The preparation, characterization, electro-chemical performance and transporting mechanism of Na1.25Cr0.25Ti1.75(PO4)(3)/C as anode material for SIBs
QY Wang and YX Luo and FP Gu and M Shui and J Shu, SOLID STATE IONICS, 352, 115368 (2020).
Due to the limited resources of lithium, sodium ion battery is regarded as the most promising alternative to lithium-ion batteries. In this study, the Cr coping and carbon coating anode material for SIBs, Na1.25Cr0.25Ti1.75(PO4)(3)/C, is synthesized by a facile sol-gel technique using polyvinyl alcohol as carbon source. The obtained products show remarkable electrochemical properties in rate-capability (148.6 mAh g(-1) at 1C, 111.8 mAh g(-1) at 2C, 91.2 mAh g(-1) at 3C, 77.8 mAh g(-1) at 4C, 68.3 mAh g(-1) at 5C, 61.8 mAh g(-1) at 6C, 57.4 mAh g(-1) at 7C), cycle-stability (65.1% capacity retention over 1000 cycles) and Coulombic efficiencies. Furthermore, the doping of Cr element reduces the mean charge/discharge potential significantly and is favorable for the construction of the whole batteries with higher average potentials. The molecular dynamics simulations of the pristine NaTi2(PO4)(3) and NaCr0.25Ti1.75(PO4)(3) tells us that the Cr doping in the lattice increases the self-diffusion coefficients of Na+ by 12 orders of magnitude. This great enhancement of the Na+ mobility is supposed to be owing to the presence of the interstice Na+ and the concerted migration of interstice Na+ and the M1 site Na+, which owns a significantly reduced energy barrier compared with that of the vacancy migration mechanism in the case of pristine NaTi2(PO4)(3).
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