The EIS testing method has a long history and many studies have been published attempting to apply it to the estimation of battery capacity.

1.  It dates back to the work of Oliver Heaviside and Emil Warburg at the end of the 19th century.
   

2.  Potentiostats were invented in the 1940s.
   

3. A Frequency Response Analyzer (FRA), which appeared in the 1970s, made impedance measurement in the high frequency range relatively easy and accelerated the use of the impedance concept in electrochemistry.
   

4.   The EIS test method has long been known for its use in the analysis of metal corrosion reaction mechanisms. The non-destructive diagnosis of coating degradation in steel bridges and electrical equipment (ISO 16773-1-4) is one example.
   

5.  In recent years, applications to rechargeable batteries have been attempted, and electrochemical researchers, mainly academics, are working on this.
   

6. The specific test method is to apply AC to the Device Under Test(DUT), measure the impedance characteristics from the response signal, estimate the equivalent circuit and analyze it.
   

7.  There are many variations in analysis methods etc.
   

8.  Challenges have been identified, such as the need for a theoretical impedance function reaction mechanism library to determine the degree of degradation, and the fact that the electrical equivalent circuit (EEC) is not a model and the available information is limited, etc. 

* Although Dr, Takagi, our co-founder, is a private edition translator of “Electrochemical Systems 3rd edition” written by John Newman, he proved that as far as business applications of battery degradation diagnosis technology, based on electrical engineering and mathematical knowledge are better suited.