γ-Fe₂O₃ Nanocrystalline Microspheres with Hybrid Behavior of Battery-Supercapacitor for Superior Lithium Storage

Abstract

Maghemite (γ-Fe2O3) nanocrystalline microspheres (MNMs) self-assembled with 52 nm nanocrystals bridged with FeOOH around grain boundaries were formed by solvothermal reaction and thermal oxidation. The unique architecture endows the MNMs with the lithium storage behavior of a hybrid battery-supercapacitor electrode: initial charge capacity of 1060 mAh g(-1) at the 100 mA g(-1) rate, stable cyclic capacity of 1077.9 mAh g(-1) at the same rate after 140 cycles, and rate capability of 538.8 mAh g(-1) at 2400 mA g(-1). This outstanding performance was attributed to the nanocrystal superiority, which shortens the Li(+) diffusion paths. The mechanism of this hybrid anode material was investigated with experimental measurements and structural analysis. The results indicate that at the first discharge, the MNM nanocrystal microsphere, whose structure can buffer the volume change that occurs during lithiation/delithiation, goes through four stages: Li(+) insertion in cation vacancies, spinel-to-rocksalt transformation, Li(+) intercalation of Li(1.75+x)Fe2O3 nanocrystals, and interfacial Li storage around nanocrystal boundaries. Only the latter two stages were reversible at and after the second charging/discharging cycle, exhibiting the hybrid behavior of a battery-supercapacitor with superior lithium storage.

Etching‐Assisted Crumpled Graphene Wrapped Spiky Iron Oxide Particles for High‐Performance Li‐Ion Hybrid Supercapacitor

“…During the early stages of long‐term cycles, the CG@SF capacity gradually decreased until the 50th cycle (as shown in Figure d), increasing continuously up to 1445 mAh g −1 during the 270th cycle, which is higher than the initial capacity (1375 mAh g −1 ). The phenomenon of increasing capacity with cycles has been reported for several nanostructured metal oxide electrodes and is commonly observed for iron oxide particles with graphene or CNT . Furthermore, the plateau region in the discharge curve (0.8 V; Figure b) decreased gradually as the cycles progressed.…”

“…During this time, the linear region became larger, greatly affecting the increase in capacity. This result can be attributed mainly to the gradual capacitive capacity increase due to Li + ion adsorption or the pseudocapacitive characteristics at the interface between the crumpled graphene and lithiated iron oxide active nanocrystals at low potential window, while battery capacity at 0.8 V from the iron oxide particles gradually decreases …”

“…Besides, iron oxide, which we used template particles for fabricating crumpled graphene, is also known as anode material of lithium‐ion battery . The iron oxide has many advantages for anode materials including a high theoretical capacity over 1000 mAh g −1 , low cost, nontoxicity, and high availability.…”

Boric Acid Assisted Reduction of Graphene Oxide: A Promising Material for Sodium-Ion Batteries

“…[1][2][3][4][5] The high demand for LIBs, however, has led to increasing concern about the limited resources and high cost of lithium. Consequently, great efforts have been spent on finding alternatives to LIBs.…”

Tailoring Iron Oxide Nanostructures for High-Capacity Lithium Storage

“…[102] γ-Fe2O3 based 3D nanostructures A variety of γ-Fe2O3 based 3D architectures have been applied in lithium storage, including γ-Fe2O3 microspheres, [98,99] N-doped carbon coated γ-Fe2O3 spheres (Figure 5e), [100] γ-Fe2O3 hollow nanoparticles, [101] Fe2O3 hierarchical hollow microboxes (Figure 5f), [102,103] hollow γ-Fe2O3@graphene core@shell hybrid, [104] polypyrrole coated γ-Fe2O3-ordered mesoporous carbon, [105] and double-shelled Fe2O3-Co3O4 hollow microcubes. [106] For example, monodisperse γ-Fe2O3 mesoporous spheres were fabricated by a surfactant-free solvothermal method with subsequent thermal transformation.…”