Regulating Pseudo-Jahn-Teller Effect and Superstructure in Layered Cathode Materials for Reversible Alkali-Ion...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• The Jahn-Teller effect (JTE) is a critical factor influencing stress in layered cathode materials during electrochemical cycling.
• Existing research indicates superstructure traces and irreversible phase transitions in pristine layered materials, even after JTE elimination.

Purpose of the Study:

• To investigate the role of pseudo-JTE in layered cathode materials, particularly P2-type Na3/4MnO2.
• To elucidate the relationship between pseudo-JTE, cationic distortion, and electrochemical degradation.
• To demonstrate how suppressing pseudo-JTE can enhance electrochemical properties.

Main Methods:

• Theoretical analysis using Taylor expansion to study cationic distortion energy.
• Experimental investigation of a model P2-type Mn-rich cathode (Na3/4MnO2) and its Li-substituted variant (Na3/4(Li1/4Mn3/4)O2).
• Advanced analytical techniques to characterize structural distortions and phase transitions.

Main Results:

• Pseudo-JTE, a second-order JTE, is identified as a widespread cause of asymmetric MnO6 octahedra distortions.
• These distortions in Na3/4(Li1/4Mn3/4)O2 lead to significant electrochemical degradation.
• Suppression of pseudo-JTE was shown to modulate phase transitions and improve electrochemical performance.

Conclusions:

• Pseudo-JTE is a more prevalent and significant factor than the conventional JTE in layered cathode materials.
• Controlling pseudo-JTE offers a new avenue for rationalizing previous approaches and enhancing the stability and performance of layered cathodes.
• This work highlights the critical importance of considering pseudo-JTE for future cathode material design.