Research On High-voltage Aqueous Sodium Ion Batteries

Aqueous sodium ion batteries（ASIBs）offer multiple advantages such as good safety performance,lower production costs and environmentally friendly,hence they are recognized as ideal energy storage system.However,due to the inherent disadvantages of easy decomposition of aqueous solutions as electrolytes,effectively expanding the electrochemical stable voltage window（ESW）of ASIBs has become a challenging subject.In addition,compared with organic sodium ion batteries,the chemical reaction process of Na⁺intercalation/extraction in aqueous solution is more complicated.Therefore,the main challenge of ASIBs is to solve the problem of easy electrolysis of the electrolyte and to find a cathode material with a higher potential and a cathode material with a lower potential.This dissertation starts from the electrolyte,the anode and cathode materials,and introduces acetonitrile（AN）into the electrolyte.So that the battery to achieve a wider ESW and higher conductivity.A pair of anode and cathode materials suitable for the electrolyte were prepared and modified to improve the overall performance of ASIBS.In this paper,a mixed electrolyte NaClO₄（H₂O）₂AN_2.4 was prepared,with an ESW of 3.0V（-1.13～1.87 V vs SCE）and a high ionic conductivity.On this basis,Na₃V₂（PO₄）₃ and Na Ti₂（PO₄）₃ were used as the cathode and anode materials to prepare full cell.It is found that the mixed electrolyte NaClO₄（H₂O）₂AN_2.4 is fully applicable in the full battery system and has good electrochemical performance.In addition,in order to increase the discharge voltage of ASIBs,FeSe₂ with a lower reaction potential was used as the anode material.The electrochemical reaction mechanism of FeSe₂ in NaClO₄（H₂O）₂AN_2.4 electrolyt is similar to that in SIBs.During the charge and discharge process,the negative electrode generates Na₂Se,Fe and Na_xFeSe₃ intermediate products.Compared with FeSe₂,FeSe₂@rGO shows better electrochemical cycling performance.The FeSe₂@rGO and the cathode material Na₃V₂（PO₄）₂F₃are used to form a full cell.The electrochemical test shows that the highest discharge platform of the full battery is 1.8V and the average discharge voltage is 1.5 V.By increasing the working voltage of ASIBs,the energy density of the full battery can be further improved.