Lithium insertion in α′-NaV2O5: Na-pillaring effect on the structural and electrochemical properties

Abstract Electrochemically formed α′-NaV 2 O 5 bronze is investigated here as cathode material for rechargeable lithium batteries. We show that the layered structure of this compound, with Na ions located between the V 2 O 5 layers, allows the reversible insertion of 1 lithium/mole of bronze at an average voltage of 2.1 V vs. Li + /Li. The Li insertion-extraction mechanism in α′-Li x NaV 2 O 5 is revealed thanks to ex situ XRD and Raman spectroscopy investigations. A narrow one-phase region occurs in the 0  1.3 NaV 2 O 5 material. The structure of the α′-LiNaV 2 O 5 is isomorphic to the pristine material. It is remarkable that only limited structural changes are found in the 0  c parameter. A high structural reversibility is evidenced, which accounts for the remarkable stable capacities achieved whatever the C rate, near 120 mAh g −1 and 60 mAh g −1 at C/10 and 1C, respectively after 60 cycles. The lithium chemical diffusion coefficient D Li , in the range 10 −9 – 10 −10  cm 2  s −1 in the 0.03 ≤ x ≤ 1.1 composition domain, is little affected by the Li concentration. The high mobility revealed for lithium ions is also supported by BVEL analysis, while a significant activation energy for Na-ions migration ascertains their immobility in the α′-NaV 2 O 5 lattice. These results demonstrate the interest of large interlayer 2D host lattices stabilized by pillaring species such as Na to achieve a stable cycling behavior, a facile guest cation insertion and to promote the ionic diffusion.