Lithium trivanadate, LiV3OQ, can be prepared in a finely dispersed form by dehydration of aqueous lithium vanadate gels. Two methods of dehydration, both easily adaptable to large-scale production, are described in this work: freeze drying and spray drying. After heat-treatment of the dried gels (xerogels) to remove loosely bound water they show a high capacity for lithium insertion, approaching four additional lithium per formula unit, and good reversibility as electrode materials for high energy density lithium cells. How the heat-treatment temperature influences the crystal structure is demonstrated as well as the electrochemical properties of the vanadium oxide.
InfroductionThe layered trivanadate, LiV3O8, 1 is an interesting alternative to V6013 for use as the positive electrode in secondary lithium cells. The intercalation chemistry of this material was pioneered by Besenhard and Schollhorn, who found it possible to insert lithium ions from a nonaqueous electrolyte2 as well as a number of hydrated cations from aqueous electrolytes.3 Early in the development Nassau and Murphy4 realized that the methods used to prepare the oxide strongly influenced its electrochemical properties. They demonstrated that LiV3O8 prepared in an amorphous, glassy state by rapid quenching from the melt had a higher initial capacity than the crystalline analogue. These findings were, howevei not pursued further in the next decade, where several research groups reported on the use of crystalline LiV3O8 as host material for lithium intercalation.5'7High initial capacities were reported for low-rate discharges, the maximum lithium uptake corresponding to more than three additional Li per formula unit, giving a stoichiometric energy density in excess of 650 Wh/kg.There has been a rather large variation between the values for the maximal lithium uptake from different research groups, but in a structural characterization of lithium inserted Lil+XV3O8, Thackeray et at.'° found that the multiplicity of the sites occupied by lithium in the fully intercalated trivanadate suggests the limiting composition Li5V3O. Recently, Manev et at. have shown how this value can be approached using a specially conditioned LiV3OQThe reported rate capability and cycling properties have, in general, not been satisfactory. Several preparation procedures have been devised to improve the performance of LiV3O8, including control of stoichiometry by rapid cooling,16 more efficient grinding,20 and addition of inert nucleation centers like silica or alumina to the melt.21 The main problem seems to be that on slow cooling, LiV3O3 crystallizes as a very hard and tough material, which is difficult to process into proper electrode structures that can maintain their integrity during deep cycling.In 1990 Pistoia et al.22 reported that fully amorphous L1V3O obtained from a precipitation technique showed significantly higher capacity, better rate capability, and longer cycle life than conventionally made crystalline LiV3O8. In the present paper we describe how an ad...
