Carbonic ester sodium ion electrolyte, preparation method and application thereof, and sodium ion battery

Abstract

The invention provides a carbonic ester sodium ion electrolyte, a preparation method and application thereof, and a sodium ion battery. According to the invention, the novel lithium salt 2-trifluoromethyl-4, 5-dicyanoimidazole lithium (LiTDI) is innovatively applied to the sodium ion electrolyte for the first time as an additive, so that the sodium metal total battery with long service life and stable wide temperature range is realized. The sodium metal battery is characterized in that the unique chemical composition of LiTDI can regulate and control the solid-electrolyte interface (SEI) of the negative electrode and the positive electrode-electrolyte interface (CEI) of the Na3V2 (PO4) 3 positive electrode in the sodium metal battery at the same time, the positive electrode and the negative electrode are both improved, and finally the performance of the whole battery is obviously improved. And the cycle stability of the sodium metal total battery can still be effectively improved by the modified electrolyte formula after circulation at a high temperature with a harsh environment and a more serious side reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium metal batteries, and in particular to a carbonate sodium ion electrolyte, a preparation method and application thereof, and a sodium ion battery. Background Art

[0002] With the booming development of large-scale energy storage systems and portable electronic devices, people have an increasing demand for high-energy and low-cost rechargeable batteries. Due to the extremely abundant sodium resources, sodium metal full batteries are considered to be one of the most promising alternatives to mainstream lithium-ion batteries. Although sodium metal has a high theoretical specific capacity (1166 mAh g -1 ) and a lower redox potential (-2.71V vs standard hydrogen electrode), but the development of a reversible and stable commercial sodium metal anode remains a huge challenge, especially when using traditional carbonate electrolytes. The unstable solid-electrolyte interface (SEI) structure on the sodium metal surface can lead to low Coulombic efficiency (CE) and uncontrollable growth of dendrites, ultimately causing battery failure or even combustion and explosion. In addition, sodium metal batteries are also plagued by positive electrode materials. Problems such as transition metal dissolution and gas generation are also closely related to the positive electrode-electrolyte interface (CEI). Therefore, regulating the SEI and CEI structures is crucial to building practical sodium metal full batteries.

[0003] In recent years, a large number of studies have been devoted to exploring how to regulate the SEI structure of sodium metal anodes in carbonate electrolytes that are compatible with most cathode materials. Strategies such as constructing artificial SEI, preparing three-dimensional conductive skeleton current collectors, and introducing electrolyte additives are all helpful in improving the cycle stability of sodium metal anodes, and the latter is undoubtedly the simplest and most effective method to regulate sodium metal SEI, and is expected to be applied on a large scale. The research and design of sodium metal battery electrolyte additives is still in the development stage, and there are few literature reports that an additive can act on and improve the positive / negative electrode interface at the same time. Therefore, it is particularly important to research and develop new electrolytes that can act on both the positive and negative electrodes at the same time, and to increase the operating temperature range of sodium metal batteries, so as to realize commercial sodium metal full batteries. Summary of the invention

[0004] The purpose of the present invention is to introduce a single lithium salt additive LiTDI into the traditional carbonate sodium ion electrolyte, while improving the structure of the negative electrode SEI and the positive electrode CEI in the sodium metal battery, so as to simply and efficiently realize a long-life, wide temperature range stable sodium metal full battery. The electrolyte formula is expected to be used on a large scale in the sodium metal electrolyte system.

[0005] The present invention is achieved in that:

[0006] The present invention provides a carbonate sodium ion electrolyte, comprising a carbonate electrolyte and a lithium salt additive;

[0007] Wherein, the lithium salt additive is 2-trifluoromethyl-4,5-dicyanoimidazole lithium.

[0008] Preferably, the mass of the 2-trifluoromethyl-4,5-dicyanoimidazole lithium is 0.01-6% of the mass of the carbonate electrolyte.

[0009] Preferably, the carbonate electrolyte comprises a sodium salt and a solvent;

[0010] The sodium salt includes at least one of NaClO4, sodium hexafluorophosphate, sodium tetrafluoroborate, and sodium bis(fluorosulfonyl)imide;

[0011] The solvent includes at least one of propylene carbonate, fluoroethylene carbonate and ethylene carbonate.

[0012] Preferably, the carbonate electrolyte further comprises a functional additive;

[0013] The functional additive includes at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate and vinyl carbonate.

[0014] Preferably, the carbonate electrolyte comprises a sodium salt and a solvent, and the solvent comprises a mixture of propylene carbonate and fluoroethylene carbonate;

[0015] The volume ratio of propylene carbonate to fluoroethylene carbonate is (0.5-2):1;

[0016] The molar concentration of the sodium salt in the carbonate electrolyte is 0.75 to 1.25 M;

[0017] Or, the carbonate electrolyte includes sodium salt and solvent, the solvent includes a mixture of propylene carbonate and ethylene carbonate; the volume ratio of ethylene carbonate to propylene carbonate is (0.5-1):1;

[0018] The molar concentration of the sodium salt in the carbonate electrolyte is 0.75-1.25M.

[0019] Preferably, the carbonate electrolyte comprises sodium salt, solvent and functional additives; the solvent comprises a mixture of propylene carbonate and ethylene carbonate; the volume ratio of ethylene carbonate to propylene carbonate is (0.5-1):1;

[0020] The sodium salt and the solvent form a mixture, the molar concentration of the sodium salt in the mixture is 0.75-1.25M, and the mass of the functional additive is 0.01-10% of the mass of the mixture.

[0021] In a second aspect, the present invention further provides a method for preparing the carbonate sodium ion electrolyte, comprising the following steps:

[0022] The carbonate sodium ion electrolyte is obtained by adding 2-trifluoromethyl-4,5-dicyanoimidazole lithium into the carbonate electrolyte.

[0023] Preferably, the method for preparing the carbonate sodium ion electrolyte comprises the following steps:

[0024] After drying, the lithium 2-trifluoromethyl-4,5-dicyanoimidazole was transferred into a glove box under an inert atmosphere;

[0025] A carbonate electrolyte is prepared in a glove box;

[0026] 2-trifluoromethyl-4,5-dicyanoimidazole lithium is added into the carbonate electrolyte to obtain a carbonate sodium ion electrolyte.

[0027] In a third aspect, the present invention further provides a use of the carbonate sodium ion electrolyte or the carbonate sodium ion electrolyte prepared by the preparation method in preparing a sodium ion battery.

[0028] In a fourth aspect, the present invention further provides a sodium ion battery, comprising the carbonate sodium ion electrolyte or the carbonate sodium ion electrolyte prepared by the preparation method.

[0029] The present invention has the following beneficial effects compared with the prior art:

[0030] 1. The carbonate sodium ion electrolyte provided by the present invention can effectively improve the cycle life and stability of the sodium metal full battery by introducing a single lithium salt additive 2-trifluoromethyl-4,5-dicyanoimidazole lithium (LiTDI) into the traditional carbonate sodium ion electrolyte;

[0031] 2. Unlike conventional single additives that only contribute to the modification of the negative electrode or positive electrode interface, the unique chemical structure of LiTDI additives enables it to synergistically regulate the structure of the sodium metal negative electrode SEI and the positive electrode CEI, simplifying the electrolyte preparation process and significantly improving the cycle stability of sodium metal. It is expected to achieve large-scale application of LiTDI additives in sodium metal battery electrolyte systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1The SEM images, cross-sectional SEM images and EDS elemental analysis results of the carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 deposited on the surface of the negative electrode sodium metal;

[0034] Figure 2 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 are assembled into Na|Cu half-cells, and the coulombic efficiency test results of the cells at 25°C are shown;

[0035] Figure 3 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were assembled into Na|Na symmetric battery stability test results;

[0036] Figure 4 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were assembled into Na|Cu half-cells, and the AC impedance spectra were measured when they were cycled for 2 cycles at 25°C;

[0037] Figure 5 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 are respectively assembled into Na|Cu half-cells and cycled for 200 cycles at 25°C.

[0038] Figure 6 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were assembled into Na|NVP full batteries, and the cycling stability test diagram was performed at 1C current density at 25°C;

[0039] Figure 7 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 are assembled into Na|NVP full batteries, and the cycle stability test results at 5C current density at 25°C are shown;

[0040] Figure 8 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 are assembled into Na|NVP full batteries, and the cycle stability test results at 1C current density at 50°C are shown;

[0041] Fig. 9The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were assembled into Na|NVP full batteries, and the cycle stability test results at 5C current density at 50°C were shown. DETAILED DESCRIPTION

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of the present application, the term "including" means "including but not limited to". Various embodiments of the present invention may be in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the numbered ranges, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated in this article, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0044] The present invention provides a carbonate sodium ion electrolyte, comprising a carbonate electrolyte and a lithium salt additive;

[0045] Wherein, the lithium salt additive is 2-trifluoromethyl-4,5-dicyanoimidazole lithium.

[0046] The carbonate sodium ion electrolyte provided by the present invention realizes a stable sodium metal battery by introducing a single lithium salt additive 2-trifluoromethyl-4,5-dicyanoimidazole lithium (i.e. 4,5-dicyano-2-trifluoromethyl-imidazole lithium, LiTDI, molecular formula C6F3LiN4) into the traditional carbonate sodium ion electrolyte. In the carbonate sodium ion electrolyte, the strongly coordinated TDI anion preferentially occupies the inner layer of the solvation structure, the CF bond in the trifluoromethyl group preferentially breaks and participates in the formation of the sodium metal negative electrode SEI, and the unique inorganic-rich structure effectively inhibits the side reactions and uncontrollable dendrite growth of the sodium metal negative electrode. At the same time, the unique electron cloud structure of TDI anions will decompose on the surface of the positive electrode material to generate inorganic-rich CEI. -CN and CNC / C=NC in TDI will complex with transition metal ions in the positive electrode material, thereby building a beneficial protective layer on the positive electrode surface, stabilizing the Na3V2(PO4)3 positive electrode crystal structure, and finally realizing a long-life, wide temperature range stable sodium metal full battery through the coordinated regulation of the positive / negative electrode interface. The electrolyte additive LiTDI is used to improve the cycle performance of sodium metal batteries, with a simple process and significant effect. The carbonate sodium ion electrolyte of the present invention only adds one additive LiTDI to achieve the optimization of negative electrode SEI and positive electrode CEI, further simplifies the process formula and reduces costs, realizes the wide temperature range operation of sodium metal batteries, and is expected to realize the large-scale application of LiTDI additives in sodium metal battery electrolyte systems.

[0047] The carbonate sodium ion electrolyte provided by the present invention, after adding LiTDI, the unique solvation structure of the electrolyte can simultaneously regulate the sodium metal negative electrode and the Na3V2(PO4)3 positive electrode, promote the formation of an inorganic-rich interface layer, effectively inhibit the side reactions of the negative electrode and the positive electrode, and finally realize a long-life, wide temperature range stable sodium metal full battery. In addition, the electrolyte formula has not been reported yet, and it has a very high degree of innovation, and the introduction of LiTDI can simultaneously achieve the regulation of the positive / negative electrode interface components and structures, the electrolyte formula regulation process is simple, and it is expected to realize the large-scale application of LiTDI additives in sodium metal battery electrolyte systems.

[0048] In some embodiments, the mass of 2-trifluoromethyl-4,5-dicyanoimidazole lithium is 0.01% to 6% of the mass of the carbonate electrolyte; preferably, the mass of 2-trifluoromethyl-4,5-dicyanoimidazole lithium is 3% to 5% of the mass of the carbonate electrolyte, specifically, the mass of 2-trifluoromethyl-4,5-dicyanoimidazole lithium is 3%, 4%, 5%, etc., of the mass of the carbonate electrolyte.

[0049] In some embodiments, the carbonate electrolyte includes a sodium salt, a solvent;

[0050] The sodium salt includes at least one of NaClO4, sodium hexafluorophosphate, sodium tetrafluoroborate, and sodium bis(fluorosulfonyl)imide;

[0051] The solvent includes at least one of propylene carbonate (PC, molecular formula: C4H6O3), fluoroethylene carbonate (FEC, molecular formula: C3H3FO3), and ethylene carbonate (EC, C3H4O3).

[0052] In some embodiments, the carbonate electrolyte further comprises a functional additive;

[0053] The functional additive includes at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, and vinyl carbonate.

[0054] In some embodiments, the carbonate electrolyte includes a sodium salt and a solvent, wherein the solvent includes a mixture of propylene carbonate and fluoroethylene carbonate;

[0055] The volume ratio of propylene carbonate and fluoroethylene carbonate is (0.5-2):1;

[0056] The molar concentration of the sodium salt in the carbonate electrolyte is 0.75 to 1.25M.

[0057] In some embodiments, the carbonate electrolyte includes a sodium salt and a solvent, wherein the solvent includes a mixture of propylene carbonate and ethylene carbonate; the volume ratio of ethylene carbonate to propylene carbonate is (0.5-1):1;

[0058] The molar concentration of the sodium salt in the carbonate electrolyte is 0.75 to 1.25M.

[0059] In some embodiments, the carbonate electrolyte includes a sodium salt, a solvent, and a functional additive; the solvent includes a mixture of propylene carbonate and ethylene carbonate; the volume ratio of ethylene carbonate to propylene carbonate is (0.5-1):1;

[0060] The sodium salt and the solvent form a mixture, the molar concentration of the sodium salt in the mixture is 0.75-1.25M, and the mass of the functional additive is 0.01-10% of the mass of the mixture.

[0061] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned carbonate sodium ion electrolyte, comprising the following steps:

[0062] The carbonate sodium ion electrolyte is obtained by adding 2-trifluoromethyl-4,5-dicyanoimidazole lithium into the carbonate electrolyte.

[0063] In some embodiments, a method for preparing a carbonate sodium ion electrolyte comprises the following steps:

[0064] S1. Dry 2-trifluoromethyl-4,5-dicyanoimidazole lithium and transfer it to a glove box under an inert atmosphere;

[0065] S2. Prepare a carbonate electrolyte in a glove box;

[0066] S3. Add 2-trifluoromethyl-4,5-dicyanoimidazole lithium to the carbonate electrolyte to obtain a carbonate sodium ion electrolyte.

[0067] In some embodiments, the inert atmosphere includes at least one of nitrogen, helium, neon, and argon.

[0068] In some embodiments, a method for preparing a carbonate sodium ion electrolyte comprises the following steps:

[0069] S1. First, the LiTDI powder was dried at 70°C in a vacuum environment for 12 h to remove any residual moisture, and then quickly transferred to a glove box with an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm in the glove box). Subsequent electrolyte preparation was carried out in this environment.

[0070] S2, then add appropriate amount of molecular sieves to various commercial carbonate electrolytes such as NaClO4 PC / FEC, NaClO4 EC / PC and NaClO4 EC / PC+FEC to remove trace amounts of water;

[0071] S3. Measure 2 to 4 g of the commercial carbonate electrolyte in S2 respectively. On the basis of the weighed mass, weigh a certain mass fraction of LiTDI additive and add it to a certain mass of carbonate sodium ion electrolyte. After standing for 12 hours, a clear and transparent modified electrolyte is obtained, namely, a carbonate sodium ion electrolyte.

[0072] In some embodiments, the commercial carbonate electrolyte is NaClO4 PC / FEC (ie, the sodium salt in the electrolyte is NaClO4, and the solvent is PC / FEC), wherein the concentration of NaClO4 is 0.75-1.25M, and the volume ratio of PC to FEC solvent is (0.5-2):1.

[0073] In some embodiments, the commercial carbonate electrolyte is NaClO4 EC / PC (ie, the sodium salt in the electrolyte is NaClO4, and the solvent is EC / PC), wherein the concentration of NaClO4 is 0.75-1.25M, and the volume ratio of EC to PC solvent is (0.5-1):1.

[0074] In some embodiments, the commercial carbonate electrolyte is NaClO4 EC / PC+PEC (i.e., the sodium salt in the electrolyte is NaClO4, the solvent is EC / PC, and it also includes a functional additive FEC), wherein NaClO4 and EC / PC form a mixture, the concentration of NaClO4 in the mixture is 0.75-1.25M, the volume ratio of EC and PC solvents is (0.5-1):1, and the mass of the functional additive FEC is 0.1-6% of the mass of the mixture formed by NaClO4 and EC / PC.

[0075] Based on the same inventive concept, the present invention also provides a use of the above-mentioned carbonate sodium ion electrolyte or the carbonate sodium ion electrolyte prepared by the above-mentioned preparation method in the preparation of a sodium ion battery.

[0076] Based on the same inventive concept, the present invention also provides a sodium ion battery, comprising the above-mentioned carbonate sodium ion electrolyte or the carbonate sodium ion electrolyte prepared by the above-mentioned preparation method.

[0077] The present invention innovatively and for the first time uses a new lithium salt, 2-trifluoromethyl-4,5-dicyanoimidazole lithium (LiTDI), as an additive in sodium ion electrolytes, to achieve a long-life, wide temperature range stable sodium metal full battery. It is characterized by the unique chemical composition of LiTDI, which can simultaneously regulate the solid-electrolyte interface (SEI) of the negative electrode and the positive electrode-electrolyte interface (CEI) structure of the Na3V2(PO4)3 positive electrode in the sodium metal battery, improve both the positive and negative electrodes, and ultimately achieve a significant improvement in the performance of the full battery. When cycling at high temperatures with more harsh environments and more serious side reactions, the modified electrolyte formula can still effectively improve the cycle stability of the sodium metal full battery.

[0078] The carbonate sodium ion electrolyte of the present invention and its preparation method and application, and sodium ion battery are further described below with specific examples. This section further illustrates the content of the present invention in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples are conventional means known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0079] Example 1

[0080] The embodiment of the present application provides a carbonate sodium ion electrolyte, including a carbonate electrolyte and a lithium salt additive;

[0081] Wherein, the lithium salt additive is 2-trifluoromethyl-4,5-dicyanoimidazole lithium;

[0082] The carbonate electrolyte includes NaClO4, propylene carbonate (PC), and fluoroethylene carbonate (FEC), the volume ratio of propylene carbonate (PC) to fluoroethylene carbonate (FEC) is 1:1, the concentration of NaClO4 in the carbonate electrolyte is 0.75M, and the mass of 2-trifluoromethyl-4,5-dicyanoimidazole lithium is 3% of the mass of the carbonate electrolyte;

[0083] The quality method of the carbonate sodium ion electrolyte comprises the following steps:

[0084] S1. First, the LiTDI powder was dried at 70°C in a vacuum environment for 12 h to remove any residual moisture, and then quickly transferred to a glove box with an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm in the glove box). Subsequent electrolyte preparation was carried out in this environment.

[0085] S2. Use a syringe to draw 5 mL of propylene carbonate (PC) solvent and transfer it to an aluminum bottle, then use another syringe to draw 5 mL of fluoroethylene carbonate (FEC) solvent and transfer it to the above aluminum bottle, mix the two appropriately to form a uniform mixed solvent, weigh 0.918 g of NaClO4 electrolyte salt and add it to the above mixed solvent, and after standing for 12 hours, obtain a clear and transparent commercial carbonate electrolyte 0.75 M NaClO4 PC / FEC (volume ratio 1:1, referred to as PF); add molecular sieves to the above electrolyte and let it stand for 12 hours to remove trace amounts of water therein;

[0086] S3. Measure 5 g of the commercial carbonate electrolyte in S2 after dehydration, add 0.15 g (mass fraction 3%) of LiTDI thereto, and after standing for 12 hours, obtain a clear and transparent modified electrolyte, which is a carbonate sodium ion electrolyte.

[0087] Example 2

[0088] The embodiment of the present application provides a carbonate sodium ion electrolyte, including a carbonate electrolyte and a lithium salt additive;

[0089] Wherein, the lithium salt additive is 2-trifluoromethyl-4,5-dicyanoimidazole lithium;

[0090] The carbonate electrolyte includes NaClO4, ethylene carbonate (EC), and propylene carbonate (PC), the volume ratio of propylene carbonate (PC) to ethylene carbonate (EC) is 1:1, the concentration of NaClO4 in the carbonate electrolyte is 1M, and the mass of 2-trifluoromethyl-4,5-dicyanoimidazole lithium is 5% of the mass of the carbonate electrolyte;

[0091] The quality method of the carbonate sodium ion electrolyte comprises the following steps:

[0092] S1. First, the LiTDI powder was dried at 70°C in a vacuum environment for 12 h to remove any residual moisture, and then quickly transferred to a glove box with an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm in the glove box). Subsequent electrolyte preparation was carried out in this environment.

[0093] S2. Place ethylene carbonate (EC) solvent on a 50°C hot plate to slowly melt, draw 5 mL of propylene carbonate (PC) solvent with a syringe and transfer it to an aluminum bottle, then quickly draw 5 mL of ethylene carbonate (EC) solvent with another syringe and transfer it to the above aluminum bottle, mix the two appropriately to a uniform mixed solvent, weigh 1.224 g of NaClO4 electrolyte salt and add it to the above mixed solvent, and after standing for 12 hours, obtain a clear and transparent commercial carbonate electrolyte 1M NaClO4 EC / PC (volume ratio 1:1); add an appropriate amount of molecular sieves to the above electrolyte and let it stand for 12 hours to remove trace amounts of water therein;

[0094] S3. Measure 5 g of the commercial carbonate electrolyte in S2 after dehydration, add 0.25 g (mass fraction 5%) of LiTDI thereto, and after standing for 12 hours, obtain a clear and transparent modified electrolyte, which is a carbonate sodium ion electrolyte.

[0095] Example 3

[0096] The embodiment of the present application provides a carbonate sodium ion electrolyte, including a carbonate electrolyte and a lithium salt additive;

[0097] Wherein, the lithium salt additive is 2-trifluoromethyl-4,5-dicyanoimidazole lithium;

[0098] The carbonate electrolyte includes NaClO4, a solvent and a functional additive;

[0099] The solvent includes ethylene carbonate (EC) and propylene carbonate (PC), and the volume ratio of propylene carbonate (PC) to ethylene carbonate (EC) is 1:1;

[0100] The functional additive is fluoroethylene carbonate (FEC);

[0101] The concentration of NaClO4 in the mixture formed by NaClO4 and the solvent is 1.2M, and the mass of the functional additive is 5% of the mass of the mixture formed by NaClO4 and the solvent;

[0102] The mass of 2-trifluoromethyl-4,5-dicyanoimidazole lithium is 3% of the mass of the carbonate electrolyte;

[0103] The quality method of the carbonate sodium ion electrolyte comprises the following steps:

[0104] S1. First, the LiTDI powder was dried at 70°C in a vacuum environment for 12 h to remove any residual moisture, and then quickly transferred to a glove box with an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm in the glove box). Subsequent electrolyte preparation was carried out in this environment.

[0105] S2, slowly melt ethylene carbonate (EC) solvent on a 50°C hot plate, first draw 5 mL of propylene carbonate solvent (PC) with a syringe and transfer it to an aluminum bottle, then quickly draw 5 mL of ethylene carbonate (EC) with another syringe and transfer it to the above aluminum bottle, mix the two appropriately to a uniform mixed solvent, weigh 1.470 g of NaClO4 electrolyte salt and add it to the above mixed solvent to obtain a mixture;

[0106] Add 5% of the total mass of the mixture to the mixture, and after standing for 12 hours, obtain a clear and transparent commercial carbonate electrolyte 1.2M NaClO4 EC / PC (volume ratio 1:1) + 5% FEC; add an appropriate amount of molecular sieves to the above electrolyte and stand for 12 hours to remove trace amounts of water;

[0107] S3. Measure 5 g of the commercial carbonate electrolyte in S2 after dehydration, add 0.15 g (mass fraction 3%) of LiTDI thereto, and after standing for 12 hours, obtain a clear and transparent modified electrolyte, which is a carbonate sodium ion electrolyte.

[0108] Comparative Example 1

[0109] This comparative example provides a carbonate sodium ion electrolyte, comprising NaClO4, propylene carbonate (PC), and fluoroethylene carbonate (FEC), wherein the volume ratio of propylene carbonate (PC) to fluoroethylene carbonate (FEC) is 1:1, and the concentration of NaClO4 in the carbonate electrolyte is 0.75M;

[0110] The quality method of the carbonate sodium ion electrolyte comprises the following steps:

[0111] S1. First, the LiTDI powder was dried at 70°C in a vacuum environment for 12 h to remove any residual moisture, and then quickly transferred to a glove box with an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm in the glove box). Subsequent electrolyte preparation was carried out in this environment.

[0112] S2. Use a syringe to draw 5 mL of propylene carbonate (PC) solvent and transfer it to an aluminum bottle, then use another syringe to draw 5 mL of fluoroethylene carbonate (FEC) solvent and transfer it to the above aluminum bottle, mix the two appropriately to a uniform mixed solvent, weigh 0.918 g of NaClO4 electrolyte salt and add it to the above mixed solvent, and after standing for 12 hours, obtain a clear and transparent commercial carbonate electrolyte 0.75 M NaClO4 PC / FEC (volume ratio 1:1, abbreviated as PF).

[0113] Performance Characterization

[0114] Figure 1 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were assembled into Na||Cu half-cells (the separator was polypropylene PP); the SEM images of the carbonate sodium ion electrolytes PF-LiTDI and PF deposited on the surface of the negative electrode sodium metal were tested respectively ( Figure 1 Top view), cross-sectional SEM image ( Figure 1 Section view) and EDS element analysis results ( Figure 1 Medium Na, F). Figure 1 PF represents the carbonate sodium ion electrolyte (PF) in Comparative Example 1, and PF+LiTDI additive represents the carbonate sodium ion electrolyte in Example 1.

[0115] Specifically, sodium ions in carbonate sodium ion electrolytes first find nucleation sites on the electrode surface, usually defects (such as steps, protrusions) or active sites on the surface. A uniform and dense SEI film is formed on the surface of sodium metal: the SEI film can effectively inhibit dendrite growth and limit the electric field enhancement at the tip.

[0116] from Figure 1 It can be seen that the sodium metal deposited by the carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 shows uniform surface distribution and a certain metallic luster, but with slight irregular deposition spots. The surface is smoother, the particles are dense and evenly distributed, and there is no obvious dendrite formation. The sodium element is evenly distributed, and the oxygen and carbon content is significantly reduced.

[0117] Figure 2 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were respectively assembled into Na|Cu half-cells (the separator was polypropylene PP), and the battery coulombic efficiency test was performed at 25°C and a current density of 1C. Figure 2PF represents the half-cell assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1, and PF-LiTDI additive represents the half-cell assembled with the carbonate sodium ion electrolyte in Example 1.

[0118] from Figure 2 It can be seen that the carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 may optimize the Na + The transmission path of ions reduces the energy loss of ions during transmission, thereby improving the Coulomb efficiency. After 80 cycles, the Coulomb efficiency is 96.1%; while in Comparative Example 1, the half-cell assembled with the carbonate sodium ion electrolyte (PF) has a Coulomb efficiency of only 66.4% after 60 cycles.

[0119] Figure 3 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were assembled into Na|Na symmetric batteries (the separator was polypropylene PP) for stability testing. Figure 3 PF represents the symmetrical battery assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1, and PF-LiTDI additive represents the symmetrical battery assembled with the carbonate sodium ion electrolyte in Example 1.

[0120] from Figure 3 It can be seen that the symmetrical battery assembled with the carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 can maintain a stable overpotential in a long cycle, indicating that it can effectively inhibit dendrites and side reactions. However, the symmetrical battery assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1 has a short circuit.

[0121] Figures 4-5 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were respectively assembled into Na|Cu half-cells (the separator was polypropylene PP), and the AC impedance spectra were measured when they were cycled for 2 and 200 cycles at 25°C. Figures 4-5 PF represents the half-cell assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1, and PF-LiTDI additive represents the half-cell assembled with the carbonate sodium ion electrolyte in Example 1.

[0122] from Figures 4-5 It can be seen that the use of the carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 significantly inhibits side reactions in long-term cycles, improves interface stability, significantly reduces the interface impedance between the electrode and the electrolyte, and is beneficial to the transmission of electrons and metal ions.

[0123] Figure 6 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were assembled into Na|NVP full batteries (the negative electrode was Na and the positive electrode was Na 3 V 2 (PO 4)3 ， The separator is polypropylene (PP), and the cycle stability test was carried out at 25°C with a current density of 1C (charged to 3.8V and discharged to 2.5V during the test). Figure 6 PF refers to the full battery assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1, and PF-LiTDI additive refers to the full battery assembled with the carbonate sodium ion electrolyte in Example 1.

[0124] from Figure 6 It can be seen that the LiTDI additive in the carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 effectively improves the interfacial stability of sodium metal and NVP positive electrode, reduces side reactions, and optimizes the sodium ion transport inside the battery; the full battery assembled with the carbonate sodium ion electrolyte in Example 1 has a discharge capacity retention rate of 88.1% after 1000 cycles at a current density of 1C at 25°C. However, the full battery assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1 has a discharge capacity retention rate of only 68.0% after 1000 cycles at a current density of 1C at 25°C.

[0125] Figure 7 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were assembled into Na|NVP full batteries (the negative electrode was Na and the positive electrode was Na 3 V 2 (PO 4)3 ， The separator is polypropylene (PP), and the cycle stability test was conducted at 25°C with a current density of 5C (charged to 3.8V and discharged to 2.5V during the test). Figure 7 PF refers to the full battery assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1, and PF-LiTDI additive refers to the full battery assembled with the carbonate sodium ion electrolyte in Example 1.

[0126] from Figure 7It can be seen that the carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 at 25°C, the LiTDI additive can improve the transport kinetics of sodium ions at a high rate of 5C, optimize the interface stability and electrochemical reaction process. Dendrite growth and irreversible loss of sodium metal, while improving the stability of the positive electrode NVP; the full battery assembled with the carbonate sodium ion electrolyte in Example 1 has a discharge capacity retention rate of 77.8% after 8000 cycles at a current density of 25°C and 5C. However, the full battery assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1 has a discharge capacity retention rate of only 21.4% after 8000 cycles at a current density of 25°C and 5C.

[0127] Figure 8 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were assembled into Na|NVP full batteries (the negative electrode was Na and the positive electrode was Na 3 V 2 (PO 4)3 ， The separator is polypropylene (PP), and the cycle stability test was conducted at 50°C with a current density of 1C (charged to 3.8V and discharged to 2.5V during the test). Figure 8 PF refers to the full battery assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1, and PF-LiTDI additive refers to the full battery assembled with the carbonate sodium ion electrolyte in Example 1.

[0128] from Figure 8 It can be seen that the carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 at 50°C, at a rate of 1C, LiTDI may reduce the electrolyte decomposition and side reactions at high temperature by stabilizing the decomposition products of the electrolyte. The decomposition of LiTDI produces the dendrite growth and irreversible loss of sodium metal, while improving the stability of the positive electrode NVP; the full battery assembled with the carbonate sodium ion electrolyte in Example 1 has a discharge capacity retention rate of 85.8% after 1000 cycles at a current density of 50°C and 1C. However, the full battery assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1 has a discharge capacity retention rate of only 66.0% after 1000 cycles at a current density of 50°C and 1C.

[0129] Fig. 9 The carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 and the carbonate sodium ion electrolyte (PF) in Comparative Example 1 were assembled into Na|NVP full batteries (the negative electrode was Na and the positive electrode was Na 3 V 2 (PO 4)3 ， The separator is polypropylene (PP), and the cycle stability test was conducted at 50°C with a current density of 5C (charged to 3.8V and discharged to 2.5V during the test). Fig. 9 PF refers to the full battery assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1, and PF-LiTDI additive refers to the full battery assembled with the carbonate sodium ion electrolyte in Example 1.

[0130] from Fig. 9 It can be seen that the capacity decay of the full battery assembled with the carbonate sodium ion electrolyte (PF-LiTDI) in Example 1 is significantly slowed down during the cycle, indicating that LiTDI suppresses the side reactions on the sodium metal surface and the irreversible loss of active sodium by optimizing the stability of the SEI film; the full battery assembled with the carbonate sodium ion electrolyte in Example 1 has a discharge capacity retention rate of 74.3% after 5000 cycles at a current density of 50°C and 5C. However, the discharge capacity retention rate of the full battery assembled with the carbonate sodium ion electrolyte (PF) in Comparative Example 1 is only 50.4% after 5000 cycles at a current density of 50°C and 5C.

[0131] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A carbonate sodium ion electrolyte, characterized in that: Including carbonate electrolyte and lithium salt additive; Wherein, the lithium salt additive is 2-trifluoromethyl-4,5-dicyanoimidazole lithium.

2. The carbonate sodium ion electrolyte according to claim 1, characterized in that The mass of the 2-trifluoromethyl-4,5-dicyanoimidazole lithium is 0.01-6% of the mass of the carbonate electrolyte.

3. The carbonate sodium ion electrolyte according to claim 1, characterized in that The carbonate electrolyte includes sodium salt and solvent; The sodium salt includes at least one of NaClO4, sodium hexafluorophosphate, sodium tetrafluoroborate, and sodium bis(fluorosulfonyl)imide; The solvent includes at least one of propylene carbonate, fluoroethylene carbonate and ethylene carbonate.

4. The carbonate sodium ion electrolyte according to any one of claims 1 to 3, characterized in that The carbonate electrolyte further includes a functional additive; The functional additive includes at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate and vinyl carbonate.

5. The carbonate sodium ion electrolyte according to any one of claims 1 to 3, characterized in that: The carbonate electrolyte includes sodium salt and solvent, and the solvent includes a mixture of propylene carbonate and fluoroethylene carbonate; The volume ratio of propylene carbonate to fluoroethylene carbonate is (0.5-2):1; The molar concentration of the sodium salt in the carbonate electrolyte is 0.75 to 1.25 M; Or, the carbonate electrolyte includes sodium salt and solvent, the solvent includes a mixture of propylene carbonate and ethylene carbonate; the volume ratio of ethylene carbonate to propylene carbonate is (0.5-1):1; The molar concentration of the sodium salt in the carbonate electrolyte is 0.75-1.25M.

6. The carbonate sodium ion electrolyte according to claim 4, characterized in that The carbonate electrolyte comprises sodium salt, solvent and functional additives; the solvent comprises a mixture of propylene carbonate and ethylene carbonate; the volume ratio of ethylene carbonate to propylene carbonate is (0.5-1):1; The sodium salt and the solvent form a mixture, the molar concentration of the sodium salt in the mixture is 0.75-1.25M, and the mass of the functional additive is 0.01-10% of the mass of the mixture.

7. The method for preparing a carbonate sodium ion electrolyte according to any one of claims 1 to 6, characterized in that: The following steps are involved: The carbonate sodium ion electrolyte is obtained by adding 2-trifluoromethyl-4,5-dicyanoimidazole lithium into the carbonate electrolyte.

8. The method for preparing a carbonate sodium ion electrolyte according to claim 7, characterized in that: The following steps are involved: After drying, the 2-trifluoromethyl-4,5-dicyanoimidazole lithium was transferred into a glove box under an inert atmosphere; A carbonate electrolyte is prepared in a glove box; 2-trifluoromethyl-4,5-dicyanoimidazole lithium is added into the carbonate electrolyte to obtain a carbonate sodium ion electrolyte.

9. Use of the carbonate sodium ion electrolyte according to any one of claims 1 to 6 or the carbonate sodium ion electrolyte prepared by the preparation method according to any one of claims 7 to 8 in preparing a sodium ion battery.

10. A sodium ion battery, characterized in that: The invention comprises the carbonate sodium ion electrolyte as claimed in any one of claims 1 to 6 or the carbonate sodium ion electrolyte prepared by the preparation method as claimed in any one of claims 7 to 8.

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