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 2 O 6, CaNb 2 O 6, and LiNb 3 O 8 . In the case of MgNb 2 O 6 and CaNb 2 O 6 only 0.27 and 0.26 Li are inserted, respectively. However, in the case of isostructural LiNb 3 O 8, 3.6 Li are inserted. The large uptake of lithium in the case of LiNb 3 O 8 compared to those of MgNb 2 O 6 and CaNb 2 O 6 is discussed with regard to the presence of framework lithium and its distribution in LiNb 3 O 8 . Ex situ XRD studies reveal that the structure is stable up to the insertion of 2.0Li/LiNb 3 O 8 . Further insertion of lithium leads to irreversible structural transformation. The initial discharge capacity of micrometer sized LiNb 3 O 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 3 O 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 3 O 8 as an attractive anode material for Li-ion batteries.