A method and system for calculating internal resistance and analyzing state of zinc-bromine flow battery
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIAN THERMAL POWER RES INST CO LTD
- Filing Date
- 2026-04-20
- Publication Date
- 2026-07-21
Smart Images
Figure CN122063479B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of electrochemical energy storage battery performance testing and state assessment, specifically relating to a method and system for calculating the internal resistance and analyzing the state of a zinc-bromine redox flow battery. Background Technology
[0002] Zinc-bromine flow batteries, as an important direction in large-scale energy storage technology, have attracted much attention due to their advantages such as high energy density and low cost. However, they face problems such as zinc dendrite growth, bromine transmembrane diffusion self-discharge, and electrolyte deterioration during operation. Key parameters such as internal resistance are needed to reflect the internal state in real time. Battery internal resistance is a core indicator for measuring ion transport, charge transfer, and mass transfer efficiency, including ohmic internal resistance (electrolyte resistance, electrode resistance, separator resistance, contact resistance) and polarization internal resistance (electrochemical polarization internal resistance, concentration polarization internal resistance).
[0003] Traditional testing methods have significant limitations: AC impedance spectroscopy requires specialized equipment, is complex to operate, and cannot be applied online; conventional DC methods can only obtain the total internal resistance and cannot distinguish the type of internal resistance; and the data changes during the testing process are not correlated with specific issues such as electrode contact, diaphragm state, and electrolyte performance. Therefore, there is an urgent need for a simple and easy-to-implement method for internal resistance analysis and state diagnosis of zinc-bromine systems. Summary of the Invention
[0004] This invention provides a method and system for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery, in order to solve the technical problems of existing zinc-bromine flow battery internal resistance testing methods, such as strong equipment dependence, inability to be applied online, only being able to obtain the total internal resistance and not being able to distinguish the type, and difficulty in associating and mapping the test data with specific internal problems of the battery.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for calculating the internal resistance and performing state analysis of a zinc-bromine flow battery includes the following steps: Perform charge-discharge-rest test on the battery, and collect the voltage-time curve during the test and the open circuit voltage at the end of the rest period; Based on the voltage-time curve during the test, the total internal resistance parameters are analyzed; Based on the total internal resistance parameters and the open-circuit voltage at the end of the resting period, a state diagnosis model is established to perform battery state analysis.
[0006] The battery charge-discharge-rest test includes a constant current charging stage, a first rest stage, a constant current discharging stage, and a second rest stage. During the constant current charging stage, the battery is charged to a preset SOC state with current I1. The first rest stage is a rest period of time t immediately following the end of the constant current charging stage. During the constant current discharging stage, the battery is discharged to a cutoff voltage U2 with current I2 after the end of the first rest stage. The second rest stage is a rest period of time t following the end of the constant current discharging stage.
[0007] During the constant current charging phase, the instantaneous voltage U at the start of charging is recorded simultaneously. c And the real-time charging voltage, and obtain the charging voltage curve U1(t) based on the real-time charging voltage; during the first resting stage, the first voltage relaxation curve and the voltage U at the beginning of the first resting stage are recorded simultaneously. rest1 The open-circuit voltage OCV1 at the end of the first settling period; during the constant current discharge phase, the real-time voltage during the discharge process is recorded to obtain the discharge voltage curve U2(t) and the voltage U at the instant of discharge start. dis During the second resting phase, the second voltage relaxation curve U is recorded. rest2 (t), and record the voltage U at the beginning of the second resting period. rest2 And the open-circuit voltage OCV2 at the end of the second resting period.
[0008] The total internal resistance parameter includes the ohmic internal resistance R. ohm Electrochemical polarization internal resistance R act Concentration polarization internal resistance R conc And the electrode material interface variation coefficient k.
[0009] The ohmic internal resistance R ohm The calculation method is as follows: After the resting period, obtain the initial charging and discharging voltage ΔU. ohm Calculate the ohmic internal resistance R ohm Ohmic internal resistance R ohm The calculation formula is: R ohm =ΔU ohm / I, where the initial voltage jump ΔU during charging and discharging. ohm I is the difference between the open-circuit voltage at the end of the resting period and the instantaneous voltage at the beginning of the discharge, and I is the test current.
[0010] The electrochemical polarization internal resistance R act The calculation formula is: R act =η act / I, where η act The electrochemical polarization voltage during the resting phase is given by η, where I is the test current and η is the electrochemical polarization voltage during the resting phase. act The calculation formula is: η act =U rest -U 10, among which, U 10 U is the instantaneous voltage after 10 seconds of rest. rest This is the voltage at the start of the settling period.
[0011] The concentration polarization internal resistance R conc The calculation formula is: (U 10 -OCV) / I, where, U 10 The instantaneous voltage after 10 seconds of rest is given, OCV is the open-circuit voltage at the end of the rest period, and I is the test current.
[0012] For carbon-plastic bipolar plate systems, an electrode material interface variation coefficient k is introduced to reflect the changes in ion conduction characteristics at the interface between the carbon-plastic bipolar plate and the current collector and electrolyte, enabling precise location of internal battery faults. This electrode material interface variation coefficient k is the ratio of the ohmic internal resistance after multiple charge-discharge cycles to the initial ohmic internal resistance, i.e., k = R. ohm' / R ohm R ohm' The internal resistance in ohms after multiple charge and discharge cycles.
[0013] Based on the total internal resistance parameters and the open-circuit voltage at the end of the resting period, a state diagnosis model is constructed, and a state diagnosis rule system is established, including rules for determining the electrode and contact state, electrolyte performance, separator state, and electrode reactivity. Specifically, the rules for determining the electrode and contact state involve monitoring the voltage during the charge-discharge-resting test of the battery and simultaneously recording the charge-discharge voltage curves, and the ohmic internal resistance R... ohm If the voltage increase is greater than 20% and irregular voltage fluctuations appear on the charge / discharge voltage curve, it is determined to be poor electrode contact or diaphragm blockage; the specific rules for judging electrolyte performance are as follows: if the concentration polarization internal resistance R conc If the concentration gradient increases by more than 30%, accompanied by a synchronous increase in the concentration relaxation time constant τ, it is determined that the electrolyte concentration is insufficient or the fluidity is reduced. The specific rule for judging the diaphragm state is as follows: if the open circuit voltage at the end of the settling period decreases at a rate greater than 0.05V during the settling time, and is accompanied by an increase in the ohmic internal resistance R... ohm If the reaction rate increases synchronously, it is determined to be a degradation of the membrane performance; the specific rule for determining the electrode reactivity is as follows: if the electrochemical polarization internal resistance R... act A significant increase of >50% indicates a reduction in active sites for zinc deposition on the negative electrode or an obstruction of bromine reduction kinetics on the positive electrode.
[0014] A system for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery includes a testing module, a total internal resistance parameter analysis module, and a state diagnosis module. The test module is used to perform charge-discharge-rest test on the battery, and collect the voltage-time curve during the test and the open circuit voltage at the end of the rest period. The total internal resistance parameter analysis module is used to analyze the total internal resistance parameter based on the voltage-time curve during the test process; The state diagnosis module is used to establish a state diagnosis model based on the total internal resistance parameters and the open-circuit voltage at the end of the resting period, and to perform battery state analysis.
[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention proposes a method for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery. It employs a multi-stage charge-discharge static testing process, acquiring voltage data in stages. This eliminates the need for high-precision offline testing equipment, allowing testing to be completed using only conventional charge-discharge and voltage acquisition components, significantly reducing reliance on specialized precision equipment. Compared to traditional internal resistance testing methods that require offline testing outside the battery operating system, this testing process can be embedded in the battery's normal operating cycle, simultaneously completing data acquisition and parameter analysis. It is adaptable to online application scenarios, enabling real-time monitoring of the battery's operating state and avoiding monitoring interruptions and data lag issues caused by offline testing.
[0016] Furthermore, this invention enables a refined differentiation of internal resistance types by precisely analyzing various internal resistance parameters and interface variation coefficients. Ohmic internal resistance reflects the conductivity of the battery's internal conductive pathways, electrochemical polarization internal resistance corresponds to the charge transfer reaction efficiency on the electrode surface, concentration polarization internal resistance is related to the electrolyte mass transfer process, and the interface variation coefficient specifically reflects the interface characteristics between the bipolar plate and other components. This refined analysis method can accurately pinpoint the specific stage of performance degradation, clarifying whether the problem lies in the conductive pathways, electrode reactions, electrolyte mass transfer, or interface contact, breaking through the bottleneck of traditional total internal resistance testing's inability to refine the source of faults.
[0017] Furthermore, differentiated judgment criteria are established for different fault types, pinpointing specific problems through changes in single or combined parameters. For example, by observing changes in ohmic internal resistance and voltage fluctuations, electrode contact or separator blockage issues can be accurately identified, avoiding the shortcomings of traditional methods that can only determine battery performance degradation but cannot pinpoint the location of the fault. By observing the coordinated changes in concentration polarization internal resistance and relaxation time constant, the specific cause of electrolyte performance abnormalities can be accurately determined, providing a clear basis for targeted maintenance. This precise correlation capability significantly improves the accuracy of fault diagnosis and reduces ineffective maintenance operations.
[0018] Furthermore, the zinc-bromine flow battery internal resistance calculation and state analysis system proposed in this invention adopts an integrated design with division of labor and collaboration. The testing module can collect multi-dimensional voltage data in real time, ensuring the integrity and timeliness of the data; the full internal resistance parameter analysis module quickly processes the collected data, avoiding errors and delays in manual calculation; and the state diagnosis module outputs diagnostic results instantly based on preset rules, achieving seamless integration of testing, analysis, and diagnosis. The entire system process is highly efficient and coherent, and can quickly provide feedback on battery status, providing timely support for battery operation adjustments and maintenance plan formulation. This significantly improves the scientific and efficient operation and management of zinc-bromine flow batteries, and extends battery life. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the voltage curves synchronously recorded during the charge-discharge-rest test of the zinc-bromine flow battery in an embodiment of the present invention; Figure 2 This is a schematic diagram of the voltage curves synchronously recorded during the charge-discharge-rest test in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the curve obtained by exponentially fitting the first voltage relaxation curve during the first resting stage in Embodiment 1 of the present invention. Figure 4 This is a schematic diagram of the charge and discharge voltage curves synchronously recorded during 50 charge-discharge-rest test cycles of the battery in an embodiment of the present invention. Figure 5 This is a schematic diagram of the curve obtained by exponentially fitting the first voltage relaxation curve of the first resting stage after performing 50 charge-discharge-resting test cycles on the battery in an embodiment of the present invention. Figure 6 This is a schematic diagram of the curve obtained by exponentially fitting the first voltage relaxation curve in the first resting stage after performing 200 charge-discharge-resting test cycles on the battery in an embodiment of the present invention. Figure 7 This is a schematic flowchart of a method for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery according to an embodiment of the present invention. Detailed Implementation
[0020] To further understand the content of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.
[0021] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[0022] Example 1 This embodiment proposes a method for calculating the internal resistance and performing state analysis of a zinc-bromine flow battery, such as... Figure 7 As shown, it includes the following steps: Perform charge-discharge-rest test on the battery, and collect the voltage-time curve during the test and the open circuit voltage at the end of the rest period; Based on the voltage-time curve during the test, the total internal resistance parameters are analyzed; Based on the total internal resistance parameters and the open-circuit voltage at the end of the resting period, a state diagnosis model is established to perform battery state analysis.
[0023] Based on the above methods and steps, this embodiment specifically includes three parts: test program design, internal resistance parameter analysis, and state diagnosis model. The specific implementation method is as follows: The battery undergoes a charge-discharge-rest period test, including a constant current charging stage, a first rest period, a constant current discharging stage, and a second rest period. During the charge-discharge-rest period test, a charge-discharge tester synchronously records the charge-discharge voltage values and plots the charge-discharge voltage curves. Figure 2 As shown; the constant current charging stage specifically involves charging with current I1 to a preset SOC (State of Charge), time t, or voltage threshold U1. During the charging process, the charging voltage curve U1(t) and the instantaneous voltage U at the start of charging are obtained based on synchronously recorded voltage values. c The first resting phase is as follows: immediately after the constant current charging phase ends, a resting time t1 is initiated. During the resting time t1, the battery voltage data is continuously and synchronously recorded to obtain the first voltage relaxation curve U. rest1 (t1), and record the voltage U at the beginning of the first resting stage. rest1 The open-circuit voltage OCV1 at the end of the first resting stage; after the first resting stage, the constant current discharge stage begins, with current I2 discharging to the cutoff voltage U2. Based on the voltage values synchronously recorded by the charge-discharge tester, the discharge voltage curve U2(t) and the instantaneous voltage U at the start of discharge are obtained. dis Immediately after the discharge ends, the second resting phase begins, with a resting time of t2. Simultaneously, based on the synchronously recorded voltage values, the second voltage relaxation curve U is recorded. rest2 (t2), and record the voltage U at the beginning of the second resting stage. rest2 And the open-circuit voltage OCV2 at the end of the second settling stage.
[0024] Based on the data collected during the above charge-discharge-rest test process, the total internal resistance parameters, including the ohmic internal resistance R, were analyzed. ohm Electrochemical polarization internal resistance R act Concentration polarization internal resistance R conc And the electrode material interface variation coefficient k. Wherein, the ohmic internal resistance R... ohm The calculation method is as follows: During a charge-discharge-rest period test, after the second rest period, the initial charge-discharge jump voltage ΔU is obtained. ohm Calculate the ohmic internal resistance R ohmOhmic internal resistance R ohm The calculation formula is: R ohm =ΔU ohm / I, where the initial voltage jump ΔU during charging and discharging. ohm I is the difference between the open-circuit voltage at the end of the settling period and the instantaneous voltage at the start of the discharge; I is the test current; the electrochemical polarization internal resistance R act The calculation formula is: R act =η act / I, where η act The electrochemical polarization voltage during the resting phase is given by η, where I is the test current and η is the electrochemical polarization voltage during the resting phase. act The calculation formula is: η act1 =U rest -U 10 , among which, U 10 U is the instantaneous voltage after 10 seconds of rest. rest This is the voltage at the start of the settling period. The concentration polarization internal resistance R... conc The calculation formula is: (U 10 -OCV) / I, where, U 10 The instantaneous voltage after 10 seconds of rest is given, OCV is the open-circuit voltage at the end of the rest period, and I is the test current. For the carbon-plastic bipolar plate system, an electrode material interface variation coefficient k is introduced. This electrode material interface variation coefficient k is the ratio of the ohmic internal resistance after multiple charge-discharge cycles to the initial ohmic internal resistance, i.e., k = R. ohm' / R ohm R ohm' The internal resistance in ohms after multiple charge-discharge cycles is R. ohm' With ohmic internal resistance R ohm The calculation method is the same, that is, the voltage value recorded synchronously after multiple charge-discharge cycles is used, and the collected electrochemical test curve is calculated according to the aforementioned steps, which mainly reflects the changes in the ion conduction characteristics of the carbon-plastic bipolar plate and the current collector / electrolyte interface.
[0025] In this embodiment, the test current I is either the charging current I1 during the constant current charging phase or the discharging current I2 during the constant current discharging phase, and the initial jump voltage ΔU during charging and discharging is... ohm The open-circuit voltage OCV1 at the end of the first settling phase and the instantaneous voltage U at the start of discharge. dis The difference, or the difference between the open-circuit voltage OCV2 at the end of the second resting phase and the instantaneous voltage U at the start of the next charging phase. c The difference; η act1 U is the electrochemical polarization voltage during the first or second settling stage. restThe voltage at the start of the first or second resting stage is denoted as , and OCV is the open-circuit voltage at the end of the first or second resting stage. To ensure the consistency of the data sources for each internal resistance parameter and to guarantee the accuracy and reliability of horizontal data comparison during subsequent state diagnosis, this embodiment uses data from the first resting stage for analyzing the total internal resistance parameters, as detailed below: The ohmic internal resistance R ohm The open-circuit voltage OCV1 at the end of the first resting stage and the instantaneous voltage U at the start of the constant current discharge stage are used. dis The difference ΔU ohm1 Perform the calculation, i.e., R ohm =ΔU ohm1 / I1, where I1 is the charging current.
[0026] Due to the resistance to charge transfer reactions on the electrode surface (such as zinc deposition / dissolution and bromine redox reactions in zinc-bromine flow batteries), the relaxation process is determined by the charge transfer kinetic rate, resulting in a short relaxation time, typically within a few seconds. For battery systems under normal operating conditions, a static voltage change within 10 seconds can approximately represent the electrochemical polarization resistance, which is sufficient to cover the electrochemical polarization relaxation process. Therefore, the electrochemical polarization resistance R... act The calculation is as follows: Based on the voltage values recorded synchronously during the charge-discharge-rest period test, the instantaneous voltage U at the 10s rest period in the first rest stage is obtained. 10 And the voltage U at the start of the first settling phase. rest1 Calculations were performed using the instantaneous voltage U during the first settling phase, which lasted 10 seconds. 10 And the voltage U at the start of the first settling phase. rest1 Calculate the electrochemical polarization voltage η during the first settling stage. act1 , that is, η act1 =U rest1 -U 10 Then, based on the electrochemical polarization voltage η of the first settling stage act1 Calculate the electrochemical polarization internal resistance R act =η act1 / I1.
[0027] The concentration polarization internal resistance R conc By analyzing the first voltage relaxation curve U during the first resting phase rest1 (t1) Perform exponential fitting on the first voltage relaxation curve U during the first resting phase. rest1 (t1) Select the curve in the interval t ≥ 10 for exponential fitting, and the fitted curve is as follows: Figure 3 As shown, the fitting formula is: U rest1(t1)=OCV1+A·e^(-t / τ), where A is the concentration polarization voltage amplitude and τ is the relaxation time constant obtained after exponential fitting; then, the concentration polarization internal resistance R is calculated based on the fitted concentration polarization voltage amplitude. conc Concentration polarization internal resistance R conc The calculation formula is: R conc =A / I1.
[0028] Based on the obtained total internal resistance parameters and the open-circuit voltage at the end of the first resting stage, a state diagnostic model is established to perform battery state analysis. First, the input parameter set of the state diagnostic model is confirmed, including the ohmic internal resistance R. ohm Concentration polarization internal resistance R conc Electrochemical polarization internal resistance R act The parameters include open-circuit voltage (OCV), electrode material interface variation coefficient (k), concentration relaxation time constant (τ), voltage fluctuation characteristics of the charge-discharge curve, and OCV decay rate. The voltage fluctuation characteristics of the charge-discharge curve are obtained by continuously recording and analyzing the voltage changes over time during the charge-discharge-rest test process. The OCV decay rate is based on the first voltage relaxation curve U... rest1 (t1), obtained by analyzing voltage values at different times. Simultaneously, baseline parameter values were set, and initial reference values for each parameter were determined through constant current charge-discharge experiments on a fault-free, stable new battery, serving as a reference standard for subsequent fault determination; and the test condition boundaries were determined: fixed electrolyte flow rate (30-60 mL / min), current density (10... The threshold values for conventional operating conditions (40mA / cm²) and resting time (≥10s) are used to avoid interference from operating condition fluctuations in model judgment.
[0029] Subsequently, fault types were categorized and diagnostic dimensions were defined, identifying four core fault categories: electrode and contact faults, electrolyte performance degradation, diaphragm degradation, and decreased electrode reactivity. Typical manifestations of each fault type were clarified, such as bromine transmembrane diffusion and pore blockage corresponding to diaphragm faults. Based on data analysis combined with the fault type classification and diagnostic dimension division, diagnostic dimensions were matched to assign a specific diagnostic dimension to each fault type, linking it to core parameters, such as the ohmic internal resistance R related to electrode and contact status. ohm The concentration polarization internal resistance R is related to voltage fluctuations and electrolyte performance. conc The relaxation time constant τ is used to avoid parameter cross-interference.
[0030] Finally, a diagnostic rule system was constructed, in which the rule for judging electrode and contact faults is as follows: The internal resistance R in ohms is set. ohm The threshold value suddenly increases by 20% of the base value, and the electrode material interface change coefficient k value continues to increase, with the increase reaching 25% of the base value; if the ohmic internal resistance R ohmIf the voltage spike is greater than 20% and the charge / discharge curve shows irregular voltage fluctuations (such as spikes or frequent jumps), it is determined to be poor electrode contact or diaphragm blockage (zinc precipitation / bromine complex deposition). If the electrode material interface change coefficient k value continues to increase by more than 25%, it is determined to be a decrease in the ion conduction performance of the bipolar plate interface.
[0031] The specific rules for determining electrolyte performance degradation faults are as follows: Set the concentration polarization internal resistance R... conc Threshold, concentration polarization internal resistance R conc The value continues to increase to 30% of the base value; if the concentration polarization internal resistance R conc If the concentration gradient increases by more than 30% and is accompanied by a simultaneous increase in the concentration relaxation time constant τ, it is determined that the electrolyte concentration is insufficient (Zn²⁺). + / Br - Losses) or decreased flowability (insufficient pump power / pipeline blockage).
[0032] The specific rules for determining diaphragm degradation faults are as follows: A threshold value for the open-circuit voltage OCV1 at the end of the first resting stage is set. The rate of decrease of the open-circuit voltage OCV1 at the end of the first resting stage within time t1 is 0.05V. If the rate of decrease of the open-circuit voltage OCV1 at the end of the first resting stage within time t1 is greater than 0.05V, and accompanied by an increase in the ohmic internal resistance R... ohm If the increase is synchronous, it is determined to be due to membrane performance degradation (increased bromine transmembrane diffusion), pore blockage, or mechanical damage.
[0033] The specific fault judgment rule for decreased electrode reaction activity is as follows: Set the electrochemical polarization internal resistance R. act Threshold, electrochemical polarization internal resistance R act Significantly increase to 50% of the base value; if the electrochemical polarization internal resistance R act If the increase is significantly greater than 50%, it is determined that the active sites of zinc deposition on the negative electrode are reduced (dendritic coverage) or the bromine reduction kinetics of the positive electrode are hindered (complexing agent failure). If it is accompanied by an abnormal value of the electrode material interface change coefficient k (deviating from the basic value ±10%), it is determined that the bipolar plate catalyst layer is degraded.
[0034] Furthermore, the ambient temperature needs to be controlled during the charge-discharge-rest period test of the battery. In this embodiment, the ambient temperature is stabilized within the range of 25±2 ℃ to eliminate the influence of temperature on the electrolyte conductivity and reaction kinetics. At the same time, the selection of the charge-discharge current density needs to match the electrolyte circulation rate to avoid situations where mass transfer limitation dominates the reaction or kinetic limitation is masked at extreme flow rates. Before conducting the charge-discharge-rest period test, the battery needs to undergo at least 3 activation cycles, charging and discharging to 75% of the rated capacity, to stabilize the interface state.
[0035] Example 2 Based on the method for calculating the internal resistance and performing state analysis of a zinc-bromine flow battery proposed in Example 1, this example uses a 60Wh zinc-bromine flow battery small test stack as the research object to perform state analysis of the 60Wh zinc-bromine flow battery. The electrolyte consists of 2M ZnBr2 + 3M KCl + 0.4M MEP (1-ethyl-1-methylpyrrolidinium bromide). The electrode material is a carbon-plastic bipolar plate, and the separator is a porous ion exchange membrane. The charge / discharge current is 2A, the charging time is 3h, charging to 75% of the battery's rated capacity, the resting time is 30min, the discharge cutoff voltage is 2V, and discharging to 55% of the battery's rated capacity.
[0036] Based on the above experimental conditions, the 60Wh zinc-bromine flow battery small test stack was subjected to three consecutive charge-discharge-rest test cycles. Each cycle repeated the test process in Example 1, and voltage data for each stage of charge and discharge were collected. In this example, the data from the first charge-discharge-rest test was used. Figure 1 As shown; the open-circuit voltage OCV1 at the end of the first resting phase is 7.119 V, t1 = 30 min, based on the first voltage relaxation curve U rest1 (t1) An exponential fit was performed to obtain the concentration polarization voltage amplitude A = 0.026V and the relaxation time constant τ = 553.082 s; the voltage U at the beginning of the first settling stage. rest1 =7.169V, instantaneous voltage U during the first resting stage after 10 seconds of rest. 10 =7.151 V; After the resting period, obtain the initial charging / discharging voltage ΔU. ohm =0.470 V, and the charge-discharge curve showed no obvious and drastic fluctuations.
[0037] Based on the above collected data, the total internal resistance parameters are analyzed as follows: Ohmic internal resistance R ohm =ΔU ohm1 / I1=0.47 / 2=0.235 Ω; Electrochemical polarization voltage η during the resting phase act = U rest1 -U 10 =7.169-7.151=0.018V, Electrochemical polarization internal resistance R act =η act1 / I1=0.018 / 2=0.009 Ω; Calculate the concentration polarization voltage amplitude A obtained after exponential fitting: Concentration polarization internal resistance R conc = A / I1=0.026 / 2=0.013 Ω; Approximate calculation of Rconc =(U 10 -OCV1) / I1=(7.151-7.119) / 2=0.016 Ω; Electrode material interface variation coefficient: k=1.
[0038] Based on the above total internal resistance parameters, and in conjunction with the diagnostic rule system described in Example 1, a state judgment is performed, and the ohmic internal resistance R... ohm= 0.235Ω, electrochemical polarization internal resistance R act =0.009Ω, concentration polarization internal resistance R conc =0.013Ω, all internal resistance parameters are within the standard range for this type of battery, and the electrode material interface variation coefficient k=1, indicating that the ion conduction characteristics of the bipolar plate and current collector / electrolyte interface are stable, with no abnormal loss or interface degradation; based on comprehensive judgment, all parameters are consistent with the characteristics of carbon-plastic bipolar plates, and the battery is judged to be in good condition.
[0039] Example 3 Based on the method for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery proposed in Example 1, this example performs 200 charge-discharge-rest test cycles on the battery of Example 2. The changes in the total internal resistance parameter and k value are tested every 50 cycles, as shown in Table 1 below: Table 1
[0040] Based on the collected voltage data and the calculation of the total internal resistance parameter and the electrode material interface variation coefficient k, the evolution law was traced, and the key data and preliminary judgments for each node are as follows: After 50 cycles: the synchronously recorded voltage values are as follows Figure 4 As shown, the first voltage relaxation curve U during the first resting phase is obtained based on the synchronously recorded voltage. rest1 (t1), the first voltage relaxation curve U during the first resting phase rest1 The curve after exponential fitting (t1) is as follows: Figure 5 As shown; Ohmic internal resistance R ohm = 0.242 Ω, electrode material interface variation coefficient k = 1.03, electrochemical polarization internal resistance R act = 0.012 Ω, indicating slight aging at the bipolar plate interface.
[0041] After 150 cycles: Ohmic internal resistance R ohm = 0.277 Ω, electrode material interface variation coefficient k = 1.18, electrochemical polarization internal resistance R act =0.024 Ω, electrochemical polarization internal resistance R act If the increment is greater than 50% of the baseline value, the bipolar plate catalyst layer is judged to be degraded. After 200 cycles: the first voltage relaxation curve U during the first resting phase. rest1 (t1), and the first voltage relaxation curve U during the first resting phase. rest1 The curve after exponential fitting (t1) is as follows: Figure 6 As shown; the open-circuit voltage OCV1 at the end of the first resting stage is 7.080 V, and the internal resistance R in ohms is... ohm = 0.294 Ω, electrode material interface variation coefficient k=1.25, electrochemical polarization internal resistance R act = 0.033 Ω, battery efficiency decreases by 9.74%, ohmic internal resistance R ohm An increase of over 25% indicates a decrease in the ion conduction performance of the bipolar plate.
[0042] Example 4 Based on the method for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery proposed in Example 1, this example proposes a system for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery, which can realize the above-mentioned method for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery, including a test module, a total internal resistance parameter analysis module, and a state diagnosis module. The test module is used to perform charge-discharge-rest test on the battery, and collect the voltage-time curve during the test and the open circuit voltage at the end of the rest period. The total internal resistance parameter analysis module is used to receive the voltage-time curve and open-circuit voltage data transmitted by the test module, and then analyze the total internal resistance parameters based on the voltage-time curve during the test process. It solves the ohmic internal resistance, electrochemical polarization internal resistance, and concentration polarization internal resistance respectively. For the carbon-plastic bipolar plate system, it can also calculate the electrode material interface change coefficient. The state diagnosis module is used to establish a state diagnosis model based on the total internal resistance parameters and the open circuit voltage at the end of the resting period, and to perform battery state analysis. By comparing the changing trends of each internal resistance parameter, the characteristics of open circuit voltage decay and the diagnostic rules, it determines the electrode and contact state, electrolyte performance, separator state and electrode reactivity one by one, and finally outputs the battery state analysis results and fault judgment conclusions, providing a basis for battery maintenance and performance optimization.
[0043] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.
Claims
1. A method for calculating the internal resistance and performing state analysis of a zinc-bromine flow battery, characterized in that, Includes the following steps: The battery undergoes a charge-discharge-rest period test, including a constant current charging stage, a first rest period, a constant current discharging stage, and a second rest period. During the constant current charging stage, the battery is charged to a preset SOC state with a current I1, and the instantaneous voltage U at the start of charging is recorded simultaneously. c The charging real-time voltage is used to obtain the charging voltage curve U1(t); the first resting stage is the resting time t after the constant current charging stage ends, during which the first voltage relaxation curve U1(t) is recorded synchronously. rest1 (t), Voltage U at the start of the first resting period rest1 and the open-circuit voltage OCV1 at the end of the first resting period; in the constant current discharge stage, after the first resting period ends, the current I2 is used to discharge to the cutoff voltage U2, the real-time voltage during the discharge process is recorded, and the discharge voltage curve U2(t) and the instantaneous voltage U at the start of discharge are obtained. dis The second settling stage is the settling time t after the constant current discharge stage ends, during which the second voltage relaxation curve U is recorded. rest2 (t), and record the voltage U at the beginning of the second resting stage. rest2 and the open-circuit voltage OCV2 at the end of the second settling phase; Based on the voltage-time curve during the test, the total internal resistance parameters, including the ohmic internal resistance R, are analyzed. ohm Electrochemical polarization internal resistance R act Concentration polarization internal resistance R conc And the electrode material interface variation coefficient k; Based on the total internal resistance parameters and the open-circuit voltage at the end of the resting period, a state diagnosis model is established, and a state diagnosis rule system is set to perform battery state analysis. The set state diagnosis rule system includes rules for determining electrode and contact states, electrolyte performance, separator states, and electrode reactivity. Specifically, the electrode and contact state determination rules involve monitoring the voltage during the charge-discharge-resting test of the battery and simultaneously recording the charge-discharge voltage curves, and the ohmic internal resistance R... ohm If the voltage increase is greater than 20% and irregular voltage fluctuations appear on the charge / discharge voltage curve, it is determined to be poor electrode contact or diaphragm blockage; if the electrode material interface change coefficient k value continues to increase greater than 25%, it is determined to be a decrease in the ion conduction performance of the bipolar plate interface; the specific rules for judging electrolyte performance are as follows: if the concentration polarization internal resistance R conc If the concentration gradient increases by more than 30%, accompanied by a synchronous increase in the concentration relaxation time constant τ, it is determined that the electrolyte concentration is insufficient or the fluidity is reduced. The specific rule for judging the diaphragm state is as follows: if the open circuit voltage at the end of the settling period decreases at a rate greater than 0.05V during the settling time, and is accompanied by an increase in the ohmic internal resistance R... ohm If the reaction rate increases synchronously, it is determined to be a degradation of the membrane performance; the specific rule for determining the electrode reactivity is as follows: if the electrochemical polarization internal resistance R... act An increase of >50% indicates a reduction in active sites for zinc deposition on the negative electrode or an obstruction of bromine reduction kinetics on the positive electrode. If this is accompanied by an abnormal value of the electrode material interface change coefficient k, it is determined to be a degradation of the bipolar plate catalyst layer.
2. The method for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery according to claim 1, characterized in that, The ohmic internal resistance R ohm The calculation method is as follows: After the resting period, obtain the initial charging and discharging voltage ΔU. ohm Calculate the ohmic internal resistance R ohm Ohmic internal resistance R ohm The calculation formula is: R ohm =ΔU ohm / I, where the initial voltage jump ΔU during charging and discharging. ohm I is the difference between the open-circuit voltage at the end of the resting period and the instantaneous voltage at the beginning of the discharge, and I is the test current.
3. The method for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery according to claim 1, characterized in that, The electrochemical polarization internal resistance R act The calculation formula is: R act =η act / I, where η act The electrochemical polarization voltage during the resting phase is given by η, where I is the test current and η is the electrochemical polarization voltage during the resting phase. act The calculation formula is: η act =U rest -U 10 , among which, U 10 U is the instantaneous voltage after 10 seconds of rest. rest This is the voltage at the start of the settling period.
4. The method for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery according to claim 1, characterized in that, The concentration polarization internal resistance R conc The calculation formula is: (U 10 -OCV) / I, where, U 10 The instantaneous voltage after 10 seconds of rest is given, OCV is the open-circuit voltage at the end of the rest period, and I is the test current.
5. The method for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery according to claim 1, characterized in that, For carbon-plastic bipolar plate systems, an electrode material interface variation coefficient k is introduced to reflect the changes in ion conduction characteristics at the interface between the carbon-plastic bipolar plate and the current collector and electrolyte, enabling precise location of internal battery faults. This electrode material interface variation coefficient k is the ratio of the ohmic internal resistance after multiple charge-discharge cycles to the initial ohmic internal resistance, i.e., k = R. ohm' / R ohm R ohm' The internal resistance in ohms after multiple charge and discharge cycles.
6. A system for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery, based on the method for calculating the internal resistance and analyzing the state of a zinc-bromine flow battery according to any one of claims 1 to 5, characterized in that, It includes a testing module, a total internal resistance parameter analysis module, and a condition diagnosis module; The test module is used to perform charge-discharge-rest test on the battery, including a constant current charging stage, a first rest stage, a constant current discharging stage, and a second rest stage. During the constant current charging stage, the battery is charged to a preset SOC state with a current I1, and the instantaneous voltage U at the start of charging is recorded simultaneously. c The charging real-time voltage is used to obtain the charging voltage curve U1(t); the first resting stage is the resting time t after the constant current charging stage ends, during which the first voltage relaxation curve U1(t) is recorded synchronously. rest1 (t), Voltage U at the start of the first resting period rest1 and the open-circuit voltage OCV1 at the end of the first resting period; in the constant current discharge stage, after the first resting period ends, the current I2 is used to discharge to the cutoff voltage U2, the real-time voltage during the discharge process is recorded, and the discharge voltage curve U2(t) and the instantaneous voltage U at the start of discharge are obtained. dis The second settling stage is the settling time t after the constant current discharge stage ends, during which the second voltage relaxation curve U is recorded. rest2 (t), and record the voltage U at the beginning of the second resting stage. rest2 and the open-circuit voltage OCV2 at the end of the second settling phase; The total internal resistance parameter analysis module is used to analyze the total internal resistance parameters, including the ohmic internal resistance R, based on the voltage-time curve during the test. ohm Electrochemical polarization internal resistance R act Concentration polarization internal resistance R conc And the electrode material interface variation coefficient k; The state diagnosis module is used to establish a state diagnosis model and set a state diagnosis rule system based on the total internal resistance parameters and the open-circuit voltage at the end of the resting period, and to perform battery state analysis. The set state diagnosis rule system includes rules for determining electrode and contact states, electrolyte performance, separator states, and electrode reactivity. Specifically, the rules for determining electrode and contact states involve monitoring the voltage during the battery's charge-discharge-resting test and simultaneously recording the charge-discharge voltage curve, and the ohmic internal resistance R... ohm If the voltage increase is greater than 20% and irregular voltage fluctuations appear on the charge / discharge voltage curve, it is determined to be poor electrode contact or diaphragm blockage; if the electrode material interface change coefficient k value continues to increase greater than 25%, it is determined to be a decrease in the ion conduction performance of the bipolar plate interface; the specific rules for judging electrolyte performance are as follows: if the concentration polarization internal resistance R conc If the concentration gradient increases by more than 30%, accompanied by a synchronous increase in the concentration relaxation time constant τ, it is determined that the electrolyte concentration is insufficient or the fluidity is reduced. The specific rule for judging the diaphragm state is as follows: if the open circuit voltage at the end of the settling period decreases at a rate greater than 0.05V during the settling time, and is accompanied by an increase in the ohmic internal resistance R... ohm If the reaction rate increases synchronously, it is determined to be a degradation of the membrane performance; the specific rule for determining the electrode reactivity is as follows: if the electrochemical polarization internal resistance R... act An increase of >50% indicates a reduction in active sites for zinc deposition on the negative electrode or an obstruction of bromine reduction kinetics on the positive electrode. If this is accompanied by an abnormal value of the electrode material interface change coefficient k, it is determined to be a degradation of the bipolar plate catalyst layer.