Device and method for recovering capacity of iron-chromium flow battery

Abstract

The invention discloses a device and a method for recovering the capacity of an iron-chromium flow battery. The device mainly comprises a battery assembly and a capacity recovery assembly, the battery assembly comprises a liquid storage tank, a circulating pump and an electric pile, and the battery assembly is used for conversion between electric energy and chemical energy; the capacity recovery assembly comprises a valve and a liquid storage tank; the method comprises the following steps: step 1, electrolyte aging: filling an electrolyte into a corresponding liquid storage tank, starting a circulating pump, starting a heating device to heat to 65-85 DEG C for charging and discharging circulation, stopping charging and discharging after circulation, and continuously operating the circulating pump to obtain the aged electrolyte; and 2, capacity recovery: adding an ammonium salt, heating the aged electrolyte through a heating device, carrying out heat preservation, and cooling to 50-65 DEG C to obtain the electrolyte with recovered capacity. According to the method, the capacity of the electrolyte can be dynamically recovered, and a relatively low capacity fading rate is kept.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid flow battery, and particularly relates to a device and method for capacity recovery of iron-chromium liquid flow battery. BACKGROUND

[0002] As a large-scale energy storage technology capable of integrating power grid, liquid flow battery can convert renewable energy with intermittence and uncertainty into stable power output. Among them, iron-chromium liquid flow battery has become one of the most promising liquid flow batteries due to its low cost, high efficiency and low toxicity. At present, this technology has been commercialized.

[0003] The electrolyte in the iron-chromium liquid flow battery is responsible for dissolving and transporting active substances to the electrode surface, so that the active substances undergo chemical reactions to complete the mutual conversion between chemical energy and electrical energy. Generally, the electrolyte of the iron-chromium liquid flow battery is composed of FeCl2·4H2O, CrCl3·6H2O and HCl. This results in the generation of hydrogen evolution side reaction and chromium ion aging while obtaining high conductivity and activity. Therefore, the electrochemical activity of the iron-chromium liquid flow battery gradually decreases during the charging and discharging cycle, and the battery capacity appears irreversible decay. In this case, the iron-chromium liquid flow battery will not have the advantage of low-cost electrolyte, and it will also not be able to meet the urgent demand for long-time energy storage. Therefore, the iron-chromium liquid flow battery urgently needs a method to improve the battery capacity.

[0004] At present, adding additives to the electrolyte is considered to be a simple and quick measure, such as In 3+ , Bi 3+ , Li + , PDTA, etc. However, in the current research results, the effect of the additive is often focused on improving the activity of the initial electrolyte. On the one hand, such additives have a certain effect on alleviating the capacity decay of the battery, but there is no report on the recovery effect after the capacity decay of the battery; on the other hand, such additives are mostly metal ions, which are not conducive to the recovery of the electrolyte and will also lead to the increase of the cost of the electrolyte. At present, there is a patent that proposes to use ammonium ions as an additive for iron-chromium electrolyte. However, in view of the current application scenarios of the iron-chromium liquid flow battery, the utilization rate of the iron-chromium electrolyte directly affects the cost and energy storage time of the iron-chromium liquid flow battery.

[0005] The existing electrolyte of the iron-chromium liquid flow battery has the problems of poor reusability and inability to recover after the capacity decay, and the present application provides a device and method for capacity recovery of the iron-chromium liquid flow battery. The method uses ammonium ions of inorganic salts as an additive, and uses a capacity recovery device. The device solves the problem of capacity decay caused by chromium ion aging by adding an ammonium salt liquid tank and cooperating with corresponding heating measures. SUMMARY

[0006] To solve the above technical problems, the application provides a battery capacity recovery device and application thereof: an additional storage tank containing an ammonium salt additive is arranged in the external circulation of a flow battery, ammonium salt is added into the battery storage tank according to the requirement, the capacity of the electrolyte is recovered by running the circulation system at a high temperature, and a low capacity attenuation rate is maintained.

[0007] According to an aspect of the application, a device for capacity recovery of an iron-chromium flow battery is provided, which mainly consists of two parts, a battery assembly and a capacity recovery assembly. The battery assembly comprises a storage tank I, a storage tank II, a circulation pump I, a circulation pump II and a stack, and is used for conversion between electrical energy and chemical energy. The capacity recovery assembly comprises a storage tank III. The left side of the stack is sequentially connected with the storage tank I and the circulation pump I, and the right side of the stack is sequentially connected with the storage tank II and the circulation pump II. The storage tank I and the circulation pump 1 are provided with a valve I. The storage tank II and the circulation pump II are provided with a valve II. The valve I and the valve II are provided with the storage tank III. The storage tank III is further connected with a temperature control box.

[0008] The storage tank I, the storage tank II and the storage tank III all have a heating function, i.e., are provided with a heating device. Effects of key components: The storage tank I is used for storing iron-chromium electrolyte.

[0009] The storage tank II is used for storing iron-chromium electrolyte.

[0010] The storage tank III is used for storing ammonium salt additives.

[0011] The circulation pump I is used for delivering iron-chromium electrolyte to the stack.

[0012] The circulation pump II is used for delivering iron-chromium electrolyte to the stack.

[0013] The valve I is used for controlling the entry of ammonium salt into the iron-chromium electrolyte.

[0014] The valve II is used for controlling the entry of ammonium salt into the iron-chromium electrolyte.

[0015] The capacity recovery of the iron-chromium flow battery is realized by arranging the valve and the circulation pump.

[0016] According to another aspect of the application, a method for capacity recovery of an iron-chromium flow battery is provided, characterized in that the method is as follows: Electrolyte aging: the initial electrolyte is filled into the liquid storage tank, the circulating pump is turned on, and the heating device is turned on to heat the liquid storage tank I and the liquid storage tank II to 50-65℃ for charging and discharging cycle, after the cycle, stop charging and discharging, the circulating pump continues to run, and the aged electrolyte is obtained; Step 2, capacity recovery: adding ammonium salt to the aged electrolyte in step 1, heating the aged electrolyte in step 1 to 65-85℃ by heating device, cooling to 50-65℃ for charging and discharging, and obtaining the electrolyte with recovered capacity.

[0017] Based on the above technical scheme, the components of the electrolyte in step 1 are ferrous salt solution, chromium salt solution, and acid solution; The ferrous salt solution is selected from at least one of ferrous chloride solution and ferrous sulfate solution; The chromium salt solution is selected from at least one of chromium chloride solution and chromium sulfate; The acid solution is selected from at least one of dilute hydrochloric acid, dilute sulfuric acid, and dilute hydrochloric acid.

[0018] Based on the above technical scheme, the components of the electrolyte in step 1 are ferrous chloride solution, chromium chloride solution, dilute hydrochloric acid, and ammonium chloride solution, wherein the concentration of the ferrous chloride solution is 1-3 mol•L -1 , the concentration of the chromium chloride solution is 1-3 mol•L -1 , and the concentration of the dilute hydrochloric acid is 3-5 mol•L -1 .

[0019] Based on the above technical scheme, the current density of the cycle in step 1 is 40-200 mA / cm 2 . The number of cycles in step 1 is 100-1000 cycles; The capacity of the electrolyte after the first charging and discharging cycle in step 1 is 800-1100 mA h.

[0020] Based on the above technical scheme, the capacity of the aged electrolyte obtained in step 1 is 400-550 mA h.

[0021] Based on the above technical scheme, the ammonium salt solution in step 2 is selected from at least one of ammonium chloride, ammonium sulfate, and ammonium bisulfate, and preferably 0.1-5 mol•L -1 of ammonium chloride solution.

[0022] Based on the above technical scheme, the content of the hexaammonium chromium ion complex in the aged electrolyte obtained in step 1 is 50-70%, and the capacity recovery is as follows: the heating device is turned on to heat the liquid storage tank III to 65-85 DEG C, and the temperature is kept for 5-30 minutes, and then reduced to 50-65 DEG C to recover the charge and discharge, and the electrolyte solution with a capacity of 700-1000 mA h is obtained. Based on the above technical scheme, the content of the hexaammonium chromium ion complex in the aged electrolyte obtained in step 1 is more than 80%, and 0.1-5 mol•L -1 Ammonium chloride, open valve II, after the electrolyte flows for 5-30 minutes, the heating device is turned on to heat the liquid storage tank III to 65-85 DEG C, and the temperature is kept for 5-30 minutes, and then reduced to 50-65 DEG C, and the electrolyte flows back to the liquid storage tank I and the liquid storage tank II, and the charge and discharge are recovered, and the electrolyte solution with a capacity of 700-1000 mA h is obtained.

[0023] Compared with the prior art, the present application has the following advantages: The technical scheme disclosed by the present application adds ammonium salt in the electrolyte, and because the splitting energy of NH 4+ in the chromium ion complex is greater than that of the hydrated ion, the ammonium chromium ion complex can exist stably in the electrolyte and cannot easily reverse to the hydrated chromium ion complex. The electrolyte liquid storage tank into which the ammonium salt is added is heated by the heating device, so that the hexaammonium chromium ion complex in the electrolyte is converted into the tetraammonium chromium ion complex which is more active and stable, thereby achieving the purpose of rapid recovery of the electrolyte capacity. At the same time, a switch valve for adding an additive is designed in the negative electrode liquid storage tank (see Figure 1 for details). A certain amount of electrolyte is extracted through the valve, and then the content of the chromium ion complex in the electrolyte is determined by ultraviolet-visible light detection. The corresponding heating temperature and heating time are set accordingly. In addition, if the electrolyte is severely aged, a certain amount of ammonium chloride can be added through the valve. After the sample detection confirms that the ammonium chromium ion complex is generated, the capacity recovery is achieved again by heating, and the dynamic recovery of the electrolyte capacity is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The battery capacity recovery device used in the present application examples 1-2 is shown in the figure (the names of the components in the figure are as follows: 1: liquid storage tank I, 2: liquid storage tank II, 3: liquid storage tank III, 4: circulating pump I, 5: circulating pump II, 6: valve I, 7: valve II, 8: temperature control box); Figure 2 The battery capacity recovery after the battery charge and discharge cycle is described in the present application example 1. DETAILED DESCRIPTION

[0025] The application will be further described in conjunction with specific embodiments, but not in any way limit the application.

[0026] The calculation formula of the adding amount of the ammonium salt in the embodiment of the application is as follows:

[0027] Formula 1; In formula 1, M represents amount of substance, mol; M represents amount of substance, mol; In addition, the ion concentration of [Cr(H2O)6Cl] 3+ can be measured by extracting part of the solution in the storage tank II.

[0028] The application provides a device for capacity recovery of an iron-chromium flow battery in the specific embodiment part, and the device is mainly composed of two parts of a battery assembly and a capacity recovery assembly; The battery assembly comprises a storage tank I, a storage tank II, a circulating pump I, a circulating pump II and an electric pile, and is used for conversion between electric energy and chemical energy; The capacity recovery assembly comprises a storage tank III; The left side of the electric pile is sequentially connected with the storage tank I and the circulating pump I, and the right side of the electric pile is sequentially connected with the storage tank II and the circulating pump II. The storage tank I is provided with a valve I between the storage tank I and the circulating pump 1; The storage tank II is provided with a valve II between the storage tank II and the circulating pump II; The valve I and the valve II are provided with the storage tank III therebetween; The storage tank III is further connected with a temperature control box.

[0029] The storage tank I, the storage tank II and the storage tank III all have a heating function, i.e., all are provided with a heating device The application further provides a method for capacity recovery of an iron-chromium flow battery in the specific embodiment part, and the method is as follows: A method for capacity recovery of an iron-chromium flow battery, characterized in that the method is as follows: Step 1, electrolyte aging: the electrolyte is loaded into the corresponding storage tank, the circulating pump is turned on, the heating device is turned on to heat to 50-65 DEG C for charging and discharging cycle, and after the cycle, the charging and discharging is stopped, and the circulating pump continues to run, and the aged electrolyte is obtained; Step 2, capacity recovery: add an ammonium salt to the aged electrolyte described in step 1, heat the aged electrolyte through a heating device, keep warm, and cool to 65-85°C to obtain an electrolyte with recovered capacity.

[0030] Based on the above technical solution, the components of the electrolyte in step 1 are ferrous salt solution, chromium salt solution, and acid solution. The ferrous salt solution is selected from at least one of ferrous chloride solution and ferrous sulfate solution.

[0031] The chromium salt solution is selected from at least one of chromium chloride solution and chromium sulfate.

[0032] The acid solution is selected from at least one of dilute hydrochloric acid, dilute sulfuric acid, and dilute hydrochloric acid.

[0033] Based on the above technical solution, the components of the electrolyte in step 1 are ferrous chloride solution, chromium chloride solution, and dilute hydrochloric acid, wherein the concentration of the ferrous chloride solution is 1-3 mol•L -1 , the concentration of the chromium chloride solution is 1-3 mol•L -1 , and the concentration of the dilute hydrochloric acid is 3-5 mol•L -1 .

[0034] Based on the above technical solution, the current density of the cycle in step 1 is 40-200 mA / cm 2 . The number of cycles in step 1 is 100-1000 cycles. The capacity of the electrolyte after the first charge-discharge cycle in the cycle in step 1 is 800-1100 mA h.

[0035] Based on the above technical solution, the capacity of the aged electrolyte obtained in step 1 is 400-550 mA h.

[0036] Based on the above technical solution, the ammonium salt solution in step 2 is selected from at least one of ammonium chloride, ammonium sulfate, and ammonium bisulfate, and is preferably ammonium chloride with a concentration of 0.1-5 mol•L -1 .

[0037] Based on the above technical solution, the content of hexaammine chromium ion complex in the aged electrolyte obtained in step 1 is 50-70%, and the capacity recovery is as follows: turn on the heating device to heat the liquid storage tank III to 65-85°C, keep warm for 5-30 minutes, then reduce to 50-65°C to recover the charge-discharge, and obtain an electrolyte solution with a capacity of 700-1000 mA h. Based on the above technical solution, the content of hexaammine chromium ion complex in the aged electrolyte obtained in step 1 is more than 80%, and 0.1-5 mol•L -1Ammonium chloride is used. Valve II is opened, and after the electrolyte flows and circulates for 5 to 30 minutes, the heating device is turned on to heat the storage tank III to 65 to 85°C. The temperature is maintained for 5 to 30 minutes, and then the temperature is lowered to 50 to 65°C. After the electrolyte flows and circulates back to the storage tanks I and II, the charging and discharging is resumed, and an electrolyte solution with a capacity of 700 to 1000 mA h is obtained.

[0038] Example 1 Adopting such Figure 1 The device shown is used for electrolyte capacity recovery testing. The device mainly consists of a battery assembly and a capacity recovery assembly. The battery assembly includes a storage tank I, a storage tank II, a circulation pump I, a circulation pump II, and a fuel cell stack. The battery assembly is used for the conversion between electrical energy and chemical energy. The capacity recovery assembly includes a storage tank III. The storage tank I and circulation pump I are connected sequentially to the left side of the fuel cell stack, and the storage tank II and circulation pump II are connected sequentially to the right side of the fuel cell stack. A valve I is installed between storage tank I and circulation pump I; a valve II is installed between storage tank II and circulation pump II; and storage tank III is installed between valve I and valve II. Storage tank III is also connected to a temperature control chamber. The fuel cell stack is assembled. The specific testing process is as follows: 50 ml of 1 mol·L⁻¹ electrolyte is added... -1 FeCl2, 1 mol·L -1 CrCl3 solution, 3 mol·L -1 Dilute hydrochloric acid was placed in storage tank I (positive electrode storage tank) and storage tank II (negative electrode storage tank), respectively. After turning on circulation pumps I and II, the heating device was turned on to heat the positive and negative electrode storage tanks to 50-65°C for charge-discharge cycling. After 100 cycles, charge-discharge was stopped, circulation pumps I and II were turned off, valve I was opened, and a small amount of electrolyte was taken. Valve I was then closed, and the aging condition of the electrolyte (i.e., electrolyte) was detected using ultraviolet-visible light. The electrolyte capacity was detected to be 600 mA h, and the content of hexaammonium chromium ion complex in the electrolyte was 50-70%. The amount of ammonium salt to be added was calculated using the formula, i.e., 0.1 mol NH4Cl powder was added to storage tank III using valve II. The heating device of storage tank III was turned on to 80°C and heated for 10 minutes, then cooled to 65°C. After the electrolyte circulated back to storage tanks I and II, charge-discharge was resumed, resulting in an electrolyte with restored capacity, i.e., 140 mA / cm³. 2 Under current density conditions, the battery capacity retention rate can still reach 91% after 100 cycles. This battery operates at 140 mA / cm². 2The first charge-discharge capacity can reach 600 mAh under the condition of current density. After 100 cycles of charge-discharge, the capacity is attenuated to 52.39% of the first cycle capacity, and the average attenuation rate is 0.47% / cycle. After the capacity recovery operation is implemented, the battery capacity is increased by 68.75%, and in the next 100 cycles of charge-discharge, the average attenuation rate is only 0.081% / cycle, greatly improving the capacity retention rate of the electrolyte. And after capacity recovery again, at the end of the 300th cycle, it can still maintain 87.99% of the capacity, and the average attenuation rate is only 0.12% / cycle, which can be restored to 40-60% before the cycle. The battery capacity recovery after the cycle is shown in Figure 2 .

[0039] Example 2 The difference from Example 1 is that the heating time in the liquid storage tank III is different, that is, after 100 cycles of battery, stop discharging, detect the capacity of the electrolyte as 300 mA h, the content of hexaammine chromium ion complex in the electrolyte is 80-85%, open the valve II, add 0.1 mol of NH4Cl powder, open the heating device of the liquid storage tank III to heat to 80℃, heat for 15 minutes, and then reduce to the operating temperature of 65℃, after the electrolyte is circulated back to the liquid storage tank I and the liquid storage tank II, the charge-discharge can be restored, at this time the electrolyte capacity is 200 mA h, which can be restored to 40-60% before the cycle. Comparative Example 1 The difference from Example 1 is that the ammonium chloride solution is replaced by In 3+ additive, and the rest of the process remains the same as Example 1. The capacity retention rate of the electrolyte is 76.8% under the condition of current density of 160 mA / cm 2 .

[0040] Comparative Example 2 The difference from Example 1 is that the ammonium chloride solution is replaced by Li + additive, and the rest of the process remains the same as Example 1. The capacity retention rate of the electrolyte is 36.3% under the condition of current density of 40 mA / cm 2 .

[0041] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, which are equivalent to equivalent embodiments, and belong to the scope of the technical solution.

Claims

1. A device for capacity recovery in iron-chromium redox flow batteries, characterized in that, The device mainly consists of two parts: a battery assembly and a capacity recovery assembly. The battery assembly includes a storage tank I, a storage tank II, a circulation pump I, a circulation pump II, and a fuel cell stack. The battery assembly is used for the conversion between electrical energy and chemical energy. The capacity recovery assembly includes a liquid storage tank III; The storage tank I and the circulation pump I are connected in sequence on the left side of the fuel cell stack, and the storage tank II and the circulation pump II are connected in sequence on the right side of the fuel cell stack. A valve I is provided between the liquid storage tank I and the circulation pump I; A valve II is provided between the liquid storage tank II and the circulation pump II; A liquid storage tank III is provided between valve I and valve II; The liquid storage tank III is also connected to the temperature control box; The liquid storage tanks I, II, and III all have heating functions, that is, they are all equipped with heating devices.

2. The apparatus according to claim 1, characterized in that, The storage tank (3) is used to hold ammonium salts.

3. A method for capacity recovery of an iron-chromium redox flow battery using the apparatus according to any one of claims 1-2, characterized in that, The method is as follows: Step 1, Electrolyte aging: The initial electrolyte is loaded into the storage tank, the circulation pump is turned on, and the heating device is turned on to heat storage tank I and storage tank II to 50~65℃ for charge-discharge cycle. After the cycle, the charge-discharge is stopped, and the circulation pump continues to run to obtain the aged electrolyte. Step 2, capacity recovery: Add ammonium salt to the aged electrolyte described in Step 1, heat the aged electrolyte described in Step 1 to 65~85℃ using a heating device, keep it at that temperature, cool it to 50~65℃, and charge and discharge it to obtain an electrolyte with restored capacity.

4. The method according to claim 3, characterized in that, In step 1, the initial electrolyte is a mixture of ferrous salt solution, chromium salt solution, and acid solution; The ferrous salt solution is selected from at least one of ferrous chloride solution and ferrous sulfate; The chromium salt solution is selected from at least one of chromium trichloride solution and chromium sulfate; The acid solution is selected from at least one of dilute hydrochloric acid and dilute sulfuric acid; The ammonium salt solution is selected from at least one of ammonium chloride, ammonium sulfate, and ammonium bisulfate.

5. The method according to claim 3, characterized in that, The electrolyte in step 1 consists of ferrous chloride solution, chromium trichloride solution, and dilute hydrochloric acid, wherein the concentration of the ferrous chloride solution is 1~3 mol•L. -1 The concentration of the chromium trichloride solution is 1~3 mol•L. -1 The concentration of dilute hydrochloric acid is 3~5 mol•L. -1 .

6. The method according to claim 3, characterized in that, The current density of the cycle described in step 1 is 40~200 mA / cm². 2 ; The number of cycles described in step 1 is 100 to 1000. The electrolyte capacity after the first charge-discharge cycle in step 1 is 800~1100 mA h.

7. The method according to claim 3, characterized in that, The capacity of the aged electrolyte obtained in step 1 is 400~550 mA h.

8. The method according to claim 3, characterized in that, The content of hexaammonium chromium ion complex in the aged electrolyte obtained in step 1 is 50-70%. The capacity recovery is specifically as follows: turn on the heating device to heat the storage tank III to 65-85℃, keep it at the temperature for 5-30 minutes, and then lower it to 50-65℃ to restore charging and discharging, so as to obtain an electrolyte solution with a capacity of 700-1000 mA h.

9. According to claim 3, the content of hexaammonium chromium ion complex in the aged electrolyte obtained in step 1 exceeds 80%, and 0.1~5 mol•L is added to storage tank III. -1 Ammonium chloride is used. Valve II is opened, and after the electrolyte flows and circulates for 5 to 30 minutes, the heating device is turned on to heat the storage tank III to 65 to 85°C. The temperature is maintained for 5 to 30 minutes, and then the temperature is lowered to 50 to 65°C. After the electrolyte flows and circulates back to the storage tanks I and II, the charging and discharging is resumed, and an electrolyte solution with a capacity of 700 to 1000 mA h is obtained.

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