Conductivity and electrochemical stability of Li+ substituted high-entropy Lix(mM0.2Co0.2Ni0.2Cu0.2Zn0.2)1-0.5xO ceramics

Abstract

In this work, high-entropy Lix(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)1-0.5xO (x = 0, 0.1, 0.2, 0.3, 0.4) ceramics with rocksalt structure were synthesized via simple sol-gel method and sintered at 1000°C. The crystal structure, crosssection micromorphology, conductivity, electronic conductivity and electrochemical stability of the sintered Lix(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)1-0.5xO ceramics were investigated by X-ray diffraction, SEM, AC-impedance, DC-polarization and cyclic voltammetry, respectively. The Lix(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)1-0.5xO ceramics present single rock-salt structure and no impurities were detected. The Li0.3(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)0.85O (x = 0.3) sample has the highest conductivity of 1.46 × 10−5 S/cm at 30°C, with an activation energy of 0.334 eV. Conductivity of the (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O ceramics is enhanced by about four orders of magnitude with the partial substitution of (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2) by lithium. The electronic conductivity of the Li0.3(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)0.85O ceramics is much lower than its ionic conductivity, which suggests that Li0.3(MgCoNiCuZn)0.85O can be treated as ionic conductor. The Li0.3(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)0.85O sample is electrochemically stable between 1.23 and 4.7 V.

Keywords

• high-entropy ceramics
• sol-gel synthesis
• solid electrolyte
• rock-salt
• ionic conductivity