Improving the cycling performance of lithium-air batteries using a nitrite salt electrolyte

Abstract

Lithium nitrate (LiNO3) has been used as the electrolyte salt for Lithium-air battery (LAB), both to protect the lithium metal anode and to generate NO2− anions that function as the redox mediator (RM) reducing the charging voltage. However, this RM effect minimally improves cycling performance because only a low NO2− concentration is produced. Instead, the use of lithium nitrite (LiNO2) as the supporting electrolyte salt can overcome this limitation. In this study, 1 M solutions of LiNO3 or LiNO2 in tetraethylene glycol dimethyl ether (TEGDME) or N-methyl-2-pyrrolidone (NMP) were prepared as LAB electrolytes. Walden plots of these electrolytes established a higher degree of dissociation in the NMP having a greater dielectric constant, thus enhancing ionic conductivity. Electrochemical impedance spectroscopy determined that an LAB cell incorporating the LiNO2/NMP electrolyte exhibited reduced diffusion resistance during discharge-charge cycling as a consequence of the enhanced RM effect of NO2− anions. Microscopic observation and pore distribution analysis of cathodes confirmed that the clogging of pores was minimized with the LiNO2/NMP electrolyte. As a result, the LAB cell using this electrolyte extended the cycle performance, more than doubling the cycle life. LiNO2 is considered to be an effective alternative for electrolyte salt for LAB.