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
Selenium sulfide/double-layered hollow carbon sphere （SeS2/DLHC） composites have been designed as high-performance cathode materials for novel Li-SeS2 batteries. In the constructed composite, SeS2 is predominantly e...Selenium sulfide/double-layered hollow carbon sphere （SeS2/DLHC） composites have been designed as high-performance cathode materials for novel Li-SeS2 batteries. In the constructed composite, SeS2 is predominantly encapsulated in the interlayer space of DLHCs with a high loading of 75% （weight percentage） and serves as the active component for lithium storage. The presence of Se in the composite and the carbon framework not only alleviate the shuttling of polysulfide, but also improve the conductivity of electrodes. Migration of active materials from the interlayer void to the hollow cavity of DLHCs after cycling, which further mitigates the loss of active materials and the shuttle effect, is observed. As a result, the SeS2/DLHC composite delivers a high specific capacity （930 mA.h.g-1 at 0.2 C） and outstanding rate capability （400 mA.h.g-1 at 6 C）, which is much better than those of SeS2/single-layered hollow carbon sphere, Se/DLHC, and S/DLHC composites. Notably, the SeS2/DLHC composite shows an ultralong cycle life with 89% capacity retention over 900 cycles at 1 C, or only 0.012% capacity decay per cycle. Our study reveals that both SeS2 and the double-layered structures are responsible for the excellent electrochemical performance.展开更多
Layered transition metal(TM) oxides are one of the most widely used cathode materials in lithium-ion batteries. The atomic configuration in TM layer of these materials is often known to be random when multiple TM elem...Layered transition metal(TM) oxides are one of the most widely used cathode materials in lithium-ion batteries. The atomic configuration in TM layer of these materials is often known to be random when multiple TM elements co-exist in the layer(e.g. Ni, Co and Mn). By contrast, the configuration tends to be ordered if the elements are Li and Mn. Here, by using special quasi-random structures(SQS) algorithm, the essential reasons of the ordering in a promising Li-rich Mn-based cathode material Li2MnO3 are investigated. The difference of internal energy and entropy between ordered and disordered materials is calculated. As a result, based on the Gibbs free energy, it is found that Li2MnO3 should have an ordered structure in TM layer. In comparison, structures with Ni-Mn ratio of 2:1 are predicted to have a disordered TM layer, because the entropy terms have larger impact on the structural ordering than internal energy terms.展开更多
Coupled with anionic and cationic redox chemistry,Li-rich/excess cathode materials are prospective high-energy-density candidates for the next-generation Li-ion batteries.However,irreversible lattice oxygen loss would...Coupled with anionic and cationic redox chemistry,Li-rich/excess cathode materials are prospective high-energy-density candidates for the next-generation Li-ion batteries.However,irreversible lattice oxygen loss would exacerbate irreversible transition metal migration,resulting in a drastic voltage decay and capacity degeneration.Herein,a metastable layered Li-excess cathode material,T2-type Li_(0.72)[Li_(0.12)Ni_(0.36)Mn_(0.52)]O_(2),was developed,in which both oxygen stacking arrangement and Li coordination environment fundamentally differ from that in conventional O3-type layered structures.By means of the reversible Li migration processes and structural evolutions,not only can voltage decay be effectively restrained,but also excellent capacity retention can be achieved upon long-term cycling.Moreover,irreversible/reversible anionic/cationic redox activities have been well assigned and quantified by various in/ex-situ spectroscopic techniques,further clarifying the charge compensation mechanism associated with(de)lithiation.These findings of the novel T2 structure with the enhanced anionic redox stability will provide a new scope for the development of high-energy-density Li-rich cathode materials.展开更多
Employing Li2CO3, NiO, Co3O4, and MnCO3 powders as starting materials, Li[Ni1/3Co1/3Mn1/3]O2 was synthesized by solid-state reaction method. Various grinding aids were applied during milling in order to optimize the s...Employing Li2CO3, NiO, Co3O4, and MnCO3 powders as starting materials, Li[Ni1/3Co1/3Mn1/3]O2 was synthesized by solid-state reaction method. Various grinding aids were applied during milling in order to optimize the synthesis process. After successive heat treatments at 650 and 950 ℃, the prepared powders were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy, and transmission electron microscopy. The powders prepared by adding salt (NaCl) as grinding aid exhibit a clear R3m layer structure. The powders by other grinding aids like heptane show some impurity peaks in the XRD pattern. The former powders show a uniform particle size distribution of less than 1 μm average size while the latter shows a wide distribution ranging from 1 to 10 μm. Energy dispersive X-ray (EDX) analysiss show that the ratio of Ni, Co, and Mn content in the powder is approximately 1/3, 1/3, and 1/3, respecively. The EDX data indicate no incorporation of sodium or chlorine into the powders. Charge-discharge tests gave an initial discharge capacity of 160 mAh·g-1 for the powders with NaCl addition while 70 mAh·g-1 for the powders with heptane.展开更多
xLi2MnO3·（1-x）Li（Ni1/3Co1/3Mn1/3）O2 （x=0.25, 0.40, 0.55） compounds were prepared by low-heating solid state reaction. In the voltage range of 2.70-4.35 V, the discharge capacity of the electrode decreased w...xLi2MnO3·（1-x）Li（Ni1/3Co1/3Mn1/3）O2 （x=0.25, 0.40, 0.55） compounds were prepared by low-heating solid state reaction. In the voltage range of 2.70-4.35 V, the discharge capacity of the electrode decreased with the increase of x, with a better cyclability. However, when cycled between 2.7 and 4.6 V, the cathodes delivered much larger capacities and their capacities increased with the introduction of Li2MnO3. Moreover, it was found that the discharge capacity gradually increased with the cycle number. The reason for this phenomenon was discussed. It was found that the relatively low cut-off potential made the activation of the Li2MnO3 component in the compound a gradual process, which caused the increasing capacity.展开更多
To improve the cyclic stability at high temperature and thermal stability, the spherical Al2O3-modified Li（Ni0.5Co0.2Mn0.3）O2 was synthesized by a modified co-precipitation method, and the physical and electrochemic...To improve the cyclic stability at high temperature and thermal stability, the spherical Al2O3-modified Li（Ni0.5Co0.2Mn0.3）O2 was synthesized by a modified co-precipitation method, and the physical and electrochemical properties were studied. The TEM images showed that Li（Ni0.5Co0.2Mn0.3）O2 was modified successfully with nano-Al2O3. The discharge capacity retention of Al2O3-modified Li（Ni0.5Co0.2Mn0.3）O2 maintained about 99% after 200 cycles at high temperature（55 ℃）, while that of the bare one was only 86%. Also, unlike bare Li（Ni0.5Co0.2Mn0.3）O2, the Al2O3-modified material cathode exhibited good thermal stability.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。
基金The authors acknowledge the financial support from the Australian Research Council, the Queensland Government, the CAS/SAFEA International Partnership Program for Creative Research Teams, the Australian National Fabrication Facility and the Australian Microscopy and Microanalysis Research Facility at the Centre for Microscopy and Microanalysis, The University of Queensland. L. Z. acknowledges the financial support from the National Natural Science Foundation of China （No. 51502226）.
文摘Selenium sulfide/double-layered hollow carbon sphere （SeS2/DLHC） composites have been designed as high-performance cathode materials for novel Li-SeS2 batteries. In the constructed composite, SeS2 is predominantly encapsulated in the interlayer space of DLHCs with a high loading of 75% （weight percentage） and serves as the active component for lithium storage. The presence of Se in the composite and the carbon framework not only alleviate the shuttling of polysulfide, but also improve the conductivity of electrodes. Migration of active materials from the interlayer void to the hollow cavity of DLHCs after cycling, which further mitigates the loss of active materials and the shuttle effect, is observed. As a result, the SeS2/DLHC composite delivers a high specific capacity （930 mA.h.g-1 at 0.2 C） and outstanding rate capability （400 mA.h.g-1 at 6 C）, which is much better than those of SeS2/single-layered hollow carbon sphere, Se/DLHC, and S/DLHC composites. Notably, the SeS2/DLHC composite shows an ultralong cycle life with 89% capacity retention over 900 cycles at 1 C, or only 0.012% capacity decay per cycle. Our study reveals that both SeS2 and the double-layered structures are responsible for the excellent electrochemical performance.
基金Supported by National Key R&D Program of China(2016YFB0700600)Soft Science Research Project of Guangdong Province(No.2017B030301013)
文摘Layered transition metal(TM) oxides are one of the most widely used cathode materials in lithium-ion batteries. The atomic configuration in TM layer of these materials is often known to be random when multiple TM elements co-exist in the layer(e.g. Ni, Co and Mn). By contrast, the configuration tends to be ordered if the elements are Li and Mn. Here, by using special quasi-random structures(SQS) algorithm, the essential reasons of the ordering in a promising Li-rich Mn-based cathode material Li2MnO3 are investigated. The difference of internal energy and entropy between ordered and disordered materials is calculated. As a result, based on the Gibbs free energy, it is found that Li2MnO3 should have an ordered structure in TM layer. In comparison, structures with Ni-Mn ratio of 2:1 are predicted to have a disordered TM layer, because the entropy terms have larger impact on the structural ordering than internal energy terms.
基金supported by the National Science Foundation under Grant No.DMR1809372。
文摘Coupled with anionic and cationic redox chemistry,Li-rich/excess cathode materials are prospective high-energy-density candidates for the next-generation Li-ion batteries.However,irreversible lattice oxygen loss would exacerbate irreversible transition metal migration,resulting in a drastic voltage decay and capacity degeneration.Herein,a metastable layered Li-excess cathode material,T2-type Li_(0.72)[Li_(0.12)Ni_(0.36)Mn_(0.52)]O_(2),was developed,in which both oxygen stacking arrangement and Li coordination environment fundamentally differ from that in conventional O3-type layered structures.By means of the reversible Li migration processes and structural evolutions,not only can voltage decay be effectively restrained,but also excellent capacity retention can be achieved upon long-term cycling.Moreover,irreversible/reversible anionic/cationic redox activities have been well assigned and quantified by various in/ex-situ spectroscopic techniques,further clarifying the charge compensation mechanism associated with(de)lithiation.These findings of the novel T2 structure with the enhanced anionic redox stability will provide a new scope for the development of high-energy-density Li-rich cathode materials.
基金This research was supportedby a grant under‘Development of Key Materials and Fundamental Tech-nology for Secondary Battery’Program of the Ministry of Commerce,Industry and Energy,Korea.
文摘Employing Li2CO3, NiO, Co3O4, and MnCO3 powders as starting materials, Li[Ni1/3Co1/3Mn1/3]O2 was synthesized by solid-state reaction method. Various grinding aids were applied during milling in order to optimize the synthesis process. After successive heat treatments at 650 and 950 ℃, the prepared powders were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy, and transmission electron microscopy. The powders prepared by adding salt (NaCl) as grinding aid exhibit a clear R3m layer structure. The powders by other grinding aids like heptane show some impurity peaks in the XRD pattern. The former powders show a uniform particle size distribution of less than 1 μm average size while the latter shows a wide distribution ranging from 1 to 10 μm. Energy dispersive X-ray (EDX) analysiss show that the ratio of Ni, Co, and Mn content in the powder is approximately 1/3, 1/3, and 1/3, respecively. The EDX data indicate no incorporation of sodium or chlorine into the powders. Charge-discharge tests gave an initial discharge capacity of 160 mAh·g-1 for the powders with NaCl addition while 70 mAh·g-1 for the powders with heptane.
基金supported by the National Natural Science Foundation of China(No.50472093,50702007)
文摘xLi2MnO3·（1-x）Li（Ni1/3Co1/3Mn1/3）O2 （x=0.25, 0.40, 0.55） compounds were prepared by low-heating solid state reaction. In the voltage range of 2.70-4.35 V, the discharge capacity of the electrode decreased with the increase of x, with a better cyclability. However, when cycled between 2.7 and 4.6 V, the cathodes delivered much larger capacities and their capacities increased with the introduction of Li2MnO3. Moreover, it was found that the discharge capacity gradually increased with the cycle number. The reason for this phenomenon was discussed. It was found that the relatively low cut-off potential made the activation of the Li2MnO3 component in the compound a gradual process, which caused the increasing capacity.
基金Funded by the National High Technology Research and Development Program of China(863 Program)(No.2015AA034600)Province Science and Technology in Anhui(No.1301021011)
文摘To improve the cyclic stability at high temperature and thermal stability, the spherical Al2O3-modified Li（Ni0.5Co0.2Mn0.3）O2 was synthesized by a modified co-precipitation method, and the physical and electrochemical properties were studied. The TEM images showed that Li（Ni0.5Co0.2Mn0.3）O2 was modified successfully with nano-Al2O3. The discharge capacity retention of Al2O3-modified Li（Ni0.5Co0.2Mn0.3）O2 maintained about 99% after 200 cycles at high temperature（55 ℃）, while that of the bare one was only 86%. Also, unlike bare Li（Ni0.5Co0.2Mn0.3）O2, the Al2O3-modified material cathode exhibited good thermal stability.
