Yulong Wu

Carbon anode materials for lithium ion batteries

Since the birth of lithium ion battery in the end of 1980s and early 1990s many kinds of anode materials have been studied. Nevertheless, graphitic carbon is still the only commercially available product. As a result, modification of carbonaceous anode materials has been a research focus. In this paper, latest progress on carbon anode materials for lithium ion batteries is briefly reviewed including research on mild oxidation of graphite, formation of composites with metals and metal oxides, coating by polymers and other kinds of carbons, and carbon nanotubes. These modifications result in great advances; novel kinds of carbon anodes will come in the near future, which will propel the development of lithium ion batteries.

Effects of heteroatoms on electrochemical performance of electrode materials for lithium ion batteries

Recent studies of lithium ion batteries focus on improving electrochemical performance of electrode materials and/or lowering cost. Doping of active materials with heteroatoms is one promising method. This paper reviews the effects of heteroatoms on anode materials such as carbon- and tin-based materials, and cathode materials such as LiCoO2, LiNiO2, LiMn2O4 and V2O5. There are favorable and unfavorable effects, which depend on the species and physicochemical states of heteroatoms and the parent electrode materials. In the application of lithium ion batteries advantageous factors should be exploited, unwelcome side effects should be avoided as far as possible. Considerable gains towards improved electrochemical performance of the electrode materials have been achieved. Nevertheless, there are still problems needing further investigation including theoretical aspects, which will in the meanwhile stimulate the investigation for better electrode materials. # 2002 Elsevier Science Ltd. All rights reserved.

Direct liquefaction of Dunaliella tertiolecta for bio-oil in sub/supercritical ethanol–water

This paper presents bio-oil preparation by direct liquefaction of Dunaliella tertiolecta (D. tertiolecta) with sub/supercritical ethanol-water as the medium in a batch autoclave with high temperature and high pressure. The results indicated that ethanol and water showed synergistic effects on direct liquefaction of D. tertiolecta. The maximum bio-oil yield was 64.68%, with an optimal D. tertiolecta conversion of 98.24% in sub/supercritical ethanol-water. The detailed chemical compositional analysis of the bio-oil was performed using an EA, FT-IR, and GC-MS. The empirical formulas of the bio-oil obtained using the ethanol-water co-solvent (40%, v/v) and sole water as the reaction medium were CH(1.52)O(0.14)N(0.06) and CH(1.43)O(0.23)N(0.09), with calorific values of 34.96 and 29.80 MJ kg(-1), respectively. XPS and SEM results showed that ethanol-water is a very effective reaction medium in the liquefaction. A plausible reaction mechanism of the main chemical component in D. tertiolecta is proposed based on our results and the literatures.

Modified natural graphite as anode material for lithium ion batteries

Abstract A concentrated nitric acid solution was used as an oxidant to modify the electrochemical performance of natural graphite as anode material for lithium ion batteries. Results of X-ray photoelectron spectroscopy, electron paramagnetic resonance, thermogravimmetry, differential thermal analysis, high resolution electron microscopy, and measurement of the reversible capacity suggest that the surface structure of natural graphite was changed, a fresh dense layer of oxides was formed. Some structural imperfections were removed, and the stability of the graphite structure increased. These changes impede decomposition of electrolyte solvent molecules, co-intercalation of solvated lithium ions and movement of graphene planes along the a-axis direction. Concomitantly, more micropores were introduced, and thus, lithium intercalation and deintercalation were favored and more sites were provided for lithium storage. Consequently, the reversible capacity and the cycling behavior of the modified natural graphite were much improved by the oxidation. Obviously, the liquid–solid oxidation is advantageous in controlling the uniformity of the products.

Anode materials for lithium ion batteries by oxidative treatment of common natural graphite

Modification of graphite has recently moved into the focus of the preparation of anode materials for lithium ion batteries. We report on an oxidative treatment by air and concentrated nitric acid solution to improve the electrochemical performance of a common natural graphite. Results from X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), thermogravimmetry (TG) and differential thermal analysis (DTA), high resolution electron microscopy (HREM), and measurements of the reversible electrochemical capacity suggest that the surface structure of natural graphite is changed and a fresh dense layer of oxides is formed. Structural imperfections are removed and the stability of the graphite structure is increased. These changes inhibit electrolyte decomposition, block intercalation of solvated lithium ions and prevent graphene planes from moving along the a-axis direction. In addition, nanochannels and micropores are introduced, and thus, lithium intercalation and deintercalation are favored and more sites are provided for lithium storage. Consequently, reversible capacity and cycling behavior of the modified natural graphite through the oxidation treatments is improved considerably. Since common natural graphite is low in cost, this method is promising for industrial application.

Thermochemical conversion of low-lipid microalgae for the production of liquid fuels: challenges and opportunities

The development of renewable biomass energy sources has attracted attention because of the potential for a sustainable fuel with a low carbon intensity. Microalgae are considered as a third generation biofuel, and have a notable advantage over other biomass in that they do not compete with food or cropland resources. The conversion of algal biomass into liquid fuels provides a long-term sustainable option for fuels production, which can be achieved in an environmentally compatible manner. Among the microalgal conversion methods, thermochemical conversion, which can make full use of all components in the algae, is viewed as one of the best conversion methods, especially for low-lipid microalgae. This article reviews recent developments in the field of algal biomass conversion into liquid fuels, with particular attention focused on the thermochemical conversion of low-lipid microalgae. We start with a brief introduction of microalgae and its biochemical components. After an overview of the main strategies involved in algal biomass conversion, we focus on the thermochemical conversion of algae, including pyrolysis and hydrothermal liquefaction and compare the two methods in detail. In addition, the catalytic upgrading of algae-derived crude bio-oil was also examined. An assessment is made of the challenges and opportunities of a commercial-scale microalgae-to-fuels process in light of mitigating technical, environmental, and logistical issues.

Pyrolysis characteristics and kinetics of aquatic biomass using thermogravimetric analyzer

The differences in pyrolysis process of three species of aquatic biomass (microalgae, macroalgae and duckweed) were investigated by thermogravimetric analysis (TGA). Three stages were observed during the pyrolysis process and the main decomposition stage could be divided further into three zones. The pyrolysis characteristics of various biomasses were different at each zone, which could be attributed to the differences in their components. A stepwise procedure based on iso-conversional and master-plots methods was used for the kinetic and mechanism analysis of the main decomposition stage. The calculation results based on the kinetic model was in good agreement with the experimental data of weight loss, and each biomass had an increasing activation energy of 118.35-156.13 kJ/mol, 171.85-186.46 kJ/mol and 258.51-268.71 kJ/mol in zone 1, 2 and 3, respectively. This study compares the pyrolysis behavior of various aquatic biomasses and provides basis for further applications of the biomass thermochemical conversion.

Effects of pretreatment of natural graphite by oxidative solutions on its electrochemical performance as anode material

Abstract Modification of natural graphite has recently moved into the focus of methods to prepare anode materials for lithium ion batteries. Here we report a treatment method for the modification of a common natural graphite employing oxidative solutions. Four solutions based on H 2 O 2 , Ce(SO 4 ) 2 , HNO 3 and (NH 4 ) 2 S 2 O 8 were employed; their effects were investigated with X-ray photoelectron spectroscopy, thermogravimmetric and differential thermal analysis, high resolution electron microscopy and measurement of electrochemical capacity. All oxidants resulted in marked improvements of reversible capacity, columbic efficiency in the first cycle and cycling behavior due to elimination of some imperfections with high activities towards lithium such as carbon chains, edge carbon atoms and sp 3 -hybridized carbon atoms, creation of more micropores/nano-channels, modification of the surface of natural graphite with a coverage of a dense layer of oxides, and improvement in stability of graphite structure. Effects of the oxidative solutions on electrochemical performance of natural graphite are compared.

Heterogeneous Catalytic Conversion of Biobased Chemicals into Liquid Fuels in the Aqueous Phase

Different biobased chemicals are produced during the conversion of biomass into fuels through various feasible technologies (e.g., hydrolysis, hydrothermal liquefaction, and pyrolysis). The challenge of transforming these biobased chemicals with high hydrophilicity is ascribed to the high water content of the feedstock and the inevitable formation of water. Therefore, aqueous-phase processing is an interesting technology for the heterogeneous catalytic conversion of biobased chemicals. Different reactions, such as dehydration, isomerization, aldol condensation, ketonization, and hydrogenation, are applied for the conversion of sugars, furfural/hydroxymethylfurfural, acids, phenolics, and so on over heterogeneous catalysts. The activity, stability, and reusability of the heterogeneous catalysts in water are summarized, and deactivation processes and several strategies are introduced to improve the stability of heterogeneous catalysts in the aqueous phase.

Anode materials for lithium ion batteries from mild oxidation of natural graphite

Mild oxidation of a natural graphite in an ammonium peroxydisulfate solution yields promising anode materials. X-ray photoelectron spectroscopy, FTIR spectroscopy, electron paramagnetic resonance, thermogravimmetry, differential thermal analysis, high resolution electron microscopy and surface area measurements provided results suggesting that oxidation eliminates some reactive structural defects in this graphite. In addition, the surface of natural graphite is recoated with a dense layer of oxides forming an effective passivating film to prevent the decomposition of electrolyte and the movement of graphene molecules along its a-axis. Consequently, its thermostability and the EPR signal increase. In addition, the numbers of nanosized pores and channels increases, which provide more inlets and outlets for lithium intercalation and deintercalation and more sites for lithium storage. As a result, the reversible lithium capacity and the coulombic efficiency in the first cycle increase significantly and the cycling behaviour improves markedly. The reproducibility of product properties can be well controlled, and this method is promising for industry.