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The intrinsic behavior of lithium fluoride in solid electrolyte interphases on lithium.

ABSTRACT: Lithium is the most attractive anode material for high-energy density rechargeable batteries, but its cycling is plagued by morphological irreversibility and dendrite growth that arise in part from its heterogeneous "native" solid electrolyte interphase (SEI). Enriching the SEI with lithium fluoride (LiF) has recently gained popularity to improve Li cyclability. However, the intrinsic function of LiF-whether chemical, mechanical, or kinetic in nature-remains unknown. Herein, we investigated the stability of LiF in model LiF-enriched SEIs that are either artificially preformed or derived from fluorinated electrolytes, and thus, the effect of the LiF source on Li electrode behavior. We discovered that the mechanical integrity of LiF is easily compromised during plating, making it intrinsically unable to protect Li. The ensuing in situ repair of the interface by electrolyte, either regenerating LiF or forming an extra elastomeric "outer layer," is identified as the more critical determinant of Li electrode performance. Our findings present an updated and dynamic picture of the LiF-enriched SEI and demonstrate the need to carefully consider the combined role of ionic and electrolyte-derived layers in future design strategies.

SUBMITTER: He M

PROVIDER: S-EPMC6955333 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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The intrinsic behavior of lithium fluoride in solid electrolyte interphases on lithium.

He Mingfu M Guo Rui R Hobold Gustavo M GM Gao Haining H Gallant Betar M BM

Proceedings of the National Academy of Sciences of the United States of America 20191217 1

Lithium is the most attractive anode material for high-energy density rechargeable batteries, but its cycling is plagued by morphological irreversibility and dendrite growth that arise in part from its heterogeneous "native" solid electrolyte interphase (SEI). Enriching the SEI with lithium fluoride (LiF) has recently gained popularity to improve Li cyclability. However, the intrinsic function of LiF-whether chemical, mechanical, or kinetic in nature-remains unknown. Herein, we investigated the ...[more]

PMID: 31848237

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Project description:The formation of a solid electrolyte interphase (SEI) between the anode surface and the electrolyte of lithium-ion batteries (LIBs) has been considered to be the most important yet the least understood issue of LIBs. To further our understanding in this regard, the density functional theory (DFT) B3PW91/6-311++G(3df,3pd) together with the implicit solvent model and the transition state theory were used for the first time to comprehensively explore the electroreduction mechanism of a novel additive, 4-chloromethyl-1,3,2-dioxathiolane-2-oxide (CMDO), and a few other solvents and additives, such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and even ethylene sulfite (ES), for comparison. The one-electron reduction potential of Li+-coordinated compounds Li+(X) for forming decomposition precursors [c-Li+(X˙-)] decreases in the following sequence: CMDO (1.9-2.2 V vs. Li+/Li) ∼ ES(1.9 V) > FEC (0.7 V) > EC (0.47 V) > PC (0.45 V) > DMC (0.38 V); this implies that CMDO is reduced prior to other solvents or additives in the mixture. Although the ring opening of [c-Li+(CMDO˙-)] is the least kinetically favorable, as reflected by the highest energy barrier (E a), i.e., CMDO (18.8-22.9 kcal mol-1) ∼ ES (23.4) > FEC (16.2) > PC (12.5) > EC (11.2) > DMC (8.0), CMDO still shows the highest overall reaction rate constant (∼1053 s-1) for forming an open ring radical [o-Li+(CMDO˙)-]. In addition, the termination reaction of [o-Li+(CMDO˙)-] for forming LiCl is thermodynamically more favorable than that of Li2SO3 or organic disulfite (LiSO3)2-R, which supports the experimental observation that the halogen-containing LiF or LiCl additives are predominant over all other halogen-containing species in the SEI layer. Moreover, the hybrid model by including the second solvation shell of Li+ via a supercluster [(CMDO)Li+(PC)2](PC)9 and the implicit solvent model (SMD) can result in a reduction potential (∼1.7 V) that is in excellent agreement with the experimental reduction peak.

Dataset Information

The intrinsic behavior of lithium fluoride in solid electrolyte interphases on lithium.

Publications

The intrinsic behavior of lithium fluoride in solid electrolyte interphases on lithium.

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