Dual Strategy in Manganese-Based Cathodes with K Expansion and Ni/Ti Compression for Stable Sodium Storage.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Manganese-based oxide cathodes for sodium-ion batteries suffer from irreversible degradation due to Mn³⁺ Jahn-Teller distortion and Mn²⁺ dissolution.
• Cyclic strain during sodiation/desodiation further exacerbates cathode instability.

Purpose of the Study:

• To develop a stable and high-performance manganese-rich cathode for sodium-ion batteries.
• To address Mn³⁺ Jahn-Teller distortion and Mn²⁺ dissolution through a dual-regulation strategy.

Main Methods:

• Synthesis of a P2-K_0.7Mn_0.8Ni_0.1Ti_0.1O₂ (KMNT) cathode material.
• Utilizing K⁺ pillars for alkali-metal layer expansion and Ni/Ti co-doping to compress transition-metal layers.
• Electrochemical testing, including cycling performance, rate capability, and operando analyses.

Main Results:

• The KMNT cathode exhibits a high average discharge voltage of ≈2.6 V (vs. Na⁺/Na) due to enhanced Mn─O interactions.
• Demonstrates a reversible specific capacity of 124 mAh g^-1 at 1 C with excellent capacity retention (98% after 200 cycles, 83% after 900 cycles at 10 C).
• Operando tests confirm a dynamic K⁺/Na⁺ exchange mechanism and the absence of Mn²⁺ formation.

Conclusions:

• The dual-regulation strategy effectively suppresses Mn³⁺ Jahn-Teller distortion and Mn²⁺ dissolution, leading to enhanced cathode stability.
• The KMNT cathode represents a significant advancement in manganese-rich cathode materials for sodium-ion batteries.
• Establishes a new paradigm for designing stable and high-performance manganese-based cathodes.