Abstract: In recent years, tremendous research effort has been aimed at increasing the energy density of supercapacitors without sacrificing high power capability so that they reach the levels achieved in batteries and at lowering fabrication costs For this purpose, two important problems have to be solved: first, it is critical to develop ways to design high performance electrode materials for supercapacitors; second, it is necessary to achieve controllably assembled supercapacitor types (such as symmetric capacitors including double-layer and pseudo-capacitors, asymmetric capacitors, and Li-ion capacitors) The explosive growth of research in this field makes this review timely Recent progress in the research and development of high performance electrode materials and high-energy supercapacitors is summarized Several key issues for improving the energy densities of supercapacitors and some mutual relationships among various effecting parameters are reviewed, and challenges and perspectives in this exciting field are also discussed This provides fundamental insight into supercapacitors and offers an important guideline for future design of advanced next-generation supercapacitors for industrial and consumer applications

Abstract: There are growing concerns over the environmental, climate, and health impacts caused by using non-renewable fossil fuels. The utilization of green energy, including solar and wind power, is believed to be one of the most promising alternatives to support more sustainable economic growth. In this regard, lithium-ion batteries (LIBs) can play a critically important role. To further increase the energy and power densities of LIBs, silicon anodes have been intensively explored due to their high capacity, low operation potential, environmental friendliness, and high abundance. The main challenges for the practical implementation of silicon anodes, however, are the huge volume variation during lithiation and delithiation processes and the unstable solid-electrolyte interphase (SEI) films. Recently, significant breakthroughs have been achieved utilizing advanced nanotechnologies in terms of increasing cycle life and enhancing charging rate performance due partially to the excellent mechanical properties of nanomaterials, high surface area, and fast lithium and electron transportation. Here, the most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in LIBs are summarized. The synthetic routes and electrochemical performance of these Si nanomaterials, and the underlying reaction mechanisms are systematically described.

Abstract: LiNixCoyMnzO2 (NCM, 0 ≤ x,y,z 4.3 V) required for high capacity is inevitably accompanied by a more rapid capacity fade over numerous cycles. Here, the degradation mechanisms of LiNi0.5Co0.2Mn0.3O2 are investigated during cycling under various cutoff voltage conditions. The surface lattice structures of LiNi0.5Co0.2Mn0.3O2 are observed to suffer from an irreversible transformation; the type of transformation depends on the cutoff voltage conditions. The surface of the pristine rhombohedral phase tends to transform into a mixture of spinel and rock salt phases. Moreover, the formation of the rock salt phase is more dominant under a higher voltage operation (≈4.8 V), which is attributable to the highly oxidative environment that triggers the oxygen loss from the surface of the material. The presence of the ionically insulating rock salt phase may result in sluggish kinetics, thus deteriorating the capacity retention. This implies that the prevention of surface structural degradation can provide the means to produce and retain high capacity, as well as stabilize the cycle life of LiNi0.5Co0.2Mn0.3O2 during high-voltage operations.

Abstract: While electrochemical water splitting is one of the most promising methods to store light/electrical energy in chemical bonds, a key challenge remains in the realization of an efficient oxygen evolution reaction catalyst with large surface area, good electrical conductivity, high catalytic properties, and low fabrication cost. Here, a facile solution reduction method is demonstrated for mesoporous Co3O4 nanowires treated with NaBH4. The high-surface-area mesopore feature leads to efficient surface reduction in solution at room temperature, which allows for retention of the nanowire morphology and 1D charge transport behavior, while at the same time substantially increasing the oxygen vacancies on the nanowire surface. Compared to pristine Co3O4 nanowires, the reduced Co3O4 nanowires exhibit a much larger current of 13.1 mA cm-2 at 1.65 V vs reversible hydrogen electrode (RHE) and a much lower onset potential of 1.52 V vs RHE. Electrochemical supercapacitors based on the reduced Co3O4 nanowires also show a much improved capacitance of 978 F g-1 and reduced charge transfer resistance. Density-functional theory calculations reveal that the existence of oxygen vacancies leads to the formation of new gap states in which the electrons previously associated with the Co-O bonds tend to be delocalized, resulting in the much higher electrical conductivity and electrocatalytic activity.

Abstract: Thin-film solar cells are made by vapor deposition of Earth-abundant materials: tin, zinc, oxygen and sulfur. These solar cells had previously achieved an efficiency of about 2%, less than 1/10 of their theoretical potential. Loss mechanisms are systematically investigated and mitigated in solar cells based on p-type tin monosulfide, SnS, absorber layers combined with n-type zinc oxysulfide, Zn(O,S) layers that selectively transmit electrons, but block holes. Recombination at grain boundaries is reduced by annealing the SnS films in H2S to form larger grains with fewer grain boundaries. Recombination near the p-SnS/n-Zn(O,S) junction is reduced by inserting a few monolayers of SnO2 between these layers. Recombination at the junction is also reduced by adjusting the conduction band offset by tuning the composition of the Zn(O,S), and by reducing its free electron concentration with nitrogen doping. The resulting cells have an efficiency over 4.4%, which is more than twice as large as the highest efficiency obtained previously by solar cells using SnS absorber layers.

Abstract: Iron oxides, such as Fe2O3 and Fe3O4, have recently received increased attention as very promising anode materials for rechargeable lithium-ion batteries (LIBs) because of their high theoretical capacity, non-toxicity, low cost, and improved safety. Nanostructure engineering has been demonstrated as an effective approach to improve the electrochemical performance of electrode materials. Here, recent research progress in the rational design and synthesis of diverse iron oxide-based nanomaterials and their lithium storage performance for LIBs, including 1D nanowires/rods, 2D nanosheets/flakes, 3D porous/hierarchical architectures, various hollow structures, and hybrid nanostructures of iron oxides and carbon (including amorphous carbon, carbon nanotubes, and graphene). By focusing on synthesis strategies for various iron-oxide-based nanostructures and the impacts of nanostructuring on their electrochemical performance, novel approaches to the construction of iron-oxide-based nanostructures are highlighted and the importance of proper structural and compositional engineering that leads to improved physical/chemical properties of iron oxides for efficient electrochemical energy storage is stressed. Iron-oxide-based nanomaterials stand a good chance as negative electrodes for next generation LIBs.

Abstract: DOI: 10.1002/aenm.201400337 synthesis of MOFs-derived porous Fe, N-based carbon catalysts supported on NRGO sheets as ORR catalysts. Here, we report the fabrication of novel nitrogen-doped coreshell-structured porous Fe/Fe 3 C@C nanoboxes supported on RGO sheets (N-doped Fe/Fe 3 C@C/RGO) by a simple pyrolysis process using graphene oxide (GO) and PB nanocubes as precursors. Such a unique structure not only offers more active sites from both nitrogen-doped Fe/Fe 3 C@C and NRGO sheets, but also shows enhanced electrical conductivity. As a result, the hybrid exhibits much better electrocatalytic activity, long-term stability, and methanol tolerance ability than the commercial Pt/C catalyst (10% Pt on Vulcan XC-72). The fabrication process for the porous N-doped Fe/Fe 3 C@C/ RGO hybrid is demonstrated in Figure 1 a. Highly uniform PB nanocubes were fi rstly synthesized using a hydrothermal method based on previous reports. [ 9a ] The obtained PB nanocubes were further dispersed in the GO solution (PB/GO) under stirring. The resulting PB/GO powders after drying at 80 °C were then annealed at 800 °C in an argon fl ow to form a core-shell-structured porous N-doped Fe/Fe 3 C@C/RGO hybrid. During this process, the continuous decomposition of PB nanocubes was accompanied by releasing nitrogen-containing gases, [ 11 ] which resulted in the formation of a porous structure accompanied with carbide reactions according to the thermogravimetric analysis (TGA) results (Figure S1, Supporting Information). Simultaneously, the nitrogen-containing species contributed to the reduction of GO and nitrogen doping in both GO and carbon shells, fi nally evolving into nitrogen-doped core-shell-structured porous Fe/Fe 3 C@C/RGO hybrids. The PB nanocubes not only act as templates/precursors, but also provide nitrogen sources for the formation of N-doped Fe/Fe 3 C@C and NRGO. Field-emission scanning electron microscopy (FESEM) images show that uniform PB nanocubes with an edge length of about 500 nm are obtained without any aggregation (Figure 1 b). An enlarged image (inset of Figure 1 b) reveals the very smooth surface over a single box. After the thermal treatment, the PB nanocubes are converted to porous N-doped Fe/Fe 3 C@C nanoboxes with a side length of around 300–400 nm (Figure 1 c). The cubic structure still remained, although its size decreased a little due to the decomposition and shrinkage during the annealing process. [ 12 ] This suggests that the PB nanocubes served as both a template and a self-sacrifi cing precursor for the formation of porous nanoboxes, which are composed of numerous Developing catalytic materials with high activity for oxygen reduction reaction (ORR) is of great signifi cance for commercial fuel cell applications. [ 1 ] Although Pt-based materials are known as the most effi cient ORR catalysts, [ 2 ] they still suffer from several serious problems, including high cost, low abundance, weak durability, crossover effect and CO poisoning; [ 3 ]

Abstract: The high-energy-density, Li-rich layered materials, i.e., xLiMO(2)(1-x)Li2MnO3, are promising candidate cathode materials for electric energy storage in plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs). The relatively low rate capability is one of the major problems that need to be resolved for these materials. To gain insight into the key factors that limit the rate capability, in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) studies of the cathode material, Li1.2Ni0.15Co0.1Mn0.55O2 [0.5Li(Ni0.375Co0.25 Mn-0.375)O(2)0.5Li(2)MnO(3)], are carried out. The partial capacity contributed by different structural components and transition metal elements is elucidated and correlated with local structure changes. The characteristic reaction kinetics for each element are identified using a novel time-resolved XAS technique. Direct experimental evidence is obtained showing that Mn sites have much poorer reaction kinetics both before and after the initial activation of Li2MnO3, compared to Ni and Co. These results indicate that Li2MnO3 may be the key component that limits the rate capability of Li-rich layered materials and provide guidance for designing Li-rich layered materials with the desired balance of energy density and rate capability for different applications.

Abstract: Layered molybdenum disulfi de (MoS 2 ) is deposited by microwave heating on a reduced graphene oxide (RGO). Three concentrations of MoS 2 are loaded on RGO, and the structure and morphology are characterized. The fi rst layers of MoS 2 are detected as being directly bonded with the oxygen of the RGO by covalent chemical bonds (Mo-O-C). Electrochemical characterizations indicate that this electroactive material can be cycled reversibly between 0.25 and 0.8 V in 1 M HClO 4 solution for hybrids with low concentrations of MoS 2 layers (LCMoS 2 /RGO) and between 0.25 and 0.65 V for medium (MCMoS 2 / RGO) and high concentrations (HCMoS 2 /RGO) of MoS 2 layers on graphene. The specifi c capacitance measured values at 10 mV s 1 are 128, 265, and 148 Fg 1 for the MoS 2 /RGO with low, medium, and high concentrations of MoS 2 , respectively, and the calculated energy density is 63 W h kg 1 for the LCMoS 2 /RGO hybrid. This supercapacitor electrode also exhibits superior cyclic stability with 92% of the specifi c capacitance retained after 1000 cycles.

Abstract: Graphene has attracted increasing attention due to its unique electrical, optical, optoelectronic, and mechanical properties, which have opened up huge numbers of opportunities for applications. An overview of the recent research on graphene and its derivatives is presented, with a particular focus on synthesis, properties, and applications in solar cells.

Abstract: A comprehensive overview and description of graphene-based nanomaterials explored in recent years for catalyst supports and metal-free catalysts for polymer electrolyte membrane (PEM) fuel cell oxygen reduction reactions (ORR) is presented. The catalyst material structures/morphologies, material selection, and design for synthesis, catalytic performance, catalytic mechanisms, and theoretical approaches for catalyst down-selection and catalyzed ORR mechanisms are emphasized with respect to the performance of ORR catalysts in terms of both activity and stability. When graphene-based materials, including graphene and doped graphene, are used as the supporting materials for both Pt/Pt alloy catalysts and non-precious metal catalyst, the resulting ORR catalysts can give superior catalyst activity and stability compared to those of conventional carbon-supported catalysts; when they are used as metal-free ORR catalysts, significant catalytic activity and stability are observed. The nitrogen-doped graphene materials even show superior performance compared to supported metal catalysts. Challenges including the lack of material mass production, unoptimized catalyst structure/morphology, insufficient fundamental understanding, and testing tools/protocols for performance optimization and validation are identified, and approaches to address these challenges are suggested.

Abstract: In lithium-sulfur batteries, small S2–4 molecules show very different electrochemical responses from the traditional S8 material. Their exact lithiation/delitiation mechanism is not clear and how to select proper electrolytes for the S2–4 cathodes is also ambiguous. Here, S2–4 and S8/S2–4 composites with highly ordered microporous carbon as a confining matrix are fabricated and the electrode mechanism of the S2–4 cathode is investigated by comparing the electrochemical performances of the S2–4 and S2–4/S8 electrodes in various electrolytes combined with theoretical calculation. Experimental results show that the electrolyte and microstructure of carbon matrix play important roles in the electrochemical performance. If the micropores of carbon are small enough to prevent the penetration of the solvent molecules, the lithiation/delithiation for S2–4 occurs as a solid-solid process. The irreversible chemically reactions between the polysulfudes and carbonates, and the dissolution of the polysulfides into the ethers can be effectively avoided due to the steric hindrance. The confined S2–4 show high adaptability to the electrolytes. The sulfur cathode based on this strategy exhibits excellent rate capability and cycling stability.

Abstract: M. Ebner, Prof. W. Vood Department of Information Technology and Electrical Engineering ETH Zurich , 8092 , Zurich , Switzerland E-mail: vwood@ethz.chD.-W. Chung, Prof. R. E. Garcia School of Materials Engineering Purdue University West Lafayette, IN , 47907 , USA .

Abstract: Taking La- and I-doped PbTe as an example, the current work shows the effects of optimizing the thermoelectric figure of merit, zT, by controlling the doping level. The high doping effectiveness allows the carrier concentration to be precisely designed and prepared to control the Fermi level. In addition to the Fermi energy tuning, La-doping modifies the conduction band, leading to an increase in the density of states effective mass that is confirmed by transport, infrared reflectance and hard X-ray photoelectron spectroscopy measurements. Taking such a band structure modification effect into account, the electrical transport properties can then be well-described by a self-consistent single non-parabolic Kane band model that yields an approximate (m*T)^(1.5) dependence of the optimal carrier concentration for a peak power factor in both doping cases. Such a simple temperature dependence also provides an effective approximation of carrier concentration for a peak zT and helps to explain, the effects of other strategies such as lowering the lattice thermal conductivity by nanostructuring or alloying in n-PbTe, which demonstrates a practical guide for fully optimizing thermoelectric materials in the entire temperature range. The principles used here should be equally applicable to other thermoelectric materials.

Abstract: DOI: 10.1002/aenm.201301584 Rechargeable batteries are important energy storage devices for the integration of renewable resources. [ 1–10 ] Lithium-ion batteries (LIBs) represent the state-of-the-art technology in high-energy batteries and have been widely applied in portable electronic devices. [ 11–19 ] However, the limited mineral reserves and high cost of lithium-based compounds hinder their expanded application in large-scale energy storage. To address this issue, rechargeable sodium-ion batteries (SIBs) working at room temperature are proposed as potential alternatives for large-scale energy storage, in particular for smart electric grids, because of the abundant supply and low cost of sodium. [ 20–23 ]

Abstract: The integration of graphene nanosheets on the macroscopic level using a self-assembly method has been recognized as one of the most effective strategies to realize the practical applications of graphene materials. Here, a facile and scalable method is developed to synthesis two types of graphene-based networks, manganese dioxide (MnO2)–graphene foam and carbon nanotube (CNT)–graphene foam, by solution casting and subsequent electrochemical methods. Their practical applications in flexible all-solid-state asymmetric supercapacitors are explored. The proposed method facilitates the structural integration of graphene foam and the electroactive material and offers several advantages including simplicity, efficiency, low-temperature, and low-cost. The as-prepared MnO2–graphene and CNT–graphene electrodes exhibit high specific capacitances and rate capability. By using polymer gel electrolytes, a flexible all-solid-state asymmetric supercapacitor was synthesized with MnO2–graphene foam as the positive electrode and CNT-graphene as the negative electrode. The asymmetric supercapacitors can be cycled reversibly in a high-voltage region of 0 to 1.8 V and exhibit high energy density, remarkable rate capability, reasonable cycling performance, and excellent flexibility.

Abstract: New non-PGM catalysts from the family of Fe-N-C pyrolyzed materials are reported. They are synthesized using a templating silica powder with iron nitrate and carbendazim (CBDZ) precursors (sacrificial support method). The synthesis involves high temperature pyrolysis, followed by etching of the sacrificial support (silica) and obtaining a “self-supported” open frame morphology catalyst. Both the temperature of heat treatment and Fe to CBDZ ratio play a crucial role in the final catalytic activity in oxygen reduction reaction (ORR). Prepared materials have extremely high durability in RDE tests, ending up with more than 94% of initial activity (by E1/2 value) after 10 000 cycles in an oxygen atmosphere, which is the result we report for the first time. Evaluation of these new M-N-C catalysts in a single membrane electrode assembly (MEA) has shown an exceptionally high open circuit voltage (OCV) of 1 V and the world's second best performance with no IR correction. MEA tests have shown high current density of 700 mA cm-2 at 0.6 V and 120 mA cm-2 at 0.8 V. In-depth structure-to-property correlation presents an evidence that Fe-Nx centers are the active sites playing a key role in oxygen reduction reaction.

Abstract: Alkaline oxygen electrocatalysis, targeting anion exchange membrane fuel cells, Zn-air batteries, and alkaline-based Li-air batteries, has become a subject of intensive investigation because of its advantages compared to its acidic counterparts in reaction kinetics and materials stability. However, significant breakthroughs in the design and synthesis of efficient oxygen reduction catalysts from earth-abundant elements instead of precious metals in alkaline media remain in high demand. Carbon composite materials have been recognized as the most promising because of their reasonable balance between catalytic activity, durability, and cost. In particular, heteroatom (e.g., N, S, B, or P) doping can tune the electronic and geometric properties of carbon, providing more active sites and enhancing the interaction between carbon structure and active sites. Importantly, involvement of transition metals appears to be necessary for achieving high catalytic activity and improved durability by catalyzing carbonization of nitrogen/carbon precursors to form highly graphitized carbon nanostructures with more favorable nitrogen doping. Recently, a synergetic effect was found between the active species in nanocarbon and the loaded oxides/sulfides, resulting in much improved activity. This report focuses on these carbon composite catalysts. Guidance for rational design and synthesis of advanced alkaline ORR catalysts with improved activity and performance durability is also presented.

Abstract: DOI: 10.1002/aenm.201400554 of the performance of PTCDA itself in SIBs, as it may have been assumed that a similar capacity fading in LIBs is to be seen in SIBs. Here, we report a high capacity and a surprisingly stable cycling life of commercially available PTCDA in SIBs. In the potential range of 1-3 V, PTCDA delivers a capacity of 145 mAh g –1 at 10 mA g –1 , an excellent rate capability (91 mAh g –1 at 1000 mA g –1 ), and good cycling stability for 200 cycles. When discharging PTCDA to 0.01 V, an extremely high capacity of 1017 mAh g –1 was obtained in the fi rst cycle. However, a low reversible capacity was observed in this potential range, coupled with a completed destroyed crystal structure of PTCDA. The commercially available PTCDA was fi rst studied by X-ray diffraction (XRD), where PTCDA displays a β-form crystalline in the monoclinic P 2 1 / c space group (Figure S1, Supporting Information). [ 11 ] The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal that PTCDA has a sub-micrometer rod-like morphology with length of ≈1 μm and width of ≈200 nm (Figure S2, Supporting Information). The electrochemical behavior of PTCDA in SIBs was evaluated by using coin cells with sodium foil as the counter/ reference electrode, glass fi ber membrane as the separator and 1.0 M NaPF 6 in ethylene carbonate/diethyl carbonate (EC:DEC = 1:1 by volume) solution as the electrolyte. As shown in Figure 1 a, the fi rst discharge process (Na ions insertion to PTCDA) mainly displays a fl at plateau at ≈2.3 V, and a discharge capacity of 134 mAh g –1 is obtained at a current rate of 10 mA g –1 . Note that the capacity contribution from Super-P in this potential range is negligible, as shown in Figure S3 (Supporting Information). This plateau should be attributed to the reduction of carbonyl groups in PTCDA along with incorporating Na ions, forming sodium enolate groups. [ 14 ] Moreover, the discharge capacity of 134 mAh g –1 indicates that two carbonyl groups in PTCDA are reduced and Na 2 PTCDA is formed, with the structure proposed in Scheme 1 b. During the following charge to 3.0 V, a major plateau is displayed at ≈2.5 V, which can be ascribed to the extraction of Na ions from the sodium enolate groups. The fl at plateaus suggest the coexistence of two phases during either sodiation or desodiation. The two phases are, most likely, Na 2 PTCDA and PTCDA. Figure 1 b shows the discharge/charge curves for the second cycle, where a new minor discharge plateau at ≈2.5 V appears and the original plateau at 2.3 V slightly evolves into two consecutive plateaus at ≈2.2 V and ≈2.1 V, suggesting a possible sequential insertion of Na ions into Na x PTCDA. After the fi rst two cycles, the electrochemical behavior of PTCDA was much stabilized, as Figure 1 c,d show the overlapping curves from third and fourth cycle and a stabilized discharge/charge capacity of ≈145 mAh g –1 . This indicates that there might be an electrochemical conditioning process for PTCDA during the initial two cycles. With relentless efforts for three decades, lithium-ion batteries (LIBs) have achieved tremendous success in powering portable electronics and electric vehicles (EVs). [ 1 ] However, there is a signifi cant challenge for LIBs that cannot possibly be addressed with technological improvement; this is the rarity and uneven global distribution of Li resources. [ 2 ] There exists a risk that the price of Li would rise so quickly due to its exhaustive and prompt use in EVs that these EVs would no longer be affordable. Therefore, it is critical to develop future battery technologies that are not limited by Li. In sharp contrast, sodium (Na) is one of the most abundant elements (6th) in the Earth’s crust. Na also shows many electrochemical properties that are similar to those of Li. [ 3 ] In the past three decades, efforts have been made on high-temperature Na batteries including Na/S and Na/NiCl 2 systems that operate at 300–350 °C. [ 4 ] Unfortunately, the high operating temperatures for these devices have hampered their wide applications. [ 5 ]

Abstract: Y. C. Mao, Prof. X. D. Wang Department of Materials Science and Engineering University of Wisconsin-Madison Madison , WI , 53706 , USA E-mail: xudong@engr.wisc.edu Y. C. Mao, H. Yang, Prof. Y. X. Tong MOE Laboratory of Bioinorganic and Synthetic Chemistry KLGHEI of Environment and Energy Chemistry School of Chemistry and Chemical Engineering Sun Yat-sen University Guangzhou , 510275 , China Prof. P. Zhao Department of Mechanical and Industrial Engineering University of Minnesota-Duluth Duluth , MN , 55812 , USA G. McConohy Department of Engineering Physics University of Wisconsin-Madison Madison , WI , 53706 , USA

Abstract: Y. Zhou, M. Leng, Z. Xia, Dr. J. Zhong, H. Song, X. Liu, B. Yang, J. Chen, K. Zhou, Prof. Y. Cheng, Prof. J. Tang Wuhan National Laboratory for Optoelectronics (WNLO) Huazhong University of Science and Technology (HUST) Wuhan 430074 , P. R. China E-mail: jtang@mail.hust.edu.cn J. Zhang, J. Han Wuhan National High Magnetic Field Center Huazhong University of Science and Technology Wuhan 430074 , P. R. China

Abstract: A new and promising P2-type layered oxide, Na5/6[Li1/4Mn3/4]O2 is prepared using a solid-state method. Detailed crystal structures of the sample are analyzed by synchrotron X-ray diffraction combined with high-resolution neutron diffraction. P2-type Na5/6[Li1/4Mn3/4]O2 consists of two MeO2 layers with partial in-plane √3a × √3a-type Li/Mn ordering. Na/Li ion-exchange in a molten salt results in a phase transition accompanied with glide of [Li1/4Mn3/4]O2 layers without the destruction of in-plane cation ordering. P2-type Na5/6[Li1/4Mn3/4]O2 translates into an O2-type layered structure with staking faults as the result of ion-exchange. Electrode performance of P2-type Na5/6[Li1/4Mn3/4]O2 and O2-type Lix[Li1/4Mn3/4]O2 is examined and compared in Na and Li cells, respectively. Both samples show large reversible capacity, ca. 200 mA h g−1, after charge to high voltage regardless of the difference in charge carriers. Structural analysis suggests that in-plane structural rearrangements, presumably associated with partial oxygen loss, occur in both samples after charge to a high-voltage region. Such structural activation process significantly influences electrode performance of the P2/O2-type phases, similar to O3-type Li2MnO3-based materials. Crystal structures, phase-transition mechanisms, and the possibility of the P2/O2-type phases as high-capacity and long-cycle-life electrode materials with the multi-functionality for both rechargeable Li/Na batteries are discussed in detail.

Abstract: Dr. H.-g. Wang, S. Yuan, D.-l. Ma, X.-l. Huang, F.-l. Meng, Prof. X.-b. Zhang State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun , 130022 , P. R. China E-mail: xbzhang@ciac.ac.cn S. Yuan, D.-l. Ma, F.-l. Meng Key Laboratory of Automobile Materials Ministry of Education, and School of Materials Science and Engineering Jilin University Changchun , 130012 , P. R. China

Abstract: DOI: 10.1002/aenm.201400610 still smaller than that of electrochemical capacitors due mainly to the use of the low dielectric constant ( ε r ) Al 2 O 3 thin fi lm as the dielectric layer ( ε r ≈ 9). The concurrent high-power capacitors are made mainly of linear dielectric polymers with an ESD of ≈1–2 J cm −3 . [ 3 ] Although the ε r values of linear dielectric polymers are generally small (≈2–5), their electric breakdown fi elds are quite high, thereby allowing the application of high voltages, which result in a relatively high ESD. [ 3 ] Nonetheless, their ESD values are not high enough, so many other materials have been studied for the purpose. Most previous research on this topic focused on AFE Pb(Zr,Ti)O 3 (PZT)-based fi lms because their ESD values are as large as ≈1 and ≈10–15 J cm −3

Abstract: High-performance flexible energy-storage devices have great potential as power sources for wearable electronics. One major limitation to the realization of these applications is the lack of flexible electrodes with excellent mechanical and electrochemical properties. Currently employed batteries and supercapacitors are mainly based on electrodes that are not flexible enough for these purposes. Here, a three-dimensionally interconnected hybrid hydrogel system based on carbon nanotube (CNT)-conductive polymer network architecture is reported for high-performance flexible lithium ion battery electrodes. Unlike previously reported conducting polymers (e.g., polyaniline, polypyrrole, polythiophene), which are mechanically fragile and incompatible with aqueous solution processing, this interpenetrating network of the CNT-conducting polymer hydrogel exibits good mechanical properties, high conductivity, and facile ion transport, leading to facile electrode kinetics and high strain tolerance during electrode volume change. A high-rate capability for TiO2 and high cycling stability for SiNP electrodes are reported. Typically, the flexible TiO2 electrodes achieved a capacity of 76 mAh g–1 in 40 s of charge/discharge and a high areal capacity of 2.2 mAh cm–2 can be obtained for flexible SiNP-based electrodes at 0.1C rate. This simple yet efficient solution process is promising for the fabrication of a variety of high performance flexible electrodes.

Abstract: Vibrations in living environments are generally distributed over a wide frequency spectrum and exhibit multiple motion directions over time, which renders most of the current vibration energy harvesters unpractical for their harvesting purposes. Here, a 3D triboelectric nanogenerator (3D-TENG) is designed based on the coupling of the triboelectrifi cation effect and the electrostatic induction effect. The 3D-TENG operates in a hybridization mode of conjuntioning the vertical contact-separation mode and the in-plane sliding mode. The innovative design facilitates harvesting random vibrational energy in multiple directions over a wide bandwidth. An analytical model is established to investigate the mechano-triboelectric transduction of 3D-TENG and the results agree well with experimental data. The 3D-TENG is able to harvest ambient vibrations with an extremely wide working bandwidth. Maximum power densities of 1.35 W m −2 and 1.45 W m −2 are achieved under out-ofplane and in-plane excitation, respectively. The 3D TENG is designed for harvesting ambient vibration energy, especially at low frequencies, under a range of conditions in daily life and has potential applications in environmental/ infrastructure monitoring and charging portable electronics.

Abstract: Half-Heusler (HH) compounds are important high temperature thermoelectric (TE) materials and have attracted considerable attention in the recent years. High figure of merit zT values of 0.8 to 1.0 have been obtained in n-type ZrNiSn-based HH compounds. However, developing high performance p-type HH compounds are still a big challenge. Here, it is shown that a new p-type HH alloy with a high band degeneracy of 8, Ti-doped FeV_(0.6)Nb_(0.4)Sb, can achieve a high zT of 0.8, which is one of the highest reported values in the p-type HH compounds. Although the band effective mass of this system is found to be high, which may lead to a low mobility, its low deformation potential and low alloy scattering potential both contribute to a reasonably high mobility. The enhanced phonon scattering by alloying leads to a reduced lattice thermal conductivity. The achieved high zT demonstrates that the p-type Ti doped FeV_(0.6)Nb_(0.4) Sb HH alloys are promising as TE materials and offer an excellent TE performance match with n-type ones for high temperature power generation.

Abstract: A unifying theory is presented to explain the lithium exchange capacity of rocksalt-like structures with any degree of cation ordering, and how lithium percolation properties can be used as a guideline for the development of novel high-capacity electrode materials is demonstrated. The lithium percolation properties of the three most common lithium metal oxide phases, the layered α-NaFeO2 structure, the spinel-like LT-LiCoO2 structure, and the γ-LiFeO2 structure, are demonstrated and a strong dependence of the percolation thresholds on the cation ordering and the lithium content is observed. The poor performance of γ-LiFeO2-type structures is explained by their lack of percolation of good Li migration channels. The spinel-like structure exhibits excellent percolation properties that are robust with respect to off-stoichiometry and some amount of cation disorder. The layered structure is unique, as it possesses two different types of lithium diffusion channels, one of which is, however, strongly dependent on the lattice parameters, and therefore very sensitive to disorder. In general it is found that a critical Li-excess concentration exists at which Li percolation occurs, although the amount of Li excess needed depends on the partial cation ordering. In fully cation-disordered materials, macroscopic lithium diffusion is enabled by ≈10% excess lithium.

Abstract: Vanadium pentoxide–reduced graphene oxide (rGO) free-standing electrodes are used as electrodes for supercapacitor applications, eliminating the need for current collectors or additives and reducing resistance (sheet resistance 29.1 Ω □−1). The effective exfoliation of rGO allows improved electrolyte ions interaction, achieving high areal capacitance (511.7 mF cm−2) coupled with high mass loadings. A fabricated asymmetric flexible device based on rGO/V2O5-rGO (VGO) consists of approximately 20 mg of active mass and still delivers a low equivalent series resistance (ESR) of 3.36 Ω with excellent cycling stability. A prototype unit of the assembled device with organic electrolyte is shown to light up eight commercial light-emitting diode bulbs.