Ya You

High-quality Prussian blue crystals as superior cathode materials for room-temperature sodium-ion batteries

High-quality Prussian blue crystals with a small number of vacancies and a low water content are obtained by employing Na4Fe(CN)6 as the single iron-source precursor. The high-quality Prussian blue shows high specific capacity and remarkable cycling stability as the cathode material for Na-ion batteries because of its excellent ion storage capability and impressive structure stability.

Sodium iron hexacyanoferrate with high Na content as a Na-rich cathode material for Na-ion batteries

AbstractOwing to the worldwide abundance and low-cost of Na, room-temperature Na-ion batteries are emerging as attractive energy storage systems for large-scale grids. Increasing the Na content in cathode materials is one of the effective ways to achieve high energy density. Prussian blue and its analogues (PBAs) are promising Na-rich cathode materials since they can theoretically store two Na+ ions per formula unit. However, increasing the Na content in PBAs cathode materials remains a major challenge. Here we show that sodium iron hexacyanoferrate with high Na content can be obtained by simply controlling the reducing agent and reaction atmosphere during synthesis. The Na content can reach as high as 1.63 per formula, which is the highest value for sodium iron hexacyanoferrate. This Na-rich sodium iron hexacyanoferrate demonstrates a high specific capacity of 150 mAh·g−1 and remarkable cycling performance with 90% capacity retention after 200 cycles. Furthermore, the Na intercalation/de-intercalation mechanism has been systematically studied by in situ Raman spectroscopy, X-ray diffraction and X-ray absorption spectroscopy analysis for the first time. The Na-rich sodium iron hexacyanoferrate can function as a plenteous Na reservoir and has great potential as a cathode material for practical Na-ion batteries.

Subzero‐Temperature Cathode for a Sodium‐Ion Battery

A subzero-temperature cathode material is obtained by nucleating cubic prussian blue crystals at inhomogeneities in carbon nanotubes. Due to fast ionic/electronic transport kinetics even at -25 °C, the cathode shows an outstanding low-temperature performance in terms of specific energy, high-rate capability, and cycle life, providing a practical sodium-ion battery powering an electric vehicle in frigid regions.

Suppressing the P2–O2 Phase Transition of Na0.67Mn0.67Ni0.33O2 by Magnesium Substitution for Improved Sodium-Ion Batteries

Room-temperature sodium-ion batteries (SIBs) have shown great promise in grid-scale energy storage, portable electronics, and electric vehicles because of the abundance of low-cost sodium. Sodium-based layered oxides with a P2-type layered framework have been considered as one of the most promising cathode materials for SIBs. However, they suffer from the undesired P2-O2 phase transition, which leads to rapid capacity decay and limited reversible capacities. Herein, we show that this problem can be significantly mitigated by substituting some of the nickel ions with magnesium to obtain Na0.67 Mn0.67 Ni0.33-x Mgx O2 (0≤x≤0.33). Both the reversible capacity and the capacity retention of the P2-type cathode material were remarkably improved as the P2-O2 phase transition was thus suppressed during cycling. This strategy might also be applicable to the modulation of the physical and chemical properties of layered oxides and provides new insight into the rational design of high-capacity and highly stable cathode materials for SIBs.

Hierarchically micro/mesoporous activated graphene with a large surface area for high sulfur loading in Li-S batteries

A hierarchically micro/mesoporous a-MEGO with a high surface area (up to 3000 m2 g−1) and large pore volume (up to 2.14 cm3 g−1) was utilized as a superior carbon host material for high sulfur loading towards advanced Li–S batteries.

Combining Nitrogen-Doped Graphene Sheets and MoS2: A Unique Film–Foam–Film Structure for Enhanced Lithium Storage

With a notable advantage in terms of capacity, molybdenum disulfide has been considered a promising anode material for building high-energy-density lithium-ion batteries. However, its intrinsically low electronic conductivity and unstable electrochemistry lead to poor cycling stability and inferior rate performance. We herein describe the scalable assembly of free-standing MoS2 -graphene composite films consisting of nitrogen-doped graphene and ultrathin honeycomb-like MoS2 nanosheets. The composite has a unique film-foam-film hierarchical top-down architecture from the macroscopic to the microscopic and the nanoscopic scale, which helps rendering the composite material highly compact and leads to rapid ionic/electronic access to the active material, while also accommodating the volume variation of the sulfide upon intercalation/deintercalation of Li. The unique structural merits of the composite lead to enhanced lithium storage.

Photocatalytic CO2 Reduction by Carbon-Coated Indium-Oxide Nanobelts

Indium-oxide (In2O3) nanobelts coated by a 5-nm-thick carbon layer provide an enhanced photocatalytic reduction of CO2 to CO and CH4, yielding CO and CH4 evolution rates of 126.6 and 27.9 μmol h-1, respectively, with water as reductant and Pt as co-catalyst. The carbon coat promotes the absorption of visible light, improves the separation of photoinduced electron-hole pairs, increases the chemisorption of CO2, makes more protons from water splitting participate in CO2 reduction, and thereby facilitates the photocatalytic reduction of CO2 to CO and CH4.

The Electrochemistry with Lithium versus Sodium of Selenium Confined To Slit Micropores in Carbon

Substitution of selenium for sulfur in the cathode of a rechargeable battery containing Sx molecules in microporous slits in carbon allows a better characterization of the electrochemical reactions that occur. Paired with a metallic lithium anode, the Sex chains are converted to Li2Se in a single-step reaction. With a sodium anode, a sequential chemical reaction is characterized by a continuous chain shortening of Sex upon initial discharge before completing the reduction to Na2Se; on charge, the reconstituted Sex molecules retain a smaller x value than the original Sex chain molecule. In both cases, the Se molecules remain almost completely confined to the micropore slits to give a long cycle life.

Nickel-Doped La0.8Sr0.2Mn1–xNixO3 Nanoparticles Containing Abundant Oxygen Vacancies as an Optimized Bifunctional Catalyst for Oxygen Cathode in Rechargeable Lithium–Air Batteries

In this work, Ni-doped manganite perovskite oxides (La0.8Sr0.2Mn(1-x)Ni(x)O3, x = 0.2 and 0.4) and undoped La0.8Sr0.2MnO3 were synthesized via a general and facile sol-gel route and used as bifunctional catalysts for oxygen cathode in rechargeable lithium-air batteries. The structural and compositional characterization results showed that the obtained La0.8Sr0.2Mn(1-x)Ni(x)O3 (x = 0.2 and 0.4) contained more oxygen vacancies than did the undoped La0.8Sr0.2MnO3 as well as a certain amount of Ni(3+) (eg = 1) on their surface. The Ni-doped La0.8Sr0.2Mn(1-x)Ni(x)O3 (x = 0.2 and 0.4) was provided with higher bifunctional catalytic activities than that of the undoped La0.8Sr0.2MnO3. In particular, the La0.8Sr0.2Mn0.6Ni0.4O3 had a lower total over potential between the oxygen evolution reaction and the oxygen reduction reaction than that of the La0.8Sr0.2MnO3, and the value is even comparable to that of the commercial Pt/C yet is provided with a much reduced cost. In the lithium-air battery, oxygen cathodes containing the La0.8Sr0.2Mn0.6Ni0.4O3 catalyst delivered the optimized electrochemical performance in terms of specific capacity and cycle life, and a reasonable reaction mechanism was given to explain the improved performance.

An O3-type NaNi0.5Mn0.5O2 cathode for sodium-ion batteries with improved rate performance and cycling stability

Layered O3-type NaNi0.5Mn0.5O2 (space group: Rm) was synthesized by a sol–gel method, and subjected to electrochemical characterization for sodium-ion batteries (SIBs). A Na//NaNi0.5Mn0.5O2 cell can deliver a reversible capacity of 141 mA h g−1 in the voltage range of 2.0–4.0 V and show a good capacity retention of 90% after 100 cycles. A highly reversible structural evolution of O3hex.–O3′mon.–P3hex.–P3′mon.–P3′′hex. upon Na+ extraction and intercalation is demonstrated to be the key factor to its excellent cycling capability. Furthermore, the apparent diffusion coefficient of Na ions in the layered O3-type NaNi0.5Mn0.5O2 composite electrode can be effectively increased by using good conductive CNTs, which is demonstrated by cyclic voltammograms and the galvanostatic intermittent titration technique. Thus even at a high rate of 2C, the O3-NaNi0.5Mn0.5O2 cathode still exhibits a high reversible capacity of 80 mA h g−1. The impressive sodium storage properties of O3-NaNi0.5Mn0.5O2 make it a promising candidate as a positive electrode material for rechargeable SIBs.