Single-Source Alkoxide Precursor Approach to Titanium Molybdate, TiMoO5, and Its Structure, Electrochemical Properties, and Potential as an Anode Material for Alkali Metal Ion Batteries.

Transition-metal oxide nanostructured materials are potentially attractive alternatives as anodes for Li ion batteries and as photocatalysts. Combining the structural and thermal stability of titanium oxides with the relatively high oxidation potential and charge capacity of molybdenum(VI) oxides was the motivation for a search for approaches to mixed oxides of these two metals. Challenges in traditional synthetic methods for such materials made development of a soft chemistry single-source precursor pathway our priority. A series of bimetallic Ti-Mo alkoxides were produced by reactions of homometallic species in a 1:1 ratio. Thermal solution reduction with subsequent reoxidation by dry air offered in minor yields Ti2Mo2O4(OMe)6(OiPr)6 (1) by the interaction of Ti(OiPr)4 with MoO(OMe)4 and Ti6Mo6O22(OiPr)16(iPrOH)2 (2) by the reaction of Ti(OiPr)4 with MoO(OiPr)4. An attempt to improve the yield of 2 by microhydrolysis, using the addition of stoichiometric amounts of water, resulted in the formation with high yield of a different complex, Mo7Ti7+xO31+x(OiPr)8+2x (3). Controlled thermal decomposition of 1-3 in air resulted in their transformation into the phase TiMoO5 (4) with an orthorhombic structure in space group Pnma, as determined by a Rietveld refinement. The electrochemical characteristics of 4 and its chemical transformation on Li insertion were investigated, showing its potential as a promising anode material for Li ion batteries for the first time. A lower charge capacity and lower stability were observed for its application as an anode for a Na ion battery.

F-Doped carbon nano-onion films as scaffold for highly efficient and stable Li metal anodes: a novel laser direct-write process.

Li metal is the most promising choice for anode in high-energy rechargeable batteries, but the dendrite growth upon cycling leads to safety concerns and poor cycle life. Herein, we demonstrate a novel and scalable approach for direct writing of a thin layer of carbon nano-onions on copper substrate to stabilize the Li metal anode and prevent the dendrite growth. The F-doped carbon nano-onion film (F-CNOF) scaffold enables reversible electroplating for over 1500 hours (300 cycles) with a coulombic efficiency of ∼100%. The F-CNOF is capable of depositing Li equivalent to a capacity of 10 mA h cm-2 (gravimetric capacity 3218 mA h g-1) at 1 mA cm-2, operating at a high current density of 6 mA cm-2. More importantly, these features of long-term cyclic stability and excellent rate capability are attributed to the very high curvature due to nano dimension (∼108 m-1) of the nano-onions that develop a very uniform Li flux due to the negative surface charge, thus preventing the dendrite formation. We have also shown via first-principles DFT calculations that the high curvature achieved herein can significantly enhance the binding energy of Li to the carbon surface, which helps to improve lithiophilicity. A full cell fabricated using Li4Ti5O12 as the positive electrode showed cyclic stability of 450 cycles.

Conversion-type Anode Materials for Alkali-Ion Batteries: State of the Art and Possible Research Directions.

In this study, the potential of conversion-type anode materials for alkali-ion batteries has been examined and analyzed in terms of the parameters of prime importance for practical alkali-ion systems. Issues like voltage hysteresis, discharge profile, rate stabilities, cyclic stabilities, irreversible capacity loss, and Columbic efficiencies have been specifically addressed and analyzed as the key subjects. Relevant studies on achieving a better performance by addressing one or more of the issues have been carefully selected and outlook has been presented on the basis of this literature. Mechanistic insights into the subject of conversion reactions are discussed in light of the use of recent and advanced techniques like in situ transmission electron microscopy, in operando X-ray diffraction, and X-ray absorption spectroscopy. Three-dimensional plots depicting the performance of different materials, morphologies, and compositions with respect to these parameters are also presented to highlight the systematic of multiparameter dependencies. Inferences are drawn from these plots in the form of a short section at the end, which should be helpful to the readers, especially young researchers. We believe that this study differs from others on the subject in being focused toward addressing the practical limitations and providing possible research directions to achieve the best possible results from conversion-type anode materials.

Hard Carbons for Sodium-Ion Battery Anodes: Synthetic Strategies, Material Properties, and Storage Mechanisms.

Sodium-ion batteries are attracting much interest due to their potential as viable future alternatives for lithium-ion batteries, in view of the much higher earth abundance of sodium over that of lithium. Although both battery systems have basically similar chemistries, the key celebrated negative electrode in lithium battery, namely, graphite, is unavailable for the sodium-ion battery due to the larger size of the sodium ion. This need is satisfied by "hard carbon", which can internalize the larger sodium ion and has desirable electrochemical properties. Unlike graphite, with its specific layered structure, however, hard carbon occurs in diverse microstructural states. Herein, the relationships between precursor choices, synthetic protocols, microstructural states, and performance features of hard carbon forms in the context of sodium-ion battery applications are elucidated. Derived from the pertinent literature employing classical and modern structural characterization techniques, various issues related to microstructure, morphology, defects, and heteroatom doping are discussed. Finally, an outlook is presented to suggest emerging research directions.

Nutty Carbon: Morphology Replicating Hard Carbon from Walnut Shell for Na Ion Battery Anode.

Efficient Na ion intercalation/deintercalation in the semigraphitic lattice of a hard carbon derived from the walnut shell is demonstrated. High-temperature (1000 °C) pyrolysis of walnut shells under an inert atmosphere yields a hard carbon with a low surface area (59 m2 g-1) and a large interplanar c axis separation of 0.39-0.36 nm as compared to 0.32 nm for graphite, suitable for Na ion intercalation/deintercalation. A stable reversible capacity of 257 mAh g-1 is observed at a current density of 50 mA g-1 for such nutshell-derived carbon (NDC) with an impressive rate performance. No loss of electrochemical performance is observed for high current cycling (100 mA g-1 → 2 A g-1 → 100 mA g-1). Additionally, the NDC shows remarkably stable electrochemical performance up to 300 charge-discharge cycles at 100 mA g-1 with a minimal drop in capacity.

Hard Carbon and Li4Ti5O12-Based Physically Mixed Anodes for Superior Li-Battery Performance with Significantly Reduced Li Content: A Case of Synergistic Materials Cooperation.

Li4Ti5O12 (LTO) and hard carbon (HC) are commonly used anodes in the Li-ion batteries. LTO has an operating voltage of 1.55 V and exhibits high-rate performance but with limited capacity. HC has high specific capacity but extremely low operating voltage. Herein, we show that a simple physical mixture of the two enhances the half-cell as well as full-cell performance through a synergistic cooperation between the materials. Specifically, the LTO-HC mixed anodes exhibit impressive performance even at high C-rates. This results from a quick internalization of Li ions by LTO followed by their distribution to HC regions via the high density of the winding internal interfaces between the two. The full cells of the LTO-HC mixed anodes with LiCoO2 (LCO) evince an enhanced operating voltage window and a well-defined plateau. Because of a reduced irreversible capacity loss in the LCO/mixed anode full cells, the overall specific capacity is better than the LCO/pristine anode full cells. Also, with the LTO-HC 20-80 anode (Li content reduced by 80%), the full cell exhibits an impressive performance when compared to pristine anodes without pre-lithiation. The LCO/mixed anode full cells have excellent cycling stability up to 500 cycles at a current density of 100 mA g-1.

From waste paper basket to solid state and Li-HEC ultracapacitor electrodes: a value added journey for shredded office paper.

Hydrothermal processing followed by controlled pyrolysis of used white office paper (a globally collectable shredded paper waste) are performed to obtain high surface area carbon with hierarchical pore size distribution. The BET specific surface area of such carbon is 2341 m(2) g(-1). The interconnected macroporous structure along with the concurrent presence of mesopores and micropores makes the material ideal for ultracapacitor application. Such waste paper derived carbon (WPC) shows remarkable performance in all solid-state supercapacitor fabricated with ionic liquid-polymer gel electrolyte. At room temperature, the material exhibits a power density of 19,000 W kg(-1) with an energy capability of 31 Wh kg(-1). The Li-ion electrochemical capacitor constructed using WPC as cathode also shows an excellent energy storage capacity of 61 Wh kg(-1).

MOF-derived crumpled-sheet-assembled perforated carbon cuboids as highly effective cathode active materials for ultra-high energy density Li-ion hybrid electrochemical capacitors (Li-HECs).

Lithium ion hybrid capacitors (Li-HECs) have attracted significant attention for use in next generation advanced energy storage technologies to satisfy the demand of both high power density as well as energy density. Herein we demonstrate the use of very high surface area 3D carbon cuboids synthesized from a metal-organic framework (MOF) as a cathode material with Li4Ti5O12 as the anode for high performance Li-HECs. The energy density of the cell is ∼65 W h kg(-1) which is significantly higher than that achievable with commercially available activated carbon (∼36 W h kg(-1)) and a symmetric supercapacitor based on the same MOF-derived carbon (MOF-DC ∼20 W h kg(-1)). The MOF-DC/Li4Ti5O12 Li-HEC assembly also shows good cyclic performance with ∼82% of the initial value (∼25 W h kg(-1)) retained after 10,000 galvanostatic cycles under high rate cyclic conditions. This result clearly indicates that MOF-DC is a very promising candidate for future P-HEVs in a Li-HEC configuration.

Synthesis of an efficient heteroatom-doped carbon electro-catalyst for oxygen reduction reaction by pyrolysis of protein-rich pulse flour cooked with SiO2 nanoparticles.

Development of a highly durable, fuel-tolerant, metal-free electro-catalyst for oxygen reduction reaction (ORR) is essential for robust and cost-effective Anion Exchange Membrane Fuel Cells (AEMFCs). Herein, we report the development of a nitrogen-doped (N-doped) hierarchically porous carbon-based efficient ORR electrocatalyst from protein-rich pulses. The process involves 3D silica nanoparticle templating of the pulse flour(s) followed by their double pyrolysis. The detailed experiments are performed on gram flour (derived from chickpeas) without any in situ/ex situ addition of dopants. The N-doped porous carbon thus generated shows remarkable electrocatalytic activity towards ORR in the alkaline medium. The oxygen reduction on this material follows the desired 4-electron transfer mechanism involving the direct reduction pathway. Additionally, the synthesized carbon catalyst also exhibits good electrochemical stability and fuel tolerance. The results are also obtained and compared with the case of soybean flour having higher nitrogen content to highlight the significance of different parameters in the ORR catalyst performance.