Structural, electrical and electrochemical properties of novel Li4+2x+yZnxMySi1-x-yO4 (where x = 0.04, y = 0.03;M = Al, Cr) ceramic electrolytes

Lisicon-type ceramic electrolytes, Li4.11Zn0.04Al0.03Si0.93O4 and Li4.11Zn0.04Cr0.03Si0.93O4, were synthesized by sol gel method. X-ray diffraction was applied to investigate the phase, structure and unit cell parameters of both solid electrolytes. The information of particles size distribution was obtained by laser particle sizer. Meanwhile, energy dispersive X-ray was used for elemental composition analysis. The complex impedance spectroscopy was carried out in the frequency range 10 Hz-10 MHz and temperature range 273 K to 773 K to study the electrical properties of the electrolytes. Both compounds were indexed to the monoclinic unit cell in the space group P21/m. The particle size in Cr substituted sample was smaller compared to that in the Al substituted sample. The EDX results showed that the chemical compositions for both compounds were very close to the designed compositions. The Li4.11Zn0.04Cr0.03Si0.93O4 compound gave slightly higher total conductivity values of 3.16 × 10−5 S cm−1 at ambient temperature and 1.78 × 10−3 S cm−1 at 773 K compared to Li4.11Zn0.04Al0.03Si0.93O4 which showed total conductivity values of 1.16 × 10−5 S cm−1 at ambient temperature and 1.12 × 10−3 S cm−1 at 773 K. The conductivity-frequency spectra were used to estimate the ionic hopping rate in the structure. The dielectric constant and dielectric loss were found to decrease with the increase of frequency but increased with the increase of temperature. Ionic transference number corresponding to Li+ ion transport determined by means of Bruce and Vincent technique is 0.93 and 0.94 for Li4.11Zn0.04Al0.03Si0.93O4 and Li4.11Zn0.04Cr0.03Si0.93O4 respectively. Linear sweep voltammetry results demonstrated that the Li4.11Zn0.04Cr0.03Si0.93O4 and Li4.11Zn0.04Al0.03Si0.93O4 ceramic electrolytes was electrochemically stable up to 4.10 V and 3.5 V versus a Li/Li+ reference electrode respectively.