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

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 K_a = 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.