High-entropy mechanism to boost ionic conductivity

Advances in solid-state batteries have primarily been driven by the discovery of superionic conducting structural frameworks that function as solid electrolytes. We demonstrate the ability of high-entropy metal cation mixes to improve ionic conductivity in a compound, which leads to less reliance on specific chemistries and enhanced synthesizability. The local distortions introduced into high-entropy materials give rise to an overlapping distribution of site energies for the alkali ions so that they can percolate with low activation energy. Experiments verify that high entropy leads to orders-of-magnitude higher ionic conductivities in lithium (Li)–sodium (Na) superionic conductor (Li-NASICON), sodium NASICON (Na-NASICON), and Li-garnet structures, even at fixed alkali content. We provide insight into selecting the optimal distortion and designing high-entropy superionic conductors across the vast compositional space. Description High entropy by design A key property for solid-state battery electrolytes is the ability to rapidly transport lithium ions. This property can be achieved by developing a percolating pathway or by increasing the mobility of the carrier ions in the electrolyte. However, standard design methods limit the selection of dopants and complicate the synthesis. Zeng et al. adapted some of the concepts of high-entropy materials to the development of solid electrolytes (see the Perspective by Botros and Janek). The addition of a mixture of high-entropy metal cations induces local disorder, thus creating overlapping site energy distributions for charge-carrying ions. This approach results in a percolating network of connected sites with a reduced energy difference and correspondingly fast lithium ion transport, as demonstrated for lithium- and sodium-based batteries. —MSL High-entropy design can lead to orders of magnitude increases in ionic conductivity regardless of the crystal framework.