Application of soft-soft base salts as supporting electrolytes in organic flow batteries based on pyridine and its derivative negative active materials

Abstract

The present invention discloses the application of soft-soft base salts as supporting electrolytes in organic flow batteries based on pyridine and its derivative negative active materials. Using soft-soft base salts as electrolyte supporting salts, the relatively large-sized soft-soft base ions provide steric hindrance protection for the ionized active molecules in electrical neutralization pairs, which is beneficial to improving the stability of redox intermediates of pyridine and its derivative negative active materials, and thus beneficial to improving the stability of the battery. The battery using soft-soft base salts has higher cycle stability than the flow batteries based on pyridine and its derivative negative materials using hard-hard base salts, soft-hard base salts, and hard-soft base salts.

Description

Technical Field

[0001] The present invention belongs to the technical field of flow batteries, and relates to the application of soft-soft-base salts as supporting electrolytes in organic flow batteries based on pyridine and its derivative negative electrode active materials. Background Art

[0002] As a new type of electrochemical energy storage facility with high capacity and low cost, flow batteries have the unique advantage that energy and power can be independently regulated. Traditional flow batteries mainly use transition metals such as vanadium and chromium as electroactive materials, and have disadvantages such as limited metal reserves, strong corrosiveness of electrolytes, serious transmembrane penetration, and slow kinetics. In order to overcome the defects of traditional flow batteries, a hot research direction is to use electrochemically active organic molecules instead of traditional inorganic electroactive substances in flow batteries. Electrochemically active organic molecules have been widely used in other fields, and many mature organic molecules can be used in flow batteries. Organic molecules are relatively easy to prepare, can be produced on a large scale at low cost, and have strong plasticity. Functionalities such as high potential, high solubility, and high compatibility with battery diaphragms can be designed through synthesis and modification.

[0003] As a complex working system, the electrolyte in a flow battery is one of the most obvious influencing factors, and it mainly undertakes the role of loading active materials and current. The electrolyte is mainly composed of a supporting electrolyte and a solvent, which not only determines the conductivity of the solution, but also affects the cycle stability of the active material in a complex battery environment. The supporting electrolyte in the electrolyte plays an important role. The supporting electrolyte should meet the following conditions: 1) It has a relatively large solubility / dissociation degree in the solvent, enabling the electrolyte to have sufficient conductivity; 2) It has a wide electrochemical window (the supporting electrolyte itself is not easily involved in electrochemical reactions); 3) It does not react with substances related to the solvent or the electrode reaction in the system.

[0004] Currently, organic phase flow batteries widely use metal ion salts based on lithium salts as supporting electrolytes, which play the role of transporting ions to conduct current and balancing the potential of redox intermediates between the positive and negative electrodes. However, organic phase flow batteries using such electrolytes often have poor reversibility. Therefore, how to improve the lifespan of organic phase flow batteries has become an urgent problem to be solved in this field.

[0005] The present invention proposes to use soft-soft-base salts to replace traditional hard-soft-base salts or hard-hard-base salts based on metal ions to solve the lifespan problem of organic phase flow batteries. Summary of the Invention

[0006] The object of the present invention is to provide an application of a soft-soft base salt as a supporting electrolyte in an organic flow battery based on a negative electrode material of pyridine and its derivatives, which is conducive to improving the application method of the supporting electrolyte for enhancing the stability of electrochemically reactive intermediates of the negative electrode active material based on pyridine and its derivatives.

[0007] The application of the soft-soft base salt of the present invention as a supporting electrolyte in an organic flow battery based on a negative electrode material of pyridine and its derivatives is specifically as follows:

[0008] Step (1): Prepare an organic electrolyte solution using a soft-soft base salt as a supporting electrolyte:

[0009] Weigh a quantitative soft-soft base salt according to the concentration, dissolve it in an organic solvent, and prepare an organic electrolyte solution with a concentration of 0.1 M to 1 M.

[0010] In the soft-soft base salt, the soft acid ion refers to a Lewis acid with few positive charges, large volume, high polarizability, easy deformability, that is, weak attraction to outer electrons, including tetrabutylammonium ion (TBA + ), tetraethylammonium ion (TEA + ), 1-butyl-1-methylpyrrolidinium ion (C4MPr + ), 1-heptyl-3-methylimidazolium ion (C7MIm + ), etc. In the soft-soft base salt, the soft base ion refers to a Lewis base that is easy to lose electrons, has a low electronegativity, is easy to be polarized and deformed, and is easy to be oxidized, that is, has a weak attraction to outer electrons, including I - , S 2- , SCN - , bis(trifluoromethanesulfonyl)imide anion (TFSI - ), trifluoromethanesulfonate anion (TFS - ), etc.

[0011] Step (2): Prepare a negative electrode electrolyte solution:

[0012] Weigh a quantitative negative electrode active material according to the concentration, add it to the organic electrolyte solution in step (1), and prepare a solution with a negative electrode active material concentration of 1 mM to 1.00 M, which is the negative electrode electrolyte solution. Among them, the negative electrode active material is one of pyridine and its derivatives.

[0013] Step (3): Prepare a positive electrode electrolyte solution:

[0014] Weigh a quantitative positive electrode active material according to the concentration, add it to the organic electrolyte solution in step (1), and prepare a solution with a positive electrode active material concentration of 0.05 M to 1.00 M, which is the positive electrode electrolyte solution. Among them, the positive electrode active material is an organic molecule with a relatively high redox potential and high solubility in an organic solvent.

[0015] Step (4): Assemble and test the flow battery:

[0016] The flow battery system includes positive and negative end plates, positive and negative current collectors, positive electrode electrolyte, porous separator, negative electrode electrolyte, and positive and negative liquid storage tanks. Under a nitrogen atmosphere, use a pipette to fill the positive and negative liquid storage tanks with the above-mentioned positive electrode electrolyte and negative electrode electrolyte respectively, seal the battery, and perform electrochemical performance tests on the battery on a battery test system.

[0017] Preferably, the soft-soft base salt is 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate.

[0018] Preferably, the organic solvent includes, but is not limited to, one or a mixture of solvents such as ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, triethylene glycol dimethyl ether, dimethyl sulfoxide, diethylene glycol dimethyl ether, vinylene sulfite, acetonitrile, etc.

[0019] Preferably, the negative electrode active material uses 4,4'-bipyridine.

[0020] Preferably, the positive electrode active material includes, but is not limited to, ferrocene.

[0021] Preferably, the porous separator is a film with high ion conductivity, including Daramic AA-800 and PP film.

[0022] Preferably, the positive and negative current collectors include, but are not limited to, graphite carbon felt, conductive carbon layer, etc.

[0023] The beneficial effects of the present invention are:

[0024] The soft-soft base salt proposed by the present invention is directly dissolved in an organic solvent and used as the electrolyte of the flow battery. As a substitute for traditional supporting electrolyte salts, it does not need to be used in combination with traditional lithium salts, and can effectively improve the electrochemical stability and reversibility of the negative electrode of the flow battery, thereby improving the overall cycle stability of the battery.

[0025] The negative electrode active material uses pyridine and its derivatives with Lewis basicity. When using hard acid salts, there will be a strong interaction between the active sites of the negative electrode active material and the hard acid cations therein, making it difficult for the negative electrode active material to be oxidized after reduction, which is not conducive to forming a reversible oxidation process. When using the soft-soft base salt (1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate) as the supporting electrolyte, the interaction between the relatively large-volume soft-soft base ions and the active material is weak and is easily dissociated during the electrochemical process. In addition, the soft-soft base ions can also provide steric hindrance protection for the ionized active molecules for charge neutralization pairing, which is beneficial to improving the stability of the redox intermediates of the negative electrode active material, and thus is beneficial to improving the stability of the battery.

[0026] Therefore, the present invention proposes to use soft acid-soft base salts as electrolyte supporting salts, which is beneficial to improving the stability of the negative electrode active material intermediate based on pyridine and its derivatives, and thus beneficial to improving the stability of the battery. The battery using soft acid-soft base salts has higher cycle stability than the flow battery based on pyridine and its derivatives negative electrode materials using hard acid-hard base salts, soft acid-hard base salts, and hard acid-soft base salts. Description of the Drawings

[0027] The present invention will be further described in the manner of exemplary embodiments, and these exemplary embodiments will be described in detail through the drawings. These embodiments are not restrictive. In these embodiments, the same numbers represent the same structures, where:

[0028] Figure 1 is the reduced density gradient isosurface map of the interaction geometry between 4,4'-bipyridine (Bpy) active molecules and several supporting electrolyte ions. Among them, (a)-(c) represent the electrolyte ions acting on the N atoms of Bpy - and (a) is Bpy - and Li + , (b) is Bpy - and tetrabutylammonium ion (TBA + ), (c) is Bpy - and 1-butyl-1-methylpyrrolidinium ion (C4MPr + ); (d)-(f) represent the electrolyte ions acting on the planar structure of Bpy - , (d) is Bpy and Li + , (e) is Bpy and tetrabutylammonium ion (TBA + ), (f) is Bpy and 1-butyl-1-methylpyrrolidinium ion (C4MPr + );

[0029] Figure 2 is the comparison of the interaction energies of 4,4'-bipyridine binding with three cations in different ways. Among them, (a) is the comparison of the interaction energies when several electrolyte ions act on the N atoms of Bpy - ; (b) is the comparison of the interaction energies when several electrolyte ions act on the planar structure of Bpy - .

[0030] Figure 3 is the surface electrostatic potential (ESP) map of the ion pairs formed by 4,4'-bipyridine with tetrabutylammonium ion TBA + , 1-butyl-1-methylpyrrolidine C4MPr + and Li + cations. Among them, (a) is Bpy and TBA+ , (b) is Bpy and C4MPr + , (c) is Bpy and Li + .

[0031] Figure 4 is the cyclic voltammogram of 4,4'-bipyridine in 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate (soft acid-soft base salt).

[0032] Figure 5 is the 100-cycle cyclic voltammogram of 4,4'-bipyridine in 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate (soft acid-soft base salt).

[0033] Figure 6 is the cyclic voltammogram of 4,4'-bipyridine in tetrabutylammonium hexafluorophosphate (soft acid-hard base salt).

[0034] Figure 7 is the 100-cycle cyclic voltammogram of 4,4'-bipyridine in tetrabutylammonium hexafluorophosphate (soft acid-hard base salt).

[0035] Figure 8 is the cyclic voltammogram of 4,4'-bipyridine in lithium bis(trifluoromethanesulfonyl)imide (hard acid-soft base salt).

[0036] Figure 9 is the cyclic voltammogram of 4,4'-bipyridine in lithium hexafluorophosphate (hard acid-hard base salt).

[0037] Figure 10 is the Coulombic efficiency, energy efficiency, and charge-discharge capacity diagram of a 0.05 M 4,4'-bipyridine / ferrocene static flow battery.

[0038] Figure 11 is the charge-discharge voltage-capacity curve diagram of a 0.05 M 4,4'-bipyridine / ferrocene static flow battery.

[0039] Figure 12 is the Coulombic efficiency, energy efficiency, and charge-discharge capacity diagram of a 0.2 M 4,4'-bipyridine / ferrocene static flow battery.

[0040] Figure 13 is the charge-discharge voltage-capacity curve diagram of a 0.2 M 4,4'-bipyridine / ferrocene static flow battery.

[0041] Figure 14 is the Coulombic efficiency, energy efficiency, and charge-discharge capacity diagram of a 0.05 M 4,4'-bipyridine / ferrocene static flow battery.

[0042] Figure 15It is a charge-discharge voltage-capacity curve graph of a 0.05M 4,4'-bipyridine / ferrocene static flow battery. Detailed implementation mode

[0043] As mentioned above, in view of the deficiencies of the prior art, the inventors of this case have proposed the technical solution of the present invention through long-term research and a large number of practices. The main basis includes at least:

[0044] The soft-soft base salt proposed by the present invention is directly dissolved in an organic solvent and used as the electrolyte of a flow battery. As a substitute for traditional supporting electrolyte salts, it does not need to be used in combination with traditional lithium salts, and can effectively improve the electrochemical stability and reversibility of the negative electrode of the flow battery, thereby enhancing the overall cycle stability of the battery.

[0045] The negative electrode active material uses pyridine and its derivatives, which have Lewis basicity. When using hard acid salts, there will be a strong interaction between the active sites of the negative electrode active material and the hard acid cations therein, making it difficult for the negative electrode active material to be oxidized after reduction, which is not conducive to forming a reversible oxidation process. When using a soft-soft base salt (1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate) as the supporting electrolyte, the interaction between the relatively large-volume soft-soft base ions and the active material is weak and is easily dissociated during the electrochemical process. In addition, the soft-soft base ions can also provide steric hindrance protection for the ionized active molecules that are electrically neutralized and paired, which is conducive to improving the stability of the redox intermediates of the negative electrode active material, and thus conducive to improving the stability of the battery.

[0046] Figure 1 It is a reduced density gradient isosurface map of the geometric relationship between 4,4'-bipyridine active molecules and several supporting electrolyte ions. Figure 2 It is a comparison of the interaction energies of 4,4'-bipyridine combined with three soft acid / hard acid ions in different ways.

[0047] Figure 1 (a), Figure 1 (d) It can be seen that when the negative electrode active material is 4,4'-bipyridine, due to the relatively small volume and concentrated charge of the hard acid type cation lithium ion, it has a strong ability to bind to the negative electrode active material (such as 4,4'-bipyridine) when combined with the negative electrode active material (such as 4,4'-bipyridine). When the negative electrode active material (such as 4,4'-bipyridine) is in the reduced state, under the electrostatic action, its interaction energy with lithium ions is more negative and the attraction is stronger. Therefore, it often leads to a decrease in the electrochemical reversibility and stability of the negative electrode material. However, Figure 1 (b), Figure 1 (c), Figure 1 (e), Figure 1 (f) It can be seen that the tetrabutylammonium cation (TBA +) with 1-butyl-1-methylpyrrolidinium cation ([C4MPr] + ) The interaction energies between the two soft acid cations and the reduced-state anode active material (such as 4,4'-bipyridine) are still at a relatively low level, with only weak van der Waals forces, which can result in a relatively high rate of binding and detachment between Bpy and the cations, facilitating the redox reaction activity of the anode material. As Figure 2 shown by the comparative data of the interaction energies of Bpy- binding to the three cations in different ways, the interaction energy between the hard acid Li + and Bpy - is one order of magnitude larger than that of the other two soft acid cations. The relatively large interaction energy makes it difficult for Li+ to dissociate / desorb during the redox reaction of Bpy, which will reduce the electrochemical reversibility and stability of Bpy, thus affecting the cycle life of the flow battery. The use of soft acid-soft base salts is beneficial to enhancing the dissociation activity of the anode active material (such as 4,4'-bipyridine), thereby promoting the progress of the Bpy redox reaction.

[0048] As Figure 3 , as shown by the surface electrostatic potential (ESP) maps of the ion pairs formed by the anode active material 4,4'-bipyridine and TBA + , C4MPr + and Li + cations, the charge of the hard acid Li + is more concentrated, which not only is not conducive to the dissociation of the cation during the oxidation of the electrode material but also cannot provide a steric protection effect, resulting in Bpy being more vulnerable to side reactions during the electrochemical process, further reducing its redox reversibility. The soft acid cations (TBA + and [C4MPr] + ) have a larger volume compared with the hard acid cation (Li + ), and the binding is more dispersed. This is not only conducive to promoting the adsorption or dissociation of ions during the redox process of the electrode material, improving the redox reversibility, and thus enhancing the battery life. In addition, the soft acid cations (TBA + and [C4MPr] + ) have a larger volume compared with the hard acid cation (Li + ). After forming ion pairs, they can effectively utilize the steric hindrance effect to provide protection for the active material, improve the stability of the reduced-state ion intermediate of the active molecule, and enhance the cycle stability of the flow battery.

[0049] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0050] The present invention provides an application of soft-soft base salts as supporting electrolytes in an organic flow battery based on a negative electrode material of pyridine and its derivatives. The specific application is as follows:

[0051] Step (1): Prepare an organic electrolyte solution using a soft-soft base salt as a supporting electrolyte:

[0052] Weigh a quantitative amount of the soft-soft base salt according to the concentration, dissolve it in an organic solvent, and prepare an organic electrolyte solution with a concentration of 0.1 M to 1 M.

[0053] The soft acid ions in the soft-soft base salt refer to Lewis acids with few or zero positive charges, large volumes, high polarizability, and easy deformation, that is, weak attraction to outer electrons, including tetrabutylammonium ion (TBA + ), tetraethylammonium ion (TEA + ), 1-butyl-1-methylpyrrolidinium ion (C4MPr + ), 1-heptyl-3-methylimidazolium ion (C7MIm + ), etc.

[0054] The soft base ions in the soft-soft base salt refer to Lewis bases that are easy to lose electrons, have low electronegativity, are easy to polarize and deform, and are easy to be oxidized, that is, weak attraction to outer electrons, including I - , S 2- , SCN - , bis(trifluoromethanesulfonyl)imide anion (TFSI - ), trifluoromethanesulfonate anion (TFS - ), etc.

[0055] Step (2): Prepare a negative electrode electrolyte solution:

[0056] Weigh a quantitative amount of the negative electrode active material according to the concentration, add it to the organic electrolyte solution in step (1), and prepare a solution with a negative electrode active material concentration of 1 mM to 1.00 M, which is the negative electrode electrolyte solution. The negative electrode active material is one of pyridine and its derivatives.

[0057] Step (3): Prepare a positive electrode electrolyte solution:

[0058] Weigh a quantitative amount of the positive electrode active material according to the concentration, add it to the organic electrolyte solution in step (1), and prepare a solution with a positive electrode active material concentration of 0.05 M to 0.50 M, which is the positive electrode electrolyte solution. The positive electrode active material is an organic molecule with a relatively high redox potential and high solubility in the organic solvent.

[0059] Step (4): Assemble and test the flow battery:

[0060] The flow battery system includes positive and negative end plates, positive and negative current collectors, positive electrolyte, porous separator, negative electrolyte, and positive and negative liquid storage tanks. Under a nitrogen atmosphere, a pipette is used to fill the positive and negative liquid storage tanks with the above-mentioned positive electrolyte and negative electrolyte respectively, and the battery is sealed. The electrochemical performance of the battery is tested on a battery test system.

[0061] Preferably, the soft-soft base salt is 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate.

[0062] Preferably, the organic solvent includes, but is not limited to, one or a mixture of solvents such as ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, triethylene glycol dimethyl ether, dimethyl sulfoxide, diethylene glycol dimethyl ether, vinylene sulfite, acetonitrile, etc.

[0063] Preferably, the negative active material uses 4,4'-bipyridine.

[0064] Preferably, the positive active material includes, but is not limited to, ferrocene.

[0065] Preferably, the porous separator is a thin film with high ionic conductivity, including Daramic AA-800 and PP film.

[0066] Preferably, the current collector includes, but is not limited to, graphite carbon felt and conductive carbon layer.

[0067] The following description is to enable those of ordinary skill in the art to make and use the present invention, and this description is provided in the context of a specific application and its requirements. For those of ordinary skill in the art, it is obvious that various changes can be made to the disclosed embodiments. Additionally, without departing from the spirit and scope of the present invention, the general principles defined in the present invention can be applied to other embodiments and application scenarios. Therefore, the present invention is not limited to the disclosed embodiments, but should be given the broadest scope consistent with the scope of the invention patent.

[0068] Example 1: Cyclic voltammetry curve test of 4,4'-bipyridine in 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate as an electrolyte supporting salt

[0069] Prepare a soft-soft base salt electrolyte based on 4,4'-bipyridine:

[0070] Weigh 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate (soft-soft base salt) and 4,4'-bipyridine, and dissolve them in an acetonitrile solvent to prepare an acetonitrile solution containing 2 mM 4,4'-bipyridine and 1 M soft-soft base salt.

[0071] Cyclic voltammetry test: The CV curve of the prepared soft-soft base salt electrolyte based on 4,4'-bipyridine was tested by cyclic voltammetry. The electrode system used was a three-electrode system, where the working electrode was a gold electrode, the counter electrode was a platinum wire electrode, the reference electrode was an Ag / AgCl electrode, and the scanning rate was 0.05 V s -1 .

[0072] Figure 4 Figure 6 is the cyclic voltammogram of 4,4'-bipyridine in 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate (soft-soft base salt).

[0073] Figure 5 Figure 10 is the cyclic voltammogram of 4,4'-bipyridine in 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate (soft-soft base salt) for 100 cycles.

[0074] The cyclic voltammogram of 4,4'-bipyridine in 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate (soft-soft base salt) has high symmetry and a narrow oxidation-reduction peak separation (<75 mV), indicating that 4,4'-bipyridine exhibits high electrochemical reversibility in the electrolyte based on these two electrolytes, and its oxidation-reduction potential is -1.87 V (vs. Ag / AgCl).

[0075] Comparative Example 1: Cyclic voltammetry test of 4,4'-bipyridine in tetrabutylammonium hexafluorophosphate (soft-hard base salt).

[0076] Preparation of soft-hard base salt electrolyte based on 4,4'-bipyridine: Weigh tetrabutylammonium hexafluorophosphate (soft-hard base salt) and 4,4'-bipyridine, dissolve them in acetonitrile solvent, and prepare an acetonitrile solution containing 2 mM 4,4'-bipyridine and 1 M soft-hard base salt.

[0077] Cyclic voltammetry test: The CV curve of the prepared soft-hard base salt electrolyte based on 4,4'-bipyridine was tested by cyclic voltammetry. The electrode system used was a three-electrode system, where the working electrode was a gold electrode, the counter electrode was a platinum wire electrode, the reference electrode was an Ag / AgCl electrode, and the scanning rate was 0.05 V s -1 .

[0078] Figure 6 Figure 28 is the cyclic voltammogram of 4,4'-bipyridine in tetrabutylammonium hexafluorophosphate (soft-hard base salt).

[0079] Figure 7 Figure 32 is the cyclic voltammogram of 4,4'-bipyridine in tetrabutylammonium hexafluorophosphate (soft-hard base salt) for 100 cycles.

[0080] The cyclic voltammogram of 4,4'-bipyridine in tetrabutylammonium hexafluorophosphate (soft acid-hard base salt) has high symmetry and a narrow oxidation-reduction peak separation (<75 mV), indicating that 4,4'-bipyridine exhibits high electrochemical reversibility in the electrolytes based on these two electrolytes, and its oxidation-reduction potential is -1.81 V (vs. Ag / AgCl).

[0081] Comparative Example 2: Cyclic voltammogram test of 4,4'-bipyridine in lithium bis(trifluoromethanesulfonyl)imide (hard acid-soft base salt)

[0082] Prepare a hard acid-soft base salt electrolyte based on 4,4'-bipyridine: Weigh lithium bis(trifluoromethanesulfonyl)imide (hard acid-soft base salt) and 4,4'-bipyridine, and dissolve them in an acetonitrile solvent to prepare an acetonitrile solution containing 2 mM 4,4'-bipyridine and 1 M hard acid-soft base salt.

[0083] Cyclic voltammogram test: Test the CV curve of the prepared hard acid-soft base salt electrolyte based on 4,4'-bipyridine by cyclic voltammetry. The electrode system used is a three-electrode system, where the working electrode is a gold electrode, the counter electrode is a platinum wire electrode, and the reference electrode is an Ag / AgCl electrode, and the scanning rate is 0.05 V s -1 。

[0084] Figure 8 is the cyclic voltammogram of 4,4'-bipyridine in lithium bis(trifluoromethanesulfonyl)imide (hard acid-soft base salt).

[0085] The cyclic voltammogram of 4,4'-bipyridine in lithium bis(trifluoromethanesulfonyl)imide (hard acid-soft base salt) shows obvious irreversibility.

[0086] Comparative Example 3: Cyclic voltammogram test of 4,4'-bipyridine in lithium hexafluorophosphate (hard acid-hard base salt)

[0087] Prepare a hard acid-hard base salt electrolyte based on 4,4'-bipyridine: Weigh lithium hexafluorophosphate (hard acid-hard base salt) and 4,4'-bipyridine, and dissolve them in an acetonitrile solvent to prepare an acetonitrile solution containing 2 mM 4,4'-bipyridine and 1 M hard acid-hard base salt.

[0088] Cyclic voltammogram test: Test the CV curve of the prepared hard acid-hard base salt electrolyte based on 4,4'-bipyridine by cyclic voltammetry. The electrode system used is a three-electrode system, where the working electrode is a gold electrode, the counter electrode is a platinum wire electrode, and the reference electrode is an Ag / AgCl electrode, and the scanning rate is 0.05 V s -1 。

[0089] Figure 9 is the cyclic voltammogram of 4,4'-bipyridine in lithium hexafluorophosphate (hard acid-hard base salt).

[0090] The cyclic voltammetry curve of 4,4'-bipyridine in lithium hexafluorophosphate (a salt of hard acid and hard base) did not show obvious redox peaks.

[0091] Application Example 1: Application of a flow battery using 4,4'-bipyridine as the negative electrode material and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate (a salt of soft acid and soft base) as the supporting electrolyte salt

[0092] Using the soft acid-soft base salt as the supporting electrolyte in an organic flow battery based on a 4,4'-bipyridine negative electrode material, the specific operation steps are as follows:

[0093] (1) Prepare an organic electrolyte with the soft acid-soft base salt as the supporting electrolyte: Calculate and weigh a quantitative amount of the soft acid-soft base salt according to the concentration, and dissolve it in the organic solvent acetonitrile to prepare an organic electrolyte with a concentration of 1 M.

[0094] (2) Prepare a negative electrode electrolyte based on the 4,4'-bipyridine negative electrode material: Calculate and weigh a quantitative amount of 4,4'-bipyridine according to the concentration, and add it to the organic electrolyte prepared in step (1) to prepare a negative electrode electrolyte with an active material concentration of 0.05 M.

[0095] (3) Prepare a positive electrode electrolyte: Calculate and weigh a quantitative amount of the ferrocene positive electrode active material according to the concentration, and add it to the organic electrolyte prepared in step (1) to prepare a positive electrode electrolyte with an active material concentration of 0.05 M.

[0096] (4) Assemble and test the flow battery: The battery system includes positive and negative end plates, positive and negative current collectors, a positive electrode, a porous separator, a negative electrode, and positive and negative liquid storage tanks. Use a pipette to fill the positive and negative liquid storage tanks with the positive / negative electrode electrolytes prepared in steps (2) and (3) respectively in a glove box filled with nitrogen, seal the battery, and perform electrochemical performance tests on the battery using a battery test system.

[0097] Figure 10 It is the Coulombic efficiency, energy efficiency, and charge-discharge capacity diagram of a 0.05 M 4,4'-bipyridine / ferrocene static flow battery.

[0098] Figure 11 It is the charge-discharge voltage-capacity curve diagram of a 0.05 M 4,4'-bipyridine / ferrocene static flow battery.

[0099] At a current density of 20 mA cm -2 the initial discharge capacity of the battery is: 9.38 Ah L -1, which is about 70.10% of the theoretical capacity, and the battery discharge voltage is 2.20V. During the charge-discharge process of 300 cycles, the battery performs stably, the Coulomb efficiency remains at about 95%, the energy efficiency remains at about 85%, the capacity retention rate of the 300th cycle is 82.60% compared with the discharge capacity of the first cycle, and the decay rate per cycle is 0.06%. It shows that when the active material is at a low concentration, the battery has high cycle stability when using soft-soft base salts as the supporting electrolyte.

[0100] Application Example 2: Application of a flow battery using 4,4'-bipyridine as the negative electrode material and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate (soft-soft base salt) as the supporting electrolyte salt

[0101] Applying the soft-soft base salt as the supporting electrolyte in an organic flow battery based on a 4,4'-bipyridine negative electrode material, the specific operation steps are as follows:

[0102] (1) Prepare an organic electrolyte with the soft-soft base salt as the supporting electrolyte: Calculate and weigh a quantitative soft-soft base salt according to the concentration, and dissolve it in the organic solvent acetonitrile to prepare an organic electrolyte with a concentration of 1M.

[0103] (2) Prepare a negative electrode electrolyte based on the 4,4'-bipyridine negative electrode material: Calculate and weigh a quantitative 4,4'-bipyridine according to the concentration, and add it to the organic electrolyte prepared in step (1) to prepare a negative electrode electrolyte with an active material concentration of 0.2M.

[0104] (3) Prepare a positive electrode electrolyte: Calculate and weigh a quantitative ferrocene positive electrode active material according to the concentration, and add it to the organic electrolyte prepared in step (1) to prepare a positive electrode electrolyte with an active material concentration of 0.2M.

[0105] (4) Assemble and test the flow battery: The battery system includes positive and negative end plates, positive and negative current collectors, a positive electrode, a porous separator, a negative electrode, and positive and negative liquid storage tanks. Use a pipette gun to fill the positive and negative liquid storage tanks with the positive / negative electrolytes prepared in steps (2) and (3) respectively in a glove box filled with nitrogen, seal the battery, and perform electrochemical performance tests on the battery on a battery test system.

[0106] Figure 12 It is the Coulomb efficiency, energy efficiency, and charge-discharge capacity diagram of a 0.2M 4,4'-bipyridine / ferrocene static flow battery.

[0107] Figure 13 It is the charge-discharge voltage-capacity curve diagram of a 0.2M 4,4'-bipyridine / ferrocene static flow battery. When the active material concentration increases, the system viscosity increases, and the complexity of the active material during the electrochemical reaction process increases. At 20mAcm -2At a current density, the initial discharge capacity of the 0.2 M 4,4'-bipyridine / ferrocene static flow battery is 5.28 Ah L -1 , which is about 98% of the theoretical capacity, and the average discharge voltage is 1.86 V. During 120 charge-discharge cycles, the battery shows stable Coulombic efficiency maintained at about 90%, and the energy efficiency is maintained at about 70%. Compared with the initial discharge capacity, the capacity retention rate at the 120th cycle is 57%, and the decay rate per cycle is 0.35%. The capacity retention rate is increased by 47% compared with that using a soft acid-hard base salt, indicating that using a soft acid-soft base salt as the supporting electrolyte can also have good battery stability when the active material is at a high concentration.

[0108] Comparative Example 4: Application of a flow battery using 4,4'-bipyridine as the negative electrode material and tetrabutylammonium hexafluorophosphate (soft acid-hard base salt) as the supporting electrolyte salt

[0109] Applying a soft acid-hard base salt as the supporting electrolyte in an organic flow battery based on a 4,4'-bipyridine negative electrode material, the specific operation steps are as follows:

[0110] (1) Prepare an organic electrolyte solution with a soft acid-hard base salt as the supporting electrolyte: Calculate and weigh a quantitative amount of soft acid-soft base salt according to the concentration, and dissolve it in the organic solvent acetonitrile to prepare an organic electrolyte solution with a concentration of 1 M.

[0111] (2) Prepare a negative electrode electrolyte solution based on a 4,4'-bipyridine negative electrode material: Calculate and weigh a quantitative amount of 4,4'-bipyridine according to the concentration, and add it to the organic electrolyte solution prepared in step (1) to prepare a negative electrode electrolyte solution with an active material concentration of 0.05 M.

[0112] (3) Prepare a positive electrode electrolyte solution: Calculate and weigh a quantitative amount of ferrocene positive electrode active material according to the concentration, and add it to the organic electrolyte solution prepared in step (1) to prepare a positive electrode electrolyte solution with an active material concentration of 0.05 M.

[0113] (4) Assemble and test the flow battery: The battery system includes positive and negative end plates, positive and negative current collectors, a positive electrode, a porous separator, a negative electrode, and positive and negative liquid storage tanks. Use a pipette gun to fill the positive and negative liquid storage tanks with the positive / negative electrode electrolyte solutions prepared in steps (2) and (3) respectively in a glove box filled with nitrogen, seal the battery, and perform electrochemical performance tests on the battery on a battery test system.

[0114] Figure 14 It is the Coulombic efficiency, energy efficiency, and charge-discharge capacity diagram of a 0.05 M 4,4'-bipyridine / ferrocene static flow battery.

[0115] Figure 15It is the charge-discharge voltage-capacity curve of a 0.05M 4,4'-bipyridine / ferrocene static flow battery.

[0116] At a current density of 20 mA cm -2 , the first-cycle discharge capacity of the battery is: 4.45 Ah L -1 , which is about 84.02% of the theoretical capacity. The battery discharge voltage is 1.75 V. During the charge-discharge process of 120 cycles, the battery has poor cycle stability. The Coulomb efficiency remains at about 95%, and the energy efficiency remains at about 85%. Compared with the first-cycle discharge capacity, the capacity retention rate of the 120th cycle is only 5.11%, and the decay rate per cycle is 0.47%. The battery performance using soft acid-hard base salts is significantly lower than that using soft acid-soft base salts, fully demonstrating the importance of using soft acid-soft base salts as supporting electrolytes in flow batteries.

Claims

1. Application of soft acid-soft base salts as supporting electrolytes in organic flow batteries based on pyridine and its derivative negative active materials, characterized in that, The soft-soft base salt is 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate.

2. The application according to claim 1, wherein In the organic flow battery, the negative electrode electrolyte is composed of a pyridine and its derivative negative electrode active material, a soft-soft base salt, and an organic solvent.

3. The application according to claim 1 or 2, characterized in that The specific application is as follows: Step (1): Prepare an organic electrolyte using the soft-soft base salt as a supporting electrolyte: Weigh a quantitative soft-soft base salt according to the concentration, dissolve it in an organic solvent, and prepare an organic electrolyte with a concentration of 0.1 M to 1 M. Step (2): Prepare the negative electrode electrolyte: Weigh a quantitative negative electrode active material according to the concentration, add it to the organic electrolyte in step (1), and prepare a solution with a negative electrode active material concentration of 1 mM to 1.00 M, which is the negative electrode electrolyte; wherein the negative electrode active material is one of pyridine and its derivatives. Step (3): Prepare the positive electrode electrolyte: Weigh a quantitative positive electrode active material according to the concentration, add it to the organic electrolyte in step (1), and prepare a solution with a positive electrode active material concentration of 0.05 M to 1.00 M, which is the positive electrode electrolyte; wherein the positive electrode active material is an organic molecule with a relatively high redox potential and a relatively high solubility in the organic solvent. Step (4): Assemble and test the flow battery.

4. The application according to claim 2, wherein The organic solvent includes one or a mixture of solvents such as ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, triethylene glycol dimethyl ether, dimethyl sulfoxide, diethylene glycol dimethyl ether, vinylene sulfite, and acetonitrile.

5. The application according to claim 1, wherein The negative electrode active material is 4,4'-bipyridine.

6. The application according to claim 3, wherein The positive electrode active material is ferrocene.

7. The application according to claim 1, wherein The flow battery includes positive and negative end plates, positive and negative current collectors, positive electrode electrolyte, porous diaphragm, negative electrode electrolyte, and positive and negative liquid storage tanks. The porous diaphragm is a film with relatively high ion conductivity, and Daramic AA-800 or PP film is used. The positive and negative current collectors are made of graphite carbon felt or a conductive carbon layer.

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