Abstract
Lithium-sulfur (Li-S) battery is a promising energy storage system due to its high energy density, cost effectiveness and environmental friendliness of sulfur. However, there are still a number of technical challenges, such as low Coulombic efficiency and poor long-term cycle life, impeding the commercialization of Li-S battery. The electrochemical performance of Li-S battery is closely related with the interfacial reactions occurring between hosting substrate and active sulfur species which are poorly conducting at fully oxidized and reduced states. Here, we correlate the relationship between the performance and interfacial reactions in the Li-S battery system, using a hollow carbon nanosphere (HCNS) with highly graphitic character as hosting substrate for sulfur. With an appropriate amount of sulfur loading, HCNS/S composite exhibits excellent electrochemical performance because of the fast interfacial reactions between HCNS and the polysulfides. However, further increase of sulfur loading leads to increased formation of highly resistive insoluble reaction products (Li2S2/Li2S) which limits the reversibility of the interfacial reactions and results in poor electrochemical performances. These findings demonstrate the importance of the interfacial reaction reversibility in the whole electrode system on achieving high capacity and long cycle life of sulfur cathode for Li-S batteries.
Highlights
IntroductionLithium-sulfur (Li-S) batteries are attracting increasing worldwide attention because of their high theoretical capacity, natural abundance, low cost, and environmental friendliness (Mikhaylik and Akridge, 2004; Wang et al, 2008, 2015; Cao et al, 2011; Jayaprakash et al, 2011; Ji et al, 2011a,b; Zheng et al, 2011, 2013a,c,d,e; Schuster et al, 2012; Su and Manthiram, 2012a,b; Evers and Nazar, 2013; Huang et al, 2014; Xiao et al, 2015)
To investigate the influence of sulfur content on the interfacial reactions and the consequent electrochemical performance of Li-S battery, hollow carbon nanosphere (HCNS)/S composites with different sulfur loading were prepared: one is loaded with sulfur content of 50 wt% S, which is close to the maximum limit as determined by the pore volume of HCNS, while the other one is loaded with significantly excessive sulfur content (80 wt% S)
Hollow carbon nanosphere-sulfur composites have been investigated as cathode materials for Li-S battery, and the electrochemical performances were correlated with the interfacial reactions occurring in the whole electrode system
Summary
Lithium-sulfur (Li-S) batteries are attracting increasing worldwide attention because of their high theoretical capacity, natural abundance, low cost, and environmental friendliness (Mikhaylik and Akridge, 2004; Wang et al, 2008, 2015; Cao et al, 2011; Jayaprakash et al, 2011; Ji et al, 2011a,b; Zheng et al, 2011, 2013a,c,d,e; Schuster et al, 2012; Su and Manthiram, 2012a,b; Evers and Nazar, 2013; Huang et al, 2014; Xiao et al, 2015). Interfacial-reaction-dependent Li-S battery polysulfides between sulfur electrode and lithium anode are the main reasons for the low utilization rate of sulfur and poor electrochemical performances of Li-S battery, including low Coulombic efficiency, high self-discharge rate, and fast capacity fading (Mikhaylik and Akridge, 2004; Wang et al, 2008; Cao et al, 2011). Other organic materials such as polythiophene (Wu et al, 2010), polypyrrole (Fu and Manthiram, 2012), polyaniline (Xiao et al, 2012b), and metal organic framework (MOF) (DemirCakan et al, 2011; Zheng et al, 2014a) have been adopted as sulfur hosting substrate and demonstrated to show good cycling performance
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