Unveiling the Synergy of Architecture and Anion Vacancy on Bi<sub>2</sub>Te<sub>3–<i>x</i></sub>@NPCNFs for Fast and Stable Potassium Ion Storage
Gaoyu Wang, Qinghua Li, Wei Zhang, Jiawei Wu, Wenbo Fan, Lixiang Wang, Zhixin Liang, Zhijiao Huang, Zeyu Lin, Guang Wang, Junling Wang, Shaoming Huang
Abstract
Large volume strain and slow kinetics are the main obstacles to the application of high-specific-capacity alloy-type metal tellurides in potassium-ion storage systems. Herein, Bi 2 Te 3– x nanocrystals with abundant Te-vacancies embedded in nitrogen-doped porous carbon nanofibers (Bi 2 Te 3– x @NPCNFs) are proposed to address these challenges. In particular, a hierarchical porous fiber structure can be achieved by the polyvinylpyrrolidone-etching method and is conducive to increasing the Te-vacancy concentration. The unique porous structure together with defect engineering modulates the potassium storage mechanism of Bi 2 Te 3, suppresses structural distortion, and accelerates K + diffusion capacity. The meticulously designed Bi 2 Te 3– x @NPCNFs electrode exhibits ultrastable cycling stability (over 3500 stable cycles at 1.0 A g –1 with a capacity degradation of only 0.01% per cycle) and outstanding rate capability (109.5 mAh g –1 at 2.0 A g –1 ). Furthermore, the systematic ex situ characterization confirms that the Bi 2 Te 3– x @NPCNFs electrode undergoes an “intercalation-conversion-step alloying” mechanism for potassium storage. Kinetic analysis and density functional theory calculations reveal the excellent pseudocapacitive performance, attractive K + adsorption, and fast K + diffusion ability of the Bi 2 Te 3– x @NPCNFs electrode, which is essential for fast potassium-ion storage. Impressively, the assembled Bi 2 Te 3– x @NPCNFs//activated-carbon potassium-ion hybrid capacitors achieve considerable energy/power density (energy density up to 112 Wh kg –1 at a power density of 1000 W kg –1 ) and excellent cycling stability (1600 cycles at 10.0 A g –1 ), indicating their potential practical applications.