Na4Fe3(PO4)2P2O7 (NFPP) is considered to be an ideal cathode material for sodium-ion batteries due to its high theoretical capacity, stable structure, small volume change, low cost, and nontoxicity. However, the inherent low electronic conductivity of polyanionic materials limits the application of this material. In this work, we improved the electronic conductivity and structural stability of the material through a dual modification synergistic strategy of manganese ion doping and surface carbon coating and prepared Na4Fe2.9Mn0.1(PO4)2P2O7@C (0.1 Mn-NFPP@C) composites by a simple mechanical-assisted chemical synthesis method. It can release 119.6 mAh g–1 at 0.1C. The capacity retention rate is 97.4% after 100 cycles at 1C and 84.8% after 3000 cycles at 10C. Many tests and calculations in this work also show that 0.1 Mn-NFPP@C modified by Mn2+ doping and carbon coating has higher electronic conductivity and electrochemical kinetics and thus exhibits better electrochemical performance.

Sodium super ion conductor (NASICON)-type Na3V2(PO4)3 (NVP) has been seen as an extremely potential cathode material in sodium-ion batteries (SIBs) because it owns many prominent merits, like an open three-dimensional channel, high-voltage platform, structural stability, etc. Nevertheless, NVP is difficult to obtain excellent electrochemical performance at high rates with the defect of low electronic conductivity, which leads to the restriction of practical application. In this paper, a nitrogen-doped carbon layer-coated Na3V2(PO4)3 composite material (NVP/NC) was synthesized by a simple sol–gel method using urea as a nitrogen source. The further test proved that NVP/NC has a better rate performance compared to NVP/C. The initial reversible capacity of NVP/NC can reach 109.18 mAh g–1 at 1 C, and the discharge specific capacity can reach 88.3 mAh g–1, even when the ultrahigh current density is 50 C. In addition, NVP/NC has excellent long cycle stability (the capacity retention rate reaches 72.89% at 50 C after 8000 cycles, and the capacity reduction rate per revolution is only about 0.0034%). Because the N-doped carbon layer provides a surface channel for electron transmission of NVP, the electronic conductivity is greatly enhanced, making NVP/NC a better composite material for SIBs. Hence, this work offers a practical process to solve the poor electronic conductivity issue of NVP.

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Li-metal has been regarded as one of the most ideal anode material candidates for next-generation lithium (Li) batteries. However, the deployment of high-energy-density Li-metal batteries (LMBs) is hindered by growth of dendrites, low coulomb efficiency, safety concerns, and limited cycle life. Herein, a 2-fluoropyridine (2-FP) additive is introduced into the fire-retardant lithium bis­(flfluorosulfonyl)­imide (LiFSI) triethyl phosphate (TEP)/hydrofluoroether (HFE)-based localized high-concentration electrolyte (LHCE), which significantly enhances the cycling stability of LMBs. The 2-FP additive successfully forms a high-quality LiF-rich interface on Li-metal anode to enhance the mechanical strength and the Li+ diffusion kinetics of the solid electrolyte interface (SEI), and it greatly optimizes the Li-metal deposition process to improve the compatibility of the electrolyte with Li-metal anode. Based on the electrolyte, the LMBs exhibit excellent cycling performance of 1000 cycles and realize 90.8% capacity retention rate at 1C. In addition, the Li||Li cells show long-term cycling stability for 2140 h and the Li||Cu cells achieve a high CE of 98.81%.

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