Electrolyte for capacitor and preparation method and application thereof
By adding a specific combination of inorganic and organic additives to the electrolyte, a stable SEI/CEI film is formed, which solves the problems of short cycle life and poor stability of sodium-ion capacitors under high voltage, and improves the high voltage cycle stability and energy density of sodium metal capacitors.
Patent Information
- Application Number
- CN202610035428.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-12
- Publication Date
- 2026-03-20
AI Technical Summary
Sodium-ion capacitors face challenges under high voltage, such as increased surface reactivity of activated carbon cathodes and instability of the double-layer structure, leading to short cycle life and poor stability. In addition, sodium metal capacitors also suffer from short cycle life and poor electrochemical stability.
A robust SEI/CEI film is formed by using a specific combination of inorganic and organic additives, including sodium tetrafluoroborate and vinylene carbonate, to regulate the structure of anionic and cationic solvent sheaths, improve interfacial stability and antioxidant properties, and is used in electrolytes.
Under high voltage conditions, it significantly improves the cycle stability and cycle life of sodium metal capacitors, and enhances the energy density and electrochemical stability of capacitors.
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Figure CN121709428A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of capacitor electrolyte technology, and more specifically, to an electrolyte for capacitors, its preparation method, and its application. Background Technology
[0002] With rapid societal development, global environmental pollution and energy crises are intensifying, and renewable energy sources (wind, solar, etc.) face challenges such as intermittency and instability. Currently, coordinating energy transition, building a clean energy system, and achieving sustainable development are urgently needed. Although lithium-ion batteries have achieved widespread commercial application, the uneven geographical distribution of lithium resources keeps their cost high. Sodium-ion batteries and sodium-ion capacitors, as novel energy storage systems, are considered the most promising alternatives to lithium-ion batteries due to their low cost and the widespread global distribution of sodium resources. However, sodium-ion batteries often use excessive metal oxides in their cathodes, leading to higher costs, and their power density is limited by electrode reaction kinetics. Compared to sodium-ion batteries, sodium-ion capacitors, with their low cost, environmental friendliness, high power density, long lifespan, and impressive energy density, have become a new generation of energy storage technology, filling the gap between lithium-ion and sodium-ion batteries in the energy storage field.
[0003] Currently, the energy density of sodium-ion capacitors is lower than that of sodium-ion batteries, because the energy density of a capacitor is E = 1 / 2CV. 2 And since E is proportional to V 2 Widening the voltage window is crucial for improving the energy density of sodium-ion capacitors, and this voltage window is primarily related to the electrolyte. Currently, the oxidation decomposition voltage of sodium-ion capacitor electrolytes is low (≤ 4.0V), significantly limiting their energy density. Current research and design of electrolytes for sodium-ion batteries largely focus on solvation structure design and electrode-electrolyte interface modification; however, due to the complexity of the electrolyte and the difficulty in effectively analyzing interfacial reaction processes, research on high-voltage electrolytes for sodium metal capacitors is extremely limited. Sodium-ion capacitors at high voltages mainly face challenges such as increased surface reactivity of the activated carbon cathode; increased ion density on the pore surface leading to side reactions; and instability of the double-layer energy storage structure.
[0004] Meanwhile, due to the high specific capacity of metallic sodium (1165 mAh g⁻¹), -1 Sodium metal is considered the most promising anode material for improving the energy density of sodium-ion capacitors due to its unique advantages, including low redox potential (-2.71 V compared to the standard hydrogen electrode). We attempted to construct sodium metal capacitors to improve the energy density of sodium-ion capacitors. However, sodium metal capacitors also face problems such as short cycle life and poor electrochemical stability due to the easy formation of fragile SEI on the sodium metal surface and the uncontrolled growth of sodium dendrites.
[0005] Therefore, the development of high-voltage electrolytes is extremely important for improving the energy density of sodium metal capacitors and promoting their commercialization. Summary of the Invention
[0006] To address the problem of severe surface reactions and unstable double-layer structure in activated carbon cathodes under high voltage (>4.3V) conditions, resulting in short cycle life and poor stability of capacitors, this invention provides an electrolyte for capacitors that enables sodium metal capacitors to exhibit excellent cycle stability under high voltage conditions.
[0007] To achieve the above objectives, the technical solution of the present invention is as follows:
[0008] An electrolyte for capacitors, the electrolyte comprising a sodium salt, an organic solvent, and additives, the additives comprising inorganic and organic additives; the inorganic additives comprising at least one of sodium tetrafluoroborate (NaBF4) and sodium difluorooxalate borate (NaDFOB); the organic additives comprising at least one of vinylene carbonate (VC), 1,3-propanesulfonate lactone (1,3-PS), vinyl sulfate (DTD), tris(2,2,2-trifluoroethyl) phosphite (TFEP), ethoxy(pentafluoro)cyclotriphosphazene (EFPN), methyl nonafluorobutyl ether (MFE), biphenyl (BP), tris(trimethylsilyl) phosphite (TMSPi), and trimethoxy(perfluorophenyl)silane (TPFS).
[0009] In some embodiments, the mass ratio of the inorganic additive to the organic additive in the electrolyte is 0.1-0.5:1.
[0010] In some embodiments, the concentration of the inorganic additive in the electrolyte is 0.1-1 wt%; and the concentration of the organic additive is 0.2-2 wt%.
[0011] In some embodiments, the concentration of sodium salt in the electrolyte is 0.8-1.2 mol / L.
[0012] In some embodiments, the sodium salt includes at least one of sodium perchlorate (NaClO4), sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium trifluoromethanesulfonate (NaOTf).
[0013] In some embodiments, the organic solvent includes at least two selected from propylene carbonate (PC), fluoroethylene carbonate (FEC), trifluoromethyl methyl ethyl carbonate (FEMC), difluoroethylene carbonate (DFEC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTME), and methyl nonafluorobutyl ether (MNE). Preferably, the organic solvent is a mixture of FEC and FEMC, which, when used as a solvent for the electrolyte, has advantages such as high voltage resistance, low melting point, and good high-temperature stability. Fluorine-containing compounds can form a more robust SEI / CEI film composed of fluorinated substances / polymers, thereby preventing possible side reactions between the electrolyte and the positive electrode surface. Further, combining small amounts of different multifunctional sodium salt additives and small organic molecule additives to regulate the anionic and cationic solvent sheath structures promotes an interfacially stable double-layer energy storage structure, constructing a stable CEI film that facilitates anion passage, and improving interfacial stability and antioxidant properties.
[0014] The present invention also provides a method for preparing an electrolyte for a capacitor according to any of the above embodiments, the method comprising the following steps:
[0015] S1. In a glove box under an argon atmosphere, with H2O < 0.1 ppm and O2 < 0.1 ppm, weigh an appropriate amount of sodium salt and dissolve it in the organic solvent and mix thoroughly to obtain a base electrolyte with a concentration of 0.8-1.2 mol / L.
[0016] S2. Add the additive to the base electrolyte and mix evenly to obtain the capacitor electrolyte.
[0017] The present invention also provides a sodium metal capacitor, wherein the sodium metal capacitor includes the above-described electrolyte for capacitors.
[0018] In some embodiments, the sodium metal capacitor further includes a positive electrode comprising activated carbon.
[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0020] This invention improves the cycle stability of the electrolyte by adding a specific combination of inorganic and organic additives to the electrolyte. When used in sodium metal capacitors, the capacitors can maintain excellent cycle stability and cycle life even when used in high voltage (>4.3V) environments. Attached Figure Description
[0021] Figure 1 The diagram shows the cycle performance of the electrolyte 1 sodium metal battery capacitor in Embodiment 1 of the present invention.
[0022] Figure 2 The diagram shows the cycle performance of the electrolyte 2 sodium metal battery capacitor in Example 2 of this invention;
[0023] Figure 3 The diagram shows the cycle performance of the electrolyte 3 sodium metal battery capacitor in Example 3 of this invention;
[0024] Figure 4 This is a circuit diagram of the electrolyte 4 sodium metal battery capacitor in Example 4 of the present invention;
[0025] Figure 5 This is a charge-discharge curve of the electrolyte 4 sodium metal battery capacitor of Example 4 of the present invention;
[0026] Figure 6 The diagram shows the cycle performance of the Na||Na symmetric battery with electrolyte 1 in Example 1 of this invention.
[0027] Figure 7 The diagram shows the cycle performance of the 4Na||Na symmetric battery with electrolyte 4 in Example 4 of the present invention. Detailed Implementation
[0028] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0030] Example 1
[0031] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), weigh an appropriate amount of sodium hexafluorophosphate and dissolve it in an organic solvent and mix thoroughly to obtain a base electrolyte with a concentration of 1 M; wherein, the organic solvent is a mixed solvent of fluoroethylene carbonate and trifluoromethyl methyl carbonate = 1:1 (v:v);
[0032] Electrolyte 1 is obtained by adding no additives to the base electrolyte.
[0033] Example 2
[0034] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), weigh an appropriate amount of sodium hexafluorophosphate and dissolve it in an organic solvent and mix thoroughly to obtain a base electrolyte with a concentration of 1 M; wherein, the organic solvent is a mixed solvent of fluoroethylene carbonate and trifluoromethyl methyl carbonate = 1:1 (v:v);
[0035] Sodium difluorooxalate borate was added to the base electrolyte and stirred until homogeneous to obtain electrolyte 2; the concentration of the additive in electrolyte 2 was 0.28 wt%.
[0036] Example 3
[0037] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), weigh an appropriate amount of sodium hexafluorophosphate and dissolve it in an organic solvent and mix thoroughly to obtain a base electrolyte with a concentration of 1 M; wherein, the organic solvent is a mixed solvent of fluoroethylene carbonate and trifluoromethyl methyl carbonate = 1:1 (v:v);
[0038] Additive trimethoxy(perfluorophenyl)silane was added to the base electrolyte and stirred until homogeneous to obtain electrolyte 3; the concentration of additive in electrolyte 3 was 1 wt%.
[0039] Example 4
[0040] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), weigh an appropriate amount of sodium hexafluorophosphate and dissolve it in an organic solvent and mix thoroughly to obtain a base electrolyte with a concentration of 1 M; wherein, the organic solvent is a mixed solvent of fluoroethylene carbonate and trifluoromethyl methyl carbonate = 1:1 (v:v);
[0041] Additives trimethoxy(perfluorophenyl)silane and sodium difluorooxalate borate were added to the base electrolyte and stirred evenly to obtain electrolyte 4; in electrolyte 4, the concentration of trimethoxy(perfluorophenyl)silane was 1 wt% and the concentration of sodium difluorooxalate borate was 0.28 wt%.
[0042] The relevant performance tests were conducted on the above electrolytes 1-4, as detailed below:
[0043] 1. Cyclic performance test of sodium metal capacitors
[0044] Na‖AC capacitors were assembled using electrolytes 1-4, with sodium metal as the negative electrode and activated carbon (AC) as the positive electrode. Constant current charge-discharge tests were performed on the assembled full cells using a blue-light testing device. The charge-discharge voltage window was set to 2-4.5V, and the current density was 2 A / g. The test results are as follows: Figures 1-5 As shown.
[0045] in, Figure 1 The diagram shows the cycle performance of the sodium metal battery capacitor with electrolyte 1 in Example 1. Figure 2 The diagram shows the cycle performance of the electrolyte 2 sodium metal battery capacitor in Example 2; Figure 3 The figure shows the cycle performance of the electrolyte 3 sodium metal battery capacitor in Example 3; Figure 4 The figure shows the cycle performance of the electrolyte 4 sodium metal battery capacitor in Example 4; Figure 5 This is a charge-discharge curve of the electrolyte 4 sodium metal battery capacitor in Example 4.
[0046] like Figures 1-5 As shown, the sodium metal capacitor using electrolyte 4 retained 81.9% of its capacity after 4000 cycles, while the sodium metal capacitor using electrolyte 1 retained 49.4% after 3000 cycles, the sodium metal capacitor using electrolyte 2 retained 63.6% after 3000 cycles, and the sodium metal capacitor using electrolyte 3 retained 76.3% after 3000 cycles. This demonstrates that the electrolyte with the additives of this invention exhibits higher capacity retention and better cycle stability at the same number of cycles.
[0047] 2. Symmetrical battery performance test
[0048] Cut sodium metal sheets were used as positive and negative electrodes to assemble a Na||Na symmetric cell for constant current deposition / stripping testing. The performance of the assembled symmetric cell was tested using a blue electrode testing device. The test results are as follows: Figures 6-7 As shown.
[0049] in, Figure 6 The diagram shows the cycle performance of the Na||Na symmetric battery with electrolyte 1 in Example 1. Figure 7 The diagram shows the cycle performance of the 4Na||Na symmetric battery with electrolyte 4 in Example 4.
[0050] like Figure 6 and Figure 7 As shown, the sodium-symmetric battery assembled with control electrolyte 1 exhibited a soft short circuit after 270 hours of cycling; the polarization voltage of the sodium-symmetric battery assembled with electrolyte 1 only began to increase after 200 hours of cycling; and the sodium-symmetric battery assembled with electrolyte 4 showed no significant polarization after 800 hours of cycling. Therefore, adding a small amount of specific additives to the electrolyte is beneficial for stabilizing the sodium metal anode and improving the cycle stability of sodium metal capacitors.
[0051] Therefore, the present invention, by employing the above-mentioned high-voltage sodium metal capacitor electrolyte and its preparation method, can effectively solve the problems of short cycle life and poor stability of existing sodium batteries, and improve the cycle life and cycle stability of sodium metal capacitor electrolyte.
[0052] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0053] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.
Claims
1. An electrolyte for capacitors, characterized in that, The mixture includes sodium salts, organic solvents, and additives, wherein the additives include inorganic and organic additives; the inorganic additives include at least one of sodium tetrafluoroborate and sodium difluorooxalate borate; and the organic additives include at least one of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, tris(2,2,2-trifluoroethyl) phosphite, ethoxy(pentafluoro)cyclotriphosphazene, methyl nonafluorobutyl ether, biphenyl, tris(trimethylsilyl) phosphite, and trimethoxy(perfluorophenyl)silane.
2. The electrolyte for capacitors according to claim 1, characterized in that, In the electrolyte, the mass ratio of the inorganic additive to the organic additive is 0.1-0.5:
1.
3. The electrolyte for capacitors according to claim 1, characterized in that, In the electrolyte, the concentration of the inorganic additive is 0.1-1 wt%; and the concentration of the organic additive is 0.2-2 wt%.
4. The electrolyte for capacitors according to any one of claims 1-3, characterized in that, The concentration of sodium salt in the electrolyte is 0.8-1.2 mol / L.
5. The electrolyte for capacitors according to any one of claims 1-3, characterized in that, The sodium salt includes at least one of sodium perchlorate, sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium trifluoromethanesulfonate.
6. The electrolyte for capacitors according to any one of claims 1-3, characterized in that, The organic solvent includes at least two of propylene carbonate, fluoroethylene carbonate, trifluoromethyl methyl carbonate, difluoroethylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, and methyl nonafluorobutyl ether.
7. The method for preparing the electrolyte for capacitors according to any one of claims 1-6, characterized in that, Includes the following steps: S1. In a glove box under an argon atmosphere, with H2O < 0.1 ppm and O2 < 0.1 ppm, weigh an appropriate amount of sodium salt and dissolve it in the organic solvent and mix thoroughly to obtain a base electrolyte with a concentration of 0.8-1.2 mol / L. S2. Add the additive to the base electrolyte and mix evenly to obtain the capacitor electrolyte.
8. A sodium metal capacitor, characterized in that, Includes the electrolyte for capacitors as described in any one of claims 1-6.
9. The sodium metal capacitor according to claim 8, characterized in that, The capacitor also includes a positive electrode, which comprises activated carbon.