A composite solid electrolyte, its preparation method and application

Abstract

The present invention provides a composite solid electrolyte, a preparation method and an application thereof. The composite solid electrolyte comprises a polymer, an additive and a lithium salt. The addition amount of the additive is 5-25% of the mass of the polymer. The additive is a two-dimensional bimetallic-organic framework material having -NH2 and / or -NO2 groups. The present invention effectively inhibits the migration of anions by using the additive, improves the Li + ion transference number. At the same time, based on the diverse pore structures and surface functions of the additive, the ion transfer path of the solid electrolyte can be shortened, the number of active sites can be increased, and the ionic conductivity of the solid electrolyte and the cycle performance of the battery can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solid electrolytes, and more particularly, to a composite solid electrolyte, a preparation method thereof, and an application thereof. Background Art

[0002] Among numerous energy storage technologies, lithium-ion batteries play an important role due to advantages such as high energy density and long lifespan. Metallic lithium has an extremely high theoretical capacity (3860 mAh / g) and the lowest electrode potential ( - 3.04 V relative to the standard hydrogen electrode), making it the best choice for the negative electrode material of the next-generation lithium-ion batteries. However, metallic lithium faces serious dendrite problems in traditional liquid electrolytes.

[0003] All-solid-state batteries can make full use of metallic lithium, and their self-assembly advantages can bring higher energy density. Generally, solid electrolytes can be divided into two categories: inorganic electrolytes and polymer electrolytes. Although inorganic electrolytes have relatively high ionic conductivity, their serious interface problems will bring large impedance, thus greatly limiting their practical applications. Polymer electrolytes have advantages such as easy film formation and low cost, and have good application potential in future all-solid-state batteries. However, polymer electrolytes have a great disadvantage: low ionic conductivity. The main reasons are as follows: ① The chain segment movement ability of polymers is limited. For example, the most common PEO polymer electrolyte is prone to crystallization, is not suitable for migrating lithium ions, and has an unstable interface; ② The movement of lithium ions depends on the coordination of polar atoms of the polymer, with poor freedom and poor mobility itself. Existing technologies generally improve ionic conductivity through copolymerization and crosslinking. However, most of these methods are complex and cumbersome, restricting their applications in actual production.

[0004] Modifying PEO polymer electrolytes by adding MOFs has been a modification direction studied more in recent years. For example, Patent CN201910367824.5 discloses a composite solid electrolyte material, a preparation method thereof, and an application thereof. By introducing a metal-organic framework material with a special topological structure and compounding it with an ion-conducting polymer matrix material and an alkali metal or alkaline earth metal salt, this electrolyte can not only be used at high temperatures but also has good ion conduction performance at lower temperatures. However, this solid electrolyte material still has the problem of low ionic conductivity at a lower temperature (25 °C), restricting its application. Summary of the Invention

[0005] Based on the above problems existing in the prior art, the inventors have found through research that in the ion migration of solid electrolytes, the migration of anions dominates, which will increase the polarization of the battery. Based on this, the present invention provides a composite solid electrolyte, which includes a high molecular polymer, an additive, and a lithium salt. The additive is used to effectively inhibit the migration of anions and improve Li +The ion transference number. Meanwhile, based on the diverse pore structures and surface functions of the additives, the ion transfer path of the solid electrolyte can be shortened, the number of active sites can be increased, and the ionic conductivity of the solid electrolyte and the cycling performance of the battery can be effectively improved.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A composite solid electrolyte, comprising a polymer, an additive, and a lithium salt, wherein the addition amount of the additive is 5-25% of the mass of the polymer; the additive is a two-dimensional bimetallic-organic framework material having -NH2 and / or -NO2 groups.

[0008] In some embodiments, the molar ratio of Li in the lithium salt + and the polar groups in the polymer is 1:10-30.

[0009] In some embodiments, the central metal ions of the bimetallic-organic framework material are Fe(III) and Co(III).

[0010] In some embodiments, the bimetallic organic framework is CoFe-BDC-NH2 and / or CoFe-BDC-NO2.

[0011] In some embodiments, the preparation of CoFe-BDC-NH2 or CoFe-BDC-NO2 comprises the following steps:

[0012] Dissolve a soluble iron salt, a soluble cobalt salt, and an organic ligand in a first organic solvent, then add deionized water, an alcohol solvent, and triethylamine, and react for more than 24 h to obtain the CoFe-BDC-NH2 or CoFe-BDC-NO2;

[0013] Wherein, the organic ligand is amino terephthalic acid or nitro terephthalic acid; the molar ratio of the soluble iron salt, the soluble cobalt salt, and the organic ligand is 1-2:3:1.

[0014] In some embodiments, the first organic solvent is dimethylformamide.

[0015] In some embodiments, the alcohol solvent is at least one of ethanol, methanol, propanol, isopropanol, butanol, and isobutanol.

[0016] In some embodiments, the preparation method of CoFe-BDC-NH2 or CoFe-BDC-NO2 further comprises the following steps:

[0017] After the reaction is complete, perform solid-liquid separation, wash the solid with propanol and ethanol, and then dry it under vacuum to obtain the final product.

[0018] In some embodiments, the molecular weight of the polymer is 10 5 ~5×10 6 g / mol.

[0019] In some embodiments, the polymer is at least one of polyethylene oxide, polymethyl methacrylate, polyacrylonitrile, polyvinylidene fluoride, and polysiloxane.

[0020] In some embodiments, the lithium salt is at least one of lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethylsulfonate, and lithium difluoroborate oxalate.

[0021] The present invention also provides a method for preparing the composite solid electrolyte according to any one of the above embodiments, the method comprising the following steps:

[0022] Adding the polymer, the additive, and the lithium salt to a second organic solvent, mixing evenly to obtain a mixed solution; then pouring the obtained mixed solution onto a template, standing still to volatilize the second organic solvent, and drying to obtain the composite solid electrolyte.

[0023] In some embodiments, the preparation method comprises the following steps:

[0024] Adding the polymer, the additive, and the lithium salt to a second organic solvent, stirring evenly to obtain a mixed solution; then pouring the obtained mixed solution onto a template, standing still for 1 - 48 h to volatilize the second organic solvent, and then drying at 50 - 120 °C to obtain the composite solid electrolyte.

[0025] In some embodiments, the second organic solvent is anhydrous acetonitrile.

[0026] The present invention also provides the application of the composite solid electrolyte according to any one of the above embodiments in the preparation of lithium - ion batteries.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The present invention applies a two - dimensional bimetallic - organic framework (MOFs) with - NH2 or - NO2 groups as an additive to the solid electrolyte. On the one hand, the metal sites on the MOFs can interact with the anions of the lithium salt in the electrolyte, effectively inhibiting the movement of the anions, providing a larger moving space for Li + , which is beneficial to the migration of Li + , and improving the Li + ion mobility; at the same time, the adsorption of the - NH2 or - NO2 groups on the MOFs on the anions further inhibits the movement of the anions, thereby further improving Li+ ion transference number. On the other hand, based on the diverse pore structures and surface functions of bimetallic MOFs, it can provide a fast ion transport channel for Li + ions, shortening the ion transfer path. The additional -NH2 or -NO2 groups promote the formation of more micropores and mesopores in MOFs during the formation process of MOFs, increasing the specific surface area of MOFs, which is beneficial to increasing the contact with the polymer and enhancing the interaction with the polymer, further improving the ionic conductivity of the solid electrolyte; after testing, for the composite solid electrolyte provided by the present invention, the Li + ion transference number can reach 0.64.

[0029] In addition, the addition of two-dimensional sheet-like MOFs can effectively disrupt the crystallization of the polymer and further promote the migration of lithium ions.

[0030] In addition, based on the increase in the lithium ion transference number, the stability of interfacial ion transport can be enhanced, thereby improving the energy density of the battery. Applying the solid electrolyte to the battery enables the battery to have a high electrochemical window (above 4.5 V), and at the same time has a high specific capacity and excellent cycling performance. Description of the Drawings

[0031] Figure 1 SEM images of the bimetallic-organic framework materials prepared in Example 1, where Figure a is the SEM image of CoFe-BDC; Figure b is the SEM image of CoFe-BDC-NO2; SEM image of CoFe-BDC-NH2;

[0032] Figure 2 TEM image and elemental distribution scanning image of CoFe-BDC prepared in Example 1;

[0033] Figure 3 TEM image and elemental distribution scanning image of CoFe-BDC-NO2 prepared in Example 1;

[0034] Figure 4 TEM image and elemental distribution scanning image of CoFe-BDC-NH2 prepared in Example 1

[0035] Figure 5 Among them, Figure a is the XRD pattern of the bimetallic-organic framework materials prepared in Example 1; Figure b is the Raman spectrum of the bimetallic-organic framework materials; Figure c is the infrared spectrum of the bimetallic-organic framework materials;

[0036] Figure 6 Cycling performance test chart of the LiFePO4 / Li battery prepared in Example 4 at a current density of 0.3C;

[0037] Figure 7Capacity test chart of the LiFePO4 / Li battery prepared in Example 4 after 200 cycles at different current densities;

[0038] Figure 8 Cycling performance test chart of the NCM523 / Li battery prepared in Example 4 at a current density of 0.2C. Detailed implementation manners

[0039] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific implementations disclosed below.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0041] Example 1

[0042] Preparation of the bimetallic-organic framework material CoFe-BDC:

[0043] 1.5 mmol of cobalt nitrate hexahydrate, 0.75 mmol of iron chloride hexahydrate and 1.5 mmol of 1,4-benzenedicarboxylic acid were added to 50 ml of dimethylformamide, and stirred and mixed evenly; then 10 ml of deionized water, 10 ml of ethanol and 10 ml of triethylamine were added, and stirred for reaction for 12 h; after the reaction was completed, the mixed solution was centrifuged for solid-liquid separation, and the solid was washed successively with acetone and ethanol, and then placed in a vacuum drying oven for drying to obtain CoFe-BDC.

[0044] Preparation of the bimetallic-organic framework material CoFe-BDC-NH2: The preparation method is the same as that of CoFe-BDC, except that the organic ligand is 2-aminoterephthalic acid.

[0045] Preparation of the bimetallic organic framework material CoFe-BDC-NO2: The preparation method is the same as that of CoFe-BDC, except that the organic ligand is 2-nitroterephthalic acid.

[0046] The bimetallic-organic framework prepared in this example was detected by SEM, and the detection results are as Figure 1 shown.

[0047] The bimetallic-organic framework prepared in this example was detected by TEM and atomic force microscope (AFM), and the detection results are as Figures 2 - 4as shown;

[0048] The bimetallic-organic framework prepared in this example was subjected to XRD, Raman spectroscopy, and infrared detection, and the detection results are as Figure 5 shown.

[0049] As Figure 1 shown, the bimetallic-organic framework prepared by the method of the present invention has a two-dimensional sheet structure.

[0050] while Figures 2 - 5 fully illustrates the structure and elemental composition of the obtained bimetallic-organic framework.

[0051] Example 2

[0052] I. Prepare CoFe-BDC-NO2 according to the method of Example 1;

[0053] II. Preparation of the solid electrolyte, including the following steps:

[0054] PEO with a molecular weight of 3×10 6 g / mol and LiClO4 were added to anhydrous acetonitrile in a molar ratio of EO to Li + of 20:1, and then CoFe-BDC-NO2 was added. The addition amount of CoFe-BDC-NO2 was 10 wt% of the mass of PEO. The mixture was stirred evenly at room temperature to obtain a mixed slurry; the mixed slurry was poured onto a polytetrafluoroethylene mold, allowed to stand, and volatilized at room temperature for more than 24 h, and then placed in a vacuum drying oven and dried under vacuum at 80 °C to obtain a composite solid electrolyte with a thickness of 100 μm, named PEO / MOFs-NO2.

[0055] The ionic conductivity of the composite solid electrolyte prepared in this example was tested at room temperature (25 °C) by a conventional method in the art. The test results were as follows: the ionic conductivity was 5.0×10 -5 S / cm; the Li + ion transference number was 0.5.

[0056] Example 3

[0057] I. Prepare CoFe-BDC-NH2 according to the method of Example 1;

[0058] II. Preparation of the solid electrolyte, including the following steps:

[0059] PEO with a molecular weight of 3×10 6 g / mol and LiClO4 were added to anhydrous acetonitrile in a molar ratio of EO to Li +It was added to anhydrous acetonitrile in a ratio of 20:1 by molar ratio, and then CoFe-BDC-NH2 was added. The addition amount of CoFe-BDC-NH2 was 10 wt% of the mass of PEO. It was stirred evenly at room temperature to obtain a mixed slurry; the mixed slurry was poured onto a polytetrafluoroethylene mold, left standing, volatilized at room temperature for more than 24 h, and then placed in a vacuum drying oven and vacuum dried at 80 °C to obtain a composite solid electrolyte with a thickness of 100 μm, named PEO / MOFs-NH2.

[0060] The ionic conductivity of the solid electrolyte prepared in this example at room temperature was 6.5×10 -5 S / cm; Li + The ion transference number was 0.64.

[0061] Comparative Example 1

[0062] I. Prepare CoFe-BDC according to the method of Example 1;

[0063] II. Preparation of the composite solid electrolyte, including the following steps:

[0064] PEO with a molecular weight of 3×10 6 g / mol, LiClO4 were added to anhydrous acetonitrile in a ratio of 20:1 by the molar ratio of EO and Li + Then CoFe-BDC was added. The addition amount of CoFe-BDC was 10 wt% of the mass of PEO. It was stirred evenly at room temperature to obtain a mixed slurry; the mixed slurry was poured onto a polytetrafluoroethylene mold, left standing, volatilized at room temperature for more than 24 h, and then placed in a vacuum drying oven and vacuum dried at 80 °C to obtain a composite solid electrolyte with a thickness of 100 μm, named PEO / MOFs.

[0065] The ionic conductivity of the solid electrolyte prepared in this comparative example was 3.5×10 -5 S / cm; Li + The ion transference number was 0.36.

[0066] Comparative Example 2

[0067] Preparation of the solid electrolyte:

[0068] PEO with a molecular weight of 3×10 6 g / mol, LiClO4 were added to anhydrous acetonitrile in a ratio of 20:1 by the molar ratio of EO and Li + It was stirred evenly at room temperature to obtain a mixed slurry; the mixed slurry was poured onto a polytetrafluoroethylene mold, left standing, volatilized at room temperature for more than 24 h, and then placed in a vacuum drying oven and vacuum dried at 80 °C to obtain a composite solid electrolyte with a thickness of 100 μm, named PEO / LiClO4.

[0069] The ionic conductivity of the solid electrolyte obtained in this comparative example was 7.1×10 -6 S / cm; the Li + ion transference number was 0.18.

[0070] Example 4

[0071] The solid electrolytes obtained in Example 3 and Comparative Example 2 were subjected to electrochemical performance tests as follows:

[0072] (1) According to the conventional method in the art, the solid electrolytes were respectively used to prepare full cells, where the positive electrode active material was commercially available LiFePO4 and the negative electrode was a lithium sheet; after the battery assembly was completed, charge-discharge cycling was carried out, and the test results are as Figure 6 shown. As Figure 6 shown, after testing, at a current density of 0.3C (1C = 170 mA / h, 60 °C), after 200 cycles, the battery prepared with the PEO / MOFs-NH2 solid electrolyte had a capacity retention of 148 mA / g; at a current density of 1C, after 200 cycles, the capacity retention was 132.29 mA / g; while the battery prepared with the PEO / LiClO4 solid electrolyte had a capacity of only 57.8 mA / g; at a current density of 1C, the capacity was 49.6 mA / g. In addition, as Figure 6 shown, after 99 cycles, the Coulomb efficiency of the battery prepared with the PEO / LiClO4 solid electrolyte was almost in a disordered state due to battery failure.

[0073] In addition, cyclic tests were also carried out at different current densities, and the capacities after 200 cycles are as Figure 7 shown.

[0074] (2) According to the conventional method in the art, the solid electrolytes were respectively used to prepare full cells, where the positive electrode active material was commercially available NCM523 (LiNi 0.5 Co 0.2 Mn 0.3 O2), and the negative electrode was a lithium sheet; after the battery assembly was completed, charge-discharge cycling was carried out at a current density of 0.2C (1C = 170 mA / h, 60 °C), and the test results are as Figure 8 shown. As Figure 8 shown, after testing, at a current density of 0.2C, after 100 cycles, the battery prepared with the PEO / MOFs-NH2 solid electrolyte had a capacity retention of 138.1 mA / g; while the battery prepared with the PEO / LiClO4 solid electrolyte had a capacity of only 55.6 mA / g.

[0075] It can be seen that the solid electrolyte prepared by the present invention has strong adaptability in different battery systems and exhibits excellent cycling performance.

[0076] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as falling within the scope described in this specification.

[0077] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A composite solid electrolyte, characterized in that, It includes a polymer, an additive, and a lithium salt. The addition amount of the additive is 5-25% of the mass of the polymer; the additive is a two-dimensional bimetallic-organic framework material having -NH2 and / or -NO2 groups; The bimetallic organic framework is CoFe-BDC-NH2 and / or CoFe-BDC-NO2; The preparation of the CoFe-BDC-NH2 or CoFe-BDC-NO2 includes the following steps: Dissolve a soluble iron salt, a soluble cobalt salt, and an organic ligand in a first organic solvent, then add deionized water, an alcohol solvent, and triethylamine, and react for more than 24 h to obtain the CoFe-BDC-NH2 or CoFe-BDC-NO2; Among them, the organic ligand is amino terephthalic acid or nitro terephthalic acid; the molar ratio of the soluble iron salt, the soluble cobalt salt, and the organic ligand is 1-2:3:

1.

2. The composite solid electrolyte according to claim 1, characterized in that, The molecular weight of the polymer is 10 5 ~5×10 6 g / mol.

3. The composite solid electrolyte according to claim 1, wherein The polymer is at least one of polyethylene oxide, polymethyl methacrylate, polyacrylonitrile, polyvinylidene fluoride, and polysiloxane.

4. The composite solid electrolyte according to claim 1, characterized in that, The lithium salt is at least one of lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethylsulfonate, and lithium difluoroborate oxalate.

5. The preparation method of the composite solid electrolyte according to any one of claims 1-4, characterized in that, It includes the following steps: Add the polymer, the additive, and the lithium salt into a second organic solvent, mix them evenly to obtain a mixed solution; then pour the obtained mixed solution onto a template, let it stand to volatilize the second organic solvent, and dry it to obtain the composite solid electrolyte.

6. The preparation method of the composite solid electrolyte according to claim 5, characterized in that, It includes the following steps: Add the polymer, the additive, and the lithium salt into a second organic solvent, stir evenly to obtain a mixed solution; then pour the obtained mixed solution onto a template, let it stand for 1-48 h to volatilize the second organic solvent, and then dry it at 50-120 °C to obtain the composite solid electrolyte.

7. Application of the composite solid electrolyte according to any one of claims 1-4 in the preparation of a lithium-ion battery.

Images