Novel Ag@Nitrogen-doped Porous Carbon Composite with High Electrochemical Performance as Anode Materials for Lithium-ion Batteries

Nano-Micro Lett. (2017) 9:32 DOI 10.1007/s40820-017-0131-y ARTICLE Novel Ag@Nitrogen-doped Porous Carbon Composite with High Electrochemical Performance as Anode Materials for Lithium-ion Batteries Yuqing Chen1 . Jintang Li1 . Guanghui Yue2 . Xuetao Luo1 Received: 5 December 2016 / Accepted: 15 January 2017 / Published online: 18 February 2017  The Author(s) 2017. This article is published with open access at Springerlink.com Highlights • • A novel Ag@nitrogen-doped porous carbon (Ag-NPC) composite was applied to lithium-ion batteries. The encapsulation of Ag nanoparticles (Ag NPs) into NPC boosts reversible capacity from 501.6 to 852 mAh g-1. Ag-NPC shows a much better cycling performance than NPC due to the synergistic effect of NPC and Ag NPs. Abstract A novel Ag@nitrogen-doped porous carbon (Ag-NPC) composite was synthesized via a facile hydrothermal method and applied as an anode material in lithium-ion batteries (LIBs). Using this method, Ag nanoparticles (Ag NPs) were embedded in NPC through thermal decomposition of AgNO3 in the pores of NPC. The reversible capacity of Ag-NPC remained at 852 mAh g-1 after 200 cycles at a current density of 0.1 A g-1, showing its remarkable cycling stability. The enhancement of the electrochemical properties such as cycling performance, reversible capacity and rate performance of Ag-NPC compared to the NPC contributed to the synergistic effects between Ag NPs and NPC. Keywords Nitrogen-doped porous carbon  Ag nanoparticles  Synergistic effects  Lithium-ion batteries 1 Introduction & Xuetao Luo 1 Fujian Key Laboratory of Advanced Materials, Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen 361005, People’s Republic of China 2 Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen, 361005, People’s Republic of China In recent years, lithium-ion batteries (LIBs) have not only been widely used for consumer electronics, but have also proved promising for electric vehicles, owing to their unique advantages, such as high energy and power density, no memory effect and environmental friendliness [1–3]. Currently, graphitic materials are the most commonly used commercial anode materials for LIBs by virtue of their 123 32 Page 2 of 11 superior cycling stability and high coulombic efficiency [4]. However, due to quite a low theoretical capacity of 372 mAh g-1, it would be hard for graphite to meet increasingly high energy requirements in electric vehicles [5]. A variety of materials have been exploited as anode materials for LIBs in the past decades, such as transitionmetal oxides [6–8], and silicon-based [9–11] or tin-based [12–14] materials, which have ultra-high theoretical capacity. Unfortunately, these materials react with lithium and are more inclined to form Li2O than Li-M alloys. Due to the fact that it is an electrochemically irreversible reaction, it results in a large irreversible capacity [15]. Silver is an appealing option for anode materials, owing to its relatively high specific capacity, which is attributed to the formation of several Ag-Li alloys (up to AgLi12) within a very low voltage range (0.25–0 V) [16]. Moreover, silver has the best electrical conductivity among all metals and excellent lithium diffusivity, which can efficiently boost the electrochemical performance [17]. However, silver also suffers from undesirable volumetric expansion during lithium insertion. To alleviate this harmful effect, different strategies have been developed, such as downsizing the particle dimensions to the nanoscale, introducing a porous structure to the solid particles and designing silver-containing composites [18–20]. Carbon is a common matrix for silver. Shilpa et al. used hollow carbon nanofibers as a buffer matrix and embedded silver nanoparticles in them through the coaxial electrospinning method [15]. Hsieh et al. dispersed silver nanorods onto graphene nanosheets by the hydrothermal method [21]. Metal organic frameworks (MOFs) have been attracting increasing attention as carbon sources for anode materials because various types of MOF precursors can result in derived carbon with a uniform, controllable, porous structure and enable innate doping of heteroatoms [22–24]. On the basis of previous research, the nanopores can facilitate rapid electrolyte transfer [25]. In addition, the heteroatomdoped carbon always performs at a higher specific capacity and outstanding cycling stability compared to the nondoped carbon [26–29]. Song et al. prepared a cage-like carbon/nano-Si composite as anode materials by the template method to embed Si nanoparticles into ZIF-8. The resulting nano-Si/C composite showed a higher reversible capacity than many Si/C composites previously reported [30]. Xie et al. fabricated a sandwich-like, graphene-based, porous nitrogen-doped carbon (PNCs@Gr) through the pyrolysis of zeolitic imidazolate framework nanoparticles grown in situ on GO (ZIF-8@GO), which exhibited outstanding electrochemical performance among carbonaceous materials used as anode materials [31]. We used ZIF-8-derived carbon as a matrix for silver nanoparticles (Ag NPs), which can provide not only rigid matrices with nanopores, but also a relatively high nitrogen 123 Nano-Micro Lett. (2017) 9:32 content. We designed a strategy to incorporate Ag NPs into N-doped porous carbon uniformly via a facile hydrothermal method without any reduction agent. When applied as the anode material for the Li-ion battery, the Ag-NPC showed excellent electrochemical performance over bare NPC, which was attributed to the synergistic effect of Ag NPs and the carbon matrix. 2 Experimental 2.1 Chemicals Methanol (CH3OH, Sinopharm Chemical Reagent Co. Ltd, [99.5%), 2-methylimidazole (C4H6N2, Sinopharm Chemical Reagent Co. Ltd., 99%), zinc nitrate (Zn(NO3)26H2O, Shanghai Titanchem Co. Ltd., [99.8%), 1-methylimidazole (C4H6N2, Sinopharm Chemical Reagent Co. Ltd., 99%) and silver nitrate (AgNO3, Sinopharm Chemical Reagent Co. Ltd.,[99.8%) were used. All reagents were used without further purification. 2.2 Preparation of N-doped Porous Carbon (NPC) ZIF-8 was synthesized according to method reported in the literature [32]. Specifically, a methanolic solution (400 mL) of 2-methylimidazole (6.48 g) and 1-methylimidazole (6.28 mL) was quickly poured into a methanolic solution (400 mL) of Zn(NO3)26H2O (5.88 g) and stirred for 2 min and then kept still for 16 h. After that, the solution was centrifuged, washed by methanol and dried at 60 C for 3 h to produce a white solid (ZIF-8). Then, the solid was ground into powder, followed by heat treatment at 800 C for 5 h under an argon atmosphere. After letting it cooldown to the room temperature, the obtained product was dispersed into an HCl solution (100 mL, 20 wt% in water) and stirred for 24 h to remove residual metallic Zn and/or ZnO. The mixture was then washed thoroughly with distilled water several times until a (...truncated)