(Invited) Impact of Functional Electrolyte Additives (Single, Multifunctional and Blended) on Advanced Performance of Nonaqueous Electrolytes
Authors: Cekic-Laskovic Isidora , von Aspern Natascha , Winter Martin 
Published: February 2020

Lithium ion batteries (LIBs) are considered as energy storage system of choice for variety of mobile and stationary applications nowadays, however fundamental knowledge on underlying principles controlling the basic processes that determine and dictate their function, operation and performance limitations as well as failure, is alarmingly required. In this underpinning way, considerable improvements and new concepts concerning the electrolyte formulations can be achieved, thus enabling electrochemical systems with high energy density, high power, long life and adequate safety at a competitive manufacturing cost. Due to the complexity of an electrolyte formulation, determined by the physicochemical properties of its components, namely inorganic fluorinated salts, organic solvents and additives, the overall cell performance comprising electrolyte/electrode interphases is inevitably accompanied by side reactions. Furthermore, chemistry of liquid electrolytes and their interaction with anode and cathode materials is complex and yet not fully understood representing the delicate balance of various properties. State-of-the-art nonaqueous aprotic electrolytes (SOTA) reveal different challenges among which electrolyte decomposition and high flammability of its constituents stand out.1 Electrolyte decomposition becomes crucial when so called “5V cathode” materials are used. One of the promising solutions refers to the application of functional electrolyte additives, added in small amounts to the electrolyte formulation to attain the demanded properties. Although different electrolyte additives have found their application in advancing the electrolyte performance, not much is understood about their role and effectiveness. Recent advances in selected ex situ, online and in situ techniques, supported by theoretical calculations and simulations, provide deeper insights into the dynamic, complex and not well-understood cell chemistry. Be means of developed methods decomposition products can be evaluated to determine main operation and failure mechanisms impacting the overall performance of given cell chemistries. Thorough study, understanding and elucidation of fundamental operation mechanisms including chemical, physical, electrochemical and interfacial processes facilitate and guide further advancement of the existing state of the art Li ion batteries. In this mechanistic game, victory is assured to those who are best able to piece together conclusions gathered from synthetic, structural, kinetic, spectroscopic as well as electrochemical studies and construct the mechanism capable of explaining obtained results.
This work comprises design, tailored synthesis and study of several fluorinated cyclic phosphorus-based containing compounds as single, bifunctional or combined high-voltage and flame retardant additives/co-solvents for advanced LIB electrolytes. The considered molecules were characterized by means of carefully selected physicochemical, electrochemical, analytical as well as structural methods2,3. This systematical approach allows to understand the structure-property-reactivity relationship of the aforementioned compounds, their impact on the overall battery chemistry, performance as well as safety and helps, to further tailor the properties of functional electrolyte additives/co-solvents for targeted application.

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