Design of Polymer Functionalized Separators for Dendrite‑Free Lithium Metal Batteries

Lithium metal batteries (LMBs) are significantly hindered by internal short circuits resulting from uncontrolled lithium dendrite growth. To address this challenge, we have developed an innovative polymer to modify conventional commercial separators, thereby mitigating lithium dendrite proliferation. This polymer is synthesized through the copolymerization of three monomers: poly(ethylene glycol) methyl ether methacrylate (PEGMA), tetramethyltetravinylcyclotetrasiloxane (TTCS), and 2‐ureido‐4[1H]‐pyrimidinone methyl methacrylate (UpyMA). The dynamic hydrogen bonds present in the UpyMA monomer confer self‐healing properties to the polymer, while the PEO chains in PEGMA facilitate enhanced Li + transport. Concurrently, TTCS interacts with Li + to improve lithium‐ion transfer, collectively contributing to the effective suppression of lithium dendrite growth. Moreover, the functional groups within the polymer not only modulate the solvation structure of the electrolyte but also partially react with Li to aid in the formation of the solid electrolyte interphase (SEI). This results in the creation of an organic/inorganic‐rich hybrid SEI that bolsters the stability of LMBs. Following the modification of the separator, the Li||Li symmetric cell demonstrates stable cycling for over 700 h. The Li||NCM811 full cell achieves stable cycling for 300 cycles with a capacity retention rate of 83.6%.