Atomic-Level Changes during Electrochemical Cycling of Oriented LiMn₂O₄ Cathodic Thin Films

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Spinel lithium manganese oxide (LiMn₂O₄) is a promising cathode material for lithium-ion batteries.
• Its practical application is limited by rapid capacity fading during electrochemical cycling.
• Understanding the structural evolution of LiMn₂O₄ is crucial for improving battery performance.

Purpose of the Study:

• To investigate the atomic-scale structural changes in LiMn₂O₄ thin films during early charge-discharge cycles.
• To correlate these structural modifications with observed changes in electrochemical properties, particularly resistivity and capacity fading.
• To elucidate the mechanisms behind conductivity degradation in LiMn₂O₄ cathodes.

Main Methods:

• Epitaxial LiMn₂O₄ thin films were subjected to electrochemical cycling.
• Atomic resolution imaging using scanning transmission electron microscopy (STEM) was employed.
• Impedance spectroscopy was used to measure changes in electrical resistivity.

Main Results:

• Defect-rich LiMn₂O₄ surfaces were observed to significantly increase battery resistivity after the first charge cycle.
• New {111} stacking faults were identified within the films, increasing with further cycling.
• These stacking faults exhibit a compressed structure, local oxygen loss, and Mn atom relaxation, hindering Li-ion migration.

Conclusions:

• Li deintercalation in LiMn₂O₄ is accompanied by structural defects like stacking faults and oxygen loss.
• These defects impede Li-ion transport, leading to increased resistivity and capacity fading.
• Minimizing defect formation during spinel cathode synthesis and cycling is essential for enhancing long-term battery performance.