All-solid-state batteries (ASSBs) with Li or Si anodes promise enhanced safety and high energy densities but face challenges with complex fabrication, stringent storage requirements, and pressure-dependent operation. Polyethylene oxide (PEO)-based composite solid electrolytes (CSEs) enable easy processing and flexible interfaces, supporting pressure-free operation and reducing costs. However, their low ionic conductivity remains a key limitation. Here, we present a rapid (similar to 5 min) and eco-friendly laser modification strategy for post-synthesized PEO CSEs, achieving enhanced ionic conductivity while retaining the attributes of simple fabrication and compatibility with Li and Si anodes under pressure-free operation. Laser engineering reduces PEO crystallinity, introduces additional Li* coordination sites, and improves interfacial stability through tailored solid electrolyte interphases. The laser-modified electrolyte enables LiFePO4//Li cells to retain 142.4 mAh g-1 after 800 cycles with 99.8 % Coulombic efficiency at 1 C and 60 degrees C. Moreover, without stack pressure, a Si anode paired with the laser-modified electrolyte delivers a high capacity of 1710.3 mAh g-1 with 56 % retention at 0.5 A g-1 after 50 cycles at 60 degrees C. Beyond performance enhancements, this work establishes a link between fluorescence emission and Li* transport in CSEs. Specifically, fluorescence shifts to shorter wavelengths correspond to shorter molecular chain lengths and lower coordination bonds, supported by time-dependent density functional theory calculations. These factors give rise to improved Li* transport. This optical probe offers a non-destructive approach for rapidly assessing electrolyte properties and enriching electrolyte design. Overall, this work demonstrates laser engineering as a practical post-synthetic strategy and highlights fluorescence as a practical indicator for advancing next-generation ASSBs. (c) 2025 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
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