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 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.