Research On Novel Aqueous Electrolytes And Their Applications In Energy Storage Devices

The essential safety of energy storage device can be realized by replacing organic electrolyte with aqueous electrolyte.Traditional aqueous electrolytes are mostly dilute metal salt solutions with a narrow electrochemical window（1.23 V）,which affects the selection of electrode materials.How to widen the narrow electrochemical window of aqueous electrolytes is a technical difficulty of aqueous battery.The key to solve this problem is to reduce the activity of free water in the aqueous electrolyte.The development of low cost and wide window aqueous electrolytes is the key to the research of aqueous battery.In this thesis,low-cost ultra-high concentration salt electrolyte of room temperature hydrated molten salt,hydrogel electrolyte based on room temperature molten salt and double cross-linked hydrogel electrolyte were designed and prepared,and innovative use of electron accelerator radiation cross-linked hydrogel electrolyte,and the physical,chemical and electrochemical properties of these electrolytes were characterized in detail,and and their applications in water storage devices were explored.The details are as follows:（1）A new type of aqueous electrolyte at room temperature molten salt（RTMS）was designed and prepared.RTMS contains almost no free water,which greatly reduces the activity of water and broadens the electrochemical window to 3.1 V.Molecular dynamics simulation was used to calculate that it has a special chain structure of NO₃^--Li-H₂O.NaCoHCF/Activated carbon（AC）and NaCoHCF/Perylene tetracarboxylic anhydride（PTCDA）water ion batteries assembled with RTMS electrolyte have excellent rate and cycling performance.The structure evolution and charge transfer mechanism of NaCoHCF electrode in RTMS were analyzed by XRD and XPS.The results show that reducing the activity of water in electrolyte is beneficial to the structure reversibility of NaCoHCF during charge and discharge.（2）In order to further reduce the activity of water,a polymer hydrogel electrolyte（E-RPE）based on RTMS was prepared by electron beam irradiation technique using a low-cost Polyethylene glycol dimethacrylate（PEGDMA）as the polymer matrix.The hydrophilic polymer framework immobilized the water molecules,which further reduced the activity of water in RTMS and the hydrogen evolution potential.The electrochemical window was widened to 3.1 V,and the ionic conductivity was as high as 4.1 ms cm^-1at room temperature.Using E-RPE as electrolyte,the NaCoHCF/AC water ion battery has not only excellent cycling stability and rate performance,but also improved its electrochemical stability at high temperature.（3）In order to further reduce the cost,a lower cost and biodegradable polyvinyl alcohol（PVA）was used as a hydrogel polymer material to replace PEGDMA,and the physical properties of PVA hydrogels under different electron beam radiation doses were explored.Rtms-pva hydrogel electrolyte was prepared by combining RTMS with PVA hydrogel prepared by radiation of 30 kGy by immersion method.The ionic conductivity of E-RPE was increased to 70.6 mS cm^-1,and its electrochemical window was about 2.5 V.Using 30 kGy RTMS-PVA as electrolyte,the assembled NaCoHCF/AC water ion battery has excellent performance,which further improves the cycling stability of NaCoHCF/AC water ion battery in E-RPE.（4）In order to give full play to the advantages of electron beam radiation technology and improve the mechanical properties of PVA hydrogel,PVA and glycerol（G）double crosslinking hydrogel electrolyte（PVA-G）was prepared without adding crosslinking agent.The physical and electrochemical properties of 30 kGy PVA-G were the best,which not only improved the mechanical properties of PVA hydrogel,but also improved the ionic conductivity as high as 22.8 mS cm^-1,and widened the electrochemical window to 2.51 V.The mixed zinc ion supercapacitor with 30 kGy PVA-G as electrolyte has a good rate performance,which broadened the application scenarios of preparing hydrogel electrolyte by electron beam radiation.