由于钠具有资源丰富和成本低廉的优势,钠离子电池再次受到科学界和工业界的广泛关注。发展低成本、性能优异的正极材料对于钠离子电池至关重要。本文通过向O3-Na_(0.90)[Cu_(0.22)Fe_(0.30)Mn_(0.48)]O_2材料中引入容易变价的Ni^(2+)得...由于钠具有资源丰富和成本低廉的优势,钠离子电池再次受到科学界和工业界的广泛关注。发展低成本、性能优异的正极材料对于钠离子电池至关重要。本文通过向O3-Na_(0.90)[Cu_(0.22)Fe_(0.30)Mn_(0.48)]O_2材料中引入容易变价的Ni^(2+)得到一种不含Mn^(3+)的钠离子电池新型正极材料O3-NaCu_(1/9)Ni_(2/9)Fe_(1/3)Mn_(1/3)O_2,该材料具有127 m A·h/g可逆比容量和3.1 V平均放电电压。由该正极与硬碳球负极组装成全电池具有248 W·h/kg的理论能量密度,高达93%的能量转化效率和优异的循环性能。展开更多
作为钠离子电池正极材料,锰基层状氧化物具有理论储钠容量高、成本低和热稳定性高等优点,但也存在因结构畸变、Na^(+)/空位有序以及过渡金属空位等带来的循环稳定性问题。研究表明,抑制过渡金属空位可有效提升锰基层状氧化物正极的电化...作为钠离子电池正极材料,锰基层状氧化物具有理论储钠容量高、成本低和热稳定性高等优点,但也存在因结构畸变、Na^(+)/空位有序以及过渡金属空位等带来的循环稳定性问题。研究表明,抑制过渡金属空位可有效提升锰基层状氧化物正极的电化学性能。为此,本工作对比研究了溶胶凝胶制备过程中高温淬火对Na_(0.67)Fe1/3Co_(1/3)Mn_(1/3)O_(2)(NFCMO)结构和性能的影响。结果表明,相比于未经高温淬火处理的NFCMO,高温液氮淬火合成的NFCMO-LN具有更高的比容量和倍率性能。NFCMO和NFCMO-LN在0.1C下的初始放电比容量分别为91.1 m Ah/g和129.8 m Ah/g;1C倍率下循环100周后的容量保留率分别为100%和90%。即使在10C的高倍率下,NFCMO-LN仍能提供56.2 m Ah/g的放电比容量。结构分析表明,高温液氮淬火能有效抑制过渡金属空位的产生,提升了材料的结构稳定性。研究结果为钠离子电池正极材料的结构设计和电化学性能优化提供了一种可行的技术途径。展开更多
A new model material of Na[Mg(Ⅱ)Mn(Ⅳ)]O, with only Mgand Mnin the transition metal layers, is synthesized for the research of anionic redox reaction. The material delivers a capacity of ～130 mAh/g with a long plate...A new model material of Na[Mg(Ⅱ)Mn(Ⅳ)]O, with only Mgand Mnin the transition metal layers, is synthesized for the research of anionic redox reaction. The material delivers a capacity of ～130 mAh/g with a long plateau at ～4.2 V in the initial charge profile, indicating anionic redox reaction(ARR) involved during the initial desodiation process. In the following cycles, the reversible capacity can reach a high value of ～210 mAh/g, which is probably derived from the participation of both ARR and Mn/Mnredox couples, further proving the charge compensation from ARR during the initial charge and following cycles. The designed cathode material without Mnhelps avoid the influence of oxygen activity from transition metals, enabling the investigation of ARR without other distractions.展开更多
The instability of thin ferroelectric films is discussed based on the close similarity of dielectric properties between bulk Bi-layered perovskites and thin BaTiO<sub>3</sub> films. The dielectric properti...The instability of thin ferroelectric films is discussed based on the close similarity of dielectric properties between bulk Bi-layered perovskites and thin BaTiO<sub>3</sub> films. The dielectric properties of pseudo-two-dimensional layered perovskites suggest that the bulk layered ferroelectric is a good model of ultra-thin ferroelectric film with a few perovskite units, free from any misfit lattice strain. It seems plausible that the ferroelectric interaction is still prominent but shows a crossover from ferroelectric to antiferroelectric along the unique c-axis (perpendicular to the film plane);with decreasing thickness, the ferroelectricity appears within the plane, which results in so-called “canted ferroelectricity”. An extra relaxation mode induced by surface effect of thin films correlates with soft mode, which results in a new intermediate phase between the paraelectric and ferroelectric phases. These evidences may indicate no critical thickness even for ferroelectric ultra- thin films.展开更多
文摘由于钠具有资源丰富和成本低廉的优势,钠离子电池再次受到科学界和工业界的广泛关注。发展低成本、性能优异的正极材料对于钠离子电池至关重要。本文通过向O3-Na_(0.90)[Cu_(0.22)Fe_(0.30)Mn_(0.48)]O_2材料中引入容易变价的Ni^(2+)得到一种不含Mn^(3+)的钠离子电池新型正极材料O3-NaCu_(1/9)Ni_(2/9)Fe_(1/3)Mn_(1/3)O_2,该材料具有127 m A·h/g可逆比容量和3.1 V平均放电电压。由该正极与硬碳球负极组装成全电池具有248 W·h/kg的理论能量密度,高达93%的能量转化效率和优异的循环性能。
文摘作为钠离子电池正极材料,锰基层状氧化物具有理论储钠容量高、成本低和热稳定性高等优点,但也存在因结构畸变、Na^(+)/空位有序以及过渡金属空位等带来的循环稳定性问题。研究表明,抑制过渡金属空位可有效提升锰基层状氧化物正极的电化学性能。为此,本工作对比研究了溶胶凝胶制备过程中高温淬火对Na_(0.67)Fe1/3Co_(1/3)Mn_(1/3)O_(2)(NFCMO)结构和性能的影响。结果表明,相比于未经高温淬火处理的NFCMO,高温液氮淬火合成的NFCMO-LN具有更高的比容量和倍率性能。NFCMO和NFCMO-LN在0.1C下的初始放电比容量分别为91.1 m Ah/g和129.8 m Ah/g;1C倍率下循环100周后的容量保留率分别为100%和90%。即使在10C的高倍率下,NFCMO-LN仍能提供56.2 m Ah/g的放电比容量。结构分析表明,高温液氮淬火能有效抑制过渡金属空位的产生,提升了材料的结构稳定性。研究结果为钠离子电池正极材料的结构设计和电化学性能优化提供了一种可行的技术途径。
基金supported by funding from Science and Technology Project of the State Grid Corporation of China("research on key technology of low-strain layered oxides for long-life Na-ion batteries",No.DG71-16-027)
文摘A new model material of Na[Mg(Ⅱ)Mn(Ⅳ)]O, with only Mgand Mnin the transition metal layers, is synthesized for the research of anionic redox reaction. The material delivers a capacity of ～130 mAh/g with a long plateau at ～4.2 V in the initial charge profile, indicating anionic redox reaction(ARR) involved during the initial desodiation process. In the following cycles, the reversible capacity can reach a high value of ～210 mAh/g, which is probably derived from the participation of both ARR and Mn/Mnredox couples, further proving the charge compensation from ARR during the initial charge and following cycles. The designed cathode material without Mnhelps avoid the influence of oxygen activity from transition metals, enabling the investigation of ARR without other distractions.
文摘The instability of thin ferroelectric films is discussed based on the close similarity of dielectric properties between bulk Bi-layered perovskites and thin BaTiO<sub>3</sub> films. The dielectric properties of pseudo-two-dimensional layered perovskites suggest that the bulk layered ferroelectric is a good model of ultra-thin ferroelectric film with a few perovskite units, free from any misfit lattice strain. It seems plausible that the ferroelectric interaction is still prominent but shows a crossover from ferroelectric to antiferroelectric along the unique c-axis (perpendicular to the film plane);with decreasing thickness, the ferroelectricity appears within the plane, which results in so-called “canted ferroelectricity”. An extra relaxation mode induced by surface effect of thin films correlates with soft mode, which results in a new intermediate phase between the paraelectric and ferroelectric phases. These evidences may indicate no critical thickness even for ferroelectric ultra- thin films.
