Cell energy density and electrolyte/sulfur ratio in Li–S cells

Hagen, Markus; Fanz, Patrik; Tübke, Jens

doi:10.1016/j.jpowsour.2014.04.018

Cited by 161 publications

(196 citation statements)

References 17 publications

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“…(i) the sulfur load must be ≥ 6 mg/cm 2 , (ii) the sulfur fraction ≥ 70%, (iii) the sulfur utilization ≥ 80%, and (iv) the electrolyte/sulfur weight ratio 3:1 or less. Similar electrolyte/sulfur ratio findings were also reported from another contribution by Hagen et al 46 Additionally, it should be noted that if optimal quantities of Li (two fold excess) and electrolyte are used for cell formulation, the typical cell life might result in dry-out of the cell.…”

Section: Energy Density Of Li-s Batteriessupporting

confidence: 86%

Introduction to Rechargeable Lithium–Sulfur Batteries

Demir‐Cakan

2017

Li-S Batteries

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Section: Energy Density Of Li-s Batteriessupporting

confidence: 86%

Introduction to Rechargeable Lithium–Sulfur Batteries

Demir‐Cakan

2017

Li-S Batteries

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“…In light of this loss mechanism, numerous strategies have been proposed to encapsulate polysulfides in the cathode, including optimization of the cathode nanomorphology (as reviewed in [6,7]), doping of polysulfide-adsorption sites [8,9], and coating of polysulfide blocking or adsorption layers [10,11]. However, most of these experimental studies are carried out with vast excess of electrolyte [12], not taking into account the fact that the electrolyte-to-sulfur mass ratio has a major influence on the sulfur utilisation [13,14,15]. In order to achieve high energy-density at cell level, the mass ratio between electrolyte and sulfur should be limited to below 3 [12].…”

Section: Introductionmentioning

confidence: 99%

Modelling transport-limited discharge capacity of lithium-sulfur cells

Zhang

Marinescu

Waluś

et al. 2016

Electrochimica Acta

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Lithium-sulfur (Li-S) battery could bring a step-change in battery technology with a potential specific energy density of 500 -600 Wh/kg. A key challenge for further improving the specific energy-density of Li-S cells is to understand the mechanisms behind reduced sulfur utilisation at low electrolyte loadings and high discharge currents. While several Li-S models have been developed to explore the discharge mechanisms of Li-S cells, they so far fail to capture the discharge profiles at high currents. In this study, we propose that the slow ionic transport in concentrated electrolyte is limiting the rate capability of Li-S cells. This transport-limitation mechanism is demonstrated through a one-dimensional Li-S model which qualitatively captures the discharge capacities of a sulfolane-based Li-S cell at different currents. Furthermore, our model predicts that a discharged Li-S cell is able regain some capacity with a short period of relaxation. This capacity recovery phenomenon is validated experimentally for different discharge currents and relaxation durations. The transport-limited discharge behavior of Li-S cells highlights the importance of optimizing the electrolyte loading and electrolyte transport property in Li-S cells.

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“…However, increasing the sulfur-to-electrolyte mass ratio lowers the sulfur utilization as well as the rate capability. [1][2][3] The charge rate of Li-S batteries is mainly limited by the large initial overpotential associated with the activation of precipitated Li 2 S, 4 as well as the slow subsequent dissolution that could lead to incomplete Li 2 S conversion at the end of charge. 5 The mechanisms behind the low discharge rate capability have been explained in terms of mass transport limitation and surface passivation caused by the accumulation of precipitated Li 2 S.…”

mentioning

confidence: 99%

What Limits the Rate Capability of Li-S Batteries during Discharge: Charge Transfer or Mass Transfer?

Zhang

Marinescu

Waluś

et al. 2017

J. Electrochem. Soc.

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Li-S batteries exhibit poor rate capability under lean electrolyte conditions required for achieving high practical energy densities. In this contribution, we argue that the rate capability of commercially-viable Li-S batteries is mainly limited by mass transfer rather than charge transfer during discharge. We first present experimental evidence showing that the charge-transfer resistance of Li-S batteries and hence the cathode surface covered by Li 2 S are proportional to the state-of-charge (SoC) and not to the current, directly contradicting previous theories. We further demonstrate that the observed Li-S behaviors for different discharge rates are qualitatively captured by a zero-dimensional Li-S model with transport-limited reaction currents. This is the first Li-S model to also reproduce the characteristic overshoot in voltage at the beginning of charge, suggesting its cause is the increase in charge transfer resistance brought by Li 2 S precipitation. Achieving a high practical energy density in Li-S batteries requires increased sulfur loading and reduced electrolyte loading at cell level. However, increasing the sulfur-to-electrolyte mass ratio lowers the sulfur utilization as well as the rate capability.1-3 The charge rate of Li-S batteries is mainly limited by the large initial overpotential associated with the activation of precipitated Li 2 S, 4 as well as the slow subsequent dissolution that could lead to incomplete Li 2 S conversion at the end of charge. 5 The mechanisms behind the low discharge rate capability have been explained in terms of mass transport limitation and surface passivation caused by the accumulation of precipitated Li 2 S.The transport limitation could arise from high electrolyte viscosity and pore-blocking due to localized Li 2 S precipitation. We recently demonstrated that a Li-S cell discharged at high current can provide extra capacity after an hour of relaxation.6 With a one-dimensional Li-S model, it was found that slow ionic transport could force polysulfides to accumulate temporarily in the separator, leading to the known reduced capacity at high discharge rates. The capacity recovery phenomenon is the result of redistribution of polysulfides across the cell during relaxation. Danner et al. 7 further demonstrated with a multiscale Li-S model that localized precipitation tends to occur at the carbon-sulfur particle surface, leading to pore-blocking and transport-limited discharge capacity for high sulfur loading.The insulating and insoluble discharge product, Li 2 S, has been shown experimentally to cover active cathode surfaces during discharge and increase the charge-transfer resistance. The relation between discharge rate and morphology of the precipitate, however, remains under debate. Based on ex-situ SEM imaging of a carbon fiber ultramicroelectrode of a Li-S cell, Fan et al. 8 revealed that Li 2 S formed as a thin, continuous coating after a fast discharge but appeared as a small number of large particles after a slow discharge. It was therefore hypothesized that ...

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Cell energy density and electrolyte/sulfur ratio in Li–S cells

Cited by 161 publications

References 17 publications

Introduction to Rechargeable Lithium–Sulfur Batteries

Introduction to Rechargeable Lithium–Sulfur Batteries

Modelling transport-limited discharge capacity of lithium-sulfur cells

What Limits the Rate Capability of Li-S Batteries during Discharge: Charge Transfer or Mass Transfer?

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