Filmforming electrolyte-additives for lithium-ion-cells

The purpose of this work is the optimization of electrolytes for lithium ion cells. Due to reductive decomposition of the electrolyte, protecting layers are formed on graphitic anodes during the first charge/discharge cycles. By proper choice of the electrolyte components, these surface layers can avoid further decomposition of the electrolyte. Common electrolytes in lithium ion cells with suitable film- forming properties suffer from their poor low-temperature behavior and the high inflammability of the used solvents. To circumnavigate these drawbacks, one has to develop new electrolytes or electrolyte additives. In this work electrolyte additives for lithium ion cells, like the organic sulfites ethylene sulfite, propylene sulfite, dimethyl sulfite or diethyl sulfite, are studied for their film-forming abilities. A strategy by decoupling the bulk-properties of the electrolyte from the film-forming properties can be chosen. The formation of the desired protecting layers is maintained by small amounts of the additive, while the main electrolyte can be chosen with respect to the desired bulk-properties. (author)