Polyimide shows great promises as the separator material in replacement of the commercial polyolefin counterparts. However, the polyimide nanoporous membranes have not yet been reported mainly due to the extremely poor processability of polyimides in dry and wet processes. In the past, only non-woven polyimide separators were demonstrated and fabricated, but exhibits low yield and mediocre mechanical strength. Here, we for the first time developed a facile solution-based synthesis of polyimide separators with outstanding mechanical strength (~1 GPa), high temperature resistance (>400 °C) and good electrolyte wettability. The method is low-cost and highly scalable for fast and large-scale fabrication, with great potential for industrial manufacturing. The batteries using the polyimide separators exhibited extraordinary rate capability, with ~30% higher capacity retention (~120 mAh/g) at a high rate of 10 C. We also demonstrated the cycling stability in the matched NMC532/Graphite full cells with commercial-level areal mass loading, which retains 91.2% of initial capacity after 200 cycles. Furthermore, we integrated dendrite detection function into the polyimide separator by a conductive interlayer inside the polyimide separator, which shows reliable early alarm of dendrite penetration. This innovation opens up the opportunity for safer batteries through separator engineering.