Electrochemical modeling of degradation effects at a wide range of temperatures for lithium ion polymer batteries
Type of DegreePhD Dissertation
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The durability of lithium-ion batteries (LiBs) drops gradually undergoing both storage and prolonged cycling conditions, which is greatly affected by the operating conditions, particularly temperatures. At high temperatures, side reaction that takes place between lithium ions and electrolyte solvents to form the solid electrolyte interphase (SEI) layer is the primary cause for degradation. At low temperatures, especially under charging, lithium ions are prone to deposit as lithium metal on instead of intercalating into the solid matrix of anode, known as “lithium plating” that becomes the predominant reason for degradation. At discharging, extra lithium ions can be released from the plated lithium resulting in the partial capacity reversed, known as “lithium stripping”. An integrated physics-based reduced order model (ROM) considering degradation effects of side reaction and lithium plating/stripping at a wide range of temperatures is proposed and validated against experiments for both fresh and cycled LiBs, which has shown the capability of predicting the cell electrochemical performances and degradation, such as capacity fade, power fade and impedance rise etc. The degradation effects, including loss of recyclable lithium ions, loss of active material, growth of SEI and deposit layer, and the consumption of electrolyte solvents are considered at the entire temperature ranges. The growth of plated lithium and secondary SEI are added as extra sources of degradation at low temperatures. The model is capable of estimating capacity and power as a function of cycle number with an overall accuracy of 3% in the case that the capacity fade is less than 30%.