A NaVO3/Gr composite exhibits enhanced electrochemical performance in SIB.

Ferroelectric oxides with large bandgaps have restricted applications in photovoltaic and photocatalytic fields. Based on recent experiments with the ferroelectric compound, LiSbO3, the stability and optoelectronic properties of a new ferroelectric compound, namely Li2SbBiO6, are investigated in this study. The calculated results demonstrate that Li2SbBiO6 satisfies the stability conditions of the elastic coefficients and phonon dynamics. Li2SbBiO6 maintains the ferroelectric polarization strength of LiSbO3 and significantly reduces the bandgap, and thus has been explored for applications in photovoltaic and photocatalytic fields. Li2SbBiO6 is a new potential ferroelectric oxide for harvesting visible light owing to its suitable bandgap and a large hole-electron effective mass ratio.

为提高LiVO3的电化学性能,通过简易溶液法制备了一系列LiVO3/石墨烯(质量分数分别为0,3％,5％,7％)复合材料.借助X射线衍射(XRD)、扫描电镜(SEM)、电化学交流阻抗测试(EIS)、恒电位间隙滴定(GITT)等表征技术,考察石墨烯包覆以及石墨烯的含量对LiVO3的晶体结构、微观形貌和电化学性能的影响.结果表明:通过溶液法可实现石墨烯包覆,石墨烯包覆能细化晶粒;随着石墨烯含量的增大,样品颗粒尺寸减小,锂离子扩散系数增大,材料电子导电率提高,因而LiVO3/石墨烯复合材料的倍率性能和循环性能都有一定程度的提升.石墨烯质量分数为5％的样品LVO/Gr-3综合性能最优,首次放电容量可达338 mAh/g,在200 mA/g的电流下循环100次,容量保持率为71.4％.

High performance anode materials are essential in realization of sodium-ion batteries. In this work, orthorhombic β-NaVO3 with nano structure was prepared by a simple solution method and investigated as anode material for sodium-ion batteries for the first time. β-NaVO3 exhibits an initial discharge capacity of 356 mAh/g at low current density and a high rate capability of 50 mAh/g at 400 mA/g. Enhanced performance were realized in β-NaVO3 /Gr composite with initial discharge capacity of 576 mAh/g at low current density and excellent cycle stability of 71% capacity retention after 100 cycles at the current density of 300 mA/g. The diffusion coefficient of sodium in β-NaVO3 was measured from galvanostatic intermittent titration techinique (GITT) (in the range of 10-16 to 10-10 cm2 s-1 ) and electrochemical impedance spectroscopies (1.8×10-16 cm2 s-1 ). Ex -situ XRD and ex- Raman results reveal that the orthorhombic crystal structure of β-NaVO3 transformed to an amorphous phase after the initial charging-discharging process.

我们通过氨水辅助的溶胶-凝胶法制备了锂离子电池正极材料LiVO3,X射线衍射图谱表明制备所得材料为纯相LiVO3,通过扫描电子显微镜观察到材料颗粒和纳米线混合的形貌.其电化学性测试结果表明,该方法制备的材料在150 mA/g的电流下,可逆容量保持为189 mAh/g,且经过20次循环后比容量保持率为98％,材料具有优异的循环性能.

通过溶胶-凝胶法制备了Cr掺杂化合物Li3V0.97Cr0.03O4,Cr掺杂样品仍然保持Li3VO4的正交晶系结构.研究表明材料的电化学性能在大于300 mA/g的放电电流下,Li3V0.97Cr0.03O4具有较未掺杂样品更优异的循环和倍率性能,在1200 mA/g的电流下,放电比容量为248 mAh/g,20次循环后比容量未见衰减.

Li2Mn1-x Fe x (PO3)4 (x = 0, 0.2, 0.4, 0.6, 0.7) solid solution phase has been successfully prepared via solid-state reaction. The Rietveld refinement results indicate that the Li2Mn1-x Fe x (PO3)4 (x = 0, 0.2, 0.4, 0.6, 0.7) solid solutions with orthorhombic structure can be obtained and the lattice parameters (including a, b, c, and V) decrease with the increasing of Fe concentration. Partial substitution of manganese with iron enhances the electrochemical performance; there, the discharge-specific capacity of the samples obviously increases from 21 mAh/g for x = 0 to 59 mAh/g for x = 0.7, which is 85 % capacity of that one lithium removal. The cyclic voltammetric (CV) curves present the Mn2+/Mn3+ redox couple situated at 4.6 and 1.8 V and Fe2+/Fe3+ redox couple located at 4.3 and 2.3 V, which can be observed in cathodic and anodic sweeps. Such a low discharge potential value for M2+/M3+ redox couple may be attributed to the zigzag [(PO3)1−] n chains in this structure.

Phase equilibria in the ternary Li2O–FeO–SiO2 system have been studied by means of X-ray powder diffraction. The experimental results show that no new lithium ferrous silicate compounds can be found in our experimental condition which may be a candidate cathode material for LIBs. The Li2O–FeO–SiO2 system can be characterized by the existence of 9 three-phase regions. In Li2O–SiO2 binary system, Li2SiO3 and Li4SiO4 are purely synthesized by solid-state reactions; other new information includes the electrochemical properties of Li2SiO3 and Li4SiO4 compounds, where the electrochemical test indicated that initial discharge-specific capacities can reach to 136 and 129 mAhg−1, respectively. Enhanced performance was exhibited after carbon coating. The initial discharge-specific capacities of carbon-coated Li2SiO3 and carbon-coated Li4SiO4 compound can reach to 230 and 220 mAhg−1 respectively. Our results show that Li2SiO3 and Li4SiO4 samples have better capacity retention except for the first discharge. No significant change can be seen in ex situ XRD patterns for Li2SiO3/C, while the lithium-ion insertion/extraction reaction may exist in Li4SiO4/C as forming solid solutions (nominated Li4+x SiO4).

A new Co-base sodium metaphosphate compound, NaCo(PO3)3, has been synthesized here by solid-state method. The crystal structure is refined by the Rietveld method, and the results reveal that NaCo(PO3)3 has an orthorhombic structure with the space group of P2 1 2 1 2 1 and lattice parameters of a = 14.2453(2) Å, b = 14.2306(1) Å, and c = 14.2603(2) Å. Its typical morphology and chemical composition are confirmed by scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). The valence states of all elements and the internal/external vibrational modes of NaCoP3O9 compound are measured by X-ray photoelectron and vibrational spectrum, where a typical feature of the (PO3)− polyanion group is observed. Meanwhile, the electrochemical properties of NaCo(PO3)3 cathode for sodium-ion batteries are also elevated and an initial discharge capacity of 33.8 mAh/g can be obtained at 0.05 C within 1.5–4.2 V. After 20 cycles, a discharge capacity of 26.7 mAh/g can be obtained and a well-kept oxidation–reduction plateau is still observed for NaCo(PO3)3 cathode, indicating the good reversibility of this metaphosphate electrode.

In this paper, we have prepared the carbon-coated Li9V3(P2O7)(3)(PO4)(2) (LVPP/C) composite via a simple carbon thermal reduction and its lithium inserted-extracted mechanism are systematically investigated. LVPP/C cathode can keep a reversible capacity of 100.6 mAhg(-1), 98.7% of the initial discharge capacity, after 50 cycles within 2.5 V-4.6 V, while an obviously capacity-fading is observed within 2.5 V-4.8 V. Meanwhile, the LVPP/C anode delivers a well rate capability and, a reversible capacity of 94.5 mAhg(-1) (1.0-2.5 V) can still be retained after 60 cycles, ranging from 0.1C to 2C and finally in 0.1C succession. A good preservation of the LVPP structure is observed during the discharge-charge process by in-situ XRD and an intercalation reaction mechanism is also confirmed for LVPP/C anode here for the first time. At last, a novel symmetrical full battery by using LVPP/C as both cathode and anode simultaneously has been successfully assembled. The investigation shows that this symmetrical cell, with an average voltage of 2.5 V, can deliver a reversible capacity of 59.8 mAhg(-1) after 30 cycles at 0.1C. (C) 2016 Elsevier Ltd. All rights reserved.

Safety behaviors of a 32 Ah prismatic lithium-ion battery are investigated under abusive charge conditions by monitoring the internal and external cell temperature variation. Results show that the cell internal temperature can reach 235 degrees C before firing, which is almost 140 degrees C higher than the cell external temperature. Although the cell resistance increases abruptly due to electrolyte oxidization when the cell is firstly overcharged to its maximum voltage (5.10 V), the cell internal temperature keeps a low temperature of 50 degrees C without notable temperature rise. However, the cathode/electrolyte interface becomes highly reactive as the cell is further overcharged. Cell internal temperature goes up to more than 200 degrees C accompanied with massively gas production when the cell is overcharged to 180% SoC. Post-overcharge analysis on both cathode and anode indicates that lithium plating during overcharge is the major cause responsible for thermal runaway because the observed cell temperature is well above the melting point of lithium metal. (C) 2015 Elsevier Ltd. All rights reserved.

The phase relations of Li2O-MnO-P2O5 ternary system under reducing atmosphere have been systematically investigated by means of X-ray diffraction. Inferior to what we expected, no other new lithium manganese phosphates exist within the Li2O-MnO-P2O5 ternary system under the reducing atmosphere. A high-pressure phase Mn-3(PO4)(2) with graftonite Fe-3(PO4)(2)-type structure can be easily obtained in the MnO-P2O5 system under the ordinary solid-state reaction conditions in H-2/Ar atmosphere and its detail structure is presented. In addition, the solid solubility of Li1+xMn1-xPO4 is determined as -0.05 <= x <= 0.03. The lattice parameters and electrochemical properties of Li1+xMn1-xPO4 with x content are investigated. The electrochemical test results show that excess Li-ion (x > 0) or the excess Mn-ion (x < 0) in LiMnPO4 has an unfavorable effect on the electrochemical properties caused by the deterioration of the lithium diffusion along the one-dimensional tunnels. (C) 2015 Elsevier B.V. All rights reserved.

The phase relation of Li2O–FeO–P2O5 ternary system under the 95 %Ar + 5 %H2 atmosphere has been systematically investigated by X-ray diffraction (XRD), and there exist 8 binary compounds, 4 ternary compounds, 2 two-phase regions, and 17 three-phase regions. No other new lithium ferrous phosphates can be existed in the Li2O–FeO–P2O5 ternary system under the 95 %Ar + 5 %H2 atmosphere. In this system, the Li1+x Fe1−x PO4 solid solution phase with the homogeneous range of −0.15 ≤ x ≤ 0.06 is determined. Their corresponding lattice parameters are obtained by the refinement results, and the results show that the lattice parameters (a, b, c, V) vary linearly with the increasing amount of excess Li-ion (x > 0) or with the increasing amount of excess Fe-ion (x < 0). The phase diagram determined in this paper can provide more information about the phase relation of Li2O–FeO–P2O5 ternary system and serve as a guide for the future investigation of lithium iron phosphates in this system.

The subsolidus phase relations in the Li2O-CoO-P2O5 system have been systematically investigated by means of X-ray diffraction (XRD) pattern. The results have confirmed 6 binary compounds, 5 ternary compounds and 17 three-phase regions. In this system, the solid-state synthesized process (under Ar/H-2 atmosphere) of LiCoPO4 using the Li2CO3, Co3O4 and NH4H2PO4 as raw materials has been investigated. The result indicates that the single-phase LiCoPO4 compound can be formed stably within the temperature range between 350 degrees C and 700 degrees C, while several intermediate or decomposition compounds have been detected outside this sintering temperature range. The electrochemical properties of these purephase LiCoPO4 powders obtained at different temperature are compared by galvanostatic charge/discharge mode and at the meantime, we also demonstrated for the first time that Li6Co5(P2O7)(4) electrode is electrochemically active. (C) 2015 Elsevier B.V. All rights reserved.

AbstractThe phase diagram of the title system under reducing atmosphere (95% Ar/5% H2) is investigated.

The carbon-coated Li3VO4 (Li3VO4/C) sample was synthesized by simple solid-state reaction method using glucose as carbon source. Rietveld refinement, XPS and element analysis results show that, though it is synthesized in the presence of carbon and reducing atmosphere, both the single-phase Li3VO4/C and the valence of vanadium of +5 can be retained. The SEM and TEM images reveal that Li3VO4/C composite has uniform particles with size less than 1 mu m. Electrochemical testing results show that Li3VO4/C at high operation temperatures holds both higher specific capacity and cyclic performance than that of low temperatures. The initial discharge capacities for the Li3VO4/C electrodes at temperatures of -20, 0, 25 and 50 degrees C are 312, 600, 760 and 721 mAh g(-1) with the coulombic efficiency of 40.45%, 72.09%, 74.34% and 73.41%, respectively. Even at a high discharge/charge rate of 15 C, the capacities of the Li3VO4/C electrodes at -20, 0, 25 and 50 degrees C still can retain about 20, 120, 370 and 450 mAh g(-1), respectively. The CV results demonstrate that the higher operation temperature can decrease the voltage polarization of the electrode, thus benefit the electrochemical performance of the Li3VO4/C electrode. In addition, the EIS results indicate that larger charge-transfer resistance and smaller lithium diffusion coefficient can be obtained at low operation temperatures, which should be one of the major reasons for its poor low-temperature performance of the Li3VO4/C electrode. (C) 2015 Elsevier B.V. All rights reserved.

A metaphosphate NaFe(PO3)(3) compound has been obtained by solid state method here. This title compound belongs to the orthorhombic structure with the space group of P212121 (No. 19) and lattice parameters of a = 143390(3) angstrom, b = 143374(2) angstrom, c = 14.3642(1) angstrom. Its structure can be described as made up of infinite (PO3)(1-) chains connected by FeO6 octahedra, while the monovalent Na cations are located in the tunnels determined by the connection of PO4 tetrahedrons and FeO6 octahedrons. Besides, the morphology, vibrational spectra, magnetic and sodium deinsertion/insertion properties of NaFe(PO3)(3) compound are also presented and discussed here for the first time, which can provide more information about the physicochemical properties of this metaphosphate compound. (C) 2015 Published by Elsevier B.V.

The carbon-coated alpha-Na2MoO4 nanoplate sample was fabricated via a facile sol-gel method involving the subsequent annealing under a reducing atmosphere to decompose the organic carbon source. X-ray diffraction with Rietveld refinement, high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) results show that single-phase alpha-Na2MoO4 can be obtained even under the presence of carbon and reducing atmosphere. When evaluated as an anode material for lithium-ion batteries, the carbon-coated alpha-Na2MoO4 nanoplate electrode displays a discharge and recharge capacity of 806mAh g (1) and 409mAh g (1) respectively in the first cycle, while a reversible discharge-charge capacity of 350mAh g (1) can be retained after 30 cycles at 30mAh g (1). A capacity of similar to 320mAh g (1) at 30mAh g (1) can still recover after 50 cycles even following the discharge/charge process with the high current density of 480mAh g (1). Meanwhile, carbon-free and carbon-coated alpha-Na2MoO4 powders fabricated via a solid state reaction were also prepared for comparison. Furthermore, the structure change of alpha-Na2MoO4 and its Li storage mechanism upon lithiation and delithiation process are studied by ex- situ XRD and TEM in below. (C) 2014 Elsevier Ltd. All rights reserved.

A series of Co-doped Li9V3−xCox(P2O7)3(PO4)2/C (x=0.00–0.10) compounds have been prepared by sol–gel method and the Rietveld refinement results indicate that pure-phase Li9V3−xCox(P2O7)3(PO4)2/C (x=0.00–0.10) compounds with trigonal structure can be obtained. Their electrochemical performance has been investigated and the results show that, although the initial specific capacity decreased with Co doping at a lower current rate, both cycle performance and rate capability have excited improvement with proper Co-doping content. Li9V2.96Co0.04(P2O7)3(PO4)2/C compound presents the best cyclic ability and rate performance. The enhancement of cyclic ability and rate performance may be attributed to enhanced specific surface area and improved lithium-ion diffusion during the proper amount of Co-doping (x=0.04) in V sites.