Mitigating Mn‐Driven Interfacial Instability in LiMn0.5Fe0.5PO4 Cathodes for Lithium‐Ion Batteries via Surface‐Intensive Ta Doping

Why It Matters

By stabilizing the Mn redox and enhancing Li⁺ transport, Ta‑doped LMFP can enable faster charging and broader temperature operation for electric‑vehicle batteries, addressing key barriers to market adoption.

Key Takeaways

• Surface‑focused Ta doping enriches LMFP particle edges.
• Li‑O bond elongation widens Li⁺ diffusion channels.
• Near‑surface Mn²⁺ rises to 59.7%, reducing Mn³⁺.
• 20 C capacity improves to 105.6 mAh g⁻¹.
• 60 °C storage retains 99.5 % capacity.

Pulse Analysis

LiMn₀.₅Fe₀.₅PO₄ (LMFP) has attracted attention as an olivine cathode that balances the high voltage of LiFePO₄ with the capacity boost from manganese. However, the material’s one‑dimensional Li⁺ channels are intrinsically slow, and the presence of Jahn‑Teller‑active Mn³⁺ accelerates polarization, especially at high charge‑rates and sub‑zero temperatures. These factors cause Mn³⁺ to concentrate near particle surfaces, leading to Mn dissolution, electrolyte decomposition, and rapid capacity fade. Overcoming both kinetic bottlenecks and surface instability is essential for LMFP to compete in electric‑vehicle applications.

The study leverages the low diffusivity of Ta⁵⁺ during solid‑state synthesis to create a surface‑intensive dopant layer. Tantalum substitutes into the transition‑metal lattice, strengthening M‑O bonds and expanding the Li‑O coordination sphere, which effectively widens the Li⁺ diffusion pathway without compromising structural integrity. By shifting the Mn oxidation balance toward Mn²⁺ (from 53.9 % to 59.7 % near the surface), the Ta‑rich shell suppresses the formation of Mn³⁺, curbing dissolution and side‑reactions. Electrochemical tests confirm a jump from 82 mAh g⁻¹ to 106 mAh g⁻¹ at 20 C, and near‑perfect capacity retention after prolonged high‑temperature storage.

These findings have direct relevance for high‑power lithium‑ion batteries, where rapid charging and operation across a wide temperature window are non‑negotiable. A cathode that maintains >99 % capacity after ten days at 60 °C and high state‑of‑charge reduces the risk of thermal runaway and extends vehicle range. The surface‑focused doping strategy also sidesteps bulk compositional trade‑offs, preserving energy density while delivering kinetic gains. As manufacturers seek cost‑effective alternatives to nickel‑rich chemistries, Ta‑doped LMFP offers a scalable pathway to robust, fast‑charging batteries.