Preparation And Electrochemical Performance Of High Performance Prussian Blue Analogues Cathode Materials For Sodium-ion Batteries

In recent years,electric energy storage technology has received extensive attention due to the rapid development of renewable energy and smart grid.Among various candidates,sodium ion batteries?SIBs?are attracting increasing attention as a complement or an alternative to lithium ion batteries?LIBs?in the applications of large-scale energy storage systems?ESSs?because of the the practically inexhaustible,ubiquitous and low-cost sodium resources as well as the similar“rocking-chair”mechanism as LIBs.High-performance cathode materials are crucial for the development of SIBs,among which Prussian blue analogues?PBAs?possess the advantages of abundant resources,ease of synthesis and environmental friendliness.Furthermore,given the unique three-dimensional channels structure of PBAs,the reversible extraction-insertion of sodium ions is accessible,enabling a high theoretical capacity and thus exhibiting a good application prospect in SIBs.This thesis focuses on the promising materials of PBAs,including Na₂MnFe?CN?₆?MnHCF?and Na₂FeFe?CN?₆?FeHCF?.The specific research contents are as follows:?1?MnHCF is desirable because of its high working voltage,high specific capacity,as well as its abundant element resources and easy preparation of sodium-rich structure.However,MnHCF as cathode material suffers from poor cycling stability and unsatisfactory rate capability due to inferior intrinsic conductivity,phase transition and transition metals dissolution,extremely limiting its practical application.To solve above issues,the MnHCF@PEDOT composites were successfully prepared by a facile in-situ polymerization method.On one hand,the phase transition and transition metals dissolution are greatly suppressed,thus rendering the prolonged cycle life.On the other hand,the capacitance storage behavior is also enhanced,enabling the improved rate performance.Consequently,the composite exhibits a high capacity of 147.9 mAh g^-1 at0.1 C,90.2 mAh g^-1 at a high rate of 20 C,and 78.2%capacity retention after 1000cycles at 10 C.Furthermore,even at a low temperature of-10?,MnHCF@PEDOT still delivers a high capacity of 87.0 mAh g^-1 and maintains 82.2%after 500 cycles.?2?FeHCF as a cathode material for SIBs generally has a bottleneck problem of low initial sodium content.FeHCF with different initial sodium contents,micromorphologies and properties were synthesized by controlling the synthesis temperature and the amounts of NaCl addition.Specifically,FeHCF exhibits decreared defects and increased sodium contents along with the enhancement of synthesis temperature.Furthermore,the electrochemical performance of FeHCF is optimal when the amount of NaCl added is 1 mol L^-1.Finally,sodium-rich FeHCF with the formula of Na_1.89Fe[Fe?CN?₆]_0.93?_0.07·2.31H₂O(?stands for the[Fe?CN?₆]^4-vacancies)was obtained under the condition of 100?and 1 mol L^-1 NaCl,with charge and discharge specific capacities of 160.3 and 146.6 mAh g^-1.