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Title: Molecular-Level Insights into the Reactivity of Siloxane-Based Electrolytes at a Lithium-Metal Anode

Abstract

A molecular-level understanding of the reactions that occur at the lithium-metal anode/electrolyte interphase is essential to improve the performance of Li–O2 batteries. Experimental and computational techniques are applied to explore the reactivity of tri(ethylene glycol)-substituted trimethylsilane (1NM3), a siloxane-based ether electrolyte, at the lithium-metal anode. In situ/ex situ X-ray diffraction and Fourier-transform infrared spectroscopy studies provide evidence of the formation of lithium hydroxide and lithium carbonates at the anode upon gradual degradation of the metallic lithium anode and the solvent molecules in the presence of oxygen. Density functional calculations performed to obtain a mechanistic understanding of the reductive decomposition of 1NM3 indicate that the decomposition does not require any apparent barrier to produce lithium hydroxide and lithium carbonates when the reduced 1NM3 solvent molecules interact with the oxygen crossing over from the cathode. This study indicates that degradation may be more significant in the case of the 1NM3 solvent, compared to linear ethers such as tetraglyme or dioxalone, because of its relatively high electron affinity. Also, both protection of the lithium metal and prevention of oxygen crossover to the anode are essential for minimizing electrolyte and anode decomposition.

Authors:
; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1222110
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Chemphyschem, 15(10):2077–2083
Country of Publication:
United States
Language:
English
Subject:
Environmental Molecular Sciences Laboratory

Citation Formats

Assary, Rajeev S., Lu, Jun, Luo, Xiangyi, Zhang, Xiaoyi, Ren, Yang, Wu, Huiming, Albishri, Hassan M., El-Hady, D. A., Al-Bogami, A. S., Curtiss, Larry A., and Amine, Khalil. Molecular-Level Insights into the Reactivity of Siloxane-Based Electrolytes at a Lithium-Metal Anode. United States: N. p., 2014. Web. doi:10.1002/cphc.201402130.
Assary, Rajeev S., Lu, Jun, Luo, Xiangyi, Zhang, Xiaoyi, Ren, Yang, Wu, Huiming, Albishri, Hassan M., El-Hady, D. A., Al-Bogami, A. S., Curtiss, Larry A., & Amine, Khalil. Molecular-Level Insights into the Reactivity of Siloxane-Based Electrolytes at a Lithium-Metal Anode. United States. doi:10.1002/cphc.201402130.
Assary, Rajeev S., Lu, Jun, Luo, Xiangyi, Zhang, Xiaoyi, Ren, Yang, Wu, Huiming, Albishri, Hassan M., El-Hady, D. A., Al-Bogami, A. S., Curtiss, Larry A., and Amine, Khalil. Mon . "Molecular-Level Insights into the Reactivity of Siloxane-Based Electrolytes at a Lithium-Metal Anode". United States. doi:10.1002/cphc.201402130.
@article{osti_1222110,
title = {Molecular-Level Insights into the Reactivity of Siloxane-Based Electrolytes at a Lithium-Metal Anode},
author = {Assary, Rajeev S. and Lu, Jun and Luo, Xiangyi and Zhang, Xiaoyi and Ren, Yang and Wu, Huiming and Albishri, Hassan M. and El-Hady, D. A. and Al-Bogami, A. S. and Curtiss, Larry A. and Amine, Khalil},
abstractNote = {A molecular-level understanding of the reactions that occur at the lithium-metal anode/electrolyte interphase is essential to improve the performance of Li–O2 batteries. Experimental and computational techniques are applied to explore the reactivity of tri(ethylene glycol)-substituted trimethylsilane (1NM3), a siloxane-based ether electrolyte, at the lithium-metal anode. In situ/ex situ X-ray diffraction and Fourier-transform infrared spectroscopy studies provide evidence of the formation of lithium hydroxide and lithium carbonates at the anode upon gradual degradation of the metallic lithium anode and the solvent molecules in the presence of oxygen. Density functional calculations performed to obtain a mechanistic understanding of the reductive decomposition of 1NM3 indicate that the decomposition does not require any apparent barrier to produce lithium hydroxide and lithium carbonates when the reduced 1NM3 solvent molecules interact with the oxygen crossing over from the cathode. This study indicates that degradation may be more significant in the case of the 1NM3 solvent, compared to linear ethers such as tetraglyme or dioxalone, because of its relatively high electron affinity. Also, both protection of the lithium metal and prevention of oxygen crossover to the anode are essential for minimizing electrolyte and anode decomposition.},
doi = {10.1002/cphc.201402130},
journal = {Chemphyschem, 15(10):2077–2083},
number = ,
volume = ,
place = {United States},
year = {Mon Jul 21 00:00:00 EDT 2014},
month = {Mon Jul 21 00:00:00 EDT 2014}
}
  • Molecular level understanding of the reactions that occur at the lithium metal anode/electrolyte interphase is essential to improve the performance of Li-O2 batteries. Experimental and computational techniques were utilized to explore the reactivity of tri(ethylene glycol)-substituted trimethylsilane (1NM3), a siloxane based ether electrolyte, at the lithium metal anode. In situ/ex situ XRD and FTIR measurements provide evidence for the formation of lithium hydroxide and lithium carbonates at the anode upon gradual degradation of the metallic lithium anode and the solvent molecules in the presence of oxygen. Density functional calculations performed to obtain mechanistic understanding of the reductive decomposition of 1NM3more » indicate that the decomposition does not require any apparent barrier to produce lithium hydroxide and lithium carbonates when the reduced 1NM3 solvent molecules interact with the oxygen crossing over from the cathode. This study indicates that the degradation of the 1NM3 solvent may be more than the linear ethers such as tetraglyme or dioxalone due to its relatively higher electron affinity. Also, this study indicates that the protection of lithium metal and prevention of oxygen crossover to the anode is essential to minimize electrolyte and anode decomposition.« less
  • Due to their high energy density and reduced cost, lithium–sulfur batteries are promising alternatives for applications such as electrical vehicles. However, a number of technical challenges need to be overcome in order to make them feasible for commercial uses. These challenges arise from the battery highly interconnected chemistry, which besides the electrochemical reactions includes side reactions at both electrodes and migration of soluble polysulfide (PS) species produced at the cathode to the anode side. The presence of such PS species alters the already complex reactivity of the Li anode. In this paper, interfacial reactions occurring at the surface of Limore » metal anodes due to electrochemical instability of the electrolyte components and PS species are investigated with density functional theory and ab initio molecular dynamics methods. It is found that the bis(trifluoromethane)sulfonimide lithium salt reacts very fast when in contact with the Li surface, and anion decomposition precedes salt dissociation. The anion decomposition mechanisms are fully elucidated. Two of the typical solvents used in Li–S technology, 1,3-dioxolane and 1,2-dimethoxyethane, are found stable during the entire simulation length, in contrast with the case of ethylene carbonate that is rapidly decomposed by sequential 2- or 4-electron mechanisms. Finally, on the other hand, the fast reactivity of the soluble PS species alters the side reactions because the PS totally decomposes before any of the electrolyte components forming Li 2S on the anode surface.« less
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  • Rechargeable lithium (Li) metal batteries with conventional LiPF6-carbonate electrolytes have been reported to fail quickly at charging current densities of about 1.0 mA cm-2 and above. In this work, we demonstrate the rapid charging capability of the Li||LiNi0.8Co0.15Al0.05O2 (NCA) cells enabled by a dual-salt electrolyte of LiTFSI-LiBOB in a carbonate solvent mixture. It is found that the thickness of solid electrolyte interphase (SEI) layer on Li metal anode largely increases with increasing charging current density. However, the cells using the LiTFSI-LiBOB dual-salt electrolyte significantly outperforms those using the LiPF6 electrolyte at high charging current densities. At the charging current densitymore » of 1.50 mA cm-2, the Li||NCA cells with the dual-salt electrolyte can still deliver a discharge capacity of 131 mAh g-1 and a capacity retention of 80% after 100 cycles, while those with the LiPF6 electrolyte start to show fast capacity fading after the 30th cycle and only exhibit a low capacity of 25 mAh g-1 and a low retention of 15% after 100 cycles. The reasons for the good chargeability and cycling stability of the cells using LiTFSI-LiBOB dual-salt electrolyte can be attributed to the good film-formation ability of the electrolyte on lithium metal anode and the highly conductive nature of the sulfur-rich interphase layer.« less