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• The metal phosphates coated P3-NaMN is synthesized via co-precipitation route. • The modified samples show a great improvement of cycling performance. • The metal phosphates coating could promote the air stability of the materials. • The coated layer could inhibit the loss of lattice oxygen in high voltage region. Cathode materials are considered to be the most critical component of the sodium-ion batteries, which determine the overall electrochemical performance of the battery to some degree. Currently, the layered oxides receive significant attention due to the high operating voltage and high capacity. However, the instability in the air and unsatisfactory cycling performance limit their commercial application. Based on excellent electrochemical performance of the P3-type Na 0.65 Mn 0.75 Ni 0.25 O 2 material, here AlPO 4 and Mg 3 (PO 4) 2 protective coatings are employed to modify P3-type Na 0.65 Mn 0.75 Ni 0.25 O 2. The metal phosphate layers cover the surfaces of the pristine particles via a co-precipitation route. It has been found that the two modified samples exhibit an obvious improvement of cycling performance with the capacity retentions about 93% at a current density of 0.2 C within 100 cycles. In addition, the coated metal phosphate layer can effectively suppress the irreversible oxidation of oxygen in the high voltage redox region. Furthermore, after exposure to the air, the coating samples still retain a high electrochemical activity. Therefore, the metal phosphates coating provides a meaningful exploration for the research and development of long-term cycling life and high air stability of cathode materials in sodium-ion batteries. [ABSTRACT FROM AUTHOR]

We present a separator modification strategy to suppress polysulfide shuttle and accelerate polysulfide conversion through transition metal coordinated g-C 3 N 4 with crystalline carbons. The Li-S batteries with Ni-C 3 N 4 /C-modified separator manifest improved electrochemical performance even at high sulfur loading and lean electrolyte condition, due to catalytic effect. • Transition metal coordinated g-C 3 N 4 with crystalline carbons is prepared. • Hybrid nanosheets efficiently prevent polysulfide diffusion by absorption effect. • This structure endows the lean-electrolyte Li-S batteries higher capacity. • Cell with Ni-C 3 N 4 /C-modified separator exhibits the best electrochemical performances. Lithium-sulfur batteries have been regarded as promising energy storage candidates because of their high energy density and low cost. However, the low electrical conductivity of sulfur, infamous polysulfides shuttle and slow redox kinetics result in fast capacity fade and poor rate capabilities. To solve these barriers, herein a modification strategy of functional separator is presented by coating transition metal coordinated graphitic carbon nitride (g-C 3 N 4) with crystalline carbons (M-C 3 N 4 /C) on the surface of a commercial separator. The coating layer exhibits both satisfactory interception ability for polysulfides shuttle and fast polysulfides conversion ability. It has been found that the uniformly distributed transition metal on g-C 3 N 4 /C acts as an active center to regulate polysulfides behavior via strong chemisorption capability and high catalytic activity towards polysulfide conversion, while the transition metal-interface guarantees the rapid electron transfer, which can consequently facilitate the utilization of active sulfur species. Notably, after considerable assessments from density functional theory calculations, spectroscopy and electrochemical performances, it can be concluded that the Ni-C 3 N 4 /C can strongly bind polysulfides and expedite polysulfides conversion kinetics as well as promote electrons/ion transfer. As a result, the lithium-sulfur batteries with Ni-C 3 N 4 /C-modified separator can deliver 999 mAh g−1 at 0.5 A g−1 with high capacity retention of 89.4% after 300 cycles. Even at a great sulfur loading of 4.6 mg cm−2 and a low electrolyte/sulfur ratio of 6 µL mg−1, a large initial capacity of 724.6 mAh g−1 is still obtained at 1.0 A g−1. The separator reported in this work initiates the exploration of transition metals coordination as dynamic regulators of high-performance lithium-sulfur batteries and also reveals an understanding of the catalytic reactions. [ABSTRACT FROM AUTHOR]