Modelling of alkali-ion battery electrolytes

Licentiate thesis, 2011

Lithium-ion batteries are omnipresent in modern electronics. They can be found in laptops, mobile phones and electric vehicles. However, there is room for both improvement, as the thermal instability of the dominant lithium salt used in batteries today, LiPF6, causes safety concerns, and more conceptual changes, as there is a limited amount of lithium available - resulting in sodium-ion batteries being a nascent field of study. This thesis looks in detail at some of the phenomena found in the electrolytes of both lithium-ion and sodium-ion batteries. These properties include the oxidative stability of the anions of the lithium and sodium salts (important for voltage and safety); the cation-anion interaction strength (important for conductivity); and also the solvation of the lithium and sodium cations in the common carbonate solvents (important for conductivity and the stability vs. the anodes/cathodes). These properties are studied for a number of both novel and well established anions. Some of the novel anions involve completely new concepts for anion design for lithium battery electrolytes. The systems are studied mostly with density functional theory (DFT) calculations and a number of other ab initio methods. These include high level calculations of benchmark quality. The applicability of DFT and the selection of DFT functionals is also studied.