CN108172871A - A method and device for in-situ monitoring of state of charge of vanadium battery electrolyte with temperature compensation - Google Patents

Abstract

The invention provides a method and device for in-situ monitoring of the state of charge of the vanadium battery electrolyte with temperature compensation. The method is: at multiple temperatures, measure the ORP values of the positive and negative electrolytes in a series of SOC states ; Establish the relationship curve Y=aX+b between the electrolyte ORP value and ln(SOC _a /(1-SOC _a )) or ln((1-SOC _c )/SOC _c ) at temperature t, and get a and b by fitting The value is related to the linear equation of temperature t, the value of X can be obtained by substituting the ORP value measured at temperature t ₁ into the formula Y=a ₁ X+b ₁ at temperature t ₁ ; and substituting X into the SOC-X database, The SOC value of the electrolyte can be obtained. This method performs real-time temperature correction on the relationship between ORP and ln(SOC _a /(1-SOC _a )) or ln((1-SOC _c )/SOC _c ), which greatly reduces the SOC test caused by temperature changes error.

Description

A method for in-situ monitoring of state of charge of vanadium battery electrolyte with temperature compensation and device

technical field

The invention relates to the technical field of in-situ monitoring of the state of charge of the electrolyte of a flow battery, in particular to a method and device for in-situ monitoring of the state of charge of the electrolyte of a vanadium battery with temperature compensation.

Background technique

At present, the methods for on-line monitoring of the state of charge of the vanadium battery electrolyte mainly include: 1) the reference stack method, that is, a small single cell is added to the electrolyte circuit, and the charge of the electrolyte is determined by detecting the terminal voltage of the small single cell state (SOC). Due to the migration of vanadium ions through the diaphragm during operation, the SOC of the positive and negative electrodes is inconsistent. Therefore, the state of charge of the electrolyte obtained by measuring the terminal voltage is the average SOC, which cannot reflect the true SOC state of the positive and negative electrolytes. 2) In the auxiliary battery method, a battery is independently installed in a section of the stack, and the battery only passes through liquid and does not pass through current. The SOC of the electrolyte is determined by detecting the open-circuit voltage of the single cell. This method has the same problem as the above-mentioned reference stack. 3) The reference solution method, which is to determine the SOC of the electrolyte by testing the potential difference between the positive and negative electrolytes of known SOC and the electrolyte passing through the pipeline. The accuracy of this method depends on the reference solution. Stablize.

In the patent CN105355946A, a method of using a reference electrode to detect the charge state of the positive and negative electrolytes is mentioned. This method measures the oxidation-reduction potential (ORP) of the positive and negative electrolytes of the battery in real time, and brings in the established open circuit voltage and ln(SOC _a /(1-SOC _a )) or ln((1-SOC _c )/SOC The relational expression of _c ) obtains the SOC of the positive and negative electrolytes of the battery in real time. This method ignores that the ORP values of the positive and negative electrolytes and the standard potential of the reference electrode are affected by temperature, so in the case of large temperature fluctuations, the error of the SOC test measured by this method will be relatively large.

Contents of the invention

The purpose of the present invention is to provide an in-situ monitoring method and device for the state of charge of the vanadium battery electrolyte with temperature compensation, so as to solve the technical problem that the prior art does not consider the influence of temperature and the error of the SOC test is large.

In order to achieve the above object, the present invention provides a method for in-situ monitoring of the state of charge of the vanadium battery electrolyte with temperature compensation, comprising the steps of:

A. At multiple temperatures, measure the open circuit voltage value ORP of the positive and negative electrolytes in a series of SOC states;

B. Establish the relationship between ORP and ln(SOC _a /(1-SOC _a )) or ln((1-SOC _c )/SOC _c ) at different temperatures Y=aX+b; a and b are related to temperature constant term of

At the positive pole, Y is the ORP _a value of the positive pole, and X is ln(SOC/ _a (1-SOC _a );

In negative pole, Y is negative pole ORP _c value, X is ln((1-SOC _c )/SOC _c );

C, make the curve of a, b value and temperature t, fit and obtain the linear equation of a, b value about temperature;

D. Substituting the real-time monitored temperature t ₁ into the linear equation of formula a and b value with respect to temperature, the values of a ₁ and b ₁ at the measured temperature can be obtained, as well as the relationship between the ORP value and ln(SOC _a /( 1-SOC _a )) or ln((1-SOC _c )/SOC _c ), abbreviated as Y=a ₁ X+b ₁ ; Substitute the ORP value measured at temperature t ₁ into the formula Y=a ₁ X value can be obtained from X+b ₁ ;

E. Iterate the X value into the SOC database to obtain the SOC value of the electrolyte;

The SOC database is a one-to-one correspondence between a SOC and ln(SOC _a /(1-SOC _a )) or a SOC and ln((1-SOC _c )/SOC _c ).

Preferably, step C is specifically:

Make the relationship curve of several items a, b and temperature in the relationship between ORP and ln(SOC _a /(1-SOC _a )) or ln((1-SOC _c )/SOC _c ), and perform a linear fitting to obtain a _t =ct+d, b _t =et+f, where c, d, e, and f are all constants.

The device using the above-mentioned temperature compensation method for in-situ monitoring of the state of charge of the vanadium battery electrolyte includes a monitoring unit, a data acquisition unit and a data processing unit. The device is installed in the vanadium battery system to realize charging of the positive and negative electrolytes. real-time monitoring;

The monitoring unit includes a temperature sensor resistant to strong acid, and the temperature sensor is installed on the pipeline and is in contact with the electrolyte;

The input end and the output end of the data acquisition unit are respectively connected with the monitoring unit and the data processing unit;

The data processing unit is a programmable logic controller PLC.

Preferably, the monitoring unit also includes a voltage detection device, and the voltage detection device is composed of a working electrode and a reference electrode; wherein the working electrode is any one of a platinum electrode, a graphite electrode, and a glassy carbon electrode, and the reference electrode can be silver Any one of silver chloride solid-state reference electrode and silver/silver sulfate solid-state reference electrode; the working electrode and reference electrode are installed on the pipeline and are in contact with the electrolyte.

Preferably, the data acquisition unit can be any one of a signal isolator, a multimeter, and an electrochemical workstation, and the input impedance of the device is greater than 10 megohms.

The present invention has the following beneficial effects:

The present invention greatly reduces the SOC loss caused by temperature changes by performing real-time temperature correction on the relationship between ORP and ln(SOC _a /(1-SOC _a )) or ln((1-SOC _c )/SOC _c ). The test error makes the detection of the state of charge of the electrolyte more accurate and convenient. The open circuit voltage and temperature of the positive and negative electrolytes are monitored in real time by the monitoring device, and the measured open circuit voltage and temperature are transmitted to the data processing unit, and the calculation logic edited in the PLC is used to solve the problem. Get the real-time SOC status of the electrolyte.

In addition to the objects, features and advantages described above, the present invention has other objects, features and advantages. Hereinafter, the present invention will be described in further detail with reference to the drawings.

Description of drawings

The accompanying drawings constituting a part of this application are used to provide further understanding of the present invention, and the schematic embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached picture:

Fig. 1 is the in-situ monitoring method flow chart of the vanadium battery positive and negative electrolyte state of charge of the preferred embodiment of the present invention;

Fig. 2 is the graph of the relationship between electrolyte ORP _a and ln (SOC _a /(1-SOC _a )) of the positive electrode electrolyte of the battery in a preferred embodiment of the present invention at different temperatures;

Fig. 3 is the relationship curve and the linear fitting curve of the electrolyte ORP _c and ln ((1-SOC _c )/SOC _c ) of the negative electrode electrolyte of the battery in a preferred embodiment of the present invention at different temperatures;

Fig. 4 is the relationship curve between the constant term a and the temperature in the relationship between ORP _a and ln((1-SOC _a )/SOC _a ) in the positive electrode relationship formula and a linear fitting curve;

Fig. 5 is the relationship curve between the constant term b and the temperature in the relationship between ORP _a and ln((1-SOC _a )/SOC _a ) in the relationship between positive electrodes and a linear fitting curve;

Fig. 6 is the relationship curve between the constant term a and the temperature in the relationship between ORP _c and ln((1-SOC _c )/SOC _c ) in the negative electrode relationship formula and a linear fitting curve;

Fig. 7 is the relationship curve between the constant item b and the temperature in the relationship between ORP _c and ln((1-SOC _c )/SOC _c ) in the negative electrode relationship formula and a linear fitting curve.

Detailed ways

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in various ways defined and covered by the claims.

Referring to Fig. 1, the device adopted in the temperature compensation method of the vanadium battery electrolyte nuclear state in-situ detection designed by the present invention includes a monitoring unit, a data acquisition unit and a data processing unit, and the device is installed in the vanadium battery system to realize positive and negative alignment. The state of charge of the electrolyte is monitored in real time.

The monitoring unit is composed of a voltage monitoring device and a temperature sensor, and the voltage detecting device is composed of a working electrode and a reference electrode. The working electrode is any one of platinum electrode, graphite electrode and glassy carbon electrode, which is used to monitor the electrode potential of the vanadium ion pair in the positive or negative electrolyte; the reference electrode can be a silver/silver chloride solid reference electrode , Any one of the silver/silver sulfate solid-state reference electrodes, which has a stable reference potential at a constant temperature; there is a potential difference between the working electrode and the reference electrode, that is, the ORP value. The working electrode, reference electrode and temperature sensor are all installed on the pipeline and are in contact with the electrolyte.

The data acquisition unit can be any one of a signal isolator, a multimeter, and an electrochemical workstation, and the input impedance is greater than 10 megohms. The data acquisition unit and the data processing unit PLC are installed in the electrical cabinet.

The open circuit voltage and temperature of the positive and negative electrolytes are monitored in real time by the monitoring device, and the measured open circuit voltage and temperature are transmitted to the data processing unit, and the calculation logic edited in the PLC is used to solve the problem. Get the real-time SOC status of the electrolyte.

The establishment of the operational logic of the PLC is based on the Nernst equation, and the steps are as follows:

In the first step, the ORP values in a series of SOC states are measured under electrolytes at different temperatures, see Table 1 and Table 2 below.

Table 1 The ORP _a value and ln((1-SOC _a )/SOC _a ) value of the cathode electrolyte measured at different temperatures and at different SOCs

Table 2 The ORP _c value and ln((1-SOC _c )/SOC _c ) value of the negative electrode electrolyte under different SOC measured at different temperatures

The second step is to establish the relationship curve between the ORP value and ln(SOC/(1-SOC)) or ln((1-SOC)/SOC) at the temperature t. The relationship curve is shown in Figure 3, which is obtained by a linear fitting The relationship between ORP value and ln(SOC/(1-SOC)) or ln((1-SOC)/SOC) Y=aX+b, where the positive electrode Y is the ORP value, and X is ln(SOC/(1-SOC )), the negative electrode Y is the ORP value, X is ln((1-SOC)/SOC), and a and b are constant terms related to temperature.

Table 3 Positive electrode ORP value and a, b value in the relational expression

Table 4 Negative electrode ORP value and a, b value in the relational expression

Through the relationship curve between ORP and ln(SOC _a /(1-SOC _a )) or ln((1-SOC _c )/SOC _c ), the constant term a, b and temperature, the constant is obtained after a linear fitting The linear equation of term and temperature, so as to obtain the relationship between ORP and temperature t and ln(SOC _a /(1-SOC _a )) or ln((1-SOC _c )/SOC _c ):

Positive electrode: Y=(0.00002t+0.0338)X+(0.0007t+0.921) 1)

Where Y is the measured ORP _a value of the positive electrode, X is ln(SOC _a /(1-SOC _a )), and t is the measured temperature.

Negative electrode: Y=(-0.00006t+0.0384)X+(-0.0006t-0.403) 2)

Where Y is the ORP _c value measured at the negative electrode, X is ln((1-SOC _c )/SOC _c ), and t is the measured temperature.

According to the real-time measurement of the positive electrode electrolyte ORPa and temperature t of the battery into the formula 1), the measured negative electrode electrolyte ORPc value and temperature t are substituted into the formula 2) to solve, and the temperature t and ORPa of the battery positive electrolyte can be obtained. Under the corresponding ln(SOCa/(1-SOCa)) and the corresponding ln((1-SOC _c )/SOC _c ) of the anode electrolyte at temperature t and ORP _c , through the positive electrode SOC _a -ln(SOC _a /(1-SOC _a )) and negative electrode SOC _c -ln ((1-SOC _c )/SOC _c ) database to perform logic operations to obtain the corresponding positive and negative electrolyte SOC values.

Therefore, the present invention establishes the relational expression of ORP and temperature t, ln(SOC _a /(1-SOC _a )) or ln ((1-SOC _c )/SOC _c ), by measuring real-time temperature t and battery catholyte or The ORP value of the negative electrolyte reduces the SOC monitoring error caused by temperature changes during actual operation.

The application measures the open circuit voltage and temperature values of the positive and negative electrolytes at different stages during the operation of the vanadium battery, and solves the above-mentioned relational formula to obtain the real-time SOC values of the positive and negative electrolytes, and compares them with the positive and negative electrolytes through redox Titration records the SOC value of electrolyte and compares, and analyzes the accuracy of SOC measured by the method involved in the present invention, the results are shown in the following table 5:

Table 5 Comparison results of real-time SOC values

From the data in the table, it can be drawn that the SOC value measured by the temperature compensation method and device for in-situ monitoring of the state of charge of the vanadium battery electrolyte provided by the present invention differs very little from the SOC value measured by redox titration , SOC deviation is less than 3%. If the equation established at 20.0°C is used to calculate the SOC of the electrolyte without temperature compensation; for example, sample 3#, when the temperature of the positive electrolyte is 35.0°C, the calculated SOC value is 86.0%, The difference with the SOC (81.2%) obtained by redox titration is 4.8%, which is 0.8% greater than the SOC difference obtained after temperature correction; for sample 5#, when the positive electrode electrolyte temperature is 40.5°C, the calculated SOC value is 37.0 %, the difference from the SOC obtained by redox titration is 7.4%, which is much larger than the 1.6% SOC difference obtained after temperature correction; and the difference will follow the difference between the temperature during voltage measurement and the temperature established by the working curve increases with the increase. In the actual operation of vanadium batteries, the temperature of the electrolyte fluctuates with the change of the ambient temperature, so it is necessary to establish a temperature-compensated electrolyte in-situ monitoring method for the vanadium battery energy storage system to monitor the operation of the battery situation.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (5)

1. A vanadium battery electrolyte charge state monitoring method in situ with temperature compensation, is characterized in that, comprises the steps: A. At multiple temperatures, measure the open circuit voltage value ORP of the positive and negative electrolytes in a series of SOC states; B. Establish the relationship between ORP and ln(SOC _a /(1-SOC _a )) or ln((1-SOC _c )/SOC _c ) at different temperatures Y=aX+b; a and b are related to temperature constant term of At the positive pole, Y is the ORP _a value of the positive pole, and X is ln(SOC/ _a (1-SOC _a ); In negative pole, Y is negative pole ORP _c value, X is ln((1-SOC _c )/SOC _c ); C, make the curve of a, b value and temperature t, fit and obtain the linear equation of a, b value about temperature; D. Substituting the real-time monitored temperature t ₁ into the linear equation of formula a and b value with respect to temperature, the values of a ₁ and b ₁ at the measured temperature can be obtained, as well as the relationship between the ORP value and ln(SOC _a /( 1-SOC _a )) or ln((1-SOC _c )/SOC _c ), abbreviated as Y=a ₁ X+b ₁ ; Substitute the ORP value measured at temperature t ₁ into the formula Y=a ₁ X value can be obtained from X+b ₁ ; E. Iterate the X value into the SOC database to obtain the SOC value of the electrolyte; The SOC database is a one-to-one correspondence between a SOC and ln(SOC _a /(1-SOC _a )) or a SOC and ln((1-SOC _c )/SOC _c ). 2. The temperature compensation method according to claim 1, wherein step C is specifically: Make the relationship curve of several items a, b and temperature in the relationship between ORP and ln(SOC _a /(1-SOC _a )) or ln((1-SOC _c )/SOC _c ), and perform a linear fitting to obtain a _t =ct+d, b _t =et+f, where c, d, e, and f are all constants. 3. use the device of the temperature compensation method of the vanadium battery electrolyte state of charge in-situ monitoring of claim 1, it is characterized in that, comprise monitoring unit, data acquisition unit and data processing unit, this device is installed in the vanadium battery system , to realize real-time monitoring of the state of charge of the positive and negative electrolytes; The monitoring unit includes a temperature sensor resistant to strong acid, and the temperature sensor is installed on the pipeline and is in contact with the electrolyte; The input end and the output end of the data acquisition unit are respectively connected with the monitoring unit and the data processing unit; The data processing unit is a programmable logic controller PLC. 4. device according to claim 3, is characterized in that, described monitoring unit also comprises voltage detection device, and voltage detection device is made up of working electrode, reference electrode; Wherein working electrode is platinum electrode, graphite electrode, glassy carbon electrode The reference electrode can be any one of the silver/silver chloride solid reference electrode and the silver/silver sulfate solid reference electrode; the working electrode and the reference electrode are installed on the pipeline, and the electrolyte touch. 5. The device according to claim 3, wherein the data acquisition unit can be any one of a signal isolator, a multimeter, and an electrochemical workstation, and the input impedance of the device is greater than 10 megohms.