There is much ongoing discussion aimed at improving the performance of next-generation lithium-ion batteries for further use in such things as electric vehicles or smart grids. In aiming for such uses, there is a need to establish a method for evaluating the establishment of safety, reliability, battery life in order to deal with such issues as rumors about problems with the secondary uses of electric batteries. The alternating current impedance method is gaining popularity as a non-damaging method that makes it possible to trace chronological changes in samples and which has the special characteristic of being able to separately measure fundamental processes using frequency responses. On the other hand, one problem with applying this method to currently marketed LIBs is the countless resulting response processes such as electrolyte resistance, current collector electrical resistance, interface reactions between the batteries north and south poles, and ion diffusion within the battery solution. The alternating current impedance method conjugates all of this data and makes analysis complex. As the actual batteries aim to increase output by lowering impedance as much as possible, this method has also faced the problem that the results interpretation is difficult because of the many reactions seen all at once.

This technology aims to establish a “usable” battery evaluation method for currently marketed LIBs using impedance analysis. While thinking about the structural aspects of the battery leading to such issues as electrolyte resistance, interface reactions between the batteries north and south poles, surface films, and ion diffusion within film and solid states, the project considers the minimum possible factors for degradation, installs an analogous circuit usable for the analysis of a wide range of frequency bands, and analyzes LIB capacity degradation based on the resulting impedance reactions. In addition, by carrying out impedance analysis under low temperature conditions, it is thought possible to conduct a correct analysis by using processes not admissible within a normal temperature range.

Currently marketed LIBs are constructed from a variety of materials through the efforts of each company. It is possible to use this analysis method for each type of LIB and to select the frequency at which analysis is run. As such, it is possible to monitor changes in the situation of LIB degradation within electric vehicles and smart grids without damaging the LIBs.

This research makes it possible to separately analyze electrochemical reaction impedance at levels not normally possible in commercial LIBs as well as different levels of solid electrolyte interfaces (SEIs), which are believed to exist at the interface between magnetic poles and electrolytes. This makes the method superior for commercial LIB degradation analysis.

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