Reprotonation-assisted self-assembly of mechanically robust aramid nanofiber/sulfated ZrO2 hybrid separator with enhanced Li+ ion transfer for lithium-metal batteries

Abstract

The incorporation of inorganic materials into separators can enhance the mechanical and thermal properties of lithium-metal batteries (LMBs). However, the loss of ionic conduction is a serious concern, while the fabrication of thin-film, free-standing nanocomposite separators remains difficult. Here, we report the reprotonation-assisted self-assembly of a mechanically robust aramid nanofiber (ANF)/sulfated ZrO2 (SZ) nanocomposite separator with enhanced Li+ ion transfer with a freestanding thickness of <15 μm for use in LMBs. The self-assembled ANFs promote the formation of thin, homogeneous films by dispersing the SZ particles with the assistance of the 3D nanofibrillar network. This distribution of SZ within the ANF matrix enhances the mechanical and ion-conduction properties of the composite. The polar sulfate groups on the SZ surface dissociate the Li salt, with the surrounding ANF network dispersing the resulting Li+ ions. The optimal hybrid separator achieves a modulus of 1.75 GPa, an ionic conductivity of 0.57 mS cm−1, and a Li+ transference number of 0.63. The hybrid separator consequently improves LMB cycling stability and Li dendrite suppression. In particular, a symmetric Li/Li cell successfully undergoes more than 1000 cycles at 1 mA cm−2 and 1 mAh cm−2, while a LiFePO4/Li cell operates successfully over 410 cycles with a capacity retention of 80% at 0.5C.