Weakly Coordinating Polyester Enables High Performance Semi-solid Polymer Electrolyte for Li–Metal Batteries

Abstract Lithium metal batteries leveraging semi-solid polymer electrolytes (SSPEs) promise to increase the energy density of Li-ion batteries. These polymer–plasticizer hybrids offer mechanical robustness, yet their performance is often limited by preferential Li+ coordination to solvating polymer matrices. Here, we demonstrate that replacing a conventional polyether with a weakly coordinating polyester, i.e., poly(caprolactone) diacrylate, mitigates this effect and fundamentally alters Li+ transport and interfacial behavior. The SSPE delivers stable cycling with 80% capacity retention after 188 cycles in full cells employing an NMC622 cathode with a 2 mA h cm–2 loading and a 25 µm Li–metal anode (N/P = 2.5).