Design Strategies of Si/C Composite Anode for Lithium-Ion Batteries.

Silicon-based materials that have higher theoretical specific capacity than other conventional anodes, such as carbon materials, Li2 TiO3 materials and Sn-based materials, become a hot topic in research of lithium-ion battery (LIB). However, the low conductivity and large volume expansion of silicon-based materials hinders the commercialization of silicon-based materials. Until recent years, these issues are alleviated by the combination of carbon-based materials. In this review, the preparation of Si/C materials by different synthetic methods in the past decade is reviewed along with their respective advantages and disadvantages. In addition, Si/C materials formed by silicon and different carbon-based materials is summarized, where the influences of carbons on the electrochemical performance of silicon are emphasized. Lastly, future research direction in the material design and optimization of Si/C materials is proposed to fill the current gap in the development of efficient Si/C anode for LIBs.

Architecting a Stable High-Energy Aqueous Al-Ion Battery.

Aqueous Al-ion batteries (AAIBs) are the subject of great interest due to the inherent safety and high theoretical capacity of aluminum. The high abundancy and easy accessibility of aluminum raw materials further make AAIBs appealing for grid-scale energy storage. However, the passivating oxide film formation and hydrogen side reactions at the aluminum anode as well as limited availability of the cathode lead to low discharge voltage and poor cycling stability. Here, we proposed a new AAIB system consisting of an AlxMnO2 cathode, a zinc substrate-supported Zn-Al alloy anode, and an Al(OTF)3 aqueous electrolyte. Through the in situ electrochemical activation of MnO, the cathode was synthesized to incorporate a two-electron reaction, thus enabling its high theoretical capacity. The anode was realized by a simple deposition process of Al3+ onto Zn foil substrate. The featured alloy interface layer can effectively alleviate the passivation and suppress the dendrite growth, ensuring ultralong-term stable aluminum stripping/plating. The architected cell delivers a record-high discharge voltage plateau near 1.6 V and specific capacity of 460 mAh g-1 for over 80 cycles. This work provides new opportunities for the development of high-performance and low-cost AAIBs for practical applications.

Vanadium-Based Materials: Next Generation Electrodes Powering the Battery Revolution?

ConspectusAs the world transitions away from fossil fuels, energy storage, especially rechargeable batteries, could have a big role to play. Though rechargeable batteries have dramatically changed the energy landscape, their performance metrics still need to be further enhanced to keep pace with the changing consumer preferences along with the increasing demands from the market. For the most part, advances in battery technology rely on the continuing development of materials science, where the development of high-performance electrode materials helps to expand the world of battery innovation by pushing the limits of performance of existing batteries. This is where vanadium-based compounds (V-compounds) with intriguing properties can fit in to fill the gap of the current battery technologies.The history of experimenting with V-compounds (i.e., vanadium oxides, vanadates, vanadium-based NASICON) in various battery systems, ranging from monovalent-ion to multivalent-ion batteries, stretches back decades. They are fascinating materials that display rich redox chemistry arising from multiple valency and coordination geometries. Over the years, researchers have made use of the inherent ability of vanadium that undergoes metamorphosis between different coordination polyhedra accompanied by transitions in the oxidation state for reversible intercalation/insertion of more than one guest ions without breaking the structure apart. Such infinitely variable properties endow them with a wide range of electronic and crystallographic structures. The former attribute varies from insulators to metallic conductors while the latter feature gives rise to layered structures or 3D open tunnel frameworks that allow facile movement of a wide range of metal cations and guest species along the gallery. Accompanied by a growing stringent requirements for energy storage applications, most V-compounds face difficulty in resolving the problems of their own lack competitiveness mostly due to their intrinsically low ionic/electronic conductivity. The key to producing vanadium-based electrodes with the desired performance characteristics is the ability to fabricate and optimize them consistently to realize certain specifications through effective engineering strategies for property modulation.In this Account, we aim to provide a comprehensive article that correlates the fundamental of charge storage mechanism to crystallographic forms and design principle for V-compounds. More importantly, the essential roles played by engineering strategies in the property modulation of V-compounds are pinpointed to further explain the rationale behind their anomalous behavior. Apart from that, we further summarize the key theoretical and experimental results of some representative examples for tuning of properties. On the other hand, advances in characterization techniques are now sufficiently mature that they can be relied upon to understand the reaction mechanism of V-compounds by tracing real-time transformation and structural changes at the atomic scale during their working state. The mechanistic insights covered in this Account could be used as a fundamental guidance for several key strategies in electrode materials design in terms of dimension, morphology, composition, and architecture that govern the rate and degree of chemical reaction.

Efficient Nitrate Synthesis via Ambient Nitrogen Oxidation with Ru-Doped TiO2 /RuO2 Electrocatalysts.

A facile pathway of the electrocatalytic nitrogen oxidation reaction (NOR) to nitrate is proposed, and Ru-doped TiO2 /RuO2 (abbreviated as Ru/TiO2 ) as a proof-of-concept catalyst is employed accordingly. Density functional theory (DFT) calculations suggest that Ruδ + can function as the main active center for the NOR process. Remarkably doping Ru into the TiO2 lattice can induce an upshift of the d-band center of the Ru site, resulting in enhanced activity for accelerating electrochemical conversion of inert N2 to active NO*. Overdoping of Ru ions will lead to the formation of additional RuO2 on the TiO2 surface, which provides oxygen evolution reaction (OER) active sites for promoting the redox transformation of the NO* intermediate to nitrate. However, too much RuO2 in the catalyst is detrimental to both the selectivity of the NOR and the Faradaic efficiency due to the dominant OER process. Experimentally, a considerable nitrate yield rate of 161.9 µmol h-1 gcat -1 (besides, a total nitrate yield of 47.9 µg during 50 h) and a highest nitrate Faradaic efficiency of 26.1% are achieved by the Ru/TiO2 catalyst (with the hybrid composition of Rux Tiy O2 and extra RuO2 by 2.79 wt% Ru addition amount) in 0.1 m Na2 SO4 electrolyte.

Oxygen doped MoS2 quantum dots for efficient electrocatalytic hydrogen generation.

In this study, we report an oxygen-doped MoS2 quantum dot (O-MoS2 QD) hybrid electrocatalyst for the hydrogen evolution reaction (HER). The O-MoS2 QDs were prepared with a one-pot microwave method by hydrazine-mediated oxygen-doping. The synthetic method is straightforward, time-saving, and can be applied in large scale preparation. Ultra-small O-MoS2 QDs with the average size of 5.83 nm and 1-4 layers can be uniformly distributed on the surface of reduced graphene oxide (RGO). Benefited from the unique structure and the doping effect of oxygen in the MoS2 QDs and the great number of active sites, the O-MoS2 QD hybrid displayed outstanding electrocatalytic performance toward HER. A low overpotential of 76 mV at 10 mA/cm2 and a Tafel slope of 58 mV/dec were obtained in an acidic solution toward HER. Additionally, the resultant O-MoS2 QD hybrid also exhibited excellent stability and durability toward HER, displaying negligible current density loss after 1000 cycles of cyclic voltammetry. The design and synthesis of the electrocatalyst in this work open up a prospective route to prepare active and stable electrocatalysts toward substituting precious metals for hydrogen generation.

Na3V2(PO4)3: an advanced cathode for sodium-ion batteries.

Sodium-ion batteries (SIBs) are considered to be the most promising electrochemical energy storage devices for large-scale grid and electric vehicle applications due to the advantages of resource abundance and cost-effectiveness. The electrochemical performance of SIBs largely relies on the intrinsic chemical properties of the cathodic materials. Among the various cathodes, rhombohedral Na3V2(PO4)3 (NVP), a typical sodium super ionic conductor (NASICON) compound, is very popular owing to its high Na+ mobility and firm structural stability. However, the relatively low electronic conductivity makes the theoretical capacity of NVP cathodes unviable even at low rates, not to mention the high rate of charging/discharging. This is a major drawback of NVPs, limiting their future large-scale applications. Herein, a comprehensive review of the recent progresses made in NVP fabrication has been presented, mainly including the strategies of developing NVP/carbon hybrid materials and elemental doping to improve the electronic conductivity of NVP cathodes and designing 3D porous architectures to enhance Na-ion transportation. Moreover, the application of NVP cathodic materials in Na-ion full batteries is summarized, too. Finally, some remarks are made on the challenges and perspectives for the future development of NVP cathodes.

Nanostructured Li3 V2 (PO4 )3 Cathodes.

To further increase the energy and power densities of lithium-ion batteries (LIBs), monoclinic Li3 V2 (PO4 )3 attracts much attention. However, the intrinsic low electrical conductivity (2.4 × 10-7 S cm-1 ) and sluggish kinetics become major drawbacks that keep Li3 V2 (PO4 )3 away from meeting its full potential in high rate performance. Recently, significant breakthroughs in electrochemical performance (e.g., rate capability and cycling stability) have been achieved by utilizing advanced nanotechnologies. The nanostructured Li3 V2 (PO4 )3 hybrid cathodes not only improve the electrical conductivity, but also provide high electrode/electrolyte contact interfaces, favorable electron and Li+ transport properties, and good accommodation of strain upon Li+ insertion/extraction. In this Review, light is shed on recent developments in the application of 0D (nanoparticles), 1D (nanowires and nanobelts), 2D (nanoplates and nanosheets), and 3D (nanospheres) Li3 V2 (PO4 )3 for high-performance LIBs, especially highlighting their synthetic strategies and promising electrochemical properties. Finally, the future prospects of nanostructured Li3 V2 (PO4 )3 cathodes are discussed.

Metal coordination polymer derived mesoporous Co3O4 nanorods with uniform TiO2 coating as advanced anodes for lithium ion batteries.

In this work, a one-dimensional Co3O4@TiO2 core-shell electrode material with superior electrochemical performance is fabricated by a convenient and controllable route. The approach involves two main steps: the homogeneous deposition of polydopamine and TiO2 layers in sequence on the cobalt coordination polymer and the thermal decomposition of the polymer matrix. The as-prepared electrode material can achieve excellent electrochemical properties and stability as an anode material for lithium ion batteries, such as a high specific capacity of 1279 mA h g(-1), good cycling stability (around 803 mA h g(-1) at a current density of 200 mA g(-1) after 100 cycles), and stable rate performance (around 520 mA h g(-1) at a current density of 1000 mA g(-1)). This dramatic electrochemical performance is mainly attributed to the excellent structural characteristics, which could improve the electrical conductivity and lithium ion mobility, as well as electrolyte permeability and architectural stability during cycling.

Using elastin protein to develop highly efficient air cathodes for lithium-O2 batteries.

Transition metal-nitrogen/carbon (M-N/C, M = Fe, Co) catalysts are synthesized using environmentally friendly histidine-tag-rich elastin protein beads, metal sulfate and water soluble carbon nanotubes followed by post-annealing and acid leaching processes. The obtained catalysts are used as cathode materials in lithium-O2 batteries. It has been discovered that during discharge, Li2O2 nanoparticles first nucleate and grow around the bead-decorated CNT regions (M-N/C centres) and coat on the catalysts at a high degree of discharge. The Fe-N/C catalyst-based cathodes deliver a capacity of 12,441 mAh g(-1) at a current density of 100 mA g(-1). When they were cycled at a limited capacity of 800 mAh g(-1) at current densities of 200 or 400 mA g(-1), these cathodes showed stable charge voltages of ∼3.65 or 3.90 V, corresponding to energy efficiencies of ∼71.2 or 65.1%, respectively. These results are considerably superior to those of the cathodes based on bare annealed CNTs, which prove that the Fe-N/C catalysts developed here are promising for use in non-aqueous lithium-O2 battery cathodes.

General Approach for MOF-Derived Porous Spinel AFe2O4 Hollow Structures and Their Superior Lithium Storage Properties.

A general and simple approach for large-scale synthesis of porous hollow spinel AFe2O4 nanoarchitectures via metal organic framework self-sacrificial template strategy is proposed. By employing this method, we can successfully synthesize uniform NiFe2O4, ZnFe2O4, and CoFe2O4 hollow architectures that are hierarchically assembled by nanoparticles. When these hollow microcubes were tested as anode for lithium ion batteries, good rate capability and long-term cycling stability can be achieved. For example, high specific capacities of 636, 449, and 380 mA h g(-1) were depicted by NiFe2O4, ZnFe2O4, and CoFe2O4, respectively, at a high current density of 8.0 A g(-1). NiFe2O4 exhibits high specific capacities of 841 and 447 mA h g(-1) during the 100th cycle when it was tested at current densities of 1.0 and 5.0 A g(-1), respectively. Discharge capacities of 390 and 290 mA h g(-1) were delivered by the ZnFe2O4 and CoFe2O4, respectively, during the 100th cycle at 5.0 A g(-1).

Nanostructured metal sulfides for energy storage.

Advanced electrodes with a high energy density at high power are urgently needed for high-performance energy storage devices, including lithium-ion batteries (LIBs) and supercapacitors (SCs), to fulfil the requirements of future electrochemical power sources for applications such as in hybrid electric/plug-in-hybrid (HEV/PHEV) vehicles. Metal sulfides with unique physical and chemical properties, as well as high specific capacity/capacitance, which are typically multiple times higher than that of the carbon/graphite-based materials, are currently studied as promising electrode materials. However, the implementation of these sulfide electrodes in practical applications is hindered by their inferior rate performance and cycling stability. Nanostructures offering the advantages of high surface-to-volume ratios, favourable transport properties, and high freedom for the volume change upon ion insertion/extraction and other reactions, present an opportunity to build next-generation LIBs and SCs. Thus, the development of novel concepts in material research to achieve new nanostructures paves the way for improved electrochemical performance. Herein, we summarize recent advances in nanostructured metal sulfides, such as iron sulfides, copper sulfides, cobalt sulfides, nickel sulfides, manganese sulfides, molybdenum sulfides, tin sulfides, with zero-, one-, two-, and three-dimensional morphologies for LIB and SC applications. In addition, the recently emerged concept of incorporating conductive matrices, especially graphene, with metal sulfide nanomaterials will also be highlighted. Finally, some remarks are made on the challenges and perspectives for the future development of metal sulfide-based LIB and SC devices.

Platinum and palladium nanotubes based on genetically engineered elastin-mimetic fusion protein-fiber templates: synthesis and application in lithium-O2 batteries.

The coupling of proteins with self-assembly properties and proteins that are capable of recognizing and mineralizing specific inorganic species is a promising strategy for the synthesis of nanoscale materials with controllable morphology and functionality. Herein, GPG-AG3 protein fibers with both of these properties were constructed and served as templates for the synthesis of Pt and Pd nanotubes. The protein fibers of assembled GPG-AG3 were more than 10 µm long and had diameters of 20-50 nm. The as-synthesized Pt and Pd nanotubes were composed of dense layers of ~3-5 nm Pt and Pd nanoparticles. When tested as cathodes in lithium-O2 batteries, the porous Pt nanotubes showed low charge potentials of 3.8 V, with round-trip efficiencies of about 65% at a current density of 100 mA g(-1).

High-performance supercapacitor electrodes based on graphene achieved by thermal treatment with the aid of nitric acid.

In this work, graphene materials have been prepared via thermal treatment of graphene oxides with the aid of intercalated nitric acid. The nitric acid not only favors the expansion of graphene but also facilitates the generation of pores into graphene. The specific surface area of such graphene frameworks is as high as 463 m(2)/g, and the pore volume reaches up to 2.23 cm(3)/g. When tested as supercapacitor electrodes, the graphene frameworks delivered an extremely high specific capacitance of ∼370 F/g while simultaneously maintained an excellent energy density of 12.9 Wh/kg and power delivery of 250 W/kg in aqueous electrolyte. These performances are much better than those of the control samples prepared without the aid of nitric acid. The porous structure and large specific surface area are believed to have contributed to the high performances.

In situ growth of NiCo(2)S(4) nanosheets on graphene for high-performance supercapacitors.

We demonstrate a facile hydrothermal method for growth of ultrathin NiCo2S4 nanosheets on reduced graphene oxide (RGO), which exhibit remarkable electrochemical performance with higher capacitance and longer cycle life than the bare NiCo2S4 hollow spheres (HSs).

Olivine-type nanosheets for lithium ion battery cathodes.

Olivine-type LiMPO4 (M = Fe, Mn, Co, Ni) has become of great interest as cathodes for next-generation high-power lithium-ion batteries. Nevertheless, this family of compounds suffers from poor electronic conductivities and sluggish lithium diffusion in the [010] direction. Here, we develop a liquid-phase exfoliation approach combined with a solvothermal lithiation process in high-pressure high-temperature (HPHT) supercritical fluids for the fabrication of ultrathin LiMPO4 nanosheets (thickness: 3.7-4.6 nm) with exposed (010) surface facets. Importantly, the HPHT solvothermal lithiation could produce monodisperse nanosheets while the traditional high-temperature calcination, which is necessary for cathode materials based on high-quality crystals, leads the formation of large grains and aggregation of the nanosheets. The as-synthesized nanosheets have features of high contact area with the electrolyte and fast lithium transport (time diffusion constant in at the microsecond level). The estimated diffusion time for Li(+) to diffuse over a [010]-thickness of <5 nm (L) was calculated to be less than 25, 2.5, and 250 µs for LiFePO4, LiMnPO4, and LiCoPO4 nanosheets, respectively, via the equation of t = L(2)/D. These values are about 5 orders of magnitude lower than the corresponding bulk materials. This results in high energy densities and excellent rate capabilities (e.g., 18 kW kg(-1) and 90 Wh kg(-1) at a 80 C rate for LiFePO4 nanosheets).

Cu doped V2O5 flowers as cathode material for high-performance lithium ion batteries.

Hierarchical Cu doped vanadium pentoxide (V2O5) flowers were prepared via a simple hydrothermal approach followed by an annealing process. The flower precursors are self-assembled with 1D nanobelts surrounding a central core. The morphological evolution is investigated and a plausible mechanism is proposed. As the cathode material for lithium ion batteries, the Cu doped V2O5 samples exhibit improved electrochemical performance compared to the un-doped ones. Among them Cu0.02V1.98O5 delivered higher reversible specific capacities, better cycling stabilities and excellent rate capabilities, e.g. 97 mA h g(-1) at 20.0 C.

Synthesis of cobalt phosphides and their application as anodes for lithium ion batteries.

A facile thermal decomposing method has been developed for the fabrication of Co(x)P nanostructures with controlled size, phase, and shape (e.g., Co(2)P rod and spheres, CoP hollow and solid particles). An amorphous carbon layer could be introduced by the carbonization of organic surfactants from the precursors. The electrochemical performance of typical CoP and Co(2)P samples as anode materials has been investigated and the CoP hollow nanoparticle with carbon coating layer depicts good capacity retention and high rate capability (e.g., specific capacity of 630 mA h g(-1) at 0.2 C after 100 cycles, and a reversible capacity of 256 mA h g(-1) can be achieved at a high current rate of 5 C).

Controlled synthesis of double-wall a-FePO4 nanotubes and their LIB cathode properties.

Double-wall amorphous FePO4 nanotubes are prepared by an oil-phase chemical route. The inward diffusion of vacancies and outward diffusion of ions through passivation layers result in double-wall nanotubes with thin walls. Such a process can be extended to prepare hollow polydedral nanocrystals and hollow ellipsoids. The double-wall FePO4 nanotubes show interesting cathode performance in Li ion batteries.

Controlled soft-template synthesis of ultrathin C@FeS nanosheets with high-Li-storage performance.

We report a facile approach to prepare carbon-coated troilite FeS (C@FeS) nanosheets via surfactant-assisted solution-based synthesis. 1-Dodecanethiol is used as both the sulfur source and the surfactant, which may form different-shaped micelles to direct the growth of nanostructures. Under appropriate growth conditions, the iron and sulfur atoms react to form thin layers of FeS while the hydrocarbon tails of 1-dodecanethiol separate the thin FeS layers, which turn to carbon after annealing in Ar. Such an approach can be extended to grow C@FeS nanospheres and nanoplates by modifying the synthesis parameters. The C@FeS nanosheets display excellent Li storage properties with high specific capacities and stable charge/discharge cyclability, especially at fast charge/discharge rates.