Al-doped LiVPO4F cathode materials LiAlxV1-xPO4F were prepared by two-step reactions based on a car-bothermal reduction (CTR) process. The properties of the Al-doped LiVPO4F were investigated by X-ray diffraction (...Al-doped LiVPO4F cathode materials LiAlxV1-xPO4F were prepared by two-step reactions based on a car-bothermal reduction (CTR) process. The properties of the Al-doped LiVPO4F were investigated by X-ray diffraction (XRD),scanning electron microscopy (SEM),and electrochemical measurements. XRD studies show that the Al-doped LiVPO4F has the same triclinic structure (space group p-↑1 ) as the undoped LiVPO4F. The SEM images exhibit that the particle size of Al-doped LiVPO4F is smaller than that of the undoped LiVPO4F and that the smallest particle size is only about 1 μm. The Al-doped LiVPO4F was evaluated as a cathode material for secondary lithium batteries,and exhibited an improved reversibility and cycleability,which may be attributed to the addition of Al^3+ ion by stabilizing the triclinic structure.展开更多
For constructing next-generation lithium-ion batteries with advanced performances,pursuit of highcapacity Li-rich cathodes has caused considerable attention.So far,the low discharge specific capacity and serious capac...For constructing next-generation lithium-ion batteries with advanced performances,pursuit of highcapacity Li-rich cathodes has caused considerable attention.So far,the low discharge specific capacity and serious capacity fading are strangling the development of Fe-based Li-rich materials.To activate the extra-capacity of Fe-based Li-rich cathode materials,a facile molten salt method is exploited using an alkaline mixture of LiOH–LiNO3–Li2O2 in this work.The prepared Li1.09(Fe0.2Ni0.3Mn0.5)0.91O2 material yields high discharge specific capacity and good cycling stability.The discharge specific capacity shows an upward tendency at 0.1 C.After 60 cycles,a high reversible specific capacity of ~250 m Ah g-1is delivered.The redox of Fe3+/Fe4+and Mn3+/Mn4+are gradually activated during cycling.Notably,the redox reaction of Fe2+/Fe3+can be observed reversibly below 2 V,which is quite different from the material prepared by a traditional co-precipitation method.The stable morphology of fine nanoparticles(100–300 nm)is considered benefiting for the distinctive electrochemical performances of Li1.09(Fe0.2Ni0.3Mn0.5)0.91O2.This study demonstrates that molten salt method is an inexpensive and effective approach to activate the extra capacity of Fe-based Li-rich cathode material for high-performance lithium-ion batteries.展开更多
Li-rich layered cathode materials have been considered the most promising candidates for large-scale Li-ion batteries due to their low cost and high reversible capacity. However, these materials have many drawbacks th...Li-rich layered cathode materials have been considered the most promising candidates for large-scale Li-ion batteries due to their low cost and high reversible capacity. However, these materials have many drawbacks that hinder commercialization, such as low initial efficiency and cyclability at elevated temperatures. To overcome these barriers, we propose an efficient and effective surface modification method, in which chemical activation (acid treatment) and LiCoPO4 coating were carried out simultaneously. During the synthesis, the lithium ions were extracted from the lattice, leading to improved Columbic efficiency, and these ions were used for the formation of LiCoPO4. The Ni and Co doped spinel phase was formed at the surface of the host material, which gives rise to the facile pathway for lithium ions. The LiCoPO4 and highly doped spinel on the surface acted as double protection layers that effectively prevented side reactions on the surface at 60℃. Moreover, the transition metal migration of the modified cathode was weakened, due to the presence of the spinel structure at the surface. Consequently, the newly developed Li-rich cathode material exhibited a high 1st efficiency of 94%, improved capacity retention of 82% during 100 cycles at 60℃, and superior rate capability of 62% at 12C (1C = 200 mA/g) rate at 24℃. In addition, the thermal stability of the modified cathode was significantly improved as compared to that of a bare counterpart at 4.6 V, showing a 60% decrease in the total heat generation.展开更多
Doping electrochemically inert elements in Li-rich layered oxide cathodes usually stabilizes the structure to improve electrochemical performance at the expense of available capacity.Here,we use an element segregation...Doping electrochemically inert elements in Li-rich layered oxide cathodes usually stabilizes the structure to improve electrochemical performance at the expense of available capacity.Here,we use an element segregation principle to realize a uniform surface doping without capacity sacrifice.On the basis of Hume-Rothery rule,element yttrium is chosen as a candidate dopant to spontaneously segregate at particle surface due to mismatched ionic size.Combined with X-ray photoelectron spectroscopy and electron energy loss spectroscopy mapping,yttrium is demonstrated uniformly distributed on particle surface.More importantly,a significant alleviation of oxygen release after surface doping is detected by operando differential electrochemical mass spectrometry.As a result,the modified sample exhibits improved reversibility of oxygen redox with 82.1%coulombic efficiency and excellent cycle performances with 84.15%capacity retention after 140 cycles.Postmortem analysis by transmission electron microscopy,Raman spectroscopy and X-ray diffraction reveal that the modified sample maintains the layered structure without a significant structure transformation after long cycles.This work provides an effective strategy with a series of elements to meet the industrial application.展开更多
A couple of layered Li-rich cathode materials Li1.2Mn0.54Ni0.13Co0.13O2 without any carbon modification are successfully synthesized by solvothermal and hydrothermal methods followed by a calcination process. The samp...A couple of layered Li-rich cathode materials Li1.2Mn0.54Ni0.13Co0.13O2 without any carbon modification are successfully synthesized by solvothermal and hydrothermal methods followed by a calcination process. The sample synthesized by the solvothermal method(S-NCM) possesses more homogenous microstructure, lower cation mixing degree and more oxygen vacancies on the surface, compared to the sample prepared by the hydrothermal method(H-NCM). The S-NCM sample exhibits much better cycling performance, higher discharge capacity and more excellent rate performance than H-NCM. At 0.2 C rate,the S-NCM sample delivers a much higher initial discharge capacity of 292.3 mAh g^-1 and the capacity maintains 235 m Ah g^-1 after 150 cycles(80.4% retention), whereas the corresponding capacity values are only 269.2 and 108.5 m Ah g^-1(40.3% retention) for the H-NCM sample. The S-NCM sample also shows the higher rate performance with discharge capacity of 118.3 mAh g^-1 even at a high rate of 10 C, superior to that(46.5 m Ah g^-1) of the H-NCM sample. The superior electrochemical performance of the S-NCM sample can be ascribed to its well-ordered structure, much larger specific surface area and much more oxygen vacancies located on the surface.展开更多
文摘Al-doped LiVPO4F cathode materials LiAlxV1-xPO4F were prepared by two-step reactions based on a car-bothermal reduction (CTR) process. The properties of the Al-doped LiVPO4F were investigated by X-ray diffraction (XRD),scanning electron microscopy (SEM),and electrochemical measurements. XRD studies show that the Al-doped LiVPO4F has the same triclinic structure (space group p-↑1 ) as the undoped LiVPO4F. The SEM images exhibit that the particle size of Al-doped LiVPO4F is smaller than that of the undoped LiVPO4F and that the smallest particle size is only about 1 μm. The Al-doped LiVPO4F was evaluated as a cathode material for secondary lithium batteries,and exhibited an improved reversibility and cycleability,which may be attributed to the addition of Al^3+ ion by stabilizing the triclinic structure.
基金supported by the Nature Science Foundations of Hebei Province (B2016210071, B2016210111)the Natural Science Foundation of Hebei Education Department (QN2016057, ZD2015082, ZC2016045)+3 种基金the National College Students’ Innovative Entrepreneurial Training Project of Chinasupported by the Chinese National 973 Program (2015CB251106)the Joint Funds of the National Natural Science Foundation of China (U1564206)Major achievements Transformation Project for Central University in Beijing
文摘For constructing next-generation lithium-ion batteries with advanced performances,pursuit of highcapacity Li-rich cathodes has caused considerable attention.So far,the low discharge specific capacity and serious capacity fading are strangling the development of Fe-based Li-rich materials.To activate the extra-capacity of Fe-based Li-rich cathode materials,a facile molten salt method is exploited using an alkaline mixture of LiOH–LiNO3–Li2O2 in this work.The prepared Li1.09(Fe0.2Ni0.3Mn0.5)0.91O2 material yields high discharge specific capacity and good cycling stability.The discharge specific capacity shows an upward tendency at 0.1 C.After 60 cycles,a high reversible specific capacity of ~250 m Ah g-1is delivered.The redox of Fe3+/Fe4+and Mn3+/Mn4+are gradually activated during cycling.Notably,the redox reaction of Fe2+/Fe3+can be observed reversibly below 2 V,which is quite different from the material prepared by a traditional co-precipitation method.The stable morphology of fine nanoparticles(100–300 nm)is considered benefiting for the distinctive electrochemical performances of Li1.09(Fe0.2Ni0.3Mn0.5)0.91O2.This study demonstrates that molten salt method is an inexpensive and effective approach to activate the extra capacity of Fe-based Li-rich cathode material for high-performance lithium-ion batteries.
文摘Li-rich layered cathode materials have been considered the most promising candidates for large-scale Li-ion batteries due to their low cost and high reversible capacity. However, these materials have many drawbacks that hinder commercialization, such as low initial efficiency and cyclability at elevated temperatures. To overcome these barriers, we propose an efficient and effective surface modification method, in which chemical activation (acid treatment) and LiCoPO4 coating were carried out simultaneously. During the synthesis, the lithium ions were extracted from the lattice, leading to improved Columbic efficiency, and these ions were used for the formation of LiCoPO4. The Ni and Co doped spinel phase was formed at the surface of the host material, which gives rise to the facile pathway for lithium ions. The LiCoPO4 and highly doped spinel on the surface acted as double protection layers that effectively prevented side reactions on the surface at 60℃. Moreover, the transition metal migration of the modified cathode was weakened, due to the presence of the spinel structure at the surface. Consequently, the newly developed Li-rich cathode material exhibited a high 1st efficiency of 94%, improved capacity retention of 82% during 100 cycles at 60℃, and superior rate capability of 62% at 12C (1C = 200 mA/g) rate at 24℃. In addition, the thermal stability of the modified cathode was significantly improved as compared to that of a bare counterpart at 4.6 V, showing a 60% decrease in the total heat generation.
基金This work was financially supported by S&T Innovation 2025 Major Special Programme of Ningbo(Grant No.2018B10081)"Lingyan"Research and Development Plan of Zhejiang Province(Grant No.2022C01071)+2 种基金the National Natural Science Foundation of China(Grant No.21773279)the Natural Science Foundation of Ningbo(Grant Nos.202003N4030,202003N4347)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2022299).
文摘Doping electrochemically inert elements in Li-rich layered oxide cathodes usually stabilizes the structure to improve electrochemical performance at the expense of available capacity.Here,we use an element segregation principle to realize a uniform surface doping without capacity sacrifice.On the basis of Hume-Rothery rule,element yttrium is chosen as a candidate dopant to spontaneously segregate at particle surface due to mismatched ionic size.Combined with X-ray photoelectron spectroscopy and electron energy loss spectroscopy mapping,yttrium is demonstrated uniformly distributed on particle surface.More importantly,a significant alleviation of oxygen release after surface doping is detected by operando differential electrochemical mass spectrometry.As a result,the modified sample exhibits improved reversibility of oxygen redox with 82.1%coulombic efficiency and excellent cycle performances with 84.15%capacity retention after 140 cycles.Postmortem analysis by transmission electron microscopy,Raman spectroscopy and X-ray diffraction reveal that the modified sample maintains the layered structure without a significant structure transformation after long cycles.This work provides an effective strategy with a series of elements to meet the industrial application.
基金supported financially by the National Key Research and Development Program(No.2017YFA0402800)the National Natural Science Foundation of China(Nos.U1732160and 11504380)
文摘A couple of layered Li-rich cathode materials Li1.2Mn0.54Ni0.13Co0.13O2 without any carbon modification are successfully synthesized by solvothermal and hydrothermal methods followed by a calcination process. The sample synthesized by the solvothermal method(S-NCM) possesses more homogenous microstructure, lower cation mixing degree and more oxygen vacancies on the surface, compared to the sample prepared by the hydrothermal method(H-NCM). The S-NCM sample exhibits much better cycling performance, higher discharge capacity and more excellent rate performance than H-NCM. At 0.2 C rate,the S-NCM sample delivers a much higher initial discharge capacity of 292.3 mAh g^-1 and the capacity maintains 235 m Ah g^-1 after 150 cycles(80.4% retention), whereas the corresponding capacity values are only 269.2 and 108.5 m Ah g^-1(40.3% retention) for the H-NCM sample. The S-NCM sample also shows the higher rate performance with discharge capacity of 118.3 mAh g^-1 even at a high rate of 10 C, superior to that(46.5 m Ah g^-1) of the H-NCM sample. The superior electrochemical performance of the S-NCM sample can be ascribed to its well-ordered structure, much larger specific surface area and much more oxygen vacancies located on the surface.