Fair performance comparison of different carbon blacks in lithium–sulfur batteries with practical mass loadings – Simple design competes with complex cathode architecture

Jozwiuk, Anna; Sommer, Heino; Janek, Jürgen; Brezesinski, Torsten

doi:10.1016/j.jpowsour.2015.07.070

Cited by 69 publications

(62 citation statements)

References 38 publications

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“…At lower discharge rates, the capacity is higher for the smaller electrolyte amount (Figure 3a, light-blue symbols, and Figure 3b, brown symbols), due to the reduced loss of active material in the dead volume of the cell. This also leads, as expected, 8,9,24,48 to a higher coulombic efficiency when electrolyte without additive is used (Figure 3a, light-blue stars). Nevertheless, one should bear in mind that decreasing the electrolyte amount even further may lead, especially for long-term cycling ( 100 cycles), to a decrease of the coulombic efficiency due to the drying up of the cell (decomposition of electrolyte due to reaction with metallic lithium), and/or, in presence of LiNO 3 , to the consumption of available additive.…”

Section: Resultssupporting

confidence: 83%

“…In other words, the Li-S cell is not only able to show reasonably good rate capability when the first cycles are performed at a rate as high as 1C, but it is even capable to deliver higher capacity than in the case when the first cycles are performed at low rates -and where, therefore, the loss of active material is occurring. This observation raises the question whether performing the first cycle at slow rate, as has been done in number of cyclability studies, 8 test (Figure 4b, purple symbols), is a consequence of processes that have occurred in the previous cycles, that is, either active-material loss by diffusion, or restricted sulfur utilization in the depth of the electrode due to the deposition of insulating Li 2 S on the electrode surface. 23 In both cases -decreasing and increasing rates ( Figure 3 and Figure 4) -the discharge rate has a significantly stronger influence on the measured capacity than the charge rate (Figure 2), showing that the discharge reactions are limiting in the Li-S system, in agreement with the findings of Kulisch et al 15 It is therefore misleading to compare the rate capability of cells where the overall cycling rate is changing (with both the charge and discharge rates being the same in individual cycles) with that where the cycling rate is only varied on charge 15,16 and where for that reason the performance might appear superior.…”

Section: Resultsmentioning

confidence: 96%

“…To confirm this hypothesis of polysulfide migration and to minimize the polysulfide diffusion, two approaches were further followed: (i) changing the rate order; that is, the rate-capability test is started with high discharge rate and the rate is decreasing, to quickly transform long-chain polysulfides into short-chain polysulfides at the initial cycling stage, and, therefore, to avoid their diffusion and loss of active material during the first cycles; (ii) decreasing the electrolyte amount to 30 μL, to limit the active-material loss by diffusion of the polysulfides into the dead space of the cell. 8,9,24,48 Figure 4a shows the rate-capability performance when the discharge rates are decreasing. The starting rate was chosen to be 1C, as it was observed in the previous tests that higher rates are not suitable to completely discharge cells containing 50 μL of electrolyte.…”

Section: Resultsmentioning

confidence: 99%

“…This approach enabled us to identify the individual effects of these experimental conditions on the rate performance. This work demonstrates that determining the rate capability of a Li-S cell is not straightforward and highlights the need to standardize, beyond electrode and cell parameters, 7,8 rate-capability-test protocols for a meaningful comparison of different Li-S systems.…”

mentioning

confidence: 99%

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Pitfalls in Li–S Rate-Capability Evaluation

Schott

Novák

Trabesinger

2016

J. Electrochem. Soc.

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Rate-capability tests are widely used to highlight advances in Li-S-system development. Here we show, by studying the individual effects of a number of cycling-and electrolyte-related parameters on a simple Li-S cell, that the rate-capability results are sensitive not only to the applied current but also to the cycling prehistory of the cell. On the one hand, the performance is affected by the order in which cycling rate is changed. Slow initial rates aggravate material loss and reduce the achievable capacity. On the other hand, the results of rate-capability tests are significantly different when the rates are varied only on the charge or only on the discharge. The charge rate does not directly affect the measured capacity, whereas the discharge rate does, especially when discharge cutoff voltages are high, due to slow discharge reactions. High charge rates, however, do affect the long-term stability, which is difficult to predict from usual rate-capability tests. Our findings also provide insights into the relative reaction rates and the influence of the general cycling procedures, underlining the importance of understanding the kinetics of Li-S systems, while designing them for high performance batteries. The lithium-sulfur (Li-S) battery is one of the most promising electrochemical systems for next-generation energy-storage applications, given the abundance of sulfur, its low toxicity, and its high theoretical specific charge of 1672 mAh g sulfur -1 (often referred as well as capacity). However, the commercialization of Li-S cells is hindered by substantial challenges, including the insulating nature of sulfur and of its discharge product Li 2 S, preventing efficient activematerial utilization, and the so-called polysulfide shuttle, leading to a loss of active material and low coulombic efficiency. Considerable improvements on the electrode and cell levels were made over the past few years, alleviating these limitations and, in turn, leading to an exponentially growing interest in Li-S batteries.1-5 From the perspective of every-day battery use, having a high rate capability is very important, and therefore rate-capability tests, in which the capacity is measured while changing the cycling rate (i.e., while changing the applied current), are often employed to complete the characterization of a battery. These tests are also widely used in the characterization of Li-S systems, to quantify the improvements brought about by various enhancements to the Li-S electrodes, electrolytes, their additives, and cells. Although it is known that Li-S cells, due to their complex chemistry, are sensitive to a wide range of parameters, 6-8 the protocols used in rate-capability tests described in the literature vary significantly. A comparison of rate performances reported in publications for Li-S cells using commercially available materials 9-12 is plotted in Figure 1. Despite their similar electrode composition (∼60 wt% sulfur, ∼30 wt% carbon black, ∼10 wt% binder (PEO or PVDF)), they display significantly different rate per...

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Section: Resultssupporting

confidence: 83%

Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Pitfalls in Li–S Rate-Capability Evaluation

Schott

Novák

Trabesinger

2016

J. Electrochem. Soc.

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“…[1][2][3][4][5][6] Nevertheless, persistent challenges associated with the sulfur cathode must be overcome for Li-S cells to become practical. For example, while sulfur cathodes have been engineered extensively for high energy density and durability, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] design rules are still lacking for high power while also attaining high specific energy.…”

Section: Introductionmentioning

confidence: 99%

Redox-Active Supramolecular Polymer Binders for Lithium–Sulfur Batteries That Adapt Their Transport Properties in Operando

Frischmann¹,

Hwa

Cairns

et al. 2016

Chem. Mater.

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π-Stacked perylene bisimide (PBI) molecules are implemented here as highly networked, redox-active supramolecular polymer binders in sulfur cathodes for lightweight and energy-dense Li-S batteries. We show that the in operando reduction and lithiation of these PBI binders sustainably reduces Li-S cell impedance relative to non-redox active conventional polymer binders. This lower impedance enables high-rate cycling in Li-S cells with excellent durability, a critical step toward unlocking the full potential of Li-S batteries for electric vehicles and aviation. INTRODUCTIONBreakthroughs in battery electrodes that enable energydense, high-power, and low-cost energy storage are necessary to catalyze a societal shift from fossil fuels to a carbon-neutral future powered by renewable energy. Of the forward-looking battery chemistries, lithium-sulfur (Li-S) cells offer certain advantages over more established Li-ion chemistries with respect to the high theoretical specific capacity of the sulfur cathode (1675 mAh g −1 vs. 272 mAh g −1 for a LiCoO 2 cathode), the low cost of sulfur (<$200 ton −1 ), the low environmental impact of sulfur, and the improved safety of the cell.

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