Next Generation Positive Electrode Materials Enabled by Nanocomposites: -Metal Fluorides-
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Next Generation Positive Electrode Materials Enabled by Nanocomposites: -Metal FluoridesF. Badwaya, N. Pereiraa,b, F. Cosandeyb, and G.G. Amatuccia,z a
Telcordia Technologies, Red Bank, NJ 07701 USA Rutgers University, Piscataway, NJ 08855 USA
b
z
e-mail: [email protected]
ABSTRACT Through the use of nanostructures and nanocomposites, the electrochemical activity of metal fluoride materials was opened as potential candidates as next generation high energy density positive electrodes for Li batteries. This class of materials, utilizing FeF3 as an example, is shown to exhibit good reversible behavior of approximately 200 mAh/g in the 3V region. The specific capacity is extended to 600 mAh/g when the discharge is extended to take into account the additional specific capacity associated with a 2V plateau. Through the use of XRD, SAED and high resolution TEM, the 2V reaction mechanism was associated to a reversible metal fluoride conversion mechanism. It is shown that LiF + Fe nanocomposite can be utilized as initial components in order to make the technology suitable for Li-ion applications. Although exhibiting relatively poor rate capabilities at this initial stage, reversible conversion metal fluorides enable for the first time the utilization of all the redox states of the constituent metal in a reversible manner in the positive electrode. This translates to 4X the specific capacity and double the energy density of today’s state of the art LiCoO2. INTRODUCTION The Li-ion battery is the premiere high-energy rechargeable energy storage technology of the present day. Unfortunately, its high performance still falls short of energy density goals in applications ranging from telecommunications to biomedical. Although a number of factors within the battery cell contribute to this performance parameter, the most crucial ones relate to how much energy can be stored in the positive and negative electrode materials of the device. The positive electrode of Li-ion batteries is dominated by the layered Li intercalation compound, LiCoO21. LiCoO2 has a practical reversible specific capacity of 150 mAh/g. Alternative electrode materials such as compounds and solid solutions consisting of LiNiO22 and LiMn2O43 4 have been introduced in the past. Although the capacity of these materials do not exceed that of LiCoO2 by a great extent, they are lower in cost and the latter is more environmentally acceptable. For the past decade there has been an extensive effort for search for new positive electrode materials. Current focus is on layered manganese compounds of the general formula LiMnO2 5and phosphate materials of the general formula LiMePO46 and Li3Me2(PO4)37where Me is a transition metal. Although operating at a lower voltage and close to the same capacity as present day LiCoO2, these materials are of interest due to their low cost and safety. However, little new ground has been revealed in the quest for positive electrode materials of higher energy density. Metal fluorides have been largely ignored as positive elec
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