G.S. Cao

In Situ Synthesis and Properties of Carbon-Coated LiFePO4 as Li-Ion Battery Cathodes

An in situ synthesis method for carbon-coated LiFePO 4 powders has been investigated in detail using inexpensive FePO 4 as an iron source and polypropylene as a reductive agent and carbon source. Thermogravimetric and differential thermal analysis of the precursor mixture indicated that the pyrolysis of polypropylene and the combination reaction of LiFePO 4 could be processed synchronously at a synthesis temperature between 500 and 800°C. X-ray diffraction analyses and scanning electron microscopy observations showed that LiFePO 4 /C composites with fine particle sizes and homogeneous carbon coating could be directly synthesized by the in situ method. The electrochemical performances of the carbon-coated LiFePO 4 powder synthesized at 700°C were evaluated using an electrochemical model cell by galvanostatic charge/discharge and cyclic voltammetry measurements. The in situ synthesized LiFePO 4 /C composite had a high electrochemical capacity of 164 mA h g - 1 at the 0.1C rate, and possessed a favorable capacity cycling maintenance at the 0.3 and 0.5C rates. The good electrochemical properties of the LiFePO 4 /C composite are suggested to originate from the good crystallinity, the fine particle sizes, and the efficient electronic conductive coating layer of the material.

A study of Zn4Sb3 as a negative electrode for secondary lithium cells

Abstract Antimony zinc alloy, Zn 4 Sb 3 , was studied as a potential material for negative electrodes of lithium-ion batteries. It was found that the reversible capacity of ball-milled Zn 4 Sb 3 in the first cycle reached 507 mA h g −1 and increased up to 580 mA h g −1 when the alloy was ball-milled with about 11.8 wt.% graphite additives. Ex-situ XRD analyses of the pure Zn 4 Sb 3 electrodes during cycling showed that several lithium-containing compounds such as LiZnSb, Li 3 Sb and LiZn have been formed successively during the insertion of lithium into Zn 4 Sb 3 . It was found that the ball-milled composite, Zn 4 Sb 3 /C 7 , possesses high initial reversible capacity, small voltage hysteresis and good capacity retention, which make this material an interesting potential electrode for lithium-ion batteries.

Improved hydrogen storage properties of MgH2 by ball milling with AlH3: preparations, de/rehydriding properties, and reaction mechanisms

Organometallically prepared AlH3 and as-received Al powders were mixed with MgH2 to improve the dehydriding and rehydriding properties of MgH2. Thermal analysis shows that the onset dehydriding temperature of MgH2 is reduced by 55 °C (or 25 °C) when mixed with AlH3 (or Al). The destabilization of MgH2 is attributed to the formation of Mg–Al alloys through the reaction between MgH2 and Al. Isothermal dehydriding measurements demonstrate that AlH3 and Al both improve the dehydriding kinetic of MgH2 to some extent, and it only takes 44 min for MgH2 + AlH3 (5.4 h for MgH2 + Al) to release 60% of the hydrogen of MgH2 at 300 °C, but 8.6 h are required for as-milled MgH2. The apparent activation energy for the dehydriding of MgH2 is reduced from 174.6 kJ mol−1 for as-milled MgH2 to 154.8 and 138.1 kJ mol−1 for MgH2 mixed with Al and AlH3 respectively; this is responsible for the improvement in the dehydriding kinetics of MgH2. Despite this, AlH3 is better in destabilizing MgH2 than the as-received Al for the fact that Al* formed in situ from the decomposition of AlH3 is oxide-free on the particle surfaces, which effectively increases the chemical activity of Al*. Furthermore, the brittleness of AlH3 makes it easier to mix MgH2 with AlH3, which would result in uniform distributions of Mg and Al and shortening of the diffusion length. Concerning the reversibility, at 300 °C and 5 MPa H2 and MgH2 are fully recovered in the dehydrided MgH2 + Al, and MgH2 + AlH3 samples after rehydriding for 10 h. The rehydriding kinetic of MgH2 is significantly enhanced for the dehydrided MgH2 + AlH3, but not in the case of the MgH2 + Al.

Electrochemical properties of some Sb or Te based alloys for candidate anode materials of lithium-ion batteries

Some antimony or tellurium based thermoelectric alloys have been prepared and studied as new candidate anode materials for lithium-ion batteries. It was found that some thermoelectric antimonides yield a volume capacity for reversible lithium storage more than twice that of state of the art carbon based materials. Ex-situ XRD analyses show that the semimetals such as antimony, bismuth and tellurium in the semiconducting thermoelectric alloys are the active elements for the lithium adsorption. However, inactive elements are also necessary for an alloy electrode to ensure the electrochemical capacity retention during cycling.

Facile synthesis of C–Fe3O4–C core–shell nanotubes by a self-templating route and the application as a high-performance anode for Li-ion batteries

In this study, we synthesized C–Fe3O4–C core–shell nanotubes through a facile chemical vapor deposition (CVD) method using Fe2O3 nanotubes as the self-templates. The hydrothermal product α-Fe2O3 hematite exhibits a tubular structure with an inner diameter of 70–100 nm, a wall thickness of 10–20 nm, and a length of 300–800 nm. After the CVD reaction in C2H2, α-Fe2O3 could be transformed into C–Fe3O4–C with the tubular structure reserved. The tubular C–Fe3O4–C is constructed by an Fe3O4 nanotube core and 5 nm thick carbon shells on both inner and outer surfaces of the Fe3O4 nanotube. The C–Fe3O4–C nanotube anode exhibits a stable cycling with a capacity over 700 mA h g−1 retained after 120 cycles at 100 mA g−1. The improved electrochemical properties of C–Fe3O4–C nanotubes compared with bare α-Fe2O3 could be attributed to the introduction of the carbon shells, which not only supplya high conductive channel and buffer matrix, but also keep the structural stability of the Fe3O4 nanotube upon cycling.

Electrochemical lithiation and delithiation of FeSb2 anodes for lithium-ion batteries

Abstract Iron antimonide, FeSb 2 , has been prepared by levitation melting. The electrochemical cycling behaviors of FeSb 2 were evaluated using lithium-ion model cell Li/LiPF 6 (EC+DMC)/FeSb 2 . It was found that the reversible capacity of FeSb 2 in the first cycle reached 507 mA h g −1 , and a reversible capacity of about 282 mA h g −1 was still maintained after 15 cycles. In our present work, we also found that the FeSb 2 /mesocarbon microbeads (MCMB) composite material possessed higher initial reversible capacity and better cycle life than pure FeSb 2 , which made it suitable for use as anode material in rechargeable lithium-ion batteries.

Electrochemical Performances of Nanosized Intermetallic Compound CoSb2 Prepared by the Solvothermal Route

Nanosized CoSb 2 powder was prepared by the solvothermal route and studied as a new candidate for anode material for secondary lithium-ion batteries. The powder was characterized by X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy in conjunction with energy dispersive X-ray analyses. It was found that the reversible capacity of the nanosized CoSb 2 in the first cycle reached 582 mA h g -1 and a capacity of 355 mA h g -1 was still maintained for more than 20 cycles. The experimental results of nanosized CoSb 2 were compared with that of a micrometer-sized one prepared by the levitation-melting/ballmilling route, which exhibited lower reversible capacity and poor cycling behavior. The superior electrochemical performance of solvothermally prepared CoSb 2 is related to the microstructure and nanoscaled particle size.