Tailoring Electrode–Electrolyte Interfaces in Lithium-Ion Batteries Using Molecularly Engineered Functional Polymers

Electrode–electrolyte interfaces
(EEIs) affect the rate
capability, cycling stability, and thermal safety of lithium-ion batteries
(LIBs). Designing stable EEIs with fast Li+ transport is
crucial for developing advanced LIBs. Here, we study Li+ kinetics at EEIs tailored by three nanoscale polymer thin films
via chemical vapor deposition (CVD) polymerization. Small binding
energy with Li+ and the presence of sufficient binding
sites for Li+ allow poly­(3,4-ethylenedioxythiophene) (PEDOT)
based artificial coatings to enable fast charging of LiCoO2. Operando synchrotron X-ray diffraction experiments suggest that
the superior Li+ transport property in PEDOT further improves
current homogeneity in the LiCoO2 electrode during cycling.
PEDOT also forms chemical bonds with LiCoO2, which reduces
Co dissolution and inhibits electrolyte decomposition. As a result,
the LiCoO2 4.5 V cycle life tested at C/2 increases over
1700% after PEDOT coating. In comparison, the other two polymer coatings
show undesirable effects on LiCoO2 performance. These insights
provide us with rules for selecting/designing polymers to engineer
EEIs in advanced LIBs.