Lithium (Li) anode has been considered to be one of the most promising candidates for energy storage systems due to its high theoretical capacity. However, the side reaction between Li-metal and electrolyte and its safety concerns are inevitable obstacles for the commercial applications of Li-metal batteries (LMBs). The cycling stability of commercial electrolyte, high-concentration electrolyte (HCE), and localized high-concentration electrolyte (LHCE) in LMBs are studied in this work. Furthermore, 2-fluoropyridine (2-FP) additive is used to significantly enhance the cycling stability of Li-metal in LHCE that contains triethyl phosphate (TEP) and bis­(2,2,2-triflfluoroethyl) ether (BTFE). The most stable cycle performance (about 2100 h) of Li||Li cell and the highest coulombic efficiency (98.82%) in the Li||Cu cell can be obtained in the system of LHCE + 2-FP (1.2 M LiFSI + TEP/BTFE + 0.01 M 2-FP). Li||LiFePO4 cell with LHCE + 2-FP exhibits the highest initial discharge capacity of 149.14 mAh g–1 and the most excellent capacity retention rate of 98.52% after 455 cycles at 1C. Moreover, the system of LHCE + 2-FP can also invest Li||LiFePO4 cell with the best rate capacity.

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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Na3V2(PO4)3 (NVP) is considered as a potential cathode material for next-generation sodium ion batteries (SIBs) because of its open Na+ diffusion channels and high operating voltage. In this paper, we design a Na3V1.9Ti0.1(PO4)3/C (Ti0.1-NVP/C) composite as a cathode for SIBs. Using Ti4+ to replace V3+ can not only stabilize the crystal structure of NVP, but also generate Na vacancies to promote Na+ diffusion and improve the intrinsic electronic conductivity of NVP. Meanwhile, the coated carbon layer provides a surface channel for the electron transport of NVP. More importantly, Ti-doped NVP activates additional Ti3+/Ti4+ and V4+/V5+ redox pairs. The synergistic effect of the two redox pairs makes the capacity of the Ti0.1-NVP/C electrode (123.3 mAh g–1 at 0.1 C) higher than the theoretical specific capacity of NVP. Ti0.1-NVP/C cathode also exhibits excellent rate capability (89.5 mAh g–1 at 30 C) and long cycle performance (retention of 62.3% at 20 C after 8000 cycles). Furthermore, the symmetric full cell of the Ti0.1-NVP/C electrode exhibits superior competitiveness. The reaction mechanism of the Ti0.1-NVP/C electrode is elucidated by ex-situ XRD and GITT measurements.