Plasticizer‐Assisted Garnet LLZO Integration in TPU‐Based Solid Composite Electrolytes for High‐Performance Solid‐State Lithium Metal Batteries

The solid composite electrolyte (SCE) system is becoming a crucial stage in the switch to all‐solid‐state batteries in order to enable excellent performance and safety. Three polymer‐based electrolytes, designated as TL‐S40, TL‐G40, and TL‐S‐G20, are examined in this work. They are composed of thermoplastic polyurethane (TPU), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), succinonitrile (SCN), and Al‐doped LLZO in varying compositions. These formulations were assessed by structural, thermal, mechanical, and electrochemical characterizations after being chosen among 38 candidates based on their ionic conductivities. TL‐G40 demonstrated the highest lithium transference number (0.22) and superior long‐term cycle stability, whereas TL‐S40 demonstrated the highest ionic conductivity (2.40 mS/cm) and voltage stability (4.90 V). The synergistic effect of SCN and LLZO‐Al was highlighted by TL‐S‐G20, which achieved the highest critical current density (308.89 A/cm 2 ) and the lowest interfacial resistance with both lithium and LFP electrodes. The thorough electrochemical assessment via galvanostatic charge–discharge and intermittent titration methods demonstrates that TL‐S‐G20 provides the most optimal electrochemical performance and interfacial stability, positioning it as a formidable contender for next‐generation flexible solid‐state battery applications.