Neutron Diffraction and Electrochemical Study of FeNb11O29/Li11FeNb11O29 for Lithium Battery Anode Applications

Lithium was found to be inserted into FeNb11O29 by reaction with n-butyllithium, producing Li11FeNb11O29 samples with good crystallinity, and the Amma crystallographic-shear structures of both compounds (a = 28.7093(6)/28.4036(4), b = 3.8256(1)/4.08447(9), c = 20.6241(4)/20.7067(2) Å, respectively) were Rietveld-refined by high-resolution neutron powder diffraction. Lithium atoms of Li11FeNb11O29 were located both in 4-fold- and in 5-fold-coordinated positions, lying respectively inside and between the 4 × 3 perovskite blocks of Nb(Fe)O6 octahedra. Electrochemical measurements on a FeNb11O29/ LixFeNb11O29 electrode vs metallic Li showed that lithium can be intercalated/deintercalated reversibly in the 1.1–2.5 V range with a stable capacity of 185 mAh/g, which roughly corresponds to 11 Li atoms per f.u. as obtained by chemical lithiation. The rather uniform structural distribution found for Li atoms is consistent with the good electrode reversibility, which makes this material promising as anode in rechargeable lithium batteries.