V2O5 xerogel electrodes with much enhanced lithium-ion intercalation properties with N2 annealing

V2O5 xerogel films were fabricated by casting V2O5 sols onto FTO glass substrates and annealing at 300 degrees 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 N-2 annealed V2O5 film. Lithium ion intercalation measurements showed that at a charge/discharge current density of 600 mAg(-1), the N-2 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 N-2 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 N-2 annealing as well as much less crystallized vanadium oxide.