Li7La3Zr2O12-Based Solid Electrolytes for Li Batteries with Voltages Beyond 5 Volts

Today’s commercial electrolytes used in lithium ion batteries, e.g. aprotic solvents with Li salts and possibly gel or polymeric stabilization, do not have sufficient electrochemical stability for high voltage cells around and above 5 V. Some sulfide, oxide and phosphate solid state materials exhibit remarkable Li ion conductivity (which can be further increased by increasing operating temperature), thus enabling them as promising candidates for solid-state Li electrolytes [1]. From the oxide class of materials, garnet-like materials based on Li₇La₃Zr₂O₁₂ were chosen for this publication due to their reasonable lithium ion conductivity (high 10^-4 Scm^-1 range at room temperature), and their stability against air and also humidity so that they can be processed in ambient conditions.

Li₇La₃Zr₂O₁₂ where Li or Zr sites are partially substituted by Aluminum, Tantalum or Yttrium, with simultaneously optimized Li content and high total Li ion conductivity were prepared and characterized with regard to crystal structure. One focal point was put on the phase formation and especially on the ratio of the cubic to tetragonal phase. The material was subsequently processed to electrolyte foils with lateral dimensions of up to 7cm×7cm and analyzed with respect to conductivity and electrochemical properties including operation as an all solid state cell using high voltage cathode materials.

References

[1] N. Kamaya et al. Nature Mat. 10 (2011) 682-686, doi: 10.1038/NMAT 3066