Microporous polymers feature shape-persistent free volume elements (FVEs), which are permeated by small molecules and ions when used as membranes for chemical separations, water purification, fuel cells and batteries^1,2,3. Identifying FVEs that have analyte specificity remains a challenge, owing to difficulties in generating polymers with sufficient diversity to enable screening of their properties. Here we describe a diversity-oriented synthetic strategy for microporous polymer membranes to identify candidates featuring FVEs that serve as solvation cages for lithium ions (Li⁺). This strategy includes diversification of bis(catechol) monomers by Mannich reactions to introduce Li⁺-coordinating functionality within FVEs, topology-enforcing polymerizations for networking FVEs into different pore architectures, and several on-polymer reactions for diversifying pore geometries and dielectric properties. The most promising candidate membranes featuring ion solvation cages exhibited both higher ionic conductivity and higher cation transference number than control membranes, in which FVEs were aspecific, indicating that conventional bounds for membrane permeability and selectivity for ion transport can be overcome⁴. These advantages are associated with enhanced Li⁺ partitioning from the electrolyte when cages are present, higher diffusion barriers for anions within pores, and network-enforced restrictions on Li⁺ coordination number compared to the bulk electrolyte, which reduces the effective mass of the working ion. Such membranes show promise as anode-stabilizing interlayers in high-voltage lithium metal batteries.

微孔聚合物具有形状持久的自由体积元素 (FVE)，当用作化学分离、水净化、燃料电池和电池^1,2,3的膜时，它会被小分子和离子渗透。识别具有分析物特异性的 FVE 仍然是一项挑战，因为难以生成具有足够多样性的聚合物来筛选其特性。在这里，我们描述了一种面向多样性的微孔聚合物膜合成策略，以确定具有作为锂离子 (Li ⁺ ) 溶剂化笼的 FVE 的候选者。该策略包括通过曼尼希反应使双（儿茶酚）单体多样化以引入 Li ⁺-FVE 内的协调功能，将 FVE 联网成不同孔隙结构的拓扑强化聚合，以及用于使孔隙几何形状和介电特性多样化的几种聚合物上的反应。具有离子溶剂化笼的最有希望的候选膜表现出比对照膜更高的离子电导率和更高的阳离子转移数，其中 FVE 是非特异性的，这表明可以克服膜渗透性和离子传输选择性的常规界限⁴。这些优势与笼存在时增强的锂^离子从电解质中的分配、孔内阴离子的更高扩散势垒以及对锂离子的网络强制限制有关^。与本体电解质相比，配位数减少了工作离子的有效质量。这种膜有望成为高压锂金属电池中的阳极稳定中间层。