Unveiling nanoplates-assembled Bi 2 MoO 6 microsphere as a novel anode material for high performance potassium-ion batte
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BSTRACT Bismuth (Bi)-based electrode has aroused tremendous interest in potassium-ion batteries (PIBs) on account of its low cost, high electronic conductivity, low charge voltage and high theoretical capacity. However, the rapid capacity fading and poor lifespan induced by the normalized volume expansion (up to ~ 406%) and serious aggregation of Bi during cycling process hinder its application. Herein, bismuth molybdate (Bi2MoO6) microsphere assembled by 2D nanoplate units is successfully prepared by a facile solvothermal method and demonstrated as a promising anode for PIBs. The unique microsphere structure and the self-generated potassium molybdate (K-Mo-O species) during the electrochemical reactions can effectively suppress mechanical fracture of Bi-based anode originated from the volume variation during charge/discharge of the battery. As a result, the Bi2MoO6 microsphere without hybridizing with any other conductive carbon matrix shows superior electrochemical performance, which delivers a high reversible capacity of 121.7 mAh·g−1 at 100 mA·g−1 over 600 cycles. In addition, the assembled perylenetetracarboxylic dianhydride (PTCDA)//Bi2MoO6 full-cell coupled with PTCDA cathode demonstrates the potential application of Bi2MoO6 microsphere. Most importantly, the phase evolution of Bi2MoO6 microsphere during potassiation/depotassiation process is successfully deciphered by ex situ X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM) technologies, which reveals a combination mechanism of conversion reaction and alloying/dealloying reaction for Bi2MoO6 anode. Our findings not only open a new way to enhance the performance of Bi-based anode in PIBs, but also provide useful implications to other alloy-type anodes for secondary alkali-metal ion batteries.
KEYWORDS Bi2MoO6, microsphere, potassium ion batteries, mechanism, anode
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Introduction
The ever-growing demand of large-scale stationary energy storage pushes energy storage devices towards cost-effective, environment friendly, high energy density and long lifespan [1–3]. While the commercial lithium-ion batteries (LIBs) cannot meet the growing demand due to the high cost, limited reserves and uneven global distribution of lithium [4, 5]. In this regard, sodium-ion and potassium-ion batteries (SIBs and PIBs, respectively) are expected to be cost-effective alternatives owing to their low cost, abundant reserves and similar physicochemical properties as those of LIBs [6–11]. Comparatively speaking, potassium possesses lower standard redox potential (–2.93 V vs. SHE) than sodium (–2.71 V vs. SHE) [12, 13], suggesting a higher working voltage and energy density for PIBs [14, 15]. However, the large ionic radius of K ion makes it difficult to intercalate into electrode material because of the higher diffusion barriers and sluggish kinetics [16]. Therefore, identifying suitable host materials with stable cyclability for PIBs so as to meet the growing demand is urgently needed. To date, the reported anode materials
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