Regulating lithium-ion transport route via adjusting lithium-ion affinity in solid polymer electrolyte

The competitive affinity of different components for lithium-ion (Li+) profoundly affects the ionic diffusion direction (namely Li+ migration route) in conductive filler-based solid polymer electrolytes (SPEs). In this work, a three-layer composite electrolyte is proposed in which a layer of PEO (polyvinyl epoxy)-LLZO (Li6.4La3Zr1.4Ta0.6O12) is sandwiched between two layers of polydopamine (PDA)-modified PEO interface (PMPI). We control the Li+ migration route in the organic matrix or inorganic filler by adjusting the Li+ affinity toward the polymer vs LLZO filler. Our DFT calculations uncover that the Li+ affinity is in the order of PDA (polydopamine)> LLZO > PEO. In this system, Li+ ions mainly travel through LLZO in PEO-LLZO electrolyte and are uniformly dispersed in the PMPI layer due to the high Li+ affinity of PDA and the homogeneous distribution of PDA in PEO matrix. Therefore, our design enables even distribution of current and eliminates growth of dendrite lithium while still providing fast ionic conduction. PDA was also found to broaden the electrochemical stability window, thus improving the compatibility of SPEs with high-voltage cathodes due to the intermolecular interaction between PDA and PEO.