Ionic Liquid-Softened Polymer Electrolyte for Anti-Drying Flexible Zinc Ion Batteries

Abstract

Using solid polymer electrolytes has been proven to be an efficient strategy to address the metal dendrites and pursuing high-voltage performance. Polyethylene oxide (PEO), as a popular polymer matrix, hardly works for zinc ion batteries due to its poor zinc ionic conductivity and the poor interfacial adhesion. Here, an ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([Emim]­OTF), was applied as a plasticizer to tune the room-temperature ionic conductivity and mechanical properties of PEO membrane electrolyte. Additional nanofillers ZnO were utilized to enhance the plasticity and modulus. With an optimized composition, the membrane exhibits a high modulus and soft mechanics, which can facilitate the reversible stripping/plating of Zn without formation of Zn dendrites. The optimized polymer electrolyte achieved an ionic conductivity of 2.3 × 10–3 S cm–1 at room temperature with a softness of 5.1 mm. By applying the resulted soft membrane electrolyte for a Zn-MnO2 battery, a capacity of 137 mAh g–1 is achieved at 30 mA g–1 even without the contribution from H+. Such an electrolyte also works for Prussian blue analogue cathodes. Importantly, the addition of [Emim]­OTF can enhance the soft contact with the electrodes, and a stable output is delivered under severe deformations for the assembled flexible devices.

Revitalizing zinc-ion batteries with advanced zinc anode design

“…However, the low ionic conductivity (o0.1 mS cm À1 ) and poor interfacial contact of SPEs at room temperature limit their further development. 171,174,175 Research has shown that the crystallinity of SPEs could be significantly reduced and ionic conductivity greatly enhanced by (1) adding inorganic nanofillers (Al 2 O 3 , SiO 2 , TiO 2 , ZnO) to lower the phase transition temperature, [176][177][178][179] and (2) blending with low molecular weight polymers likes polyvinylidene fluoride (PVDF) 23 and branched aramid nanofibers. 180 Zhi's group 23,179 prepared a polyvinylidene fluoride-hexafluoropropylene/polyethylene oxide (PVDF-HFP/PEO) all-solid polymer electrolyte with high ionic conductivity (16.9 mS cm À1 ), excellent flexibility and mechanical properties, which significantly inhibited both the HER and dendrite growth.…”

“…171,174,175 Research has shown that the crystallinity of SPEs could be significantly reduced and ionic conductivity greatly enhanced by (1) adding inorganic nanofillers (Al 2 O 3 , SiO 2 , TiO 2 , ZnO) to lower the phase transition temperature, [176][177][178][179] and (2) blending with low molecular weight polymers likes polyvinylidene fluoride (PVDF) 23 and branched aramid nanofibers. 180 Zhi's group 23,179 prepared a polyvinylidene fluoride-hexafluoropropylene/polyethylene oxide (PVDF-HFP/PEO) all-solid polymer electrolyte with high ionic conductivity (16.9 mS cm À1 ), excellent flexibility and mechanical properties, which significantly inhibited both the HER and dendrite growth. Solid-state ZIBs based on PVDF-HFP/PEO exhibit excellent cycling stability and rate capability, enabling the operation in a wide temperature range from À20 1C to 70 1C.…”

Advances in polymer electrolytes for solid-state zinc–air batteries

“…More importantly, polymer electrolytes with high softness properties can enhance soft contact with the electrode and still provide a stable output in the event of severe deformation of the assembled flexible device. 132,133 It is feasible to confer high binding properties on solid polymer electrolytes by additives or modifiers or by substance bonding reactions. Zincophilic additives can induce 16 111 uniform zinc deposition during battery operation, which can effectively promote bonding and stability between interfaces.…”

High-performance solid-state zinc-ion batteries enabled by flexible and highly Zn2+ conductive solid-polymer electrolyte

“…24,29 Besides, the addition of EMIM Otf IL causes a phase transition of PVA-inter-PEG from crystalline to amorphous, facilitates the segmental motions of polymer chains and enhances the Zn 2+ conductivity. 22,24,[30][31][32] Also, the EMIM + of ionic-liquid may compete with CF 3 SO 3 − , release Zn 2+ from the zinc salt, and enhance the Zn 2+ concentration for conduction. 24 Therefore, the higher the concentration of EMIM Otf IL, the higher the Zn 2+ conductivity that could be expected.…”