Microstructure Design And Electrochemical Properties Of Functinal Polymer Gel Electrolytes

To date the low mechanical performance,ionic conductivity,operating voltage window and poor safety of gel electrolytes severely limited the property of energy storage devices,thus calling for new breakthrough in performance.Herein,we report the strategy for design and construction of unprecedented functional polymer gels,to overcome the performance barriers of electrolytes and enable investigation on microstructures and properties of supercapacitors.A type of self-healing stretchable hydrogels(PAD/H₂SO₄)was fabricated based on the ionic associations between–COO^-/SO₃^-and quaternary ammonium groups as well as hydrogen bonds.By adjusting interactions and dynamic structures,the zwitterionic supramolecular PAD/H₂SO₄ electrolyte exhibits high tensile strength(1.80 MPa)and large stretchability(2900%).Moreover,the self-healing efficiency is over 90%after breaking.The ionic conductivity of the PAD/H₂SO₄electrolyte is 57mS cm^-1 at room temperature,and is stable even after cyclic cutting/healing.Acting as electrolyte,conducting polymer PANI was in situ polymerized onto the entire surface of the PAD/H₂SO₄ to prepare the integrated all-gel-state supercapacitor(PAD/H₂SO₄-PANI).The integrated design not only improves the transmission efficiency of electrons and ions,but also avoids the disconnection of electrode and electrolyte during physical deformation or damage.Furthermore,the integrated supercapacitor can be stretched to 20 times of its original size,and is self-healable at room temperature.The supercapacitor achieves excellent areal capacitance of 430mF cm^-2 at 0.5mA cm^-2 and rate capability,which can be repeatable for at least 50 cutting/healing cycles.A major stumbling block in large-scale adoption of high-energy-density electrochemical devices has been safety issues.Here methyl cellulose(MC)is used as stimuli-responsive material in the smart electrolyte,for its capable of thermo-reversible gelation in aqueous solution at elevated temperature.Along with temperature increasing,the electrolyte undergoes a thermally-activated sol-gel transition,which results in a decreased ions concentration and broken circuit,since the hydrophobic segment in MC molecular is tangled to inhibit the motion of ions.The practicability of the thermal switching behavior in electrochemical storage devices was demonstrated by fabricating symmetric coin-type supercapacitors using activated carbon(AC)as electrodes,while drastically decrease in capacity of approximately 85%loss is observed due to absence of ions upon heating at 70?.To broaden the operating voltage window and thus improving the energy density of Micro-supercapacitors,self-stand ionogels are designed based on the PEO-Li⁺metal-ligand coordination and hydrogen-bonding dual-dynamic network.As a result,limiting potential of about-4 to 4 V and excellent thermal stabilities above 380 and 350?(Figure 5e)can be attained when BMIMTFSI and BMIMBF₄ are confined into ionogels via hydrogen bonding between the ILs and the polymer matrix,making them promising alternatives for devices with extreme temperature tolerance and high operating voltage window.Owing to the dual-dynamic network,the ionogels exhibit high tensile strength and large stretchability as well as high mechanical healing efficiency(up to 96.5%).The ionic conductivities of the BMIMTFSI-P and BMIMBF₄-P electrolytes are 4.7 and 1.07mS cm^-1 at room temperature,and are stable even after cyclic cutting/healing.Based on the ionogels,a novel flexible micro-supercapacitor prototype is proposed benefiting from the substrate-alterable DIW technology,whereas the electrode material is directly printed onto the stretchable and self-healable ionogel that acts as a flexible substrate and gel-electrolyte simultaneously.The operating voltage window of the self-healable micro-supercapacitors is up to 3V.According to the Ragone plot,the maximum energy density reaches 81.88?Wh cm^-2 at a power density of 0.75mW cm^-2.