Iron-based mixed phosphate Na4Fe3(PO4)2P2O7 (NFPP) is one of the most promising cathodes for sodium-ion batteries due to its good rate capability and long lifespan, while its practical application is hindered by sluggish ionic/electronic kinetics and interfacial instability. Herein, we report a novel solid-source ammonium fluoride (NH4F) plasma-driven synergistic "Trinity" engineering strategy to realize simultaneous reconstruction of NFPP cathodes in bulk, interface, and surface architectures. Mechanistic investigations reveal that the coupling reactions between the NH4F plasma and NFPP lattice/surface trigger simultaneous bulk F-substitution and F/N interface doping as well as surface reconstruction. Specifically, the bulk F- substitution strengthens Fe─O bonding and widens Na+ channels. Concurrently, plasma-generated radicals promote the formation of F/N co-doped carbon network and NaF at the interface, while also promoting the development of a NaF-rich cathode electrolyte interphase at the surface via modulating the NFPP/electrolyte status. This trinity engineering establishes fast transport pathways and a stable cathode electrolyte interface, effectively minimizing charge transfer impedance while suppressing deleterious side reactions. Consequently, the optimized cell exhibits high capacity and superior high-rate cycling life with 95.5% retention after 6000 cycles at 30 C. The developed plasma-driven approach offers mechanistic insights for the synergistic optimization of polyanionic cathodes for advanced sodium ion storage.
Wang et al. (Sun,) studied this question.
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