Functional materials for rechargeable batteries

Joining copper oxide nanotube arrays driven by the nanoscale Kirkendall effect

Various annealing conditions (environment, temperature, and duration) are applied to study the nanoscale Kirkendall effect of copper (Cu) nanowire (NW) arrays on a Si substrate. The results show that an appropriate amount of oxygen supply is crucial for uniform transformation from Cu NWs (average diameter ∼50 nm) into Cu oxide nanotube arrays. An annealing duration of 30 min at 200 °C in a low vacuum environment reveals that the voids are not uniformly distributed at the Cu/Cu oxide interface. This suggests that void growth is due to surface diffusion of Cu along void surfaces. Annealing above 200 °C for 60 min resulted in complete transformation from Cu NWs into Cu oxide nanotubes. X-ray photoelectron spectroscopy characterization indicates that the Cu oxides formed at 200 °C and 300 °C are Cu₂O and CuO, respectively. It is demonstrated that the transformation from Cu NW arrays into Cu oxide nanotube arrays can be combined with the joining of stacked Si chips in a single-process step with reasonable joint shear strength. Transmission electron microscopy-electron energy loss spectroscopy elemental mapping analysis reveals that the joint interface is Cu oxide. The outward diffusion of Cu driven by the nanoscale Kirkendall effect is believed to enhance the joining process. By controlling the environment, temperature, and duration, joined Cu₂O or CuO nanotube stacked chips can be achieved, which serve as a platform for the further development of nanostructured, stacked devices.

In situ deposition of hierarchical architecture assembly from Sn-filled CNTs for lithium-ion batteries

In this paper, we have demonstrated a hierarchical architecture assembly from Sn-filled CNTs, which was in situ deposited on Cu foils to form binder-free electrode by incorporating flame aerosol deposition (FAD) with chemical vapor deposition (CVD) processes. The reversible capacity of Sn-filled CNTs hierarchical architecture anode exhibited above 1000 mA h g(-1) before 30th cycle and stabilized at 437 mA h g(-1) after 100 cycles at a current density of 100 mA g(-1). Even at as high as 2 A g(-1), the capacity still maintained 429 mA h g(-1). The desirable cycling life and rate capacities performance were attributed to great confinement of tin in the interior of CNTs and the superior conducting network constructed by the 3D hierarchical architecture. The novel, rapid and scalable synthetic route was designed to prepare binder-free electrode with high electrochemical performance and avoid long-time mixing of active materials, binder, and carbon black, which is expected to be one of promising preparation of Sn/C anodes in lithium-ion batteries.

Li3V2(PO4)3@C core-shell nanocomposite as a superior cathode material for lithium-ion batteries

Li3V2(PO4)3@C core-shell nanoparticles with typical sizes of 20-40 nm were synthesized using a hydrothermal-assisted sol-gel method. Ascorbic acid and PEG-400 were adopted as carbon sources and reductants. The uniform Li3V2(PO4)3@C nanocomposite obtained was composed of a Li3V2(PO4)3 core with high-phase purity and a graphitized carbon shell, which was characterized using XRD, SEM, TEM, and Raman analysis. The nanocomposite exhibited a remarkably high rate capability and long cyclability, delivering a discharge capacity of 138 mA h g(-1) at 5 C within a voltage range of 3-4.8 V and the capacity retention was 86% after 1000 cycles. The superior electrochemical performance of Li3V2(PO4)3@C indicates that it has potential for application as a cathode material in advanced rechargeable lithium-ion batteries.

Novel luminescent soft materials of terpyridine-containing ionic liquids and europium(III)

Herein, we describe novel luminescent soft materials via reaction of Eu(3+)-coordinated carboxyl functionalized ionic liquids with terpyridine-functionalized imidazolium salts that are built from an imidazolium ring substituted on one side with a terpyridine derivative and, on the opposite side, a paraffin chain of various lengths. The obtained materials are either pastelike substances or viscous fluids, depending on the anions of the carboxyl functionalized ionic liquids. The soft luminescent materials were investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetry (TG), and luminescence spectroscopy. The soft materials show bright red emission irradiated with UV light, because of the energy transfer from terpyridine-functionalized imidazolium salts to the Eu(3+) ions. The absolute quantum yields of the materials were determined and the energy transfer efficiency was estimated according to the reported method.

A flexible TiO₂(B)-based battery electrode with superior power rate and ultralong cycle life

A flexible film electrode is fabricated by growing TiO2 (B) nanosheets on electrospun carbon nanofiber fabric. The hybrid electrode exhibits remarkable electrochemical performance with high reversible capacity, excellent rate capability, and ultralong cycle life for thousands of cycles, which makes it highly attractive for high-power flexible lithium-ion batteries.

Microwave-assisted synthesis of dual-conducting Cu2O@Cu-graphene system with improved electrochemical performance as anode material for lithium batteries

Two by two: A low-cost, fast, and green microwave-assisted approach has been developed for the controlled synthesis of core-shell Cu2O@Cu/graphene hybrids. With the unique dual-conducting system consisting of graphene support and Cu layer on the surface of the Cu2O nanoparticles, the as-obtained hybrids exhibited significantly enhanced lithium ion battery performance as anode materials.

Functional mesoporous materials for energy applications: solar cells, fuel cells, and batteries

This feature article presents recent progress made in the synthesis of functional ordered mesoporous materials and their application as high performance electrodes in dye-sensitized solar cells (DSCs) and quantum dot-sensitized solar cells (QDSCs), fuel cells, and Li-ion batteries. Ordered mesoporous materials have been mainly synthesized using two representative synthetic methods: the soft template and hard template methods. To overcome the limitations of these two methods, a new method called CASH was suggested. The CASH method combines the advantages of the soft and hard template methods by employing a diblock copolymer, PI-b-PEO, which contains a hydrophilic block and an sp(2)-hybridized-carbon-containing hydrophobic block as a structure-directing agent. After discussing general techniques used in the synthesis of mesoporous materials, this article presents recent applications of mesoporous materials as electrodes in DSCs and QDSCs, fuel cells, and Li-ion batteries. The role of material properties and mesostructures in device performance is discussed in each case. The developed soft and hard template methods, along with the CASH method, allow control of the pore size, wall composition, and pore structure, providing insight into material design and optimization for better electrode performances in these types of energy conversion devices. This paper concludes with an outlook on future research directions to enable breakthroughs and overcome current limitations in this field.

Single-ion BAB triblock copolymers as highly efficient electrolytes for lithium-metal batteries

Electrochemical energy storage is one of the main societal challenges of this century. The performances of classical lithium-ion technology based on liquid electrolytes have made great advances in the past two decades, but the intrinsic instability of liquid electrolytes results in safety issues. Solid polymer electrolytes would be a perfect solution to those safety issues, miniaturization and enhancement of energy density. However, as in liquids, the fraction of charge carried by lithium ions is small (<20%), limiting the power performances. Solid polymer electrolytes operate at 80 °C, resulting in poor mechanical properties and a limited electrochemical stability window. Here we describe a multifunctional single-ion polymer electrolyte based on polyanionic block copolymers comprising polystyrene segments. It overcomes most of the above limitations, with a lithium-ion transport number close to unity, excellent mechanical properties and an electrochemical stability window spanning 5 V versus Li(+)/Li. A prototype battery using this polyelectrolyte outperforms a conventional battery based on a polymer electrolyte.

Gram-scale synthesis of ultrasmall SnO2 nanocrystals with an excellent electrochemical performance

The gram-scale synthesis of ultrasmall SnO2 nanocrystals has been successfully realized via a solvothermal process, during which the solvent used plays an important role in inhibiting the growth and aggregation of the nanocrystals. When investigating their electrochemical behaviour, the nanocrystal electrode shows an excellent performance in capacity retention and a better rate capacity.

In situ fabrication of porous graphene electrodes for high-performance energy storage

In the development of energy-storage devices, simultaneously achieving high power and large energy capacity at fast rate is still a great challenge. In this paper, the synergistic effect of structure and doping in the graphene is demonstrated for high-performance lithium storage with ulftrafast and long-cycling capabilities. By an in situ constructing strategy, hierarchically porous structure, highly conductive network, and heteroatom doping are ideally combined in one graphene electrode. Compared to pristine graphene, it is found that the degree of improvement with both structure and doping effects is much larger than the sum of that with only structure effect or doping effect. Benefitting from the synergistic effect of structure and doping, the novel electrodes can deliver a high-power density of 116 kW kg(-1) while the energy density remains as high as 322 Wh kg(-1) at 80 A g(-1) (only 10 s to full charge), which provides an electrochemical storage level with the power density of a supercapacitor and the energy density of a battery, bridging the gap between them. Furthermore, the optimized electrodes exhibit long-cycling capability with nearly no capacity loss for 3000 cycles and wide temperature features with high capacities ranging from -20 to 55 °C.

Alkanethiol-passivated ge nanowires as high-performance anode materials for lithium-ion batteries: the role of chemical surface functionalization

We demonstrate that dodecanethiol monolayer passivation can significantly enhance the anode performance of germanium (Ge) nanowires in lithium-ion batteries. The dodecanethiol-passivated Ge nanowires exhibit an excellent electrochemical performance with a reversible specific capacity of 1130 mAh/g at 0.1 C rate after 100 cycles. The functionalized Ge nanowires show high-rate capability having charge and discharge capacities of ∼555 mAh/g at high rates of 11 C. The functionalized Ge nanowires also performed well at 55 °C, showing their thermal stability at high working temperatures. Moreover, full cells using a LiFePO(4) cathode were assembled and the electrodes still have stable capacity retention. An aluminum pouch type lithium cell was also assembled to provide larger current (∼30 mA) for uses on light-emitting-diodes (LEDs) and audio devices. Investigation of the role of organic monolayer coating showed that the wires formed a robust nanowire/PVDF network through strong C-F bonding so as to maintain structure integrity during the lithiation/delithiation process. Organic monolayer-coated Ge nanowires represent promising Ge-C anodes with controllable low carbon content (ca. 2-3 wt %) for high capacity, high-rate lithium-ion batteries and are readily compatible with the commercial slurry-coating process for cell fabrication.

Facile shape control of Co(3)O(4) and the effect of the crystal plane on electrochemical performance

Co(3)O(4) with three different crystal plane structures - cubes bounded by {001}planes, truncated octahedra enclosed by {111} and {001} planes, and octahedra with exposed {111}planes - is synthesized using a very simple one-step hydrothermal method. The three kinds of Co(3)O(4) exhibit significantly different electrochemical performances and the effect of different exposed crystal planes on the electrochemical performance of Co(3)O(4) is comprehensively studied.

Facile synthesis of novel tunable highly porous CuO nanorods for high rate lithium battery anodes with realized long cycle life and high reversible capacity

Various CuO nanostructures have been well studied as anode materials for lithium ion batteries (LIBs); however, there are few reports on the synthesis of porous CuO nanostructures used for anode materials, especially one-dimensional (1D) porous CuO. In this work, novel 1D highly porous CuO nanorods with tunable porous size were synthesized in large-quantities by a new, friendly, but very simple approach. We found that the pore size could be controlled by adjusting the sintering temperature in the calcination process. With the rising of calcination temperature, the pore size of CuO has been tuned in the range of ∼0.4 nm to 22 nm. The porous CuO materials have been applied as anode materials in LIBs and the effects of porous size on the electrochemical properties were observed. The highly porous CuO nanorods with porous size in the range of ∼6 nm to 22 nm yielded excellent high specific capacity, good cycling stability, and high rate performance, superior to that of most reported CuO nanocomposites. The CuO material delivers a high reversible capacity of 654 mA h g(-1) and 93% capacity retention over 200 cycles at a rate of 0.5 C. It also exhibits excellent high rate capacity of 410 mA h g(-1) even at 6 C. These results suggest that the facile synthetic method of producing a tunable highly porous CuO nanostructure can realize a long cycle life with high reversible capacity, which is suitable for next-generation high-performance LIBs.

Facile approach to prepare porous CaSnO₃ nanotubes via a single spinneret electrospinning technique as anodes for lithium ion batteries

CaSnO₃ nanotubes are successfully prepared by a single spinneret electrospinning technique. The characterized results indicate that the well-crystallized one-dimensional (1D) CaSnO₃ nanostructures consist of about 10 nm nanocrystals, which interconnect to form nanofibers, nanotubes, and ruptured nanobelts after calcination. The diameter and wall thickness of CaSnO₃ nanotubes are about 180 and 40 nm, respectively. It is demonstrated that CaSnO₃ nanofiber, nanotubes, and ruptured nanobelts can be obtained by adjusting the calcination temperature in the range of 600-800 °C. The effect of calcination temperature on the morphologies of electrospun 1D CaSnO₃ nanostructures and the formation mechanism leading to 1D CaSnO₃ nanostructures are investigated. As anodes for lithium ion batteries, CaSnO₃ nanotubes exhibit superior electrochemical performance and deliver 1168 mAh g⁻¹ of initial discharge capacity and 565 mAh g⁻¹ of discharge capacity up to the 50th cycle, which is ascribed to the hollow interior structure of 1D CaSnO₃ nanotubes. Such porous nanotubular structure provides both buffer spaces for volume change during charging/discharging and rapid lithium ion transport, resulting in excellent electrochemical performance.

Recent advances in metal oxide-based electrode architecture design for electrochemical energy storage

Metal oxide nanostructures are promising electrode materials for lithium-ion batteries and supercapacitors because of their high specific capacity/capacitance, typically 2-3 times higher than that of the carbon/graphite-based materials. However, their cycling stability and rate performance still can not meet the requirements of practical applications. It is therefore urgent to improve their overall device performance, which depends on not only the development of advanced electrode materials but also in a large part "how to design superior electrode architectures". In the article, we will review recent advances in strategies for advanced metal oxide-based hybrid nanostructure design, with the focus on the binder-free film/array electrodes. These binder-free electrodes, with the integration of unique merits of each component, can provide larger electrochemically active surface area, faster electron transport and superior ion diffusion, thus leading to substantially improved cycling and rate performance. Several recently emerged concepts of using ordered nanostructure arrays, synergetic core-shell structures, nanostructured current collectors, and flexible paper/textile electrodes will be highlighted, pointing out advantages and challenges where appropriate. Some future electrode design trends and directions are also discussed.

Natural DNA-modified graphene/Pd nanoparticles as highly active catalyst for formic acid electro-oxidation and for the Suzuki reaction

Natural DNA has been considered as a building block for developing novel functional materials. It is abundant, renewable, and biodegradable and has a well-defined structure and conformation with many unique features, which are difficult to find in other polymers. Herein, calf thymus DNA modified graphene/Pd nanoparticle (DNA-G-Pd) hybrid materials are constructed for the first time using DNA as a mediator, and the prepared DNA-G-Pd hybrid shows high catalytic activity for fuel cell formic acid electro-oxidation and for organic Suzuki reaction. The main advantages of using DNA are not only because the aromatic nucleobases in DNA can interact through π-π stacking with graphene basal surface but also because they can chelate Pd via dative bonding in such defined sites along the DNA lattice. Our results indicate that isolated, homogeneous, and ultrafine spherical Pd nanoparticles are densely in situ decorated on DNA-modified graphene surfaces with high stability and dispersibility. The prepared DNA-G-Pd hybrid has much greater activity and durability for formic acid electro-oxidation than the commercial Pd/C catalyst and polyvinylpyrrolidone-mediated graphene/Pd nanoparticle (PVP-G-Pd) hybrid used for direct formic acid fuel cells (DFAFCs). Besides, the DNA-G-Pd hybrid can also be an efficient and recyclable catalyst for the organic Suzuki reaction in aqueous solution under aerobic conditions without any preactivation. Since DNA can chelate various transition metal cations, this proof-of-concept protocol provides the possibility for the tailored design of other novel catalytic materials based on graphene with full exploitation of their properties.

Enzyme responsive materials: design strategies and future developments

Enzyme responsive materials (ERMs) are a class of stimuli responsive materials with broad application potential in biological settings. This review highlights current and potential future design strategies for ERMs and provides an overview of the present state of the art in the area.