Abstract
At present Li-ion batteries are the premier rechargeable energy storage technology and they offer a promising future as a power source for high energy density battery applications. Unfortunately, their high performance still falls short of energy density goals in many military ground battery and soldier portable applications. Although a number of factors within the battery cell contribute to this performance parameter, the most crucial one relates to how much energy can be stored in the positive and negative electrode materials of the lithium ion battery. Very little focus had been shown in the research of the electrochemistry of transition metal fluorides until Rutgers, The State University of New Jersey began its investigation. The reason for this apparent lack of interest in these compounds was that their intrinsic properties appeared to make them less desirable as possible electrode materials for lithium batteries. Metal fluorides are notorious for their poor electronic conductivity due to the large bandgap induced by the highly ionic character of the metal-halogen bond. This point had kept them away from the radar screen in the search for improved electrode materials for rechargeable lithium batteries. Iron-based compounds are of interest for batteries because of their low cost and low toxicity.
Amatucci and coworkers found that metal fluorides such as iron and bismuth fluorides can be fabricated as high capacity reversible cathodes for rechargeable lithium batteries by converting them into nanoscale electrode materials [1]. We have found that metal fluorides such as iron fluoride prepared with nanoscale particles are able to support appreciable electron conductivity and function as reversible electrodes in non-aqueous lithium ion batteries. The iron fluoride, FeF3, in specially formulated nanoscale particles is able to support appreciable electron conductivity by the shortening of bulk path lengths and augmentation of electron tunneling. These nanocomposites can be prepared through a variety of methods which are practical on a large scale. Electro Energy has fabricated laboratory test cells from cathodes prepared from a mixture of the metal fluoride and high surface carbon. The cell incorporates standard lithium ion battery separators and organic liquid electrolytes. The key technology is the nanocomposite cathode prepared by sophisticated methods which enable the composite electrode mixture, formed from slurry using a suitable solvent, and coating the electrode onto a substrate which is then dried and compacted to achieve the desired density for optimum electrochemical performance.
The paper summarizes the test results gathered from laboratory test cells fabricated from the FeF3 cathode material. The cells were tested at various rates and temperatures and life cycle tested to characterize the capability of the cathode material to meet DoD application requirements. The greatest risk anticipated in the development of this technology is extending beyond the laboratory cell level into the large cell and battery level. In this regard, Electro Energy's wafer lithium cell is ideal for prototype cell development, the cells are easy to construct and initial cell development work can be done using single layer anodes and cathodes [2, 3, 4 and 5].