High-Performance Oriented V2O5 Thin Films Prepared by DC Sputtering for Rechargeable Lithium Microbatteries

Crystalline thin films of vanadium pentoxide have been deposited by dc sputtering using a vanadium target. Depending on the power applied, two set of samples 800 nm thick characterized by a 001 or an h00 preferred orientation have been synthesized. Investigation of their respective electrochemical properties as positive electrode for rechargeable lithium microbatteries has been performed in liquid electrolyte. The h00 oriented deposits exhibit a better electrochemical behavior in terms of rate capability, polarization, and cycling properties in the voltage range 3.8/2.8 V. Specific capacities of 25 and 40 mAh/cm2 are recovered after 50 cycles at 10 muA/cm2 in the potential windows 3.8/2.8 and 3.8/2.15 V, respectively. A better electronic conductivity combined with a high porosity induced by a specific morphology are thought to be responsible for this attractive behavior. X-ray diffraction experiments clearly indicate Li insertion results in a continuous increase of the interlayer distance c and a contraction of the a parameter with x in LixV2O5 (0 < x < 1) without the emergence of the delta phase as expected in the bulk material. Using the same procedure, a 2.4 mum thick V2O5 film has been prepared with the h00 preferred orientation to optimize the cycling performance. An excellent rechargeability has been proved in the voltage range 3.8/2.8 V because a specific capacity of 70 mAh/cm2 is still available at a high current density of 100 muA/cm2, showing a good kinetic behavior and a good adherence to the substrate. The present study suggests very thick h00-oriented V2O5 deposits can be prepared with high specific capacities and long cycle life.