Metal Chloride-Graphite Compounds as Cathode and Anode Materials for Batteries
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SERGE FLANDROIS AND FRANCIS BARON Centre de Recherche Paul Pascal, Universite' de Bourdeaux,
33405 TALENCE,
FRANCE
ABSTRACT Graphite intercalation compounds can be used as electrode materials in batteries owing to the high electronic conductivity of carbon layers and the easy diffusion of ions Moreover intercalation has the between the layers. beneficial effect of impeding some parasitic reactions After a brief detrimental to good electrode reversibility. review of recent proposals, emphasis is given to transition It is shown that, besides the nickel metal chlorides. chloride-graphite compound proposed two years ago as a cathode material for alkaline batteries, other metal chlorides intercalated into graphite are excellent cathode or anode materials. INTRODUCTION Graphite intercalation compounds have already been proposed as electrode mateadvantage of these materials is the high elecrials in batteries [1-8]. The first trical conductivity of graphitic layers which increases generally after intercalation. However any electrode reaction implies the presence of both electrons and ions. A high ionic conductivity is thus needed for the electrochemical reactions to occur. This is not obvious for graphite compounds;nevertheless we will see that a certain ionic conductivity is observed at least for some ions. Intercalation compounds have another advantage : the host structure (graphite lattice) can protect the active material (the guest) from harmful reactions for example dissolution in the electrolyte. The proposals of using graphite intercalation compounds as electrode materials to be mentioned which is also the concern various types of batteries. The first only one commercialized at the present time is based on the electrochemical couple Li/CF [1J. This system has interesting characteristics for miniature batteries used as power sources for small size electronic equipment. Its main qualities are high voltage (the initial OCV is around 3 volt), light weight, discharge capabilities over a wide temperature range, voltage stability and good shelf life. As early as 1928, graphite oxide was proposed as a cathodic depolarizer in Leclanch6 cells [23. However, because of its price and its hazardous nature, MnO2 preferred. More recently, graphite oxide has been proposed as the cathois still de in lithium cells [3]. A very high theoretical energy density of 1200 Wh/kg (calculated on the weight of anode and cathode only) makes this cell a serious candidate as a novel battery. Many other intercalation compounds can be used as the cathode of lithium ARMAND and TOUZAIN [4] have listed theoretical EMFs and energy densities cells. The more promising ones appear to be intercalation for more than one hundred. compounds with fluorometallate ions, such as PFE, AsF'6 or SbFr. MAXIMOVITCH et al. L5J have tested some metal chloride - graphite compounds as chlorine reservoirs for Al/Cl 2 batteries. The electrolyte was an NaCI-AlCI3 mixture which melts at about 110*C. The OCV after charging was about 2.1% The best results were obtained for C 3
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