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Oxygen‐deficient TiP2O7‐y is synthesized by solvothermal and high‐temperature solid‐phase methods. X‐ray powder diffraction (XRD) test data analyses reveal that the solvothermal reaction time can affect the density of oxygen defects in the TiP2O7‐y. Fourier transform infrared spectra (FT‐IR) shows that there is a blue shift in the P−O bond because of the presence of oxygen vacancies. It is strongly demonstrated that oxygen vacancies exist in TiP2O7‐y because electron paramagnetic resonance (EPR) shows sharp peaks at g=2.003. Oxygen vacancy modulated TiP2O7‐y with exposed (541) face shows long cycling stability and super high‐rate capabilities. The initial discharge capacity of TiP2O7‐y, which was prepared after solvothermal reaction for 18 h, reached 828.4 mAh g−1. It can still maintain 246.9 mAh g−1, at 0.5 A g−1, after 500 cycles. Even cycled at 5 A g−1, the reversible rate capacity was maintained at 209.7 mAh g−1. Oxygen vacancies can not only improve the electronic conductivity of TiP2O7‐y but also increase the lithium‐ion diffusion rate. [ABSTRACT FROM AUTHOR]

Nanoparticle Na3V2(PO4)3/C materials with different polyacrylonitrile contents can be successfully synthesized using precipitation method. As an energy storage material used in the production of lithium batteries which is also compared with pure of that, the Na3V2(PO4)3/C not only has a larger capacity, but also has a very high cycle stability. In particular, the initial discharge capacities of the Na3V2(PO4)3/C sample annealed at 750°C containing 10 wt% of polyacrylonitrile are 130.9 and 122.2 mAh g−1 at current densities of 0.5 and 1 C, respectively; the corresponding coulomb efficiencies are 97.3 and 99.5%. It is also worth noting that the capacity retention can reach as high as 92.7% for 500 cycles at 1 C. [ABSTRACT FROM AUTHOR]

Summary: Herein, a series of lithium‐sodium hybrid ion Na3−xLixV2(PO4)3/C (x = 2.5, 2.0, 1.5, 1.0, 0.5) as cathode materials are prepared by sol‐gel method. The lithium storage properties of Na3−xLixV2(PO4)3/C reveal that the lithium sodium ratio has a strong influence on material structure and the electrochemical properties. The multiple voltage platforms are observed at charge and discharge curve for the Na0.5Li2.5V2(PO4)3 material, as it contains rhombohedral and monoclinic Li3V2(PO4)3 phases, whereas a single voltage platform can be observed when x is less than 2, which are mixtures of Na3V2(PO4)3 with rhombohedral structure and Li3V2(PO4)3 with rhombohedral structure. Notably, NaLi2V2(PO4)3/C prepared by the calcination at 700°C for 8 hours contains a single rhombohedral phase. And when the charging and discharging voltage at the range 2.5 to 4.5 V and current density at 0.5C, NaLi2V2(PO4)3/C and Na2.5Li0.5V2(PO4)3/C are prepared by the pre‐calcination at 400°C for 4 hours and subsequent calcination at 750°C for 8 hours exhibit high first‐cycle specific discharge capacities of 124.8 and 130.0 mAh·g−1. The capacities are 118.4 and 115.1 mAh·g−1 after 50 cycles, indicating excellent capacity retention. [ABSTRACT FROM AUTHOR]

With their advantages of abundant raw material reserves, safety, and low toxicity and cost, sodium-ion batteries (SIBs) have gained increasing attention in recent years. Thanks to a high theoretical specific capacity (124 mAh g -1 ), a high operating voltage (about 3.2 V), and a very stable three-dimensional layered structure, sodium ferric fluorophosphate (Na 2 FePO 4 F, NFPF) has emerged as a strong candidate to be used as a cathode material for SIBs. However, applications are currently limited due to the low electronic conductivity and slow ion diffusion rate of NFPF, which result in a low actual specific capacity and a high rate performance. In this study, the authors used a high-temperature solid-phase technique to produce Na 2-x Li x FePO 4 F/C (0 ≤ x ≤ 2) and evaluated the impact on electrode performance of materials with different Na + and Li + contents (values of x). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were also used to analyze the material's crystal structure and nanostructure. The results show that the material had the best room-temperature performance when x = 0.5. At a charge-discharge rate of 0.1 C, the first discharge-specific capacity of the resulting Na 1.5 Li 0.5 FePO 4 F/C cathode material was 122.9 mAh g -1 (the theoretical capacity was 124 mAh g -1 ), and after 100 cycles, it remained at 118 mAh g -1 , representing a capacity retention rate of 96.2% and a Coulomb efficiency of 98%. The findings of this study demonstrate that combining lithium and sodium ions improves the electrochemical performance of electrode materials.

In this investigation, a lithium-free cathode material, Na 0.7 MnO 2.05 -Na 0.91 MnO 2 , was synthesized by the solid phase method. The intercalation mechanism and partial phase transformation mechanism of NMO600 were clarified by in situ X-ray diffraction and impedance. The design of the heterostructure is favourable for improving the lithium ion storage of NMO600, which can deliver a discharge capacity of 83.12 mA h g -1 at 1 A g -1 and keep 61.71 mA h g -1 after 700 cycles.