Understanding the role of lithium polysulfide solubility in limiting lithium-sulfur cell capacity

Shen, Chao; Xie, Jianxin; Zhang, Mei; Andrei, Petru; Hendrickson, Mary; Plichta, Edward J.; Zheng, Jim P.

doi:10.1016/j.electacta.2017.07.123

“…Actually, the low electrolyte usage is as important as high sulfur content and tap density for Li–S battery with high energy density. Nevertheless, reducing the amount of electrolyte may increase the viscosity and impede ionic diffusion after LiPS species dissolving into electrolyte, leading to the poor utilization of sulfur active material and severe performance degradation . However, in our case, with low electrolyte/sulfur ratio of 10 and 8 µL mg −1 , the composite still presents high reversible discharge capacity and stable cycling performance at 0.2C rate (Figure S14b, Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

Conductive CoOOH as Carbon‐Free Sulfur Immobilizer to Fabricate Sulfur‐Based Composite for Lithium–Sulfur Battery

Wang

¹

,

Wang

²

,

Liu

³

et al. 2019

Adv Funct Materials

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Lithium-sulfur battery is recognized as one of the most promising energy storage devices, while the application and commercialization are severely hindered by both the practical gravimetric and volumetric energy densities due to the low sulfur content and tap density with lightweight and nonpolar porous carbon materials as sulfur host. Herein, for the first time, conductive CoOOH sheets are introduced as carbon-free sulfur immobilizer to fabricate sulfur-based composite as cathode for lithium-sulfur battery. CoOOH sheet is not only a good sulfur-loading matrix with high electron conductivity, but also exhibits outstanding electrocatalytic activity for the conversion of soluble lithium polysulfide. With an ultrahigh sulfur content of 91.8 wt% and a tap density of 1.26 g cm −3 , the sulfur/CoOOH composite delivers high gravimetric capacity and volumetric capacity of 1199.4 mAh g −1 -composite and 1511.3 mAh cm −3 at 0.1C rate, respectively. Meanwhile, the sulfurbased composite presents satisfactory cycle stability with a slow capacity decay rate of 0.09% per cycle within 500 cycles at 1C rate, thanks to the strong interaction between CoOOH and soluble polysulfides. This work provides a new strategy to realize the combination of gravimetric energy density, volumetric energy density, and good electrochemical performance of lithium-sulfur battery.

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“…TheE /S ratio is lower than what has been deemed as the minimum (about 5.2 mL E mg À1 S )t of ully dissolve LPS for the commonly-used LSB electrolyte based on amixed solvent of equal volumes of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME). [14] Remarkably,t he electrode still shows high specific capacities with well-defined voltage profiles in the current density range from 0.2 to 0.8 mA cm À2 (Figure 3c), although the electrolyte amount is not enough to fully dissolve the LPS intermediates.N otably, the electrode can be continuously discharged and charged for 50 cycles at 0.8 mA cm À2 with as table specific capacity of about 830 mAh g À1 ,c orresponding to an areal capacity of about 5.0 mAh cm À2 (Figure 3d), although the Coulombic efficiency (CE), especially at lower rates,isnot ideal because of an amplified shuttle effect in the LPS-saturated electrolyte. [15] Thecapability of tolerating the low E/S ratio is directly related to the catalytic power of MoP.Incontrast, the CNT-S electrode without MoP stops working normally at current densities of 0.6 mA cm À2 or higher,m anifesting substantially increased overpotentials and reduced capacities (Supporting Information, Figure S8).…”

Section: Angewandte Chemiementioning

confidence: 93%

Electrocatalysis in Lithium Sulfur Batteries under Lean Electrolyte Conditions

Yang

¹

,

Zhong

²

,

Shi

³

et al. 2018

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The presence of electrocatalysis in lithium-sulfur batteries has been proposed but not yet sufficiently verified. In this study,m olybdenum phosphide (MoP) nanoparticles are shown to play ad efinitive electrocatalytic role for the sulfur cathode working under lean electrolyte conditions featuring alow electrolyte/active material ratio:the overpotentials for the charging and discharging reactions are greatly decreased. As aresult, sulfur electrodes containing MoP nanoparticles show faster kinetics and more reversible conversion of sulfur species, leading to improvements in charging/discharging voltage profiles,c apacity,r ate performance,a nd cycling stability. Taking advantage of the electrocatalytic properties of MoP, high-performance sulfur electrodes were successfully realized that are steadily cyclable at ah igh areal capacity of 5.0 mAh cm À2 with ac hallenging electrolyte/sulfur (E/S) ratio of 4 mL E mg À1 S .Lithium sulfur batteries (LSBs) have as uperior theoretical specific energy of 2600 Wh kg À1 ,b ut an unsatisfactory cycle life. [1] Thecathode material of LSBs,namely sulfur,islimited in cycling stability,d espite its high theoretical specific capacity of 1675 mAh g À1 . [2] Thec apacity decay is tightly associated with the dissolution and diffusion of lithium polysulfide (LPS) intermediates in the electrolyte,w hich on the one hand facilitates the kinetics of electrochemical conversion [3] but on the other hand causes loss of active material and side reactions. [4] Using polar material surfaces, for example,f unctionalized carbons, [5] metal oxides, [6] sulfides, [7] phosphides, [8] nitrides, [9] and metal-organic frameworks, [10] to confine LPS via chemical interactions has been found to be one of the most effective ways for improving the cycling stability of sulfur electrodes.B esides immobilizing LPS on the cathode,i ti sa lso crucial to ensure their rapid electrochemical conversion and thus capacity contribution. Fori nstance,w eh ave recently reported on molybdenum phosphide (MoP) nanoparticles serving an electrocatalystlike function for stabilizing the sulfur cathode. [8b] While the extension of cycle life was significant, electrocatalysis was only preliminarily implied by the larger cyclic voltammetry current on the MoP-modified electrode in aL PS electrolyte. Herein, we report anew observation of akey evidence for the electrocatalytic role played by MoP nanoparticles in LSBs:reduction of overpotential for the charging/discharging reactions of the sulfur cathode,w hich is only obvious under lean electrolyte conditions (that is,w ith al ow electrolyte/ active material ratio). Fora no rdinary sulfur electrode,t he average charging/discharging voltage hysteresis at ac urrent density of 0.8 mA cm À2 increases greatly to 0.43 Vw hen the electrolyte/sulfur (E/S; mL E mg À1 S )ratio is lowered to 6. With MoP nanoparticles incorporated in the electrode structure, the voltage hysteresis is reduced to 0.18 V. MoP effectively catalyzes the electrochemical conversion reactions of sulfur, which helps the...

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“…[14] Remarkably,t he electrode still shows high specific capacities with well-defined voltage profiles in the current density range from 0.2 to 0.8 mA cm À2 (Figure 3c), although the electrolyte amount is not enough to fully dissolve the LPS intermediates.N otably, the electrode can be continuously discharged and charged for 50 cycles at 0.8 mA cm À2 with as table specific capacity of about 830 mAh g À1 ,c orresponding to an areal capacity of about 5.0 mAh cm À2 (Figure 3d), although the Coulombic efficiency (CE), especially at lower rates,isnot ideal because of an amplified shuttle effect in the LPS-saturated electrolyte. TheE /S ratio is lower than what has been deemed as the minimum (about 5.2 mL E mg À1 S )t of ully dissolve LPS for the commonly-used LSB electrolyte based on amixed solvent of equal volumes of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME).…”

mentioning

confidence: 99%

Electrocatalysis in Lithium Sulfur Batteries under Lean Electrolyte Conditions

Yang

¹

,

Zhong

²

,

Shi

³

et al. 2018

View full text Add to dashboard Cite

The presence of electrocatalysis in lithium-sulfur batteries has been proposed but not yet sufficiently verified. In this study,m olybdenum phosphide (MoP) nanoparticles are shown to play ad efinitive electrocatalytic role for the sulfur cathode working under lean electrolyte conditions featuring alow electrolyte/active material ratio:the overpotentials for the charging and discharging reactions are greatly decreased. As aresult, sulfur electrodes containing MoP nanoparticles show faster kinetics and more reversible conversion of sulfur species, leading to improvements in charging/discharging voltage profiles,c apacity,r ate performance,a nd cycling stability. Taking advantage of the electrocatalytic properties of MoP, high-performance sulfur electrodes were successfully realized that are steadily cyclable at ah igh areal capacity of 5.0 mAh cm À2 with ac hallenging electrolyte/sulfur (E/S) ratio of 4 mL E mg À1 S .Lithium sulfur batteries (LSBs) have as uperior theoretical specific energy of 2600 Wh kg À1 ,b ut an unsatisfactory cycle life. [1] Thecathode material of LSBs,namely sulfur,islimited in cycling stability,d espite its high theoretical specific capacity of 1675 mAh g À1 . [2] Thec apacity decay is tightly associated with the dissolution and diffusion of lithium polysulfide (LPS) intermediates in the electrolyte,w hich on the one hand facilitates the kinetics of electrochemical conversion [3] but on the other hand causes loss of active material and side reactions. [4] Using polar material surfaces, for example,f unctionalized carbons, [5] metal oxides, [6] sulfides, [7] phosphides, [8] nitrides, [9] and metal-organic frameworks, [10] to confine LPS via chemical interactions has been found to be one of the most effective ways for improving the cycling stability of sulfur electrodes.B esides immobilizing LPS on the cathode,i ti sa lso crucial to ensure their rapid electrochemical conversion and thus capacity contribution. Fori nstance,w eh ave recently reported on molybdenum phosphide (MoP) nanoparticles serving an electrocatalystlike function for stabilizing the sulfur cathode. [8b] While the extension of cycle life was significant, electrocatalysis was only preliminarily implied by the larger cyclic voltammetry current on the MoP-modified electrode in aL PS electrolyte. Herein, we report anew observation of akey evidence for the electrocatalytic role played by MoP nanoparticles in LSBs:reduction of overpotential for the charging/discharging reactions of the sulfur cathode,w hich is only obvious under lean electrolyte conditions (that is,w ith al ow electrolyte/ active material ratio). Fora no rdinary sulfur electrode,t he average charging/discharging voltage hysteresis at ac urrent density of 0.8 mA cm À2 increases greatly to 0.43 Vw hen the electrolyte/sulfur (E/S; mL E mg À1 S )ratio is lowered to 6. With MoP nanoparticles incorporated in the electrode structure, the voltage hysteresis is reduced to 0.18 V. MoP effectively catalyzes the electrochemical conversion reactions of sulfur, which helps the...

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Understanding the role of lithium polysulfide solubility in limiting lithium-sulfur cell capacity

Cited by 65 publications

References 37 publications

Conductive CoOOH as Carbon‐Free Sulfur Immobilizer to Fabricate Sulfur‐Based Composite for Lithium–Sulfur Battery

Conductive CoOOH as Carbon‐Free Sulfur Immobilizer to Fabricate Sulfur‐Based Composite for Lithium–Sulfur Battery

Electrocatalysis in Lithium Sulfur Batteries under Lean Electrolyte Conditions

Electrocatalysis in Lithium Sulfur Batteries under Lean Electrolyte Conditions

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