The Properties And Application Of Sodium Alginate In Aqueous Zinc Ion Batteries

The safety problem and high price of organic electrolyte restrict the further development and wide application of traditional lithium-ion batteries.Compared with organic electrolyte,aqueous electrolyte has a broader development prospect because of its safety and environmental friendly.Aqueous zinc-ion batteries have many advantages,such as large amount of zinc,environment friendly,high theoretical specific capacity,low redox potential,and have attracted great interests.However,there are still some problems need to be solved.For example,battery binder needs to be dissolved in organic solution,and the corrosion of hydrolyzed solution and dendrite could lead the short circuit.If the above two problems can be overcome effectively,zinc-ion batteries will have greater development.In this paper,sodium alginate（SA）was applied to prepare the binder and gel electrolyte for zinc-ion batteries.（1）Firstly,the water soluble SA is employed as a binder in aqueous Zn batteries,because SA could cross-link with Zn²⁺ion to form a water insoluble and mechanical super strong binder for electrodes.An aqueous Zn||Li Fe PO₄ cell is used to demonstrate SA binder for Li Fe PO₄ cathodes.At the same concentration,SA has higher viscosity than PVDF.FT-IR showed that SA and Zn²⁺coordinated.The Contact Angle test showed that the electrode electrolyte prepared by SA had better wettability.The SEM of the positive electrode before and after the cycle showed that the SA electrode plate was intact,and the PVDF electrode plate had cracks.The capacity retention of the SA electrode at 0.2C is 93.7%,while that of the PVDF electrode is only 84.7%.When the temperature drops to-5?C,the capacity retention of the SA electrode（97.3%）is 5%higher than that of the PVDF electrode（92.3%）.EIS results show that SA electrodes have lower impedance than PVDF electrodes.（2）In the second section,organic-inorganic gel electrolyte was prepared from polysilicate acid hydrolyzed and SA.The Zn||Li Fe PO₄ cell were assembled with the Li Fe PO₄positive electrode sheet containing SA binder.The ionic conductivity of the electrolyte is1.144×10^-2 S/cm,the fracture stress is 6.7 MPa,the electrochemical window is 0～2.435V,and the flame retardancy is good.The Zn-Li Fe PO₄ cells were assembled with this electrolyte and cycled for 300 cycles at 1 C,with a capacity retention rate of 74.9%.SEM and XRD tests showed that the gel electrolyte could effectively inhibit the generation of zinc dendrite and improve the performance of the batteries.