Sulfur/graphitic hollow carbon sphere nano-composite as a cathode material for high-power lithium-sulfur battery
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NANO EXPRESS
Open Access
Sulfur/graphitic hollow carbon sphere nano-composite as a cathode material for high-power lithium-sulfur battery Eon Sung Shin, Min-Seop Kim, Won Il Cho* and Si Hyoung Oh*
Abstract The intrinsic low conductivity of sulfur which leads to a low performance at a high current rate is one of the most limiting factors for the commercialization of lithium-sulfur battery. Here, we present an easy and convenient method to synthesize a mono-dispersed hollow carbon sphere with a thin graphitic wall which can be utilized as a support with a good electrical conductivity for the preparation of sulfur/carbon nano-composite cathode. The hollow carbon sphere was prepared from the pyrolysis of the homogenous mixture of the mono-dispersed spherical silica and Fe-phthalocyanine powder in elevated temperature. The composite cathode was manufactured by infiltrating sulfur melt into the inner side of the graphitic wall. The electrochemical cycling shows a capacity of 425 mAh gā1 at 3 C current rate which is more than five times larger than that for the sulfur/carbon black nano-composite prepared by simple ball milling. Keywords: Lithium-sulfur battery; Hollow carbon sphere; Graphitic carbon; Nano-composite; Cathode
Background The advent of new commercial markets for the hybrid electric vehicle and the large-scale energy storage system urges the development of novel battery systems with much higher energy density and lower price than the conventional Li-ion battery based on the transition metal oxide and graphite [1,2]. For decades, lithium-sulfur battery has been investigated as a viable candidate to meet these requirements due to its high theoretical energy density of over 2,500 Wh/kg and the low material cost of sulfur [3,4]. The lithiumsulfur battery utilizes a series of conversion reactions of elemental sulfur (S8) to lithium sulfide (Li2S) on the cathode, resulting in a high cathodic capacity of 1,678 mAh gā1. These reactions involve complex intermediate steps, where various lithium polysulfides (Li2Sn, 3 < n < 8) participate as temporary soluble species [5,6]. Since the solubilized lithium polysulfides can cause a significant shuttle reaction, and thus, an excessive overcharge behavior may occur during the
* Correspondence: [email protected]; [email protected] Center for Energy Convergence Research, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul, 136-791, South Korea
charge process, the dissolution of polysulfide species needs to be suppressed as much as possible. So far, many attempts have been made to control this phenomenon, with a partial success including an addition of mesoporous metal oxide to cathode [7], an encapsulation of sulfur nanoparticles by hollow metal oxide [8], and an adoption of the highly concentrated electrolyte system [9]. The other fundamental challenge of Li-S battery is associated with the insulating low electrical conductivity of sulfur (approximately 5.0 Ć 10ā14 S/cm) which leads to poor electrochemical performance even at moderate current r
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