Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)
Session: 1
Room: Park Tower 8217
Rickey Terrell - University of Cincinnati
Co-Author(s): Eric McShane, University of California Berkeley; Kyle Diederichsen, University of California Berkeley; Dr. Bryan McCloskey, University of California Berkeley
Li-ion batteries are a popular power generation choice for portable electronics and have most recently seen increased interest in transportation applications. This widespread use has generated a demand for batteries to be developed with improved electrochemical performance. However, this is difficult to achieve due to the transport limitations of the battery electrolyte. Specifically, electrolytes with low transference numbers—defined as the fraction of Li+ cation conductivity compared to the overall electrolyte conductivity—create undesired ion concentration gradients that lead to decreased charge rates. Thus, the utilization of high transference number electrolytes (HTNE) is promising in fast charging battery applications. Two HTNEs of interest are polyelectrolytes and solvent-in-salt electrolytes. Polyelectrolytes utilize polymers as a Li salt, which restricts anionic movement. Conversely, the solvent-in-salt technique maximizes the concentration of the Li salt in the electrolyte solution. In both approaches, the increase in the transference number is also coupled with shifts in other transport properties that may additionally impact battery performance. Here we have recorded viscosity and conductivity measurements to elucidate relationships between solution composition and measured solution transport properties of interest. In the examined solvent-in-salt systems, solvent choice influenced the viscosity by altering the preference of the Li salt to form solvation shells with the solvent molecules. In polyelectrolytes, increases in polymer molecular weight resulted in increased viscosity. Coupled with the result that conductivity remains constant upon increase of polymer molecular weight, this data shows that Li+ ion transport is independent of bulk electrolyte viscosity. In most electrolyte solutions, viscosity correlates to diffusion. However, this result implies a more complex diffusion mechanism is responsible for ion transport in polyelectrolyte systems which requires further study. The characterization completed in this study reveals new information about HTNE transport properties which will inform future synthesis of electrolytes, resulting in higher performing Li-ion batteries.
Funder Acknowledgement(s): 1. Amgen and 2. University of California Berkeley
Faculty Advisor: Dr. Bryan McCloskey, bmcclosk@berkeley.edu
Role: I completed the electrolyte synthesis, characterization, and analysis of collected data. The synthesis of the High Transference Number Electrolytes required combining various lithium salts in the solvents under Argon. Characterization of the electrolytes was completed by measuring viscosity, using an electromagnetically spinning viscometer, and conductivity, using a 4-pole conductivity probe. Data was analyzed to determine relationships between transport properties.