An all-electronic heteropoly acid electrolyte and high energy density flow battery

Abstract

The application discloses a kind of full electronic heteropoly acid electrolyte and high energy density flow battery, heteropoly acid electrolyte is based on proton coupling electron transfer method design, is by heteropoly acid active substance and proton promoter jointly composed water-based electrolyte, the heteropoly acid is Keggin configuration H a [XM 12 O 40 ] or Dawson configuration H b [X2M 18 O 62 ], the proton promoter is inorganic acid and organic acid that can provide proton supply.This heteropoly acid electrolyte realizes H6[P2W 18 O 62 ] heteropoly acid 1~18 theoretical electron range full electronic capacity (i.e. 0~100%SoC (State-of-charge, charge state)) stable charge-discharge cycle.Heteropoly acid-based flow battery direct charge-discharge protocol and step charge-discharge protocol are developed, and the flow battery shows multi-electron transfer, high volume capacity and high energy density characteristics.The application breaks through the bottleneck that traditional heteropoly acid electrolyte system cannot be stably charged and discharged at high charge state of heteropoly acid, and fundamentally solves the problem of low energy density caused by single / double electron transfer in traditional flow battery system.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically, it relates to an all-electron heteropolyacid electrolyte and a high-energy-density flow battery. Background Technology

[0002] With the accelerated global transition to renewable energy, the total installed capacity of renewable energy had increased to 4448 GW by the end of 2024 (data from the International Energy Agency), and is projected to provide nearly 90% of electricity by 2050, becoming a crucial guarantee for addressing climate change and meeting ever-growing energy demands. However, the intermittency and volatility of solar / wind power generation necessitate breakthrough innovations in energy storage technologies to ensure grid reliability and maximize the utilization of renewable energy.

[0003] Redox flow batteries, as a promising new electrochemical energy storage technology, possess inherent safety, long lifespan, strong stability, scalability, and renewability. They can effectively alleviate the instability and intermittency issues caused by solar and wind power, making them a core option for renewable energy grid integration, power system peak shaving and valley filling, backup power supplies for special scenarios, and energy storage devices. However, in the current research and development and commercial application of flow battery technology, the widely used vanadium-based, iron-chromium-based, zinc-bromine-based, sulfur-based, and halogen-based flow battery systems still suffer from the fundamental limitation of relatively low overall energy density due to single / double electron transfer mechanisms.

[0004] Heteropolyacids (also known as polyoxometalates) are a class of inorganic oxygen-containing polyacid compounds composed of high-valence oxidation states of former transition metal ions as framework atoms, and heteroatoms coordinated and bridged with oxygen atoms in a certain structure and proportion. As recognized "electron reservoirs" and "electron sponges," heteropolyacids possess the potential for multi-electron transfer and the realization of high-energy-density flow battery electrolytes. However, in the course of decades of research, the actual electrolyte utilization and state of charge (SoC) of heteropolyacid electrolytes have reached a critical bottleneck, typically only achieving below 33.3%. 6+ →W 5+ For 1e - According to the transfer meter, at 100% SoC, classic Keggin and Dawson configuration heteropolyacids can each transfer 12e. - and 18e - However, according to literature and patent reports on flow batteries, heteropolyacid electrolytes generally exhibit a state of charge below 33.3% and poor cycling stability. For example: H3[PW 12 O 40 Achieving 4e - 30 charge-discharge cycles during transfer (33.33% SOC) [1]; H6[CoW 12 O 40 ] achieves 4e - 30 cycles of charge-discharge at transfer (33.33% SOC) [2, 3] ; H4[SiW 12 O 40 ] achieves 2e - 155 cycles of charge-discharge at transfer (16.67% SOC) [4] ; Li5[BW 12 O 40 ] achieves 2e - 300 cycles of charge-discharge at transfer (16.67% SOC) [5] ; H6[P2W 18 O 62 ] achieves 6e - 450 cycles of charge-discharge at transfer (33.33% SOC) [6] , and 16e - 20 cycles of charge-discharge at transfer (88.9% SOC) [7] .

[0005] The above references are as follows:

[0006] [1] FENG Ting, WANG Haining, LIU Yiyang, ZHANG Jin, XIANG Yan, LU Shanfu. A redox flow battery with high capacity retention using 12-phosphotungstic acid / iodine mixed solution as electrolytes[J]. Journal of Power Sources, 2019, 436: 226831.

[0007] [2] LIU Yiyang, LU Shanfu, WANG Haining, YANG Chunmei, SU Xin, XIANG Yan. An Aqueous Redox Flow Battery with a Tungsten–Cobalt Heteropolyacid as the Electrolyte for both the Anode and Cathode[J]. Advanced Energy Materials, 2017, 7(8): 1601224.

[0008] [3] Beijing University of Aeronautics and Astronautics. A novel keggin cobalt tungstate flow battery: 201610539016.9[P]. 2018-11-30.

[0009] [4] FRIEDL Jochen, HOLLAND-CUNZ Matthaea V., CORDING Faye, PFANSCHILLING Felix L., WILLS Corinne, MCFARLANE William, SCHRICKER Barbara, FLECK Robert, WOLFSCHMIDT Holger, STIMMING Ulrich. Asymmetric polyoxometalate electrolytes for advanced redox flow batteries[J]. Energy & Environmental Science, 2018, 11(10): 3010-3018.

[0010] [5] YANG Le, HAO Yahui, LIN Jiande, LI Ke, LUO Siheng, LEI Jie, HAN Yanhong, YUAN Ruming, LIU Guokun, REN Bin, CHEN Jiajia. POM Anolyte for All-Anion Redox Flow Batteries with High Capacity Retention and Coulombic Efficiency at Mild pH[J]. Advanced Materials, 2022, 34(7): 2107425.

[0011] [6] AI Fei, WANG Zengyue, LAI Nien-Chu, ZOU Qingli, LIANG Zhuojian, LU Yi-Chun. Heteropoly acid negolytes for high-power-density aqueous redox flow batteries at low temperatures[J]. Nature Energy, 2022, 7(5): 417-426.

[0012] [7] CHEN Jia-Jia, SYMES Mark D., CRONIN Leroy. Highly reduced and protonated aqueous solutions of [P2W 18 O 62 ] 6- for on-demand hydrogen generationand energy storage[J]. Nature Chemistry, 2018, 10(10): 1042-1047. SUMMARY

[0013] In order to solve the problem that the above-mentioned heteropoly acid electrolyte can only operate in a low charge state, the application provides a full-electron heteropoly acid electrolyte and a high-energy-density flow battery, and realizes a maximum 100% charge state of the heteropoly acid electrolyte and stable charge-discharge cycle performance.

[0014] In order to achieve the above-mentioned purpose, the application discloses a full-electron heteropoly acid electrolyte and a high-energy-density flow battery, and the heteropoly acid electrolyte is designed based on a proton-coupled electron transfer method and is a water-based electrolyte composed of a heteropoly acid active substance and a proton promoter. a [XM 12 O 40 ] or a Dawson structure H b [X2M 18 O 62 ]. Wherein, X represents a central heteroatom, such as P, Si, B, Co, Fe, Zn, etc., M represents a framework metal atom, such as W, Mo, V, etc., and a and b are integers. The proton promoter is an inorganic acid and an organic acid that can provide proton supply. The heteropoly acid electrolyte realizes stable charge-discharge cycles within the full-electron capacity of H6[P2W 18 O 62 ] heteropoly acid 1~18 theoretical electrons (i.e. 0~100% SoC (State-of-charge, charge state)).

[0015] The traditional heteropoly acid electrolyte does not consider the synergistic proton-coupled electron transfer mechanism, resulting in the heteropoly acid active substance in the charging reduction process being in a "proton starvation" state, the mismatch between the proton supply and the electron transfer causing the reduction potential of the heteropoly acid to drop sharply (the battery charging voltage increases sharply, and it cannot be charged to the preset capacity), and the further distortion and instability of the heteropoly acid cluster structure, so that the heteropoly acid electrolyte can only be cycled at a low charging state level and cannot be operated stably for a long time at a high charging state. The application adds a special proton promoter to the heteropoly acid electrolyte to meet the needs of the synergistic proton coupling in the charging reduction process of the heteropoly acid active substance, solves the "proton starvation" problem existing in the traditional electrolyte system, makes the reduction potential of the heteropoly acid active substance in the high reduction state transition smoothly, prevents the sharp increase of the battery charging voltage, and ensures the stable operation of the heteropoly acid-based flow battery. The application breaks through the bottleneck that the traditional heteropoly acid electrolyte system cannot be charged and discharged stably at a high charging state of the heteropoly acid, and fundamentally solves the problem of low energy density caused by single / double electron transfer in the traditional flow battery system.

[0016] Preferably, the proton promoter includes inorganic acid and organic acid, the inorganic acid is one or more of sulfuric acid, hydrochloric acid, phosphoric acid and hydrobromic acid, and the organic acid is one or more of oxalic acid, formic acid, acetic acid, citric acid and tartaric acid.

[0017] Specifically, the heteropoly acid is preferably Dawson configuration H6[P2W 18 O 62 ] and the like.

[0018] Preferably, the molar ratio of the heteropoly acid to H + in the proton promoter is 1:1 to 1:25. The concentration of the proton promoter is determined by the required proton concentration in the charging process of the heteropoly acid and the solubility of the heteropoly acid in the proton promoter.

[0019] The concentration of the heteropoly acid is 0.1 to 0.8 mol / L, preferably 0.2 to 0.5 mol / L.

[0020] 0.3 mol / L H6[P2W 18 O 62 ] as the negative electrolyte active substance, 600 cycles (more than 1020 h) of flow battery charging and discharging were carried out at 66.7% SoC (12-electron theoretical capacity) as the charging cutoff condition, during which the 94.85 AhL -1 discharge capacity was maintained without obvious capacity attenuation, the average coulombic efficiency was 98.51%, and the energy density was 103.75 Wh L -1 ; 0.2 mol / L H6[P2W 18 O 62As the negative electrolyte active material, the discharge capacity reached 233.48 Ah L and the energy density reached 235.01 Wh L at 100% SoC (18-electron theoretical capacity) as the charge cut-off condition for the flow battery charge-discharge cycle. -1 The discharge capacity did not have obvious capacity decay, the average coulombic efficiency was 97.92%, and the energy density was 99.13 Wh L. -1 ; and 0.5 mol / L H6[P2W 18 O 62 As the negative electrolyte active material, the discharge capacity reached 233.48 Ah L and the energy density reached 235.01 Wh L at 100% SoC (18-electron theoretical capacity) as the charge cut-off condition for the flow battery charge-discharge cycle. -1 The discharge capacity did not have obvious capacity decay, the average coulombic efficiency was 97.92%, and the energy density was 99.13 Wh L. -1 The above-mentioned representative flow battery based on H6[P2W 18 O 62 ] heteropoly acid runs smoothly, and the running time, cycle number, maximum discharge capacity and energy density are much higher than those reported in the literature, indicating that the full-electron heteropoly acid electrolyte disclosed in the patent has great originality and advancement.

[0021] The second aspect of the application provides a high-energy-density flow battery, which comprises a negative electrode connected to a negative electrolyte, a positive electrode connected to a positive electrolyte, and a proton exchange membrane, preferably, the battery further comprises a circulating pump, a current collector, a graphite plate with flow channels, a gasket, an end plate, etc., the negative electrolyte is the above-mentioned heteropoly acid electrolyte which can be charged and discharged in the full-electron range, the positive electrode and the negative electrode are graphite felt or carbon felt, the current collector is preferably a gold-plated copper plate, and the graphite plate with flow channels is preferably a serpentine flow channel.

[0022] With the increase of the concentration of heteropoly acid active material in the heteropoly acid electrolyte, more protons are needed in theory. However, there is a practical problem that the solubility of heteropoly acid in water-based acidic medium will be lower than that in water without adding an additive, which makes the proton promoter in the heteropoly acid electrolyte unable to match the theoretical proton concentration required for the reduction of heteropoly acid, and further leads to the poor stability of the flow battery in the full-electron capacity range of heteropoly acid charge-discharge cycle. Therefore, for whether the proton promoter in the heteropoly acid electrolyte can match the theoretical proton concentration required for the reduction of heteropoly acid, the third aspect of the application constructs a direct charge-discharge protocol and a step-by-step charge-discharge protocol for heteropoly acid-based flow battery, to break through the control of the speed-limiting step in the charging process of heteropoly acid, and ensure the stable and reliable operation of the heteropoly acid flow battery.

[0023] The direct charge-discharge protocol is to directly perform the flow battery charge-discharge cycle with 1 to n electron theoretical capacity as a preset charge cut-off condition. The step-by-step charge-discharge protocol is to first perform a charge-discharge cycle with 1 to n electron theoretical capacity as a charge cut-off condition respectively, and then continue to perform the flow battery direct charge-discharge cycle with n electron theoretical capacity

[0024] Specifically,

[0025] When the theoretical required proton concentration mc is less than the proton concentration provided by the proton promoter, the heteropoly acid m electron theoretical capacity is used as the preset charge cut-off condition to directly perform the flow battery charge-discharge cycle.

[0026] When the theoretical required proton concentration nc is greater than the proton concentration provided by the proton promoter, the step-by-step charge-discharge protocol needs to be adopted when the heteropoly acid 100% SoC charge-discharge cycle, mainly including the following steps:

[0027] S1, the 1 to n electron theoretical capacity of the heteropoly acid is used as the charge cut-off condition, and the flow battery charge-discharge cycle is performed under the 1 to n electron theoretical capacity respectively;

[0028] S2, continue to perform the flow battery direct charge-discharge cycle with n electron theoretical capacity;

[0029] The calculation formula of the theoretical electron capacity of the heteropoly acid is , wherein C is the theoretical capacity, n is the number of unit heteropoly acid molecule redox electron transfer, m is any integer value in the range of 1 to n including n, c is the active material concentration of the heteropoly acid, v is the volume of the heteropoly acid electrolyte, and F is the Faraday constant (96485.33289, C / mol);

[0030] The mc is the theoretical required proton concentration calculated by strictly following the cooperative proton coupled electron transfer process when the c concentration of the heteropoly acid active material is transferred by m electrons, that is, the heteropoly acid cooperates with a unit proton for each unit electron transfer.

[0031] The SoC represents the state of charge (State-of-charge) of the heteropoly acid active material, and the present application identifies that each framework metal atom in the heteropoly acid obtains 1 electron when the heteropoly acid is maximally charged with n electrons, at which time the 100% SoC of the heteropoly acid corresponds. Therefore, the classic Keggin structure H a [XM 12 O 40 ] or Dawson structure H b [X2M 18 O 62 ] heteropoly acid can be maximally charged with 12 electrons and 18 electrons respectively. The calculation formula of SoC is Wherein n is the number of the highest transfer of redox electrons of a unit heteropoly acid molecule, and m is an arbitrary integer value in the range of 1-n, inclusive.

[0032] The proton concentration provided by the proton promoter is the proton concentration provided by the strong acid, medium-strong acid, and weak acid proton promoters when ionized in the heteropoly acid electrolyte.

[0033] The charging cutoff condition is the double cutoff of the calculated theoretical electronic capacity and voltage (1.65-1.8 V), and the charging cutoff is met when any condition is met; the discharging cutoff condition is the voltage cutoff (0 V).

[0034] Through the above technical solution, the application achieves the following beneficial effects:

[0035] 1. The heteropoly acid electrolyte designed in the application adds a special proton promoter, which meets the needs of the synergistic proton coupling of the charging and reduction process of the heteropoly acid active material, solves the "proton starvation" problem existing in the traditional electrolyte system, makes the reduction potential of the heteropoly acid in the high reduction state transition smoothly, and prevents the battery from charging voltage from increasing sharply to prevent charging to the preset capacity, ensuring the stable operation of the heteropoly acid-based flow battery; fundamentally solves the problems of poor cycle stability and low energy density of the heteropoly acid-based flow battery.

[0036] 2. The application constructs a direct charging and discharging protocol and a step-by-step charging and discharging protocol for a heteropoly acid-based flow battery to break through the control of the speed-limiting step in the charging process of the heteropoly acid, ensuring the stable and reliable operation of the heteropoly acid-based flow battery. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a schematic diagram of a heteropoly acid-based flow battery prototype;

[0038] Figure 2 is a H6[P2W 18 O 62 ] heteropoly acid-based flow battery full electronic capacity charging and discharging process performance diagram, wherein a is the coulombic efficiency and discharge capacity-cycle diagram, and b is the voltage-capacity diagram;

[0039] Figure 3 is a flow battery charging and discharging cycle diagram of 0.2 mol / L H6[P2W 18 O 62 ] negative electrolyte at 100% SoC (18 electronic capacity) in Example 1;

[0040] Figure 4 is a flow battery charging and discharging cycle diagram of 0.3 mol / L H6[P2W 18 O 62 ] negative electrolyte at 33.3% SoC (6 electronic capacity) in Example 2;

[0041] Figure 5 is the charge-discharge cycle diagram of 0.3 mol / L H6[P2W 18 O 62 ] negative electrolyte at 66.7% SoC (12 electron capacity) flow battery in Example 3;

[0042] Figure 6 is the charge-discharge cycle diagram of 0.3 mol / L H6[P2W 18 O 62 ] negative electrolyte at 100% SoC (18 electron capacity) flow battery in Example 4;

[0043] Figure 7 is the charge-discharge cycle diagram of 0.3 mol / L H6[P2W 18 O 62 ] negative electrolyte without the addition of a proton promoter at 100% SoC (18 electron capacity) flow battery in Comparative Example 2;

[0044] Figure 8 is the charge-discharge cycle diagram of 0.5 mol / L H6[P2W 18 O 62 ] negative electrolyte at 100% SoC (18 electron capacity) flow battery in Example 5. DETAILED DESCRIPTION

[0045] The specific embodiments of the present application are described in detail below in conjunction with the examples. It should be understood that the specific embodiments described herein are only for illustration and explanation of the present application and are not intended to limit the present application.

[0046] H6[P2W 18 O 62 ] heteropoly acid as an active material, and a negative electrolyte is prepared according to a new electrolyte formula. The electrolyte formula of each example and comparative example is shown in Table 1:

[0047] The heteropoly acid negative electrolyte is 8 mL, and the active material of the positive electrolyte is vanadyl sulfate (VOSO4). In order to ensure that the performance during the cycle process is mainly affected by the negative heteropoly acid electrolyte, the theoretical capacity of the positive electrolyte is set to five times the theoretical capacity of the negative electrolyte, and the volume is obtained by reverse calculation through the theoretical capacity formula C=26.8ncv.

[0048] Table 1: Electrolyte formula and charge-discharge method of each example and comparative example

[0049]

[0050] The heteropoly acid negative electrolyte of each embodiment is assembled into a flow battery with positive electrolyte, proton exchange membrane, positive and negative electrode materials, test fixture, etc. Figure 1 ) and its charge-discharge battery performance is tested, and the results are shown in Table 2.

[0051] Comparative Example 1 is 0.3 mol / L H6[P2W 18 O 62 ] as the negative electrolyte of the flow battery, and is subjected to a direct charge-discharge protocol, as a comparison with the step charge-discharge protocol, the results are shown in Figure 6 .

[0052] Table 2 Charge-discharge performance of batteries of each embodiment and comparative example

[0053]

[0054] From Table 2 and the figure, it can be seen that:

[0055] Through the step charge-discharge protocol, 0.3 mol / L H6[P2W 18 O 62 ] as the electrolyte active material, with its 1-18 electron theoretical capacity as the charge cutoff condition, each 3 cycles are carried out. At 100 mA cm -2 , after 54 charge-discharge cycles (more than 90 hours), the discharge capacity gradually increases to 141.87 Ah L -1 , which is equivalent to the discharge capacity of 0.3 mol / L H6[P2W 18 O 62 ] at 100% SoC, the average coulombic efficiency of the whole cycle process is 98.3%, and the energy efficiency is 81.3%, indicating that H6[P2W 18 O 62 ] heteropoly acid has stable full-electron (1-18 electron) redox ability through the reversible conversion of W 6+ and W 5+ in the cluster Figure 2 , Example 4.

[0056] Through the direct charge-discharge protocol of the flow battery, 0.2 mol / L H6[P2W 18 O 62 ] as the negative electrolyte active material, at 100% SoC (18 electron theoretical capacity) as the charge cutoff condition, 400 cycles (more than 674 hours) are carried out. During the period, the discharge capacity does not decrease significantly, the average discharge capacity is 94.47 Ah L -1 , the average coulombic efficiency is 97.92%, and the energy density is 99.13 Wh L -1, indicating that 0.2 mol / L H6[P2W 18 O 62 ] can be cycled stably at 100% SoC by direct charge-discharge protocol (Example 1). Figure 3

[0057] By liquid flow battery direct charge-discharge protocol, 0.3 mol / L H6[P2W 18 O 62 ] as negative electrolyte active material, at 33.3% SoC (6-electron theoretical capacity) as the charge cut-off condition, 300 cycles (more than 254 hours) were carried out. During the period, the discharge capacity did not decrease significantly, the average discharge capacity was 47.14 Ah L -1 , the average coulombic efficiency was 97.71%, and the energy density was 48.44 Wh L -1 , indicating that 0.3 mol / L H6[P2W 18 O 62 ] can be cycled stably at 33.3% SoC by direct charge-discharge protocol (Example 2). Figure 4

[0058] By liquid flow battery direct charge-discharge protocol, 0.3 mol / L H6[P2W 18 O 62 ] as negative electrolyte active material, at 66.7% SoC (12-electron theoretical capacity) as the charge cut-off condition, 600 cycles (more than 1024 hours) were carried out. During the period, the discharge capacity did not decrease significantly, the average discharge capacity was 94.85 Ah L -1 , the average coulombic efficiency was 98.51%, and the energy density was 103.75 Wh L -1 , indicating that 0.3 mol / L H6[P2W 18 O 62 ] can be cycled stably at 66.7% SoC by direct charge-discharge protocol (Example 3). Figure 5

[0059] By liquid flow battery step charge-discharge protocol, 0.3 mol / L H6[P2W 18 O 62 ] as negative electrolyte active material, at 100% SoC (18-electron theoretical capacity) as the charge cut-off condition, 300 cycles (more than 762 hours) were carried out. During the period, the discharge capacity did not decrease significantly, the average discharge capacity was 141.55 Ah L -1 ​​​, with an average coulombic efficiency of 97.81% and an energy density of 148.13 Wh L -1 , indicating that 0.3 mol / L H6[P2W 18 O 62 ] could not be cycled stably at 100% SoC without sufficient protons provided by the proton promoter (Example 4 and Comparative Example 1). 18 62 O 18 O 62 ] as the negative electrolyte active material at 100% SoC (18-electron theoretical capacity) as the charge cut-off condition for 28 cycles (over 66 hours). The discharge capacity continuously decayed from 139.88 Ah L -1 to 94.08 Ah L -1 , indicating that 0.3 mol / L H6[P2W 18 O 62 ] could not be cycled stably at 100% SoC without sufficient protons provided by the proton promoter (Example 4 and Comparative Example 1). Figure 6

[0060] Without the addition of a proton promoter, i.e. under the condition of "proton starvation" in which no protons are supplied in the negative heteropoly acid electrolyte, 0.3 mol / L H6[P2W 18 O 62 ] heteropoly acid triggered the cut-off voltage only when charged to 91.06 Ah L -1 , and could not be charged to 100% SoC (corresponding to an 18-electron theoretical capacity of 144.72 Ah L -1 ), i.e. could not form an effective charge-discharge cycle in the full electron range. Therefore, in combination with the results of the examples, it can be found that the condition of the proton promoter supplying protons in the heteropoly acid electrolyte plays an extremely important role in maintaining the stability of the full-electron reduction of H6[P2W 18 O 62 ] heteropoly acid (Comparative Example 2). Figure 7

[0061] Through the flow battery step charge-discharge protocol, 0.5 mol / L H6[P2W 18 O 62 ] as the negative electrolyte active material was cycled for 40 cycles (over 177 hours) at 100% SoC (18-electron theoretical capacity) as the charge cut-off condition. During the cycle, the discharge capacity did not significantly decay, with an average discharge capacity of 233.48 Ah L​​​-1 , average coulombic efficiency of 96.80%, and energy density of 235.01 Wh L -1 , indicating that the solubility of H6[P2W 18 O 62 ] is limited, and under the condition that the proton promoter cannot provide sufficient protons, 0.5 mol / L H6[P2W 18 O 62 ] can be stably charged and discharged by the step charging and discharging protocol at 100% SoC Figure 8 , Example 5).

[0062] It should be noted that the abbreviations "CE" in the above pictures represent "Coulombic Efficiency", "EE" represents "Energy Efficiency", "DC" represents "Discharge capacity", "M" represents "mol / L" (unit of concentration), "direct" represents "direct charging and discharging protocol", and "step" represents "step charging and discharging protocol". The above discharge capacity (unit: Ah L -1 ) and energy density (unit: Wh L -1 ) are based on the volume of the negative electrode electrolyte.

[0063] Considering the ionization equilibrium of strong and weak acids in aqueous solution, when calculating the total proton concentration (mol / L) of the negative electrode electrolyte, the total proton concentration is given in the form of a range, with the minimum value being the sum of the protons of the completely ionized strong acid and the first step ionized strong acid, and the maximum value being the minimum value plus the protons of the remaining ionization of the strong acid and the complete ionization of the weak acid.

[0064] Among them, H2C2O4 (oxalic acid) and H3PO4 (phosphoric acid) are polybasic strong acids, and are considered to be completely ionized in the first step, and other steps are partially ionized; tartaric acid, citric acid, and malic acid are polybasic weak acids, and are considered to be initially un-ionized due to the influence of the initial acidity of the electrolyte. And strong acid and polybasic weak acid can gradually completely ionize protons by promoting ionization equilibrium in the process of reducing heteropoly acid.

[0065] Heteropoly acid shows acidity in solution, and is considered to be completely ionized, but this part of the proton is mainly used for the action of the counterion of the heteropoly acid cluster itself. In addition, as a solute molecule, the solubility of heteropoly acid in acidic aqueous solution gradually decreases with the increase of acidity, so at higher concentrations of heteropoly acid (such as 0.5 mol / L H6[P2W 18 O 62 ]), it is not possible to add enough proton promoter in the negative electrode electrolyte, and there is still a practical situation of "proton starvation".

[0066] The above describes the preferred embodiments of the present application in detail, but the present application is not limited to the specific details in the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0067] In addition, it should be noted that each specific technical feature described in the above-described specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0068] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should be considered as disclosed by the present application.

Claims

1. A full-electronic heteropoly acid negative electrolyte, characterized in that, The electrolyte is a water-based electrolyte jointly promoted by a heteropoly acid and a proton promoter, the heteropoly acid is a Keggin structure H a [XM 12 O 40 ] or a Dawson structure H b [X2M 18 O 62 ], wherein X represents a central heteroatom, M represents a skeleton metal atom, and a and b are integers; the proton promoter includes an inorganic acid and an organic acid, the inorganic acid is one or more of sulfuric acid, hydrochloric acid, phosphoric acid, and hydrobromic acid, the organic acid is one or more of oxalic acid, formic acid, acetic acid, citric acid, and tartaric acid, and the molar ratio of H + in the heteropoly acid to the proton promoter is 1:1 to 1:

25.

2. The all-electronic heteropoly acid negative electrolyte according to claim 1, characterized in that, The heteropoly acid is of Dawson configuration H6[P2W 18 O 62 ], Keggin configuration H3[PW 12 O 40 ] or H4[SiW 12 O 40 ].

3. The all-electron heteropolyacid negative electrolyte according to claim 1, characterized by, The concentration of the heteropoly acid is 0.2-0.5 mol / L.

4. A high energy density flow battery, characterized in that, The negative electrode is connected to the negative electrolyte, the positive electrode is connected to the positive electrolyte, and the proton exchange membrane is provided.

5. The method for charging and discharging the high-energy-density flow battery of claim 4, characterized in that, When the theoretically required proton concentration mc is less than the proton concentration provided by the proton promoter, the m-electron theoretical capacity of the heteropoly acid can be directly used as the preset charging cutoff condition for the flow battery charging and discharging cycle; When the theoretically required proton concentration nc is greater than the proton concentration provided by the proton promoter, a step charging and discharging form needs to be adopted for the flow battery charging and discharging cycle at 100% SoC of the heteropoly acid, including the following steps: S1. Using 1-m-electron theoretical capacity of the heteropoly acid as the charging cutoff condition, respectively, the flow battery charging and discharging cycle is performed at 1-m-electron capacity; S2. Continue to directly charge and discharge the flow battery at n-electron capacity; Wherein the calculation formula of the theoretical electron capacity of the heteropoly acid is C=26.8ncv, wherein C is the theoretical capacity, n is the number of redox electrons of a unit heteropoly acid molecule, m is an arbitrary integer value in the range of 1-n including n, c is the active material concentration of the heteropoly acid, and v is the volume of the heteropoly acid electrolyte; The charging cutoff condition is the double cutoff of the calculated theoretical electron capacity and voltage, and any one condition is the charging cutoff; The discharging cutoff condition is the voltage cutoff.

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