Electrode-electrolyte interphase engineering for O3-type Na[Ni0.5Mn0.5]O2 cathode via trace LiPF6 incorporation

O3-type layered Na[Ni 0.5 Mn 0.5 ]O 2 (NM5050) is recognized as a cost-effective, energy-dense cobalt-free cathode solution for sodium-ion batteries (SIBs). However, its performance is fundamentally limited by the compounded effects of bulk structural degradation and interfacial instability. The higher standard reduction potential of the Na/Na + redox couple relative to Li/Li + leads to unfavorable thermodynamics and sluggish kinetics of interphase formation, resulting in a cathode-electrolyte interphase (CEI) that is insufficiently robust to protect the cathode surface against chemo-mechanical failure. Herein, trace LiPF 6 is employed as a functional additive within the baseline 1 M NaPF 6 propylene carbonate/fluoroethylene carbonate (PC/FEC) electrolyte to stabilize NM5050. This incorporation significantly enhances both the cycling stability and rate capability, maintaining 89.5% and 68.1% capacity retention after 100 and 200 cycles, respectively, within a 2.0-4.0 V window. Cross-sectional imaging reveals that LiPF 6 -containing electrolyte effectively suppresses intergranular microcracks. Simultaneously, differential capacity analysis confirms the enhanced reversibility of the hexagonal P3’ → O3’ phase transition, ensuring long-term structural integrity. X-ray photoelectron spectroscopy identifies an inorganic-rich, Li-containing CEI as the primary factor for stabilization, and electrochemical impedance spectroscopy corroborates a reduction in charge-transfer resistance. This straightforward strategy can provide valuable insights into the trace-additive-driven interphase modulation to suppress chemo-mechanical failure in O3-type layered cathodes.