Chuanqi Feng

Low-temperature synthesis of polypyrrole-coated LiV3O8 composite with enhanced electrochemical properties

A composite, Liv 3 O 8 -polypyrrole (PPy), was synthesized by a low-temperature solution route followed by an in situ polymerization method. The as-prepared powders consisted of nanosized PPy distributed homogeneously within the layered lithium trivanadate. The electrochemical properties of Liv 3 O 8 -PPy composite were systematically investigated and compared with bare lithium trivanadate. It was found that the electrochemical performance of the Liv 3 O 8 -PPy composite was significantly enhanced, with a specific capacity of ∼ 183 mAh g -1 retained after 100 cycles. This suggests that nanostructured PPy could work well as a polymer-conducting matrix and also as a binding material to improve the overall electrochemical properties of the Liv 3 O 8 when used as a cathode material in lithium-ion batteries.

Synthesis of hollow GeO2 nanostructures, transformation into Ge@C, and lithium storage properties

In this work, we synthesize mesoporous and hollow germanium@carbon nanostructures through simultaneous carbon coating and reduction of a hollow ellipsoidal GeO2 precursor. The formation mechanism of GeO2 ellipsoids and the ratio of Ge4+ to Sn4+ as the starting materials are also investigated. Compared to the solid ellipsoidal Ge@carbon (Ge@C-3), the hollow ellipsoidal Ge@C-1 sample exhibits better cycling stability (100% capacity retention after 200 cycles at the 0.2 C rate) and higher rate capability (805 mA h g−1 at 20 C) compared to Ge@C-3 due to its unique hollow structure; therefore, this hollow ellipsoidal Ge@carbon can be considered as a potential anode material for lithium ion batteries.

Hollow carbon spheres with encapsulated germanium as an anode material for lithium ion batteries

A novel composite consisting of hollow carbon spheres with encapsulated germanium (Ge@HCS) was synthesized by introducing a germanium precursor into the porous-structured hollow carbon spheres. The carbon spheres not only function as a scaffold to hold the germanium and thus maintain the structural integrity of the composite, but also increase the electrical conductivity. The voids and vacancies that are formed after the reduction of germanium dioxide to germanium provide free space for accommodating the volume changes during discharging–charging processes, thus preventing pulverization. The obtained Ge@HCS composite exhibits excellent lithium storage performance, as revealed by electrochemical evaluation.

Hydrothermal synthesis of molybdenum disulfide for lithium ion battery applications

Abstract Molybdenum disulfide nanoflakes were synthesized by a simple hydrothermal process using sodium molybdate and thiourea as reactants at a relatively low temperature. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that the samples have the structure of 2H-MoS 2 and the morphology of nanoflakes with the average thickness around 5–10 nm. The results of electrochemical properties indicate that the morphology and size of MoS 2 particles have effects on their capacity when they are used as the anode for lithium ion battery. The as-prepared MoS 2 samples have high reversible discharge capacity up to 994.6 mA·h·g −1 for the MoS 2 -1 electrode and 930.1 mA·h·g −1 for the MoS 2 -2 electrode and show excellent cycling performances. The MoS 2 -1 electrode has a better cycling stability than the MoS 2 -2 electrode due to their difference in the uniformity of the samples.

K0.25Mn2O4 nanofiber microclusters as high power cathode materials for rechargeable lithium batteries

K0.25Mn2O4 microclusters assembled from single-crystalline nanofibers were synthesized via a hydrothermal process at different temperatures. The possibility of using these materials as cathode material for lithium ion batteries was studied for the first time. The charge/discharge results showed that the K0.25Mn2O4 nanofiber microclusters synthesized at 120 °C exhibit excellent lithium storage properties, with a high reversible capability (360 mA h g−1 at current density of 100 mA g−1) and stable lithium-ion insertion/de-insertion reversibility. The charge/discharge mechanism in lithium ion batteries was studied and proposed for the first time. During the charge process, K+ was extracted from the electrode, which made active vacated sites suitable for lithium ion intercalation and was beneficial for increasing capacity.

Synthesis and Characterization of Cobalt-Doped WS2 Nanorods for Lithium Battery Applications

Cobalt-doped tungsten disulfide nanorods were synthesized by an approach involving exfoliation, intercalation, and the hydrothermal process, using commercial WS2 powder as the precursor and n-butyllithium as the exfoliating reagent. XRD results indicate that the crystal phase of the sample is 2H-WS2. TEM images show that the sample consists of bamboo-like nanorods with a diameter of around 20 nm and a length of about 200 nm. The Co-doped WS2 nanorods exhibit the reversible capacity of 568 mAh g−1 in a voltage range of 0.01–3.0 V versus Li/Li+. As an electrode material for the lithium battery, the Co-doped WS2 nanorods show enhanced charge capacity and cycling stability compared with the raw WS2 powder.

Unique Urchin-like Ca2Ge7O16 Hierarchical Hollow Microspheres as Anode Material for the Lithium Ion Battery.

Germanium is an outstanding anode material in terms of electrochemical performance, especially rate capability, but its developments are hindered by its high price because it is rare in the crust of earth, and its huge volume variation during the lithium insertion and extraction. Introducing other cheaper elements into the germanium-based material is an efficient way to dilute the high price, but normally sacrifice its electrochemical performance. By the combination of nanostructure design and cheap element (calcium) introduction, urchin-like Ca2Ge7O16 hierarchical hollow microspheres have been successfully developed in order to reduce the price and maintain the good electrochemical properties of germanium-based material. The electrochemical test results in different electrolytes show that ethylene carbonate/dimethyl carbonate/diethyl carbonate (3/4/3 by volume) with 5 wt% fluoroethylene carbonate additive is the most suitable solvent for the electrolyte. From the electrochemical evaluation, the as-synthesized Ca2Ge7O16 hollow microspheres exhibit high reversible specific capacity of up to 804.6 mA h g−1 at a current density of 100 mA g−1 after 100 cycles and remarkable rate capability of 341.3 mA h g−1 at a current density of 4 A g−1. The growth mechanism is proposed based on our experimental results on the growth process.

In-situ One-step Hydrothermal Synthesis of a Lead Germanate-Graphene Composite as a Novel Anode Material for Lithium-Ion Batteries

Lead germanate-graphene nanosheets (PbGeO3-GNS) composites have been prepared by an efficient one-step, in-situ hydrothermal method and were used as anode materials for Li-ion batteries (LIBs). The PbGeO3 nanowires, around 100–200 nm in diameter, are highly encapsulated in a graphene matrix. The lithiation and de-lithiation reaction mechanisms of the PbGeO3 anode during the charge-discharge processes have been investigated by X-ray diffraction and electrochemical characterization. Compared with pure PbGeO3 anode, dramatic improvements in the electrochemical performance of the composite anodes have been obtained. In the voltage window of 0.01–1.50 V, the composite anode with 20 wt.% GNS delivers a discharge capacity of 607 mAh g−1 at 100 mA g−1 after 50 cycles. Even at a high current density of 1600 mA g−1, a capacity of 406 mAh g−1 can be achieved. Therefore, the PbGeO3-GNS composite can be considered as a potential anode material for lithium ion batteries.

Hierarchical Structural Evolution of Zn2GeO4 in Binary Solvent and Its Effect on Li-ion Storage Performance

Zinc germinate (Zn2GeO4) with a hierarchical structure was successfully synthesized in a binary ethylenediamine/water (En/H2O) solvent system by wet chemistry methods. The morphological evolution process of the Zn2GeO4 was investigated in detail by tuning the ratio of En to H2O in different solvent systems, and a series of compounds with awl-shaped, fascicular, and cross-linked hierarchical structures was obtained and employed as anode materials in lithium-ion batteries. The materials with fascicular structure exhibited excellent electrochemical performance, and a specific reversible capacity of 1034 mA h g-1 was retained at a current density of 0.5 A g-1 after 160 cycles. In addition, the as-prepared nanostructured electrode also delivered impressive rate capability of 315 mA h g-1 at the current density of 10 A g-1. The remarkable electrochemical performances could be ascribed to the following aspects. First, each unit in the three-dimensional fascicular structure can effectively buffer the volume expansions during the Li+ extraction/insertion process, accommodate the strain induced by the volume variation, and stabilize its whole configuration. Meanwhile, the small fascicular units can enlarge the electrode/electrolyte contact area and form an integrated interlaced conductive network which provides continuous electron/ion pathways.

AlPO4 coated LiNi1/3Co1/3Mn1/3O2 for high performance cathode material in lithium batteries

The surface of layered LiNi1/3Co1/3Mn1/3O2 was coated with AlPO4 by co-precipitation method and followed by heat treatment. The prepared samples were characterized by XRD and SEM. The samples coated with AlPO4 exhibited both improved rate and cycle capacity compared with the pristine LiNi1/3Co1/3Mn1/3O2. Especially, the sample coated with 1 wt% AlPO4 showed outstanding cyclability. The electrochemical impedance spectroscopy (EIS) results indicated that the AlPO4 coating layer significantly suppressed the increase of charge-transfer resistance (Rct). The activation energy of the charge transfer processes at the electrode/electrolyte interface was reduced by AlPO4 coating. These results indicate that AlPO4 coated LiNi1/3Co1/3Mn1/3O2 could be a promising cathode material for lithium ion batteries.