DCIR, ACIR, EIS

https://www.linkedin.com/pulse/what-dcir-acir-eis-meaning-all-three-whats-difference-connection/

LIB(lithium-ion batteries)의 R(저항, resistance)을 테스트하기 위해, DCIR, ACIR 및 EIS의 세 가지 방법을 사용합니다.
그렇다면 이 세 가지 방법의 테스트 원리는 무엇일까요?
물리적 의미는 무엇일까요?
세 가지 방법의 차이점은 무엇인가요?
어떤 연관성이 있나요?

이 세 가지 충전방법의 차이점을 이해하려면, 먼저 “전류 저항”을 설명하는 다양한 “단어”를 파악해야합니다.

1.    저항이란?  (What is resistance?)

The resistance does not necessarily refer to the resistance device but describes the obstruction of a device or material to the current flowing through it. Its essence is to irreversibly convert electrical energy into other forms of energy. Resistance is a special case when the impedance is 0 in the reactance part.2.    

저항은 반드시 “저항 장치”를 지칭하는 것이 아니라, 장치나 물질이 흐르는 전류를 방해하는 것을 말합니다.
저항의 본질은 전기 에너지를 다른 형태의 에너지로 비가역적으로 변환하는 것입니다.
저항은 reactance(리액턴스) 부분에서 impedance(임피던스)가 0인 특별한 경우입니다.

2. What is Impedance?

임피던스는 회로 (또는 장치)를 설명하는 기본 개념입니다.
특정 전압의 경우 전류는 다음과 같습니다. 임피던스는 순간 전압을 전류로 나눈 값으로 정의됩니다.
Impedance includes resistance, tolerance and sensibility. 임피던스에는 저항, 허용 오차 및 감도가 포함됩니다.
저항의 본질은 전기 에너지의 소실입니다.
정전 용량의 본질은 전기 에너지를 공간 또는 유전체에 전기장의 형태로 저장하는 것이며,
유도 용량의 본질은 전기 에너지를 공간 또는 자기 유전체에 자기장의 형태로 저장하는 것입니다.
용량성 에너지와 유도성 에너지 모두 전기 에너지를 저항처럼 열 에너지 소비로 전환하는 대신,
다른 시간에 방출할 수 있는 저장된 전기 에너지입니다.
그러나 커패시턴스와 인덕턴스는 회로의 특정 순간에 전압-전류 비율에 큰 영향을 미칩니다. 따라서 임피던스는 저항, 허용 오차, 감도를 결합한 합성 파라미터로 정의되며, 임피던스의 식은 다음과 같이 복잡합니다:
Z= R+ jX
복소수의 실수 부분은 소산된 전기 에너지의 저항을 나타내고,
허수 부분은 저장된 전기 에너지의 리액턴스를 나타냅니다.
저항은 신호 진폭의 감쇠를 나타내고, 리액턴스는 신호 위상의 변화를 나타냅니다.
reactance (capacitance, inductance) 리액턴스 (커패시턴스, 인덕턴스)는 가역적 전기 자기장의 에너지 형태를 변환하는 것이며 전자기장 이론에 따르면이 변환 과정은 신호에 반영되는 전기 또는 자기장의 변화율과 관련이 있기 때문에 신호의 주파수는 신호의 주파수입니다.
즉, 임피던스의 리액턴스 부분은 주파수와 관련이 있습니다.
다음은 저항 부분, 커패시턴스 부분, 인덕턴스 부분의 임피던스 표현입니다:
ZR=R ZL=jwL ZC=1/(jwC)

3. What kinds of “words” describe current resistance in the battery?

4.  What is the ohm resistance, interface impedance, charge transfer impedance and diffusion impedance of the battery?

The ohm resistance should be called ohmic resistance, because the ohmic resistance only contains the resistance part and does not take into account tolerance and sensibility. Ohm internal resistance is mainly divided into three parts, one is ion resistance, the other is electronic resistance, and the third is contact resistance. Ion resistance: The resistance to the transmission of lithium ions inside the battery is mainly affected by positive and negative electrode materials, diaphragms and electrolytes. Electron resistance: the resistance to electron transmission. It is mainly affected by the contact between the active substance and the collecting fluid, the active substance itself, the plate parameters, and the collecting fluid substrate. Contact resistance: The contact resistance is mainly formed by the contact between the particles of the active substance and between the active substance and the collector. The contact resistance is mainly affected by the adhesion of the positive and negative slurry.Interface impedance: the resistance of Li ions through the SEI membrane.Charge transfer impedance: It is reflected in the adsorption ability of the interface to ions and the ability of charge transfer to cause ions to undergo electrochemical reactions on the interfaceDiffusion impedance: resistance to the diffusion of Li ions in active substances and electrolytes.

5. What is ohm polarization, electrochemical polarization and concentration polarization of batteries?

In the case of external current passing through, because the ohm resistance causes local charges to accumulate, so that the current is greater than the resistance provided by the ohmic resistance (R ohm). This phenomenon is called ohm polarization, ohm polarization internal resistance = (R test ohm) – (R ohm). Electrochemical polarization and concentration polarization are also the same. For a more specific explanation, please refer to the article (lithium electricity – why is it difficult for lithium-ion batteries to charge at low temperatures? Why does a lithium-ion battery have an irreversible capacity loss after cycling at low temperature?) The above definition of internal resistance of the battery is people’s simplified description of lithium-ion batteries. In fact, the battery is a com‐ plex electrochemical system. The total impedance of this process can be abstracted into three electrical components, namely:

• Internal resistance RΩ: internal resistance of electrolyte and electrode. Double-layer capacitor Cdl: derived from the inactive ions in the electrolyte, no chemical reaction occurs, only the charge distribution is changed. Faraday impedance Zf: derived from the active ions in the electrolyte, with redox re‐ actions and charge transfer.
Charge transfer and mass transfer These two processes can be abstracted as: charge transfer resistance (Rct) and War‐ burg impedance (ZW) respectively.Therefore, every particle that undergoes an electrochemical reaction can be represented by the following circuit diagram:Then, the ideal state model of the entire lithium-ion battery is shown in the following figure: (In the ideal state, there is no side reaction, only the de-embedding and embedding of Li particles)After understanding the meaning of various “words” and the ideal model of lithium-ion batteries, let’s analyze DCIR, ACIR, EIS.I.  What is DCIR?DCIR (Direct Current Internal Resistance) DC internal resistance test.



Picture credits- HIOKI

The measured DC internal resistance includes all the resistance in the battery: {Ohm internal resistance, interface impedance, charge transfer impedance, diffusion impedance} and {Ohm polarization internal resistance, electrochemical polarization internal resistance and concentration polarization internal resistance}. Because there is a significant change in the spatial position of Li ions during the test, it is called dynamic resistance. DCIR is to use a specific magnification current (I) to charge and discharge for a certain period of time (t), to record the battery voltage (U1) before charge and discharge and the voltage after charge and discharge (U2), including: R=（U2-U1）/I We believe that the value of the DC internal resistance test is the impedance shown by the lithium-ion battery in the working process.The purpose of testing the DC resistance is to obtain the impedance of the battery in actual working conditions.II.                What is ACIR?ACIR (Alternating Current Internal Resistance) AC internal resistance test.



The reason why alternating current is used to test the resistance of the battery is that we want to eliminate the impact of polarization and directly measure the resistance of the properties of the substance to the current.When using alternating current, f=1/TWhen the frequency is large enough, the period of the current is smaller. In a short period of time, the Li ion has no time to move for a long distance but moves back and forth from the original position.



Therefore, when the frequency is large enough, it is assumed that:1. The charge does not move, so there will be no accumulation of charge, and the charge distribution does not change, so it is believed that there will be no polarization. 2. Similarly, because the charge distribution does not change, the capacitance will not change. 3. The position of the Li ion has not changed, so there will be no diffusion behavior, so there is no diffusion impedance in the circuit.III. What is EIS?



Electrochemical Impedance Spectrum (EIS): is a non-destructive parameter determination and effective battery kinetic behavior measurement method. A sine wave voltage signal with a frequency of w1 and a small amplitude is ap‐ plied to the battery system, and the system generates a sine wave current response with a frequency of w2. The ratio between the excitation voltage and the response current is the impedance spectrum of the electrochemical system.It can be found that ACIR and EIS are tested in the same way, using AC pow‐er for testing. However, ACIR is only tested at a certain frequency, while EIS is tested at a frequency range. The two purposes are different. The purpose of ACIR is to test the ohmic resistance of the battery, so what is the purpose of EIS? The EIS includes Nyquist diagram and Bode diagram. The common Nyquist diagram in the battery is as follows:For the above Nyquist diagram, we may ask why it is divided by frequency. What is the meaning of each division? For the ultra-high frequency part, f=100K Hz, the period of alternating cur‐ rent is particularly small, which can be understood that the Li ions vibrate in situ and generate inductance. The intersection of the curve and the horizontal coordinates is R ohm, which is considered to be the ohm resistance of the battery. For the high-frequency part, due to the limitation of the alternating current cycle, the moving distance of Li ions is limited, and it can only move for a very small period of time. At this time, we will discuss the Li ions in different positions separately:1. The Li ions in the electrolyte, in this small moving position, are subjected to little resistance; 2. The Li ions in the positive and negative materials may not have been separated from the original lattice site in this small moving position, so the resistance is also very small; 3. The Li ion located at the interface; the moving distance is just the part of the inter‐ face. The Li ion is constantly entering and exiting,and is subjected to greater resistance.



To sum up, in the high-frequency part, Li ions are resisted from all aspects. But among them, the contribution of the interface is the largest, so we think that high frequency represents the interface impedance. For the intermediate frequency part, the cycle of the alternating current is enough to support the Li ion to move for a distance. So, the Li ions in the electrolyte have moved away. Who will fill the gap? Of course, it is the Li ions in the active material, but if the Li ions in the active material want to be de-embedded, an electrochemical reaction is required, so it is believed that the charge transfer impedance contribution is very large at this time, so the intermediate frequency is assigned to the charge transfer impedance. For the low-frequency part, f=0.01 Hz, the Li ion at this time has enough time to enter and exit the interface, and can also complete the electro chemical process. Then the fully assembled Li ions are already on the way to diffusion. At this time, the Li ions are subjected to more impedance from diffusion, so the low-frequency part is used to characterize the diffusion impedance. In summary, EIS is tested using alternating current within a certain frequency range. Through the different degrees of response of different components to different frequency currents, each part of the circuit is split, and then artificially stipulates that each segment corresponds to a certain component. Infact, in the EIS test, the overall circuit participates in each frequency, and each component contributes. Therefore, the purpose of EIS is to amplify the performance of specific components through different frequencies, so as to make a general division and achieve specific analysis of a certain component.About Semco – Established in 2006, Semco Infratech has secured itself as the number 1 lithium-ion battery assembling and testing solutions provider in the country. Settled in New Delhi, Semco gives turnkey solutions for lithium-ion battery assembling and precision testing with an emphasis on Research and development to foster imaginative, future-proof products for end users.