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Nitrogen/Oxygen Dual-doped Carbon Nanofibers as an Electrocatalytic Interlayer for a High Sulfur Content Lithium-Sulfur Battery. Tianji Gao, Zhihao Yu, Zheng-Hong Huang, and Ying Yang ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b01840 • Publication Date (Web): 07 Dec 2018 Downloaded from http://pubs.acs.org on December 9, 2018
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ACS Applied Energy Materials
Nitrogen/Oxygen Dual-doped Carbon Nanofibers as an Electrocatalytic Interlayer for a High Sulfur Content Lithium-Sulfur Battery
Tianji Gaoa, Zhihao Yua, Zheng-Hong Huangb, Ying Yanga*
a
State Key Laboratory of Control and Simulation of Power System and Generation
Equipments, Tsinghua University, Beijing 100084, China b Laboratory of Advanced Materials, Department of Materials Science and Engineering,
Tsinghua University, Beijing 100084, China Corresponding author: Ying Yang. *Email:
[email protected] Key words: lithium-sulfur battery; interlayer; nitrogen/oxygen dual-doped carbon nanofibers; catalytic effect; scalable; electrospun; large sulfur loading
Abstract A self-standing nitrogen/oxygen dual-doped carbon nanofiber matrix is prepared based on polymer chain design and electrospinning followed by a one-step carbonization. The interlayer can substantially suppress the shuttle effect and improve the charge-discharge performance of lithium-sulfur battery because of the catalytic effect and strong adsorption effect between interlayer and lithium polysulfides. With a sulfur areal loading of 4.54 mg cm−2 and a sulfur mass content of 80% at the whole electrode level, the discharge specific capacity of the initial cycle is 947 mA h g-1 and it also contains more than 908 mA h g-1 and 800 mA h g-1 after 100 and 200 cycles at 0.1 C with such an interlayer. It is found that the capacity contribution from octasulfur to dilithium tetrasulfide is improved 35% and the utilization ratio of dilithium tetrasulfide to lithium
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sulfide improved 76% with an interlayer, which is the main reason for the improvement of the capacity. We believe that the cell configuration presented here coupled with further improvements of the sulfur electrode could help to alleviate some of the persistent problems in lithium-sulfur cells.
1. Introduction The high demand of energy storage devices for electric vehicles and large-scale energy storage has triggered the exploration of new electrochemical systems, such as lithiumsulfur (Li-S) batteries with a high theoretical capacity of 1675 mA h g-1 and a high energy density of 2600 W h kg-1 [1-6]. Despite the considerable advantages of Li-S battery, the rapid capacity decay of Li-S batteries is a significant obstacle for practical applications. “Lithium polysulfides (LiPSs) shuttle effect” is one of the main factors of capacity fading in Li-S battery [710]. However, the LiPSs dissolution is an inevitable step for the fast kinetics of electrochemical reaction in cathodes. Numerous efforts have been made to alleviate the LiPSs shuttle effect [11-18], in which inserting a barrier layer between cathode and separator is a straightforward and effective strategy. Graphene [11, 12], carbon nano tube [13, 14], carbon papers [15, 16] and carbon nanofiber matrix [12, 13] have been investigated for trapping LiPSs. Although the cycling stability has been improved, the non-polar carbon materials show week physical adsorptions of LiPSs. Doping heteroatoms into carbon substrates is a feasible way to adjust the non-polar property of carbon materials. Various heteroatoms, such as nitrogen (N), oxygen (O) and boron (B), have been single-doped [19] or dual-doped [20-23] into carbon substrates [16-18] in various electrochemical systems, such as electrocatalysts in lithium oxygen batteries, Li-S batteries and supercapacitors [24, 25]. There are many
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methods for doping these atoms into carbon, including surface treatment with concentrated acid (e.g. sulfuric acid (H2SO4), nitric acid (HNO3)), or under different atmospheres (oxygen (O2), hydrogen (H2) and ammonia (NH3)) or designing polymer precursor before carbonization [11, 26, 27]. Among these methods, polymer precursor synthesis based on monomer molecule structure design is believed as a controllable method to prepared heteroatoms-doped carbon. The properties of carbon including conductivity and pore structure can be easily controlled during the carbonization process. It is believed that the matrix structure interlayer with functionalized surface can limit LiPSs shuttle effect with strong chemical adsorption [28-30]. Polyanilinegraphene oxide membrane [31], rice paper based carbon felt [32], H2SO4/HNO3 treated carbon paper [33], N-rich polyimide electrospun nanofibers [19] were reported to be used as an interlayer to improve the electrochemical stability of Li-S battery. However, most of the approaches are based on single atom doping and the process is relatively complicated and expensive. Another issue for practical applications of Li-S battery is the low sulfur content in the cathode, with a typical reported value
