Open accessJournal Article

# Effects of fluorinated solvents on electrolyte solvation structures and electrode/electrolyte interphases for lithium metal batteries.

02 Mar 2021-Proceedings of the National Academy of Sciences of the United States of America (Proceedings of the National Academy of Sciences)-Vol. 118, Iss: 9
Abstract: Electrolyte is very critical to the performance of the high-voltage lithium (Li) metal battery (LMB), which is one of the most attractive candidates for the next-generation high-density energy-storage systems. Electrolyte formulation and structure determine the physical properties of the electrolytes and their interfacial chemistries on the electrode surfaces. Localized high-concentration electrolytes (LHCEs) outperform state-of-the-art carbonate electrolytes in many aspects in LMBs due to their unique solvation structures. Types of fluorinated cosolvents used in LHCEs are investigated here in searching for the most suitable diluent for high-concentration electrolytes (HCEs). Nonsolvating solvents (including fluorinated ethers, fluorinated borate, and fluorinated orthoformate) added in HCEs enable the formation of LHCEs with high-concentration solvation structures. However, low-solvating fluorinated carbonate will coordinate with Li+ ions and form a second solvation shell or a pseudo-LHCE which diminishes the benefits of LHCE. In addition, it is evident that the diluent has significant influence on the electrode/electrolyte interphases (EEIs) beyond retaining the high-concentration solvation structures. Diluent molecules surrounding the high-concentration clusters could accelerate or decelerate the anion decomposition through coparticipation of diluent decomposition in the EEI formation. The varied interphase features lead to significantly different battery performance. This study points out the importance of diluents and their synergetic effects with the conductive salt and the solvating solvent in designing LHCEs. These systematic comparisons and fundamental insights into LHCEs using different types of fluorinated solvents can guide further development of advanced electrolytes for high-voltage LMBs.

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Topics: Electrolyte (56%), Solvation (55%), Solvation shell (54%)
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6 results found

Journal Article
Xueying Zheng1, Liqiang Huang1, Wei Luo1, Haotian Wang1  +5 moreInstitutions (2)
10 May 2021-ACS energy letters
Abstract: The solid-electrolyte interphase (SEI) is known to dictate the performance of a Li metal anode, where its inorganic compositions are primarily responsible for Li+ conduction, electron insulation, a...

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Topics: Electrolyte (55%), Solvation (50%)

6 Citations

Journal Article
Zhang Cao1, Xueying Zheng2, Qunting Qu1, Yunhui Huang2  +1 moreInstitutions (2)
01 Sep 2021-Advanced Materials
Abstract: Silicon (Si) anodes are advantageous for application in lithium-ion batteries in terms of their high theoretical capacity (4200 mAh g-1 ), appropriate operating voltage (<0.4 V vs Li/Li+ ), and earth-abundancy. Nevertheless, a large volume change of Si particles emerges with cycling, triggering unceasing breakage/re-formation of the solid-electrolyte interphase (SEI) and thereby the fast capacity degradation in traditional carbonate-based electrolytes. Herein, it is demonstrated that superior cyclability of Si anode is achievable using a nonflammable ether-based electrolyte with fluoroethylene carbonate and lithium oxalyldifluoroborate dual additives. By forming a high-modulus SEI rich in fluoride (F) and boron (B) species, a high initial Coulombic efficiency of 90.2% is attained in Si/Li cells, accompanied with a low capacity-fading rate of only 0.0615% per cycle (discharge capacity of 2041.9 mAh g-1 after 200 cycles). Full cells pairing the unmodified Si anode with commercial LiFePO4 (≈13.92 mg cm-2 ) and LiNi0.5 Mn0.3 Co0.2 O2 (≈17.9 mg cm-2 ) cathodes further show extended service life to 150 and 60 cycles, respectively, demonstrating the superior cathode-compatibility realized with a thin and F, B-rich cathode electrolyte interface. This work offers an easily scalable approach in developing high-performance Si-based batteries through Si/electrolyte interphase regulation.

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Topics: Electrolyte (56%), Anode (54%)

2 Citations

Book Chapter
01 Jan 2021-
Topics: Lithium (76%)

1 Citations

Journal Article
Kisung Park1, Youngseong Jo1, Bonhyeop Koo1, Hongkyung Lee1  +1 moreInstitutions (1)
Abstract: The safe, stable cycling of Li-metal batteries (LMBs) over wide temperature ranges is crucial for practical applications, even in extreme environments. Although LMB performance has been enhanced using various high-concentration electrolytes (HCEs) with hydrofluoroether dilution, efficient operation over a wide temperature range remains elusive. This study elucidated the factors that enable LMB cycling in a wide temperature range (5–60 °C) by exploiting a model HCE composed of lithium bis(fluorosulfonyl)imide and 1,2-dimethoxyethane as well as an HCE diluted with 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE). Comprehensive analyses revealed that TTE dilution plays an essential role at lower temperatures by enhancing Li+ ion transport in the concentrated electrolyte while maintaining the original solvation structure. Furthermore, as the performance-determining factor for high-temperature cycling, TTE involvement in the solid–electrolyte interphase (SEI) reinforced the thermal stability. Thus, TTE dilution is crucial for both facile mass transport and thermally stable SEI formation. The resulting Li dendrite suppression and high Li Coulombic efficiency enable the realization of LMBs with a wide operating temperature range.

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Topics: Temperature cycling (53%), Hydrofluoroether (53%)

1 Citations

Journal Article
Abstract: Organic cations are essential components of locally concentrated ionic liquid electrolytes (LCILEs), but receive little attention. Herein, we demonstrate their significant influence on the electrochemical performance of lithium metal batteries via a comparison study of two LCILEs employing either 1‑butyl‑1-methylpyrrolidinium cation (Pyr14+) or 1-ethyl-3-methylimidazolium cation (Emim+). It is demonstrated that the structure of the organic cation in LCILEs has only a limited effect on the Li+- bis(fluorosulfonyl)imide anion (FSI−) coordination. Nonetheless, the coordination of FSI− with the organic cations is different. The less coordination of FSI− to Emim+ than to Pyr14+ results in the lower viscosity and faster Li+ transport in the Emim+-based electrolyte (EmiBE) than the Pyr14+-based electrolyte (PyrBE). Additionally, the chemical composition of the solid-electrolyte interphase (SEI) formed on lithium metal is affected by the organic cations. A more stable SEI growing in the presence of Emim+ leads to a higher lithium plating/stripping Coulombic efficiency (99.2%). As a result, Li/EmiBE/LiNi0.8Mn0.1Co0.1O2 cells exhibit a capacity of 185 mAh g−1 at 1C discharge (2 mA cm−2) and capacity retention of 96% after 200 cycles. Under the same conditions, PyrBE-based cells show only 34 mAh g−1 capacity with 39.6% retention.

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Topics: Lithium (57%), Ionic liquid (54%), Electrolyte (54%) ... read more

##### References
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27 results found

Journal Article
Georg Kresse1, Daniel P. Joubert2Institutions (2)
15 Jan 1999-Physical Review B
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.

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Topics: Cauchy stress tensor (53%)

46,297 Citations

Journal Article
Abstract: The parametrization and testing of the OPLS all-atom force field for organic molecules and peptides are described. Parameters for both torsional and nonbonded energetics have been derived, while the bond stretching and angle bending parameters have been adopted mostly from the AMBER all-atom force field. The torsional parameters were determined by fitting to rotational energy profiles obtained from ab initio molecular orbital calculations at the RHF/6-31G*//RHF/6-31G* level for more than 50 organic molecules and ions. The quality of the fits was high with average errors for conformational energies of less than 0.2 kcal/mol. The force-field results for molecular structures are also demonstrated to closely match the ab initio predictions. The nonbonded parameters were developed in conjunction with Monte Carlo statistical mechanics simulations by computing thermodynamic and structural properties for 34 pure organic liquids including alkanes, alkenes, alcohols, ethers, acetals, thiols, sulfides, disulfides, a...

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Topics: Ab initio (56%), , Molecular orbital (50%)

10,389 Citations

Journal Article
Kang Xu1Institutions (1)
16 Sep 2004-Chemical Reviews
Abstract: 2.1. Solvents 4307 2.1.1. Propylene Carbonate (PC) 4308 2.1.2. Ethers 4308 2.1.3. Ethylene Carbonate (EC) 4309 2.1.4. Linear Dialkyl Carbonates 4310 2.2. Lithium Salts 4310 2.2.1. Lithium Perchlorate (LiClO4) 4311 2.2.2. Lithium Hexafluoroarsenate (LiAsF6) 4312 2.2.3. Lithium Tetrafluoroborate (LiBF4) 4312 2.2.4. Lithium Trifluoromethanesulfonate (LiTf) 4312 2.2.5. Lithium Bis(trifluoromethanesulfonyl)imide (LiIm) and Its Derivatives 4313

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Topics: Lithium perchlorate (71%), Lithium (70%),  ... read more

4,694 Citations

Journal Article
Dingchang Lin1, Yayuan Liu1, Yi Cui2, Yi Cui1Institutions (2)
Abstract: Lithium-ion batteries have had a profound impact on our daily life, but inherent limitations make it difficult for Li-ion chemistries to meet the growing demands for portable electronics, electric vehicles and grid-scale energy storage. Therefore, chemistries beyond Li-ion are currently being investigated and need to be made viable for commercial applications. The use of metallic Li is one of the most favoured choices for next-generation Li batteries, especially Li-S and Li-air systems. After falling into oblivion for several decades because of safety concerns, metallic Li is now ready for a revival, thanks to the development of investigative tools and nanotechnology-based solutions. In this Review, we first summarize the current understanding on Li anodes, then highlight the recent key progress in materials design and advanced characterization techniques, and finally discuss the opportunities and possible directions for future development of Li anodes in applications.

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2,828 Citations

Journal Article
Kang Xu1Institutions (1)
29 Oct 2014-Chemical Reviews

2,632 Citations

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