Charger with capacity measurement function

Abstract

A charger (10) with a diagnostic function according to the present invention comprises: a charging means (14) that charges a secondary battery (2) by constant current charging, charges the secondary battery by switching to constant voltage charging after the battery terminal voltage of the secondary battery (2) reaches a prescribed voltage, and terminates charging when the charging current becomes a prescribed current; a determination means that determines a value of the charging state at the end of charging to be 0.95; a measurement means (4) that measures the battery terminal voltage immediately before the end of charging and the battery terminal voltage immediately after the end of charging; and a capacity calculation means that calculates the battery capacity of the secondary battery (2) on the basis of the value of the charging state, the battery terminal voltage immediately before the end of charging, and the battery terminal voltage immediately after the end of charging.

Description

Charger with capacity measurement function

[0001] The present invention relates to measuring and indicating a battery's State of Health (SOH) at the end of charge.

[0002] Conventional chargers only have the function of fully charging a battery or supplementary charging. To check the amount of electricity that can be stored in a battery, you either start charging the battery from a fully discharged state and measure the total amount of electricity (measured in coulombs or Ah) until the battery is fully charged, or start discharging the battery after fully charging it and measure the total amount of discharge.

[0003] However, in reality, it is rare to charge from a fully discharged state or discharge from a fully charged state, so a capacity measuring device that requires a battery to be fully discharged (or fully charged) in order to measure capacity is not practical.

[0004] When the battery capacity of an EV decreases, the motor horsepower drops sharply. Therefore, it is necessary to constantly check the battery capacity, especially when the battery is installed in a vehicle. Checking battery performance is an extremely important issue for the safety and reliability of equipment that uses batteries as an energy source.

[0005] Matsuda et al., "Introduction to Electrochemistry," Maruzen Co., Ltd. (November 1999); Itagaki et al., "Electrochemical Impedance Method," Maruzen Publishing (July 2011); Koyama et al., "Evolution of Lithium-Ion Secondary Batteries and Evaluation / Analysis Technology," Nikkan Kogyosha Monthly Magazine "Industrial Materials," Vol. 69 (July 2021)

[0006] For example, Non-Patent Documents 2 and 3 state that static internal resistance measured by the AC impedance method is a battery performance index, and disclose a method for calculating a performance ratio from an impedance ratio relative to a reference battery.

[0007] Furthermore, Patent Document 2 and the like disclose a method for observing complex response characteristics according to a combination of an electrolyte and an electrode, and Patent Document 4 discloses a method for calculating power storage performance from the electrochemical characteristics of an electrode.

[0008] However, electrical measurements require measuring the overall characteristics of the flow of electrons due to oxidation-reduction at the electrodes and the flow of ions in the electrolyte, making it difficult to measure the electrode performance that determines the battery capacity separately. Many methods have been attempted in the past, but all have had various practical and implementation difficulties and have been limited to use in specialized applications.

[0009] An object of the present invention is to calculate the capacity by performing a predetermined measurement when charging is terminated.

[0010] The charger with diagnostic function of the present invention is characterized by comprising: charging means for charging a secondary battery by constant current charging, switching to constant voltage charging after the battery terminal voltage of the secondary battery reaches a predetermined voltage, and terminating charging when the charging current reaches a predetermined current; determining means for determining a value of the state of charge at the end of charging; measuring means for measuring the battery terminal voltage just before the end of charging and the battery terminal voltage just after the end of charging; and capacity calculating means for calculating the battery capacity of the secondary battery based on the value of the state of charge, the battery terminal voltage just before the end of charging, and the battery terminal voltage just after the end of charging.

[0011] In the charger with diagnostic function according to the present invention, the value of the state of charge is preferably 0.95.

[0012] According to the present invention, the capacity can be measured simply by fully charging the battery from any state.

[0013] 1 is a schematic diagram of a charger with a diagnostic function according to an embodiment of the present invention; 2 is a diagram showing the behavior of voltage and current when measuring physical quantities necessary for capacity calculation according to an embodiment of the present invention; and 3 is a breakdown of the measured voltage in each state according to an embodiment of the present invention.

[0014] 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.

[0015] The 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 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 battery 2 is a lithium-ion secondary battery.

[0016] During charging, the medium that reaches the reaction interface of the negative electrode from the positive electrode side reacts with electrons flowing in from the outside through an electrochemical reaction and is carried on the negative electrode. Research into this process has been conducted by great predecessors such as Boltzmann-Maxwell and Arrhenius, and is still widely known and applied as a basic principle today.

[0017] This invention was achieved by utilizing these fundamental principles and theorems and applying and developing electrical, electronic, and microcomputer technologies that have evolved over time.

[0018] The diagnostic function-equipped charger 10 comprises a measurement unit 12, a power unit 14, and a control unit 16. The diagnostic function-equipped charger 10 has the function of measuring the capacity by simply fully charging the battery 2 from any state. During charging, the terminal voltage is monitored by the voltmeter 4, and the current is monitored by the ammeter 6.

[0019] The power unit 14 can supply the desired current and voltage to the battery 2 according 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 current injection, voltage application, and voltage / current measurement can be performed at desired timing.

[0020] The measurement unit 12, power unit 14, and control unit 16 make it possible to measure the current and voltage just before the end of charging, and the voltage just after the end of charging. It is generally known that the speed of a battery's chemical reaction is about 1 ms. This means that a drop in the battery terminal voltage occurs about 1 ms after the current is cut off. Based on this, it can be said that there is no problem in determining the time just before the end of charging 1 ms before the current cut off signal is sent, and the time just after the end of charging 2 ms after the current cut off signal is sent. <Research and Analysis of Battery Operation Related to the Present Invention>

[0021] The present invention allows the physical quantities necessary to calculate battery capacity to be obtained simply by measuring the voltage difference using a specified method immediately before and after the end of charging. The technology underlying the energy storage performance test involves monitoring the battery 2 voltage immediately after injecting a certain amount of electrical energy. This is the Ad. I. C&C charging method, which repeats this process until the set battery voltage is reached.

[0022] 2 shows the voltage and current just before the end of charging. Charging is performed at a constant current, and when a predetermined voltage is reached, charging is switched to constant voltage charging.

[0023] The relationship between the current I and the overvoltage Δv and the dynamic internal resistance DIR is given by: (Patent Document 4)

[0024] Here, K ００ is a constant depending on the electrode material, C r,f * is 1 / 100 of SOC, f=F / RT [1 / V]. (R [J / mol・T]: gas constant, F [Q / mol]: Faraday constant, T [K]: absolute temperature)

[0025] Also K 00 Between the capacitance Q and the holds true. (Patent Document 4)

[0026] In FIG. 2, the charging current is I and the charge termination current is I ０ (This is stated in the battery specifications, and is 0.1 I in this case.) When charging is terminated, the SOC is set to 95% (C r,f * = 0.95) and set it. ｍａｘ When this V is reached, the charging mode is switched from CC to CV. ｍａｘ The electrical characteristics of the electrolyte and the physical characteristics of the electrodes are also specified in the battery specifications, such as 4.2 V for cobalt-carbon and 3.6 V for iron phosphate-carbon.

[0027] Voltage just before cut-off V ｍａｘ and the voltage V immediately after the cutoff (within 0.1 seconds) ΔV ｆ and the charge termination current I ０The relational expression is <Formula 3> is.

[0028] From this, <Formula 4> When the SOC at the end of charging is set to 95%, This becomes:

[0029] This K 00 From Equation 1, the overvoltage Δv at an arbitrary SOC at the charging current I is determined. For example, when the SOC is 50%, Δv and DIR take the minimum values, as shown in Equation 5. The physicochemical meaning of Δv in the above description will now be clarified.

[0030] The electromotive force is defined as the static potential difference between the positive and negative electrodes. That is, it is the equilibrium potential when there is no current flowing in or out of the battery, and there is no potential difference due to the imbalance or movement of ions inside the battery. It usually refers to the potential difference after 10 or so hours of non-operation.

[0031] The battery terminal voltage V(t+) during charging is calculated by the electromotive force V ｅｍｔ (t) and Δη due to the form of ions in the electrolyte and the fused form of ions ｅｑ (t), and the reaction potential difference ΔV(t) due to the electrode reaction. <Equation 6> The battery terminal voltage V(t-) immediately after the end of charging is the electromotive force V ｅｍｆ (t) and Δη due to the form of ions in the electrolyte and the fused form of ions ｅｑ (t) is the sum of (Formula 7).

[0032] Δη ｅｑ (t) is the time constant T １ , diffusion resistance R １ , and the time constant T ２ , diffusion resistance R ２ It is expressed as a series connection of two tank circuits with the following formula:

[0033] From the Nernst relationship, the charge concentration C, which indicates the SOC, ｒ ＊ (t) is the electromotive force V ｅｍｆ (t) is determined. <Formula 9>

[0034] However, V ｅｍｆ (t) is the sum of the potential drop of the negative electrode and the potential rise of the positive electrode with respect to the increase in t, and the coefficient 1 / f in the formula takes into account the rate-determining influence of both electrodes and the influence of mobility, and applies the coefficient α specific to the battery, making it 1 / αf. ｓｔ is a constant specific to the battery material depending on the combination of the positive electrode and negative electrode.

[0035] From Equation 6 and Equation 7, <Equation 10> is obtained.

[0036] Since both V(t+) and V(t-) are measured quantities, ΔV(t) can be calculated from Equation 10. ΔV in Equation 4 ｆ (t) is ΔV(t) just before and after the end of charging, so from these measurements, K ００ This shows that Q can be calculated from Equation 2. It also suggests that Q can be calculated by following a similar procedure when fully discharging. This can be applied to BMS, etc. <Features of the present invention>

[0037] Charging is essential for practical use of secondary batteries. However, conventional methods have not been able to obtain the battery's State of Health (SOH) during charging. Two methods are considered for obtaining this information: first fully charging the battery and then measuring the charge until it is fully discharged, or vice versa. However, going through the trouble of charging and discharging the battery to obtain the SOH is time-consuming and inefficient.

[0038] Therefore, it is necessary to estimate the internal state of the battery from measurements of voltage, current, etc., and calculate the capacity. In battery diagnosis using the impulse method or impedance method, the electrochemical operating constants of a standard battery are known in advance, and the constants of the target battery are compared. These constants must be referenced as correlation matrix constants of many factors depending on the battery's operating history and the operating environment during that history, etc., and various challenges exist in analysis and interpretation. A feature of the present invention is that the DIR, which is an index of the size of the lithium ion reaction area of ​​the electrode, can be obtained by measuring the charge voltage immediately before and after the end of charging, and the electrode capacity can be calculated from this. <Effects of the present invention>

[0039] Battery charging, which involves replenishing or replenishing an energy tank with electrical energy, has the disadvantage that, unlike gasoline tanks, the tank's capacity and performance change. Therefore, proper use that takes these changes into account is important when using energy, but it has traditionally been difficult to recognize these changes. This invention makes it possible to easily check changes each time a battery is charged, improving the safety and reliability of battery-powered devices.

[0040] Furthermore, the current performance (capacity) of the battery can be confirmed each time it is charged, and analysis of the battery's history data allows prediction of the battery's characteristics and creation of a future usage plan for the battery, thereby confirming its safety in use and guaranteeing trust and peace of mind.

Claims

1. A charger with diagnostic function, comprising: charging means for charging a secondary battery with constant current charging, switching to constant voltage charging after the battery terminal voltage of the secondary battery reaches a predetermined voltage, and terminating charging when the charging current reaches a predetermined current, determining means for determining a value of the state of charge at the end of charging as 0.95, measuring means for measuring the battery terminal voltage immediately before the end of charging and the battery terminal voltage immediately after the end of charging, and capacity calculating means for calculating the battery capacity of the secondary battery using formulas 2 and 4 based on the value of the state of charge, the battery terminal voltage immediately before the end of charging, and the battery terminal voltage immediately after the end of charging. <Formula 2> <Formula 4> Io: Current when charging is terminated f: F / RT R [J / mol T]: Gas constant F [Q / mol]: Faraday constant T [K]: Absolute temperature ΔVf: Potential difference between the voltage immediately before charging is terminated and the voltage immediately after it is cut off

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