Supramolecular Polyanions as Effective Interphase Layers for Anode-Free Lithium Metal Batteries

Abstract

Supramolecular polymers (SPs) driven by host-guest interactions have seen considerable advancements over the past decade, but the guest species involved are predominantly neutral molecules or cations. Strong and dependable macrocycle-anion interactions for supramolecular polymerization are highly sought after, yet the functionalities of this class of SPs featuring negatively charged backbones remain largely unexplored. Here we report a novel host-guest interaction between one tetraurea macrocycle and two organophosphate anions with high affinity (association constant Ka = 1.06 × 109 M−2). It can serve as noncovalent joints to efficiently link low-molecular-mass polyethylene oxide (PEO) diorganophosphates into long linear SPs. Being used as an interphase layer in anode-free lithium (Li) metal batteries, the polymer material promotes Li+ absorption and desolvation through electrostatic attractions, and enables fast Li+ transport by the alternatingly arranged anionic linkages and PEO units in the polymer main chain. As a result, the SP layer homogenizes Li+ flux to achieve uniform Li deposition, and significantly improves the electrochemical performance of LiFePO4 full batteries by a factor of 285% with cycling stability over 200 cycles. These findings pave the way for a new family of anion-based SPs with tunable architectures and compositions, and suggest their promising applications in future batteries.