Graphene Wrapped FeSe₂ Nano‐Microspheres with High Pseudocapacitive Contribution for Enhanced Na‐Ion Storage

Abstract

Pseudocapacitance is a Faradaic process that involves surface or near surface redox reactions. Increasing the pseudocapacitive contribution is one of the most effective means to improve the rate performance of electrode materials. In this study, graphene oxide is used as a template to in situ synthesize burr globule‐like FeSe2/graphene hybrid (B‐FeSe2/G) using a facile one‐step hydrothermal method. Structural characterization demonstrates that graphene layers not only wrap the surfaces of FeSe2 particles, but also stretch into the interior of these particles, as a result of which the unique nano‐microsphere structure is successfully established. When serving as anode material for Na‐ion batteries, B‐FeSe2/G hybrid displays high electrochemical performance in the voltage range of 0.5–2.9 V. The B‐FeSe2/G hybrid has high reversible capacity of 521.6 mAh·g−1 at 1.0 A g−1. Meanwhile, after 400 cycles, high discharge capacity of 496.3 mAh g−1 is obtained at a rate of 2.5 A g−1, with a high columbic efficiency of 96.6% and less than 1.0% loss of discharge capacity. Even at the ultrahigh rate of 10 A g−1, a specific capacity of 316.8 mAh g−1 can be achieved. Kinetic analyses reveal that the excellent performance of the B‐FeSe2/G hybrid is largely attributed to the high pseudocapacitive contribution induced by the special nano‐micro structure.

Interfacial Bonding of Metal‐Sulfides with Double Carbon for Improving Reversibility of Advanced Alkali‐Ion Batteries

“…But, as shown in Figure 3a and Figure S1 (Supporting Information), its smooth surface indicates the well crystalline, perhaps enabling the shrinking of energy distribution, which further results in the inferior surface‐controlling electrochemical contributions. [ 19 ] As expected, the slight aggregations are triggered by the introducing of carbon‐precursor in Figure 3c and Figure S1 (Supporting Information). Some tiny particles were tightly wrapped by carbon layer to protect the active materials, while some obtained fractured carbon sheets are beneficial for the ions shuttling.…”

Metal‐Organic‐Framework‐Derived FeSe2@Carbon Embedded into Nitrogen‐Doped Graphene Sheets with Binary Conductive Networks for Rechargeable Batteries

“…As shown in Figure (d), the Fe 2p spectrum of FeSe 2 /C exhibits two main peaks at 710.3 and 723.9 eV, corresponding to Fe 2p 3/2 and Fe 2p 1/2 of iron selenide, respectively. Several other fitting peaks originate from the formation of iron oxide by surface oxidation of FeSe 2 and satellite peaks . The peaks observed at 707.1 and 720.3 eV for FeSe 2 /C@NGS are attributed to metallic iron …”

Effect of Crystal Structures on Electrochemical Performance of Hierarchically Porous CoSe2 Spheres as Anodes for Sodium‐Ion Batteries

“…Notably, it is worth noting that the CV profiles of the o‐CoSe 2 overlap well without any discrepancy from the second cycle, which means excellent reversibility and stability due to the unique hierarchical porous architecture. In contrast, due to rather serious microstructure change during the c‐CoSe 2 electrode activation at the first charge and discharge process, the CV profiles of the c‐CoSe 2 spheres about the reduction and oxidation peaks do not overlap and exhibit poor stability …”

“…By contrast, the c‐CoSe 2 electrode deliver rather low capacity after 100 cycles. The o‐CoSe 2 spheres have higher specific surface area and more optimized layered porous structure, which not only improve conductivity by shortening transport length of ion and electron, but also improve the structure stability of the electrode during the cycling, thereby leading to superior performance …”