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Utilizing the anionic redox reaction opens new approaches for the development of new battery cathode materials with extra capacities. Although, it suffers from several obstacles such as voltage hysteresis and sluggish kinetics. In this paper, a new layered chalcogenide-based on dual anionic-redox reaction is reported. The newly designed layered NaCrSSe exhibits the capacity of almost all Na+ intercalation/deintercalation (137 mAh g-1 at 50 mA g-1), and a unique charge/discharge feature with a small polarization of 0.15 V and high energy efficiencies of ~92% in initial cycles. Furthermore, a superior high-rate charge capacity of 115.5mAh g-1 (83.7% retention) was achieved at 27.8 C (4000 mA g-1), which is impressive in all bulk materials for sodium-ion batteries. Systematic characterization studies on structure evolution and DFT calculation show the charge compensation of S and Se anions during cycling. These results will enrich the anion redox chemistry and provide valuable information for developing new anion redox based cathode materials with high capacity and fast kinetics.

Chromium-based layered cathode materials suffer from the irreversible disproportionation reaction of Cr4+ to Cr3+ and Cr6+, which hinders the reversible multi-electron redox of Cr ions in layered cathodes, and limits their capacity and reversibility. To address this problem, a novel O3-type layer-structured transition metal oxide of NaCr1/3Fe1/3Mn1/3O2 (NCFM) was designed and studied as a cathode material. A high reversible capacity of 186 mA h g−1 was achieved at a current rate of 0.05C in a voltage range of 1.5 to 4.2 V. X-ray diffraction revealed an O3 → (O3 + P3) → (P3 + O3′′) → O3′′ phase-transition pathway for NCFM during charge. X-ray absorption, X-ray photoelectron and electron energy-loss spectroscopy measurements revealed the electronic structure changes of NCFM during Na+ deintercalation/intercalation processes. It is confirmed that the disproportionation reaction of Cr4+ to Cr3+ and Cr6+ can be effectively suppressed by Fe3+ and Mn4+ substitution. These results demonstrated that the reversible multi-electron oxidation/reduction of Cr ions can be achieved in NCFM during charge and discharge accompanied by CrO6 octahedral distortion and recovery.

Transition metal compounds of FeSe and CuWO4 thin films have been successfully fabricated by using R.F. sputtering method. Although two kinds of transition metal compounds of FeSe and CuWO4 thin films can react with sodium electrochemically, they exhibit different electrochemical features. The nanosized metal Fe is highly dispersed into Na2Se matrix and metal Cu is extruded from Na2WO4 mixture after the FeSe/Na and CuWO4/Na cells are discharged, respectively. The conversion reaction mechanism between FeSe and Na2Se is proposed for the FeSe/Na cell. While the displacement reaction mechanism for CuWO4/Na cell is proposed for the first time based on the transmission electron microscopy (TEM) and selected area electron diffraction (SAED) data. These various mechanisms make transition metal compounds interesting materials for rechargeable sodium ion batteries.

A single-phase quinary layer transition metal oxide of NaNi1/4Co1/4Fe1/4Mn1/8Ti1/8O2 was synthesized as a high-rate-capability and long-life cathode material for sodium-ion batteries.

Metal–air batteries are important power sources for electronics and vehicles because of their remarkable high theoretical energy density and low cost. In this work, we firstly investigate the electrochemical properties of sodium air batteries (SABs) with the addition of ferrocene in the electrolyte. Combining charge–discharge measurements with field-emission transmission electron microscopy images of the discharged air cathodes, our results have demonstrated that two different pathways with ferrocene as an electrocatalyst and involved in the electrochemistry during the charge process might be governed by the morphological features of the electrode caused by the deposition of Na2O2 in SABs. The SAB with ferrocene as a catalyst exhibits a high cycling performance of up to 230 cycles with a high capacity of 1000 mA h g−1.

High rate capability and long cycle life are challenging goals for the development of room temperature sodium-ion batteries. Here we report a new single phase quaternary O3-type layer-structured transition metal oxide Na(NiCoFeTi)1/4O2 synthesized by a simple solid-state reaction as a new cathode material for sodium-ion batteries. It can deliver a reversible capacity of 90.6 mA h g−1 at a rate as high as 20C. At 5C, 75.0% of the initial specific capacity can be retained after 400 cycles with a capacity-decay rate of 0.07% per cycle, demonstrating a superior long-term cyclability at high current density. X-ray diffraction and absorption characterization revealed reversible phase transformations and electronic structural changes during the Na+ deintercalation/intercalation process. Ni, Co and Fe ions contribute to charge compensation during charge and discharge. Although Ti ions do not contribute to the charge transfer, they play a very important role in stabilizing the structure during charge and discharge by suppressing the Fe migration. In addition, Ti substitution can also smooth the charge–discharge plateaus effectively, which provides a potential advantage for the commercialization of this material for room temperature sodium-ion batteries.

The electrochemical performance of most transition metal oxides based on the conversion mechanism is greatly restricted by inferior cycling stability, rate capability, high overpotential induced by the serious irreversible reactions, low electrical conductivity, and poor ion diffusivity. To mitigate these problems, highly porous Mn

The key factors governing the single-phase or multi-phase structural change behaviors during the intercalation/deintercalation of guest ions have not been well studied and understood yet. Through systematic studies of orthorhombic Fe2(MoO4)3 electrode, two distinct guest ion occupation paths, namely discrete one for Li and pseudo-continuous one for Na, as well as their relationship with single-phase and two-phase modes for Na1 and Li1, respectively during the intercalation/deintercalation process have been demonstrated. For the first time, the direct atomic-scale observation of biphasic domains (discrete occupation) in partially lithiated Fe2(MoO4)3 and the one by one Na occupation (pseudo-continuous occupation) at 8d sites in partially sodiated Fe2(MoO4)3 are obtained during the discharge processes of Li/Fe2(MoO4)3 and Na/Fe2(MoO4)3 cells respectively. Our combined experimental and theoretical studies bring the new insights for the research and development of intercalation compounds as electrode materials for secondary batteries., Comment: Scientific Reports, 2015

A Cu2Se electrode on a copper grid substrate has been directly fabricated by a facile post-selenized method and tested as a positive material for sodium ion batteries. Cu2Se exhibits large reversible capacities (about 250 mA h g(-1)), good cyclic stabilities and low polarization. These results indicate that Cu2Se is a promising candidate as a cathode material for sodium ion batteries.