Ultrafine Fe3O4Quantum Dots on Hybrid Carbon Nanosheets for Long-Life, High-Rate Alkali-Metal Storage

State-of-the-Art Electrode Materials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) were investigated as recently as in the seventies. However, they have been overshadowed for decades, due to the success of lithium-ion batteries that demonstrated higher energy densities and longer cycle lives. Since then, the witness a re-emergence of the SIBs and renewed interest evidenced by an exponential increase of the publications devoted to them (about 9000 publications in 2019, more than 6000 in the first six months this year). This huge effort in research has led and is leading to an important and constant progress in the performance of the SIBs, which have conquered an industrial market and are now commercialized. This progress concerns all the elements of the batteries. We have already recently reviewed the salts and electrolytes, including solid electrolytes to build all-solid-state SIBs. The present review is then devoted to the electrode materials. For anodes, they include carbons, metal chalcogenide-based materials, intercalation-based and conversion reaction compounds (transition metal oxides and sulfides), intermetallic compounds serving as functional alloying elements. For cathodes, layered oxide materials, polyionic compounds, sulfates, pyrophosphates and Prussian blue analogs are reviewed. The electrode structuring is also discussed, as it impacts, importantly, the electrochemical performance. Attention is focused on the progress made in the last five years to report the state-of-the-art in the performance of the SIBs and justify the efforts of research.

Recent Progress in Iron-Based Electrode Materials for Grid-Scale Sodium-Ion Batteries

Grid-scale energy storage batteries with electrode materials made from low-cost, earth-abundant elements are needed to meet the requirements of sustainable energy systems. Sodium-ion batteries (SIBs) with iron-based electrodes offer an attractive combination of low cost, plentiful structural diversity and high stability, making them ideal candidates for grid-scale energy storage systems. Although various iron-based cathode and anode materials have been synthesized and evaluated for sodium storage, further improvements are still required in terms of energy/power density and long cyclic stability for commercialization. In this Review, progress in iron-based electrode materials for SIBs, including oxides, polyanions, ferrocyanides, and sulfides, is briefly summarized. In addition, the reaction mechanisms, electrochemical performance enhancements, structure-composition-performance relationships, merits and drawbacks of iron-based electrode materials for SIBs are discussed. Such iron-based electrode materials will be competitive and attractive electrodes for next-generation energy storage devices.

Sodium-ion batteries: present and future

Energy production and storage technologies have attracted a great deal of attention for day-to-day applications. In recent decades, advances in lithium-ion battery (LIB) technology have improved living conditions around the globe. LIBs are used in most mobile electronic devices as well as in zero-emission electronic vehicles. However, there are increasing concerns regarding load leveling of renewable energy sources and the smart grid as well as the sustainability of lithium sources due to their limited availability and consequent expected price increase. Therefore, whether LIBs alone can satisfy the rising demand for small- and/or mid-to-large-format energy storage applications remains unclear. To mitigate these issues, recent research has focused on alternative energy storage systems. Sodium-ion batteries (SIBs) are considered as the best candidate power sources because sodium is widely available and exhibits similar chemistry to that of LIBs; therefore, SIBs are promising next-generation alternatives. Recently, sodiated layer transition metal oxides, phosphates and organic compounds have been introduced as cathode materials for SIBs. Simultaneously, recent developments have been facilitated by the use of select carbonaceous materials, transition metal oxides (or sulfides), and intermetallic and organic compounds as anodes for SIBs. Apart from electrode materials, suitable electrolytes, additives, and binders are equally important for the development of practical SIBs. Despite developments in electrode materials and other components, there remain several challenges, including cell design and electrode balancing, in the application of sodium ion cells. In this article, we summarize and discuss current research on materials and propose future directions for SIBs. This will provide important insights into scientific and practical issues in the development of SIBs.

Flexible Paper-like Free-Standing Electrodes by Anchoring Ultrafine SnS2 Nanocrystals on Graphene Nanoribbons for High-Performance Sodium Ion Batteries

Ultrafine SnS₂ nanocrystals-reduced graphene oxide nanoribbon paper (SnS₂-RGONRP) has been created by a well-designed process including in situ reduction, evaporation-induced self-assembly, and sulfuration. The as-formed SnS₂ nanocrystals possess an average diameter of 2.3 nm and disperse on the surface of RGONRs uniformly. The strong capillary force formed during evaporation leads to a compact assembly of RGONRs to give a flexible paper structure with a high density of 0.94 g cm^-3. The as-prepared SnS₂-RGONRP composite could be directly used as free-standing electrode for sodium ion batteries. Due to the synergistic effects between the ultrafine SnS₂ nanocrystals and the conductive, tightly connected RGONR networks, the composite paper electrode exhibits excellent electrochemical performance. A high volumetric capacity of 508-244 mAh cm^-3 was obtained at current densities in the range of 0.1-10 A g^-1. Discharge capacities of 334 and 255 mAh cm^-3 were still kept, even after 1500 cycles tested at current densities of 1 and 5 A g^-1, respectively. This strategy provides insight into a new pathway for the creation of free-standing composite electrodes used in the energy storage and conversion.

Self-crosslink assisted synthesis of 3D porous branch-like Fe3O4/C hybrids for high-performance lithium/sodium-ion batteries

Porous branch-like Fe₃O₄/C hybrids synthesized by a simple carbonization of self-crosslinked Fe-alginate show high-performance in lithium/sodium-ion batteries.

Amorphous Fe2O3/Graphene Composite Nanosheets with Enhanced Electrochemical Performance for Sodium-Ion Battery

With the increasing use of sodium-ion batteries (SIBs), developing cost-effective anode materials, such as metal oxide, for Na-ion storage is one of the most attractive topics. Due to the obviously larger ion radius of Na than that of Li, most metal oxide electrode materials fail to exhibit the same high performance for SIBs like that of Li-ion batteries. Herein, iron oxide was employed to demonstrate a concept that rationally designing an amorphous structure should be useful to enhance Na-ion storage performance of a metal oxide. Amorphous Fe₂O₃/graphene composite nanosheets (Fe₂O₃@GNS) were successfully synthesized by a facile approach as anodes for SIBs. It reveals that amorphous Fe₂O₃ nanoparticles with an average diameter of 5 nm were uniformly anchored on the surface of graphene nanosheets by the strong C-O-Fe oxygen-bridge bond. Compared to well-crystalline Fe₂O₃, amorphous Fe₂O₃@GNS exhibited superior sodium storage properties such as high electrochemical activity, high initial Coulombic efficiency of 81.2%, and good rate performance. At a current density of 100 mA/g, amorphous Fe₂O₃@GNS composites show a specific capacity of 440 mAh/g, which is obviously higher than the specific capacity of 284 mAh/g of crystalline Fe₂O₃. Even at a high current density of 2 A/g, amorphous Fe₂O₃@GNS composites still exhibit a specific capacity as high as 219 mAh/g. The excellent electrochemical performance should be attributed to the amorphous structures of Fe₂O₃ as well as strongly interfacial interaction between Fe₂O₃ and GNS, which not only accommodate more electrochemical active sites and provide the more transmission channels for sodium ions but also benefit electron transfer as well as effectively buffer the volume change of host materials during sodiation and desodiation. This concept for designing amorphous iron oxide anodes for SIBs is also expected to facilitate preparation of various amorphous nanostructure of other metal oxides and improve their Na-ion storage performance.