A pore-structured Si alloy anode using an unzipping polymer for a lithium ion battery

Abstract

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. Schematic diagram of the porous electrode fabrication process using polymethyl methacrylate (PMMA) and the electrochemical test results obtained from the 3-dimensional structures.