Electrochemical Stability of PEDOT:PSS As Cathodic Binder for Li-Ion Batteries

Cathodes in Li-ion batteries are composites and consist of redox active compounds such as metal oxides (LiCoO₂, LiMn₂O₄, LiNi_xMn_yCo_zO₂) or metal phosphates (LiFePO₄), and electrochemically inactive components with different functionalities. Organic polymers such as polyvinylidene difluoride (PVDF) are used as binder that forms a supporting matrix for the active material particles (1, 2). The properties of the binder significantly influence the electronic/ionic conductivity and the mechanical properties of the electrodes and the battery behavior (3). Since the commonly used binders are electrically insulating, additives such as carbon black and carbon nanotubes are added to the electrodes. However, the addition of redox inactive compounds reduces the total electrode capacity and has a crucial influence on the battery performance and stability.

          In our recent work we proposed a new electrode concept for LiFePO₄ cathodes, where poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) plays a dual role of binder and conducting additive (4). The new composite cathodes were prepared free of any other conductive additives such as carbon black or carbon nanotubes. The results show that an increasing PEDOT:PSS content leads to a decrease in the overvoltage and correspondingly to an improvement in the rate capability of resulting electrodes.

          In this contribution we report the electrochemical behavior of PEDOT:PSS casted on an Al current collector in an aprotic Li-containing electrolyte in the potential range 2.5 to 4.2 V. In addition, the influence of the temperature on the electrochemical performance of the polymer was examined in the temperature range 10 °C to 50 °C by cyclic voltammetry and electrochemical impedance spectroscopy. The obtained results show, that the polymer is electrochemically inactive in the applied potential window and remains in the oxidized conductive state. The polymer film shows high electrochemical stability and only slight changes in the impedance are visible during multiple cycling.

Reference

1. I. Krylova, Prog. Org. Coat., 42, 119 (2001).

2. S. Babinec, H. Tang, A. Talik, S. Hughes, G. Meyers, J. Power Sources, 174, 508 (2007).

3. B. Lestriez, C. R. Chim, 13, 1341 (2010).

4. P. R. Das, L. Komsiyska, O. Osters, G. Wittstock, J. Electrochem. Soc 162 (4) 674 (2015).