Siloxane-based hybrid capacitor electrolyte with low lithium salt concentration, wide temperature range and high voltage as well as preparation method and application of siloxane-based hybrid capacitor electrolyte

Abstract

The invention discloses a siloxane-based hybrid capacitor electrolyte with low lithium salt concentration, wide temperature range and high voltage and a preparation method and application thereof, and the siloxane-based hybrid capacitor electrolyte comprises a siloxane organic solvent, an organic lithium salt and an inorganic lithium salt, wherein the siloxane organic solvent is one or two of a functional siloxane solvent and a functional siloxane solvent. According to the siloxane-based hybrid capacitor electrolyte, the advantages of excellent thermal stability and electrochemical stability of a siloxane solvent, high lithium ion conductivity and the like are fully utilized, the advantages of weak solvation ability, good interface stability and the like of the siloxane solvent are exerted, and intrinsic desolvation kinetics and interface charge and mass transfer kinetics are optimized from the atomic level; the negative ion adsorption sequence is optimized by further combining low lithium salt concentration and an organic-inorganic lithium salt coupling strategy, and good operation of the hybrid energy storage capacitor under the working conditions of wide temperature range and high voltage is ensured on the premise of realizing low preparation cost.

Description

Technical Field

[0001] The present invention belongs to the field of hybrid capacitor energy storage, and relates to a hybrid capacitor electrolyte, and specifically to a siloxane-based hybrid capacitor electrolyte with low lithium salt concentration, wide temperature range, and high voltage, and a preparation method and application thereof. Background Art

[0002] The development of new energy storage technologies and equipment with high specific energy, high power, long life, and wide temperature range is of great significance for high-proportion renewable energy generation, smoothing power fluctuations of new energy grid-connected, providing instantaneous power, and improving the power supply capacity of backup power. Although traditional lithium-ion batteries have high energy density, they have obvious shortcomings in high-power applications and rapid charging and discharging; although supercapacitors have high power density and long cycle life, their low energy density cannot meet high specific energy requirements. Hybrid capacitor energy storage technology combines the advantages of supercapacitors and electrochemical batteries. While improving the energy density of the energy storage system, it can achieve higher power density, longer cycle life and higher safety performance. It is one of the effective solutions recognized by academia and industry.

[0003] At present, commercial hybrid capacitor electrolytes are carbonate electrolytes. Carbonate solvents have high melting points, and the desolvation kinetics of lithium ions are slow at low temperatures, which seriously affects the rate performance of hybrid capacitors; under high temperature and high pressure, the poor thermal stability and electrochemical stability of carbonate solvents will lead to continuous decomposition of the solvent, which will cause the electrode / electrolyte interface to be continuously broken and reshaped, resulting in serious side reactions, leading to a continuous increase in the internal resistance of the capacitor, which in turn seriously affects the electrochemical performance of the hybrid capacitor. Compared with traditional carbonate solvents, siloxane solvents have a wide temperature range and can still remain in a liquid state at -80 degrees Celsius, which is conducive to the rapid migration of lithium ions; the highly electron-aggregated C=O in ethylene carbonate has a strong ion-dipole interaction with lithium ions, which seriously limits the desolvation kinetics of lithium ions, while the polar covalent bonding between oxygen atoms and silicon atoms in siloxane solvents can effectively disperse the electron aggregation on -O-, thereby showing a weaker ion-dipole interaction and accelerating the desolvation kinetics of lithium ions at the atomic scale. At the same time, siloxane can construct a silicon-rich electrode / electrolyte interface in situ on the electrode surface, ensuring the stable operation of the hybrid capacitor energy storage device under extreme conditions such as high temperature and high pressure. Summary of the invention

[0004] Based on the above technical background, the present invention provides a low lithium salt concentration, wide temperature range, high voltage siloxane-based hybrid capacitor electrolyte and its preparation method and application. The siloxane-based hybrid capacitor electrolyte fully utilizes the advantages of siloxane solvent thermal stability, excellent electrochemical stability and high lithium ion conductivity, and gives full play to the advantages of siloxane solvent weak solvation ability and good interface stability, optimizes the intrinsic desolvation kinetics and interface charge and mass transfer kinetics from the atomic level, and further combines low lithium salt concentration and organic-inorganic lithium salt coupling strategy to optimize the anion adsorption sequence, and ensures the good operation of the hybrid energy storage capacitor under wide temperature range and high voltage conditions under the premise of achieving low preparation cost.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A siloxane-based hybrid capacitor electrolyte with low lithium salt concentration, wide temperature range and high voltage, comprising a siloxane organic solvent, an organic lithium salt and an inorganic lithium salt, wherein:

[0007] The siloxane organic solvent is one or both of a functionalized siloxane solvent and a functionalized siloxane solvent;

[0008] The siloxane solvent is one or more of trimethylsiloxane, triethylsiloxane, propyltrimethoxysilane, propyltriethoxysilane, vinyltrimethoxysilane and vinyltriethoxysilane;

[0009] The functionalized siloxane solvent is one or more of 3-mercaptopropyltriethoxysilane, isocyanatepropyltriethoxysilane, and 3-aminopropyltriethoxysilane;

[0010] The inorganic lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium nitrate;

[0011] The organic lithium salt is one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorooxalatoborate), and lithium bis(fluorosulfonyl)imide;

[0012] The molar ratio of the organic lithium salt to the inorganic lithium salt is 0.1-0.5:0.01-0.5;

[0013] In the siloxane-based hybrid capacitor electrolyte, the total concentration of the organic lithium salt and the inorganic lithium salt is 0.1 to 0.5 mol / L.

[0014] A method for preparing the above-mentioned low lithium salt concentration, wide temperature range, and high voltage siloxane-based hybrid capacitor electrolyte comprises the following steps:

[0015] Step 1, adding siloxane solvent, functionalized siloxane solvent, organic lithium salt, and inorganic lithium salt, and stirring until the mixed solution is clear and transparent;

[0016] Step 2: Add molecular sieves to ensure that the molecular sieves are fully in contact with the solution to promote the adsorption of water and impurities, and obtain a siloxane-based hybrid capacitor electrolyte, wherein:

[0017] The mass ratio of the molecular sieve to the siloxane-based hybrid capacitor electrolyte is 1:5-15.

[0018] The above-mentioned low lithium salt concentration, wide temperature range, and high voltage siloxane-based hybrid capacitor electrolyte can be applied to a hybrid lithium ion capacitor, wherein the hybrid capacitor includes a positive electrode material, a negative electrode material, and a separator, wherein:

[0019] A siloxane-based hybrid capacitor electrolyte is provided between the positive electrode material and the negative electrode material;

[0020] The positive electrode material is not limited to coal-based porous carbon, activated carbon, commercial supercapacitor carbon, lithium iron phosphate, ternary positive electrode materials, etc. Commercial hybrid capacitor positive electrode materials can be used in the present invention;

[0021] The negative electrode material is not limited to titanium-based oxides, niobium-based oxides, soft carbon, hard carbon, and commercial hybrid capacitor negative electrode materials can be used in the present invention;

[0022] The separator includes but is not limited to polypropylene separator, cellulose separator, glass fiber separator, and commercial separators can be used in the present invention.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. Siloxane solvents have good electrochemical stability, thermal stability and weak solvation ability, which can effectively weaken the ion-dipole effect and accelerate the desolvation process of lithium ions at low temperatures.

[0025] 2. Functionalized siloxane solvents can construct inorganic-rich electrode / electrolyte interfaces in situ, enabling fast interfacial transport kinetics to achieve high-rate performance.

[0026] 3. The lithium salt design strategy of organic-inorganic composite lithium salts can optimize the anion adsorption order and meet the diverse needs under a wide temperature range and high voltage.

[0027] 4. The siloxane-based hybrid capacitor electrolyte of the present invention fully utilizes the advantages of siloxane solvents such as high lithium salt solubility, extremely low freezing point and high thermal stability, ensuring that the hybrid capacitor electrolyte can work efficiently within a wide temperature range. At the same time, some functionalized siloxane solvents (thiol, cyano and amino) are introduced to optimize the electrolyte solvation structure while constructing a stable electrode / electrolyte interface with high ion flux and high Young's modulus on the positive and negative electrode surfaces, thereby ensuring that the hybrid capacitor has excellent cycle stability and high-power working capability.

[0028] 5. The siloxane-based hybrid capacitor electrolyte of the present invention has low cost, simple preparation, and good large-scale application scenarios;

[0029] 6. The siloxane-based hybrid capacitor electrolyte of the present invention uses a high-stability siloxane electrolyte and a polyvalent lithium salt in a coordinated manner, so that the electrolyte not only has good low-temperature performance and fast charging performance, but also exhibits good rate capability under high temperature and high pressure conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a linear scan graph of carbonate electrolyte;

[0031] Figure 2 It is the linear scanning diagram of siloxane electrolyte;

[0032] Figure 3 is the cycle performance diagram;

[0033] Figure 4 The charge and discharge curves at different current densities. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further described below in conjunction with the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0035] Example 1

[0036] The embodiment provides a siloxane-based hybrid capacitor electrolyte with low lithium salt concentration, wide temperature range and high voltage. The siloxane-based hybrid capacitor electrolyte uses lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate as lithium salts, trimethylsiloxane and 3-mercaptopropyltriethoxysilane as solvents, the molar ratio of lithium bis(fluorosulfonyl)imide to lithium tetrafluoroborate is 2:0.3, the volume ratio of trimethylsiloxane to 3-mercaptopropyltriethoxysilane is 8:2, and the total concentration of lithium salt is 0.23 mol / L. The mixed lithium salt of lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate is added to the mixed solvent of trimethylsiloxane and 3-mercaptopropyltriethoxysilane, and stirred at a speed of 100 r / min for 0.5 hours until the mixed solution is clear and transparent, and 10% (mass fraction) of molecular sieves is added, and water is further removed to obtain an electrolyte that can work at -50 degrees Celsius.

[0037] Example 2

[0038] The present embodiment provides a siloxane-based hybrid capacitor electrolyte with low lithium salt concentration, wide temperature range and high voltage. The siloxane-based hybrid capacitor electrolyte uses lithium bis(fluorosulfonyl)imide, lithium bis(fluorooxalate)borate and lithium tetrafluoroborate as lithium salts, 3-aminopropyltriethoxysilane and 3-mercaptopropyltriethoxysilane as solvents, the molar ratio of lithium bis(fluorosulfonyl)imide, lithium bis(fluorooxalate)borate and lithium tetrafluoroborate is 1:1:0.5, the volume ratio of 3-aminopropyltriethoxysilane and 3-mercaptopropyltriethoxysilane is 1:1, and the total lithium salt concentration is 0.25 mol / L. A mixed lithium salt of lithium bis(fluorosulfonyl)imide, lithium bis(fluorooxalatoborate) and lithium tetrafluoroborate is added to a mixed solvent of 3-aminopropyltriethoxysilane and 3-mercaptopropyltriethoxysilane, and stirred at a speed of 150 r / min for 1 hour until the mixed solution becomes clear and transparent, and 10% (mass fraction) molecular sieve is added to further remove water to obtain an electrolyte that can operate at -40 to +80 degrees Celsius.

[0039] Example 3

[0040] The present embodiment provides a siloxane-based hybrid capacitor electrolyte with low lithium salt concentration, wide temperature range and high voltage. The siloxane-based hybrid capacitor electrolyte uses lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorooxalate)borate and lithium tetrafluoroborate as lithium salts, uses isocyanatepropyltriethoxysilane, 3-aminopropyltriethoxysilane and 3-mercaptopropyltriethoxysilane as solvents, the molar ratio of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorooxalate)borate and lithium tetrafluoroborate is 9:1:1, the volume ratio of isocyanatepropyltriethoxysilane, 3-aminopropyltriethoxysilane and 3-mercaptopropyltriethoxysilane is 8:1:1, and the total lithium salt concentration is 0.33 mol / L. A mixed lithium salt of bis(trifluoromethylsulfonyl)imide, lithium difluorooxalatoborate and lithium tetrafluoroborate is added to a mixed solvent of isocyanatepropyltriethoxysilane, 3-aminopropyltriethoxysilane and 3-mercaptopropyltriethoxysilane, and stirred at a speed of 200 r / min for 2 hours until the mixed solution becomes clear and transparent, and 10% (mass fraction) molecular sieves are added to further remove water to obtain an electrolyte that can operate at a high voltage of 4.6V.

[0041] Figure 3 is the cycle performance diagram of the electrolyte in this embodiment, Figure 3 It can be seen that the electrolyte has good cycle stability. Figure 4 is the charge and discharge curve of the electrolyte under different current densities in this embodiment, Figure 4 It can be seen that the electrolyte has good high-rate charge and discharge capabilities.

[0042] Example 4

[0043] This embodiment provides a siloxane-based hybrid capacitor electrolyte with low lithium salt concentration, wide temperature range, and high voltage. The siloxane-based hybrid capacitor electrolyte uses lithium bis(trifluoromethylsulfonyl)imide and lithium bis(fluorooxalate)borate as lithium salts, and uses isocyanatepropyltriethoxysilane and 3-aminopropyltriethoxysilane as solvents. The molar ratio of lithium bis(trifluoromethylsulfonyl)imide to lithium bis(fluorooxalate)borate is 9:1, the volume ratio of isocyanatepropyltriethoxysilane to 3-aminopropyltriethoxysilane is 9:1, and the total lithium salt concentration is 0.5 mol / L. A mixed lithium salt of lithium bis(trifluoromethylsulfonylimide) and lithium bis(fluorooxalatoborate) is added to a mixed solvent of triethoxypropylisocyanatesilane and 3-aminopropyltriethoxysilane, and stirred at a speed of 300 r / min for 2 hours until the mixed solution becomes clear and transparent, and 10% (mass fraction) molecular sieve is added to further remove water to obtain an electrolyte that can operate at 80 degrees Celsius and a high voltage of 4.6V.

[0044] Example 5

[0045] The present embodiment provides a low lithium salt concentration, low temperature resistant siloxane-based hybrid capacitor electrolyte, wherein the siloxane-based hybrid capacitor electrolyte uses lithium bis(fluorosulfonyl)imide and lithium bis(fluorooxalate)borate as lithium salts and trimethylsiloxane as solvent. The molar ratio of lithium bis(fluorosulfonyl)imide to lithium bis(fluorooxalate)borate is 15:1, and the total concentration of lithium salt is 0.32 mol / L. Add the mixed lithium salt of lithium bis(fluorosulfonyl)imide and lithium bis(fluorooxalate)borate to the trimethylsiloxane solvent, stir at a speed of 200 r / min for 2 hours until the mixed solution is clear and transparent, add 10% (mass fraction) molecular sieves, and further remove water to obtain an electrolyte that can work at -60 degrees Celsius.

[0046] Example 6

[0047] A wide temperature range hybrid capacitor was assembled using titanium niobate (TNO) as the negative electrode, coal-based porous carbon as the positive electrode, and the electrolyte in Example 3 as the hybrid capacitor electrolyte.

[0048] Comparative Example 1

[0049] This comparative example provides a commercial carbonate electrolyte, wherein 1 mol / L lithium hexafluorophosphate is dissolved in ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, wherein the volume ratio of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate is 1:1:1. A hybrid capacitor is prepared using the electrolyte.

[0050] Figure 1 The electrochemical window of commercial carbonate electrolytes. Figure 2 This is the electrochemical window of the electrolyte in Example 4. By comparison, it can be clearly found that the siloxane-based electrolyte has good electrochemical stability.

Claims

1. A siloxane-based hybrid capacitor electrolyte with low lithium salt concentration, wide temperature range and high voltage, characterized in that The siloxane-based hybrid capacitor electrolyte includes a siloxane organic solvent, an organic lithium salt, and an inorganic lithium salt, wherein: the siloxane organic solvent is one or both of a functionalized siloxane solvent and a functionalized siloxane solvent; the molar ratio of the organic lithium salt to the inorganic lithium salt is 0.1-0.5:0.01-0.5, and the total concentration of the organic lithium salt and the inorganic lithium salt is 0.1-0.5 mol / L.

2. The low lithium salt concentration, wide temperature range, high voltage siloxane-based hybrid capacitor electrolyte according to claim 1, characterized in that The siloxane solvent is one or more of trimethylsiloxane, triethylsiloxane, propyltrimethoxysilane, propyltriethoxysilane, vinyltrimethoxysilane and vinyltriethoxysilane.

3. The low lithium salt concentration, wide temperature range, high voltage siloxane-based hybrid capacitor electrolyte according to claim 1, characterized in that The functionalized siloxane solvent is one or more of 3-mercaptopropyltriethoxysilane, isocyanatepropyltriethoxysilane and 3-aminopropyltriethoxysilane.

4. The low lithium salt concentration, wide temperature range, high voltage siloxane-based hybrid capacitor electrolyte according to claim 1, characterized in that The inorganic lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate and lithium nitrate.

5. The low lithium salt concentration, wide temperature range, high voltage siloxane-based hybrid capacitor electrolyte according to claim 1, characterized in that The organic lithium salt is one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorooxalatoborate), and lithium bis(fluorosulfonyl)imide.

6. A method for preparing a low lithium salt concentration, wide temperature range, and high voltage siloxane-based hybrid capacitor electrolyte according to any one of claims 1 to 5, characterized in that The method comprises the following steps: Step 1, adding siloxane solvent, functionalized siloxane solvent, organic lithium salt, and inorganic lithium salt, and stirring until the mixed solution is clear and transparent; Step 2: adding molecular sieves to ensure that the molecular sieves are fully in contact with the solution to promote the adsorption of water and impurities, thereby obtaining a siloxane-based hybrid capacitor electrolyte.

7. The method for preparing a low lithium salt concentration, wide temperature range, and high voltage siloxane-based hybrid capacitor electrolyte according to claim 6, characterized in that The mass ratio of the molecular sieve to the siloxane-based hybrid capacitor electrolyte is 1:5-15.

8. Use of the low lithium salt concentration, wide temperature range, and high voltage siloxane-based hybrid capacitor electrolyte according to any one of claims 1 to 5 in a hybrid lithium ion capacitor.

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