All-solid-state lithium batteries (ASSLBs) hold immense promise as next-generation energy storage systems. A crucial aspect

of ASSLB development lies in achieving high energy density, which demands the high mass loadings of cathode active material.

However, thick cathode with high mass loading may introduce various challenges, such as interfacial resistance between

electrolytes and electrodes, suboptimal ion conduction, and limited battery lifespan. To address these challenges, composite

cathode has been engineered by integrating solid-state electrolytes into conventional cathodes to enhance ion transport.

Solid polymer electrolytes (SPEs), in particular, stand out for their ability to mitigate interfacial issues during cycling due

to their elasticity and fl exibility compared to their inorganic counterparts. This review off ers a comprehensive overview of

eff orts to incorporate SPEs into catholytes for ASSLBs. It begins with a discussion on catholyte composition, emphasizing

the properties of their constituent components. Subsequently, it provides a concise overview of electrochemical transport

and measurement techniques. The review then delves into effi cient and cost-eff ective fabrication processes, highlighting

their signifi cance. Finally, it underscores the crucial role of SPEs in advancing the development of catholytes for the future.