A three-phase membraneless flow battery based on salting-out effect

Abstract

The application discloses a three-phase membrane-free flow battery based on salting-out effect. The three-phase membrane-free flow battery takes insoluble phase based on salting-out effect as ion exchange membrane, and takes another phase as positive electrolyte and negative electrolyte respectively, and dissolves positive and negative electroactive substances respectively. The electroactive substance is redox substance without metal deposition / dissolution. Compared with water-based organic flow battery taking ion exchange membrane as diaphragm, the flow battery of the application can be compared with the water-based organic flow battery in terms of battery cycle performance, and uses industrial available chemical substances without molecular modification, greatly reducing the cost of the battery. Compared with membrane-free flow battery taking two mutually insoluble electrolyte solutions as positive and negative electrolyte, the flow battery of the application has superior battery performance, high design flexibility and high safety. The three-phase membrane-free flow battery has certain advantages in cycle stability, cost, expandability and safety.

Description

Technical Field

[0001] This invention relates to a three-phase membrane-free flow battery based on the salting-out effect, belonging to the fields of flow battery and energy storage technology. Background Technology

[0002] Given the dwindling fossil fuel resources and the continued development of clean energy sources (wind, solar, etc.), energy storage technologies that combine high efficiency, safety, and stability have attracted widespread attention. As an electrochemical energy storage technology using solution-phase redox materials as energy carriers, flow batteries are highly favored for their high safety, scalability, and energy conversion efficiency. After more than forty years of development, all-vanadium and Zn / Br flow batteries have achieved commercial applications. However, with increasing demands on energy storage technology and the pursuit of green chemistry, the high toxicity and high cost of vanadium compounds, as well as the strong acidity of their use, limit the further application of all-vanadium flow batteries. Flow batteries using elemental metals (such as Zn and Cd) as redox materials still struggle to overcome the safety issues caused by dendrite growth; furthermore, the coupling of energy and power significantly reduces their scalability.

[0003] In recent years, flow batteries using organic electroactive materials as redox couples have become one of the hot topics in flow battery research due to their molecular modifiability, low cost, and high elemental abundance. Unlike the deposition / dissolution process of metal elements on the electrode surface, the redox process of organic electroactive materials occurs almost entirely in the solution phase, thus avoiding battery safety issues caused by potential deposition / dissolution problems. Furthermore, the redox reaction in the solution phase allows for independent design of power and energy, which is beneficial for the practical application of flow batteries.

[0004] However, although the use of organic electroactive materials is expected to reduce the cost of flow batteries and ensure their sustainable application, cost analysis has found that the widely used ion exchange membrane accounts for 20-40% of the total cost (Li. et al. Adv. Sci. 2022, 2105468, Musbaudeen. et al. Renew. Sust. Energ. Rev. 2017, 70, 506-518), and the decline in battery performance caused by factors such as ion exchange membrane contamination, reduced durability, and corrosion is also a challenge. To reduce the cost of flow batteries, membrane-free flow batteries have emerged. For example, Navalpotro et al. (Angew. Chem. Int. Ed. 2017, 56, 12460–12465) first proposed a membrane-free flow battery based on two immiscible electrolyte solutions. By partitioning p-benzoquinone and p-phenol in immiscible ionic liquids and aqueous solutions respectively, they effectively constructed a membrane-free flow battery. Although its coulombic efficiency is high, the battery performance is poor, mainly in terms of low energy density, low voltage efficiency, and high cost. Meng et al. (Joule, 2020, 4, 953-966) proposed a self-stratified battery that uses 2,2,6,6-tetramethylpiperidine-1-oxygen radical (TEMPO) dissolved in tetraethylene glycol dimethyl ether (TEGDME) and ZnSO4 dissolved in aqueous solution as the positive and negative electrode solutions, respectively. Stable cycling of the battery was achieved under external stirring conditions. This work provides a new idea for the design of flow batteries. However, the battery's dependence on stirring and the side reactions (such as hydrogen evolution), dendrite growth, self-discharge, and power and energy coupling caused by the use of Zn negative electrode cannot be ignored.

[0005] In summary, balancing the interrelationships among battery performance, cost, environmental protection, and safety is one of the important directions for the development of flow batteries. Developing flow batteries that combine safety, stability, low cost, and high scalability is an important prerequisite and development direction for realizing large-scale energy storage using flow batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a three-phase, membrane-free, metal-free (meaning that the redox material used does not contain metal) flow battery based on the salting-out effect, which is a membrane-free flow battery with high cycle stability, low cost, green safety, high scalability, and flexible design.

[0007] The present invention provides a three-phase membraneless flow battery based on the salting-out effect, wherein the insoluble phase based on the salting-out effect serves as an ion exchange membrane, which reduces cross-contamination of redox substances while ensuring the free passage of electrolyte ions, and the other phase serves as the positive electrode electrolyte and the negative electrode electrolyte, respectively dissolving the positive electrode active material and the negative electrode active material.

[0008] In the three-phase membrane-free flow battery of the present invention, both the positive electrode active material and the negative electrode active material are redox materials that do not contain metal deposition / dissolution;

[0009] Both the positive electrode active material and the negative electrode active material are 2,2,6,6-tetramethylpiperidine-1-oxygen radical (TEMPO), 2,5-di-tert-butyl-1,4-dimethoxybenzene, viologen compounds or quinone compounds;

[0010] The viologen compounds include methyl viologen, bis-(trimethylammonium)propyl viologen, and bis-(trimethylammonium)ethyl viologen;

[0011] The quinone compounds include p-benzoquinone and disodium salt of 9,10-anthraquinone-2,7-disulfonic acid;

[0012] The positive electrode active material and the negative electrode active material are preferably TEMPO and methyl viologen (MV).

[0013] In the three-phase membraneless flow battery of the present invention, the aqueous phase used for the salting-out effect is an aqueous solution of at least one of MgSO4, Li2SO4, Na2SO4, (NH4)2SO4, K2SO4 and Al2(SO4)3, preferably an aqueous solution of MgSO4, and the organic phase is an organic solution of quaternary ammonium salt or bis(trifluoromethanesulfonyl)imide.

[0014] The concentration of inorganic salts in the aqueous solution is 0.8M to 2.0M, preferably 1.8M;

[0015] The organic solvent used in the organic solution is any one of propylene carbonate (PC), acetonitrile (MeCN), ethylene glycol dimethyl ether (DME), and tetraethylene glycol dimethyl ether (TEGDME);

[0016] The concentration of quaternary ammonium salt or bis(trifluoromethanesulfonyl)imide in the organic solution is 0.5–1.5 M, preferably 1.2 M;

[0017] The specific preparation process is as follows: Prepare an aqueous solution A containing a certain concentration of inorganic salt, and prepare a non-aqueous solution B containing a certain concentration of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or quaternary ammonium salt. After thoroughly mixing equal volumes of solutions A and B, allow them to stand and separate into layers (the separation process of the two phases can also be accelerated by centrifugation, etc.), to obtain the upper layer solution (abbreviated as TP, insoluble phase) and the lower layer solution (abbreviated as BP).

[0018] In the three-phase membrane-free flow battery of the present invention, the positive electrode electrolyte is filled in the positive electrode cavity, the negative electrode electrolyte is filled in the negative electrode cavity, and the insoluble phase is placed between the positive electrode electrolyte and the negative electrode electrolyte.

[0019] Preferably, when the negative electrode active material of the three-phase membrane-free flow battery is methyl viologen, bis(trifluoromethanesulfonyl)imide is used as the paired anion;

[0020] When the positive electrode active material of the three-phase membraneless flow battery is 2,2,6,6-tetramethylpiperidine-1-oxy radical, bis(trifluoromethanesulfonyl)imide is used as the anion.

[0021] In the three-phase membrane-free flow battery of the present invention, the concentration of the positive electrode active material in the positive electrode electrolyte is 0.05–5.2 M;

[0022] The concentration of the negative electrode electroactive material in the negative electrode electrolyte is 0.05–2.1 M.

[0023] In this invention, the positive electrode current collector and the negative electrode current collector of the three-phase membrane-free flow battery are both made of stainless steel or graphite rods. Graphite rods are preferred as the positive / negative electrode current collectors. The graphite rods are cleaned and dried before use.

[0024] The electrode material of the three-phase membraneless flow battery is carbon felt, carbon cloth or carbon, preferably carbon felt as the positive / negative electrode. Before use, the carbon felt is ultrasonically cleaned in acetone, ethanol and water for 30 minutes in sequence, and then vacuum dried at 60°C.

[0025] Carbon fiber is used to connect the positive current collector to the positive electrode and the negative current collector to the negative electrode, thereby establishing electrical contact between the electrode and the current collector.

[0026] The testing of the three-phase membraneless flow battery of the present invention can be carried out in an H-shaped electrolytic cell. The H-shaped electrolytic cell has two grooves on both sides for placing the positive / negative electrolyte and electrodes, respectively. The middle cavity of the H-shaped electrolytic cell is used to place TP (insoluble phase).

[0027] The advantages of this invention over the prior art are as follows:

[0028] This invention provides a novel flow battery, which utilizes a phase separated by the salting-out effect to act as an ion exchange membrane (reducing cross-contamination of redox substances while ensuring a certain level of conductivity). This successfully constructs a three-phase membrane-free flow battery based on the salting-out effect, and demonstrates good performance in terms of battery cost, battery performance, and safety. It is a potential membrane-free flow battery that can be applied to next-generation energy storage.

[0029] Compared with other types of flow batteries, it has the following main advantages:

[0030] Compared to organic flow batteries that use ion exchange membranes as separators in aqueous systems, the flow battery of this invention is comparable to (and even superior to) some membrane-containing flow batteries in terms of battery cycle performance. Furthermore, the electroactive materials of the flow battery of this invention are industrially available chemical substances that do not require molecular modification, which greatly reduces the cost of the battery.

[0031] Table 1 Comparison of the battery performance of the present invention with that of membrane-based aqueous organic flow batteries

[0032]

[0033]

[0034] [1]TBLiu,XLWei,ZMNie,V.Sprenkle,W.Wang,Adv.Energy Mater.2016,6,1501449.

[0035] [2]YHLiu,MAGoulet,LCTong,YZLiu,YLJi,L.Wu,RGGordon,MJAziz,ZJYang,TWXu,Chem 2019,5,1861-1870.

[0036] [3]J.Luo,B.Hu,C.Debruler,TLLiu,Angew.Chem.,Int.Ed.2018,57,231-235.

[0037] [4] T.Janoschka, N.Martin, MDHager, USSchubert, Angew.Chem., Int.Ed.2016, 55, 14425-14428.

[0038] [5] B. Liu, CWTang, H. Jiang, G. Jia, T. Zhao, ACS Sustain. Chem. Eng. 2021, 9, 6258-6265.

[0039] [6]T.Janoschka,N.Martin,U.Martin,C.Friebe,S.Morgenstern,H.Hiller,MDHager,USSchubert,

[0040] Nature 2015, 527, 78-81.

[0041] [7]H.Fan,WDWu,M.Ravivarma,HBLi,B.Hu,JFLei,YYFeng,XHSun,JXSong,TLLiu,Adv.Funct.Mater.2022,32,2203032.

[0042] Note: The abbreviations of the above substances can be found in the corresponding references for their molecular structures, which are not listed here. Tables 2 and 3 are similar and will not be elaborated upon further.

[0043] Compared to flow batteries that use organic phases as solvents, the electrolyte of this invention is non-flammable. Figure 8 This demonstrates the battery's safety, and the organic solvent used is propylene carbonate, which has low toxicity, thus offering advantages in both safety and cost. Furthermore, the battery exhibits superior cycle performance (see Table 2) and greater flexibility.

[0044] Table 2 Comparison of the battery performance of the present invention with that of membrane-containing organic redox flow batteries

[0045]

[0046] [1]WTDuan,RSVemuri,JDMilshtein,S.Laramie,RDDmello,JHHuang,L.Zhang,DHHu,M.

[0047] Vijayakumar,W.Wang,J.Liu,RMDarling,L.Thompson,K.Smith,JSMoore,FRBrushett,XL

[0048] Wei,J.Mater.Chem.A 2016,4,5448-5456.

[0049] [2]WTDuan,JHHuang,JAKowalski,IAShkrob,M.Vijayakumar,E.Walter,BFPan,Z.Yang,JD

[0050] Milshtein,B.Li,C.Liao,ZCZhang,W.Wang,J.Liu,JSMoore,FRBrushett,L.Zhang,XL

[0051] Wei, ACS Energy Lett. 2017, 2, 1156-1161.

[0052] [3]C.Zhang,Y.Qian,Y.Ding,L.Zhang,X.Guo,Y.Zhao,G.Yu,Angew.Chem.,Int.Ed.2019,58,7045-7050.

[0053] [4]B.Liu,CWTang,C.Zhang,GCJia,TSZhao,Chem.Mater.2021,33,978-986.

[0054] [5]YHZhen,CJZhang,JSYuan,YDLi,J.Mater.Chem.A 2021,9,22056-22063.

[0055] [6]

[0056] [7]G.Kwon,K.Lee,MHLee,B.Lee,S.Lee,SKJung,K.Ku,J.Kim,SYPark,JEKwon,K.Kang,Chem 2019,5,2642-2656.

[0057] [8]D.Xu,C.Zhang,Y.Zhen,Y.Li,ACS Appl.Mater.Interfaces 2021,13,35579-35584.

[0058] [9]JHHuang,Z.Yang,M.Vijayakumar,WTDuan,A.Hollas,BFPan,W.Wang,XLWei,L.Zhang,Adv.Sustain.Syst.2018,2,1700131.

[0059] Compared to membrane-free flow batteries that use two immiscible electrolyte solutions as positive and negative electrodes, the flow battery of this invention exhibits superior battery performance (significantly improved cycle stability), high design flexibility, and high safety.

[0060] Table 3 Comparison of the battery performance of the present invention with that of a membraneless flow battery.

[0061]

[0062] In the table, CE represents coulombic efficiency and VE represents voltage efficiency.

[0063] [1]P.Navalpotro,C.Neves,J.Palma,MGFrire,JAPCoutinho,R.Marcilla,Adv.Sci.2018,5,1800576.

[0064] [2]P.Navalpotro,J.Palma,M.Anderson,R.Marcilla,Angew.Chem.,Int.Ed.2017,56,12460-12465.

[0065] [3] P. Navalpotro, C. Trujillo, I. Montes, C. Neves, J. Palma, MG Freire, JAP Coutinho, R. Marcilla, Energy Storage Mater. 2020, 26, 400-407.

[0066] [4] A. Chakraborty, R. Bock, R. Green, K. Luker, G. Menard, L. Sepunaru, ACSAppl.Energ.Mater.2023, 6, 605-610.

[0067] Cost estimation: Based on the report by Li et al. (Li, et al. Adv. Sci. 2022, 2105468), and assuming that the electrolyte and separator together account for 45% of the total battery cost, the total cost estimate provided by this invention is $77.1 / kWh, which is lower than the $100 / kWh target set by the U.S. Department of Energy.

[0068] Table 4. Material cost analysis of this three-phase membraneless flow battery.

[0069]

[0070] Data source:

[0071] (1)http: / / www.condicechem.com /

[0072] (2)Wei,et al.ACS Energy Lett.2017,2,2187-2204

[0073] (3) Alibaba.com

[0074] In summary, the three-phase membrane-free flow battery of this invention has certain advantages in terms of cycle stability, cost, scalability, and safety. It is one of the few membrane-free flow batteries that can combine multiple advantages. Attached Figure Description

[0075] Figure 1 Photographs (a) showing the layering of a solution containing 1.8 M MgSO4 in the aqueous phase and 1.2 M LiTFSI in the PC phase, and (b) showing the distribution of the four electroactive materials in TP and BP.

[0076] Figure 2 Cyclic voltammograms of 5 mM TEMPO and 5 mM MVTFSI at different scan rates in the BP phase are shown. The working electrode is a glassy carbon electrode with a diameter of 3 mm.

[0077] Figure 3 The cyclic voltammetry curves of 1 mM TEMPO and 1 mM MVTFSI in the BP phase are shown, with a scan rate of 50 mV·s. -1 The working electrode is a carbon felt measuring 7mm × 7mm × 5mm, and carbon fiber is used to connect the carbon felt to the working electrode wiring.

[0078] Figure 4 This is a battery performance characterization of Example 1 of the present invention, wherein Figures a and b show the cycle and charge / discharge performance of the battery at different current densities; Figure c shows the battery performance at a current density of 15 mA·cm⁻¹. -2 The charge / discharge curves at the maximum achievable energy utilization; Figures d and e show the stability analysis and charge / discharge curves after 120 cycles (225 h).

[0079] Figure 5 This is an analysis of the total voltammetry (TP) of the separating positive and negative electrode electrolytes after long-term cycling of the battery in Example 1 of this invention. Figure a shows the cyclic voltammetry curves of TP before and after long-term cycling, with a scan rate of 50 mV·s. -1 The working electrode is a glassy carbon electrode with a diameter of 3 mm. Figure b shows the UV-Vis spectral analysis of TP after long cycling.

[0080] Figure 6 This is a self-discharge analysis of the battery after long-term cycling in Embodiment 1 of the present invention. Figure a shows the battery charge-discharge curve, with a setting of 4.5t. c Observe the self-discharge behavior of the battery. Figure b shows the curves of coulombic efficiency and charge / discharge capacity retention during the self-discharge process.

[0081] Figure 7This is a practical application test of the battery in Embodiment 1 of the present invention. Figures a and b show the lighting conditions of the bulb before and after the battery forms a circuit, with the bulb off.

[0082] Figure 8 This is a solution flammability test, where Figure a and Figure b show the situation when the flame approaches BP and enters BP, respectively. Detailed Implementation

[0083] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0084] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0085] Unless otherwise specified, all commonly used chemical reagents used in this invention are commercially available products and have not undergone secondary purification. The deionized water used in the experiment was prepared in the laboratory and has a resistivity of 18.25 MΩ·cm.

[0086] All battery performance tests were performed on the LAND-CT2001A (manufactured by Wuhan Landian Electronics Co., Ltd.).

[0087] In addition, the electrochemical cyclic voltammetry of the battery was performed on a CHI 660E (manufactured by Shanghai Chenhua Instrument Co., Ltd.), with electrolyte solutions of 5 mM TEMPO and 5 mM MVTFSI (MV 2+ BP (a 1:2 complex with TFSI-).

[0088] Example 1

[0089] 1. Synthesis of MVTFSI

[0090] Aqueous solutions of 0.4 M MVCl2 (i.e., 10.28 g MVCl2 dissolved in 100 mL of water) and 0.81 M LiTFSI (i.e., 22.52 g LiTFSI dissolved in 50 mL of water) were prepared separately. LiTFSI solution was added to the MVCl2 solution under stirring, and the reaction was allowed to proceed for 30 min at a stirring rate of 300–600 rpm. After the reaction was complete, stirring was stopped, and the mixed solution and precipitate were transferred to a cleaned sintered glass funnel. Unreacted MVCl2 and LiTFSI were then filtered out using a sintered glass funnel. The solution was washed three times with deionized water (40 mL × 3). The washed MVTFSI was then transferred to a vacuum oven at 60 °C and dried for 24 h to obtain solid MVTFSI.

[0091] 2. Electrochemical property testing

[0092] 10 mL of BP solutions with concentrations of 5 mM TEMPO and MVTFSI were prepared respectively, and then placed in an electrolytic cell. A glassy carbon electrode was used as the working electrode, and a Pt disk electrode was used as the counter electrode. Ag + Cyclic voltammetry was performed using / Ag as the reference electrode. Figure 2 Cyclic voltammetry curves at different scan rates show that the electrochemical reaction is diffusion-controlled rather than surface-controlled. Furthermore, using a carbon felt as the working electrode at 50 mV·s... -1 At a scan speed of [speed], the following can be obtained Figure 3 Due to the porous and unactivated structure of the carbon felt, its reversibility is worse, but this has little impact on its use in subsequent experiments (constant current charging / discharging).

[0093] 3. Battery assembly:

[0094] (1) Mix equal volumes of an aqueous solution containing 1.8M MgSO4 (i.e., 21.672g MgSO4 prepared into 100mL of aqueous solution) with a PC solution containing 1.2M LiTFSI (34.450g LiTFSI prepared into 100mL of PC solution), allow to stand and separate into layers, then separate the layers to obtain the upper layer solution TP and the lower layer solution BP, as follows. Figure 1 Figure a shows TEMPO, and Figure b shows TEMPO. + MV 2+ and MV ·+ The distribution images of the four redox substances in TP and BP show that all four redox substances have a high distribution ratio, which is beneficial to maintaining the stability of battery performance.

[0095] (2) Prepare a battery positive electrode solution with a concentration of 0.2M TEMPO: Weigh 0.7813g of TEMPO and place it in a beaker, then add 10mL of BP to dissolve it. After it is completely dissolved, transfer it to a 25mL volumetric flask and make up to volume. This is the battery positive electrode solution.

[0096] (3) Prepare a battery negative electrode solution with a concentration of 0.5M MVTFSI: Weigh 9.3250g MVTFSI into a beaker, then add 15mL BP to dissolve it. After it is completely dissolved, centrifuge to remove a very small amount of precipitated liquid, and transfer the solution to a 25mL volumetric flask and make up to volume. This is the battery negative electrode solution.

[0097] (4) Take 5 mL of solution from the 25 mL volumetric flask containing the positive / negative electrode solution and put it into a 15 mL centrifuge tube. Continuously bubble nitrogen into the positive / negative electrode electrolyte for more than 15 min. To avoid the effect of bubbling nitrogen on the solution volume, the solvent needs to be added according to the specific situation during the experiment.

[0098] (5) Take 10 mL of TP into a 15 mL centrifuge tube and continuously purge nitrogen gas for more than 20 min.

[0099] (6) Treatment of H-shaped electrolytic cells: Before the experiment, the electrolytic cells were ultrasonically cleaned with acetone, ethanol and water, and then dried in a hot air drying oven at 60°C and naturally cooled to room temperature.

[0100] (7) The carbon felt is pretreated by cutting it into a suitable size and shape, then placing it in a beaker and ultrasonically cleaning it in acetone, ethanol and water for 30 minutes in sequence. After cleaning, the inner wall of the beaker is dried in an electric heating drying oven until there is no obvious water mist. Then it is vacuum dried at 60°C for 24 hours and then naturally cooled to room temperature.

[0101] (8) The graphite rod is pretreated by ultrasonic cleaning in ethanol and acetone for 5 minutes, followed by vacuum drying.

[0102] (9) Connect the carbon felt to the graphite rod. Establish direct electrical contact between the carbon felt and the graphite rod. To reduce the connection resistance, use carbon fiber for fixation.

[0103] (10) Place the carbon felt and graphite rod in the grooves at both ends of the H-shaped electrolytic cell, use a glass rod to fully flatten the carbon felt, and then transfer the electrolytic cell to the glove box.

[0104] (11) Assemble the battery in the glove box. Transfer the positive / negative electrolyte and TP into the glove box, and then add a certain volume of positive electrolyte and negative electrolyte to the grooves on both sides respectively (1.4 mL for battery testing, add the solution using a pipette).

[0105] (12) After the process in (5), let it stand and remove any air bubbles that may be present in the carbon felt. Then slowly add TP to the H-shaped electrolytic cell to completely cover BP. In order to avoid TP directly contacting the carbon felt, attention should be paid to the liquid addition rate during the experiment.

[0106] (13) Seal the H-shaped electrolytic cell with a polytetrafluoroethylene cap, and use hot melt adhesive to seal any possible leaks of solution / air. After the hot melt adhesive has completely cured, subsequent experiments can be carried out.

[0107] (14) Connect the current collector to the external circuit to test the battery.

[0108] 4. Battery Testing Conditions: After assembly and 6 hours of resting, testing begins. The battery is tested using a constant current charge / discharge mode with voltage cutoff conditions: a charging cutoff voltage of 1.6V and a discharging cutoff voltage of 0.2V. A graphite rod is used as the current collector. A specific current is applied for charging / discharging as needed. The battery is tested in a glove box under N2 atmosphere. First, the battery rate performance is tested by varying the charge / discharge current density to observe changes in capacity and coulombic efficiency. Figure 4 Figure a shows that, due to polarization, the battery capacity gradually decreases with increasing current density, but the coulombic efficiency remains high, demonstrating the battery's stability. Figure 4 Figure b shows the charge / discharge curves at different current densities, which further demonstrates that battery polarization increases with increasing current density.

[0109] The battery's long-cycle performance is achieved at a current density of 15 mA·cm⁻¹. -2 The process was carried out under these conditions, and the charge / discharge curve with the highest energy utilization rate was selected. Figure 4 Figure c shows that its energy utilization rate is higher than 95%. Figure 4 The middle d-figure shows the long-cycle performance of the battery, revealing good stability during 120 cycles (225 hours). Figure 4 The representative charge / discharge curves shown in Figure e further demonstrate that this flow battery produces no byproducts.

[0110] 5. Electrolyte Analysis After Cycling: After long-term cycling of the battery, 1 mL of positive / negative electrode electrolyte and 5 mL of the upper "membrane electrolyte" were taken for subsequent analysis (due to the limited solution volume in a single electrolytic cell, solutions from multiple parallel electrolytic cells can be combined for analysis). The electrochemical testing conditions for the upper solution were: working electrode: glassy carbon electrode; counter electrode: platinum electrode; reference electrode: AgCl / Ag electrode (KCl saturated); scan rate: 50 mV·s. -1 The resulting cyclic voltammetry curve is as follows: Figure 5 Figure a shows that the composition (electrochemical properties) of the "diaphragm electrolyte" remains essentially unchanged before and after long-term cycling. The UV-Vis spectrophotometric conditions for the upper layer solution were: direct UV-Vis analysis of the upper layer solution with a path length of 1 cm. The test results are as follows... Figure 5 Figure b shows that, based on the spectral results, the cross-contamination of electroactive substances is estimated to be less than 0.5% after a long cycle of 225 hours.

[0111] 6. Battery self-discharge analysis after cycling: After long-term cycling, self-discharge analysis was performed using a constant current charge / discharge mode. The difference from the above test conditions was that a 4.5t charge / discharge was used. c (That is, 4.5 times the charging time) is the resting time to observe voltage changes, which yields... Figure 6 .according to Figure 6 Figure a shows that during the settling time (4.5t)... c The voltage inside the chamber was slightly reduced. According to step 10, there was less than 0.5% cross-contamination after 225 hours of cycling. Therefore, it can be basically determined that a very small amount of side reaction or self-discharge is the main reason for the voltage drop during the resting period. Figure 6 The decrease in efficiency and capacity as the number of loops increases, as shown in Figure b, further confirms the above conclusion.

[0112] 7. Practical application test of the battery: Charge the battery to 100% SOC, then connect a light bulb in series to test the battery output. The working voltage of the light bulb is 2.2~2.4V. The test results are shown in [link to test results]. Figure 7 As can be seen, the battery can be charged / discharged stably and has a relatively stable output power.

[0113] Example 2:

[0114] The pretreatment of carbon felt and graphite rods, the preparation of solutions, and the detailed assembly process of the battery are as described in Example 1. They will only be briefly explained here and will not be repeated.

[0115] (1) Mix equal volumes of an aqueous solution containing 1.8M MgSO4 and a PC solution containing 0.8M LiTFSI thoroughly, let stand to allow the layers to separate, and then separate the layers to obtain the upper layer solution TP and the lower layer solution BP.

[0116] (2) Dissolve a certain concentration (0.05M) of TEMPO and MVCl2 (chloride) in BP to obtain the positive electrode solution and the negative electrode solution of the battery.

[0117] (3) Place the carbon felt in the grooves at both ends of the H-shaped electrolytic cell, and then add the positive electrode electrolyte and the negative electrode electrolyte to the grooves on both sides respectively.

[0118] (4) Add TP to the H-shaped electrolytic cell to completely cover the positive / negative electrode solutions.

[0119] (5) Use graphite rods to connect carbon felts. The connection between the graphite rods and carbon felts is made using carbon fiber.

[0120] Battery testing conditions: After assembly and resting for 6 hours, the test begins. The battery adopts constant current charging / discharging mode, with the cutoff condition being voltage cutoff, i.e., the charging cutoff voltage is 1.6V and the discharging cutoff voltage is 0.2V. The graphite rod is used as the current collector, and a certain current is applied according to the experimental requirements.

[0121] Example 3:

[0122] The pretreatment of carbon felt and graphite rods, the preparation of solutions, and the detailed assembly process of the battery are as described in Example 1. They will only be briefly explained here and will not be repeated.

[0123] The electrolytic cell in this embodiment differs from that in Embodiment 1. In Embodiment 1, the H-shaped electrolytic cell has concave sides for placing the carbon felt electrode and the positive / negative electrode solution, and the upper part is connected to the "diaphragm electrolyte" to connect the entire electrolytic cell. Here, the lower part of the electrolytic cell is open, while the upper part is separated to serve as a storage area for the carbon felt and the positive / negative electrode solution.

[0124] (1) Mix equal volumes of an aqueous solution containing 1.8M MgSO4 and a MeCN solution containing 1.2M LiTFSI thoroughly, let stand to allow the layers to separate, and then separate the layers to obtain the upper layer solution TP and the lower layer solution BP. The upper layer solution is the MeCN phase rich in LiTFSI, and the lower layer solution is the aqueous solution rich in MgSO4.

[0125] (2) Preparation of positive electrode solution: Accurately prepare 50mM TEMPO battery positive electrode solution.

[0126] (3) Preparation of negative electrode solution: Accurately prepare 50mM MVTFSI battery negative electrode solution.

[0127] (4) Remove N2 from the electrolyte: continuously introduce N2 into the positive electrode liquid, negative electrode liquid and BP for more than 15 minutes.

[0128] (5) Add a certain amount of BP to the H-shaped electrolytic cell. Stop adding the solution once the lower connected part is completely filled.

[0129] (6) Slowly add the positive and negative electrode solutions (1.5 mL each) to the H-shaped electrolytic cell at the same time.

[0130] (7) After the solution in step (6) is mechanically balanced, place carbon felt (which has been connected to the graphite rod in advance) into the positive / negative electrode solution. To maintain balance, carbon felt on both sides needs to be placed at the same time.

[0131] (8) Place the carbon felt to completely immerse it in TP and remove any air bubbles that may be generated using a pointed syringe.

[0132] (9) Test with an external battery testing system.

[0133] Battery testing conditions: After assembly and resting for 6 hours, the test begins. The battery adopts constant current charging and discharging mode, with the cutoff condition being voltage cutoff, i.e., the charging cutoff voltage is 1.6V and the discharging cutoff voltage is 0.2V. The graphite rod is used as the current collector, and a certain current is applied according to the needs of the experiment.

Claims

1. A three-phase membrane-free flow battery based on the salting-out effect, characterized in that: Based on the salting-out effect, the insoluble phase is used as an ion exchange membrane, and the other phase is used as the positive electrode electrolyte and the negative electrode electrolyte, respectively, to dissolve the positive electrode active material and the negative electrode active material. The salting-out effect uses an aqueous phase of at least one of MgSO4, Li2SO4, Na2SO4, (NH4)2SO4, K2SO4 and Al2(SO4)3, and an organic phase of an organic solution of quaternary ammonium salt or bis(trifluoromethanesulfonyl)imide.

2. The three-phase membrane-free flow battery according to claim 1, characterized in that: Both the positive electrode active material and the negative electrode active material are redox substances that do not contain metal deposition / dissolution.

3. The three-phase membrane-free flow battery according to claim 2, characterized in that: Both the positive electrode active material and the negative electrode active material are 2,2,6,6-tetramethylpiperidine-1-oxy radical, 2,5-di-tert-butyl-1,4-dimethoxybenzene, viologen compounds, or quinone compounds.

4. The three-phase membrane-free flow battery according to claim 3, characterized in that: The organic solvent used in the organic solution is any one of propylene carbonate, acetonitrile, ethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

5. The three-phase membrane-free flow battery according to any one of claims 1-4, characterized in that: The positive electrode electrolyte is filled in the positive electrode cavity, the negative electrode electrolyte is filled in the negative electrode cavity, and the insoluble phase is placed between the positive electrode electrolyte and the negative electrode electrolyte.

6. The three-phase membrane-free flow battery according to any one of claims 1-4, characterized in that: When the negative electrode electroactive material is methyl viologen, bis(trifluoromethanesulfonyl)imide is used as the paired anion; When the positive electrode active material is 2,2,6,6-tetramethylpiperidine-1-oxy free radical, bis(trifluoromethanesulfonyl)imide is used as the anion.

7. The three-phase membrane-free flow battery according to any one of claims 1-4, characterized in that: In the positive electrode electrolyte, the concentration of the positive electrode active material is 0.05~5.2 M; The concentration of the negative electrode electroactive material in the negative electrode electrolyte is 0.05~2.1 M.

8. The three-phase membrane-free flow battery according to any one of claims 1-4, characterized in that: The positive and negative current collectors of the three-phase membraneless flow battery are both made of stainless steel or graphite rods. The electrode material of the three-phase membraneless flow battery is carbon felt, carbon cloth, or carbon paper.

9. The three-phase membrane-free flow battery according to claim 8, characterized in that: Carbon fiber is used to connect the positive current collector to the positive electrode and the negative current collector to the negative electrode.

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