Battery electrode microstructure strongly affects the mixed ionic / electronic conduction in electrodes that is necessary to achieve rapid charging / discharging, especially in very thick electrodes. Thick electrodes having low porosity will not provide access of the full electrode structure to electrolyte ions, which will limit the effective capacity at high rates. One strategy for combating this limitation is to incorporate macroscopic pores into the electrode. Electrolyte-filled macropores provide an electrolyte reservoir that can provide ions needed for rapid charging / discharging of a thick electrode, due to the shorter overall distance that ions have to travel during charge / discharge. This talk will present recent work on the use of freeze tape casting with water-based electrode slurries to create thick electrodes having large macroscopic through-pores that run perpendicular to the electrode plane. Electrodes having similar mass loading can be charged / discharged more rapidly when these macropores are present, compared with electrodes that do not have macropores. Implications of the work for fabrication of very thick electrodes capable of rapid charging / discharging will be discussed.