A PDOL composite electrolyte, its preparation method and application

Abstract

The present invention belongs to the technical field of solid-state batteries, and specifically discloses a PDOL composite electrolyte, a preparation method thereof, and an application thereof. The PDOL composite electrolyte provided by the present invention comprises a sodium salt, 1,3-dioxolane, a fluorinated solvent, a nitrile plasticizer, and a zirconia-based inorganic filler. Among them, the sodium salt can not only provide free sodium ions, but also serve as an initiator for 1,3-dioxolane to promote the formation of highly stable PDOL from 1,3-dioxolane; the fluorinated solvent can form a stable interfacial film on the surface of the negative electrode, and the nitrile plasticizer can further promote the dissolution of 1,3-dioxolane and improve the conversion rate of 1,3-dioxolane monomers; the zirconia-based inorganic filler further improves the degree of polymerization and stability of PDOL; the battery containing the PDOL composite electrolyte provided by the present invention has excellent first-cycle Coulombic efficiency, capacity retention rate, and discharge specific capacity under high-voltage conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state batteries, and particularly relates to a PDOL composite electrolyte and a preparation method and application thereof. Background Art

[0002] Due to the abundant and widespread distribution of sodium resources, sodium-ion batteries are considered to be attractive energy storage devices for large-scale applications in the next generation. However, the development of sodium metal batteries also faces major challenges. There are a large number of carbonate-based organic electrolytes in traditional sodium-ion batteries. Although liquid electrolytes have high conductivity and excellent wettability on the electrode surface, the high reactivity of sodium metal in the battery will lead to poor electrochemical stability between the negative electrode and the traditional liquid electrolyte. There are problems such as flammability, explosiveness, easy leakage during use, and the easy generation of sodium dendrites during multiple cycles, which can cause battery short circuits. Therefore, in order to solve this problem, safe, stable, and efficient solid-state sodium batteries have received increasing attention.

[0003] The emergence of solid-state sodium batteries is expected to solve the safety problems of sodium-ion batteries because solid electrolytes can mechanically inhibit the growth of sodium dendrites and have high electrical conductivity, strong mechanical strength, sufficient chemical stability, and a wide electrochemical window. Currently, solid electrolytes can be divided into organic polymer electrolytes, inorganic solid electrolytes, and composite solid electrolytes. However, a key problem is that poor contact may occur between the solid electrolyte and the electrode material, resulting in a large interfacial resistance and affecting the performance of solid-state batteries. To solve the above problems, the in-situ polymerization method can effectively eliminate geometric gaps. By in-situ initiating the formation of long-chain polymers from liquid monomers, it can simultaneously achieve close contact between the electrolyte and the electrode and greatly reduce the interfacial resistance. Poly(1,3-dioxolane) (PDOL), as a long-chain polymer, has excellent sodium-ion transport ability and high electrochemical stability under normal pressure when applied in sodium-ion batteries. Solid or gel-state PDOL electrolytes exhibit excellent cycling performance. However, existing PDOL electrolytes are all prepared from 1,3-dioxolane (DOL) monomers, and there are problems such as low conversion rate of DOL monomers in existing PDOL electrolytes. When applied to batteries, there is a problem of poor oxidation stability, usually lower than 4V. The oxidation ring structure in DOL monomer molecules is prone to ring opening to generate free radicals under high-voltage conditions above 4V. The chemical properties of short-chain segments are similar to those of monomers, and the ends are easily affected by the electric field under high-voltage conditions, thus generating free radicals or small-molecule products. Once free radicals are generated, they will react with other components in the electrolyte system (such as solvents, sodium salts, etc.), accelerating the degradation of the entire system and reducing the electrochemical performance of the battery. This limits the application of PDOL electrolytes in high-voltage batteries. Therefore, it is of great significance to provide a PDOL composite electrolyte and its preparation method to improve the conversion rate of DOL monomers in PDOL electrolytes and the stability of PDOL, and thus improve the electrochemical performance of sodium metal batteries under high voltage. Summary of the Invention

[0004] In view of this, aiming at the problems of low conversion rate of DOL monomers in existing PDOL electrolytes, poor stability of PDOL, and thus poor electrochemical performance of sodium metal batteries under high voltage, the present invention provides a PDOL composite electrolyte, its preparation method, and its application.

[0005] To solve the above technical problems, the technical solution provided by the present invention is:

[0006] In the first aspect of the present invention, a PDOL composite electrolyte is provided. The PDOL composite electrolyte comprises the following raw material components: sodium salt, 1,3-dioxolane, fluorinated solvent, nitrile plasticizer, and zirconia-based inorganic filler;

[0007] The nitrile plasticizer is a mixture of succinonitrile and adiponitrile;

[0008] The fluorinated solvent is a mixture of perfluorobutyl-substituted ethylene carbonate, perfluorohexyl-substituted ethylene carbonate, and perfluorooctyl-substituted ethylene carbonate.

[0009] Compared with the prior art, in the PDOL composite electrolyte provided by the present invention, a sodium salt is selected as an initiator. A small amount of the sodium salt decomposes in the electrolyte to generate Lewis groups, which can combine with the oxygen atoms on 1,3-dioxolane and open the ring of 1,3-dioxolane. The CH 2 group at the end of 1,3-dioxolane exhibits Lewis acidity and further initiates a chain reaction by reacting with other molecules or substances in the PDOL composite electrolyte to form PDOL with high stability. Moreover, the sodium salt can also provide more free sodium ions, thereby improving the electrochemical performance of the battery by increasing the ionic conductivity; the fluorinated solvent, as a functional additive for the negative electrode, will form a SEI layer rich in NaF on the surface of the sodium metal negative electrode under high pressure. The formed interfacial film has high quality and high stability, thereby improving the electrochemical performance of the battery; a specific nitrile plasticizer greatly improves the solubility of the sodium salt in 1,3-dioxolane monomer, further increasing the conversion rate of DOL monomer, making the prepared PDOL composite electrolyte have a high degree of polymerization and high stability. When applied under high-pressure conditions, it also has excellent first-cycle Coulomb efficiency, capacity retention rate, and discharge specific capacity; there are a large number of Lewis acid sites on the surface of zirconia-based inorganic fillers, including Zr 4+ and Y 3+ and oxygen vacancies, etc., which can further promote the polymerization of unreacted 1,3-dioxolane, thereby further increasing the conversion rate of 1,3-dioxolane monomer, and thus increasing the degree of polymerization and stability of PDOL. The prepared PDOL composite electrolyte can still have excellent electrochemical performance under high-pressure conditions. Moreover, the zirconia-based inorganic filler also has a NASICON structure, which further improves the sodium ion conduction ability and the ion exchange rate at the electrode interface, further improving the electrochemical performance of the battery.

[0010] In the PDOL composite electrolyte provided by the present invention, the conversion rate of 1,3-dioxolane monomer is as high as 98.5%. PDOL has both a high degree of polymerization and high stability. The fluorinated solution can form a stable interfacial film on the electrode surface. When applied under high-pressure conditions, it has excellent first-cycle Coulomb efficiency, capacity retention rate, and discharge specific capacity.

[0011] Preferably, based on the sum of the volumes of 1,3-dioxolane and the fluorinated solvent being 100%, the volume content of 1,3-dioxolane is 80% - 95%, and the volume content of the fluorinated solvent is 5% - 20%.

[0012] Preferably, the addition amount of the nitrile plasticizer is 10%-15% of the mass of the 1,3-dioxolane.

[0013] The preferred dosage is beneficial to further improve the solubility of the sodium salt, and further improve the electrochemical performance of the battery by enhancing the polymerization ability of 1,3-dioxolane.

[0014] Preferably, the addition amount of the zirconia-based inorganic filler is 2%-5% of the mass of the 1,3-dioxolane.

[0015] Preferably, based on the sum of the volumes of 1,3-dioxolane and the fluorinated solvent being 100%, the concentration of the sodium salt in the PDOL composite electrolyte is 1 mol / L - 1.2 mol / L.

[0016] The preferred usage amounts of the sodium salt and the zirconia-based inorganic filler can greatly enhance the polymerization ability of 1,3-dioxolane, increase the conversion rate of 1,3-dioxolane, and further improve the electrochemical performance of the battery.

[0017] Preferably, the sodium salt is sodium hexafluorophosphate.

[0018] The preferred sodium salt can further improve the stability of the prepared PDOL composite electrolyte, and further enhance the high-voltage resistance ability of the battery.

[0019] More preferably, the fluorinated solvent is a mixture of ethylene carbonate with perfluorobutyl-substituted methylene, ethylene carbonate with perfluorohexyl-substituted methylene, and ethylene carbonate with perfluorooctyl-substituted methylene.

[0020] More preferably, the ethylene carbonate with perfluorobutyl-substituted methylene is and the ethylene carbonate with perfluorohexyl-substituted methylene is and the ethylene carbonate with perfluorooctyl-substituted methylene .

[0021] Preferably, the mass ratio of perfluorobutyl-substituted ethylene carbonate, perfluorohexyl-substituted ethylene carbonate, and perfluorooctyl-substituted ethylene carbonate in the fluorinated solvent is (3 - 3.5) : (3 - 3.5) : (4 - 4.5).

[0022] Preferably, the mass ratio of succinonitrile to adiponitrile in the nitrile plasticizer is 1 : (1 - 1.5).

[0023] Preferably, the zirconia-based inorganic filler is yttria-stabilized zirconia.

[0024] The present invention further defines the specific components of the fluorinated solvent, nitrile plasticizer, and zirconia-based inorganic filler, which is beneficial to further improve the high-voltage resistance performance of the battery.

[0025] The second aspect of the present invention provides a method for preparing the above PDOL composite electrolyte, which includes the following steps:

[0026] Mix the weighed sodium salt, 1,3-dioxolane, fluorinated solvent, nitrile plasticizer and zirconia-based inorganic filler evenly, and then react the mixture at 70 °C - 72 °C to obtain the PDOL composite electrolyte.

[0027] Preferably, the reaction time is 12 h - 13 h.

[0028] The third aspect of the present invention provides the application of the above PDOL composite electrolyte or the PDOL composite electrolyte prepared by the above method in a sodium metal battery. Description of the Drawings

[0029] Figure 1 It is the SEM image of the PDOL composite electrolyte prepared in Example 1 of the present invention. Detailed Embodiments

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and the drawings. 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.

[0031] Example 1

[0032] This example provides a PDOL composite electrolyte raw material, which includes the following raw material components: sodium hexafluorophosphate, 1,3-dioxolane, fluorinated solvent, nitrile plasticizer and yttria-stabilized zirconia;

[0033] Among them, based on the sum of the volumes of 1,3-dioxolane and fluorinated solvent being 100%, the content of 1,3-dioxolane is 80%, and the content of the fluorinated solvent is 20%;

[0034] Based on the sum of the volumes of 1,3-dioxolane and fluorinated solvent being 100%, the concentration of sodium hexafluorophosphate in the PDOL composite electrolyte is 1 mol / L;

[0035] The addition amount of the nitrile plasticizer is 15% of the mass of the 1,3-dioxolane;

[0036] The addition amount of yttria-stabilized zirconia is 5% of the mass of the 1,3-dioxolane;

[0037] The fluorinated solvent is a mixture of ethylene carbonate with perfluorobutyl-substituted methylene, ethylene carbonate with perfluorohexyl-substituted methylene and ethylene carbonate with perfluorooctyl-substituted methylene with a mass ratio of 3:3:4; the nitrile plasticizer is a mixture of succinonitrile and adiponitrile with a mass ratio of 1:1.

[0038] Example 2

[0039] This example provides a PDOL composite electrolyte raw material, including the following raw material components: sodium hexafluorophosphate, 1,3-dioxolane, fluorinated solvent, nitrile plasticizer, and yttria-stabilized zirconia;

[0040] Among them, based on the sum of the volumes of 1,3-dioxolane and the fluorinated solvent being 100%, the content of 1,3-dioxolane is 95%, and the content of the fluorinated solvent is 5%;

[0041] Based on the sum of the volumes of 1,3-dioxolane and the fluorinated solvent being 100%, the concentration of sodium hexafluorophosphate in the PDOL composite electrolyte is 1.2 mol / L;

[0042] The addition amount of the nitrile plasticizer is 10% of the mass of the 1,3-dioxolane;

[0043] The addition amount of yttria-stabilized zirconia is 2% of the mass of the 1,3-dioxolane;

[0044] The fluorinated solvent is a mixture of ethylene carbonate with perfluorobutyl-substituted methylene, ethylene carbonate with perfluorohexyl-substituted methylene, and ethylene carbonate with perfluorooctyl-substituted methylene with a mass ratio of 3.5:3.5:4.5; the nitrile plasticizer is a mixture of succinonitrile and adiponitrile with a mass ratio of 1:1.5.

[0045] Example 3

[0046] This example provides a PDOL composite electrolyte raw material, including the following raw material components: sodium hexafluorophosphate, 1,3-dioxolane, fluorinated solvent, nitrile plasticizer, and yttria-stabilized zirconia;

[0047] Among them, based on the sum of the volumes of 1,3-dioxolane and the fluorinated solvent being 100%, the content of 1,3-dioxolane is 90%, and the content of the fluorinated solvent is 10%;

[0048] Based on the sum of the volumes of 1,3-dioxolane and the fluorinated solvent being 100%, the concentration of sodium hexafluorophosphate in the PDOL composite electrolyte is 1.1 mol / L;

[0049] The addition amount of the nitrile plasticizer is 12% of the mass of the 1,3-dioxolane;

[0050] The addition amount of yttria-stabilized zirconia is 3% of the mass of the 1,3-dioxolane;

[0051] The fluorinated solvent is a mixture of ethylene carbonate with perfluorobutyl-substituted methylene, ethylene carbonate with perfluorohexyl-substituted methylene, and ethylene carbonate with perfluorooctyl-substituted methylene in a mass ratio of 3.1:3.3:4.2; the nitrile plasticizer is a mixture of succinonitrile and adiponitrile in a mass ratio of 1:1.2.

[0052] Example 4

[0053] This example provides a PDOL composite electrolyte raw material. Compared with Example 1, the difference is that:

[0054] The nitrile plasticizer is a mixture of succinonitrile and adiponitrile in a mass ratio of 1:3;

[0055] Other components are the same as those in Example 1.

[0056] Example 5

[0057] This example provides a PDOL composite electrolyte raw material. Compared with Example 1, the difference is that:

[0058] Sodium hexafluorophosphate is replaced with sodium bis(trifluoromethylsulfonyl)imide;

[0059] Other components are the same as those in Example 1.

[0060] Comparative Example 1

[0061] This comparative example provides a PDOL composite electrolyte raw material. Compared with Example 1, the difference is that:

[0062] The fluorinated solvent is limited to only using ethylene carbonate with perfluorobutyl-substituted methylene;

[0063] Other components are the same as those in Example 1.

[0064] Comparative Example 2

[0065] This comparative example provides a PDOL composite electrolyte raw material. Compared with Example 1, the difference is that:

[0066] Adiponitrile is replaced with an equal amount of succinonitrile;

[0067] Other components are the same as those in Example 1.

[0068] Comparative Example 3

[0069] This comparative example provides a PDOL composite electrolyte raw material. Compared with Example 1, the difference is that:

[0070] Yttria-stabilized zirconia is replaced with an equal amount of silica;

[0071] Other components are the same as those in Example 1.

[0072] Comparative Example 4

[0073] This comparative example provides an electrolyte raw material, including the following raw material components: sodium hexafluorophosphate, diethylene glycol dimethyl ether, and 1,3-dioxolane;

[0074] Among them, the volume ratio of diethylene glycol dimethyl ether to 1,3-dioxolane is 1:1;

[0075] Based on the sum of the volumes of diethylene glycol dimethyl ether, 1,3-dioxolane, and sodium hexafluorophosphate being 100%, the concentration of sodium hexafluorophosphate in the electrolyte raw material is 1 mol / L.

[0076] The electrolyte raw materials provided in Examples 1 to 5 and Comparative Examples 1 to 4 were respectively dropped into button cells (button cell model 2032), and the dropping amount was 5 mL. The sodium metal, glass fiber separator, and positive electrode were immersed in the PDOL composite electrolyte raw material. Before pressing, the button cells were placed in the heating transition chamber of the glove box and heated at 70 °C for 12 h. Finally, the heated button cells were pressed to obtain sodium metal button cells containing the electrolyte;

[0077] Among them, the positive electrode was prepared from sodium nickel iron manganese phosphate of the P2 type high-voltage layered electrode material, conductive agent carbon black, and binder polyvinylidene fluoride according to a mass ratio of 80%:10%:10%;

[0078] The glass fiber separator was GF-D, with a thickness of 0.68 mm, and the diameter of the cut separator was 10 mm.

[0079] The sodium metal button cells containing the electrolytes of Examples 1 to 5 and Comparative Examples 1 to 4 were subjected to constant current charge-discharge tests at room temperature using a Neware battery tester. They were activated for 2 cycles at a current density of 0.02 A·g -1 , and then operated in subsequent cycles (2.0 V - 4.4 V) at a current density of 0.2 A·g -1 . The first-cycle discharge specific capacity, first-cycle Coulombic efficiency, and 100-cycle capacity retention rate at 0.2 A·g -1 were recorded. The specific test results are shown in Table 1: -1 The first-cycle discharge specific capacity, first-cycle Coulombic efficiency, and 100-cycle capacity retention rate at 0.2 A·g

[0080] Table 1

[0081]

[0082] Judging from the test data of applying the PDOL composite electrolyte raw material provided in the examples of the present invention to the battery, the PDOL composite electrolyte provided by the present invention has excellent electrochemical performance. When applied to the battery, it can significantly improve the first-cycle discharge specific capacity and first-cycle Coulombic efficiency of the battery and improve the cycle performance.

[0083] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A PDOL composite electrolyte, characterized in that: The PDOL composite electrolyte is composed of the following raw material components: sodium salt, 1,3-dioxolane, fluorinated solvent, nitrile plasticizer and zirconium oxide inorganic filler; The nitrile plasticizer is a mixture of succinonitrile and adiponitrile in a mass ratio of 1:(1-1.5); The fluorinated solvent is a mixture of perfluorobutyl substituted ethylene carbonate, perfluorohexyl substituted ethylene carbonate and perfluorooctyl substituted ethylene carbonate in a mass ratio of (3-3.5):(3-3.5):(4-4.5); Taking the sum of the volumes of 1,3-dioxolane and the fluorinated solvent as 100%, the volume content of the 1,3-dioxolane is 80%-95%, and the volume content of the fluorinated solvent is 5%-20%; The sodium salt is sodium hexafluorophosphate; The zirconium oxide-based inorganic filler is yttria-stabilized zirconium oxide.

2. The PDOL composite electrolyte according to claim 1, characterized in that The amount of the nitrile plasticizer added is 10%-15% of the mass of the 1,3-dioxolane; and / or The amount of the zirconium oxide inorganic filler added is 2%-5% of the mass of the 1,3-dioxolane; and / or Based on the sum of the volumes of 1,3-dioxolane and the fluorinated solvent being 100%, the concentration of the sodium salt in the PDOL composite electrolyte is 1 mol / L-1.2 mol / L.

3. The PDOL composite electrolyte according to claim 1, characterized in that The fluorinated solvent is a mixture of perfluorobutyl substituted methylene ethylene carbonate, perfluorohexyl substituted methylene ethylene carbonate and perfluorooctyl substituted methylene ethylene carbonate.

4. The PDOL composite electrolyte according to claim 3, characterized in that The perfluorobutyl substituted methylene ethylene carbonate is , the perfluorohexyl substituted methylene ethylene carbonate is , the perfluorooctyl substituted methylene ethylene carbonate .

5. A method for preparing the PDOL composite electrolyte according to any one of claims 1 to 4, characterized in that: The weighed sodium salt, 1,3-dioxolane, fluorinated solvent, nitrile plasticizer and zirconium oxide inorganic filler are mixed evenly, and then the mixture is reacted at 70° C.-72° C. to obtain a PDOL composite electrolyte.

6. The method for preparing the PDOL composite electrolyte according to claim 5, characterized in that: The reaction time is 12h-13h.

7. Use of the PDOL composite electrolyte according to any one of claims 1 to 4 or the PDOL composite electrolyte prepared by the preparation method of the PDOL composite electrolyte according to claim 5 or 6 in a sodium metal battery.

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