Perfluoropolyether‐terminated Single‐ion Polymer for Enhancing Performance of PEO‐based Solid Polymer Electrolyte

Solid-state electrolytes are receiving increasing attention in lithium metal batteries due to the advantage of high energy density. Poly(ethylene oxide) (PEO) electrolyte possesses good compatibility with lithium salts. However, PEO suffers from a low lithium-ion transference number and poor high-voltage resistance, which significantly hinder its application in lithium metal batteries. Herein, a perfluoropolyether-terminated single-ion polymer (PFPE-polymer) is designed and synthesized in this contribution. By incorporating the PFPE-polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into PEO via casting, the polymer electrolyte (PFPE-SE) is successfully prepared. Compared to PEO-based electrolytes, PFPE-SE forms a solid electrolyte interface (SEI) layer and inhibits the growth of lithium dendrites on the anode. At 70 °C, the lithium-ion transference number <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mo>(</mml:mo> <mml:msub><mml:mi>t</mml:mi> <mml:mrow><mml:mi>L</mml:mi> <mml:msup><mml:mi>i</mml:mi> <mml:mo>+</mml:mo></mml:msup> </mml:mrow> </mml:msub> <mml:mo>)</mml:mo></mml:mrow> <mml:annotation>$( {{{t}_{L{{i}^ + }}}} )$</mml:annotation></mml:semantics> </mml:math> and the electrochemical window reach 0.72 and 4.7 V, respectively. When tested at a discharge rate of 0.5 C, the Li|PFPE-SE|LFP cell exhibits a specific capacity of 156.0 mAh g^-1, with a capacity retention of 74.3% after 230 cycles, superiority the performance of the electrolyte prepared by mixing PEO with LiTFSI. This work presents a promising polymer electrolyte strategy for achieving high-performance lithium metal batteries, leveraging the in situ construction of the SEI layer and the utilization of a single-ion polymer.