2019 Fiscal Year Annual Research Report
安全電池実現のための適切添加剤を用いた先端的非引火性電解液の理論的設計
| Project/Area Number |
19F19040
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| Research Institution | Nagoya University |
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Principal Investigator |
長岡 正隆 名古屋大学, 情報学研究科, 教授 (50201679)
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| Co-Investigator(Kenkyū-buntansha) |
BOUIBES AMINE 名古屋大学, 情報学研究科, 外国人特別研究員
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| Project Period (FY) |
2019-04-25 – 2021-03-31
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| Keywords | Computational design / Nonflammable electrolyte / Dilution / SEI film formation / Red Moon methodology |
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| Outline of Annual Research Achievements |
The main goal of this study is to design computationally a non-flammable electrolyte for a practical safe Li-ion batteries (LIB). For that, we focused on the new concept of highly salt-concentrated (HC) electrolyte based on non-flammable trimethyl-phosphate (TMP) solvent. The microscopic mechanism of its solid electrolyte interphase (SEI) layer formation was firstly investigated using Red Moon methodology. It was revealed that a large amount of salt anions is localized on the SEI surface in HC electrolyte, enhancing the network formation of a dense inorganic layer with SEI salt-derived species. In addition, it was shown that the size of TMP molecule prevents itself from entering in SEI layer, leading to the formation of a pure dense inorganic SEI layer, which should considerably improve the stability of SEI layer and would bring about a long lifetime of advanced safe LIB. Next, we aimed to “dilute” such HC TMP-based electrolyte in order to address its low ionic conductivity and high viscosity. For that, new hydrofluoroethers (HFE) were designed with high degree of fluorination. Using MD calculations, the miscibility was firstly verified from the change of Gibbs free energy. Then, the transport and structural properties were investigated using MD and QM calculations. A significant increase of ionic conductivity was obtained in dilute TMP-based electrolyte. These highly fluorinated HFEs showed a very poor coordination ability leading to the construction of a localized concentrated electrolyte, which is strongly requested for the formation of a stable salt-derived SEI film.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
Very good results were obtained regarding the transport properties of diluted TMP-based electrolyte using new designed hydrofluoroethers (NewHFE) molecules. The NewHFE:TMP-based electrolyte resulted a high ionic conductivity even to that of diluted electrolyte based on Bis (trifluoroethyl) ether (BTFE) cosolvent. Usually, the diluted electrolyte based on BTFE cosolvent showed the highest conductivity among other hydrofluoroethers cosolvents. In addition, the NewHFE molecules have high degree of fluorination than the well-known Tetrafluoroethyl tetrafluoropropyl ether (TTE), which is considered as an efficient additive to enhance the SEI film stability and charge-discharge cycling performance.
Good results also are expected regarding the formation of stable ductile SEI film in the NewHFE:TMP-based electrolyte because of the high degree of fluorination and very poor coordination ability of the present NewHFE molecules.
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| Strategy for Future Research Activity |
Actually, I am summarizing the obtained results of the microscopic effect for each HFE diluents regarding the structural and transport properties of bulk diluted electrolytes.
As future work in this year, the microscopic effect of different HFE diluents on the SEI film formation in TMP-based electrolyte will be investigated. Once the primary reactions for SEI film formation are obtained, Red Moon method will be used over a number of samples in order to obtain the atomic structures of SEI films. Then, a number of SEI film properties will be investigated in order to evaluate the structural stability and its ductile-brittle behavior. For that, the molecular configuration of the reaction products as well as the cavity will be investigated in the obtained SEI film. In addition to that, the topology of SEI film will be analyzed using Persistent Homology methodology. Afterword, the mechanical properties such as elastic constants, bulk and shear modulus will be calculated in order to analyze the mechanical stability and predict the most ductile SEI.
The final results will be presented in a suitable symposium (Pacifichem2020) and the detail-rich three or more papers will be published in highly reputed journals.
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Research Products
(5 results)
