THE IMPACT OF CHARGE/DISCHARGE RATE ON CAPACITY FADE ON COMPOSITE STRUCTURED CATHODES IN LITHIUM ION BATTERIES

摘要

We develop a cohesive understanding the effect of rate of cycle on the composite structure of a lithium ion battery. Electrochemical techniques are used to evaluate capacity, resistance, and rate capability. Together, capacity and resistance measurements are used to segregate chemical-induced degradation (associated with resistance rise and capacity loss) from mechanical-induced degradation (primarily associated with capacity loss) in the cathode for different c-rate cycling. Meanwhile, rate capability measurements reveal the impact of chemical and physical degradation on utilization of the electrodes at various c-rates. Raman spectroscopy is used to directly measure Li~+ inventory losses caused by film growth on the composite anode surface and evaluate how it contributes to capacity loss measured electrochemically. Lastly, microscopy techniques assess mechanical damage in LiCoO_2 particles in the form of micro-cracks and dislocation defects which are thought to impede solid-state Li ion diffusion. This was demonstrated through diffusivity measurements using galvanostatic intermittent titration techniques.