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Na-based batteries have shown substantial progress in recent years and are promising candidates for mitigating the supply risks associated with Li-based batteries. In this Review, Na and Li batteries are compared in terms of fundamental principles and specific materials. Principles for the rational design of a Na battery architecture are discussed. Recent prototypes are surveyed to demonstrate that Na cells offer realistic alternatives that are competitive with some Li cells in terms of performance. Sodium batteries are promising candidates for mitigating the supply risks associated with lithium batteries. This Review compares the two technologies in terms of fundamental principles and specific materials, and assesses the performance of commercial prototype sodium cells.

In order to become commercially viable, sodium-ion batteries need to deliver long cycle life with good capacity and energy density while still ensuring safety. Electrolyte plays a key role forming solid electrolyte interphase (SEI) layers at low potential, which affects the thermal stability and cycle life of the anode materials under consideration. In this study, an ether-based non-flammable electrolyte, 1 M NaBF4 in tetraglyme, is tested for sodium storage using a non-carbonaceous anode material Na2Ti3O7/C, and the results are compared with those obtained with the popularly used carbonate-based electrolyte, 1 M NaClO4 in ethylene carbonate (EC) and propylene carbonate (PC) (v/v = 1:1). The Na2Ti3O7/C versus Na cells using 1 M NaBF4 in tetraglyme show a much higher first cycle Coulombic efficiency (73%) than those using 1 M NaClO4 in EC/PC (33%). Thermal stability studies using differential scanning calorimetry (DSC) conclusively show that Na2Ti3O7/C electrodes cycled with 1 M NaBF4 in tetraglyme are more thermally stable than the one cycled with 1 M NaClO4 in EC/PC. Further investigations on the formation of SEI layers were performed using attenuated total reflection-Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and DSC studies. These studies unambiguously demonstrate that the SEI formed on Na2Ti3O7/C using 1 M NaBF4 in tetraglyme is not only less resistive but also more stable than the SEI formed using 1 M NaClO4 in EC/PC.

Here, we present a comprehensive study of choice of electrolyte, anode and cathode to develop commercially viable non-flammable sodium-ion battery. We report hard carbon (HC) vs. Na using ether-based non-flammable electrolyte (1 ​M NaBF4 in tetraglyme) and compare storage performance, thermal stability and SEI formation with those obtained using carbonate-based electrolyte (1 ​M NaClO4 in EC:PC = 1:1 v/v). The results shows that 1 ​M NaBF4 in tetraglyme works as a better electrolyte than carbonate-based electrolyte for HC anode. We present and compare storage performances of pristine and aliovalent-doped Na3V2(PO4)3 (NVP) vs. Na. Doped-NVP outperforms pristine cathode in terms of specific capacity and rate capability. 18650-type non-flammable sodium-ion cells fabricated using modified NVP vs. HC exhibits energy density of 60 ​Wh kg−1. When discharged at a high rate close to 5C, the cell successfully retains 83% of its storage capacity obtained at low rate. When cycled at C/5, doped NVP vs. HC 18650 ​cell retains 90% of its initial capacity after 200 cycles.

P3-Na0.9Fe0.5Mn0.5O2 is reported as a new P-type cathode material for Na-ion batteries. The P3 structure can accommodate 0.9 mole of Na-ions leading to a high discharge capacity of 155 mA h g−1 and does not require sacrificial salts for full-cell operation. Operando X-ray diffraction and ex situ X-ray absorption studies are also reported.

Here, we introduce a fire-retarding electrolyte for sodium-ion batteries using fire-retardant triethyl phosphate (TEP) as a solvent. 3% vinylene carbonate (VC) is added to enhance its stability.

A novel, water-stable and high energy density cathode material Na0.9Cu0.12Ni0.10Fe0.30Mn0.43Ti0.05O2 (NCNFMT) is reported here along with a thorough understanding of structural events during battery operation. Systematic substitutions are carried out, which lead to increase in specific energy densities of this family of cathodes from 274.6 W h kgcathode−1 (NCFM – Na0.9Cu0.22Fe0.30Mn0.48O2) to 304.2 W h kgcathode−1 (NCFMT – Na0.9Cu0.22Fe0.30Mn0.43Ti0.05O2) and finally to 350.7 W h kgcathode−1 (NCNFMT – Na0.9Cu0.12Ni0.10Fe0.30Mn0.43Ti0.05O2). Operando X-ray diffraction reveals phase transformations and ex situ EXAFS shows the evolution of local environments around transition metals during charge/discharge. Monoclinic distortions in the NCFM material during O3–P3 phase transformations are suppressed by Ti4+ substitution leading to improvements in the cycling performance of NCFMT. Cu–O octahedral sites exhibit huge Jahn–Teller distortion: Ni2+ substitution in place of Cu2+ not only leads to more ordered Ni–O, but it also helps extract more Na ions from the O3 cathode structure, thus boosting the capacity while also showing good cycling stability due to the highly reversible bond-length and local environmental changes as revealed by EXAFS analyses. X-ray photoelectron spectroscopy shows a titanium-rich surface for NCFMT and NCNFMT which helps improve water-stability. The capacity retention after 200 cycles at 0.2C is 84%, 96% and 90% for NCFM, NCFMT and NCNFMT respectively. The delivered storage capacities of NCFM, NCFMT and NCNFMT are 21 mA h g−1, 47 mA h g−1 and 60 mA h g−1 respectively at 3C. 18650 type Na-ion batteries using the NCNFMT cathode material against a hard carbon anode are also reported to demonstrate potential scalability of the NCNFMT cathode and efficacy of a 1 M NaBF4 tetraglyme electrolyte system for the first time. 18650 cells deliver a specific energy density of 62 W h kgtotal_18650_weight−1 with 90% energy efficiency, thus being suitable for large scale energy storage applications.

In this manuscript, the impact of operating conditions such as voltage window, and operating temperature on electrochemical performance and cycle life of Zn-substituted Na3.2V1.8Zn0.2(PO4)3 (NVZP) vs hard carbon (HC) coin cells filled with 1 mol dm−3 NaBF4 in tetraglyme is presented. Initially, the cells are cycled for 500 times at C/2 charge and 1 C discharge in three different voltage windows (4.20–1.00 V, 4.05–1.00 V and 4.05–1.50 V) and at two temperatures (28 °C and 40 °C) and are subjected to periodic internal resistance and impedance measurements. The elemental composition of the electrodes harvested after cycling reveals that vanadium dissolution with accompanying deposition on the HC electrode and irreversible loss of sodium causes increased cell impedance. The identified degradation mechanisms, which causes severe capacity fade, are found to be accelerated in the cells cycled over wider voltage windows, particularly at elevated temperature. The best cycling performance and lowest impedance are recorded for the cells cycled within 4.05–1.50 V at 28 °C owing to negligible vanadium dissolution. Under these optimized testing conditions, a prototype 18650 cell, shows impressive capacity retention of 77% after 1000 cycles.

Introduction to SPIE Defense and Commercial Sensing conference 11722: Energy Harvesting and Storage: Materials, Devices, and Applications XI

In order to become commercially viable, sodium-ion batteries need to deliver long cycle life with good capacity and energy density while still ensuring safety. Electrolyte plays a key role forming solid electrolyte interphase (SEI) layers at low potential, which affects the thermal stability and cycle life of the anode materials under consideration. In this study, an ether-based non-flammable electrolyte, 1 M NaBF

International audience; Sodium rich iron hexacyanoferrates were prepared by coprecipitation, hydrothermal route, and under reflux, with or without dehydration. They were obtained with different structures described in cubic, orthorhombic or rhombohedral symmetry, with variable compositions in sodium, water and cationic vacancies, and with a variety of morphologies. This series of sodium rich Prussian Blue Analogs allowed to address the relationship between synthesis conditions, composition, structure, morphology and electrochemical properties in Na-ion batteries. A new orthorhombic phase with the Na 1.8 Fe 2 (CN) 6 •0.7H 2 O composition synthesized by an hydrothermal route at 140°C is reported for the first time, whereas a phase of Na 2 Fe 2 (CN) 6 •2H 2 O composition obtained under reflux, previously described with a monoclinic structure, shows in fact a rhombohedral structure.

P3-Na0.9Fe0.5Mn0.5O2 is reported as a new P-type cathode material for Na-ion batteries. The P3 structure can accommodate 0.9 mole of Na-ions leading to a high discharge capacity of 155 mA h g-1 and does not require sacrificial salts for full-cell operation. Operando X-ray diffraction and ex situ X-ray absorption studies are also reported.

We report the synthesis, characterization, and performance evaluation of tungsten (W) incorporated vanadium oxide (VO2) nanocomposite cathode material for improved lithium storage performance. VO2 nanorods, 100–200 nm in diameter and 1–3 μm in length are synthesized using a hydrothermal method. W incorporation at different weight percent results in the VO2 morphology shifting from rods to a sheet type structure. The lithium storage performance of VO2 has improved remarkably by increasing the loading of W to an optimal level, which influence the intercalation/ deintercalation of lithium ions into the expanded lattices of VO2. The maximum specific capacity observed for the optimal VO2/W4 composite was 381 mAh/g at a current density of 0.1 C. Cyclic voltammetry measurements showed the presence of an electroactive V3+/V4+ redox couple, leading to lower peak separation and voltage polarization differences. Superior charge storage performance was observed with the VO2/W4 composite as compared to the VO2 based devices.

NASICON-structured Li1+xZr2-xLax(PO4)3 (x = 0–0.2) solid electrolytes are prepared by sol-gel method. The influence of substitution of La3+ for Zr4+ on the ionic conductivity, morphology, and structure of the parent compound LiZr2(PO4)3 (LZP) is investigated. Rietveld refinement of powder x-ray diffraction data reveals that the La3+ substitution stabilizes the LZP in the highly conducting rhombohedral R 3 ¯ c phase at room temperature. La3+ substituted LZP display enhanced ionic conductivity, showing the highest ionic conductivity of 0.72 × 10−4 S/cm at room temperature for the composition Li1.1Zr1.9La0.1(PO4)3. The improvement in conductivity of LZP with another aliovalent substituent, Mg2+, whose ionic radii is similar to Zr4+ (0.72 A) is also investigated. Further, the activation energy decreases from 0.53 eV for the parent LZP to 0.42 eV for x = 0.1 La3+ substituted LZP. Lithium-ion transference number obtained by direct current polarization for Li1.1Zr1.9La0.1(PO4)3 is 0.99, confirming the high ionic conducting nature of the solid electrolyte. Cyclic voltammetry recorded for Li1.1Zr1.9La0.1(PO4)3 shows electrochemical stability window up to ∼4.0 V vs. Li. In particular, La3+ substituted NASICON-type LZP (x = 0.1) exhibits good chemical and structural stability after exposing to air, water, Li metal, acidic and basic solutions.

In this article, we report a high-performing fluorophosphate-based cathode material for sodium-ion battery, namely NaVPO4F, synthesised by a facile one-step soft template method. We compared physical and electrochemical properties between the NaVPO4F materials synthesised using V2O3 and V2O5 as starting precursors. FESEM images show that the samples consist of particles of size in the range 200–800 nm. The synthesised NaVPO4F using V2O5 cycled vs. sodium metal at 0.1 C is able to deliver a high discharge capacity of 133 mAh g−1, with a flat discharge plateau at 3.33 V. At a moderate current rate of 1 C, it still manages to achieve a reversible discharge capacity of 121 mAh g−1, and retains 82% of its initial capacity after 2500 cycles. Notably, this electrode material exhibits impressive long-term cyclability at high rates, where it is able to retain 81 and 77% of respective initial discharge capacities even after 10,000 cycles at 10 and 20 C. This durable performance of NaVPO4F using V2O5 precursor is attributed to the good electrode surface integrity owing to negligible volume changes as confirmed by FESEM experiment.

Viability of room-temperature rechargeable in-situ sodium plated batteries (INPBs) with bare Cu current collector foil as anode is reported which operated by sodium plating-stripping on Cu foil during each charge-discharge cycle, respectively. Using 1M NaBF4 in tetraglyme electrolyte, an Na2Fe2(CN)6//Cu INPB delivered 336Wh/kg specific energy density with 76% retention in 100cycles. Keywords: In-situ sodium plating, Anode-free, Current collector anode, Non-dendritic, NaBF4 in tetraglyme, Na2Fe2(CN)6

The individual physico-chemical processes in lithium-ion batteries namely solid-state diffusion and charge transfer polarization are difficult to be tracked by impedance spectroscopy due to simultaneous contributions from cathode and anode. A deeper understanding of various polarization processes in lithium-ion batteries is important to enhance storage performance and cycle life. In this context, the polarization processes occurring in cylindrical 18650 cells comprising different cathodes against graphite anode (LiNi 0.2 Mn 0.2 Co 0.6 O 2 vs. graphite; LiNi 0.6 Mn 0.2 Co 0.2 O 2 vs. graphite; LiNi 0.8 Co 0.15 Al 0.05 O 2 vs. graphite and LiFePO 4 vs. graphite) are investigated by deconvolution of impedance spectra across various states of charge. Further, cathodes and anodes are extracted from the investigated 18650-type cells and tested in half-cells against Li-metal as well as in symmetric cell configurations to understand the contribution of cathode and anode to the full cells of various battery chemistries studied. Except for the LiFePO 4 vs. graphite cell, the polarization resistance in graphite of other cells are found to be higher than those of the investigated cathodes, proving that the polarization in lithium-ion battery is largely influenced by the graphitic anode. Furthermore, the charge transfer polarization resistance encountered by the cathodes investigated in this work is found to be a strong function of the states of charge.

Here we report a polyanion-based cathode material for sodium-ion batteries, Na 2 MnSiO 4 , registering impressive sodium storage performances with discharge capacity of 210 mAh g −1 at an average voltage of 3 V at 0.1 C, along with excellent long-term cycling stability (500 cycles at 1 C). Insertion/extraction of ∼1.5 mol of sodium ion per formula unit of the silicate-based compound is reported and the utilisation of Mn 2+ ⇋ Mn 4+ redox couple is also demonstrated by ex-situ XPS. Besides, this study involves a systematic investigation of influence of the electrolyte additive (with different content) on the sodium storage performance of Na 2 MnSiO 4 . The electrolyte additive forms an optimum protective passivation film on the electrode surface, successfully reducing manganese dissolution.

One of the key requirements of large-scale grid-storage systems is development of inexpensive and safe batteries. Sodium-ion batteries using earth-abundant Fe or Ti based cathodes and anodes would be ideal candidates for such storage systems. Herein, a new phase of Na-rich and all Fe Prussian Blue Analogue, monoclinic Na2Fe2(CN)6.2H2O, is reported as a potential cathode for such grid-storage sodium-ion batteries. This water-insoluble and air-stable cathode can deliver 85 mAh g−1 at an average discharge voltage of 3 V vs Na/Na+ with excellent cycle life (3,000 cycles). Many facets about its sodium storage characteristics are discussed with particular emphasis on the role of interstitial water on the sodium storage performance and its conversion to the dehydrated rhombohedral phase. Its compatibility with a newly developed non-flammable glyme-based liquid electrolyte, 1M NaBF4 in tetraglyme, is also disclosed along with general electrochemical and thermal characterization of this electrolyte for sodium-ion battery application. Finally, three different types of full cells are revealed with either monoclinic or rhombohedral phase as cathode and graphite or the recently reported Na2Ti3O7 Na3-xTi3O7 pathway of Na2Ti3O7 as anode. Full cell energy densities of 70–90 Wh kg−1 (using cumulative cathode and anode weights) could be obtained without any pre-cycling steps. This new cathode and safe electrolyte may hold great promise toward development of inexpensive, non-flammable and highly stable grid-storage sodium-ion batteries.

In this article, we propose key design criteria to synthesis carbon coated α-Li3V2(PO4)3 positive electrode material for high power lithium batteries. A facile and scalable one-pot soft template method is adopted to synthesize α-Li3V2(PO4)3/C (LVP/C), which exhibits unique morphology of micron-size mesoporous secondary particles comprising interconnected primary nanoparticles showing good storage and rate performances with long cycle life. This cathode material displays high discharge capacities of 178, 90 and 59 mAh.g−1 at 0.1C, 30C and 80C, respectively. The mesoporous LVP/C with a 3D lithium diffusion network exhibits better rate performance (90 mAh.g−1 at 30C) as compared to the known phosphate, silicate or oxide cathode materials for lithium-ion batteries (LIBs). In addition, LVP/C electrode material retains 80% (at 1C) and 100% (at 20C) of its initial capacity after 1,000 cycles. The phase transitions during delitiation/litiation are discussed at different cutoff voltages, corresponding to the number of moles of lithium involved in the redox reactions. The reversibility of electrochemical extraction/insertion processes are confirmed using operando XRD measurements. Observed storage performances can be attributed not only to high crystallinity of LVP/C calcined at 800°C for 6 h; also to the unique mesoporous architecture of this carbon coated cathode material forming high packing density during the soft template synthesis. Obtained dense packed mesoporous architecture of LVP/C allows favourable (i) electrolyte wettability for lithium-incorporation from the electrolyte and (ii) long electronic wiring by the well-connected carbon coating towards the current collector.

We report here thermal behaviour and various components of heat loss of 18650-type LiFePO4/graphite cell at different testing conditions. In this regard, the total heat generated during charging and discharging processes at various current rates (C) has been quantified in an Accelerating Rate Calorimeter experiment. Irreversible heat generation, which depends on applied current and internal cell resistance, is measured under corresponding charge/discharge conditions using intermittent pulse techniques. On the other hand, reversible heat generation which depends on entropy changes of the electrode materials during the cell reaction is measured from the determination of entropic coefficient at various states of charge/discharge. The contributions of irreversible and reversible heat generation to the total heat generation at both high and low current rates are evaluated. At every state of charge/discharge, the nature of the cell reaction is found to be either exothermic or endothermic which is especially evident at low C rates. In addition, electrochemical impedance spectroscopy measurements are performed on above 18650 cells at various states of charge to determine the components of internal resistance. The findings from the impedance and thermal loss analysis are helpful for understanding the favourable states of charge/discharge for battery operation, and designing better thermal management systems.

We report the synthesis of low and high temperature polymorphs of Li 2 MnSiO 4 and dependence of lithium storage performance on such polymorphs. Two polymorphs namely, Pmn 2 1 (low temperature/orthorhombic polymorph) and P 2 1 / n (high temperature/monoclinic polymorph) are isolated by controlling the calcination temperature. Among them the electrochemical performance of Pmn 2 1 is found to be better than P 2 1 / n . Orthorhombic polymorph ( Pmn 2 1 ) of carbon coated Li 2 MnSiO 4 exhibits an impressive discharge capacity of 262 mAh g −1 at 0.1C and rate performance up to 5C; in contrast P 2 1 / n delivers only a discharge capacity of 164 mAh g −1 at 0.1C at room temperature. Notably, the capacity of Pmn 2 1 phase is almost 1.5–2 times higher than P 2 1 / n phase at all current rates. Capacity retention of 90% is reported for orthorhombic polymorph until 30 cycles at 0.1C. Further the voltage profiles and polarization of orthorhombic phase are much better than the monoclinic phase. Such perceivable differences in the rate performances and voltage profiles is argued to be due to variations in the activation energy barrier and hopping distance of lithium-ion in the crystal structures. Besides the role of polymorphism, we also show here that the structural stability during cycling is critical in retaining high storage performance.

A new sodium storage pathway is unveiled for the anode Na2Ti3O7 which involves the newly discovered intermediate phase of Na3 − xTi3O7. Details about this Na2Ti3O7 ⇋ Na3 − xTi3O7 sodium storage pathway and how it relates to the conventional Na2Ti3O7 ⇋ Na4Ti3O7 pathway are mentioned. This Na2Ti3O7 ⇋ Na3 − xTi3O7 pathway has the lowest redox voltage of 0.2 V vs Na/Na+ ever reported for any non-carbon based sodium-ion battery anode along with moderately high capacity approaching 89 mAh/g, negligible polarization, excellent rate performance (up to 80 C, or 45 s response) and good cycle life till 1500 cycles. These results indicate this pathway's potential as an anode for sodium-ion batteries meant for diverse applications. Keywords: Na2Ti3O7, Na3 − xTi3O7, Lowest voltage anode, Voltage step, Sodium-ion battery

Deployment of micro-grids using renewable energy (solar and wind power) requires large-scale electrical energy storage (EES) systems. Currently, lithium-ion batteries (LIBs) are leading candidates for EES. High power density LIBs addressing intermittency of renewables use expensive lithium titanate as anode. Besides, lithium is a scarce resource. Sodium, on the other hand, is the sixth most abundant element on the Earth’s crust. Sodium-ion batteries (NIBs) operating at ambient temperature are expected to be durable, safe and inexpensive. Regardless of the relatively lower energy density of NIBs, they can effectively be employed in micro-grid applications, where the weight and footprint requirement are not severe. We present here recently developed non-flammable sodium-ion conducting glyme based electrolyte displaying excellent storage performance of low voltage anodes as well as high voltage cathodes for sodium-ion cells. Employing this liquid electrolyte, non-flammable sodium-ion cells (18650-type) have been fabricated using rhombohedral Prussian Blue analogoue1 or sodium vanadium phosphate as cathode and hard carbon as anode with energy density in the range 40 – 60 Wh/kg (kg refers to the total 18650 full cell weight) and impressive 4C rate performance. This ultra-safe commercial type sodium-ion cells have relatively higher energy density than the reported aqueous (non-flammable) commercial NIBs. We further present thermal (DSC analyses) and safety parameters (heat losses and internal resistance evaluations) of the above 18650 cells which help in developing thermal management systems for NIB packs for possible micro-grids (100-500 kWh) to address the intermittency of renewable energy.

We report here the potential competency of MnCO3 versus MnO2 for supercapacitor applications. MnCO3 was synthesized by a hydrothermal method using KMnO4 as a manganese source and either sugar or pyrrole as carbon source. MnCO3 synthesized using sugar and pyrrole as carbon source is referred hereafter as MnCO3(s) and MnCO3(p), respectively. The synthesized products were characterized by powder X-ray diffraction, scanning electron microscopic and transmission electron microscopic studies. Microscopic studies revealed that MnO2 possesses micro-flower-like morphology constructed by self-assembled nano-petals. While the morphology of MnCO3(s) is sub-micron size particles of different shape, the morphology of MnCO3(p) is crystalline particles of 10–20 nm dia. The capacitive characteristics of MnO2, MnCO3(s) and MnCO3(p) were evaluated in aqueous 0.1 M Mg(ClO4)2 electrolyte between 0 and 1 V using cyclic voltammetry and galvanostatic charge/discharge cycling. Specific capacitance (SC) values of 216 and 296 F g−1 obtained for MnCO3(s) and MnCO3(p) are 35 and 85 % higher than SC value of 160 F g−1 obtained for MnO2, respectively. Besides better capacitive storage characteristics, MnCO3(s) and MnCO3(p) have also exhibited better rate capability and cycle life than MnO2.

Two new organic dyes based on trifluorenylamine donor and cyanoacrylic acid acceptor have been synthesized and characterized by optical and electrochemical measurements and density functional theory calculations. It is found that the trifluorenylamine donor is beneficial to red-shift the absorption and to lower the oxidation potential when compared to the triphenylamine donor. The variations in the photovoltaic performance of the dyes are corroborated by the dye loading data, incident photon to current conversion efficiency and the interfacial kinetic parameters estimated from the intensity modulated photovoltage/photocurrent spectral measurements. A dye with fluorene and bithiophene segments in the π-linker exhibited device efficiency up to 5.8%. The enhanced power conversion efficiency exhibited by this dye when compared to its analogue containing diphenylaminofluorne donor is attributed to its superior anti-aggregation ability and the comparatively prolonged electron lifetime.

Nanostructured pure Na2FePO4F was synthesised by a soft template method, followed by high-energy ball milling (HEBM) process and post-heat treatment. Physical and electrochemical properties of this sample were compared with as-prepared (pristine) sample. FESEM images recorded on the ball milled samples showed that the particles were of spherical morphology, with particle size centred around 100 nm. BET analysis illustrated a correlation between the surface area of the material with the electrochemical performance. Rietveld refinement of XRD patterns of the pristine and the HEBM samples together with the obtained reliability factor values demonstrated lower percentage of antisite disorder in HEBM sample. Compared to the pristine sample, which delivered an initial discharge capacity of only 87 mA h g−1, the HEBM sample showed an impressive storage capacity of 116 mA h g−1 at 0.1 C. Furthermore, at 1 C after 200 cycles, the ball milled sample displayed stable cyclability, retaining almost 80% of its initial discharge capacity, with an average coulombic efficiency of 99.4%. The improved sodium storage performance as compared to the pristine sample is discussed in terms of the reduced antisite disorder and associated sodium ion diffusion.

Palladium nanoparticles decorated graphene (Gra/Pd nanocomposite) was synthesized by simultaneous chemical reduction of graphene oxide and palladium salt in a single step. The negatively charged graphene oxide (GO) facilitates uniform distribution of Pd 2+ ions onto its surface. The subsequent reduction by hydrazine hydrate provides well dispersed Pd nanoparticles decorated graphene. Different amount of Pd nanoparticles on graphene was synthesized by changing the volume to weight ratio of GO to PdCl 2 . X-ray diffraction studies showed FCC lattice of Pd with predominant (1 1 1) plane. SEM and TEM studies revealed that thin graphene nanosheets are decorated by Pd nanoparticles. Raman spectroscopic studies revealed the presence of graphene nanosheets. The electro-catalytic activity of Gra/Pd nanocomposites toward methanol and ethanol oxidation in alkaline medium was evaluated by cyclic voltammetric studies. 1:1 Gra/Pd nanocomposite exhibited good electro-catalytic activity and efficient electron transfer. The kinetics of electron transfer was studied using chronoamperometry. Improved electro-catalytic activity of 1:1 Gra/Pd nanocomposite toward alcohol oxidation makes it as a potential anode for the alcohol fuel cells.

The galvanostatic cycling of electrode materials in lithium or sodium batteries is assumed to arise just from the contribution of the working electrode, with the counter electrode seen as always operating at a fixed potential. In this manuscript, we demonstrate a hitherto unreported phenomenon which involves a voltage step seen in the discharge profiles at high rates of two-phase electrode materials in sodium batteries that is produced not from a change in potential of the working electrode, but from an increase in polarization of the counter electrode. The choice of solvent used is critical in this context, with the phenomenon existing for EC:PC and not for PC solvent. It arises due to a passivation layer formed on the sodium counter electrode. The voltage step is observed only in the presence of sodium metal as the counter electrode, as it is not seen in full sodium-ion cells. Keywords: Voltage step, EC:PC solvent, Counter electrode polarization, Passivation layer, Sodium-ion battery, Unusual phenomenon

Sodium-ion batteries (NIBs) have been emerging as one of the most promising candidates for stationary storage applications such as telecommunication towers, micro-grids etc., mainly because Na is one of the most abundant elements on the Earth’s crust.1,2 NIB operating at ambient temperature is expected to be durable, safe and inexpensive. Regardless of the relatively lower energy density of NIBs, they can be effectively employed for stationary applications, where the weight and footprint requirements are not severe.3 However, identifying appropriate anode, cathode, electrolyte, as well as the combination of these three components have always been challenging to develop robust NIB.4,5 In this talk, we will present investigation of the storage performance, thermal stability6 and SEI layers of four notable anodes, viz., hard carbon, graphite, TiO2 and Na2Ti3O7 7 using ether-based non-flammable electrolyte: 1M NaBF4 in tetraglyme and compare with the results obtained with commonly used carbonate-based electrolyte: 1M NaClO4 in EC:PC. We report better storage performance with higher first cycle coulombic efficiency of above anodes tested against metallic Na using ether-based electrolyte compared to carbonate-based electrolytes. Thermal studies, ATR-FTIR and impedance spectroscopy recorded at fully sodiated and fully desodiated states of these four anodes further confirm that a more stabilized SEI is formed by ether-based electrolyte. Above studies further suggests that the ether-based electrolyte is much safer for NIBs compared to carbonate-based electrolytes such as 1M NaClO4 in EC:PC. For the cathode, Na3V2(PO4)3 (NVP) was chosen due to a high redox potential of 3.37 V vs. Na/Na+. By employing a highly scalable synthesis procedure8 two types of NVP are prepared: pristine NVP and modified NVP by aliovalent doping. Sodium storage performances (specific capacity, rate performance and cycle life) of modified NVP outperforms the pristine NVP. The observed superior storage performance in modified NVP is attributed to enhanced activity of vanadium (V3+ to V4+ and V4+ to V5+)9 as confirmed by XPS studies and higher chemical diffusion coefficient. We also present storage performance, XPS studies, measurement of heat loss and internal resistance of 18650-type non-flammable NIB cells made using NVP (pristine- and modified- NVP) vs. HC with 1M NaBF4 in tetraglyme as electrolyte. The 18650 cell of pristine NVP vs. HC shows low energy density (47 Wh.kg− 1), moderate rate performance and poor cyclability. On the other hand, the 18650 cell of modified NVP vs. HC exhibits improved energy density (60 Wh.kg− 1) and enhanced rate and cyclic performances. Further, we report lesser heat generation in modified NVP vs. HC cell compared to pristine NVP vs. HC cell. Corresponding internal resistance of these 18650 cells measured at different depths of discharge (DoD) and temperature intervals reveal improved chemical diffusion coefficient, and substantial reduction in charge transfer resistance of the modified NVP vs. HC cell caused by aliovalent doping of NVP. The work presented here for introducing a safe NIB technology for stationary storage application is an illustration of R&D with a long value chain: scale-up production of cathode materials, commercial type cell fabrication, investigation of storage performance, estimation of heat generation, quantification of heat loss in terms of internal resistance. This translational R&D at NUS thus bridges academics and industries. References: B. Dunn, H. Kamath and J.-M. Tarascon, Science, 2011, 334, 928-935. N. Yabuuchi, K. Kubota, M. Dahbi and S. Komaba, Chemical Reviews, 2014, 114, 11636-11682. M. Armand and J.-M. Tarascon, Nature, 2008, 451, 652-657. J. Wang, Y. Yamada, K. Sodeyama, E. Watanabe, K. Takada, Y. Tateyama and A. Yamada, Nature Energy, 2018, 3(1), 22–29. C. Delmas, Advanced Energy Materials, 2018, 8(17), 1–9. A.Ponrouch, E. Marchante, M. Courty, J. M. Tarascon and M. R. Palacin, Energy and Environmental Science, 2012, 5(9), 8572–8583. J. Xu, C. Ma, M. Balasubramanian and Y. S. Meng, Chemical Communications, 2014, 3, 1–4. 8. Saravanan, C. W. Mason, A. Rudola, K. H. Wong, P. Balaya, Advanced Energy Materials, 2013, 3, 444-450. F. Lalère, V. Seznec, M. Courty, R. David, J. N. Chotard and C. Masquelier, Journal of Materials Chemistry A, 2015, 3, 16198-16205.

An architecture featuring carbon coated, interconnected nano-grains constructed with mesopores is developed for LiMnPO 4 cathode material. This architecture facilitates enhanced lithium ionic and electronic transports; favours improved lithium storage performance. Mesoporous LiMnPO 4 /C electrode delivers discharge capacity of 140 mAh g −1 at 0.05 C using galvanostatic cycling mode. This best electrochemical response of LiMnPO 4 /C at constant current mode is complemented by diffusion studies using cyclic voltammetry and impedance spectroscopy. Further, the interdependence of lithium storage performance on carbon content, milling time (2, 4, 6 and 10 h), grain size and porous characteristics (surface area, pore size and pore volume) is also discussed. Finally, the feasibility of LiMnPO 4 /C cathode is evaluated against Li 4 Ti 5 O 12 /C anode in a full cell.

Sodium storage in α-MoO3 anode material is reported here for the first time. Upon cycling in the voltage window 0.04–3.0 V, MoO3 anode delivers first cycle sodiation and desodiation capacities of 771 and 410 mAh g−1. The average sodiation and desodiation potentials of the stable cycles lie below 1.0 V with attractive voltage profiles. MoO3 anode also shows favorable rate performance and long cycle life over 500 cycles. Keywords: Sodium-ion battery, Anode material, Conversion reaction, High rate performance, Long term cyclability, Full cell testing

Sodium ion batteries are attractive for the rapidly emerging large-scale energy storage market for intermittent renewable resources. Currently a viable cathode material does not exist for practical non-aqueous sodium ion battery applications. Here we disclose a high performance, durable electrode material based on the 3D NASICON framework. Porous Na3V2(PO4)3/C was synthesized using a novel solution-based approach. This material, as a cathode, is capable of delivering an energy storage capacity of ∼400 mWh/g vs. sodium metal. Furthermore, at high current rates (10, 20 and 40 C), it displayed remarkable capacity retention. Equally impressive is the long term cycle life. Nearly 50% of the initial capacity was retained after 30,000 charge/discharge cycles at 40 C (4.7 A/g). Notably, coulombic efficiency was 99.68% (average) over the course of cycling. To the best of our knowledge, the combination of high energy density, high power density and ultra long cycle life demonstrated here has never been reported before for sodium ion batteries. We believe our findings will have profound implications for developing large-scale energy storage systems for renewable energy sources.

Metal oxide semiconductors are promising interfacial materials for organic photovoltaics (OPVs) because of their electrical properties and solution processability. In this article, we report the fabrication of poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) OPV devices incorporating solution-based NiO interfacial layers that show promising enhancements of the device photocurrent and stability. We discuss the impact of parasitic shunt and series resistances on device performance as well as the ambient degradation of these devices, studied with intensity modulated photocurrent spectroscopy (IMPS). The results showed that charge extraction was predominantly affected by degradation via decrease in carrier mobility and increased trapping/recombination, revealing the physical mechanism behind the degradation observed. 2012 Elsevier Ltd. All rights reserved.

A critical component in bulk-heterojunction (BHJ) organic photovoltaics (OPVs) is the charge-selective interfacial layer, which plays a vital role in achieving high device performance and stability. Here, we present the performance of molybdenum oxide (MoOx) hole selective interfacial layers for BHJ OPVs based on poly(3-hexylthiophene) (P3HT) donor and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) acceptor, prepared by a facile, low-temperature solution process. The results showed that the MoOx films enhanced device efficiency and stability in comparison to reference devices containing the conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) interfacial layer. Furthermore, a high fill factor (∼69%) close to the theoretical maximum value predicted for the P3HT:PCBM BHJ system was achieved. Despite their hole selective nature, ultraviolet photoemission spectroscopy (UPS) revealed that the MoOx films were n-type. This hole selective behavior can be explained by invoking band b...

The present work demonstrates the usefulness of nickel oxide as a hole transporting material in solid state dye-sensitized solar cells (SSDSSCs). We report on the photovoltaic performances of sensitized TiO2/NiO heterojunctions, and demonstrate that the TiO2 film thickness and morphology, as well as NiO film thickness, have significant effects on the photovoltaic behaviour of TiO2/NiO SSDSSC. Under 1 sun AM1.5G simulated illumination, the SSDSSCs demonstrated best photovoltaic performance with a short circuit photocurrent density, open circuit voltage, fill factor and efficiency of 0.91 mA cm−2, 780 mV, 40% and 0.3%, respectively. This study draws attention to the feasibility of enhancing the photovoltaic performance in SSDSSC devices through development of appropriately designed sensitized TiO2/NiO heterojunctions.