3D Printing of Electron/Ion-Flux Dual-Gradient Anodes for Dendrite-Free Zinc Batteries.

3D porous Zn-metal anodes have aroused widespread interest for Zn-ion batteries (ZIBs). Nevertheless, the notorious "top-growth" dendrites caused by the intrinsic top-concentrated ions and randomly distributed electrons may ultimately trigger a cell failure. Herein, an electron/ion-flux dual-gradient 3D porous Zn anode is reported for dendrite-free ZIBs by adopting 3D printing technology. The 3D-printed Zn anode with layer-by-layer bottom-up attenuating Ag nanoparticles (3DP-BU@Zn) establishes dual-gradient electron/ion fluxes, i.e., an internal bottom-up gradient electron flux created by bottom-rich conductive Ag nanoparticles, and a gradient ion flux resulting from zincophilic Ag nanoparticles which pump ions toward the bottom. Meanwhile, the 3D-printing-enabled hierarchical porous structure and continuously conducting network endow unimpeded electron transfer and ion diffusion among the electrode, dominating a bottom-preferential Zn deposition behavior. As a result, the 3DP-BU@Zn symmetrical cell affords highly reversible Zn plating/stripping with an extremely small voltage hysteresis of 17.7 mV and a superior lifespan over 630 h at 1 mA cm-2 and 1 mAh cm-2 . Meanwhile, the 3DP-BU@Zn//VO2 full cell exhibits remarkable cyclic stability over 500 cycles. This unique dual-gradient strategy sheds light on the roadmap for the next-generation safe and durable Zn-metal batteries.