C.Y. Chung

Solvothermal synthesis of nano-LiMnPO4 from Li3PO4 rod-like precursor: reaction mechanism and electrochemical properties

A simple one-pot solvothermal approach is employed to synthesize LiMnPO4 (LMP) nanomaterials by using Li3PO4 nanorods and MnSO4·H2O as the precursors. Various experimental parameters, such as volume ratio of polyethylene glycol 600 (PEG600) to water, reactant feeding order, reaction time and pH value, are discussed. The phase and morphology changes of the product were characterized by XRD and TEM. A reaction mechanism is proposed based on the characteristic results. The charge–discharge properties show that the LMP nanomaterials synthesized at 180 °C for 4 h at a pH value of 6.46 followed by sintering with glucose at 600 °C for 3 h under argon atmosphere present the highest discharge capacity of 147 mA h g−1 at 0.05 C rate (i.e. 8.55 mA g−1 of current rate) under a galvanostatic charging–discharging mode, and it can retain 93% of the initial capacity of 46.6 mA h g−1 after cycling 200 times at 1 C rate. Cyclic voltammetry (CV) was also used to investigate the carbon coated LMP electrode.

Fabrication of LiF/Fe/Graphene nanocomposites as cathode material for lithium-ion batteries.

Homogeneous LiF/Fe/Graphene nanocomposites as cathode material for lithium ion batteries have been synthesized for the first time by a facile two-step strategy, which not only avoids the use of highly corrosive reagents and expensive precursors but also fully takes advantage of the excellent electronic conductivity of graphene. The capacity remains higher than 150 mA h g(-1) after 180 cylces, indicating high reversible capacity and stable cyclability. The ex situ XRD and HRTEM investigations on the cycled LiF/Fe/G nanocomposites confirm the formation of FeF(x) and the coexistence of LiF and FeF(x) at the charged state. Therefore, the heterostructure nanocomposites of LiF/Fe/Graphene with nano-LiF and ultrafine Fe homogeneously anchored on graphene sheets could open up a novel avenue for the application of iron fluorides as high-performance cathode materials for lithium-ion batteries.

Rugated porous Fe3O4 thin films as stable binder-free anode materials for lithium ion batteries

Rugated porous Fe3O4 thin films were synthesized by a facile multi-pulse electrochemical anodization method. The fabricated Fe3O4 films are directly grown on Fe, featuring nano-channels with periodically rugated channel walls running throughout the film thickness direction. Electrochemical measurements show that the as-prepared Fe3O4 films readily serve as high-performance anode materials for lithium ion batteries with a specific capacity of 1100, 880 and 660 mA h g−1 at 0.1, 0.2, and 0.5 C, respectively, which compared favorably with the conventional straight-channel counterparts fabricated by DC anodization. Moreover, the cycling capability test of the novel electrode at 0.1 C for 100 cycles shows a steady charge/discharge platform, indicating a high cycling stability and structural robustness. The observed improvements of the rugated Fe3O4 films as lithium ion battery anode materials are attributed to their special periodic rugated nanostructures.

Effect of f.c.c. antiferromagnetism on martensitic transformation in Fe-Mn-Si based alloys

Abstract By using resistance measurement and dynamic mechanical analysis, critical points of Fe–Mn–Si and Fe–Mn–Si based shape memory alloys (SMA) were determined and the effect of f.c.c. antiferromagnetism on the thermal and stress-induced martensitic transformation, i.e. f.c.c.(γ)→h.c.p.(e), was studied. With the increase of Mn content in the alloys, critical points M s , M f , A s and A f decrease and the Neel temperature T N increases until the thermal martensite has been suppressed completely. As the T N approaches M s the f.c.c. antiferromagnetism will extend the temperature range of the martensitic transformation to −150°C. After the thermal martensite is completely suppressed by the antiferromagnetic state, the martensitic transformation can also be induced to a great extent by stress, as confirmed by the measurement of an internal friction peak during the reverse martensitic transformation.

Layered Li2MnO3·3LiNi0.5−xMn0.5−xCo2xO2 microspheres with Mn-rich cores as high performance cathode materials for lithium ion batteries

Layered Li2MnO3·3LiNi0.5-xMn0.5-xCo2xO2 (x = 0, 0.05, 0.1, 0.165) microspheres with Mn-rich core were successfully synthesized by a simple two-step precipitation calcination method and intensively evaluated as cathode materials for lithium ion batteries. The X-ray powder diffractometry (XRD) results indicate that the growth of Li2MnO3-like regions is impeded due to the presence of cobalt (Co) in the material. The field-emission scanning electron microscopy (FESEM) data reveal the core-shell-like structure with a Mn-rich core in the as-prepared particles. The charge-discharge testing reveals that the capacity is markedly improved by adding Co. The activation of the cathode after Co doping becomes easier and can be accomplished completely when charged to 4.6 V at the C/40 rate in the initial cycle. Superior electrochemical performances are obtained for samples with x = 0.05 and 0.1. The corresponding initial discharge capacities are separately 281 and 285 mA h g(-1) at C/40 between 2 and 4.6 V at room temperature. After 250 cycles at C/2, the respective capacity retentions are 71.2% and 70.4%, which are better compared to the normal Li-excess Li2MnO3·3LiNi0.4Mn0.4Co0.2O2 sample with a uniform distribution of Mn element in the particles. The initial discharge capacities of both samples are approximately 250 mA h g(-1) at a rate of C/2 between 2 and 4.6 V at 55 °C after activation. Furthermore, the samples are investigated by electrochemical impedance spectroscopy (EIS) at room and elevated temperature, revealing that the key factor affecting electrochemical performance is the charge transfer resistance in the particles.

Remarkable biocompatibility enhancement of porous NiTi alloys by a new surface modification approach: In-situ nitriding and in vitro and in vivo evaluation

An in-situ nitriding method has been developed to modify the outer surface and the pore walls of both open and closed pores of porous NiTi shape memory alloys (SMAs) as part of their sintering process. XRD and XPS examinations revealed that the modified layer is mainly TiN. The biocompatibility of the in-situ nitrided sample has been characterized by its corrosion resistance, cell adherence, and implant surgery. The in-situ nitrided porous NiTi SMAs exhibit much better corrosion resistance, cell adherence, and bone tissue induced capability than the porous NiTi alloys without surface modification. Furthermore, the released Ni ion content in the blood of rabbit is reduced greatly by the in-situ nitriding. The excellent biocompatibility of in-situ nitrided sample is attributed to the formation of the TiN layer on all the pore walls including both open and closed pores.

Facile synthesis of porous Li-rich layered Li[Li0.2Mn0.534Ni0.133Co0.133]O2 as high-performance cathode materials for Li-ion batteries

Lithium-rich layered metal oxides have drawn much recent attention due to their high rechargeable capacity of 250–300 mA h g−1. Herein, we report the synthesis of porous Li[Li0.2Mn0.534Ni0.133Co0.133]O2 metal oxide powders using a facile polymer-thermolysis method. X-ray powder diffractometry (XRD) results show that a well-crystallized layered structure was obtained when the calcination temperatures reach 800 °C. Pores in the range of 100–200 nm are observed using scanning electron microscopy (SEM). The porous Li[Li0.2Mn0.534Ni0.133Co0.133]O2 synthesized at 850 °C shows much superior electrochemical performance to the sample synthesized by the traditional coprecipitation-calcination method, with a high initial coulombic efficiency of 87% and initial discharge capacity of 245.4 mA h g−1 at 15 mA g−1 in the voltage window 2–4.6 V. A capacity retention of 81% was obtained after 300 cycles at 300 mA g−1. The higher capacity and improved rate performance of porous Li[Li0.2Mn0.534Ni0.133Co0.133]O2 can be predominantly attributed to enhanced Li+ intercalation kinetics resulting from the highly porous structure.

Structure and electrochemical performance of nanosized Li1.1(Ni0.35Co0.35Mn0.30)O2 powders for lithium-ion battery

Pure Li1.1Ni0.35Co0.35Mn0.30O2 nanosized powders have been successfully synthesized by improved hydroxide co-precipitation method, and characterized with X-ray powder diffraction and scanning electron microscopy (SEM). The electrochemical properties of cathodes and Li1.1Ni0.35Co0.35Mn0.30O2/Li4Ti5O12 full cells have been studied by charge–discharge tests and cyclic voltammetry. The Li1.1Ni0.35Co0.35Mn0.30O2 powders have a typical layered hexagonal crystal structure with an average particle size of about 780 nm. The cathodes exhibit high capacities and good cycling performance. The initial discharge capacity of the cathodes is 154.8 mAhg-1 at 0.5 C between 2.5 V and 4.3 V, and the capacity retention keeps 80.6% after 50 charge–discharge cycles. The Li1.1Ni0.35Co0.35Mn0.30O2/Li4Ti5O12 cells also deliver high specific capacities, good cycling stability and rate capability. This work demonstrates that Li1.1Ni0.35Co0.35Mn0.30O2 is a promising cathode material for lithium-ion batteries.

Kinetics of Li+ transport and capacity retention capability of HT- LiCoO2 films

In this work, HT-LiCoO2 films with preferential c-axis orientation were prepared using pulsed laser deposition. The kinetics of lithium ion transport through the HT-LiCoO2 film was investigated by applying potentiostatic intermittent titration technique (PITT). The capacity retention capability of the HT-LiCoO2 film was studied using constant-current (CC) cycling. PITT measurement showed that the lithium chemical diffusion coefficient () of the HT-LiCoO2 films reached as high as 10−8–10−10 cm2 s−1 and the value of in the two-phase coexistence region was lower than that in other single-phase regions. CC cycling revealed that the HT-LiCoO2 film delivered an initial discharge capacity of 40 μAh μm−1 cm−2 and the discharge capacity decreased to 22.4 μAh μm−1 cm−2 after 100 CC cycles. The observation was found to be caused by the continuous formation of the spinel phase (LiCo2O4 or Co3O4).

Microstructural characteristics and biocompatibility of a Type-B carbonated hydroxyapatite coating deposited on NiTi shape memory alloy

Microstructural characteristics and biocompatibility of a Type-B carbonated hydroxyapatite (HA) coating prepared on NiTi SMA by biomimetic deposition were characterized using XRD, SEM, XPS, FTIR and in vitro studies including hemolysis test, MTT cytotoxicity test and fibroblasts cytocompatibility test. It is found CO(3)(2-) groups were present as substitution of PO(4)(3-) anions in HA crystal lattice due to Type-B carbonate. The growth of Type-B carbonated HA coating in SBF containing HCO(3)(-) ions is stable during all periods of biomimetic deposition. The carbonated HA coating has better blood compatibility than the chemically-polished NiTi SMA. There was a good cell adhesion to this HA coating surface and cell proliferation in the vicinity of the coating was better than that for the chemically-polished NiTi SMA. Thus biomimetic deposition of this carbonated HA coating is a promising way to improve the biocompatibility of NiTi SMA for implant applications.