Li9SiAlO8: A Lithium Ion Electrolyte for Voltages above 5.4 V

The solid solution compound represents a single‐phase derivative formally composed of 50 atom percent (a/o) and 50 a/o . It exhibits an ionic conductivity at 25°C. The total electronic conductivity in contact with elemental lithium or highly positively polarized electrodes is found to be around four orders of magnitude smaller. Detailed studies under different conditions and in different cell types are presented. In the asymmetric cell type (−) (+), the tantalum electrode served as an arbitrary positive electrode simulating different lithium activities due to the applied external voltage. Upon extreme polarization ( E vs. ) below 100°C, stable tarnishing layers were formed at the ‐electrode interfaces, thus resisting further decomposition, which makes a suitable electrolyte for investigating cathodes which exhibit very high positive voltages vs. lithium. Moreover, chemical stability experiments show this electrolyte to be inert against elemental lithium and up to at least 100 and 500°C, respectively. crystallizes in a monoclinic unit cell having the parameters a = 5.108(4) Å, b = 5.388(4) Å, c = 6.205(6) Å, and β = 90.40(9)°.