Reversible electrodeposition of metals at liquid-solid interfaces is a requirement for long cycle life in rechargeable batteries that utilize metals as anodes. The process has been studied extensively from the perspective of the electrochemical transformations that impact reversibility, however the fundamental challenges associated with maintaining morphological control when a intrinsically crystalline solid metal phase emerges from an electrolyte solution have been less studied, but provide important opportunities for progress. Here we propose a crystal growth stabilization method to reshape the initial growth and orientation of crystalline metal electrodeposits. The method takes advantage of polymer-salt complexes (PEG-Zn2+-aX-) (a=1,2,3) formed spontaneously in aqueous electrolytes containing zinc (Zn2+) and halide (X-) ions to regulate electro-crystallization of Zn. It is shown that when X = I, the complexes facilitate electrodeposition of Zn in a hexagonal closest packed (HCP) morphology with preferential orientation of the (002) plane parallel to the electrode surface. This facilitates exceptional morphological control of Zn electrodeposition at planar substrates and leads to high anode reversibility and unprecedented cycle life. Preliminary studies of the practical benefits of the approach are demonstrated in Zn-I2 full battery cells, designed in both coin cell and single-flow battery cell configurations. In both contexts, we find that control of the Zn crystallography enables batteries with long-term cycling stability at high areal capacity. The crystal growth stabilization method therefore provides an exciting pathway toward low-cost and large-scale storage of electrical energy.