High-performance mesoporous γ-Fe2O3 sphere/graphene aerogel composites towards enhanced lithium storage

Transition metal oxides have recently been demonstrated as highly attractive anodes for high-capacity lithium ion batteries, whose electrochemical properties could be further improved through rational architecture design and incorporating reliable conductive network. Herein, mesoporous γ-Fe₂O₃ spheres/graphene aerogel composites were synthesized via a solvothermal pathway followed by suitable annealing. Experimental results reveal the uniform mesoporous structure and well-dispersed γ-Fe₂O₃ spheres with the size of 300-400 nm embedded in the mesopores of the graphene aerogel network. Compared with α-Fe₂O₃/graphene aerogel and pure γ-Fe₂O₃, the as-synthesized composite delivers, at the first cycle, a high discharging capacity of 1080 mAh g^-1 at current density of 200 mA g^-1. Even at much higher current density of 8000 mA g^-1, satisfactory discharging capacities of 421.5 mAh g^-1 can still be achieved. Upon 100 charging-discharging cycles, the specific capacity of as high as 890.5 mAh g^-1 at 200 mA g^-1 is maintained. The enhanced electrochemical properties could be attributed to their favorable three-dimensional graphene aerogel network, which accounts for the improved structural stability and electronic conductivity of γ-Fe₂O₃ during the lithiation/delithiation process.

Achieving Ultrahigh Capacity with Self-Assembled Ni(OH)2 Nanosheet-Decorated Hierarchical Flower-like MnCo2O4.5 Nanoneedles as Advanced Electrodes of Battery-Supercapacitor Hybrid Devices

Self-assembled Ni(OH)₂ nanosheet-decorated hierarchical flower-like MnCo₂O_4.5 nanoneedles were synthesized via a cost-effective and facile hydrothermal strategy, aiming to realize a high-capacity advanced electrode of a battery-supercapacitor hybrid (BSH) device. It is demonstrated that the as-synthesized hierarchical flower-like MnCo₂O_4.5@Ni(OH)₂-nanosheet electrode exhibits a high specific capacity of 318 mAh g^-1 at a current density of 3 A g^-1 and still maintains a capacity of 263.5 mAh g^-1 at a higher current density of 20 A g^-1, with an extremely long cycle lifespan of 87.7% capacity retention after 5000 cycles. Moreover, using the unique core-shell structure as the cathode and hollow Fe₂O₃ nanoparticles/reduced graphene oxide as the anode, the BSH device delivers a high energy density of 56.53 Wh kg^-1 when the power density reaches 1.9 kW kg^-1, and there is an extraordinarily good cycling stability with the capacity retention rate of 90.4% after 3000 cycles. It is believed that the superior properties originate from desirable core-shell structures alleviating the impact of volume changes as well as the existence of two-dimensional Ni(OH)₂ nanosheets with more active sites, thereby improving the cycle stability and achieving ultrahigh capacity. These results will provide more access to the rational material design of diverse nanostructures toward high-performance energy storage devices.

Assembling a double shell on a diatomite skeleton ternary complex with conductive polypyrrole for the enhancement of supercapacitors

Double shell FeOOH/PPy on a diatomite ternary complex was assembled via two-step hydrothermal and in situ polymerization routes.

A Zinc Cobalt Sulfide Nanosheet Array Derived from a 2D Bimetallic Metal-Organic Frameworks for High-Performance Supercapacitors

Porous ternary metal sulfide integrated electrode materials with abundant electroactive sites and redox reactions are very promising for supercapacitors. Herein, a porous zinc cobalt sulfide nanosheet array on Ni foam (Zn-Co-S/NF) was constructed by facile growth of 2D bimetallic zinc/cobalt-based metal-organic framework (Zn/Co-MOF) nanosheets with leaf-like morphology on NF, followed by additional sulfurization. The Zn-Co-S/NF nanosheet array acted directly as a supercapacitor electrode showing much better electrochemical performance (2354.3 F g^-1 and 88.6 % retention over 1000 cycles) when compared with zinc cobalt sulfide powder (355.3 F g^-1 and 75.8 % retention over 1000 cycles), which originates from good electrical conductivity and mechanical stability, abundant electroactive sites, and facilitated transportation of electrons and electrolyte ions due to the unique nanosheet array structure. An asymmetric supercapacitor (ASC) device assembled from Zn-Co-S/NF and activated carbon electrodes can deliver a highest energy density of 31.9 Wh kg^-1 and a maximum power density of 8.5 kW kg^-1 . Most importantly, this ASC also shows good cycling stability (71.0 % retention over 10000 cycles). Furthermore, a red LED can be powered by two connected ASCs, and thus as-synthesized Zn-Co-S/NF has great potential for practical applications.

Hybridizing Fe3O4 nanocrystals with nitrogen-doped carbon nanowires for high-performance supercapacitors

The nanocomposite hybridizing Fe₃O₄ nanocrystals with N-doped carbon nanowires exhibits great performances for supercapacitors.