Although lithium ion batteries are considered as system of choice for variety of mobile and stationary applications, fundamental knowledge is alarmingly required to uncover the underlying principles controlling the basic processes that determine and dictate their function, operation, performance limitations as well as failure. In this underpinning way, considerable improvements and new concepts in respect to the stable electrode active materials and electrolyte formulations can be achieved leading to electrochemical systems with long life, high energy density, high power and adequate safety at a competitive manufacturing cost. Due to the complexity of electrolyte formulation, determined by the physicochemical properties of its components, namely inorganic fluorinated salts, organic solvents and additives, the desired operation performance is always accompanied by inevitable side reactions. Recent advances in selected ex situ, online and in situ techniques, combined with theoretical approach, outline and provide deeper insight into the dynamic, complex and not well-understood cell chemistry. In this mechanistic game, victory is assured to those who are best able to piece together conclusions obtained from synthetic, structural, kinetic, spectroscopic as well as electrochemical studies and construct the mechanism capable of explaining the results. Thorough investigation and elucidation of those fundamental, mechanisms including chemical, physical, electrochemical and interfacial processes guide and strengthen the further advancement of the existing state of the art Li ion batteries and stimulate development of the next generation rechargeable batteries.

Since an electrolyte has a complex starting composition, analytical and electrochemical techniques have to be developed and applied for the numerous individual species that are present in the system. By means of developed analysis methods, decomposition products can be evaluated to determine operation and failure mechanisms as depicted in Figure 1.