Filler-free cellulose nanofiber composite papers with excellent mechanical properties for efficient electromagnetic interference shielding.

The vast majority of conductive polymer composites (CPCs) currently available for electromagnetic interference (EMI) shielding rely on inorganic conductive fillers to construct conductive networks. However, the strategy inevitably causes some compromises in the biocompatibility, biodegradability, and mechanical properties of CPCs. In this work, the filler-free and high conductive cellulose nanofiber (CNF) composite papers containing poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) doped by lithium bis(trifloromethanesulfonyl) imide (Li-TFSI) are reported. The resultant Li-TFSI@PEDOT:PSS/CNF (LPPC) composite papers exhibit an exceptional absolute EMI shielding effectiveness of 14,525.5 dB∙cm, surpassing the reported values of many CPCs-based EMI shielding materials containing inorganic fillers. Li-TFSI can induce the structural reorganization of PEDOT chains. The conductivity of Li-TFSI@PEDOT:PSS was boosted with the enhancement of the crystalline order and oxidation level of PEDOT chains. Furthermore, the obtained LPPC composite papers demonstrate outstanding mechanical properties with a tensile strength of 44.42 MPa and EMI shielding stability with a retention ratio of up to 97 %, which are desirable for EMI shielding in wearable devices. Therefore, this work provides a feasible strategy to construct filler-free CPCs-based EMI shielding materials, which are expected to provide electromagnetic protection for the next flexible devices.