Instantaneous battery deterioration degree measuring instrument

Abstract

[Problem] To provide an instantaneous battery deterioration degree measuring instrument capable of accurately measuring the degree of deterioration of a secondary battery in a short time. [Solution] An instantaneous battery deterioration degree measuring instrument is characterized by including: a measurement unit that obtains a potential difference ΔＶ and a current I after a lapse of a predetermined period of time from a start of application of a current when a constant current is applied to a secondary battery, the predetermined period of time being required for constant current control to become stabilized, or at an end of application of the current; and a capacity calculation unit that calculates the capacity of the secondary battery from the voltage difference ΔＶand the current I.

Description

Instantaneous battery deterioration meter

[0001] The present invention relates to an instantaneous battery deterioration meter.

[0002] Conventionally, to measure the degree of deterioration of a secondary battery, the battery is charged to full charge, and then the cumulative amount of electricity until it is fully discharged is measured, and the performance of the secondary battery is evaluated based on the resulting numerical value, but this series of operations takes several hours. Here, the degree of deterioration SOH (State of Health) is an index that represents the health and deterioration state of a battery, and is expressed as a percentage (%) of the full charge capacity (Ah) at the time of deterioration, when the rated capacity (Ah) is taken as 100%.

[0003] However, from the perspective of a secondary battery user, performance recognition is essential in the manufacturing process of devices that use secondary batteries, as well as in the inspection process that ensures the safety and reliability of the secondary batteries to be installed, and is an important pre-check item for the next process. Making this performance recognition possible in a short time was an extremely important challenge both physically and economically.

[0004] Patent No. 6839883

[0005] According to the above-mentioned Patent Document 1, the state of health (SOH) of a secondary battery can be measured in a short time. However, in the method of Patent Document 1, a time lag occurs between the application of an overvoltage and the response of the current, and measurement errors due to the mass transfer rate in the electrolyte cannot be avoided.

[0006] An object of the present invention is to provide an instantaneous battery deterioration measuring device that can measure the deterioration level of a secondary battery accurately and in a short time.

[0007] The instantaneous battery degradation measuring device of the present invention is characterized by comprising a measuring unit that determines the potential difference ΔV and the current I at the start of current flow when applying a constant current to a secondary battery, after a predetermined period has passed during which the constant current control has stabilized, or at the end of current flow, and a capacity calculation unit that calculates the capacity of the secondary battery from the voltage difference ΔV and the current I.

[0008] In the instantaneous battery degradation meter according to the present invention, the capacity calculation unit includes means for calculating a true overvoltage δ by substituting the voltage difference ΔV into Equation 12, and means for calculating a power storage ratio SOC based on Equation 18, and f = F / RT [1 / V] Gas constant R [J / mol T] Faraday constant F [Q / mol] Absolute temperature T [K] <Formula 18> Molar concentration of the reducing agent in the battery: C ｒ ＊ = 1 / 100 of the storage ratio SOC Battery electromotive voltage: V ｅｍｆ Battery nominal voltage: V st f=F / RT [1 / V] Gas constant R [J / mol・T] Faraday constant F [Q / mol] Absolute temperature T [K] Battery-specific coefficient α

[0009] In addition, in the instantaneous battery deterioration measuring device according to the present invention, there is provided a means for calculating a true overvoltage δmin when the storage rate SOC is 50% by substituting the true overvoltage δ and the storage rate SOC into Equation 16, and a means for calculating a current element I based on Equation 17. ００ and a means for calculating the current I / the current element I ＯＯ Using the battery specific coefficient K ００ and a means for calculating K ＯＯ and a means for calculating the capacity of the secondary battery using (1 / √2). <Formula 16> Molar concentration of the reducing agent in the battery: C ｒ ＊ = 1 / 100 of the power storage ratio SOC True overvoltage: δ True overvoltage at a power storage ratio SOC of 50%: δmin <Formula 17>

[0010] According to the present invention, the degree of deterioration of a secondary battery can be measured accurately and in a short time.

[0011] Fig. 1 is a schematic diagram of a battery degradation level measuring device according to an embodiment of the present invention; Fig. 2 is a diagram showing the behavior of voltage and current when measuring physical quantities necessary for capacity calculation in an embodiment of the present invention; Fig. 3 is a diagram showing measurement results of the behavior of voltage and current when measuring physical quantities necessary for capacity calculation in an embodiment of the present invention; Fig. 4 is a flowchart showing a procedure for measuring the degradation level of a secondary battery using a battery degradation level measuring device according to an embodiment of the present invention.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following, like elements in all the drawings are designated by like reference numerals, and redundant description will be omitted.

[0013] The secondary battery 2 has a mechanism for retaining electrical energy, which is externally injected in the form of a current, internally in the form of a change in the state of chemical substances, so-called Gibbs energy. The potential inside the secondary battery 2 is expressed in terms of the Gibbs energy level, and the energy associated with the potential difference defined by the difference in the fundamental levels of the negative and positive electrodes that make up the battery and the abundance ratio of the working medium is equivalent to the injected electrical energy. An example of the secondary battery 2 is a lithium-ion secondary battery.

[0014] The terminal voltage of the secondary battery 2 is monitored by a voltmeter 4 and the current is monitored by an ammeter 6 .

[0015] The instantaneous battery deterioration level measuring instrument 10 also has the function of measuring and identifying preliminary information such as the material and configuration of the target battery type, with the aim of being able to measure the deterioration level SOH of the secondary battery 2 in a short period of time (e.g., 1 second).

[0016] The instantaneous battery deterioration meter 10 measures the battery terminal voltage V when a constant current is applied. ｎ and current I, and has the function of diagnosing the degree of battery deterioration by measuring the voltage and current at short time intervals (within 1 second).

[0017] The instantaneous battery degradation level measuring device 10 includes a measuring unit 12, a power unit 14, and a control unit 16 having a capacity calculation unit 18. The measuring unit 12 includes a voltmeter 4 and an ammeter 6.

[0018] The power unit 14 can supply the desired current and voltage to the secondary battery 2 in response to signals from the control unit 16. The current and voltage are measured by the voltmeter 4 and ammeter 6 of the measurement unit 12. The power unit 14 and measurement unit 12 are controlled by the control unit 16, and are capable of injecting current, applying voltage, and measuring voltage and current at desired timing.

[0019] V ｅｍｆ is measured and the SOC is calculated using Equation 18.

[0020] The control unit 16 controls the power unit 14 to apply a constant current to the secondary battery 2 for a short period of time (for example, 1 second). The battery terminal voltage Vn and current I of the secondary battery 2 are measured during or after application of the constant current. V ｎ The difference (Figure 2 ΔV is V １ -V ０ Or V ２ -V ３ ) and calculates ΔV from the data of ΔV and I, and the control unit 16 calculates the degree of deterioration SOH and displays the calculated SOH on the display unit.

[0021] FIG. 2 is a voltage and current diagram showing ΔV at the start and end of current flow when a constant current is passed through the secondary battery 2 for a short period of time (about 1 second).

[0022] Furthermore, as shown in Figure 2, when a constant current is applied (or when the constant current is cut off), it is necessary to measure the potential difference ΔV that occurs across the resistance component due to the electrode reaction. This is expected to occur within 1 ms. After this, the main phenomenon is the transient phenomenon of the LC component of the electrolyte of the secondary battery 2, so measurements should not be taken at this time.

[0023] In reality, when a constant current is applied, the voltage and current oscillate up and down until the constant current control stabilizes, as indicated by the circle in Figure 3, and it takes time for the control to converge to a constant current, so it is preferable to observe the falling waveform.

[0024] The instantaneous battery degradation meter 10 according to an embodiment of the present invention can measure the degradation level of a secondary battery 2 simply by passing a constant current through the secondary battery 2 for a short period of time and measuring the value of the constant current and the ΔV at the start and end of the current flow. The technology underlying the measurement of power storage performance involves injecting a certain amount of electrical energy and then immediately monitoring the voltage of the secondary battery 2. This is a charging method (see Japanese Patent No. 3752249) in which this process is repeated until a set battery voltage is reached.

[0025] Next, we will explain the operation of the instantaneous battery degradation level measuring device 10. Figure 4 is a flowchart showing the procedure for detecting battery performance in a short time (about 1 second) using the instantaneous battery degradation level measuring device 10.

[0026] First, a constant current is applied to the secondary battery 2 for about 1 second, and the voltage at the end of the current flow (V ２ ) is measured (S2), and the current I is measured (S4). These controls are performed by the control unit 16.

[0027] After steps S2 and S4, the current flowing through the secondary battery 2 is interrupted (S6). Then, the current falling curve is successively observed to detect the moment when the current flowing through the secondary battery 2 falls to 0 (1% or less of the current I) (S8).

[0028] The voltage at the moment when the current flowing through Current 2 becomes 0 (V in Figure 2) ３ After step S10, the value of the overvoltage ΔV is calculated using Equation 11 (S12). <Equation 11>

[0029] After S12, the true overvoltage δ that satisfies the formula 12 is calculated (S14). <Formula 12>

[0030] In order to find the true overvoltage δ, the successive asymptotic method is used. Specifically, the initial value of δ is set to half (1 / 2) of ΔV (S16). After S16, ΔVn is found using Equation 13 (S17). <Equation 13>

[0031] Next, it is determined whether the difference between ΔVn and the true ΔV is within 0.1 mV (S18). If it is determined in step S18 that the difference is not within 0.1 mV, δn is increased by 0.1 mV (S20), and the process returns to step S17.

[0032] In the step S18, if it is determined that the difference is within 0.1 mV, the true overvoltage δ is determined (S22). ｅｍｆ to standard voltage V ｓｔ Subtract (=V ｅｍｆ -V ｓｔ ) and calculate the difference (S24). ｓｔ is read from the battery specifications and is the electromotive force V ｅｍｆ is measured before S2 or S24.

[0033] After S24, the charge ratio SOC is calculated using Equation 18 (S26). Here, α is a correction coefficient that is used when the charge ratio SOC is significantly different from the battery capacity Q value. The α value differs depending on the type of electrode, so it is calculated experimentally. <Equation 18>

[0034] After step S26, the SOC coefficient is calculated using Equation 15 (S28). The coefficient for an SOC of 50% is 1. <Equation 15>

[0035] After step S28, the true overvoltage δmin at an SOC of 50% is calculated from δ and the SOC coefficient using Equation 16 (S30). <Equation 16>

[0036] After the step S30, the current element I is calculated using Equation 17. ００ (S32). During constant current charging, the overvoltage δ and SOC (Cr ＊ ) relationship is Cr ＊ As approaches the limit (0 or 1), δ becomes large and, as mentioned above, Cr ＊ The minimum value is reached at 0.5. The time integral of the constant current I is the injected quantity of electricity Q (the battery capacity Q value), and this integral value I ｏ is generally true regardless of the battery, and the current element I ｏｏ The current I is multiplied by the electrode activation coefficient Kｏｏ The capacity Q is calculated by multiplying the integral of the current element by the same coefficient. ＊ (1-Cr ＊ ) = 0.5, it is maximum, and in order to keep the current constant, δ is the minimum value δ ｍｉｎ At that time, I ｏ current element I ｏｏ This is expressed by the following equation: <Equation 17>

[0037] After the step of S32, the battery specific coefficient K ００ = I / I ＯＯ After S34, Q=K ＯＯ The capacity is calculated by (1 / √2) (S36).

[0038] As described above, the instantaneous battery degradation meter 10 has the remarkable effect of being able to perform high-speed, highly accurate degradation diagnosis by passing a constant current through the secondary battery 2 for a short period of time (about 1 second) and calculating ΔV at the start or end of the current flow. In addition, the instantaneous battery degradation meter 10 has the advantage that it does not need to stabilize the power supply within several ms (several milliseconds), making it possible to inexpensively manufacture a power supply device that applies an overvoltage.

Claims

1. An instantaneous battery degradation meter comprising: a measuring unit that determines the potential difference ΔV and current I at the start of current flow when applying a constant current to a secondary battery, after a predetermined period has passed during which constant current control has stabilized, or at the end of current flow; and a capacity calculation unit that calculates the capacity of the secondary battery from the voltage difference ΔV and current I.

2. In the instantaneous battery degradation meter according to claim 1, the capacity calculation unit comprises: means for calculating a true overvoltage δ by substituting the voltage difference ΔV into formula 12; means for calculating a charge storage ratio SOC based on formula 18; and means for calculating a charge storage ratio SOC based on formula 12. f = F / RT [1 / V] Gas constant R [J / mol T] Faraday constant F [Q / mol] Absolute temperature T [K] <Formula 18> Molar concentration of the reducing agent in the battery: C ｒ ＊ = 1 / 100 of the storage ratio SOC Battery electromotive voltage: V ｅｍｆ Battery nominal voltage: V st f=F / RT [1 / V] Gas constant R [J / mol・T] Faraday constant F [Q / mol] Absolute temperature T [K] Battery-specific coefficient α 3. The instantaneous battery degradation measuring device according to claim 2, further comprising: means for substituting the true overvoltage δ and the power storage ratio SOC into Equation 16 to calculate a true overvoltage δmin when the power storage ratio SOC is 50%; and means for calculating a current element I based on Equation 17. ００ and a means for calculating the current I / the current element I ＯＯ Using the battery specific coefficient K ００ and a means for calculating K ＯＯ An instantaneous battery deterioration meter comprising: a means for calculating the capacity of the secondary battery using (1 / √2); and <Formula 16> Molar concentration of the reducing agent in the battery: C ｒ ＊ = 1 / 100 of the power storage ratio SOC True overvoltage: δ True overvoltage at a power storage ratio SOC of 50%: δmin <Formula 17>

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