Mechanisms of lithiation in carbon and silicon anodes for lithium-ion batteries

Abstract

As the demand for energy increases globally, advanced energy storage materials must be developed to support renewable energy conversion technologies. Lithium-ion batteries (LIBs) are among the most promising energy storage methods technologies for mobile applications, but the mechanisms governing their operation and degradation remain incompletely understood. This thesis presents investigations of carbon- and silicon-based LIB anodes and compares their strengths and weaknesses for energy storage applications. First, we report an ultrafast alternative to graphite for high-power demand applications: a "herringbone" molecular crystal of hexa-perihexabenzocoronene (HBC). The unique lithiation mechanism of HBC is revealed via electrochemical, structural, and operando techniques, unveiling the structural origin of its pseudocapacitive character. Second, we report a cost-effective and high-capacity SiO x/Gr | | NMC811 battery system for high energy-density applications. Advanced electrochemical characterization techniques including in-situ electrochemical dilatometry were employed to the understand its impressive electrochemical stability for such a high energy density cell. This work reveals a hidden degradation mechanism that is masked by continuous lithium-ion emission into the system over the course of aging. Third, we will briefly discuss a new methodology developed for the compositional analysis of Si/C composite anodes, a recently commercialized technology for mobile LIB applications. This thermal gravimetric method reveals distinct silicon environments that render important implications for the composite electrochemistry. Altogether, these three reports provide new mechanistic insights into how lithium is inserted into carbon and silicon anodes, how its transport rate can be increased, and how its degradation can be prevented over the course of aging.