Electrochemical Study of Li-Ion Battery Anode (Graphite) and Cathode (NMC811) Surface Film Formation By in-Situ Scanning Probe Microscopy

Abstract

Lithium ion battery usage has grown significantly in recent years. To obtain the best from the li-ion battery technology, it is important to understand both advantages and the limitations from the fundamental point of view. In lithium-ion batteries, layer structured graphite is the most commonly used anode material and NMC is one of the modern choices of cathode materials for high capacity Li-ion batteries in the electric vehicle applications [1,2,3].During the first charging process, the electrochemical reduction of electrolyte components gets deposited on the surface of anode resulting solid electrolyte interface (SEI) layer formation [4,5,6]. It is widely accepted that the batteries benefit from a proper SEI formation, as it can improve their lifetime, cycle life, power capability and safety [7].Morphological structure of SEI layer formed on HOPG and cathode electrolyte interface (CEI) layer formed on NMC plays an important role in lithium-ion battery (LIB), particularly for its cyclability and safety. For the development of high-performance LIB’s, it is crucial to understand the SEI layer formation on anode side [8] and the less studied corresponding layer formed on cathode side termed as CEI, whose composition and role are debated [9].Microscopic techniques, which include scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are the most powerful tools to measure the electric current and surface topography [10,11]. Within this work, we present in-situ electrochemical atomic force microscopic (EC-AFM) studies of surface reaction and topographic evolution of SEI and CEI layers formed on HOPG and NMC811 substrates. EC-AFM morphological analysis is also complemented with XPS (X-ray Photoemission Spectroscopy) characterisation for elemental composition, which brings a new insight in the comparison of SEI/CEI decomposition products. Acknowledgements: This work is partially supported by Faraday Institution (EP/S003053/1) and North-East Centre of Energy Materials-NECEM (EP/R021503/1) funded by EPSRC.