Understanding the High Cation Transference in Poly(pentyl malonate) Electrolyte

The development of new battery electrolyte rests on the molecular level understanding of ion transport. The recently synthesised poly(pentyl malonate) (PPM) electrolyte exhibits promising cation transference, limiting current and electrochemical stability over the benchmark poly(ethylene) oxide (PEO) electrolyte. We elucidate the molecular origin of the faster Li⁺ dynamics in PPM by using molecular dynamics simulations. The current fraction of Li⁺ and ionic conductivity obtained from the Onsager approach quantitatively agree with experimental measurements at all salt concentrations. While the ionic conductivity is comparable with the state of the art PEO-based electrolyte, the current fraction is more than 3 fold of that in PEO. In contrast to the tight chelation of Li⁺ by single PEO chain, the simulation reveals the coordination of Li⁺ involves more than one PPM chains. The distinct multi-chain coordination in PPM is also reflected by the different molecular origin of the scattering peak that arises with increasing salt concentration. Dynamically, this multi-chain coordination in PPM promotes the frequent jumping of Li⁺, which overcomes the moderately infrequent interchain hopping in PEO electrolytes. A larger cation-cation correlation than anion-anion correlation can be realized in PPM electrolyte, hence enabling the high current fraction.