Inducing weak and negative Jahn-Teller distortions to alleviate structural deformations for stable sodium storage.

In the quest for efficient supercapacitor materials, manganese-based layered oxide cathodes stand out for their cost-effectiveness and high theoretical capacity. However, their progress is hindered by the Jahn-Teller (J-T) distortion due to the unavoidable Mn 4+ to Mn 3+ reduction during ion storage processes. Our study addresses this challenge by stabilizing the K 0.5 MnO 2 cathode through strategic Mg 2+ substitution. This substitution leads to an altered Mn 3+ electronic configuration, effectively mitigating the strong J-T distortion during ion storage processes. We provide a comprehensive analysis combining experimental evidence and theoretical insights, highlighting the emergence of the weak and negative J-T effects with reduced structural deformation during electrochemical cycling. Our findings reveal that the K 0.5 Mn 0.85 Mg 0.15 O 2 cathode exhibits remarkable durability, retaining 96.0% of initial capacitance after 8000 cycles. This improvement is attributed to the specific electronic configurations of Mn 3+ ions, which play a crucial role in minimizing volumetric changes and counteracting structural deformation typically induced by the strong J-T distortion. Our study not only advances the understanding of managing J-T distortion in manganese-based cathodes but also opens new avenues for designing high-stability supercapacitors and other energy storage devices by tailoring electrode materials based on their electronic configurations.