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The additive of self-terminated oligomers with hyper-branched architecture (STOBA) in Li(Ni0.4Co0.2Mn0.4)O2 (LNCM) cathodes of lithium ion batteries improves the battery stability and capacity. In this study, the surface chemistry of pristine LNCM electrodes with and without the STOBA additive was analyzed by means of X-ray photoelectron spectroscopy and the surface morphology was observed by scanning electron microscopy. It was found that STOBA covers LNCM particles uniformly and the formation of chemical bonding between nitrogen atoms in STOBA and metallic atoms in LNCM was discovered. This bonding may cause the uniform coverage of STOBA on LNCM. The formation of STOBA layer on LNCM improves the coverage of the binder poly(vinylidene fluoride) and inhibits the formation of LiF. [ABSTRACT FROM AUTHOR]

Abstract: This study developed a novel and inexpensive method for fabricating size-tunable tapered antireflective nanopillars on a polycarbonate (PC) film using hybrid nano-patterning lithography consisting of nanosphere lithography (NSL) and nanoimprint lithography (NIL). The optical properties of the antireflective surfaces can be controlled by the CrN nanomold morphologies resulting from the different reactive ion etching conditions. The nanomold surface of CrN nanohole arrays has a low surface energy at the interface and has an anti-sticking property that can be applied in the problem of the sticking during demolding. A high-performance antireflective tapered nanopillar layer was successfully imprinted on a PC film surface using a contactless gas assisted pressing process along with a CrN nanomold prepared by NSL. The optical properties of antireflective characteristic of the PC tapered nanostructures were analyzed. Such antireflective surfaces are promising for fabrication of high light transmittance and antireflective optical materials to be used in many important fields. [Copyright &y& Elsevier]

Spherical composite oxide Li1.5Ni0.25Mn0.75O2.5 (or 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2) powder as a Li-ion battery cathode has been synthesized by high-temperature calcination of a mixture containing Li2CO3 and (Ni0.25Mn0.75)CO3, which is synthesized by a continuous co-precipitation method. The evolution in the microstructure of the oxide during calcination is studied mainly by transmission X-ray microscopy (TXM), complemented by X-ray diffraction and thermogravimetry, and it can be divided into three major stages. The first stage takes place below 400 °C, and is characterized by the decomposition of the transition metal carbonates to form amorphous oxides, leading to the formation of internal cracks due to extensive densification. The second stage occurs between 400 and 800 °C, and involves complete Li1.5Ni0.25Mn0.75O2.5 formation and the development of a unique radially-distributed pore structure. The third stage takes place above 800 °C and during prolonged heating at 900 °C, and is characterized by grain growth and change into a randomly distributed tortuous pore structure. TXM 3D-elemental analysis gives statistical evidence showing heterogeneity in the distributions of Ni and Mn, which causes capacity loss and might be a common problem encountered in the two-step precipitation–calcination process. The electrochemical performance of the resulting Li1.5Ni0.25Mn0.75O2.5 powder exhibits complex dependence on the microstructure. The radially distributed pore pattern and small grain size produced by moderate heating favor the rate performance of the composite oxide cathode by reducing charge-transfer resistance and enhancing apparent Li ion solid-state diffusivity. A large grain size resulting from prolonged heating, on the other hand, reduces the formation of the spinel MnO2 domain upon de-lithiation of the Li2MnO3 component of the composite oxide. [ABSTRACT FROM AUTHOR]

Reduced graphene materials were prepared by different reducing approaches of graphite oxide, including chemical reduction and thermal reduction. In this study, the characteristics of reduced graphene and the lithium storage behavior of graphene-based anodes were investigated by SEM, BET, TPD, FTIR as well as C/D tests and Raman measurements. The electrochemical behaviors of reduced graphene materials were sensitive to reduction process, of which the capacity varying from 717 to 230 mAh/g. The enhanced capacity should not be predominantly attributed to exceptional high surface area and enlarged d-spacing, but rather more possible for existence of functional groups along with structure defects. [ABSTRACT FROM AUTHOR]

As an anode for Li-ion batteries, Si has a high theoretical capacity but suffers from dramatic volume variations during cycles of lithiation/de-lithiation (L/D). Attempt is made to increase cycle stability of Si electrode by incorporating 'pre-set' voids into the electrode matrix to partially accommodate volume expansion. A metal-assisted chemical etching (MACE) method, in which Si is partially etched in the solution containing AgNO3 and HF, has been evaluated for synthesize porous Si particles. It has been found that the particle porosity exhibits complex dependence on etching time, oxidant concentration and temperature. Porous Si particles containing predominantly mesopores have been produced by the MACE method, but the maximumporosity has been limited to be ca. 25%. The resulting porous Si is subsequently coated with a C layer and subjected to cycles of electrochemical L/D. The C-coated porous Si electrode exhibits high capacity and remarkably improved cycle stability as compared with non-porous Si electrode. [ABSTRACT FROM AUTHOR]

Abstract: The charge/discharge capacity and cycle stability at high C-rate of LiFePo4 (LFPO) electrodes using three types of Al current collectors, including smooth un-etched Al foil, anodization-etched Al foil, and the etched Al foil covered with a conformal C coating grown at 600°C in CH4, were investigated. The results unequivocally demonstrate the strong effects exerted by the surface structure and composition of the Al current collectors on the power performance. In particular, the use of the C-coated current collector not only remarkably increases the power-delivering capability, by 3–7-fold based on different comparison criteria, of the LFPO electrode, but also greatly enhances its cycle stability under high C-rate (5C). The rate enhancement exceeds that of a low-temperature organic-bound C-coating reported in the literature. The enhancements are consistent with observed reduction in overall charge-transfer resistance, which can be attributed to the removal of the native insulating oxide surface layer of the current collector and to the improved adhesion at the active layer/current collector interface. This current collector is also applicable to other cathode and anode (e.g., Li4Ti5O12) materials of Li-ion batteries for the same beneficial effects. [Copyright &y& Elsevier]

Abstract: LiFePO4/mesocarbon microbead (MCMB) cells of which the carbon electrodes were, respectively, coated with different metal layers were characterized for their charge/discharge cycle performance at 55°C. The examined metals included Au, Cu, Fe, Ni, Co, and Ti, and the superficial layers were 30–50nm in thickness and deposited by vacuum sputtering. It was found that the presence of a either Au or Cu layer remarkably reduces capacity fading, while the rest metals only accelerate fading. There was observed a consistent trend between the capacity fading rate and the amount of the soild-electrolyte-interphase (SEI) deposition; the faster the capacity fading, the greater amount of SEI materials appearing on the surface of cycled carbon electrode. Microscopic and composition analyses indicates that the superficial Au and Cu layers act as a sieve to collect the Fe ions that result form erosion of LiFePO4 before they diffuse into the interior of the carbon electrode, and that the so-deposited Fe particles do not show the tendency to catalyze the SEI formation, as in contrast to those directly deposited on the carbon surfaces. [Copyright &y& Elsevier]

Abstract: The fading mechanism of Li ion batteries with two different anode materials was discussed in this study. Anode materials were spherical type of meso-phase carbon micro bead (MCMB) and flake type of pitch coated graphite (PCG). This battery used LiMn2O4 as the cathode materials. The LiMn2O4/MCMB battery had higher rate capability than the LiMn2O4/PCG battery. However, the LiMn2O4/PCG battery had only 20% capacity retention after 70 cycling tests, while the LiMn2O4/MCMB battery had 95% capacity retention. The X-ray diffraction (XRD) and X-ray photospectroscopy (XPS) were used to analyze the structure of active materials and the solid electrolyte interface (SEI) films on the electrodes. It was found that structure of PCG anode and LiMn2O4 cathode was maintained as pristine structure by XRD analysis. The carbonate was easier to decompose on PCG surface than on the MCMB surface by XPS analysis. It was suggested that the electrolyte decomposition on PCG surface might be play a major role for the LiMn2O4/PCG battery fading. [Copyright &y& Elsevier]

Abstract: Structural transformation taking place during charge/discharge of the LiFePO4 electrode in an organic Li-ion electrolyte has been studied by in situ synchrotron X-ray diffraction (XRD) concurrently with electrochemical analysis. The data reveal complex structural transformation patterns which result from significantly delayed structural transformation, even at low to moderate current rates (C/10∼1C). The extent of the deviation is affected by charge/discharge conditions as well as history, and strong deviation appears detrimental to electrode cycle life. Furthermore, the two-phase characteristic of the Li+ insertion/extraction reactions is found to persist even within one metastable crystal structure. The result suggests the presence of domain structures that are probably caused by the strong electron/ion site coulombic interaction as previously suggested. [Copyright &y& Elsevier]

Abstract: Rate equation of LiFePO4 formation via solid-state reaction has been studied by using a model system: Li(CH3COO)+FePO4 in a reducing atmosphere. Kinetic data were acquired by using in-situ synchrotron X-ray diffraction technique, and the analysis was based on a non-isothermal methodology, which shows that the reaction rate is well described by the rate-equation: [F 0.7/(1− F)0.7]=1.56×1011 exp(−24,100/T)t, where F is the fractional conversion to LiFePO4, T, the calcination temperature (K), and t is the calcination time (min). The equation indicates that the formation of LiFePO4 is intrinsically a fast reaction: 95% conversion can be achieved between 550 and 600°C in a few hours. Nevertheless, the reaction could be significantly hindered if gas-phase diffusion processes of reactant/product species become rate-limiting, and the gas-flow pattern relative to the powder bed during synthesis thus has a decisive effect on the reaction rate in large-scale synthesis. Single-phased, nanocrystalline LiFePO4 powder having an average crystal size of 35nm can be synthesized by calcination using flow-through configuration at 600°C in merely 2h, and the powder exhibits a capacity of ∼140mAhg−1. [Copyright &y& Elsevier]

Abstract: Nanosized LiNi1/3Co1/3Al1/3O2 with an α-NaFeO2 structure has been successfully synthesized via a water-in-oil microemulsion method. Well-crystallized LiNi1/3Co1/3Al1/3O2 was obtained after heating at 800°C for merely 3h. The particle size of the microemulsion-derived powders was around 30nm. The results of electrochemical analysis revealed that the synthesized powders exhibited higher discharge capacity at elevated temperatures than at room temperature. The Co3+/Co4+ redox reactions are considered to play an important role in the discharge capacity and capacity retention of synthesized LiNi1/3Co1/3Al1/3O2. [Copyright &y& Elsevier]

Abstract: LiNi1/3Co1/3Mn1/3O2 powders have been successfully prepared via a newly developed microwave-hydrothermal method. Monophasic powders with an α-NaFeO2 structure were obtained. The particle sizes of the microwave-derived powders were in submicron order (0.2–0.3 μm) and were much smaller than those of the powders synthesized via coprecipitation reaction (1–3 μm). The microwave-hydrothermal route not only shortened the required reaction time but also improved the electrochemical performance of the product. Electrochemical analysis indicated that the microwave-derived LiNi1/3Co1/3Mn1/3O2 powders exhibited a higher capacity than those derived from coprecipitation method. The capacity fading ratio of the microwave-derived powders was lower than that of the powders obtained via coprecipitation route, according to the results of high C-rate tests. [Copyright &y& Elsevier]

Abstract: The interior microstructures of Sn particles developed during electrochemical lithiation/de-lithiation have been revealed by in situ X-ray transmission microscopy (TXM). The Li-alloying particles exhibited the formation of core–shell internal structure along with crack formation within the lithiated zone during the first lithiation. The extent and speed of the expansion process was shown to be a strong function of particle size. Upon completion of the first de-lithiaiton, the particles only partially (∼10%) contracted, while re-crystallization of Sn continued to take place within the interior of the particles during a following idle period. The re-crystallization process alleviated the pulverization problem and led to the formation of porous Sn particles, which exhibited remarkably attenuated dimensional variations during subsequent cycles. [Copyright &y& Elsevier]

Abstract: LiFePO4 particles were coated with TiO2 (molar ratio=3%) via a sol–gel process, and the effects of the coating on cycle performance of LiFePO4 cathode at 55°C against either a Li or a C (mesocarbon microbead) anode were investigated. It was found that, while the coating reduces capacity fading of the LiFePO4/Li cell, it imposes a deteriorating effect on the LiFePO4/C cell. Analyses on cell impedance and electrode surface morphology and composition showed that the oxide coating reduced Fe dissolution from the LiFePO4 cathode and hence alleviated the impedance increase associated with the erosion process. This leads to reduced capacity fading as observed for the LiFePO4/Li cell. However, the oxide coating itself was eroded upon cycling, and the dissolved Ti ions were subsequently reduced at the anode surface. Ti deposit on the C anode was found to be more active than Fe in catalyzing the formation of the solid-electrolyte interphase (SEI) layer, causing accelerated capacity decay for the LiFePO4/C cell. The results point out the importance of evaluating the effect of cathode coating material on the anode side, which has generally been overlooked in the past studies. [Copyright &y& Elsevier]

Abstract: Spherical particle morphology of Li1.1Ni1/3Co1/3Mn1/3O2 cathode material was carefully controlled by spray drying the slurry containing mixed oxides pre-calcined at 900°C. The as-dried powders were then treated in a microwave-processing cavity with different power and time. The microwave-processing cavity is a designed elliptically resonant cavity with double foci. One focusing zone concentrated microwave energy to treat the as-dried cathode material. After microwave-treated power of 200W for 15min at least, high purity of Rocksalt structure showed high ratio of integrated intensities of (003)/(104), larger than 1.1, and double peaks (006)/(102) and (108)/(110) split up clearly based on X-ray diffraction patterns. After 200W microwave treating for 15min, the discharge capacity of the obtained Li1.1Ni1/3Co1/3Mn1/3O2 powders was 120mAhg−1 by charging from 4.3 to 2.5V at room temperature. Furthermore, discharge capacity larger than 140mAhg−1 can be obtained for treating with 200W microwave energy for 30min. Nevertheless, the discharge capacity was less than 100mAhg−1 treated with 1100°C/24h by conventional furnace. The microwave-treated Li1.1Ni1/3Co1/3Mn1/3O2 cathode material sustains capacity less than 5% degradation after 50 cycles test. The results of microwave process show promise properties requirement for commercial applications. [Copyright &y& Elsevier]