Electrolyte and preparation and application thereof

Abstract

The invention discloses an electrolyte and preparation and application thereof. The electrolyte comprises a positive electrolyte and a negative electrolyte, the positive electrolyte is an aqueous solution in which vanadium ions, ammonium ions and acid radical ions are dissolved, and the negative electrolyte is an aqueous solution in which nickel ions, cobalt ions and acid radical ions are dissolved. The preparation method of the electrolyte comprises the following steps: dissolving vanadium oxide and / or vanadium salt by adopting inorganic strong acid, filtering and taking filtrate to obtain a first solution; adjusting the average valence state of vanadium ions in the first solution to 4 by adopting an oxidizing agent or a reducing agent, and filtering to take filtrate to obtain a second solution; adding ammonium salt into the second solution, and dissolving to obtain a positive electrode electrolyte; dissolving metal nickel and / or nickel salt and metal cobalt or cobalt salt by adopting inorganic strong acid, filtering and taking filtrate to obtain a third solution; and adding water into the third solution, and adjusting the concentrations of nickel ions and cobalt ions to obtain the negative electrode electrolyte. The invention can ensure that the battery outputs electric energy more stably, shows excellent electrochemical performance and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to a battery electrolyte and a preparation method thereof, and in particular to a liquid flow battery electrolyte and a preparation and application thereof. Background Art

[0002] All-vanadium liquid flow battery is a redox battery with vanadium as the active material in a circulating liquid state. At present, the technology of vanadium liquid flow battery has gradually matured. It uses vanadium ions of different valence states to store electrical energy in sulfuric acid electrolyte, and circulates the electrolyte in the battery stack through an external pump, thereby generating an electrochemical reaction and converting chemical energy into electrical energy. This battery has the advantages of high safety, long cycle life, environmental friendliness, fast response speed and easy adjustment of capacity scale.

[0003] Existing vanadium flow batteries have the following defects and shortcomings:

[0004] 1. High initial installation cost: At present, the initial installation cost of all-vanadium liquid flow batteries is relatively high, mainly concentrated in key components such as electrolyte, stack, control system, etc. This is mainly due to factors such as the scarcity of vanadium ore resources, the complexity of electrolyte preparation, and the high cost of stack materials. Therefore, all-vanadium liquid flow batteries still face certain challenges in large-scale commercial applications.

[0005] 2. Low energy density: The performance of all-vanadium flow batteries is restricted by the concentration of vanadium ions in the positive electrolyte. Specifically, since there is an upper limit to the solubility of vanadium ions in aqueous solutions, when the concentration exceeds this critical value, high-valent pentavalent vanadium ions are easy to precipitate to form solid V2O5 precipitation. This phenomenon limits the increase in electrolyte concentration, which in turn affects the energy density of the battery, making all-vanadium flow batteries relatively inferior in terms of energy storage. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide an electrolyte with high energy density and low cost. Another purpose of the present invention is to propose a method for preparing an electrolyte to solve the problem of how to prepare an electrolyte for a redox flow battery. The third purpose of the present invention is to propose the application of the electrolyte in a flow battery to solve the problem of how to prepare a vanadium nickel cobalt flow battery.

[0007] Technical solution: The electrolyte described in the present invention includes a positive electrode electrolyte and a negative electrode electrolyte, the positive electrode electrolyte is an aqueous solution dissolved with vanadium ions, ammonium ions, and acid ions, and the negative electrode electrolyte is an aqueous solution dissolved with nickel ions, cobalt ions, and acid ions.

[0008] The present invention introduces a nickel-cobalt-based energy storage medium into the negative electrode electrolyte system of the liquid flow battery, aiming to utilize its excellent redox properties to achieve efficient reversible conversion between nickel ions and nickel and between cobalt ions and cobalt, thereby broadening the electrochemical activity range of the negative electrode material. Compared with the problem that the divalent vanadium ions in the negative electrode electrolyte of the traditional all-vanadium liquid flow battery are easily oxidized to trivalent vanadium ions, which makes it difficult to maintain the valence state balance, the nickel-cobalt-based energy storage medium used in the present invention exhibits higher stability in the air, effectively avoiding the battery performance degradation caused by valence state imbalance, and ensuring the safe and stable operation of the battery system. In addition, the nickel-cobalt-based energy storage medium selected in the present invention shows a more significant raw material cost advantage compared to the traditionally used vanadium-based energy storage medium.

[0009] The present invention incorporates a vanadium-based energy storage medium into the battery positive electrode structure, and with its excellent redox activity, realizes a highly efficient and reversible electrochemical conversion process between low-valent vanadium ions and high-valent vanadium ions.

[0010] Preferably, the initial valence state of the vanadium ions in the positive electrode electrolyte is tetravalent, and the initial valence states of the nickel ions and cobalt ions are both divalent.

[0011] Preferably, the vanadium ions are provided by vanadium oxides and / or vanadium salts, the nickel ions are provided by metallic nickel and / or nickel salts, the cobalt ions are provided by metallic cobalt or cobalt salts, and the ammonium ions are provided by ammonium salts of organic acids.

[0012] Preferably, the vanadium oxide and / or vanadium salt includes at least one of V2O5, VO2, V2O3, (VO2)2SO4, VOSO4, VO2Cl, VOCl2, VCl3, and VCl2; the nickel salt includes at least one of Ni(NO3)2, NiSO4, C4H6NiO4, and NiCl2; the cobalt salt includes at least one of Co(NO3)2, CoSO4, C4H6CoO4, and CoCl2; and the ammonium salt of the organic acid includes triammonium citrate and / or ammonium oxalate.

[0013] Preferably, the acid ions in the positive electrode electrolyte and the negative electrode electrolyte are independently selected from at least one of sulfate, nitrate and chloride ions.

[0014] The second aspect of the present invention discloses a method for preparing the above electrolyte, comprising the following steps:

[0015] (1) using a strong inorganic acid to dissolve vanadium oxide and / or vanadium salt, and filtering the filtrate to obtain a first solution;

[0016] (2) using an oxidizing agent or a reducing agent to adjust the average valence of vanadium ions in the first solution to tetravalent, and filtering the filtrate to obtain a second solution;

[0017] (3) adding ammonium salt to the second solution, dissolving it and adding a certain volume of water to obtain a positive electrode electrolyte;

[0018] (4) using an inorganic strong acid to dissolve the metal nickel and / or nickel salt and the metal cobalt or cobalt salt, and filtering the filtrate to obtain a third solution;

[0019] (5) Adding water to the third solution to adjust the concentrations of nickel ions and cobalt ions to obtain a negative electrode electrolyte.

[0020] Preferably, in step (1), the inorganic strong acid is selected from at least one of sulfuric acid, nitric acid and hydrochloric acid, and the molar ratio of the inorganic strong acid to the vanadium element is 1-2:1.

[0021] Preferably, in step (2), the oxidant is V2O5, and the reductant is oxalic acid; in step (3), the final concentration of vanadium ions in the positive electrode electrolyte is 0.5-2.0 mol / L, and the concentration of ammonium ions is 0.001-0.003 mol / L.

[0022] Preferably, in step (4), the inorganic strong acid is selected from at least one of sulfuric acid, nitric acid and hydrochloric acid, and the molar ratio of the inorganic strong acid to the nickel element is 1-2:1; in step (5), the final concentration of nickel ions in the negative electrode electrolyte is 0.25-1.0 mol / L, and the final concentration of cobalt ions is 0.5-1.5 mol / L.

[0023] According to a third aspect of the present invention, the above electrolyte is used in the preparation of a liquid flow battery.

[0024] The redox pairs of the positive and negative electrodes of the vanadium nickel cobalt flow battery obtained by assembling the above electrolytes are VO2 + / VO 2+ 、Ni 2+ / Ni and Co 2+ / Co, the standard potential difference is 1.25-1.28V, and the VO2 + Ions lose electrons to form VO 2+ ions, Ni in the negative electrolyte 2+ is reduced to form Ni, while Co 2+ The reduced Co is deposited on the negative electrode, and the discharge process is the opposite. The reaction equation of the vanadium nickel cobalt flow battery is:

[0025] Ni 2+ +2e - →Ni

[0026] Co 2+ +2e - →Co

[0027] VO 2++H2O→VO2 + +2H + +e -

[0028] Ni 2+ +Co 2+ +4VO 2+ +4H2O=Ni+Co+4VO2 + +8H +

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0030] Compared with the all-vanadium liquid flow battery, the liquid flow battery based on the coupling of vanadium-based energy storage medium and nickel-cobalt-based energy storage medium proposed in the present invention has achieved a significant reduction in the cost of electrolyte on the basis of ensuring the advantage of high energy density. The introduction of nickel-cobalt-based energy storage medium effectively solves the problem of the instability and high price of low-priced vanadium in the negative electrode of the current all-vanadium liquid flow battery. The electrolyte system can ensure a more stable output of electrical energy for the battery, exhibit excellent electrochemical performance, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the charging process of vanadium nickel cobalt flow battery;

[0032] Figure 2 Schematic diagram of the discharge process of vanadium nickel cobalt flow battery. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0034] Embodiment 1: An electrolyte comprises a positive electrode electrolyte and a negative electrode electrolyte, wherein the positive electrode electrolyte is an aqueous solution in which vanadium ions, ammonium ions and acid ions are dissolved, and the negative electrode electrolyte is an aqueous solution in which nickel ions, cobalt ions and acid ions are dissolved.

[0035] The initial valence of the vanadium ions in the positive electrolyte is 4, and the initial valence of the nickel ions and the cobalt ions are both 2. The acid radical ions in the positive electrolyte and the negative electrolyte are independently selected from at least one of sulfate, nitrate, and chloride.

[0036] The vanadium ions are provided by vanadium oxides and / or vanadium salts, the nickel ions are provided by metal nickel and / or nickel salts, the cobalt ions are provided by metal cobalt or cobalt salts, and the ammonium ions are provided by ammonium salts of organic acids.

[0037] The preparation method of the above electrolyte is as follows:

[0038] (1) dissolving (VO2)2SO4 with sulfuric acid at a molar ratio of acid to vanadium element of 1:1, and filtering the filtrate to obtain a first solution;

[0039] (2) using oxalic acid as a reducing agent to adjust the average valence of vanadium ions in the first solution to tetravalence, with a molar ratio of the reducing agent to the vanadium ions being 1:1, and filtering the filtrate to obtain a second solution;

[0040] (3) Add triammonium citrate to the second solution, dissolve it, and add a certain volume of water to obtain a positive electrode electrolyte, ensuring that the final concentration of vanadium ions in the positive electrode electrolyte is 2.0 mol / L and the concentration of ammonium ions is 0.001 mol / L.

[0041] (4) dissolving NiCl2 and CoCl2 with hydrochloric acid at a molar ratio of acid to nickel element of 2:1, and filtering the filtrate to obtain a third solution;

[0042] (5) Adding water to the third solution to adjust the final concentration of nickel ions to 1.0 mol / L and the final concentration of cobalt ions to 1.0 mol / L to obtain a negative electrode electrolyte.

[0043] Example 2: A method for preparing an electrolyte is as follows:

[0044] (1) dissolving VO2Cl with hydrochloric acid at a molar ratio of acid to vanadium element of 2:1, and filtering the filtrate to obtain a first solution;

[0045] (2) using oxalic acid as a reducing agent to adjust the average valence of vanadium ions in the first solution to tetravalence, with a molar ratio of the reducing agent to the vanadium ions being 1:1, and filtering the filtrate to obtain a second solution;

[0046] (3) adding ammonium oxalate to the second solution, and adding a certain volume of water after dissolving to obtain a positive electrode electrolyte, ensuring that the final concentration of vanadium ions in the positive electrode electrolyte is 2.0 mol / L and the concentration of ammonium ions is 0.002 mol / L.

[0047] (4) dissolving NiSO4 and CoSO4 with sulfuric acid at a molar ratio of acid to nickel element of 1:1, and filtering the filtrate to obtain a third solution;

[0048] (5) Water is added to the third solution to adjust the final concentration of nickel ions to 0.5 mol / L and the final concentration of cobalt ions to 0.5 mol / L to obtain a negative electrode electrolyte.

[0049] Example 3: A method for preparing an electrolyte is as follows:

[0050] (1) dissolving V2O5 with nitric acid at a molar ratio of acid to vanadium element of 2:1, and filtering the filtrate to obtain a first solution;

[0051] (2) using oxalic acid as a reducing agent to adjust the average valence of vanadium ions in the first solution to tetravalence, with a molar ratio of the reducing agent to the vanadium ions being 1:1, and filtering the filtrate to obtain a second solution;

[0052] (3) Adding triammonium citrate to the second solution, and adding a certain volume of water to obtain a positive electrode electrolyte after dissolving, so as to ensure that the final concentration of vanadium ions in the positive electrode electrolyte is 0.5 mol / L and the concentration of ammonium ions is 0.003 mol / L.

[0053] (4) dissolving Ni(NO3)2 and Co(NO3)2 using nitric acid at a molar ratio of acid to nickel element of 2:1, and filtering the filtrate to obtain a third solution;

[0054] (5) Water is added to the third solution to adjust the final concentration of nickel ions to 0.25 mol / L and the final concentration of cobalt ions to 0.5 mol / L to obtain a negative electrode electrolyte.

[0055] Embodiment 4: A method for preparing an electrolyte is as follows:

[0056] (1) dissolving (VO2)2SO4 with sulfuric acid at a molar ratio of acid to vanadium element of 1:1, and filtering the filtrate to obtain a first solution;

[0057] (2) using oxalic acid as a reducing agent to adjust the average valence of vanadium ions in the first solution to tetravalence, with a molar ratio of the reducing agent to the vanadium ions being 1:1, and filtering the filtrate to obtain a second solution;

[0058] (3) adding ammonium oxalate to the second solution, and adding a certain volume of water to obtain a positive electrode electrolyte after dissolution, so as to ensure that the final concentration of vanadium ions in the positive electrode electrolyte is 1.5 mol / L and the concentration of ammonium ions is 0.001 mol / L.

[0059] (4) dissolving C4H6NiO4 and C4H6CoO4 with hydrochloric acid at a molar ratio of acid to nickel element of 2:1, and filtering the filtrate to obtain a third solution;

[0060] (5) Adding water to the third solution, adjusting the final concentration of nickel ions to 1.0 mol / L and the final concentration of cobalt ions to 1.5 mol / L, to obtain a negative electrode electrolyte.

[0061] Comparative Example 1: The rest is the same as Example 1, except that:

[0062] No CoCl2 was added in step (4).

[0063] Comparative Example 2: The rest is the same as Example 1, except that:

[0064] No NiCl2 was added in step (4).

[0065] Comparative Example 3: The rest is the same as Example 1, except that:

[0066] In step (4), NiCl2 and CoCl2 are replaced by VCl2.

[0067] Comparative Example 4: The rest is the same as Example 1, except that:

[0068] Replace NiCl2 in step (4) with FeCl2.

[0069] Comparative Example 5: The rest is the same as Example 1, except that:

[0070] Replace CoCl2 in step (4) with ZnCl2.

[0071] Comparative Example 6: The rest is the same as Example 1, except that:

[0072] In step (3), triammonium citrate is replaced by ammonium chloride.

[0073] The electrolytes prepared in Examples 1-4 and Comparative Examples 1-6 were used to assemble a flow battery in the following manner:

[0074] (1) Prepare the required battery modules, electrodes, ion exchange membranes, electrolytes, pipes, valves and other components

[0075] (2) Build a stable battery assembly frame, install battery modules and connect battery assemblies according to design requirements.

[0076] (3) Install pipes and valves to ensure that the electrolyte can circulate smoothly in the battery components.

[0077] (4) Inject electrolyte for performance testing to ensure that the performance and connection of the battery components are normal and that the battery system can operate stably.

[0078] like Figure 1 and Figure 2 As shown, the working principle of the vanadium nickel cobalt flow battery assembled using Examples 1-4 is as follows:

[0079] 1. Negative electrode: During the charging process, divalent nickel ions are reduced to nickel and divalent cobalt ions are reduced to cobalt; during the discharging process, the negative electrode nickel is oxidized to divalent nickel ions and the cobalt is oxidized to divalent cobalt ions. Through the action of the diaphragm, the products and intermediates between the negative electrode and the positive electrode do not interfere with each other, ensuring the independent redox reaction of the vanadium-nickel-cobalt based energy storage medium.

[0080] During the charging process, a reduction reaction of the nickel-cobalt energy storage medium occurs:

[0081] Ni 2+ +2e- →Ni

[0082] Co 2+ +2e - →Co

[0083] During the discharge process, an oxidation reaction of the titanium-chromium energy storage medium occurs:

[0084] Ni→Ni 2+ +2e -

[0085] Co→Co 2+ +2e -

[0086] 2. Positive electrode: During the charging process, the 4-valent vanadium ions in the positive electrode are oxidized to 5-valent vanadium ions on the positive electrode carbon felt; during the discharging process, the 5-valent vanadium ions in the positive electrode undergo a reduction reaction to generate 4-valent vanadium ions. Through the action of the diaphragm, the products and intermediates between the negative electrode and the positive electrode do not interfere with each other, ensuring the independent redox reaction of the vanadium-based energy storage medium.

[0087] During the charging process, the 4-valent vanadium ions undergo an oxidation reaction to form 5-valent vanadium ions:

[0088] VO 2+ +H2O→VO2 + +2H + +e -

[0089] During the discharge process, the reduction reaction of pentavalent vanadium ions occurs to form tetravalent vanadium ions:

[0090] VO2 + +2H + +e - →VO 2+ +H2O

[0091] 3. Coupling system: Place the negative electrode containing nickel-cobalt-based energy storage medium and the positive electrode containing vanadium-based energy storage medium in the same system, and separate them by a diaphragm to ensure that the reactions between the positive and negative electrodes are carried out separately. Ensure that there is an external circuit connection between the two systems to ensure that the new liquid flow battery system can be used for electrical energy storage and output.

[0092] Total charging reaction: Ni 2+ +Co 2+ +4VO 2+ +4H2O=Ni+Co+4VO2 + +8H +

[0093] Total discharge reaction: Ni+Co+4VO2 + +8H + =Ni2+ +Co 2+ +4VO 2+ +4H2O.

[0094] The energy density of the flow battery and the efficiency of the stack outlet were tested, and the results are as follows:

[0095] Table 1 Effect of different electrolytes on battery performance

[0096] Group Energy density (Wh / L) Stack outlet efficiency (%) Example 1 22.5 74 Example 2 21.8 71 Example 3 21.1 70 Example 4 20.7 72 Comparative Example 1 13.5 37 Comparative Example 2 12.6 29 Comparative Example 3 16.2 61 Comparative Example 4 11.6 25 Comparative Example 5 14.4 43 Comparative Example 6 16.1 56

[0097] It can be seen from the results in Table 1 that when nickel ions or cobalt ions are used alone as the electrolyte of the negative electrode in Comparative Examples 1-2, the overall performance of the flow battery is not only significantly lower than that of Example 1, but is even significantly lower than that of Comparative Example 3 (i.e., the all-vanadium flow battery), indicating that the nickel or cobalt elements alone cannot significantly improve the performance of the vanadium flow battery, but will have a negative impact on the performance of the vanadium flow battery. In Comparative Examples 4-5, replacing the nickel element with the iron element or the cobalt element with the zinc element will also lead to a significant decline in the performance of the vanadium flow battery, and the battery performance is significantly lower than that of Example 1 and Comparative Example 3. The energy density and electrical efficiency of the all-vanadium flow battery in Example 1 are greatly improved compared with those in Comparative Example 3, indicating that the negative electrode electrolyte system constructed by the combined use of nickel and cobalt elements can significantly improve the electrical performance of the vanadium flow battery. Comprehensive Comparative Examples 1-5 show that the nickel element and the cobalt element in the negative electrode electrolyte synergistically improve the electrical performance of the vanadium flow battery, and both are indispensable. Comparative Example 6 shows that, as ammonium salt additives, only organic acid ammonium salts can adapt to the nickel-cobalt composite system and fully improve the electrochemical properties of the system. Although inorganic acid ammonium salts can also provide ammonium ions, they cannot further improve and exert the electrochemical properties of the nickel-cobalt composite system.

Claims

1. An electrolyte, characterized in that: It comprises a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte is an aqueous solution in which vanadium ions, ammonium ions and acid ions are dissolved. The negative electrode electrolyte is an aqueous solution in which nickel ions, cobalt ions and acid ions are dissolved.

2. The electrolyte according to claim 1, characterized in that: The initial valence state of the vanadium ions in the positive electrode electrolyte is tetravalent, and the initial valence states of the nickel ions and the cobalt ions are both divalent.

3. The electrolyte according to claim 2, characterized in that: The vanadium ions are provided by vanadium oxides and / or vanadium salts, the nickel ions are provided by metal nickel and / or nickel salts, the cobalt ions are provided by metal cobalt or cobalt salts, and the ammonium ions are provided by ammonium salts of organic acids.

4. The electrolyte according to claim 3, characterized in that: The vanadium oxide and / or vanadium salt includes at least one of V2O5, VO2, V2O3, (VO2)2SO4, VOSO4, VO2Cl, VOCl2, VCl3, and VCl2; the nickel salt includes at least one of Ni(NO3)2, NiSO4, C4H6NiO4, and NiCl2; the cobalt salt includes at least one of Co(NO3)2, CoSO4, C4H6CoO4, and CoCl2; and the ammonium salt of the organic acid includes triammonium citrate and / or ammonium oxalate.

5. The electrolyte according to claim 1, characterized in that: The acid ions in the positive electrode electrolyte and the negative electrode electrolyte are independently selected from at least one of sulfate, nitrate and chloride ions.

6. The method for preparing the electrolyte according to any one of claims 1 to 5, characterized in that: The steps include: (1) using a strong inorganic acid to dissolve vanadium oxide and / or vanadium salt, and filtering the filtrate to obtain a first solution; (2) using an oxidizing agent or a reducing agent to adjust the average valence of vanadium ions in the first solution to tetravalent, and filtering the filtrate to obtain a second solution; (3) adding ammonium salt to the second solution, dissolving it and adding a certain volume of water to obtain a positive electrode electrolyte; (4) using an inorganic strong acid to dissolve the metal nickel and / or nickel salt and the metal cobalt or cobalt salt, and filtering the filtrate to obtain a third solution; (5) Adding water to the third solution to adjust the concentrations of nickel ions and cobalt ions to obtain a negative electrode electrolyte.

7. The method for preparing the electrolyte according to claim 6, characterized in that: In step (1), the inorganic strong acid is selected from at least one of sulfuric acid, nitric acid and hydrochloric acid, and the molar ratio of the inorganic strong acid to the vanadium element is 1-2:

1.

8. The method for preparing the electrolyte according to claim 6, characterized in that: In step (2), the oxidant is V2O5, and the reductant is oxalic acid; in step (3), the final concentration of vanadium ions in the positive electrode electrolyte is 0.5-2.0 mol / L, and the concentration of ammonium ions is 0.001-0.003 mol / L.

9. The method for preparing the electrolyte according to claim 6, characterized in that: In step (4), the inorganic strong acid is selected from at least one of sulfuric acid, nitric acid and hydrochloric acid, and the molar ratio of the inorganic strong acid to the nickel element is 1-2:1; in step (5), the final concentration of nickel ions in the negative electrode electrolyte is 0.25-1.0 mol / L, and the final concentration of cobalt ions is 0.5-1.5 mol / L.

10. Use of the electrolyte according to any one of claims 1 to 5 in a liquid flow battery.

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