Ion correlation and negative lithium transference in polyelectrolyte solutions.

Area of Science:

• Electrochemistry
• Polymer Science
• Materials Science

Background:

• Polyelectrolyte solutions (PESs) are explored for high conductivity and lithium transference numbers (t+).
• PESs aim to increase t+ by slowing anion motion via polymer backbone anchoring.
• Increasing anion charge can counteract this effect, decreasing t+.

Purpose of the Study:

• Directly measure ion mobilities in a model non-aqueous PES.
• Investigate competing effects influencing conductivity and t+.
• Determine the viability of short-chained PESs as high transference number electrolytes.

Main Methods:

• Electrophoretic Nuclear Magnetic Resonance Spectroscopy (eNMR) to measure ion mobilities.
• Direct measurement of ion movement in an electric field.
• Calculation of Onsager transport coefficients.

Main Results:

• Below entanglement limit, conductivity and t+ decrease with increasing polymer degree of polymerization.
• Observed Li+ moving in the opposite direction of the electric field (negative transference number) in polyanions with ≥10 repeat units.
• t+ increases with increasing Li+ concentration.
• Anion-anion and cation-anion correlations reduce t+ in non-entangled PESs.

Conclusions:

• Short-chained polyelectrolyte solutions are not viable for high transference number electrolytes.
• Ion correlations significantly impact electrolyte performance.
• Understanding ion correlations is crucial for designing advanced electrolytes for batteries.