Proton type electrolyte based on strong solvation weakening strategy for fluorine ion battery and application of proton type electrolyte

Abstract

The invention belongs to the technical field of new energy, and particularly relates to a proton type electrolyte based on a strong solvation weakening strategy for a fluorine ion battery and application of the proton type electrolyte. Aiming at the technical problems of poor reaction kinetics and electrochemical reversibility of the existing fluorine ion battery, the invention provides the protic electrolyte based on the strong solvation weakening strategy for the fluorine ion battery, and the protic electrolyte consists of fluorine ion salt, a solvation regulator containing a hydroxyl or amino structure and a protic solvent. Through the solvation regulator based on hydrogen bond interaction, excessive solvation of a protic solvent to fluorine ions is weakened, and reaction kinetics and reversibility are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy, and relates to a liquid electrolyte for a high-performance room-temperature secondary fluoride ion battery, and specifically relates to a protonic electrolyte for a fluoride ion battery based on a strong solvation weakening strategy and its application. Background Art

[0002] Achieving the energy electrification of key industries such as transportation and aviation is an important measure to address the depletion of fossil fuels and the climate crisis. However, commercial lithium-ion batteries still cannot meet the energy density requirements of such a large-scale industrial application. Moreover, with the commercial development and application of lithium batteries for decades, the depletion problem of lithium resources has emerged year by year, directly affecting the development and cost of related chemicals. Therefore, developing a new battery chemical system with high specific energy and relatively low cost has great industrial and academic value.

[0003] Different from lithium-ion shuttle batteries, the valence of lithium ions changes when they shuttle back and forth between the negative electrodes. For fluoride ion batteries, the shuttling of fluoride ions between the positive and negative electrodes does not produce a change in valence state, but only plays a role in balancing charges.

[0004] Although belonging to the same high-specific-energy battery system based on multivalent electron transfer, different from multivalent cation batteries, such as magnesium / aluminum ion batteries, the strong Coulomb interaction between magnesium / aluminum ions and host materials results in poor ion migration kinetics, thus causing poor reaction kinetics. For fluoride ion batteries, in addition to the theoretical energy density being as high as over 5000 Wh / L, the Coulomb interaction between monovalent fluoride ions and host materials is weak, so ion migration is relatively easy and the reaction kinetics is good.

[0005] However, as an emerging battery system, the main difficulty of fluoride ion batteries lies in the lack of a suitable electrolyte to ensure the reversible operation of the battery, especially in low-temperature or even room-temperature environments. Although the ion transport performance of liquid electrolytes at room temperature is significantly better than that of solid electrolytes, one of the main difficulties is that the strong solvation of fluoride salts in proton solvents makes it usually difficult for fluoride ions to desolvate and participate in the electrode electrochemical reaction in such solvents, resulting in poor reaction kinetics and electrochemical reversibility of the constructed fluoride ion battery. Summary of the Invention

[0006] Aiming at the above problems, the purpose of the present invention is to provide a protonic electrolyte for a room-temperature fluoride ion battery based on a strong solvation weakening strategy and its application.

[0007] On the one hand, the present invention provides a protonic electrolyte for a fluoride ion battery based on a strong solvation weakening strategy, which is composed of a fluoride salt, a solvation regulator containing a hydroxyl or amino structure, and a proton solvent. In the present invention, the role of the solvation regulator belongs to a functional additive of the electrolyte. And the volume of the solvation regulator + the volume of the proton solvent is the total volume of the electrolyte. In addition, in the present invention, the composition of the electrolyte does not contain a highly conductive electronic material to avoid the possibility of electronic conduction in the electrolyte. The composition of the electrolyte also does not contain commonly used organic solvents such as esters and ethers in electrolytes, thereby further reducing the cost of the electrolyte and improving the environmental friendliness of the electrolyte.

[0008] Preferably, the fluoride salt is an inorganic fluoride salt, preferably including at least one of cesium fluoride, potassium fluoride, rubidium fluoride, and sodium fluoride.

[0009] Preferably, the solvation regulator containing a hydroxyl or amino structure contains only 1-2 hydroxyls or amino groups, and contains an anion part to complex with the cation part of the fluoride salt to promote the dissociation of the fluoride salt, preferably including at least one of choline chloride, choline bromide, choline, and aniline hydrochloride; the proton solvent is a solvent that can provide protons to form hydrogen bond association or form a coordination cation with solute molecules, and is a molecule that can provide at least two protons, preferably including at least one of ethylene glycol, ethylenediamine, and propylene glycol. For example, considering that the smaller the anion size of the regulator, the better, and taking into account the raw material cost, the solvation regulator adopted in the present invention is choline chloride; considering the possible steric hindrance effect of the chain length of the proton solvent on fluoride ion shuttle, the shorter the chain length, the better, and the alcohol-based proton solvent has weaker corrosiveness than the ammonia-based proton solvent, so the proton solvent adopted in the present invention is preferably short-chain alcohols. And since the ternary or more polyhydric alcohols have too strong hydrogen bond interactions, resulting in too high viscosity, ethylene glycol is finally adopted as the proton solvent in the present invention. Since the interaction between the hydroxyl group of choline chloride and the hydroxyl group of ethylene glycol weakens the strong solvation of ethylene glycol on fluoride ions through its hydroxyl group, it is convenient for fluoride ions to desolvate.

[0010] Preferably, the concentration of the solvation regulator containing a hydroxyl or amino structure does not exceed 40%, preferably 8% - 40%, more preferably 16% - 25% (the percentages here are all mole percentages).

[0011] Preferably, the concentration of the fluoride salt does not exceed 200 mg / mL, preferably 50 - 200 mg / mL, more preferably 76.0 - 151.9 mg / mL.

[0012] In the present invention, the strong solvation effect of ethylene glycol on fluoride ions caused by hydrogen bonding is weakened through the hydrogen bonding interaction between the hydroxyl groups on choline chloride and the hydroxyl groups of ethylene glycol. An appropriate amount of a mixture of choline chloride and ethylene glycol is vigorously stirred at room temperature (for example, 12 hours) in a glove box filled with argon to obtain a basic solvent, and then an appropriate amount of cesium fluoride is added and stirring is continued vigorously (for example, 12 hours) to obtain the corresponding electrolyte solution.

[0013] On the other hand, the present invention provides a fluoride ion soft-pack battery, comprising: a protonic electrolyte for a fluoride ion battery based on a strong solvation weakening strategy.

[0014] Preferably, it further comprises: a positive electrode, wherein the positive electrode comprises at least one of a composite of copper fluoride and carbon, a composite of metallic copper and carbon, a composite of bismuth fluoride and carbon, and a composite of metallic bismuth and carbon.

[0015] Preferably, it further comprises: a negative electrode, wherein the negative electrode comprises at least one of metallic lead, tin, magnesium, and zinc.

[0016] Preferably, it further comprises: a positive electrode current collector; the positive electrode current collector comprises at least one of aluminum foil and carbon-coated aluminum foil.

[0017] Preferably, it further comprises: a negative electrode current collector; the negative electrode current collector comprises at least one of copper foil and carbon cloth.

[0018] Advantages of the present invention: (1) In the present invention, through a solvation regulator based on hydrogen bonding interaction, the over-solvation of fluoride ions by a proton solvent is weakened, improving the reaction kinetics and reversibility; (2) In the present invention, by optimizing the concentration of the regulator, the wetting ability of the electrolyte on the separator and the redox stability of the electrolyte are further enhanced, the fluoride ion transference number is increased, the fluoride ion solvation structure in the electrolyte is optimized, facilitating the desolvation of fluoride ions, enhancing the interfacial reaction kinetics, and improving the reversibility of the fluoride ion battery; (3) In the present invention, copper fluoride is used as the positive electrode material of the battery to achieve a high reaction platform and a large-capacity charge-discharge behavior. Description of the drawings

[0019] Figure 1 It is a flowchart for the preparation of the electrolyte solution in Example 1; Figure 2 It is the room temperature ionic conductivity of the glass fiber separator infiltrated with the prepared electrolyte solution in Example 2; Figure 3 It is the room temperature ionic conductivity of the prepared electrolyte solution in Example 3; Figure 4The test of the fluoride ion transference number in the electrolyte prepared in Example 3 includes the constant voltage polarization and the impedance diagrams before and after it (see the inset). Figure 5 The electrochemical window of the electrolyte prepared in Example 4. Figure 6 The physical and sectional structure diagrams of the soft-pack battery assembled in Example 5. Figure 7 The long cycle performance of the 2032-type button fluoride ion battery assembled with the electrolyte containing different choline chloride concentrations prepared based on Example 5, using Al foil as the positive current collector, copper fluoride as the positive electrode material, and metallic lead as the negative electrode material. Figure 8 The rate performance of the button fluoride ion battery in Example 5. Figure 9 The electrochemical curves of the fluoride ion soft-pack battery assembled with the LE3 ratio electrolyte which is the optimal one screened by the button battery performance in Example 5, using Al foil as the positive current collector, copper fluoride as the positive electrode material, metallic lead as the negative electrode material, and copper foil as the negative current collector. Figure 10 The long cycle performance of the soft-pack fluoride ion battery in Example 5. Detailed implementation manners

[0020] The present invention will be further described by the following implementation manners. It should be understood that the following implementation manners are only used to illustrate the present invention and do not limit the present invention.

[0021] In the present disclosure, the protonic electrolyte for fluoride ion batteries includes: fluoride salts, a solvation regulator containing hydroxyl or amino groups, and a proton solvent.

[0022] In an optional implementation manner, the fluoride ion salt is an inorganic fluoride salt, preferably including at least one of cesium fluoride, potassium fluoride, rubidium fluoride, and sodium fluoride. Among them, the concentration of the fluoride ion salt is 0 to 200 mg / mL and not 0, preferably 50 to 200 mg / mL, and more preferably 76.0 to 151.9 mg / mL.

[0023] In an alternative embodiment, the solvation regulator containing a hydroxyl or amino group contains only 1 to 2 hydroxyl or amino groups, and contains an anionic moiety for complexing with the cationic moiety of the fluoride salt to promote the dissociation of the fluoride salt. Preferably, the solvation regulator containing a hydroxyl or amino group includes at least one of choline chloride, choline bromide, choline, and aniline hydrochloride. The protonic solvent is a solvent that can provide protons to form hydrogen bond association or form a coordination cation with the solute molecules, and is a molecule that can provide at least two protons. Preferably, it includes at least one of ethylene glycol, ethylenediamine, and propylene glycol. For example, when choline chloride is used as the solvation regulator, the interaction between the hydroxyl group of choline chloride and the hydroxyl group of ethylene glycol weakens the strong solvation effect of ethylene glycol on fluoride ions through its hydroxyl group, thus facilitating the desolvation of fluoride ions.

[0024] In an alternative embodiment, when the concentration of the solvation regulator is expressed as the molar ratio of the number of choline chloride molecules to the total number of solvent molecules (i.e., choline chloride + ethylene glycol), the concentration of the regulator is 0 to 40% and not 0, preferably 8% to 40%, more preferably 16% to 25% (the percentages here are all mole percentages). In the present invention, the content of the solvation regulator has a great influence on the battery performance. In particular, electrolytes with different concentrations of the solvation regulator have a greater impact on the long-cycle and rate performance of the battery.

[0025] Taking choline chloride and ethylene glycol as examples, the preparation method of the protonic electrolyte for fluoride ion batteries is exemplarily described below. Among them, the hydrogen bond interaction between the hydroxyl group on choline chloride and the hydroxyl group of ethylene glycol weakens the strong solvation effect of ethylene glycol on fluoride ions caused by hydrogen bond interaction. It should be noted that other solvation regulators containing hydroxyl or amino groups and protonic solvents are also applicable to this preparation process.

[0026] A mixture of an appropriate amount of choline chloride and ethylene glycol is vigorously stirred at room temperature for 6 to 12 hours in a glove box filled with argon to obtain a base solvent.

[0027] An appropriate amount of fluoride salt is added to the base solvent, and stirring is continued vigorously for 12 to 24 hours to obtain the corresponding electrolyte.

[0028] Examples are further given below to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, rather than being limited to the specific values in the following examples.

[0029] Example 1: Preparation of a protonic electrolyte based on a choline chloride regulator: Weigh 0.4552 g, 1.0014 g, 1.6691 g, and 2.5036 g of choline chloride, add 2 mL of ethylene glycol, and stir at room temperature for 6 hours to form a homogeneous and transparent solution; label them as S1 / S2 / S3 / S4, and pure ethylene glycol as S0. Then add 151.9 mg of cesium fluoride and stir vigorously for 12 hours to obtain the prepared electrolytes LE0 (0 mol%), LE1 (8 mol%), LE2 (17 mol%), LE3 (25 mol%), and LE4 (33 mol%). The preparation process is as shown in the appendix Figure 1 as follows.

[0030] Example 2: Testing the ionic conductivity of the wetting diaphragm: Using a stainless steel sheet with a diameter of 15.5 mm as the electrode and a glass fiber disc with a diameter of 19 mm as the diaphragm, based on the electrolyte of Example 1, assemble a CR2032 type coin-shaped symmetric battery, test its electrochemical impedance and calculate the ionic conductivity. The voltage is 10 mV and the frequency range is 10 M - 1 Hz. As Figure 2 shown, the room temperature ionic conductivity of the wetting diaphragm is in the range of 0.65 mS / cm - 2.17 mS / cm. When the mole fraction of choline chloride in the total solvent molecules is 25 mol% (i.e., LE3), the ionic conductivity of the wetting diaphragm is the highest, reaching 2.17 mS / cm, which means that the LE3 electrolyte has the best wettability to the diaphragm.

[0031] Example 3: Preparation of the electrode material and testing of the ionic transport performance of the electrolyte: 1) Preparation of the electrode: Grind and mix commercial anhydrous stannous fluoride, tin powder, and Ketjenblack in a mass ratio of 4:4:1 until homogeneous. Then mix the mixture with the conductive agent Super-P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 9:1 by grinding until homogeneous, add an appropriate amount of N-methylpyrrolidone (NMP) to make a homogeneous slurry, and coat it on a clean copper foil current collector. After natural drying, transfer it to a vacuum oven at 60 °C and dry for 12 hours. Cut the dried copper foil loaded with tin and stannous fluoride into discs with a diameter of 10 mm; 2) Test the room temperature ionic conductivity of electrolytes with different salt concentrations using an ionic conductivity meter. As Figure 3 shown, when the mole fraction of choline chloride in the total solvent molecules is 17 mol% (i.e., LE2), the ionic conductivity of the electrolyte is the highest, reaching 10.12 mS / cm; 3) In an argon atmosphere glove box with both the water value and oxygen value less than 0.1 ppm, assemble a CR2032 type coin-shaped symmetric battery based on the above electrode for testing the fluoride ion transference number in the electrolyte. As Figure 4 shown, taking the LE3 electrolyte as an example, its fluoride ion transference number is 0.36.

[0032] Example 4: Electrochemical Window Test of Electrolyte Using an Al foil as the positive electrode and a lead foil as the negative electrode, a CR2032 coin cell was assembled based on the electrolyte of Example 1. The scan rate was set at 1 mV / s. As shown Figure 5 in the figure, the continuous increase in the content of choline chloride strengthened the redox stability of the electrolyte system. When the content was the highest (i.e., LE4, 33 mol%), the electrochemical window was the widest, at -0.8 V - 2.2 V.

[0033] Example 5: Preparation, Assembly and Testing of Cathode Materials 1) Preparation of the cathode: Commercial anhydrous copper fluoride and Ketjen black were ball-milled at a mass ratio of 8:2 and a rotation speed of 600 rpm / min for 5 hours. The ball-milled mixture of copper fluoride and carbon was uniformly mixed with the conductive agent Super-P and the binder polyvinylidene fluoride (PVDF) at a mass ratio of 7:2:1 by grinding, and an appropriate amount of N-methylpyrrolidone (NMP) was added to make a uniform slurry, which was then coated on a clean aluminum foil current collector. After natural drying, it was transferred to a vacuum oven at 60 °C and dried for 12 hours. The dried aluminum foil loaded with copper fluoride was cut into square electrode sheets, which were used as the cathode material electrodes; 2) Assembly and testing of the battery: In an argon atmosphere glove box with a water value and an oxygen value both less than 0.1 ppm, a 2032 coin cell was assembled for electrochemical performance testing. Among them, the positive electrode was the above-prepared copper fluoride positive electrode sheet, the negative electrode was metallic lead, the electrolyte was the above-prepared electrolyte, and the separator was Glass fiber. After the preliminary screening of the coin cell performance, the most preferred electrolyte was selected to assemble a soft-pack battery. Among them, the cathode, anode and separator materials were the same as those of the above coin cell, and the negative current collector was a metallic copper foil. As shown Figure 6 in the figure, the soft-pack battery was assembled in a stacking manner, and it could also be extended to a winding manner;

[0034] To test the electrochemical performance of the fluoride ion battery based on the electrolyte prepared in Example 1, the assembled coin cell was placed on a BlueTEC CT2001A for constant current charge and discharge testing. The current density was 50 mA / g, the discharge cut-off voltage was -0.3 V, and the charge cut-off voltage was 0.6 V. The long cycle and rate performance of the coin cell were as shown Figures 7 - 8 in the figure. Among the different concentrations of the regulator, the fluoride ion battery with the electrolyte formulation at a concentration of 25% had the best long cycle performance and rate performance. Therefore, a soft-pack battery was also assembled with the electrolyte prepared with this best electrolyte formulation later. Its discharge cut-off voltage was -0.3 V and the charge cut-off voltage was 0.5 V. The electrochemical performance of this soft-pack fluoride ion battery was as shown Figures 9 - 10As shown. Compared with the fluoride ion batteries reported so far, this soft-pack battery has a larger capacity (the initial capacity is 6.72 mAh, that is, 525 mA h / g), a longer cycle life (more than 150 cycles), and a high Coulomb efficiency close to 100% after stabilization.

[0035] Finally, it is necessary to state here that the above embodiments are only used to further illustrate the technical solutions of the present invention in detail, and cannot be understood as a limitation on the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the protection scope of the present invention.

Claims

1. A protonic electrolyte for fluoride ion batteries based on a strong solvation weakening strategy, characterized in that, It is composed of a fluoride salt, a solvation regulator containing a hydroxyl or amino group structure, and a proton solvent.

2. The protonic electrolyte for fluoride ion batteries based on the strong solvation weakening strategy according to claim 1, characterized in that, The fluoride salt is an inorganic fluoride salt, preferably including at least one of cesium fluoride, potassium fluoride, rubidium fluoride, and sodium fluoride.

3. The protonic electrolyte for fluoride ion batteries based on the strong solvation weakening strategy according to any one of claims 1 or 2, characterized in that, The solvation regulator containing a hydroxyl or amino group structure contains only 1-2 hydroxyl or amino groups and contains an anion part to complex with the cation part of the fluoride salt to promote the dissociation of the fluoride salt; preferably, the solvation regulator containing a hydroxyl or amino group structure includes at least one of choline chloride, choline bromide, choline, and aniline hydrochloride; The proton solvent is a solvent that can provide protons to form hydrogen bond association or form a coordination cation with solute molecules and is a molecule that can provide at least two protons; preferably, the proton solvent includes at least one of ethylene glycol, ethylenediamine, and propylene glycol.

4. The protonic electrolyte for fluoride ion batteries based on the strong solvation weakening strategy according to any one of claims 1-3, characterized in that The concentration of the solvation regulator containing a hydroxyl or amino group structure does not exceed 40 mol%, preferably 8 mol% - 40 mol%, more preferably 16 mol% - 25 mol%.

5. The protonic electrolyte for fluoride ion batteries based on the strong solvation weakening strategy according to any one of claims 1-4, characterized in that, The concentration of the fluoride salt does not exceed 200 mg / mL, preferably 50 - 200 mg / mL, more preferably 76.0 - 151.9 mg / mL.

6. A fluoride-ion soft-pack battery, characterized in that, Including: The protonic electrolyte for a fluoride ion battery based on a strong solvation weakening strategy according to any one of claims 1-5.

7. The soft-pack fluoride ion battery according to claim 6, wherein, Further including: A positive electrode, which includes at least one of a composite of copper fluoride and carbon, a composite of metallic copper and carbon, a composite of bismuth fluoride and carbon, and a composite of metallic bismuth and carbon.

8. The fluoride ion battery according to claim 6 or 7, characterized in that, Further including: A negative electrode, which includes at least one of metallic lead, tin, magnesium, and zinc.

9. The soft-pack fluoride ion battery according to claim 7, characterized in that, Further including: A positive electrode current collector; the positive electrode current collector includes at least one of aluminum foil and carbon-coated aluminum foil.

10. The soft-pack fluoride ion battery according to claim 8, characterized in that, Further including: A negative electrode current collector; the negative electrode current collector includes at least one of copper foil and carbon cloth.

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