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Herein, we report the transition metal dependent deprotonation of layered type materials during their high voltage (>4.5 V vs. Li/Li+) operation as a potential degradation cause in an electrochemical system.

The layered oxide Na0.67CoO2 with Na+ occupying trigonal prismatic sites between CoO2 layers exhibits a remarkably high room temperature oxygen evolution reaction (OER) activity in alkaline solution. The high activity is attributed to an unusually short O-O separation that favors formation of peroxide ions by O--O- interactions followed by O2 evolution in preference to the conventional route through surface O-OH- species. The dependence of the onset potential on the pH of the alkaline solution was found to be consistent with the loss of H+ ions from the surface oxygen to provide surface O- that may either be attacked by solution OH- or react with another O-; a short O-O separation favors the latter route. The role of a strong hybridization of the O-2p and low-spin CoIII/CoIV π-bonding d states is also important; the OER on other CoIII/CoIV oxides is compared with that on Na0.67CoO2 as well as that on IrO2.

Silicon has attracted much attention as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and rich resource abundance. However, the practical battery use of Si is challenged by its low conductivity and drastic volume variation during the Li uptake/release process. Tremendous efforts have been made on shrinking the particle size of Si into nanoscale so that the volume variation could be accommodated. However, the bare nano-Si material would still pulverize upon (de)lithiation. Moreover, it shows an excessive surface area to invite unlimited growth of solid electrolyte interface that hinders the transportation of charge carriers, and an increased interparticle resistance. As a result, the Si nanoparticles gradually lose their electrical contact during the cycling process, which accounts for poor thermodynamic stability and sluggish kinetics of the anode reaction versus Li. To address these problems and improve the Li storage performance of nano-Si anode, proper structural design should be applied on the Si anode. In this perspective, we will briefly review some strategies for improving the electrochemistry versus Li of nano-Si materials and their derivatives, and show opinions on the optimal design of nanostructured Si anode for advanced LIBs.

LiNi0.5Mn1.5O4 thin films were coated on stainless steel substrates by radio-frequency sputtering at room temperature for a lithium-ion battery. The cathode films were post-annealed at 500, 600 and 700 °C to study (i) the impact of annealing temperature on the crystallization of the cathode film and (ii) the reactivity between the cathode film and the stainless steel substrate. X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy were adopted to characterize the thin films. The electrochemical properties of the LiNi0.5Mn1.5O4 cathodes were investigated with cyclic voltammetry and galvanostatic charge/discharge tests. As the annealing temperature increased from 500 to 600 °C, the crystallinity and electrochemical characteristics of LiNi0.5Mn1.5O4 both improved. However, as the annealing temperature further increased to 700 °C, the phase purity and the electrochemical performance were greatly deteriorated. Combined chemical analyses with time-of-flight secondary ion mass spectrometry depth profiling and energy-dispersive X-ray spectroscopy in scanning transmission electron microscopy mapping have indicated that the cross-diffusion of metal ions between LiNi0.5Mn1.5O4 and the stainless steel substrate takes place at a temperature higher than 600 °C, which was attributed as a main origin of the phase change in the LiNi0.5Mn1.5O4 cathode layer and electrochemistry degradations of lithium-ion battery.

LiNi0.5Mn1.5O4 (LNMO) cathode thin films were prepared on Pt-coated stainless steel (SS) substrates by radio-frequency magnetron sputtering. The layers were post-annealed at 500, 600 and 700 °C to study the impact of thermal treatment on the crystallization of the cathode material. As the annealing temperature increases, interdiffusion occurs between the substrate and the LNMO film, which degrades the electrochemical properties of the cathode film. In order to mitigate this problem, an In-Sn-O (ITO) interlayer was introduced between Pt and the SS substrate. The ITO film is electrochemically stable and acts as an effective diffusion barrier between the substrate and the LNMO layer, which results in improved electrochemical properties of the LNMO film for a lithium ion battery.

Consider the almost insulator for pure Li3VO4 with a band gap of 3.77 eV, to significantly improve the electrical conductivity, the novel Li3V1–xMoxO4 (x = 0.00, 0.01, 0.02, 0.05, and 0.10) anode materials were prepared successfully by simple sol–gel method. Our calculations show that, by substitute Mo6+ for V5+, the extra electron occupied the V 3p empty orbital and caused the Fermi level shift up into the conduction band, where the Mo-doped Li3VO4 presents electrical conductor. The V/I curve measurements show that, by Mo doping in V site, the electronic conductivity of the Li3VO4 was increased by 5 orders of magnitude. And thence the polarization was obviously reduced. EIS measurement results indicated that by Mo-doping a higher lithium diffusion coefficient can be obtained. The significantly increased electronic conductivity combined the higher lithium diffusion coefficient leads to an obvious improvement in reversible capacity and rate performance for the Mo-doped Li3VO4. The resulting Li3V1–xMoxO4 (x...

Summary The greater availability of sodium (Na) over lithium (Li) motivates development of a Na-ion battery that can compete with a Li-ion battery. In these batteries, both electrodes consist of hosts into which Li + or Na + can be inserted reversibly. Graphite has been the anode host for Li-ion batteries, but the Na + ion is too large to be inserted easily between the flat graphene layers of common graphite. We report the synthesis and electrochemical performance of N-doped carbon nanofibers and tubules with an organic-liquid electrolyte and a large fraction of graphitic carbon and larger spacing (0.38–0.44 nm) between carbon sheets; the carbon hollow tubules yield ultrastable (10,000 cycles), high-rate capabilities of Na + intercalation and deintercalation with reversible capacities up to 346 mAh g −1 .

The development of all-solid-state rechargeable batteries is plagued by a large interfacial resistance between a solid cathode and a solid electrolyte that increases with each charge–discharge cycle. The introduction of a plastic–crystal electrolyte interphase between a solid electrolyte and solid cathode particles reduces the interfacial resistance, increases the cycle life, and allows a high rate performance. Comparison of solid-state sodium cells with 1) solid electrolyte Na3Zr2(Si2PO4) particles versus 2) plastic–crystal electrolyte in the cathode composites shows that the former suffers from a huge irreversible capacity loss on cycling whereas the latter exhibits a dramatically improved electrochemical performance with retention of capacity for over 100 cycles and cycling at 5 C rate. The application of a plastic–crystal electrolyte interphase between a solid electrolyte and a solid cathode may be extended to other all-solid-state battery cells.

Vulcanized rubber products contain polymer backbones crosslinked with sulfur to improve mechanical strength. Burning of waste rubber products emits toxic gases, and recycling of rubber by breaking the C–S bond with costly reagents and heat is also haunted by environmental concerns. The crosslinked polymers can be extracted chemically at room temperature and, by a simple solution-drop method, used to prepare a bifunctional cathode layer on the cathode current collector of a Li–S battery. The C–S bond of the crosslinking sulfur can be broken reversibly in a discharge/recharge cycle to provide a sulfur source, and the broken carbon bond can capture a lithium polysulfide soluble in a liquid organic electrolyte by forming a C–Li–S bond during discharge. During charge, the Li is extracted and the C–S bond is reformed. However, added sulfur powder is also needed in the cathode of a Li–S battery. The data also provide a low-cost way to recycle waste rubber electrochemically.

Low-cost, single-step synthesis of hollow nanotubes of N-doped carbon deposited on CoS is enabled by the simultaneous use of three functionalities of polyacrylonitrite (PAN) nanofibers: 1) a substrate for loading active materials, 2) a sacrificial template for creating hollow tubular structures, and 3) a precursor for in situ nitrogen doping. The N-doped carbon in hollow tubes of CoS provides a high-capacity anode of long cycle life for a rechargeable Li-ion or Na-ion battery cell that undergoes the conversion reaction 2 A++2 e−+CoS →Co+A2S with A=Li or Na.

Sodium extraction behavior in the rhombohedral Na3MnTi(PO4)3 with the NASICON structure was investigated and shown to have a 0.5 eV separation of the localized-electron Mn3+/Mn2+ and Mn4+/Mn3+ redox energies. Used as a cathode in a sodium-ion half-cell, the redox couples of Mn3+/Mn2+ and Mn4+/Mn3+ exhibit two voltage plateaus located at about 3.6 and 4.1 V vs Na+/Na, respectively. Na3MnTi(PO4)3 also exhibits a small volume change after the extraction of two sodium ions, and the NASICON structure is well-maintained after repeated extraction and insertion of sodium ions.

Dendrite-free, reversible plating and stripping of Li into and from a metallic-lithium anode from an organic-liquid electrolyte is demonstrated. A porous cellulose-based membrane used for skin care absorbs the electrolyte and is wet by metallic lithium. The membrane separator was tested in symmetric lithium cells and in Li(S) rechargeable coin cells assembled in the charged state.

In this paper, High performance torque control based on the flux mapping of 48V Wound Rotor Synchronous Motor has been studied to improve torque control. Flux map considering MTPA (Maximum Torque Per Ampere), MFPT (Minimum Flux Per Torque), Maximum efficiency point at the same torque command and flux command for each field current was produced. Current map using flux mapping of Each field current was applied to the MTPA, MFPT. Generating a current vector locus was to determine the characteristics of the operation region. Through the Matlab/Simulink simulation, difference between speed-torque map and flux map was represented. The suggested flux map was tested actual experiments on a dynamometer.

Garnet-structured Li7La3Zr2O12 is a promising solid Li-ion electrolyte for all-solid-state Li-metal batteries and Li-redox-flow batteries owing to its high Li-ion conductivity at room temperature and good electrochemical stability with Li metal. However, there are still three major challenges unsolved: (1) the controversial electrochemical window of garnet, (2) the impractically large resistance at a garnet/electrode interface and the fast lithium-dendrite growth along the grain boundaries of the garnet pellet, and (3) the fast degradation during storage. We have found that these challenges are closely related to a thick Li2CO3 layer and the Li–Al–O glass phase on the surface of garnet materials. Here we introduce a simple method to remove Li2CO3 and the protons in the garnet framework by reacting garnet with carbon at 700 °C; moreover, the amount of the Li–Al–O glass phase with a low Li-ion conductivity in the grain boundary on the garnet surface was also reduced. The surface of the carbon-treated garnet...

Solid-oxide Li+ electrolytes of a rechargeable cell are generally sensitive to moisture in the air as H+ exchanges for the mobile Li+ of the electrolyte and forms insulating surface phases at the electrolyte interfaces and in the grain boundaries of a polycrystalline membrane. These surface phases dominate the total interfacial resistance of a conventional rechargeable cell with a solid-electrolyte separator. We report a new perovskite Li+ solid electrolyte, Li0.38 Sr0.44 Ta0.7 Hf0.3 O2.95 F0.05 , with a lithium-ion conductivity of σLi =4.8×10-4 S cm-1 at 25 °C that does not react with water having 3≤pH≤14. The solid electrolyte with a thin Li+ -conducting polymer on its surface to prevent reduction of Ta5+ is wet by metallic lithium and provides low-impedance dendrite-free plating/stripping of a lithium anode. It is also stable upon contact with a composite polymer cathode. With this solid electrolyte, we demonstrate excellent cycling performance of an all-solid-state Li/LiFePO4 cell, a Li-S cell with a polymer-gel cathode, and a supercapacitor.

Where the anode of an alkali-metal rechargeable battery has the Fermi energy above the LUMO of the electrolyte, an important fraction of the working ions of a cell become irreversibly trapped in a passivating solid-electrolyte-interphase (SEI) layer formed at the anode surface on the initial charge, thus reducing the reversible capacity of the cathode. To compensate for this irreversible loss in a rechargeable sodium-ion battery, a cathode additive that can supply extra Na+ ions should be explored. In this work, we have characterized the chemical and electrochemical properties of orthorhombic Na2NiO2 for this purpose. Through a combined electrochemical and structural characterization, Na2NiO2 is found to be transformed irreversibly to NaNiO2, and the crystalline NaNiO2 is operating as a cathode in the following charge and discharge reactions. We have evaluated electrochemical characteristics of Na2NiO2 and confirmed that it is a suitable cathode additive to compensate for the irreversible Na+ loss at the ...

Amorphous silicon (a-Si) has been intensively explored as one of the most attractive candidates for high-capacity and long-cycle-life anode in Li-ion batteries (LIBs) primarily because of its reduced volume expansion characteristic (∼280%) compared to crystalline Si anodes (∼400%) after full Li(+) insertion. Here, we report one-dimensional (1-D) electrospun Si-based metallic glass alloy nanofibers (NFs) with an optimized composition of Si60Sn12Ce18Fe5Al3Ti2. On the basis of careful compositional tailoring of Si alloy NFs, we found that Ce plays the most important role as a glass former in the formation of the metallic glass alloy. Moreover, Si-based metallic glass alloy NFs were wrapped by reduced graphene oxide sheets (specifically Si60Sn12Ce18Fe5Al3Ti2 NFs@rGO), which can prevent the direct exposure of a-Si alloy NFs to the liquid electrolyte and stabilize the solid-electrolyte interphase (SEI) layers on the surfaces of rGO sheets while facilitating electron transport. The metallic glass nanofibers exhibited superior electrochemical cell performance as an anode: (i) Si60Sn12Ce18Fe5Al3Ti2 NFs show a high specific capacity of 1017 mAh g(-1) up to 400 cycles at 0.05C with negligible capacity loss as well as superior cycling performance (nearly 99.9% capacity retention even after 2000 cycles at 0.5C); (ii) Si60Sn12Ce18Fe5Al3Ti2 NFs@rGO reveals outstanding rate behavior (569.77 mAh g(-1) after 2000 cycles at 0.5C and a reversible capacity of around 370 mAh g(-1) at 4C). We demonstrate the potential suitability of multicomponent a-Si alloy NFs as a long-cycling anode material.

Transition-metal phosphates (TMPs) are potential materials for large-scale applications of lithium ion batteries (LIBs). Yet, high-voltage TMP cathodes have not met commercial success due to ill understood failure mechanisms. In this article we studied the surface chemistry of Li3V2(PO4)3 composite electrodes using X-ray photoelectron spectroscopy (XPS) post-electrochemical cycling in a stable electrochemical window of 3.0–4.2 V vs Li/Li+ and in the wider window of 3.0–4.8 V vs Li/Li+ where a dramatic fade in capacity is noted. In addition, we performed aging experiments in LiPF6 EC/DEC electrolyte with no electrochemical bias applied to investigate a possible spontaneous solid electrolyte interphase (SEI) formation as has been described for lithium transition-metal oxide (LixMyOz) electrodes. An SEI was found on the Li3V2(PO4)3 composite electrodes cycled in both potential windows and after aging with similar chemical compositions including ethers, alkoxides, esters, carboxylates, and carbonates as well ...

Despite great interest in a Li–S battery, soluble polysulfides as charge/discharge intermediates pose an important challenge to realize commercial Li–S batteries. For building physical barriers to reduce a diffusional loss of those species, chemical surface-trap-sites have been proposed, but experimental evidence about the trapping interaction hasn't been reported. Here, highly crosslinked polymer-electrolyte coating layers with electron-donating groups were designed to bind lithium polysulfides. An ester group with a high spatial density was shown to be a strong candidate to bind lithium polysulfides. Spectroscopic evidence for the presence of lithium bonds between the lithium polysulfides and the electron-donating groups is reported for the first time. An electrochemical charge/discharge model is also proposed, which can explain the electrochemical behavior within the insulating polymer layer.

A low-cost, thin, flexible, and mechanically robust alkali-ion electrolyte separator is shown to allow fabrication of a safe rechargeable alkali-ion battery with alternative cathode strategies. A Na-ion battery with an insertion host as cathode and a Li-ion battery with a redox flow-through cathode are demonstrated to cycle without significant fade. The separator membrane is a composite of Al2O3 particles and cross-linked ethylene-oxide chains; it can be fabricated at low cost into a large-area thin membrane that blocks dendrites from an alkali-metal anode. To block a soluble ferrocene redox molecule from crossing from the cathode side to the anode in a Li-ion battery with a redox-flow cathode, a thin mixed Li+/electronic-conducting film has been added to the cathode side of the composite separator. An osmosis issue was minimized by balancing concentrations of solutes on the two sides of the separator where the cathode side contains a soluble redox molecule.

In this paper, an algorithm is suggested to detect an offset angle of the absolute rotor position sensor after the initial assembly of a PMSG. Unlike previous studies in a stationary state, this one is not designed to detect an electrical angle but rather the absolute position of the rotor is detected while operating the generator. Also,a position sensor, current sensors and voltage sensor were used to ensure reliability. This technique completes the detection of the sensor offset in two steps. In the first step, a zero-crossing of the EMF is measured using a voltage sensor to detect the electrical angle offset when the alternator is actuated by the engine. In the second step, a high frequency current is injected along the d-axis on-line during the control of the generation, eventually to obtain the inductance using a DFT (Discrete Fourier Transform), and then to ultimately extract the final electrical angle offset through the comparison of the inductance magnitude. The suggested algorithm was validated with PSIM simulation and, furthermore, was tested with actual experiments on a dynamometer.Keywords: PMSG, initial position, zero-crossing, inductance, DFT (Discrete Fourier Transform)

Carbon nanofibers encapsulating Si nanoparticles (CNFs/SiNPs) were prepared via an electrospinning method and chemically functionalized with 3-aminopropyltriethoxysilane (APS) to be grafted onto graphene oxide (GO). As a result, the thin and flexible GO, which exhibits a negative charge in aqueous solution, fully wrapped around the APS-functionalized CNFs with a positive surface charge via electrostatic self-assembly. After the formation of chemical bonds between the epoxy groups on GO and the amine groups in APS via an epoxy ring opening reaction, the GO was chemically reduced to a reduced graphene oxide (rGO). Electrochemical and morphological characterizations showed that capacity loss by structural degradation and electrolyte decomposition on Si surface were significantly suppressed in the rGO-wrapped CNFs/SiNPs (CNFs/SiNPs@rGO). Superior capacities were consequently maintained for up to 200 cycles at a high current density (1048 mA h g(-1) at 890 mA g(-1)) compared to CNFs/SiNPs without the rGO wrapping (304 mA h g(-1) at 890 mA g(-1)). Moreover, the resistance of the SEI layer and charge transfer resistance were also considerably reduced by 24% and 88%, respectively. The described graphene wrapping offers a versatile way to enhance the mechanical integrity and electrochemical stability of Si composite anode materials.

A tailored conversion-reaction anode material of 1-D MoS2 nanofibers with a vine-like shape composed of MoS2 nanoflakes delivers exceptionally high Na capacity and exhibits excellent rate properties. The improved cycleability of the MoS2 nanofiber electrode is achieved by a uniform TiO2 coating, which effectively minimized the sulfur dissolution.

Polyimide (PI) nanofibers with an average diameter of 300 nm, possessing superior electrolyte wettability and thermal stability, are synthesized by electrospinning a poly(amic acid) (PAA) solution followed by an imidization process. The large pore volume of the PI nanofiber mat can facilitate faster Li+-ion transport and greater rate capability, but it also cause an irreversible increase in cell impedance during long term cycling. To overcome these problems, thin Al2O3 over-layers are coated on both sides of a PI separator via a dip-coating process. The Al2O3-coated PI separators exhibit enhanced capacity, cyclability (95.53% retention after 200 cycles at 1 C), and rate capabilities (78.91% at 10 C) compared to the bare PI separator (68.65% at 10 C) and a commercial polypropylene separator (18.25% at 10 C) with a limited increase of cell impedance.

Does the Li4Ti5O12 electrode need a carbon additive in lithium-ion batteries? We answered this question in our previous work by showing that the partially reduced Ti4+ on the surface of Li4Ti5O12 could provide enough electronic conductivity to initiate the electrochemical process. In this work, we discuss the generally accepted fact that a solid electrolyte interphase (SEI) is hardly formed on the surface of the Li4Ti5O12 electrode owing to its high redox potential by using the carbon-free Li4Ti5O12 electrode to exclude the influences of carbon. In contrast to the previous argument, Li4Ti5O12 was found to have certain reactivity towards electrolytes at room and high temperature (60 °C). Moreover, in the presence of carbon in the electrode (i.e. the conventional electrode formulation), the reactivity of the electrode towards an electrolyte was significantly increased at high temperatures. These results were discussed based on surface analyses and electrode morphology observation before and after cycling, and correlated with the electrochemical performance.

A stable hydrophobic ionic crystalline solid comprised of the N-propyl-N-methylpiperidinium cation and hexafluorophosphate anion PP13PF6 exhibits a remarkably wide electrochemical window of 7.2 V. This high purity crystalline ionic salt has versatility for use as an electrolyte in the electrodeposition of reactive metals such as tin. Moreover, this ionic salt can be used as a solid state electrolyte in Li-ion batteries. Theoretical calculations indicate that this solid state electrolyte has vacant sites that are preferential for Li-ion conductivity with an energy barrier of 0.4 eV. Further, the ionic crystals exhibit molecular rotations which facilitate facile Li-ion transport.

By a novel in situ chemical vapor deposition, activated N-doped hollow carbon-nanotube/carbon-nanofiber composites are prepared having a superhigh specific Brunauer–Emmett–Teller (BET) surface area of 1840 m(2) g(–1) and a total pore volume of 1.21 m(3) g(–1). As an anode, this material has a reversible capacity of ~1150 mAh g(–1) at 0.1 A g(–1) (0.27 C) after 70 cycles. At 8 A g(–1) (21.5 C), a capacity of ~320 mAh g(–1) fades less than 20% after 3500 cycles, which makes it a superior anode material for a Li-ion battery.

Two distinctive one-dimensional (1-D) carbon nanofibers (CNFs) encapsulating irregularly and homogeneously segregated SnCo nanoparticles were synthesized via electrospinning of polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN) polymers containing Sn-Co acetate precursors and subsequent calcination in reducing atmosphere. CNFs synthesized with PVP, which undergoes structural degradation of the polymer during carbonization processes, exhibited irregular segregation of heterogeneous alloy particles composed of SnCo, Co3Sn2, and SnO with a size distribution of 30-100 nm. Large and exposed multiphase SnCo particles in PVP-driven amorphous CNFs (SnCo/PVP-CNFs) kept decomposing liquid electrolyte and were partly detached from CNFs during cycling, leading to a capacity fading at the earlier cycles. The closer study of solid electrolyte interphase (SEI) layers formed on the CNFs reveals that the gradual growth of fiber radius due to continuous increment of SEI layer thickness led to capacity fading. In contrast, SnCo particles in PAN-driven CNFs (SnCo/PAN-CNFs) showed dramatically reduced crystallite sizes (10 nm) of single phase SnCo nanoparticles which were entirely embedded in dense, semicrystalline, and highly conducting 1-D carbon matrix. The growth of SEI layer was limited and saturated during cycling. As a result, SnCo/PAN-CNFs showed much improved cyclability (97.9% capacity retention) and lower SEI layer thickness (86 nm) after 100 cycles compared to SnCo/PVP-CNFs (capacity retention, 71.9%; SEI layer thickness, 593 nm). This work verifies that the thermal behavior of carbon precursor is highly responsible for the growth mechanism of SEI layer accompanied with particles detachment and cyclability of alloy particle embedded CNFs.

Li6Zr2O7 crystallizes in a framework structure with Li occupying 1D channels in three distinguishable square–pyramidal sites. Rao et al. have reported a factor 100 increase in Li+ conductivity at 300 °C by substitution of Ta(V) for Zr(IV). We demonstrate here that a similar enhancement in Li-ion conductivity can also be achieved by incorporation of interstitial Li in the formula unit Li6+xZr2−xMxO7 (M = Y or In). Insertion of x = 0.15 Li in the form of Li6+xZr2−xMxO7 can be obtained by simple solid state synthesis. In order to know the limit of Li insertion into Li6Zr2O7, we demonstrated electrochemical insertion into Li6+xZr1.5Ti0.5O7 of excess Li to at least x ≈ 0.17 at room temperature. The Lithium activation energy was 0.63 eV for Li6.15Zr1.85Y0.15O7.

Monoclinic α-Li3V2(PO4)3 has a complex 3-D metal phosphate framework that provides mobility for all three lithium ions, giving it the highest gravimetric capacity (197 mAh/g) of all the transition-metal phosphates. Along with its high gravimetric capacity, its thermal and electrochemical stability make it of great interest as a cathode material for lithium-ion energy storage devices. Raman spectroscopy has proven to be a unique analytical tool for studying electrode materials of lithium-ion batteries due to its ability to probe structural changes at the level of chemical bonds. In this work, the calculated Raman spectrum of α-Li3V2(PO4)3 provided by density functional theory is presented along with symmetry assignments for all of the calculated and observed modes through Raman microscopy. Furthermore, the phase stability of microcrystalline α-Li3V2(PO4)3 was studied as a function of irradiation power density. Follow-up thermal studies confirm that two structural phase transitions, β and γ, occur at elevat...

Each cell of a battery stores electrical energy as chemical energy in two electrodes, a reductant (anode) and an oxidant (cathode), separated by an electrolyte that transfers the ionic component of the chemical reaction inside the cell and forces the electronic component outside the battery. The output on discharge is an external electronic current I at a voltage V for a time Δt. The chemical reaction of a rechargeable battery must be reversible on the application of a charging I and V. Critical parameters of a rechargeable battery are safety, density of energy that can be stored at a specific power input and retrieved at a specific power output, cycle and shelf life, storage efficiency, and cost of fabrication. Conventional ambient-temperature rechargeable batteries have solid electrodes and a liquid electrolyte. The positive electrode (cathode) consists of a host framework into which the mobile (working) cation is inserted reversibly over a finite solid-solution range. The solid-solution range, which is reduced at higher current by the rate of transfer of the working ion across electrode/electrolyte interfaces and within a host, limits the amount of charge per electrode formula unit that can be transferred over the time Δt = Δt(I). Moreover, the difference between energies of the LUMO and the HOMO of the electrolyte, i.e., electrolyte window, determines the maximum voltage for a long shelf and cycle life. The maximum stable voltage with an aqueous electrolyte is 1.5 V; the Li-ion rechargeable battery uses an organic electrolyte with a larger window, which increase the density of stored energy for a given Δt. Anode or cathode electrochemical potentials outside the electrolyte window can increase V, but they require formation of a passivating surface layer that must be permeable to Li(+) and capable of adapting rapidly to the changing electrode surface area as the electrode changes volume during cycling. A passivating surface layer adds to the impedance of the Li(+) transfer across the electrode/electrolyte interface and lowers the cycle life of a battery cell. Moreover, formation of a passivation layer on the anode robs Li from the cathode irreversibly on an initial charge, further lowering the reversible Δt. These problems plus the cost of quality control of manufacturing plague development of Li-ion rechargeable batteries that can compete with the internal combustion engine for powering electric cars and that can provide the needed low-cost storage of electrical energy generated by renewable wind and/or solar energy. Chemists are contributing to incremental improvements of the conventional strategy by investigating and controlling electrode passivation layers, improving the rate of Li(+) transfer across electrode/electrolyte interfaces, identifying electrolytes with larger windows while retaining a Li(+) conductivity σ(Li)10(-3) S cm(-1), synthesizing electrode morphologies that reduce the size of the active particles while pinning them on current collectors of large surface area accessible by the electrolyte, lowering the cost of cell fabrication, designing displacement-reaction anodes of higher capacity that allow a safe, fast charge, and designing alternative cathode hosts. However, new strategies are needed for batteries that go beyond powering hand-held devices, such as using electrode hosts with two-electron redox centers; replacing the cathode hosts by materials that undergo displacement reactions (e.g. sulfur) by liquid cathodes that may contain flow-through redox molecules, or by catalysts for air cathodes; and developing a Li(+) solid electrolyte separator membrane that allows an organic and aqueous liquid electrolyte on the anode and cathode sides, respectively. Opportunities exist for the chemist to bring together oxide and polymer or graphene chemistry in imaginative morphologies.

A K-Na liquid alloy allows a dendrite-free high-capacity anode; its immiscibility with an organic liquid electrolyte offers a liquid-liquid anode-electrolyte interface. Working with a sodiated Na2 MnFe(CN)6 cathode, the working cation becomes K+ to give a potassium battery of long cycle life with an acceptable capacity at high charge/discharge rates.

Despite the great achievement in understanding the materials properties and powder engineering of LiFePO4, the chemical bonding at the surface has been almost ignored. Herein, we demonstrate that the undercoordinated Fe2+/Fe3+ redox couple at the surface gives a high barrier for charge transfer, but it can be stabilized by nitrogen or sulfur adsorption. The surface modification improves greatly the charge transfer kinetics and the charge/discharge performance of a LiFePO4 cathode. Density functional theory (DFT) calculation estimates the origin of the improvement in terms of an electronic and ionic contribution based on a surface model probed by time of flight secondary ion mass spectrometry (TOF-SIMS); the calculation agrees well with an experimental rate-constant analysis.

Anatase TiO2 has been suggested as a potential sodium anode material, but the low electrical conductivity of TiO2 often limits the rate capability, resulting in poor electrochemical properties. To address this limitation, we propose graphene-wrapped anatase TiO2 nanofibers (rGO@TiO2 NFs) through an effective wrapping of reduced graphene oxide (rGO) sheets on electrospun TiO2 NFs. To provide strong electrostatic interaction between the graphene oxide (GO) sheets and the TiO2 NFs, poly(allylamine hydrochloride) (PAH) was used to induce a positively charged TiO2 surface by the immobilization of the -NH3+ group and to promote bonding with the negatively charged carboxylic acid (-COO−) and hydroxyl (-O−) groups on the GO. A sodium anode electrode using rGO@TiO2 NFs exhibited a significantly improved initial capacity of 217 mAh g−1, high capacity retention (85% after 200 cycles at 0.2C) and a high average Coulombic efficiency (99.7% from the second cycle to the 200th cycle), even at a 5C rate, compared to those of pristine TiO2 NFs. The improved electrochemical performances stem from highly conductive properties of the reduced GO which is effectively anchored to the TiO2 NFs.

This study presents a design of a high-speed photon counting readout circuit for spectral computed tomography detectors. We propose a novel front-end architecture aimed to reduce a dead time by introducing dual signal paths in each pixel. A prototype chip is fabricated with 0.18um six-metal standard CMOS process that consists of 16 × 16 pixels and periphery circuits. Each pixel has 200um pixel pitch and contains two signal paths. The switching circuit in the pixel allows a single signal path to connect with the input pad at a time. As a result, the proposed dual-path readout scheme shows a 3-times higher speed than that of a conventional single-path readout scheme.

In bacteria, many DNA-protein interactions that initiate transcription, replication and recombination require the mediation of DNA architectural proteins such as IHF and HU. For replication initiation, plasmid P1 requires three origin binding proteins: the architectural protein HU, a plasmid-specific initiator, RepA, and the Escherichia coli chromosomal initiator, DnaA. The two initiators bind in the origin of replication to multiple sites, called iterons and DnaA boxes respectively. We show here that all five known DnaA boxes can be deleted from the plasmid origin provided the origin is extended by about 120 bp. The additional DNA provides an IHF site and most likely a weak DnaA binding site, because replacing the putative site with an authentic DnaA box enhanced plasmid replication in an IHF-dependent manner. IHF most likely brings about interactions between distally bound DnaA and RepA by bending the intervening DNA. The role of IHF in activating P1 origin by allowing DnaA binding to a weak site is reminiscent of the role the protein plays in initiating the host chromosomal replication.

Spenel lithium manganese oxides with a nominal composition of LiMn 2 O 4 are prepared by using a conventional ceramic synthesis method and are coated by a chemical deposition of silver particles. The silver-coated nano-particle LiMn 2 O 4 shows excellent cycleability at 2 C galvanostatic conditions. The high surface electronic conductivity caused by the metal coating reduces cell polarization. The results indicate that such surface treatment of cathode powders should be an effective way to improve cycle-life with high current retention.

LiFePO4 is a potential candidate for the cathode material of the lithium secondary batteries. Co-precipitation method and microwave heating were adopted to study about LiFePO4. The samples were characterized by X-ray diffraction, scanning electron microscope, particle-size analysis, ICP composition analysis and electrochemical methods. Olivine phase LiFePO4 was successfully synthesized in a few minutes. The specific capacity, cycle property and rate capability were impressive as compared with previous reports. The microwave heating method using activated carbon is a very simple and useful tool to control the iron oxidation state to 2+ without reductive gas flow. Keywords: Co-precipitation, Carbon addition, Microwave heating, Activated carbon, Reductive atmosphere

Insertion into the garnet Li3Nd3W2O12 of four Li per formula unit shows excellent reversibility. The W sites share edges with Nb sites, but they are isolated from one another, so the W-5 d electrons remain strongly correlated with the W(V)/W(IV) redox energy at 0.8–0.85 eV and the W(VI)/W(V) at 0.4–0.55 eV below Li+/Li. Different Li+-ion orderings in the interstitial space are able to keep up with the Li insertion to a 0.2 °C rate, but not to a 0.5 °C rate. A reversible capacity fades at 1 °C rate is attributed mainly to the poor electronic conductivity of the garnet. Keywords: Lithium garnet, Tungsten redox energies, Solid electrolyte

LiCoO2 thin films have received attention as cathodes of thin-film microbatteries in these days. In this study, LiCoO2 thin films were fabricated by a sol–gel spin coating method and an annealing process. They were deposited on Pt(111) and Pt(200) substrates to investigate the effect of orientation of current collector. The crystallinity, microstructure and electrochemical properties of final films are also studied by XRD, SEM and galvanostatic charge/discharge cycling test. Films heat-treated under appropriate conditions exhibit high capacity and good crystallinity so those films are considered to be candidates as cathodes for thin-film microbatteries.

In this paper, we report a preliminary study on the electrical and optical properties of the first P-on-N SiPM prototype developed at KAIST with a collaboration of NNFC. The sensors were fabricated on a 200 mm n-type silicon epitaxial-layer wafer via customized CMOS process at NNFC. Measurements on the reverse current were carried out on a wafer-level with an auto-probing station and breakdown voltage was found as 32.3 V. As for optical characterization, gain, dark count rate, and photon detection efficiency have been measured as a function of bias voltage at room temperature. In particular, we show that the device had a comparable gain of ~ 106 with respect to conventional PMTs and had a peak sensitivity in blue light regime. Furthermore, we attempt to explain possible causes of some of phenomena seen from the device characterization.