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.