Nitrogen-Doped Carbon-Encapsulated SnO₂@Sn Nanoparticles Uniformly Grafted on Three-Dimensional Graphene-like Networks as Anode for High-Performance Lithium-Ion Batteries

A peculiar nanostructure consisting of nitrogen-doped, carbon-encapsulated (N–C) SnO₂@Sn nanoparticles grafted on three-dimensional (3D) graphene-like networks (designated as N–C@SnO₂@Sn/3D-GNs) has been fabricated via a low-cost and scalable method, namely an in situ hydrolysis of Sn salts and immobilization of SnO₂ nanoparticles on the surface of 3D-GNs, followed by an in situ polymerization of dopamine on the surface of the SnO₂/3D-GNs, and finally a carbonization. In the composites, three-layer core–shell N–C@SnO₂@Sn nanoparticles were uniformly grafted onto the surfaces of 3D-GNs, which promotes highly efficient insertion/extraction of Li⁺. In addition, the outermost N–C layer with graphene-like structure of the N–C@SnO₂@Sn nanoparticles can effectively buffer the large volume changes, enhance electronic conductivity, and prevent SnO₂/Sn aggregation and pulverization during discharge/charge. The middle SnO₂ layer can be changed into active Sn and nano-Li₂O during discharge, as described by SnO₂ + Li⁺ → Sn + Li₂O, whereas the thus-formed nano-Li₂O can provide a facile environment for the alloying process and facilitate good cycling behavior, so as to further improve the cycling performance of the composite. The inner Sn layer with large theoretical capacity can guarantee high lithium storage in the composite. The 3D-GNs, with high electrical conductivity (1.50 × 10³ S m^–1), large surface area (1143 m² g^–1), and high mechanical flexibility, tightly pin the core–shell structure of the N–C@SnO₂@Sn nanoparticles and thus lead to remarkably enhanced electrical conductivity and structural integrity of the overall electrode. Consequently, this novel hybrid anode exhibits highly stable capacity of up to 901 mAh g^–1, with ∼89.3% capacity retention after 200 cycles at 0.1 A g^–1 and superior high rate performance, as well as a long lifetime of 500 cycles with 84.0% retention at 1.0 A g^–1. Importantly, this unique hybrid design is expected to be extended to other alloy-type anode materials such as silicon, germanium, etc

FeNC catalysts decorated with NiFe₂O₄ to enhance bifunctional activity for Zn–Air batteries

Rechargeable Zn–air battery is a promising next-generation energy storage device attributed to its high energy density, excellent safety, and low cost. However, its commercialization is hampered by sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at air electrodes. Herein, we have designed, fabricated, and demonstrated a highly efficient ORR/OER electrocatalyst, NiFe2O4/FeNC, using low-cost materials via a facile synthesis route. NiFe2O4 is successfully loaded on Fe/N-doped carbon (FeNC) through bonding to Fe3C in FeNC. Due to the existence of high ORR active sites such as FeN4 and Fe and N-doped carbon moieties, the half-wave potential of the ORR reaches a high value of 0.83 V. While benefited from NiFe2O4 with high OER activity and the synergistic effect between NiFe2O4 and FeNC, the overpotential is 310 mV at 10 mA cm–2 in the OER. The voltage difference between charging–discharging operations in the Zn–air battery employing the NiFe2O4/FeNC electrocatalyst only increases by 0.16 V after cycling for 100 h (600 cycles) at 10 mA cm–2, which is much lower than 1.28 V using the best commercial Pt/C and RuO2 catalysts. </p

Hierarchically Bicontinuous Porous Copper as Advanced 3D Skeleton for Stable Lithium Storage

Rechargeable lithium metal anodes (LMAs) with long cycling life have been regarded as the “Holy Grail” for high-energy-density lithium metal secondary batteries. The skeleton plays an important role in determining the performance of LMAs. Commercially available copper foam (CF) is not normally regarded as a suitable skeleton for stable lithium storage owing to its relatively inappropriate large pore size and relatively low specific surface area. Herein, for the first time, we revisit CF and address these issues by rationally designing a highly porous copper (HPC) architecture grown on CF substrates (HPC/CF) as a three-dimensional (3D) hierarchically bicontinuous porous skeleton through a novel approach combining the self-assembly of polystyrene microspheres, electrodeposition of copper, and a thermal annealing treatment. Compared to the CF skeleton, the HPC/CF skeleton exhibits a significantly improved Li plating/stripping behavior with high Coulombic efficiency (CE) and superior Li dendrite growth suppression. The 3D HPC/CF-based LMAs can run for 620 h without short-circuiting in a symmetric Li/Li@Cu cell at 0.5 mA cm^–2, and the Li@Cu/LiFePO₄ full cell exhibits a high reversible capacity of 115 mAh g^–1 with a high CE of 99.7% at 2 C for 500 cycles. These results demonstrate the effectiveness of the design strategy of 3D hierarchically bicontinuous porous skeletons for developing stable and safe LMAs

Supplementary information files for FeNC catalysts decorated with NiFe2O4 to enhance bifunctional activity for Zn–Air batteries

Supplementary files for article FeNC catalysts decorated with NiFe2O4 to enhance bifunctional activity for Zn–Air batteries  Rechargeable Zn–air battery is a promising next-generation energy storage device attributed to its high energy density, excellent safety, and low cost. However, its commercialization is hampered by sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at air electrodes. Herein, we have designed, fabricated, and demonstrated a highly efficient ORR/OER electrocatalyst, NiFe2O4/FeNC, using low-cost materials via a facile synthesis route. NiFe2O4 is successfully loaded on Fe/N-doped carbon (FeNC) through bonding to Fe3C in FeNC. Due to the existence of high ORR active sites such as FeN4 and Fe and N-doped carbon moieties, the half-wave potential of the ORR reaches a high value of 0.83 V. While benefited from NiFe2O4 with high OER activity and the synergistic effect between NiFe2O4 and FeNC, the overpotential is 310 mV at 10 mA cm–2 in the OER. The voltage difference between charging–discharging operations in the Zn–air battery employing the NiFe2O4/FeNC electrocatalyst only increases by 0.16 V after cycling for 100 h (600 cycles) at 10 mA cm–2, which is much lower than 1.28 V using the best commercial Pt/C and RuO2 catalysts.  </p

Mn₃O₄ Quantum Dots Supported on Nitrogen-Doped Partially Exfoliated Multiwall Carbon Nanotubes as Oxygen Reduction Electrocatalysts for High-Performance Zn–Air Batteries

Highly efficient and low-cost nonprecious metal electrocatalysts that favor a four-electron pathway for the oxygen reduction reaction (ORR) are essential for high-performance metal–air batteries. Herein, we show an ultrasonication-assisted synthesis method to prepare Mn₃O₄ quantum dots (QDs, ca. 2 nm) anchored on nitrogen-doped partially exfoliated multiwall carbon nanotubes (Mn₃O₄ QDs/N-p-MCNTs) as a high-performance ORR catalyst. The Mn₃O₄ QDs/N-p-MCNTs facilitated the four-electron pathway for the ORR and exhibited sufficient catalytic activity with an onset potential of 0.850 V (vs reversible hydrogen electrode), which is only 38 mV less positive than that of Pt/C (0.888 V). In addition, the Mn₃O₄ QDs/N-p-MCNTs demonstrated superior stability than Pt/C in alkaline solutions. Furthermore, a Zn–air battery using the Mn₃O₄ QDs/N-p-MCNTs cathode catalyst successfully generated a specific capacity of 745 mA h g^–1 at 10 mA cm^–2 without the loss of voltage after continuous discharging for 105 h. The superior ORR activity of Mn₃O₄ QDs/N-p-MCNTs can be ascribed to the homogeneous Mn₃O₄ QDs loaded onto the N-doped carbon skeleton and the synergistic effects of Mn₃O₄ QDs, nitrogen, and carbon nanotubes. The interface binding energy of −3.35 eV calculated by the first-principles density functional theory method illustrated the high stability of the QD-anchored catalyst. The most stable adsorption structure of O₂, at the interface between Mn₃O₄ QDs and the graphene layer, had the binding energy of −1.17 eV, greatly enhancing the ORR activity. In addition to the high ORR activity and stability, the cost of production of Mn₃O₄ QDs/N-p-MCNTs is low, which will broadly facilitate the real application of metal–air batteries