Search

Hard carbon and microcrystalline graphite (MG) core-shell structured composite materials are prepared, and their electrochemical performances as an anode material for lithium-ion batteries are reported. The composite materials are obtained by coating a mixture of MG and pitch onto hard carbon particles, followed by heating at 1200 °C under an argon atmosphere for 1 h. The surface of the hard carbon is subsequently covered with a layer of the MG/pitch carbon composite. In the coating layer of the MG/pitch carbon composite, the MG particles are divided into nanoscale graphite sheets, and uniformly dispersed within the pitch of carbon matrix. The composite particles have a rounded shape, especially when the content of MG increases, which can improve their packing density compared to hard carbon having sharp edges. Anodes prepared from these composite materials exhibit enhanced electrochemical performances, including a high reversible capacity, high initial coulombic efficiency, high charging/discharging rate capability, and desirable cycling stability. [ABSTRACT FROM AUTHOR]

Abstract: A shell/core Co-incorporated LiMn2O4 cathode material was synthesized by a facile modified sol–gel process, using highly dispersed Mn3O4 nanoparticles as the Mn source. Structural characterization revealed that the shell layer, which was 5–10nm thick, and composed of spinel LiMn1.83Co0.17O4, grew homogeneously on the spinel LiMn2O4 core with a size of ~50nm. Electrochemical results showed that electrochemical performance of the shell/core cathode material compared favorably with that of the Co-doped LiMn2O4 counterparts. Also its rate capability and cycling performance were apparently superior to those of pristine LiMn2O4 synthesized under the same conditions. The shell/core cathode material exhibited a discharge capacity of 127mAhg−1 at a current rate of 0.5C (where 1C=148mAg−1), and retained a capacity of 103mAhg−1 at 10C, showing 81% capacity retention. After 200 cycles at 1C and 25°C, it delivered a capacity of 123mAhg−1, retaining 98% of its initial capacity. After 100 cycles at 1C and 55°C, it showed a capacity of 118mAhg−1, preserving 94% of its initial capacity. Its excellent electrochemical performance along with the facile synthesis process allowed the shell/core cathode material to serve as a promising cathode for high-performance Li-ion batteries. [Copyright &y& Elsevier]

Abstract: Olivine structured LiFePO4/C cathode was synthesized via a freeze-drying route and followed by microwave heating with two kinds of carbon sources: PEG-4000 (organic) and Super p (inorganic). XRD patterns indicate that the as-prepared sample has an olivine structure and carbon modification does not affect the structure of the sample. Image of SEM shows a uniform and optimized particles size, which greatly improves the electrochemical properties. TEM result reveals the amorphous carbon around the surface of the particles. At a low rate of 0.1C, the LiFePO4/C sample presents a high discharge capacity of 157.8mAhg−1 which is near the theoretical capacity (170mAhg−1), and it still attains to 149.1mAhg−1 after 200 cycles. It also exhibits an excellent rate capacity with high discharge capacities of 143.2mAhg−1, 137.5mAhg−1, 123.7mAhg−1 and 101.6mAhg−1 at 0.5C, 1.0C, 2.0C and 5.0C, respectively. EIS results indicate that the charge transfer resistance of LiFePO4 decreases greatly after carbon coating. [Copyright &y& Elsevier]

Abstract: With an aim to broaden the understanding of the factors that govern electrochemical performance of lithium-rich layered oxide, the influences of insufficient lithium on reversible capacity, cyclic stability and rate capability of the oxide as cathode of lithium ion battery are investigated in this study. Various concentrations of lithium precursor are introduced to synthesize a target composition Li[Li0.13Ni0.30Ni0.57]O2, and the resulting products are characterized with inductively coupled plasma spectrum, scanning electron microscope, X-ray diffraction, Raman spectroscopy, and electrochemical measurements. The results indicate that the lithium content in the resulting oxide decreases with reducing the concentration of lithium precursor from 10wt%-excess lithium to stoichiometric lithium, due to insufficient compensation for lithium volatilization during synthesis process at high temperature. However, all these oxides still exhibit typically structural and electrochemical characteristics of lithium-rich layered oxides. Interestingly, with decreasing the Li content in the oxide, its reversible capacity increases due to relatively higher content of active transition-metal ions, while the cyclic stability degrades severely because of structural instability induced by higher content of Mn3+ ions and deeper lithium extraction. [Copyright &y& Elsevier]

• Amorphisation and recrystallisation technique was employed for simulated synthesis. • Composite nanosheets (2D) and nanoporous (3D) materials were generated. • XRDs and microstructures showed presence of layered-spinel intergrowths. • Bulk and nanoporous LiMn 2 O 4 can withstand stresses associated with cycling. Mechanical stresses originate from various factors, such as mechanical load, operational vibration, diffusion during cycling, and thermal expansion coefficients. Li-ion intercalation causes lattice expansion that will impart stress on neighbouring regions and ion mechanical degradation within the layers, which leads to weaker battery performance and eventual failure. The current study reports on the advances in the simulated synthesis of nanosheet, nanoporous, and bulk ternary LiMn 2 O 4 spinel from an atomic perspective, during which amorphisation and recrystallisation techniques were employed and the microstructures reflect the spinel and layered heterostructures. Analysis of mechanical and structural properties is carried out via stress-strain, x-ray diffraction (XRD), radial distribution functions (RDF) graphs, and molecular graphics systems before and after subjection to strain. Subsequently, molecular graphics for the nanoporous material indicated a rigid tunnel framework, whilst the bulk framework showed tilting upon compression. These structural deformations within the bulk might prevent efficient Li transport into/out of the electrode materials. [ABSTRACT FROM AUTHOR]

Abstract: Porous separator functions to electrically insulate the negative and positive electrodes yet communicate lithium ions between the two electrodes when infiltrated with a liquid electrolyte. The separator must fulfill numerous requirements (e.g. permeability, wettability, and thermal stability) in order to optimize the abuse tolerance and electrochemical performance of a battery. Non-woven mat separators have advantages such as high porosity and heat resistance. However, their applications in lithium ion batteries are very limited as their inadequate pore structures could cause accelerated battery performance degradation and even internal short. This work features the development of thermally stable non-woven composite separators using a low cost paper-making process. The composite separators offer significantly improved thermal dimensional stability and exhibit superior wettability by the liquid electrolyte compared to a conventional polypropylene separator. The open porous structures of the non-woven composite separators also resulted in high effective ionic conductivities. The electrochemical performance of the composite separators was tested in coin cells. Stable cycle performances and improved rate capabilities have been observed for the coin cells with these composite separators. [Copyright &y& Elsevier]

Abstract: Electrochemical impedance spectroscopy (EIS) has been widely utilized as an experimental method for understanding the internal mechanisms and aging effect of lithium ion battery. However, the impedance interpretation still has a lot of difficulties. In this study, a multi-physics based EIS simulation approach is developed to study the cycling effect on the battery impedance responses. The SEI film growth during cycling is coherently coupled with the complicated charge, mass and energy transport processes. The EIS simulation is carried out by applying a perturbation voltage on the electrode surface, and the numerical results on cycled cells are compared with the corresponding experimental data. The effect of electrical double layer, electrode open circuit potential as well as the diffusivity of binary electrolyte are simulated on battery impedance responses. The influence of different SEI growth rate, thermal conditions and charging-discharging rate during cycling are also studied. This developed method can be potentially utilized for interpretation and analysis of experimental EIS results. [Copyright &y& Elsevier]

Solvothermal approach is used to synthesize LiMn0.9Fe0.1PO4 (LMFP) nanomaterial for Li-ion batteries (LIBs). Experimental parameters such as feeding sequences, reaction time and reaction temperature are discussed and the obtained LMFP are characterized by XRD, SEM and TEM. To understand the formation of LMFP, a reaction mechanism is proposed. The proposed mechanism indicates that the suitable concentration of MLi (M = Fe, Mn) antisite defect can improve the electrochemical performance of the material. The charge–discharge data of obtained LMFP shows that the LiMn0.9Fe0.1PO4 material synthesized at 180 °C for 4 h and then sintering with sucrose at 650 °C for 5 h under argon protection has the highest discharge capacity, which is 149.2 mAh g−1 at 0.1C rate. [ABSTRACT FROM AUTHOR]

To understand the influence of structure and atom sites on the electrochemical properties of Sn-based anode materials, the lithium intercalation-deintercalation mechanisms into SnNiCu and SnNiCu phases were studied using the first-principle plane wave pseudo-potential method. Calculation results showed that both SnNiCu and SnNiCu were unsuitable anode materials for lithium ion batteries. The Sn-based anode structure related to the number of interstitial sites, theoretical specific capacity, and volume expansion ratio. Different atom sites led to different forces at interstitial sites, resulting in variations in formation energy, density of states, and hybrid orbital types. In order to validate the calculated model, the SnNiCu alloy anode material was synthesized through a chemical reduction-codeposition approach. Experimental results proved that the theoretical design was reasonable. Consequently, when selecting Sn-based alloy anodes, attention should be paid to maximizing the number of interstitial sites and distributing atoms reasonably to minimize forces at these sites and facilitate the intercalation and deintercalation of lithium ion. [ABSTRACT FROM AUTHOR]

Abstract: Fe2O3-graphite (Fe2O3-G) composites have been facilely and effectively synthesized via ball milling. Structural features and electrochemical properties of the Fe2O3-G composites as anodes for lithium-ion batteries are investigated. The Fe2O3-G composites benefit from the close contact of nanocrystalline Fe2O3 with the graphite matrix, which improves the electronic conductivity and restrains the volume variation during cycling. The composite with 20% graphite shows the highest reversible capacity up to 491.1 mAh g−1 after 55 cycles with good rate capability. Due to the superior electrochemical performance, the Fe2O3-G composites prepared via ball milling could be promising as anode materials with high capacity, low-cost for lithium-ion batteries. [Copyright &y& Elsevier]

Highlights: [•] Carbon-coated V2O5 was synthesized in a scalable and easy method using a carbon form as a template. [•] Electrochemical performance of the carbon-coated V2O5 was significantly improved compared to nano-sized V2O5. [•] The carbon-coated V2O5 calcined at 400°C showed enhanced capacity retention and rate capabilities. [ABSTRACT FROM AUTHOR]

Abstract: Amorphous hydrated iron (III) phosphate has been synthesized by a coordinate precipitation method from equimolecular Fe(NO3)3 and (NH4)2HPO4 solutions at an elevated temperature. Hydrated iron (III) phosphate samples and the corresponding LiFePO4/C products were characterized by XRD and SEM. The electrochemical behavior was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The LiFePO4/C fabricated from as-synthesized FePO4 delivered discharge capacities of 162.5, 147.3, 133.0, 114.7, 97.2, 91.3 and 88.5mAhg−1 at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, 3C and 4C with satisfactory capacity retention, respectively. [Copyright &y& Elsevier]

Abstract: Uniform Fe3O4/PPy composite nanospheres (FPCNs) with Fe3O4 nanoparticles embedded in PPy nanospheres (∼200nm) were prepared by a hydrothermal process followed by an ultrasonication assisted polymerization. For the first time, FPCNs were used as anode for lithium ion batteries, demonstrating enhanced electrochemical performance with high reversible capacity (544mAhg−1 after 300 cycles), remarkable capacity retention (98% of the initial capacity after 300 cycles), as well as good rate capability (332 mAh g−1 at 2000mAg−1). The spherical PPy matrix in FPCNs possesses three functions: 1) buffering the structural variation of Fe3O4 nanoparticles during charging/discharging process; 2) preventing the aggregation of Fe3O4 nanoparticles; 3) avoiding the direct contact between Fe3O4 nanoparticles and the electrolyte. The results observed in this study may shed some light on the investigation of MOx/polymer composite electrode materials. [Copyright &y& Elsevier]

Abstract: The interconnected LiMn2O4 fibers have been synthesized by using easily accessible cellulose filter paper as template. SEM and TEM images indicate the fibers are porous and constructed by nano grains. Without surface modification, the fibers exhibit superior high-rate capabilities and good cycling stability. The discharge capacities at 0.5C and 20C are 123 and 101mAhg−1 respectively, and about 78.9% of its initial capacity can be retained after 1000 cycles at 5C. The superior rate performance and excellent cyclability can be attributed to the porous fiber structure, single crystalline and exposed {111} facet. [Copyright &y& Elsevier]

Abstract: LiAlO2-coated LiNi1/3Mn1/3Co1/3O2 powders were prepared by a sol–gel method associated with ultra-sonication, and the obtained LiAlO2-coated LiNi1/3Mn1/3Co1/3O2 was investigated as positive electrode materials for all-solid-state batteries with sulfide-based solid electrolytes. All-solid-state lithium batteries were assembled with the obtained LiAlO2-coated LiNi1/3Mn1/3Co1/3O2 powders and with amorphous Li3PS4 as solid electrolytes. The charge–discharge cycle performance of the all-solid-state cells was improved by the LiAlO2-coating on LiNi1/3Mn1/3Co1/3O2 powders. The LiAlO2 coating was effective in suppressing an increasing of the interfacial resistance between the LiNi1/3Mn1/3Co1/3O2 electrode material and the sulfide based solid electrolyte, Li3PS4, during charge–discharge cycling. The battery with the 1.0mol% LiAlO2-coated LiNi1/3Mn1/3Co1/3O2 showed an initial discharge capacity of 134 mAhg−1 and the battery retained the capacity more than 124 mAhg −1 even after 400 charge–discharge cycles at a current density of 11 mAg −1 at room temperature. [Copyright &y& Elsevier]

Highlights: [•] To improve the electrochemistry of LiMn2O4 by partial substitution of Li by Na. [•] Na-substitution can improve the cycling stability. [•] A new, low-cost method to improve its electrode properties due to low-cost of Na resource. [ABSTRACT FROM AUTHOR]

Highlights: [•] We prepared three types of SnO2/TiO2 composite nanofibers via a facile electrospinning method. [•] Both SnO2 and TiO2 in these fibers are identified as a rutile phase by XRD and Raman Spectroscopy. [•] Composite nanofibers show superior electrochemical performance to pure TiO2 and SnO2fibers. [•] The enhanced cycling stability is due to the space confinement provided by the stable TiO2 matrix. [ABSTRACT FROM AUTHOR]

A novel wet method of (NH4)3AlF6 coating was explored to enhance the electrochemical performance of Mn-based solid-solution cathode material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2. The X-ray powder diffraction patterns show that the coating material is pure-phase (NH4)3AlF6 and both pristine and coated samples can be indexed to hexagonal α-NaFeO2 layered structure with space group of R-3m. The field-emission scanning electron microscope images and the energy dispersive X-ray spectroscopy show that (NH4)3AlF6 is successfully coated on the surface of active particle. The (NH4)3AlF6 coated electrodes exhibit improved electrochemical performance, for instance, the initial charge-discharge efficiency was promoted by 5% (NH4)3AlF6 coating, the 1wt.% and 3wt.% coated electrodes deliver elevated cycling ability which is ascribed to the lower resistance between electrode and electrolyte as indicated by AC impedance measurement at different cycles. In addition, the coated-electrodes also give enhanced rate capability particularly for 1wt.% NAF-coated electrode performing surprising capacity of 143.4 mAh g−1 at 5C higher than that of 109.4 mAh g−1 for pristine electrode. Furthermore, the 1wt.% NAF-coated electrode also shows improved cycle and rate performance at 55°C. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we report on the development and demonstration of physically consistent three-dimensional models for Lithium Ion Battery (LIB) cells. The discharge behavior of a LIB is a multiphysics and multiscale problem that is simulated using coupled models for thermal, electrical, and electrochemical phenomena. The individual physics models and software are integrated into a new open computational framework for battery simulations which was designed to support a variety of modeling formulations and computer codes. Several cell configurations (unrolled cell, unrolled cell with current collectors, large capacity pouch cell, and cylindrical cell) that show the importance of coupled simulations are simulated using this approach and discussed. A validation study is presented for the pouch cell discharged under high rates to demonstrate the accuracy of the proposed modeling framework. [Copyright &y& Elsevier]

Abstract: Nano-Si embedded Si7Ti4Ni4 is synthesized with the melt spinning method, which is facile, and applicable to mass-production. Si7Ti4Ni4, the buffer material, is electrochemically inactive toward lithium. Nevertheless, Si7Ti4Ni4 has good electrical conductivity, in the order of 105 S m−1, which is more conductive than amorphous carbon that is usually used as a coating material for active material. Furthermore, the surrounding grain boundaries of Si7Ti4Ni4 effectively relax volume expansion of Si. Therefore, it plays a critical role in maintaining the structure of electrode and the integrity of active materials. As a result, nano-Si embedded in Si7Ti4Ni4 shows outstanding cycle performance over 50 cycles at 400 mA g−1, and it maintains 86% of its specific capacity at 3200 mA g−1, compared with that of 400 mA g−1. This indicates that nano-Si embedded in Si7Ti4Ni4 can be a promising anode material for lithium ion batteries. [Copyright &y& Elsevier]

Abstract: LiVO3 materials are synthesized by combustion method with oxalic acid as fuel. Owing to its relatively low crystallization and small particle size, the LiVO3 calcined at 450 °C for 2 h displays optimal electrochemical performances, delivering a high discharge capacity of 298.4 mAh g−1 and 262.5 mAh g−1 between 1.0 and 3.5 V at a current density of 50 mA g−1 and 500 mA g−1 respectively, and exhibiting good cyclic stability. In this work, the chemical diffusion coefficient of Li+ (D Li+) in the LiVO3 electrode is determined by electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). The value calculated by EIS is in the range of 10−9–10−8 cm2 s−1, while it calculated by GITT is 10−9.5–10−8 cm2 s−1. [Copyright &y& Elsevier]

Abstract: The structure and electrochemical properties of epitaxial thin film LiNi0.5Mn1.5O4 electrodes are investigated for lithium ion secondary batteries applications. The orientation and thickness of the LiNi0.5Mn1.5O4 films are controlled by changing the substrate orientation and the pulse laser deposition time, respectively. The lattice parameters of the films increase with film thickness and the manganese valence decreases without any change in the nickel valence. Regardless of their orientation, all the films exhibit reversible capacities of 80–130 mAh g−1. The dependence of the discharge capacity on film thickness indicates a nanosize effect. The electrochemical properties of the high voltage spinel system are significantly dependent on their electronic properties, lattice orientations, and film thicknesses of the electrodes. [Copyright &y& Elsevier]

Abstract: The effects of graphene and C coating modifications on electrochemical performance of silicon nanoparticle (SiNP)/graphene composite anode were investigated. Graphene with varying sheet sizes (238, 160 and 113 nm) were used as an anode material where a cycling performance dependence on the sheet size (edge sites and sheet disorder) was observed. Temperature-dependent N doping of graphene resulted in graphene with N (5.97% w/w) presenting three binding configurations: 72.1% pyridinic N, 22.4% pyrrolic N and 5.5% graphitic N. The nitrided graphene displayed improved cycling capacity and minimized performance decay, principally due to the pyridinic N. Galvanostatic cycling using increasing current density rates (500–2500 mA g−1) of SiNP composites with C coating/deposition showed improvements in both capacity retention and rate performance. A polyacrylonitrile (PAN)-based coating scheme was used to produce a N-containing (2.20%) C coating which displayed the best high performance improvements, attributable to the minimization of direct solid-electrolyte interphase (SEI) formation and improvement in the conduction path. Optimization of the methods to achieve the best modification characteristics might enable performance improvements that maximize the capabilities of the materials. [Copyright &y& Elsevier]

Highlights: [•] MnCo2O4 nanowire array is prepared by a fast and facile hydrothermal method. [•] MnCo2O4 nanowire array exhibits noticeable pseudocapacitive properties. [•] The as-prepared nanowire array is also a promising material for Li-ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: Li-excess Li[Li0.18Ni0.15Co0.15Mn0.52]O2 layered cathode material is prepared by the sol-gel method. The material is aged in a LiPF6 based electrolyte and then is subjected to a series of structural and electrochemical analyses. X-ray diffraction shows that aging in electrolyte does not change the C2/m ordering of the material crystal lattice. But the surface of the material is etched by the electrolyte which is confirmed by transmission electron microscope and Raman scattering. This causes dissolution of some transition metal elements (especially Ni and Co) and formation of a spinel-like surface layer. Also, some by-products resulted from the electrolyte decomposition are detected on the surface of the material. Electrochemical impedance spectroscopy shows that aging in electrolyte severely hinders the electrochemical kinetics of the material. Cyclic voltammetry indicates that the aged sample has large electrode polarization which prevents the oxygen loss process and the activation of Mn4+ ions. As a result, the discharge capacity of the aged sample continuously increases from 134 mAh g−1 to 215 mAh g−1 in the initial several cycles. [Copyright &y& Elsevier]

Nanoporous Si was obtained by means of metal-assisted chemical etching. Li ion insertion-extraction was tested by voltammetric and galvanostatic electrochemical cycling in conventional 1 M LiPF ethylene carbonate/dimethyl carbonate EC/DMC and in 1 M LiTFSI 1-butyl-1-methyl-pyrrolidinium bis (trifluoromethyl) sulfonylimide [BMP] [TFSI] electrolytes. The nanoporous Si demonstrated high reversibility when cycled in 1 M LiPF EC/DMC electrolyte and showed superior activity compared to the non-structured sample. In contrast to the organic carbonate electrolyte, the material cycling in ionic liquid media showed reduced capacity and reversibility of the Li ion exchange. The latter results were discussed in terms of the high viscosity of the ionic liquid and ineffective cathodic passivation of the Si substrate in the ionic liquid-based electrolyte. Scanning electron microscopy imaging showed minor morphological changes due to the large volume change during Li insertion. No signs of crack formation and propagation were detected during the time span of the measurement. [ABSTRACT FROM AUTHOR]

Highlights: [•] Equilibrium potential curves for lithium intercalation electrode. [•] Activity correction and phase transition treatment for intercalation electrode. [•] Single particle model with effective diffusivity for lithium intercalation process. [•] Accurate simulation of discharge/charge prediction. [Copyright &y& Elsevier]

Abstract: LiMn2O4/LiNi0.5Mn1.5O4 composite with LiMn2O4 substrate and LiNi0.5Mn1.5O4 surface layer is proposed and prepared through sol–gel method. The resulting samples have been characterized by XRD and SEM measurements, in terms of which the impurity-free phase, uniform particle morphology have been proved. Charge–discharge test, XPS measurement combining with TEM observation confirm the existence of LiNi0.5Mn1.5O4 surface layer. Comparing with the bare LiMn2O4, the LiNi0.5Mn1.5O4-coated LiMn2O4 phase presents significantly improved cycling stability, especially at 60°C. Additionally, the rate capability and thermal safety of LiMn2O4 are greatly enhanced after being coated by LiNi0.5Mn1.5O4. ICP-AES measurement, structural analysis, and impedance experiment indicate that the improved electrochemical property of LiNi0.5Mn1.5O4-coated LiMn2O4 should be attributed to the alleviated dissolution loss of manganese, strengthened structural stability, and improved SEI property. [Copyright &y& Elsevier]

Highlights: [•] An improved sol–gel method was developed to synthesize Li3V2(PO4)3/C cathode material. [•] The pH value had an obvious influence on the morphologies of the prepared powders. [•] Powders prepared at pH=4 had uniform size distribution with little agglomeration. [•] Powders prepared at pH=9 had a small particle size. [•] Discharge capacity and cycle performance were improved by changing pH value. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fe2O3/graphene composite was prepared by a facile one-pot hydrothermal process. [•] Fe2O3 nanoparticles with diameter of 40–60nm anchors on the graphene sheets. [•] Fe2O3/graphene composite shows excellent lithium storage property. [•] Electrochemical impedance spectra were analyzed. [ABSTRACT FROM AUTHOR]

Abstract: The effects of Cr coating are studied with respect to improving the electrochemical characteristics of carbon-coated silicon monoxide anodes in rechargeable Li cells. The Cr coating is applied by ion beam sputtering. Analyses of the coating are carried out by EDX, SEM, TEM, and EPMA. A coin cell (CR2032) with a carbon-coated SiO x anode coated with Cr and a lithium cobalt oxide (LCO) cathode is assembled in an argon-filled glove box. The charged capacity of the Cr-coated SiO x –C/LCO cell is 1127 mAh g−1 in the 1st cycle at 0.1 C, while that of the uncoated SiO x –C/LCO cell is 956 mAh g−1. In addition, the Cr-coated SiO x –C/LCO cell has a discharged capacity of 733 mAh g−1, which is higher than that of the uncoated cell (635 mAh g−1). Furthermore, the discharge capacity retention ratio (100th:2nd) of the Cr-coated cell is 75% while that of the uncoated cell is 69%. The rate capability of the Cr-coated cell is superior to that of the uncoated cell. Cr has good electrical conductivity, enabling more Li ions to be stored in the Cr-coated cell than in the uncoated cell. Investigations into the improved electrochemical characteristics are carried out through the analyses of impedance, voltage profile, and cycle data. [Copyright &y& Elsevier]

First-principles prediction of enhancement in the electrochemical potential of LiCoO with aluminum substitution has been realized through earlier experiments. For safer and less expensive Li-ion batteries, it is desirable to have a similar enhancement for alternative cathode materials, LiFePO and LiCoPO. Here, we present first-principles density functional theory based analysis of the effects of aluminum substitution on electrochemical potential of LiCoO, LiFePO and LiCoPO. While Al substitution for transition metal results in increase in electrochemical potential of LiCoO, it leads to reduction in LiFePO and LiCoPO. Through comparative topological analysis of charge density of these materials, we identify a ratio of Bader charges that correlates with electrochemical potential and determine the chemical origin of these contrasting effects: while electronic charge from lithium is transferred largely to oxygen in LiCoO, it gets shared by the oxygen and Co/Fe in olivine phosphates due to strong covalency between O and Co/Fe. Our work shows that covalency of transition metal-oxygen bond plays a key role in determining battery potential. [ABSTRACT FROM AUTHOR]

Abstract: Undoped and 2 wt% vanadium (V5+) doped TiO2 samples are prepared in polyol medium by low-temperature solvothermal method. The as-prepared samples are annealed at 400 °C for 5 h in an air atmosphere to increase the crystallinity. The XRD pattern shows that pure anatase TiO2 is formed in both the doped and undoped samples. The maximum sizes of nanoparticles are found to be 300 nm and 15 nm with spherical shaped morphology for undoped TiO2 and V5+ doped TiO2 samples respectively. In addition, 2 wt% V5+ doped sample exhibits excellent electrochemical performance with high reversible specific capacity and excellent rate capability compared to the undoped case. This improvement can be attributed to the substitution of the Ti4+ ions by V5+ ions in the TiO2 lattice and create more Ti4+ vacancies in the lattice. This action may lead to the generation of apparently more number of free holes in the doped p-type semiconductor. Therefore, the increased hole concentration in the valence band can contribute to the electrical conductivity of the doped sample. Vanadium doping also influences the sample crystallinity and reduces the particle size, which provides a larger active surface area than that of undoped TiO2. [Copyright &y& Elsevier]

Abstract: Morphology-controlled LiMn0.9Fe0.1PO4 nanoplatelets as high performance cathode material for lithium ion batteries have been synthesized via a simple ascorbic acid-assisted solvothermal process in water-ethanol solvent. The phase structure and morphology of the products were characterized by XRD, SEM and TEM. The results reveal that decreasing the crystallite size along b-axis direction and increasing the surface area of (010) plane can shorten Li+ diffusion path and increase the electrode reaction activity. The LiMn0.9Fe0.1PO4 nanoplatelet holds the high capacity of 145 mA h g−1, 134 mA h g−1, 119 mA h g−1, 97 mA h g−1 and 68 mA h g−1 at 0.1 C, 0.5 C, 1 C, 5 C and 10 C respectively, and it can retain 75% of the initial reversible capacity even after 100 cycles at 10 C rate. [Copyright &y& Elsevier]

Abstract: An electrochemical model is developed to investigate capacity recovery methods for cycled lithium ion batteries. Different capacity recovery methods are evaluated and compared. The center recovery method for commercial batteries is found to be impractical because it causes severe solid surface concentration gradients which may harm the batteries. On the contrary, the center recovery method for novel batteries with porous current collector sheets is better than the bottom recovery method because smaller solid surface concentration gradients are detected and less relaxation time is required during capacity recovery. Capacity recovery methods which discharge negative electrodes is superior to those which discharge positive electrodes of cycled batteries as smaller solid surface concentration gradients is generated and less relaxation time is required at the same discharging current. [Copyright &y& Elsevier]

Abstract: Cube-like and plate-like Li[Li0.2Mn0.54Ni0.13Co0.13]O2 particles are obtained after treated in LiCl and KCl molten salts at 800 °C, respectively, comparing to the ball-like original particles calcined in air. The oxide treated in KCl molten salt with large specific area of 17.05 m2 g−1 delivers high discharge capacities of 254.1 mAh g−1 and 168.5 mAh g−1 at current densities of 200 mA g−1 and 2000 mA g−1, respectively. In addition, enhanced cycle stability with capacity retention of 94.9% after 80 cycles at charge–discharge current densities of 200 mA g−1 is obtained for the oxide treated in LiCl molten salt with sacrifice of a little capacity. Such electrochemical performance change is proved to be independent of Li+ diffusion coefficient. It appears that the treatment in molten salts can effectively reform the electrochemical performances of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode materials for various applications. [Copyright &y& Elsevier]

Highlights: [•] Facile, fast and low-cost urea synthesis of porous SnO2 anode for lithium ion battery. [•] Porous SnO2 anode delivers excellent electrochemical performances. [•] High surface area, good electric contact and easier Li+ diffusion give high performances. [•] Finer the sizes of the SnO2 nanoparticles better the cycling stability. [ABSTRACT FROM AUTHOR]

In this study, we propose a new filler material (Zn4O(1,4-benzenedicarboxylate)3 metal-organic framework, MOF-5), which is successfully prepared and incorporated in poly(ethylene oxide) (PEO) based composite polymer electrolyte (CPE) by an in-situ method for improving electrochemical properties in lithium ion battery. A highest ionic conductivity of 3.16 × 10−5 S cm−1 at 25 °C for the composition of PEO-LiN(SO2CF3)2 (ethylene oxide (EO):Li = 10:1)/10 wt% MOF-5 is obtained. The anodic steady window of the electrolyte is 4.57 V at 60 °C, which is decided by the decomposition voltage of MOF-5. The interfacial resistances of Li/CPE/Li cells become more stable upon storage compared for that without MOF-5. The reversible capacities of LiFePO4/Li solid cells increase at both 60 °C and 80 °C due to the decrease of the cell polarization. In addition, the capacity retention is 45% after 100 cycles at 1 C rate at 80 °C, while there is a sharp decay after 30 cycles in the cells without MOF-5 filling. These results show that MOF-5 is useful to enhance electrochemical properties of composite polymer electrolyte for solid lithium ion battery. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical impedance spectroscopy for lithium ion batteries has recently gained increasing attention due to its ability of non-invasive evaluation of important electrochemical parameters. Commonly used three-electrode test cells, however, proved unreliable due to asymmetric current line distributions, causing severe distortions of impedance spectra. Finite element method (FEM) simulations can visualize these current lines at different frequencies and simulate impedance spectra at given geometries. By applying FEM simulations to a recently developed coaxial impedance test cell, limiting conditions for reliable impedance measurements could be identified. Using a reference electrode in coaxial position yields sufficiently reliable results as long as the electrode misalignment is small compared to the electrolyte thickness and edge effects are prevented. [Copyright &y& Elsevier]

Abstract: Rechargeable lithium-ion batteries (LIBs) are currently accepted to be one of the most suitable energy storage resources in portable electronic devices because of their high gravimetric and volumetric energy density. To understand the behavior of Li+ ions on electrochemical lithium extraction/insertion process, we performed in situ 7Li nuclear magnetic resonance (NMR) measurements for LiCoO2 cathode in a plastic cell battery, and the spectral evolutions of the 7Li NMR signal of Li x CoO2 (0≤ x ≤1) were well investigated. Very narrow solid solution region of Li x CoO2 (∼0.99≤ x <1) was explicitly defined from the large intensity reduction of LiCoO2 signal at ∼0ppm, which is related to the localized nature of the electronic spin of paramagnetic Co4+ ion formed at the very early delithiation stage. With further decreasing the signal intensity of LiCoO2, a Knight-shifted signal corresponding to an electrically conductive Li x CoO2 phase emerged at x =0.97, which then monotonously decreased in intensity for x <0.75 in accordance with the electrochemical lithium de-intercalation from Li x CoO2. These observations acquired in situ fully confirm the earlier studies obtained in ex situ measurements, although the present study offers more quantitative information. Moreover, it was shown that the peak position of the NMR shift for Li x CoO2 moved as a function of lithium content, which behavior is analogous to the change in its c lattice parameter. Also, the growth and consumption of dendritic/mossy metallic lithium on the counter electrode was clearly observed during the charge/discharge cycles. [Copyright &y& Elsevier]

Highlights: [•] Cation-incorporated Li3V2(PO4)3/C have been systematically investigated. [•] Cation incorporation in Li3V2(PO4)3 does not change the monoclinic structure but form solid solution. [•] Fe-incorporation shows the best electrochemical performance whereas Ni-incorporation shows the poorest performance. [•] A clear profile of cation incorporation with Fe, Co, Ni, Mn ions in Li3V2(PO4)3/C is obtained. [ABSTRACT FROM AUTHOR]

Abstract: The complex nature of lithium ion batteries makes the tracking of individual physical processes difficult. However, having a good knowledge thereof is indispensable for a continuous improvement of cell performance and lifetime. In this study, the impedance response of a commercial 18650 cell was investigated within a wide frequency range (100 kHz–2 μHz) by combining electrochemical impedance spectroscopy and time domain measurements. In parallel, the original 18650 cell was opened. Thus, the electrode materials could be tested in an experimental test set-up using a reference electrode, which allowed the separation of anode and cathode processes. The different kinds of impedance data sets were de-convoluted in the space of relaxation times, enabling a refined separation of physical processes like charge transfer or solid state diffusion. This multistep approach, which is not tied to a particular electrochemistry, allowed the identification of the dominating physical processes being hidden in the impedance spectrum of the original 18650 cell. [Copyright &y& Elsevier]

Highlights: [•] Li2+x Mn1−x P x Si1−x O4/C are novel cathode materials for lithium ion batteries. [•] Single phase Li2+x Mn1−x P x Si1−x O4/C is formed when x is not higher than 0.05. [•] Li2.05Mn0.95P0.05Si0.95O4/C (x =0.05) has the best electrochemical properties. [ABSTRACT FROM AUTHOR]

Abstract: Zn2V2O7 nanorods were successfully synthesized by a hydrothermal route for the application in the Lithium ion batteries. The effects of the reacting time on the Zn2V2O7 nanorods as well as the corresponding electrochemical properties were investigated. Results show that the obtained sample under the optimum condition possesses high crystallinity; the width and the thickness are in the range of 40–60nm and 20–40nm, respectively. Based on the observations, a possible growth mechanism of Zn2V2O7 nanorods could be described as a reacting–exfoliating–splitting process. Besides, the Zn2V2O7 nanorods used as anode materials in rechargeable lithium-ion battery can exhibit a highly reversible discharge/charge capacity and excellent rate property at a current density as high as 0.1Ag−1. This might be attributed to the intrinsic characteristics of the layered structure of Zn2V2O7 nanorods. [Copyright &y& Elsevier]

Abstract: LiNi1/3Co1/3Mn1/3O2 (LNCM) with a well-ordered layered structure, confirmed by X-ray diffraction, was synthesized by the chemical-wet synthesis incorporated with (i) a pulse microwave-assisted heating of LNCM precursors and (ii) a carbon coating technique. The microwave irradiation periods (i.e., 5–20min) and amount of carbon additive (i.e., glucose content: 0.1–0.75%) served as key factors in modifying as-prepared LNCM powders. The electrochemical performance of as-prepared LNCM cathodes was well characterized by cyclic voltammetry and charge–discharge cycling at 0.1–5C. Both appropriate microwave heating and carbon coating significantly improve discharge capacity, rate capability, and cycling stability of LNCM cathodes. This improved performance can be attributed to the facts that an appropriate microwave heating of LNCM precursors induces low cation mixing of the layered lattices and the carbon coating enables the creation of outer circuit of charge-transfer pathway, preventing cathode corrosion from direct contact to the electrolyte. The C-coated LNCM cathode shows the increased capacity retention from 70.2 to 93.3% after 50 cycles at 1C. On the basis of the experimental results, both the microwave heating and the carbon coating provide a feasible potential way to improve the electrochemical performance of LNCM cathode, benefiting the development of Li-ion batteries. [Copyright &y& Elsevier]

Highlights: [•] Polymer-derived SiCN and SiOC ceramics are studied as anode for Li-ion batteries. [•] Ceramic precursors are modified in order to increase the carbon content. [•] Ceramic matrix stabilizes free carbon phase. [•] Stabilizing role is lost once the amount of carbon exceeds a threshold value. [Copyright &y& Elsevier]

Abstract: Li2MnSiO4 cathode materials doped with various cationic ions, Ga3+, Al3+, and Mg2+, are synthesized and their microstructure and electrochemical properties are investigated. The samples doped with trivalent ions, especially Ga3+, lead to a higher charge/discharge capacity and initial efficiency with well-dispersed nanoparticle formation. We can realize that the enhanced electrochemical performance of the specific ion doped Li2MnSiO4 cathodes originated from the uniformly distributed nanoparticles rather than the additional lithium insertion/extraction of the given cathode materials induced by the charge compensation. [Copyright &y& Elsevier]

Abstract: Lithium-rich layered cathode Li1.2Mn0.54Ni0.13Co0.13O2 is synthesized by a co-precipitation method followed by high-temperature treatment and surface coated with different amount of amorphous FePO4. The microstructure and electrochemical performance of the as-prepared cathode materials are investigated systematically. It is demonstrated that the Li1.2Mn0.54Ni0.13Co0.13O2 particles are uniformly coated with amorphous FePO4. With proper amount of amorphous FePO4 coating layer, significant improvements in discharge capacity, initial Coulombic efficiency, rate capability, cycle performance, and thermal stability are achieved at room temperature. Specifically, the 3 wt.% FePO4-coated cathode exhibits the highest discharge specific capacities (271.7 mAh g−1 at C/20), improved initial Coulombic efficiency (85.1%), and best cyclability (discharge capacity of 202.6 mAh g−1 at C/2 after 100 cycles), while the 1 wt.% FePO4-coated cathode displays the best rate capability (194.3 mAh g−1 at 1 C rate and 167.9 mAh g−1 at 2 C rate). The charge–discharge curves and electrochemical impedance spectra reveal that the improved electrochemical performances are due to the suppression of both the oxygen vacancy elimination at the end of the first charge and side reactions of the cathode with the electrolyte, as well as the decrease in charge transfer polarization by the FePO4 coating layer. [Copyright &y& Elsevier]

Abstract: The cobalt sulfides/graphene nanosheets (GNS) composite is prepared by a facile one-pot solvothermal route in the presence of graphene oxide sheets (GOS). XRD, SEM and TEM characterizations show that sphere-like cobalt sulfides particles with an average size of about 150 nm, which are complicated phases of CoS2, CoS and Co9S8, are highly dispersed on or wrapped in the creasy graphene. The selective nucleation and growth of cobalt sulfides particles on GOS make the particles more uniform in morphology and size. The as-fabricated cobalt sulfides/GNS composite exhibits very high electrochemical lithium storage reversible capacity of about 1018 mAh g−1. Moreover, the cobalt sulfides/GNS composite still remains reversible capacity of above 950 mAh g−1 after 50 cycles at a current density of 100 mA g−1 as well as at the different current densities from 100 to 1000 mA g−1, proving its excellent cycling durability and high-rate capability. The superior electrochemical performances of the composite may be attributed to the robust composite structure and superior conductivity, high charger mobility, large surface area and good flexibility of graphene. [Copyright &y& Elsevier]

Abstract: Carbon coated LiMn0.5Fe0.5PO4 solid solution materials (LiMn0.5Fe0.5PO4/C) are synthesized by rheological phase reaction with stearic acid as carbon source, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET and TG/DTG. The results show that well-crystallized olivine structure LiMn0.5Fe0.5PO4 nanoplatelets with no obvious impurity phase are obtained. The as-synthesized materials are served as cathode of lithium ion battery and investigated by galvanostatic charge/discharge tests. The results demonstrate that, in comparison with the LMFP materials of different Mn:Fe ratio (LiMn0.2Fe0.8PO4/C and LiMn0.8Fe0.2PO4/C) synthesized by the same route of rheological phase reaction, the LiMn0.5Fe0.5PO4/C exhibit excellent rate specific capability, and can deliver discharge capacity of 138, 99, 80, 72, 67 and 55 mAh g−1 at respectively 0.1, 1, 5, 10, 15 and 20C rates. Moreover, the electrode possesses good cycle stability. A specific capacity of 100 mAh g−1 at 1C after 300 cycles of charge–discharge at room temperature is reached, which represents 95% of capacity retention. The significantly improved electrochemical performances of the LiMn0.5Fe0.5PO4/C cathode are attributed to the uniformly distributed particles and the enhancement of conductivity that is originated from the surface coating of carbon on primary particles. [Copyright &y& Elsevier]