Electrochemical investigation of Al-Li/Li _x FePO₄ cells in oligo(ethylene glycol) dimethyl ether/LiPF₆

1 M LiPF₆ dissolved in oligo(ethylene glycol) dimethyl ether with a molecular weight, 500 g mol^-1 (OEGDME500, 1 M LiPF ₆), was investigated as an electrolyte in experimental Al-Li/LiFePO₄ cells. More than 60 cycles were achieved using this electrolyte in a Li-ion cell with an Al-Li alloy as an anode sandwiched between two Li _x FePO₄ electrodes (cathodes). Charging efficiencies of 96-100% and energy efficiencies of 86-89% were maintained during 60 cycles at low current densities. A theoretical investigation revealed that the specific energy can be increased up to 15% if conventional LiC₆ anodes are replaced by Al-Li alloy electrodes. The specific energy and the energy density were calculated as a function of the active mass per electrode surface (charge density). The results reveal that for a charge density of 4 mAh cm^-2 about 160 mWh g^-1 can be reached with Al-Li/LiFePO₄ batteries. Power limiting diffusion processes are discussed, and the power capability of Al-Li/LiFePO₄ cells was experimentally evaluated using conventional electrolytes.