An online evaluation method and system for a vanadium flow battery health state

Abstract

The application relates to an online evaluation method and system for the health state of a vanadium flow battery. The method part mainly comprises the following steps: in the calibration stage, a reference capacity integral is obtained by integrating the current in the first voltage to the second voltage interval of a reference battery, and a function relationship between the voltage change of the positive and negative electrodes and the capacity change is established; in the subsequent operation stage, a current capacity integral is obtained by integrating the current in the first voltage to the second voltage interval of the reference battery, and based on the function relationship between the voltage change of the positive and negative electrodes and the capacity change established in the calibration stage, the current positive and negative electrode capacity changes are obtained according to the current positive and negative electrode voltage changes; the ratio of the current capacity integral to the reference capacity integral is taken as the health state of the whole system, the difference between the current positive and negative electrode capacity changes is taken as the irreversible capacity, and the rest is reversible capacity. The application can realize accurate evaluation of the online health state of a vanadium flow battery system, and can distinguish reversible capacity from irreversible capacity.

Description

Technical Field

[0001] This application relates to the field of vanadium redox flow battery technology, and in particular to an online assessment method and system for the health status of vanadium redox flow batteries. Background Technology

[0002] Vanadium redox flow battery (VRFB) is a new type of large-scale energy storage technology. Due to its advantages such as recyclable electrolyte, high safety and long life, it is widely used in power grid frequency regulation, peak shaving and distributed energy storage scenarios.

[0003] However, with increasing operating time, battery systems experience varying degrees of performance degradation, manifested as capacity reduction, decreased voltage efficiency, increased ion cross-linking, and liquid level imbalance. Therefore, accurately assessing the battery's State of Health (SOH) is crucial for ensuring stable system operation. The commonly accepted definition of battery SOH is the ratio of the current maximum usable capacity to the system's nominal capacity: SOH = (Current maximum usable capacity / Nominal capacity) × 100%.

[0004] Current estimates of SOH are mainly based on the following methods:

[0005] 1. Equivalent Circuit Model (ECM) method: This method infers SOH by measuring changes in internal resistance and polarization voltage. However, the model is too simplified and cannot reflect the complex electrochemical reaction characteristics.

[0006] 2. Electrochemical model method: relies on concentration difference and reaction kinetic equations for parameter inversion, but has many parameters, complex calculations and is sensitive to the operating environment.

[0007] 3. Incremental Capacity Analysis (ICA) or Differential Voltage Analysis (DVA): This method calculates capacity change characteristics using charge and discharge data and is widely used in lithium battery systems. However, in flow batteries, the crosstalk between vanadium ions at the positive and negative electrodes is quite severe, requiring offline / online mixing for real-time balancing. The ICA / DVA method introduces significant errors in flow battery systems.

[0008] The above method has the following problems: it is not accurate enough for assessing the online health status of the all-vanadium redox flow battery system, and it cannot distinguish between reversible capacity and irreversible capacity.

[0009] Therefore, overcoming the problems of insufficient accuracy in assessing the online health status of vanadium redox flow battery systems and the inability to distinguish between reversible and irreversible capacity in existing technologies is a challenge to be solved in this technical field. Summary of the Invention

[0010] To address the aforementioned deficiencies or improvement needs of existing technologies, and to resolve the issues of insufficient accuracy in online health status assessment of vanadium redox flow battery systems and the inability to distinguish between reversible and irreversible capacity, this application provides an online health status assessment method and system for vanadium redox flow batteries. By setting up a reference battery, an auxiliary positive electrode, and an auxiliary negative electrode, a functional relationship between the baseline capacity integral, positive and negative electrode voltage changes, and capacity changes is established during the calibration phase. In the subsequent operation phase, after obtaining the current capacity integral, the overall health status of the system can be directly calculated. After obtaining the current positive and negative electrode voltage changes, the current positive and negative electrode capacity changes can be obtained based on the aforementioned functional relationship between voltage and capacity changes. Furthermore, irreversible and reversible capacities can be calculated based on these current capacity changes. This solution enables accurate online health status assessment of vanadium redox flow battery systems and can distinguish between reversible and irreversible capacity.

[0011] The embodiments of this application adopt the following technical solutions:

[0012] Firstly, this application provides an online assessment method for the health status of a vanadium redox flow battery, comprising:

[0013] A reference battery, an auxiliary positive electrode, and an auxiliary negative electrode are provided; wherein, the reference battery is connected in parallel with the main fuel cell stack, and the auxiliary positive electrode and the auxiliary negative electrode are connected to the positive and negative electrodes of the reference battery, respectively;

[0014] During the calibration phase, the reference capacity integral is obtained by integrating the current over the first voltage to the second voltage range of the reference battery, and a functional relationship between the changes in positive and negative electrode voltages and the changes in capacity is established.

[0015] In the subsequent operation phase, the current integral is obtained by integrating the current in the first voltage to second voltage range of the reference battery, and the current positive and negative electrode capacity change is obtained based on the functional relationship between the positive and negative electrode voltage change and the capacity change established in the calibration phase.

[0016] The ratio of the current capacity integral to the baseline capacity integral is taken as the current overall health status of the system. The difference between the current positive and negative electrode capacity changes is taken as the irreversible capacity, and the rest are reversible capacities.

[0017] By adopting the above technical solution, a reference battery, an auxiliary positive electrode, and an auxiliary negative electrode are set up. During the calibration phase, a functional relationship between the baseline capacity integral, positive and negative electrode voltage changes, and capacity changes is established. In the subsequent operation phase, after obtaining the current capacity integral, the overall health status of the system can be directly calculated. After obtaining the current positive and negative electrode voltage changes, the current positive and negative electrode capacity changes can be obtained based on the aforementioned functional relationship between positive and negative electrode voltage changes and capacity changes. Furthermore, irreversible and reversible capacities can be calculated based on the current positive and negative electrode capacity changes. The above solution can achieve accurate online health status assessment of the vanadium redox flow battery system and can distinguish between reversible and irreversible capacities.

[0018] In some embodiments, the first voltage and the second voltage are the voltages between the positive and negative terminals of the reference battery.

[0019] By adopting the above technical solution, the first voltage and the second voltage of the reference battery form an overall measurement range standard. During the calibration phase, the capacity increment obtained by integrating the current within this range can be used as the baseline capacity integral when SOH=100%, providing a reference benchmark for subsequent SOH estimation.

[0020] In some embodiments, establishing the functional relationship between positive and negative electrode voltage changes and capacity changes specifically includes:

[0021] Establish a functional relationship between the change in positive electrode voltage and the change in capacity; wherein, the change in positive electrode voltage is the voltage change between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode;

[0022] Establish a functional relationship between the change in negative electrode voltage and the change in capacity; wherein, the change in negative electrode voltage is the voltage change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode.

[0023] By adopting the above technical solutions, functional relationships between voltage and capacity changes between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode, and between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode, can be established respectively. This allows for the differentiation of capacity changes between the positive and negative electrodes, providing a basis for subsequent determination of irreversible and reversible capacity.

[0024] In some embodiments, establishing the functional relationship between positive electrode voltage change and capacity change specifically includes:

[0025] The voltage signal between the positive terminal of the reference battery and the positive terminal of the auxiliary electrode is collected at the moment when the reference battery reaches the first voltage, and recorded as V11; the voltage signal between the positive terminal of the reference battery and the positive terminal of the auxiliary electrode is collected at the moment when the reference battery reaches the second voltage, and recorded as V11'; at the same time, the corresponding voltage V1 is recorded at certain intervals of current integral capacity dQ during the process. 11 V1 12V1 13 ...V1 1n Among them, V1 11 =V11,V1 1n =V11';

[0026] Establish the functional relationship between positive electrode voltage change and capacity change:

[0027] dq1 = f(dv1) = a * (dv1) 2 +b*(dv1)+c; where the sequence dv1 is V1 12 -V1 11 V1 13 -V1 11 ...V1 1n -V1 11 The dq1 sequence is dQ, 2dQ, 3dQ, ..., (n-1)*dQ; a, b, and c are the parameters to be identified, and the parameters are identified by the least squares method.

[0028] By adopting the above technical solution, the functional relationship between voltage change and capacity change between the reference battery positive electrode and the auxiliary electrode positive electrode can be established. Subsequently, the corresponding positive electrode side voltage change can be obtained through this functional relationship and directly substituted into the function to calculate the positive electrode side capacity change.

[0029] In some embodiments, establishing the functional relationship between the negative electrode voltage change and the capacity change specifically includes:

[0030] At the moment when the reference battery reaches the first voltage, the voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode is collected and recorded as V21; at the moment when the reference battery reaches the second voltage, the voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode is collected and recorded as V21'; simultaneously, at certain intervals of current integral capacity dQ during the process, the corresponding voltage V2 is recorded. 11 V2 12 V2 13 ...V2 1n Among them, V2 11 =V21,V2 1n =V21';

[0031] Establish the functional relationship between the change in negative electrode voltage and the change in capacitance:

[0032] dq2 = g(dv2) = d*(dv2) 2 +e*(dv2)+f; where the dv2 sequence is V2 12 -V2 11 V2 13 -V2 11 ...V2 1n -V2 11The dq2 sequence is dQ, 2dQ, 3dQ, ..., (n-1)*dQ; d, e, and f are the parameters to be identified, and the parameters are identified by the least squares method.

[0033] By adopting the above technical solution, the functional relationship between voltage change and capacity change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode can be established. Subsequently, the corresponding voltage change on the negative electrode side can be obtained through this functional relationship and directly substituted into the function to calculate the capacity change on the negative electrode side.

[0034] In some embodiments, the functional relationship between positive and negative electrode voltage changes and capacity changes established during the calibration phase, and the determination of the current positive and negative electrode capacity changes based on the current positive and negative electrode voltage changes, specifically includes:

[0035] Obtain the voltage signals V12 and V12' between the positive terminal of the reference battery and the positive terminal of the auxiliary electrode when the reference battery reaches the first voltage and the second voltage respectively in the current cycle;

[0036] Calculate the current positive electrode voltage change ΔV12 = V12 - V12'; substitute ΔV12 into the function dq1 = f(dv1) to obtain the current positive electrode capacity change ΔQ. pos =f(ΔV12)

[0037] Obtain the voltage signals V22 and V22' between the negative terminal of the reference battery and the negative terminal of the auxiliary electrode when the reference battery reaches the first voltage and the second voltage respectively in the current cycle;

[0038] Calculate the current negative electrode voltage change ΔV22 = V22 - V22'; substitute ΔV22 into the function dq2 = g(dv2) to obtain the current negative electrode capacity change ΔQ. neg =g(ΔV22;

[0039] The method of using the difference between the current positive and negative electrode capacities as the irreversible capacity specifically includes: irreversible capacity DQ. irrev =|(|ΔQ pos |−|ΔQ neg |)|.

[0040] By adopting the above technical solution, based on the voltage signal change between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode, the current positive electrode capacity change on the positive electrode side can be obtained based on the aforementioned function; similarly, based on the voltage signal change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode, the current negative electrode capacity change on the negative electrode side can be obtained based on the aforementioned function; and then the irreversible capacity can be obtained by the difference between the current positive electrode capacity change and the current negative electrode capacity change, thus realizing the distinction between irreversible capacity and reversible capacity.

[0041] In some embodiments, the method further includes: after performing a mixing or refilling operation, a recalibration phase and a subsequent operation phase.

[0042] By adopting the above technical solution, when the system restores the valence equilibrium and concentration uniformity of the electrolyte through mixing or refilling, the previously identified characteristic functions f(dv1) and g(dv2) may have deviated from the actual voltage-to-capacity function, including changes in the reference capacity. Therefore, a parameter self-correction process needs to be performed to recalibrate and obtain a new set of parameters to ensure the accuracy and continuity of SOH estimation.

[0043] In some embodiments, it also includes:

[0044] During the calibration phase, the voltage V41 between the positive and negative terminals of the auxiliary electrode is collected.

[0045] During subsequent operation, the voltage V4 between the positive and negative terminals of the auxiliary electrode will be periodically measured. n ;

[0046] ΔV4=|V4 n -V41|, when ΔV4 exceeds the preset threshold, an alarm is issued, and the voltage V4 is adjusted through external operation. n Restored to V41 status.

[0047] By adopting the above technical solution, although data is collected for a short time at a specific sampling moment, potential drift of the positive and negative electrodes of the auxiliary electrode may still occur during long-term operation due to ion migration or local concentration difference, thereby affecting the accuracy of subsequent voltage sampling and the stability of SOH estimation. To address this, a state monitoring and self-maintenance mechanism for the positive and negative electrodes of the auxiliary electrode is introduced. When the voltage change between the positive and negative electrodes of the auxiliary electrode exceeds a preset threshold, the voltage between the positive and negative electrodes of the auxiliary electrode is restored by manually replenishing the electrolyte or by oxidation-reduction.

[0048] Secondly, this application provides an online health status assessment system for vanadium redox flow batteries, employing the online health status assessment method for vanadium redox flow batteries as described in the first aspect, including a main stack, a reference cell, an auxiliary positive electrode, an auxiliary negative electrode, and a control and calculation module, wherein:

[0049] The positive electrode of the reference battery is connected to the positive electrode of the main battery stack via a liquid circuit, and the negative electrode of the reference battery is connected to the negative electrode of the main battery stack via a liquid circuit.

[0050] The positive electrode of the auxiliary electrode is connected to the positive electrode of the reference battery through a liquid circuit, and a first solenoid valve is provided in the liquid circuit; the negative electrode of the auxiliary electrode is connected to the negative electrode of the reference battery through a liquid circuit, and a second solenoid valve is provided in the liquid circuit; the positive electrode of the auxiliary electrode and the negative electrode of the auxiliary electrode are connected through a liquid circuit, and a third solenoid valve is provided in the liquid circuit.

[0051] The control and calculation module is used to control the instantaneous switching of each solenoid valve and to collect the voltage between each liquid circuit at the corresponding moment. It calculates the health status and distinguishes between reversible and irreversible capacity by voltage changes and capacity increments.

[0052] By adopting the above technical solution, the main battery stack, reference battery, auxiliary electrode positive and auxiliary electrode negative are connected based on the liquid circuit. The switching of each liquid circuit is controlled by the solenoid valves installed on the liquid circuit. The control and calculation module realizes the instantaneous switching of each solenoid valve to collect the corresponding data. Then, the overall health status of the system is calculated based on the collected data, and the reversible capacity and irreversible capacity are distinguished.

[0053] In some embodiments, both the positive and negative auxiliary electrodes are half-cells, and each of the positive and negative electrode chambers of the positive and negative auxiliary electrodes is provided with a corresponding electrolyte.

[0054] By adopting the above technical solution, the positive and negative electrode chambers of the auxiliary electrode positive and negative electrodes contain electrolytes with corresponding specific SOCs. For example, the positive electrode contains VO2 with a SOC concentration of 50%. + With VO 2+ Electrolyte, negative electrode contains V at a concentration corresponding to 50% SOC 3+ With V 2+ Electrolyte.

[0055] In summary, this application includes at least the following beneficial technical effects:

[0056] 1. A reference battery, an auxiliary positive electrode, and an auxiliary negative electrode are set up. During the calibration phase, a functional relationship is established between the baseline capacity integral, the positive and negative electrode voltage changes, and the capacity change. In the subsequent operation phase, after obtaining the current capacity integral, the overall health status of the system can be directly calculated. After obtaining the current positive and negative electrode voltage changes, the current positive and negative electrode capacity changes can be obtained based on the previously established functional relationship between positive and negative electrode voltage changes and capacity changes. Furthermore, irreversible and reversible capacities can be calculated based on these current capacity changes. This scheme enables accurate online health status assessment of the vanadium redox flow battery system and can distinguish between reversible and irreversible capacities.

[0057] 2. When the system restores the valence equilibrium and concentration uniformity of the electrolyte through mixing or refilling, the previously identified characteristic functions f(dv1) and g(dv2) may have deviated from the actual voltage-to-capacity function, and the reference capacity may also change. Therefore, a parameter self-correction process needs to be performed to recalibrate and obtain a new set of parameters to ensure the accuracy and continuity of SOH estimation.

[0058] 3. Although data is collected for a short period of time at a specific sampling moment, potential drift of the positive and negative electrodes of the auxiliary electrode may still occur during long-term operation due to ion migration or local concentration differences, thereby affecting the accuracy of subsequent voltage sampling and the stability of SOH estimation. To address this, a state monitoring and self-maintenance mechanism for the positive and negative electrodes of the auxiliary electrode is introduced. When the voltage change between the positive and negative electrodes of the auxiliary electrode exceeds a preset threshold, the voltage between the positive and negative electrodes of the auxiliary electrode is restored by manually replenishing the electrolyte or by oxidation-reduction. Attached Figure Description

[0059] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0060] Figure 1 A flowchart illustrating an online health status assessment method for a vanadium redox flow battery provided in this application embodiment;

[0061] Figure 2 An extended flowchart of step 102 provided in the embodiments of this application;

[0062] Figure 3 An architecture diagram of an online health status assessment system for vanadium redox flow batteries provided in this application embodiment;

[0063] Figure 4 The flowchart illustrates the operation of the control and calculation module provided in the embodiments of this application. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Furthermore, the technical features involved in the various embodiments described below can be combined with each other as long as they do not conflict with each other. The application will now be described in detail with reference to the accompanying drawings and embodiments. Example 1

[0065] like Figure 1 As shown in the figure, this application provides an online assessment method for the health status of a vanadium redox flow battery, and the specific steps are as follows.

[0066] Step 101: Set up a reference battery, an auxiliary positive electrode, and an auxiliary negative electrode; wherein, the reference battery is connected in parallel with the main battery stack, the auxiliary positive electrode and the auxiliary negative electrode are connected to the positive and negative electrodes of the reference battery respectively, and the auxiliary positive electrode and the auxiliary negative electrode are connected to each other. All of the above connections are liquid circuit connections, and each liquid circuit is equipped with a solenoid valve for on / off control.

[0067] Step 102: In the calibration phase, the current is integrated over the first voltage to the second voltage range of the reference battery to obtain the baseline capacity integral, and a functional relationship between the positive and negative electrode voltage changes and the capacity change is established. Here, the first voltage and the second voltage are the voltages between the positive and negative electrodes of the reference battery. The first and second voltages of the reference battery form a unified measurement range standard. During the calibration phase, the capacity increment obtained by integrating the current within this range can be used as the baseline capacity integral when SOH = 100%, providing a reference benchmark for subsequent SOH estimation.

[0068] refer to Figure 2 As shown, in step 102 above, establishing the functional relationship between the positive and negative voltage changes and the capacity changes specifically includes the following steps.

[0069] Step 1021: Establish a functional relationship between the positive electrode voltage change and the capacity change; wherein, the positive electrode voltage change is the voltage change between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode. Specifically, at the moment when the reference battery reaches the first voltage, the voltage signal between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode is collected and recorded as V11; at the moment when the reference battery reaches the second voltage, the voltage signal between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode is collected and recorded as V11'; simultaneously, at certain intervals during the process, the voltage V1 corresponding to the current integral capacity dQ is recorded. 11 V1 12 V1 13 ...V1 1n Among them, V1 11 =V11,V1 1n =V11'; Establish the functional relationship between positive voltage change and capacity change: dq1=f(dv1)=a*(dv1) 2 +b*(dv1)+c; where the sequence dv1 is V1 12 -V1 11 V1 13 -V1 11 ...V1 1n -V1 11The dq1 sequence is dQ, 2dQ, 3dQ, ..., (n-1)*dQ; a, b, and c are the parameters to be identified, which are identified using the least squares method. Through the above technical solution, a functional relationship between the voltage and capacity changes between the reference battery's positive electrode and the auxiliary electrode's positive electrode can be established. Subsequently, this functional relationship can be used to obtain the corresponding positive electrode side voltage change and directly substitute it into the function to calculate the positive electrode side capacity change.

[0070] Step 1022: Establish a functional relationship between the negative electrode voltage change and the capacity change; wherein, the negative electrode voltage change is the voltage change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode. Specifically, at the moment when the reference battery reaches the first voltage, the voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode is collected and denoted as V21; at the moment when the reference battery reaches the second voltage, the voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode is collected and denoted as V21'; simultaneously, at certain intervals during the process, the voltage V2 corresponding to the current integral capacity dQ is recorded. 11 V2 12 V2 13 ...V2 1n Among them, V2 11 =V21,V2 1n =V21'; Establish the functional relationship between the change in negative electrode voltage and the change in capacity: dq2=g(dv2)=d*(dv2) 2 +e*(dv2)+f; where the dv2 sequence is V2 12 -V2 11 V2 13 -V2 11 ...V2 1n -V2 11 The dq2 sequence is dQ, 2dQ, 3dQ, ..., (n-1)*dQ; d, e, and f are the parameters to be identified, which are identified using the least squares method. Through the above technical solution, a functional relationship between the voltage and capacity changes between the reference battery's negative electrode and the auxiliary electrode's negative electrode can be established. Subsequently, this functional relationship can be used to obtain the corresponding voltage change on the negative electrode side and directly substitute it into the function to calculate the capacity change on the negative electrode side.

[0071] By establishing the functional relationships between voltage and capacity changes between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode, and between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode, respectively, the capacity changes between the positive and negative electrodes can be distinguished, providing a basis for subsequent determination of irreversible and reversible capacity.

[0072] Step 103: In the subsequent operation phase, the current integral is obtained by integrating the current over the first voltage to the second voltage range of the reference battery. Based on the functional relationship between the positive and negative electrode voltage changes and capacity changes established during the calibration phase, the current positive and negative electrode capacity changes are obtained according to the current positive and negative electrode voltage changes. Specifically, the voltage signals V12 and V12' between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode are obtained when the reference battery reaches the first voltage and the second voltage respectively in the current cycle; the current positive electrode voltage change ΔV12 = V12 - V12' is calculated; ΔV12 is substituted into the function dq1 = f(dv1) to obtain the current positive electrode capacity change ΔQ. pos =f(ΔV12); Obtain the voltage signals V22 and V22' between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode when the reference battery reaches the first voltage and the second voltage respectively in the current cycle; Calculate the current negative electrode voltage change ΔV22 = V22 - V22'; Substitute ΔV22 into the function dq2 = g(dv2) to obtain the current negative electrode capacity change ΔQ. neg =g(ΔV22)

[0073] Step 104: The ratio of the current capacity integral to the baseline capacity integral is taken as the overall health status of the current system. The difference between the current positive and negative electrode capacity changes is taken as the irreversible capacity, and the rest are reversible capacities. Specifically, taking the difference between the current positive and negative electrode capacity changes as the irreversible capacity includes: irreversible capacity DQ. irrev =|(|ΔQ pos |−|ΔQ neg |)|.

[0074] Through steps 103 and 104, based on the voltage signal change between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode, the current positive electrode capacity change on the positive electrode side can be obtained based on the aforementioned function; similarly, based on the voltage signal change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode, the current negative electrode capacity change on the negative electrode side can be obtained based on the aforementioned function; then, the irreversible capacity is obtained by the difference between the current positive electrode capacity change and the current negative electrode capacity change, thus realizing the distinction between irreversible capacity and reversible capacity.

[0075] By adopting the above technical solution, a reference battery, an auxiliary positive electrode, and an auxiliary negative electrode are set up. During the calibration phase, a functional relationship between the baseline capacity integral, positive and negative electrode voltage changes, and capacity changes is established. In the subsequent operation phase, after obtaining the current capacity integral, the overall health status of the system can be directly calculated. After obtaining the current positive and negative electrode voltage changes, the current positive and negative electrode capacity changes can be obtained based on the aforementioned functional relationship between positive and negative electrode voltage changes and capacity changes. Furthermore, irreversible and reversible capacities can be calculated based on the current positive and negative electrode capacity changes. The above solution can achieve accurate online health status assessment of the vanadium redox flow battery system and can distinguish between reversible and irreversible capacities.

[0076] In some embodiments, the system further includes a recalibration phase and subsequent operation phase after performing a mixing or refilling operation. Through the above technical solution, when the system restores the valence equilibrium and concentration uniformity of the electrolyte through a mixing or refilling operation, the previously identified characteristic functions f(dv1) and g(dv2) may have deviated from the actual voltage-to-capacity function, including changes in the reference capacity. Therefore, a parameter self-correction process and a recalibration phase are required to obtain a new set of parameters to ensure the accuracy and continuity of the SOH estimation.

[0077] In some embodiments, the method further includes: during the calibration phase, acquiring the voltage V41 between the positive and negative terminals of the auxiliary electrode; and during subsequent operation phases, periodically acquiring the voltage V4 between the positive and negative terminals of the auxiliary electrode. n ;ΔV4=|V4 n -V41|, when ΔV4 exceeds the preset threshold, an alarm is issued, and the voltage V4 is adjusted through external operation. n Return to V41 state. Although the above technical solution allows for short-term data acquisition at specific sampling times, long-term operation may still result in potential drift at the positive and negative electrodes of the auxiliary electrode due to ion migration or local concentration differences, affecting subsequent voltage sampling accuracy and SOH estimation stability. Therefore, a state monitoring and self-maintenance mechanism for the positive and negative electrodes of the auxiliary electrode is introduced. If the voltage change between the positive and negative electrodes exceeds a preset threshold, the voltage between them is restored through manual electrolyte replenishment or redox reactions. Example 2

[0078] Based on the online assessment method for the health status of vanadium redox flow batteries provided in Example 1, this Example 2 provides an online assessment system for the health status of vanadium redox flow batteries, which applies the online assessment method for the health status of vanadium redox flow batteries as described in Example 1.

[0079] refer to Figure 3 As shown, the online health status assessment system for vanadium redox flow batteries of this application includes a main stack, a reference cell, an auxiliary positive electrode, an auxiliary negative electrode, and a control and calculation module.

[0080] The main battery stack is a vanadium redox flow battery stack, comprising a positive electrode chamber and a negative electrode chamber, which are respectively connected to the positive and negative electrolyte circulation systems. Specifically, the positive electrode of the main battery stack is connected to the positive electrolyte tank, and the negative electrode of the main battery stack is connected to the negative electrolyte tank.

[0081] The reference battery is a complete full cell, and its corresponding liquid circuit is connected in parallel with the liquid circuits of the positive and negative electrode electrolytes of the main battery stack. Specifically, the positive electrode of the reference battery is connected to the positive electrode of the main battery stack through a liquid circuit, and the negative electrode of the reference battery is connected to the negative electrode of the main battery stack through a liquid circuit.

[0082] The auxiliary electrode positive and negative electrodes are two half-cells, and their liquid circuits are connected to the positive and negative liquid circuits of the reference cell respectively via solenoid valves. The positive and negative electrode chambers contain electrolytes corresponding to a specific SOC, for example, the positive electrode contains VO2 with a SOC concentration of 50%. + With VO 2+ Electrolyte, negative electrode contains V at a concentration corresponding to 50% SOC 3+ With V 2+ Electrolyte. Specifically, the positive electrode of the auxiliary electrode is connected to the positive electrode of the reference battery through a liquid circuit, and a first solenoid valve is provided on the liquid circuit; the negative electrode of the auxiliary electrode is connected to the negative electrode of the reference battery through a liquid circuit, and a second solenoid valve is provided on the liquid circuit; the positive electrode of the auxiliary electrode and the negative electrode of the auxiliary electrode are connected through a liquid circuit, and a third solenoid valve is provided on the liquid circuit.

[0083] For the aforementioned liquid circuit connection and solenoid valve control structure, the reference battery and auxiliary electrode are controllably connected via liquid circuits, specifically including the following liquid circuits: Reference positive electrode liquid circuit: The positive electrode of the reference battery is connected to the positive electrode of the main stack via a liquid circuit; simultaneously, the positive electrode of the reference battery is connected to the positive electrode of the auxiliary electrode via a liquid circuit. A first solenoid valve S1 is installed on the liquid circuit to control its on / off state. Reference negative electrode liquid circuit: The negative electrode of the reference battery is connected to the negative electrode of the main stack via a liquid circuit; simultaneously, the negative electrode of the reference battery is connected to the negative electrode of the auxiliary electrode via a liquid circuit. A second solenoid valve S2 is installed on the liquid circuit to control its on / off state. Auxiliary electrode interconnection liquid circuit: An interconnection liquid circuit is provided between the positive and negative electrodes of the auxiliary electrode. A third solenoid valve S3 is installed on the liquid circuit to control the on / off state of the electrolyte channel between the two auxiliary electrodes. The liquid circuits connecting the positive electrode of the reference battery to the positive electrode of the auxiliary electrode, the connecting pipes connecting the negative electrode of the reference battery to the negative electrode of the auxiliary electrode, and the liquid circuits for interconnection between the auxiliary electrodes can be designed using ion-connected U-shaped pipes to minimize ion crosstalk during voltage sampling when the solenoid valve is turned on.

[0084] The control and calculation module controls the instantaneous switching of each solenoid valve and collects the voltage between each liquid path at the corresponding moment. It calculates the health status and distinguishes between reversible and irreversible capacity by analyzing voltage changes and capacity increments. Specifically, the control and calculation module collects the following signals: voltage V1 between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode; voltage V2 between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode; voltage V3 between the positive and negative electrodes of the reference battery; and voltage V4 between the positive and negative electrodes of the auxiliary electrode. The control and calculation module collects the system current, calculates the charge integral, and controls the switching sequence of each solenoid valve according to a set strategy. It opens the solenoid valve at a specified sampling moment to establish an instantaneous ion channel, immediately closes it after collecting the voltage, and calculates the state of equilibrium (SOH) based on the voltage changes and capacity increments.

[0085] The above technical solution connects the main battery stack, reference battery, positive auxiliary electrode, and negative auxiliary electrode through a liquid circuit. The switching of each liquid circuit is controlled by solenoid valves installed on the liquid circuit. The control and calculation module realizes the instantaneous switching of each solenoid valve to collect corresponding data. Then, the overall health status of the system is calculated based on the collected data, and reversible capacity and irreversible capacity are distinguished.

[0086] refer to Figure 4 As shown, the specific operation flow of the control and calculation module includes the following steps.

[0087] (1) System initialization and establishment of SOH=100% baseline.

[0088] During the initial system operation or offline calibration phase (which can be understood as a state of SOH=100%), within the specified temperature and flow range, and within the set voltage range (the overall voltage of the reference battery changes from V3 to V3'), the following steps are executed sequentially during this process:

[0089] 1. At the moment when the reference battery reaches voltage V3, open the solenoid valve S1 on the liquid line between the positive terminal of the reference battery and the positive terminal of the auxiliary electrode, and collect the voltage signal V11 between them. After the collection is completed, close the solenoid valve S1. At the moment when the reference battery reaches voltage V3', open the solenoid valve S1 on the liquid line between the positive terminal of the reference battery and the positive terminal of the auxiliary electrode again, and collect the voltage V11' between them. After the collection is completed, close the solenoid valve S1, and obtain the corresponding pressure difference ΔV11 = V11 - V11'. At the same time, at certain current integration capacity dQ (dQ should be as small as possible, determined according to the capability of the control and calculation module and the actual current integration range, or the entire range can be divided equally based on experience), record the corresponding voltage V1. 11 V1 12 V1 13 ...V1 1n Among them, V111 =V11,V1 1n =V11'.

[0090] 2. At the corresponding time points in the previous step, open and close the solenoid valve S2 on the liquid circuit between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode, and collect the corresponding voltage signals V21 and V21' to obtain the corresponding pressure difference ΔV21=V21-V21', and the voltage point V2 corresponding to dq. 11 V2 12 V2 13 ...V2 1n Among them, V2 11 =V21,V2 1n =V21'.

[0091] 3. After the system is running normally and during subsequent periodic cycles, open the solenoid valve S3 on the liquid line between the positive and negative terminals of the auxiliary electrode at regular intervals to collect the voltage signal V41 between them.

[0092] During the above process, the corresponding solenoid valve should be closed immediately after the corresponding voltage acquisition is completed to isolate the ion channel and avoid electrochemical interference between different half-cells. Within the reference cell voltage range of V3 and V3', the control and calculation module integrates the current to obtain the capacity increment DQ. 100 This is the integral of the baseline capacity when SOH = 100%. This baseline capacity includes both the reversible (recoverable) capacity and the irreversible (loss) capacity of the battery, providing a reference for subsequent SOH estimation. To reduce calculation errors, the interval between V3 and V3' can be appropriately expanded, for example, to correspond to the voltage range between 50% and 100% capacity.

[0093] (2) Parameter identification of voltage for capacity change.

[0094] For V1 1n With V2 1n Parameter identification is performed based on the functional relationship between the change in capacity and the capacity:

[0095] dq1 = f(dv1) = a * (dv1) 2 +b*(dv1)+c;

[0096] Among them, the dv1 sequence is V1 12 -V1 11 V1 13 -V1 11 ...V1 1n -V1 11 The dq1 sequence is dQ, 2dQ, 3dQ, ..., (n-1)*dQ; a, b, and c are the parameters to be identified, which can be identified by the least squares method.

[0097] Similarly, the Q2 function can be identified:

[0098] dq2 = g(dv2) = d*(dv2) 2 +e*(dv2)+f; where the dv2 sequence is V2 12 -V2 11 V2 13 -V2 11 ...V2 1n -V2 11 The dq2 sequence is dQ, 2dQ, 3dQ, ..., (n-1)*dQ; d, e, and f are the parameters to be identified, and the parameters are identified by the least squares method.

[0099] (3) SOH estimation during operation.

[0100] During each subsequent charge and discharge cycle of the system, when the reference battery voltage reaches points V3 to V3', and the operating conditions (temperature, flow rate, etc.) meet the same flow rate and temperature range specified in the initial data acquisition, the solenoid valve is controlled to periodically open and close in sequence, and the voltage at each point is collected.

[0101] 1. Open and close the solenoid valve S1 of the reference battery positive electrode and the auxiliary electrode positive electrode liquid circuit, collect the corresponding voltages V12 and V12', and calculate the voltage change ΔV12=V12-V12' in this range;

[0102] 2. Open and close the solenoid valve S2 of the liquid circuit between the negative terminal of the reference battery and the negative terminal of the auxiliary electrode, collect the corresponding voltages V22 and V22', and calculate the voltage change ΔV22=V22-V22' within this range;

[0103] 3. Open and close the auxiliary electrode inter-electrode solenoid valve S3, and collect the voltage V4;

[0104] 4. Synchronously collect the current within the voltage range of the reference battery from V3 to V3' and perform capacity integration to obtain the capacity increment DQ corresponding to this cycle. n Integral DQ with the current capacity n Integral DQ with the baseline capacity 100 The ratio of the current system SOH is used as the current system SOH. total :

[0105] SOH total =DQ n / DQ 100 ×100%;

[0106] SOH total =SOH reversible +SOH irreversible ;

[0107] Where SOH totalIt consists of two parts, one of which is the reversible (recoverable) capacity SOH. reversible This portion of the capacity can be recovered through methods such as mixing positive and negative electrode electrolytes; the other portion is irreversible (unrecoverable) capacity SOH. irreversible This portion of the capacity cannot be restored by mixing the solution; it requires replenishing vanadium ions to restore it to its initial state.

[0108] (4) Calculation of reversible capacity and irreversible capacity.

[0109] The capacity of the reversible portion is due to the energy exchange between the positive and negative electrolytes. Without the loss of vanadium ions, the change in vanadium ion concentration at one electrode would be symmetrical to the change at the other electrode, thus reflecting a change in usable capacity. The capacity changes corresponding to the positive and negative electrodes are calculated using the previously identified dv and dq mapping functions f(dv) and g(dv):

[0110] ΔQ pos =f(ΔV12)

[0111] ΔQ neg =g(ΔV22;

[0112] If |ΔQ pos |≈|ΔQ neg | indicates that the concentration changes of vanadium ions on both sides are relatively consistent, and the change in system capacity is mainly caused by the migration of vanadium ions, both of which are reversible capacities.

[0113] If |ΔQ pos | and |ΔQ neg If the difference is large (this difference threshold can be determined by the maximum error between the identification functions f() and g() and the actual test quantity), then there is an irreversible loss. The irreversible capacity loss can be calculated using the following formula:

[0114] DQ irrev =|(|ΔQ pos |−|ΔQ neg |)|;

[0115] SOH irreversible =DQ irrev / DQ 100 ×100%;

[0116] In this way, the system calculates the total SOH, reversible SOH, and irreversible SOH of the battery in real time during operation. This provides a reference for maintenance schemes such as electrolyte mixing, secondary use, and electrolyte replenishment.

[0117] (5) Self-correction scheme after mixing or refilling.

[0118] When the system restores the electrolyte's valence equilibrium and concentration uniformity through mixing or refilling, the previously identified characteristic functions f(dv1) and g(dv2) may have deviated from the actual voltage-to-capacity function, including the initial capacity DQ. 100 The values ​​can also change, so a parameter self-correction process needs to be performed to ensure the accuracy and continuity of the SOH estimation. For example, initialize the SOH to 100%, and re-acquire data according to step (1), and perform parameter identification according to step (2).

[0119] (6) Auxiliary reference electrode status monitoring and self-maintenance mechanism.

[0120] Although the solenoid valve only opens briefly at specific sampling moments, potential drift at the positive and negative electrodes of the auxiliary electrode can still occur during long-term operation due to ion migration or local concentration differences, thus affecting the accuracy of subsequent voltage sampling and the stability of SOH estimation. Therefore, this application introduces a state monitoring and self-maintenance mechanism for the positive and negative electrodes of the auxiliary electrode, as follows:

[0121] The voltage V41 collected in step (1) should remain stable for a period of time; during system operation, the voltage state V4 between the positive and negative electrodes of the auxiliary electrode should be collected periodically (e.g., every few cycles or after each mixing). n And compared with V41, ΔV4=|V4 n -V41|, when ΔV4 exceeds a preset threshold (e.g., 10mV~20mV, specifically determined based on the SOC-OCV data and allowable error), it is determined that the auxiliary reference electrode has significant ion crosstalk or concentration imbalance. When the above phenomenon occurs, it can be restored by manually replenishing the electrolyte or by redox reactions, so that the sampling voltage value of V4 returns to the V41 state.

[0122] In summary, this application achieves accurate state of health (SOH) determination and dynamic correction of vanadium redox flow batteries in different operating cycles by introducing an auxiliary reference electrode system, capacity integration benchmark calibration, and reversible / irreversible capacity separation and correction algorithm, which has the following beneficial effects.

[0123] 1. This application establishes an adaptive benchmark of steady-state SOH=100% through capacity integration, realizing a unified health assessment standard under different cyclic conditions.

[0124] 2. By establishing a mathematical function for voltage range and capacity change through the dv–dq relationship, the reversible and irreversible capacities of the vanadium redox flow battery can be accurately separated and determined.

[0125] 3. By recalibrating the dv–dq parameters after mixing or refilling, the algorithm can adaptively correct the function parameters and maintain the accuracy of SOH calculation.

[0126] 4. By monitoring the voltage drift of the positive and negative electrodes of the auxiliary electrode and performing liquid replenishment or redox maintenance, the stability of the auxiliary reference electrode potential and the accuracy of the measurement are ensured.

[0127] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An online assessment method for the health status of a vanadium redox flow battery, characterized in that, include: A reference battery, an auxiliary positive electrode, and an auxiliary negative electrode are provided; wherein, the reference battery is connected in parallel with the main fuel cell stack, and the auxiliary positive electrode and the auxiliary negative electrode are connected to the positive and negative electrodes of the reference battery, respectively; During the calibration phase, the reference capacity integral is obtained by integrating the current over the first voltage to the second voltage range of the reference battery, and a functional relationship between the changes in positive and negative electrode voltages and the changes in capacity is established. In the subsequent operation phase, the current integral is obtained by integrating the current in the first voltage to second voltage range of the reference battery, and the current positive and negative electrode capacity change is obtained based on the functional relationship between the positive and negative electrode voltage change and the capacity change established in the calibration phase. The ratio of the current capacity integral to the baseline capacity integral is taken as the current overall health status of the system. The difference between the current positive and negative electrode capacity changes is taken as the irreversible capacity, and the rest are reversible capacities.

2. The online assessment method for the health status of a vanadium redox flow battery according to claim 1, characterized in that, The first voltage and the second voltage are the voltages between the positive and negative terminals of the reference battery.

3. The online assessment method for the health status of a vanadium redox flow battery according to claim 1, characterized in that, The establishment of the functional relationship between positive and negative electrode voltage changes and capacity changes specifically includes: Establish a functional relationship between the change in positive electrode voltage and the change in capacity; wherein, the change in positive electrode voltage is the voltage change between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode; Establish a functional relationship between the change in negative electrode voltage and the change in capacity; wherein, the change in negative electrode voltage is the voltage change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode.

4. The online assessment method for the health status of a vanadium redox flow battery according to claim 3, characterized in that, The establishment of the functional relationship between positive electrode voltage change and capacity change specifically includes: The voltage signal between the positive terminal of the reference battery and the positive terminal of the auxiliary electrode is collected at the moment when the reference battery reaches the first voltage, and recorded as V11; the voltage signal between the positive terminal of the reference battery and the positive terminal of the auxiliary electrode is collected at the moment when the reference battery reaches the second voltage, and recorded as V11'; at the same time, the corresponding voltage V1 is recorded at certain intervals of current integral capacity dQ during the process. 11 V1 12 V1 13 ...V1 1n Among them, V1 11 =V11,V1 1n =V11'; Establish the functional relationship between positive electrode voltage change and capacity change: dq1 = f(dv1) = a * (dv1) 2 +b*(dv1)+c; where the sequence dv1 is V1 12 -V1 11 V1 13 -V1 11 ...V1 1n -V1 11 The dq1 sequence is dQ, 2dQ, 3dQ, ..., (n-1)*dQ; a, b, and c are the parameters to be identified, and the parameters are identified by the least squares method.

5. The online assessment method for the health status of a vanadium redox flow battery according to claim 4, characterized in that, The establishment of the functional relationship between negative electrode voltage change and capacity change specifically includes: At the moment when the reference battery reaches the first voltage, the voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode is collected and recorded as V21; at the moment when the reference battery reaches the second voltage, the voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode is collected and recorded as V21'; simultaneously, at certain intervals of current integral capacity dQ during the process, the corresponding voltage V2 is recorded. 11 V2 12 V2 13 ...V2 1n Among them, V2 11 =V21,V2 1n =V21'; Establish the functional relationship between the change in negative electrode voltage and the change in capacitance: dq2 = g(dv2) = d*(dv2) 2 +e*(dv2)+f; where the dv2 sequence is V2 12 -V2 11 V2 13 -V2 11 ...V2 1n -V2 11 The dq2 sequence is dQ, 2dQ, 3dQ, ..., (n-1)*dQ; d, e, and f are the parameters to be identified, and the parameters are identified by the least squares method.

6. The online assessment method for the health status of a vanadium redox flow battery according to claim 5, characterized in that, The functional relationship between positive and negative electrode voltage changes and capacity changes established during the calibration phase, specifically including the following to derive the current positive and negative electrode capacity changes based on the current positive and negative electrode voltage changes: Obtain the voltage signals V12 and V12' between the positive terminal of the reference battery and the positive terminal of the auxiliary electrode when the reference battery reaches the first voltage and the second voltage respectively in the current cycle; Calculate the current positive electrode voltage change ΔV12 = V12 - V12'; substitute ΔV12 into the function dq1 = f(dv1) to obtain the current positive electrode capacity change ΔQ. pos =f(ΔV12) Obtain the voltage signals V22 and V22' between the negative terminal of the reference battery and the negative terminal of the auxiliary electrode when the reference battery reaches the first voltage and the second voltage respectively in the current cycle; Calculate the current negative electrode voltage change ΔV22 = V22 - V22'; substitute ΔV22 into the function dq2 = g(dv2) to obtain the current negative electrode capacity change ΔQ. neg =g(ΔV22; The method of using the difference between the current positive and negative electrode capacities as the irreversible capacity specifically includes: irreversible capacity DQ. irrev =|(|ΔQ pos |−|ΔQ neg |)|.

7. The online assessment method for the health status of a vanadium redox flow battery according to any one of claims 1-6, characterized in that, Also includes: After mixing or refilling the solution, the calibration phase and subsequent operation phase are repeated.

8. The online assessment method for the health status of a vanadium redox flow battery according to any one of claims 1-6, characterized in that, Also includes: During the calibration phase, the voltage V41 between the positive and negative terminals of the auxiliary electrode is collected. During subsequent operation, the voltage V4 between the positive and negative terminals of the auxiliary electrode will be periodically measured. n ; ΔV4=|V4 n -V41|, when ΔV4 exceeds the preset threshold, an alarm is issued, and the voltage V4 is adjusted through external operation. n Restored to V41 status.

9. An online health status assessment system for vanadium redox flow batteries, employing the online health status assessment method for vanadium redox flow batteries as described in any one of claims 1-8, characterized in that, It includes the main fuel cell stack, reference cell, auxiliary electrode positive, auxiliary electrode negative, and control and computing module, among which: The positive electrode of the reference battery is connected to the positive electrode of the main battery stack via a liquid circuit, and the negative electrode of the reference battery is connected to the negative electrode of the main battery stack via a liquid circuit. The positive electrode of the auxiliary electrode is connected to the positive electrode of the reference battery through a liquid circuit, and a first solenoid valve is provided in the liquid circuit; the negative electrode of the auxiliary electrode is connected to the negative electrode of the reference battery through a liquid circuit, and a second solenoid valve is provided in the liquid circuit; the positive electrode of the auxiliary electrode and the negative electrode of the auxiliary electrode are connected through a liquid circuit, and a third solenoid valve is provided in the liquid circuit. The control and calculation module is used to control the instantaneous switching of each solenoid valve and to collect the voltage between each liquid circuit at the corresponding moment. It calculates the health status and distinguishes between reversible and irreversible capacity by voltage changes and capacity increments.

10. The online health status assessment system for vanadium redox flow batteries according to claim 9, characterized in that, Both the positive and negative auxiliary electrodes are half-cells, and each of the positive and negative electrode chambers contains a corresponding electrolyte.

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