Electrochemical lithium and sodium intercalation into the tantalum-rich layered chalcogenides Ta2Se and Ta2Te3

Two-layered tantalum chalcogenides are evaluated as alkali metal intercalat ion hosts in lithium and sodium electrochemical cells. The metal-rich pseud o-two-dimensional solid Ta2Se shows a poor intercalation behaviour. Lithium reacts with the selenide by deintercalating selenium from the blocks of Ta -related b.c.c. structure leading to a collapse of the structure and the fo rmation of tantalum metal. Sodium is reversibly intercalated to a limited e xtent leading to complex structural changes in the selenide, as revealed by electron diffraction. The two-dimensional telluride Ta2Te3 allows a topota ctic intercalation of lithium below 1 F/mol, while a more extended reaction leads to sample amorphization. The better intercalation behaviour of this solid can be related with the one-atom thick metal layer and the van der Wa als gap separating tellurium atoms of successive layers. Sodium can be reve rsibly intercalated into Ta2Te3 in sodium cells which show a good cycling b ehaviour. Exposure of the intercalated solid to water vapour allows the pre paration of hydrated products with a monolayer or a bilayer of water molecu les solvating sodium in the interlayer space. (C) 1999 Elsevier Science S.A . All rights reserved.