Hanna He

Annealed NaV3O8 nanowires with good cycling stability as a novel cathode for Na-ion batteries

In this work, NaV3O8 nanowires are proposed as a novel cathode for a Na-ion battery for the first time. The as-prepared nanowires are characterized well by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Sodium insertion/extraction properties of as-prepared nanowires with or without thermal treatment are compared. It is found that thermal treatment could remove some crystal water in the host, resulting in a contracted crystal volume. In comparison with the untreated sample, although the reversible discharge capacity of annealed NaV3O8·xH2O nanowires is decreased from 169.6 mA h g−1 to 145.8 mA h g−1 when cycled at 10 mA g−1, it shows good capacity retention of ca. 91.1% after 50 cycles, much higher than that (51.9%) of the untreated sample. Annealed NaV3O8 nanowires exhibit much better cycling stability and charge–discharge plateaus during the Na-ion insertion/extraction processes, which should be attributed to the contracted crystal volume and the increased crystallinity.

Iron-Doped Cauliflower-Like Rutile TiO2 with Superior Sodium Storage Properties

Developing advanced anodes for sodium ion batteries is still challenging. In this work, Fe-doped three-dimensional (3D) cauliflower-like rutile TiO2 was successfully synthesized by a facile hydrolysis method followed by a low-temperature annealing process. The influence of Fe content on the structure, morphology, and electrochemical performance was systematically investigated. When utilized as a sodium ion battery anode, 6.99%-Fe-doped TiO2 exhibited the best electrochemical performance. This sample delivered a very high reversible capacity (327.1 mAh g-1 at 16.8 mA g-1) and superior rate performance (160.5 mAh g-1 at 840 mA g-1), as well as long-term cycling stability (no capacity fading at 1680 mA g-1 over 3000 cycles). Density functional theory (DFT) calculations combined with experimental results indicated that the significantly improved sodium storage ability of the Fe-doped sample should be mainly due to the increased oxygen vacancies, narrowed band gap, and lowered sodiation energy barrier, which enabled much higher electronic/ionic conductivities and more favorable sodium ion intercalation into rutile TiO2.

LixV2O5/LiV3O8 nanoflakes with significantly improved electrochemical performance for Li-ion batteries

Poor cycling stability and rate capability are the main challenges for LiV3O8 as the cathode material for Li-ion batteries. Here a novel strategy involving the self-transformation of superficial LiV3O8 in a reducing atmosphere (H2–Ar) was reported to fabricate LixV2O5/LiV3O8 nanoflakes. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) results demonstrate that LixV2O5/LiV3O8 nanoflakes could be in situ formed and that the thickness of the LixV2O5 layer is controllable. When used as a cathode for a Li-ion battery, the LixV2O5/LiV3O8 nanoflakes exhibit significantly improved cycling stability with a capacity retention of ca. 82% over 420 cycles at a 1 C-rate (1 C = 300 mA g−1), and much better rate performance compared with bare LiV3O8. The improvement of the electrochemical performance could be attributed to the unique core–shell structure, in which the ultrathin LixV2O5 layer could not only protect the internal LiV3O8 from dissolution, but also increase the Li ion diffusion coefficient and suppress the charge-transfer resistance, as verified by electrochemical impedance spectroscopy (EIS) and XRD results.

Plasma-Induced Amorphous Shell and Deep Cation-Site S Doping Endow TiO2 with Extraordinary Sodium Storage Performance

Structural design and modification are effective approaches to regulate the physicochemical properties of TiO2 , which play an important role in achieving advanced materials. Herein, a plasma-assisted method is reported to synthesize a surface-defect-rich and deep-cation-site-rich S doped rutile TiO2 (R-TiO2-x -S) as an advanced anode for the Na ion battery. An amorphous shell (≈3 nm) is induced by the Ar/H2 plasma, which brings about the subsequent high S doping concentration (≈4.68 at%) and deep doping depth. Experimental results and density functional theory calculations demonstrate greatly facilitated ion diffusion, improved electronic conductivity, and an increased mobility rate of holes for R-TiO2-x -S, which result in superior rate capability (264.8 and 128.5 mAh g-1 at 50 and 10 000 mA g-1 , respectively) and excellent cycling stability (almost 100% retention over 6500 cycles). Such improvements signify that plasma treatment offers an innovative and general approach toward designing advanced battery materials.

Adjusting the Yolk-shell Structure of Carbon Spheres to Boost the Capacitive K+ Storage Ability

Carbon materials continue to be a focus of rapid innovative application in potassium-ion batteries (KIBs) owing to their abundant resources. However, K+ storage of carbon electrodes is limited by the intercalation chemistry which brings a large structural change and sluggish potassiation kinetics. In this work, we synthesized a series of hierarchical porous yolk–shell carbon sphere (HYCS) materials through an extended Stober reaction. By controlling the concentration of tetraethyl orthosilicate (TEOS), their morphologies, including pore volume, specific surface area and yolk ratios, can be well adjusted. Quantitative analysis reveals that these adjusted materials show enhanced capacitive behavior, which leads to fast reaction kinetics and enhanced K+ adsorption capability. Furthermore, the capacitance contribution can be controlled through adjusting the yolk–shell nanostructures. The optimized sample with the largest pore volume (1.47 cm3 g−1) and the highest specific surface area (703.1 cm2 g−1) possesses the best rate performance with capacities of 314 and 121 mA h g−1 at 50 and 5000 mA g−1, respectively. These achievements signify that structural adjustment is an effective approach for constructing high-performance K+ storage materials.