An on-line monitoring method for soc of a dissolution-precipitation type metal-air flow battery

Abstract

The application discloses an on-line monitoring method for SOC of a dissolution-deposition type metal air flow battery, and relates to the field of metal air flow batteries. The method comprises the following steps: assembling a dissolution-deposition type metal air flow battery system, placing a negative electrolyte storage tank under a weighing device, injecting discharge-state electrolyte, and recording the initial volume of the electrolyte; starting a negative circulating pump, lowering the liquid level in the storage tank, recording the height of the liquid level after the liquid level is stable, calculating the volume of the solution in the storage tank at this time, and recording the mass of the storage tank; calculating the mass change of the storage tank at any charging and discharging moment; calculating the amount-of-substance change of reactants according to the mass change, calculating the charging electric quantity according to Faraday's law, obtaining the SOC at this moment by using the ratio of the charging electric quantity to the theoretical capacity of the battery, and realizing on-line monitoring of the SOC. The method is simple and effective, and can avoid SOC monitoring deviation caused by metal self-corrosion and self-discharge of the dissolution-deposition type metal air flow battery and small open-circuit voltage change.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal-air flow battery, and particularly relates to a method for monitoring the SOC of a dissolution-deposition type metal-air flow battery. BACKGROUND

[0002] The metal-air flow battery is a new type of electrochemical energy storage technology, which has the advantages of high efficiency, environmental protection, independent power and capacity, and is widely used in the fields of small mobile power supply, power supply of small portable electronic devices, and power supply of underwater military devices. The dissolution-deposition type metal-air flow battery is a new type of flow battery, and the active material is deposited on the porous electrode and dissolved in the supporting electrolyte during the charging and discharging process. Therefore, under different state of charge (SOC) conditions, the deposition amount of the active material on the electrode surface is different, which causes the difference in the concentration of the electrolyte, and further affects the quality of the electrolyte in the storage tank. That is, the dissolution-deposition type metal-air flow battery storage tank quality information can be used for the SOC online monitoring of the dissolution-deposition type metal-air flow battery.

[0003] The SOC is equal to the ratio of the remaining power to the theoretical power of the battery in numerical value, and the monitoring accuracy is an important technical index of the battery management system, which has an important influence on the overall performance, service life and safety of the battery. The existing SOC monitoring methods mainly include the ampere-hour integration method, the open circuit voltage method and the internal resistance method. The ampere-hour integration method estimates the SOC of the battery by accumulating the charged or discharged power when the battery is charging or discharging. On the one hand, there is a long-term cumulative error, and on the other hand, due to the self-corrosion and self-discharge of the deposited metal, a part of the power is lost, which leads to the fact that the ampere-hour integration method cannot reflect the true SOC of the metal-air flow battery. The open circuit voltage method indirectly fits the one-to-one correspondence between the open circuit voltage of the battery and the SOC of the battery according to the change relationship between the open circuit voltage of the battery and the concentration of the active material in the battery. This method needs to stand the battery or battery pack for a long time on the one hand, and on the other hand, the difference in the open circuit voltage of the metal-air battery under different SOC conditions is very small, which leads to a large error in the SOC monitoring by the open circuit voltage method. The internal resistance method has the problems of difficulty in estimating the internal resistance and difficulty in realizing in hardware.

[0004] Since the deposition and dissolution of the active material on the electrode surface of the dissolution-deposition type metal-air flow battery reflect the information of the change of the concentration of the active material, which directly corresponds to the difference in the quality of the electrolyte in the storage tank, the method for monitoring the SOC of the battery is simple in equipment, avoids the problems of small difference in open circuit voltage and difficulty in estimating the internal resistance, and can effectively avoid the monitoring deviation caused by the self-corrosion and self-discharge of the metal, thereby improving the SOC monitoring accuracy. SUMMARY

[0005] Purpose of the invention: To address the difficulties and large monitoring deviations in SOC monitoring of dissolution-deposition metal-air flow batteries, this invention proposes an online monitoring method for SOC of dissolution-deposition metal-air flow batteries. This method avoids the problems of insignificant open-circuit voltage differences and difficulties in estimating internal resistance, and can effectively avoid monitoring deviations caused by metal self-corrosion and self-discharge, thereby improving the accuracy of SOC monitoring.

[0006] Technical Solution: To achieve the objectives of this invention, the technical solution adopted is: an online monitoring method for the state of charge (SOC) of a dissolution-deposition type metal-air flow battery, comprising the following steps:

[0007] Step 1: Assemble a dissolution-deposition type metal-air flow battery system, including a flow battery device and an electrolyte storage tank, which are connected by pipelines and a circulation pump. The flow battery device includes a positive electrode, a negative electrode, a diaphragm, and a fixing plate. Both the positive and negative electrodes use inert porous electrodes. A weighing device is installed at the electrolyte storage tank.

[0008] Step 2: Inject the discharged electrolyte into the electrolyte storage tank, record the volume V0 of the injected electrolyte, and calculate the theoretical battery capacity C0 = FzV0c / 3600, where F is the Faraday constant, z is the charge number of the electrode reaction, c is the initial concentration of the active material in the electrolyte, and 3600 is the conversion rate between hours and seconds.

[0009] Step 3: Start the circulation pump. The electrolyte in the tank enters the pipeline and the flow battery device through the circulation pump. The electrolyte level in the tank drops and the volume decreases. When the liquid level stabilizes and the volume of electrolyte in the tank no longer changes, record the height of the liquid level at this time. Calculate the solution volume V1 in the tank at this time based on the cross-sectional area of ​​the tank and record the mass m0 of the tank at this time (SOC=0).

[0010] Step 4: Run the battery under a certain charge and discharge regime, and record the mass m of the storage tank at any time t. t At this point, the mass difference between the tank and the mass when the SOC is 0 is Δm = m0 - m t (Unit: g);

[0011] Step 5: The mass difference of the storage tank at time t is caused by the deposition of active material on the porous electrode surface in the battery. According to Faraday's law: Q = zξF, where Q is the charge, ξ is the reaction progress (the amount of material deposited or dissolved), and F is the Faraday constant, combined with the mass difference of the storage tank, the SOC at time t can be calculated by the following formula, thereby realizing online monitoring of SOC.

[0012]

[0013] Where: M is the molar mass of the sediment, in g / mol; C0 is the theoretical capacity of the battery, in Ah.

[0014] Further, the dissolution-deposition type metal air flow battery of step 1 includes a zinc-based air flow battery, a tin-based air flow battery, an iron-based air flow battery, a manganese-based air flow battery, a lead-based air flow battery, a nickel-based air flow battery, a lithium-based air flow battery, a magnesium-based air flow battery, and a combination of the above batteries.

[0015] Further, the porous electrode of step 1 includes a carbon felt electrode, a graphite felt electrode, a carbon fiber electrode, or an electrode obtained by modifying, modifying, or compounding the above electrode.

[0016] Further, the electrolyte of step 2 refers to one of an organic electrolyte or an inorganic electrolyte.

[0017] Further, the charging and discharging system of step 4 includes constant current charging and discharging, constant voltage charging and discharging, constant power charging and discharging, constant resistance charging and discharging, or a combination of the above four.

[0018] Beneficial effects: Compared with the prior art, the technical scheme of the present application has the following beneficial technical effects:

[0019] The present application utilizes the change of the liquid storage tank mass during the charging process of the dissolution-deposition type metal air flow battery to monitor the SOC online, which is essentially to establish a corresponding relationship between the change of the liquid storage tank mass caused by the phase change of the active material and the SOC, so as to directly correspond to the reaction progress of the active material, avoid the problem of unclear open circuit voltage difference and difficult internal resistance estimation, and effectively avoid the monitoring deviation caused by metal self-corrosion and self-discharge, thereby improving the SOC monitoring accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a structural diagram of a dissolution-deposition type metal air flow battery (before the circulation pump is started);

[0021] Figure 2 is a structural diagram of a dissolution-deposition type metal air flow battery (after the circulation pump is started);

[0022] Among them, ① is the negative electrode of the battery; ② is the diaphragm; ③ is the positive electrode of the battery; ④ is the fixed clamping plate; ⑤ is the electrolyte storage tank; ⑥ is the electrolyte; ⑦ is the weighing device; ⑧ is the circulation pump; ⑨ is the liquid flow battery device. DETAILED DESCRIPTION

[0023] The technical scheme of the present application will be further described below in combination with the drawings and examples.

[0024] The online monitoring method of the dissolution-deposition type metal air flow battery SOC described in the present application specifically includes the following steps:

[0025] Step 1, assemble the dissolution-deposition type zinc-air flow battery system, as shown in Figure 1 , including a flow battery device and an electrolyte storage tank, both of which are connected through a pipeline and a circulating pump, the flow battery device includes a positive electrode, a negative electrode, a separator and a fixing clamp, wherein the positive electrode and the negative electrode both use inert porous electrodes, and a weighing device is installed at the electrolyte storage tank;

[0026] Step 2, inject 1L discharged electrolyte into the electrolyte storage tank, the electrolyte composition is 6mol / L KOH+2mol / L ZnCl2, record the volume of the injected electrolyte V0=1L, and calculate the theoretical capacity of the battery C0=FzV0c / 3600=96485×2×1×2 / 3600=107.2Ah, wherein F is the Faraday constant, z is the charge number of the electrode reaction, c is the initial concentration of the active substance in the electrolyte, and 3600 is the conversion rate of hours and seconds;

[0027] Step 3, start the circulating pump, as shown in Figure 2 , the electrolyte in the storage tank enters the pipeline and the flow battery device through the circulating pump, the electrolyte in the storage tank decreases in volume, and when the liquid level is stable, the volume of the electrolyte in the storage tank no longer changes, record the height of the liquid level at this time 15cm, according to the cross-sectional area of the storage tank 50.24cm 2 , calculate the volume of the solution in the storage tank at this time (SOC=0) V1=753.6mL, and record the mass of the storage tank at this time m0=1158.2g;

[0028] Step 4, charge the battery with a constant current of 20A, record the mass of the storage tank at 2.5h m t =1112.1g, the mass difference of the storage tank at this time and the mass at SOC=0 is Δm=m t =46.1g;

[0029] Step 5, the mass difference of the storage tank at the SOC state at time t is caused by the deposition of active substances on the surface of the porous electrode in the battery; according to Faraday's law: Q=zξF, Q is the electric quantity, ξ is the reaction progress (the amount of deposited or dissolved substances), F is the Faraday constant, combined with the mass difference of the storage tank, the SOC at time t is calculated by the following formula, thereby realizing online monitoring of the SOC.

[0030]

[0031] , wherein: M is the molar mass of Zn, unit g / mol; C0 is the theoretical capacity of the battery, unit Ah.

[0032] By comparing with the SOC at this moment (20A x 2.5h / 107.2Ah = 46.64%), the relative deviation of the SOC measurement in this embodiment is (46.81-46.64) / 46.64 = 3.6‰. Therefore, the present application avoids the measurement of the open circuit voltage and the internal resistance of the battery, and overcomes the influence of the self-corrosion and self-discharge of the zinc electrode on the SOC monitoring deviation, and obtains an online monitoring method for the SOC of the dissolution-deposition type metal air flow battery with high precision.

Claims

1. A method for online monitoring of the state of charge (SOC) of a dissolution-deposition type metal-air flow battery, characterized in that: Includes the following steps: Step 1: Assemble a dissolution-deposition type metal-air flow battery system, including a flow battery device and an electrolyte storage tank, which are connected by pipelines and a circulation pump. The flow battery device includes a positive electrode, a negative electrode, a diaphragm, and a fixing plate. Both the positive and negative electrodes use inert porous electrodes. A weighing device is installed at the electrolyte storage tank. Step 2: Inject the discharged electrolyte into the electrolyte storage tank, record the volume V0 of the injected electrolyte, and calculate the theoretical battery capacity C0 = FzV0c / 3600, where F is the Faraday constant, z is the charge number of the electrode reaction, and c is the initial concentration of the active material in the electrolyte. Step 3: Start the circulation pump. After the liquid level in the tank stops changing, record the liquid level. Calculate the volume of electrolyte V1 in the tank at this time based on the cross-sectional area of ​​the tank, and record the mass m0 of the tank when SOC = 0. Step 4: Run the battery under a certain charge and discharge regime, and record the mass m of the storage tank at any time t. t At this point, the mass difference between the tank and the mass when the SOC is 0 is Δm = m0 - m t ; Step 5: The mass difference of the storage tank at time t is calculated according to Faraday's law: Q = zξF, where Q is the amount of electricity, ξ is the reaction progress, i.e. the amount of substance deposited or dissolved, and F is the Faraday constant. Combined with the mass difference of the storage tank, the SOC at time t is calculated by the following formula, thereby realizing online monitoring of SOC. Where M is the molar mass of the sediment; C0 is the theoretical capacity of the battery.

2. The monitoring method according to claim 1, characterized in that: The dissolution-deposition type metal-air flow battery described in step 1 includes zinc-based air flow batteries, tin-based air flow batteries, iron-based air flow batteries, manganese-based air flow batteries, lead-based air flow batteries, nickel-based flow air batteries, lithium-based flow air batteries, magnesium-based flow air batteries, and combinations of the above batteries.

3. The monitoring method according to claim 1, characterized in that: The porous electrode described in step 1 includes a carbon felt electrode, a graphite felt electrode, a carbon fiber electrode, or an electrode obtained by modifying, altering, or compositing the above electrodes.

4. The monitoring method according to claim 1, characterized in that: The electrolyte mentioned in step 2 refers to either an organic electrolyte or an inorganic electrolyte.

5. The monitoring method according to any one of claims 1-4, characterized in that: The charging and discharging regime described in step 4 includes constant current charging and discharging, constant voltage charging and discharging, constant power charging and discharging, constant resistance charging and discharging, or a combination of the above four.

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