Li-rich layered oxide materials have attracted increasing attention because of their high specific capacity(>250 mAh g^(-1)). However, these materials typically suffer from poor cycling stability and low rate perfo...Li-rich layered oxide materials have attracted increasing attention because of their high specific capacity(>250 mAh g^(-1)). However, these materials typically suffer from poor cycling stability and low rate performance. Herein, we propose a facile and novel metal-organic-framework(MOF) shell-derived surface modification strategy to construct NiCo nanodots decorated(~5 nm in diameter) carbon-confined Li_(1.2)Mn_(0.54) Ni_(0.13)Co_(0.13)O_2 nanoparticles(LLO@C&NiCo). The MOF shell is firstly formed on the surface of as-prepared Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2 nanoparticles via low-pressure vapor superassembly and then is in situ converted to the NiCo nanodots decorated carbon shell after subsequent controlled pyrolysis.The obtained LLO@C&NiCo cathode exhibits enhanced cycling and rate capability with a capacity retention of 95% after 100 cycles at 0.4 C and a high capacity of 159 mAh g^(-1) at 5 C, respectively, compared with those of LLO(75% and 105 mAh g^(-1)). The electrochemical impedance spectroscopy and selected area electron diffraction analyses after cycling demonstrate that the thin C&NiCo shell can endow LLO with high electronic conductivity and structural stability, indicating the undesired formation of the spinel phase initiated from the particle surface is efficiently suppressed. Therefore, this presented strategy may open a new avenue on the design of high-performance electrode materials for energy storage.展开更多
Lithium-rich layered oxides(LLOs)have been extensively studied as cathode materials for lithium-ion batteries(LIBs)by researchers all over the world in the past decades due to their high specific capacities and high c...Lithium-rich layered oxides(LLOs)have been extensively studied as cathode materials for lithium-ion batteries(LIBs)by researchers all over the world in the past decades due to their high specific capacities and high charge-discharge voltages.However,as cathode materials LLOs have disadvantages of significant voltage and capacity decays during the charge-discharge cycling.It was shown in the past that fine-tuning of structures and compositions was critical to the performances of this kind of materials.In this report,LLOs with target composition of Li1.17Mn0.50Ni0.24Co0.09O2 were prepared by carbonate co-precipitation method with different pH values.X-ray powder diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscope(TEM),and electrochemical impedance spectroscopies(EIS)were used to investigate the structures and morphologies of the materials and to understand the improvements of their electrochemical performances.With the pH values increased from 7.5 to 8.5,the Li/Ni ratios in the compositions decreased from 5.17 to 4.64,and the initial Coulombic efficiency,cycling stability and average discharge voltages were gained impressively.Especially,the material synthesized at pH=8.5 delivered a reversible discharge capacity of 263 mAhg−1 during the first cycle,with 79.0%initial Coulombic efficiency,at the rate of 0.1 C and a superior capacity retention of 94%after 100 cycles at the rate of 1 C.Furthermore,this material exhibited an initial average discharge voltage of 3.65 V,with a voltage decay of only 0.09 V after 50 charge-discharge cycles.The improved electrochemical performances by varying the pH values in the synthesis process can be explained by the mitigation of layered-to-spinel phase transformation and the reduction of solid-electrolyte interface(SEI)resistance.We hope this work can shed some light on the alleviation of voltage and capacity decay issues of the LLOs cathode materials.展开更多
采用喷雾干燥法和沉淀法,制备了表面修饰TiO2（B）（2wt%、4wt%、6wt%和8wt%）的富锂层状氧化物Li（Li0.17Ni0.2Mn0.58Co0.05）O2正极材料。X射线衍射（XRD）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）结构测试分析结果表明,修饰T...采用喷雾干燥法和沉淀法,制备了表面修饰TiO2（B）（2wt%、4wt%、6wt%和8wt%）的富锂层状氧化物Li（Li0.17Ni0.2Mn0.58Co0.05）O2正极材料。X射线衍射（XRD）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）结构测试分析结果表明,修饰TiO2（B）后样品的体相结构仍然保持初始样品的层状结构,仅氧化物颗粒表面附着有少量TiO2（B）纳米晶。示差扫描量热测试（DSC）表明,与初始样品比较,修饰TiO2（B）后样品的热稳定性得到明显改善。在2.0~4.8 V范围内进行恒流电化学性能测试。研究显示,在0.1C（1C=300 m A/g）倍率下,修饰4wt%TiO2（B）样品的首次放电比容量可达296.4 m Ah/g,首次库伦效率则由初始样品的77.7%提升到修饰TiO2（B）后样品的84.3%,100周循环后电极容量保持率由初始样品的69.5%提升到修饰TiO2（B）后样品的80.2%。即使在阶梯倍率的2C倍率下,修饰4wt%TiO2（B）的样品仍具有较高的电化学容量（166.5 m Ah/g）。以上研究结果表明,表面修饰TiO2（B）纳米晶可以显著改善富锂层状氧化物Li（Li0.17Ni0.2Mn0.58Co0.05）O2的热稳定性和电化学性能。展开更多
采用聚合物热解的方法合成了富锂正极材料Li[Li0.2Co0.13Ni0.13Mn0.54]O2（RLMO）,并对其进行硼磷玻璃（BPG）表面包覆。经过X射线衍射（XRD）、扫描电镜（SEM）、透射电镜（TEM）实验表明,材料颗粒尺寸在100~200 nm范围,其表面明显具...采用聚合物热解的方法合成了富锂正极材料Li[Li0.2Co0.13Ni0.13Mn0.54]O2（RLMO）,并对其进行硼磷玻璃（BPG）表面包覆。经过X射线衍射（XRD）、扫描电镜（SEM）、透射电镜（TEM）实验表明,材料颗粒尺寸在100~200 nm范围,其表面明显具有非晶包覆层,且表面包覆不会改变材料的主体结构。在2.0~4.8 V范围内进行恒流充放电测试表明,非晶硼磷玻璃包覆材料（BPG-RLMO）具有更高的首次放电比容量（279.5 m Ah/g,30 m A/g）、高的首次库仑效率（91.3%）和优异的循环稳定性（100次循环后容量保持率为86.4%,30 m A/g）。这些结果表明非晶硼磷玻璃包覆可有效抑制电解液的表面分解和所引起的表面结构破坏,提高了材料的首次库仑效率和循环稳定性,为高性能富锂正极材料的发展提供一种可借鉴途径。展开更多
以柠檬酸为螯合剂,采用溶胶-凝胶法通过调节煅烧温度和陈化时间制备了不同粒径的富锂正极材料Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2。结果表明材料的粒径随煅烧温度增加,逐渐增大;随着陈化时间的增加,呈现先增大后变小的趋势。当煅...以柠檬酸为螯合剂,采用溶胶-凝胶法通过调节煅烧温度和陈化时间制备了不同粒径的富锂正极材料Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2。结果表明材料的粒径随煅烧温度增加,逐渐增大;随着陈化时间的增加,呈现先增大后变小的趋势。当煅烧温度为850℃,陈化时间为10 d时,材料具有最优的电化学性能,尤其是倍率性能。在2.0~4.8 V的电压范围内以0.1 C充放电循环60周后放电比容量仍为206.7 m Ah·g-1,2.0 C时的放电比容量为125.6 m Ah·g-1。展开更多
应用共沉淀结合固相烧结合成了富锂层状氧化物(Li-rich layered oxide,LLO)Li1.2Ni0.13Co0.13Mn0.54O2.对制备的富锂材料用氧化石墨烯(Graphene Oxide,GO)包覆后,再经300oC空气中煅烧,制备了石墨烯(Graphene,Gra)卷绕包覆的复合材料(LLO...应用共沉淀结合固相烧结合成了富锂层状氧化物(Li-rich layered oxide,LLO)Li1.2Ni0.13Co0.13Mn0.54O2.对制备的富锂材料用氧化石墨烯(Graphene Oxide,GO)包覆后,再经300oC空气中煅烧,制备了石墨烯(Graphene,Gra)卷绕包覆的复合材料(LLO/Gra).使用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)及电化学方法表征所得样品.结果表明,富锂层状氧化物均匀地卷绕在石墨烯中.与原始富锂材料相比,石墨烯包覆后的复合材料表现出更加优异的电化学性能.尤其是石墨烯卷绕可以改善富锂材料的导电性,提高材料的放电倍率性能,在2.0至4.8 V电压范围内,0.1C(20 m A·g-1)电流充放电下,容量达270 m Ah·g-1,1C倍率下复合物的放电容量接近200 m Ah·g-1,比原始LLO材料170 m Ah·g-1提高了15%.展开更多
The mechanism research of structure-related reactions on Li_2MnO_3 is important to enhance the electrochemical performance of lithium-manganese-rich layered oxides.Although there are some reports on the structure evol...The mechanism research of structure-related reactions on Li_2MnO_3 is important to enhance the electrochemical performance of lithium-manganese-rich layered oxides.Although there are some reports on the structure evolution of Li_2MnO_3 during cycling process,the employed research techniques are very limited,mainly in/ex-situ X-ray diffraction,X-ray absorption and transmission electron microscopy.Here,atomic pair distribution function,a method to study the local atomic arrangement on the basis of average spectroscopic information,is used for the first time to study the local structure evolution of Li_2MnO_3 during electrochemical charge/discharge cycles.The results clearly demonstrate that Mn^(3+)/Mn^(4+) redox couple is activated and Mn ions are reduced during discharging process.Some Mn ions in Mn layers can significantly migrate to Li layers and occupy the octahedral sites.As a result,a portion of inserted Li ions can occupy the face-shared tetrahedron sites,accompanied by the formation of local spinel-like structure.This work provides an important and suitable method based on the average spectroscopic information to investigate the local structure of electrode materials of lithium-ion batteries as well as other advanced battery systems.展开更多
因高能量密度和高能量转换效率,锂离子电池已被广泛应用于便携式电子设备和电动交通中。富锂层状结构氧化物以高达300 m Ah·g^-1的可逆容量成为能量密度350 Wh·kg^-1及以上动力锂离子电池的重要候选正极材料。但是,欲使这类...因高能量密度和高能量转换效率,锂离子电池已被广泛应用于便携式电子设备和电动交通中。富锂层状结构氧化物以高达300 m Ah·g^-1的可逆容量成为能量密度350 Wh·kg^-1及以上动力锂离子电池的重要候选正极材料。但是,欲使这类材料获得实际应用,就必须解决循环过程中结构衰退带来的一系列问题。本文重点介绍近几年来笔者所领导的研究组通过元素筛选实现材料的表面和体相掺杂,通过全新的结构设计稳定材料结构和性能方面的努力。同时,为使读者对国内外重要研究组在相关方面的研究进展也有所了解,我们也将从元素替代、结构一体化表面修饰(包括多层表面修饰和浓度梯度材料)、表面包覆和表面掺杂等方面介绍他们的重要研究成果。最后,将对该类材料的未来发展方向作出展望并给出我们的一些思考。展开更多
基金supported by the National Key Research and Development Program of China(2016YFA0202603)the National Basic Research Program of China(2013CB934103)+4 种基金the Programme of Introducing Talents of Discipline to Universities(B17034)the National Natural Science Foundation of China(51521001)the National Natural Science Fund for Distinguished Young Scholars(51425204)the Fundamental Research Funds for the Central Universities(WUT:2016III001 and 2016-YB-004)financial support from China Scholarship Council(201606955096)
文摘Li-rich layered oxide materials have attracted increasing attention because of their high specific capacity(>250 mAh g^(-1)). However, these materials typically suffer from poor cycling stability and low rate performance. Herein, we propose a facile and novel metal-organic-framework(MOF) shell-derived surface modification strategy to construct NiCo nanodots decorated(~5 nm in diameter) carbon-confined Li_(1.2)Mn_(0.54) Ni_(0.13)Co_(0.13)O_2 nanoparticles(LLO@C&NiCo). The MOF shell is firstly formed on the surface of as-prepared Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2 nanoparticles via low-pressure vapor superassembly and then is in situ converted to the NiCo nanodots decorated carbon shell after subsequent controlled pyrolysis.The obtained LLO@C&NiCo cathode exhibits enhanced cycling and rate capability with a capacity retention of 95% after 100 cycles at 0.4 C and a high capacity of 159 mAh g^(-1) at 5 C, respectively, compared with those of LLO(75% and 105 mAh g^(-1)). The electrochemical impedance spectroscopy and selected area electron diffraction analyses after cycling demonstrate that the thin C&NiCo shell can endow LLO with high electronic conductivity and structural stability, indicating the undesired formation of the spinel phase initiated from the particle surface is efficiently suppressed. Therefore, this presented strategy may open a new avenue on the design of high-performance electrode materials for energy storage.
基金the National Natural Science Foundation of China(No.21271145)the National Science Foundation of Hubei Province(No.2015CFB537)+1 种基金the Science and Technology Innovation Committee of Shenzhen Municipality(No.JCYJ20170306171321438)the financial support for this investigation.
文摘Lithium-rich layered oxides(LLOs)have been extensively studied as cathode materials for lithium-ion batteries(LIBs)by researchers all over the world in the past decades due to their high specific capacities and high charge-discharge voltages.However,as cathode materials LLOs have disadvantages of significant voltage and capacity decays during the charge-discharge cycling.It was shown in the past that fine-tuning of structures and compositions was critical to the performances of this kind of materials.In this report,LLOs with target composition of Li1.17Mn0.50Ni0.24Co0.09O2 were prepared by carbonate co-precipitation method with different pH values.X-ray powder diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscope(TEM),and electrochemical impedance spectroscopies(EIS)were used to investigate the structures and morphologies of the materials and to understand the improvements of their electrochemical performances.With the pH values increased from 7.5 to 8.5,the Li/Ni ratios in the compositions decreased from 5.17 to 4.64,and the initial Coulombic efficiency,cycling stability and average discharge voltages were gained impressively.Especially,the material synthesized at pH=8.5 delivered a reversible discharge capacity of 263 mAhg−1 during the first cycle,with 79.0%initial Coulombic efficiency,at the rate of 0.1 C and a superior capacity retention of 94%after 100 cycles at the rate of 1 C.Furthermore,this material exhibited an initial average discharge voltage of 3.65 V,with a voltage decay of only 0.09 V after 50 charge-discharge cycles.The improved electrochemical performances by varying the pH values in the synthesis process can be explained by the mitigation of layered-to-spinel phase transformation and the reduction of solid-electrolyte interface(SEI)resistance.We hope this work can shed some light on the alleviation of voltage and capacity decay issues of the LLOs cathode materials.
文摘采用喷雾干燥法和沉淀法,制备了表面修饰TiO2（B）（2wt%、4wt%、6wt%和8wt%）的富锂层状氧化物Li（Li0.17Ni0.2Mn0.58Co0.05）O2正极材料。X射线衍射（XRD）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）结构测试分析结果表明,修饰TiO2（B）后样品的体相结构仍然保持初始样品的层状结构,仅氧化物颗粒表面附着有少量TiO2（B）纳米晶。示差扫描量热测试（DSC）表明,与初始样品比较,修饰TiO2（B）后样品的热稳定性得到明显改善。在2.0~4.8 V范围内进行恒流电化学性能测试。研究显示,在0.1C（1C=300 m A/g）倍率下,修饰4wt%TiO2（B）样品的首次放电比容量可达296.4 m Ah/g,首次库伦效率则由初始样品的77.7%提升到修饰TiO2（B）后样品的84.3%,100周循环后电极容量保持率由初始样品的69.5%提升到修饰TiO2（B）后样品的80.2%。即使在阶梯倍率的2C倍率下,修饰4wt%TiO2（B）的样品仍具有较高的电化学容量（166.5 m Ah/g）。以上研究结果表明,表面修饰TiO2（B）纳米晶可以显著改善富锂层状氧化物Li（Li0.17Ni0.2Mn0.58Co0.05）O2的热稳定性和电化学性能。
文摘采用聚合物热解的方法合成了富锂正极材料Li[Li0.2Co0.13Ni0.13Mn0.54]O2（RLMO）,并对其进行硼磷玻璃（BPG）表面包覆。经过X射线衍射（XRD）、扫描电镜（SEM）、透射电镜（TEM）实验表明,材料颗粒尺寸在100~200 nm范围,其表面明显具有非晶包覆层,且表面包覆不会改变材料的主体结构。在2.0~4.8 V范围内进行恒流充放电测试表明,非晶硼磷玻璃包覆材料（BPG-RLMO）具有更高的首次放电比容量（279.5 m Ah/g,30 m A/g）、高的首次库仑效率（91.3%）和优异的循环稳定性（100次循环后容量保持率为86.4%,30 m A/g）。这些结果表明非晶硼磷玻璃包覆可有效抑制电解液的表面分解和所引起的表面结构破坏,提高了材料的首次库仑效率和循环稳定性,为高性能富锂正极材料的发展提供一种可借鉴途径。
文摘以柠檬酸为螯合剂,采用溶胶-凝胶法通过调节煅烧温度和陈化时间制备了不同粒径的富锂正极材料Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2。结果表明材料的粒径随煅烧温度增加,逐渐增大;随着陈化时间的增加,呈现先增大后变小的趋势。当煅烧温度为850℃,陈化时间为10 d时,材料具有最优的电化学性能,尤其是倍率性能。在2.0~4.8 V的电压范围内以0.1 C充放电循环60周后放电比容量仍为206.7 m Ah·g-1,2.0 C时的放电比容量为125.6 m Ah·g-1。
文摘应用共沉淀结合固相烧结合成了富锂层状氧化物(Li-rich layered oxide,LLO)Li1.2Ni0.13Co0.13Mn0.54O2.对制备的富锂材料用氧化石墨烯(Graphene Oxide,GO)包覆后,再经300oC空气中煅烧,制备了石墨烯(Graphene,Gra)卷绕包覆的复合材料(LLO/Gra).使用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)及电化学方法表征所得样品.结果表明,富锂层状氧化物均匀地卷绕在石墨烯中.与原始富锂材料相比,石墨烯包覆后的复合材料表现出更加优异的电化学性能.尤其是石墨烯卷绕可以改善富锂材料的导电性,提高材料的放电倍率性能,在2.0至4.8 V电压范围内,0.1C(20 m A·g-1)电流充放电下,容量达270 m Ah·g-1,1C倍率下复合物的放电容量接近200 m Ah·g-1,比原始LLO材料170 m Ah·g-1提高了15%.
基金supported by the National Natural Science Foundation of China(No.U21A20170)the Ministry of Science and Technology of China(No.2019YFE0100200,2019YFA0705703,and 2021YFB2501900)。
基金supported financially by the Beijing Natural Science Foundation (B) (KZ201610005003)National Natural Science Foundation of China (51622202, U1507107, 21603009 and 51802009)+1 种基金National Key R&D Program of China (2018YFB0104302)Guangdong Science and Technology Project (2016B010114001)
文摘The mechanism research of structure-related reactions on Li_2MnO_3 is important to enhance the electrochemical performance of lithium-manganese-rich layered oxides.Although there are some reports on the structure evolution of Li_2MnO_3 during cycling process,the employed research techniques are very limited,mainly in/ex-situ X-ray diffraction,X-ray absorption and transmission electron microscopy.Here,atomic pair distribution function,a method to study the local atomic arrangement on the basis of average spectroscopic information,is used for the first time to study the local structure evolution of Li_2MnO_3 during electrochemical charge/discharge cycles.The results clearly demonstrate that Mn^(3+)/Mn^(4+) redox couple is activated and Mn ions are reduced during discharging process.Some Mn ions in Mn layers can significantly migrate to Li layers and occupy the octahedral sites.As a result,a portion of inserted Li ions can occupy the face-shared tetrahedron sites,accompanied by the formation of local spinel-like structure.This work provides an important and suitable method based on the average spectroscopic information to investigate the local structure of electrode materials of lithium-ion batteries as well as other advanced battery systems.
文摘因高能量密度和高能量转换效率,锂离子电池已被广泛应用于便携式电子设备和电动交通中。富锂层状结构氧化物以高达300 m Ah·g^-1的可逆容量成为能量密度350 Wh·kg^-1及以上动力锂离子电池的重要候选正极材料。但是,欲使这类材料获得实际应用,就必须解决循环过程中结构衰退带来的一系列问题。本文重点介绍近几年来笔者所领导的研究组通过元素筛选实现材料的表面和体相掺杂,通过全新的结构设计稳定材料结构和性能方面的努力。同时,为使读者对国内外重要研究组在相关方面的研究进展也有所了解,我们也将从元素替代、结构一体化表面修饰(包括多层表面修饰和浓度梯度材料)、表面包覆和表面掺杂等方面介绍他们的重要研究成果。最后,将对该类材料的未来发展方向作出展望并给出我们的一些思考。
