High-entropy hydroxide composite solid electrolyte and preparation method thereof

Abstract

The invention provides a high-entropy hydroxide composite solid electrolyte and a preparation method thereof, and belongs to the technical field of electrolytes. The preparation method comprises the following steps: dissolving lithium chloride and chlorine salts of a plurality of transition metals in a solution, adjusting the pH value to be alkaline by using alkali liquor, and carrying out closed reaction; cooling, filtering and drying the closed reaction product, then carrying out heat treatment, and grinding to obtain the high-entropy hydroxide, the preparation method comprises the following steps: dissolving a polymer and poly (bis (2, 2, 2-trifluoroethoxy) azo nitrogen alkene) in a solvent to obtain a polymer solution; and adding the high-entropy hydroxide and lithium salt into the polymer solution, forming a film, and drying to obtain the composite solid electrolyte. The composition of the composite solid electrolyte is stable in air, the ionic conductivity is greatly improved, meanwhile, the composite solid electrolyte has good mechanical strength, growth and puncture of lithium dendrites can be inhibited, and then the safety of a lithium battery is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytes, and particularly relates to a high-entropy hydroxide composite solid electrolyte and a preparation method thereof. Background Art

[0002] Compared with traditional liquid lithium-ion batteries, all-solid-state lithium batteries using solid electrolytes have the advantages of high safety, high energy density, long cycle life, etc., and are expected to solve problems such as low energy density, easy leakage, easy corrosion, and easy combustion of electrolytes in lithium-ion batteries. As the core component of solid-state lithium batteries, solid electrolytes can be divided into inorganic solid electrolytes, polymer solid electrolytes, and organic-inorganic composite solid electrolytes. Inorganic or polymer solid electrolytes cannot meet the actual application requirements of solid-state batteries. Therefore, organically combining inorganic electrolytes and polymer electrolytes to design organic-inorganic composite electrolytes and realizing the functional synergistic effects of each component will be one of the effective ways to develop high-performance solid-state lithium batteries. At present, there are still many problems in composite electrolytes, such as low ionic conductivity, poor electro / thermal stability of electrolytes, and poor interfacial stability with electrodes.

[0003] High-entropy materials are a new type of materials. At present, there are few studies on using high-entropy materials for solid electrolytes. Bérardan et al. first studied the use of high-entropy oxides for solid electrolytes and synthesized rock-salt-structured (Mg,Co,Ni,Cu,Zn)1-xLixO and (Mg,Co,Ni,Cu,Zn)10-2xLixGaxO high-entropy oxides, with an ionic conductivity reaching 1 mS cm -1 at 80 °C, but the electrochemical stability of the electrolyte still needs to be improved (J. Mater. Chem. A, 2016, 4, 9536-9541). Strauss et al. synthesized a series of halogen-rich lithium thiogermanate-type high-entropy sulfide materials and quantitatively analyzed the occupancy of S 2- / Cl - / Br - on the anion sublattice of the materials. The results show that the ionic conductivity of solid electrolytes can be improved by adjusting the complexity of the composition (Angew. Chem. Int. Ed., 2023, 62, e202314155). Patents (CN118899528A, CN117039128A, etc.) prepared solid electrolyte materials such as high-entropy garnet-structured high-entropy oxides and high-entropy polymers. However, the currently prepared high-entropy electrolytes face problems such as poor stability in air, harsh preparation conditions, difficult processing, and low ionic conductivity.

[0004] In view of this, the present application is specifically proposed. Summary of the Invention

[0005] The object of the present invention is to provide a high-entropy hydroxide composite solid electrolyte and a preparation method thereof, aiming to solve the problems of low ionic conductivity and poor stability of existing high-entropy electrolytes.

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

[0007] In the first aspect, the present invention provides a preparation method of a high-entropy hydroxide composite solid electrolyte, including the following steps:

[0008] Dissolve lithium chloride and chlorides of several transition metals in a solution, adjust the pH value to alkaline with an alkali solution, and carry out a closed reaction;

[0009] Cool, filter, and dry the closed reaction product, then carry out heat treatment, and then grind to obtain high-entropy hydroxide;

[0010] Dissolve a polymer and poly(bis(2,2,2-trifluoroethoxy)phosphazene) in a solvent to obtain a polymer solution;

[0011] Add the high-entropy hydroxide and lithium salt to the polymer solution, form a film, and dry to obtain a composite solid electrolyte.

[0012] In the second aspect, the present invention also provides a high-entropy hydroxide composite solid electrolyte prepared by the above preparation method.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) The composite solid electrolyte of the present invention containing high-entropy hydroxide, lithium salt, poly(bis(2,2,2-trifluoroethoxy)phosphazene), and polymer has a stable composition in air, and the preparation method is simple, which can greatly improve the safety and efficiency of the solid electrolyte synthesis process.

[0015] (2) The present invention conducts heat treatment on the closed reaction product, and its morphology changes from granular to flaky, which can reduce the crystallinity of the polymer and at the same time reduce the transmission distance of lithium ions in the high-entropy hydroxide. In addition, after heat treatment, the vacancy defects of the product increase, and the layer spacing also decreases. These are all beneficial to increasing the ionic conductivity of lithium ions in the composite electrolyte.

[0016] (3) The composite solid electrolyte of the present invention is used in a lithium metal all-solid-state battery, and has stable thermal / electrochemical properties. Due to its good interface wettability, the electrolyte interface can greatly reduce the interface impedance and inhibit the side reactions at the solid electrolyte interface, achieving high ionic conductivity. Poly(bis(2,2,2-trifluoroethoxy)phosphazene), polymer and lithium salt generate inorganic LiF, and at the same time the composite solid electrolyte has good mechanical strength, which can inhibit the growth and puncture of lithium dendrites, thereby realizing the safety of lithium batteries. Description of the Drawings

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following accompanying drawings only show some embodiments of the present invention and should not be regarded as limiting the scope of the present invention.

[0018] Figure 1 It is a SEM image of the sealed reaction product Li(FeCoNiCuZn)OH in Example 1 of the present invention before heat treatment after drying;

[0019] Figure 2 It is a SEM image of the sealed reaction product Li(FeCoNiCuZn)OH in Example 1 of the present invention after heat treatment. Detailed Embodiments

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The material ratios not shown in the embodiments or comparative examples of the present invention can be any ratio, and the ratio relationship without indicating the unit is the mass ratio.

[0021] The first aspect of the embodiment of the present invention provides a preparation method of a high-entropy hydroxide composite solid electrolyte, including the following steps:

[0022] Dissolve lithium chloride and chlorides of several transition metals in water or ethylene glycol to form a solution, adjust the pH value to alkaline with an alkali solution, and carry out a sealed reaction;

[0023] Cool, filter, and dry the sealed reaction product, then carry out heat treatment, and then grind to obtain a high-entropy hydroxide;

[0024] Dissolve a polymer and poly(bis(2,2,2-trifluoroethoxy)phosphazene) in a solvent to obtain a polymer solution;

[0025] Add the high-entropy hydroxide and lithium salt to the polymer solution, form a film, and dry to obtain a composite solid electrolyte.

[0026] In some optional embodiments, the several transition metals include at least four of Li, Fe, Co, Ni, Cu, Zn, Cd, Cr, Mo, Mn, V, preferably five.

[0027] In some preferred embodiments, the chlorides of the several transition metals are used in equimolar amounts. Any ratio relationship that deviates from this ratio but does not make a substantial difference should be regarded as falling within the ratio range defined by the present invention.

[0028] In some more preferred embodiments, in terms of molar amount, the amount of lithium chloride used is the same as the total amount of the chlorides of the several transition metals. For example, if chlorides of five transition metals are used, the amount of lithium chloride used is about 5 times the amount of the chlorides of the five transition metals. Any deviation from this ratio but not resulting in a substantial difference shall be regarded as falling within the ratio range defined by the present invention.

[0029] In some preferred embodiments, adjusting the pH value to alkaline means adjusting the pH value to 10.

[0030] In some alternative embodiments, the alkali solution is sodium hydroxide.

[0031] Further, the temperature of the closed reaction is 80 - 180 °C, and the time of the closed reaction is 5 - 15 hours.

[0032] Further, the temperature of the heat treatment is 200 - 500 °C, and the time of the heat treatment is 1 - 3 hours. Generally, it is considered that the high-entropy compound can be formed after the closed reaction product is dried. However, in the present invention, the closed reaction product is heat-treated, and it is found that its morphology changes from granular to flaky, which can reduce the crystallinity of the polymer and at the same time reduce the transport distance of lithium ions in the high-entropy hydroxide. In addition, after the heat treatment, the vacancy defects of the product increase, and the interlayer spacing also decreases. All of these are beneficial to increasing the ionic conductivity of lithium ions in the composite electrolyte.

[0033] In some alternative embodiments, the polymer includes poly(ethylene oxide) (PEO) and / or poly(vinylidene fluoride - hexafluoropropylene) (PVDF - HFP).

[0034] In some alternative embodiments, the lithium salt includes LiTFSI and / or LiFSI.

[0035] Further, the mass ratio of poly(bis(2,2,2 - trifluoroethoxy)phosphazene) to the polymer is 1:1 - 1:3.

[0036] Further, when adding the high-entropy hydroxide and the lithium salt to the polymer solution, taking the sum of the masses of the high-entropy hydroxide, the lithium salt, the polymer, and poly(bis(2,2,2 - trifluoroethoxy)phosphazene) as the total mass, the addition amount of the high-entropy hydroxide is 2% - 30% of the total mass.

[0037] Further, the addition amount of the lithium salt is 8% - 30% of the total mass.

[0038] The second aspect of the embodiments of the present invention provides a high-entropy hydroxide composite solid electrolyte prepared by the preparation method described above.

[0039] Performance testing method:

[0040] In a glove box under an argon atmosphere, a symmetric cell was assembled with the prepared high-entropy hydroxide composite solid electrolyte and a stainless-steel sheet to test the ionic conductivity; lithium iron phosphate was used as the positive electrode, and a lithium sheet was used as the negative electrode. A cell was assembled with the composite solid electrolyte to test the rate performance.

[0041] The following is an illustration with specific examples.

[0042] Example 1

[0043] This example provides a preparation method for a high-entropy hydroxide composite solid electrolyte:

[0044] Chlorides of Li, Fe, Co, Ni, Cu, Zn, etc. with a molar ratio of 5:1:1:1:1:1 were dissolved in water to form a solution. The solution was titrated with sodium hydroxide solution to a pH of 10, and then added to a homogeneous reaction kettle, sealed, heated to 160 °C, and reacted at a constant temperature for 10 hours. After cooling to room temperature, the solid-liquid mixture was filtered and dried to obtain high-entropy hydroxide Li(FeCoNiCuZn)OH. The SEM image of its ground sample is as Figure 1 shown. Subsequently, it was heat-treated at 400 °C for 1 hour. After grinding, the SEM image is as Figure 2 shown. It can be seen that the microscopic morphology of the high-entropy hydroxide changed significantly before and after heat treatment, changing from granular to flaky.

[0045] PVDF-HFP and poly(bis(2,2,2-trifluoroethoxy)phosphazene) with a mass ratio of 2.5:1 were dissolved in DMF to form a polymer solution. Taking the total mass of high-entropy hydroxide, lithium salt, PVDF-HFP, and poly(bis(2,2,2-trifluoroethoxy)phosphazene) as the total mass, 20% of the total mass of lithium salt (LiTFSI) and 5% of the total mass of Li(FeCoNiCuZn)OH were then dissolved in the above polymer solution, and a film was formed on a polytetrafluoroethylene plate and dried to obtain a composite solid electrolyte. After testing, at 25 °C, the ionic conductivity reached 2.1 mS / cm, the capacity reached 160 mAh / g at 0.1 C, 120 mAh / g at 0.5 C, and 93 mAh / g at 1 C.

[0046] Example 2

[0047] This example provides a preparation method for a high-entropy hydroxide composite solid electrolyte:

[0048] Chlorides of Li, Fe, Co, Ni, Mn, Cu, etc. with a molar ratio of 5:1:1:1:1:1 are dissolved in water to form a solution. The solution is titrated with sodium hydroxide solution to a pH of 10, and then added to a homogeneous reaction kettle, sealed, heated to 120 °C, and reacted at a constant temperature for 8 hours. After cooling to room temperature, the solid-liquid mixture is filtered, dried, heat-treated at 200 °C for 3 hours, and ground to obtain high-entropy hydroxide Li(FeCoNiMnCu)OH.

[0049] PVDF-HFP and poly(bis(2,2,2-trifluoroethoxy)phosphazene) with a mass ratio of 2.5:1 are dissolved in DMF to form a polymer solution. Taking the total mass of high-entropy hydroxide, lithium salt, PVDF-HFP, and poly(bis(2,2,2-trifluoroethoxy)phosphazene) as the total mass, then 25% of the total mass of lithium salt (LiTFSI) and 10% of the total mass of Li(FeCoNiMnCu)OH are dissolved in the above polymer solution, and a film is formed on a polytetrafluoroethylene plate and dried to obtain a composite solid electrolyte. After testing, at 25 °C, the ionic conductivity reaches 0.86 mS / cm, the capacity at 0.1 C reaches 153 mAh / g, the capacity at 0.5 C reaches 127 mAh / g, and the capacity at 1 C reaches 101 mAh / g.

[0050] Example 3

[0051] This example provides a preparation method of a high-entropy hydroxide composite solid electrolyte:

[0052] Chlorides of Li, Fe, Co, Ni, V, Cr, etc. with a molar ratio of 5:1:1:1:1:1 are dissolved in ethylene glycol to form a solution. The solution is titrated with sodium hydroxide solution to a pH of 10, and then added to a homogeneous reaction kettle, sealed, heated to 160 °C, and reacted at a constant temperature for 10 hours. After cooling to room temperature, the solid-liquid mixture is filtered, dried, heat-treated at 300 °C for 2 hours, and ground to obtain high-entropy hydroxide Li(FeCoNiVCr)OH.

[0053] PVDF-HFP and poly(bis(2,2,2-trifluoroethoxy)phosphazene) with a mass ratio of 2.5:1 are dissolved in DMF to form a polymer solution. Taking the total mass of high-entropy hydroxide, lithium salt, PVDF-HFP, and poly(bis(2,2,2-trifluoroethoxy)phosphazene) as the total mass, then 30% of the total mass of lithium salt (LiTFSI) and 15% of the total mass of Li(FeCoNiVCr)OH are dissolved in the above polymer solution, and a film is formed on a polytetrafluoroethylene plate and dried to obtain a composite solid electrolyte. After testing, at 25 °C, the ionic conductivity reaches 0.72 mS / cm, the capacity at 0.1 C reaches 148 mAh / g, the capacity at 0.5 C reaches 125 mAh / g, and the capacity at 1 C reaches 99 mAh / g.

[0054] Example 4

[0055] This example provides a method for preparing a high-entropy hydroxide composite solid electrolyte:

[0056] Chlorides of Li, Fe, Co, Ni, Cr, Mn, etc. with a molar ratio of 5:1:1:1:1:1 are dissolved in water to form a solution. The solution is titrated to a pH value of 10 using a sodium hydroxide solution, and then added to a homogeneous reaction kettle, sealed, heated to 180 °C, and kept at a constant temperature for 5 hours. After cooling to room temperature, the solid-liquid mixture is filtered, dried, heat-treated at 200 °C for 3 hours, and ground to obtain high-entropy hydroxide Li(FeCoNiCrMn)OH.

[0057] PEO and poly(bis(2,2,2-trifluoroethoxy)phosphazene) with a mass ratio of 2.5:1 are dissolved in DMF to form a polymer solution. Taking the total mass of the high-entropy hydroxide, lithium salt, PEO, and poly(bis(2,2,2-trifluoroethoxy)phosphazene) as the total mass, then 10% of the total mass of lithium salt (LiTFSI) and 30% of the total mass of Li(FeCoNiCrMn)OH are dissolved in the above polymer solution, and a film is formed on a polytetrafluoroethylene plate and dried to obtain a composite solid electrolyte. After testing, at 60 °C, the ionic conductivity reaches 0.32 mS / cm, the capacity reaches 150 mAh / g at 0.1C, the capacity reaches 125 mAh / g at 0.5C, and the capacity reaches 91 mAh / g at 1C.

[0058] Example 5

[0059] This example provides a method for preparing a high-entropy hydroxide composite solid electrolyte:

[0060] Chlorides of Li, Fe, Co, Ni, Cu, Cd, etc. with a molar ratio of 5:1:1:1:1:1 are dissolved in water to form a solution. The solution is titrated to a pH value of 10 using a sodium hydroxide solution, and then added to a homogeneous reaction kettle, sealed, heated to 150 °C, and kept at a constant temperature for 8 hours. After cooling to room temperature, the solid-liquid mixture is filtered, dried, heat-treated at 200 °C for 3 hours, and ground to obtain high-entropy hydroxide Li(FeCoNiCuCd)OH.

[0061] Dissolve PEO and poly(bis(2,2,2-trifluoroethoxy)phosphazene) with a mass ratio of 2.5:1 in DMF to form a polymer solution. Take the sum of the masses of the high-entropy hydroxide, lithium salt, PEO, and poly(bis(2,2,2-trifluoroethoxy)phosphazene) as the total mass. Subsequently, dissolve 20% of the total mass of the lithium salt (LiFSI) and 5% of the total mass of Li(FeCoNiCuCd)OH in the above polymer solution, and form a film on a polytetrafluoroethylene plate and dry it to obtain a composite solid electrolyte. After testing, at 60 °C, the ionic conductivity reaches 0.25 mS / cm, the capacity at 0.1 C reaches 140 mAh / g, the capacity at 0.5 C reaches 115 mAh / g, and the capacity at 1 C reaches 92 mAh / g.

[0062] Example 6

[0063] This example provides a preparation method for a high-entropy hydroxide composite solid electrolyte:

[0064] Dissolve chlorides of Li, Fe, Co, Ni, Cu, Zn, etc. with a molar ratio of 5:1:1:1:1:1 in water to form a solution. Use sodium hydroxide solution to titrate this solution to a pH of 10, then add it to a homogeneous reaction kettle, seal it, heat it to 160 °C, and keep it at a constant temperature for 12 hours. After cooling to room temperature, filter, dry the solid-liquid mixture, heat-treat it at 500 °C for 1 hour, and grind it to obtain the high-entropy hydroxide Li(FeCoNiCuZn)OH.

[0065] Dissolve PEO and poly(bis(2,2,2-trifluoroethoxy)phosphazene) with a mass ratio of 2.5:1 in DMF to form a polymer solution. Take the sum of the masses of the high-entropy hydroxide, lithium salt, PEO, and poly(bis(2,2,2-trifluoroethoxy)phosphazene) as the total mass. Subsequently, dissolve 30% of the total mass of the lithium salt (LiTFSI) and 10% of the total mass of Li(FeCoNiCuCd)OH in the above polymer solution, and form a film on a polytetrafluoroethylene plate and dry it to obtain a composite solid electrolyte. After testing, at 60 °C, the ionic conductivity reaches 0.61 mS / cm, the capacity at 0.1 C reaches 147 mAh / g, the capacity at 0.5 C reaches 121 mAh / g, and the capacity at 1 C reaches 96 mAh / g.

[0066] Comparative Example 1

[0067] The difference from Example 1 is that there is no such heat treatment process. After testing, at 25 °C, the ionic conductivity reaches 0.05 mS / cm, the capacity at 0.1 C reaches 157 mAh / g, the capacity at 0.5 C reaches 108 mAh / g, and the capacity at 1 C reaches 75 mAh / g.

[0068] From the comparison between Example 1 and Comparative Example 1, it can be seen that in Comparative Example 1, without heat treatment, the ionic conductivity of the composite solid electrolyte decreased by two orders of magnitude, and the rate performance also decreased significantly.

[0069] Comparative Example 2

[0070] The difference from Example 1 is that the temperature of the heat treatment is 170 °C. After testing, at 25 °C, the ionic conductivity reaches 0.09 mS / cm, the capacity at 0.1C reaches 160 mAh / g, the capacity at 0.5C reaches 115 mAh / g, and the capacity at 1C reaches 78 mAh / g.

[0071] From the comparison between Example 1 and Comparative Example 2, it can be seen that in Comparative Example 2, due to the too low heat treatment temperature, the ionic conductivity of the composite solid electrolyte still decreased by two orders of magnitude, and the rate performance decreased slightly.

[0072] The above are only the preferred embodiments of the present invention and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for preparing a high entropy hydroxide composite solid electrolyte, characterized in that: The steps include: Dissolve lithium chloride and several transition metal chloride salts in a solution, adjust the pH to alkaline with alkali solution, and seal the reaction; The closed reaction product is cooled, filtered, dried, then heat treated, and then ground to obtain a high entropy hydroxide; dissolving the polymer and poly(bis(2,2,2-trifluoroethoxy)phosphazene) in a solvent to obtain a polymer solution; The high entropy hydroxide and lithium salt are added to the polymer solution to form a film, which is then dried to obtain a composite solid electrolyte.

2. The preparation method according to claim 1, characterized in that: The several transition metals include at least four of Li, Fe, Co, Ni, Cu, Zn, Cd, Cr, Mo, Mn, and V; And / or, the chloride salts of the several transition metals are used in equimolar amounts.

3. The preparation method according to claim 1 or 2, characterized in that: In terms of moles, the amount of lithium chloride used is the same as the total amount of chloride salts of the several transition metals.

4. The preparation method according to claim 1, characterized in that: The step of adjusting the pH value to alkalinity is adjusting the pH value to 10; And / or, the alkali solution is sodium hydroxide.

5. The preparation method according to claim 1, characterized in that: The temperature of the closed reaction is 80-180° C., and the closed reaction time is 5-15 hours.

6. The preparation method according to claim 1, characterized in that: The temperature of the heat treatment is 200-500° C., and the time of the heat treatment is 1-3 hours.

7. The preparation method according to claim 1, characterized in that: The polymer includes polyethylene oxide and / or polyvinylidene fluoride-hexafluoropropylene; And / or, the lithium salt includes LiTFSI and / or LiFSI.

8. The preparation method according to claim 1 or 7, characterized in that: The mass ratio of the poly(bis(2,2,2-trifluoroethoxy)phosphazene) to the polymer is 1:1-1:

3.

9. The preparation method according to claim 1, characterized in that: When the high entropy hydroxide and the lithium salt are added to the polymer solution, the total mass is the sum of the masses of the high entropy hydroxide, the lithium salt, the polymer, and the poly(bis(2,2,2-trifluoroethoxy)phosphazene), and the amount of the high entropy hydroxide added is 2%-30% of the total mass; And / or, the amount of lithium salt added is 8%-30% of the total mass.

10. A high entropy hydroxide composite solid electrolyte, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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