Guanhua Jin

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.

Aqueous rechargeable lithium batteries using NaV6O15 nanoflakes as high performance anodes

Poor cycling performance is still the big challenge for aqueous rechargeable lithium batteries (ARLBs), in which the instability of the anode is considered to be the main issue. In this work, NaV6O15 nanoflakes were synthesized by a two-step approach and a NaV6O15//LiMn2O4 ARLB system with superior cycling performance was constructed. The galvanostatic charge–discharge result demonstrates an initial discharge capacity of 110.7 mA h g−1 (based on anode mass) at 150 mA g−1 and the capacity retention of ca. 90% and 80% at 300 mA g−1 after 100 and 400 cycles, respectively. Such superior cycling performance of ARLBs is mainly due to the intrinsic 3-D tunneled structure of NaV6O15, nanoflake morphology and relatively stable electrode surface, as verified by the X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) results of the tested electrodes. Moreover, a simple single-phase reaction mechanism during the lithium ion insertion/extraction process is observed for NaV6O15 by XRD analysis.

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.

Electrochemical behavior and cyclic fading mechanism of LiNi0.5Mn0.5O2 electrode in LiNO3 electrolyte

Electrochemical behavior of layered LiNi0.5Mn0.5O2 in LiNO3 aqueous solution and its cyclic fading mechanism in electrolytes with different pH values were investigated. CV results show that LiNi0.5Mn0.5O2 has good electrochemical reversible behaviors in 5 mol/L LiNO3 solution. Meanwhile, the electrode in 5 mol/L LiNO3 with pH value of 12 demonstrates the best electrochemical stability. Based on the electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) results, it is proposed that suppressed charge-transfer resistance is the major reason, which is probably ascribed to the more stable electrode surface and less structure change.