Engineering strategies based on “nanostructuring” and “active/inactive composites” are commonly used separately to improve the performance of alkali‐ion battery electrodes. Here, these two strategies are merged to further enhance the performance of alloy‐type alkali‐ion battery anodes. Specifically, macroporous antimony (Sb)/magnesium fluoride (MgF2) active/inactive composite material is used as a high‐performance Na‐ion battery anode. The porous Sb phase with pore size in the sub‐micrometer range acts as the electrochemically active component and the electrochemically inactive dense MgF2 phase acts as a mechanical buffer. Na‐ion battery anodes made of porous Sb/MgF2 active/inactive composites are reversibly sodiated for over 300 cycles, delivering a capacity of ≈551 mAh g−1 after 300 cycles at a C‐rate of C/2. This performance is remarkable because the porous Sb/MgF2 composite is not made of mesoporous structures. Furthermore, the cycling longevity of this porous Sb/MgF2 composite outperforms the common nanostructured Sb‐based Na‐ion battery anode materials. This good performance is attributed to the “porous active/inactive” configuration, where the dense inactive mechanical buffer phase absorbs part of the phase transformation‐induced stresses, while porosity in the active phase helps to accommodate the phase transformation induced volume expansions and electrolyte transfer into the bulk of this composite.

Nanoporous metals used in various electrochemical applications including electrochemical actuators, electrocatalysts, supercapacitors, and batteries exhibit an irreversible volume shrinkage during their formation by dealloying, the origin of which remains obscure. Here we use dilatometry techniques to measure the irreversible shrinkage in nanoporous Au in situ during electrochemical dealloying. A linear contraction up to ∼9% was recorded. To identify the origin of this dimensional change, we borrow the time-dependent isothermal shrinkage model from sintering theory, which we use to fit the dimensional changes measured in our nanoporous Au during dealloying. This shrinkage model suggests that bulk transport through plastic flow is the primary mass transport mechanism responsible for the material contraction in dealloying. Based on the current understanding of the mechanism of porosity formation in dealloying, mass transport through surface diffusion of undissolved materials is critical in the process. The present work sheds new light in the sense that bulk transport through plastic flow seems also to play an important role in dealloying.

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