(286d) The Role of Polymer Composite Binder on Mechanics and Performance of Lithium Ion Battery Electrodes

Battery electrodes are complex multiphase composites which must provide efficient bicontinuous networks for transport of electrons (through the particle phase) and positive lithium ions (through the electrolyte filled pores of the electrode). A crucial but often neglected element of battery electrodes is the binder, typically a mixture of polyvinylidene fluoride (PVDF) and carbon black.  The binder has two primary roles – to provide mechanical integrity and to improve electrical conduction of the electrodes.  Migration of the binder has also been implicated as a potential mechanism of capacity fade in rechargeable lithium ion batteries.

We will present experimental characterization of the polymer binder for battery applications.  Mechanical properties of the composite binder will be shown for both dry films and also binder swollen with carbonate electrolytes used in rechargeable batteries.  Additionally we will examine the impact of mechanical stresses on the retention electrolyte and also the electrical conductivity.

Mesoscale simulations will be presented using experimentally determined three dimensional structures of battery cathodes.  As batteries charge and discharge, the particles within the electrodes expand and contract as lithium is transferred into and out of the active material.  The role of complex particle geometry and polymer binder properties on peak mechanical stresses due to particle swelling during cycling will be examined.  Implications for battery performance and cycling stability will be discussed.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.