Sol–gel preparation of V2O5 sheets and their lithium storage behaviors studied by electrochemical and in-situ X-ray diffraction techniques

Abstract In this paper, V 2 O 5 sheets and bulks are prepared by a low temperature sol–gel method with and without tartaric acid as chelating agent, respectively. Owing to short diffusion pathways for lithium ions, V 2 O 5 sheets display the reversible lithium storage capacities of 243.2, 167.5, 124.3 mAh g −1 at 0.2C, 1C and 2C in 1.5–4.1 V, respectively. Electroanalytical results reveal that the chemical diffusion coefficient (3.4×10 −12 cm 2 s −1 ) in Li-deficient Li x V 2 O 5 sheets ( x =0.681) is almost one order of magnitude higher than that (3.7×10 −13 cm 2 s −1 ) in Li-rich phase ( x =2.824). As a result, V 2 O 5 sheets show an outstanding capacity retention of 92.7% after 22 cycles due to 0.912 Li per formula storage in Li-deficient Li x V 2 O 5 at 2C. In-situ structural analysis shows that the electrochemical reactions of V 2 O 5 sheets with Li are associated with the formation of α-Li x V 2 O 5 , e-Li x V 2 O 5 , δ-Li x V 2 O 5 and γ-Li x V 2 O 5 in 1.5–4.1 V. In the reverse delithiation process, γ-Li x V 2 O 5 can transforms back into δ-Li x V 2 O 5 , e-Li x V 2 O 5 and α-Li x V 2 O 5 , but cannot return to the pristine V 2 O 5 . Upon an over-lithiation process to 0.0 V, the crystal structure of Li x V 2 O 5 ( x >3) sheets will collapse and cannot be rebuilt in 0.0–4.1 V.