Enhancing the Filler Utilization of Composite Gel Electrolytes via In Situ Solution‐Processable Method for Sustainable Sodium‐Ion Batteries

Abstract The composite gel electrolyte (CGE), which combines the advantages of inorganic solid‐state electrolytes and solid polymer electrolytes, is regarded as the ultimate candidate for constructing batteries with high safety and superior electrode‐electrolyte interface contact. However, the ubiquitous agglomeration of nanofillers results in low filler utilization, which seriously reduces structural uniformity and ion transport efficiency, thus restricting the development of consistent and durable batteries. Herein, a solution‐processable method to in situ construct CGE with high filler utilization is introduced. The homogeneous metal–organic framework fillers contribute to uniform ionic and electronic filed distribution, realizing a stable electrode‐electrolyte interface. Consequently, the CGE with high filler utilization achieves an ultra‐long lifespan of 10 000 cycles with a capacity retention of 80.2%. This work provides guidance for constructing high‐performance CGEs in electrochemical energy‐storage devices.