Enhanced cycling stability and suppressed voltage decay of LiMn0.8Fe0.2PO4/C by Zn-gradient doping

Abstract

The practical application of manganese-rich lithium manganese iron phosphate, i.e., LiMn_0.8Fe_0.2PO₄, is limited by poor cycling stability and severe voltage decay. In this study, a novel and facile Zn-gradient doping strategy has been employed to enhance the structural stability and lithium-ion de-intercalation kinetics, thereby suppressing the voltage decay of LiMn_0.8Fe_0.2PO₄/C (LMFP/C). Compared to the pristine LMFP/C, the Zn-gradient doped LiMn_0.8Fe_0.2PO₄/C (Zn-LMFP/C) exhibits significantly enhanced cycling stability with the capacity retention increasing from 64.11% to 97.47% and suppressed voltage decay with the energy retention increasing from 60.75% to 96.06% after 300 cycles at 1C. Furthermore, the reversible capacity of Zn-LMFP/C is 157.21 mA h g⁻¹ at 0.1C and 138.88 mA h g⁻¹ at 5C, much higher than those of most of the Mn-rich LMFP/C materials reported in previous literature. Cyclic voltammetry (CV) and Galvanostatic Intermittent Titration Technique (GITT) results show that the delithiation/lithiation kinetics of Zn-LMFP/C are notably enhanced. Further first-principles calculations confirm that Zn-LMFP/C possesses superior structural stability and lithium-ion diffusion kinetics. These findings underscore the effectiveness of gradient doping in improving the electrochemical stability of LMFP, providing a promising strategy to mitigate voltage decay and enhance the long-term performance of high-capacity cathode materials for lithium-ion batteries.