Sodium intercalation into α- and β-VOSO4

Received: 12.02.2019. Accepted: 19.03.2019. Published: 29.03.2019.Na-ion battery is one of the best alternatives to Li-ion battery. Abundance of sodium on earth is three orders of magnitude higher than lithium, which should make Na-ion battery technology cheaper. But alkaline-ion battery prices, which tend to increase because of the massive world demand, also depend on the choice of electrode materials. Therefore, cost-effective electrode development remains an important subject of research because this will allow Na-ion battery to be even more competitive. Electrochemical performances of anhydrous VOSO4 as electrode for Na-ion battery are reported in this letter. Two anhydrous phases of vanadyl sulfate have been studied. The first one, α-VOSO4, shows that up to 0.8 sodium per formula unit (Na/f.u.) can be intercalated in this phase, and a reversible intercalation of 0.4 Na/f.u. has been observed with a strong polarization. The second one, β-VOSO4, can intercalate up to 0.9 Na/f.u. with a reversible inter- calation of 0.4 Na/f.u. leading to a reversible capacity of 64 mAh/g

Sodium intercalation into α- and β-VOSO4

Received: 12.02.2019. Accepted: 19.03.2019. Published: 29.03.2019.Na-ion battery is one of the best alternatives to Li-ion battery. Abundance of sodium on earth is three orders of magnitude higher than lithium, which should make Na-ion battery technology cheaper. But alkaline-ion battery prices, which tend to increase because of the massive world demand, also depend on the choice of electrode materials. Therefore, cost-effective electrode development remains an important subject of research because this will allow Na-ion battery to be even more competitive. Electrochemical performances of anhydrous VOSO4 as electrode for Na-ion battery are reported in this letter. Two anhydrous phases of vanadyl sulfate have been studied. The first one, α-VOSO4, shows that up to 0.8 sodium per formula unit (Na/f.u.) can be intercalated in this phase, and a reversible intercalation of 0.4 Na/f.u. has been observed with a strong polarization. The second one, β-VOSO4, can intercalate up to 0.9 Na/f.u. with a reversible inter- calation of 0.4 Na/f.u. leading to a reversible capacity of 64 mAh/g

Interface modification of clay and graphene platelets reinforced epoxy nanocomposites: a comparative study

The interface between the matrix phase and dispersed phase of a composite plays a critical role in influencing its properties. However, the intricate mecha-nisms of interface are not fully understood, and polymer nanocomposites are no exception. This study compares the fabrication, morphology, and mechanical and thermal properties of epoxy nanocomposites tuned by clay layers (denoted as m-clay) and graphene platelets (denoted as m-GP). It was found that a chemical modification, layer expansion and dispersion of filler within the epoxy matrix resulted in an improved interface between the filler mate-rial and epoxy matrix. This was confirmed by Fourier transform infrared spectroscopy and transmission electron microscope. The enhanced interface led to improved mechanical properties (i.e. stiffness modulus, fracture toughness) and higher glass transition temperatures (Tg) compared with neat epoxy. At 4 wt% m-GP, the critical strain energy release rate G1c of neat epoxy improved by 240 % from 179.1 to 608.6 J/m2 and Tg increased from 93.7 to 106.4 �C. In contrast to m-clay, which at 4 wt%, only improved the G1c by 45 % and Tg by 7.1 %. The higher level of improvement offered by m-GP is attributed to the strong interaction of graphene sheets with epoxy because the covalent bonds between the carbon atoms of graphene sheets are much stronger than silicon-based clay

Experiments with ODYSSE: Opportunistic Duty cYcle Based Routing for wirelesS Sensor nEtworks

International audienceIn this paper, we propose, design and experiment an energy efficient protocol for Wireless Sensor Networks (WSNs) named Opportunistic Duty cYcle based routing protocol for wirelesS Sensor nEtworks (ODYSSE). The main key innovation of ODYSSE is that it judiciously makes use of three mechanisms. The first one is duty cycling which consists in randomly switching on/off transceivers to save energy. The second one is opportunistic routing in which the next hop is not rigidly fixed: any node closer to the destination might become a relay. The third one, is source coding using LDPC, Low-Density Parity-Check codes. With asynchronous duty cycling as a starting point, the above techniques fit perfectly, yielding a robust low complexity protocol for highly constrained nodes. ODYSSE is implemented and installed in an experimental testbed composed of 45 Arduino nodes communicating with IEEE 802.15.4 (XBee) modules deployed in the large-scale platform FIT IoT-LAB. Results show that the performance obtained is very satisfying in both following scenarios: high load (images) and light load (reporting of infrequent event)

Sodium intercalation into α- and β-VOSO4

International audienceNa-ion battery is one of the best alternatives to Li-ion battery. Abundance of sodium on earth is three orders of magnitude higher than lithium, which should make Na-ion battery technology cheaper. But alkaline-ion battery prices, which tend to increase because of the massive world demand, also depend on the choice of electrode materials. Therefore, cost-effective electrode development remains an important subject of research because this will allow Na-ion battery to be even more competitive. Electrochemical performances of anhydrous VOSO4 as electrode for Na-ion battery are reported in this letter. Two anhydrous phases of vanadyl sulfate have been studied. The first one, α-VOSO4, shows that up to 0.8 sodium per formula unit (Na/f.u.) can be intercalated in this phase, and a reversible intercalation of 0.4 Na/f.u. has been observed with a strong polarization. The second one, β-VOSO4, can intercalate up to 0.9 Na/f.u. with a reversible intercalation of 0.4 Na/f.u. leading to a reversible capacity of 64 mAh/g

Magnetic properties of LiNi0.5Mn1.5O4 spinels prepared by wet chemical methods

International audienceWe present the magnetic properties of LiNi0.5Mn1.5O4 spinels prepared by the sol–gel and pyrolysis techniques. Structural properties show that the material synthesized by pyrolysis method exhibit an ordered spinel structure. Characterization methods include SQUID magnetometry and ESR spectroscopy. Magnetic measurements have evidenced the ferromagnetic ordering below T c 1⁄4 129 K in LiNi0.5Mn1.5O4. Results show that actually no impurity phase is detected in LiNi0.5Mn1.5O4, thus the ferrimagnetic behavior is attributed to an intrinsic property of this material. The magnetic order in this case is trivially a collinear ferrimagnetic ordering in which both the Ni sublattice and the Mn sublattice are ferromagnetic. ESR measurements show a two-component signal with a complex shape. The dominant band is assigned to Mn4+ ions that are the only paramagnetic entities in this compound