Design Of Zinc Ion Hydrogel Electrolytes And The Application In Flexible Energy Storage Devices

Miniaturization,integration and flexibility are the tendency of future consumer electronics,which calls for strict requirements for the energy density,safety and shape deformability of energy storage devices.Recently,aqueous Zn metal batteries have received extensive attention for their characteristics of low cost,high safety and volume energy density.However,the bottlenecks in dendrite growth,passivation,and corrosion of Zn anode as well as the utilization and cycling reversibility of cathode vastly restrict their practical application.The stability and compatibility to electrode of electrolytes are crucial for the electrochemical performances of the Zn ion batteries.One of the main solutions is to utilize hydrogel electrolytes.On the one hand,they could serve as separator and electrolyte simultaneously,on the other,improve the stability of electrodes and cycle performance of the batteries with extended application into flexible energy storage.Nowadays,developing zinc ion hydrogel electrolytes with high ionic conductivity,excellent mechanical performance and wide thermal adaptability has attracted extensive attention.In this thesis,a series of researches have been carried out based on gelatin natural polymer matrix.The main contents and conclusions of the article are as follows:?1?The design of stable interface between gelatin hydrogel electrolyte and electrodes as well as performance research of high-safety solid-state Zn-Li Mn₂O₄ cells:Taking advantage of the unique thermo-reversibility of the gelatin,stable solid-state Zn ion batteries with intact contact between GHEs and electrodes was fabricated by in situ gelation of the GHE coated on the electrodes.The electrochemical tests of Zn in liquid electrolytes and GHEs show that the corrosion of Zn in GHE descends dramatically and the corresponding Zn symmetric cells are able to cycle stably for over 1200 h.In comparison with liquid Zn-LMO full cells,the solid-state ones exhibit obviously lower self-discharge and largely improved cycle stability.Furthermore,they deliver excellent safety and flexibility under a series of extreme conditions indicating the great potential for wearable device applications.?2?An inorganic salt reinforced Zn²⁺-conducting solid-state electrolyte for ultra-stable Zn metal batteries:In addition to thermo-reversibility,gelatin exhibits Hofmeister effect and inorganic salt solutions show a significant effect on its physical properties.GSE-x were prepared by immersion in salt solution at various concentrations.When the salt concentration increases,the water content lower,while mechanical strength and thermo-stability enhance.Among of them,GSE-2.5 exhibits balanced ionic conductivity(8.95 m S cm^-1),tensile strength?2.78 MPa?and melting temperature?54.5°C?.The assembled Zn symmetric cell and Zn-Mn O₂ full present excellent electrochemical performance.Furthermore,the fabricated solid-sate batteries deliver superior safety and stability under harsh conditions such as being cut,immersed in water,bent,hammered and drilled.?3?Ultra-stable gelatin/Alginate-Zn composite hydrogel electrolyte synergistically reinforced by inorganic salt soaking strategy:Based on the Hofmeister effect of gelatin in sulfate solution and ionic crosslinking of alginate sodium with multi-valent cations,a double network composite hydrogel electrolyte with good mechanical performance and high thermo-stability,ionic conductivity was designed.The research results prove that composite hydrogel exhibits higher thermo-stability than gelatin single hydrogel?G₅A₀?,and when the alginate solution?3 wt%?content increases,the ionic conductivity enhances with mechanical strength reducing.Especially,G₂A₃ having proper ionic conductivity(7.55 m S cm^-1)and mechanical strength?1.4 MPa?endows the plating/stripping of Zn electrode with high coulombic efficiency and reversibility.Furthermore,in comparison with G₅A₀ and G₃A₂,the solid-state Zn-Li Fe PO₄ full cell based on G₂A₃ delivers excellent rate performance and cycling stability.?4?Anti-freezing gelatin organo-hydrogel electrolytes for flexible low-temperature tolerant aqueous Zn ion batteries:By utilizing binary solvent?EG/H₂O?dispersion medium,a stable and low temperature tolerant gelatin organo-hydrogel electrolytes?GOHEs?for Zn ion batteries was prepared.Their ionic conductivities are obviously higher than that of gelatin hydrogel electrolytes?GOHE-0?at-20°C,whose ionic conductivity is only 0.61 m S cm^-1.The results of electrochemical tests at different temperature show that the assembled Zn/GOHE-2/Zn symmetric cell cycles stably from25 to-20°C,whereas the polarization voltage of Zn symmetric cell based on GOHE-0 suffers from sharply increasing.In comparison with Zn/GOHE-5/LFP,the Zn/GOHE-2/LFP full cells deliver superior rate performance and cycling stability,exhibiting a capacity retention of 93.6% for 5000 cycles at 200 m A g^-1.