Stabilizing sulfur cathodes using nitrogen-doped graphene as a chemical immobilizer for LiS batteries
Graphical abstract
High performance LiS batteries was designed by using nitrogen-doped graphene as a chemical immobilizer to bind lithium polysulfides and stabilize sulfur in the cathode.
Introduction
Lithium–sulfur (LiS) battery is a promising candidate for next generation energy storage systems due to its high theoretical specific capacity (1675 mAh g−1) and energy density (∼2600 Wh kg−1). Moreover, the low cost, environmental friendliness and wide availability of sulfur makes it attractive for battery applications [1], [2], [3], [4]. However, the practical application of the LiS batteries has been impeded due to a series of obstacles such as low electrical conductivity of sulfur/lithium sulfides, low Coulombic efficiency caused by the dissolving and shuttling of soluble lithium polysulfides (LiPSs), and large volume expansion/shrinkage of sulfur during lithiation/delithiation processes [5], [6], [7], [8].
To address the above issues, graphene based electrodes have attracted considerable interest for applications in LiS batteries due to their high electrical conductivity and large surface area [9], such as graphene wrapped sulfur cathode [10], three-dimensional hierarchical graphene network encapsulated sulfur electrode [11], unstacked double-layer graphene confined sulfur cathode [12], and graphene sandwiched sulfur structure [13]. As a high conductivity, porous and flexible framework, graphene was incorporated into the electrodes to overcome the shortcomings of LiS batteries, such as the insulating nature of sulfur, “shuttle effect” of LiPSs during repeated electrochemical charge/discharge cycles, and large volume expansion problems. However, these designs are still limited by the weak interactions (related to physical adsorption/confinement) between the graphene matrix and the sulfur species, which are not sufficient for alleviating polysulfides dissolution into the electrolyte. Besides hetero-atoms doping in the carbon materials as the strategy to bring chemical binding with lithium polysulfides, other promising chemical adsorbents such as transition metal oxides or sulphides have recently been introduced into LiS battery system to immobilize lithium polysulfides [14], [15], [16], [17]. However, the use of non-conductive metal oxides as polysulfide immobilizers will affect the rate performance of the electrodes. Therefore, an ideal conductive substrate should not only host non-polar sulfur, but also strongly adsorb (or bind) polar polysulfide species to extend the battery cycle life and achieve high utilization of active sulfur.
Generally, chemically-derived graphene from graphene oxide (GO) is decorated with abundant oxygen-containing functional groups (e.g. hydroxyl (COH), carboxyl (–COOH), carbonyl (CO), epoxyl (COC)), and lattice defects (e.g. atom vacancy, distortion, and dangling bonds) on the lateral surface or at edges [18], [19]. It is well demonstrated that non-metal heteroatoms can be easily incorporated into the graphene network, which has proven to be a very effective approach to tune the electrical and chemical environment of the carbon surface for electrochemical reactions [20]. Among different non-metal heteroatoms, nitrogen (N) is a very popular doping element that could act as a Lewis base in the lattice of graphene and interacts with other molecules [21], such as LiPSs and final discharge lithium sulfides, to significantly improve the electrochemical performance of LiS batteries. For example, N-doped porous carbon [22], [23], N-doped carbon nanotubes [24], [25] and N-doped graphene [26], [27], [28] were applied as the conductive substrates to improve the performance of LiS batteries. In these studies, Wang’s group proposed that the existence of N in the mesoporous carbon will promote the formation of bonds between sulfur atoms and nitrogen-related functional groups on the carbon [22]. However, the effect of N-dopants on the soluble LiPSs that are generated during the electrochemical reaction of a LiS battery are not well-understood. Further, it is still ambiguous as to which types of N-dopants are the most effective immobilizers to restrict the dissolution of LiPSs and what is the detailed interaction mechanism between N-dopants and LiPSs.
Herein, we propose a facile strategy towards high-performance LiS battery by using N-doped graphene as chemical immobilizer to stabilize sulfur and its discharge products. To provide the proof-of-the-concept, the raw material of GO was annealed in ammonia atmosphere serving as sulfur host (denoted as N-G), in side-by-side comparison to GO treated in argon (denoted as A-G). The results lead to insights about the roles played by the doped N heteroatom in graphene network on the electrochemical reaction. As a result, a high capacity of ∼1200 mAh g−1, excellent cycling stability, and good rate capability of a N-G-based LiS battery are achieved.
Section snippets
Synthesis of GO
GO was fabricated using natural graphite flakes by a modified Hummers’ method [29]. The concentration of the GO suspension obtained was 1.8 mg mL−1.
Synthesis of N-G and A-G
N-G was prepared by annealing GO at 400 °C under NH3 gas flow. Briefly, 100 mg of GO was put in the middle of a quartz tube furnace in NH3 flow of 50 sccm. It was then heated to 400 °C with a ramp of 5 °C min−1 and held at this temperature for 2 h. The resultant N-G samples were obtained after the furnace was naturally cooled to room temperature. In
Results and discussion
The graphene-sulfur composites were prepared by thermal-diffused sulfur into N-G and A-G samples at 155 °C [30], [31]. SEM images reveal that both N-G-S and A-G-S have a curly morphology with a thin, wrinkled laminated structure (Fig. 1a,c and Fig. S1a). The elemental composition was analyzed by EDS that shows the presence of C, O, and S in the N-G-S and A-G-S composites (Fig. 1b, Fig. S2), while N element only appears in the N-G-S sample, indicating the successful incorporation of N atoms into
Conclusion
In summary, a stabilized sulfur cathode was achieved by using nitrogen modified graphene as chemical immobilizer for LiS batteries. The N-doped graphene cathode with ∼70% of sulfur exhibits a high specific capacity, fast reaction dynamics, good rate performance, and stable cycling performance with only 0.051% capacity decay per cycle up to 300 cycles. When the current density increased to 6 A g−1, the specific capacity is still retained up to ∼330 mA h g−1. The enhanced performance can be
Acknowledgements
This work was supported by MOST (2014CB932402) and National Science Foundation of China (Nos.51521091, 51525206, 51172239, 51372253 and U1401243), “Strategic Priority Research Program” of the Chinese Academy of Sciences (XDA01020304, XDA09010104), the Key Research Program of the Chinese Academy of Sciences (Grant No. KGZD-EW-T06), and Research Supported by the CAS/SAFEA International Partnership Program for Creative Research Teams.
References (46)
Energy storage materials: a perspective
Energy Storage Mater.
(2015)- et al.
Carbon materials for Li–S batteries: functional evolution and performance improvement
Energy Storage Mater.
(2016) - et al.
Multi-functional separator/interlayer system for high-stable lithium-sulfur batteries: progress and prospects
Energy Storage Mater.
(2015) - et al.
Graphene materials for lithium–sulfur batteries
Energy Storage Mater.
(2015) - et al.
Free-standing TiO2 nanowire-embedded graphene hybrid membrane for advanced Li/dissolved polysulfide batteries
Nano Energy
(2015) - et al.
The reduction of graphene oxide
Carbon
(2012) - et al.
Synthesis and exfoliation of isocyanate-treated graphene oxide nanoplatelets
Carbon
(2006) - et al.
Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide
Carbon
(2007) - et al.
The low temperature performance of Li-ion batteries
J. Power Sources
(2003) - et al.
Understanding the interactions between lithium polysulfides and N-doped graphene using density functional theory calculations
Nano Energy
(2016)
Li-O2 and Li-S batteries with high energy storage
Nat. Mater
Nanostructured sulfur cathodes
Chem. Soc. Rev.
Rechargeable lithium–sulfur batteries
Chem. Rev.
New approaches for high energy density lithium-sulfur battery cathodes
Acc. Chem. Res.
Carbon-sulfur composites for Li-S batteries: status and prospects
J. Mater Chem. A
Graphene-wrapped sulfur particles as a rechargeable lithium-sulfur battery cathode material with high capacity and cycling stability
Nano Lett.
Tailoring microstructure of graphene-based membrane by controlled removal of trapped water inspired by the phase diagram
Adv. Funct. Mater
Unstacked double-layer templated graphene for high-rate lithium–sulphur batteries
Nat. Commun.
A graphene–pure-sulfur sandwich structure for ultrafast, long-life lithium–sulfur batteries
Adv. Mater
Powering lithium–sulfur battery performance by propelling polysulfide redox at sulfiphilic hosts
Nano Lett.
Balancing surface adsorption and diffusion of lithium-polysulfides on nonconductive oxides for lithium-sulfur battery design
Nat. Commun.
Vertically oriented arrays of ReS2 nanosheets for electrochemical energy storage and electrocatalysis
Nano Lett.
Hierarchically aminated graphene honeycombs for electrochemical capacitive energy storage
J. Mater Chem.
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