Surface and interfacial engineering of P2-type layered oxides through Li/Mg/Si tri-doping toward stable and fast sodium-ion transport

Interfacial engineering is a decisive factor in stabilizing layered oxide cathodes for sodium-ion batteries (SIBs). Here, a synergistic Li/Mg/Si tri-doping strategy is introduced to simultaneously modulate the bulk lattice and interfacial chemistry of a P2-type Na 0.7 Li 0.03 Mg 0.05 Ni 0.25 Mn 0. 6 Si 0.07 O 2 (LMNMS) cathode. The dopants expand the c-axis lattice (11.195 Å) and strengthen surface transition metal (TM)-O covalency, yielding improved Na + diffusion kinetics and interfacial stability. X-ray photoelectron spectroscopy (XPS) and in situ Raman analyses reveal reduced surface oxygen vacancies (15% vs. 22% in the undoped sample) and suppressed electrolyte-induced oxygen redox, effectively mitigating the P2 → O2 phase transition. Electrochemical impedance spectroscopy confirms a 45% decrease in charge-transfer resistance, indicating enhanced interfacial charge transport. Benefiting from this coupled bulk-surface optimization, LMNMS delivers a high reversible capacity of 165 ± 3.2 mAh g −1 at 0.1C, an excellent rate performance (92 ± 2.5 mAh g −1 at 5C), and 90.5 ± 1.8% capacity retention after 200 cycles. This work highlights how multi-site doping tailors both the electronic and chemical nature of electrode interfaces, offering a design paradigm for high-performance and interface-stable sodium-ion batteries.