硫/水热碳球复合材料的制备及对锂硫电池倍率性能的影响

在锂硫电池正极材料的研究中,碳材料可以有效改善电池倍率及循环性能.为了提高锂硫电池的高倍率放电性能,通过水热合成的方法,制备了由非均匀粒径碳球组成的碳材料.与硫热合成后,硫均匀分布在碳材料表面及周围,复合材料含硫量为52wt%.0.2C放电电流下,首次放电比容量为1174mAh·g^-1,100次循环后放电比容量为788mAh·g^-1.在4C的放电电流下,放电比容量稳定维持在600mAh·g^-1,循环过程中,库伦效率高于90%.该碳材料有良好的导电网络,且制备方便,成本低廉,对于穿梭效应和放电过程中的膨胀效应有一定的抑制作用,是一种优秀的正极材料.     

Polyantimonides as anode materials in battery applications

Antimony containing compounds have drawn interest as anode materials in Li batteries due to their high Li packing density and the resulting volumetric charge density. Reasonable specific capacities outperforming graphite by a factor of 2 have been reported for antimonides and polyantimonides. Together with good cycling stabilities, rate capabilities and a high potential level against Li metal, both classes of materials are discussed as potential candidates to substitute carbonaceous hosts. Unfortunately, severe volume expansion during the reaction with lithium takes place which has to be taken into account during optimization of the systems. This feature demands size tailoring and electrode optimization to push the electrochemical performance and the lifetime of half cells and full batteries in applicable dimensions. While antimonides are more or less intermetallic compounds, performing a conversion reaction to electrochemical active (in most cases Sb) and non-active species, polyantimonides can offer a greater flexibility due to their anisotropic structural features. Polyantimonides, containing simple dumbbells up to layered arrangements of covalently bonded antimony, can provide voids or interstitials for insertion and intercalation of lithium. The chance to preserve such favourable structural features during this process is in principle higher than for antimonides where conversion reactions to other species take place.Herein we report on structural features and electrochemical performance of antimony containing active materials for anodes in lithium batteries. Our focus lies on recent developments in polyantimonides chemistry but we will also address the scientific progress with antimonides.     

Preparation of Yolk‐Shell and Filled Co9S8 Microspheres and Comparison of their Electrochemical Properties

In this study, we report the first preparation of phase‐pure Co₉S₈ yolk–shell microspheres in a facile two‐step process and their improved electrochemical properties. Yolk–shell Co₃O₄ precursor microspheres are initially obtained by spray pyrolysis and are subsequently transformed into Co₉S₈ yolk–shell microspheres by simple sulfidation in the presence of thiourea as a sulfur source at 350 °C under a reducing atmosphere. For comparison, filled Co₉S₈ microspheres were also prepared using the same procedure but in the absence of sucrose during the spray pyrolysis. The prepared yolk–shell Co₉S₈ microspheres exhibited a Brunauer–Emmett–Teller (BET) specific surface area of 18 m² g^?1 with a mean pore size of 16 nm. The yolk–shell Co₉S₈ microspheres have initial discharge and charge capacities of 1008 and 767 mA h g^?1 at a current density of 1000 mA g^?1, respectively, while the filled Co₉S₈ microspheres have initial discharge and charge capacities of 838 and 638 mA h g^?1, respectively. After 100 cycles, the discharge capacities of the yolk–shell and filled microspheres are 634 and 434 mA h g^?1, respectively, and the corresponding capacity retentions after the first cycle are 82 % and 66 %.     

Excellent Performance of Few‐Layer Borocarbonitrides as Anode Materials in Lithium‐Ion Batteries

Borocarbonitrides (B_xC_yN_z) with a graphene‐like structure exhibit a remarkable high lithium cyclability and current rate capability. The electrochemical performance of the B_xC_yN_z materials, synthesized by using a simple solid‐state synthesis route based on urea, was strongly dependent on the composition and surface area. Among the three compositions studied, the carbon‐rich compound B_0.15C_0.73N_0.12 with the highest surface area showed an exceptional stability (over 100 cycles) and rate capability over widely varying current density values (0.05–1 A g^?1). B_0.15C_0.73N_0.12 has a very high specific capacity of 710 mA h g^?1 at 0.05 A g^?1. With the inclusion of a suitable additive in the electrolyte, the specific capacity improved drastically, recording an impressive value of nearly 900 mA h g^?1 at 0.05 A g^?1. It is believed that the solid–electrolyte interphase (SEI) layer at the interface of B_xC_yN_z and electrolyte also plays a crucial role in the performance of the B_xC_yN_z .     

2 D Manganese Vanadate Nanoflakes as High‐Performance Anode for Lithium‐Ion Batteries

Nanometer‐sized flakes of MnV₂O₆ were synthesized by a hydrothermal method. No surfactant, expensive metal salt, or alkali reagent was used. These MnV₂O₆ nanoflakes present a high discharge capacity of 768 mA h g^?1 at 200 mA g^?1, good rate capacity, and excellent cycling stability. Further investigation demonstrates that the nanoflake structure and the specific crystal structure make the prepared MnV₂O₆ a suitable material for lithium‐ion batteries.     

Flame Spray Pyrolysis for Finding Multicomponent Nanomaterials with Superior Electrochemical Properties in the CoOx‐FeOx System for Use in Lithium‐Ion Batteries

High‐temperature flame spray pyrolysis is employed for finding highly efficient nanomaterials for use in lithium‐ion batteries. CoO_x‐FeO_x nanopowders with various compositions are prepared by one‐pot high‐temperature flame spray pyrolysis. The Co and Fe components are uniformly distributed over the CoO_x‐FeO_x composite powders, irrespective of the Co/Fe mole ratio. The Co‐rich CoO_x‐FeO_x composite powders with Co/Fe mole ratios of 3:1 and 2:1 have mixed crystal structures with CoFe₂O₄ and Co₃O₄ phases. However, Co‐substituted magnetite composite powders prepared from spray solutions with Co and Fe components in mole ratios of 1:3, 1:2, and 1:1 have a single phase. Multicomponent CoO_x‐FeO_x powders with a Co/Fe mole ratio of 2:1 and a mixed crystal structure with Co₃O₄ and CoFe₂O₄ phases show high initial capacities and good cycling performance. The stable reversible discharge capacities of the composite powders with a Co/Fe mole ratio of 2:1 decrease from 1165 to 820 mA h g^?1 as the current density is increased from 500 to 5000 mA g^?1; however, the discharge capacity again increases to 1310 mA h g^?1 as the current density is restored to 500 mA g^?1.     

Nano-crystalline FeOOH mixed with SWNT matrix as a superior anode material for lithium batteries

Nano-crystalline FeOOH particles(5～10 nm) have been uniformly mixed with electric matrix of single-walled carbon nanotubes(SWNTs)for forming FeOOH/SWNT composite via a facile ultrasonication method. Directly using the FeOOH/SWNT composite(containing 15 wt%SWNTs) as anode material for lithium battery enhances kinetics of the Li+insertion/extraction processes, thereby effectively improving reversible capacity and cycle performance, which delivers a high reversible capacity of 758 mAh g-1under a current density of 400 mA g-1even after 180 cycles, being comparable with previous reports in terms of electrochemical performance for FeOOH anode. The good electrochemical performance should be ascribed to the small particle size and nano-crystalline of FeOOH, as well as the good electronic conductivity of SWNT matrix.     

Hydrothermal exfoliated molybdenum disulfide nanosheets as anode material for lithium ion batteries

Ultrathin MoS2nanosheets were prepared in high yield using a facile and effective hydrothermal intercalation and exfoliation route. The products were characterized in detail using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The results show that the high yield of MoS2nanosheets with good quality was successfully achieved and the dimensions of the immense nanosheets reached 1 μm–2 μm. As anode material for Li-ion batteries, the as-prepared MoS2nanosheets electrodes exhibited a good initial capacity of 1190 mAh g-1and excellent cyclic stability at constant current density of 50 mA g-1. After 50 cycles, it still delivered reversibly sustained high capacities of 750 mAh g-1.     

Revealing the Reaction and Fading Mechanism of FeSe2 Cathodes for Rechargeable Magnesium Batteries

Rechargeable Mg batteries (RMBs) are advantageous large-scale energy-storage devices because of the high abundance and high safety, but exploring high-performance cathodes remains the largest difficulty for their development. Compared with oxides and sulfides, selenides show better Mg-storage performance because the weaker interaction with the Mg²⁺ cation favors fast kinetics. Herein, nanorod-like FeSe₂ was synthesized and investigated as a cathode for RMBs. Compared with microspheres and microparticles, nanorods exhibit higher capacity and better rate capability with a smaller particle size. The FeSe₂ nanorods show a high capacity of 191 mAh g⁻¹ at 50 mA g⁻¹ and a good rate performance of 39 mAh g⁻¹ at 1000 mA g⁻¹. Ex situ characterizations demonstrate the Mg²⁺ intercalation mechanism for FeSe₂, and a slight conversion reaction occurs on the surface of the particles. The capacity fading is mainly because of the dissolution of Fe²⁺, which is caused by the reaction between Fe²⁺ and Cl⁻ of the electrolyte during the charge process on the surface of the particles. The surface of FeSe₂ is mainly selenium after long cycling, which may also dissolve in the electrolyte during cycling. The present work develops a new type of Mg²⁺ intercalation cathode for RMBs. More importantly, the fading mechanism revealed herein has considered the specificity of Mg battery electrolyte and would assist a better understanding of selenide cathodes for RMBs.     

Chemistry-Performance Relationships of Polymer Gel-Electrolytes for Mg−S and Li−S Batteries: Influence of Network Cation Solvation Capacity on Polymer-Polysulfide Interactions

Metal-sulfur batteries are a promising next-generation energy storage technology, offering high theoretical energy densities with low cost and good sustainability. An active area of research is the development of electrolytes that address unwanted migration of sulfur and intermediate species known as polysulfides during operation of metal-sulfur batteries, a phenomenon that leads to low energy efficiency and short life-spans. A particular class of electrolytes, gel polymer electrolytes, are especially attractive for their ability to repel polysulfides on the basis of structure, electrostatics, and other polymer properties. Herein, within the context of magnesium- and lithium-sulfur batteries, we investigate the impact of gel polymer electrolyte cation solvation capacity, a property related to network dielectric constant and chemistry, on sulfur/polysulfide-polymer interactions, an understudied property-performance relationship. Polymers with lower cation solvation capacity are found to permanently absorb less polysulfide active material, which increases sulfur utilization for Li−S batteries and significantly increases charge efficiency and life-span for Li−S and Mg−S batteries.