NEW CATHODE MATERIALS FOR RECHARGEABLE LITHIUM BATTERIES - THE 3-D FRAMEWORK STRUCTURES LI3FE2(XO4)(3) (X = P, AS)

Electrochemical insertion of lithium into four Li3Fe2(XO4)(3) polymorp hs (X = P or As) with 3-D framework structures was carried out in ''Li /LiClO4(PC:DME)/cathode'' coin cells, Approximately 2 Li per formula u nit could be reversibly inserted into the three different structures, which corresponds to the reduction of all Fe3+ to Fe2+ between 2.5 and 3.5 V vs lithium. The position of the Fe3+/Fe2+ redox couple below th e lithium-anode Fermi energy is nearly independent uf the structure an d of whether X = P or As, There rs, however, a clear dependence of (i) the shape of the V-cc vs x curves for Li3+xFe2(XO4)(3) and (ii) the c harge-discharge rare capabilities on the crystal structure of the cath ode material, (C) 1998 Academic Press.