A Lithium/Dissolved Sulfur Battery with an Organic Electrolyte

Abstract

Prototype cells of the configuration Li/,~SM S as Li2S,, THF, 1M LiAsF6/C have been characterized with regard to capacity, rate, and rechargeability. Virtually 100% of the theoretical capacity could be realized at 50~ at rates below 1.0 mA/cm 2. In high rate cell configurations, 75% cathode utilization is possible at ,-.4 mA/cm 2 (C/3-C/4rate). The capacities at high rate are enhanced by Lewis acids, although the ultimate cause of rate limitation is passivation of the current collector by discharge products. The self-discharge rates of Li in contact with 4-5M S (as Li2Sn) solutions reveal capacity losses of 0.5%/day at 25~ to 4.4%/day at 71~ Based on the experimental results, a practical energy density of ~300 W-hr kg-' is possible using a standard cell design. Results on the battery's rechargeability are briefly reviewed.An ambient temperature Li/S battery utilizing an organic electrolyte has many attractive possibilities, among them high energy density, and the use of relatively low cost, relatively safe materials. Previous attempts to develop such a cell have involved the incorporation of insoluble Ss directly into the current collector (1-3). In general, very poor discharge efficiencies were obtained. One explanation put forth for these results is that some of the Ss was reduced to soluble polysulfide, Sn -2, which "escaped" from the cathode current collector and self-discharged on the Li anode (4). One recent moderately successful approach to increasing the S utilization efficiency was to add a Lewis acid, BF3, supposedly to suppress polysulfide formation (4, 5).The highest rate Li batteries, such as Li/SOC12 (6-8) and Li/SO2 (9, 10), have employed liquid cathodes. Here, very good electrical contact is maintained between the cathode material and the current collector through all phases of discharge. Both Ss and its ultimate discharge product, Li2S, are electrical insulators. Thus, it is likely that insulation of the cathode material, rather than S,~ -~ formation, led to poor results for Li/S cells. In our experience, the reaction between Li and dissolved Sn -2 is very slow, and the formation of dissolved Sn -2 enhances cathode utilization. In this regard, the explanation of the effect of BF8 on sulfur utilization is not very convincing.In contrast to most previous work on Li/S batteries, we have chosen to investigate a system where the S is completely dissolved in the electrolyte, as Li2S~ (11,12). Hence, the theoretical cell reaction becomes

Improving lithium–sulphur batteries through spatial control of sulphur species deposition on a hybrid electrode surface

“…The fabricated batteries based on nanofiber electrodes also displayed excellent cycling stabilities, effectively resolving the fast capacity fading commonly observed in Li-S batteries with highconcentration polysulphides as starting materials 34,42 . The typical charge/discharge voltage profile of the fabricated cell in the following cycles ( Supplementary Fig.…”

“…Different from the previous sulphur encapsulation strategy, we turn our attention to spatial control of solid-state charge/discharge products in the cathode in order not to lose the activity of some dissolved S species. There are three issues to be considered on the deposition of S species: the uncontrolled random deposition of S or Li x S on limited surface area of electrodes could lead to the formation of large agglomerates that are electrochemically inactive 8,29,33 ; the slow redox kinetics of polysulphides on the surface of certain electrodes could result in the low utilization of sulphur during charge and discharge 34 ; and solid S species might bind weakly and detach away from the electrode surface and thus become inactive 27 . To address these issues related to the deposition of S species, the electrode surface in a Li-S battery should be able to control the deposition of polysulphides and have strong binding with the deposited sulphur species.…”

Lithium–sulphur batteries with a microporous carbon paper as a bifunctional interlayer

“…The early-stage research in Li-S batteries was initiated three decades ago 6,7 , but the spotlight did not return to this battery system until there was a renewed interest in electric vehicles in recent years. The major impediments to the development of Li-S batteries are low active material utilization, poor cycle life and low charge efficiency 8 .…”

Well-dispersed sulfur anchored on interconnected polypyrrole nanofiber network as high performance cathode for lithium-sulfur batteries

“…The sharp redox peaks with stable overlapping features confirm high reversibility and an excellent stability of the composite electrode upon operation in lithium battery [28]. In the cathodic (reduction) sweep, the peaks at 2.4 and 2.0 V can be observed, which are assigned to the reduction of element sulfur (S 8 ) to soluble lithium polysulfides (Li 2 S n , 4 n 8) and further conversion of these lithium polysulfides into insoluble Li 2 S 2 and Li 2 S, respectively [29]. The only one anodic peak at 2.4 V corresponds to the reversible transformation of Li 2 S 2 and Li 2 S to Li 2 S 8 [30].…”