For engineering applications like electric vehicles, reducing the mass and volume of the incorporated batteries improves the overall performance. To this end, the concept of a structural battery combines load bearing and battery functionality in a single composite material. One such material is based on multi-functional properties of carbon fibers [1]. In the positive electrode, the active material is incorporated in a coating on these fibers. This coating has a similar structure as porous electrodes in conventional Li-ion batteries: Li storing particles are embedded in a porous binder matrix saturated with a liquid electrolyte. Our aim is to develop a multi-scale-model describing the electro-chemo-mechanical coupling mechanisms in this type of microstructure. As an intermediate step, we focus on creating a framework to capture the processes at the interfaces between the different phases. On the fine-scale, the considered primary fields are the mechanical displacement, chemical potential and electric potential. The model is based on small strain kinematics, linear-elastic quasi-static deformation, linear diffusion, electro-statics and linear couplings between the electro-chemical and mechanical processes. Nonlinear constitutive relations are considered for the chemical potential inside the bulk material and the reaction kinetics at the particle-electrolyte interface. A two-scale procedure is developed based on the concept of variationally consistent homogenization. On the sub-scale, we consider a Representative Volume Element (RVE) with a resolved three phase microstructure. A dual potential approach (cf. [2]) is employed to derive an effective macro-scale model which can capture effects resulting from the jump in electro-chemical potential at the particle-electrolyte interface. Together with the RVE problem, a FE² procedure can be used for simulations and to gain understanding of the system behavior. [1] D. Carlstedt, K. Runesson, F. Larsson, V. Tu, R. J¨ anicke, L.E. Asp, Computational modelling of structural batteries accounting for stress-assisted convection in the electrolyte, Int J Solids Struct, 238, 111343, 2021. [2] D. Rollin, F. Larsson, K. Runesson, R. J¨ anicke, Variationally consistent homogenization of diffusion in particle composites with material interfaces using dual macroscale chemical potentials, Comput Mech, 76, 409-427, 2025.