Comment on “Cycling Li-O
            <sub>2</sub>
            batteries via LiOH formation and decomposition”

Shen, Yue; Zhang, Wang; Chou, Shulei; Dou, Shi Xue

doi:10.1126/science.aaf1399

Cited by 48 publications

(41 citation statements)

References 7 publications

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“…We demonstrate, in contrast to the work of Shen et al, that the chemical reactivity between LiOH and the triiodide ion (I 3 -) to form IO 3 -indicates that LiOH can be removed on charging; the electrodes do not clog, even after multiple cycles, confirming that solid products are reversibly removed.…”

contrasting

confidence: 99%

Response to Comment on “Cycling Li-O ₂ batteries via LiOH formation and decomposition”

Liu

Kim

Carretero‐González

et al. 2016

Science

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We described a lithium-oxygen (Li-O 2 ) battery comprising a graphene electrode, a dimethoxyethane-based electrolyte, and H 2 O and lithium iodide (LiI) additives, lithium hydroxide (LiOH) being the predominant discharge product. We demonstrate, in contrast to the work of Shen et al., that the chemical reactivity between LiOH and the triiodide ion (I 3 -) to form IO 3 -indicates that LiOH can be removed on charging; the electrodes do not clog, even after multiple cycles, confirming that solid products are reversibly removed. We reported on a lithium-oxygen battery that formed LiOH as the predominant discharge product, formed from a reduced graphene oxide (rGO) electrode, a dimethoxyethane (DME)-based electrolyte, and H 2 O and LiI additives (1). On the basis of observed oxygen release, we suggested the following charge reaction.We also clearly stated, "We stress, however, that the equilibria that occur in the presence of oxygen, water, and iodine are complex, often involving a series of polyanions (including IO -and its protonated form); further mechanistic studies are required to understand the role of these complex equilibria in the redox processes" (1). Some of these equilibria are as follows (2) 3IShen et al. First, removal of LiOH in lithium-oxygen batteries below 3.2 V has previously been observed-e.g., with ruthenium-based catalysts and tetraglyme (4)/dimethyl sulfoxide (5)-based electrolytes and added water. Because the catalyst does not alter the equilibrium voltage, the equilibrium itself must be altered. In another Technical Response (6), we argued that the free-energy change of reaction 1 on moving from an aqueous to nonaqueous electrolyte system cannot be ignored and will change the equilibrium potential. Of note, we have observed that LiOH can be quantitatively removed via reactions 2 to 5, I 3 -reacting to form IO 3 -and I -and suggesting an alternative mechanism [see figure 1 in (6) for details], the rate depending strongly on the amount of water and LiTFSI concentrations present in the system (Fig. 1). Reaction 1 is a four-electron process and will be strongly affected by the nature of the electrode; further studies are required to determine the relative rates of reaction 1 versus reactions 3 to 5 and the potential role that catalysts may play in determining this.2) Shen et al. (3) observed in a transparent cell that the electrolyte color darkens on cycling due to I 3 -accumulation. They concluded that the first discharge involves the formation of LiOH via O 2 reduction at~2.6 V [figure 1B in (3)] but that the subsequent charge process involves the direct oxidation of I -to I 3 -, rather than the removal of LiOH, subsequent discharge processes, also observed at~2.6 V, being a combination of further LiOH formation and I 3 -reduction. Because our ultraviolet (UV)-visible experiments show that the kinetics for reactions 2 to 5 are highly dependent on the water content [figure 1 in (6)], we suggest that the conditions used in Shen et al.´s experiment, 5 A/g for a charge/discharge capacity of 1 Ah/g-...

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confidence: 99%

Response to Comment on “Cycling Li-O ₂ batteries via LiOH formation and decomposition”

Liu

Kim

Carretero‐González

et al. 2016

Science

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“…[18b] Shen et al also reported that LiOH cannot be decomposed by I 3 À upon charging. [24] Zhou andc o-workers proposed that H 2 Oc ould reduce the amount of the side reactions catalyzed by LiI. By increasing the alkalinity of the H 2 O-containinge lectrolyte, the number of side reactions could be reduced and Li 2 O 2 formed.…”

Section: Halogen Rm Charmentioning

confidence: 99%

Promoting Li–O₂ Batteries With Redox Mediators

Shen

Zhang

et al. 2019

ChemSusChem

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Li–O2 batteries have a high theoretical specific energy, 3500 Wh kg−1; however, its practical capacity is far below this value and limited by the passivation with the insulating discharge product Li2O2. The nonconductive nature of Li2O2 also impedes the charging process, leading to a low coulombic efficiency and high overpotential on charge even at a moderate rate. To address these challenges, redox mediators could be used both during discharge and charge to transfer electrons between O2/electrode surface or Li2O2/electrode surface to overcome the passivation of Li2O2, which would facilitate the discharge and charge process. The capacity and current density were significantly improved using the redox mediators, thus representing a promising strategy to achieve a high energy density for Li–O2 batteries.

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“…The catalytic mechanism of Ru in Li–O 2 batteries operating via LiOH was further investigated by Liu et al With 50 000 ppm H 2 O in a 1 m LiTFSI/DMSO electrolyte, Ru/SP showed that the charge potential decreased to 3.1 V and that LiOH was the only discharge product at 4000–500 000 ppm H 2 O. Note that the decomposition potential of LiOH was generally ≈3.42 V in alkaline solution and 3.82 V in neutral solution in the absence of catalysts . In this system, Ru facilitates LiOH formation by shifting the reaction equilibrium (2Li 2 O 2 + 2H 2 O → 4 LiOH + O 2 ) toward the products.…”

Section: Other Energy Carriersmentioning

confidence: 97%

“…With H 2 O as the dominant proton source, the voltage gap was reduced to 0.2 V with 0.05 m LiI via LiOH formation based on rGO in 0.25 m LiTFSI/DME electrolyte. The possibility of this reaction was disputed, specifically in regard to whether LiOH can be thermodynamically oxidized by triiodide (

{normalI}_{3}^{-}

) . Shen et al observed that

{normalI}_{3}^{-}

ions were not consumed with the significant accumulation of LiOH.…”

Section: Other Energy Carriersmentioning

confidence: 99%

Defect Chemistry in Discharge Products of Li–O₂ Batteries

et al. 2018

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Li–O2 batteries, possessing the highest theoretical specific energy density among all known Li‐ion‐based batteries, demonstrate great potential as energy storage devices for powering electric vehicles. However, their battery performance is significantly limited by the insulating nature of the discharge product Li2O2, which has a wide bandgap (4–5 eV), resulting in high charge overpotential. Defect engineering of the discharge product emerges as a very promising strategy to improve the electrical conductivity and hence reduce the charge overpotential. The aim of this review is to highlight recent advances and progress in understanding and controlling the defect chemistry of discharge products in Li–O2 batteries. First, the theoretical perspectives of defects in Li2O2 are reviewed, with particular emphasis on defect design and engineering strategies to significantly improve the charge transport properties of Li2O2. Then intermediate defects in Li2O2 formed during the discharge and charge processes and materials with induced defects, including Li2− x O2, doped Li2O2, Li2O2 with surface/grain boundaries, and amorphous Li2O2, which are tailored by engineered catalysts and electrolyte additives are discussed. Finally, other alternative energy carriers for new energy storage chemistry of Li–O2 batteries, such as lithium superoxide, lithium hydroxide, and lithium carbonate, will also be discussed.

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Comment on “Cycling Li-O ₂ batteries via LiOH formation and decomposition”

Cited by 48 publications

References 7 publications

Response to Comment on “Cycling Li-O ₂ batteries via LiOH formation and decomposition”

Response to Comment on “Cycling Li-O ₂ batteries via LiOH formation and decomposition”

Promoting Li–O₂ Batteries With Redox Mediators

Defect Chemistry in Discharge Products of Li–O₂ Batteries

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Comment on “Cycling Li-O 2 batteries via LiOH formation and decomposition”

Cited by 48 publications

References 7 publications

Response to Comment on “Cycling Li-O 2 batteries via LiOH formation and decomposition”

Response to Comment on “Cycling Li-O 2 batteries via LiOH formation and decomposition”

Promoting Li–O2 Batteries With Redox Mediators

Defect Chemistry in Discharge Products of Li–O2 Batteries

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Product

Resources

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Comment on “Cycling Li-O ₂ batteries via LiOH formation and decomposition”

Response to Comment on “Cycling Li-O ₂ batteries via LiOH formation and decomposition”

Response to Comment on “Cycling Li-O ₂ batteries via LiOH formation and decomposition”

Promoting Li–O₂ Batteries With Redox Mediators

Defect Chemistry in Discharge Products of Li–O₂ Batteries