Synthesis and electrochemical characterization of lithium vanadium phosphate

Abstract

In a world where the miniaturization and the portability of electronic devices is king, batteries play an ever-increasingly important role. They are vital components in many consumer electronics such as cell phones and PDAs, in medical devices, and in novel applications, such as unmanned vehicles and hybrids. As the power demands of these devices increases, battery performance must improve accordingly. This thesis is an introductory investigation into the electrochemical properties of a promising new battery cathode material: lithium vanadium phosphate (Li3V2(PO4)3) (LVP). Studies of other members of the phospho-olivine family, which LVP is a part of, indicate that the olivines have high lithium diffusivity but low electronic conductivity. LVP is part of the phosphor- olivine family, which traditionally has been shown to have high lithium diffusivity but low electronic conductivity. LVP was synthesized via a solid-state reaction and cast into composite cathodes. (90/5/5 ratio of LVP, Super P Carbon, and PVDF.) These composite cathodes were used in lithium anode, LiPF6 liquid electrolyte, Swage-type cells that were galvanostatically cycled from 3.OV to 4.2V and from 3.4V to 4.8V at C/20 rates. Electrochemical impedance spectroscopy was carried out on an LVP / liquid electrolyte / LVP cells from 0.01Hz to 1MHz. Finally, temperature conductivity measurements were taken from a die-pressed LVP bar. The results of the experimentation indicate that LVP has much promise as a new battery cathode material, but there are still a number of concerns to address.

(cont.) LVP has a higher operating voltage (4.78V) than the current Li-ion battery standard (3.6V), but there are issues with becoming amorphous, cycleability, and active material accessibility. From the EIS data, passivating films on the surface of the LVP cathode do not seem to be a factor in limiting performance. The conductivity data gives a higher than expected conductivity (4.62* 10-4 S/cm).