A one-step method to prepare a magnesium electrolyte salt is provided. According to the method, the magnesium electrolyte is obtained by reacting a Grignard reagent and a fluorinated aryl borane. In addition, formation of monomeric or dimeric magnesium ion is determined by the choice of the Grignard reagent. The magnesium electrolyte may be non-chlorinated and non-corrosive. A magnesium battery containing the magnesium electrolyte is also provided.