Among the candidate batteries, sodium-ion batteries are in the spotlight because of their sufficient, low-cost, and widely distributed sodium resources. Layered transition metal oxides exhibit intrinsic structural instability owing to multiple phase changes. The low theoretical capacity of polyanionic compounds restricts their future application, and organic cathode materials are easily dissolved in the electrolyte and have poor conductivity. Fortunately, Prussian blue and its analogs (PB and PBAs) cathode materials show extraordinary potential because of their three-dimensional rigid open framework, high theoretical specific capacity, adjustable structure, and facile synthesis. However, the Fe(CN)6 vacancies and coordination water inevitably generated in the crystal during synthesis limit its further application in energy storage. To solve the above problems, most researchers have optimized the intrinsic structure to improve the quality of the crystal or focused on modifying the surface to enhance the interface stability. Considering the structure-properties relationship, this paper first discusses the PB and PBAs' chemical composition and crystal structure. On this basis, strategies for optimizing the structure of PB and PBAs were analyzed from three aspects: material synthesis, ion doping, and unique structure design. In addition, the latest research progress on the modification of PB and PBA materials is elaborated. Moreover, the future development prospects are discussed, to provide a theoretical reference for developing higher-performance PB and PBAs materials.
Keywords:sodium ion battery
;
prussian blue analogues
;
structure construction
;
structural optimization
CHEN Na. Research progress on the construction and optimization of Prussian blue material structure for sodium-ion batteries[J]. Energy Storage Science and Technology, 2023, 12(11): 3340-3351
例如,过渡金属氧化物Na x MO2(M=Mn、Co、Ni、V、Fe等过渡金属元素)比容量较高,但因其在电极反应过程中频繁的相变以及较差的空气稳定性,导致电池的循环稳定性差[10-11];聚阴离子类化合物Na x M y (X a O b )zZ w (M=Fe、V、Ni、Co等过渡金属元素;X=P、Si、S等非金属元素;Z=F-、OH-等阴离子),虽然有较为合适的结构和适合Na+脱嵌的较大孔隙,但是低的电导率和电池比容量限制了其在钠离子电池储能领域的进一步应用[12];有机正极材料理论比容量高、来源丰富、环境友好,但是易溶解在有机电解液当中且自身导电性较差[15-16]。幸运的是,近些年研究人员通过改变普鲁士蓝(PB)的化学组成、骨架结构等发现了一系列具有高理论比容量(170 mAh/g)和刚性三维骨架结构的普鲁士蓝类似物(PBAs)。PBAs可调节的结构和简单的制备方法使得其成为最有潜力的正极材料之一[20-24]。
Fig. 1
The schematic illustration of optimizing PB and PBAs
1 PB及PBAs的基础结构
PB和PBAs的化学组成可以表示为A x MA[MB(CN)6] y·ϒ(1-y)·nH2O,0≤x≤2,0<y≤1,典型晶体结构如图2(a)所示[20]。其中A表示Na+、K+等碱金属或者碱土金属中的一种或者几种,MA和MB表示过渡金属元素中的一种或者几种,ϒ表示MB(CN)6空位,H2O表示结晶水、吸附水和沸石水。MA和MB可以是一种过渡金属元素,都是铁时则为典型的PB,主要通过它们的价态来区分。中心离子周围配体的强度决定过渡金属离子的自旋态,低自旋态MB与C相连,高自旋态MA与N相连,MAN6和MBC6两个八面体由—CN—连接共同组成了PBAs的三维刚性开放骨架,为Na+的快速运输提供了合适的通道。
图2
Pb和PbAs骨架的晶体结构示意图,完整A x MA[MB(CN)6] (左) 及理想缺陷的A x MA[MB(CN)6]0.75·ϒ 0.25·nH2O (右) 的晶体骨架,理想缺陷每个晶胞中存在25%Fe(CN)6 空位[20]
Fig. 2
Left: An intact A x MA[MB(CN)6] framework without structural defects, Right: An ideally defective A x MA[MB(CN)6]0.75·ϒ 0.25·nH2O framework with 25% Fe(CN)6 vacancies existing in each unit cell[20]
Fig. 4
(a) A~F SEM image (A), HAADF-STEM image (B), and EDS elemental mappings (C~F) of hexapod EDTA-NMF with etching for 60 h. All scale bars represent 500 nm; (b) Etching mechanism of NMF with Na2EDTA; (c) Cycling performances of two NMFs at 500 mA/g and the Coulombic efficiency of hexapod EDTA-NMF[30]
Fig. 5
(a) Long-term cycling stability of PW-HN and PB-Bulk at 10 C[32]; (b) Long-term cycling stability of LD-PB and D-PB at 100 C and (c) the role of competing coordination agent in the synthesis process of PB and the calculation of the binding energies between iron ion and different coordination agents[39]
除了在过渡金属离子位进行元素调整外,碱位掺杂也逐渐用于优化晶体体相。如Sun等[53]通过在电解液中添加Ba2+制备了Ba掺杂在Na位的Na x Ba y Fe[Fe(CN)6]。计算结果表明,Ba2+成功阻止了间隙水的进入,进一步稳定了材料的结构,大大提高了Na+扩散速率。Na x Ba y Fe[Fe(CN)6]的初始库仑效率高达99.32%,6 C下仍有83.41 mAh/g的比容量。为了抑制Mn的Jahn-Teller效应,Yang等[24]利用拓扑外延工艺制备了K2Mn[Fe(CN)6](KMF)亚微米八面体,并将其组装成八面体超结构作为钠离子电池正极(图7)。KMF的自组装行为提高了结构稳定性,减少了与电解质的副反应。在插层过程中,部分KMF会变为MnHCF,由于KMF中的Jahn-Teller失真比NMF中的弱,KMF可以作为稳定器来破坏NMF的长程Jahn-Teller,从而抑制了整体的畸变,在0.1 A/g、0.5 A/g下循环1500次、1300次后容量保持率为80%。
除核壳结构之外,研究人员也进行了更多创新性的探索。如为了减轻Ni的惰性对比容量的影响,Aifantis等[59]采用简单的共沉淀法制备了浓度梯度结构的Na x Ni y Mn1-y Fe(CN)6·nH2O颗粒。与均相相比,逐渐增加的Ni含量减轻了电化学诱导应力和在Na+插层过程中的累积损伤,0.2 C下100次循环后未观察到明显的颗粒断裂,大大提升了MnHCF的长循环性能。材料在0.2 C下展示出110 mAh/g的可逆比容量,在5 C下1000次循环后仍然有93%的保持率。令人印象深刻的是,Chen等[54]通过使用对苯二甲酸蚀刻PB的方法制备了具有阶梯立方空心结构的T-PB样品,并通过溶剂热反应合成了含CMK-3的T-PB。阶梯状空心大体积立方体以及与CMK-3颗粒紧密接触的微小立方体形成了连续的大导电网络。特殊的结构以及高的比表面积、电导率确保了Na+和电子的快速迁移,显示出快速的Na+储存动力学。在3200 mA/g的电流密度下,仍能提供87 mAh/g的比容量。Huang等[55]通过自模板法,逐步蚀刻模板ZIF-67模板制备了空心结构的CoFeHCF。结果表明,这种中空结构缓解了Na+插入和脱出过程中晶格的体积变化,而且缩短了离子的迁移路径。
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... 例如,过渡金属氧化物Na x MO2(M=Mn、Co、Ni、V、Fe等过渡金属元素)比容量较高,但因其在电极反应过程中频繁的相变以及较差的空气稳定性,导致电池的循环稳定性差[10-11];聚阴离子类化合物Na x M y (X a O b )zZ w (M=Fe、V、Ni、Co等过渡金属元素;X=P、Si、S等非金属元素;Z=F-、OH-等阴离子),虽然有较为合适的结构和适合Na+脱嵌的较大孔隙,但是低的电导率和电池比容量限制了其在钠离子电池储能领域的进一步应用[12];有机正极材料理论比容量高、来源丰富、环境友好,但是易溶解在有机电解液当中且自身导电性较差[15-16].幸运的是,近些年研究人员通过改变普鲁士蓝(PB)的化学组成、骨架结构等发现了一系列具有高理论比容量(170 mAh/g)和刚性三维骨架结构的普鲁士蓝类似物(PBAs).PBAs可调节的结构和简单的制备方法使得其成为最有潜力的正极材料之一[20-24]. ...
... 例如,过渡金属氧化物Na x MO2(M=Mn、Co、Ni、V、Fe等过渡金属元素)比容量较高,但因其在电极反应过程中频繁的相变以及较差的空气稳定性,导致电池的循环稳定性差[10-11];聚阴离子类化合物Na x M y (X a O b )zZ w (M=Fe、V、Ni、Co等过渡金属元素;X=P、Si、S等非金属元素;Z=F-、OH-等阴离子),虽然有较为合适的结构和适合Na+脱嵌的较大孔隙,但是低的电导率和电池比容量限制了其在钠离子电池储能领域的进一步应用[12];有机正极材料理论比容量高、来源丰富、环境友好,但是易溶解在有机电解液当中且自身导电性较差[15-16].幸运的是,近些年研究人员通过改变普鲁士蓝(PB)的化学组成、骨架结构等发现了一系列具有高理论比容量(170 mAh/g)和刚性三维骨架结构的普鲁士蓝类似物(PBAs).PBAs可调节的结构和简单的制备方法使得其成为最有潜力的正极材料之一[20-24]. ...
... 例如,过渡金属氧化物Na x MO2(M=Mn、Co、Ni、V、Fe等过渡金属元素)比容量较高,但因其在电极反应过程中频繁的相变以及较差的空气稳定性,导致电池的循环稳定性差[10-11];聚阴离子类化合物Na x M y (X a O b )zZ w (M=Fe、V、Ni、Co等过渡金属元素;X=P、Si、S等非金属元素;Z=F-、OH-等阴离子),虽然有较为合适的结构和适合Na+脱嵌的较大孔隙,但是低的电导率和电池比容量限制了其在钠离子电池储能领域的进一步应用[12];有机正极材料理论比容量高、来源丰富、环境友好,但是易溶解在有机电解液当中且自身导电性较差[15-16].幸运的是,近些年研究人员通过改变普鲁士蓝(PB)的化学组成、骨架结构等发现了一系列具有高理论比容量(170 mAh/g)和刚性三维骨架结构的普鲁士蓝类似物(PBAs).PBAs可调节的结构和简单的制备方法使得其成为最有潜力的正极材料之一[20-24]. ...
... 例如,过渡金属氧化物Na x MO2(M=Mn、Co、Ni、V、Fe等过渡金属元素)比容量较高,但因其在电极反应过程中频繁的相变以及较差的空气稳定性,导致电池的循环稳定性差[10-11];聚阴离子类化合物Na x M y (X a O b )zZ w (M=Fe、V、Ni、Co等过渡金属元素;X=P、Si、S等非金属元素;Z=F-、OH-等阴离子),虽然有较为合适的结构和适合Na+脱嵌的较大孔隙,但是低的电导率和电池比容量限制了其在钠离子电池储能领域的进一步应用[12];有机正极材料理论比容量高、来源丰富、环境友好,但是易溶解在有机电解液当中且自身导电性较差[15-16].幸运的是,近些年研究人员通过改变普鲁士蓝(PB)的化学组成、骨架结构等发现了一系列具有高理论比容量(170 mAh/g)和刚性三维骨架结构的普鲁士蓝类似物(PBAs).PBAs可调节的结构和简单的制备方法使得其成为最有潜力的正极材料之一[20-24]. ...
... 例如,过渡金属氧化物Na x MO2(M=Mn、Co、Ni、V、Fe等过渡金属元素)比容量较高,但因其在电极反应过程中频繁的相变以及较差的空气稳定性,导致电池的循环稳定性差[10-11];聚阴离子类化合物Na x M y (X a O b )zZ w (M=Fe、V、Ni、Co等过渡金属元素;X=P、Si、S等非金属元素;Z=F-、OH-等阴离子),虽然有较为合适的结构和适合Na+脱嵌的较大孔隙,但是低的电导率和电池比容量限制了其在钠离子电池储能领域的进一步应用[12];有机正极材料理论比容量高、来源丰富、环境友好,但是易溶解在有机电解液当中且自身导电性较差[15-16].幸运的是,近些年研究人员通过改变普鲁士蓝(PB)的化学组成、骨架结构等发现了一系列具有高理论比容量(170 mAh/g)和刚性三维骨架结构的普鲁士蓝类似物(PBAs).PBAs可调节的结构和简单的制备方法使得其成为最有潜力的正极材料之一[20-24]. ...
... 例如,过渡金属氧化物Na x MO2(M=Mn、Co、Ni、V、Fe等过渡金属元素)比容量较高,但因其在电极反应过程中频繁的相变以及较差的空气稳定性,导致电池的循环稳定性差[10-11];聚阴离子类化合物Na x M y (X a O b )zZ w (M=Fe、V、Ni、Co等过渡金属元素;X=P、Si、S等非金属元素;Z=F-、OH-等阴离子),虽然有较为合适的结构和适合Na+脱嵌的较大孔隙,但是低的电导率和电池比容量限制了其在钠离子电池储能领域的进一步应用[12];有机正极材料理论比容量高、来源丰富、环境友好,但是易溶解在有机电解液当中且自身导电性较差[15-16].幸运的是,近些年研究人员通过改变普鲁士蓝(PB)的化学组成、骨架结构等发现了一系列具有高理论比容量(170 mAh/g)和刚性三维骨架结构的普鲁士蓝类似物(PBAs).PBAs可调节的结构和简单的制备方法使得其成为最有潜力的正极材料之一[20-24]. ...
... PB和PBAs的化学组成可以表示为A x MA[MB(CN)6] y·ϒ(1-y)·nH2O,0≤x≤2,0<y≤1,典型晶体结构如图2(a)所示[20].其中A表示Na+、K+等碱金属或者碱土金属中的一种或者几种,MA和MB表示过渡金属元素中的一种或者几种,ϒ表示MB(CN)6空位,H2O表示结晶水、吸附水和沸石水.MA和MB可以是一种过渡金属元素,都是铁时则为典型的PB,主要通过它们的价态来区分.中心离子周围配体的强度决定过渡金属离子的自旋态,低自旋态MB与C相连,高自旋态MA与N相连,MAN6和MBC6两个八面体由—CN—连接共同组成了PBAs的三维刚性开放骨架,为Na+的快速运输提供了合适的通道. ...
... [20]Left: An intact A x MA[MB(CN)6] framework without structural defects, Right: An ideally defective A x MA[MB(CN)6]0.75·ϒ 0.25·nH2O framework with 25% Fe(CN)6 vacancies existing in each unit cell[20]Fig. 2
Schematic illustration of the conventional coprecipitation method (I) and the citrate-assisted controlled crystallization process (II)[20]Fig. 32.2 水热法
... 例如,过渡金属氧化物Na x MO2(M=Mn、Co、Ni、V、Fe等过渡金属元素)比容量较高,但因其在电极反应过程中频繁的相变以及较差的空气稳定性,导致电池的循环稳定性差[10-11];聚阴离子类化合物Na x M y (X a O b )zZ w (M=Fe、V、Ni、Co等过渡金属元素;X=P、Si、S等非金属元素;Z=F-、OH-等阴离子),虽然有较为合适的结构和适合Na+脱嵌的较大孔隙,但是低的电导率和电池比容量限制了其在钠离子电池储能领域的进一步应用[12];有机正极材料理论比容量高、来源丰富、环境友好,但是易溶解在有机电解液当中且自身导电性较差[15-16].幸运的是,近些年研究人员通过改变普鲁士蓝(PB)的化学组成、骨架结构等发现了一系列具有高理论比容量(170 mAh/g)和刚性三维骨架结构的普鲁士蓝类似物(PBAs).PBAs可调节的结构和简单的制备方法使得其成为最有潜力的正极材料之一[20-24]. ...
... 除了在过渡金属离子位进行元素调整外,碱位掺杂也逐渐用于优化晶体体相.如Sun等[53]通过在电解液中添加Ba2+制备了Ba掺杂在Na位的Na x Ba y Fe[Fe(CN)6].计算结果表明,Ba2+成功阻止了间隙水的进入,进一步稳定了材料的结构,大大提高了Na+扩散速率.Na x Ba y Fe[Fe(CN)6]的初始库仑效率高达99.32%,6 C下仍有83.41 mAh/g的比容量.为了抑制Mn的Jahn-Teller效应,Yang等[24]利用拓扑外延工艺制备了K2Mn[Fe(CN)6](KMF)亚微米八面体,并将其组装成八面体超结构作为钠离子电池正极(图7).KMF的自组装行为提高了结构稳定性,减少了与电解质的副反应.在插层过程中,部分KMF会变为MnHCF,由于KMF中的Jahn-Teller失真比NMF中的弱,KMF可以作为稳定器来破坏NMF的长程Jahn-Teller,从而抑制了整体的畸变,在0.1 A/g、0.5 A/g下循环1500次、1300次后容量保持率为80%. ...
... Electrochemical performance of Prussian blue cathode materials for sodium-ion batteriesTable 1
... [30](a) A~F SEM image (A), HAADF-STEM image (B), and EDS elemental mappings (C~F) of hexapod EDTA-NMF with etching for 60 h. All scale bars represent 500 nm; (b) Etching mechanism of NMF with Na2EDTA; (c) Cycling performances of two NMFs at 500 mA/g and the Coulombic efficiency of hexapod EDTA-NMF[30]Fig. 4
... [32];(b) LD-PB和D-PB在100C下的长循环曲线及 (c) 螯合剂在PB合成中的作用和铁离子与不同螯合剂结合能的计算[39](a) Long-term cycling stability of PW-HN and PB-Bulk at 10 C[32]; (b) Long-term cycling stability of LD-PB and D-PB at 100 C and (c) the role of competing coordination agent in the synthesis process of PB and the calculation of the binding energies between iron ion and different coordination agents[39]Fig. 5
... [32]; (b) Long-term cycling stability of LD-PB and D-PB at 100 C and (c) the role of competing coordination agent in the synthesis process of PB and the calculation of the binding energies between iron ion and different coordination agents[39]Fig. 5
(a) Long-term cycling stability of PW-HN and PB-Bulk at 10 C[32]; (b) Long-term cycling stability of LD-PB and D-PB at 100 C and (c) the role of competing coordination agent in the synthesis process of PB and the calculation of the binding energies between iron ion and different coordination agents[39]Fig. 5
... 除了在过渡金属离子位进行元素调整外,碱位掺杂也逐渐用于优化晶体体相.如Sun等[53]通过在电解液中添加Ba2+制备了Ba掺杂在Na位的Na x Ba y Fe[Fe(CN)6].计算结果表明,Ba2+成功阻止了间隙水的进入,进一步稳定了材料的结构,大大提高了Na+扩散速率.Na x Ba y Fe[Fe(CN)6]的初始库仑效率高达99.32%,6 C下仍有83.41 mAh/g的比容量.为了抑制Mn的Jahn-Teller效应,Yang等[24]利用拓扑外延工艺制备了K2Mn[Fe(CN)6](KMF)亚微米八面体,并将其组装成八面体超结构作为钠离子电池正极(图7).KMF的自组装行为提高了结构稳定性,减少了与电解质的副反应.在插层过程中,部分KMF会变为MnHCF,由于KMF中的Jahn-Teller失真比NMF中的弱,KMF可以作为稳定器来破坏NMF的长程Jahn-Teller,从而抑制了整体的畸变,在0.1 A/g、0.5 A/g下循环1500次、1300次后容量保持率为80%. ...
... 除核壳结构之外,研究人员也进行了更多创新性的探索.如为了减轻Ni的惰性对比容量的影响,Aifantis等[59]采用简单的共沉淀法制备了浓度梯度结构的Na x Ni y Mn1-y Fe(CN)6·nH2O颗粒.与均相相比,逐渐增加的Ni含量减轻了电化学诱导应力和在Na+插层过程中的累积损伤,0.2 C下100次循环后未观察到明显的颗粒断裂,大大提升了MnHCF的长循环性能.材料在0.2 C下展示出110 mAh/g的可逆比容量,在5 C下1000次循环后仍然有93%的保持率.令人印象深刻的是,Chen等[54]通过使用对苯二甲酸蚀刻PB的方法制备了具有阶梯立方空心结构的T-PB样品,并通过溶剂热反应合成了含CMK-3的T-PB.阶梯状空心大体积立方体以及与CMK-3颗粒紧密接触的微小立方体形成了连续的大导电网络.特殊的结构以及高的比表面积、电导率确保了Na+和电子的快速迁移,显示出快速的Na+储存动力学.在3200 mA/g的电流密度下,仍能提供87 mAh/g的比容量.Huang等[55]通过自模板法,逐步蚀刻模板ZIF-67模板制备了空心结构的CoFeHCF.结果表明,这种中空结构缓解了Na+插入和脱出过程中晶格的体积变化,而且缩短了离子的迁移路径. ...
... 除核壳结构之外,研究人员也进行了更多创新性的探索.如为了减轻Ni的惰性对比容量的影响,Aifantis等[59]采用简单的共沉淀法制备了浓度梯度结构的Na x Ni y Mn1-y Fe(CN)6·nH2O颗粒.与均相相比,逐渐增加的Ni含量减轻了电化学诱导应力和在Na+插层过程中的累积损伤,0.2 C下100次循环后未观察到明显的颗粒断裂,大大提升了MnHCF的长循环性能.材料在0.2 C下展示出110 mAh/g的可逆比容量,在5 C下1000次循环后仍然有93%的保持率.令人印象深刻的是,Chen等[54]通过使用对苯二甲酸蚀刻PB的方法制备了具有阶梯立方空心结构的T-PB样品,并通过溶剂热反应合成了含CMK-3的T-PB.阶梯状空心大体积立方体以及与CMK-3颗粒紧密接触的微小立方体形成了连续的大导电网络.特殊的结构以及高的比表面积、电导率确保了Na+和电子的快速迁移,显示出快速的Na+储存动力学.在3200 mA/g的电流密度下,仍能提供87 mAh/g的比容量.Huang等[55]通过自模板法,逐步蚀刻模板ZIF-67模板制备了空心结构的CoFeHCF.结果表明,这种中空结构缓解了Na+插入和脱出过程中晶格的体积变化,而且缩短了离子的迁移路径. ...
... 除核壳结构之外,研究人员也进行了更多创新性的探索.如为了减轻Ni的惰性对比容量的影响,Aifantis等[59]采用简单的共沉淀法制备了浓度梯度结构的Na x Ni y Mn1-y Fe(CN)6·nH2O颗粒.与均相相比,逐渐增加的Ni含量减轻了电化学诱导应力和在Na+插层过程中的累积损伤,0.2 C下100次循环后未观察到明显的颗粒断裂,大大提升了MnHCF的长循环性能.材料在0.2 C下展示出110 mAh/g的可逆比容量,在5 C下1000次循环后仍然有93%的保持率.令人印象深刻的是,Chen等[54]通过使用对苯二甲酸蚀刻PB的方法制备了具有阶梯立方空心结构的T-PB样品,并通过溶剂热反应合成了含CMK-3的T-PB.阶梯状空心大体积立方体以及与CMK-3颗粒紧密接触的微小立方体形成了连续的大导电网络.特殊的结构以及高的比表面积、电导率确保了Na+和电子的快速迁移,显示出快速的Na+储存动力学.在3200 mA/g的电流密度下,仍能提供87 mAh/g的比容量.Huang等[55]通过自模板法,逐步蚀刻模板ZIF-67模板制备了空心结构的CoFeHCF.结果表明,这种中空结构缓解了Na+插入和脱出过程中晶格的体积变化,而且缩短了离子的迁移路径. ...