  We present a coupled continuum formulation for the electrostatic, chemical,
thermal and mechanical processes in battery materials. Our treatment applies on
the macroscopic scale, at which electrodes can be modelled as porous materials
made up of active particles held together by binders and perfused by the
electrolyte. Starting with the description common to the field, in terms of
reaction-transport partial differential equations for ions, variants of the
classical Poisson equation for electrostatics, and the heat equation, we add
mechanics to the problem. Our main contribution is to model the evolution of
porosity as a consequence of strains induced by intercalation, thermal
expansion and mechanical stresses. Recognizing the potential for large local
deformations, we have settled on the finite strain framework. We present a
detailed computational study of the influence of the dynamically evolving
porosity, upon ion distribution, electrostatic potential fields,
charge-discharge cycles and mechanical force generated in the cell.
