Insights into the LiMn₂O₄ Cathode Stability in Aqueous Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Spectroscopy

Background:

• Lithium manganese oxide (LiMn2O4) cathodes exhibit significant stability in aqueous electrolytes, a stark contrast to their performance in conventional organic electrolytes used in lithium-ion batteries (LIBs).
• Understanding the underlying mechanisms for this enhanced stability is crucial for developing next-generation energy storage solutions.
• Conventional characterization methods often lack the resolution to probe the nanoscale and atomic-scale changes occurring during battery cycling.

Purpose of the Study:

• To elucidate the mechanisms behind the enhanced stability of LiMn2O4 cathodes in aqueous electrolytes.
• To investigate the phase and defect evolution within LiMn2O4 cathodes during cycling using advanced characterization techniques.
• To provide a comprehensive assessment of LiMn2O4 cathode behavior in aqueous environments.

Main Methods:

• Utilized variable energy positron annihilation lifetime spectroscopy (VEPALS) for atomic-scale defect analysis.
• Employed tip-enhanced Raman spectroscopy (TERS) for nanoscale surface analysis and dynamic change detection.
• Applied macro-Raman spectroscopy for micrometer-scale investigation of crystalline order.
• Integrated multiple spectroscopic techniques to provide complementary insights across various length scales.

Main Results:

• VEPALS identified cationic defects and subnanometer pores that collapse during cycling.
• TERS detected the formation and dissolution of Mn3O4 and SO4^2- accumulation at grain boundaries.
• Macro-Raman spectroscopy indicated a slow degradation of crystalline quality over time.
• Combined techniques revealed multifaceted insights into phase and defect evolution during cycling.

Conclusions:

• The enhanced stability of LiMn2O4 cathodes in aqueous electrolytes is linked to specific defect evolution pathways.
• Advanced spectroscopic methods offer unprecedented insights into the dynamic behavior of battery materials.
• Findings provide a mechanistic understanding to guide the development of stable aqueous lithium-ion batteries.