Microstructural Aspects of Electrode Material Degradation Mechanisms in Li-ion Batteries

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Li-ion batteries are state-of-the-art energy storage systems that are being employed in a wide range of rechargeable portable electronic devices and also considered for mass-produced hybrid and electric vehicles. Understanding microstructural aspects of the electrode degradation mechanism during charging and discharging of Li-ion batteries is of key importance in order to design energy efficient batteries with low impedance growth and high capacity. The proposed research program aims at developing advanced characterization methods for identifying the micromechanisms of surface and subsurface damage in negative battery electrodes produced typically from graphite or silicon. The implementation of an in-situ observation system during electrochemical tests using a digital optical microscope and a Raman spectrometer will determine severity of surface degradation damage due to exfoliation and fragmentation of particles on electrode surfaces. The compositional changes that occur during the electrolyte decomposition and formation of solid electrolyte interface will be simultaneously identified. Application of FIB and TEM microscopy to samples excised from model electrode materials, such as HOPG with graphene layers parallel and normal to the interface, and Si samples with known crystallographic orientations, will elucidate details of crack initiation and propagation processes that operate in these electrodes. Attention will be given to the determination of local stresses and stress intensities at crack tips that are expected to rationalize the role of the intercalation products in controlling the crack growth rates. The results will be summarized in the form of diagrams or Electrode Damage Maps that will show the damage features as a function of cycling time and temperature, voltage scan rate and the electrolyte composition. By correlating the microscopic information to electrochemical performance, new design methods for improved electrode microstructures will arise. At least six HQP will be trained to the benefit of emerging energy materials sectors of the Canadian economy.