Modulating the discharge capacity and cycling performance of the LiMn0.6Fe0.4PO4 cathode for lithium-ion batteries via titanium introduction

Abstract

LiMn_0.6Fe_0.4PO₄ has garnered considerable attention due to its higher operating voltage and theoretical energy density in comparison to the commercial LiFePO₄. However, LiMn_0.6Fe_0.4PO₄ still encounters challenges of discharge capacity and cycling performance. To address these issues, Ti doping is implemented through a scalable solid-state method to substitute the Mn site in the LiMn_0.6Fe_0.4PO₄ crystal structure. LiMn_0.57Ti_0.03Fe_0.4PO₄ exhibits superior specific capacities of 151.4 and 139.3 mAh g⁻¹ at 0.2 and 1C, respectively, with an impressive capacity retention rate of 87.4% after 500 cycles at 1C. It is found that the lithium-ion diffusion channel is broadened and the lithium-ion diffusion rate is enhanced (∼10⁻¹² S cm⁻¹) by a combination of structural and electrochemical studies. Interestingly, lithium-ion diffusion ability is greatly improved during the Mn²⁺/Mn³⁺ than the Fe²⁺/Fe³⁺ couple. Moreover, the electronic conductivity has also been enhanced. Furthermore, structure stability between Li_xMn_0.6Fe_0.4PO₄ and Mn_0.6Fe_0.4PO₄ phases is dramatically boosted during delithiation/lithiation. This study elucidates the comprehensive mechanism of the role of Ti doping and opens up new technology space to improve the discharge capacity and cycling performance of lithium-ion batteries.