Method for measuring internal resistance of battery

Abstract

The disclosed method is a method for measuring the internal resistance of a battery. The measurement method includes: an energization step of charging or discharging a battery; a measurement step for measuring the open-circuit voltage of the battery at and after the completion of the charging or discharging; and a calculation step for individually calculating at least one resistance component included in the internal resistance on the basis of a voltage change in the open-circuit voltage measured in the measurement step and a current value flowing through the battery due to charging or discharging at the end. In the calculation step, the at least one resistance component is calculated on the basis of the slope of a line obtained by plotting the voltage change in a graph having the square root of the elapsed time from the end as the horizontal axis and the open-circuit voltage as the vertical axis.

Description

Technical Field

[0001] The present disclosure relates to a method for measuring the internal resistance of a battery. Background Art

[0002] The internal resistance of a battery is particularly important in evaluating the performance of a battery and evaluating the state of a battery (for example, a deteriorated state). Therefore, methods for measuring the internal resistance have been proposed in the past.

[0003] Patent document 1 (Japanese Patent Publication No. 2017-111860) discloses the following secondary battery control system, which includes: a data accumulation unit, which obtains and accumulates usage history data of the secondary battery including the current and voltage of the secondary battery corresponding to the usage time of the secondary battery; a data selection unit, which selects data of a predetermined range from the usage history data accumulated by the data accumulation unit; an internal degradation parameter calculation unit, which calculates internal degradation parameters corresponding to the degradation state of the capacity and internal resistance of the secondary battery based on the data selected by the data selection unit; and a degradation state estimation unit, which estimates the degradation state of the secondary battery based on the internal degradation parameters calculated by the internal degradation parameter calculation unit.

[0004] Patent document 2 (International Publication No. 2020 / 012720) discloses the following secondary battery parameter estimation device, which comprises: a voltage acquisition unit, which acquires the voltage of a secondary battery; a current acquisition unit, which acquires the current of the secondary battery; a parameter estimation unit, which estimates multiple parameters including the internal resistance of the secondary battery in an equivalent circuit model corresponding to the secondary battery based on the voltage acquired by the voltage acquisition unit and the current acquired by the current acquisition unit; an internal resistance derivation unit, which derives the internal resistance of the secondary battery in a manner different from the manner estimated by the parameter estimation unit; and a determination unit, which determines whether to use the multiple parameters estimated by the parameter estimation unit to replace the parameters of the secondary battery based on a comparison result of the internal resistance estimated by the parameter estimation unit and the internal resistance derived by the internal resistance derivation unit.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-111860

[0008] Patent Document 2: International Publication No. 2020 / 012720 Summary of the invention

[0009] Problems to be solved by the invention

[0010] Various methods have been proposed as methods for measuring the internal resistance of a battery. However, in the conventional methods, it is difficult to measure the resistance components constituting the internal resistance of a battery individually by a simple method. Under such circumstances, one of the purposes of the present disclosure is to provide a method for measuring the resistance components constituting the internal resistance of a battery individually by a simple method.

[0011] Technical solutions to solve problems

[0012] One aspect of the present disclosure relates to a method for measuring the internal resistance of a battery. The method includes: a power-on step of charging or discharging the battery; a measuring step of measuring the open circuit voltage of the battery at the end of the charging or discharging and thereafter; and a calculating step of separately calculating at least one resistance component included in the internal resistance based on the voltage change of the open circuit voltage measured in the measuring step and the current value flowing through the battery due to the charging or discharging at the end, wherein the at least one resistance component is calculated based on the slope of a line obtained by plotting the voltage change in a graph with the square root of the elapsed time from the end as the horizontal axis and the open circuit voltage as the vertical axis.

[0013] Effects of the Invention

[0014] According to the measuring method of the present disclosure, the resistance component constituting the internal resistance of a battery can be measured individually by a simple method.

[0015] The novel features of the present invention, which relate to both the structure and content of the present invention, together with other objects and features of the present invention, will be better understood from the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a diagram for explaining the measurement method of the present disclosure.

[0017] Figure 2 This is a diagram for explaining an example of the measurement method implemented in Example 1.

[0018] Figure 3 This is a diagram for explaining the measurement method performed in Example 2.

[0019] Figure 4 This is a graph showing the measurement results of Example 2. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present disclosure are illustrated, but embodiments of the present disclosure are not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes illustrated, but other numerical values ​​and other materials can be applied as long as the invention of the present disclosure can be implemented. In this specification, a description such as "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be replaced by "above numerical value A and below numerical value B". In the following description, when a lower limit and an upper limit are illustrated for numerical values ​​of specific physical properties, conditions, etc., any of the illustrated lower limits and any of the illustrated upper limits can be arbitrarily combined as long as the lower limit is not above the upper limit.

[0021] (Method for measuring internal resistance of battery)

[0022] The measurement method of the present embodiment is a method for measuring the internal resistance R of a battery. Hereinafter, the measurement method is sometimes referred to as "measurement method (M)". There is no particular limitation on the battery whose internal resistance can be measured by the measurement method (M). Examples of batteries measured by the measurement method (M) include secondary batteries and primary batteries. There are no particular limitations on the secondary batteries and primary batteries to be measured. Examples of secondary batteries to be measured include lithium-ion batteries, lithium metal secondary batteries, sodium metal secondary batteries, nickel-hydrogen batteries, lead storage batteries, and the like. Examples of primary batteries to be measured include manganese dry batteries, alkaline dry batteries, air batteries, and the like.

[0023] The measuring method (M) includes three steps (procedures) of a current supply step, a measuring step, and a calculating step, which will be described below.

[0024] (Electrification process)

[0025] The power-on process is a process of charging or discharging the battery to be measured. It is preferred that the current value (charging or discharging current value) in the power-on process does not change at the end stage of the power-on process. In order to perform a highly reliable measurement, it is preferred that the current value in the power-on process is constant within 10 seconds before the end. The current value Ie (charging or discharging current value) at the end of the power-on process can be in the range of 0.01 to 100 times (for example, 0.1 to 10 times) of 1C of the battery. By setting the current value Ie to this range, the measurement can be performed with particularly high reliability. In addition, 1C is the current value of 1 hour rate. The current value of 1C is calculated by the formula 1C (A) = rated capacity (Ah) / 1 (h).

[0026] (Measurement process)

[0027] The measuring step is a step of measuring the open circuit voltage Vop of the battery at the end of charging or discharging in the energizing step and thereafter. When the energizing step is completed, the open circuit voltage Vop of the battery changes over time. In the measuring step, the change in voltage is measured over time.

[0028] (Calculation process)

[0029] The calculation step is a step of separately calculating at least one resistance component Re included in the internal resistance R based on the voltage change Vch (volt) of the open circuit voltage Vop (volt) measured in the measurement step and the current value Ie (ampere) flowing through the battery due to the charge or the discharge at the end. In the calculation step, the at least one resistance component Re is calculated based on the slope of a line (hereinafter sometimes referred to as "line L") obtained by plotting the voltage change Vch in a graph with the square root TR of the elapsed time T from the end as the horizontal axis and the open circuit voltage Vop as the vertical axis.

[0030] As a result of various studies, the inventors of the present application have newly discovered that the resistance components constituting the internal resistance R can be calculated individually based on the above-mentioned line L. The present disclosure is based on this new insight. According to the method of the present disclosure, multiple resistance components can be calculated individually. In other words, according to the method of the present disclosure, the internal resistance can be divided into multiple resistance components and calculated. According to the method of the present disclosure, it is possible to know the magnitude of different resistance components, and therefore, it is particularly useful in evaluating the performance of the battery and the state of the battery (such as the deteriorated state). In addition, the internal resistance R and the resistance components constituting the internal resistance R can be simply measured.

[0031] The ratio of each resistance component can be known according to the measurement method (M). Based on the ratio of each resistance component, the performance evaluation of the battery and the estimation of the degradation state of the battery can be performed in more detail. In addition, based on the absolute value of each resistance component, the performance evaluation of the battery and the estimation of the degradation state of the battery can also be performed in more detail.

[0032] The resistance component Re can be calculated using the above-mentioned current value Ie and a plurality of voltage values ​​(hereinafter sometimes referred to as "voltage value V(I)"). The plurality of voltage values ​​V(I) include the following voltage values. In addition, I of V(I) represents the order of voltage values, starting from the reference voltage value V(0), and then being set to voltage values ​​V(1), V(2), ... in sequence.

[0033] (1) A reference voltage value serving as an open circuit voltage at the end of the energization process (hereinafter sometimes referred to as a “reference voltage value V(0)”).

[0034] (2) At least one voltage value V(I) (where 1≤I) obtained by extrapolating at least one straight line SL of at least one straight line portion appearing on line L in the above graph to the end of the energization process. Here, the end of the energization process is the origin of the horizontal axis of the above graph (the square root of the elapsed time T TR=0).

[0035] The voltage value V(I) (where 1≤I) is determined based on the slope of the straight line portion of the line L. The number of the at least one straight line SL may be 1, 2 or more, or 4 or less (e.g., 3 or less or 2 or less). When the number of the straight line SL is 1, it is preferred to derive a voltage value V(I) along the square root TR of the elapsed time T (seconds) in the range of 0 to 3 (s 1 / 2 ) is a straight line of a linear portion of the range. By drawing this straight line SL, the resistance component with a fast response speed can be calculated.

[0036] According to the measurement method (M), the internal resistance R (the total value of all resistance components Re) can also be obtained. In this case, a straight line SL is drawn along the portion of the line L where the voltage change disappears and becomes substantially parallel to the horizontal axis, and the voltage value V(I) is obtained using the straight line SL. In addition, the internal resistance R can be obtained by using the reference voltage value V(0), the voltage value V(I), and the current value Ie. Alternatively, the internal resistance R can be obtained by adding the resistance components Re.

[0037] The straight line SL may include a line extending along the square root TR of the elapsed time T (seconds) between 0 and 3 (s 1 / 2 ) and a straight line along the portion where the voltage change disappears and becomes substantially parallel to the horizontal axis. Based on these straight lines, the resistance component with a fast response speed and the internal resistance R can be calculated.

[0038] As a method for determining the linear portion of the line L and extracting the straight line SL, the following methods can be used. As a first method, a method of visually determining and extracting the straight line can be cited. As a second method, a method of determining the straight line based on s 1 / 2 A method of drawing a straight line within a range where the value of the line L is constant after differentiation. A third method is to superimpose the voltage change and s as the square root TR decreases. 1 / 2 In addition, when focusing on the portion related to the electronic resistance that changes rapidly with the voltage change, a method of deriving a regression line based on a plurality of voltage values ​​measured within several tens of milliseconds after the end of the energization process can be cited.

[0039] In the measuring method (M), the resistance component can be obtained by dividing the voltage difference between two voltage values ​​(for example, two adjacent voltage values) among the plurality of voltage values ​​V(I) by the current value Ie.

[0040] An example of a method for calculating the internal resistance R and the resistance component Re will be described with reference to the drawings. Figure 1 This is a graph showing the change over time of the open circuit voltage Vop after the secondary battery is discharged at the current value Ie (ampere). Figure 1 The graph is a graph measured after the charge and discharge cycle test of the secondary battery of Example 1 described later. The vertical axis is the open circuit voltage Vop (volts). The horizontal axis is the square root TR (s) of the time T (seconds: s) elapsed from the end of discharge. 1 / 2 ). The position of 0 on the horizontal axis indicates the end of discharge. The position of 10 on the horizontal axis indicates the elapsed time of 100 seconds, and the position of 30 on the horizontal axis indicates the elapsed time of 900 seconds.

[0041] Figure 1 The line L is obtained by plotting the voltage change of the open circuit voltage Vop. Figure 1 As shown, line L has four straight line portions, and four straight lines SL(1) to SL(4) are drawn along these portions. In addition, straight line SL(4) indicates the value after 3600 seconds when substantially no change in the open circuit voltage Vop is observed.

[0042] The open circuit voltage Vop when the square root TR is 0 is the reference voltage value V(0). Figure 1 The voltage values ​​V(1) to V(4) shown are the voltage values ​​when the straight lines SL(1) to SL(4) are extrapolated to the end of discharge (square root TR = 0). In other words, the voltage value V(I) (where 1 ≤ I) is the voltage value at the intersection of the extension line of the straight line SL(I) and the vertical axis (Y axis) of TR = 0.

[0043] exist Figure 1 In the example of , four resistance components Re(1) to Re(4) can be obtained. Re(1) is obtained by the following formula.

[0044] Re(1)(Ω)=(V(1)-V(0)) / Ie

[0045] That is, the first resistance component Re(1) is obtained by dividing the voltage difference between two adjacent voltage values ​​V(0) and V(1) among the plurality of voltage values ​​by the current value Ie. Similarly, each resistance component Re(I) is obtained by the following equation.

[0046] Re(I)=(V(I)-V(I-1)) / Ie

[0047] The internal resistance R of the entire battery can be obtained by adding up the resistance components or by the following formula: R = (V(4) - V(0)) / Ie

[0048] Re(1) is considered to be a resistance component with particularly fast response, and is a resistance component related to the mobility of electrons and electrolyte, that is, the movement of electrons in the electrode composed of an active material layer and a current collector, and the ion mobility in the electrolyte. Re(2) is considered to be a resistance component with fast response, and is a resistance component related to the charge transfer resistance, that is, the reaction between the active material and the ions in the electrolyte. Re(3) may be a resistance component related to the process of transporting ions in the gaps present in the electrode and filled with electrolyte. Re(4) may be a resistance component related to the process of ion diffusion in the active material as a solid. In addition, it is not necessary to draw a straight line SL along all the straight line portions to calculate the corresponding resistance components, and only the required resistance components can be calculated. For example, only the resistance component with particularly fast response can be calculated. For example, it is possible to draw a straight line SL along the square root TR of 3 (s 1 / 2 ) is used to draw a straight line SL from the linear portion of the area below , and only the resistance component with a particularly fast response is calculated.

[0049] In the measurement method (M), in the above-mentioned measurement step, the open circuit voltage Vop may be measured at every predetermined time or every time the above-mentioned voltage change reaches a predetermined value. The predetermined time may be in the range of 0.001 to 10 seconds (e.g., in the range of 0.1 to 1 second). The predetermined value of the voltage change may be in the range of 0.1 to 100 mV (e.g., in the range of 1 to 10 mV).

[0050] In the measurement method (M), in the above measurement step, the open circuit voltage Vop may be measured every 0.1 second or every time the voltage change reaches 5 mV until at least 10 seconds have passed since the end of charging or discharging. Thereafter, the measurement interval may be further increased or the measurement may be continued at the same measurement interval.

[0051] The present disclosure provides a measuring device for measuring the internal resistance of a battery using a measuring method (M). The measuring device has a structure for executing the measuring method (M). For example, the measuring device may include: a device for charging and discharging the battery (a device for implementing a power-on process), a device for measuring the open circuit voltage of the battery (a device for implementing a measuring process), and a device for analyzing the measured values ​​and calculating the internal resistance (resistance component) (a device for implementing a calculation process). The device for charging and discharging the battery and the device for measuring the open circuit voltage of the battery are not particularly limited, and known devices can be used. The device for implementing the calculation process may include a processing unit and a storage device. A program for executing the above-mentioned calculation process is stored in the storage device. The measured values ​​measured in the measuring process are also stored in the storage device. The processing unit executes the stored program to calculate the internal resistance (resistance component) based on the measured values. In the storage device, a program for executing the power-on process and the measuring process according to the determined steps may also be stored. The processing unit can control the device based on these programs.

[0052] (Note)

[0053] The above description discloses the following technology.

[0054] (Technology 1)

[0055] A method for measuring the internal resistance of a battery, comprising:

[0056] A power-on process for charging or discharging the battery;

[0057] a measuring step of measuring an open circuit voltage of the battery at or after the end of the charging or the discharging; and

[0058] a calculation step of separately calculating at least one resistance component included in the internal resistance based on the voltage change of the open circuit voltage measured in the measurement step and the current value flowing through the battery due to the charge or the discharge at the end,

[0059] In the calculation step, the at least one resistance component is calculated based on a slope of a line obtained by plotting the voltage change in a graph having a square root of the elapsed time from the end as the horizontal axis and the open circuit voltage as the vertical axis.

[0060] (Technique 2)

[0061] According to the determination method described in technique 1,

[0062] The resistance component is calculated using the current value and a plurality of voltage values,

[0063] The plurality of voltage values ​​include:

[0064] as a reference voltage value of the open circuit voltage at the end; and

[0065] At least one voltage value obtained by extrapolating at least one straight line along at least one straight line-like portion appearing on the line in the graph to the end point.

[0066] (Technique 3)

[0067] According to the determination method described in technique 2,

[0068] The resistance component is obtained by dividing a voltage difference between two adjacent voltage values ​​among the plurality of voltage values ​​by the current value.

[0069] (Technique 4)

[0070] The measuring method according to any one of techniques 1 to 3,

[0071] In the measuring step, the open circuit voltage is measured at predetermined time intervals or whenever the voltage change reaches a predetermined value.

[0072] (Technique 5)

[0073] The measuring method according to any one of techniques 1 to 4,

[0074] In the measuring step, the open circuit voltage is measured every 0.1 seconds or every time the voltage change reaches 5 mV until at least 10 seconds have passed from the end.

[0075] Example

[0076] Hereinafter, the present disclosure will be described in more detail by way of examples.

[0077] (Example 1)

[0078] In Example 1, a charge-discharge cycle test was performed on a secondary battery using a layered oxide containing Li, Ni, and Mn as a positive electrode active material and lithium metal as a negative electrode active material. The charge-discharge cycle test was performed by repeatedly charging at a current value of 0.7 C and discharging at a current value of 0.15 C. In addition, measurements were performed before and after the charge-discharge cycle test according to the measurement method (M).

[0079] Figure 2 The graph obtained by the measurement step of the measurement method (M) before the charge and discharge cycle test is shown. Figure 2 The graph of FIG. 1 is a graph showing the change over time of the open circuit voltage Vop after the secondary battery was charged to 3.7 V at a current value of 0.7 C and then discharged at a current value (current value Ie) of 0.15 C for 1051 seconds. Figure 2 The line L is a line obtained by plotting the voltage change of the open circuit voltage Vop. Figure 1 The change with time of the open circuit voltage Vop after the charge and discharge cycle test is shown.

[0080] and Figure 1 same, Figure 2 There are four straight line portions on line L, and four straight lines SL(1) to SL(4) are drawn along them. In addition, straight line SL(4) shows the value after 3600 seconds, when there is virtually no change in the open circuit voltage Vop. Furthermore, by extrapolating these straight lines SL(1) to SL(4) to the end of discharge (square root TR=0), voltage values ​​V(1) to V(4) are obtained (not shown). Furthermore, based on the reference voltage value V(0) which is the open circuit voltage Vop at the end of discharge and the voltage values ​​V(1) to V(4), the internal resistance R and the first to fourth resistance components Re(1) to Re(4) are calculated by the above method.

[0081] Moreover, based on Figure 1 The graph shown calculates the internal resistance R and resistance components Re (1) to (4) of the secondary battery after the charge and discharge cycle test. Table 1 shows the calculation results.

[0082] Table 1

[0083]

[0084] As shown in Table 1, it can be seen that the resistance components Re(1) and Re(2) also significantly increased among the resistance components through the charge and discharge cycle test.

[0085] (Example 2)

[0086] In Example 2, the state of charge (SOC) of the secondary battery was changed, and the internal resistance was measured according to the measurement method (M). The secondary battery was assembled in the same manner as in Example 1, except that the restraint pressure was increased to 2.7 times. Furthermore, charging at a current value of 0.7C and discharging at a current value of 0.15C were repeated.

[0087] Next, the secondary battery was charged to change the charging state. In addition, the battery was discharged at a current value of 1 C for 30 seconds under different charging states, and the voltage change after discharge was measured. In addition, the internal resistance of the secondary battery was calculated by the measurement method (M). Figure 3 The voltage changes before and after discharge in each charging state are shown. Figure 3 The higher the battery voltage on the horizontal axis, the higher the charging state.

[0088] Will Figure 3Table 2 shows the results of calculating the resistance of the secondary battery at points (a) to (e).

[0089] Table 2

[0090]

[0091] As shown in Table 2, the resistance component Re(2) changes in a U-shape as the charge state changes. In addition, in the fully charged state, the resistance components Re(3) and Re(4) increase significantly.

[0092] The battery voltage was set to 3.7V, 3.9V, 4.2V, and 4.5V, and the resistance component of the internal resistance was calculated by the measurement method (M) at each voltage. Specifically, at each voltage, the measurement was performed by the measurement method (M) after discharging at a current value of 0.15C for 1051 seconds. In addition, the AC impedance measurement was performed during the discharge process. The results of the internal resistance calculated by the measurement method (M) are shown in Figure 1. Figure 4 In addition, Figure 4 , the Nyquist plot measured at each voltage is shown rotated 90° counterclockwise.

[0093] like Figure 4 As shown, the internal resistance R at 3.7 V is 157Ω, which is approximately half of that of the secondary battery in Example 1.

[0094] according to Figure 4 It is believed that the resistance component Re(1) corresponds to the arc on the high frequency side of the Nyquist diagram, and the resistance component Re(2) corresponds to the arc on the low frequency side of the Nyquist diagram. The resistance components Re(3) and Re(4) may correspond to the resistance related to ion transport and the diffusion resistance.

[0095] (Example 3)

[0096] In Example 3, a charge-discharge cycle test was performed on a secondary battery using a layered oxide containing Li, Ni, Co, and Al as a positive electrode active material and a mixture of graphite and silicon as a negative electrode active material. The charge-discharge cycle test repeatedly performed charging at a current value of 0.7C and discharging at a current value of 0.15C. In addition, the battery was charged to 3.8V and discharged at a current value of 0.15C for 1051 seconds, and then measured by the measurement method (M). The results of calculating the resistance of the secondary battery are shown in Table 3.

[0097] Table 3

[0098]

[0099] In this battery, the open circuit voltage Vop continued to change 3600 seconds after the discharge was completed, so the resistance component Re(4) was not calculated. On the other hand, the resistance components Re(1) to Re(3) were calculated.

[0100] Industrial Applicability

[0101] The present disclosure can be used for a method for measuring the internal resistance of a battery.

[0102] Although the present invention has been described in conjunction with the present preferred embodiment, such disclosure should not be interpreted in a limiting manner. By reading the above disclosure, a person skilled in the art of the present invention will undoubtedly understand various modifications and changes. Therefore, the attached claims should be interpreted as including all modifications and changes that do not depart from the true spirit and scope of the present invention.

Claims

1. A method for measuring the internal resistance of a battery, comprising: A power-on process for charging or discharging the battery; a measuring step of measuring an open circuit voltage of the battery at the end of the charging or the discharging and thereafter; as well as a calculation step of separately calculating at least one resistance component included in the internal resistance based on the voltage change of the open circuit voltage measured in the measurement step and the current value flowing through the battery due to the charge or the discharge at the end, In the calculation step, the at least one resistance component is calculated based on a slope of a line obtained by plotting the voltage change in a graph having a square root of the elapsed time from the end as the horizontal axis and the open circuit voltage as the vertical axis.

2. The assay method according to claim 1, The resistance component is calculated using the current value and a plurality of voltage values, The plurality of voltage values ​​include: as a reference voltage value of the open circuit voltage at the end; and At least one voltage value obtained by extrapolating at least one straight line along at least one straight line-like portion appearing on the line in the graph to the end point.

3. The assay method according to claim 2, The resistance component is obtained by dividing a voltage difference between two adjacent voltage values ​​among the plurality of voltage values ​​by the current value.

4. The assay method according to claim 1 or 2, In the measuring step, the open circuit voltage is measured at predetermined time intervals or whenever the voltage change reaches a predetermined value.

5. The assay method according to claim 1 or 2, In the measuring step, the open circuit voltage is measured every 0.1 seconds or every time the voltage change reaches 5 mV until at least 10 seconds have passed from the end.

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