Charger with capacity measurement function

Abstract

To provide a charger with a diagnostic function that calculates a capacity by performing a predetermined measurement when charging is terminated.SOLUTION: A charger with a diagnostic function, is characterized by comprising: charging means for charging a secondary battery by constant current charging, switching to the consent voltage charging after a battery terminal voltage of the secondary battery reaches a predetermined voltage to perform charging, and terminating charging when a charging current becomes a predetermined current; determining means for determining a value of a charging state when the charging is terminated; measuring means for measuring the battery terminal voltage immediately before the charging is terminated and the battery terminal voltage immediately after the charging is terminated; and capacity calculating means for calculating a battery capacity of the second battery based on the value of the charging state, the battery terminal voltage immediately before the charging is terminated, and the battery terminal voltage immediately after the charging is terminated.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventional chargers only had the function of fully charging a battery or supplementary charging. When checking the amount of electricity that can be stored in a battery, either the battery was fully discharged and then charging was started, and the total amount of electricity (units are coulombs or Ah) was measured until the battery was fully charged, or the battery was fully charged and then discharging was started, and the total amount discharged was measured.

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

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

[0005] [Patent Document 1] Patent No. 3752249 [Patent Document 2] Patent No. 3869838 [Patent Document 3] Patent No. 6589080 [Patent Document 4] Patent No. 6839883 [Non-Patent Document 1] Matsuda et al. "Introduction to Electrochemistry" Maruzen Co., Ltd. (November 1999) [Non-Patent Document 2] Itagaki, "Electrochemical Impedance Method," Maruzen Publishing (July 2011) [Non-Patent Document 3] Koyama et al., "Evolution of Lithium-ion Secondary Batteries and Their Evaluation and Analysis Technologies," Nikkan Kogyosha Monthly Magazine "Industrial Materials" vol. 69 (July 2021) Summary of the Invention [Problem to be solved by the invention]

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

[0008] However, electrical measurements require the measurement of the overall characteristics of the flow of electrons due to the oxidation and reduction of the electrodes and the flow of ions in the electrolyte, making it difficult to measure the electrode performance that determines the capacity of the battery separately. Many methods have been attempted in the past, but all of them have various difficulties in terms of practical application and implementation, and are limited to use for special purposes.

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

[0010] The charger with diagnostic function of the present invention is characterized by comprising: a 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 becomes a predetermined current; a determination means for determining a value of the state of charge at the end of charging; a measurement 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 a capacity calculation means for calculating the battery capacity of the secondary battery 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.

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

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

[0013] [Figure 1] 1 is a schematic diagram of a charger with diagnostic function in an embodiment according to the present invention; [Diagram 2] 1 shows behavior of voltage and current when measuring physical quantities necessary for capacitance calculation in an embodiment according to the present invention. [Diagram 3] 1 is a breakdown of measured voltages in each state in an embodiment according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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, the same elements in all the drawings are designated by the same reference numerals, and duplicated explanations will be omitted.

[0015] The battery 2 has a mechanism for retaining the electric energy injected from the outside in the form of a current in the form of a change in the state of a chemical substance, so-called Gibbs energy. The potential inside the battery 2 is expressed by the Gibbs energy level, and the energy associated with the potential difference defined by the basic level difference between the negative and positive electrodes constituting the battery and the abundance ratio of the working medium is equivalent to the injected electric 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 the electrons flowing in from the outside through an electrochemical reaction and is supported by the negative electrode. Research on this process was conducted by great predecessors such as Boltzmann-Maxwell and Arrhenius, and is still widely known and applied today as a basic principle.

[0017] This invention was made possible by utilizing these fundamental principles and theorems and applying current developments in electrical, electronic and microcomputer technology.

[0018] Charger 10 with diagnostic function comprises a measurement unit 12, a power unit 14, and a control unit 16. Charger 10 with diagnostic function has the function of measuring the capacity by simply fully charging battery 2 from any state. During charging, the terminal voltage is monitored by voltmeter 4, and the current is monitored by 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 it is possible to inject current, apply voltage, and measure voltage and current at the 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 chemical reaction in a battery is about 1 ms. This means that the battery terminal voltage drops about 1 ms after the current is cut off. Based on this, it can be said that there is no problem in setting the time 1 ms before the current cut off signal as just before the end of charging, and 2 ms after the current cut off signal as just after the end of charging. <Research and analysis of battery operation related to the present invention>

[0021] This invention is capable of obtaining the physical quantities necessary to calculate the battery capacity simply by measuring the voltage difference using a specified method just before and just after the end of charging. The technology that is the basis for testing the energy storage performance is to monitor the voltage of battery 2 immediately after injecting a certain amount of electrical energy. This is the Ad.IC&C charging method, which repeats this process and ends when the set battery voltage is reached.

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

[0023] The relationship between current I and overvoltage Δv and the dynamic internal resistance DIR are <Formula 1> It is represented as JPEG2025006734000002.jpg43100. (Patent Document 4)

[0024] Here, K 00 is a constant depending on the electrode material, C r,f * is 1 / 100 of SOC, and 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 and the capacity Q <Formula 2> JPEG2025006734000003.jpg1933 is established. (Patent Document 4)

[0026] In FIG. 2, the charging current is I, the charge end current is I0 (listed in the battery specifications, here 0.1I), and the SOC at the time of charge end is 95% (C r,f * = 0.95) and set it. The battery terminal voltage is V max When this voltage is reached, the charging will switch from CC charging to CV charging. max The electrical characteristics of the electrolyte and the physical characteristics of the electrodes are specified in the battery specifications, for example, 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 interruption (within 0.1 seconds) f The relationship between the charge end current I0 and <Formula 3> JPEG2025006734000004.jpg1586 It is.

[0028] From this <Formula 4> JPEG2025006734000005.jpg2074 is derived. When the SOC at the end of charging is set to 95% JPEG2025006734000006.jpg2184 It becomes.

[0029] This K 00 From equation 1, the overvoltage Δv at any SOC with charging current I is determined. For example, when SOC is 50%, Δv and DIR are at their minimum values. <Formula 5> JPEG2025006734000007.jpg3269 is derived. 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. In other words, it is the equilibrium potential when there is no current flowing in or out of the battery, and there is no potential difference caused by the imbalance or movement of ions inside the battery, and it usually refers to the potential difference after 10 hours of non-operation.

[0031] During charging, the battery terminal voltage V(t+) is 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) associated with the electrode reaction. <Formula 6> JPEG2025006734000008.jpg1077The battery terminal voltage V(t-) immediately after the charging operation is completed 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). <Formula 7> JPEG2025006734000009.jpg1057

[0032] Δη eq (t) is represented by a series connection of two tank circuits with time constant T1, diffused resistance R1, and time constant T2, diffused resistance R2. <Formula 8> JPEG2025006734000010.jpg994

[0033] According to the Nernst relationship, the stored charge concentration C indicates the SOC. r * (t) is the electromotive force V emf Confirm (t). <Formula 9> JPEG2025006734000011.jpg1975

[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. The coefficient 1 / f in the formula takes into account the rate-limiting effects of both electrodes and the effects of mobility, and is set to 1 / αf by applying the coefficient α specific to the relevant battery. Note that V stis a constant specific to the battery material for the combination of the positive electrode and the negative electrode.

[0035] From formula 6 and formula 7 <Formula 10> The result is JPEG2025006734000012.jpg1153.

[0036] Since both V(t+) and V(t-) are measured quantities, ΔV(t) can be calculated from Equation 10. f Since (t) is ΔV(t) just before and after the end of charging, from these measurements, K 00 It is shown that Q can be calculated from Equation 2. It is also suggested 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. There are two ways to obtain this: first fully charge the battery and then measure the charge until it is fully discharged, or vice versa. However, going to the trouble of charging and discharging the battery just to obtain the SOH takes time and is not efficient.

[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 and impedance method, the electrochemical operating constants of a standard battery are known in advance, and the constants of the target battery are compared, and these constants must be referenced as correlation matrix constants of many factors depending on the battery's operating history and the operating environment at that time, etc., and various problems exist in analysis and interpretation. The feature of this invention is that the DIR, which is an index of the size of the reaction area of ​​lithium ions on 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 it. <Effects of the present invention>

[0039] Battery charging, which supplements and replenishes an energy tank with electrical energy, has the disadvantage that the tank's capacity and performance change, unlike a gasoline tank. Therefore, when using energy, it is important to use it appropriately while taking these changes into account, but it has been difficult to recognize these changes in the past. With the present invention, it is possible to easily check the changes every time charging, improving the safety and reliability of battery-powered devices.

[0040] In addition, the current performance (capacity) of the battery can be confirmed each time it is charged, and from data analysis of its history, it is possible to predict the characteristics of the target battery and create a plan for its future use, thereby confirming its safety in use and ensuring trust and peace of mind.

Claims

1. a charging means for charging a secondary battery by constant current charging, switching to constant voltage charging after a battery terminal voltage of the secondary battery reaches a predetermined voltage, and terminating charging when the charging current reaches a predetermined current; a determination means for determining a value of the state of charge at the end of charging; A measuring means for measuring the battery terminal voltage immediately before and after the end of charging; a capacity calculation means for calculating a battery capacity of the secondary battery 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; A charger with a diagnostic function comprising:

2. 2. The charger with diagnostic function according to claim 1, 4. A charger with diagnostic function, wherein the value of the state of charge is 0.95.

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