In Situ Ion–Exchange Synthesis of Fe₃O₄ Nanosheets with 3D Hierarchically Porous Carbon Frameworks for High‐Performance Energy Storage

Abstract

Since their commercialization in the 1990s, [1] lithium (Li)-ion batteries (LIBs) dominate the market for consumer electronics and electric vehicles because of their high-energy density and long cycle life. [2][3][4] However, the low power density of batteries gradually cannot meet the demands for faster charge/discharge ability with superior energy density in electric vehicles. [5] Thus, it is especially important to develop new electrode materials for LIBs with high-energy/power density, long cycle life, and low cost. In addition, the limited reserves of Li resources increase the LIB cost and hinder the development of existing energy-storage systems. [6,7] Another promising way is to find alternatives to Li, such as sodium (Na), which is almost three orders of magnitude higher than Li in reserves, and has relatively lower cost. [8][9][10] However, Na-ion batteries (NIBs) also have many problems, such as the lower negative redox potential and larger size of Na ions than those of Li ions. These make the performance of NIBs uncompetitive against that of LIBs. [11,12] Generally, electrode materials that can deliver high-energy/power density are strongly required for both LIBs and NIBs at present.High-energy density delivered at rapid charge/discharge rate requires the electrode materials to have 1) abundant redox reaction sites for charge storage and 2) fast internal solid-state ion-diffusion kinetics and high electronic conductivity. [4] However, most electrode materials with high theoretical capacities, such as Si, [13][14][15] Sn, [16,17] transitionmetal oxides (TMOs), [18][19][20][21][22][23] etc., usually undergo low electrical/ ionic conductivity or huge volume changes, which limits the battery performance. For instance, Fe 3 O 4 is a promising anode material for batteries due to its high theoretical capacity (926 mA h g À1 ), high reversibility, eco-friendliness, and low cost. However, this material tends to aggregate during fabrication and be pulverized during cycling, leading to a much lower actual capacity. [24,25] A strategy to address these problems is to create electrode materials with their active components controllable in size and morphology, and dispersing continuously and uniformly on an electrical conductive framework with a large number of internal channels for rapid ion transport. [26,27] Carbon frameworks are regarded as an optimal choice for composites with Fe 3 O 4 for LIBs or NIBs anodes due to the robust structure, good electrical/ionic conductivity, and low cost. To date, researchers have successfully developed many novel methods to prepare Fe 3 O 4 /carbon hybrids, such as etching method, [28] spontaneous deposition of metallic salts, [29] hydrothermal method, [30,31] and electrostatic spinning. [32,33] However, these methods involve complex preparation processes and are still far from commercial

Fe3O4/Fe/FeS Tri‐Heterojunction Node Spawning N‐Carbon Nanotube Scaffold Structure for High‐Performance Sodium‐Ion Battery

“…Even when compared to the previously reported Fe 3 O 4based materials, the FHNCS exhibited superior rate capability (Figure 4e). [14,20,24,[48][49][50] The distinguished rate capability was caused by the fast Na + and electron transfer rate due to the unique structure. The cycling stability was checked by the galvanostatic charge-discharge test.…”

“…e) A comparison of the rate capability. [14,20,24,[48][49][50] f, g) The cycling stability at a current density of 0.5 and 1.0 A g À1 .…”

“…d) The galvanostatic charge-discharge curves of FHNCS at different current densities. e) A comparison of the rate capability [14,20,24,[48][49][50]. f, g) The cycling stability at a current density of 0.5 and 1.0 A g À1 .…”