Electrochemical properties of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C cathode materials synthesized via ethylene glycol-assisted solvothermal method

The Li₃V₂(PO₄)₃/C (LVP/C) cathode materials for lithium-ion batteries were synthesized via ethylene glycol-assisted solvothermal method. The phase composition, phase transition temperature, morphology, and fined microstructure were studied using X-ray diffraction (XRD), differential thermal analyzer (DTA), scanning electron microscope (SEM), and transmission electron microscope (TEM), respectively. The electrochemical properties, impedance, and electrical conductivity of LVP/C cathode materials were tested by channel battery analyzer, the electrochemical workstation, and the Hall test system, respectively. The results shown that the appropriate amount of water added to ethylene glycol solvent contributes to the synthesis of pure phase LVP. The LVP₁₀/C cathode material can exhibit discharge capacities of 128, 126, 126, 123, 124, and 114 mAh g^?1 at 0.1, 0.5, 2, 5, 10, and 20 C in the voltage range of 3.0–4.3 V, respectively. Meanwhile, it shows also a stable cycling performance with the capacity retention of 89.6% after 180 cycles at 20 C.     

Nano Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> as sulfur host for high-performance Li-S battery

S/Li₄Ti₅O₁₂ cathode with high lithium ionic conductivity was prepared for Li-S battery. Herein, nano Li₄Ti₅O₁₂ is used as sulfur host and fast Li⁺ conductor, which can adsorb effectively polysulfides and improve remarkably Li⁺ diffusion coefficient in sulfur cathode. At 0.5 C, S/Li₄Ti₅O₁₂ cathode has a stable discharge capacity of 616 mAh g^?1 at the 700th cycle and a capacity loss per cycle of 0.0196% from the second to the 700th cycle, but the corresponding values of S/C cathode are 437 mAh g^?1 and 0.0598%. Even at 2 C, the capacity loss per cycle of S/Li₄Ti₅O₁₂ cathode is only 0.0273% from the second to the 700th cycle. The results indicate that Li₄Ti₅O₁₂ as the sulfur host plays a key role on the high performance of Li-S battery due to reducing the shuttle effect and enhancing lithium ionic conductivity.     

Conductivity and spectroscopic studies of Li<Subscript>2</Subscript>O-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

Lithium vanadium-borate glasses with the composition of 0.3Li₂O–(0.7-x)B₂O₃–xV₂O₅ (x?=?0.3, 0.325, 0.35, 0.375, 0.4, 0.425, 0.45, and 0.475) were prepared by melt-quenching method. According to differential scanning calorimetry data, vanadium oxide acts as both glass former and glass modifier, since the thermal stability of glasses decreases with an increase in V₂O₅ concentration. Fourier transform infrared spectroscopy data show that the vibrations of [VO₄] structural units occur at V₂O₅ concentration of 45 mol%. It is established that the concentration of V⁴⁺ ions increases exponentially with the growth of vanadium oxide concentration. Direct and alternative current measurements are carried out to estimate the contribution both electronic and ionic conductivities to the value of total conductivity. It is shown that the electronic conductivity is predominant in the total one. The glass having the composition of 0.3Li₂O-0.275B₂O₃-0.475V₂O₅ shows the highest electrical conductivity that has the value of 7.4?×?10^?5 S cm^?1 at room temperature.     

Enhanced electrochemical performance of lithium ion battery cathode Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C

Li-ion battery cathode material lithium-vanadium-phosphate Li₃V₂(PO₄)₃ was synthesized by a carbon-thermal reduction method, using stearic acid, LiH₂PO₄, and V₂O₅ as raw materials. And stearic acid acted as reductant, carbon source, and surface active agent. The effect of its content on the crystal structure and electrochemical performance of Li₃V₂(PO₄)₃/C were characterized by XRD and electrochemical performance testing, respectively. The results showed that the content of carbon source has no significant effect on the crystal structure of lithium vanadium phosphate. Lihtium vanadium phosphate obtained with 12.3% stearic acid demonstrated the best electrochemical properties with a typical discharge capacity of 119.4 mAh/g at 0.1 C and capacity retention behavior of 98.5% after 50 cycles. And it has high reversible discharge capacity of 83 mAh/g at 5 C with the voltage window of 3 to 4.3 V.     

Electrochemical comparison of LiFe<Subscript>0.4</Subscript>Mn<Subscript>0.595</Subscript>Cr<Subscript>0.005</Subscript>PO<Subscript>4</Subscript>/C and LiMnPO<Subscript>4</Subscript>/C cathode materials

A comparison of electrochemical performance between LiFe_0.4Mn_0.595Cr_0.005PO₄/C and LiMnPO₄/C cathode materials was conducted in this paper. The cathode samples were synthesized by a nano-milling-assisted solid-state process using caramel as carbon sources. The prepared samples were investigated by XRD, SEM, TEM, energy-dispersive X-ray spectroscopy (EDAX), powder conductivity test (PCT), carbon-sulfur analysis, electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge cycling. The results showed that LiFe_0.4Mn_0.595Cr_0.005PO₄/C exhibited high specific capacity and high energy density. The initial discharge capacity of LiFe_0.4Mn_0.595Cr_0.005PO₄/C was 163.6 mAh g^?1 at 0.1C (1C = 160 mA g^?1), compared to 112.3 mAh g^?1 for LiMnPO₄/C. Moreover, the Fe/Cr-substituted sample showed good cycle stability and rate performance. The capacity retention of LiFe_0.4Mn_0.595Cr_0.005PO₄/C was 98.84 % over 100 charge-discharge cycles, while it was only 86.64 % for the pristine LiMnPO₄/C. These results indicated that Fe/Cr substitution enhanced the electronic conductivity for the prepared sample and facilitated the Li⁺ diffusion in the structure. Furthermore, LiFe_0.4Mn_0.595Cr_0.005PO₄/C composite presented high energy density (606 Wh kg^?1) and high power density (574 W kg^?1), thus suggested great potential application in lithium ion batteries (LIBs).     

Investigations on the synthesis and electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C by different methods

Li₃V₂(PO₄)₃/C samples were synthesized by two different synthesis methods. Their influence on electrochemical performances of Li₃V₂(PO₄)₃/C as cathode materials for lithium-ion batteries was investigated. The structure and morphology of Li₃V₂(PO₄)₃/C samples were characterized by X-ray diffraction and scanning electron microscopy. Electrochemical performance was characterized by charge/discharge, cyclic voltammetry, and alternating current (AC) impedance measurements. Li₃V₂(PO₄)₃/C with smaller grain size showed better performances in terms of the discharge capacity and cycle stability. The improved electrochemical properties of the Li₃V₂(PO₄)₃/C were attributed to the decreasing grain size and enhanced electrical conductivity produced via low temperature route. AC impedance measurements also showed that the Li₃V₂(PO₄)₃/C synthesized by low temperature route significantly decreased the charge-transfer resistance and shortened the migration distance of lithium ion.     

Multi-hierarchical nanosheet-assembled chrysanthemum-structured Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C as electrode materials for high-performance sodium-ion batteries

The structure and morphology of sodium vanadium phosphate (Na₃V₂(PO₄)₃) play a vital role in enhancing the electrochemical performance of sodium-ion batteries due to the inherent poor electronic conductivity of the phosphate framework. In order to improve this drawback, a new chrysanthemum-structured Na₃V₂(PO₄)₃/C material has been successfully assembled with multi-hierarchical nanosheets via a hydrothermal method. Continuous scattering nanosheets in chrysanthemum petals are beneficial in reducing energy consumption during the process of sodium ion diffusion, on which the carbon-coated surface can significantly increase overall conductivity. The as-prepared sample exhibits outstanding electrochemical performance due to its unique structure. It rendered a high initial specific capacity of 117.4?mAh?g^?1 at a current density of 0.05 C. Further increasing the current density to 10 C, the initial specific capacity still achieves 101.3?mAh?g^?1 and remains at 87.5?mAh?g^?1 after 1000 cycles. In addition, a symmetrical sodium-ion full battery using the chrysanthemum-structured Na₃V₂(PO₄)₃/C materials as both the cathode and anode has been successfully fabricated, delivering the capacity of 62?mAh?g^?1 at 1?C and achieving the coulombic efficiency at an average of 96.4% within 100 cycles. These results indicate that the new chrysanthemum-structured Na₃V₂(PO₄)₃/C can provide a new idea for the development of high-performance sodium-ion batteries.     

Synthesis,thermal and electrical behavior of the superprotonic conductor phase in Rb<Subscript>3</Subscript>(HSeO<Subscript>4</Subscript>)<Subscript>2.5</Subscript>(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>0.5</Subscript> compound

The Rb₃(HSeO₄)_2.5(H₂PO₄)_0.5 compound was prepared and its thermal behavior and electric properties were investigated. The thermogravimetry (TGA) analysis and the differential scanning calorimetric (DSC) show the presence of a structural phase transition of the title compounds at 374 K which is confirmed by the variation of fp and σ_dc as a function of temperature. The complex impedance of the Rb₃(HSeO₄)_2.5(H₂PO₄)_0.5 compound has been investigated in the temperature range of 295–453 K and in the frequency range 209 Hz–1 MHz. The impedance plots show semicircle arcs at different temperatures, and an electrical equivalent circuit has been proposed to explain the impedance results. The circuits consist of the parallel combination of bulk resistance Rp and constant phase elements CPE₁ in series with fractal capacity CPE₂. The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. The conductivity dc follows the Arrhenius relation. The near value of activation energies obtained from the analysis of modulus, conductivity data, and circuit equivalent confirm that the transport is through the ion hopping mechanism, dominated by the motion of the H⁺ proton in the structure of the investigated materials.     

Impedance spectroscopy analysis of Li<Subscript>2</Subscript>SnO<Subscript>3</Subscript>

In this work, Li₂SnO₃ has been synthesized by the sol–gel method using acetates of lithium and tin. Thermogravimetric analysis (TGA) has been applied to the precursor of Li₂SnO₃ to determine the suitable calcination temperature. The formation of the compound calcined at 800 °C for 9 h has been confirmed by X-ray diffraction (XRD) analysis. The Li₂SnO₃ is then pelletized and electrically characterized by using electrochemical impedance spectroscopy (EIS) in the frequency range from 50 Hz to 1 MHz. The complex impedance spectra clearly show the dominating presence of the grain boundary effect on electrical properties whereas the complex modulus plots reveal two semicircles which are due to the grain (bulk) and grain boundary. The spectra of imaginary parts of both impedance and modulus versus frequency show the existence of peaks with the modulus plots exhibiting two peaks that are ascribed to the grain and grain boundary of the material. The peak maximum shifts to higher frequency with an increase in temperature and the broad nature of the peaks indicates the non-Debye nature of Li₂SnO₃. The activation energy associated with the dielectric relaxation obtained from the electrical impedance spectra is 0.67 eV. From the electric modulus spectra, the activation energies related to conductivity relaxation in the grain and grain boundary of Li₂SnO₃ are 0.59 and 0.69 eV, respectively. The conductivity–temperature relationship is thermally assisted and obeys the Arrhenius rule with the activation energy of 0.66 eV. The conduction mechanism of Li₂SnO₃ is via hopping.     

Thermal properties and ionic conductivity of Li<Subscript>1,3</Subscript>Ti<Subscript>1,7</Subscript>Al<Subscript>0,3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> solid electrolytes sintered by field-assisted sintering

Li_1,3Ti_0,7Al_0,3(PO₄)₃ (LATP) powder was obtained by a conventional melt-quenching method and consolidated by field-assisted sintering technology (FAST) at different temperatures. Using this technique, the samples could be sintered to relative densities in the range of 93 to 99 % depending on the sintering conditions. Ionic and thermal conductivity were measured and the results are discussed under consideration of XRD and SEM analyses. Thermal conductivity values of 2 W/mK and ionic conductivities of 4?×?10^?4 Scm^?1 at room temperature were obtained using relatively large particles and a sintering temperature of 1000 °C at an applied uniaxial pressure of 50 MPa.     

AC conductivity and mechanism of conduction study of lithium barium pyrophosphate Li<Subscript>2</Subscript>BaP<Subscript>2</Subscript>O<Subscript>7</Subscript> using impedance spectroscopy

The Li₂BaP₂O₇ compound has been obtained by the conventional solid-state reaction and characterized by X-ray powder diffraction. The title material crystallizes in the monoclinic system with C2/c space group. Electrical properties of the compound have been studied using complex impedance spectroscopy in the frequency range 200 Hz–5 MHz and temperature range 589–724 K. Temperature dependence of the DC conductivity and modulus was found to obey the Arrhenius law. The obtained values of activation energy are different which confirms that transport in the titled compound is not due to a simple hopping mechanism. AC conductivity measured follows the power-law dependence σ _AC?～?ω ^s typical for charge transport. Therefore, the experimental results are analyzed with various theoretical models. Temperature dependence of the power law exponent s strongly suggests that tunneling of large polarons is the dominant transport process.     

Improved structural stability and electrochemical performance of Na<Subscript>3</Subscript>V<Subscript>2</Subscript> (PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode material by Cr doping

Cr-doped sodium vanadium phosphate (NVP) in the form of Na₃V_2-xCr_x(PO₄)₃ (x = 0, 0.02, 0.04, 0.08, 0.10) is synthesized via a facile sol-gel route as cathode materials for sodium ion batteries. The structure and morphology of these materials are systematically characterized by x-ray diffraction (XRD), Fourier-infrared spectra (FT-IR), and scanning electron microscope (SEM). XRD analysis reveals that with the increasing amount of Cr, the crystallographic parameters show a descending trend. Electrochemical tests show that the cycle stability and the specific capacity of the sodium ion batteries can be significantly improved by doping Cr into NVP. Among all the Cr-doped cathode materials, Na₃V_1.92Cr_0.08(PO₄)₃ achieves the highest capacity of 112.2 mAh g^?1 and the capacity retention is 97.2 % after 50 cycles. Electrochemical impedance spectroscopy measurements demonstrate that Cr doping is an effective method to reduce the contact resistance of interparticles by suppressing irreversible phase transformation at low sodium contents.     

Investigation on lithium ion conductivity and structural stability of yttrium-substituted Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript>

Advanced Li-air battery architecture demands a high Li⁺ conductive solid electrolyte membrane that is electrochemically stable against metallic lithium and aqueous electrolyte. In this work, an investigation has been carried out on the microstructure, Li⁺ conduction behaviour and structural stability of Li₇La_3-x Y _x Zr₂O₁₂ (x = 0.125, 0.25 and 0.50) prepared by conventional solid-state reaction technique. The phase analysis of Li₇La_3-x Y _x Zr₂O₁₂ (x = 0.125, 0.25 and 0.50) sintered at 1200 °C by powder X-ray diffraction (PXRD) and Raman confirms the formation of high Li⁺ conductive cubic phase (\( Ia\overline{3}d \)) lithium garnets. Among the investigated lithium garnets, Li₇La_2.75Y_0.25Zr₂O₁₂ sintered at 1200 °C exhibits a maximized room temperature total (bulk + grain boundary) Li⁺ conductivity of 3.21 × 10^?4 S cm^?1 along with improved relative density of 96 %. The preliminary investigation on the structural stability of Li₇La_2.75Y_0.25Zr₂O₁₂ in the solutions of 1 M LiCl, dist. H₂O and 1 M LiOH at 30 °C/50 °C indicates that the Li₇La_2.75Y_0.25Zr₂O₁₂ is relatively stable against 1 M LiCl and dist. H₂O. Further electrochemical investigation is essential for practical application of Li₇La_2.75Y_0.25Zr₂O₁₂ as protective solid electrolyte membrane in aqueous Li-air battery.     

Crystal structure analysis of Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> powder prepared by wet chemical reaction and solid-state reaction by using X-ray diffraction (XRD)

Lithium phosphate (Li₃PO₄) is one of the promising solid electrolyte materials for lithium-ion battery because of its high ionic conductivity. A crystalline form of Li₃PO₄ had been prepared by two different methods. The first method was wet chemical reaction between LiOH and H₃PO₄, and the second method was solid-state reaction between Li₂O and P₂O₅. Crystal structure of Li₃PO₄ white powder had been investigated by using an X-ray diffraction (XRD) analysis. The results show that Li₃PO₄ prepared by wet chemical reaction belongs to orthorhombic unit cell of β-Li₃PO₄ with space group Pmn2₁. Meanwhile, Li₃PO₄ powder prepared by solid-state reaction belongs to orthorhombic unit cell of γ-Li₃PO₄ with space group Pmnb and another unknown phase of Li₄P₂O₇. The impurity of Li₄P₂O₇ was due to phase transformation in solid state reaction during quenching of molten mixture from high temperature. Ionic conductivity of Li₃PO₄ prepared by solid-state reaction was ～3.10^?7 S/cm, which was higher than Li₃PO₄ prepared by wet chemical reaction ～4.10^?8 S/cm. This increasing ionic conductivity may due to mixed crystal structures that increased Li-ion mobility in Li₃PO₄.     

Synthesis and electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C by organic solvent replacement drying method

A series of Li₃V₂(PO₄)₃/C composite cathodes have been prepared by the organic solvent replacement drying method. Five kinds of organic solvent including ethyl alcohol, butyl alcohol, 2-methoxyethanol, 1,2-propylene glycol, and ethylene glycol were used in the drying process to replace the water respectively. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge tests were employed to analyze the crystal structure, morphology, and electrochemical properties of the as-prepared materials. The results show that the organic solvent has a great influence on the secondary particle size of the as-synthesized materials. Special emphasis is placed on the sample prepared with 1,2-propylene glycol, which has the smallest average particle size and uniform distribution, thus leading to the best high rate performance and long-term cycling stability. The electrode exhibits average specific discharge capacities of 127.6, 128.3, 127.7, 126.7, 125.5, 124.4, 121.9, and 117.0 mAh g^?1 at 0.1, 0.2, 0.5, 1, 3, 5, 10, and 20C, respectively. More encouragingly, this sample delivers an outstanding cycle life with capacity retention of up to 94.68% even after 1000 cycles at 20C. Moreover, EIS results demonstrate that this sample has the minimum resistance and the largest apparent lithium ion diffusion coefficient (1.569 × 10^?7 cm² s^?1) which can facilitate to the Li⁺ diffusion during the charge/discharge process. Our results indicate that this preparation strategy can be facile and versatile for the synthesis of other high-rate and high-capacity intercalation materials.     

Synthesis and characterization of Li<Subscript>1-x</Subscript>Tb<Subscript>x</Subscript>NiPO<Subscript>4</Subscript> solid solution as cathode materials for lithium ion battery application

Modified Pechini-type polymerizable precursor method has been used to prepare nanosized Li_1-xTb_xNiPO₄ (x = 0, 0.03, 0.05, and 0.07) solid solutions to obtain homogeneous with controlled stoichiometry and smaller particle size. The reaction temperature was determined by thermogravimetric (TG/DTA) analysis. X-ray diffraction analysis reveals the formation of orthorhombic structure and the calculated crystallite sizes are found to be in the range of 75–89 nm. Morphological, compositional, and vibrational properties were performed by SEM, EDAX, and FTIR, respectively. Conductivity measurements were carried out at room temperature by AC impedance analysis. The Li_0.97Tb_0.03Ni_0.99PO₄ sample shows one order of higher conductivity than pure LiNiPO₄. Higher concentration of terbium samples such as Li_0.95Tb_0.05Ni_0.99PO₄ and Li_0.93Tb_0.07Ni_0.99PO₄ lead to decrease of conductivity. The frequency dependency of dielectric permittivity, dielectric loss, and electric modulus of Li_1-x Tb_xNiPO₄ solid solutions are studied. The frequency-dependent plot of modulus reveals that the conductivity relaxation is of non-Debye type.     

Electrochemical behavior of carbonic precursor with Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>nanostructured material in hybrid battery system

The nanostructured Na₃V₂(PO₄)₃ (NVP) cathode material has been synthesized using the sol-gel route for different molar fractions of citric acid as a carbon source during the synthesis. The nanostructured NVP as cores with carbonic shell structures are fabricated with two different citric acid molar ratios. The thermal treatment has been optimized to convert the amorphous carbon shell into graphitic carbon to realize the better electrical conductivity and thus effective electron transfer during the electrochemical charge transfer process. The X-ray diffraction measurements confirmed the rhombohedral crystallographic phase (space group R-3c) with average crystallite size ~28 ± 5 nm. The coin cells are assembled in a hybrid rechargeable electrochemical cell configuration with lithium as a counter electrode and LiPF₆-EC:DEC:DMC (1:1:1 ratio) as the electrolyte. The electrochemical charge/discharge measurements are carried out at C/10 and C/20 rates and the measured specific capacities are 80 and 120 mAhg^?1 for samples with lower and higher citric acid molar ratios, respectively. The studies suggest that NVP can be used as an effective cathode material in hybrid electrochemical cells, and a higher concentration of citric acid may result in the effective carbonic shell for optimal electron transfer and thus enhanced electrochemical performance.     

Lithium diffusion in Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based electrodes: a joint analysis of electrochemical impedance,cyclic voltammetry,pulse chronoamperometry,and chronopotentiometry data

In order to establish the mechanism and to determine the parameters of lithium transport in electrodes based on lithium-vanadium phosphate (Li₃V₂(PO₄)₃), the kinetic model was designed and experimentally tested for joint analysis of electrochemical impedance (EIS), cyclic voltammetry (CV), pulse chronoamperometry (PITT), and chronopotentiometry (GITT) data. It comprises the stages of sequential lithium-ion transfer in the surface layer and the bulk of electrode material’s particles, including accumulation of lithium in the bulk. Transfer processes at both sites are of diffusion nature and differ significantly, both by temporal (characteristic time, τ) and kinetic (diffusion coefficient, D) constants. PITT data analysis provided the following D values for the predominantly lithiated and delithiated forms of the intercalation material: 10^?9 and 3 × 10^?10 cm² s^?1, respectively, for transfer in the bulk and 10^?12 cm² s^?1 for transfer in the thin surface layer of material’s particles. D values extracted from GITT data are in consistency with those obtained from PITT: 3.5–5.8 × 10^?10 and 0.9–5 × 10^?10 cm² s^?1 (for the current and currentless mode, respectively). The D values obtained from EIS data were 5.5 × 10^?10 cm² s^?1 for lithiated (at a potential of 3.5 V) and 2.3 × 10^?9 cm² s^?1 for delithiated (at a potential 4.1 V) forms. CV evaluation gave close results: 3 × 10^?11 cm² s^?1 for anodic and 3.4 × 10^?11 cm² s^?1 for cathodic processes, respectively. The use of complex experimental measurement procedure for combined application of the EIS, PITT, and GITT methods allowed to obtain thermodynamic E,c dependence of Li₃V₂(PO₄)₃ electrode, which is not affected by polarization and heterogeneity of lithium concentration in the intercalate.     

Synthesis and electrochemical characterization of graphene nanoflakes and LiFe<Subscript>0.97</Subscript>Ni<Subscript>0.03</Subscript>PO<Subscript>4</Subscript>/C for lithium-ion battery

The graphene nanoflakes and olivine-type LiFe_0.97Ni_0.03PO₄/C (LFNP3/C) samples have been synthesized as anode and cathode materials, respectively. Physicochemical characterization of the graphene nanoflakes and LFNP3/C material were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD patterns reveal the formation of the pure phase of both the synthesized samples. SEM micrographs disclose the formation of spherically shaped nanosized particles for LFNP3/C while graphene shows flake-type morphology. CR2032 half and full coin cells were assembled for electrochemical testing of the synthesized samples. Cyclic voltammetry (CV) results indicate that the graphene-based half-cells, i.e., GN1H and GN2H, possess reduction peak/plateau around 0.17 V while LFNP3/C cathode shows discharging voltage plateau at 3.4 V vs. Li/Li⁺. The discharge capacities were found to be 700, 900, and 153 mAhg^?1 for GN1H, GN2H, and LFNP3/C half-cells vs. Li/Li⁺, respectively. Among full cells, LFPGN1F with γ = 0.75 (mass/capacity balancing factor) shows better charging/discharging profile at each C-rate as compared to LFPGN2F with γ = 0.55. LFPGN1F delivered an initial discharge capacity of around 154 mAhg^?1 at 0.1C and even at a high discharge rate of 1C, it retained ~97% of the discharge capacity as compared to the initial cycle at the same rate.     

High-temperature complex impedance and modulus spectroscopic studies of doped Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> ferroelectric ceramics

Lead-free Na_0.5Bi_0.5TiO₃ (NBT) and (1 ? x)Na_0.5Bi_0.5TiO₃ + xBaTiO₃ with x = 0.1 and 0.2 (where x = 0.1 and 0.2 are named as NBT1 and NBT2, respectively), (1 ? y)Na_0.5Bi_0.5TiO₃ + yBa_0.925Nd_0.05TiO₃ with y = 0.1 and 0.2 (where y = 0.1 and 0.2 are named as NBT3 and NBT4, respectively)-based relaxor ferroelectric ceramics were prepared using the sol-gel method. The crystal structure was investigated by X-ray diffraction (XRD) at room temperature (RT). The XRD patterns confirmed the presence of the rhombohedral phase in all the samples. The electrical properties of the present NBT-based samples were investigated by complex impedance and the modulus spectroscopy technique in the temperature range of RT–600 °C. The AC conductivity was found to increase with the substitution of Ba²⁺ ions to the NBT sample whereas it significantly decreased with the addition of Nd³⁺ ions. The more anion vacancies in Ba-added samples and the lower anion vacancies in Nd-added samples were found to be responsible for higher and lower conductivities, respectively.