add inorganic fillers to organic solid electrolytes to increase mechanical and other lithium characteristics. However, how to improve the interface contact between solid electrolytes and positive and negative electrodes, and how to improve the electrical performance and life of solid-state batteries are still urgent problems to be solved. Summary of the invention

[0004] In response to the above technical problems, the present application provides a modified solid electrolyte and a preparation method and application thereof.

[0005] To achieve the above objectives, this application proposes the following technical solutions: In a first aspect, a modified solid electrolyte is provided, comprising: a first solid electrolyte layer and a second solid electrolyte layer, wherein the first solid electrolyte layer comprises a first polymer, a first oxide and a first lithium salt, and the second solid electrolyte layer comprises a second polymer, a second oxide and a second lithium salt; the first oxide is obtained by calcining and decomposing a first MOF material, and the first MOF material is a MOF material of at least one of Ni, Co and Mn; the second oxide is obtained by calcining and decomposing a second MOF material, and the second MOF material is a MOF material of Li.

[0006] In a second aspect, a method for preparing a modified solid electrolyte is provided, comprising: S1, calcining the first MOF material in an oxidizing atmosphere to obtain a first oxide; preparing a mixed solution A using a first polymer, a first oxide and a first lithium salt as raw materials, and coating and drying the mixed solution A to obtain a modified positive electrode side solid electrolyte; S2. calcining the second MOF material in an oxidizing atmosphere to obtain a second oxide; using the second polymer, the second oxide and the second lithium salt as raw materials to prepare a mixed solution B, coating the mixed solution B on the surface of the modified positive electrode side solid electrolyte, and drying to obtain a modified solid electrolyte.

[0007] In a third aspect, a solid-state battery is provided, comprising a positive electrode, a negative electrode and a modified solid electrolyte, wherein the modified solid electrolyte is the aforementioned modified solid electrolyte or a modified solid electrolyte prepared by the aforementioned preparation method.

[0008] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: The modified solid electrolyte provided includes a positive electrode side solid electrolyte composed of an oxide obtained by decomposing MOF materials of Ni, Co, and Mn, a first lithium salt, and a first polymer, and a negative electrode side electrolyte composed of an oxide obtained by decomposing MOF materials of Li, a second lithium salt, and a second polymer. The modified solid electrolyte is conducive to the formation of a lithium-rich SEI film and uniform deposition of lithium ions on the surface of lithium metal, reduces the growth of lithium dendrites, can reduce the dissolution of positive electrode materials, improves the interface contact between the solid electrolyte and the electrode, enhances ionic conductivity and cycle stability, and increases the energy storage performance and life of solid-state lithium-ion batteries.

[0009] The modified solid electrolyte method provided is simple to operate and has green and clean production conditions. It can realize large-scale synthesis and efficient preparation of high-performance solid electrolytes for lithium-ion batteries, and provides a reference and basis for the study of contact modification between solid electrolytes and positive and negative electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0011] Figure 1 This is the SEM image of modified oxide A prepared in step (1) of Example 1.

[0012] Figure 2 The cycle performance diagram of the solid-state battery assembled with the solid electrolyte prepared in Examples 1 to 5 and Comparative Examples 1 to 4. DETAILED DESCRIPTION

[0013] The applicant has found through research that by providing a positive electrode side solid electrolyte layer including a nanoporous oxide obtained by calcining and decomposing MOF materials of Ni, Co, and Mn, a first polymer, and a first lithium salt, and providing a negative electrode side solid electrolyte layer including a nanoporous oxide obtained by calcining and decomposing MOF materials of Li, a second polymer, and a second lithium salt, a lithium-rich SEI film and a uniform deposition of lithium ions can be formed on the surface of lithium metal, the growth of lithium dendrites can be reduced, the dissolution of the positive electrode material can be reduced, the interface contact between the solid electrolyte and the electrode can be improved, the ionic conductivity and cycle stability can be enhanced, and the energy storage performance and life of the solid-state lithium-ion battery can be significantly improved.

[0014] Specifically, some embodiments of the present invention provide a modified solid electrolyte, including: a first solid electrolyte layer and a second solid electrolyte layer, the first solid electrolyte layer including a first polymer, a first oxide and a first lithium salt, the second solid electrolyte layer including a second polymer, a second oxide and a second lithium salt; the first oxide is obtained by calcining and decomposing a first MOF material, the first MOF material is a MOF material of at least one of Ni, Co and Mn; the second oxide is obtained by calcining and decomposing a second MOF material, the second MOF material is a MOF material of Li.

[0015] The present invention adds nano oxides obtained by calcining nickel-cobalt-manganese MOF in the electrolyte on the positive electrode side, and adds nano lithium oxides obtained by calcining lithium MOF materials on the negative electrode side. The oxides obtained by calcining MOF-based materials can inherit the nano size of MOF materials and have special morphology (good particle size uniformity, small size, complete lattice, porous structure), which is conducive to the dispersion in polymer solid electrolytes, and improves the specific surface, reduces the agglomeration and crystallization of polymers, and can also increase lithium ion transmission channels and improve ion transmission. The nano oxides obtained by calcining nickel, cobalt or manganese nano MOF materials on the positive electrode side can reduce the corrosion of the electrolyte to the positive electrode material on the one hand, and inhibit the decomposition of the transition metal of the positive electrode material on the other hand, increase the structural stability of the battery as a whole, and increase the compatibility with the positive electrode interface. The nano lithium oxides obtained by calcining lithium MOF materials on the negative electrode side are helpful to form a lithium-rich SEI film on the surface of lithium metal, and the lithium-rich state of the interface is helpful to the uniform deposition of lithium ions and reduce the growth of lithium dendrites. In general, the use of specific metal oxides to fill the positive and negative electrodes is conducive to increasing the interface contact, improving ion conductivity and cycle stability.

[0016] In some preferred embodiments, the first polymer and the second polymer are at least one of PVDF, PVDF-HFP, and PVDF-CTFE.

[0017] In some preferred embodiments, the first lithium salt is LiBF 4、LiPF 6 、LiAsF 6 At least one of .

[0018] In some preferred embodiments, the second lithium salt is LiFSI, LiTFSI, LiClO 4 At least one of .

[0019] In some preferred embodiments, the mass ratio of the first polymer, the first oxide and the first lithium salt is 7-12:5-10:6-10.

[0020] In some preferred embodiments, the mass ratio of the second polymer, the second oxide and the second lithium salt is 7-12:5-10:6-10.

[0021] Some embodiments provide a method for preparing a modified solid electrolyte, comprising: S1, calcining the first MOF material in an oxidizing atmosphere to obtain a first oxide; preparing a mixed solution A using a first polymer, a first oxide and a first lithium salt as raw materials, and coating and drying the mixed solution A to obtain a modified positive electrode side solid electrolyte; S2. calcining the second MOF material in an oxidizing atmosphere to obtain a second oxide; using the second polymer, the second oxide and the second lithium salt as raw materials to prepare a mixed solution B, coating the mixed solution B on the surface of the modified positive electrode side solid electrolyte, and drying to obtain a modified solid electrolyte.

[0022] In some preferred embodiments, the first polymer and the second polymer are at least one of PVDF, PVDF-HFP, and PVDF-CTFE.

[0023] In some preferred embodiments, the first lithium salt is LiBF 4 、LiPF 6 、LiAsF 6 In some preferred embodiments, the second lithium salt is LiFSI, LiTFSI, LiClO 4 The applicant has found through research that the first lithium salt and the second lithium salt are preferred to further improve the battery performance.

[0024] In some preferred embodiments, in step S1, the calcination temperature is 500-700°C, for example, 500°C, 520°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C, 700°C, etc., and the calcination time is 1.5-4h, for example, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0025] In some preferred embodiments, in step S2, the calcination temperature is 450-600°C, such as 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C, etc., and the calcination time is 1-2h, such as 1h, 1.2h, 1.5h, 1.8h, 2h, etc. Studies have shown that if the calcination temperature is too high, the resulting oxide will agglomerate, increase the volatilization of Li, and reduce the performance of the solid electrolyte. If the calcination temperature is too low, the organic components will not be completely decomposed, which will also reduce the performance of the solid electrolyte.

[0026] In some preferred embodiments, the first MOF material is at least one of ZIF-67 (Co), MOF-74 (Ni), and ZIF-90 (Mn); the size of the first MOF material is 200~500nm, for example, 200nm, 250nm, 300nm, 350℃, 400℃, 450nm, 500nm, etc.

[0027] In some preferred embodiments, the second MOF material is at least one of Li-BTC-MOF, Li-ZIF-MOF, and Li-UIO-MOF; the size of the second MOF material is 50~300nm, for example, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, etc.

[0028] In some preferred embodiments, in the mixed solution A, the concentration of the polymer is 70-120 g / L, such as 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, etc. According to research, if the polymer concentration is too high, the reduction of lithium content will affect the transmission of lithium ions, and if the polymer concentration is too low, the bonding effect will be poor, which is not conducive to the mechanical strength of the membrane.

[0029] In some preferred embodiments, in the mixed solution A, the concentration of the first oxide is 50-100 g / L, such as 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, etc. Studies have shown that if the concentration of the oxide is too high, a good lithium ion transmission channel cannot be established, and if the concentration is too low, the modification effect on the electrolyte is deteriorated.

[0030] In some preferred embodiments, in the mixed solution A, the concentration of the lithium salt is 60-100 g / L, such as 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, etc. Studies have shown that too high a lithium salt concentration will reduce the uniformity of the solid electrolyte, and too low a lithium salt concentration will hinder lithium ion transmission.

[0031] In some preferred embodiments, the solvent of the mixed solution A is at least one of N,N-dimethylformamide, N-methylpyrrolidone and tetrahydrofuran.

[0032] In some preferred embodiments, in the mixed solution B, the concentration of the polymer is 70-120 g / L, for example, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, etc.

[0033] In some preferred embodiments, in the mixed solution B, the concentration of the second oxide is 50-100 g / L, for example, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, etc.

[0034] In some preferred embodiments, in the mixed solution B, the concentration of the lithium salt is 60-100 g / L, for example, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, etc.

[0035] In some preferred embodiments, the solvent of the mixed solution B is at least one of N,N-dimethylformamide, N-methylpyrrolidone and tetrahydrofuran.

[0036] In some preferred embodiments, in step S1, the thickness of the scraper used for coating is 200-300 μm, such as 200 μm, 220 μm, 250 μm, 280 μm, 300 μm, etc. If the scraper is too thick, the film will be too thick, resulting in an increase in the particle size of lithium ion transmission and an increase in resistance, while if the scraper is too thin, the film will be too thin.

[0037] In some preferred embodiments, in step S2, the coating is performed using a scraper with a thickness of 100-200 μm, such as 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, etc.

[0038] In some embodiments, the oxidizing atmosphere is one or both of air and oxygen.

[0039] Some embodiments of the present invention provide a solid-state battery, comprising a positive electrode, a negative electrode and a modified solid electrolyte, wherein the modified solid electrolyte is the aforementioned modified solid electrolyte or a modified solid electrolyte prepared by the aforementioned preparation method.

[0040] The active material of the positive electrode is an oxide of lithium and metal M, where M is one or more of Ni, Co, and Mn. For example, it can be a layered ternary positive electrode material, a spinel-like nickel cobalt manganese oxide material, a layered or spinel lithium manganese oxide material, a layered or spinel lithium cobalt oxide material, a layered or spinel lithium nickel oxide material, a layered or spinel lithium nickel manganese oxide, a layered or spinel nickel cobalt oxide material, a layered or spinel lithium cobalt manganese oxide material / lithium-rich manganese-based positive electrode material, etc.

[0041] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the specification, but the protection scope of the present invention is not limited to the following specific embodiments.

[0042] Example 1 (1) ZIF-67 with a particle size of 300 nm was heated at 600 °C for 2 hours in an oxygen environment to obtain modified oxide A. The SEM image is shown in Figure 1 As shown, from Figure 1 It can be seen that the particle size of the modified oxide A is nanometer-scale (particle size is 80~500nm); 10g PVDF-HFP, 7g modified oxide A and 8g LiPF 6 Add into 100 ml of N,N-dimethylformamide and stir to obtain a mixed solution A, apply the mixed solution A on a glass plate with a scraper with a thickness of 200 μm, and fully dry to obtain a modified positive electrode side solid electrolyte; (2) Li-BTC-MOF with a particle size D50 of 150 nm was heated at 500°C for 1.5 hours in an oxygen environment to obtain a modified oxide B. 10 g PVDF-HFP, 7 g modified oxide B and 8 g LiFSI were added to 100 ml N,N-dimethylformamide and stirred to obtain a mixed solution B. The mixed solution B was applied to the modified positive electrode side solid electrolyte prepared in step (1) with a 100 μm scraper and dried to obtain a modified solid electrolyte.

[0043] Comparative Example 1 (1) Take 24.4g ZIF-67 with a particle size D50 of 300nm, 10g PVDF-HFP and 8g LiPF 6 Add into 100 ml of N,N-dimethylformamide and stir to obtain a mixed solution A, apply the mixed solution A on a glass plate with a scraper with a thickness of 200 μm, and fully dry to obtain a modified positive electrode side solid electrolyte; (2) 50 g of Li-BTC-MOF with a particle size D50 of 150 nm, 10 g of PVDF-HFP and 8 g of LiFSI were added to 100 ml of N,N-dimethylformamide and stirred thoroughly to obtain a mixed solution B. The mixed solution B was applied onto the modified positive electrode side solid electrolyte prepared in step (1) with a 100 μm scraper and dried thoroughly to obtain a modified solid electrolyte.

[0044] Comparative Example 2 (1) Take 7g cobalt tetroxide, 10g PVDF-HFP and 8g LiPF 6 Add into 100 ml of N,N-dimethylformamide and stir to obtain a mixed solution A, apply the mixed solution A on a glass plate with a scraper with a thickness of 200 μm, and fully dry to obtain a modified positive electrode side solid electrolyte; (2) Take 7 g Li 2 O, 10 g PVDF-HFP and 8 g LiFSI were added into 100 ml N,N-dimethylformamide and stirred thoroughly to obtain a mixed solution B. The mixed solution B was coated on the modified positive electrode side solid electrolyte prepared in step (1) with a 100 μm scraper and dried thoroughly to obtain a modified solid electrolyte.

[0045] Comparative Example 3 (1) Take ZIF-67 with a particle size of 300 nm and heat it at 600 °C for 2 hours in an oxygen environment to obtain modified oxide A; take 7 g of modified oxide A, 10 g of PVDF-HFP and 8 g of LiPF 6 Add into 100 ml of N,N-dimethylformamide and stir to obtain a mixed solution A, apply the mixed solution A on a glass plate with a scraper with a thickness of 200 μm, and fully dry to obtain a modified positive electrode side solid electrolyte; (2) Take 7 g of modified oxide A, 10 g of PVDF-HFP and 8 g of LiFSI, add them into 100 ml of N,N-dimethylformamide and stir them thoroughly to obtain a mixed solution B. Apply the mixed solution B on the modified positive electrode side solid electrolyte prepared in step (1) with a 100 μm scraper and fully dry to obtain a modified solid electrolyte.

[0046] Comparative Example 4 (1) Take 10g PVDF-HFP and 8g LiPF 6 Add into 100 ml of N,N-dimethylformamide and stir to obtain a mixed solution A, apply the mixed solution A on a glass plate with a scraper with a thickness of 200 μm, and fully dry to obtain a modified positive electrode side solid electrolyte; (2) Li-BTC-MOF with a particle size D50 of 150 nm was heated at 500°C in an oxygen environment for 1.5 hours to obtain a modified oxide B. 7 g of the modified oxide B, 10 g of PVDF-HFP and 8 g of LiFSI were added to 100 ml of N,N-dimethylformamide and stirred to obtain a mixed solution B. The mixed solution B was applied on the modified positive electrode side solid electrolyte prepared in step (1) with a 100 μm scraper and dried to obtain a modified solid electrolyte.

[0047] Example 2 (1) MOF-74 with a particle size of 200 nm was heated at 500 °C for 4 hours in an oxygen environment to obtain modified oxide A. 7 g PVDF-HFP, 8 g modified oxide A and 10 g LiBF 4 Add into 100 ml of N,N-dimethylformamide and stir to obtain a mixed solution A, apply the mixed solution A on a glass plate with a scraper with a thickness of 200 μm, and fully dry to obtain a modified positive electrode side solid electrolyte; (2) Li-ZIF-MOF with a particle size D50 of 150 nm was heated at 450°C for 2 hours in an oxygen environment to obtain a modified oxide B. 7 g PVDF-HFP, 8 g modified oxide B and 10 g LiTFSI were added to 100 ml N,N-dimethylformamide and stirred to obtain a mixed solution B. The mixed solution B was coated on the modified positive electrode side solid electrolyte prepared in step (1) with a 100 μm scraper and dried to obtain a modified solid electrolyte.

[0048] Example 3 (1) ZIF-90 with a particle size of 300 nm was heated at 700 °C for 1.5 hours in an oxygen environment to obtain modified oxide A. 12 g PVDF-HFP, 5 g modified oxide A and 6 g LiAsF 6 Add into 100 ml of N,N-dimethylformamide and stir to obtain a mixed solution A, apply the mixed solution A on a glass plate with a scraper with a thickness of 200 μm, and fully dry to obtain a modified positive electrode side solid electrolyte; (2) Li-UIO-MOF with a particle size of 150 nm was heated at 600 °C for 1 hour in an oxygen environment to obtain modified oxide B. 12 g PVDF-HFP, 5 g modified oxide B and 6 g LiClO 4 Add into 100 ml of N,N-dimethylformamide and stir thoroughly to obtain a mixed solution B. Apply the mixed solution B onto the modified positive electrode side solid electrolyte prepared in step (1) with a 100 μm scraper and dry thoroughly to obtain a modified solid electrolyte.

[0049] Example 4 (1) ZIF-67 with a particle size D50 of 300 nm was taken and kept at 600°C for 2 hours in an oxygen environment to obtain a modified oxide A. 10 g PVDF-HFP, 7 g modified oxide A and 8 g LiFSI were added to 100 ml N,N-dimethylformamide and stirred to obtain a mixed solution A. The mixed solution A was coated on a glass plate with a scraper with a thickness of 200 μm and dried to obtain a modified positive electrode side solid electrolyte. (2) Li-BTC-MOF with a particle size of 150 nm was heated at 500 °C in an oxygen environment for 1.5 hours to obtain modified oxide B. 10 g PVDF-HFP, 7 g modified oxide B and 8 g LiPF 6 Add into 100 ml of N,N-dimethylformamide and stir thoroughly to obtain a mixed solution B. Apply the mixed solution B onto the modified positive electrode side solid electrolyte prepared in step (1) with a 100 μm scraper and dry thoroughly to obtain a modified solid electrolyte.

[0050] Example 5 (1) ZIF-67 with a particle size of 300 nm was heated at 800 °C for 1.5 hours in an oxygen environment to obtain modified oxide A. 10 g PVDF-HFP, 7 g modified oxide A and 8 g LiPF 6 Add into 100 ml of N,N-dimethylformamide and stir to obtain a mixed solution A, apply the mixed solution A on a glass plate with a scraper with a thickness of 200 μm, and fully dry to obtain a modified positive electrode side solid electrolyte; (2) Li-BTC-MOF with a particle size D50 of 150 nm was heated at 700°C for 1 hour in an oxygen environment to obtain a modified oxide B. 10 g PVDF-HFP, 7 g modified oxide B and 8 g LiFSI were added to 100 ml N,N-dimethylformamide and stirred to obtain a mixed solution B. The mixed solution B was applied to the modified positive electrode side solid electrolyte prepared in step (1) with a 100 μm scraper and dried to obtain a modified solid electrolyte.

[0051] The solid electrolyte sheets prepared in the above-mentioned embodiments and comparative examples were cut into discs with a diameter of 19 mm to serve as the electrolyte of the battery. The lithium foil was cut into discs with a diameter of 16 mm to serve as the negative electrode. The commercial six-series (622) ternary positive electrode material was mixed with the conductive agent acetylene black (AB) and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was used as the solvent. The mixture was placed in a small beaker and stirred at a speed of 800 r / min for 2 hours to obtain a slurry. The slurry was coated on the current collector aluminum foil using an automatic coating machine, placed flat on tempered glass and transferred to a vacuum drying oven at 85°C for 4 hours, and the circular pole piece with a diameter of 12 mm was punched and dried at 105°C in a vacuum drying oven for 4 hours. It was placed in a glove box filled with argon atmosphere with a water content and oxygen content of less than 0.01 ppm for 4 hours to reduce the moisture adsorbed by the pole piece during the transfer process, and served as the positive electrode of the battery. The positive electrode sheet was placed in contact with the positive electrode side of the electrolyte and the negative electrode sheet was placed in contact with the other side, and then assembled into a CR2032 button cell in a glove box.

[0052] After the battery was assembled and aged for 12 hours, the charge and discharge test was performed. The sample was cycled 100 times at a voltage of 2.8~4.3V and a current density of 0.1C. The data of the first discharge capacity and the discharge capacity after 100 cycles are shown in Table 1. The cycle performance diagram is shown in Figure 2 shown.

[0053] At the same time, a stainless steel-stainless steel battery was assembled to test the EIS curve at a frequency of 100,000~1 Hz at room temperature, and the ionic conductivity at room temperature was obtained by fitting calculation. The obtained data are shown in Table 1.

[0054] Table 1 Combining Table 1 and Figure 2 It can be seen that compared with Comparative Example 1, which directly uses MOF materials as electrolyte components, Examples 1 to 3 use porous nano-oxides obtained after calcining an equal amount of MOF materials as electrolyte components, which can significantly improve lithium ion conductivity and first discharge specific capacity, and the improvement of cycle performance is more obvious. After analysis, this may be because, on the one hand, the special structure of the porous nano-oxide obtained after calcination can improve the ion transmission effect, and on the other hand, the porous nano-oxide obtained after calcining the MOF material makes the solid electrolyte structure more stable, that is, it can construct a more stable ion transmission channel.

[0055] Compared with Comparative Example 2, Examples 1 to 3 use the same amount of oxide as the electrolyte component, which can significantly improve the lithium ion conductivity, first discharge specific capacity and cycle performance. After analysis, this may be due to the special structure and chemical composition of the oxide obtained by calcining the MOF material. For example, the MOF material is a material with uniform particle size, small size and complete lattice. The particle size, size and lattice of the metal oxide obtained by calcining can effectively inherit the MOF material to form nano-scale porous particles, which is helpful for the dispersion of the particle oxide in the solid electrolyte, reducing the agglomeration and crystallization of the polymer, and increasing the lithium ion transmission channel.

[0056] Compared with the modified electrolytes prepared in Comparative Examples 3 and 4, the first discharge specific capacity, cycle performance and lithium ion conductivity of the modified electrolyte assembled battery prepared in Example 1 are significantly improved, and the battery assembled in Comparative Example 4 fails in the cycle process, which indicates that the types of oxides in the electrolytes on the positive and negative electrode sides have a significant impact on the performance of the solid electrolyte. After analysis, this may be because nickel, cobalt or manganese oxides are selected on the positive electrode side. On the one hand, it can reduce the corrosion of the electrolyte to the ternary positive electrode material, and on the other hand, it can inhibit the decomposition of the transition metal of the positive electrode material, increase the overall structural stability of the battery, and increase the compatibility with the positive electrode interface. The addition of nano lithium oxide obtained by calcining lithium MOF materials on the negative electrode side helps to form a lithium-rich SEI film on the surface of lithium metal. At the same time, the lithium-rich state of the interface helps to uniformly deposit lithium ions and reduce the growth of lithium dendrites.

[0057] Compared with the battery assembled with the solid electrolyte prepared in Example 1, the capacity and ion conductivity of the battery assembled with the solid electrolyte prepared in Example 4 are reduced, and the cycle performance is significantly reduced, which shows that it is particularly important to select suitable lithium salts for the solid electrolyte on the positive electrode side and the solid electrolyte on the negative electrode side. Compared with the battery assembled with the solid electrolyte prepared in Example 1, the capacity and ion conductivity of the battery assembled with the solid electrolyte prepared in Example 5 are reduced, and the cycle performance is significantly reduced. After analysis, this may be because the calcination temperature is too high, which has an adverse effect on the obtained oxide.

[0058] Comparing the performance of the battery assembled with the electrolyte prepared in Example 1 and Example 4, it can be seen that the type of positive and negative lithium salts will affect the performance of the battery. Comparing the performance of the battery assembled with the electrolyte prepared in Example 1 and Example 5, it can be seen that the calcination temperature of the MOF material will also affect the performance of the battery.

[0059] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A modified solid electrolyte, characterized in that: include: A first solid electrolyte layer and a second solid electrolyte layer, the first solid electrolyte layer includes a first polymer, a first oxide and a first lithium salt, and the second solid electrolyte layer includes a second polymer, a second oxide and a second lithium salt; the first oxide is obtained by calcining and decomposing a first MOF material, and the first MOF material is a MOF material of at least one of Ni, Co and Mn; the second oxide is obtained by calcining and decomposing a second MOF material, and the second MOF material is a MOF material of Li.

2. The modified solid electrolyte according to claim 1, characterized in that The first polymer and the second polymer are at least one of PVDF, PVDF-HFP, and PVDF-CTFE; The first lithium salt is at least one of LiBF4, LiPF6, and LiAsF6; The second lithium salt is at least one of LiFSI, LiTFSI, and LiClO4; The mass ratio of the first polymer, the first oxide and the first lithium salt is 7-12:5-10:6-10; The mass ratio of the second polymer, the second oxide and the second lithium salt is 7-12:5-10:6-10.

3. The method for preparing a modified solid electrolyte according to claim 1 or 2, characterized in that: include: S1. calcining the first MOF material in an oxidizing atmosphere to obtain a first oxide; A mixed solution A is prepared by using a first polymer, a first oxide and a first lithium salt as raw materials, and the mixed solution A is coated and dried to obtain a modified positive electrode side solid electrolyte; S2. calcining the second MOF material in an oxidizing atmosphere to obtain a second oxide; using the second polymer, the second oxide and the second lithium salt as raw materials to prepare a mixed solution B, coating the mixed solution B on the surface of the modified positive electrode side solid electrolyte, and drying to obtain a modified solid electrolyte.

4. The method for preparing the modified solid electrolyte according to claim 3, characterized in that: In step S1, the calcination temperature is 500-700°C, and the calcination time is 1.5-4h; In step S2, the calcination temperature is 450-600°C, and the calcination time is 1-2 hours.

5. The method for preparing the modified solid electrolyte according to claim 3, characterized in that: The first MOF material is at least one of ZIF-67 (Co), MOF-74 (Ni), and ZIF-90 (Mn); the size of the first MOF material is 200-500 nm; The second MOF material is at least one of Li-BTC-MOF, Li-ZIF-MOF, and Li-UIO-MOF; the size of the second MOF material is 50-300 nm.

6. The method for preparing the modified solid electrolyte according to claim 3, characterized in that: In the mixed solution A, the concentration of the polymer is 70-120 g / L; In the mixed solution A, the concentration of the first oxide is 50-100 g / L; In the mixed solution A, the concentration of the lithium salt is 60-100 g / L; The solvent of the mixed solution A is at least one of N,N-dimethylformamide, N-methylpyrrolidone and tetrahydrofuran.

7. The method for preparing a modified solid electrolyte according to claim 3, characterized in that: In the mixed solution B, the concentration of the polymer is 70-120 g / L; In the mixed solution B, the concentration of the second oxide is 50-100 g / L; In the mixed solution B, the concentration of the lithium salt is 60-100 g / L; The solvent of the mixed solution B is at least one of N,N-dimethylformamide, N-methylpyrrolidone and tetrahydrofuran.

8. The method for preparing the modified solid electrolyte according to claim 3, characterized in that: In step S1, the coating is performed using a scraper with a thickness of 200-300 μm; In step S2, the coating is performed using a scraper with a thickness of 100-200 μm.

9. A solid-state battery, characterized in that: The invention comprises a positive electrode, a negative electrode and a modified solid electrolyte, wherein the modified solid electrolyte is the modified solid electrolyte according to claim 1 or 2 or the modified solid electrolyte prepared by the preparation method according to any one of claims 3 to 8.

10. The solid-state battery according to claim 9, characterized in that: The positive electrode active material is an oxide of Li and M, where M is one or more of Ni, Co and Mn.

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