Gel polymer electrolyte composition, gel polymer electrolyte and sodium-ion battery thereof

Abstract

The present application provides a kind of gel polymer electrolyte composition, gel polymer electrolyte and sodium ion battery thereof.The gel polymer electrolyte composition includes sodium salt, non-aqueous solvent, sodium phosphate salt additive, initiator and monomer as shown below, wherein R1-R4 are each independently selected from substituted or unsubstituted C1-C6 hydrocarbon group.The gel polymer electrolyte obtained by the synergistic effect of sodium phosphate salt additive and double bond-containing monomer has lower viscosity, and when applied to sodium ion battery, the high-temperature cycle performance and safety performance of sodium ion battery at high voltage can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a gel polymer electrolyte composition, a gel polymer electrolyte, and a sodium-ion battery thereof. Background Technology

[0002] The large-scale development of the energy storage market and the continuous expansion of energy storage application scenarios have placed higher demands on the economic efficiency and safety of energy storage technologies. As the chemical energy storage technology closest to lithium-ion batteries, sodium-ion batteries possess advantages such as abundant sodium resources, low cost, and excellent rate and low-temperature performance, creating enormous potential for their large-scale application. Therefore, sodium-ion batteries can serve as an important supplementary technology to lithium-ion batteries in the field of large-scale energy storage, possessing significant economic value and strategic importance.

[0003] However, compared to lithium-ion batteries, sodium-ion batteries currently suffer from lower energy density and gas generation during cycling. This is because sodium ions have a larger radius than lithium ions, resulting in more severe volume changes and more complex phase transitions in the cathode materials, especially layered transition metal oxides, during sodium ion insertion / extraction, leading to poorer surface structure stability. Furthermore, at the same voltage, the sodium cathode is at a higher potential and has greater surface residual capacity, exacerbating cycling and gas generation problems.

[0004] Sodium-ion batteries using commercially available liquid electrolytes are insufficient to meet the requirements. On the one hand, liquid electrolytes undergo severe decomposition reactions on the surface of electrode materials under high temperature and high pressure conditions, leading to battery performance degradation. On the other hand, the low flash point solvents used in liquid electrolytes have poor safety at elevated temperatures.

[0005] Using solid polymer electrolytes can fundamentally improve battery safety. However, compared to liquid electrolytes, solid polymer electrolytes have poor ionic conductivity. Moreover, currently available polymer electrolytes with high ionic conductivity use polyether polymers such as polyethylene oxide (PEO) as the polymer matrix, but polyether polymers have poor oxidation resistance, resulting in low battery operating voltage and low battery energy density.

[0006] Therefore, there is an urgent need to develop a gel polymer electrolyte with high operating voltage, excellent electrical performance, and good safety performance to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a gel polymer electrolyte composition, a gel polymer electrolyte, and a sodium-ion battery thereof, so as to improve the electrochemical performance and safety performance of sodium-ion batteries.

[0008] To achieve the above objectives, a first aspect of the present invention provides a gel polymer electrolyte composition comprising a sodium salt, a non-aqueous solvent, an initiator, a sodium phosphate salt additive, and monomers as shown below:

[0009]

[0010] R1 to R4 are each independently selected from substituted or unsubstituted C1 to C6 hydrocarbon groups.

[0011] Compared with the prior art, the sodium phosphate additive of the present invention serves two purposes: firstly, it acts as a sodium replenisher for sodium-ion batteries, sacrificing itself to replenish the active sodium lost during the first charge-discharge cycle and improving the coulombic efficiency of the first cycle; secondly, it forms a NaP-rich layer during the first formation stage. x O y The components, after being deposited onto the surfaces of the positive and negative electrodes, form a stable SEI film. Monomers containing double bonds can polymerize at reduced potentials, resulting in a lower SEI impedance on the negative electrode surface; furthermore, the monomer has a smaller molecular weight, leading to a lower viscosity gel electrolyte after polymerization. Therefore, this invention utilizes the synergistic effect of sodium phosphate additives and monomers containing double bonds to obtain a novel gel electrolyte with lower viscosity, significantly improving the electrical and safety performance of sodium-ion batteries under high voltage.

[0012] Ideally, R1 and R2 are the same, and R3 and R4 are the same.

[0013] Preferably, R1 to R2 and R3 to R4 are each independently selected from C2 to C6 alkenyl groups, C2 to C6 cyclic saturated or unsaturated alkyl groups.

[0014] Preferably, R1 to R2 and R3 to R4 are each independently selected from C2 to C4 alkenyl groups and C2 to C6 cyclic saturated alkyl groups.

[0015] Preferably, R1 to R2 and R3 to R4 are each independently selected from C3 alkenyl groups and C2 cyclic saturated alkyl groups.

[0016] Preferably, the monomer is selected from at least one of the following compounds A1 to A3:

[0017]

[0018] Preferably, the sodium phosphate salt additive includes at least one of the following compounds: B1 and B2:

[0019]

[0020] The preparation method of compound B2 is as follows: compound 1 and sodium methoxide are reacted in methanol solution at 15-25°C for 2-3 hours, the reaction solution is then concentrated, and finally the concentrated solution is recrystallized with dichloromethane to obtain compound B2. The structural formula of compound 1 is shown below:

[0021]

[0022] Preferably, the monomer accounts for 1% to 5% by mass in the gel polymer electrolyte, specifically, but not limited to, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%.

[0023] Preferably, the sodium phosphate salt additive is present in the gel polymer electrolyte composition at a mass percentage of 0.01% to 0.5%, specifically, but not limited to, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, and 0.5%.

[0024] Preferably, the initiator is selected from any one of azobisisobutyronitrile, 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), tert-butylperoxide-2-ethylhexanoate (TBPEH), di-tert-butylperoxide (DTBP), and dilauryl peroxide (LPO). The initiator accounts for 0.01% to 5% by mass in the gel polymer electrolyte composition, specifically, but not limited to, 0.01%, 0.05%, 1%, 2%, 3%, and 5%.

[0025] Preferably, the sodium salt is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium trifluoromethanesulfonate (NaCF3SO3), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium bis(oxalate-borate)borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorooxalate-borate (NaODFB), sodium difluorodioxalate-phosphate (NaDODFP), and sodium bis(fluorosulfonyl)imide (NaFSI).

[0026] Preferably, the sodium salt constitutes 8% to 14% by mass in the gel polymer electrolyte composition, specifically, but not limited to, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.3%, 11.8%, 12.0%, 12.5%, 12.8%, 13.0%, 13.4%, 13.7%, and 14%.

[0027] Preferably, the non-aqueous solvent is selected from at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butyl acetate (Ba), γ-butyrolactone (BL), propyl propionate (PP), ethyl propionate (EP), and ethyl butyrate (EB).

[0028] A second aspect of the present invention provides a gel polymer electrolyte prepared by polymerization of the above-described gel polymer electrolyte composition.

[0029] A third aspect of the present invention provides a sodium-ion battery, comprising a positive electrode and a negative electrode, and further comprising the aforementioned gel polymer electrolyte.

[0030] Preferably, the positive electrode comprises a positive electrode material, the positive electrode material comprising a layered oxide, the layered oxide having the chemical formula Na. x M (1-y-z) Fe y Mn z O2, wherein M is independently selected from at least one of Co, Ni, Cu, Mg, Zn, Al, Sn, Ga, Cr, Sr, V, and Ti, 0 <x≤1,0≤y≤1,0≤z≤1,y+z≤1。

[0031] Preferably, the negative electrode comprises a negative electrode material selected from at least one of alkali metals, soft carbon, and hard carbon. Detailed Implementation

[0032] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0034] There are no particular restrictions on the purity of any raw materials used in this invention. However, it is preferred to use analytical grade or conventional purity in the field of sodium-ion battery electrolytes.

[0035] The sodium-ion battery of the present invention includes a positive electrode, a negative electrode, and a gel polymer electrolyte. The gel polymer electrolyte is prepared by polymerization of a gel polymer electrolyte composition. The gel polymer electrolyte composition includes a sodium salt, a non-aqueous solvent, a sodium phosphate salt additive, an initiator, and a monomer.

[0036] The sodium salt is selected from sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium trifluoromethanesulfonate (NaCF3SO3), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium bis(oxalate-borate)borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorooxalate-borate (NaODFB), sodium difluorodioxalate-phosphate (NaDODFP), and sodium bis(fluorosulfonyl)imide (NaFSI). In this invention, the sodium salt is preferably sodium hexafluorophosphate (NaPF6), and the sodium salt accounts for 8% to 14% of the total mass of the gel polymer electrolyte composition, specifically, but not limited to, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.3%, 11.8%, 12.0%, 12.5%, 12.8%, 13.0%, 13.4%, 13.7%, and 14%, preferably 10% to 12%.

[0037] The non-aqueous solvent is selected from at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene carbonate (PC), butyl acetate (Ba), γ-butyrolactone (BL), propyl propionate (PP), ethyl propionate (EP), and ethyl butyrate (EB). In this invention, the non-aqueous solvent is preferably a mixture of ethyl propionate (EP), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) to achieve more stable cycle performance.

[0038] The initiator is selected from any one of azobisisobutyronitrile, 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), tert-butylperoxide-2-ethylhexanoate (TBPEH), di-tert-butylperoxide (DTBP), and dilauryl peroxide (LPO). In this invention, the initiator is preferably azobisisobutyronitrile (AIBN). The initiator accounts for 0.01% to 5% of the total mass of the gel polymer electrolyte composition, specifically, but not limited to, 0.01%, 0.05%, 1%, 2%, 3%, and 5%.

[0039] The monomer is selected from at least one of the following compounds A1 to A3, and the monomer accounts for 1 to 5% of the total mass of the gel polymer electrolyte composition, specifically, but not limited to, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%.

[0040]

[0041] The sodium phosphate additive is at least one selected from the group consisting of compound B1 and compound B2. The sodium phosphate additive accounts for 0.01% to 0.5% of the total mass of the gel polymer electrolyte composition, specifically including but not limited to 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.26%, 0.3%, 0.35%, 0.4%, 0.45%, and 0.5%.

[0042]

[0043] Wherein, the preparation method of compound B2 is as follows: compound 1 and sodium methoxide react in a methanol solution at 15 to 25°C for 2 to 3 hours, the reaction solution is then concentrated, and finally the concentrated solution is recrystallized with dichloromethane to obtain compound B2. The structural formula of compound 1 is shown below:

[0044]

[0045] The positive electrode comprises a positive electrode material, and the positive electrode material comprises a layered oxide having a chemical formula of Na x M (1-y-z) Fe y Mn z O2, wherein M is independently at least one selected from the group consisting of Co, Ni, Cu, Mg, Zn, Al, Sn, Ga, Cr, Sr, V and Ti, 0<x≤1, 0≤y≤1, 0≤z≤1, y+z≤1. In the present invention, M is selected as Ni, x=1, y=0.2, z=0.3.

[0046] The negative electrode comprises a negative electrode material, and the negative electrode material is at least one selected from the group consisting of alkali metal, soft carbon and hard carbon. Among them, soft carbon is amorphous carbon that can be graphitized at a high temperature above 2500°C, while hard carbon is difficult to graphitize even after high-temperature treatment, thereby exhibiting stronger sodium storage capacity and lower working potential, therefore the negative electrode material of the present invention is preferably hard carbon.

[0047] Example 1

[0048] (1) Preparation of gel polymer electrolyte composition prepolymer:

[0049] In an argon atmosphere, an electrolyte is prepared in a vacuum glove box with a moisture content < 1 ppm. In a dry argon atmosphere glove box, ethyl propionate (EP), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed according to a weight ratio of EP:EMC:DEC=2:1:2, then compound A1 and compound B1 are added, after dissolving and fully stirring, NaPF6 and AIBN are added, and the mixture is uniformly mixed to obtain a gel polymer electrolyte composition prepolymer.

[0050] (2) Preparation of the positive electrode:

[0051] NaNi ternary material sodium ferromanganate 5 / 10 Fe 2 / 10 Mn 3 / 10 O2, binder PVDF and conductive agent SuperP are mixed evenly in a mass ratio of 95:1:4 to prepare a sodium-ion battery positive electrode slurry of a certain viscosity. The mixed slurry is coated on both sides of aluminum foil, dried and rolled to obtain the positive electrode sheet.

[0052] (3) Preparation of negative electrode:

[0053] Hard carbon, conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) are mixed in a mass ratio of 95:1.5:1.0:2.5 to form a slurry. The mixture is then coated on both sides of copper foil, dried, and rolled to obtain the negative electrode sheet.

[0054] (4) Preparation of sodium-ion batteries:

[0055] The positive electrode, separator, and negative electrode are stacked to form a square cell. The cell is packaged with polymer and filled with the sodium-ion battery gel polymer electrolyte composition prepolymer prepared above. The cell is reacted at 60-70°C for 2-4 hours to obtain the gel polymer electrolyte. After formation, capacity testing and other processes, a sodium-ion battery with a capacity of 1000mAh is produced.

[0056] The gel polymer electrolyte formulations for each embodiment and comparative example are shown in Table 1. The steps for preparing the gel polymer electrolyte composition and the sodium-ion battery are the same as in Example 1.

[0057] Table 1

[0058]

[0059]

[0060] The gel polymer electrolytes and sodium-ion batteries prepared in Examples 1-16 and Comparative Examples 1-4 were subjected to wettability tests, high-temperature cycle tests, and safety performance tests under the following specific test conditions. The performance test results are shown in Table 2.

[0061] (1) Infiltration test

[0062] Take positive and negative electrode sheets and cut them into circular pieces with a diameter of 16 mm. Drop the gel electrolyte onto the surface of the positive and negative electrode sheets and then test the time it takes for the gel electrolyte to disappear. The shorter the time it takes for the gel electrolyte to disappear, the better the wettability of the electrolyte.

[0063] (2) High-temperature cycling performance test

[0064] The sodium-ion batteries of Examples 1-16 and Comparative Examples 1-4 were subjected to one 0.5C / 0.5C charge and discharge cycle at 45°C (battery discharge capacity C0), with an upper limit voltage of 4.2V. Then, they were subjected to 300 cycles of 0.5C / 0.5C charge and discharge at high temperature (battery discharge capacity C1). The capacity retention rate was calculated as (C1 / C0) * 100%.

[0065] (3) Safety performance test

[0066] Under normal temperature (25°C) conditions, the sodium-ion batteries of Examples 1-16 and Comparative Examples 1-4 were charged at a constant current of 1C until the charging termination voltage (10V) was reached. Then, constant voltage charging was applied until the charging current rate dropped to 0.05C, at which point charging was stopped and the batteries were allowed to stand for 2.5 hours. The batteries were then placed in a test chamber, which was heated at a rate of 5°C / min. Once the temperature inside the chamber reached 160°C ± 2°C, it was kept constant for 1 hour. A battery that did not smoke, catch fire, or explode was considered to have passed the test; otherwise, it failed.

[0067] Table 2

[0068]

[0069] As can be seen from the performance test results of Examples 1-16 and Comparative Examples 1-4 in Table 2, the sodium-ion battery containing the gel polymer electrolyte of the present invention has good high-temperature cycle performance and safety performance. The specific analysis is as follows:

[0070] As can be seen from the comparison of Examples 1 to 6, the sodium-ion battery prepared using the monomer compound A3 has better wetting performance. This is because compound A3 has more double bonds, and the polymer formed by it has lower viscosity, thus resulting in better wetting performance.

[0071] A comparison of Examples 1, 3, and 5 with Examples 2, 4, and 6 shows that using compound B1 as an additive exhibits superior high-temperature cycling performance. This may be because compound B1 contains multiple cyclic sodium phosphate skeletons, which form an organic NaP-rich structure during the initial formation stage. x O y It contains inorganic components such as Na3PO4 and Na3PO3, which have lower solubility in carbonate solvents, resulting in a more stable SEI film and more stable high-temperature cycling performance in the later stages.

[0072] Compared with Example 1, Comparative Example 1 has poor safety performance and high-temperature cycling performance because it does not contain sodium phosphate salt additive compound B1 and monomer compound A1; Comparative Example 2 does not contain monomer compound A1, so it has poor safety performance and high-temperature cycling performance; Comparative Example 3 does not contain sodium phosphate salt additive compound B1, so it has poor high-temperature cycling performance; Comparative Example 4 has a chain-like phosphate structure, so it has poor high-temperature cycling performance.

[0073] The sodium phosphate additive of this invention serves two purposes: firstly, it acts as a sodium replenisher in sodium-ion batteries, sacrificing the active sodium lost during the first charge-discharge cycle to improve the first-cycle coulombic efficiency; secondly, it forms a NaPxOy-rich component during the initial formation stage, resulting in a more stable SEI film after deposition on the positive and negative electrode surfaces; and thirdly, the sodium phosphate additive of this invention possesses a cyclic framework, particularly compound B1, which has multiple cyclic sodium phosphate frameworks, forming an organic NaP-rich component during the initial formation stage. x O y The invention incorporates inorganic components such as Na3PO4 and Na3PO3, which have lower solubility in carbonate solvents, resulting in a more stable SEI film and improved high-temperature cycling performance. The monomer containing double bonds in this invention can polymerize at a reduced potential, forming an SEI on the negative electrode surface with lower SEI resistance; furthermore, the monomer has a smaller molecular weight, leading to a lower viscosity gel electrolyte after polymerization. Therefore, this invention utilizes the synergistic effect of sodium phosphate additives and monomers containing double bonds to obtain a novel gel electrolyte with lower viscosity, significantly improving the electrical and safety performance of sodium-ion batteries under high voltage.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A gel polymer electrolyte composition, characterized in that, Includes sodium salts, non-aqueous solvents, initiators, sodium phosphate additives, and monomers as shown below: R1 to R4 are each independently selected from substituted or unsubstituted C1 to C6 hydrocarbon groups; The sodium phosphate salt additive includes at least one of compound B1 and compound B2: Compound B1 and compound B2.

2. The gel polymer electrolyte composition according to claim 1, characterized in that, The monomer is selected from at least one of the following compounds A1 to A3: Compound A1, Compound A2, Compound A3.

3. The gel polymer electrolyte composition according to any one of claims 1 to 2, characterized in that, The monomer accounts for 1% to 5% by mass in the gel polymer electrolyte composition.

4. The gel polymer electrolyte composition according to any one of claims 1 to 2, characterized in that, The sodium phosphate salt additive is present in the gel polymer electrolyte composition at a mass percentage of 0.01% to 0.5%.

5. The gel polymer electrolyte composition according to any one of claims 1 to 2, characterized in that, The initiator is selected from any one of azobisisobutyronitrile, 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), tert-butylperoxide-2-ethylhexanoate, di-tert-butylperoxide, and dilauroyl peroxide.

6. The gel polymer electrolyte composition according to any one of claims 1 to 2, characterized in that, The sodium salt is selected from at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalate-borate), sodium difluorophosphate, sodium di(oxalate-borate), sodium di(oxalate-difluorophosphate), and sodium bis(oxalate-imide).

7. The gel polymer electrolyte composition according to any one of claims 1 to 2, characterized in that, The non-aqueous solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate, and ethyl butyrate.

8. A gel polymer electrolyte, characterized in that, It is obtained by polymerization of the gel polymer electrolyte composition according to claim 1.

9. A sodium-ion battery, comprising a positive electrode and a negative electrode, characterized in that, It also includes the gel polymer electrolyte of claim 8.

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