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<p>The ubiquitous Li<sub>3</sub>PO<sub>4</sub> impurity phase and sluggish Li<sup>+</sup> diffusion kinetics severely limit the electrochemical performance of LiMn<sub>0.6</sub>Fe<sub>0.4</sub>PO<sub>4</sub> (LMFP) synthesized via the solvothermal method. Herein, a synergistic strategy combining Li-site Na<sup>+</sup> doping with process optimization is proposed. By reducing the Li/(Mn + Fe) molar ratio to 2.7:1 and extending the reaction time to 15&#xa0;h at 180&#xa0;°C, the Li<sub>3</sub>PO<sub>4</sub> impurity is completely eliminated. Rietveld refinement reveals that Na<sup>+</sup> substitution at Li sites induces an anisotropic lattice expansion. Specifically, the a-axis is elongated by 0.100%, thereby widening the cross section of the one-dimensional Li<sup>+</sup> diffusion channel along the [010] direction. X-ray photoelectron spectroscopy confirms a decreased Mn3⁺ fraction on the particle surface, alleviating the Jahn–Teller distortion. At the optimal doping level of 1 at%, the material delivers a discharge specific capacity of 141.8 mAh g<sup>−1</sup> at 0.1 C (21.0% higher than that of the undoped sample) and 72.9 mAh g<sup>−1</sup> at 5 C, along with a capacity retention of 95.3% after 200 cycles at 1 C. Equivalent circuit modeling shows that 1% Na doping reduces the charge-transfer resistance from 149.3 to 84.4&#xa0;Ω and increases the apparent Li<sup>+</sup> diffusion coefficient by approximately 7.1 times. This work provides a reproducible process window for synthesizing phase-pure LMFP and establishes a clear structure–performance relationship for Li-site doping.</p>

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Enhancing electrochemical performance of LiMn0.6Fe0.4PO4 cathode via Li-site Na+ doping

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Xing Xu,
  • Yuanhui Liu,
  • Juanjuan Cheng,
  • Longfei Liu,
  • Yun Ou

摘要

The ubiquitous Li3PO4 impurity phase and sluggish Li+ diffusion kinetics severely limit the electrochemical performance of LiMn0.6Fe0.4PO4 (LMFP) synthesized via the solvothermal method. Herein, a synergistic strategy combining Li-site Na+ doping with process optimization is proposed. By reducing the Li/(Mn + Fe) molar ratio to 2.7:1 and extending the reaction time to 15 h at 180 °C, the Li3PO4 impurity is completely eliminated. Rietveld refinement reveals that Na+ substitution at Li sites induces an anisotropic lattice expansion. Specifically, the a-axis is elongated by 0.100%, thereby widening the cross section of the one-dimensional Li+ diffusion channel along the [010] direction. X-ray photoelectron spectroscopy confirms a decreased Mn3⁺ fraction on the particle surface, alleviating the Jahn–Teller distortion. At the optimal doping level of 1 at%, the material delivers a discharge specific capacity of 141.8 mAh g−1 at 0.1 C (21.0% higher than that of the undoped sample) and 72.9 mAh g−1 at 5 C, along with a capacity retention of 95.3% after 200 cycles at 1 C. Equivalent circuit modeling shows that 1% Na doping reduces the charge-transfer resistance from 149.3 to 84.4 Ω and increases the apparent Li+ diffusion coefficient by approximately 7.1 times. This work provides a reproducible process window for synthesizing phase-pure LMFP and establishes a clear structure–performance relationship for Li-site doping.