Yanjun 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.

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.

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.

Characterization of glucagon-like peptide 2 receptor (GLP2R) gene in chickens: functional analysis, tissue distribution, and developmental expression profile of GLP2R in embryonic intestine

This study characterized the glucagon-like peptide 2 receptor (GLP2R) gene of chickens because relatively little is known about the underlying mechanism of GLP2 actions in nonmammalian species. With the use of reverse transcription PCR, we first cloned the chicken GLP2R (cGLP2R) from adult intestine, which was predicted to encode a 529-amino acid receptor precursor. With the use of a pGL3-CRE luciferase reporter system, we demonstrated that cGLP2R expressed in Chinese hamster ovary cells could be potently activated by cGLP2 (half maximal effective concentration, 1.06 nM) but not by its structurally related peptides, including the newly identified glucagon-like peptide, indicating that cGLP2R is a functional receptor specific to cGLP2. Reverse transcription PCR assay revealed that cGLP2R mRNA was widely expressed in adult chicken tissues, including pancreas and various parts of the gastrointestinal tract. With the use of quantitative real-time reverse transcription PCR assays, we further investigated the mRNA expression of cGLP2R and its potential downstream mediators, epidermal growth factor receptor (EGFR) ligands (heparin-binding EGF-like growth factor, epiregulin, and amphiregulin), in the distal duodenum of developing embryos. The mRNA expression levels of GLP2R and EGFR ligands (heparin-binding EGF-like growth factor and amphiregulin) were shown to increase (P < 0.05 or 0.01) during the late embryonic stages (E16 and E20), implying a potential coordinated action of GLP2 and EGFR ligands on embryonic intestine development. Taken together, our findings not only establish a molecular basis to explore the physiological roles of GLP2 in birds, but they also provide comparative insights into the roles of GLP2R and its ligand in vertebrates, such as its roles in embryonic intestine development.

Macroporous network Li3V2(PO4)3/C cathode material with excellent high-rate performance for lithium-ion batteries

Macroporous network Li3V2(PO4)3/C was successfully synthesized by rheological phase method using ethanol and 1,2-propylene glycol as a mixed solvent. At the same time, Li3V2(PO4)3/C via a single ethanol solvent was prepared for comparison. XRD analysis of the two samples confirmed the formation of high purity and well-crystallized Li3V2(PO4)3/C. The SEM results reveal that there is a significant difference in morphologies between the two samples, the one by single ethanol shows a flake-like morphology, while the other one presents a macroporous network morphology. The sample with a macroporous network morphology shows discharge capacities of 154, 138, 130, 120, 101, 93, 83 and 70 mA h g−1 at 1C, 3C, 5C, 10C, 20C, 30C, 40C and 50C (1C = 150 mA g−1) in the voltage range of 3.0–4.8 V, respectively, which are better than those of the Li3V2(PO4)3/C sample with a flake-like morphology. In summary, it is demonstrated that the Li3V2(PO4)3/C cathode material using a mixed solvent can deliver a significantly improved high rate performance in the voltage range of 3.0–4.8 V, which can be mainly ascribed to the macroporous network morphology.

Cobalt-doped lithium-rich cathode with superior electrochemical performance for lithium-ion batteries

Li-rich Mn-based Co-doped Li1.231Mn0.615−0.75xNi0.154CoxO2 (x = 0, 0.02, 0.05, 0.07, 0.10, 0.12, 0.15, 0.20, 0.25) cathode materials were prepared by a facile combustion method. X-ray diffraction analysis indicates that the crystal structure of materials has been modified by the doped cobalt ions. The capacity differential results obtained from the galvanostatic charge–discharge process within 2.0 and 4.8 V (vs. Li/Li+) indicate that the cobalt doped in the material could conduce to lithium ions re-embedded into the structure and increase the electrical properties. Compared with the electrochemical properties of these materials, the optimum doped sample is Li1.231Mn0.525Ni0.154Co0.12O2 (x = 0.12), which delivers an extreme minimum irreversible capacity of 59.1 mA h g−1 with the highest coulombic efficiency of 82.6%, and its discharge specific capacity maintains 180.7 mA h g−1 at 1 C rate after 50 cycles.

Synthesis of a novel tunnel Na0.5K0.1MnO2 composite as a cathode for sodium ion batteries

A novel tunnel Na0.5K0.1MnO2 composite assembled by two different tunnel structures of Na0.44MnO2 and KMn8O16 is synthesized by a co-precipitation method. Bundles of microrods and small nanorods could be observed in the Na0.5K0.1MnO2 composite. The composite possesses high crystallinity and large stacking faults. When used as a cathode for sodium ion batteries, the composite exhibits a high specific capacity, excellent cyclability and superior rate capability. A high reversible discharge capacity of 142.3 mA h g−1 could be delivered at 0.1C, with 94.7 mA h g−1 retained after 100 cycles. Also 82.2 mA h g−1 could be maintained after 300 cycles at 1.0C. More than 70 mA h g−1 could be obtained at a high rate of 4.0C. The outstanding electrochemical performances may be attributed to the combined tunnel structures, one-dimensional rod-like morphology and massive structural stacking faults.

Effective enhancement of the electrochemical performance of layered cathode Li1.5Mn0.75Ni0.25O2.5 via a novel facile molten salt method

A series of nanocrystalline lithium-rich cathode materials Li1.5Mn0.75Ni0.25O2.5 have been prepared by a novel synthetic process, which combines the co-precipitation method and a modified molten salt method. By using a moderate excess of 0.5LiNO3–0.5LiOH eutectic salts as molten media and reactants, the usage of deionized water or alcohol in the subsequent wash process is successfully reduced, compared with the traditional molten salt method. The materials with different excess Li salt content, Li/M (M = Ni + Mn) = 1.55, 1.65, 1.75, 1.85, 1.95, 2.05, molar ratio, show distinct differences in their structure and charge–discharge characteristics. The structural characterization demonstrates that the sample with a ratio of Li/M = 1.85 has a more well-defined α-NaFeO2 structure and a more enlarged Li layer spacing. It also exhibits the best comprehensive electrochemical behavior with the highest coulombic efficiency, the best rate capability and optimal cycling stability. More specifically, it delivers a dramatically improved initial coulombic efficiency of 87.86%, and a discharge capacity of 129 mA h g−1 even at an ultra-high current density of 2000 mA g−1 (10C). Meanwhile a superior cycling stability is also observed with a high discharge capacity of 251 mA h g−1 and a retention of 98% at 0.2C after 50 cycles. Our results reveal that this method is facile and feasible to synthesize a high rate and high capacity lithium-rich material.

Thermal studies on Li(CH 3 CN) 4 PF 6 and Li(C 4 H 10 O 2 ) 2 PF 6 complexes by the TG–DTA–MS and DSC

Li(CH3CN)4PF6 and Li(C4H10O2)2PF6 complexes are important intermediates created in the synthetic process of high-purity LiPF6 electrolyte via transformation method. The thermal decomposition behavior of as-prepared Li(CH3CN)4PF6 and Li(C4H10O2)2PF6 crystals in pure nitrogen atmosphere has been studied by means of thermogravimetric–differential thermal analysis coupled with mass spectrometry (TG–DTA–MS). Results suggest that the decomposition of Li(CH3CN)4PF6 complex can be roughly divided into a three-stage process, and CH3CN is the primary gas product of decomposition process for Li(CH3CN)4PF6 in open Al2O3 pans. Further insight into Li(C4H10O2)2PF6 crystal indicates that it undergoes a similar decomposition process to Li(CH3CN)4PF6. Accordingly, the detailed deduction of the thermal decomposition mechanism formulas for them was presented in this paper. Besides, the thermal behaviors of Li(CH3CN)4PF6 and Li(C4H10O2)2PF6 complexes in hermetic aluminum pan were also investigated by differential scanning calorimetry (DSC).