Highly Concentrated Electrolytes for Rechargeable Lithium Batteries
Doctoral thesis, 2020
In this thesis both the fundamentals and various approaches to application of HCEs to lithium batteries are studied. First, LiTFSI–acetonitrile electrolytes of different salt concentrations were studied with respect to electrochemical stability including chemical analysis of the passivating solid electrolyte interphases (SEIs) on the graphite electrodes. However, some problems with solvent reduction remained, why second, LiTFSI–ethylene carbonate (EC) HCEs were employed vs. Li metal electrodes. Safety was improved by avoiding volatile solvents and compatibility with polymer separators was proven, making the HCE practically useful. Third, the transport properties of HCEs were studied with respect to salt solvation, viscosity and conductivity, and related to the rate performance of battery cells. Finally, LiTFSI–EC based electrolytes were tested vs. high voltage NMC622 electrodes.
The overall impressive electrochemical stability improvements shown by HCEs do not generally overcome the inherent properties of the constituent parts and parasitic reactions ultimately leads to cell failure. Furthermore, improvements in ionic transport cannot be expected in most HCEs; on the contrary, the reduced conductivity leads to a lower rate capability. Based on this knowledge, turning to a concept of electrolyte compositions where the inherent drawbacks of HCEs are circumvented leads to surprisingly good electrolytes even for Li metal battery cells, and with additives, Al dissolution can be prevented also when using NMC622 electrodes.
Highly concentrated electrolyte
Li metal battery
Chalmers, Physics, Materials Physics
Critical evaluation of the stability of highly concentrated LiTFSI - Acetonitrile electrolytes vs. graphite, lithium metal and LiFePO4 electrodes
Journal of Power Sources,; Vol. 384(2018)p. 334-341
Highly Concentrated LiTFSI-EC Electrolytes for Lithium Metal Batteries
ACS Applied Energy Materials,; Vol. 3(2020)p. 200-207
Interactions and Transport in Highly Concentrated LiTFSI-based Electrolytes
ChemPhysChem,; Vol. 21(2020)p. 1166-1176
V. Nilsson, P. Johansson, K. Edström and R. Younesi – Additives and Separators for LiTFSI–EC Electrolytes vs. Lithium metal, Graphite and NMC622 Electrodes
Dagens litiumjonbatterier och nästa generations batterier är kemiskt komplicerade system. Att de alls fungerar beror på att kemiska nedbrytningsprodukter inuti batteriet sätter sig på elektrodytorna och passiverar dessa.
För att öka batterisäkerheten utan att tappa livslängd och energitäthet har nya batterielektrolyter testats. Dessa är baserade på mindre skadliga kemikalier och använder en extremt hög saltkoncentration som säkerställer att elektrolyterna är mindre lättflyktiga och reaktiva. Elektrolyterna kan användas för att skapa säkrare litiumbatterier för olika tillämpningar.
The lithium-ion batteries of today and the next generation of batteries are chemically complicated systems. The fact that they even work is thanks to fortunate chemical degradation, which forms passivating decomposition products on the electrode surfaces.
To increase the safety of the batteries while maintaining or improving the energy density and lifetime, a new kind of electrolytes were tested for application in lithium batteries. These electrolytes are based on less harmful chemicals and feature an extremely high salt concentration, which ensures that they are less volatile and reactive. The electrolytes can be used to design safer lithium batteries for various applications.
Other Chemical Engineering
Areas of Advance
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4727
Chalmers University of Technology
PJ-salen, Fysikgården 2B, Göteborg
Opponent: Serena Corr, The University of Sheffield, Storbritannien