Modelling transport-limited discharge capacity of lithium-sulfur cells

Zhang, Teng; Marinescu, Monica; Waluś, Sylwia; Offer, Gregory J.

doi:10.1016/j.electacta.2016.10.032

Cited by 66 publications

(73 citation statements)

References 37 publications

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“…Mass transport limitations, which are not accounted for in this zero dimensional model, have been shown to limit the power rate. 26 The effect of cathode passivation by the insulating precipitate Li 2 S at low states of charge, which has been associated with increased overpotential at the beginning of charging, 27 is also disregarded here. It should be noted, however, that Zhang et al have shown that this effect can be attributed instead to transport limited reaction kinetics.…”

Section: Model Limitations-inmentioning

confidence: 99%

Irreversible vs Reversible Capacity Fade of Lithium-Sulfur Batteries during Cycling: The Effects of Precipitation and Shuttle

Marinescu

O’Neill

Zhang

et al. 2017

J. Electrochem. Soc.

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Lithium-sulfur batteries could deliver significantly higher gravimetric energy density and lower cost than Li-ion batteries. Their mass adoption, however, depends on many factors, not least on attaining a predictive understanding of the mechanisms that determine their performance under realistic operational conditions, such as partial charge/discharge cycles. This work addresses a lack of such understanding by studying experimentally and theoretically the response to partial cycling. A lithium-sulfur model is used to analyze the mechanisms dictating the experimentally observed response to partial cycling. The zero-dimensional electrochemical model tracks the time evolution of sulfur species, accounting for two electrochemical reactions, one precipitation/dissolution reaction with nucleation, and shuttle, allowing direct access to the true cell state of charge. The experimentally observed voltage drift is predicted by the model as a result of the interplay between shuttle and the dissolution bottleneck. Other features are shown to be caused by capacity fade. We propose a model of irreversible sulfur loss associated with shuttle, such as caused by reactions on the anode. We find a reversible and an irreversible contribution to the observed capacity fade, and verify experimentally that the reversible component, caused by the dissolution bottleneck, can be recovered through slow charging. This model can be the basis for cycling parameters optimization, or for identifying degradation mechanisms relevant in applications. Lithium sulfur (LiS) batteries have the potential to provide a step change in performance, compared to Li-ion batteries, with an expected practical energy density of 700 Wh kg −1 compared to that of the intercalation Li-ion batteries, of 210 Wh kg −1 . 1,2 Added benefits, such as a potential low cost due to the abundance of the active materials, low toxicity and relative safety, 3 make them an attractive energy storage solution for a wide variety of applications, such as space exploration 4 and low temperature energy delivery. 5 However, the relatively low power capabilities, significant self discharge and low cycle life have so far hindered mainstream adoption of LiS cells. Degradation mechanisms such as lithium anode corrosion, self discharge and low coulombic efficiency have all been related to the polysulfide shuttle. As a result, most effort in the research community is currently directed toward decreasing the amount of shuttle through material design, and assessing the properties of the proposed materials through coin cell characterization.We argue that equally important for accelerating the adoption of this battery chemistry is the understanding of how real cells behave under real operating conditions, which often include incomplete charge/discharge cycles, noisy current loads and rest periods at various states of charge (SoC). Understanding and detecting the mechanisms leading to degradation, such as capacity fade, are intermediate steps crucial to predicting cycle life. Such understanding can...

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Section: Model Limitations-inmentioning

confidence: 99%

Irreversible vs Reversible Capacity Fade of Lithium-Sulfur Batteries during Cycling: The Effects of Precipitation and Shuttle

Marinescu

O’Neill

Zhang

et al. 2017

J. Electrochem. Soc.

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“…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.…”

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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“…The capacity due to this sulfur is considered as recovered capacity. This is a common effect [8] and has been briefly reported for LiS batteries in [9,10].…”

Section: Dod (%)mentioning

confidence: 92%

“…So far, the recovery effect of a single DOD as an additional result of a self-discharge experiment was published in [10]. Furthermore, a remarkable recovery effect at a 100% DOD level was published in [9]. The purpose of this work is the quantification of the recovering capacity of the cell and subsequently its veritable usage capacity.…”

Section: Capacity Recovery Effectmentioning

confidence: 99%

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Capacity Recovery Effect in Lithium Sulfur Batteries for Electric Vehicles

Maurer

Commerell

Hintennach

et al. 2018

WEVJ

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Lithium sulfur batteries have a promisingly high theoretical specific energy density of about 2600 Wh/kg and an expected practical specific energy density of about 500-600 Wh/kg. Therefore, it is a highly promising future energy storage technology for electric vehicles. Beside these advantages, this technology shows a low cell capacity at high discharge currents. Due to the capacity recovery effect, up to 20% of the total cell capacity becomes available again with some rest time. This study shows a newly-developed capacity recovery model for lithium sulfur batteries. Due to the long rest periods of electric vehicles, this effect has an important influence on the usable cell capacity and depth of discharge in lithium sulfur batteries.

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Modelling transport-limited discharge capacity of lithium-sulfur cells

Cited by 66 publications

References 37 publications

Irreversible vs Reversible Capacity Fade of Lithium-Sulfur Batteries during Cycling: The Effects of Precipitation and Shuttle

Irreversible vs Reversible Capacity Fade of Lithium-Sulfur Batteries during Cycling: The Effects of Precipitation and Shuttle

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

Capacity Recovery Effect in Lithium Sulfur Batteries for Electric Vehicles

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