Rechargeable Lithium Sulfur Battery

Abstract

This paper reports on the investigation of rate capability and cycle characteristics of a lithium sulfur battery. The second discharge region where solid Li 2 S is formed on the surface of the carbon matrix in the cathode was highly sensitive to cathode thickness and discharge rate. The scanning electron microscope ͑SEM͒ observation suggests that thick Li 2 S layer formed at the surface of the cathode causes the diminution of the second discharge region at high discharge rate. Upon repeated cycle, the delocalization of the surface Li 2 S layer happened, however, the irreversible Li 2 S gradually increased with cycle as evidence by ͑SEM͒ and wave dispersive spectroscopy measurements, causing capacity fade. The formation of the irreversible Li 2 S was more significant for higher rates of discharge. It is believed that the destruction of the carbon matrix by stress generated during the localized deposition of Li 2 S is responsible for the formation of irreversible Li 2 S.The successful development of a lithium sulfur battery which has been regarded as one of the candidates for next generation battery requires extensive research on the electrochemical behaviors under various operation conditions. 1-7 We demonstrated previously that the Li 2 S is formed on the carbon matrix in the cathode. In addition, little Li 2 S remained uncharged on carbon matrix of the cathode even at 100% depth of charge. 8 In this paper, the performance changes of the lithium/sulfur ͑Li/S͒ battery and the morphological changes of the sulfur cathode with discharge rate, cathode thickness, and cycles are reported. From the practical point of view, information on the behaviors of the Li/S battery with the changes of these factors are highly important in design and further improvement of the Li/S battery. The changes in the morphology of the cathode with discharge rate and cycle number were detected by means of scanning electron microscopy ͑SEM͒ and wave dispersive spectroscopy ͑WDS͒ measurements. Based on the SEM and WDS analysis, we tried to find a structural factor of the sulfur cathode that affects the rate capability and cycle characteristics of the Li/S batteries. ExperimentalThe sulfur ͑purity: 99.8%, Aldrich͒ was ground by ball-mixing method to reduce the particle size to 3-8 m before use. The sulfur cathode was prepared by doctor blade-coating of the slurry of sulfur ͑purity: 99.98%, Aldrich͒ and super-P ͑MMM carbon͒, a conducting agent, on one side of aluminum current collector. The resulting cathode consists of 56.7 wt % of sulfur, 27.3 wt % of super-P, and 16 wt % of poly͑butadiene-co-styrene͒ based binder. The thickness of the cathode layer measured with a thickness gauge ͑Mitutoyo digimatic indicator 407-320͒ was varied as 15, 30, and 60 m. The capacity and density of the resulting cathodes are summarized in Table I. The Li metal foil ͑Teckraf͒ with thickness of 240 m was used as an anode. The lithium sulfur ͑Li/S͒ cells were fabricated by winding the cathode (250 ϫ 40 mm), Li metal anode (260 ϫ 45 mm), and separator ͑Celgard 3501, H...

A Microstructurally Resolved Model for Li-S Batteries Assessing the Impact of the Cathode Design on the Discharge Performance

“…While the lack of accurately determined parameters limits the predictive power the suggested capacity limiting mechanism -the clogging of inter-particular pores in the cathode region closest to the separator -has been identified experimentally. 42 Hence our model is capable of making qualitative predictions about such cathode micro-structural effects on the discharge performance. The decrease in mesoporosity is larger than the increase in Li 2 S (solid) volume fraction (Figure 7b), with additional losses caused due to the choking of mesopore entrances.…”

“…[40][41][42] The solvated polysulfides (S 2− y(soln) ) may react with lithium ions (Li + (soln) ) and produce insoluble lithium polysulfide that precipitates (Li 2 S y(solid) ). These chemical reactions are reversible, hence termed as precipitation/dissolution reactions (Table II), and indexed by curly brackets "{}".…”

Solvent Effects on Polysulfide Redox Kinetics and Ionic Conductivity in Lithium-Sulfur Batteries

“…4 Several technical barriers have limited the advancement of lithiumsulfur (Li-S) batteries, including rapid capacity fade, low rate capability, and low materials utilization. [5][6][7][8][9] During discharge of a Li-S cell, elemental S is initially reduced to form soluble polysulfide species Li 2 S x (4 ≤ x ≤ 8) which exist in complex solution-phase equilibria. Upon further discharge, the short chain polysulfides are further reduced and precipitate as Li 2 S until the discharge end state is reached.…”

Optimization of S/Mno2 Composite Cathode Material for Lithium Sulfur Batteries

“…The rechargeable lithium-sulfur (Li-S) battery has attracted immense assiduity in the last several years [4][5][6] owing to its high energy density (theoretically 2567 Wh/kg) and high theoretical specific capacity (1675 mAh/g). It exhibits higher specific capacity and specific energy (with lithium anode) than any other known cathode active materials [7,8] . In addition to, sulfur is abundant in nature, inexpensive and environmental harmless.…”