A Flexible Ionic Liquid Gelled PVA‐Li₂SO₄ Polymer Electrolyte for Semi‐Solid‐State Supercapacitors

Abstract

The development of fl exible energy devices is dramatically increasing the requirement of gel polymer electrolyte (GPE) with mechanical robustness and excellent transport effi ciency of ion or solute. Some GPEs such as poly(vinylidene fl uoride) (PVDF) with glass fi bers, [ 12 ] nonwoven fabrics, [ 13 ] etc. have been reported for fl exible batteries. There is a remarkable ions migration effi ciency in these GPEs, which provides breakthrough electrochemical performances. Poly(vinyl alcohol) (PVA) hydrogel is a widely used GPE substrate for supercapacitors. [ 5,14 ] However, current ionic conducting gels, which just consist of PVA hydrogels and inorganic salts, acid or alkali dissolved in water, are brittle and exhibit poor mechanical strength due to the damage of inorganic ions to the hydrogen bond between PVA polymer chains and water molecules. Furthermore, metal electrodes can be corroded by acid in the GPE during the charge-discharge process. Therefore, GPE with neutral salts is a promising new research fi eld for semi-solid-state supercapacitors. However, excess inorganic ions would infl uence the mechanical strength of the gels because of the coagulation with PVA chains in water. Consequently, the ionic conductivities of GPE are generally low (0.1-10 mS cm −1 ) due to the limitation of salts content (generally lower than 20 wt%) in gels. Up to date, the problem that inorganic salts cannot be added into gel polymer substrate in large quantities has not been settled.Common neutral GPE contains much water, and the potential window of the aqueous GPE is limited to the ideal maximum value of 1.23 V, usually used in the range of 0-0.80 V which also places restrictions on the application of such supercapacitors. And aqueous GPE cannot maintain a stable appearance with the gradual loss of water which also infl uences the electrochemical behavior of supercapacitors. [ 15 ] Ionic liquids (ILs) recently attain more attention in the applications of energy storage, such as semi-solid-state supercapacitors, because of their wide operation potential, high thermal and electrochemical stability as conducting medium relative to inorganic salts. However, their low conductivities restrict the electrochemical performance in semi-solid-state supercapacitors. [ 1,16,17 ] The ionic conductivity can be improved further with a wide operation electrochemical window after the addition of neutral inorganic salts in the GPE, which opens up new access to high-performance EDLCs, but related researches are lacked.

Na2SO4‐Polyacrylamide Electrolytes and Enabled Solid‐State Electrochemical Capacitors

“…Previous development of neutral pH polymer electrolytes relied on poly(vinyl alcohol) (PVA) as the polymer host, but there is potential incompatibility between sulfate salts and PVA that might implicate their long‐term stability. Although Li 2 SO 4 −PVA and Na 2 SO 4 −PVA have been adapted for solid‐state ECs, their ionic conductivities and long‐term performance stability are still unclear.…”

Dissolution–Crystallization Transition within a Polymer Hydrogel for a Processable Ultratough Electrolyte

“…Furthermore, among the three supercapacitors, the A 0 D 15 –NaAc 1.2 based supercapacitor presents an excellent energy density of 28.3 Wh kg −1 at a power density of 200 W kg −1 , much greater than that of the A 15 D 0 –NaAc 1.2 based supercapacitor (19.0 Wh kg −1 ) and the A 7.5 D 7.5 –NaAc 1.2 based supercapacitor (25.7 Wh kg −1 ) (Figure g). All these supercapacitors offer better performance than most aqueous supercapacitors in energy density because of their higher operating voltage . For practical application purposes, we also evaluated the leakage current and self‐discharge of the A 0 D 15 –NaAc 1.2 based supercapacitor.…”

An Omni‐Healable Supercapacitor Integrated in Dynamically Cross‐Linked Polymer Networks

“…The key to the fabrication was the use of poly(vinyl alcohol) grafted with N,N,N ‐trimethyl‐1‐(oxiran‐2‐yl)methanaminium chloride (PVA‐ g ‐TMAC) that was synthesized through a ring‐opening reaction (Figure S1, Supporting Information) . The grafting of quaternary ammonium groups effectively reduces the coagulation of PVA chains caused by the salt‐out effect, which improves the malleability and salt‐tolerance of the resulting copolymer. At first, a hydrogel electrolyte was prepared by cross‐linking PVA‐ g ‐TMAC via dynamic diol‐borate ester bonding in the presence of KCl and borax (Figure a) .…”