A new class of materials for lithium-ion batteries: iron(III) borates

The first electrochemical investigation of transition metal berate structur es are reported, focusing on FeBO3 and Fe3BO6. In Fe3BO6, uptake of lithium initiates a two-phase process that results in framework disintegration, as expected from structural considerations and formation of an amorphous mate rial that reversibly cycles lithium with a specific capacity of 450 mhA/g a t an average potential of 1.6 V, in the regime of anode applications. Subst itution of Fe(III) with other metals in the Fe3BO6 lattice is found to be d etrimental to cycling behavior. Reduction of the particle size results in a reversible capacity up to 700 mAh/g, albeit with some fading on cycling. ( C) 2001 Elsevier Science B.V. All rights reserved.