Low hole polaron migration barrier in lithium peroxide

Abstract

We present computational evidence of polaronic hole trapping and migration in lithium peroxide (Li[subscript 2]O[subscript 2]), a material of interest in lithium-air batteries. We find that the hole forms in the π* antibonding molecular orbitals of the peroxide (O2[superscript 2−]) anion, and that this trapped hole induces significant local lattice distortion, forming a polaron. Our study finds migration barriers for the free polaron to be between 68 and 152 meV, depending on the hopping direction. This low barrier suggests that this material might not be as insulating as previously assumed, provided that the formation of carriers can be achieved. One transport limitation may arise from lithium vacancies, which we find to strongly bind to the polaron. This result, in combination with previous experimental results, suggests that electronic conductivity in this material is likely to be determined by vacancy diffusion.