Electrodeposition of aluminum from ionic liquids has been considered a promising approach to low-temperature aluminum electrolysis. In this study, we first investigated the electrochemical stability of 1-ethyl-3-methylimidazolium chloride ([Emim][Al2Cl7]) electrolyte, which is a typically used electrolyte for aluminum electrodeposition. It was found that part of imidazole ions decomposed on the cathode during the electrolysis process, especially when the temperature was at or over 353 K. In order to enhance the stability of the electrolyte, we further studied the effects of lithium salt and lithium bis(oxalato)borate (LiBOB), on the electrochemical stability of the [Emim][Al2Cl7] ionic liquid system. It was found that the electrochemical window of the electrolyte was broadened from 2.59 to 2.74 V at 373 K by addition of 1 mol% LiBOB. With the existence of LiBOB, the reduction current density of Al2Cl7- increased before -0.58 V and the electrodissolution of Al was more complete. The possible mechanism on the LiBOB increases the stability of the electrolyte systems also discussed based on our theoretical calculations.