Improved performance of Li-S battery with hybrid electrolyte by interface modification
Introduction
Lithium metal is one of the most promising candidates as an anode material for next-generation energy storage systems due to its high specific capacity (3860 mA h g− 1) and the low negative electrochemical potential (− 3.04 V versus the standard hydrogen electrode) [1], [2]. When coupled with a sulfur cathode, a rechargeable lithium-sulfur (Li-S) battery is expected to yield high theoretical specific energy of 2600 W h kg− 1, based on a redox reaction that reversibly interconverts sulfur (S8) and Li2S [3]. In addition, sulfur is low cost, highly natural abundant and environmental friendly. However, the practical realization of Li–S batteries is currently hindered by numerous scientific and technical challenges.
The most critical problem is believed to be associated with the intermediate lithium polysulfides (Li2Sn, n = 4–8) that are highly soluble in many organic solvents based electrolytes [4], [5], [6]. The dissolved polysulfides, formed at the beginning of discharge, could shuttle between the cathode and anode through the commonly used porous polymer separator. This shuttle process induces irreversible loss of active materials from the cathode, corrosion of Li metal anode, low coulombic efficiency, rapid capacity fading, and high self-discharge rates [7], [8]. Nevertheless, the dissolution of polysulfides is inevitable and essential for effective utilization of the active material in a Li-S cell [9], [10]. In the discharge process, the soluble polysulfides dissolve into the electrolyte solution enabling the subsequent sulfur to be exposed to the conductive agent and the reduction process to progressively move forward. In the charge process, the dissolved polysulfide species can facilitate the electrochemical conversion of the insoluble discharge products Li2S2/Li2S [11], [12]. We have previously reported a novel type of Li-S cell employing a hybrid electrolyte (HE) [13]. The hybrid electrolyte was composed of the liquid electrolyte and a lithium ion conductor that acts as the separator. The NASICON-type structured Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid electrolyte, which physically block the dissolution and diffusion of polysulfides could solve the shuttling problem. Meanwhile, the liquid electrolyte takes advantage of the dissolved polysulfides which offer fast charge/discharge rates and favor fast electrochemical kinetics of the cathode.
However, a redistribution of polysulfides on the electrode is unavoidable no matter what kind of treatment is done on the initial sulfur cathodes [14]. The redistribution of sulfur in the cell would cause the capacity fading once the soluble polysulfides detach from the cathode into the liquid electrolyte [15], [16], [17]. Gradually, sulfur loses intimate contact with carbon matrix. Electronically isolated and electrochemically inactive Li2S does not take part in the electrochemical oxidation during charge state owing to the lack of carbon matrix. The formation of irreversible Li2S becomes severe as cycling proceeds and the available conducting surface is decreased gradually, leading to the decreasing of discharge capacity. To make full use of the dissolved sulfur-containing active materials, a carbon coating layer facing sulfur cathode is introduced onto one side of the solid electrolyte. As shown in Fig. 1, the carbon-coating layer serves as an upper current collector to facilitate electron transport as well as to improve the wettability of solid electrolyte towards the liquid electrolyte. The migration of the polysulfides is physically blocked by the solid electrolyte and the shuttle effect is prevented. A lithium sulfur battery with enhanced electrochemical performance is demonstrated with an initial discharge capacity of 1409 mA h g− 1 and a reversible specific capacity of 1000 mA h g− 1 after 50 cycles at 0.2C rate.
Section snippets
Carbon coated Li1.5Al0.5Ge1.5(PO4)3 pellet fabrication
The Li1.5Al0.5Ge1.5(PO4)3 ceramic electrolyte is synthesized by the solid state reaction method. The detailed preparation process is previously reported [13], [18]. The obtained ceramic pellet, with the thickness of 0.7 mm and diameter of 17.4 mm, has a conductivity of 1.7 × 10− 4 S/cm at room temperature. This value is in good agreement with results reported by several previous literatures [19], [20], [21], [22]. The electronically conductive carbon is a mixture of acetylene black (AB) and carbon
Results and discussion
Fig. 2a presents cross-sectional image of the carbon coated LAGP ceramic electrolyte. The carbon coating layer is stacked well on the surface of the LAGP ceramic and is about 5 μm thick on average. The carbon material is composed of a uniformly dispersed mixture of AB and CNT, as shown in the TEM image (Fig. 2b). Fig. 2c shows the top surface morphology of the carbon coating layer which shows a uniform porous structure without visible agglomeration. The digital photo of the pristine ceramic
Conclusion
In summary, this work clearly demonstrates that by modifying the ceramic electrolyte with a carbon coating layer, a highly efficient interface is achieved in the ceramic-liquid hybrid Li-S cell. The carbon coating layer obviously increases the conducting surface between cathode and the ceramic electrolyte where high reutilization of the adsorbed dissolved polysulfide species is realized, leading to significant enhancement in the reversibility and rate capability. The resultant Li-S cell shows
Acknowledgements
We are grateful to the support of the Natural Science Foundation of China (NSFC) No. 51402330, No. 51372262, No. 51472261 and the high resolution earth observation system major special project youth innovation foundation of China No. GFZX04060103. The authors thank Prof. B. V. R. Chowdari (School of Materials science and Engineering, Nanyang Technological University, Singapore) for helpful discussion.
References (35)
J. Power Sources
(2013)- et al.
J. Power Sources
(2014) - et al.
Solid State Ionics
(2004) - et al.
J. Power Sources
(2011) - et al.
J. Power Sources
(2015) - et al.
J. Power Sources
(2014) - et al.
Nature
(2001) - et al.
Nat. Commun.
(2015) - et al.
Nat. Commun.
(2014) - et al.
Acc. Chem. Res.
(2013)
Acc. Chem. Res.
Adv. Energy Mater.
J. Electrochem. Soc.
J. Electrochem. Soc.
J. Am. Chem. Soc.
J. Electrochem. Soc.
Phys. Chem. Chem. Phys.
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