Showing papers in "Advanced Energy Materials in 2012"
TL;DR: In this paper, both negative and positive electrode materials in NIB are briefly reviewed, and it is concluded that cost-effective NIB can partially replace Li-ion batteries, but requires further investigation and improvement.
Abstract: Lithium (Li)-ion batteries (LIB) have governed the current worldwide rechargeable battery market due to their outstanding energy and power capability. In particular, the LIB's role in enabling electric vehicles (EVs) has been highlighted to replace the current oil-driven vehicles in order to reduce the usage of oil resources and generation of CO2 gases. Unlike Li, sodium is one of the more abundant elements on Earth and exhibits similar chemical properties to Li, indicating that Na chemistry could be applied to a similar battery system. In the 1970s-80s, both Na-ion and Li-ion electrodes were investigated, but the higher energy density of Li-ion cells made them more applicable to small, portable electronic devices, and research efforts for rechargeable batteries have been mainly concentrated on LIB since then. Recently, research interest in Na-ion batteries (NIB) has been resurrected, driven by new applications with requirements different from those in portable electronics, and to address the concern on Li abundance. In this article, both negative and positive electrode materials in NIB are briefly reviewed. While the voltage is generally lower and the volume change upon Na removal or insertion is larger for Na-intercalation electrodes, compared to their Li equivalents, the power capability can vary depending on the crystal structures. It is concluded that cost-effective NIB can partially replace LIB, but requires further investigation and improvement.
2,885 citations
TL;DR: In this article, the authors summarized thirty years' research efforts in the field of organic compounds for rechargeable lithium batteries and compared the cell performances of these materials, providing a comprehensive overview of the area, and straightforwardly revealing the advantages/disadvantages of each class of materials.
Abstract: Organic compounds offer new possibilities for high energy/power density, cost-effective, environmentally friendly, and functional rechargeable lithium batteries. For a long time, they have not constituted an important class of electrode materials, partly because of the large success and rapid development of inorganic intercalation compounds. In recent years, however, exciting progress has been made, bringing organic electrodes to the attention of the energy storage community. Herein thirty years' research efforts in the field of organic compounds for rechargeable lithium batteries are summarized. The working principles, development history, and design strategies of these materials, including organosulfur compounds, organic free radical compounds, organic carbonyl compounds, conducting polymers, non-conjugated redox polymers, and layered organic compounds are presented. The cell performances of these materials are compared, providing a comprehensive overview of the area, and straightforwardly revealing the advantages/disadvantages of each class of materials.
1,096 citations
TL;DR: In this paper, the authors discuss the increasing cost and an uneven geological distribution of the lithium source in recent years, and the need to increase the demand of lithium must grow proportionately and perhaps unsustainably.
Abstract: New energy technologies are critical to address global concerns regarding energy shortages and environmental issues. Lithiumbased batteries are currently the technology of choice to develop renewable energy technology and electric vehicles due to their high energy density. In this context, if electric vehicles are to gain a signifi cant share of future automobile markets, battery production and, therefore, the demand of lithium must grow proportionately and perhaps unsustainably. Therefore there is growing concern regarding the increasing cost and an uneven geological distribution of lithium source in recent years. [ 1 ]
979 citations
TL;DR: In this article, it was shown that nitrogen-doped graphene (NG) has high catalytic activity toward the oxygen-reduction reaction (ORR), which often limits the performance of the cathode in a fuel cell or a metalair battery.
Abstract: excellent thermal conductivity, [ 2 ] and a high optical transparency. [ 3 ] These properties lead to very promising applications of graphene in electronic devices, [ 4 ] transparent electrodes, [ 5 ] and energy-storage devices. [ 6 , 7 ] Recently, it was found that graphene has an extraordinary catalytic activity. [ 8–14 ] For example, N-doped graphene has a high catalytic activity toward the oxygen-reduction reaction (ORR). [ 8 ] Furthermore, graphene oxide (GO), an important derivative of graphene, is an effi cient catalyst for oxidation and hydration reactions of various alcohols, [ 9 ] whereas reduced GO can be used for catalyzing the hydrogenation of nitrobenzene. [ 10 ] Studies have shown that the heteroatoms in graphene derivatives, such as N and O, play a critical role in their catalytic activities. [ 10 , 15 , 16 ] Thus, the introduction of dopants into the graphene lattice has been the focus of much research in order to achieve a high catalytic activity toward target reactions. Among various doped graphenes, nitrogen-doped graphene (NG) has attracted much attention because of its high catalytic activity toward the ORR – the electrode reaction that often limits the performance of the cathode in a fuel cell or a metalair battery. Conventional Pt-based catalysts have a high intrinsic catalytic activity toward the ORR, but suffer from the drawbacks of high cost, poor long-term stability, and susceptibility to the crossover effect, which hinder the commercial viability of Ptloaded fuel cells. [ 17 ] Thus the search for an alternative catalyst, such as NG, is of great importance in replacing these expensive Pt-based catalysts. To prepare NG, chemical-vapor deposition in the presence of N-containing precursors is the most-common method; [ 18 ] arc discharge of graphite electrodes in a H 2 /pyridine or H 2 /NH 3 atmosphere can also produce NG. [ 19 ] However, the extremely low yield and high cost of these methods limit their application only to fundamental studies. Later, it was found that GO can be
817 citations
TL;DR: The luminescent solar concentrator (LSC) is a simple device at its heart, employing a polymeric or glass waveguide and luminecent molecules to generate electricity from sunlight when attached to a photovoltaic cell as mentioned in this paper.
Abstract: Research on the luminescent solar concentrator (LSC) over the past thirty-odd years is reviewed. The LSC is a simple device at its heart, employing a polymeric or glass waveguide and luminescent molecules to generate electricity from sunlight when attached to a photovoltaic cell. The LSC has the potential to find extended use in an area traditionally difficult for effective use of regular photovoltaic panels: the built environment. The LSC is a device very flexible in its design, with a variety of possible shapes and colors. The primary challenge faced by the devices is increasing their photon-to-electron conversion efficiencies. A number of laboratories are working to improve the efficiency and lifetime of the LSC device, with the ultimate goal of commercializing the devices within a few years. The topics covered here relate to the efforts for reducing losses in these devices. These include studies of novel luminophores, including organic fluorescent dyes, inorganic phosphors, and quantum dots. Ways to limit the surface and internal losses are also discussed, including using organic and inorganic-based selective mirrors which allow sunlight in but reflect luminophore-emitted light, plasmonic structures to enhance emissions, novel photovoltaics, alignment of the luminophores to manipulate the path of the emitted light, and patterning of the dye layer to improve emission efficiency. Finally, some possible ‘glimpses of the future’ are offered, with additional research paths that could result in a device that makes solar energy a ubiquitous part of the urban setting, finding use as sound barriers, bus-stop roofs, awnings, windows, paving, or siding tiles.
779 citations
TL;DR: In this paper, a brief overview of the critical issues relevant to air-electrodes in metal-air batteries is presented, and some recent advancements in the development of non-precious catalysts for ORR in Li-air and Znair batteries are highlighted, including transition metal oxides, low-dimensional carbon-based structures, and other catalysts such as transition metal macrocycles and metal nitrides.
Abstract: Electrical energy storage and conversion is vital to a clean, sustainable, and secure energy future. Among all electrochemical energy storage devices, metal-air batteries have potential to offer the highest energy density, representing the most promising systems for portable (electronics), mobile (electrical vehicles), and stationary (micro-grids) applications. To date, however, many fundamental issues are yet to be overcome to realize this potential. For example, efficient catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air-electrode are yet to be developed to significantly reduce the polarization loss in metal-air batteries, which severely hinders the rate capability, energy efficiency, and operational life. In this progress report, a brief overview is first presented of the critical issues relevant to air-electrodes in metal-air batteries. Some recent advancements in the development of non-precious catalysts for ORR in Li-air and Zn-air batteries are then highlighted, including transition metal oxides, low-dimensional carbon-based structures, and other catalysts such as transition-metal macrocycles and metal nitrides. New directions and future perspectives for metal-air batteries are also outlined.
635 citations
TL;DR: In this paper, the current market trends of lithium ion batteries are discussed as a primary topic, followed by an overview of anode and cathode material candidates of the battery for xEVs and ESSs based on their electrochemical properties.
Abstract: Application targets of lithium ion batteries (LIBs) are moving from small-sized mobile devices of information technology to large-scale electric vehicles (xEVs) and energy storage systems (ESSs). Environmental issues and abruptly increasing power demands are pushing high performance energy storage devices or systems onto markets. LIBs are one of the most potential candidates as the energy storage devices mainly due to their high energy densities with fairly good rate capabilities and a fairly long cycle life. As battery systems become larger in terms of stored energy as well as physical size, the safety concerns should be more seriously cared. Each application target has its own specification so that electrode materials should be chosen to meet requirements of the corresponding application. This report diagnoses the current market trends of LIBs as a primary topic, followed by giving an overview of anode and cathode material candidates of LIBs for xEVs and ESSs based on their electrochemical properties.
604 citations
TL;DR: In this paper, a review highlights methods of synthesizing porous electrode materials by templating and template-free methods and discusses how the structural features of porous electrodes influence their electrochemical properties.
Abstract: Numerous benefits of porous electrode materials for lithium ion batteries (LIBs) have been demonstrated, including examples of higher rate capabilities, better cycle lives, and sometimes greater gravimetric capacities at a given rate compared to nonporous bulk materials. These properties promise advantages of porous electrode materials for LIBs in electric and hybrid electric vehicles, portable electronic devices, and stationary electrical energy storage. This review highlights methods of synthesizing porous electrode materials by templating and template-free methods and discusses how the structural features of porous electrodes influence their electrochemical properties. A section on electrochemical properties of porous electrodes provides examples that illustrate the influence of pore and wall architecture and interconnectivity, surface area, particle morphology, and nanocomposite formation on the utilization of the electrode materials, specific capacities, rate capabilities, and structural stability during lithiation and delithiation processes. Recent applications of porous solids as components for three-dimensionally interpenetrating battery architectures are also described.
598 citations
TL;DR: In this paper, the state of the art, achievements, and challenges in the field of high-voltage cathode materials for Li-ion cells are reviewed and analyzed, and some suggestions regarding possible approaches for future development are also presented.
Abstract: The ever-increasing demand for high-performing, economical, and safe power storage for portable electronics and electric vehicles stimulates RD in Li-ion cells, the objective of current research is to develop a 5-volt cell, and at the same time to maintain high specific charge capacity, excellent cycling, and safety. Since current anode materials possess working potentials fairly close to the potential of a lithium metal, the focus is on the development of cathode materials. This work reviews and analyzes the current state of the art, achievements, and challenges in the field of high-voltage cathode materials for Li-ion cells. Some suggestions regarding possible approaches for future development in the field are also presented.
583 citations
TL;DR: In this paper, the role of atomic disorder on the cation sub-lattice, as well as phase separation of Cu2ZnSnS4 into ZnS and CuSnS3, on the material performance for light-to-electricity conversion in photovoltaic devices are discussed.
Abstract: Quaternary semiconducting materials based on the kesterite (A2BCX4) mineral structure are the most promising candidates to overtake the current generation of light-absorbing materials for thin-film solar cells. Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) and their alloy Cu2ZnSn(Se,S)4 consist of abundant, low-cost and non-toxic elements, unlike current CdTe and Cu(In,Ga)Se2 based technologies. Zinc-blende related structures are formed by quaternary compounds, but the complexity associated with the multi-component system introduces difficulties in material growth, characterization, and application. First-principles electronic structure simulations, performed over the past five years, that address the structural, electronic, and defect properties of this family of compounds are reviewed. Initial predictions of the bandgaps and crystal structures have recently been verified experimentally. The calculations highlight the role of atomic disorder on the cation sub-lattice, as well as phase separation of Cu2ZnSnS4 into ZnS and CuSnS3, on the material performance for light-to-electricity conversion in photovoltaic devices. Finally, the current grand challenges for materials modeling of thin-film solar cells are highlighted.
576 citations
TL;DR: In this article, a three-dimensional macroporous carbon film composed of interwoven connected carbon fibers containing around 10wt% oxygen and 8 wt% nitrogen was synthesized by carbonizing a common livestock biowaste in the form of chicken eggshell membranes.
Abstract: Supercapacitor electrode materials are synthesized by carbonizing a common livestock biowaste in the form of chicken eggshell membranes. The carbonized eggshell membrane (CESM) is a three-dimensional macroporous carbon film composed of interwoven connected carbon fibers containing around 10 wt% oxygen and 8 wt% nitrogen. Despite a relatively low surface area of 221 m2 g−1, exceptional specific capacitances of 297 F g−1 and 284 F g−1 are achieved in basic and acidic electrolytes, respectively, in a 3-electrode system. Furthermore, the electrodes demonstrate excellent cycling stability: only 3% capacitance fading is observed after 10 000 cycles at a current density of 4 A g−1. These very attractive electrochemical properties are discussed in the context of the unique structure and chemistry of the material.
IBM1
TL;DR: In this article, high performance Cu2ZnSnS4 photovoltaic devices are demonstrated using electrodeposition of metal stacks and annealing of a CuZnS precursor in a sulfur atmosphere.
Abstract: High-performance Cu2ZnSnS4 photovoltaic devices are demonstrated using electrodeposition of metal stacks and annealing of a CuZnSn precursor in a sulfur atmosphere. A champion electroplated Cu2ZnSnS4 solar cell achieves a power conversion efficiency of 7.3%, which is a record efficiency for electrodeposited Cu2ZnSnS4 solar devices. The device performance points to electrodeposition and annealing as a low-cost and viable approach to earth-abundant solar cell fabrication.
TL;DR: In this paper, a polyaniline-coated sulfur/conductive carbon-black (PANI@S/C) composites with different contents of sulfur are prepared via two facile processes including ball-milling and thermal treatment of the conductive carbon black and sublimed sulfur, followed by an in situ chemical oxidative polymerization of the aniline monomer in the presence of the S/C composite and ammonium persulfate.
Abstract: Polyaniline-coated sulfur/conductive-carbon-black (PANI@S/C) composites with different contents of sulfur are prepared via two facile processes including ball-milling and thermal treatment of the conductive carbon black and sublimed sulfur, followed by an in situ chemical oxidative polymerization of the aniline monomer in the presence of the S/C composite and ammonium persulfate. The microstructure and electrochemical performance of the as-prepared composites are investigated systematically. It is demonstrated that the polyaniline, with a thickness of ≈5–10 nm, is coated uniformly onto the surface of the S/C composite forming a core/shell structure. The PANI@S/C composite with 43.7 wt% sulfur presents the optimum electrochemical performance, including a large reversible capacity, a good coulombic efficiency, and a high active-sulfur utilization. The formation of the unique core/shell structure in the PANI@S/C composites is responsible for the improvement of the electrochemical performance. In particular, the high-rate charge/discharge capability of the PANI@S/C composites is excellent due to a synergistic effect on the high electrical conductivity from both the conductive carbon black in the matrix and the PANI on the surface. Even at an ultrahigh rate (10C), a maximum discharge capacity of 635.5 mA h per g of sulfur is still retained for the PANI@S/C composite after activation, and the discharge capacity retention is over 60% after 200 cycles.
TL;DR: The Hundred-Talent Project of the Chinese Academy of Sciences (CAS) as discussed by the authors is a hundred-talent project of the National Natural Science Foundation of China (NNF).
Abstract: National High Technology Research and Development Program of China [2009AA033101]; National Basic Research Program of China [2009CB220104]; National Natural Science Foundation of China [50972164]; Chinese Academy of Sciences Project [KJCX2-YW-W26]; Hundred-Talent Project of the Chinese Academy of Sciences
TL;DR: In this article, the authors proposed pseudocapacitive transition-metal oxides and electronically conducting polymers based on faradic redox charge storage to achieve higher energy density than those of electrochemical double layer capacitive carbon materials.
Abstract: 1–4 ] However, super-capacitors deliver an unsatisfactory energy density. Intensive efforts have been devoted to the enhancement of their energy density to make it comparable to that of rechargeable batteries. Among the supercapacitor electrode materials, pseudocapacitive transition-metal oxides and electronically conducting polymers based on faradic redox charge storage have attracted signifi cant attention because of their higher energy density than those of electrochemical double-layer capacitive carbon materials.
TL;DR: In this article, the phenomenology and fundamental thermodynamics of magnetocaloric materials are discussed, as well as the hysteresis behavior often found in first-order materials.
Abstract: Magnetocaloric materials with a Curie temperature near room temperature have attracted significant interest for some time due to their possible application for high-efficiency refrigeration devices. This review focuses on a number of key issues of relevance for the characterization, performance and implementation of such materials in actual devices. The phenomenology and fundamental thermodynamics of magnetocaloric materials is discussed, as well as the hysteresis behavior often found in first-order materials. A number of theoretical and experimental approaches and their implications are reviewed. The question of how to evaluate the suitability of a given material for use in a magnetocaloric device is covered in some detail, including a critical assessment of a number of common performance metrics. Of particular interest is which non-magnetocaloric properties need to be considered in this connection. An overview of several important materials classes is given before considering the performance of materials in actual devices. Finally, an outlook on further developments is presented.
TL;DR: In this paper, the authors reviewed the latest advances in the exploration and development of battery systems and relative materials and briefly commented on and discussed the main approaches, achievements, and challenges in this field.
Abstract: Building a low-carbon society supported by sustainable energy is a worldwide topic. The aqueous lithium-ion battery (LIB) has been demonstrated to be one of the most promising stationary power sources for sustainable energies such as wind and solar power. The aqueous LIB may solve both the safety problem associated with the lithium-ion batteries which use highly toxic and flammable organic solvents, and the poor cycling life associated with commercialized aqueous rechargeable batteries including lead-acid and nickel-metal-hydride systems. During the past decades, many efforts have been made to improve the performance of the aqueous lithium-ion battery. The present work reviews the latest advances in the exploration and development of battery systems and relative materials. Also the main approaches, achievements, and challenges in this field are briefly commented on and discussed.
TL;DR: In this article, an overview of the efforts to understand oxygen reduction/evolution and capacity limitations in these systems, and of electrode and electrolyte materials that are suitable for non-aqueous and hybrid (nonaqueous/aqueous) cells.
Abstract: With the increasing importance of electrified transport, the need for high energy density storage is also increasing. Possible candidates include Li-O2 batteries, which are the subject of rapidly increasing focus worldwide despite being in their infancy of understanding. This excitement owes to the high energy density of Li-O2 (up to 2-3 kWh kg−1), theoretically much higher compared to that of other rechargeable systems, and the open “semi-fuel” cell battery configuration that uses oxygen as the positive electrode material. To bring Li-O2 batteries closer to reality as viable energy storage devices, and to attain suitable power delivery, understanding of the underlying chemistry is essential. Several concepts have been proposed in the last year to account for the function and target future design of Li-O2 batteries and these are reviewed. An overview is given of the efforts to understand oxygen reduction/evolution and capacity limitations in these systems, and of electrode and electrolyte materials that are suitable for non-aqueous and hybrid (nonaqueous/aqueous) cells.
TL;DR: In this article, the electrochemical properties of Nb2O5 were investigated and it was shown that the orthorhombic and pseudohexagonal phases of the material undergo fast faradaic reactions that lead to high specific capacitance in short charging times.
Abstract: Capacitive energy storage offers several attractive properties compared to batteries, including higher power, faster charging, and a longer cycle life. A key limitation to this electrochemical energy-storage approach is its low energy density and, for this reason, there is considerable interest in identifying pseudocapacitor materials where faradaic reactions are used to achieve greater charge storage. This paper reports on the electrochemical properties of Nb2O5 and establishes that crystalline phases of the material undergo fast faradaic reactions that lead to high specific capacitance in short charging times. In particular, the specific capacitance for the orthorhombic phase at infinite sweep rate reaches ≈400 F g−1, which exceeds that of birnessite MnO2 in nonaqueous electrolyte and is comparable to RuO2 at the same extrapolated rate. The specific capacitances of the orthorhombic and pseudohexagonal phases are much greater than that of the amorphous phase, suggesting that the faradaic reactions which lead to additional capacitive energy storage are associated with Li+ insertion along preferred crystallographic pathways. The ability for Nb2O5 to store charge at high rates despite its wide bandgap and low electronic conductivity is very different from what is observed with other transition metal oxides.
TL;DR: In this paper, a mesoporous MoS with a high surface area and narrow pore-size distribution is synthesized by a vacuum assisted impregnation route, achieving a high rate capacity of 608 mAh g at the discharge current of 10 A g (-15C).
Abstract: Highly ordered mesoporous MoS with a high surface area and narrow pore-size distribution is synthesized by a vacuum assisted impregnation route. The mesoporous MoS demonstrates an expanded d spacing of 0.66 nm. The mesoporous MoS electrode achieves an excellent high rate capacity of 608 mAh g at the discharge current of 10 A g (-15C), which places MoS as a viable next generation high power source for electric vehicles.
TL;DR: In this article, the development of high-performance power sources has become an urgent and increasing demand in various portable electronics and sensor networks, such as portable electronics, backup power sources, and pacemakers.
Abstract: Owing to the rapidly growing global energy consumption, the development of high-performance power sources has become an urgent and increasing demand in various fi elds such as portable electronics and sensor networks. [ 1–3 ] As a result of their excellent characteristics, such as superior power density, fast charge/discharge rates, and long cycle lifetime, supercapacitors (SCs, also known as electrochemical capacitors or ultracapacitors), which bridge the gap between high specifi c energy batteries and high specifi c power conventional capacitors, have been employed as state-of-the-art energy storage systems and widely used in consumer electronics, backup power sources, and pacemakers. [ 4–7 ]
TL;DR: In this paper, a nonaqueous lithium-ion redox flow battery employing organic molecules is proposed and investigated, where 2,5-Di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and a variety of molecules derived from quinoxaline are employed as initial highpotential and lowpotential active materials, respectively.
Abstract: A non-aqueous lithium-ion redox flow battery employing organic molecules is proposed and investigated. 2,5-Di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and a variety of molecules derived from quinoxaline are employed as initial high-potential and low-potential active materials, respectively. Electrochemical measurements highlight that the choice of electrolyte and of substituent groups can have a significant impact on redox species performance. The charge-discharge characteristics are investigated in a modified coin-cell configuration. After an initial break-in period, coulombic and energy efficiencies for this unoptimized system are ∼70% and ∼37%, respectively, with major charge and discharge plateaus between 1.8-2.4 V and 1.7-1.3 V, respectively, for 30 cycles. Performance enhancements are expected with improvements in cell design and materials processing.
TL;DR: In this article, a transmission electron microscope (TEM) has been designed to study the structural evolution of individual nanowire or nanoparticle electrodes with near-atomic resolution in real time.
Abstract: Understanding the microscopic mechanisms of electrochemical reaction and material degradation is crucial for the rational design of high-performance lithium ion batteries (LIBs). A novel nanobattery assembly and testing platform inside a transmission electron microscope (TEM) has been designed, which allows a direct study of the structural evolution of individual nanowire or nanoparticle electrodes with near-atomic resolution in real time. In this review, recent progresses in the study of several important anode materials are summarized. The consistency between in situ and ex situ results is shown, thereby validating the new in situ testing paradigm. Comparisons between a variety of nanostructures lead to the conclusion that electrochemical reaction and mechanical degradation are material specific, size dependent, and geometrically and compositionally sensitive. For example, a highly anisotropic lithiation in Si is observed, in contrast to the nearly isotropic response in Ge. The Ge nanowires can develop a spongy network, a unique mechanism for mitigating the large volume changes during cycling. The Si nanoparticles show a critical size of ∼150 nm below which fracture is averted during lithiation, and above which surface cracking, rather than central cracking, is observed. In carbonaceous nanomaterials, the lithiated multi-walled carbon nanotubes (MWCNTs) are drastically embrittled, while few-layer graphene nanoribbons remain mechanically robust after lithiation. This distinct contrast manifests a strong ‘geometrical embrittlement’ effect as compared to a relatively weak ‘chemical embrittlement’ effect. In oxide nanowires, discrete cracks in ZnO nanowires are generated near the lithiation reaction front, leading to leapfrog cracking, while a mobile dislocation cloud at the reaction front is observed in SnO2 nanowires. This contrast is corroborated by ab initio calculations that indicate a strong chemical embrittlement of ZnO, but not of SnO2, after a small amount of lithium insertion. In metallic nanowires such as Al, delithiation causes pulverization, and the product nanoparticles are held in place by the surface Li-Al-O glass tube, suggesting possible strategies for improving electrode cyclability by coatings. In addition, a new in situ chemical lithiation method is introduced for fast screening of battery materials by conventional TEM. Evidently, in situ nanobattery experiments inside TEM are a powerful approach for advancing the fundamental understanding of electrochemical reactions and materials degradation and therefore pave the way toward rational design of high-performance LIBs.
TL;DR: In this article, three different theoretical approaches are presented to identify pathways to organic solar cells with power conversion efficiencies in excess of 20% and the dielectric constant is introduced as a central parameter for efficient solar cells.
Abstract: Three different theoretical approaches are presented to identify pathways to organic solar cells with power conversion efficiencies in excess of 20%. A radiation limit for organic solar cells is introduced that elucidates the role of charge-transfer (CT) state absorption. Provided this CT action is sufficiently weak, organic solar cells can be as efficient as their inorganic counterparts. Next, a model based on Marcus theory of electronic transfer that also considers exciton generation in both the electron donor and electron acceptor is used to show how reduction of the reorganization energies can lead to substantial efficiency gains. Finally, the dielectric constant is introduced as a central parameter for efficient solar cells. By using a drift–diffusion model, it is found that efficiencies of more than 20% are within reach.
TL;DR: In this paper, a mesoporous Li4Ti5O12/C nanocomposite is synthesized by a nanocasting technique using the porous carbon material CMK-3 as a hard template.
Abstract: A mesoporous Li4Ti5O12/C nanocomposite is synthesized by a nanocasting technique using the porous carbon material CMK-3 as a hard template. Modified CMK-3 template is impregnated with Li4Ti5O12 precursor, followed by heat treatment at 750 °C for 6 h under N2. Li4Ti5O12 nanocrystals of up to several tens of nanometers are successfully synthesized in micrometer-sized porous carbon foam to form a highly conductive network, as confirmed by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and nitrogen sorption isotherms. The composite is then evaluated as an anode material for lithium ion batteries. It exhibits greatly improved electrochemical performance compared with bulk Li4Ti5O12, and shows an excellent rate capability (73.4 mA h g−1 at 80 C) with significantly enhanced cycling performance (only 5.6% capacity loss after 1000 cycles at a high rate of 20 C). The greatly enhanced lithium storage properties of the mesoporous Li4Ti5O12/C nanocomposite may be attributed to the interpenetrating conductive carbon network, ordered mesoporous structure, and the small Li4Ti5O12 nanocrystallites that increase the ionic and electronic conduction throughout the electrode.
TL;DR: In this article, a hierarchical structure composed of Ni3S2 nanosheets grown on carbon nanotube (CNT) backbone is fabricated by a rational multi-step transformation route, which is shown to exhibit excellent performance in both supercapacitors and photocatalytic H2 production.
Abstract: One-dimensional (1D) hierarchical structures composed of Ni3S2 nanosheets grown on carbon nanotube (CNT) backbone (denoted as CNT@Ni3S2) are fabricated by a rational multi-step transformation route. The first step involves coating the CNT backbone with a layer of silica to form CNT@SiO2, which serves as the substrate for the growth of nickel silicate (NiSilicate) nanosheets in the second step to form CNT@SiO2@NiSilicate core-double shell 1D structures. Finally the as-formed CNT@SiO2@NiSilicate 1D structures are converted into CNT-supported Ni3S2 nanosheets via hydrothermal treatment in the presence of Na2S. Simultaneously the intermediate silica layer is eliminated during the hydrothermal treatment, leading to the formation of CNT@Ni3S2 nanostructures. Because of the unique hybrid nano-architecture, the as-prepared 1D hierarchical structure is shown to exhibit excellent performance in both supercapacitors and photocatalytic H2 production.
TL;DR: In this paper, the authors present efficient all-polymer solar cells comprising two different low-bandgap naphthalenediimide (NDI)-based copolymers as acceptors and regioregular P3HT as the donor.
Abstract: The authors present efficient all-polymer solar cells comprising two different low-bandgap naphthalenediimide (NDI)-based copolymers as acceptors and regioregular P3HT as the donor. It is shown that these naphthalene copolymers have a strong tendency to preaggregate in specific organic solvents, and that preaggregation can be completely suppressed when using suitable solvents with large and highly polarizable aromatic cores. Organic solar cells prepared from such nonaggregated polymer solutions show dramatically increased power conversion efficiencies of up to 1.4%, which is mainly due to a large increase of the short circuit current. In addition, optimized solar cells show remarkable high fill factors of up to 70%. The analysis of the blend absorbance spectra reveals a surprising anticorrelation between the degree of polymer aggregation in the solid P3HT:NDI copolymer blends and their photovoltaic performance. Scanning near-field optical microscopy (SNOM) and atomic force microscopy (AFM) measurements reveal important information on the blend morphology. It is shown that films with high degree of aggregation and low photocurrents exhibit large-scale phase-separation into rather pure donor and acceptor domains. It is proposed that, by suppressing the aggregation of NDI copolymers at the early stage of film formation, the intermixing of the donor and acceptor component is improved, thereby allowing efficient harvesting of photogenerated excitons at the donor–acceptor heterojunction.
TL;DR: In this article, the authors investigated the power conversion efficiency of small-molecule-based organic photovoltaic (OPV) cells for an alternate of silicon semiconductor-based solar cells.
Abstract: In the past few years, great progress has been made in organic photovoltaic (OPV) cells for an alternate of silicon semiconductorbased solar cells. OPV has the advantages of clean, low-cost, flexibility, and the possibility of roll-to-roll production.[1–4] Currently, most of the works have been focused on polymer donor molecules using bulk heterojunction (BHJ) architecture and [6,6]-phenyl-C61–butyric acid methyl ester (PC61BM) as the acceptor.[5,6] Indeed, in addition to the currently better OPV performance than small molecules, polymers have the advantages for such as better film forming quality and so on.[7] However, it cannot be denied that there are disadvantages for polymer-based OPV, such as batch to batch reproducibility, difficulty of purification, and so on. In contrast, small molecules intrinsically do not have such flaws;[8] additionally, their band structures could be tuned easily with much more choices of chemical modification. Furthermore, small molecules generally have higher charge mobility and open voltages.[9,10] However, even with these advantages, small-molecule-based OPV cells have not been investigated as intensively as that of their polymer counterparts because one of the major problems for small molecules is their generally poor film quality when using the simple solution spinning process.[11] This has been hampering their performance, and indeed their power conversion efficiencies (PCEs) (4%–5%)[12–18] are still significantly lower compared with that (>7%)[19–25] from polymers. It is thus expected that better PCE could be achieved when their intrinsic bad film quality and morphology in BHJ architecture could be improved combining with their other advantages. But to achieve this, careful molecule design has to be carried out to address many factors collectively, including their molar absorption, morphology compatibility with the acceptors for a better film quality, and so on.