Charge Delocalization on BO₄^– Centers to Improve Conductivity on Single Lithium Ion Conducting Polymer Electrolytes: A Computational/Experimental Approach

Single lithium ion conducting polymer electrolytes (SLICPEs) could be one of the best options for safer lithium ion batteries, only if new strategies can be envisaged to improve their ionic conduction properties. In this work, we examine the effect of two strategies to improve the ionic conductivity of SLICPE based on sp 3 boron atoms linkers by PEG chains, namely, partial cross-linking and modification of the electron-withdrawing properties of the substituents attached to the BO 4 – groups. The molecular structure analysis, determined by density functional theory, shows an important variation on the electron density of the BO 4 – group with the presence of electron-withdrawing groups, allowing lower Li + –polymer interaction energy and lower activation energy for Li + hopping; these results confirm the changes in the chemical environment of B and Li established by NMR. The increase of the electron-withdrawing capacity of the substituent groups on the BO 4 – groups decreases their electronic density, increases the length of the BO 4 – –Li + bond distance, and allows higher mobility of Li + in the partially cross-linked SLICPE structure. The ionic conductivity measurements obtained by electrochemical impedance spectroscopy (EIS) reveal that the effect of the diminution of electron density in the BO 4 – groups and its effect on the mobility of Li + in the polymer matrix are mainly observed at temperatures higher than T m, where the system has enough energy to break electrostatic short-range interactions within the polymer matrix, which limits the mobility of the polymer matrix.