Rechargeable zinc (Zn) batteries are safe, sustainable, and energy-dense alternatives to Li-ion batteries. Recent advances, such as monolithic Zn-sponge electrodes, have enabled long cycle lives by suppressing the formation of short-circuiting dendrites even after deep levels of discharge and charge. A substantial barrier, however, to their widespread adoption has been their poor mechanical integrity. Our previous Zn-sponge electrodes had uniaxial compressive strengths near 0.01 MPa. With such a compressive strength, the sponge electrode can break under its own weight if cantilevered with planar dimensions beyond 1 cm with a thickness of 0.2 cm. If the mechanical strength were enhanced while preserving electrochemical performance, Zn-sponge electrodes could be used in next-generation grid-storage, electric-vehicle, and personal-electronic batteries. Here, we present a manufacturing process that optimizes the reinforcing zinc-oxide shell over the fused zinc-sponge core. The presence of the oxide shell boosts the compressive strength of the sponge with respect to our previous version by 9,900%, yielding a plateau stress of 1 MPa. This increase in strength enables the fabrication of large, thin Zn-sponge electrodes (12×12×0.2 cm) for large-format applications. When paired with a nickel electrode, the reinforced Zn-sponge electrode displays rechargeability and high system energy density.