Solid-state materials containing rotatable polyanions, such as B12 H122-, constitute a peculiar class of ionic conductors due to their unique transport behavior, where rotating polyanions promote phase transitions to disordered phases with several orders of magnitude enhancement in cation conductivities. A major drawback is the high temperature required to activate rotation and thereby low conductivities at room temperature. Here, we elucidate a mechanism to drastically reduce the temperature based on the use of pseudorotation in high-H coordination hydride complexes. We demonstrate this mechanism for an existing complex transition metal hydride Li5MoH11 containing MoH93-, and we present a strong potential of this material to unprecedentedly exhibit a high lithium ion conductivity of 7.9 × 10-2 S cm-1 at room temperature.
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