Patricia H. Smith

In situ XAS investigation of the oxidation state and local structure of vanadium in discharged and charged V2O5 aerogel cathodes

We have examined the evolution of the oxidation state and atomic structure of vanadium(V) in discharged and charged nanophase vanadium pentoxide (V2O5) aerogel cathodes under in situ conditions using X-ray absorption spectroscopy (XAS). We show that the oxidation state of V in V2O5 aerogel cathode heated under vacuum (100 mTorr) at 220 8C for 20.5 h is similar to that of V in a commercially obtained sample of orthorhombic V2O5. In addition, lithium (Li) insertion during the first cycle of discharging leads to the reduction of V(V) to V(IV) and V(IV) to V(III) in a manner consistent with the stoichiometry of the sample (i.e. Lix V2O5). Li extraction during charging leads to oxidation of V(III) to V(IV) and then V(IV) to V(V). Furthermore, the oxidation state of V in fully charged cathodes remains unchanged with cycling (upto at least the 16th cycle) from that of V in the control V2O5 aerogel cathode. However, the average oxidation state of V in discharged V2O5 cathodes increased with cycling. Moreover, the local structure of V in the discharged state has a higher degree of symmetry than that of the fully charged state. A significant change in the structure of the V/V correlation of discharged cathodes is observed with cycling indicating the formation of electrochemically irreversible phases. # 2002 Elsevier Science Ltd. All rights reserved.

A survey of available underwater electric propulsion technologies and implications for platform system safety

The majority of unmanned undersea vehicle (UUV) and autonomous underwater vehicle (AUV) applications are electrically powered, deriving their energy from chemical reactions within a battery. Unlike thermal engines, where chemical energy is metered into a combustion chamber, batteries are unique in the storage of all energy content within a limited material construction. Fuel cells are a logical cross between the concepts of electric storage battery and thermal engine. The requirements for military and some civilian AUVs demand increased battery energy density and volume compared to the overall AUV vehicle. Batteries, like fuel cells. are most cost-effective when they may be recharged and reutilized. The aspects of increased energy density, intrinsic power capability and electrical or mechanical recharging present a significant challenge in designing a power supply system that is safe under all conditions for the AUV and for the deployment platform. This paper will provide an overview of common AUV propulsion systems and discuss aspects of vehicle integration and vehicle and launch platform safety with respect to recharging, refurbishing or refueling an AUV system.

High pulse power batteries for air deployable Navy applications

The US Navy needs a high-power battery for an advanced sonobuoy. Several chemistries and designs have been examined and reported upon. The main focus at this point is on thermal batteries and lithium/sulfur dioxide (Li/SO/sub 2/) batteries. Other chemistries have been evaluated (e.g. lithium/manganese dioxide and lithium/thionyl chloride), however only lithium/sulfur dioxide and thermals have the combination of high power, energy, and low cost (producibility) that is required.