Abstract: Highest reported efficiency cesium lead halide perovskite solar cells are realized by tuning the bandgap and stabilizing the black perovskite phase at lower temperatures. CsPbI2Br is employed in a planar architecture device resulting in 9.8% power conversion efficiency and over 5% stabilized power output. Offering substantially enhanced thermal stability over their organic based counterparts, these results show that all-inorganic perovskites can represent a promising next step for photovoltaic materials.

Abstract: Ni-rich layered oxides and Li-rich layered oxides are topics of much research interest as cathodes for Li-ion batteries due to their low cost and higher discharge capacities compared to those of LiCoO2 and LiMn2O4. However, Ni-rich layered oxides have several pitfalls, including difficulty in synthesizing a well-ordered material with all Ni3+ ions, poor cyclability, moisture sensitivity, a thermal runaway reaction, and formation of a harmful surface layer caused by side reactions with the electrolyte. Recent efforts towards Ni-rich layered oxides have centered on optimizing the composition and processing conditions to obtain controlled bulk and surface compositions to overcome the capacity fade. Li-rich layered oxides also have negative aspects, including oxygen loss from the lattice during first charge, a large first cycle irreversible capacity loss, poor rate capability, side reactions with the electrolyte, low tap density, and voltage decay during extended cycling. Recent work on Li-rich layered oxides has focused on understanding the surface and bulk structures and eliminating the undesirable properties. Followed by a brief introduction, an account of recent developments on the understanding and performance gains of Ni-rich and Li-rich layered oxide cathodes is provided, along with future research directions.

Abstract: DOI: 10.1002/aenm.201501874 its spherical morphology well without surface cracking of the spheres, which explains its excellent capacity retention of 83% after 100 cycles. HCS is obtained by a hydrothermal reaction of dissolved sucrose, followed by pyrolysis. [ 10 ] The obtained product comprises carbon microspheres with diameters of around 5–10 μm ( Figure 1 a), and these spheres are of a fairly porous surface texture, as shown in the high resolution transmission electron microscopy (HRTEM) image (Figure 1 b). HCS exhibits a Brunauer–Emmett–Teller (BET) specifi c surface area of 65 m 2 g −1 . The nongraphitic hard carbon nature of HCS is revealed by X-ray diffraction (XRD) and Raman spectra. The XRD pattern of HCS shows a broad (002) peak, indicating a small stacking height of graphene layers, i.e., an average L c of ca. 1.4 nm estimated according to the Scherrer equation (Figure 1 c). Compared to the d-spacing of 0.335 nm in crystalline graphite, HCS exhibits an average inter-layer distance of ca. 0.400 nm, revealed by the position of the (002) peak. The Raman spectrum of HCS is very typical for nongraphitic carbon materials, which contains the D-band more intensive than the G-band, where they are assigned to A 1g vibration mode of sp 2 carbon rings caused by defects and E 2g vibration mode of sp 2 carbon atoms, respectively (Figure 1 d). We fi rst investigated the charge/discharge properties of the HCS electrode in KIBs, as compared to NIBs. Figure 2 a shows the typical potassiation/depotassiation potential profi les, where there is a high-potential sloping region and a low-potential quasiplateau region. Considering the available alkali metal ion storage mechanisms for hard carbon anodes, the two potential regions should correspond to K-ion insertion into different substructures or structural sites inside HCS, i.e., edges or defective sites of turbostratic nanodomains (TNs), inter-layer space inside TNs, and voids between TNs. [ 11 ] At C/10 (28 mAh g −1 ), the HCS/K cell presents a reversible capacity of 262 mAh g −1 in the depotassiation process, which is lower than 322 mAh g −1 from the HCS/Na cells (Figure 2 b). Furthermore, it is worthwhile pointing out that a capacity contribution of 200 mAh g −1 , 60% of the total capacity in HCS/Na cells, comes from its plateau region, where the sodiation potential is below 0.1 V versus Na + /Na. In contrast, it is only ca. 50 mAh g −1 , less than 20% of its total capacity in HCS/K cells, that is gained at potentials lower than 0.1 V versus K + /K. The difference in redox potentials between HCS/K and HCS/Na cells is more evident in the corresponding d Q /d V profi les (Figure 2 c,d). The HCS/K cell exhibits its potassiation and depotassiation peaks at 0.2 and 0.33 V versus K + /K, respectively, while both sodiation and desodiation peaks in the HCS/Na cell are lower than 0.1 V versus Na + /Na. When metal ion insertion occurs at potentials too close to the plating of the corresponding metal, dendrite formation can be a serious concern, particularly at high current rates. Great needs for electrochemical energy storage come from not only transportation but also stationary applications, e.g., home solar-power storage, microgrids, and load leveling. [ 1 ] However, for state-of-the-art lithium-ion batteries (LIBs), lithium is simply too rare to be deployed in stationary facilities. [ 2 ] Therefore, there arises tremendous interest in alternative Earth-abundant metalion batteries, among which, sodium-ion batteries (NIBs) attract most attention due to the abundance of sodium and its similar “rocking chair” operation principle as LIBs. [ 3 ] Great progress has been made on new electrode materials for NIBs. [ 4 ]

Abstract: Grid-scale energy storage systems (ESSs) that can connect to sustainable energy resources have received great attention in an effort to satisfy ever-growing energy demands. Although recent advances in Li-ion battery (LIB) technology have increased the energy density to a level applicable to grid-scale ESSs, the high cost of Li and transition metals have led to a search for lower-cost battery system alternatives. Based on the abundance and accessibility of Na and its similar electrochemistry to the well-established LIB technology, Na-ion batteries (NIBs) have attracted significant attention as an ideal candidate for grid-scale ESSs. Since research on NIB chemistry resurged in 2010, various positive and negative electrode materials have been synthesized and evaluated for NIBs. Nonetheless, studies on NIB chemistry are still in their infancy compared with LIB technology, and further improvements are required in terms of energy, power density, and electrochemical stability for commercialization. Most recent progress on electrode materials for NIBs, including the discovery of new electrode materials and their Na storage mechanisms, is briefly reviewed. In addition, efforts to enhance the electrochemical properties of NIB electrode materials as well as the challenges and perspectives involving these materials are discussed.

Abstract: The electrochemical stability window of solid electrolyte is overestimated by the conventional experimental method using a Li/electrolyte/inert metal semiblocking electrode because of the limited contact area between solid electrolyte and inert metal. Since the battery is cycled in the overestimated stability window, the decomposition of the solid electrolyte at the interfaces occurs but has been ignored as a cause for high interfacial resistances in previous studies, limiting the performance improvement of the bulk-type solid-state battery despite the decades of research efforts. Thus, there is an urgent need to identify the intrinsic stability window of the solid electrolyte. The thermodynamic electrochemical stability window of solid electrolytes is calculated using first principles computation methods, and an experimental method is developed to measure the intrinsic electrochemical stability window of solid electrolytes using a Li/electrolyte/electrolyte-carbon cell. The most promising solid electrolytes, Li10GeP2S12 and cubic Li-garnet Li7La3Zr2O12, are chosen as the model materials for sulfide and oxide solid electrolytes, respectively. The results provide valuable insights to address the most challenging problems of the interfacial stability and resistance in high-performance solid-state batteries.

Abstract: NiFe-based (oxy)hydroxides are highly active catalysts for the oxygen evolution reaction in alkaline electrolyte solutions. These catalysts can be synthesized in different ways leading to nanomaterials and thin films with distinct morphologies, stoichiometries and long-range order. Notably, their structure evolves under oxygen evolution operating conditions with respect to the as-synthesized state. Therefore, many researchers have dedicated their efforts on the identification of the catalytic active sites employing in operando experimental methods and theoretical calculations. These investigations are pivotal to rationally design materials with outstanding performances that will constitute the anodes of practical commercial alkaline electrolyzers. The family of NiFe-based oxyhydroxide catalysts reported in recent years is addressed and the actual state of the research with special focus on the understanding of the oxygen-evolution-reaction active sites and phase is described. Finally, an overview on the proposed oxygen-evolution-reaction mechanisms occurring on NiFe-based oxyhydroxide electrocatalysts is provided.

Abstract: Mixed transition-metal oxides (MTMOs), including stannates, ferrites, cobaltates, and nickelates, have attracted increased attention in the application of high performance lithium-ion batteries. Compared with traditional metal oxides, MTMOs exhibit enormous potential as electrode materials in lithium-ion batteries originating from higher reversible capacity, better structural stability, and high electronic conductivity. Recent advancements in the rational design of novel MTMO micro/nanostructures for lithium-ion battery anodes are summarized and their energy storage mechanism is compared to transition-metal oxide anodes. In particular, the significant effects of the MTMO morphology, micro/nanostructure, and crystallinity on battery performance are highlighted. Furthermore, the future trends and prospects, as well as potential problems, are presented to further develop advanced MTMO anodes for more promising and large-scale commercial applications of lithium-ion batteries.

Abstract: It is demonstrated that amorphous cobalt boride (Co2B) prepared by the chemical reduction of CoCl2 using NaBH4 is an exceptionally efficient electrocatalyst for the oxygen evolution reaction (OER) in alkaline electrolytes and is simultaneously active for catalyzing the hydrogen evolution reaction (HER). The catalyst achieves a current density of 10 mA cm−2 at 1.61 V on an inert support and at 1.59 V when impregnated with nitrogen-doped graphene. Stable performance is maintained at 10 mA cm−2 for at least 60 h. The optimized catalyst, Co2B annealed at 500 °C (Co2B-500) evolves oxygen more efficiently than RuO2 and IrO2, and its performance matches the best cobalt-based catalysts reported to date. Co2B is irreversibly oxidized at OER conditions to form a CoOOH surface layer. The active form of the catalyst is therefore represented as CoOOH/Co2B. EXAFS observations indicate that boron induces lattice strain in the crystal structure of the metal, which potentially diminishes the thermodynamic and kinetic barrier of the hydroxylation reaction, formation of the OOH* intermediate, a key limiting step in the OER.

Abstract: Sodium-ion batteries (SIBs) have attracted more and more attention for scalable electrical energy storage due to the abundance and wide distribution of Na resources. However, the anode still remains a great challenge for the application of SIBs. Here the production of uniform hard carbon microtubes (HCTs) made from natural cotton through one simple carbonization process and their application as an anode are reported. The study shows that the electrochemical performance of the HCTs is seriously affected by the carbonization temperature due to the difference in their microstructure and heteroatomic content. The HCTs carbonized at 1300 °C deliver the highest reversible capacity of 315 mAh g−1 and good rate capability due to their unique tubular structure. This contribution not only provides a new approach for the preparation of hard carbon materials with unique tubular microstructure using natural inspiration, but it also deepens the fundamental understanding of the sodium storage mechanism.

Abstract: X. Jia, G. Chen, Prof. X. Kang Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education College of Chemistry and Materials Science Northwest University Xi’an 710069 , P. R. China X. Jia, Dr. Y. Zhao, G. Chen, Dr. L. Shang, R. Shi, Prof. L.-Z. Wu, Prof. C.-H. Tung, Prof. T. Zhang Key Laboratory of Photochemical Conversion and Optoelectronic Materials Technical Institute of Physics and Chemistry Chinese Academy of Sciences Beijing 100190 , P. R. China E-mail: tierui@mail.ipc.ac.cn Prof. G. I. N. Waterhouse School of Chemical Sciences The University of Auckland Auckland 1142 , New Zealand

Abstract: Metal sulfide hollow nanostructures (MSHNs) have received intensive attention as electrode materials for electrical energy storage (EES) systems due to their unique structural features and rich chemistry. Here, we summarize recent research progress in the rational design and synthesis of various metal sulfide hollow micro-/nanostructures with controlled shape, composition and structural complexity, and their applications to lithium ion batteries (LIBs) and hybrid supercapacitors (HSCs). The current understanding of hollow structure control, including single-shelled, yolk-shelled, multi-shelled MSHNs, and their hybrid micro-/nanostructures with carbon (amorphous carbon nanocoating, graphene and hollow carbon), is focused on. The importance of proper structural and compositional control on the enhanced electrochemical properties of MSHNs is emphasized. A relationship between structural and compositional engineering with improved electrochemical activity of MSHNs is sought, in order to shed some light on future electrode design trends for next-generation EES technologies.

Abstract: The lithium-sulfur battery is a compelling energy storage system because its high theoretical energy density exceeds Li-ion batteries at much lower cost, but applications are thwarted by capacity decay caused by the polysulfide shuttle. Here, proof of concept and the critical metrics of a strategy to entrap polysulfides within the sulfur cathode by their reaction to form a surface-bound active redox mediator are demonstrated. It is shown through a combination of surface spectroscopy and cyclic voltammetry studies that only materials with redox potentials in a targeted window react with polysulfides to form active surface-bound polythionate species. These species are directly correlated to superior Li-S cell performance by electrochemical studies of high surface area oxide cathodes with redox potentials below, above, and within this window. Optimized Li-S cells yield a very low fade rate of 0.048% per cycle. The insight gained into the fundamental surface mechanism and its correlation to the stability of the electrochemical cell provides a bridge between mechanistic understanding and battery performance essential for the design of high performance Li-S cells.

Abstract: Though polypyrrole (PPy) is widely used in flexible supercapacitors owing to its high electrochemical activity and intrinsic flexibility, limited capacitance and cycling stability of freestanding PPy films greatly reduce their practicality in real-world applications. Herein, we report a new approach to enhance PPy's capacitance and cycling stability by forming a freestanding and conductive hybrid film through intercalating PPy into layered Ti3C2 (l-Ti3C2, a MXene material). The capacitance increases from 150 (300) to 203 mF cm−2 (406 F cm−3). Moreover, almost 100% capacitance retention is achieved, even after 20 000 charging/discharging cycles. The analyses reveal that l-Ti3C2 effectively prevents dense PPy stacking, benefiting the electrolyte infiltration. Furthermore, strong bonds, formed between the PPy backbones and surfaces of l-Ti3C2, not only ensure good conductivity and provide precise pathways for charge-carrier transport but also improve the structural stability of PPy backbones. The freestanding PPy/l-Ti3C2 film is further used to fabricate an ultra-thin all-solid-state supercapacitor, which shows an excellent capacitance (35 mF cm−2), stable performance at any bending state and during 10 000 charging/discharging cycles. This novel strategy provides a new way to design conductive polymer-based freestanding flexible electrodes with greatly improved electrochemical performances.

Abstract: Molecular hydrogen can be generated renewably by water splitting with an artificial-leaf device, which essentially comprises two electrocatalyst electrodes immersed in water and powered by photovol ...

Abstract: Increasing worldwide energy demands and rising CO2 emissions have motivated a search for new technologies to take advantage of renewables such as solar and wind energies. Redox flow batteries (RFBs) with their high power density, high energy efficiency, scalability (up to MW and MWh), and safety features are one suitable option for integrating such energy sources and overcoming their intermittency. However, resource limitation and high system costs of current RFB technologies impede wide implementation. Here, a total organic aqueous redox flow battery (OARFB) is reported, using low-cost and sustainable methyl viologen (MV, anolyte) and 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-HO-TEMPO, catholyte), and benign NaCl supporting electrolyte. The electrochemical properties of the organic redox active materials are studied using cyclic voltammetry and rotating disk electrode voltammetry. The MV/4-HO-TEMPO ARFB has an exceptionally high cell voltage, 1.25 V. Prototypes of the organic ARFB can be operated at high current densities ranging from 20 to 100 mA cm2, and deliver stable capacity for 100 cycles with nearly 100% Coulombic efficiency. The MV/4-HO-TEMPO ARFB displays attractive technical merits and thus represents a major advance in ARFBs.

Abstract: Lithium-ion batteries (LIBs) have dominated the portable electronics industry and solid-state electrochemical research and development for the past two decades. In light of possible concerns over the cost and future availability of lithium, sodium-ion batteries (SIBs) and other new technologies have emerged as candidates for large-scale stationary energy storage. Research in these technologies has increased dramatically with a focus on the development of new materials for both the positive and negative electrodes that can enhance the cycling stability, rate capability, and energy density. Two-dimensional (2D) materials are showing promise for many energy-related applications and particularly for energy storage, because of the efficient ion transport between the layers and the large surface areas available for improved ion adsorption and faster surface redox reactions. Recent research highlights on the use of 2D materials in these future ‘beyond-lithium-ion’ battery systems are reviewed, and strategies to address challenges are discussed as well as their prospects.

Abstract: F. Pei, Dr. X. L. Fang Pen-Tung Sah Institute of Micro-Nano Science and Technology Xiamen University Xiamen , Fujian 361005 , China E-mail: x.l.fang@xmu.edu.cn T. H. An, J. Zang, X. J. Zhao, Dr. M. S. Zheng, Prof. Q. F. Dong, Prof. N. F. Zheng State Key Laboratory for Physical Chemistry of Solid Surfaces Collaborative Innovation Center of Chemistry for Energy Materials and Engineering Research Center for Nano-Preparation Technology of Fujian Province College of Chemistry and Chemical Engineering Xiamen University Xiamen , Fujian 361005 , China E-mail: nfzheng@xmu.edu.cn

Abstract: Energy crisis is one of the most urgent and critical issues in our modern society. Currently, there is an increasing demand for efficient, low-cost, light-weight, flexible and environmentally benign, small-, medium-, and large-scale energy storage devices, which can be used to power smart grids, portable electronic devices, and electric vehicles. Novel electrode materials, with a high energy density at high power are urgently needed for realizing high-performance energy storage devices. The recent development in the field of 2D materials, including both graphene and other layered systems, has shown promise for a wide range of applications. In particular, graphene analogues, due to their remarkable electrochemical properties, have shown great potential in energy-related applications. This review aims at providing an overview of current research and important advances on the development of 2D materials beyond graphene for supercapacitors and batteries. The major challenges to be tackled, and more generally the future directions in the field, are also highlighted.

Abstract: Dr. Y. F. Li, Dr. R. X. Jin, Prof. Y. Xing, Dr. X. C. Liu Jilin Provincial Key Laboratory of Advanced Energy Materials Department of Chemistry Northeast Normal University Changchun 130024, P. R. China E-mail: xingy202@nenu.edu.cn Dr. J. Q. Li, Dr. S. Y. Song State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun 130022, P. R. China E-mail: songsy@ciac.ac.cn Prof. M. Li Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education South-Central University for Nationalities Wuhan 430074, P. R. China Prof. R. C. Jin Department of Chemistry Carnegie Mellon University Pittsburgh, PA 15213, USA

Abstract: D. Xu, Prof. J. Cai, Prof. L. Zhang College of Chemistry and Molecular Sciences Wuhan University Wuhan 430072 , China E-mail: zhangln@whu.edu.cn Dr. C. Chen, Prof. J. Xie State Key Laboratory of Advanced Electromagnetic Engineering and Technology School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan 430074 , P. R. China E-mail: xiejia@hust.edu.cn Dr. B. Zhang, Prof. L. Miao Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan 430074 , P. R. China Prof. Y. H. Huang State Key Laboratory of Materials Processing and Die & Mould Technology School of Materials Science and Engineering Huazhong University of Science and Technology Wuhan 430074 , P. R. China

Abstract: Dr. S. Q. Wang, L. Xia, Prof. H. H. Wang School of Chemistry and Chemical Engineering South China University of Technology Guangzhou 510640 , China E-mail: hhwang@scut.edu.cn Dr. L. Zhang, Prof. H. H. Wang School of Chemical Engineering The University of Adelaide SA 5005 , Australia L. Yu, Prof. X. W. Lou School of Chemical and Biomedical Engineering Nanyang Technological University 62 Nanyang Drive Singapore 637459 , Singapore E-mail: xwlou@ntu.edu.sg

Abstract: DOI: 10.1002/aenm.201600221 yields a synergism for the HER. [ 25 ] In accordance with the “volcano plot,” the activity for the evolution of hydrogen is a function of the M H (metal hydride) bond strength and exhibits a peak value for metal Pt, which has an optimal M H bond strength. [ 26 ] Therefore, designing a material on the molecular scale which combines an M H-weak metal (Ni) with an M H-strong metal (Mo) is a feasible method to acquire ideal catalysts. Sasaki’s group synthesized NiMoN x nanosheets on carbon support [ 21 ] and mixed close-packed Co 0.6 Mo 0.14 N 2 particles [ 20 ] via annealing corresponding precursors under ammonia gas. Both of the materials show the high HER electrocatalytic activity with low overpotential and small Tafel slope. In addition to the pristine activity of the catalysts, a variety of other parameters can limit their performance, such as roughness, conductivity, stability of the catalyst, the attachment of catalysts on electrodes. [ 27 ]

Abstract: Metal-organic frameworks (MOFs) with high surface area and tunable chemical structures have attracted tremendous attention. Recently, there has been increasing interest in deriving advanced materials from MOFs for electrochemical energy storage and conversion. This progress report highlights recent breakthroughs in electrocatalysis by using MOF-based novel catalysts, such as in oxygen reduction and evolution, hydrogen evolution and carbon dioxide reduction. The advantages of preparing electrocatalysts from MOFs are introduced and discussed. Then, the development of MOF derived electrocatalysis-active products, such as heteroatom-doped carbon, metal oxide (MO), metal sulfide (MS), metal carbide (MC), metal phosphide (MP) and their hybrids with carbon, are summarized. The detailed functions of these materials in representative electrocatalysis systems are also reviewed. The demonstrated examples will provide understanding in preparing highly active and stable electrocatalysts. The progress report concludes with the future applications of MOF-based materials in the field of electrocatalysis.

Abstract: Lithium ion batteries (LIBs) possess energy densities higher than those of the conventional batteries, but their lower power densities and poor cycling lives are critical challenges for their applications to electric vehicles (EVs) or grid stations. The energy and power densities, as well as the life of LIBs are dependent on electrodes where sluggish diffusion control process and structural stability are the main concerns. Here, the lithium storage mechanism of anode materials and the Goodenough diagram to explain the potential of cell and key parameters to determine the performance of an anode are highlighted. The cost reduction parameters and the availability of anode materials for future batteries on the basis of their resources and performances will be discussed. Further, the recent progress on anode nanostructures and solutions to the associated challenges will be outlined. The use of several techniques to determine the dynamic variations in nanostructures including both structural and chemical changes of electrode nanostructures during cycling as well as the limitations for high load applications will be explained. Finally, the concluding remarks will highlight the characteristics for both anode and cathode for better choice of electrode combinations in the full batteries.

Abstract: Facile design of low-cost and highly active catalysts from earth-abundant elements is favorable for the industrial application of water splitting. Here, a simple strategy to synthesize an ultrathin molybdenum disulfide/nitrogen-doped reduced graphene oxide (MoS2/N-RGO-180) nanocomposite with the enlarged interlayer spacing of 9.5 A by a one-step hydrothermal method is reported. The synergistic effects between the layered MoS2 nanosheets and N-doped RGO films contribute to the high activity for hydrogen evolution reaction (HER). MoS2/N-RGO-180 exhibits the excellent catalytic activity with a low onset potential of −5 mV versus reversible hydrogen elelctrode (RHE), a small Tafel slope of 41.3 mV dec−1, a high exchange current density of 7.4 × 10−4 A cm−2, and good stability over 5 000 cycles under acidic conditions. The HER performance of MoS2/N-RGO-180 nanocomposite is superior to the most reported MoS2-based catalysts, especially its onset potential and exchange current density. In this work, a novel and simple method to the preparation of low-cost MoS2-based electrocatalysts with the extraordinary HER performance is presented.

Abstract: Hard carbons are considered among the most promising anode materials for Na-ion batteries. Understanding their structure is of great importance for optimizing their Na storage capabilities and therefore achieving high performance. Herein, carbon nanofibers (CNFs) are prepared by electrospinning and their microstructure, texture, and surface functionality are tailored through carbonization at various temperatures ranging from 650 to 2800 degrees C. Stepwise carbonization gradually removes the heteroatoms and increases the graphitization degree, enabling us to monitor the corresponding electrochemical performance for establishing a correlation between the CNFs characteristics and Na storage behavior. Outstandingly, it is found that for CNFs carbonized at above 2000 degrees C, a single voltage Na uptake plateau at similar or equal to 0.1 V with a capacity of similar or equal to 200 mAh g(-1). This specific performance may be nested in the higher degree of graphitization, lower active surface area, and different porous texture of the CNFs at such temperatures. It is demonstrated via the assembly of a CNF/Na2Fe2(SO4)(3) cell the benefit of such CNFs electrode for enhancing the energy density of full Na-ion cells. This finding sheds new insights in the quest for high performance carbon based anode materials.

Abstract: Low-cost and resourceful transition metal phosphides (TMPs) have gradually received wide acceptance in the energy industry through exhibiting comparable catalytic activity and long-term stability to traditional catalysts (e.g., Pt/C, LiCoO2, LiFePO4, etc.). With the emergence of the research hotspot of TMPs, probing their mechanism of catalytic energy conversion and storage inspired by the superb structure of metal-phosphorus chelate is of great significance. To this end, recent developments in TMPs with various crystal structures and morphologies have attracted much attention. The design of TMPs ranging from the choice of different transition metals to phosphorus sources has been intensively explored. This research has indicated that multidimensional morphologies of TMPs prominently enrich the patterns of charge storage and electron transportation, and ultra-nanoscaled TMPs obtained by multiple tools and techniques might challenge the threshold of electrocatalytic reactions. Here, recent developments in synthetic strategies of TMPs from different precursors are classified. The underlying mechanism between the structural and crystallographic characteristics and the tuned properties of TMPs in energy applications is also presented. Additionally, the key trends in structure and morphology characterization of TMPs are highlighted. Future perspectives on the challenges and opportunities facing TMPs catalysts are thereby proposed.

Abstract: The development of sodium-ion batteries for large-scale applications requires the synthesis of electrode materials with high capacity, high initial Coulombic efficiency (ICE), high rate performance, long cycle life, and low cost. A rational design of freestanding anode materials is reported for sodium-ion batteries, consisting of molybdenum disulfide (MoS2) nanosheets aligned vertically on carbon paper derived from paper towel. The hierarchical structure enables sufficient electrode/electrolyte interaction and fast electron transportation. Meanwhile, the unique architecture can minimize the excessive interface between carbon and electrolyte, enabling high ICE. The as-prepared MoS2@carbon paper composites as freestanding electrodes for sodium-ion batteries can liberate the traditional electrode manufacturing procedure, thereby reducing the cost of sodium-ion batteries. The freestanding MoS2@carbon paper electrode exhibits a high reversible capacity, high ICE, good cycling performance, and excellent rate capability. By exploiting in situ Raman spectroscopy, the reversibility of the phase transition from 2H-MoS2 to 1T-MoS2 is observed during the sodium-ion intercalation/deintercalation process. This work is expected to inspire the development of advanced electrode materials for high-performance sodium-ion batteries.

Abstract: Sodium-ion batteries (SIBs) are now being actively developed as low cost and sustainable alternatives to lithium-ion batteries (LIBs) for large-scale electric energy storage applications. In recent years, various inorganic and organic Na compounds, mostly mimicked from their Li counterparts, have been synthesized and tested for SIBs, and some of them indeed demonstrate comparable specific capacity to the presently developed LIB electrodes. However, the lack of suitable cathode materials is still a major obstacle to the commercial development of SIBs. Here, we present a brief review on the recent developments of SIB cathodes, with a focus on low cost and high energy density materials (> 450 Wh kg−1 vs Na) together with discussion of their Na-storage mechanisms. The considerable differences in the structural requirements for Li- and Na-storage reactions mean that it is not sufficient to design SIB cathode materials by simply mimicking LIB materials, and therefore great efforts are needed to discover new materials and reaction mechanisms to further develop variable cathodes for advanced SIB technology. Some directions for future research and possible strategies for building advanced cathode materials are also proposed here.