Syntheses And Performance Study Of Ionic Conductors(H~+,Li~+)

The gradual development of electrochemical energy devices with high energy density and high safety performance provides an effective strategy for solving the energy crisis.The ionic conductors,as the key component of these energy devices,determine the storage and transfer of ions within these energy devices,thereby affecting their final performance.Traditional ionic conductors have low conductivity,low safety factor,and high interface resistance,which are difficult to meet the current requirements for high-energy-density energy devices.Therefore,it is imminent to design and synthesize new ionic conductor materials.In this thesis,aiming at the fast ionic conductors,ionic conductors with high ionic conductivity and stable performance are prepared by improving the concentration of transportable ions,constructing the ionic conduction network,and promoting the dissociation of ions.In addition,some strategies,such as in-situ solidification and polymer coating,are used to reduce the interface impedance of energy devices,thereby improving the electrochemical performance.The specific research ideas are as follows:1.A new type of proton conductors,amorphous chromium oxyhydroxide,Cr O（OH）·x H₂O,is synthesized by in-situ hydrolysis of metal salt by sol-gel method.Cr O（OH）·x H₂O has a high water absorption value of 450 mg g^-1,which is helpful for the trapping of a large number of water molecules and the construction of the continuous and ordered hydrogen bond network.At 90°C and 98%relative humidity,Cr O（OH）·x H₂O achieved an ultra-high proton conductivity of 0.31 S cm^-1with an activation energy of 0.39e V,following the proton hopping mechanism.Then,as a proton conducting filler,Cr O（OH）·x H₂O is added to sulfonated polyetheretherketone（SPEEK）to form SPEEK-Cr O（OH）membrane,for studying the application potential of Cr O（OH）·x H₂O in proton exchanging membrane.The composite membrane shows a proton conductivity comparable to that of commercial Nafion,0.17 S cm^-1at 80°C,with no decrease for over 36h.This work sheds light on a simple and feasible strategy to prepare metal oxyhydroxides as efficient proton conductors.2.In this chapter,polyoxometalates（POMs）with the proton conduction properties and redox properties are used to prepare solid polymer electrolytes,to synergistically improve the capacitance and energy density of solid-state supercapacitors（SCs）with active polyaniline electrodes.Then researching the electrochemical matching activity between the types of POMs(H₃PMo₁₂O₄₀and H₃PW₁₂O₄₀)and the electrode activity,and it is found that the molybdenum-based H₃PMo₁₂O₄₀has higher redox activity,and can provide a higher pseudo-capacitance of SCs together with polyaniline.The interfacial resistance of SCs is greatly reduced by in-situ coagulation of the electrolyte at the electrodes.Taking advantage of the high proton conductivity of H₃PW₁₂O₄₀and high redox activity of H₃PMo₁₂O₄₀,the SCs with the mixed H₃PMo₁₂O₄₀&H₃PW₁₂O₄₀as electrolytes have a capacitance of 7.69 F cm^-2(3840 F g^-1)at a current density of 0.5 m A cm^-2and an energy density of 533μWh cm^-2(266.6 Wh kg^-1).In addition,benefiting from the abundant hydrogen bond network between POMs and polymers,POMs-based electrolytes exhibit excellent self-healing ability.This work improves the capacitance of solid-state supercapacitors by using molecular polyoxometalates as proton conducting and redox electrolytes,and the strategy is also applicable to other energy devices.3.The dissociation effect of zwitterions（MIMPS）on polyoxometalates（POMs）is used to improve the proton conductivity of polyoxometalate-based electrolytes and further improve the capacitive performance of polyaniline supercapacitors.MIMPS can promote the dissolution and dissociation of POMs in polymer solutions,releasing more mobile protons,which is conducive to the rapid proton transport.The supercapacitors with MIMPS have a higher capacitive performance with an areal capacitance of 13 F cm^-2at a current density of0.5 m A cm^-2,while the areal capacitance of the capacitors without MIMPS is only 9.5 F cm^-2.In addition,supercapacitors with MIMPS have a lower interfacial impedance,indicating that the adding of MIMPS can not only achieve extremely high conductivity,but also reduce the conductive interface impedance.This work provides a new strategy for optimizing the overall performance of polyoxometalate-based electrolytes in supercapacitors.4.In this chapter,addressing the low conductivity and high interfacial impedance of solid electrolytes,using covalent organic framework（TPBD）and polyethylene oxide（PEO）to preparate a solid-state electrolyte（TPBD-Li PF₆@PEO）,and then applying it to solvent-free solid-state Li-ion batteries.Solid-state NMR experiments and density functional theory calculations indicate that the strong interaction between the-C=O sites in TPBD and Li⁺ions greatly promote the dissociation of Li PF₆.The coating of PEO polymer reduces the grain boundary resistance between ionic conductors,optimizes the Li⁺ion transport network,and improves interfacial ion transport in solid-state batteries.At room temperature,TPBD-Li PF₆@PEO offers a high ionic conductivity of 0.543 m S cm^-1.The Li Fe PO₄|TPBD-Li PF₆@PEO|Li battery with no added liquid electrolyte exhibits a specific capacity of 140 m Ah g^-1at 0.2 C and a coulombic efficiency of 99.6%after 200 cycles at room temperature.This work provides practical ideas and suggestions for the preparation of solid-state electrolytes and the development of solid-state energy devices.