Functional Design of Nitrile-Based Electrolyte Components

Abstract

Introduction One of the crucial points for next generation lithium batteries is the development of high performance electrolyte components (e.g. electrolyte solvents, conducting salts and additives) to replace current LiPF6-based liquid systems. Novel electrolytes should guarantee high thermal and electrochemical stability, high ionic conductivity, long term stability of anode and cathode interfaces as well as they should lead to stable SEI films.[1-2] On the other hand, electrolyte components should be nonflammable, nontoxic and environmentally friendly. This work is focused on applying basic chemical principles like inductive effects, sterical hindrance, increasing electronegativity and modification with fluoride splitting groups to model new nitrile-based electrolyte components (cf. Fig. 1).[3-4] The physicochemical properties of these new electrolyte components were investigated and different modification steps were compared. Results and Discussion Increasing the +I effect, induced by electron donating substituents and the sterical hindrance of the nitrile-based electrolyte solvents led to highly cathodic stable nitrile-siloxane-solvents which are as well stable against metallic lithium in comparison to simple nitrile-based solvents like acetonitrile.[5] Additionally, they exhibit low vapor pressures and are in general nonflammable. The here mentioned nitrile-based conducting salts show high anodic stabilities ranging from 4.5-5.6 V vs. Li/Li+ and in the cathodic region, they are stable down to the lithium metal stripping/plating process. In comparison to commonly used LiPF6, the lithium salts show very high thermal stabilities starting from 300 °C and raises to 500 °C with growing sterical hindrance. Furthermore, BF3-modification of additive components led to stable passivation layers on aluminum current collectors and therefore to a better suppression of Al-dissolution, even in the presence of LiTFSI in carbonate type solvents. To sum it up, investigation and application of basic concepts on nitrile-based electrolyte components offer a simple tool for an easy tailoring.