V2O5 xerogel electrodes with much enhanced lithium-ion intercalation properties with N2annealing

Abstract

V₂O₅ xerogel films were fabricated by casting V₂O₅ sols onto FTO glass substrates and annealing at 300 °C for 3 hours in nitrogen and air. The films annealed in nitrogen and air possessed different grain size and crystallinity. Optical absorption measurements and electrochemical impedance analyses revealed a reduced optical bandgap and enhanced electrical conductivity of N₂ annealed V₂O₅ film. Lithium ion intercalation measurements showed that at a charge/discharge current density of 600 mAg⁻¹, the N₂ annealed sample possessed noticeably better lithium ion storage capability. In contrast to the air annealed sample, which started with a discharge capacity of 152 mAhg⁻¹ but after 50 cycles the capacity had decreased to a low value of only 44 mAhg⁻¹, the N₂ annealed sample started with a low value of 68 mAhg⁻¹ but the capacity increased sharply to a high value of 158 mAhg⁻¹ at the 24^th cycle, followed by little capacity degradation in later cycles and after 50 cycles, the discharge capacity was still as high as 148 mAhg⁻¹. Much improved lithium ion intercalation capacity and cyclic stability could be attributed to surface defects V⁴⁺ and/or V³⁺ and associated oxygen vacancies introduced by N₂annealing as well as much less crystallized vanadium oxide.