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

Abstract

The first electrochemical investigation of transition metal borate structures are reported, focusing on FeBO 3 and Fe 3BO 6. In Fe 3BO 6, uptake of lithium initiates a two-phase process that results in framework disintegration, as expected from structural considerations and formation of an amorphous material that reversibly cycles lithium with a specific capacity of 450 mhA/g at an average potential of 1.6 V, in the regime of anode applications. Substitution of Fe(III) with other metals in the Fe 3BO 6 lattice is found to be detrimental to cycling behavior. Reduction of the particle size results in a reversible capacity up to 700 mAh/g, albeit with some fading on cycling.