Effect of solid loading on the processing and behavior of PEDOT:PSS binder based composite cathodes for lithium ion batteries

• PEDOT:PSS is used as binder in carbon black free cathodes for Li-ion batteries.
• Rheology and coating behavior of binder/active material slurries has been studied.
• Agglomerate distribution in the electrode changes with solid loading of the slurry.
• Physical properties and battery behavior depends on solid loading of the slurry.

Rheological measurements were used to study the flow behavior of composite slurries consisting of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) polyelectrolyte complex as binder and LiFePO4 as a model active material for the preparation of positive electrodes for lithium ion batteries. Various aqueous slurries containing 92% LiFePO4 and 8% PEDOT:PSS with different solid loadings were prepared. All slurries showed solid-like behavior due to formation of a network structure of LiFePO4 bridged by PEDOT:PSS chains. However, the solid loading of the slurries influences the distribution of the agglomerates and the binder affecting also the thickness, the adhesion and the electrical conductivity of the coatings casted from the different slurries under the same conditions. Hence, the electrochemical performance of single cells prepared with these coating changed with the solid loading of the slurry. The optimum electrochemical performance is achieved with slurries containing 40% solid loading.