A differential capacitance measurement method, device, electronic equipment and medium

Abstract

The present application discloses a differential capacitance measurement method, device, electronic device and medium. The differential capacitance measurement method includes: obtaining multiple charging currents corresponding to different moments of a cell to be tested in a preset cell state; wherein the charging current is measured by charging the cell to be tested at a constant voltage after the cell to be tested is connected in series with an external resistor; based on the multiple charging currents, determining the decay time constant in the relationship model of the decay of the charging current over time; obtaining the ratio of the decay time constant to the resistance value of the external resistor to obtain the differential capacitance of the cell to be tested in the preset cell state. The above scheme realizes the measurement of the overall differential capacitance of the cell.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a differential capacitance measurement method, device, electronic equipment and medium. Background Art

[0002] The differential capacitance of a battery cell is an important parameter of the battery and can be used to analyze the characteristics of the battery cell. For example, it can be used to analyze the double-layer characteristics inside the battery cell, the adsorption and desorption mechanism, potential range and degree of electrode surfactants, the surface state and true surface area of ​​the electrode, and whether the battery cell is abnormal. How to measure the differential capacitance of the battery cell has become an urgent problem to be solved. Summary of the invention

[0003] The present application at least provides a differential capacitance measurement method, device, electronic device and medium.

[0004] The present application provides a differential capacitance measurement method, comprising: obtaining a plurality of charging currents corresponding to different moments of a battery cell to be tested in a preset battery cell state; wherein the charging current is measured by charging the battery cell to be tested at a constant voltage after the battery cell to be tested is connected in series with an external resistor; based on the plurality of charging currents, determining a decay time constant in a relationship model of the decay of the charging current over time; obtaining a ratio of the decay time constant to the resistance value of the external resistor to obtain the differential capacitance of the battery cell to be tested in the preset battery cell state.

[0005] In the above scheme, the battery cell to be tested in a preset battery cell state with an external resistor connected in series is charged at a constant voltage, the decay time constant is obtained by analyzing the charging current, and the differential capacitance in the preset battery cell state is determined based on the ratio of the decay time constant to the resistance value of the external resistor, thereby realizing the measurement of the differential capacitance of the battery cell as a whole.

[0006] In some embodiments, based on multiple charging currents, determining the decay time constant in the relationship model of the charging current decaying with time includes: using multiple charging currents and the moments corresponding to each charging current to fit the relationship model of the charging current decaying with time; obtaining the decay time constant in the relationship model.

[0007] In the above scheme, the charging current is fitted to obtain a model of the current changing with time, so that the decay time constant in the model can be obtained to determine the differential capacitance.

[0008] In some embodiments, the decay time constant represents the time for the charging current to decay to a target current, the target current is the sum of the steady-state current and the adjustment current, the adjustment current is the product of the difference current and a preset value, the preset value is the inverse of the natural constant, and the difference current is the difference between the initial charging current and the steady-state current.

[0009] In the above scheme, the decay time constant can be the time it takes for the charging current to decay to the target current, which is related to the speed at which the charging current decays.

[0010] In some embodiments, there is at least one external resistor, and after obtaining the decay time constant corresponding to each external resistor, the ratio of the decay time constant to the resistance value of the external resistor is obtained to obtain the differential capacitance of the battery cell to be tested in a preset battery cell state, including: when there is one external resistor, obtaining the ratio of the decay time constant corresponding to the external resistor to the resistance value of the external resistor as the differential capacitance of the battery cell to be tested in the preset battery cell state; when there are multiple external resistors, obtaining a ratio representation value as the differential capacitance of the battery cell to be tested in the preset battery cell state, the ratio representation value represents the concentration trend of the ratios corresponding to each external resistor, and the ratio corresponding to the external resistor is the ratio between the decay time constant corresponding to the external resistor and the resistance value of the external resistor.

[0011] In the above scheme, there may be one or more external resistors. By directly obtaining the ratio or the ratio characterization value, the differential capacitance under the preset battery cell state can be determined. The number of external resistors can be flexibly selected to meet different application needs.

[0012] In some embodiments, a ratio representation value is obtained as the differential capacitance of the battery cell to be tested in a preset battery cell state, including: using the decay time constant corresponding to each external resistor and the resistance value of each external resistor to fit a direct proportional function, the direct proportional function has the resistance value as the independent variable and the decay time constant as the dependent variable; obtaining the proportional coefficient of the direct proportional function as the differential capacitance of the battery cell to be tested in the preset battery cell state.

[0013] In the above scheme, the resistance value and the attenuation time constant are directly proportional. A directly proportional function can be obtained by fitting, and the proportional coefficient is used as a ratio representation value, thereby realizing the determination of the differential capacitance.

[0014] In some embodiments, the resistance of the external resistor is several times greater than the internal resistance of the battery cell to be tested.

[0015] In the above scheme, the resistance value of the external resistor can be set at several times of the internal resistance to meet the needs of differential capacitance measurement.

[0016] In some embodiments, the resistance of the external resistor is between 0.1Ω and 1Ω.

[0017] In the above scheme, the resistance value of the external resistor can be set between 0.1Ω and 1Ω to meet the needs of differential capacitance measurement.

[0018] In some embodiments, the preset battery cell state includes the battery cell temperature being a preset temperature and the charge state being a preset charge state; constant voltage charging is charging the battery cell to be tested in the preset battery cell state using a target power supply voltage, and the target power supply voltage is equal to the battery cell voltage of the battery cell to be tested before constant voltage charging, wherein the charge state of the battery cell to be tested can be adjusted by constant current charging of the battery cell to be tested.

[0019] In the above scheme, the state of charge is adjusted by constant current charging, and the voltage of the battery cell in the preset battery cell state is used as the voltage value of constant voltage charging to achieve constant voltage charging.

[0020] In some embodiments, after obtaining the differential capacitance of the battery cell to be tested under different preset battery cell states, the method further includes: using the differential capacitance corresponding to different charge states at the same battery cell temperature to construct a first change curve of the differential capacitance of the battery cell to be tested versus the charge state.

[0021] In the above solution, a first variation curve is constructed to accurately represent the differential capacitance of the battery cell to be tested.

[0022] In some embodiments, after obtaining the differential capacitance of the battery cell to be tested under different preset battery cell states, the method further includes: using the differential capacitance corresponding to different battery cell temperatures under the same charge state to construct a second variation curve of the differential capacitance of the battery cell to be tested with the battery cell temperature.

[0023] In the above solution, a second variation curve is constructed to accurately represent the differential capacitance of the battery cell to be tested.

[0024] In some embodiments, after obtaining the ratio of the decay time constant to the resistance value of the external resistor to obtain the differential capacitance of the battery cell to be tested in a preset battery cell state, it also includes: obtaining the steady-state current and voltage difference of the battery cell to be tested, the steady-state current is the current after the battery cell to be tested is charged to a steady state at a constant voltage, and the voltage difference is the voltage change of the battery cell to be tested after it has been left stationary for a preset time; using the steady-state current and the preset time, obtaining a first charge of the battery cell to be tested within the preset time; and using the voltage difference and the differential capacitance, obtaining a second charge of the battery cell to be tested within the preset time; obtaining the charge difference between the first charge and the second charge, the charge difference characterizing the accuracy of the differential capacitance.

[0025] In the above scheme, the charge amount is calculated in two ways and the two charge amounts are compared to reflect the accuracy of the differential capacitance measurement.

[0026] The present application provides a differential capacitance measuring device, including a first acquisition module, a calculation module, and a second acquisition module, wherein the first acquisition module is used to acquire a plurality of charging currents corresponding to different moments of a battery cell to be tested in a preset battery cell state; wherein the charging current is measured by charging the battery cell to be tested at a constant voltage after the battery cell to be tested is connected in series with an external resistor; the calculation module is used to determine, based on the plurality of charging currents, a decay time constant in a relationship model of the decay of the charging current over time; and the second acquisition module is used to acquire a ratio of the decay time constant to the resistance value of the external resistor, so as to obtain the differential capacitance of the battery cell to be tested in the preset battery cell state.

[0027] The present application provides an electronic device, including a memory and a processor, wherein program instructions are stored in the memory, and when the program instructions are executed by the processor, any of the above-mentioned differential capacitance measurement methods is implemented.

[0028] The present application provides a computer-readable storage medium having program instructions stored thereon, and when the program instructions are executed by a processor, any of the above-mentioned differential capacitance measurement methods is implemented.

[0029] In the above scheme, the battery cell to be tested in a preset battery cell state with an external resistor connected in series is charged at a constant voltage, the decay time constant is obtained by analyzing the charging current, and the differential capacitance in the preset battery cell state is determined based on the ratio of the decay time constant to the resistance value of the external resistor, thereby realizing the measurement of the differential capacitance of the battery cell as a whole.

[0030] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings herein are incorporated into the specification and constitute a part of the specification. These drawings illustrate embodiments consistent with the present application and are used together with the specification to illustrate the technical solution of the present application.

[0032] Figure 1 is a flow chart of a differential capacitance measurement method provided by some embodiments of the present application;

[0033] Figure 2 is a schematic diagram of a circuit for charging a battery cell to be tested provided in some embodiments of the present application;

[0034] Figure 3 is a schematic diagram of a relationship model of charging current decaying over time provided in some embodiments of the present application;

[0035] Figure 4 is a schematic diagram of a relationship model corresponding to different resistance values ​​provided in some embodiments of the present application;

[0036] Figure 5 is a schematic diagram of a direct proportional function provided in some embodiments of the present application;

[0037] Figure 6 is a schematic diagram of a framework of a differential capacitance measuring device provided in some embodiments of the present application;

[0038] Figure 7 is a schematic diagram of a framework of an electronic device provided in some embodiments of the present application;

[0039] Figure 8 It is a schematic diagram of the framework of the computer-readable storage medium provided in some embodiments of the present application. DETAILED DESCRIPTION

[0040] The scheme of the embodiment of the present application is described in detail below in conjunction with the drawings of the specification.

[0041] In the following description, for the purpose of explanation rather than limitation, specific details such as specific subsystem structures, interfaces, and technologies are provided to facilitate a thorough understanding of the present application.

[0042] The term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the objects associated before and after are in an "or" relationship. In addition, "many" in this article means two or more than two. In addition, the term "at least one" in this article means any combination of at least two of any one or more of a plurality of, for example, including at least one of A, B, and C, can mean including any one or more elements selected from the set consisting of A, B, and C.

[0043] The differential capacitance of the battery cell is an important parameter of the battery and can be used to analyze the characteristics of the battery cell. For example, it can be used to analyze the double-layer characteristics inside the battery cell, the adsorption and desorption mechanism, potential range and degree of electrode surfactants, the surface state of the electrode and the real surface area, and it can be used to determine whether the battery cell is abnormal. However, the determination of the differential capacitance of the battery cell as a whole cannot be achieved in the prior art. In the differential capacitance determination method disclosed in the embodiment of the present application, the battery cell to be tested in a preset battery cell state with an external resistor connected in series is charged at a constant voltage, the decay time constant is obtained by analyzing the charging current, and the differential capacitance in the preset battery cell state is determined based on the ratio of the decay time constant to the resistance value of the external resistor, which can achieve the determination of the differential capacitance of the battery cell as a whole.

[0044] The differential capacitance measurement method disclosed in the embodiment of the present application can be applied to battery cells, and the type of battery cells is not limited.

[0045] See also Figure 1 , Figure 1: is a flow chart of a differential capacitance measurement method provided by some embodiments of the present application. Specifically, the method may include:

[0046] Step S110: obtaining a plurality of charging currents corresponding to different moments of the battery cell to be tested in a preset battery cell state.

[0047] The multiple charging currents are measured at different times during the constant voltage charging of the battery cell to be tested, and the constant voltage charging is performed after the battery cell to be tested is connected in series with an external resistor.

[0048] See also Figure 2 , Figure 2 It is a schematic diagram of a circuit for charging a battery cell to be tested provided in some embodiments of the present application.

[0049] like Figure 2 A in the figure shows a circuit diagram after the battery cell to be tested is connected in series with an external resistor Rout, and the battery cell to be tested is charged at a constant voltage with Vout as the charging voltage.

[0050] Among them, a simplified schematic diagram of the internal circuit of the battery cell to be tested is also shown, wherein Ra represents the ohmic impedance of the battery cell to be tested, Rct represents the electrochemical reaction impedance of the battery cell to be tested, Rw represents the diffusion impedance of the battery cell to be tested, and C represents the capacitance of the battery cell to be tested, which represents the ability to store charge and energy.

[0051] After the battery cell to be tested in the preset battery state is connected in series with an external resistor, the battery cell to be tested is charged at a constant voltage. During the charging process, multiple charging currents are measured at different times.

[0052] Among them, one or more external resistors can be set for the battery cell to be tested, and different external resistors have different resistance values. The battery cell to be tested is connected in series with each external resistor, and multiple charging currents corresponding to each external resistor are measured to obtain the decay time constant corresponding to each external resistor.

[0053] In a specific application scenario, resistors of different resistance values ​​may be selected as external resistors. Alternatively, a variable resistance box may be used as an external resistor, and its resistance value may be adjusted. Alternatively, external resistors of different resistance values ​​may be simulated by a device.

[0054] Step S120: Based on the multiple charging currents, determine a decay time constant in a relationship model of the decay of the charging current over time.

[0055] It is understandable that during the charging process, the charging current of the battery cell decays over time, and the relationship between the charging current and time conforms to a certain model, and the model parameters include the decay time constant. Among them, the decay time constant is related to the speed of current decay, or it can be understood that the decay time constant is related to the time to reach the equilibrium current. Based on multiple charging currents, the relationship model of the charging current decay of the battery cell to be tested over time can be determined, and the decay time constant is obtained.

[0056] The amount of the charging current can be set according to actual application requirements.

[0057] In some embodiments, a plurality of charging currents and the time instants corresponding to the charging currents may be used to fit a relationship model of the charging current decaying with time, and at this time, the decay time constant in the relationship model may be obtained.

[0058] In a specific application scenario, the decay time constant represents the time for the charging current to decay to the target current. The target current is the sum of the steady-state current and the adjustment current. The adjustment current is the product of the difference current and the preset value. The difference current is the difference between the initial charging current and the steady-state current. The preset value is the reciprocal of the natural constant.

[0059] See also Figure 3 , Figure 3 It is a schematic diagram of the relationship model of charging current decaying with time provided in some embodiments of the present application.

[0060] Figure 3 The middle dashed line is the curve of the actual measured charging current changing with time, and the implementation is the curve of the charging current changing with time predicted by the model.

[0061] The relationship model of charging current decaying with time can be expressed as the following formula:

[0062]

[0063] Where t represents time, i t represents the charging current at time t, i0 represents the initial charging current, that is, the charging current at t=0, i 稳态 It represents the current value when the charging current reaches the steady state, i1 represents the difference current, which is the difference between the initial charging current and the steady-state current, and τ is the decay time constant.

[0064] The relationship model characterizes that: the charging current at the current moment is equal to the difference between the initial charging current and the target product, the target product is the product between the difference current and the target difference, the target difference is the difference between the predetermined value and the exponential function, and the exponential function is based on the base of the natural logarithm and has the negative of the ratio of the target moment to the decay time constant as the exponent.

[0065] When t=τ, the charging current .

[0066] Step S130: obtaining a ratio of the decay time constant to the resistance value of the external resistor to obtain a differential capacitance of the battery cell to be tested under a preset battery cell state.

[0067] In some embodiments, there is one external resistor, and the ratio of the attenuation time constant to the resistance value of the external resistor can be directly used as the differential capacitance of the battery cell to be tested in a preset battery cell state.

[0068] In some embodiments, when there are multiple external resistors, the corresponding attenuation time constant and resistance value can be obtained for each external resistor, and on this basis, the differential capacitance of the battery cell to be tested in a preset battery cell state can be determined.

[0069] For each external resistor, a ratio of its corresponding attenuation time constant and its resistance value can be calculated, and the ratio can also represent the differential capacitance of the battery cell under a preset battery cell state.

[0070] Furthermore, a ratio characterization value may be obtained and determined as the differential capacitance of the battery cell to be tested under a preset battery cell state. The ratio characterization value may characterize the concentration trend of the ratios corresponding to the external resistors.

[0071] In some embodiments, the ratios corresponding to the external resistors may be first obtained, and then the ratio characterization values ​​may be obtained based on all the ratios. For example, an average value of the ratios may be determined.

[0072] In some embodiments, the decay time constant corresponding to each external resistor and the resistance value of each external resistor can be used to fit a proportional function, where the resistance value of the external resistor is used as the independent variable and the decay time constant is used as the dependent variable. The proportional coefficient of the proportional function is used as the differential capacitance of the battery cell to be tested under the preset battery cell state.

[0073] In a specific application scenario, there is a positive proportional relationship between the decay time constant τ and the resistance value R of the external resistor, which can be expressed as the following formula: τ=kR. R is the independent variable, τ is the dependent variable, and the proportional coefficient k is an unknown parameter. An external resistor corresponds to a set of decay time constants and resistance values. A positive proportional function is obtained by fitting multiple sets of decay time constants and resistance values, where the proportional coefficient k can be used as the differential capacitance C.

[0074] In the above scheme, the battery cell to be tested in a preset battery cell state with an external resistor in series is charged at a constant voltage, the decay time constant is obtained by analyzing the charging current, and the differential capacitance is determined based on the ratio of the decay time constant to the resistance value of the external resistor, thereby realizing the measurement of the differential capacitance of the entire battery cell. Moreover, this test will not damage the battery cell, thus realizing non-destructive testing.

[0075] Setting multiple external resistance values ​​can reduce system errors, such as the impact of noise fluctuations from circuit components and the environment on measurement results, and improve measurement accuracy.

[0076] It can be understood that the resistance of the external resistor Rout is several times greater than the internal resistance of Ra / Rct / Rw / the cell to be tested. Figure 2 The circuit diagram shown in a can be simplified as Figure 2 In the circuit diagram given in b, the simplified circuit is a capacitor C and an external resistor Rout connected in series.

[0077] The multiples can be set according to actual application needs. The relevant resistance values ​​of the cell to be tested can be predetermined, and then the resistance value of the external resistor Rout can be set for the cell to be tested, so that the resistance value of the external resistor Rout is greater than the multiple Ra / Rct / Rw / internal resistance value of the cell to be tested.

[0078] In some embodiments, the resistance of the external resistor Rout is greater than 10 times the internal resistance of Ra / Rct / Rw / the battery cell to be tested.

[0079] In a specific application scenario, considering that the Ra / Rct / Rw of the battery cell to be tested is usually at the mΩ level, the resistance of the external resistor Rout can be set to between 0.1Ω and 1Ω.

[0080] It can be understood that in a circuit where a capacitor and a resistor are connected in series, the time constant for charging and discharging the capacitor is , =RC. Time constant Reflects the charging and discharging speed of the capacitor. The time constant is proportional to the resistance and capacitance. If the resistance and capacitance are small, the time constant is also small, and the capacitor charges and discharges at a faster speed. On the contrary, if the resistance and capacitance are large, the time constant is large, and the capacitor charges and discharges slowly. The constant voltage charging circuit is simplified as a circuit with a capacitor and a resistor in series, so it can be considered that the constant voltage charging circuit meets =RC.

[0081] Among them, the decay time constant τ in the relationship model of the charging current decaying with time during constant voltage charging and the aforementioned time constant Both reflect the speed at which the capacitor reaches the equilibrium current. It can be found that the decay time constant τ is the time constant , the resistance of the external resistor is R, and the differential capacitance of the cell to be tested is C. =RC. Therefore, based on the ratio of the decay time constant to the resistance value of the external resistor, the differential capacitance of the cell to be tested under the preset cell state can be accurately determined.

[0082] In a specific application scenario, the relationship model of charging current decaying over time can be expressed as follows:

[0083]

[0084] The decay time constant can be expressed as follows:

[0085]

[0086] In some embodiments, the above constant voltage charging test may be performed on the battery cell to be tested in a preset battery cell state, and the preset battery cell state may include the battery cell temperature being a preset temperature and the state of charge (SOC) being a preset state of charge. The battery cell to be tested is at a preset temperature during the constant voltage charging test, and the battery cell is at a preset state of charge when the constant voltage charging test starts.

[0087] When multiple external resistors are set for the cell to be tested, each external resistor is connected in series with the cell to be tested and then constant voltage charging is performed. The resistance value of the external resistor changes, but the preset cell state of the cell to be tested remains unchanged. Thus, the decay time constant corresponding to each external resistor when the cell is in the preset cell state can be obtained, which is used to determine the differential capacitance of the cell in this preset cell state.

[0088] It should be noted that the differential capacitance is affected by many factors, including the cell temperature and state of charge. Therefore, a single test can obtain the differential capacitance of the cell under test in a certain preset cell state. The preset temperature and / or state of charge can be adjusted to make the cell in different preset cell states, and the cells under test in different preset cell states can be tested respectively to obtain the differential capacitance in different preset cell states.

[0089] In some embodiments, the method may further include analyzing differential capacitance at different cell temperatures at the same state of charge, and / or analyzing differential capacitance at different states of charge at the same temperature.

[0090] In some embodiments, constant voltage charging is to use a target power supply voltage to charge a battery cell to be tested in a preset battery cell state, wherein the target power supply voltage may be equal to the battery cell voltage of the battery cell to be tested before constant voltage charging, that is, the battery cell voltage of the battery cell to be tested in a preset battery cell state, when the battery cell temperature is a preset temperature, and the charge state is a preset charge state.

[0091] In a specific application scenario, a conventional electrochemical charging and discharging device is used as a power source for constant voltage charging. The port of the detection circuit is connected to the pole ear (column) of the battery cell.

[0092] In one implementation scenario, the battery cell to be tested may be charged with a constant current to adjust the charge state of the battery cell to be tested.

[0093] It should be noted that at the same cell temperature, different states of charge correspond to different cell voltages. The state of charge of the cell can be adjusted by adjusting the constant current charging time, and the cell voltage will change accordingly. The cell voltage can also be directly measured and the cell voltage after constant current charging can be adjusted to adjust the cell state of charge.

[0094] In a specific application scenario, when the cell temperature is a preset temperature, the cell to be tested is charged with a constant current and the cell voltage is measured, that is, the cell voltage in the preset cell state is obtained, which can be used as the target power supply voltage.

[0095] In a specific application scenario, when the cell temperature is a preset temperature, the cell to be tested is charged with a constant current to adjust the state of charge and cell voltage of the cell. After the adjustment is completed, the cell voltage is measured as the target power supply voltage. At least one external resistor is set for the cell to be tested, and after the cell to be tested is connected to each external resistor, the cell to be tested is charged with a constant voltage using the target power supply voltage, and the charging current is measured at different times during the constant voltage charging process.

[0096] In some embodiments, at the same cell temperature, different cell voltages correspond to different states of charge, and differential capacitances corresponding to multiple states of charge (cell voltages) at the same cell temperature are obtained to construct a first variation curve of differential capacitance of the cell to be tested versus state of charge (cell voltage). In a specific application scenario, the horizontal axis may be the state of charge SOC or the cell voltage V, and the vertical axis may be the differential capacitance, which may be represented by C(V).

[0097] In some implementation scenarios, different states of charge can be set at the same battery cell temperature. Specifically, the state of charge can be adjusted by adjusting the constant current charging duration, and multiple preset constant current charging durations can be set to correspond to multiple states of charge. After the adjustment is completed, the battery cell voltage is measured as the target power supply voltage. Alternatively, the change in the state of charge can be indicated by measuring the change in the battery cell voltage, and multiple preset battery cell voltages can be set to correspond to multiple states of charge. Adjust the battery cells to be tested to each preset battery cell voltage, and then use the corresponding preset battery cell voltage as the target power supply voltage for constant voltage charging test.

[0098] In some embodiments, differential capacitances of the battery cell to be tested corresponding to a plurality of different battery cell temperatures at the same state of charge are obtained, and a second variation curve of the differential capacitance of the battery cell to be tested versus the battery cell temperature is constructed.

[0099] It should be noted that when the state of charge remains unchanged, the change in cell temperature will cause the voltage to change. The duration of constant current charging can be fixed so that the cell to be tested is at the same state of charge, and the cell voltage after constant current charging can be measured as the target power supply voltage.

[0100] In a specific application scenario, the horizontal axis may be the battery cell temperature T, and the vertical axis may be the differential capacitance, which may be represented by C(T).

[0101] In some embodiments, after obtaining the differential capacitance of the cell to be tested in a preset cell state, the differential capacitance may be verified. The process of verifying a differential capacitance may include obtaining the steady-state current and voltage difference of the cell to be tested, obtaining the first charge of the cell to be tested within the preset time using the steady-state current and the preset time, and obtaining the second charge of the cell to be tested within the preset time using the voltage difference and the differential capacitance; and obtaining the charge difference between the first charge and the second charge.

[0102] The voltage difference may represent the voltage change of the cell to be tested in a preset cell state after being left at rest for a preset time. It may be the difference between the target power supply voltage and the measured voltage. The cell voltage of the cell to be tested at the beginning of the rest is the target power supply voltage, and the measured voltage may be the value obtained by measuring the cell at the end of the rest.

[0103] The steady-state current is the current after the battery cell to be tested is charged at a constant voltage to a steady state.

[0104] It is understandable that the change in the amount of charge of the self-discharge of the battery cell to be tested within a preset time can be determined in two ways. One is the constant voltage charging test current method, which is determined by the self-discharge current and the preset time, wherein the steady-state current can be used as the self-discharge current. The other is the voltage difference method, which is determined based on the voltage difference and the differential capacitance. The charges obtained by the two methods are compared, so that the accuracy of the differential capacitance determined by the above method can be verified.

[0105] The preset time can be set according to actual application needs.

[0106] In a specific application scenario, the cell voltage of the cell to be tested is adjusted to be equal to the target power supply voltage, the cell to be tested is placed for a preset time Δt, and the cell voltage is measured. The voltage difference ΔOCV is calculated using the measured voltage and the target power supply voltage.

[0107] In a specific application scenario, the target power supply voltage can be used to charge the battery cell at a constant voltage to determine the steady-state current i 稳态, wherein the constant voltage charging may be the constant voltage charging test in the aforementioned embodiment, or the constant voltage charging test may be performed again without an external resistor. The steady-state current may be determined based on a relationship model of the charging current decaying over time, or may be directly measured after the constant voltage charging current is stabilized.

[0108] It is understood that for both the constant voltage charging test and the voltage differential test, the cell temperature is the same and remains constant during the test. The state of charge or cell voltage is the same at the start of the test.

[0109] Within the preset time Δt, the first charge of the self-discharge reaction of the battery cell is ΔQ1= i 稳态 ×Δt. The second charge is ΔQ2 = C × ΔOCV. The first charge is compared with the second charge, and the difference between the two can indicate the accuracy of the differential capacitance.

[0110] In a specific application scenario, the preset time may be 24 hours. The charge difference between the first charge and the second charge is less than 3‰, indicating that the value determined based on the ratio of the decay time constant to the resistance value of the external resistor is the differential capacitance, and the obtained differential capacitance is relatively accurate.

[0111] See also Figure 4 , Figure 4 It is a schematic diagram of a relationship model corresponding to different resistance values ​​provided in some embodiments of the present application.

[0112] The external resistors with different resistance values ​​are connected in series with the battery cells to be tested, and the relationship model of the charging current decaying with time corresponding to each resistance value is obtained. Among them, Rout1<Rout2<Rout3<Rout4.

[0113] Among them, the steady-state current is equal to the self-discharge current of the battery cell. It is a parameter that is independent of the external resistance value. It is determined by the characteristics of the battery cell and is related to the design, chemical system, manufacturing defects, etc. of the battery cell. The smaller the resistance of the external resistor, the faster the target current is reached, and the corresponding decay time constant is smaller, τ1<τ2<τ3<τ4. Target current ≈ .

[0114] See also Figure 5 , Figure 5 It is a schematic diagram of a direct proportional function provided in some embodiments of the present application.

[0115] The resistance value R of the external resistor is used as the independent variable, and the decay time constant τ is used as the dependent variable. The decay time constant τ, the resistance value R of the external resistor, and the differential capacitance C of the battery cell to be tested satisfy =RC.

[0116] A proportional function is obtained by fitting multiple sets of resistance values ​​and decay time constants, and the slope is the differential capacitance of the cell to be tested. The fitting can be performed based on the least squares method.

[0117] See also Figure 6 , Figure 6 It is a schematic diagram of the framework of a differential capacitance measuring device provided in some embodiments of the present application.

[0118] The differential capacitance measuring device 60 includes a first acquisition module 61, a calculation module 62 and a second acquisition module 63. The first acquisition module 61 is used to obtain multiple charging currents corresponding to different moments of the battery cell to be tested in a preset battery cell state; wherein the charging current is measured by constant voltage charging of the battery cell to be tested after the battery cell to be tested is connected in series with an external resistor; the calculation module 62 is used to determine the decay time constant in the relationship model of the decay of the charging current over time based on multiple charging currents; the second acquisition module 63 is used to obtain the ratio of the decay time constant to the resistance value of the external resistor, so as to obtain the differential capacitance of the battery cell to be tested in the preset battery cell state.

[0119] In the above scheme, the battery cell to be tested in a preset battery cell state with an external resistor connected in series is charged at a constant voltage, the decay time constant is obtained by analyzing the charging current, and the differential capacitance in the preset battery cell state is determined based on the ratio of the decay time constant to the resistance value of the external resistor, thereby realizing the measurement of the differential capacitance of the battery cell as a whole.

[0120] In some embodiments, the calculation module 62 is used to determine the decay time constant in the relationship model of the decay of the charging current over time based on multiple charging currents, specifically including: using multiple charging currents and the moments corresponding to each charging current to fit the relationship model of the decay of the charging current over time; obtaining the decay time constant in the relationship model.

[0121] In the above scheme, the charging current is fitted to obtain a model of the current changing with time, so that the decay time constant in the model can be obtained to determine the differential capacitance.

[0122] In some embodiments, the decay time constant represents the time for the charging current to decay to a target current, the target current is the sum of the steady-state current and the adjustment current, the adjustment current is the product of the difference current and a preset value, the preset value is the inverse of the natural constant, and the difference current is the difference between the initial charging current and the steady-state current.

[0123] In the above scheme, the decay time constant can be the time it takes for the charging current to decay to the target current, which is related to the speed at which the charging current decays.

[0124] In some embodiments, there is at least one external resistor. After obtaining the attenuation time constant corresponding to each external resistor, the second acquisition module 63 is used to obtain the ratio of the attenuation time constant to the resistance value of the external resistor to obtain the differential capacitance of the battery cell to be tested in a preset battery cell state, specifically including: when there is one external resistor, obtaining the ratio of the attenuation time constant corresponding to the external resistor to the resistance value of the external resistor as the differential capacitance of the battery cell to be tested in the preset battery cell state; when there are multiple external resistors, obtaining a ratio representation value as the differential capacitance of the battery cell to be tested in the preset battery cell state, the ratio representation value represents the concentration trend of the ratios corresponding to each external resistor, and the ratio corresponding to the external resistor is the ratio between the attenuation time constant corresponding to the external resistor and the resistance value of the external resistor.

[0125] In the above scheme, there may be one or more external resistors. By directly obtaining the ratio or the ratio characterization value, the differential capacitance under the preset battery cell state can be determined. The number of external resistors can be flexibly selected to meet different application needs.

[0126] In some embodiments, the second acquisition module 63 is used to obtain a ratio representation value as the differential capacitance of the battery cell to be tested in a preset battery cell state, specifically including: using the decay time constant corresponding to each external resistor and the resistance value of each external resistor to fit a direct proportional function, the direct proportional function has the resistance value as the independent variable and the decay time constant as the dependent variable; obtaining the proportional coefficient of the direct proportional function as the differential capacitance of the battery cell to be tested in a preset battery cell state.

[0127] In the above scheme, the resistance value and the attenuation time constant are directly proportional. A directly proportional function can be obtained by fitting, and the proportional coefficient is used as a ratio representation value, thereby realizing the determination of the differential capacitance.

[0128] In some embodiments, the resistance of the external resistor is several times greater than the internal resistance of the battery cell to be tested.

[0129] In the above scheme, the resistance value of the external resistor can be set at several times of the internal resistance to meet the needs of differential capacitance measurement.

[0130] In some embodiments, the resistance of the external resistor is between 0.1Ω and 1Ω.

[0131] In the above scheme, the resistance value of the external resistor can be set between 0.1Ω and 1Ω to meet the needs of differential capacitance measurement.

[0132] In some embodiments, the preset battery cell state includes the battery cell temperature being a preset temperature and the charge state being a preset charge state; constant voltage charging is charging the battery cell to be tested in the preset battery cell state using a target power supply voltage, and the target power supply voltage is equal to the battery cell voltage of the battery cell to be tested before constant voltage charging, wherein the charge state of the battery cell to be tested can be adjusted by constant current charging of the battery cell to be tested.

[0133] In the above scheme, the state of charge is adjusted by constant current charging, and the voltage of the battery cell in the preset battery cell state is used as the voltage value set for constant voltage charging to achieve constant voltage charging.

[0134] In some embodiments, the differential capacitance measuring device 60 includes an analysis module for constructing a first change curve of the differential capacitance of the battery cell to be tested with the charge state by using the differential capacitance corresponding to different charge states at the same battery cell temperature after obtaining the differential capacitance of the battery cell to be tested under different preset battery cell states.

[0135] In the above solution, a first variation curve is constructed to accurately represent the differential capacitance of the battery cell to be tested.

[0136] In some embodiments, the differential capacitance measuring device 60 includes an analysis module for obtaining the differential capacitance of the battery cell to be tested under different preset battery cell states, and then using the differential capacitance corresponding to different battery cell temperatures under the same charge state to construct a second change curve of the differential capacitance of the battery cell to be tested with the battery cell temperature.

[0137] In the above solution, a second variation curve is constructed to accurately represent the differential capacitance of the battery cell to be tested.

[0138] In some embodiments, the differential capacitance measuring device 60 includes a verification module, which is used to obtain the ratio of the decay time constant to the resistance value of the external resistor to obtain the differential capacitance of the battery cell to be tested in a preset battery cell state, and then obtain the steady-state current and voltage difference of the battery cell to be tested, wherein the steady-state current is the current after the battery cell to be tested is charged to a steady state at a constant voltage, and the voltage difference is the voltage change of the battery cell to be tested after it has been left stationary for a preset time; using the steady-state current and the preset time, obtain the first charge of the battery cell to be tested within the preset time; and using the voltage difference and the differential capacitance, obtain the second charge of the battery cell to be tested within the preset time; obtain the charge difference between the first charge and the second charge, and the charge difference characterizes the accuracy of the differential capacitance.

[0139] In the above scheme, the charge amount is calculated in two ways and the two charge amounts are compared to reflect the accuracy of the differential capacitance measurement.

[0140] See also Figure 7 , Figure 7 It is a schematic diagram of the framework of an electronic device provided in some embodiments of the present application.

[0141] The electronic device 70 includes a memory 71 and a processor 72, and the processor 72 is used to execute program instructions stored in the memory 71. When the program instructions are executed by the processor 72, any of the above-mentioned differential capacitance measurement methods is implemented. In a specific implementation scenario, the electronic device 70 may include, but is not limited to: computer equipment, electrical equipment, microcomputers, desktop computers, servers, and in addition, the electronic device 70 may also include mobile devices such as laptops and tablet computers, which are not limited here.

[0142] Specifically, the processor 72 is used to control itself and the memory 71 to implement any of the above-mentioned differential capacitance determination methods. The processor 72 can also be called a CPU (Central Processing Unit). The processor 72 may be an integrated circuit chip with signal processing capabilities. The processor 72 can also be a general-purpose processor, a digital signal processor (Digital Signal Processor, DSP), an application-specific integrated circuit (Application Specific Integrated Circuit, ASIC), a field-programmable gate array (Field-Programmable Gate Array, FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc. In addition, the processor 72 can be implemented by an integrated circuit chip.

[0143] See also Figure 8 , Figure 8 It is a schematic diagram of the framework of the computer-readable storage medium provided in some embodiments of the present application.

[0144] The computer-readable storage medium 80 stores program instructions 81 that can be executed by a processor. When the program instructions 81 are executed by the processor, they are used to implement any of the above-mentioned differential capacitance measurement methods.

[0145] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0146] In the several embodiments provided in the present application, it should be understood that the disclosed methods and devices can be implemented in other ways. For example, the device implementation described above is only schematic. For example, the division of modules or units is only a logical function division. There may be other division methods in actual implementation, such as units or components can be combined or integrated into another subsystem, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, and the indirect coupling or communication connection of devices or units can be electrical, mechanical or other forms.

[0147] In addition, each functional unit in each embodiment of the present application can be integrated into a processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of a software functional unit. If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or part of the contribution to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor (processor) to perform all or part of the steps of the methods of each implementation method of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program code.

Claims

1. A differential capacitance measurement method, characterized in that: include: Acquire multiple charging currents corresponding to different moments of the battery cell to be tested in a preset battery cell state; wherein the charging current is measured by charging the battery cell to be tested at a constant voltage after the battery cell to be tested is connected in series with an external resistor; Based on the multiple charging currents, determine a decay time constant in a relationship model of the charging current decaying with time, wherein the decay time constant represents the time for the charging current to decay to a target current, wherein the target current is the sum of a steady-state current and an adjustment current, wherein the adjustment current is the product of a difference current and a preset value, wherein the preset value is the inverse of a natural constant, and wherein the difference current is the difference between an initial charging current and the steady-state current; The ratio of the decay time constant to the resistance value of the external resistor is obtained to obtain the differential capacitance of the battery cell to be tested in the preset battery cell state.

2. The method according to claim 1, characterized in that: The step of determining, based on the multiple charging currents, a decay time constant in a relationship model in which the charging current decays over time comprises: Using the multiple charging currents and the time corresponding to each of the charging currents, fitting a relationship model of the charging current decaying over time; Obtain a decay time constant in the relationship model.

3. The method according to claim 1, characterized in that: There is at least one external resistor, and after obtaining the decay time constant corresponding to each external resistor, obtaining the ratio of the decay time constant to the resistance value of the external resistor to obtain the differential capacitance of the battery cell to be tested in the preset battery cell state includes: In the case where there is one external resistor, obtaining a ratio of a decay time constant corresponding to the external resistor to a resistance value of the external resistor as a differential capacitance of the battery cell to be tested in the preset battery cell state; In the case where there are multiple external resistors, a ratio characterization value is obtained as the differential capacitance of the battery cell to be tested in the preset battery cell state, and the ratio characterization value characterizes the concentration trend of the ratios corresponding to the external resistors, and the ratio corresponding to the external resistor is the ratio between the attenuation time constant corresponding to the external resistor and the resistance value of the external resistor.

4. The method according to claim 3, characterized in that The step of obtaining a ratio representation value as a differential capacitance of the battery cell to be tested in the preset battery cell state includes: Using the decay time constant corresponding to each of the external resistors and the resistance value of each of the external resistors, a proportional function is fitted, wherein the proportional function takes the resistance value as an independent variable and the decay time constant as a dependent variable; The proportional coefficient of the direct proportional function is obtained as the differential capacitance of the battery cell to be tested under the preset battery cell state.

5. The method according to claim 1, characterized in that The resistance of the external resistor is several times greater than the internal resistance of the battery cell to be tested; And / or, the resistance of the external resistor is between 0.1Ω and 1Ω.

6. The method according to claim 1, characterized in that The preset cell state includes a cell temperature being a preset temperature and a charge state being a preset charge state; the constant voltage charging is to charge the cell to be tested in the preset cell state using a target power supply voltage, and the target power supply voltage is equal to the cell voltage of the cell to be tested before the constant voltage charging, wherein the charge state of the cell to be tested can be adjusted by constant current charging of the cell to be tested.

7. The method according to claim 6, characterized in that After obtaining the differential capacitance of the battery cell to be tested under different preset battery cell states, the method further includes: Using the differential capacitance corresponding to different states of charge at the same battery cell temperature, construct a first variation curve of the differential capacitance of the battery cell to be tested versus the state of charge; And / or, after obtaining the differential capacitance of the battery cell to be tested under different preset battery cell states, the method further includes: The differential capacitance corresponding to different battery cell temperatures under the same state of charge is used to construct a second variation curve of the differential capacitance of the battery cell to be tested versus the battery cell temperature.

8. The method according to claim 1, characterized in that: After obtaining the ratio of the decay time constant to the resistance value of the external resistor to obtain the differential capacitance of the battery cell to be tested in the preset battery cell state, the method further includes: Obtaining a steady-state current and voltage difference of the battery cell to be tested, wherein the steady-state current is the current after the battery cell to be tested is charged to a steady state at a constant voltage, and the voltage difference is the voltage change of the battery cell to be tested after being left stationary for a preset time; Using the steady-state current and the preset time, obtaining a first charge amount of the battery cell to be tested within the preset time; and Using the voltage difference and the differential capacitance, obtaining a second charge of the battery cell to be tested within the preset time; A charge difference between the first charge amount and the second charge amount is obtained, where the charge difference represents the accuracy of the differential capacitance.

9. A differential capacitance measuring device, characterized in that: include: A first acquisition module is used to acquire a plurality of charging currents corresponding to different moments of a cell to be tested in a preset cell state; wherein the charging current is measured by charging the cell to be tested at a constant voltage after the cell to be tested is connected in series with an external resistor; a calculation module, configured to determine, based on the multiple charging currents, a decay time constant in a relationship model of the decay of the charging current over time, wherein the decay time constant represents the time for the charging current to decay to a target current, wherein the target current is the sum of a steady-state current and an adjustment current, wherein the adjustment current is the product of a difference current and a preset value, wherein the preset value is the reciprocal of a natural constant, and wherein the difference current is the difference between an initial charging current and the steady-state current; The second acquisition module is used to acquire the ratio of the attenuation time constant to the resistance value of the external resistor to obtain the differential capacitance of the battery cell to be tested under the preset battery cell state.

10. An electronic device, characterized in that: The method comprises a memory and a processor, wherein the memory stores program instructions, and the program instructions are used to execute the method according to any one of claims 1 to 8 when executed by the processor.

11. A computer-readable storage medium having program instructions stored thereon, characterized in that: When the program instructions are executed by a processor, the method according to any one of claims 1 to 8 is implemented.

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