FeNb11O29, anode material for high-power lithium-ion batteries: Pseudocapacitance and symmetrisation unravelled with advanced electrochemical and in situ/operando techniques

In the last years of research on new anode materials for advanced Lithium-Ion Batteries (LIBs), niobium-based oxides are raising growing attention due to very high theoretical capacities and high working potential that can prevent the formation of lithium dendrites, ensuring the safety of the batteries. Most of them crystallizes in open Wadsley–Roth shear structures, which show large Li-ion diffusion coefficients and promising applications in energy storage systems. In this paper, the complex structural and electrochemical features of FeNb11O29 are unravelled with in situ Raman Spectroscopy, operando X-Ray Diffraction and electrochemical techniques. The intrinsic pseudocapacitance shown by the iron niobate is correlated to large channels in its structure that cause weak Li+-host interactions and very little charge-transfer resistances. The symmetrisation of the octahedral framework that occurs after the reduction of Nb5+ cations, detected for the first time, seems to be the key of the electrochemistry of FeNb11O29, which shows excellent features for advanced high-power density LIBs.