All-electron heteropolyacid electrolyte and high-energy-density flow battery

Abstract

The invention discloses an all-electron heteropolyacid electrolyte and a high-energy-density flow battery, the heteropolyacid electrolyte is designed based on a proton coupling electron transfer method, the heteropolyacid electrolyte is an aqueous electrolyte composed of a heteropolyacid active substance and a proton accelerator, the heteropolyacid is of a Keggin configuration Ha [XM12O40] or a Dawson configuration Hb [X2M18O62], and the proton accelerator is a proton accelerator. The proton accelerant is inorganic acid and organic acid capable of providing proton supply. According to the heteropolyacid electrolyte, stable charge-discharge cycle of full electron capacity (namely 0-100% SoC (state of charge)) in a theoretical electron range of H6 [P2W18O62] heteropolyacid 1-18 is realized. A direct charging and discharging protocol and a stepping charging and discharging protocol of the heteropolyacid-based flow battery are developed, and the flow battery has the characteristics of multi-electron transfer, high volume capacity and high energy density. The invention breaks through the long-standing bottleneck that the traditional heteropolyacid electrolyte system cannot realize stable charge-discharge cycle in a heteropolyacid high-charge state, and fundamentally solves the problem of low energy density caused by single / double electron transfer in the traditional flow battery system.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and in particular relates to an all-electronic heteropolyacid electrolyte and a high-energy-density liquid flow battery. Background Art

[0002] With the accelerated global transition to renewable energy, total installed renewable energy capacity has grown to 4,448 GW by the end of 2024 (according to the International Energy Agency), and is projected to provide nearly 90% of electricity by 2050, becoming a crucial component in addressing climate change and meeting growing energy demand. However, the intermittent and volatile nature of solar and wind power generation requires breakthrough innovations in energy storage technology to ensure grid reliability and maximize the use of renewable energy.

[0003] As a promising new electrochemical energy storage technology, redox flow batteries offer inherent safety, long life, strong stability, scalability, and renewability. They can effectively alleviate the instability and intermittency issues associated with solar and wind power, making them a key option for renewable energy grid integration, peak-shaving and valley-shifting in power systems, and backup power and energy storage devices for special scenarios. However, in the current development and commercialization of flow battery technology, widely used flow battery systems, such as all-vanadium, iron-chromium, zinc-bromine, sulfur, and halogen-based, still suffer from the fundamental limitation of generally low 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-valent oxidation states of pre-transition metal ions as skeleton atoms, and heteroatoms coordinated and bridged with oxygen atoms in a certain structure and proportion. As a recognized "electron reservoir" and "electron sponge", heteropolyacids have the potential to transfer multiple electrons and realize high-energy density flow battery electrolytes. However, during decades of research, the actual electrolyte utilization rate and charging state of heteropolyacid electrolytes have reached a critical bottleneck, that is, they can usually only reach a charging state (SoC) of less than 33.3%. With W 6+ →W 5+ 1e - Transfer meter, at 100% SoC, the classic Keggin and Dawson configuration heteropoly acids can transfer 12e - and 18e - However, according to the literature and patent reports on liquid flow batteries, the heteropoly acid electrolyte is basically in a state of charge below 33.3% and has a poor cycle stability. For example: H3[PW 12 O 40 ]Achieve 4e - 30 charge and 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: [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. [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. [3] Beijing University of Aeronautics and Astronautics. A novel keggin cobalt tungsten acid flow battery: 201610539016.9[P]. 2018-11-30. [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. [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. [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. [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 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.

[0006] 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)).

[0007] 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.

[0008] 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.

[0009] Specifically, the heteropoly acid is preferably Dawson configuration H6[P2W 18 O 62 ] and the like.

[0010] 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.

[0011] The concentration of the heteropoly acid is 0.1 to 0.8 mol / L, preferably 0.2 to 0.5 mol / L.

[0012] 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.

[0013] The second aspect of the present 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.

[0014] 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 any 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 the question of 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 present 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.

[0015] The direct charge-discharge protocol is to directly perform the flow battery charge-discharge cycle by taking 1-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 respectively by taking 1-n electron theoretical capacity as a charge cut-off condition, and then continue to directly perform the flow battery charge-discharge cycle by taking n electron theoretical capacity Specifically, 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 taken as a preset charge cut-off condition, and the flow battery charge-discharge cycle can be directly performed. 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: S1, taking 1-n electron theoretical capacity of the heteropoly acid as a charge cut-off condition, respectively, performing a flow battery charge-discharge cycle under 1-n electron theoretical capacity; S2, continuing to directly perform the flow battery charge-discharge cycle by taking n electron theoretical capacity; The calculation formula of the theoretical electron capacity of the heteropoly acid is , wherein C is the theoretical capacity, n is the number of redox electron transfer per unit heteropoly acid molecule, m is any integer value in the range of 1-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); 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; The SoC represents the state of charge (State-of-charge) of the heteropoly acid active material. The present application identifies that the heteropoly acid can be charged to n electrons at most when each framework metal atom in the heteropoly acid obtains one electron, and at this 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 charged to 12 electrons and 18 electrons at most, respectively. The calculation formula of SoC is , wherein n is the highest number of redox electron transfer per unit heteropoly acid molecule, and m is any integer value in the range of 1-n including n.

[0016] The proton concentration provided by the proton promoter is the proton concentration provided by the strong acid, medium-strong acid, weak acid type proton promoter when ionized in the heteropoly acid electrolyte; The charging cut-off condition is double cut-off of the calculated theoretical electron capacity and voltage (1.65~1.8 V), and the charging cut-off is met when any condition is met; the discharging cut-off condition is voltage cut-off (0 V).

[0017] Through the above technical solution, the application has the following beneficial effects: 1. The heteropoly acid electrolyte of the application is added with a special proton promoter, which meets the needs of the synergistic proton coupling of the charging reduction process of the heteropoly acid active substance, solves the problem of "proton starvation" existing in the traditional electrolyte system, makes the reduction potential of the heteropoly acid in the high reduction state transition smoothly, prevents the battery from charging voltage from increasing sharply and charging to the preset capacity, and ensures the stable operation of the heteropoly acid based flow battery; fundamentally solve the problems of poor cycle stability and low energy density of the heteropoly acid based flow battery.

[0018] 2. The application constructs a direct charging and discharging protocol and a step charging and discharging protocol special for the heteropoly acid based flow battery, so as to break through the control of the speed limiting step in the charging process of the heteropoly acid, and ensure the stable and reliable operation of the heteropoly acid based flow battery. DETAILED DESCRIPTION

[0019] Figure 1 is a schematic diagram of a heteropoly acid based flow battery prototype; Figure 2 is a heteropoly acid based flow battery H6[P2W 18 O 62 ] 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; Figure 3 is the flow battery charging and discharging cycle diagram of 0.2 mol / L H6[P2W 18 O 62 ] negative electrolyte at 100% SoC (18 electron capacity) in example 1; Figure 4 is the flow battery charging and discharging cycle diagram of 0.3 mol / L H6[P2W 18 O 62 ] negative electrolyte at 33.3% SoC (6 electron capacity) in example 2; Figure 5 is the flow battery charging and discharging cycle diagram of 0.3 mol / L H6[P2W 18 O 62 ] negative electrolyte at 66.7% SoC (12 electron capacity) in example 3; Figure 6is 0.3 mol / L H6[P2W 18 O 62 ] catholyte in Example 4 at 100% SoC (18 electron capacity) flow battery charge-discharge cycle diagram; Figure 7 is 0.3 mol / L H6[P2W 18 O 62 ] catholyte without proton promoter addition in Comparative Example 2 at 100% SoC (18 electron capacity) flow battery charge-discharge cycle diagram; Figure 8 is 0.5 mol / L H6[P2W 18 O 62 ] catholyte in Example 5 at 100% SoC (18 electron capacity) flow battery charge-discharge cycle diagram. DETAILED DESCRIPTION

[0020] The specific embodiments of the present application are described in detail below with reference to the examples. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present application, and are not intended to limit the present application.

[0021] H6[P2W 18 O 62 ] heteropoly acid as an active material, and prepared into a catholyte according to a new electrolyte formula. The electrolyte formula of each example and comparative example is shown in Table 1: Among them, the heteropoly acid catholyte is 8 mL, and the active material of the anolyte is vanadyl sulfate (VOSO4). In order to ensure the performance during the cycle process, the theoretical capacity of the anolyte is set to five times the theoretical capacity of the catholyte, and the volume is obtained by reverse calculation through the theoretical capacity formula C = 26.8nCV.

[0022] Table 1: Electrolyte formula and charge-discharge method of each example and comparative example

[0023] The heteropoly acid catholyte of each example is assembled into a flow battery (Flow Battery) with the anolyte, 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.

[0024] Comparative Example 1 is 0.3 mol / L H6[P2W 18 O 62 ] as the catholyte of the flow battery, and the direct charge-discharge protocol is used as the comparison with the step charge-discharge protocol, and the results are shown in Figure 6 .

[0025] Table 2. Charge-discharge performance of batteries of each example and comparative example

[0026] From Table 2 and the figures, it can be seen that: Through the step charging-discharging protocol, 0.3 mol / L H6[P2W 18 O 62 ] as the electrolyte active material, with its 1-18 electron theoretical capacity as the charging cutoff condition, each 3 cycles were carried out. At 100 mA cm -2 , after 54 charge-discharge cycles (more than 90 hours), the discharge capacity gradually increased 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).

[0027] 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 charging cutoff condition, 400 cycles (more than 674 hours) were carried out. During the period, the discharge capacity did not decrease significantly, the average discharge capacity was 94.47 Ah L -1 , the average coulombic efficiency was 97.92%, and the energy density was 99.13 Wh L -1 , indicating that under the condition of sufficient protons provided by the proton promoter, 0.2 mol / L H6[P2W 18 O 62 ] can be stably charged and discharged by the direct charge-discharge protocol at 100% SoC ( Figure 3 , Example 1).

[0028] Through the direct charge-discharge protocol of the flow battery, 0.3 mol / L H6[P2W 18 O 62As negative electrolyte active material, 0.3 mol / L H6[P2W O] was cycled at 33.3% SoC (6-electron theoretical capacity) as charge cut-off condition for 300 cycles (more than 254 hours) by flow battery direct charge-discharge protocol. During the period, the discharge capacity did not show obvious decay, 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 under the condition that the proton promoter provides sufficient protons, 0.3 mol / L H6[P2W 18 O 62 ] can be stably charged and discharged at 33.3% SoC by the direct charge-discharge protocol of the flow battery Figure 4 , Example 2).

[0029] As negative electrolyte active material, 0.3 mol / L H6[P2W 18 O 62 ] was cycled at 66.7% SoC (12-electron theoretical capacity) as charge cut-off condition for 600 cycles (more than 1024 hours) by flow battery direct charge-discharge protocol. During the period, the discharge capacity did not show obvious decay, 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 under the condition that the proton promoter provides sufficient protons, 0.3 mol / L H6[P2W 18 O 62 ] can be stably charged and discharged at 66.7% SoC by the direct charge-discharge protocol of the flow battery Figure 5 , Example 3).

[0030] As negative electrolyte active material, 0.3 mol / L H6[P2W 18 O 62 ] was cycled at 100% SoC (18-electron theoretical capacity) as charge cut-off condition for 300 cycles (more than 762 hours) by flow battery step charge-discharge protocol. During the period, the discharge capacity did not show obvious decay, the average discharge capacity was 141.55 Ah L -1 , the average coulombic efficiency was 97.81%, and the energy density was 148.13 Wh L -1 , indicating that limited by the solubility of H6[P2W 18 O 62 ], under the condition that the proton promoter cannot provide sufficient protons, 0.3 mol / L H6[P2W 18 O 62]At 100% SoC, stable charge-discharge cycling can be achieved by the step charge-discharge protocol. However, under the condition that the proton promoter cannot provide sufficient protons, direct charge-discharge protocol by flow battery, at 0.3 mol / L H6[P2W 18 O 62 ]as the negative electrolyte active material, at 100% SoC (18-electron theoretical capacity) as the charge cut-off condition, 28 cycles (more than 66 hours) were carried out. During this period, the discharge capacity decreased from 139.88 Ah L -1 to 94.08 Ah L -1 , indicating that under the condition that the proton promoter cannot provide sufficient protons, 0.3 mol / L H6[P2W 18 O 62 ]cannot be stably charged and discharged at 100% SoC by the direct charge-discharge protocol ( Figure 6 , Example 4 and Comparative Example 1).

[0031] Under the condition of "proton starvation" without the addition of proton promoters, i.e. without the supply of protons in the negative heteropoly acid electrolyte, 0.3 mol / L H6[P2W 18 O 62 ]heteropoly acid can only be charged to 91.06 Ah L -1 trigger the cut-off voltage, and cannot be charged to 100% SoC (corresponding to the 18-electron theoretical capacity of 144.72 Ah L -1 ), that is, it cannot 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 supply of protons by the proton promoter 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 ( Figure 7 , Comparative Example 2).

[0032] By the step charge-discharge protocol of the flow battery, 0.5 mol / L H6[P2W 18 O 62 ]as the negative electrolyte active material, at 100% SoC (18-electron theoretical capacity) as the charge cut-off condition, 40 cycles (more than 177 hours) were carried out. During this period, the discharge capacity did not decrease significantly, the average discharge capacity was 233.48 Ah L -1 , the average coulombic efficiency was 96.80%, and the energy density was 235.01 Wh L -1 , indicating that limited by the solubility of H6[P2W 18 O 62 ], under the condition that the proton promoter cannot provide sufficient protons, 0.5 mol / L H6[P2W 18 O62 ]At 100% SoC, stable charge-discharge cycles can be performed by a step charge-discharge protocol (see FIG. 1) Figure 8 Example 5.

[0033] 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", "direct" represents "direct charge-discharge protocol", and "step" represents "step charge-discharge protocol". The discharge capacity (unit: Ah L -1 ) and energy density (unit: Wh L -1 ) are converted based on the volume of the negative electrolyte.

[0034] Considering the ionization equilibrium of strong and weak acids in aqueous solution, when calculating the total proton concentration (mol / L) of the negative electrolyte, the total proton concentration is given in the form of a range. The minimum value of the total proton concentration is the sum of the protons of the completely ionized strong acid and the first ionized strong acid. The maximum value of the total proton concentration is the minimum value plus the protons of the remaining ionization of the strong acid and the complete ionization of the weak acid.

[0035] 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 partially ionized in the other steps. 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. In addition, strong acids and polybasic weak acids can gradually ionize completely by promoting the ionization equilibrium during the reduction of heteropoly acid.

[0036] Heteropoly acids show acidity in solution and are considered to be completely ionized, but this part of the proton is mainly used for the action of counterions of heteropoly acid clusters. In addition, as a solute molecule, the solubility of heteropoly acid in acidic aqueous solution gradually decreases with the increase of acidity. Therefore, when the concentration of heteropoly acid is higher (such as 0.5 mol / L H6[P2W 18 O 62 ] in the negative electrolyte, there is still a practical situation of "proton starvation" when enough proton promoters cannot be added.

[0037] The above describes the preferred embodiments of the present application, but the present application is not limited to the specific details in the above embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, and these simple modifications all belong to the protection scope of the present application.

[0038] It should be further noted that each of the various technical features described in the above embodiments can be combined with any other technical features in any suitable manner, and the present application is not limited to the combinations explicitly described herein, in order to avoid unnecessary repetition, the present application will not describe each possible combination.

[0039] Furthermore, any combination of the various embodiments of the present application can be made, as long as it does not deviate from the spirit of the present application, it should also be considered as disclosed by the present application.

Claims

1. An all-electronic heteropolyacid electrolyte, characterized in that The electrolyte is an aqueous electrolyte promoted by a heteropoly acid and a proton promoter. The heteropoly acid is a Keggin configuration H a [XM 12 O 40 ] or Dawson configuration 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.

2. The all-electronic heteropolyacid electrolyte according to claim 1, characterized in that 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, tartaric acid, and malic acid.

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

4. The all-electronic heteropolyacid electrolyte according to claim 1, wherein The concentration of the heteropoly acid is 0.2-0.5 mol / L.

5. The all-electronic heteropolyacid electrolyte according to claim 1, characterized in that The heteropoly acid and the H in the proton promoter + The molar ratio is 1:1~1:

25.

6. A high energy density flow battery, characterized in that: The invention comprises a negative electrode connected to a negative electrode electrolyte, a positive electrode connected to a positive electrode electrolyte, and a proton exchange membrane, wherein the negative electrode electrolyte is the all-electronic heteropolyacid electrolyte according to any one of claims 1 to 5.

7. The charge and discharge protocol of the high energy density flow battery according to claim 6, characterized in that: When the theoretical required proton concentration mc ≤ the proton concentration provided by the proton promoter, the flow battery charge and discharge cycle can be directly carried out using the heteropoly acid m-electron theoretical capacity as the preset charging cutoff condition; When the theoretical required proton concentration nc is greater than the proton concentration provided by the proton promoter, a step-by-step charge-discharge protocol is required for the charge-discharge cycle with 100% SoC of the heteropoly acid, including the following steps: S1. Using the 1~n electron theoretical capacity of the heteropoly acid as the charging cutoff condition, a flow battery charge-discharge cycle was performed at each of the 1~n electron capacities; S2, continue to perform direct charge and discharge cycles of the flow battery with n electron capacity; 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 per unit heteropoly acid molecule, m is any integer value in the range of 1 to n including n, c is the concentration of the heteropoly acid active substance, and v is the volume of the heteropoly acid electrolyte; The charge cut-off condition is a dual cut-off of the calculated theoretical electron capacity and voltage. If either condition is met, the charge is cut-off; the discharge cut-off condition is a voltage cut-off.

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