Potential sweep and potential step experiments were carried out using a nickel microelectrode (50 mum diameter) to study the kinetics of the Li/Li+ couple as well as lithium reactivity and passivation in poly(ethylene glycol dimethyl ether) (PEGM, MW = 400) containing LiAsF6, LiCF3SO3, and LiBr. Kinetic parameters such as exchange current density, transfer coefficient, and the activation energy of the charge transfer reaction were obtained. It was found that lithium reactivity in PEGM solution containing LiBr is much higher than in that containing LiAsF6 or LiCF3SO3. Lithium passivation appears to result from its reaction with the reducible anion, AsF6- or CF3SO3-, and a passivation mechanism is suggested.