Crystal Structure Modification Enhanced FeNb11O29 Anodes for Lithium-Ion Batteries

The recently explored FeNb11O29 is an advanced anode material for lithium-ion batteries, owing to its high specific capacity and safety. However, it suffers from poor rate capability. To tackle this issue, a crystal structure modification is employed. Defective FeNb11O29 (FeNb11O27.9) is fabricated by using a one-step solid-state reaction method in N-2. FeNb11O27.9 has the same ortho-rhombic shear ReO3 crystal structure (Amma space group) as FeNb11O29, but a larger unit-cell volume and 3.8% O2- vacancies (vs. all O2- ions), which improve the Li+-ion diffusion coefficient by a factor of 88.3%. The contained Nb4+ ions with free 4d electrons significantly increase the electronic conductivity by three orders of magnitude. Consequently, FeNb11O27.9 shows improved pseudocapacitive behavior and electrochemical properties. In comparison with FeNb11O29, FeNb11O27.9 exhibits a higher reversible capacity of 270 mAhg(-1) with a higher first-cycle coulombic efficiency of 90.6% at 0.1 C. At 10 C, FeNb11O27.9 still retains a high capacity of 145 mAhg(-1) with low capacity loss of 6.9% after 200 cycles, in contrast to the values of 99 mAhg(-1.) and 11.1% obtained for FeNb11O29.