Batteries are now essential components of our daily lives, whether it is in mobile phones, in portable computers, for starting the car engine or for powering the satellite that sends radio communication signals down to earth [1-3]. Further, electric vehicles (EVs) including hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs) and pure battery electric vehicles (BEVs) are predicted to dominate the vehicle market [4].
However, understanding and predicting the behaviour of the internal degradation mechanisms (e.g. double layer capacitance and solid electrolyte interface formation) responsible for the ageing of the batteries throughout their lifetime is of utmost importance [5-7]. In the literature, impedance measurement is recognised as an effective non-destructive technique [8, 9] which can be used for the investigation of these mechanisms in combination with electrochemical characterisation and modelling [10, 11].
For this purpose, electrochemical impedance spectroscopy (EIS) technique is used in this research for the analysis of the impedance spectra of LiNi0.4Mn0.4Co0.2O2 batteries and their electrodes with ageing. In this aim, accelerated ageing was performed on battery cells by cycling them at 1C (20A) charge and 1C (20A) discharge current rates, under high temperatures (35°C and 45°C). The impedance spectra at 20%, 50% and 80% State of Charge (SoC) of a full cell and its anode and cathode at the beginning of life (prior to the cycling) are shown in Figs. 1 and 2. In comparison to this, Fig. 2 emphasises the changes in the impedance curves of a cell cycled at 35°C already after 100 and 200 cycles.
In this work, the explanation of the evolution of the impedance spectra observed at different milestones of the ageing (up to 800 full cycles) is achieved through modelling. Therefore, both electrochemical as well as equivalent circuit impedance modelling methods are carried out in parallel. From the evolution of both models parameters sets, the ageing mechanisms reflected by the change in the impedance spectra of the cell and its electrodes are identified and will be presented. Moreover, from the comparison of both parameters sets, a useful correlation between the physical meaning of the equivalent circuit components and the electrochemical parameters was derived and will be also presented.
Original languageEnglish
Publication statusPublished - 2016
Event6th Baltic Electrochemistry Conference - Electrochemistry of Functional Interfaces and Materials - Helsinki, Finland
Duration: 15 Jun 201617 Jun 2016

Conference

Conference6th Baltic Electrochemistry Conference - Electrochemistry of Functional Interfaces and Materials
CountryFinland
CityHelsinki
Period15/06/1617/06/16

ID: 22126710