Li/Ti Doping Modulates Biphasic Compatibility: A Synergistic Strategy for High-Performance Composite-Phase Sodium-Ion Batteries

Abstract

Biphasic composite structures have been proven to be an effective design strategy for improving the performance of sodium-ion batteries (SIBs). However, current biphasic regulation strategies rarely consider the synergistic effect of multielement co-doping. This study employs Na0.75Ni0.3Fe0.15Mn0.55O2 as the matrix material and regulates its O3/P2 biphasic structure via synergistic doping based on the characteristics of lithium (Li) and titanium (Ti) elements. The results demonstrate that Li+ efficiently adjusts the O3/P2 phase ratio, while Ti4+ stabilizes the crystal lattice. The synergistic effect of Li and Ti co-doping endows the Na0.75Li0.05Ni0.3Fe0.15Mn0.4Ti0.1O2 cathode with a dual-phase structure with a high O3-phase proportion. The optimized material delivers a specific capacity of 135 mAh g–1 at 0.05 C with an initial Coulombic efficiency of 99% and retains 86.1% of its initial capacity after 200 cycles at 1 C. This work provides a feasible strategy for the design of high-performance layered oxide cathodes for SIBs.