Facilitated Dissociation of Water in the Presence of Lithium Metal at Ambient Temperature as a Requisite for Lithium–Gas Reactions

Shang, Jin; Shirazian, Saeed

doi:10.1021/acs.jpcc.8b01817

“…Generally comparing our results with previous investigations of water reactivity with Li metal surface, our results are consistent with Shang et al 80 who found the final products of H 2 O reacting with a Li surface to include LiOH, a small amount of LiH, H 2 gas, and various water complexes.…”

Section: Resultssupporting

confidence: 93%

“…2.3, metallic surface effects are neglected in the reaction network, and to confirm that water splitting is indeed spontaneous within our level of theory, we used a cluster DFT model consisting of 32 Li atoms and found that the reaction is almost barrierless (see SI Sec III) and consistent with previous work (0.12 eV). 80 We note that although water reduction reactions are usually considered to be equivalent to hydrogen evolution reaction (HER), this is a simplified picture as the detailed mechanisms involve adsorbed species H ads and OH ads . 80,81 Hence, the as-formed hydride ion, most likely created through water splitting on the Li surface, is presumably stabilizing the TS structures along the path and the overall barrier (0.72 eV as the rate-limiting barrier, Struct 4 → TS 3) is much lower than that for the black path in Figure 4 (a).…”

Section: Resultsmentioning

confidence: 99%

“…80 We note that although water reduction reactions are usually considered to be equivalent to hydrogen evolution reaction (HER), this is a simplified picture as the detailed mechanisms involve adsorbed species H ads and OH ads . 80,81 Hence, the as-formed hydride ion, most likely created through water splitting on the Li surface, is presumably stabilizing the TS structures along the path and the overall barrier (0.72 eV as the rate-limiting barrier, Struct 4 → TS 3) is much lower than that for the black path in Figure 4 (a). Further investigation is necessary to determine the plausibility of this path and whether cooperative effects could further lower the barrier in this pathway.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Data-Driven Prediction of Formation Mechanisms of Lithium Ethylene Monocarbonate with an Automated Reaction Network

Xie¹,

Spotte-Smith²,

Patel³

et al. 2021

Preprint

0

View full text Add to dashboard Cite

<div><div><div><p>Interfacial reactions are notoriously difficult to characterize and robust prediction of the chemical evolution and associated functionality of the resulting surface film is one of the grand challenges of materials chemistry. The solid–electrolyte interphase (SEI), critical to the operation of Li-ion batteries (LIB), exemplifies such a surface film and despite decades of work, considerable controversy remains regarding the major components of the SEI as well as their formation mechanisms. In this work, we present pioneering results of a newly developed data-driven reaction network addressing the recent question whether lithium ethylene monocarbonate (LEMC) or lithium ethylene dicarbonate (LEDC) is the major organic component of the LIB SEI. Our data-driven, automated methodology is based on a systematic generation of relevant species using a general fragmentation/recombination procedure which provides the basis for our vast thermodynamic reaction landscape, calculated with density functional theory (DFT). The graph implementation of the reaction landscape is subsequently explored using shortest pathfinding algorithms, identifying reactions to LEMC from EC, Li+ and H2O under the electron chemical potential of Li metal. Confirming the viability of our approach, the reaction network automatically recovers previously-proposed formation mechanisms of LEMC from EC and LEDC through hydrolysis, among which the direct hydrolysis of EC under basic conditions is found to be the most kinetically favorable. We also identify several other new reaction pathways to LEMC, illustrating the complex and competitive landscape of possible electrochemical electrolyte decomposition reactions. For example, we recover a LEMC formation mechanism that generates lithium hydride as a by-product and a radical mechanism through breaking the (CH2)O–C(–O)OLi bond in LEDC, neither of which has been proposed previously. Most importantly, we find that all identified paths, which are also kinetically favorable under the explored conditions, require water as a reactant. This condition severely limits the amount of LEMC that can form, as compared to LEDC, a conclusion that has direct impact on our understanding of SEI formation in Li-ion energy storage systems. Finally, we emphasize that our framework demonstrates robust, automated, data-driven predictions of novel interfacial reaction mechanisms and this framework is generally applicable to other reactive systems.</p></div></div></div>

show abstract

“…2.3, metallic surface effects are neglected in the reaction network, and to confirm that water splitting is indeed spontaneous within our level of theory, we used a cluster DFT model consisting of 32 Li atoms and found that the reaction is almost barrierless (see SI Sec III) and consistent with previous work (0.12 eV). 80 We note that although water reduction reactions are usually considered to be equivalent to hydrogen evolution reaction (HER), this is a simplified picture as the detailed mechanisms involve adsorbed species H ads and OH ads . 80,81 Hence, the as-formed hydride ion, most likely created through water splitting on the Li surface, is presumably stabilizing the TS structures along the path and the overall barrier (0.72 eV as the rate-limiting barrier, Struct 4 → TS 3) is much lower than that for the black path in Figure 4 (a).…”

Section: Direct Reaction Paths To Lemc From Ec LImentioning

confidence: 99%

Data-Driven Prediction of Formation Mechanisms of Lithium Ethylene Monocarbonate with an Automated Reaction Network

Xie

¹

,

Spotte-Smith²,

Patel³

et al. 2021

Preprint

View full text Add to dashboard Cite

<div><div><div><p>Interfacial reactions are notoriously difficult to characterize and robust prediction of the chemical evolution and associated functionality of the resulting surface film is one of the grand challenges of materials chemistry. The solid–electrolyte interphase (SEI), critical to the operation of Li-ion batteries (LIB), exemplifies such a surface film and despite decades of work, considerable controversy remains regarding the major components of the SEI as well as their formation mechanisms. In this work, we present pioneering results of a newly developed data-driven reaction network addressing the recent question whether lithium ethylene monocarbonate (LEMC) or lithium ethylene dicarbonate (LEDC) is the major organic component of the LIB SEI. Our data-driven, automated methodology is based on a systematic generation of relevant species using a general fragmentation/recombination procedure which provides the basis for our vast thermodynamic reaction landscape, calculated with density functional theory (DFT). The graph implementation of the reaction landscape is subsequently explored using shortest pathfinding algorithms, identifying reactions to LEMC from EC, Li+ and H2O under the electron chemical potential of Li metal. Confirming the viability of our approach, the reaction network automatically recovers previously-proposed formation mechanisms of LEMC from EC and LEDC through hydrolysis, among which the direct hydrolysis of EC under basic conditions is found to be the most kinetically favorable. We also identify several other new reaction pathways to LEMC, illustrating the complex and competitive landscape of possible electrochemical electrolyte decomposition reactions. For example, we recover a LEMC formation mechanism that generates lithium hydride as a by-product and a radical mechanism through breaking the (CH2)O–C(–O)OLi bond in LEDC, neither of which has been proposed previously. Most importantly, we find that all identified paths, which are also kinetically favorable under the explored conditions, require water as a reactant. This condition severely limits the amount of LEMC that can form, as compared to LEDC, a conclusion that has direct impact on our understanding of SEI formation in Li-ion energy storage systems. Finally, we emphasize that our framework demonstrates robust, automated, data-driven predictions of novel interfacial reaction mechanisms and this framework is generally applicable to other reactive systems.</p></div></div></div>

show abstract

“…Water can react rapidly with Li metal to generate lithium hydroxide (LiOH) and release hydrogen and a large amount of heat [11]. Moreover, the presence of water also favorably promotes the reactions between Li and other gas constituents [12,13]. Such intractable moist-air sensitivity not only makes the initial states of Li metal spotty, but also easily causes fire and even explosion during operation.…”

Section: Introductionmentioning

confidence: 99%