Toward Stable, High-Energy, Partially Disordered Mn-Rich Spinel Cathodes by Revealing and Mitigating Surface...

Area of Science:

• Materials Science
• Electrochemistry
• Sustainable Energy

Background:

• Manganese-rich cathodes offer a sustainable alternative for high-performance batteries.
• Limited cyclability in these cathodes is often attributed to manganese dissolution and cathode-anode crosstalk.
• The Jahn-Teller (J-T) effect of Mn³⁺ is implicated in these degradation pathways, particularly in spinel structures like LiMn₂O₄.

Purpose of the Study:

• To investigate the role of the Jahn-Teller effect in Mn dissolution and structural degradation of spinel cathodes.
• To tailor the degree of disorder in spinel cathodes to control the manganese redox range and J-T activity.
• To explore strategies for mitigating Mn dissolution and improving the cyclability of Mn-rich cathodes.

Main Methods:

• Tailoring the degree of disorder in spinel cathode materials.
• Cycling batteries at segmented voltage windows to isolate J-T active and inactive ranges.
• Analyzing surface degradation mechanisms using electrochemical techniques.
• Investigating the effect of electrolyte acidity on Mn³⁺ disproportionation and cathode stability.

Main Results:

• Mn dissolution was found to be less significant below 3.6 V vs. Li/Li⁺, despite a stronger J-T effect.
• Cycling beyond 3.6 V induced severe degradation, including tetragonal phase formation and Mn²⁺-rich surfaces, accelerating Mn dissolution.
• Reducing electrolyte acidity suppressed Mn³⁺ disproportionation, leading to a stable dopant-free Mn-only cathode with 250 mAh g⁻¹ specific capacity.
• Electrolyte engineering effectively minimized Mn³⁺ disproportionation, enabling stable operation and avoiding crosstalk.

Conclusions:

• The Jahn-Teller effect's role in Mn dissolution is voltage-dependent and can be managed by controlling the cycling window.
• Electrolyte engineering, specifically reducing acidity, is a viable strategy to stabilize Mn-rich cathodes and prevent crosstalk.
• Mn-rich cathodes can achieve high specific capacity and improved cyclability, offering a sustainable path for next-generation batteries.