CN115856685A - Method for measuring internal resistance of all-vanadium redox flow battery in different charging and discharging states - Google Patents
Method for measuring internal resistance of all-vanadium redox flow battery in different charging and discharging states Download PDFInfo
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Abstract
The invention belongs to the technical field of analysis and test of all-vanadium redox flow batteries, and discloses a method for measuring internal resistance of an all-vanadium redox flow battery in different charging and discharging states. The all-vanadium redox flow battery system carries out constant-current charging and discharging two cycles through a charging and discharging instrument, and then measures the internal resistance of the battery in the charging process and the internal resistance of the battery in the discharging process. (4) The invention provides the internal resistance measurement method which is simple to operate, accurate in measurement data and free of negative influence on the all-vanadium redox flow battery.
Description
Technical Field
The invention belongs to the technical field of analysis and test of all-vanadium redox flow batteries, and particularly relates to a method for measuring ohmic internal resistance, electrochemical polarization internal resistance and concentration polarization internal resistance of an all-vanadium redox flow battery in different charging and discharging states.
Background
The energy storage technology can solve the problem of difficulty caused by intermittent and fluctuating nature energy. The all-vanadium redox flow system battery has the advantages of high efficiency, high response speed, intrinsic safety, ultra-long cycle life, capacity and power which can be independently designed, no geographic environment limitation and the like, is suitable for smoothing of wind-solar power generation on a supply side, can also be suitable for electric energy management on a demand side, and is particularly suitable for large-scale energy storage power stations.
The internal resistance is an important technical index for measuring the performance of the battery, and the battery with small internal resistance has stronger large-current discharge capacity. Therefore, the research on the internal resistance of the battery is a vital work in the battery industry, and the internal resistance of the all-vanadium redox flow battery mainly comprises ohmic internal resistance, electrochemical internal resistance and concentration polarization internal resistance.
At present, the HPPC method is mainly used for testing the resistance in the field of lithium batteries, but the electrolyte of the all-vanadium redox flow battery is flowing liquid and is characterized in that large concentration polarization exists between a battery flowing inlet and a battery flowing outlet, and the HPPC measuring method ignores the concentration polarization internal resistance and is difficult to apply to the all-vanadium redox flow battery.
CN113805086A chinese patent "a method for quickly estimating internal resistance of lithium ion battery", measures ohmic internal resistance and polarization internal resistance of lithium battery, wherein an estimated value of ohmic internal resistance also includes electrochemical polarization internal resistance; the measurement time for the internal polarization resistance is relatively long, and a certain self-discharge effect exists, so that the measured value is inaccurate. Secondly, the specific numerical values of the ohmic internal resistance, the electrochemical polarization internal resistance and the concentration polarization internal resistance of the lithium battery cannot be measured by the measuring method.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a method for measuring the internal resistance of an all-vanadium redox flow battery in different charging and discharging states, which realizes the analysis and measurement of ohmic polarization internal resistance, electrochemical polarization internal resistance and concentration polarization internal resistance of the all-vanadium redox flow battery through the real-time monitoring open-circuit voltage function of an alternating current internal resistance instrument and a charging and discharging instrument.
The above purpose of the invention is realized by the following technical scheme: a method for measuring internal resistance of an all-vanadium redox flow battery in different charging and discharging states (the flow is shown in figure 2) comprises the following steps:
1. performing constant-current charge and discharge two cycles on the all-vanadium redox flow battery system through a charge and discharge instrument;
2. measuring the internal resistance of the battery in the charging process: when measuring the internal resistance of the charging process within the low SOC range (0-90%), directly charging the battery to a corresponding SOC value at constant current, then laying aside for 5-15 min, recording the open-circuit voltage of the battery in real time by an instrument during the laying aside process, recording the data at the frequency of 0.1-2 s/point, measuring the ohmic internal resistance of the battery by the instrument during the laying aside process, and continuing constant current discharging after the laying aside is finished; when measuring the internal resistance in the charging process within the high SOC range (90-100%), continuing constant voltage charging to the test SOC value after the constant current charging is finished, then laying aside for 5-15 min, recording the voltage value and measuring the ohmic internal resistance in the laying aside process, continuing constant current discharging after the laying aside is finished, and finishing the test;
3. measuring the internal resistance of the battery in the discharging process: constant current charging is carried out firstly, constant voltage charging is carried out continuously until the SOC =100%, then constant current discharging is carried out until the SOC value to be measured is achieved, the battery is placed for 5-15 min, data are recorded and measured through a charging and discharging instrument and an alternating current internal resistance instrument in the placing process, constant current discharging is carried out continuously after the placing is finished, and the test is completed.
Further, the all-vanadium redox flow battery system (fig. 1) in step 1 is composed of a main battery, an SOC battery, a positive liquid storage tank, a negative liquid storage tank, a pipeline, a magnetic pump and a charging and discharging instrument, wherein the main battery comprises a main battery positive electrode and a main battery negative electrode, the main battery positive electrode is connected with the positive liquid storage tank and the magnetic pump in a closed loop mode through the pipeline, the main battery negative electrode is connected with the negative liquid storage tank and the other magnetic pump in a closed loop mode through the pipeline, the main battery positive electrode and the main battery negative electrode are respectively connected with the SOC battery and the charging and discharging instrument through the pipeline, and the SOC battery is connected with a voltage detection device.
Compared with the prior art, the invention has the beneficial effects that:
(1) According to the method for testing the internal resistance of the all-vanadium redox flow battery, the total internal resistance, the ohmic polarization internal resistance, the total internal resistance of electrochemical polarization and the concentration polarization internal resistance of the battery system can be calculated by using the open-circuit voltage change curve and the data of the battery system. According to the method, the ohmic polarization internal resistance of the all-vanadium redox flow battery is directly measured according to the alternating current internal resistance instrument, so that the ohmic internal resistance, the electrochemical polarization internal resistance and the concentration polarization internal resistance of the all-vanadium redox flow battery can be accurately measured respectively;
(2) In the research and development process of the all-vanadium redox flow battery, in order to improve the overall performance of the battery, structural design is carried out on an electrode frame, an electrode, a flow channel and the like, the influence of different structures on the battery performance is evaluated only by the battery efficiency, and the voltage efficiency needs to be specifically analyzed. The method can accurately measure the ohmic polarization internal resistance, the electrochemical polarization internal resistance and the concentration polarization internal resistance of different all-vanadium redox flow batteries, and provides a basis for voltage efficiency analysis, battery performance and the like of the batteries;
(3) According to the resistance values of the ohmic polarization internal resistance, the electrochemical polarization internal resistance and the concentration polarization internal resistance, the improvement can be made on the aspects of battery materials, battery structures and the like, and the direction is indicated for the next research and development;
(4) The internal resistance measuring method provided by the invention is simple to operate, accurate in measured data and free of negative influence on the all-vanadium redox flow battery.
Drawings
The invention will be further explained with reference to the drawings and the detailed description
FIG. 1 is a schematic structural diagram of an all-vanadium redox flow battery system according to the invention;
FIG. 2 is a flow chart of the internal resistance test of the all-vanadium redox flow battery of the invention;
FIG. 3 is a schematic diagram of the open-circuit voltage variation of the battery system during the resting process after charging according to the present invention;
FIG. 4 is a graph showing the change of internal resistances of the all-vanadium redox flow battery system along with the change of charging SOC;
FIG. 5 is a schematic diagram of the open circuit voltage variation of the battery system during the discharge resting process of the present invention;
FIG. 6 is a schematic diagram of SOC (state of charge) variation curves of internal resistances of the all-vanadium redox flow battery system along with discharge.
FIG. 1. Main battery; 2. a charge-discharge instrument; SOC battery; 4. a positive liquid storage tank; 5. a negative pole liquid storage tank; 6. a magnetic pump; 7. a pipeline; 8. a voltage detection device; 11. a main battery positive electrode; 12. a main battery negative electrode.
Detailed Description
The invention is described in more detail below with reference to specific examples, without limiting the scope of the invention. Unless otherwise specified, the experimental methods adopted by the invention are all conventional methods, and experimental equipment, materials, reagents and the like used in the experimental method can be obtained from commercial sources.
Example 1
The all-vanadium redox flow battery system used in the experiment is a 5kW galvanic pile consisting of 18 monocells, the electrolyte is sulfuric acid system electrolyte, the total volume of the electrolyte is 320L, and the volumes of positive and negative electrolytes are 160L respectively. The battery system is connected with the SOC battery in series on the liquid path, the open-circuit voltage of the SOC battery can be monitored in real time, and the SOC of the battery system can be read in real time through the open-circuit voltage of the SOC battery. The carbon felt electrode is used in the battery system, the size of the electrode is 570mm multiplied by 220mm, and the constant current charging and discharging current density is 150mA/cm 2 . The battery system operating temperature is in the range of 36 +/-1 ℃.
The internal resistance value measuring method in the charging process comprises the following steps: charging the battery to a corresponding SOC value by constant current or constant current and constant voltage, standing for 10min, recording the open-circuit voltage of the battery in real time by a charge-discharge instrument in the standing process, recording the data at a frequency of 0.5 s/point, measuring the ohmic polarization internal resistance of the battery by using an alternating current internal resistance instrument in the standing process, and continuing constant current discharge to 1V after the standing is finished.
According to the method for measuring the internal resistance value in the charging process, the change curve of the open-circuit voltage of the battery system in the resting process after charging is shown in fig. 3, wherein point A is the open-circuit voltage of the battery system when the battery system is charged to the SOC value, point B is the position of 0.5s in the resting process and is the starting point of the slow drop of the open-circuit voltage after the instantaneous drop of the open-circuit voltage, and point D is the starting point of the steady stage of the open-circuit voltage of the battery system.
Open circuit voltage records of the standing process after the charging is carried out until the SOC values are respectively 10%, 30%, 50%, 70% and 90% are shown in table 1, internal resistance values of the all-vanadium redox flow battery when the all-vanadium redox flow battery is charged to different SOC values can be calculated according to the table 1, and the results are shown in table 2. The change curve of each internal resistance with the charging SOC is shown in fig. 4.
The internal resistance calculation method is (U) A -U B )/I＝R ohm +R act ，(U B -U D )/I＝R com ，R ohm +R act Is the sum of ohmic polarization internal resistance and electrochemical polarization internal resistance, R con Is the concentration polarization internal resistance. Furthermore, R ohm Can be directly measured by an alternating current internal resistance instrument.
TABLE 1 open-circuit voltage recording table in the laying process after charging
TABLE 2 internal resistance results for different SOC during charging
Example 2
The all-vanadium redox flow battery system used in the experiment is a galvanic pile which is composed of 18 monocells and has the power of 5kW, sulfuric acid system electrolyte is used as the electrolyte, the total volume of the electrolyte is 320L, and the volumes of positive and negative electrolyte are 160L respectively. The battery system is connected with the SOC battery in series on the liquid path, the open-circuit voltage of the SOC battery can be monitored in real time, and the SOC of the battery system can be read in real time through the open-circuit voltage of the SOC battery. The carbon felt electrode is used in the battery system, the size of the electrode is 570mm multiplied by 220mm, and the constant current charging and discharging current density is 150mA/cm 2 . The battery system operating temperature is in the range of 36 +/-1 ℃. According to the internal resistance value measuring method in the discharging process, the change curve of the open-circuit voltage of the battery system in the laying process after discharging is shown in fig. 5, wherein point A is the open-circuit voltage of the battery system when discharging to the SOC value, point B is the position of 0.5s in the laying process and is the starting point of the slow rising of the open-circuit voltage after the instantaneous rising, and point D is the starting point of the stable stage of the open-circuit voltage of the battery system.
Open circuit voltage records in the standing process after discharging to SOC values of 10%, 30%, 50%, 70% and 90% are shown in table 3, internal resistance values of the all-vanadium redox flow battery when discharging to different SOC values can be calculated according to table 3, and the results are shown in table 4. The SOC variation curve of each internal resistance of the battery with discharge is shown in fig. 6.
TABLE 3 open-circuit voltage recording table in laying process after discharge
TABLE 4 internal resistance results for different SOC during discharge
According to the results of fig. 4 and 6, the ohm polarization internal resistance is the largest and the electrochemical polarization internal resistance is the smallest in the internal resistances of the all-vanadium redox flow battery. The ohmic polarization internal resistance is basically kept unchanged along with the change of the SOC in the charging process and the discharging process, because the ohmic polarization internal resistance is mainly influenced by the experimental temperature, and the all-vanadium redox flow battery always keeps the experimental temperature at about 36 ℃ in the running process, the measured ohmic polarization internal resistance basically has no change, which indicates the reliability of the testing method. At the end of charging and discharging, the difficulty of charge transfer is increased, and the difficulty of electrochemical reaction of the positive electrode and the negative electrode is increased, so that the electrochemical polarization internal resistance is obviously increased.
The measurement results of the examples are in accordance with the conventional principles. The result shows that the ohmic polarization internal resistance, the electrochemical polarization internal resistance and the concentration polarization internal resistance of the all-vanadium redox flow battery in different SOC states can be effectively and accurately measured by the method, and the method has important significance on the aspects of pile performance evaluation and the like.
The embodiments described above are merely preferred embodiments of the invention, rather than all possible embodiments of the invention. Any obvious modifications to the above would be obvious to those of ordinary skill in the art, but would not bring the invention so modified beyond the spirit and scope of the present invention.
Claims (2)
1. A method for measuring internal resistance of an all-vanadium redox flow battery in different charge and discharge states is characterized by comprising the following steps:
s1, performing constant-current charge and discharge two cycles on an all-vanadium redox flow battery system through a charge and discharge instrument;
s2, measuring the internal resistance of the battery in the charging process: when measuring the internal resistance of the low SOC range (0-90%) in the charging process, directly charging the battery to a corresponding SOC value in a constant current manner, then laying aside for 5-15 min, recording the open-circuit voltage of the battery in real time by an instrument in the laying aside process, wherein the data recording frequency is 0.1-2 s/point, simultaneously measuring the ohmic internal resistance of the battery by using the instrument in the laying aside process, and continuing the constant current discharge after the laying aside is finished; when measuring the internal resistance in the charging process within the high SOC range (90-100%), continuing constant voltage charging to the test SOC value after the constant current charging is finished, then laying aside for 5-15 min, recording the voltage value and measuring the ohmic internal resistance in the laying aside process, continuing constant current discharging after the laying aside is finished, and finishing the test;
s3, measuring the internal resistance of the battery in the discharging process: constant current charging is carried out firstly, constant voltage charging is carried out continuously until the SOC =100%, then constant current discharging is carried out until the SOC value to be measured is achieved, the battery is placed for 5-15 min, data are recorded and measured through a charging and discharging instrument and an alternating current internal resistance instrument in the placing process, constant current discharging is carried out continuously after the placing is finished, and the test is completed.
2. The method for measuring the internal resistance of the all-vanadium redox flow battery in different charging and discharging states in the step 1 is characterized in that the all-vanadium redox flow battery system in the step 1 is composed of a main battery (1), an SOC battery (3), a positive liquid storage tank (4), a negative liquid storage tank (5), a pipeline (7), a magnetic pump (6) and a charging and discharging instrument (2), wherein the main battery (1) comprises a main battery positive electrode (11) and a main battery negative electrode (12), the main battery positive electrode (11) is in closed-loop connection with the positive liquid storage tank (4) and the magnetic pump (6) through the pipeline (7), the main battery negative electrode (12) is in closed-loop connection with the negative liquid storage tank (5) and the other magnetic pump (6) through the pipeline (7), the main battery positive electrode (11) and the main battery negative electrode (12) are respectively connected with the SOC battery (3) and the charging and discharging instrument (2) through the pipeline (7), and the SOC battery (3) is connected with a voltage detection device (8).
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