ИСТИНА

DRT conversion is a relatively new method of analysis of electrochemical impedance data based on the representation of the investigated system in the form of a distribution of serially connected RC (resistor and capacitor) elements. The main advantage of the method is that the parameters of such elements need not be specified beforehand and are determined directly in the process of impedance analysis. Thus, the method does not require a-priori introduction of equivalent circuits, which is an undeniable advantage. The method is quite powerful as it is able to separate a large number of components of the impedance spectrum. The number of these components also need not be introduced beforehand and is determined directly in the process of the DRT analysis. As a result, the DRT method is becoming a widely accepted tool for the impedance analysis of electrochemical systems including lithium electrochemical systems. In this work, we have verified the correctness of the DRT conversion method and validated this method in relation to real lithium-ion battery systems. The properties of the electrochemical systems such as composition, exposure, degree of charge/discharge of battery were varied and the parameters of the DRT transformation were determined. In particular, we chose electrodes that were based on lithium ferrophosphate but employed the binders that radically differed in their properties (PEDOT:PSS and PVDF), Also the effects of conductive additives such as single-walled carbon nanotubes and electrode treatment with heat or pressure up to 5 MPa were analyzed. As a result, we were able to fully match the peaks of the resulting distribution with the processes occurring in the cell. Moreover, based on this analysis, we were able to detect some features that were not previously described in the literature. For example, we found that the impedance of highly conductive electrodes is determined by the additive rather than the nature of the binder used. This is really an unexpected finding that could allow researchers to expand the range of binders used in lithium-ion battery systems as well as focus their attention on their other characteristics such as adhesion to the current collector, flexibility, extensibility, etc. It has also been shown that pressing the electrode reduces only the resistance related to the binder but does not affect the capacity of the active material in the electrode and the transport of lithium ions in it.