Phase behavior and electrochemical properties of lithium-doped N-methyl-N-propyl-piperidinium perchlorate

There are cathode materials for lithium-ion batteries that can operate at high voltages. However, they cannot be used in electrochemical power sources without electrolytes with a wide electrochemical window. Organic ionic plastic crystals (OIPC) are good candidates as the main component of the electrolytes for electrochemical power sources due to their properties. OIPC based on quaternary ammonium salts are stable in a wide temperature range, non-volatile, non-flammable, and have good electrochemical stability and relatively high ionic conductivity. In this work, several electrolytes were investigated in the binary system N-methyl-N-propylpiperidinium perchlorate ([N₁₃pip]ClO₄)–lithium perchlorate. The formation of a new phase was revealed, which is a double salt of the composition 2[N₁₃pip]ClO₄·3LiClO₄. The expected phase diagram of the system is constructed. Electrolytes [N₁₃pip]ClO₄–LiClO₄ containing 0.07–0.29 mol fraction LiClO₄ have a high ionic conductivity ~ 10⁻³ S/cm at temperatures above 110–120 °C. It was shown that the electrochemical stability window of the obtained electrolytes reaches 4.9 V. Electrolytes with a mole fraction of LiClO₄ x = 0.07 and 0.18 showed electrochemical stability for 150 charge–discharge cycles with lithium electrodes at a current density of 0.05 mA/cm². Thus, the solid electrolytes in the [N₁₃pip]ClO₄–LiClO₄ system have a high lithium conductivity and may be used in intermediate-temperature lithium batteries.