CN115207426A - Boron-based negative electrode electrolyte and organic flow battery comprising same - Google Patents

Abstract

The invention discloses an organic boron negative electrode electrolyte and an organic flow battery comprising the same; the organic boron negative electrode electrolyte comprises active molecules, wherein the active molecules are beta-diketonate boron compounds, beta-diamido-esterboron compounds or beta-ketoester urethane boron compounds. The organic flow battery disclosed by the invention has the advantages of low cost, high energy density, excellent battery performance and the like.

Description

Boron-based negative electrode electrolyte and organic flow battery comprising same

Technical Field

The disclosure relates to the field of electrochemical technologies, and in particular, to an organic flow battery using a novel boron organic compound as a negative electrode electrolyte.

Background

In recent years, renewable energy sources, such as wind and solar, have been considered as an alternative, clean method of power generation to meet the increasing demand for electricity. However, due to the intermittency, weather and time variability of renewable energy sources, the supply of electric power and human demand need large-scale energy storage devices for regulation, in the existing energy storage technology, a redox flow battery is used as a low-cost and safe energy storage device, has the advantages of mutual independence of power and capacity, good expandability, long cycle life and the like, can store solar energy, wind energy and the like at the peak value, and then releases the energy at the valley value, thereby providing possibility for the new energy sources to be incorporated into an intelligent integrated power grid. A typical flow battery primarily includes a reservoir, a battery reactor, and a peristaltic pump. The positive and negative active materials are stored in the liquid storage tank, reach the cell stack through the driving of the pump, and generate oxidation-reduction reaction in the cell stack, and electrons flow to an external circuit through the current collector.

The organic molecules of the currently studied organic flow battery systems have structural designability, and parameters such as potential, solubility and kinetic diffusion coefficient of electroactive organic substances can be optimized by increasing functional groups. Especially in recent years, more and more researches are focused on developing nonaqueous organic electroactive molecules with wider electrochemical windows, wherein the nonaqueous organic electroactive molecules comprise benzoquinones, phenazines, TEMPO and ferrocene organic active molecules which all show better electrochemical performance. However, the reported molecules have disadvantages of high synthesis cost of the molecules and low energy density of the battery. The organic boron organic molecules as the cathode electrolyte active substance have the advantages of low cost, low oxidation-reduction potential, high solubility in organic solvents and the like, have great potential utilization value, and are not reported when the organic boron electroactive substance is used as the cathode electrolyte of the organic flow battery.

Disclosure of Invention

To solve the existing problems, the present disclosure provides a renewable energy storage system with high efficiency and low cost.

The present disclosure provides a boron-based negative electrolyte comprising:

an active molecule; wherein the active molecule is a beta-diketonate boron compound, a beta-diamido-ester boron compound or a beta-ketoester urethane boron compound.

In embodiments of the present disclosure, the active molecule is represented by formula I:

wherein R and R ₁ And R ₂ Each independently represents a hydrogen atom, an alkyl group or a phenyl group.

In embodiments of the present disclosure, the alkyl group is a linear or branched alkyl group, including: -CH ₃ 、-CH(CH ₃ ) ₂ 、-C(CH ₃ ) ₃ (ii) a Said phenyl group comprising-C ₆ H ₅ 。

In the disclosed embodiment, R is H, and R is ₁ And R ₂ Are all-C (CH) ₃ ) ₃ 。

In embodiments of the present disclosure, the active molecule is represented by formula II:

wherein R is ₁ -R ₁₀ Each independently represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group or one of the following functional groups: -CH ₃ 、-CH(CH ₃ ) ₂ 、-OCH ₂ CH ₂ OCH ₃ 、-O(CH ₂ CH ₂ O) _n CH ₃ (n＝1、2、3、4)、-O(CH ₂ CH ₂ O) _n CH ₂ CH ₃ (n＝1、2、3、4)、-O(CH ₂ CH ₂ O) _n OH (n =1, 2, 3, 4); ar and Ar' represent aryl groups.

In embodiments of the present disclosure, the active molecule is represented by formula III:

wherein R is ₁ -R ₅ Each independently represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group or one of the following functional groups: -CH ₃ 、-CH(CH ₃ ) ₂ 、-OCH ₂ CH ₂ OCH ₃ 、-O(CH ₂ CH ₂ O) _n CH ₃ (n＝1、2、3、4)、-O(CH ₂ CH ₂ O) _n CH ₂ CH ₃ (n＝1、2、3、4)、-O(CH ₂ CH ₂ O) _n OH (n =1, 2, 3, 4); ar represents an aryl group.

In embodiments of the disclosure, the alkyl group includes a straight or branched chain saturated or unsaturated C ₁ -C ₁₀ Alkyl, said alkoxy including straight or branched saturated or unsaturated C ₁ -C ₁₀ An alkoxy group; the aryl group is a monocyclic or polycyclic aryl group including: phenyl, naphthyl, azulenyl, anthracenyl, fluorenyl, pyrenyl, phenanthrenyl, biphenyl, and terphenyl, or the aryl group is one or more alkyl chains including saturated or unsaturated alkyl chains or C ₁ -C ₁₀ Alkoxy or a heteroatom aryl group, wherein the heteroatom comprises a halogen atom, -SH, -SR, -NO, -CN, -OH, amino.

In the disclosed embodiments, the R ₂ 、R ₄ 、R ₇ 、R ₉ Are all H, R ₁ 、R ₅ 、R ₆ 、R ₁₀ Are all-CH ₃ Said R is ₃ And R ₈ Are all-CH ₃ or-OCH ₂ CH ₂ OCH ₃ 。

The present disclosure also provides an organic flow battery comprising the boron-based negative electrolyte as described in any of the above.

In an embodiment of the present disclosure, the organic flow battery further comprises a positive electrolyte; the positive electrolyte includes a positive electrolyte active material; wherein the active substance of the positive electrode electrolyte is 2, 5-di-tert-butyl-1-methoxy-4- [2' -methoxyethoxy ] benzene.

In an embodiment of the present disclosure, the organic flow battery further includes:

an organic solvent comprising: acetonitrile, ethylene glycol dimethyl ether, propylene carbonate, dichloromethane, dimethyl sulfoxide and N-methylpyrrolidone;

a supporting electrolyte comprising: tetraethylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, lithium bistrifluoromethylsulfonimide, tetraethylammonium perfluoroalkylsulfonylimide, lithium perchlorate;

a separator comprising: polypropylene, polyethylene, polystyrene, and polytetrafluoroethylene; wherein the isolating membrane is a porous film with the pore diameter of 5-200 nanometers;

a carbon electrode, comprising: carbon felt, graphite felt, carbon cloth, carbon paper; wherein the carbon electrode is a porous electrode with the fiber diameter of 1-20 microns and the porosity of 50-98%;

a bipolar plate, comprising: graphite plate, conductive plastic plate, conductive rubber plate; wherein the conductivity of the bipolar plate is 50-800mS/cm.

The technical scheme of the present disclosure has the following positive effects:

the present disclosure provides a non-aqueous redox flow battery system having a high open circuit voltage and high energy density, wherein the negative electrolyte active molecules have (1) a very low redox potential; (2) high electrochemical stability; (3) high solubility in acetonitrile.

Drawings

The features, advantages and technical and industrial significance of the disclosed embodiments will be described below with reference to the accompanying drawings, in which like reference numerals refer to like elements.

Fig. 1 is a schematic illustration of an alternative chemical structure of a boron-based negative electrolyte active material of an embodiment of the present disclosure.

Fig. 2 is a schematic diagram of a cyclic voltammetry summary of boron beta-diketonate in accordance with an embodiment of the present disclosure.

Fig. 3 is a schematic of cyclic voltammetry for compound 1 of an embodiment of the present disclosure.

Fig. 4 is a schematic of cyclic voltammetry for compound 2 of an embodiment of the disclosure.

Fig. 5 is a schematic of cyclic voltammetry for compound 3 of an embodiment of the present disclosure.

Fig. 6 is a schematic of cyclic voltammetry for compound 4 of an embodiment of the present disclosure.

Fig. 7 is a schematic of cyclic voltammetry for compound 5 of an embodiment of the disclosure.

Fig. 8 is a schematic of cyclic voltammetry for compound 5 of the disclosed embodiments at different scan rates.

FIG. 9 is a schematic drawing of the Randles-Sevcik structure of Compound 5 of an embodiment of the disclosure.

FIG. 10 is a TEABF dissolved in an embodiment of the present disclosure ₄ Cyclic voltammogram of compound 5/DBMB of/MeCN.

Fig. 11 is a schematic illustration of the effect of current density on charge and discharge capacity of an embodiment of the disclosure.

Fig. 12 is a schematic illustration of the effect of current density on coulombic efficiency, voltage efficiency, and energy efficiency of an embodiment of the disclosure.

Fig. 13 is a schematic of battery performance of an embodiment of the disclosure.

Fig. 14 is a schematic of cyclic voltammetry for compound 6 of an embodiment of the disclosure.

Fig. 15 is a schematic of cyclic voltammetry for compound 7 of an embodiment of the present disclosure.

Fig. 16 is a schematic of cyclic voltammetry for compound 8 of an embodiment of the disclosure.

Detailed Description

The present disclosure will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams each illustrating only a basic structure of the present disclosure in a schematic manner, and thus show only the constitution related to the present disclosure.

A redox flow battery is a chargeable and dischargeable secondary battery, and an electrochemically active material is reversibly charged and discharged through a reversible redox reaction in a reaction process. Redox flow batteries are typically composed of several major components, namely a negative reservoir, a positive reservoir, a battery pack, a separator membrane, and a peristaltic pump. In the charging process, the cathode electrolyte active molecules accept electrons to perform a reduction reaction, and the anode electrolyte active molecules perform an oxidation reaction. During the discharge process, the reduced cathode electrolyte active molecules are oxidized by losing electrons to restore to the original cathode electrolyte active molecular compounds, and the oxidized anode electrolyte active molecules are subjected to a reduction reaction to restore to the original anode electrolyte active molecules. The separator is located in the center of the reaction cell to allow charged ions to pass through while preventing the two electrolytes from mixing.

To overcome the disadvantages of high material cost and low battery energy density of existing organic active molecules, the present disclosure proposes boron-based redox cathode electrolyte active materials for redox flow batteries. Fig. 1 and 2 are schematic diagrams of the chemical structures of negative electrode electrolyte active materials representative of embodiments of the present disclosure. The β -diketonatoboron or a derivative thereof used as the negative electrode electrolyte active material may be selected, for example, from β -diketonatoboron of the general formula (I):

wherein R and R ₁ And R ₂ Which may be identical or different, represent a hydrogen atom, or a linear (or branched) alkyl group: -CH ₃ 、-CH(CH ₃ ) ₂ (e.g. using ⁱ Pr)、-C(CH ₃ ) ₃ (e.g. using ^t Bu), or phenyl (e.g. -C) ₆ H ₅ ). Preferably, R is H, R ₁ And R ₂ Are all-C (CH) ₃ ) ₃ (e.g. using ^t Bu)。

In embodiments of the present disclosure, the beta-diamidoborole or derivative thereof may also be selected from beta-diketonatoboroles having the general formula (II):

wherein R is ₁ -R ₁₀ Which may be identical or different, represent a hydrogen atom, or a halogen atom, or one of the following functional groups: -CH ₃ 、-CH(CH ₃ ) ₂ (e.g. using ⁱ Pr)、-OCH ₂ CH ₂ OCH ₃ 、-O(CH ₂ CH ₂ O) _n CH ₃ (n can be 1,2, 3, 4), -O (CH) ₂ CH ₂ O) _n CH ₂ CH ₃ (n can be 1,2, 3, 4), -O (CH) ₂ CH ₂ O) _n OH (n can be 1,2, 3, 4), or selected fromStraight or branched, saturated or unsaturated C ₁ -C ₁₀ Alkyl or alkoxy. In embodiments of the present disclosure, the aryl groups, which may be the same or different, represent monocyclic or polycyclic aryl groups. The aryl group herein includes, for example, but is not limited to, phenyl, naphthyl, azulenyl, anthracenyl, fluorenyl, pyrenyl, phenanthryl, bi (di) benzene, and terphenyl. Aryl also denotes one or more aryl groups containing saturated or unsaturated alkyl chains, or saturated or unsaturated C ₁ -C ₁₀ Alkoxy, or other functional groups with heteroatoms, such as halogen atoms, -SH, -SR, -NO, -CN, -OH, amino, or other heteroaryl groups. Preferably, R ₂ 、R ₄ 、R ₇ 、R ₉ Are all H, R ₁ 、R ₃ 、R ₅ 、R ₆ 、R ₈ 、R ₁₀ Are all-CH ₃ (ii) a Or preferably R ₂ 、R ₄ 、R ₇ 、R ₉ Are all H, R ₁ 、R ₅ 、R ₆ 、R ₁₀ Are all-CH ₃ ，R ₃ And R ₈ Are all-OCH ₂ CH ₂ OCH ₃ 。

The organic solvent used in these nonaqueous redox flow battery systems may be acetonitrile (MeCN), ethylene glycol dimethyl ether (DME), propylene carbonate, methylene chloride, dimethyl sulfoxide, N-methylpyrrolidone; preferably, the organic solvent is acetonitrile (MeCN).

The supporting electrolyte may be tetraethylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, lithium bistrifluoromethylsulfonimide, tetraethylammonium tetrafluoromethylsulfonimide, lithium perchlorate; preferably, the supporting electrolyte is tetraethylammonium tetrafluoroborate.

The polymer porous membrane is one of the following: polypropylene, polyethylene, polystyrene and polytetrafluoroethylene, wherein the pore size of the separator is between 5 and 200 nm. Preferably, the polymer porous membrane is polypropylene, and the pore size is about 64nm.

The porous carbon electrode may be a carbon felt, a graphite felt, a carbon cloth or a carbon paper. The fiber diameter is about 1-20 μm, and the porosity is 50-98%. Preferably, the porous carbon electrode is a graphite felt, wherein the fibers haveHas a wire diameter of about 10 μm and a diameter of about 1.39g/cm ³ Density and a porosity of 93%.

The compact carbon bipolar plate can be a graphite plate, a conductive plastic plate or a conductive rubber plate, and the conductivity of the compact carbon bipolar plate is about 50-800mS/cm; the bipolar plates may or may not be provided with flow channels. Preferably, the dense carbon bipolar plate is a graphite plate engraved with flow channels and has a conductivity of 320mS/cm.

The working principle of the nonaqueous organic flow battery is as follows: upon charging, the negative electrode redox-active molecules acquire electrons to generate reduced negatively-charged radical products, while the positive electrode electrolyte loses electrons to generate oxidized state products. During discharge, the negative redox active molecules lose electrons, and the positive electrolyte returns to its original state after receiving the electrons.

Synthesis of Compound 1

5mL (48.7 mmol) of acetylacetone was dissolved in 20mL of toluene. To the reaction mixture was added 6mL (48.7 mmol) of boron trifluoride diethyl etherate. Connect the reaction flask to a KOH scrubber and continue to supply N ₂ . After heating the reaction mixture at 90 ℃ for 18 hours, all solvents and unreacted starting materials were removed by vacuum distillation and a pale yellow solid was obtained as the desired product compound 1. Yield: 6.82 g, 95%.

¹ H NMR(400MHz,CDCl ₃ ):δ6.01(s,1H),2.27(s,6H). ¹³ C NMR(100MHz,CDCl ₃ ):δ192.4,101.9,23.9. ¹¹ B NMR(128MHz,CDCl ₃ ):δ2.14。

Synthesis of Compound 2

1mL (8.59 mmol) of 3-methyl-2, 4-pentanedione was dissolved in 10mL of toluene. To the reaction mixture was added 1.06mL (8.59 mmol) of boron trifluoride diethyl etherate. Connect the reaction flask to a KOH scrubber and continue to supply N ₂ . After heating the reaction mixture at 50 ℃ for 14 hours, all solvents and unreacted starting materials were removed by vacuum distillation and a tan solid was obtained as the desiredThe product, compound 2. Yield: 1.32 g, 95%.

¹ H NMR(400MHz,CDCl ₃ ):δ2.31(s,6H),1.93(s,3H). ¹³ C NMR(100MHz,CDCl ₃ ):δ190.4,107.2,22.8,11.9. ¹¹ B NMR(128MHz,CDCl ₃ ):δ1.74。

Synthesis of Compound 3

1mL (9.34 mmol) of 2, 6-dimethyl-3, 5-heptanedione was dissolved in 10mL of toluene. To the reaction mixture was added 1.15mL (9.34 mmol) of boron trifluoride diethyl etherate. Connect the reaction flask to a KOH scrubber and continue to supply N ₂ . After heating the reaction mixture at 60 ℃ for 16 hours, all solvents and unreacted starting materials were removed by vacuum distillation and a pale yellow oil was obtained as the desired product compound 3. Yield: 1.2 g, 63%.

¹ H NMR(400MHz,CDCl ₃ ):δ5.96(s,1H),2.72(septet,J＝6.8Hz,2H),1.26(d,J＝6.8Hz,12H). ¹³ C NMR(100MHz,CDCl ₃ ):δ200.1,96.4,36.4,19.2. ¹¹ B NMR(128MHz,CDCl ₃ ):δ2.44。

Synthesis of Compound 4

130mg (0.764 mmol) or 2, 6-trimethylheptane-3, 5-dione were dissolved in 5mL of toluene. To the reaction mixture was added 1.15mL (0.764 mmol) of boron trifluoride diethyl ether. Connect the reaction flask to a KOH scrubber and continue to supply N ₂ . After heating the reaction mixture at 50 ℃ for 14 hours, all solvents and unreacted starting materials were removed by vacuum distillation and a pale yellow oil was obtained as the desired product compound 4. Yield: 128 mg, 77%.

¹ H NMR(400MHz,CDCl ₃ ):δ6.04(s,1H),2.72(septet,J＝6.8Hz,2H),1.27(s,9H),1.25(d,J＝6.8Hz,6H). ¹³ C NMR(100MHz,CDCl ₃ ):δ202.1,200.3,94.8,39.4,36.6,27.2,19.2. ¹¹ B NMR(128MHz,CDCl ₃ ):δ2.48。

Synthesis of Compound 5:

to a solution of 2,2,6,6-tetramethyl-3,5-heptanedione (1ml, 4.79mmol,1 eq) in toluene (10 ml) was added boron trifluoride diethyl etherate (0.592ml, 4.79mmol,1 eq). Connect the reaction flask to a KOH scrubber, continuously supply N ₂ . The mixture was heated at 50 ℃ for 15 hours. After removal of the solvent and unreacted starting material by vacuum distillation, the white solid obtained was tBuBF ₂ (890 mg, 80%) Compound (I). ¹ H NMR(400MHz，CDCl ₃ )：δ6.14(s，1H)，1.28(s，18H)。 ¹³ C NMR(100MHz，CDCl ₃ )：δ202.4,92.9,39.6,27.3。 ¹¹ B NMR(128MHz，CDCl ₃ )：δ2.66。

Compound 6:4, 6-di-tert-butyl-2, 2-difluoro-1, 3-diphenyl-1, 2-dihydro-1, 3. Lambda ⁴ ,2λ ⁴ Synthesis of (Diazaborane)

6mL (65.7 mmol) of aniline and 10.2mL (69.7 mmol) of triethylamine were dissolved in 150mL of tetrahydrofuran. 8.5mL of trimethylacetyl chloride (69.0 mmol) was added dropwise to the reaction mixture at 0 ℃ and then stirred at room temperature for 3 hours. The white precipitate was filtered to obtain a filtrate. After vacuum drying and hexane washing, a white solid, i.e., the amide product, N-phenylpivalamide, was obtained. Yield: 11.36 g (98%). 5g (28.2 mmol) of N-phenylpivalamide are suspended in 10.3mL (141.2 mmol) of thionyl chloride. The reaction flask was connected to a KOH scrubber and N was continuously supplied ₂ And heated at 70 ℃ for 2 hours. All solvents were then removed in vacuo and the desired product was extracted with hexane to give N-phenylneovaloylchloride asA yellow oil of formula (la). Yield: 5.432 g (99%). 2g (10.22 mmol) of N-phenylpivalyl chloride are dissolved in 8mL of diethyl ether. 15.7mL (20.44 mmol) of 1.3M methyllithium was added slowly to diethyl ether at-78 deg.C and at room temperature under N ₂ The mixture was stirred for 5 hours, then carefully quenched with ice and water and extracted with diethyl ether. After removal of the solvent in vacuo, the resulting oil is purified by vacuum distillation to give a colorless oil, such as 3, 3-dimethyl-N-phenylbutan-2-imine. Yield: 1.4 g (78%). 0.5g (2.85 mmol) of 3, 3-dimethyl-N-phenylbutane-2-imine and 0.436mL (2.91 mmol) of N, N, N ', N' -tetramethylethylenediamine are dissolved in 6mL of hexane. Then 1.82mL (2.91 mmol) of n-butyllithium in 1.6M hexane were slowly added at-78 ℃. The mixture was stirred at room temperature overnight, and then 0.558g (2.85 mmol) of N-phenylpivaloyl chloride was added dropwise in 5mL of hexane. After refluxing the reaction flask for 3 hours, the desired product was extracted with ether and water. The organic layer was obtained, then dried by addition of anhydrous magnesium sulfate and dried in vacuo, and then used as a reactant in the next step without further purification. 0.36g (1.08 mmol) of this reactant (2, 6-tetramethyl-N) ³ ，N ⁵ Diphenylheptane-3, 5-diimine) was dissolved in 5mL of toluene. To the reaction mixture was added 0.133mL (1.08 mmol) of boron trifluoride diethyl etherate. Connect the reaction flask to a KOH scrubber and continue to supply N ₂ . After heating the reaction mixture at 50 ℃ for 12 hours, all solvents and unreacted starting materials were removed by vacuum distillation and the white solid was further purified by column chromatography to obtain the desired product compound 6 as a white solid. Yield: 80mg, 19%.

¹ H NMR(400MHz,CDCl ₃ ):δ7.31(m,6H),7.18(m,4H),5.98(s,1H),1.14(s,18H). ¹¹ B NMR(128MHz,CDCl ₃ ):δ2.02(t). ¹⁹ F NMR(376MHz,CDCl ₃ ):δ-138.1。

Compound 7:4, 6-di-tert-butyl-2, 2-difluoro-1, 3-dimethyl-1, 2-dihydro-1, 3. Lambda ⁴ ,2λ ⁴ -dinitrogenSynthesis of heteroboronine

9.23mL (65.7 mmol) of 2.4,6-trimethylaniline and 9.71mL (69.7 mmol) of triethylamine were dissolved in 150mL of tetrahydrofuran. 8.5mL of trimethylacetyl chloride (69.0 mmol) was added dropwise to the reaction mixture at 0 ℃ and then refluxed for 2 hours. The white precipitate was filtered to obtain a filtrate. After vacuum drying and hexane washing, the white solid amide product N-homotriacyl pivalamide is obtained. Yield: 14 g (97%). 10g (45.6 mmol) of N-homotriacyl pivaloamide are suspended in 16.6mL (228 mmol) of thionyl chloride. The reaction flask was connected to a KOH scrubber, and N was continuously supplied ₂ And heated at 70 ℃ for 3 hours. All solvents were then removed in vacuo and the desired product was extracted with hexane to obtain a pale yellow oil, i.e., N-homotriacylneovalyl chloride. Yield: 10.77 g (99%). 3.5g (14.7 mmol) of N-homotriacylpivaloyl chloride are dissolved in 14mL of diethyl ether. 34mL (44.2 mmol) of diethyl ether dissolved with 1.3M methyllithium was added slowly at-78 deg.C and at room temperature under N ₂ The mixture was stirred for 2 hours, then carefully quenched with ice and water and extracted with ether. After removal of the solvent in vacuo, the resulting oil was purified by vacuum distillation to obtain a colorless oil, i.e., N-mesitylene-3, 3-dimethylbutane-2-imine. Yield: 2.56 g (80%). 0.5g (2.3 mmol) of N-mesitylene-3, 3-dimethylbutane-2-imine and 0.379mL (2.53 mmol) of N, N, N ', N' -tetramethylethylenediamine were dissolved in 3mL of hexane. Then, 1.87mL (2.99 mmol) of hexane in which 1.6M n-butyllithium was dissolved was slowly added at-78 ℃. The mixture was stirred at room temperature overnight, then 0.547g (2.3 mmol) of N-homotriacylneoglutaminechloride was added dropwise in 4mL of hexane. After refluxing the reaction flask for 2 hours, the desired product was extracted with ether and water. An organic layer was obtained, and then dried by adding anhydrous magnesium sulfate and dried in vacuum. The mixture was recrystallized from refluxing hexane to give N as a pale yellow solid ³ ，N ⁵ -dimethyl-2, 6-tetramethylheptane-3, 5-diimine. Yield: 650 mg (68%). Mixing 100mg of N ³ ，N ⁵ -dimethyl-2, 6-tetramethylheptane-3, 5-diimine (0.24 mmol) was dissolved in 7mL of toluene. 0.1mL of triethylamine (0.72 mmol) was slowly added at room temperature, and stirred at the same temperature for 30 minutes. To the reaction mixture was added 0.177mL (1.43 mmol) of boron trifluoride diethyl etherate. Connect the reaction flask to a KOH scrubber and continue to supply N ₂ . After heating the reaction mixture at 100 ℃ for 15 hours, 1mL of water was added to stop the reaction, and the product was extracted with toluene, washed several times with water, and purified by column chromatography to obtain compound 7 as a pale yellow solid. Yield: 102 mg, 91%.

¹ H NMR(400MHz,CDCl ₃ ):δ6.78(s,4H),5.89(s,1H),2.22(s,6H),2.21(s,12H),1.13(s,18H). ¹¹ B NMR(128MHz,CDCl ₃ ):δ2.19(t). ¹⁹ F NMR(376MHz,CDCl ₃ ):δ-139.9。

Compound 8:4, 6-di-tert-butyl-1, 3-bis (2, 6-diisopropylphenyl) -2, 2-difluoro-1, 2-dihydro-1, 3. Lambda ⁴ ,2λ ⁴ Synthesis of (diazaborine)

12.4mL (65.7 mmol) of 2.6-diisopropylaniline and 9.71mL (69.7 mmol) of triethylamine were dissolved in 150mL of tetrahydrofuran. 8.5mL of trimethylacetyl chloride (69.0 mmol) was added dropwise to the reaction mixture at 0 ℃ and then refluxed for 2 hours. The white precipitate was filtered to obtain a filtrate, and then the precipitate was extracted twice with tetrahydrofuran. After drying in vacuo and washing with hexane, the amide product N- (2, 6-diisopropylphenyl) pivaloamide was obtained as a white solid. Yield: 12.2 g (70%). 10g (38.3 mmol) of N- (2, 6-diisopropylphenyl) pivaloamide are suspended in 13.9mL (191.3 mmol) of thionyl chloride. The reaction flask was connected to a KOH scrubber, and N was continuously supplied ₂ And heated at 70 ℃ for 3 hours. All solvents were then removed under vacuumAnd the desired product was extracted with hexane to obtain a yellow oil in the form of N- (2, 6-diisopropylphenyl) pivaloyl chloride. Yield: 10.65 g (99%). 3.0g (10.72 mmol) of N- (2, 6-diisopropylphenyl) pivaloyl chloride was dissolved in 10mL of diethyl ether. 24.7mL (32.2 mmol) of diethyl ether dissolved with 1.3M methyllithium was added slowly at-78 deg.C and at room temperature under N ₂ The mixture was stirred for 5 hours, then carefully quenched with ice and water and extracted with ether. After removal of the solvent in vacuo, the resulting oil was purified by vacuum distillation to obtain a colorless oil, i.e., N- (2, 6-diisopropylphenyl) -3, 3-dimethylbutane-2-imine. Yield: 2.1 g (76%). 0.5g (1.93 mmol) of N- (2, 6-diisopropylphenyl) -3, 3-dimethylbutane-2-imine and 0.318mL (2.12 mmol) of N, N, N ', N' -tetramethylethylenediamine were dissolved in 3mL of hexane. Then, 1.57mL (2.51 mmol) of hexane in which 1.6M n-butyllithium was dissolved was slowly added at-78 ℃. The mixture was stirred at room temperature overnight, and then 0.539g (1.93 mmol) of N- (2, 6-diisopropylphenyl) pivaloyl chloride was added dropwise to 3mL of hexane. After refluxing the reaction flask for 2 hours, the desired product was extracted with ether and water. An organic layer was obtained, and then dried by adding anhydrous magnesium sulfate and dried in vacuum. The mixture was recrystallized from refluxing hexane and stored at-30 ℃ overnight, then washed with cold pentane to give N ³ ，N ⁵ Bis (2, 6-diisopropylphenyl) -2, 6-tetramethylheptane-3, 5-diimine as a white solid. Yield: 698 mg (72%). 80mg of N ³ ，N ⁵ Bis (2, 6-diisopropylphenyl) -2, 6-tetramethylheptane-3, 5-diimine (0.16 mmol) was dissolved in 5mL of toluene. 0.111mL of triethylamine (0.796 mmol) was slowly added at room temperature, and stirred at the same temperature for 30 minutes. 0.196mL (1.59 mmol) of boron trifluoride diethyl etherate was added to the reaction mixture at 0 ℃. Connect the reaction flask to a KOH scrubber and continue to supply N ₂ . After heating the reaction mixture at 100 ℃ for 24 hours, 1mL of water was added to stop the reaction, and the product was extracted with toluene, washed several times with water, and purified by column chromatography to obtain compound 8 as a pale yellow solid. Yield: 10.5 mg, 12%.

¹ H NMR(400MHz,CDCl ₃ ):δ7.21(t,2H),7.07(d,4H),5.69(s,1H),3.12(sep,4H),1.28(d,12H),1.22(d,12H),1.13(s,18H). ¹¹ B NMR(128MHz,CDCl ₃ ):δ2.50(t). ¹⁹ F NMR(376MHz,CDCl ₃ ):δ-127.5。

Cyclic voltammetry test

0.01mmol of beta-diketonatoboron or beta-diaminoesterboron or beta-ketonatourethaneboron or derivatives thereof was weighed out and dissolved in 5ml of a 0.5mol/L solution of tetraethylammonium tetrafluoroborate (TEABF 4) in anhydrous acetonitrile. The solution was then stirred to form a homogeneous solution with a molarity of 2mmol/L and maintained under a nitrogen atmosphere. A three-electrode system is adopted, silver nitrate/silver is used as a reference electrode, a platinum column electrode is used as a counter electrode, and a glassy carbon electrode is used as a working electrode to carry out cyclic voltammetry test. The scan rate was 100mV/s.

Referring to fig. 3 to 7, fig. 3 to 7 are schematic views of cyclic voltammetry of compounds 1-5 according to the embodiments of the present disclosure. The examples of the present disclosure first investigated the redox reversibility of the smallest diketonate boron analog 1. In MeCN/TBABF ₄ The reduction of 1 showed a completely irreversible redox couple. Next, the effect of the R' -group on redox reversibility was investigated by adding one more methyl group to 1. However, like 1,2 observed irreversible redox with no reoxidation current, indicating that the radical anion generated was unstable and that substitution on the R' -group may not improve redox reversibility. These results have prompted us to focus on the relationship between the volume of the R-group and the redox reversibility. It is hypothesized that the use of bulky R-groups may increase reversibility by enhancing steric hindrance of the reducing radical anion. As expected, isopropyl derivative 3 and asymmetric compound 4 showed a significant improvement in redox reversibility. Unfortunately, they are still quasi-reversible, despite being liquid and miscible in organic solvents such as MeCN. The symmetric di-tert-butyl species 5 is at-1.83V (vs Ag/Ag) ⁺ ) The following shows a reversible redox signal.

0.01mmol of beta-diketonatoboron or beta-diaminoesterboron or beta-ketonatourethaneboron or derivatives thereof was weighed out and dissolved in 5ml of a 0.5mol/L solution of tetraethylammonium tetrafluoroborate in anhydrous acetonitrile. The solution was then stirred to form a homogeneous solution with a molarity of 2mmol/L and maintained under a nitrogen atmosphere. A three-electrode system is adopted, silver nitrate/silver is used as a reference electrode, a platinum column electrode is used as a counter electrode, and a glassy carbon electrode is used as a working electrode to carry out cyclic voltammetry testing. The scanning speeds were 20mV/s, 50mV/s, 100mV/s, 200 and 500mV/s.

Referring to FIGS. 8 to 10, FIG. 8 is a schematic diagram of cyclic voltammetry of compound 5 of the example of the present disclosure at different scan rates, FIG. 9 is a schematic diagram of Randles-Sevcik structure of reduction wave and oxidation wave of compound 5 of the example of the present disclosure, and FIG. 10 is a schematic diagram of 0.5M EABF at a scan rate of 100mV/s ₄ Cyclic voltammogram of a 2mM mixture of 5/DBMB in MeCN. Different scan rate experiments show that the redox reaction of 5 is diffusion controlled.

Redox flow battery rate performance testing

In a glove box, 1.6mmol of beta-diketonate boron or beta-diamino ester boron or beta-keto ester urethane boron or derivatives thereof are weighed as cathode electrolyte active molecules and dissolved in 16mL of 0.5mol/L tetraethylammonium tetrafluoroborate anhydrous acetonitrile solution. The molar concentration was 0.1mol/L and shaken to form a homogeneous solution. 472mg of 2, 5-di-tert-butyl-1-methoxy-4- [2' -methoxyethoxy ] benzene (dbmb) was then weighed out as positive electrode electrolyte and added to the previously prepared homogeneous solution. The molar concentration is 0.1mol/L. The cells were then assembled into a sandwich shape in the following order: the first phenolic aldehyde plate, the first aluminum end plate, the first gold-plated copper collector plate, the first graphite plate, the first electrode, the first polytetrafluoroethylene gasket and the first polymer microporous membrane are stacked, and the second polytetrafluoroethylene gasket, the second electrode, the second graphite plate, the second gold-plated copper collector plate, the second aluminum end plate and the second phenolic resin are stacked. The prepared 16mL of mixed electrolyte solution was divided into two equal parts (8 mL each) and injected into two closed electrolyte tanks. Then, the inlet and outlet of the storage tank with the flow pump and the inlet and outlet of the anode and cathode flow fields of the battery are connected, and the electrolyte is driven to circulate at the flow rate of 40mL/min by the peristaltic pump.

Referring to fig. 11 and 12, fig. 11 shows charge and discharge performance of an assembled battery using β -diketonate boron (5) as a negative electrolyte active molecule and dbmb as a positive electrolyte active molecule, and fig. 12 shows the effect of current density on Coulombic Efficiency (CE), voltage Efficiency (VE), and Energy Efficiency (EE) of the disclosed embodiments. Using 20mA/cm ² 、30mA/cm ² 、40mA/cm ² And 50mA/cm ² The rate capability was tested at different current densities, so that it was known from 20mA/cm ² To 50mA/cm ² In the middle of the above-mentioned two-dimensional strain, each increase is 10mA/cm ² The capacity of (c) is changed. As shown in FIGS. 11 and 12, the coulombic efficiency was from 20mA/cm ² 60% of the time increased to 50mA/cm ² 80% of the time, indicating that under different currents, the active substances have less shuttling on two sides of the membrane, and the electrochemical reversibility of the active molecules is good. In addition, the voltage efficiency drops from 92% to 80% due to the increase in overpotential between the charge/discharge processes. From a rate performance study of the battery, 40mA/cm was selected in the disclosed examples ² The current density of (2) is set as an optimum current density and a charge-discharge cycle is performed for a long time.

Long cycle test for redox flow batteries

In a glove box, 1.6mmol of beta-diketonate boron (5) was weighed and dissolved in 16mL of a 0.5mol/L tetraethylammonium tetrafluoroborate solution in anhydrous acetonitrile. The molar concentration was 0.1mol/L and the mixture was shaken to form a homogeneous solution. 472mg of 2, 5-di-tert-butyl-1-methoxy-4- [2' -methoxyethoxy ] benzene (dbmb) was then weighed as a positive electrode electrolyte and added to the previously prepared homogeneous solution. In the 16mL mixed electrolyte solution, the molar concentration of the positive electrode electrolyte and the negative electrode electrolyte was 0.1mol/L. The cell was then assembled in the following order to form a sandwich shape: the first phenolic aldehyde plate, the first aluminum end plate, the first gold-plated copper collector plate, the first graphite plate, the first electrode, the first polytetrafluoroethylene gasket and the first polymer microporous membrane are stacked, and the second polytetrafluoroethylene gasket, the second electrode, the second graphite plate, the second gold-plated copper collector plate, the second aluminum end plate and the second phenolic resin are stacked. The prepared 16mL of mixed electrolyte solution was divided into two equal parts (8 mL each) and injected into two closed electrolyte tanks. Then, the inlet and outlet of the reservoir with the flow pump and the inlet and outlet of the positive and negative flow fields of the cell were connected and the cycle was driven by the peristaltic pump at a flow rate of 40 mL/min.

Referring to FIG. 13, FIG. 13 shows 0.1M 5/DBMB in 0.5M TEABF ₄ Stability, efficiency and capacity of/MeCN. Fig. 13 shows cycle performance such as charge/discharge capacity and efficiency of a flow battery using β -diketonate boron (5) as a negative electrode electrolyte active molecule and dbmb as a positive electrode electrolyte active molecule. The flow battery achieved stable efficiency (CE 80%, EE 68%, VE 85% in the first 80 cycles). However, a gradual capacity fade was observed after 80 cycles with a capacity retention of 50%, corresponding to a capacity retention of 99.4% per cycle. In general, the disclosed embodiments confirm that the organoboron-based compounds may be negative electrolyte active molecules that achieve high solubility, have high electrochemical stability, low redox potential, and high energy density, and provide important insights into the future development of boron-based redox active electrolytes in organic flow battery technology.

Referring to fig. 14, fig. 14 is a schematic view of cyclic voltammetry of compound 6 according to an embodiment of the present disclosure. Compound 6 shown in fig. 14: 4, 6-di-tert-butyl-2, 2-difluoro-1, 3-diphenyl-1, 2-dihydro-1, 3. Lambda ⁴ ,2λ ⁴ The diazaborane showed about-2.2V (vs Ag/Ag) ⁺ ) Oxidation reduction potential of (a).

Referring to fig. 15, fig. 15 is a schematic view of cyclic voltammetry of compound 7 according to the embodiment of the present disclosure. Compound 7 shown in fig. 15: 4, 6-di-tert-butyl-2, 2-difluoro-1, 3-dimethyl-1, 2-dihydro-1, 3. Lambda ⁴ ,2λ ⁴ The diazaborate salt showed about-2.5V (vs Ag/Ag) ⁺ ) Very low redox potential.

Referring to fig. 16, fig. 16 is a schematic view of cyclic voltammetry of compound 8 according to an embodiment of the present disclosure. Compound 8 shown in figure 16: 4, 6-di-tert-butyl-1, 3-bis (2, 6-diisopropylphenyl) -2, 2-difluoro-1, 2-dihydro-1, 3. Lambda ⁴ ,2λ ⁴ Diazaboronine exhibits about-2.45V (vs Ag/Ag) ⁺ ) Very low redox potential.

The boron-based negative electrolyte active molecules presented in this disclosure are useful in organic nonaqueous flow batteries. The battery takes beta-diketonate boron molecules with higher solubility, good electrochemical reversibility and chemical stability, beta-diammine boron molecules with extremely low redox potential or beta-ketoester urethane boron molecules as negative electrolyte active substances, and takes DBMB or other organic positive electrolytes as positive electrolyte active molecules. The organic nonaqueous flow battery with low cost, high energy density and excellent battery performance is constructed.

It should be understood that the specific embodiments described above are merely illustrative of the present disclosure and are not intended to limit the present disclosure. Obvious variations or modifications derived from the spirit of the present disclosure are still within the scope of the present disclosure.

In the present specification, whenever reference is made to "an exemplary embodiment", "a preferred embodiment", "one embodiment", or the like, it is intended that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment/implementation, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in other ones of the implementations described throughout.

The embodiments of the present disclosure are described above in detail. However, aspects of the present disclosure are not limited to the above-described embodiments. Various modifications and substitutions may be made to the above-described embodiments without departing from the scope of the present disclosure.

Claims (11)

1. A boron-based negative electrolyte comprising:

an active molecule;

wherein the active molecule is a beta-diketonate boron compound, a beta-diamido-ester boron compound or a beta-ketoester urethane boron compound.

2. The boron-based negative electrolyte of claim 1, wherein the active molecule is of formula I:

wherein R, R ₁ And R ₂ Each independently represents a hydrogen atom, an alkyl group or a phenyl group.

3. The boron-based negative electrolyte of claim 2, wherein the alkyl group is a linear or branched alkyl group comprising: -CH ₃ 、-CH(CH ₃ ) ₂ 、-C(CH ₃ ) ₃ (ii) a Said phenyl group comprising-C ₆ H ₅ 。

4. The boron-based negative electrode electrolyte of claim 2, wherein R is H, and R is H ₁ And R ₂ Are all-C (CH) ₃ ) ₃ 。

5. The boron-based negative electrolyte of claim 1, wherein the active molecule is represented by formula II:

wherein R is ₁ -R ₁₀ Each independently represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group or one of the following functional groups: -CH ₃ 、-CH(CH ₃ ) ₂ 、-OCH ₂ CH ₂ OCH ₃ 、-O(CH ₂ CH ₂ O) _n CH ₃ (n＝1、2、3、4)、-O(CH ₂ CH ₂ O) _n CH ₂ CH ₃ (n＝1、2、3、4)、-O(CH ₂ CH ₂ O) _n OH (n =1, 2, 3, 4); ar and Ar' represent aryl groups.

6. The boron-based negative electrolyte of claim 1, wherein the active molecule is of formula III:

wherein R is ₁ -R ₅ Each independently represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group or one of the following functional groups: -CH ₃ 、-CH(CH ₃ ) ₂ 、-OCH ₂ CH ₂ OCH ₃ 、-O(CH ₂ CH ₂ O) _n CH ₃ (n＝1、2、3、4)、-O(CH ₂ CH ₂ O) _n CH ₂ CH ₃ (n＝1、2、3、4)、-O(CH ₂ CH ₂ O) _n OH (n =1, 2, 3, 4); ar represents an aryl group.

7. The boron-based negative electrode electrolyte of claim 5 or 6, wherein the alkyl group comprises a linear or branched, saturated or unsaturated C ₁ -C ₁₀ Alkyl, said alkoxy including straight or branched chain saturated or unsaturated C ₁ -C ₁₀ An alkoxy group; the aryl group is a monocyclic or polycyclic aryl group including: phenyl, naphthyl, azulenyl, anthracenyl, fluorenyl, pyrenyl, phenanthrenyl, biphenyl and terphenyl, or the aryl group is one or more alkyl chains including saturated or unsaturated alkyl chains or C ₁ -C ₁₀ Alkoxy or heteroatom aryl, wherein the heteroatom comprises a halogen atom, -SH, -SR, -NO, -CN, -OH, amino.

8. The boron-based negative electrode electrolyte according to claim 5 or 6, wherein R is ₂ 、R ₄ 、R ₇ 、R ₉ Are all H, R ₁ 、R ₅ 、R ₆ 、R ₁₀ Are all-CH ₃ Said R is ₃ And R ₈ Are all-CH ₃ or-OCH ₂ CH ₂ OCH ₃ 。

9. An organic flow battery comprising the boron-based negative electrolyte of any of claims 1-8.

10. The organic flow battery of claim 9, further comprising a positive electrolyte; the positive electrolyte includes a positive electrolyte active material; wherein the active substance of the positive electrode electrolyte is 2, 5-di-tert-butyl-1-methoxy-4- [2' -methoxyethoxy ] benzene.

11. The organic flow battery of claim 9, further comprising:

an organic solvent comprising: acetonitrile, ethylene glycol dimethyl ether, propylene carbonate, dichloromethane, dimethyl sulfoxide and N-methylpyrrolidone;

a supporting electrolyte comprising: tetraethylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, lithium bistrifluoromethylsulfonimide, tetraethylammonium perfluoroalkylsulfonylimide, lithium perchlorate;

a separator comprising: polypropylene, polyethylene, polystyrene, and polytetrafluoroethylene; wherein, the isolating membrane is a porous film with the pore diameter of 5-200 nanometers;

a carbon electrode, comprising: carbon felt, graphite felt, carbon cloth, carbon paper; wherein the carbon electrode is a porous electrode with the fiber diameter of 1-20 microns and the porosity of 50-98%;

a bipolar plate, comprising: graphite plates, conductive plastic plates and conductive rubber plates; wherein the conductivity of the bipolar plate is 50-800mS/cm.

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