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Herein, hierarchically structured microgrid frameworks of Co3O4 and carbon composite deposited on reduced graphene oxide (Co3O4@C/rGO) are demonstrated through the three‐dimensioinal (3D) printing method, where the porous structure is controllable and the height and width are scalable, for dendrite‐free Na metal deposition. The sodiophilicity, facile Na metal deposition kinetics, and NaF‐rich solid electrolyte interphase (SEI) formation of cubic Co3O4 phase are confirmed by combined spectroscopic and computational analyses. Moreover, the uniform and reversible Na plating/stripping process on 3D‐printed Co3O4@C/rGO host is monitored in real time using in situ transmission electron and optical microscopies. In symmetric cells, the 3D printed Co3O4@C/rGO electrode achieves a long‐term stability over 3950 at 1 mA cm−2 and 1 mAh cm−2 with a superior Coulombic efficiency (CE) of 99.87% as well as 120 h even at 20 mA cm−2 and 20 mAh cm−2, far exceeding the previously reported carbon‐based hosts for Na metal anodes. Consequently, the full cells of 3D‐printed Na@Co3O4@C/rGO anode with 3D‐printed Na3V2(PO4)3@C‐rGO cathode (≈15.7 mg cm−2) deliver the high specific capacity of 97.97 mAh g−1 after 500 cycles with a high CE of 99.89% at 0.5 C, demonstrating the real operation of flexible Na metal batteries. [ABSTRACT FROM AUTHOR]

Abstract Herein, hierarchically structured microgrid frameworks of Co3O4 and carbon composite deposited on reduced graphene oxide (Co3O4@C/rGO) are demonstrated through the three‐dimensioinal (3D) printing method, where the porous structure is controllable and the height and width are scalable, for dendrite‐free Na metal deposition. The sodiophilicity, facile Na metal deposition kinetics, and NaF‐rich solid electrolyte interphase (SEI) formation of cubic Co3O4 phase are confirmed by combined spectroscopic and computational analyses. Moreover, the uniform and reversible Na plating/stripping process on 3D‐printed Co3O4@C/rGO host is monitored in real time using in situ transmission electron and optical microscopies. In symmetric cells, the 3D printed Co3O4@C/rGO electrode achieves a long‐term stability over 3950 at 1 mA cm−2 and 1 mAh cm−2 with a superior Coulombic efficiency (CE) of 99.87% as well as 120 h even at 20 mA cm−2 and 20 mAh cm−2, far exceeding the previously reported carbon‐based hosts for Na metal anodes. Consequently, the full cells of 3D‐printed Na@Co3O4@C/rGO anode with 3D‐printed Na3V2(PO4)3@C‐rGO cathode (≈15.7 mg cm−2) deliver the high specific capacity of 97.97 mAh g−1 after 500 cycles with a high CE of 99.89% at 0.5 C, demonstrating the real operation of flexible Na metal batteries.

Herein, hierarchically structured microgrid frameworks of Co 3 O 4 and carbon composite deposited on reduced graphene oxide (Co 3 O 4 @C/rGO) are demonstrated through the three-dimensioinal (3D) printing method, where the porous structure is controllable and the height and width are scalable, for dendrite-free Na metal deposition. The sodiophilicity, facile Na metal deposition kinetics, and NaF-rich solid electrolyte interphase (SEI) formation of cubic Co 3 O 4 phase are confirmed by combined spectroscopic and computational analyses. Moreover, the uniform and reversible Na plating/stripping process on 3D-printed Co 3 O 4 @C/rGO host is monitored in real time using in situ transmission electron and optical microscopies. In symmetric cells, the 3D printed Co 3 O 4 @C/rGO electrode achieves a long-term stability over 3950 at 1 mA cm -2 and 1 mAh cm -2 with a superior Coulombic efficiency (CE) of 99.87% as well as 120 h even at 20 mA cm -2 and 20 mAh cm -2 , far exceeding the previously reported carbon-based hosts for Na metal anodes. Consequently, the full cells of 3D-printed Na@Co 3 O 4 @C/rGO anode with 3D-printed Na 3 V 2 (PO 4 ) 3 @C-rGO cathode (≈15.7 mg cm -2 ) deliver the high specific capacity of 97.97 mAh g -1 after 500 cycles with a high CE of 99.89% at 0.5 C, demonstrating the real operation of flexible Na metal batteries., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Lithium metal has the highest theoretical energy density and the lowest redox potential among Li-ion battery anodes, but often suffers from Li dendrite-related safety problem. Here, we describe a hierarchical Ni monolith of interconnected crystalline microwires covered with vertical nanosheets synthesized for a recoverable host of dendrite-free Li. The metallic Ni–Li anode exhibits high capacity, high Coulombic efficiency and high-rate cyclability (over 690 cycles at an ultrahigh current density of 40.0 mA cm−2). The Ni monolith, derived from the chain chelation of acetate anions, nickel cations and hydrazine molecules, features high conductivity, high flexibility, low density, hierarchical pores and lithiophilic surface oxidation. This special structure enables fast electrolyte wetting, Li+ flux homogenization and uniform electric field to seed Li metal, which can work as a recyclable, light and conductive host inhibiting dendritic Li growth at various current densities. Our investigation demonstrates that the cheap acetate nickel salt can be used to fabricate nanostructured Li host for Li-ion battery anode. Image 1 • Lithiophilic Ni microwire-nanosheet monolith is synthesized for Li anode host. • Soluble chain complex of Ni(Ac) 2 and N 2 H 4 is crucial for the monolith formation. • Dendrite-free Li anode reaches 690 cycles at high current density of 40 mA cm−2. [ABSTRACT FROM AUTHOR]