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In the present study, an in-depth investigation on the structural transformation in a mesoporous γ-MnO2 cathode during electrochemical reaction in a zinc-ion battery (ZIB) has been undertaken. A combination of in situ Synchrotron XANES and XRD studies reveal that the tunnel-type parent γ-MnO2 undergoes a structural transformation to spinel-type Mn(III) phase (ZnMn2O4) and two new intermediary Mn(II) phases, namely, tunnel-type γ-ZnxMnO2 and layered-type L-ZnyMnO2, and that these phases with multioxidation states coexist after complete electrochemical Zn-insertion. On successive Zn-deinsertion/extraction, a majority of these phases with multioxidation states is observed to revert back to the parent γ-MnO2 phase. The mesoporous γ-MnO2 cathode, prepared by a simple ambient temperature strategy followed by low-temperature annealing at 200 °C, delivers an initial discharge capacity of 285 mAh g–1 at 0.05 mA cm–2 with a defined plateau at around 1.25 V vs Zn/Zn2+. Ex situ HR-TEM studies of the discharged electr...

Cappearstocontributetoitsimpressiveelectrochemicallithiumstorageproperties among the prepared electrodes. The pyro-synthetic strategy aids in developing nanostructured battery electrodes withporous morphologies and appears to offer promise for being developed as an energy saving process for large-scale applications.© The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative CommonsAttribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/),whichpermitsnon-commercialreuse,distribution,andreproductioninanymedium,providedtheoriginalworkisnotchangedinanyway and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0511507jes]All rights reserved.Manuscript submitted February 2, 2015; revised manuscript received March 29, 2015. Published April 8, 2015.

In the present study, a metal-organic framework (MOF) derived from a facile water-assisted green precipitation technique is employed to synthesize phase-pure cobalt vanadate (Co

A nonstoichiometric sodium manganese oxide (NaxMnO2 + d) cath- ode useful for sodium batteries was synthesized by an ambient-temperature strategy that involved facile reduction of aqueous sodium permanganate in sodium iodide and subsequent heat treatment at 6008C. Combined powder X-ray diffraction and synchrotron X- ray diffraction analyses confirmed the annealed sample to belong to aN a xMnO2 phase with a P2-hexagonal structure. The ICP-AES results con- firmed the stoichiometry of the sample to be Na0.53MnO2 + d. Electron microsco- py studies revealed the particle size of the electrode to be in the range of a few hundred nanometers. The Na0.53MnO2 + d cathode delivered an average discharge capacity of 170 mA h g � 1 with a stable plateau at 2.1 V for the initial 25 cycles versus sodium. Ex situ XANES studies con- firmed the reversible intercalation of sodium into Na0.53MnO2 + d and suggest- ed the accommodation of over-stoi- chiometric Mn 4 + ions to contribute to- wards the performance of the elec- trode.

LiFePO 4 cathodes with secondary nanorod structures and nano-plate morphologies were synthesized by varying the reaction time in a polyol refluxing process without the use of any characteristic structure directing agents. The X-ray diffraction studies indicate the highly crystalline nature of the prepared samples. Electron microscopy investigations revealed the morphology of the samples after 1 to 16 h polyol reaction to be secondary nanorod bundles whereas the olivine sample recovered after 32 h polyol reaction displayed nano-plate morphology. The dimensions of the obtained samples varied from a few tens to a few hundred nanometers. When employed in a lithium test cell, the LiFePO 4 cathodes reacted for 1, 4, 8, 16 and 32 h delivered discharge capacities of 161, 162, 171, 143 and 155 mAhg − 1 , respectively, with a well-defined plateau at 3.4 V and impressive capacity retentions until 50 cycles. Interestingly, among the prepared electrodes, the LiFePO 4 nanorod bundle cathode prepared under 1 h reaction time maintained the highest average reversible capacities of 123 and 103 mAhg − 1 at C-rates as high as 3.2 and 6.4 C. The crystal growth mechanism during the polyol refluxing method can be explained by the stages of precursor dissolution and nucleation, oriented crystal growth and alignment by self-assembly, aggregation and partial dissolution and complete re-crystallization.

In the present study, carbon-coated lithium iron phosphate (LiFePO4/C) is prepared directly by a polyol-assisted pyro-synthesis performed under reaction times of a few seconds in open-air conditions. The polyol solvent, tetraethylene glycol (TTEG), acts as a low-cost fuel to facilitate combustion and the released exothermic energy promotes the nucleation and growth processes of the olivine nanoparticles. In addition, phosphoric acid (used as the phosphorous source) acts as a catalyst to accelerate polyol carbonization. The structure analysis of the as-prepared LiFePO4/C using X-ray, neutron diffraction and 7Li NMR studies suggested the efficacy of the rapid technique to produce highly crystalline phase-pure olivine nanocrystals. The electron microscopy and particle-size distribution studies revealed that the average particle diameters lie below 100 nm and confirmed the presence of a surface carbon layer of 2–3 nm thickness. The thermal and elemental studies indicated that the carbon content in the sample was approximately 5 %. The prepared LiFePO4/C cathode delivered capacities of 162 mA h g-1 at 0.1 °C rates with impressive capacity retention for extended cycling. The polyol-assisted pyro-synthesis, which evades the use of external energy sources, is not only a straightforward, simple and timely approach but also offers opportunities for large-scale LiFePO4/C production.

Olivine structured LiFePO4/carbon composites with different amounts of carbon were prepared by a modified two-step solid-state reaction. The iron citrate used as both iron and carbon sources in the reaction resulted in the formation of carbon coatings on the olivine particles as the mixed precursors were heated at three different initial-step temperatures of 200, 300 and 400 °C followed by a second-step annealing at moderate temperatures of 700 °C. The obtained final powders with varying carbon contents were systematically analyzed by characterization techniques of thermo-gravimetric analysis, X-ray powder diffraction, field-emission scanning electron microscopy, and field-emission transmission electron microscopy prior to electrochemical testing in order to determine the structural and calcination effects on the electrochemical properties of the composites. The field-emission transmission electron microscopy images revealed that the morphology of the LiFePO4 composites consist of agglomerated particles surrounded by carbon as a conductive material. Among the prepared samples, the LiFePO4/carbon composite calcined at initial-step temperature of 300 °C showed the highest discharge capacity and the best rate capability in the voltage range of 2.5–4.2 V.

Herein, we report on a high-discharge-rate Na

The high capacity and low potential make Li-metal ideal anode material for high energy density batteries. However, its poor cyclability and safety issue prevent the practical use of Li-metal for rechargeable batteries. The degradation of Li-metal is mainly caused by dendrite formation of deposited Li and decomposition of liquid electrolyte at the interface between Li-metal and a separator. We modified the interfacial structure using aromatic porous layer (APL) to form stable SEI layer and minimize dendritic growth of Li-metal. Without APL, the surface of SEI/Li-meal was rough, and there were small cracks. However, APL led to formation of smooth SEI/Li-metal surface. In addition, the use of APL changed the structure of Li dendrite from a sharp needle-like shape to a blunt flower-like shape, which reduces the problematic electrolyte decomposition reaction. For this reason, APL improved cycling efficiency of Li dendrite. We tested a NMC/Cu cell to investigate the cycling efficiency of Li-dendrite. The cell assembled with APL showed 2 times higher efficiency compared to that of normal NMC/Cu cell. Due to stable interface between Li-metal and separator, the cyclability of a NMC/Li-metal cell with APL was remarkably improved. After 100 cycles, the residual capacity of the APL cell was 3 times higher than that of the conventional NMC/Li-metal cell.

Lithium ion Batteries (LIBs) are the most popular tools as energy storage systems for electric vehicles (EVs), large-scale energy storage system (ESS) owing to their high energy density, power properties. However, LIBs are complex systems which are not yet revealed completely for their degradation mechanism. In general, the loss of Lithium during cycling, depletion and decomposition of the electrolyte, structural collapse of active materials and resistance increase are the most probable reasons for the degradation of LIBs. To diagnose LIBs, we have focused to make a unitary degradation cell which has referred reason during cycling. Herein, we fabricate Li loss cell intentionally as specified value and figure out how different capacities between intended values and real value in cells. Furthermore, we investigate what different in electrochemical impedance between the fresh cell and the unitary degradation cell.

Reduced graphene oxide (rGO) sheets were synthesized by a modified Hummer's method without additional reducing procedures, such as chemical and thermal treatment, by appropriate drying of graphite oxide under ambient atmosphere. The use of a moderate drying temperature (250°C) led to mesoporous characteristics with enhanced electrochemical activity, as confirmed by electron microscopy and N 2 adsorption studies. The dimensions of the sheets ranged from nanometres to micrometres and these sheets were entangled with each other. These morphological features of rGO tend to facilitate the movement of guest ions larger than Li + . Impressive electrochemical properties were achieved with the rGO electrodes using various charge-transfer ions, such as Li + , Na + and K + , along with high porosity. Notably, the feasibility of this system as the carbonaceous anode material for sodium battery systems is demonstrated. Furthermore, the results also suggest that the high-rate capability of the present rGO electrode can pave the way for improving the full cell characteristics, especially for preventing the potential drop in sodium-ion batteries and potassium-ion batteries, which are expected to replace the lithium-ion battery system

An efficient synthesis is used for the first time to prepare CuO/reduced graphene oxide nanocomposite anode materials for lithium ion batteries. Initially, copper oxide (CuO) nanoparticles are synthesized via a simple, facile and inexpensive microwave-assisted method within short reaction times (

In present study, fluorine substituted Li1.23Ni0.13Co0.14Mn0.56O2−zFz (z = 0–0.20) are synthesized by simple and low-temperature co-precipitation process and observed enhancement in their electrochemical properties are investigated as function of fluorine substitutions. 19F MAS NMR analyses revealed the presence of fluorine as metal fluoride on the surface, and as oxy-fluoride in bulk Li1.23Ni0.13Co0.14Mn0.56O2−zFz. Li1.23Ni0.13Co0.14Mn0.56O2−zFz (z = 0.15) showed improved cycling performance and reduced cell impedance as a result of the fluorine doping. In addition, fluorine substitution controlled the amount of stabilizing transition metals in the lithium layers of spinel-like regions, which in turn resulted in countering the capacity loss and voltage decay compared to Li1.23Ni0.13Co0.14Mn0.56O2.

Urea-assisted auto-combustion synthesis was used for the easy and scalable preparation of TiO2 nanoparticles for use as anodes in lithium-ion batteries. The prepared TiO2 powder was annealed at 300 °C, 400 °C, 500 °C and 600 °C to optimize the system and assess the effects of particle size on electrochemical properties. X-ray diffraction patterns confirmed that pure anatase phase TiO2 formed at up to 500 °C, above which mixed phases of anatase and rutile emerged. Field-emission transmission electron microscopy showed that spherical particles of 8–25 nm were formed. The electrochemical performances of annealed TiO2 samples were tested by charging/discharging, C-rate measurement and electrochemical impedance spectroscopy. It was clearly found that the crystal particle size has a striking impact on the Li insertion behavior and lithium storage capability. TiO2 nanoparticles electrode annealed at lower temperature 300 °C showed high rate capability, excellent capacity retention and high electrical conductivity due to its very small particles and nonideal crystal lattices.

The real time detection of quantitative oxygen release from the cathode is performed by in-situ Gas Chromatography as a tool to not only determine the amount of oxygen release from a lithium-ion cell but also to address the safety concerns. This in-situ gas chromatography technique monitoring the gas evolution during electrochemical reaction presents opportunities to clearly understand the effect of surface modification and predict on the cathode stability. The oxide cathode, 0.5Li2MnO3∙0.5LiNi0.4Co0.2Mn0.4O2, surface modified by amorphous cobalt-phosphate nanoparticles (a-CoPO4) is prepared by a simple co-precipitation reaction followed by a mild heat treatment. The presence of a 40 nm thick a-CoPO4 coating layer wrapping the oxide powders is confirmed by electron microscopy. The electrochemical measurements reveal that the a-CoPO4 coated overlithiated layered oxide cathode shows better performances than the pristine counterpart. The enhanced performance of the surface modified oxide is attributed to the uniformly coated Co-P-O layer facilitating the suppression of O2 evolution and offering potential lithium host sites. Further, the formation of a stable SEI layer protecting electrolyte decomposition also contributes to enhanced stabilities with lesser voltage decay. The in-situ gas chromatography technique to study electrode safety offers opportunities to investigate the safety issues of a variety of nanostructured electrodes.

We report on the solvothermal preparation of pure Li 4 Ti 5 O 12 and Li 4 Ti 5 O 12 /graphene (15 wt% and 30 wt%) nanocomposites anode for high-performance lithium-ion batteries. Structure and morphology studies of the nanocomposites by X-ray diffraction, field-emission scanning electron microscopy and field-emission transmission electron microscopy reveal Li 4 Ti 5 O 12 nanoparticles embedded onto the graphene nanosheets. On comparison to pure spinel Li 4 Ti 5 O 12 , the electrochemical performances of the Li 4 Ti 5 O 12 /graphene nanocomposites indicate higher capacities and enhanced cycle performances within the voltage domain of 1.0–2.5 V, under current rates as high as 10.4 C. The production of phase pure Li 4 Ti 5 O 12 nanoparticles ensures the short ion-diffusion paths while the presence of graphene facilitates improved structural network and hence enhanced electronic transport in the prepared nanocomposites. These factors eventually amount to impressive electrochemical properties.

This paper reports a co-precipitation synthesis of TiP 2 O 7 –graphene (10 wt%) nanocomposite and pure TiP 2 O 7 nanoparticles for the use as an advanced anode material for high performance lithium-ion batteries. The structure and morphology of the compounds are characterized by powder X-ray diffraction, field-emission scanning electron microscopy and field-emission transmission electron microscopy techniques. The electrochemical performances were evaluated in coin type Li-ion test cells. This TiP 2 O 7 –graphene nanocomposite displayed superior Li-ion battery performance with a large reversible capacity, excellent cyclic performance and good rate capability at a current density of 0.1 mA cm −2 . At an elevated current density of 6.4 mA cm −2 , the nanocomposite anode delivered a capacity of 98.4 mAh g −1 , which is much higher than that of pure TiP 2 O 7 (0.56 mAh g −1 ). The impressive electrochemical performance of the nanocomposite was ascribed to the synergistic effect of the high surface area nanoparticles in conjunction with the good electronic conductivity of graphene. The graphene nanosheets not only provide an electronically conducting network, but also tend to prevent the aggregation of the high surface area TiP 2 O 7 nanoparticles. Further, the graphene nanosheets can act as buffer layers to accommodate the volume change during the Li-ion insertion/extraction processes in the TiP 2 O 7 nanoparticles.

A nanostructured Mn

Nanocrystalline LiFePO4/C has been synthesized under a very short period of time (90 sec) using a polyol-assisted microwave heating synthesis technique. The X-ray diffraction (XRD) data indicates that the rapidly synthesized materials correspond to phase pure olivine. Post-annealing of the as-prepared sample at 600 °C in argon atmosphere yields highly crystalline LiFePO4/C. The morphology of the samples studied using scanning electron microscopy (SEM) reveals the presence of secondary particles formed from aggregation of primary particles in the range of 30-50 nm. Transmission electron microscopy (TEM) images reveal a thin carbon layer coating on the surface of the primary particle. The charge/discharge studies indicate that the as-prepared and annealed LiFePO4/C samples delivered initial discharge capacities of 126 and 160 mA h g-1, respectively, with good capacity retentions at 0.05 mA cm-2 current densities. The post-annealing process indeed improves the crystallinity of the LiFePO4 nanocrystals, which enhances the electrode performance of LiFePO4/C.

Carbon-coated nano-sized LiMnPO4/C particles are synthesized by polyol method using low-cost glucose as the carbon source. The X-ray diffraction patterns of the synthesized samples are well indexed to the orthorhombic olivine-LiMnPO4 structure. The morphology studies using FE-SEM and HR-TEM images clearly illustrate thin layered carbon coatings on LiMnPO4 particles of sizes ranging between 50~100 nm. The LiMnPO4/C particles delivers an initial discharge capacity of 151 mA h g-1 at a current density of 1.6 mA g-1 in the voltage range of 2.5-4.3 V with impressive capacity retentions.

Hierarchical meso-/macroporous anatase TiO2 was synthesized by the hydrolysis of a titanium metal-organic framework precursor followed by calcination in air. This unique porous feature enables the superior rate capability and excellent cycling stability of anatase TiO2 as an anode for rechargeable lithium-ion batteries.

Thermo–mechanical treatment was employed in this study to optimize the strength and conductivity of Cu–Fe–Ag microcomposites. The strength/conductivity properties of Cu–Fe–Ag microcomposites drawn to η = 4.8 without intermediate heat treatments (NH) were observed to be 1006 MPa/39% IACS and those drawn to η = 6.3 with three intermediate heat treatments (IH-3) were 939 MPa/56.2% IACS. A substantial increase of conductivity was obtained at the expense of a modest loss of the strength by the employment of intermediate heat treatments. The precipitation of impurities and alloying elements during intermediate heat treatment is thought to increase the conductivity due to the reduced impurity scattering. The activation volume was measured to be 170 b 3 for the as-drawn Cu–Fe–Ag (IH-2). Numerous particles were observed in Cu matrix and the spacing between these particles (∼30 nm) were found to be comparable to the activation length (170 b = 43 nm). The most probable rate controlling mechanism of Cu–Fe–Ag microcomposites is suggested to be the interaction between dislocations and precipitates in Cu matrix.

/C cathode delivered an initial discharge capacity of 163 mAh/g (98% of theoretical value) at C/20 rate withimpressive capacity retentions until 50 cycles attributed to the combined contributions of surface coating and porous structure thatserve as facile electrical conduits for ion/electron transport.© 2012 The Electrochemical Society. [DOI: 10.1149/2.003204eel] All rights reserved.Manuscript submitted May 30, 2012; revised manuscript received July 2, 2012. Published August 24, 2012.

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.

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.

Despite nanomaterials with unique properties playing a vital role in scientific and technological advancements of various fields including chemical and electrochemical applications, the scope for exploration of nano-scale applications is still wide open. The intimate correlation between material properties and synthesis in combination with the urgency to enhance the empirical understanding of nanomaterials demand the evolution of new strategies to promising materials. Herein we introduce a rapid pyro-synthesis that produces highly crystalline functional nanomaterials under reaction times of a few seconds in open-air conditions. The versatile technique may facilitate the development of a variety of nanomaterials and, in particular, carbon-coated metal phosphates with appreciable physico-chemical properties benefiting energy storage applications. The present strategy may present opportunities to develop "design rules" not only to produce nanomaterials for various applications but also to realize cost-effective and simple nanomaterial production beyond lab-scale limitations.

In this study, anatase-type titanium dioxide (TiO2) anodes were prepared by a polyol-assisted pyro-synthetic process followed by mild annealing in the range of 300 to 600 °C. The XRD studies confirmed the formation of anatase-type TiO2 and the Scherrer formula aided in establishing the average crystallite size to be less than 50 nm for all of the prepared samples. Electron microscopy studies revealed the average particle-size to be in the range between 5 and 50 nm whereas the adsorption studies demonstrated the mesoporous characteristics of all the prepared samples and the 500 °C electrode, in particular, exhibited tri-porosity. This unique tri-porous feature in combination with the sufficiently high particle crystallinity appears to contribute to the impressive electrochemical lithium storage (154.7 and 116.4 mAh g-1 at 3.2 and 6.4 C, respectively) in the 500 °C electrode. Furthermore, the pyro-synthetic strategy aids in developing nanostructured battery electrodes with porous morphologies and appears promising to be developed as an energy saving process for large-scale applications.

Metal-organic framework (MOF) based synthesis of battery electrodes has presently become a hot topic of significant research interest. Considering the complications to prepare Co3V2O8 due to the criticality of its stoichiometric composition, we report here by a simple MOF formation by solvothermal technique followed by air annealing to synthesize Co3V2O8 for use as potential anodes for lithium battery applications. Structrual investigations by X-ray diffraction, X-ray photoelectron spectroscopy, high resolution electron microscopy, and surface area studies revealed that the phase pure Co3V2O8 nanoparticles are inter connected to form a sponge-like morphology with porous properties. Electrochemical measurements exposed the excellent lithium storage (~ 1000 mAhg-1 at 200 mAg-1) and retention properties (500 mAhg-1 at 1000 mAg-1 after 700 cycles) of the prepared Co3V2O8 electrode. A notable rate performance of 430 mAhg-1 at 3200 mAg-1 was also observed and ex-situ analysis confirmed the morphological and structural stability of this material after long cycles performance. These results validate that the unique nanostructured morphology arising from the use of the ordered array of MOF networks is favorable for improving the cyclability and rate capability in battery electrodes. The synthetic strategy presented herein may provide solutions to develop phase pure mixed metal oxides for high performance electrodes for useful energy storage applications. Figure 1

In commercially available Li-ion cells, cobalt-based oxide is utilized as the cathode material, but its high cost and low thermal stability prohibit the large-scale use such as Energy Storage Systems (ESS) and Electric Vehicles (EV). Lithium iron phosphate (LiFePO4) and lithium vanadium phosphate (Li3V2(PO4)3) exhibit good thermal stability and high operating voltage, which make them the most promising cathode candidates so far. Despite of their advantages, LiFePO4 and Li3V2(PO4)3 also have some drawbacks. For instance, LiFePO4 has a stable voltage platform and its cyclic attenuation rate is almost negligible, but its relatively low capacity and low voltage limit its energy density and consequently limits its use. Li3V2(PO4)3 has a higher voltage, however, it suffers from its stepped voltage platforms and severe cycle attenuation. In order to combine the advantages from both materials, many research groups have attempted by designing hybrid materials since the doping approach can only improve the main material without combining the advantages of two different active materials. In this work, we focus on obtaining nanostructured materials as well as hybrid materials by using pyro-synthetic method which is very effective for production of highly crystalline carbon coated nanomaterials under very short reaction times in open-air conditions. Further, the pyro-synthetic route using polyol medium will be beneficial for producing nanomaterials in terms of time and cost effectiveness because the combustion strategy is also applied to this strategy. Moreover, poly alcohols or polyols such as ethylene glycol and di/tri/tetra ethylene glycol can play multi-roles of a solvent, a reducing agent and a carbon source. We have successfully synthesized 0.66LiFePO4•0.33Li3V2(PO4)3 nanocomposites with high crystallinity by one-step pyro-synthetic strategy using the polyol at low temperature. The as-prepared sample without any additional heat treatment showed average particle size of about 30 – 60 nm and spherical shape as observed by SEM studies. After moderate heat-treatment was applied, the particle sizes of 0.66LFP•0.33LVP increased due to crystal growth of monoclinic phase of LVP accompanied by particle agglomeration. When tested for lithium-ion cell, the nanoparticles composite electrode demonstrated impressive electrochemical properties with enhanced energy density. Furthermore, it showed high reversible capacity of 145.65 mAh g-1 at 0.1C and exhibited remarkable capacity of 119 mAh g-1 at 6.4C. After cycled at 6.4C, the electrode can recover to 85% of its initial capacity when the current density returned back to 0.1C indicating the excellent rate capabilities of the present electrode.

The present study reports on a highly rate capable NASICON-structured NaTi2(PO4)3/ reduced graphene oxide (NTP/rGO) composite electrode synthesized by polyol-assisted pyro synthesis for Na-ion batteries (NIBs). X-ray diffraction (XRD) studies confirmed the presence of a rombohedral NaTi2(PO4)3 phase in the composite while Raman spectroscopy studies helped to identify the existence of rGO in the composite. Electron microscopy studies established that NaTi2(PO4)3 nanoparticles of average sizes ranging between 20 and 30 nm were uniformly distributed and embedded on the GO sheets. When tested for sodium storage properties, the obtained NTP/rGO composite electrode registered high rate capacities (95 mAh g-1 at 9.2 C and 78 mAh g-1 at 36.8 C) when compared to that of the NTP/C electrode (~1 mAh g-1 at 9.2 and 36.8 C). The enhanced performance of the composite electrode can be attributed to the nano-sized NaTi2(PO4)3 particles with shorter diffusion path lengths embedded on the rGO sheets with enhanced electrolyte/electrode contact areas that ultimately leads to an improvement in the electrical conductivity at high current densities. Ex-situ XANES studies confirmed reversible Na-ion intercalation/de-intercalation into/from NTP/rGO. The study thus demonstrates that the NaTi2(PO4)3/rGO nanocomposite electrode is a promising candidate for the development of high power/energy density anodes for NIBs.

This study reports the use of a layered-type birnessite δ-MnO2 nano-flake cathode for eco-friendly zinc-ion battery (ZIB) applications. The present δ-MnO2 was prepared via the simple low temperature thermal decomposition of KMnO4. The X-ray diffraction (XRD) pattern of the samples was well indexed to the δ-MnO2 phase. Field emission SEM and TEM images of the δ-MnO2 revealed flake-like morphologies with an average diameter of 200 nm. The electrochemical properties, investigated by cyclic voltammetry and constant current charge-discharge measurements, revealed that the nano-flake cathode exhibited first discharge capacity of 122 mAh g-1 under a high current density of 83 mA g-1 versus zinc. The discharge capacity thereafter increased until it reached 252 mAh g-1 in the fourth cycle. On the hundredth cycle, the electrode registered a discharge capacity of 112 mAh g-1. Coulombic efficiencies of nearly 100% were maintained on prolonged cycling and thereby indicate the long cycle stability of the δ-MnO2. Besides, the realization of specific capacities of 92 and 30 mAh/g at high current densities of 666 and 1333 mA/g, respectively, clearly demonstrates the decent rate capabilities of δ -MnO2 nano-flake cathode. These results may facilitate the utilization of layered-type birnessite δ-MnO2 in ZIB applications.

Nowadays, extensive researches to overcome the world energy crisis has emphasized the urgent necessity of developing sustainable energy storage systems. The rechargeable lithium-ion battery (LIB) dominates today's battery market for portable device applications. Nonetheless, the crucial issues concerning its safety, eco-friendliness, and cost-effectiveness, as well as the controversies associated with the availability of lithium resources, have led to the continuous exploration of new battery chemistries. Sodium-ion, potassium-ion, and aluminum-ion batteries are promising alternative since these devices are based on relatively abundant and cheap sodium, potassium, and aluminum elements, respectively. However, these battery systems also suffer from complicated issues of safety, processing costs, and environmental concerns. Earlier efforts for developing a rechargeable aqueous zinc-ion battery (ZIB), which facilitates energy storage application via zinc-ion insertion/extraction, has opened the way for the realization of safe, environmentally benign and cost-effective next generation energy storage system. ZIB is still in the stage of early phase of development, therefore, fundamental studies concentrating on the zinc-ion insertion mechanism is an attractive goal to pursue. In this work, we used nanorod alpha-type manganese dioxide cathode for ZIB application. Alpha-type manganese deioxide was prepared by a simple hydrothermal synthesis. SEM and TEM studies showed rod-type sample with approximately 20 and 200 nm of width and length, respectively. The nanorod cathode exhibited an initial discharge capacity of 176.8 mAh g-1 at a current density of 83 mA g-1 and demonstrated nearly 100% Coulombic efficiencies under prolonged cycling when tested for zinc storage properties. Rate performance measurements revealed that specific capacities of 43.33 and 31.48 mAh g-1 were registered at current densities as high as 1333 and 1666 mA g-1. A combination of ex-situ synchrotron XRD and XAS studies confirmed the reversibility of electrochemical zinc-ion insertion into [2x2] tunnels of the alpha-type manganese dioxide host structure. The host exhibits structural stability by accommodating an unit cell volume expansion of approximately 3.12% during Zn-insertion. The present study hence paves the way for further development of rechargeable aqueous ZIB as an alternative ideal energy storage system due to its excellent safety and reliability. Figure 1

A Li-ion battery cathode with target stoichiometry LiTi0.08Fe0.92PO4 was prepared by doping excess amount of Ti4+ into the olivine structure using solid-state reaction at 700 °C. X-ray diffraction (XRD) results of the prepared sample confirmed the presence of a major olivine phase in addition to few impurity phases including the ion-conducting NASICON-type Li3Fe2(PO)4 and Li2TiFe(PO4)3 phases. Further, the calculated lattice parameter values appear to confirm Ti-doping in LiFePO4. Electron microscopy and particle distribution studies revealed a slight increase in the average particle-sizes in addition to fragmented particles and the presence of surface carbon coating on the sample particles. EDX mapping studies revealed a fair distribution of Ti4+ ions in the prepared sample. When examined as a cathode in a non-aqueous lithium cell at room temperature, LiTi0.08Fe0.92PO4 delivered high specific capacities and good capacity retentions (≤ 2% capacity loss after 50 cycles). Besides, the cathode delivered impressive rate capabilities as specific capacities of 160 and 110 mAhg-1 at 0.1 and 11.4 C, respectively, were retained. Although the average particle-size was slightly higher, the presence of ion-conducting NASICON-type species appear to contribute to the enhanced electrical conductivity and hence to the cathode performance of LiTi0.08Fe0.92PO4.

The increasing demand for energy storage devices has motivated the need to find environmentally friendly, high energy density, and cost-effective materials for energy storage and suitable synthesis techniques. In this work, we report a simple and cost-effective chemical route, in which intermediate Ni1/3Co1/3Mn1/3(OH)2 product was primarily prepared using a simple redox synthesis technique at ambient temperature. Lithiation reactions were then performed at higher temperatures to develop the final layered Lix(Ni1/3Co1/3Mn1/3)O2 structure (where x= 1.0 and 1.05). The lithium content was varied in order to analyze the effect of excess lithiation on the structural and electrochemical properties of the layered-type Li(Ni1/3Co1/3Mn1/3)O2 cathode. The XRD studies clearly confirmed the formation of layered-type structures corresponding to hexagonal α-NaFeO2 (space group R-3m). The ICP studies confirmed the stoichiometric chemical composition (Li(Ni0.32Co0.33Mn0.31)O2) of the prepared samples. FE-SEM images revealed that the particle growth occurred when the particles were heated at elevated temperatures of 950°C, and the average particle diameter was around a few micrometers. The electrochemical tests performed versus lithium indicated that competitive specific capacity values were registered for all the prepared cathodes and the capacity retention was impressive on repeated charge/discharge cycling within the potential range of 3.0 – 4.3 V and a current density of 14 mA/g. In particular, the Li(Ni0.32Co0.33Mn0.31)O2 sample demonstrated the highest capacity retention value (~ 99%) after 50 cycles and better rate performances of 104, 91, 76, and 67 mAh/g at higher current densities of 229, 457, 914, and 1429 mA/g respectively.

Hierarchical meso-/macroporous anatase TiO2 (HPT) was synthesized from the hydrolysis of a titanium metal-organic framework precursor followed by calcination in air. The HPT possesses bimodal and hierarchical porosity: mesopores with pore diameters of 12, 16 and 28 nm along with macropores with pore diameters of up to 185 nm.This unique porous feature enables the superior rate capability and excellent cycling stability of anatase TiO2 as an anode for rechargeable lithium-ion batteries(LIBs). At a rate of 5 C, the specific discharge capacity of the HPT electrode is about 155 mA h g-1. After 200 cycles at 5 C charging/discharging rates, the capacity loss was only ~6.5 %. The superior rate capability and excellent cycling stability make HPT a promising anode material for fast rechargeable LIBs. Figure 1

In response to the ever-increasing global demand for electronic devices, Lithium-ion batteries have taken an important place in meeting this demand since they provide high voltage, high energy density, and are light weight. Nanostructured binary metal oxides (BMOs) which exhibit high theoretical capacity as a result of a conversion reaction. Among the BMOs, the manganese-based oxide hausmannite (Mn3O4) has attracted much attention due to it being low –cost and environmentally benign. A nanostructured Mn3O4/C electrode was prepared by a one-step polyol-assisted pyro-synthesis without any post-heat treatments. The as-prepared Mn3O4/C revealed nanostructured morphology comprised of secondary aggregates formed from carbon-coated primary particles of average diameters ranging between 20 and 40 nm, as evidenced from the electron microscopy studies. The N2 adsorption studies reveal a hierarchical porous feature in the nanostructured electrode. The nanostructured morphology appears to be related to the present rapid combustion strategy. The nanostructured porous Mn3O4/C electrode demonstrated impressive electrode properties with reversible capacities of 666 mAh/g at a current density of 33 mA/g, good capacity retentions (1141 mAh/g with 100% Coulombic efficiencies at the 100th cycle), and rate capabilities (307 and 202 mAh/g at 528 and 1056 mA/g, respectively) when tested as an anode for lithium-ion battery applications.

A facile and cost-effective urea-assisted autocombustion strategy has been designed for the fabrication of Co3O4/CoFe2O4 nanocomposite and pure CoFe2O4 anode materials followed by annealing at 700 and 900 °C for 6 h, respectively. To confirm the exact structure, Rietiveld analysis was performed on the Synchrotron XRD pattern of both the CoFe2O4 samples annealed at 700 and 900 °C. The results clearly depicts the formation of two phases (Co3O4:CoFe2O4) with the ratio of [76.3(5):23.6(3)%] in the sample annealed at 700 °C sample, while single phase CoFe2O4 formation was observed for the sample annealed at 900 °C. It has also been found that the designed nanocomposite sample is composed of small nanoparticles (50–100 nm), while the size of pure CoFe2O4 particles is in the range from 600 nm to 1 μm. When applied as an anode material, the obtained Co3O4/CoFe2O4 nanocomposite electrode exhibits high reversible capacity as well as excellent cycling stability and better rate capability in comparison to a pure CoFe2O4 electrode. The enhanced electrochemical performance of the nanocomposite can be attributed to the intimate interconnection between Co3O4 and CoFe2O4, along with the nanosize range of particles and high surface area, which not only favor fast kinetic properties facilitating electron transportation and Li+ ion insertion/deinsertion but also relieve the stress caused by volume changes during the numerous charge/discharge cycles and suppress the degradation of the material.

Since 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. 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 mAh/g versus sodium and potassium at current densities of 10 and 5 mA/g, respectively. This finding facilitates the feasible development of several amorphous electrodes with similar phase behavior for energy-storage applications. Figure 1

Abstract Commercially available lithium-ion batteries comprised of LiCoO2 as the cathode and graphite as the anode. Graphite is being considered for use as the anode material for lithium-ion batteries for several reasons, such as the fact that the Li+ ions can easily intercalate/de-intercalate into/from the graphite structure, low irreversible capacity at the first cycle, a flat and low potential profile, a long cycle life, abundant and relatively low cost. However, in spite of its advantages, graphite has several drawbacks, such as its low energy density, low theoretical capacity (372 mAh g-1), easy exfoliation and safety issues related to lithium deposition. These drawbacks limit its application to electric vehicles, hybrid electric vehicles and plug-in hybrid electric vehicles. Therefore, searching for new electrode materials which can act as an alternative to graphite with a high specific capacity and excellent electrical conductivity is an urgent task in building the next-generation high-power lithium-ion batteries, in order to fulfill the ever-growing demand in various consumer electronic devices. Recently, ZnMn2O4 has been considered as one of the most attractive compounds, because of the low oxidation (delithiation) potential of zinc and manganese nanoparticles: 1.2 V and 1.5 V, respectively, which ultimately increase the battery output voltage compared to that provided by simple binary metal oxides. Furthermore, zinc and manganese are abundant, environmentally friendly, and relatively inexpensive compared to nickel and cobalt. Interestingly, ZnMn2O4 can store Li+ions through both conversion and alloying reactions, because Zn, one of the products of the conversion reaction. However, as in the case of other anodes, the poor electric conductivity and large volume change of the ZnMn2O4 nanostructures during the electrochemical reaction lead to a fast capacity decrease. However, a few attempts have been made to overcome the aforementioned drawbacks of ZnMn2O4 by focusing on controlling the morphology accompanied with synthesis of nano-sized particles and graphene based nanocomposites using expensive and tedious methods. Nanostructured materials have become a subject of great interest in a variety of mechanical, electrical and optical applications, due to their unique physico-chemical properties. Therefore we are synthesized ZnMn2O4/C nanoparticles by one step polyol assisted pyro-synthesis for use as the anode in rechargeable lithium ion batteries without any post heat treatment. The as-prepared ZnMn2O4/C is tetragonal with a spherical particle size in the range of 10–30 nm. Electrochemical measurements were performed using the as-prepared powders as the active material for a lithium-ion cell. The nanoparticle electrode delivered an initial charge capacity of 666.1 mAh g1 and exhibited a capacity retention of 81% (539.4 mAh g-1) after 50 cycles. The capacity enhancement in the as-prepared ZnMn2O4/C may be explained on the basis of the polyol medium that enables to develop a sufficient carbon network that can act as electrical conduits during electrochemical reactions. The carbon network appears to enhance the particle-connectivity and hence improve the electronic conductivities. References [1] A.K. Rai, L.T. Anh, C.J. Park, J. Kim, Ceram. Int., 39, 6611, (2013). [2] F.M. Courtel, Y. Abu-Lebdeh, I.J. Davidson, Electrochim. Acta, 71, 123, (2012). [3] Z. Bai, N. Fan, C. Sun, Z. Ju, C. Guo, J. Yang, Y. Qian, Nanoscale, 5, 2442, (2013). [4] L. Xiao, Y. Yang, J. Yin, Q. Li, L. Zhang, J. Power Sources, 194, 1089, (2009). Figure 1

Despite nanomaterials with unique properties playing a vital role in scientific and technological advancements of various fields including chemical and electrochemical applications, the scope for exploration of nano-scale applications is still wide open. The intimate correlation between material properties and synthesis in combination with the urgency to enhance the empirical understanding of nanomaterials demand the evolution of new strategies to promising materials. Herein we introduce a rapid pyro-synthesis (Fig.1.) that produces highly crystalline functional nanomaterials under reaction times of a few seconds in open-air conditions. The versatile technique may facilitate the development of a variety of nanomaterials and, in particular, carbon-coated metal phosphates with appreciable physico-chemical properties benefiting energy storage applications. The present strategy may present opportunities to develop ‘‘design rules’’ not only to produce nanomaterials for various applications but also to realize cost-effective and simple nanomaterial production beyond lab-scale limitations. Figure 1

In this study, a nanorod-type α-MnO2 cathode prepared by a facile hydrothermal reaction was utilized for rechargeable aqueous zinc-ion battery (ZIB) applications. Electron microscopy studies revealed rod-type particles with approximately 20 and 200 nm of width and length, respectively. When tested for zinc storage properties, the nanorod cathode exhibited an initial discharge capacity of 176.8 mAh/g at a current density of 83 mA/g and demonstrated nearly 100% Coulombic efficiencies under prolonged cycling. Further, rate performance measurements revealed that specific capacities of 43.33 and 31.48 mAh/g were attained at current densities as high as 1333 and 1666 mA/g. Ex-situ XAS investigations confirmed the reversibility of electrochemical Zn-insertion into the a-MnO2 electrode. Moreover, a combination of ex-situ synchrotron XRD studies, visualization and pattern-fitting software programs not only established the electrochemical Zn-insertion into the host a-MnO2 structure but also indicated that the unit cell volume of the [2x2] tunnels in the a-MnO2 host expands by approximately 3.12% during Zn-insertion. The present study thus paves the way for further development of aqueous ZIB as an ideal energy storage system due to its excellent safety and reliability.

A non-stoichiometric composition of sodium manganese oxide (NaxMnO2+δ) cathode useful for sodium batteries was synthesized by an ambient temperature strategy that involves the facile reduction of aqueous sodium permanganate in sodium iodide and subsequent heat treatment at 600 °C. A combined powder X-ray diffraction (PXRD) and synchrotron X-ray diffraction (SXRD) analyses confirmed the annealed sample to belong to a NaxMnO2 phase with a P2-hexagonal structure. The ICP results confirmed the stoichiometry of the sample to be Na0.53MnO2+δ. Electron microscopy studies revealed the particle size of the electrode to be in the range of a few hundred nanometers. The Na0.53MnO2+δ cathode delivered average discharge capacities of 170 mAhg-1 with a stable plateau at 2.1 V for the initial 25 cycles versus sodium. Ex-situ XANES studies confirmed the reversible intercalation of sodium into Na0.53MnO2+δ and suggested the accommodation of over-stoichiometric Mn4+ ions to contribute towards electrode performance. Figure 1

Mono-dispersed and densely packed, LiFePO4 cathodes with high rate performance versus lithium were synthesized using a two-step polyol process. The particle-size distribution and packing density of LiFePO4 nanoparticles were fine-tuned via separation of the nucleation and particle growth processes in the polyol medium by varying reaction time and temperature. Precisely, the LiFePO4 samples were synthesized by heating the reaction mixtures at 200 °C for various reaction times (0, 1, 3 and 6 h) to facilitate nucleation and thereafter the solution temperature was raised and maintained at 320 °C to facilitate the crystal growth process. XRD studies confirmed the formation of olivine phase in all the samples. The FE-SEM, FE-TEM and particle-size distribution studies illustrate that the particle-size of olivine nanocrystals may be tuned to approximately 200 nm by controlling the aging time at 200 °C or in other words separating the nucleation and crystal growth process. The olivine cathodes synthesized by maintaining 3-6 h aging time demonstrate improved discharge capacities and cycle performances in comparison to those of the remaining samples. In particular, the 6 h olivine cathode registered average discharge capacities of 130, 87 and 64 mAh/g at 5 C, 10 C and 15.7 C current rates respectively.

Earlier efforts to develop an aqueous zinc-ion battery (ZIB), which facilitates energy storage/conversion via Zn-ion intercalation/de-intercalation, has paved the way not only to realizing safe and environmentally benign energy devices, but also to reducing the processing costs of next generation batteries. [1,2] From the viewpoint of developing low-cost and environmentally safe rechargeable batteries that can be easily scaled up for large-scale production, the present study reports on a high surface area mesoporous tunnel-type γ-MnO2 cathode obtained by a simple template-free ambient temperature strategy and subsequent annealing at low temperatures for ZIB applications. An in-depth study on the structural transformation in a mesoporous γ-MnO2 cathode during electrochemical reaction in a zinc-ion battery (ZIB) has been conducted. A combination analyses of in-situ synchrotron XANES and XRD reveal that the tunnel-type parent γ-MnO2 experiences a structural transformation to spinel-type Mn(III) phase (ZnMn2O4) and two new intermediary Mn(II) phases namely, tunnel-type γ-ZnxMnO2 and layered-type L-ZnyMnO2 and that these phases with multioxidation states co-exist after complete electrochemical Zn-intercalation. On sequential Zn-de-intercalation, a majority of these phases with multi-oxidation states was observed to revert back to the parent γ-MnO2 phase. The mesoporous γ-MnO2 cathode exhibits an initial discharge capacity of 285 mAh g-1 at 0.05 mA cm-2 with a defined plateau at around 1.25 V vs. Zn/Zn2+. Further, ex-situ HR-TEM studies of the discharged electrode aided to identify the lattice fringe widths corresponding to the Mn(III) and Mn(II) phases and the stoichiometric composition estimated by ICP appear to be in agreement with the in-situ findings. References C. Xu, B. Li, H. Du, F. Kang, Angew. Chem. Int. Ed., 51, 933, (2012). C. Yuan, Y. Zhang, Y. Pan, X. Liu, G. Wang, D. Cao, Electrochim. Acta, 116, 404 (2014).

Correction to: NPG Asia Materials (2014) 6, e138; doi:10.1038/am.2014.98; published online 17 October 2014 After the online publication of this article, the authors noticed an error in the Acknowledgements section. The correct statements in the Acknowledgements section of this article should have read as below.