Sodium ion storage performance and mechanism in orthorhombic V2O5 single-crystalline nanowires

A fundamental understanding of the electrochemical reaction process and mechanism of electrodes is very crucial for developing high-performance electrode materials. In this study, we report the sodium ion storage behavior and mechanism of orthorhombic V2O5 single-crystalline nanowires in the voltage window of 1.0-4.0 V (vs. Na/Na+). The single-crystalline nanowires exhibit a large irreversible capacity loss during the first discharge/charge cycle, and then show excellent cycling stability in the following cycles. At a current density of 100 mA g(-1), the nanowires electrode delivers initial discharge/charge capacity of 217/88 mA h g(-1), corresponding to a Coulombic efficiency of only 40.5%; after 100 cycles, the electrode remains a reversible discharge capacity of 78 mA h g(-1) with a fading rate of only 0.09% per cycle compared with the 2(nd)cycle discharge capacity. The sodium ion storage mechanism was investigated, illustrating that the large irreversible capacity loss in the first cycle can be attributed to the initially formed single-crystalline alpha '-NaxV2O5(0.02 <x< 0.88), in which sodium ions cannot be electrochemically extracted and the alpha '-Na(0.88)V(2)O(5)can reversibly host and release sodium ionsviaa single-phase (solid solution) reaction, leading to excellent cycling stability. The Na+ diffusion coefficient in alpha '-Na(x)V(2)O(5)ranges from 10(-12) to 10(-11.5) cm(2)s(-1)as evaluated by galvanostatic intermittent titration technique (GITT).