WO2021091360A1

WO2021091360A1 - Method and apparatus for extracting entropy of electrochemical element using heat generation response according to electric signal input

Info

Publication number: WO2021091360A1
Application number: PCT/KR2020/015657
Authority: WO
Inventors: 이상국; 조준호; 테네시기욤; 한석균
Original assignee: 한국과학기술원
Priority date: 2019-11-08
Filing date: 2020-11-09
Publication date: 2021-05-14

Abstract

Provided is a method of extracting the entropy of an electrochemical device, the method comprising the steps of: applying a current including a frequency component to the electrochemical element; measuring a change in heat or temperature of the electrochemical element generated by the applied current; separating the frequency component of the measured change in heat or temperature, and specifying a frequency component that is one or two times the applied current; separating heat generation components including resistance heat generation and entropy heat generation from the specified frequency component and the change in temperature; and extracting the entropy of the electrochemical element through a combination of the ratio of the heat generation components and the absolute magnitude of the resistance heat generation.

Description

Method and apparatus for extracting entropy of electrochemical device using heat response according to electrical signal input

The present invention relates to a method and apparatus for extracting entropy of an electrochemical device using a heat response according to an electrical signal input, and more particularly, by measuring heat generated by a voltage or current input, the entropy of the electrochemical device can be extracted therefrom. The present invention relates to an apparatus and an entropy extraction method and apparatus for extracting entropy through signal processing from measurement of temperature, voltage, and current of an electrochemical device.

Entropy extraction technology for electrochemical devices can be classified dynamically/statically according to the real-time nature of the extraction process, and conventional static entropy extraction technology includes ETM (Electro Thermodynamic Measurement), and dynamic entropy extraction technology such as Calorimetry, IRET, etc. Has been developed.

TM technology is a method of calculating entropy according to the second law of thermodynamics by heating or cooling an element to be measured to give a temperature change, and measuring a change in open circuit voltage (OCV) accordingly. However, this requires a device for changing the external temperature of the electrochemical device, and requires several to tens of hours for thermal equilibrium and relaxation of the open circuit voltage. ETIS (Electro-thermal Impedance Spectroscopy) technology changes the current applied to the battery, measures the surface temperature accordingly, and extracts the entropy by calculating the amount of heat.

In addition, ETIS technology has the hassle of requiring EIS (Electrochemical Impedance Spectroscopy) measurement in advance in order to remove heat generated by resistance components and induce only heat of entropy when applying current to the battery. Also, it is necessary to measure the amount of heat from temperature. The disadvantage is that additional experiments are required to measure the heat transfer function to be used in the calculation process.

In order to solve the above-described problem, the present invention is a device capable of measuring the heat generation according to the current input, and extracting the entropy of the electrochemical element therefrom; And an entropy extraction method of an electrochemical device that extracts entropy through signal processing from measurement of the temperature (surface temperature or internal temperature), voltage, and current of the device to be measured.

In order to solve the above problems, the present invention is a method for extracting entropy of an electrochemical device, comprising: applying a current including a frequency component to the electrochemical device; Measuring heat or temperature change of the electrochemical device generated by the applied current; Separating a frequency component of the measured heat or temperature change, and specifying a frequency component that becomes one or two times the applied current; Dividing a heating component consisting of resistance heating and entropy heating from the specified frequency component and temperature change; And extracting the entropy of the electrochemical device through a combination of the ratio of the exothermic components and the absolute magnitude of the resistance heating.

In one embodiment of the present invention, the resistance heating of the heating component is calculated from the impedance and voltage or current of the electrochemical device.

In an embodiment of the present invention, the calculating of the entropy is performed in a manner of calculating an absolute value of entropy heating by using the calculated resistance heating value and ratio information of the derived heating components.

The present invention provides an apparatus for extracting entropy of an electrochemical device, comprising: a power supply unit for applying a current including a frequency component to the electrochemical device; A measurement unit for measuring voltage and current of the electrochemical device; A temperature measuring unit measuring the temperature of the electrochemical device; And a signal processing unit for extracting entropy from the voltage and current measured by the measuring unit and the temperature measured by the temperature measuring unit, wherein the signal processing unit includes resistance heating from voltage, current, and temperature information measured from the electrochemical device. The exothermic component consisting of and entropy heating is classified, and entropy is measured according to the combination of the ratio of the heating components and the absolute total size of the resistance heating.

In one embodiment of the present invention, the current has a frequency component, and the signal processing unit separates the resistance heating and entropy heating from a frequency component that becomes one or two times the applied current among the frequency components, and the resistance heating Is calculated from the impedance and voltage or current of the electrochemical device.

In one embodiment of the present invention, the temperature measuring unit includes a temperature measuring device that measures the temperature of the electrochemical element by attaching it to the surface of the electrochemical element, inserting it inside, or measuring the impedance.

When extracting the entropy of a lithium-ion battery, etc. using the heat-generating response according to the current input according to the present invention, the measurement time is faster than that of a system that extracts entropy from the existing battery, and in principle, it does not require external temperature change In addition, there is an advantage that it can be applied to batteries in which charging/discharging is ongoing. In addition, based on this, it can be applied to all fields in which the battery is used, and entropy information extracted in real time or non-real time from the battery can be used for analyzing the internal state of the battery, predicting the amount of heat generated by the battery, and managing safety.

1 is a step diagram of a method for extracting entropy of an electrochemical device according to an embodiment of the present invention.

2 is a block diagram of an extraction device for implementing an entropy extraction method according to the present invention.

FIG. 3 is a more detailed embodiment of the signal processing unit of FIG. 2, and schematically illustrates detailed steps of an operation in which an entropy value is derived from a corresponding part.

4 is a schematic diagram of each of the technical steps in a process of extracting entropy by applying the measuring device and the measuring method of the present invention to a battery.

5 is a measurement result obtained by extracting entropy for a lithium ion battery (pouch cell type) by the inventors of the present invention implementing an entropy extraction apparatus and method according to the present invention, and an ETM method widely recognized as a conventional standard measurement method. It is a figure compared with the measurement result by (this also carried out by the present inventors).

Hereinafter, a preferred embodiment of the present invention will be described in detail. In describing the present invention, when it is determined that a detailed description of a related known technology may obscure the subject matter of the present invention, a detailed description thereof will be omitted. Throughout the specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

The present invention is intended to illustrate specific embodiments and to be described in detail in the detailed description, since various transformations may be applied and various embodiments may be provided. However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all conversions, equivalents, and substitutes included in the spirit and scope of the present invention.

The terms used in the present invention are used only to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present invention, terms such as include or have are intended to designate the existence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features or It is to be understood that the presence or addition of numbers, steps, actions, components, parts, or combinations thereof does not preclude the possibility of preliminary exclusion.

In order to solve the above-described problem, the present invention is a method of extracting entropy of an electrochemical device (battery, fuel cell, supercapacitor, etc.), and in more detail, by measuring heat generation according to voltage or current input, the entropy of the electrochemical device is extracted therefrom. Provides a way to do it. More specifically, it provides a method of extracting entropy through signal processing from measurement of temperature, voltage, and current of an electrochemical device.

To this end, the present invention distinguishes the heating component consisting of resistance heating and entropy heating from the voltage, current, and temperature information measured from the electrochemical device, and calculates the entropy according to the ratio of the heating components and the combination of the absolute total size of the resistance heating. Extract.

Referring to FIG. 1, the method includes applying a current including a frequency component to an electrochemical device; Measuring heat or temperature change of the electrochemical device generated by the applied current in real time; Separating a frequency component of the measured heat or temperature change, and specifying a frequency component that becomes one or two times the applied current; Dividing a heating component consisting of resistance heating and entropy heating from the specified frequency component and temperature change; And extracting the entropy of the electrochemical device through a combination of the ratio of the exothermic components and the absolute magnitude of the resistance heating.

In addition, the present invention provides an extraction device for implementing the above-described entropy extraction method, which is shown in FIG. 2.

Referring to Figure 2, the entropy extraction apparatus according to an embodiment of the present invention includes a power supply for applying a current including a frequency component to the electrochemical device; A measurement unit for measuring voltage and current of the electrochemical device; A temperature measuring unit measuring the temperature of the electrochemical device; And a signal processing unit for extracting entropy from the voltage and current measured by the measurement unit and the temperature measured by the temperature measurement unit. In particular, the signal processing unit for extracting entropy according to the present invention distinguishes a heating component consisting of resistance heating and entropy heating from the voltage, current, and temperature information measured from the electrochemical device, and the ratio of the heating components and the resistance heating Entropy is measured according to the combination of the absolute total size of, which will be described in more detail below according to a specific embodiment of the present invention.

The extraction method according to an embodiment of the present invention includes: i) mounting a measuring device including a measuring device and a temperature measuring device measuring device to a device to be measured; (ii) applying an electrical signal to the device; (iii) measuring the voltage, current and temperature of the electrochemical device using the measuring equipment; (iv) separating the temperature components; (v) deriving the ratio of the reversible heat amount (entropy heat) and the irreversible heat amount (resistance heat); Calculating impedance; (vii) calculating irreversible calories; And (viii) extracting entropy.

In the present invention, entropy means "change of entropy per unit mole (ΔS, [J/(mol*K)])" as a chemical reaction occurs through charging/discharging. This is a value corresponding to "the amount of heat generated per unit mole * per temperature" of a reversible chemical reaction occurring inside an electrochemical device such as a battery. However, considering that the rate of chemical reaction (mol per hour, [mol/sec]) corresponds to "current /{Faraday constant (F) * ionic charge (Q)}" in the electrochemical device, " “Entropy” can also be interpreted as a physical quantity corresponding to “per unit current * reversible heating rate per temperature [W/(A*K)]”.

In the present invention, irreversible heat (Qi), resistance heat, or resistance heating is Joule heat corresponding to ^{I 2} R by DC resistance component (R) when current (I) flows through a battery or a general circuit. heat) is generated and this is called Qi. This means "Joule heat per unit mole [J/mol]" generated by internal resistance during charging/discharging of the battery. In addition, a number of resistance heating values may exist for one battery according to electrical/chemical/thermal conditions (SoC, temperature, voltage, etc.).

In the present invention, reversible heat (Qr), entropy heat, or entropy heat is ΔG from the definition of Gibbs energy (ΔG) in thermodynamics when an enthalpy change (Enthalpy, ΔH) occurs in an arbitrary chemical reaction. = ΔH-T ΔS is established, and at this time, the amount of heat corresponding to TΔS is defined as Qr. Qr is also the same unit as Qi, and means "change of heat per unit mole [J/mol]".

The sign of the entropy heating value may be a positive sign (+) or a negative sign (-), and if the sign has a negative sign, it means endothermic heat (external heat is absorbed by the battery; usually a temperature drop). In addition, a number of entropy heating values may exist for one battery according to electrical/chemical/thermal conditions (SoC, temperature, voltage, etc.).

In the present invention, a schematic experimental process for extracting entropy in real time is as shown in the following examples and FIGS. 2 and 3.

Hereinafter, an embodiment in which the present invention is applied to extracting entropy for a battery will be described in detail according to a method.

i) Mounting a measuring device including a measuring device and a temperature measuring device on the battery

It can measure voltage, current, and temperature in real time (or near-real time, requiring a sampling rate of several to tens of times per second or more), and for voltage and current, the appropriate range (approximately 5 volts for 18650 single cells). , 5 amps), and install it on the battery.

The present invention is a measurement method in which the response speed and precision of a temperature measuring device are important, and the temperature measuring device is attached to the surface of the battery, so that the heat of the battery can be transferred as quickly and without distortion as possible, and if necessary, a thermal compound, etc. The heat transfer medium of is used.

Alternatively, the temperature measuring device may be inserted into the battery, and through this, it is possible to achieve a more direct measurement of heat generated from components such as electrodes and electrolytes in the battery. Alternatively, a temperature measurement device is not implemented in the form of a separate element, and the temperature measurement is a method of measuring the temperature of the battery in real time (or semi-real time, sampling rate several to hundreds of times/second) by measuring the impedance value of the battery. A temperature measuring device to which the technology is applied may also be used. In other words. The temperature measuring device according to the invention is all within the scope of the invention, as long as it can at least measure the heat generated from the battery components.

As described above, a battery with a temperature measuring device can be placed in a temperature chamber maintained at a constant temperature and entropy can be extracted, and at room temperature without using a constant temperature chamber, or in use or not in use, charging/ Entropy can also be extracted when a battery is installed in an electric/electronic device that is being discharged.

(ii) applying current to the battery

Apply a sine wave current to a battery that is not in use or is being charged/discharged. When a sine wave current is applied to a battery during charging/discharging, it means that a sine wave current corresponding to the AC component is additionally given in a situation where a current bias equal to the amount of charging/discharging exists.

That is, as a function of time t, assuming the charging/discharging current as F(t), and expressing the sinusoidal current as A sin(wt + k), if a sinusoidal current is applied to the battery under charging/discharging, F It means that the current corresponding to (t) + A sin(wt + k) is applied.

Also, when a sinusoidal current is applied to a battery that is not in use, a current of A sin (wt + k) flows through the battery. The sine wave may be a pure sine wave, or a quasi-sine wave (Modified sine wave) may be used, and more generally, all current signals including frequency components are potentially used. And all of which are within the scope of the present invention.

As described above, when current flows through the battery, an electrochemical reaction occurs. The battery exhibits a specific voltage due to a combination of the characteristics of the electrochemical reaction itself or the internal resistance of the battery.

When the current changes over time in the form of a sine wave, in general, the voltage of the battery also has a property of changing over time (in a form similar to a sine wave). The current of the battery may cause an endothermic or exothermic reaction inside the battery. As a result, heat enters and exits, leading to a change in the temperature of the battery surface.

The voltage, current, and temperature of the battery are measured almost simultaneously with the process of applying a sinusoidal current to the battery to obtain data.

(iii) measuring the voltage, current and temperature of the battery using the measuring equipment

Measure voltage, current, and temperature for a battery to which sinusoidal current is applied. In this process, data is continuously acquired and information about the voltage, current, and temperature of the battery is obtained. In this process, the surface temperature or the internal temperature of the battery is measured and used as the temperature data value of the battery.

(iv) separating the temperature components

Inside the battery to which the sinusoidal current is applied, two types of heat in and out occur due to the influence of the current, Qr (reversible heat) and Qi (irreversible heat). Qi is the entry and exit of heat by the DC resistance of the battery, and Qr is the entry and exit of heat by the entropy change (TΔS) of the internal chemical reaction of the battery.

The amount of change in the battery temperature is determined as each temperature change component ΔTr and ΔTi resulting from the components of the two columns. It is expressed as the change in temperature ΔT = ΔTr + ΔTi, and the temperature component ΔTr by Qr and the temperature component ΔTi by Qi are added to form the temperature change ΔT.

The sinusoidal current has a characteristic that the direction changes with time, and the magnitudes of Qi and Qr also change with time (there is a frequency component). Assuming that the sinusoidal frequency is f, Qi has a frequency of f, and Qr has a frequency of 2*f. As a result, the frequency of the temperature component ΔTr is 2f, and the frequency of ΔTi is indicated as f.

When measured in an actual temperature measuring device, since the two temperature components are measured as ΔT = Δ Tr + ΔTi, the process of separating this through digital signal processing (DSP) follows. The measured temperature data is separated into a frequency f component and a frequency 2f component through a Fourier transform (FFT or DFT), an analog filter, or a digital filter.

( v) Deriving the ratio of the reversible heat amount (entropy heat) and the irreversible heat amount (resistance heat)

The amount of heat per hour generated by the battery can be expressed as dQ/dt = Q'. Two components of heat generation (Qi, Qr) can also be differentiated over time (t) and expressed as Qi' and Qr'.

If the heat transfer function from a closed system such as a battery to the outside of the system is G(f), there is a relationship of the surface temperature change ΔT = Q'/ G(f). A simple RC circuit approximation is possible by assuming that the heat capacity of the battery is C and the heat resistance to the outside is R, where G(f) is a function of frequency and 2*G(f) = G(2f) is established. . In other words, from ΔT = Q'/ G(f) ΔTr = Qr' / (2*G(f)), ΔTi = Qi' / G(f), ΔTi / ΔTr= 2*Qi'/ by dividing the two equations Qr'. Therefore, if the size ratio ΔTi / ΔTr of the two separated temperature components is calculated, the heat quantity ratio Qi'/Qr' can be estimated therefrom.

(vi) calculating impedance

In the present invention, it is necessary to extract the battery impedance in a situation in which the sinusoidal current of the battery is applied. For this, impedance is extracted from the measured voltage and current values.

In general, batteries have a non-linear response characteristic. When a sinusoidal current is applied to the battery, the resulting voltage across the battery may not be a pure sinusoidal wave. In addition, when a sine wave is applied while charging/discharging the battery itself, current and voltage include a DC bias component in addition to the sine wave component.

The voltage V(t) and current of the battery over time are I(t). In voltage and current, an AC component and a DC component are commonly mixed. Excluding the DC component, when the AC components of voltage and current are v(t) and i(t), respectively, it is calculated as impedance z(t) = v(t) / i(t).

(vii) calculating irreversible calories

From the impedance z(t) calculated as above, the heating value per hour = (i(t)^2) * Real(z(t)) can be calculated using the fact that the heating value of the resistance is determined by the real component of the impedance. have.

It can be assumed that z(t) is almost constant over a relatively long period of time (tens of periods of a sine wave). That is, z(t) is constant over a fairly wide range of t. Since i(t) is a sinusoidal wave, it is generally expressed as i(t) = A * sin(w*t + k).

Calorific value per hour = d Qi / dt = Qi'

=A^2 * (sin(w*t + k) )^2 * Real(z(t))

= Real(z(t)) * (1/2) * A^2 * (1-cos( 2*w*t + 2*k ))

As a result, it has a 2*f frequency. However, since the component measured by the actual temperature measuring device in "Correction per Hour" is an AC component, the remaining AC components excluding the DC component are Qi' = Real(z(t)) * (-1/2) * A^2 * cos (2wt + 2k).

Therefore, when setting the current applied to the battery as i(t) = A * sin(w*t + k), the theoretically calculated Qi' = Real(z(t)) * (-1/2) * A It is estimated as ^2 * cos(2wt + 2k).

(vii) extracting entropy

As above, when setting the current applied to the battery as i(t) = A * sin(w*t + k), Qi' = Real(z(t)) * (-1/2) * A^2 * It was estimated as cos(2wt + 2k).

In addition, in step 5, the heat quantity ratio Qi'/Qr' can be derived from the temperature ratio ΔTi / ΔTr. The specific process is as follows.

Entropy change per unit mole of battery internal chemical reaction = ΔS, and entropy change of electron 1C = ΔS / F (where F is Faraday's constant, ~ 96485 coulomb)

From the second law of thermodynamics, the "reversible heat amount" leaving the system is calculated as Qr = T* ΔS, so at a specific temperature T, the "reversible heat amount" by electron 1C = T*Δ S/F, where the current is the amount of charge per hour. it means.

Thus, reversible heat per hour at a specific temperature T = I*T*ΔS/F = dQr/dt = Qr'. In this way, the relationship between Qr' and entropy can be obtained.

Reversible heat per hour at temperature T = I*T*ΔS/F = dQr/dt = Qr'. If you set the current as i(t) = A * sin(w*t + k)

Qr' = A*sin(w*t +k) *T *ΔS/F

Qi' = eal(z(t)) * (-1/2) * A^2 * cos(2wt + 2k)

Since there is a relationship of the ratio of heat quantity Qi'/Qr' = ΔTi / ΔTr = 2*Qi'/Qr', in the situation where i(t) = A * sin(w*t + k) current is input to the battery, Δ If you measure Ti / ΔTr and know the value for impedance z(t), temperature T,

ΔTi / ΔTr = 2*Qi'/Qr' = 2*(Real(z(t)) * (-1/2) * A^2 * cos(2wt + 2k)) / (A*sin(w*t +k) *T *ΔS/F) and

From this, the entropy ΔS value is extracted as ΔS = (-A*F/T) * (ΔTi / ΔTr) * (Real(z(t))*cos(2wt+2k)/sin(wt+k)) can do.

FIG. 3 is a more detailed embodiment of the signal processing unit of FIG. 2, illustrating detailed steps of an operation for deriving an entropy value according to the above-described method, and in FIG. 4, a measuring apparatus and a measuring method of the present invention are applied to a battery. Thus, each of the technical steps in the process of extracting entropy is schematically illustrated.

5 is a measurement result obtained by extracting entropy for a lithium ion battery (pouch cell type) by the inventors of the present invention implementing an entropy extraction apparatus and method according to the present invention, and an ETM method widely recognized as a conventional standard measurement method. It is a diagram compared with the measurement result by (this is also carried out by the present inventors).

Referring to FIG. 5, when entropy is extracted according to the method and apparatus according to FIGS. 1 to 4, the same entropy extraction value can be obtained without measuring a separate heat transfer function as compared to the prior art that required the conventional EIS measurement. You can see what you can do.

As described above, specific parts of the present invention have been described in detail, and it is clear that these specific techniques are only preferred embodiments for those of ordinary skill in the art, and the scope of the present invention is not limited thereby. something to do. Accordingly, it will be said that the substantial scope of the present invention is defined by the appended claims and their equivalents.

The present invention has the advantage that the measurement time is faster than that of a system that extracts entropy from an existing battery, does not require external temperature change in principle, and can be applied to a battery in which charging/discharging is in progress. Can be applied to

Claims

As a method of extracting entropy of an electrochemical device,

Applying a current including a frequency component to the electrochemical device;

Measuring heat or temperature change of the electrochemical device generated by the applied current;

Separating a frequency component of the measured heat or temperature change, and specifying a frequency component that becomes one or two times the applied current;

Dividing a heating component consisting of resistance heating and entropy heating from the specified frequency component and temperature change;

And extracting the entropy of the electrochemical device through a combination of the ratio of the exothermic components and the absolute magnitude of the resistance heating.
The method of claim 1,

The resistive heating of the heating component is calculated from the impedance and voltage or current of the electrochemical device.
The method of claim 1,

The calculating of the entropy is performed in a manner of calculating an absolute value of entropy heating by using the calculated resistance heating value and the ratio information of the derived heating components.
As an entropy extraction device of an electrochemical device,

A power supply unit for applying a current including a frequency component to the electrochemical device;

A measurement unit for measuring voltage and current of the electrochemical device;

A temperature measuring unit measuring the temperature of the electrochemical device;

A signal processing unit for extracting entropy from the voltage and current measured by the measurement unit and the temperature measured by the temperature measurement unit,

The signal processing unit classifies a heating component composed of resistance heating and entropy heating from the voltage, current, and temperature information measured from the electrochemical device, and calculates entropy according to a combination of the ratio of the heating components and the absolute total size of the resistance heating. An apparatus for extracting entropy of an electrochemical device, characterized in that to measure.
The method of claim 4,

Entropy extraction device of an electrochemical device, characterized in that the current has a frequency component.
The method of claim 5,

The signal processing unit separates the resistance heating and entropy heating from a frequency component that becomes one or two times the applied current among the frequency components,

The resistive heating is an apparatus for extracting entropy of an electrochemical device, characterized in that calculated from impedance and voltage or current of the electrochemical device.
The method of claim 5,

The temperature measuring unit includes a temperature measuring device for measuring the temperature of the electrochemical element by attaching to the surface of the electrochemical element, inserting it inside, or measuring the impedance of the electrochemical element.