Study Of Prussian Blue And Manganese Oxide Cathode For Aqueous Sodium-ion Battery

Aqueous sodium ion batteries have obvious advantages aiming for low-cost energy storage application,since they are composed of resource-rich sodium based active materials and high safety aqueous electrolytes.The cathode material with large specific capacity and high stability is one of the bottlenecks restricting the development of aqueous sodium ion batteries.In this study,co-doped Prussian blue cathode materials were synthesized and their stability was improved with solid hydrogel electrolyte.Furthermore,aqueous sodium ion cell was developed using highly active a-MnO₂ material as the cathode and Na⁺pre-intercalated sodium phosphate as anode.The electrochemical properties of the novel cell were investigated.The main research contents and results obtained in this study are as follows:?1?Preparation of co-doped Prussian blue cathode materials and the stability improvement in gel electrolytes.A series of Prussian blue compounds co-doped by Co-Ni,Fe-Ni and Mn-Ni pairs were prepared by a co-precipitation method.The as-obtained materials were assembled with sodium titanium phosphate anode and their electrochemical performance was characterized in 1.7mol sodium sulfate electrolyte.For the Mn-Ni co-doped Prussian blue compounds,their specific capacity can be increased by the change of the valence of Mn ion meanwhile the structural stability of Prussian blue can be improved by the doping of Ni.These can increase the specific capacity and improve the cycling performance for the co-doped material.Based on the comparison of the electrochemical performance of different Mn and Ni doping ratio?Mn:Ni=1:1 Mn:Ni=1:5 Mn:Ni=1:4?,an optimal ration of Mn:Ni=1:4 was chosen.The specific discharge capacity of the compound reaches at 138 m Ah/g.On the other hand,due to the potential dissolution of Prussian blue materials in aqueous electrolyte,the specific capacity of the cell decreased upon the cycles.In the study,the highly dispersed gas phase SiO₂ was mixed with electrolyte salt to form a solid gel sodium ion electrolyte.The Mn-Ni co-doped Prussian blue material was cycled with the as-proposed the solid-gel electrolyte.The results show that the gel electrolyte could greatly hindered the dissolution of Prussian blue material.The initial capacity of the cell was 138m Ah/g and the capacity retention rate remained90%after 450 cycles.?2?Design and characterization of a novel sodium ion cell with highly active?-MnO₂ cathode and Na⁺pre-intercalated sodium phosphate anodeAqueous sodium ion battery based on manganese oxide and sodium titanium phosphate has obvious advantage in cost.In this study,a novel sodium ion cell was developed and fabricated with manganese dioxide as cathode and sodium titanium phosphate as anode.Firstly,the cell composed of sodium titanium phosphate and Li Mn₂O₄ was electrochemically charged and discharged.As the charging voltage was set as 1.85v,a Na+pre-intercalated sodium phosphate was obtained.The sodium rich titanium phosphate anode was assembled with the as-prepared?-MnO₂with high activity.The 1.7mol/l sodium sulfate solution was used as the electrolyte.To improve the stability of manganese oxide based active materials,0.1mol/l manganese sulfate was added into the above electrolyte.The specific capacity?based on manganese oxide?of the cell can reach 80m Ah/g with a good cycling stability.A high capacity retention rate can be observed at more than 100 cycles.The X-ray diffraction analysis of the reaction products shows that there is sodium ion intercalation reaction in the charge and discharge process for the?-MnO₂active material,forming sodium manganese-sodium compound.This result indicates that the designed aqueous sodium-ion cell based on manganese oxide cathode and sodium rich titanium phosphate anode has a high reversibility of sodium ion intercalation/extraction.