Generality Rules and Synergistic Effect of Mitigating the Jahn-Teller Effect by Multisites Compositionally Complex Doping.

Abstract

The Jahn-Teller (JT) deformation triggers severe structural distortion and large capacity fading in the cathode materials of alkali-ion batteries. Although conventional doping containing over 20 dopant species has been demonstrated to suppress the JT effect, how the short-range and cooperative JT effect are regulated remains an open question. Recently, the new compositionally complex (high entropy) doping has been validated in various oxide cathodes and achieved "zero strain", but the reported "synergistic effect" is largely factual reporting with a limited fundamental understanding of the link between multicomponents and the JT effect. By comparing a group of spinel LiMn₂O₄ (LMO) cathodes with tridoping sites containing one, three, or five dopants' species, the present work shows that MnO₆ octahedral distortion systematically decreases, whereas capacity retention and structure stability systematically increase as the number of dopants' species increases. We propose the generality rules that Mn-site doping breaks the linear continuous short-range JT distortion while 16c-sites doping disturbs the d_z²-orbital collinear ordering and mitigates the cooperative JT effect. Moreover, our complex doping strategy further buffers and rotates the JT strain, resulting in isotropic moderate volume distortion. Based on this synergic effect, both the short-range and cooperative JT effect are significantly suppressed in our synthesized multisites multicomponent doped LMO.