Polyimide-engineered sodium titanate anode for sodium storage with improved structure and interface stability

Abstract

Na2Ti3O7 (NTO) anode has been long-term plagued by the rapid capacity decay due to the irreversible structural evolution and interfacial side reaction at low sodium insertion potential. Most reported investigations about NTO anode mainly focus on designing nanostructure to shorten ion diffusion and increase the electrochemical activity. However, few attentions have been paid to promote the cycle stability of bulk NTO. Surface/interface engineering through the incorporation of well-designed coating layer has been verified an effective strategy to stabilize the structure and interface of the electrodes. Herein, a polyimide-engineered bulk Na2Ti3O7 (NTO@PI) is proposed to promote its structure and interface stability upon cycles. The continuous PI layer with intrinsic flexibility as a protection skin can suppress the self-relaxation of discharged product and promote the structural stability during cycles. Meanwhile, PI protective layer with superior chemical stability not only hinders the side reaction occurred at NTO/electrolyte interface, but also serves as a barrier layer to preclude the erosion of H2O when exposed to air. Moreover, the PI layer with intrinsic ionic conductivity is capable of boosting Na-ion transportation from electrolyte into the NTO lattice as well. This work stresses a rational strategy for the surface/interface regulation of long-lasting and practical Ti-based anodes.