 Polymethyl methacrylate (PMMA), which has the thermal property of unzipping, was used as a pore-forming agent during electrode fabrication to solve the chronic volume expansion problem in silicon (Si) anodes for lithium ion batteries (LIBs). PMMA-treated Si alloy electrodes have low volume expansion resulting in low deformation during lithiation. To maximize the effect of a porous structure, the pore diameter in the electrode was controlled. The best cycling stability was obtained when using 10 μm diameter PMMA. After 100 cycles at the 0.5-C rate a bare electrode retained 39% capacity, whereas an electrode using 10 μm diameter PMMA retained 62%. The outstanding capacity retention obtained from porous electrodes originated from the optimized porous architecture. Furthermore, PMMA-treated electrodes provide the lowest resistance in a cell by facilitating fast electron and ion transport, enhancing battery performance. Hence, for cycle-guaranteed Si-based LIBs these porous electrodes could provide an alternative or supplementary structure to other more complex manufacturing processes.