Numerical simulations based on phase-field methods render comprehensive insights into the complex phenomena during the evolution of microstructures. Microscopic solid-state phase transitions are highly affected by chemical as well as by mechanical driving forces and therefore the accurate calculation of chemo-mechanical configurational forces in the transition region is essential. In this work, we present a thermodynamically consistent multiphase-field model for chemo-mechanically driven phase transformation processes. A mechanical model based on the mechanical jump conditions on singular surfaces is coupled with a thermodynamically consistent multiphase-field approach for diffusive phase transformation processes. The approach employs a diffuse interface formalism accounting for curvature effects and recovering the sharp interface solutions. As applications, we discuss a nano-particle battery model starting from intercalation in a defect-free, single-crystalline platelet. We show how faster in-plane diffusion promotes phase separation while higher C-rates and coherency strain lead to the opposite effect. This work highlights the importance to consider pre-existing grain boundaries for nucleation at higher-order junctions, heterogeneity of the intercalation fluxes and grain-by-grain filling behaviour. Anisotropic elastic deformation leads to high stresses at the evolving phase boundaries, especially at high misorientations between neighbouring grains. Coupled with quantitative modeling of crack propagation, we will describe degradation by fracture in polycrystals in future works.