Nanostructured Li₂S–C Composites as Cathode Material for High-Energy Lithium/Sulfur Batteries

Abstract

With a theoretical capacity of 1166 mA·h·g(-1), lithium sulfide (Li(2)S) has received much attention as a promising cathode material for high specific energy lithium/sulfur cells. However, the insulating nature of Li(2)S prevents the achievement of high utilization (or high capacity) and good rate capability. Various efforts have been made to ameliorate this problem by improving the contact between Li(2)S and electronic conductors. In the literature, however, a relatively high capacity was only obtained with the Li(2)S content below 50 wt %; therefore, the estimated cell specific energy values are often below 350 W·h·kg(-1), which is insufficient to meet the ever-increasing requirements of newly emerging technologies. Here, we report a cost-effective way of preparing nanostructured Li(2)S-carbon composite cathodes by high-energy dry ball milling of commercially available micrometer-sized Li(2)S powder together with carbon additives. A simple but effective electrochemical activation process was used to dramatically improve the utilization and reversibility of the Li(2)S-C electrodes, which was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. We further improved the cycling stability of the Li(2)S-C electrodes by adding multiwalled carbon nanotubes to the nanocomposites. With a very high specific capacity of 1144 mA·h·g(-1) (98% of the theoretical value) obtained at a high Li(2)S content (67.5 wt %), the estimated specific energy of our cell was ∼610 W·h·kg(-1), which is the highest demonstrated so far for the Li/Li(2)S cells. The cells also maintained good rate capability and improved cycle life. With further improvement in capacity retention, nanostructured Li(2)S-C composite cathodes may offer a significant opportunity for the development of rechargeable cells with a much higher specific energy.

Li2S nano spheres anchored to single-layered graphene as a high-performance cathode material for lithium/sulfur cells

“…Among the many candidates, the lithium-ion battery (LIB) is considered as "state-of-the-art" and has been used for portable devices and electric vehicles [1][2][3][4][5][6][7]. However, the traditional LIB seems to be insufficient for practical application in emerging markets due to the limited specific energy of the cell, which indicates that remarkable developments are necessary for applications such as electric vehicles [8][9][10].…”

“…Furthermore, sulfur, which is ubiquitous in nature, is environmentally benign and low-cost. [4,[8][9][10][11][12][13][14][15] Li/S cells have become one of the most promising rechargeable cell systems, showing great potential in meeting the rigorous needs for electrical vehicles and grid-scale stationary storage. Despite their advantages, Li/S cells still are affected by some intrinsic drawbacks.…”

“…In addition, another difficulty of the Li/S cells is the use of a metallic lithium anode, which is associated with dendrite formation on the surface of the Li metal anode caused by the inhomogeneous current distribution during cycling, leading to serious safety hazards and cell shorting [30][31][32]. Fully lithiated lithium sulfide (Li 2 S) with a theoretical specific capacity of 1169 mA h g À 1 Li 2 S has become a more desirable cathode material for the Li/S cell due to its capability of pairing with a lithium-free anode such as silicon and some tin compounds which can obviate the safety concerns of the lithium metal anode when using sulfur [10,[33][34][35][36][37][38][39][40][41]. Li 2 S particles, as the end discharge product of the Li/S cell, shrink during charging and generate empty space to accommodate the volume expansion of sulfur particles during lithiation (discharge), thus the mechanical failure of the cathode can be alleviated, resulting in improved cycle life for the Li/S cell.…”

“…Sharing the same reaction mechanisms, Li 2 S cathodes inevitably encounter the same problems as for sulfur cathodes such as the dissolution of polysulfides into most liquid electrolytes, and its "shuttle effect" which can induce low utilization of active material, low coulombic efficiency and severe degradation of the cycle life. Meanwhile the low electronic and ionic conductivity of Li 2 S also cause low sulfur utilization and poor rate capability of the sulfur cathode [10,44]. To address the abovementioned problems, many approaches have emerged to improve the electrochemical performance of the Li 2 S cathode, for example employing Li 2 S nanoparticles, and encapsulating Li 2 S with carbon, [1,10,35] conductive polymers or transition metal disulfides [37,45].…”

A systematic approach to high and stable discharge capacity for scaling up the lithium–sulfur battery

“…Improving the discharge capacity, however, to near to the theoretical level and minimizing the capacity fading phenomenon are the burning questions that need to be solved, which involve solving the problems of polysulfide dissolution and the shuttling effect of polysulfide [3]. Extensive research has been conducted on different techniques: loading the sulfur onto carbon materials [4][5][6][7][8][9], engineering the cathode surface [10][11][12], using different electrolytes and binders [13,14], and applying different additives, specifically conductive polymers [15,16], to minimize the problems.…”