Lithium insertion into niobates with columbite-type structure: Interplay between structure-composition and crystallite size

We have studied lithium insertion into three columbite type compounds MgNb 2O6, CaNb 2O 6, and LiNb 3O 8. In the case of MgNb 2O6 and CaNb 2O6 only 0.27 and 0.26 Li are inserted, respectively. However, in the case of isostructural LiNb 3O 8, 3.6 Li are inserted. The large uptake of lithium in the case of LiNb 3O 8 compared to those of MgNb 2O6 and CaNb 2O6 is discussed with regard to the presence of framework lithium and its distribution in LiNb 3O 8. Ex situ XRD studies reveal that the structure is stable up to the insertion of 2.0Li/LiNb 3O 8. Further insertion of lithium leads to irreversible structural transformation. The initial discharge capacity of micrometer sized LiNb 3O 8 is 234 mAh g -1. However it shows a large irreversible capacity loss in the first charge and the reversible capacity fades to 45 mAh g -1 on cycling. Further, we have synthesized nanocrystalline LiNb 3O 8 by polymeric complex method with the aim to improve its electrochemical performance. The nanocrystalline sample shows an initial discharge capacity of 265 mAh g -1 and the reversible capacity is 145 mAh g -1 even after 50 cycles, rendering nanocrystalline LiNb 3O 8 as an attractive anode material for Li-ion batteries. © 2011 American Chemical Society.