<italic>In</italic>-<italic>situ</italic> carboxylate-armoring polyimide@polyimide separator for inhibiting dendrites in lithium metal batteries

The formation of lithium (Li) dendrites remains a critical barrier to the practical implementation of lithium-metal batteries (LMBs). Herein, we present an in-situ carboxylated polyimide (CPI)-armoring polyimide (PI) nanofiber membrane (CPI@PI) as an advanced separator. Density functional theory calculations unveil that the carboxyl groups in CPI exhibit a strong binding energy with Li+ (−3.33 eV), enabling efficient Li+ dissociation and uniform transmission. Additionally, the multifunctional CPI nanolayer reduces the average pore size of the CPI@PI membrane to 0.62 μm while enhancing the mechanical modulus to 1.2 GPa, effectively curtailing the formation of dendrites. These features endow the CPI@PI separator with a high Li+ transference number (0.61) and a low nucleation overpotential (57 mV). Remarkably, Li||Li symmetric cells equipped with the CPI@PI separator displays a tiny voltage polarization during 700 h at 1.0 mA cm−2, which substantially outperforms that of commercial Celgard separator. Moreover, the CPI@PI-based Li||NCM523 full cells achieve an outstanding specific capacity of 96.3 mAh g−1 at 5 C. This work offers a pragmatic strategy to advance dendrite suppression in LMBs, marking a significant step toward their practical application.