【作者】 王伟；

【导师】 赵强； 李峥；

【作者基本信息】 电子科技大学 ， 工程硕士（专业学位）， 2021， 硕士

【摘要】 随着绿色能源的发展,人们对大规模储能设备的需求日渐提升。锂离子电池由于价格较高,因此不适用于大规模储能应用。与锂元素相比,钠元素具有价格便宜并且分布广泛的优点。此外,钠元素与锂元素化学性质相近。在此情况下,钠离子电池作为新一代离子电池成为研究热点。但是,由于钠离子半径比锂离子半径大,导致传统锂离子电池正极材料并不适用于钠离子电池,所以需要开发全新的钠离子电池正极材料。普鲁士蓝材料具有开放的框架结构,能提供存储钠离子的空间,因此作为钠离子电池正极材料成为研究热点。在众多普鲁士蓝材料中,低成本和高能量密度的亚铁氰锰钠（NaMnHCF）是钠离子电池有希望的正极材料。然而传统的共沉淀方法合成的NaMnHCF不仅含有较多的缺陷和结晶水,同时材料中的Mn³⁺具有明显的Jahn-Teller效应,此外,NaMnHCF还容易与电解液发生副反应,这些会明显影响材料的电化学性能。针对以上所述,本论文开展了以下的工作:（1）本研究从络合剂作用机理出发,通过优化络合剂的添加方式,大幅降低合成过程中络合剂的浓度,从而在保证材料结构完整的同时,降低材料的颗粒尺寸,实现了NaMnHCF材料电化学性能的进一步提升。在此基础上,本研究探究了颗粒团聚以及结晶水对NaMnHCF前期活化过程的影响。对于结晶性高的NaMnHCF材料而言,颗粒团聚对材料的前期活化过程影响很小,但是,通过对NaMnHCF材料进行脱水处理,本研究成功消除了材料的活化过程,并且脱水后的材料其电荷转移阻抗更低,这是由于结晶水会影响NaMnHCF材料氧化还原中心的活性,同时,在材料中钠离子含量较高的情况下,结晶水对钠离子传输过程的阻碍更加明显。此外,不同圈数的CV测试表明NaMnHCF的前期活化过程实际上是材料的脱水过程。（2）本研究采用过渡金属离子交换法对NaMnHCF材料进行改性。将NaMnHCF材料在含有M²⁺（M=Ni、Co、Cu、Zn等元素）的水溶液中进行搅拌,在不改变形貌的情况下NaMnHCF材料会在表面生成一层含有M元素的改性层。改性层具有抑制NaMnHCF材料与电解液发生副反应的作用,同时还有利于钠离子在材料中的传输。改性后的材料在1C的电流密度下循环1000圈仍具有80 m A h g^-1的比容量,并且在10C的电流密度下可以提供86.7 m Ah g^-1的比容量,相比于未改性的材料而言(1C下循环1000圈后为29 m Ah g^-1和10C下为78.3 m Ah g^-1),其长循环稳定性和倍率性能均有明显提升。更多还原

【Abstract】 With the development of green energy,the demand for large-scale energy storage devices is increasing.Because of the high cost,lithium-ion batteries are not suitable for large-scale energy storage applications.Compared with lithium,sodium has the advantage of being cheap and abundant in the nature.In addition,the chemical properties of sodium and lithium are similar.In this case,sodium ion battery as a new generation of ion battery has become a research hotspot.However,because the radius of sodium ion is larger than that of lithium ion,the traditional cathode materials for lithium ion batteries are not suitable for sodium ion batteries.Therefore,new cathode materials for sodium ion batteries need to be developed.Prussian blue material has an open frame structure,which can provide suitable voids for storing sodium ions,so they have become a research hotspot as cathode materials for sodium ion batteries.Among many prussian blue materials,sodium manganese hexacyanoferrate（NaMnHCF）with low cost and high energy density is show grate promise.However,the NaMnHCF materials synthesized by traditional coprecipitation method contain significant number of defects and crystal water,and the Mn³⁺has obvious Jahn-Teller effect.In addition,NaMnHCF is prone to side reactions with the electrolyte,which will significantly affect the electrochemical performance of the material.In view of the above,the following studies were carried out:（1）By optimizing the addition method,the concentration of the complexing agent in the synthesis process was significantly reduced.The synthesized NaMnHCF shows the advantages of high structure integrity and small particle size,which further improves the electrochemical performance.In addition,the effects of particle agglomeration and crystal water on the electrochemical properties of NaMnHCF were studied.For those with high crystallinity,particle agglomeration has a certain influence on the electrochemical properties,but it is not the most dominant factor.However,by dehydrating the NaMnHCF material,we successfully eliminated the activation process of the material,and the dehydrated material has a lower charge transfer impedance because the crystal water will adversely affect the activity of the redox center of NaMnHCF.At the same time,when the sodium ion content is high,the crystal water is more likely to hinder the sodium ion diffusion.In addition,comparision of the CV tests indicated that the activation process of NaMnHCF material actually involve the dehydration process of the material.（2）NaMnHCF material was modified by transition-metal ion exchange method.After the NaMnHCF powders were stirred in an aqueous solution containing M²⁺（M=Ni,Co,Cu,Zn,etc.）,a coating layer containing M element will be formed on the surface of NaMnHCF material.The modified layer can inhibit the side reaction between the electrode and electrolyte,and is also beneficial to the transport of sodium ions in the material.It is found that the surface modified NaMnHCF still has a specific capacity of80 m Ah g^-1after 1000 cycles,and can provide a specific capacity of 86.7 m Ah g^-1at a current density of 10C.Compared with the unmodified material(29 m Ah g^-1after 1000cycles at 1C and 78.3 m Ah g^-1 at 10C),the long-term stability and the rate performance of the modified NaMnHCF were significantly improved.更多还原