Capacity fading induced by unstable surface chemical properties and intrinsic structural degradation is a critical challenge for the commercial utilization of Ni-rich cathodes. Here, a highly stabilized Ni-rich cathode with enhanced rate capability and cycling life is constructed by coating the molybdenum compound on the surface of LiNi 0.815 Co 0.15 Al 0.035 O 2 secondary particles. The infused Mo ions in the boundaries not only induce the Li 2 MoO 4 layer in the outermost but also form an epitaxially grown outer surface region with a NiO-like phase and an enriched content of Mo 6+ on the bulk phase. The Li 2 MoO 4 layer is expected to reduce residential lithium species and promote the Li + transfer kinetics. The transition NiO-like phase, as a pillaring layer, could maintain the integrity of the crystal structure. With the suppressed electrolyte−cathode interfacial side reactions, structure degradation, and intergranular cracking, the modified cathode with 1% Mo exhibits a superior discharge capacity of 140 mAh g −1 at 10 C, a superior cycling performance with a capacity retention of 95.7% at 5 C after 250 cycles, and a high thermal stability.

No abstract

No abstract

The Na+ superionic conductor (NASICON)‐type Na3V2(PO4)3 cathodes have attracted extensive interest due to their high structural stability and fast Na+ mobility. However, the substitution of vanadium with low‐cost active elements remains imperative due to high cost of vanadium, to further boost its application feasibility. Herein, a novel ternary NASICON‐type Na4VMn0.5Fe0.5(PO4)3/C cathode is designed, which integrates the advantages of large reversible capacity, high voltage, and good stability. The as‐obtained Na4VMn0.5Fe0.5(PO4)3/C composite can deliver an excellent rate capacity of 96 m Ah g‐1 at 20 C and decent cycling durability of 94% after 3000 cycles at 20 C, which is superior to that of Na4VFe(PO4)3/C and Na4VMn(PO4)3/C. The synergetic contributions of multimetal ions and facilitated Na+ migration of the Na4VMn0.5Fe0.5(PO4)3/C cathode are confirmed by the first‐principles calculations. The processive reduction/oxidation involved in Fe2+/Fe3+, Mn2+/Mn3+, V3+/V4+/V5+ redox couples are also revealed upon the charging/discharging process by ex situ soft X‐ray absorption spectroscopy. The reversible structure evolution and small volume change during the electrochemical reaction is demonstrated by in situ X‐ray diffraction characterization. The rational design of NASICON‐type cathodes by regulating composition with substitution of multimetal ions can provide new perspectives for high‐performance Na‐ion batteries.