SiCN/C-ceramic composite as anode material for lithium ion batteries

The choice of electrode and electrolyte materials to design lithium batteries is limited due to the chemical reactivity of the used materials during the intercalation/deintercalation process. Amorphous silicon carbonitride (SiCN) ceramics are known to be chemically stable in corrosive environments and exhibit disordered carbonaceous regions making it potentially suitable to protect graphite from exfoliation. The material studied in this work was synthesized by mixing commercial graphite powder with the crosslinked polysilazane VL20^®. Pyrolysis of the polymer/graphite compound at appropriate temperatures in inert argon atmosphere resulted in the formation of an amorphous SiCN/graphite composite material. First electrochemical investigations of pure SiCN and of the SiCN/C composite are presented here. A reversible capacity of 474 mA hg⁻¹ was achieved with a sample containing 25 wt% VL20^® and 75 wt% graphite. The measured capacity exceeds that of the used graphite powder by a factor of 1.3 without any fading over 50 cycles.     

Gelatin-pretreated carbon particles for potential use in lithium ion batteries

Graphite anodes for use in lithium ion batteries were prepared from graphite particles pretreated in a gelatin solution. The content of gelatin in the final anode material was determined from the difference in mass of graphite particles before and after the treatment with gelatin and by thermogravimetric analysis. Forces between a gelatin-coated glass particle and graphite surface were measured in solution using an atomic force microscope. The effect of gelatin content on the characteristics of first charge-discharge cycle is measured and commented in terms of a simple passivation model.     

Response characteristics of all-solid-state pH sensor using Li5YSi4O12 glass

A new type of all-solid-state pH sensor was investigated for the monitoring of pH in high temperature. The all-solid-state pH sensor consists of two half-cells: indicator electrode using the Li₅YSi₄O₁₂ glass and an Ag/AgCl reference electrode coated with Nafion film. A stable Nafion film was achieved by heat treating at 100 °C for 1 h. The electromotive force (EMF) of the all-solid-state pH sensor decreased linearly with pH increase in water in accordance with the Nernst's equation. The all-solid-state pH sensor operated stably up to 80 °C. The sensitivity of the all-solid-state pH sensor against pH was high, and the EMF was also scarcely influenced by the presence of inorganic ions such as Li⁺, Na⁺ and Cl⁻. It was practically confirmed by the pH titration test that the all-solid-state pH sensor behaved similar to the commercial pH meter with the conventional glass electrode. In addition, the all-solid-state pH sensor showed same equivalence point both at high temperature and low temperature operations.     

Preparation and characterization of basic carbonates as novel anode materials for lithium-ion batteries

Three basic carnobates, (PbCO₃)₂·Pb(OH)₂, NiCO₃·2Ni(OH)₂·4H₂O, and CuCO₃·Cu(OH)₂, are prepared and used for the first time as anode materials for lithium-ion batteries. Electrochemical results show that (PbCO₃)₂·Pb(OH)₂, NiCO₃·2Ni(OH)₂·4H₂O and CuCO₃·Cu(OH)₂ can deliver high initial discharge capacities of 1175.8, 1742.6 and 1356.2 mAh g⁻¹, respectively. The lithium storage mechanisms of basic metal carbonates are observed by various electrochemical, ex-situ and in-situ methods during the initial charge–discharge cycle. It can be found that basic metal carbonates decompose into metal (M=Pb, Ni or Cu), Li₂CO₃, LiOH and H₂O upon the preliminary discharge. With further lithiation, the active metal can alloy with Li to form several Li_xM phases. During the reverse charge process, Li extraction from the de-alloying reaction, M/Li₂CO₃ and M/LiOH mixtures can be observed. However, the cycling efficiency is low. Electrochemically inactive particles generated from pulverization, structural collapse and electronic contact loss result in the large irreversible capacity and low initial cycling efficiency. By using carbon black as conductive additive and buffer layer, the electrochemical properties of composite can be greatly improved. Carbon black–(PbCO₃)₂·Pb(OH)₂ composite shows a reversible charge capacity of 244.7 mAh g⁻¹ after 20 cycles, which is much higher than the value (77.2 mAh g⁻¹) of the pristine sample.     

Enhanced thermoelectric properties of carbon fiber reinforced cement composites

Thermoelectric properties of carbon fiber reinforced cement composites (CFRCs) have attracted relevant interest in recent years, due to their fascinating ability for harvesting ambient energy in urban areas and roads, and to the widespread use of cement-based materials in modern society. The enhanced effect of the thin pyrolytic carbon layer (formed at the carbon fiber/cement interface) on transport and thermoelectric properties of CFRCs has been studied. It has been demonstrated that it can enhance the electrical conduction and Seebeck coefficient of CFRCs greatly, resulting in higher power factor 2.08 µW m⁻¹ K⁻² and higher thermoelectric figure of merit 3.11×10⁻³, compared to those reported in the literature and comparable to oxide thermoelectric materials. All CFRCs with pyrolytic carbon layer, exhibit typical semiconductor behavior with activation energy of electrical conduction of 0.228-0.407 eV together with a high Seebeck coefficient. The calculation through Mott’s formula indicates the charge carrier density of CFRCs (10¹⁴–10¹⁶ cm⁻³) to be much smaller than that of typical thermoelectric materials and to increase with the carbon layer thickness. CFRCs thermal conductivity is dominated by phonon thermal conductivity, which is kept at a low level by high density of micro/nano-sized defects in the cement matrix that scatter phonons and shorten their mean free path. The appropriate carrier density and mobility induced by the amorphous structure of pyrolytic carbon is primarily responsible for the high thermoelectric figure of merit.     

Influence of the composition-induced structure evolution on the electrocaloric effect in Bi0.5Na0.5TiO3-based solid solution

The present work investigated the influence of the composition induced structure evolution on the electrocaloric effect in lead-free (0.935−x)Bi_0.5Na_0.5TiO₃–0.065BaTiO₃–xSrTiO₃ (BNBST, BNBSTx) ceramics. It was found that broad ∆T peak could be observed for all compositions and the electrocaloric strength α (α=ΔT_max/ΔE) in BNBST0.02 could reach as high as 0.27 K mm/kV. The increase of the SrTiO₃ concentration led to a shift of ∆T_max to a lower temperature, resulting in a large near room-temperature electrocaloric strength α of 0.17 K mm/kV in BNBST0.22.     

Multiferroic behavior of heterostructures composed of lanthanum and bismuth ferrite

Heterostructured thin films of lanthanum ferrite (LFO) and bismuth ferrite (BFO) with different thicknesses were successfully obtained by a soft chemical method. The films were deposited by spin-coating and annealed at 500 °C for 2 h. The XRD pattern confirmed the purity of the thin films, where no additional peaks associated with impurity phases were present. The morphology analysis showed spherical grains with a random size distribution. The grain sizes increased with the number of BFO layers. The average grain size varied from 43 nm to 68 nm. The best dielectric results were obtained for the film with 6 LFO sublayers and 4 BFO top layers, in which the dielectric constant showed low dispersion. Since the capacitance-voltage curve for the film 6-LFO/4-BFO is symmetrical around null voltage, it can be inferred that this heterostructure has few mobile ions and accumulated charges on the film-substrate interface. In this film, polarization remains almost constant during 10¹² cycles before the onset of degradation, which shows the very high resistance of the films to fatigue. Magnetoelectric coefficient measurements of the films revealed the formation of hysteresis loops, and a maximum value of 12 V/cmOe was obtained for the magnetoelectric coefficient in the longitudinal direction; this value is much higher than that previously reported for pure BFO thin films.     

The effect of Zn ion substitution on electromagnetic properties of low-temperature fired Z-type hexaferrite

The influence of Zn substitution on the densification, microstructure, lattice parameters and electromagnetic properties of planar Z-type hexaferrites, which have stoichiometric composition of Ba₃Co_2(10.8−x)Zn_2xCu_0.4Fe₂₄O₄₁, were investigated. The results show that the Zn²⁺ substitution has no obvious effect on the densification, but Z-type hexagonal phase can form and demonstrate typical planar anisotropic characteristics of soft magnetic materials (σ_r6.20 emu/g) in the range of x0.25. The of lattice parameters of planar a (0.588 nm) and axial c (5.25 nm) remain stable. At the certain temperatures, the sintered hexaferrites with an optimal density of about 4.62 g/cm³ show better electromagnetic properties for x=0.15 than the samples without Zn²⁺ incorporation: initial permeability of about 9.0, cut-off frequency of above 800 MHz, resisitivity of above 3.20 Ω cm and dielectric constant of less than 35.     

Facile synthesis of MTaO4 (M = Al,Cr and Fe) metal oxides and their application as anodes for lithium-ion batteries

Ternary metal oxides have attracted much attention in energy storage fields. Herein, tantalum-based oxides MTaO₄ (M = Al, Cr and Fe) are synthesized by a facile co-precipitation method, and their performance as lithium-ion battery anodes are evaluated. Among them, the FeTaO₄ electrode presents superior electrochemical performance compared to the MTaO₄ (M = Al and Cr) and a reversible capacity of more than 200?mAh?g^?1 can be maintained after 100 cycles, while a capacity of 53.6 and 128.9?mAh?g^?1 can be obtained at the same condition for AlTaO₄ and CrTaO₄, respectively. The explanation that FeTaO₄ exhibits the excellent electrochemical performance in MTaO₄ (M = Al, Cr and Fe) are further discussed.     

A CTAB-assisted hydrothermal synthesis of VO2(B) nanostructures for lithium-ion battery application

Nanostructured VO₂(B) was synthesized via a combined hydrothermal method using V₂O₅ as a source material and oxalic acid powder as a reductant. Especially, cetyltrimethylammonium bromide (CTAB) was used as template and then three different morphologies of the VO₂(B): nanobelts, nanoflowers and nanoflakes were obtained through the change of the experimental conditions. The morphology and crystalline structure of the prepared products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Furthermore, the electrochemical charge–discharge cycling properties of the VO₂(B) nanostructures in lithium-ion battery were investigated. The results indicated that the belt-like, flower-like and flake-like VO₂(B) nanostructures have the initial specific discharge capacity of 205.2, 254.0 and 56.0 mA h g⁻¹, and that the morphology of VO₂(B) nanostructures can deeply affect the service performance of batteries. According to the experiments, this CTAB-assisted hydrothermal method provides an insight into the preparation and application of nanostructured VO₂(B) as cathode material in lithium-ion battery.     

Enhanced thermoelectric effect of carbon fiber reinforced cement composites by metallic oxide/cement interface

Thermoelectric power of carbon fiber reinforced cement composites was firstly enhanced efficiently by metallic oxide microparticles in the cement matrix. The absolute Seebeck coefficient of these composites increased steadily with increasing metallic oxide content and achieved 4–5 folds of the original one. The largest absolute thermoelectric power of +100.28 µV/°C was obtained for the composite with 5.0 wt% Bi₂O₃ microparticles. The carrier scattering of the interface between oxide microparticles and cement matrix is probably attributed to the Seebeck effect enhancement.     

Structure,electrochemical impedance and Raman spectroscopy of lithium-niobium-titanium-oxide ceramics for LTCC technology

Resultsof Electrochemical Impedance Spectroscopy (EIS) are reported for lithium-niobium-titanium-oxide (LNTO) ceramics synthesized by a solid-state reaction method with two functional additives (MoO₃ or ZnO) in the temperature range 323 K - 573 K and frequencies between 10^?1 Hz and 10⁷ Hz. Scanning electron microscopy (SEM) reveals a textured morphology of rod and plate-like particles that are typical for M-phase LNTO materials, while X-ray diffraction (XRD) analysis confirms the formation of an M-phase member compound with an approximate structure of Li₇Nb₃Ti₅O₂₁. Complex impedance analysis indicates that its overall electrical resistivity behavior depends mostly on the grain boundary processes. EIS analysis shows a negative temperature coefficient of resistance behavior (NTCR) in a defined temperature range in two LNTOs and thermal activation of the conduction mechanisms. The low dielectric constants of 5.5 and 12.1 at 1 MHz were found for the first and second LNTOs, respectively. Complimentary Raman spectroscopic measurements, despite very large crystallographic unit cell of LNTO, reveal only a small number of lines, which is the consequence of a “molecular” nature of materials.     

High-rate properties of LiFePO4/carbon composites as cathode materials for lithium-ion batteries

Electrochemical properties of LiFePO₄/carbon composites were investigated to achieve a high-rate lithium electrode performance. LiFePO₄/carbon composites were synthesized by a hydrothermal reaction of a solution of FeSO₄·7H₂O, H₃PO₄, and LiOH·H₂O mixed with carbon powders under nitrogen atmosphere followed by annealing under 1% H₂–99% Ar atmosphere. Particle size of the obtained LiFePO₄/carbon composites observed by scanning electron microscopy was less than 100 nm. At a high current density of 1000 mA g⁻¹, the LiFePO₄/carbon composites showed a high discharge capacity of 113 mA h g⁻¹, and a flat discharge potential plateau was observed around 3.4 V. The discharge capacity at the high current density, 85% of that at a low current density of 30 mA g⁻¹, is a quite high value for LiFePO₄ cathodes. Homogeneous microstructure consisting of small particles contributed to the high-rate properties of the LiFePO₄/carbon composites.     

Microwave-induced small size effect of (Ba,Sr)3MgSi2O8:0.06Eu, 0.1Mn phosphor for 660 nm-featured bio-lighting

The 660 nm-featured (Ba, Sr) ₃MgSi₂O₈:0.06Eu^{2 +}, 0.1Mn²⁺(AMS-EM) phosphor in violet for red/blue bio-lighting LEDs was prepared by 2.45 GHz microwave (MW) high temperature firing procedure. The phase-pure host phase, (Ba, Sr) ₃MgSi₂O₈, was formed to be responsible for simultaneous red band emission from Mn ion and blue band emission from Eu ion, while the formation of an impurity phase of Sr₂SiO₄ responsible for 505 nm-peaked green band emission for Eu ion was effectively suppressed owing to MW fast-heating procedure. Small sized and agglomeration-free phosphor particles were either observed, which was probably resulted from suppressing the grain growth in as-formed host particles, compared with conventional high-temp solid state (SS) reaction firing procedure. These results indicate that high-temp MW firing procedure is suitable for preparing this simultaneously red- and blue-emitting AMS-EM phosphor in the application of bio-lighting for plant cultivation.     

Behavior of some potassium tungstates in the course of electrochemical lithium insertion

Electrochemical lithium insertion has been studied in K₂WO₄, K₂W₃O₁₀ and K₂W₄O₁₃ through galvanostatic intermittent titration technique. We have monitored structural changes in the host matrix as lithium insertion proceeds through in situ X-ray diffraction experiments. In particular, K₂WO₄ showed to be unable to insert lithium in appreciable amounts. The maximum amount of lithium inserted in each oxide leads to specific capacities of 18 Ah/kg for K₂WO₄, 220 Ah/kg for K₂W₃O₁₀ and 265 Ah/kg for K₂W₄O₁₃. Nevertheless, due to irreversible structural transformations in the host matrix, such capacities were dramatically lost after the first cycle.     

Structural,optical, and electrical properties of cellulose/titanate nanosheets composite with enhanced protection against gamma irradiation

Two-dimensional (2D) materials have emerged as a promising functional filler in nanocomposites due to their unique anisotropy and resilience to harsh conditions. We report herein the use of Ti_0.91O₂ nanosheets as a protective component against γ-irradiation to cellulose paper. The titanate nanosheets were prepared via a sequence of solid-state synthesis of lepidocrocite-type Cs_0.7Ti_1.825O₄, proton exchange to H_0.7Ti_1.825O₄·H₂O, and exfoliation with tetrabutylammonium hydroxide. The nanosheets were incorporated into the commercial cellulose filter paper by a simple dip coating up to 0.6 mg cm⁻², equivalent to 10 wt% TiO₂. The nanosheets distribution was demonstrated by energy dispersive X-ray (EDX) mapping, synchrotron radiation X-ray tomographic microscopy (SRXTM), and atomic force microscopy (AFM). It is found that γ-irradiation (up to 50 kGy) destroyed the cellulose Iβ crystallinity of uncoated paper, but this is less pronounced in the cellulose/titanate nanosheets composite. This was also confirmed by the lack of a 235 nm-absorption characteristics of irradiation-induced decomposition product(s) in nanosheets-containing papers, which also exhibit UVA shielding property. The coated samples remained white while the uncoated ones were darkened with γ-irradiation. In addition, the nanosheets-coated papers showed dielectric permittivity, loss tangent, and AC conductivity which were invariant of the γ-dose, unlike those from the uncoated ones. Our work demonstrates the use of lead-free Ti_0.91O₂ nanosheets as a γ-shielding component to slow down/prevent structural, optical, and electrical properties damages in cellulose paper, which could extend to other nature-derived materials.     

Influence of oxygen ion enrichment on optical,mechanical, and electrical properties of LSCF perovskite nanocomposite

La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) is a mixed ionic electronic conductor with excellent surface catalytic activity for oxygen reduction. This work demonstrated that introduction of pure oxygen ion conductor to LSCF particles can significantly influence in-plane electronic conduction at the surface of LSCF-samarium-doped ceria (SDC) composite. The composite functional layer was prepared by mixing 50?wt% SDC particles with LSCF particles obtained from glycine–nitrate process. Homogeneous LSCF-SDC composite layer deposited by screen printing on an SDC substrate has been studied with and without LSCF current-collecting layer (CCL). The microstructural, optical, Raman, mechanical and electrical properties, and interfacial polarization resistance (R_p) of the prepared powders were evaluated. Results revealed that addition of oxygen ion conductor SDC exerted negligible effect on the phase structure and specific surface area but significantly influenced the band gap, oxygen vacancies, and electrical conductivity of LSCF. SDC addition significantly increased area specific resistance (ASR) of LSCF from 0.138?Ω?cm² to 0.481?Ω?cm² at 800?°C, thereby blocking the conduction path among LSCF particles. R_p value of LSCF-SDC composite can be improved by more than six times by enlarging the in-plane electronic conduction with thin CCL. Electrochemical measurement revealed that LSCF CCL reduced the R_p value, resulting in the lowest ASR of 0.087?Ω?cm² at 800?°C for the LSCF–SDC composite.     

Lowering sensitivity of anode materials for lithium ion batteries towards humidity

Sensitivity of anode materials towards humidity is an important factor for the performance of lithium ion batteries. Here it is demonstrated for the first time that the sensitivity of composite anode materials prepared of metals such as copper and silver with natural graphite can be strikingly lowered. The composites are prepared by adsorbing metal ions from solutions onto the surface of natural graphite followed by heat-treatment at high temperature. Results from X-ray photoelectron spectroscopy, high resolution electron microscopy, thermogravimmetry, differential thermal analysis, and capacity measurements indicate that the deposited metals exist in two forms, viz. metallic and carbidic M_xC (M=Cu and Ag), and remove/cover (i.e. deactivated) the active hydrophilic sites at the surface of graphite. As a result, in the presence of high humidity the composites absorb less water, and the obtained electrochemical performance including reversible capacity, coulombic efficiency in the first cycle and cycling behavior is markedly improved. This approach provides a potentially powerful method to manufacture lithium ion batteries under less critical conditions.     

Adjustable dielectric properties of Li2CuxZn1−xTi3O8 (x=0 to 1) ceramics with low sintering temperature

Single-phase dielectric ceramics Li₂Cu_xZn_1−xTi₃O₈ (x=0–1) were synthesized by the conventional solid-state ceramic route. All the solid solutions adopted Li₂MTi₃O₈ cubic spinel structure in which Li/M and Ti show 1:3 order in octahedral sites whereas Li and M are distributed randomly in tetrahedral sites with the degree of Li/M cation mixing varying from 0.5 to 0.3. The substitution of Cu for Zn effectively lowered the sintering temperatures of the ceramics from 1050 to 850 °C and significantly affected the dielectric properties. As x increased from 0 to 0.5, τ_f gradually increased while the dielectric constant (ε_r) and quality factor value (Q×f) gradually decreased, and a near-zero τ_f of 1.6 ppm/°C with ε_r of 25.2, Q×f of 32,100 GHz could be achieved for Li₂Cu_0.1Zn_0.9Ti₃O₈ ceramic sintered at 950 °C, which make it become an attractive promising candidate for LTCC application. As x increases from 0.5 to 1, the dielectric loss significantly increases with AC conductivity increasing up to 2.3×10⁻⁴ S/cm (at 1 MHz).     

The effect of lithium oxide on the threshold field of ZnO varistors

Lithium oxide in form of Li₂CO₃ solution is added with contents of 0–200 ppm to two ZnO-based varistors standard formulations, once with Sb₂O₃ and the other without. According to Li₂CO₃ concentration, both threshold field and energy absorption capability evolution are studied. It is found that with the benefit of antimony, the lithium allows reaching high threshold field but concomitantly, low energy absorption capability. Without antimony, threshold fields up to 300 V/mm are attained, associated with a fair energy absorption capability. With 100 ppm of Li₂CO₃, optimum couple of values (315 V/mm; 115 J/cm³) is achieved. With 200 ppm of Li₂CO₃, threshold field exceeds 500 V/mm but energy absorption capability falls below 50 J/cm³. Correlations with SEM microstructures observations suggest that lithium increases voltage barrier height by decreasing donor density and that spinel phases (Zn₇Sb₂O₁₂) have detrimental effects on the electrical absorption capability by limiting the density of current, reducing the effective current path from one ZnO grain to another.