Understanding electronic structure and interfaces of positive electrodes for lithium ion batteries

Abstract

Lithium ion batteries are the currently the best commercial battery in the market and they are used as energy storage devices for mobile phones, laptops, and other portable electronic devices. This is due to their balance of high energy density with high power density compared to other electrochemical energy devices. Also, these days the automotive industry wants to use lithium ion batteries to electric vehicles to reduce the pollution and independence to oil. Although lithium ion batteries are currently one of the best energy storage devices, there is still an ample room for improvement. One of the key parameters to study is electrode/electrolyte interface of electrodes. EEI on the negative electrode, also known as Solid Electrolyte Interphase (SEI) has the well-known structure with organic and inorganic compounds. Although EEI on negative electrodes is well known, it is not the case for positive electrodes. Numerous studies have been done on positive electrodes; however, there is still a need for systematic study of these interfaces on positive electrodes. This thesis is about understanding the reactivity and interactions of Li-ion battery positive electrode materials with the electrolyte. By understanding reactions at the EEI, we can develop a way to improve cycle life and safety of lithium ion batteries. To unambiguously pinpoint the electrode/electrolyte interface layers on different positive electrode materials, 100 % active materials are used as positive electrodes instead of composite electrodes.