Benhe Zhong

Subunits controlled synthesis of α-Fe2O3 multi-shelled core–shell microspheres and their effects on lithium/sodium ion battery performances

Two kinds of Fe2O3 core–shell microspheres were synthesized. The Fe2O3 sample obtained using ethanol (E–Fe2O3) contains a shell and a core assembled by nanoparticles with a diameter of ∼150 nm and the surface is fairly smooth. Fe2O3 with optimized subunits was produced using water (W–Fe2O3). The core is assembled by smaller nanoparticles of ∼50 nm. The thicker shell and exterior surface possess porous nanorods. These peculiar subunits endow W–Fe2O3 with a higher specific surface area, more pore volume and larger nanopores. W–Fe2O3 displayed 733.1 mA h g−1 at 6000 mA g−1, which is more than two times that of E–Fe2O3 (306.5 mA h g−1). Encouragingly, W–Fe2O3 also expressed relatively promising sodium ion battery performances. The significantly different performances between E–Fe2O3 and W–Fe2O3 can be almost entirely attributed to their distinctive subunits. The study demonstrated that enhanced lithium/sodium ion storage properties can be achieved by adjusting the subunits.

L-Histidine-assisted template-free hydrothermal synthesis of α-Fe2O3 porous multi-shelled hollow spheres with enhanced lithium storage properties

Unique α-Fe2O3 porous multi-shelled hollow spheres (α-Fe2O3 PMSHSs) have been prepared by a simple template-free hydrothermal method followed by annealing in air. For the first time, L-histidine was used as a morphology controlling agent in the synthesis process. The α-Fe2O3 PMSHSs had a relatively high surface area of 14.2 m2 g−1 and a pore volume of 0.07 cm3 g−1. When used as an anode material for lithium ion batteries, the α-Fe2O3 PMSHSs exhibited high specific capacity, good cycling stability, and excellent rate performance. A stable and reversible capacity of 869.9 mA h g−1 could be maintained at a charge–discharge current density of 400 mA g−1 after 300 cycles. Superior rate capability had also been demonstrated by testing the material at different current densities. The α-Fe2O3 PMSHSs could deliver a capacity as high as 833.3 mA h g−1 at 800 mA g−1, and a capacity of 498.1 mA h g−1 at 6000 mA g−1. The superior electrochemical performance of the α-Fe2O3 PMSHSs is attributed to the hierarchical porosity, special micro/nanostructure, shorter electron and lithium ion diffusion pathways, and easy penetration of the electrolyte.

Preparation of sodium trimetaphosphate and its application as an additive agent in a novel polyvinylidene fluoride based gel polymer electrolyte in lithium sulfur batteries

Six-membered cyclic sodium trimetaphosphate with strong electronegativity and an excellent capability of chelating metal cations was prepared via a convenient calcining method and used as an additive agent in a PVDF-based gel polymer electrolyte membrane for lithium sulfur batteries after being ion-exchanged with Li+ cations. The membrane and its application in lithium sulfur batteries were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), linear sweep voltammetry (LSV), charge–discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Results show that this novel gel polymer electrolyte exhibits a high ionic conductivity of 2–4 mS cm−1 between 17 and 76 °C and has promising characteristics for use in lithium sulfur batteries. The “shuttle effect”, which is the critical issue for lithium sulfur batteries, is restrained because of using the gel polymer electrolyte with the trimetaphosphate added to it.

A further electrochemical investigation on solutions to high energetical power sources: isomerous compound 0.75Li1.2Ni0.2Mn0.6O2·0.25LiNi0.5Mn1.5O4

An isomerous layered/spinel 0.75Li1.2Ni0.2Mn0.6O2·0.25LiNi0.5Mn1.5O4 cathode material with outstanding electrochemical properties has been synthesized by a reasonable design of introducing high-power spinel LiNi0.5Mn1.5O4 material to fill up the surface gaps of pristine lithium-rich layered Li1.2Ni0.2Mn0.6O2 material with a molar ratio of 25 : 75. Morphological characterization reveals that the octahedral spinel LiNi0.5Mn1.5O4 particles are successfully coated into the surface gaps of the Li1.2Ni0.2Mn0.6O2 secondary particle, forming a special alternant structure with spherical and octahedral particles on the surface. Interestingly, some hollow sections are also observed in 0.75Li1.2Ni0.2Mn0.6O2·0.25LiNi0.5Mn1.5O4 material, confirmed from the TEM images. The structural characterization demonstrates that this isomerous compound is more well-defined α-NaFeO2 configured, more enlarged in Li layer spacing and lower in cation disordered degree. The exquisite morphology and ideal structure endow this nanocrystal-assembled composite significantly enhanced electrochemical performance with high capacity, good rate capability and excellent cycling stability, compared with the pristine Li1.2Ni0.2Mn0.6O2. It delivers a discharge capacity of 135 mA h g−1 even at an ultrahigh current density of 2000 mA g−1 (10 C). Moreover, the superior cycling stability is also observed with high discharge capacities of 254 mA h g−1 and 222 mA h g−1 at 0.5 C and 1 C after 100 cycles with capacity retention of 98% and 94%, respectively. Moreover, the fast-charging test results are indicative of the fact that this layered/spinel cathode could be used in practical application. Its discharge capacity is 176 mA h g−1 at 1 C after 50 cycles with the charge rate of 10 C. Furthermore, the composite can endure high current charging and discharging even at a high cut-off potential (5.0 V), whereas the pristine Li1.2Ni0.2Mn0.6O2 material cannot. Therefore, we absolutely believe that this isomerous layered/spinel 0.75Li1.2Ni0.2Mn0.6O2·0.25LiNi0.5Mn1.5O4 cathode is a promising candidate for the commercial development of advanced LIBs.

Electrochemical performance of LiFePO4-Li3V2(PO4)3 composite material prepared by solid-hydrothermal method

LiFePO4-Li3V2(PO4)3 composites were synthesized by solid-hydrothermal method and by ball milling, respectively. The electrochemical performance of the solid-hydrothermally obtained materials (C-LFVP) was significantly improved compared with LiFePO4 (LFP) and Li3V2(PO4)3 (LVP), and it was also much better than that of the ball-milled LiFePO4-Li3V2(PO4)3 (P-LFVP). C-LFVP and P-LFVP both had four REDOX peaks (voltage plateaus), which coincided with that of LFP and LVP. Some new trace substances were found in C-LFVP which had more perfect morphology, this was responsible for the better electrochemical performance of C-LFVP than P-LFVP.

Influence of vanadium compound coating on lithium-rich layered oxide cathode for lithium-ion batteries

A vanadium compound is applied as a coating material to improve the electrochemical performance of the lithium-rich layered oxide Li1.2Mn0.6Ni0.2O2. The physicochemical properties of the material before and after coating are characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (FT-IR). Results reveal that LiδV2O5 (δ is very small) is successfully coated on the as-prepared material, and the crystal properties of the powder have been modified after coating. The formation of the LiδV2O5 coating layer is a result of some Li-ions diffusing from the Li1.2Mn0.6Ni0.2O2 particle to the coating layer at the interface. The material before and after coating serve as the cathode for lithium-ion batteries and were investigated by galvanostatic measurements within a voltage range of 2.0–4.8 V (vs. Li/Li+). The initial coulombic efficiency (CE1) of Li1.2Mn0.6Ni0.2O2 is improved from 71.8% to 87.7% due to the LiδV2O5 coating layer, which can act as an insertion host to accept the lithium ions that could not be inserted back into the bulk lattice during the first discharge process. Additionally, the electrochemical performances (cycling performance and rate capability) of the modified Li1.2Mn0.6Ni0.2O2 are very superior to the pristine one. The significantly improved electrochemical performances are attributed primarily to: (i) the modified crystal properties after coating; (ii) the amelioration of the charge-transfer resistance after coating; (iii) the coating layer which can contribute to stabilizing the electrode surface by suppressing the side reactions between electrode and electrolyte.

Preparation of carbon aerogel by ambient pressure drying and its application in lithium/sulfur battery

Formaldehyde, resorcinol, and sodium acetate were used to synthesize the carbon aerogels by ambient pressure drying. The effect of the ratio of resorcinol and sodium acetate for carbon aerogels was researched by scanning electron microscope and Brunauer-Emmett-Teller characterizations. Then the carbon aerogels were applied in synthesizing sulfur/carbon aerogel composites through a melting method, the specific capacity and cycle performance of lithium/sulfur batteries that adopted the prepared composites as cathodes were measured by galvanostatic discharge–charge. X-ray diffraction, conductivity measurement, cyclic voltammetry, and electrochemical impedance spectra tests were also carried out to help explain the electrochemical performance. Finally, the carbon aerogel with the best properties was chosen for the comparative study of replacement of water by acetone as solvent in the preparation of carbon aerogels. According to our study, the carbon aerogel prepared by ambient pressure drying with high electrical conductivity, controllable pore structure, and high specific surface area was proposed to be used for lithium/sulfur batteries, and the key factors to the performance of carbon aerogel/sulfur composites were discussed.

Chromium (VI) adsorption from wastewater using porous magnetite nanoparticles prepared from titanium residue by a novel solid-phase reduction method

Porous magnetite nanoparticles were successfully synthesized by reduction of titanium residue with pyrite under nitrogen protection, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, vibrating sample magnetometer, X-ray photoelectron spectroscope, zeta potential and Brunauer-Emmett-Teller method. The XRD analysis confirmed the formation of porous magnetite nanoparticles with single spinel structure. The SEM image demonstrated that porous magnetite nanoparticles displayed spherical shape with the average diameter of ~51nm. The surface area of porous magnetite nanoparticles with high magnetic moment (78emu·g-1) was 11.1m2g-1. The experimental results revealed that equilibrium adsorption behavior of Cr(VI) was well described by Langmuir isotherm model with the maximum adsorption capacity of 14.49mgg-1 at 298.15K, and kinetic data was found to fit well with pseudo-second-order model. The adsorption rate for Cr(VI) was controlled by both boundary layer diffusion and intraparticle diffusion. Thermodynamics analysis showed that the adsorption processes of Cr(VI) were endothermic and spontaneous. In addition, the adsorption of Cr(VI) on porous magnetite nanoparticles was classified as chemisorption adsorption, which depended on electrostatic attraction accompanied with reduction of Cr(VI) to Cr(III). Porous magnetite nanoparticles were readily regenerated and used repeatedly for Cr(VI) adsorption at least five cycles. Furthermore, the experimental results indicate that porous magnetite nanoparticles have a promising application for Cr(VI) adsorption from wastewater.

The roles of nickel/manganese in electrochemical cycling of lithium-rich Mn-based nickel cathode materials

Lithium-rich oxides have attracted much attention due to their potential application as cathode materials in lithium ion batteries, but still suffer from voltage decay and capacity fading upon cycling. Understanding the effect of active-mass elements on the deterioration of cycling performance would be beneficial for finding a suitable route to address these challenging problems. Herein, a Li-rich Mn-based nickel oxide Li1.231Mn0.592Ni0.2O2 was synthesized. We have mainly employed dQ/dV plots to elucidate the electrochemical process changes during cycling. Our results demonstrate that the influence of Ni is more sensitive than that of Mn, and the Ni redox peak is gradually disappeared upon cycling, but the electrode reaction of Mn is relatively stable with the shape of the corresponding dQ/dV plots are unchanged, though a small shift to low potential occurs. Moreover, the capacity contribution of Ni is decreased with the extent of cycling, but the capacity contribution of Mn is increased.

Hollow Li1.2Mn0.54Ni0.13Co0.13O2 micro-spheres synthesized by a co-precipitation method as a high-performance cathode material for Li-ion batteries

Hollow Li1.2Mn0.54Ni0.13Co0.13O2 micro-spheres were successfully synthesized by a co-precipitation method. The micro-spheres deliver an initial discharge capacity of 296 mA h g−1 and a coulombic efficiency of 83.4% at a current density of 30 mA g−1. Furthermore, the micro-spheres exhibit an excellent rate capability (150 mA h g−1 at a current density of 1500 mA g−1) and a high reversible discharge capacity of 227 mA h g−1 after 100 cycles at a current density of 60 mA g−1.