A high-volumetric-capacity bismuth nanosheet/graphene electrode for potassium ion batteries
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Published online 1 September 2020 | https://doi.org/10.1007/s40843-020-1493-1
A high-volumetric-capacity bismuth nanosheet/ graphene electrode for potassium ion batteries 1,2†
Linchao Zeng
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ABSTRACT Potassium ion batteries (PIBs) with high-volumetric energy densities are promising for next-generation low-cost energy storage devices. Metallic bismuth (Bi) with a structure similar to graphite, is a promising anode material for PIBs due to its high theoretical volumetric capacity −3 (3763 mA h cm ) and relatively low working potential (−2.93 V vs. standard hydrogen electrode). However, it experiences severe capacity decay caused by a huge volume expansion of Bi when alloying with potassium. This study reports a flexible and free-standing Bi nanosheet (BiNS)/reduced graphene oxide composite membrane with designed porosity close to the expansion ratio of BiNS after charging. The controlled pore structure improves the electron and ion transport during cycling, and strengthens the structural stability of the electrode during potassiation and depotassiation, leading to excellent electrochemical performance for potassium-ion storage. In particular, it delivers a high reversible −3 volumetric capacity of 451 mA h cm at the current density of −1 0.5 A g , which is much higher than the previously reported commercial graphite material. Keywords: potassium ion batteries, high volumetric energy density, bismuth nanosheet, controlled pore structure, graphite
INTRODUCTION Recently, energy storage devices with high volumetric energy density and low cost have become more and more important for commercial applications [1–5]. Potassium ion battery (PIB), a newly developed energy storage system, is a promising candidate due to the low standard + electrochemical potential of K /K (−2.93 V vs. standard hydrogen electrode SHE) and the abundance of potassium resource in the earth’s crust [6–13]. Graphite is a commercialized anode material for batteries, showing a 1 2 3
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, Minsu Liu , Peipei Li , Guangmin Zhou , Peixin Zhang and Ling Qiu
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limited theoretical volumetric capacity of about −3 627.7 mA h cm [14]. To improve the volumetric energy density of PIBs, many anode materials with high theoretical volumetric capacity and low charge-discharge platforms are explored, including antimony (Sb), bismuth (Bi), tin oxide (SnO2), and phosphorus (P) [9,15–18]. Among them, Bi is an outstanding candidate for PIBs because of its high theoretical volumetric capacity of −3 3763 mA h cm and relatively low working potential [19–22]. However, Bi endures a large volume expansion of ~411% during the charge and discharge processes, resulting in severe capacity decay. In addition, the large + size of K (1.38 Å) could hinder the ion transport [15,17,23]. In the previous studies, constructing porous structures is a common strategy to inhibit the volume expansion, which provides extra space to accommodate the expansion [20,21,24]. However, the volumetric capacity of electrodes is also sacrificed to the range of 100– −3 300 mA h cm [1]. T
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