Safe operation is crucial for lithium (Li) batteries, and therefore, developing separators with dendrite-detection function is of great scientific and technological interest. However, challenges have been encountered when integrating the function into commercial polyolefin separators. Among all polymer candidates, polyimides (PIs) are prominent due to their good thermal/mechanical stability and electrolyte wettability. Nevertheless, it is still a challenge to efficiently synthesize PI separators, let alone integrate additional functions. In this work, a novel yet facile solution synthesis was developed to fabricate a nanoporous PI separator. Specifically, recyclable LiBr was utilized as the template for nanopores creation while the polymer was processed at the intermediate stage. This method proves not only to be a facile synthesis with basic lab facility but also to have promising potential for low-cost industrial production. The as-synthesized PI separator exhibited excellent thermal/mechanical stability and electrolyte wettability, the latter of which further improves the ionic conductivity and thus battery rate capability. Notably, stable full-cell cycling for over 200 cycles with a PI separator was further achieved. Based on this method, the fabrication of an all-integrated PI/Cu/PI bifunctional separator for dendrite detection can be fulfilled. The as-fabricated all-integrated separators prove efficient as early alarms of Li penetration, opening up the opportunity for safer battery design by separator engineering.