High-Density Anchoring toward Ultra-Thin Polymer Electrolytes with High Electrochemical Stability

All-solid-state lithium batteries (ASSLBs) have attracted considerable attention because of their excellent safety and high energy density. However, application of ASSLBs is significantly impeded by the lack of solid-state electrolytes with ultra-thinness, high mechanical strength, and high electrochemical stability. Herein, we address this dilemma by designing an ultra-thin agarose-based electrolyte through a high-density anchoring strategy. The high-density anchoring is achieved by the supramolecular interaction between agarose (AG) and tannic acid (TA), which effectively restricts the free rotation of hydroxyl groups on AG backbones and forms Li-ion migration channels between AG chains. These characteristics endow the ultra-thin polymer electrolyte (UTPE) with a high mechanical strength, a wide electrochemical window (4.5 V), and a high lithium-ion transference number of 0.45 at 25 °C. A solid-state LiFePO4||Li battery with a 20 μm UTPE displays outstanding cyclability with a specific capacity of 141 mAh g–1 over 300 cycles at a 0.5 C rate. A LiNi0.5Mn0.2Co0.3O2||Li battery using the UTPE delivers a specific capacity of 93.9 mAh g–1 over 100 cycles at a 0.1 C rate at 2.5–4.2 V, showing a retention rate of 75.0% at room temperature. Furthermore, solid-state LiFePO4||Li pouch cells exhibit remarkable safety even after being folded, cut, and penetrated by the nail. This study offers a promising strategy to address the mechanical strength and electrochemical stability issues of solid polymer electrolytes, which has potential applications in high-energy-density ASSLBs.