Safe electrolytes based on Glyoxylic-Acetals for Lithium- and Sodium-ion batteries

Within this thesis, the glyoxylic-acetals 1,1,2,2-tetramethoxyethane (TMG) and 1,1,2,2-tetraethoxyethane (TEG) have been investigated as electrolyte solvents for lithium-ion and sodium-ion batteries. TMG and TEG provide higher flash and boiling points compared to linear organic carbonates while simultaneously offering low melting points. Moreover, these solvents are available on a large scale, as they are industrially used as solubilizing agents. In the first part of this thesis, TMG and TEG are investigated as solvent components for lithium-ion battery electrolytes. Mixtures of TMG or respectively TEG with organic carbonate solvents are analyzed towards their physicochemical and electrochemical properties. Moreover, the effects of glyoxylic-acetals on the solid-electrolyte-interphase (SEI) formation on silicon-graphite composite electrodes are analyzed by electrochemical and spectroscopical means. The second part of the thesis concentrates on transferring the subject of glyoxylic-acetal-based electrolytes from lithium-ion to sodium-ion batteries (SIBs). Electrolytes containing these solvents are analyzed towards their viscosity, flash point, ionic conductivity and thermal stability, as well as tested in lab-scale SIBs. Furthermore the synthesis of a novel hard carbon material from brewer's spent grain is presented and the material is applied in combination with TEG containing electrolytes in lithium-, sodium- and potassium-ion battery half cells. The third part of this work is dedicated to the characterization of glyoxylic acetals as solvents in gel-polymer electrolytes. The objective of this approach is to combine the favorable thermal properties provided by TEG with the advantage of a leakage-safe electrolyte system.