A Na 3 V 2 (PO 4 ) 3 /C cathode synthesized by a polyol-assisted pyrosynthetic reaction and subsequent sintering delivered a discharge capacity of 235 mA h g À1 , corresponding to an extraction of 4 Na per formula with steady capacity retention and impressive rate capabilities that maintain 56% of theoretical capacity at 2.67 C.

In response to the ever-increasing global demand for viable energy-storage systems, sodium and potassium batteries appear to be promising alternatives to lithium ion batteries because of the abundance, low cost and environmental benignity of sodium/ potassium. Electrical energy storage via ion-intercalation reactions in crystalline electrodes is critically dependent on the sizes of the guest ions. Herein, we report on the use of a porous amorphous iron phosphate synthesized using ambient temperature strategies as a potential host that stores electrical energy through the feasible insertion of mono-/di-/tri-valent ions. A combination of ex situ studies reveals the existence of a reversible amorphous-to-crystalline transition in this versatile electrode during electrochemical reactions with monovalent sodium, potassium and lithium. This reconstitutive reaction contributes to realizing specific capacities of 179 and 156 mAhg − 1 versus sodium and potassium at current densities of 10 and 5 mAg − 1 , respectively. This finding facilitates the feasible development of several amorphous electrodes with similar phase behavior for energy-storage applications. NPG Asia Materials (2014) 6, e138; doi:10.1038/am.2014.98; published online 17 October 2014 INTRODUCTIONSince 1990, the global demand for electricity has increased twice as much as the demand for energy overall, and the demand for electricity is expected to further increase by more than two-thirds over the next 20 years. Energy storage/conversion technologies have therefore become a crucial research topic as we seek to make society sustainable. In particular, electrical energy storage is critical not only for supporting electronic, vehicular and load-leveling applications but also for efficiently commercializing renewable solar and wind power. Rechargeable Li-ion batteries with an output energy exceeding 90% have emerged as one of the most effective electrochemical energystorage technologies, and these batteries power most modern-day electronic devices. 1 Despite substantial research to enhance Li-ion batteries for high-power applications, aspects such as their availability, cost and safety still remain to be fully addressed. 2 The controversies surrounding the accessible global lithium reserves and the anticipated energy demand may greatly impact the cost of Li-ion batteries in the long term. 3 Although advancing Li-ion battery technologies for electric vehicle applications is attractive, the quest for alternative energy sources for smart grid-scale storage applications has recently gained significant momentum. Rechargeable sodium and potassium batteries offer tremendous potential because they utilize inexpensive, abundant and environmentally benign sodium/potassium elements. [4][5][6][7][8][9] However,

A monoclinic Li3V2(PO4)3/C (LVP/C) cathode for lithium battery applications was synthesized by a polyol-assisted pyro-synthesis. The polyol in the present synthesis acts not only as a solvent, reducing agent and a carbon source but also as a low-cost fuel that facilitates a combustion process combined with the release of ultrahigh exothermic energy useful for nucleation process. Subsequent annealing of the amorphous particles at 800°C for 5 h is sufficient to produce highly crystalline LVP/C nanoparticles. A combined analysis of X-ray diffraction (XRD) and neutron powder diffraction (NPD) patterns was used to determine the unit cell parameters of the prepared LVP/C. Electron microscopic studies revealed rod-type particles of length ranging from nanometer to micrometers dispersed among spherical particles with average particle-sizes in the range of 20–30 nm. When tested for Li-insertion properties in the potential windows of 3–4.3 and 3–4.8 V, the LVP/C cathode demonstrated initial discharge capacities of 131 and 196 mAh/g (~100% theoretical capacities) at 0.15 and 0.1 C current densities respectively with impressive capacity retentions for 50 cycles. Interestingly, the LVP/C cathode delivered average specific capacities of 125 and 90 mAh/g at current densities of 9.6 C and 15 C respectively within the lower potential window.

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Nanocrystalline anatase TiO 2 was synthesized from a triethylene glycol solution of titanium isopropoxide ͓Ti͑O-iPr͒ 4 ͔ by refluxing at 270°C for 12 h. The thermal stability and effect of particle size on the corresponding electrochemical performances were investigated by annealing the prepared sample at various temperatures; namely, 300, 400, 500, 600, 700, 800, and 900°C. The X-ray diffraction patterns of the samples clearly revealed that the maximum temperature for the formation of pure anatase phase was 700°C beyond which the presence of rutile polymorph became significant. The field emission-transmission electron microscopy images of the obtained samples showed uniform and considerably dispersed particles with fairly homogeneous distributions and average sizes of 8-50 nm. The electrochemical measurements indicated considerable charge-discharge capacities devoid of major capacity fading during extended cycles, due to their electrochemically beneficial highly crystalline traits, nanosized particles, and uniform distribution.