Performance and capacity fade of V 2O 5–lithium polymer batteries at a moderate–low temperature

Abstract

Lithium metal–polymer electrolyte batteries with improved utilization of the active material at a moderate–low temperature (65°C) were realized. Low molecular weight poly(ethylene glycol) (PEG, MW=2000) was used as the lithium-ion conductive matrix in the composite cathode. The cathode active material was crystalline V 2O 5. A blend of poly(ethylene oxide) (PEO, MW=4×10 6) and PEG was used as a solid polymer electrolyte (SPE). The transport properties of the SPE were evaluated at various temperatures. A specific conductivity as high as 1.0×10 −4 S cm −1 was calculated at 45°C. The temperature dependence of the interfacial resistances between lithium/SPE and cathode material/PEG was evaluated. The lithium/SPE interfacial resistance decreases linearly with the temperature. The charge transfer resistance between the cathode material and PEG reaches a minimum at 60°C and it does not decrease with a further temperature increase. The data clearly show that the battery is able to work at a temperature as low as 60°C. The operating temperature was set at 65°C and the battery performance was evaluated at different discharge rates. An energy density of about 500 W h kg −1 and a power density of about 150 W kg −1 were achieved cycling the cell in about 3.3 h at 0.20 mA cm −2. Prolonged cycling showed a capacity fading of about 0.45% per cycle. This value does not differ very much from the value found cycling the cell in liquid electrolyte. The fade in capacity was associated with an increase of cell resistance. The evolution of the lithium/SPE and cathode material/PEG interfaces resistances was monitored. The interfacial resistance increases with time, but its value is not so high as to explain the increase of the total resistance of the cell. Anyhow, this additional resistance could be responsible for the difference in the capacity fading when cycling the cell in polymer electrolyte instead of in liquid electrolyte.