Large-scale electric energy storage is a key enabler for the use of renewable energy. Recently, the room-temperature Na-ion battery has been rehighlighted as an alternative low-cost technology for this application. However, significant challenges such as energy density and long-term stability must be addressed. Herein, we introduce a novel cathode material, Na1.5VPO4.8F0.7, for Na-ion batteries. This new material provides an energy density of ~600 Wh kg(-1), the highest value among cathodes, originating from both the multielectron redox reaction (1.2 e(-) per formula unit) and the high potential (~3.8 V vs Na(+)/Na) of the tailored vanadium redox couple (V(3.8+)/V(5+)). Furthermore, an outstanding cycle life (~95% capacity retention for 100 cycles and ~84% for extended 500 cycles) could be achieved, which we attribute to the small volume change (2.9%) upon cycling, the smallest volume change among known Na intercalation cathodes. The open crystal framework with two-dimensional Na diffusional pathways leads to low activation barriers for Na diffusion, enabling excellent rate capability. We believe that this new material can bring the low-cost room-temperature Na-ion battery a step closer to a sustainable large-scale energy storage system.

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A novel, Na-pillared LiMnPO4 with an alluaudite structure that allows fast lithium diffusion with stable electrochemical cycling as a cathode in lithium batteries.

A variety of electrochemical applications of mixed ionic-electronic conductor compounds hinge on their variety of mass and charge transport properties, e.g., ionic conductivity, electronic conductivity, conductivity with suppressed transfer of either electrons or ions, chemical diffusivity, and permeability. All these transport properties of a compound may be represented completely by an Onsager transport coefficient matrix. Here we introduce a simple electrochemical method to measure all the Onsager coefficients for a mixed conductor oxide with known nonstoichiometry (δ), apply it to construct the Onsager matrix for the system of La(2)NiO(4+δ), and derive thereby its transport properties to compare with the literature values available.

To initiate resistance switching phenomena, it is usually necessary to apply a strong electric field to a sample. This forming process poses very serious obstacles in real nanodevice applications. In unipolar resistance switching (URS), it is well known that the forming originates from soft dielectric breakdown. However, the forming in bipolar resistance switching (BRS) is poorly understood. In this study, we investigated the forming processes in Pt/Ta₂O₅/TaOx/Pt and Pt/TaOx/Pt nanodevices, which showed BRS and URS, respectively. By comparing the double- and single-layer systems, we were able to observe differences in the BRS and URS forming processes. Using computer simulations based on an 'interface-modified random circuit breaker network model', we could explain most of our experimental observations. This success suggests that the BRS forming in our Pt/Ta₂O₅/TaOx/Pt double-layer system can occur via two processes, i.e., polarity-dependent resistance switching in the Ta₂O₅ layer and soft dielectric breakdown in the TaOx layer. This forming mechanism can be used to improve the performance of BRS devices. For example, we could improve the endurance properties of Pt/Ta₂O₅/TaOx/Pt cells by using a small forming voltage.