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We have prepared two types TiO2(B)-carbon composites from Lepidocrocite-type compounds (K0.86Li0.26Ti1.72O4) heated at 700 and 900°C under presence of carbon nanotube (CNT) and glucose as carbon sources. The XRD data shows that it contains a single phase of TiO2(B) and the existence of carbon was confirmed by Raman spectra. TEM image confirms that TiO2(B) primary particles and carbon nanotube are scattered randomly and contact tightly in the composite. Carbon content in the composite was found to be 5 - 8% and CNT is the major carbonaceous material. The charge and discharge curves of TiO2(B)-carbon composite prepared from precursor heated at 700°C resemble with that of amorphous TiO2. The calculated discharge capacity of the composite is 323mAhg−1 at a cut off voltage of 0.9V, which is higher than that of bare TiO2(B). It is suggested that the electrochemical performance of this material is strongly influenced by both the operating temperature and cut off voltage. The discharge capacity can reach 198mAhg−1 at 4.5C rate at a cut off voltage 1.3V and the coulombic efficiency is over 99.8% after 10th cycles. [ABSTRACT FROM AUTHOR]

The influence of the vanadium substituted LiNi0.5Co0.2Mn0.3O2 (LNCM-532) cathode materials on the structure and electrochemical properties were investigated by means of X-ray diffraction, Rietveld refinement, scanning electron microscope, X-ray photoelectric spectroscopy, energy dispersive spectrometer, electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge/discharge tests. XRD, EDS, XPS results show that vanadium is successfully substituted for the transitional metal in LiNi0.5Co0.2Mn0.3O2 crystal lattice. Rietveld refinement results show that suitable vanadium substitution leads to low cation mixing. Electrochemical tests show that the discharge capacity of Li[Ni0.5Co0.2Mn0.3]0.97V0.03O2 at 5 C remains 72.2% of that at 0.1 C, while the capacity retention is only 58.9% for LiNi0.5Co0.2Mn0.3O2. LiNi0.5Co0.2Mn0.3O2 exhibits the capacity retention of 93.9% at 1 C after 50 cycles. After substituting, the capacity retention of Li[Ni0.5Co0.2Mn0.3]0.97V0.03O2 is increased to 96.3% at 1 C. EIS measurement indicates that vanadium substitution contributes to the better lithium ion diffusion and the lower charge transfer resistance. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

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]

This study, for the first time, synthesized carboxymethyl cellulose lithium (CMC-Li) by a two-step method and applied it to modified electrode material by electrospinning and as a binder on a lithium ion battery. By electrospinning, nano CMC-Li fiber and CMC-Li/9, 10-anthraquinone (AQ) composite fiber were obtained successfully and coated AQ electrode material. AQ was uniformly distributed in fibers, and then CMC-Li/AQ composite fiber was carbonized to obtain the carbon nanofiber/AQ/Li [CAL] composite as lithium battery anode material. Also for the first time we investigated substituting aqueous CMC-Li with different degrees of substitution (DS) for oily polyvinylidene fluoride (PVDF) as a lithium battery binder to assemble the battery with CAL for electrochemical performance tests. Compared with PVDF binder, cells with CMC-Li for a binder have excellent advantages, such as higher discharge capacity (226.4 mAh g), safer cycle performance, lower cost and being more eco-friendly. Furthermore, the cell with CMC-Li with high DS performed better than the cell with low DS. This method also applies to other electrode materials. [ABSTRACT FROM AUTHOR]

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: 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: 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 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]

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]

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: 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: 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]

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]

We report a Mn substitution strategy to tailor the morphology, size, surface of LiCo1-xMnxPO4 (x=0·2, 0·5 and 0·8) materials using a facile organic acid mediated hydrothermal approach. The results show that the Mn substitution plays a profound role in reducing the particle size, stabilising the surface, and improving the diffusivity of LiCo1-xMnxPO4 materials, thus leading to much enhanced electrochemical performance compared with LiCoPO4. However, when excessive Mn (e.g. x=0·8) is present in the olivine crystal, the performance of LiCo1-xMnxPO4 degrades, possibly due to Jahn-Teller lattice distortion. As a result, the LiCo0·5Mn0·5PO4 displays the best electrochemical performance in terms of capacity delivery, cyclability and rate capability. Therefore, the Mn substitution in LiCoPO4 could be an efficient way to achieve high energy density and long cycle life for high voltage materials. [ABSTRACT FROM AUTHOR]

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: 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]