High‐Performance PVDF‐HFP Quasi‐Solid‐State Polymer Electrolyte Achieved by Multivalent Cation for Ultra‐Rate and Long‐Cycle‐Life Sodium Metal Batteries

ABSTRACT

Here, a multivalent cationic salt, indium trifluoromethanesulfonate (In(OTf) ₃ ), is introduced into a poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) quasi‐solid‐state polymer electrolyte (QSSPE). Due to the multivalent of In ³⁺ , which causes intense cation–dipole interactions between In ³⁺ and the −CF ₂ dipoles, these interactions drive the rotation of the backbone of the α‐phase chains, align all the −CF ₂ dipoles toward the cations, and thus significantly increases the β‐phase content. This transition increases both the dipole moment of polymer chains and the dielectric constant of polymer matrix, which shortens the Na ⁺ transport pathway, promotes the dissociation of NaClO ₄ , and restricts the mobility of ClO ₄ ⁻ . Consequently, the QSSPE exhibits high ionic conductivity (1.31 × 10 ⁻³ S cm ⁻¹ ) and Na ⁺ transference number (0.75). Additionally, whether at the anode or the cathode, In(OTf) ₃ preferentially decomposes, forming compact, thin and inorganic‐rich SEI and CEI that remarkably improves both the cycling stability and rate capability of cells. The Na||Na cell demonstrates stable over 1800 h. The Na||Na ₃ V ₂ (PO ₄ ) ₃ cell retains 93% capacity after 7000 cycles at 8 C and functions stably under −20°C and 80°C. The Na||Na ₃ V ₂ (PO ₄ ) ₂ O ₂ F cell can cycle stably for 1000 cycles at 2 C. Moreover, pouch cells also exhibit long‐cycle lifespans, verifying the practical potential of the QSSPE.