Magnesium hydroxide is an important chemi- cal, and is usually obtained from seawater or brine via precipitation process. The particle size distribution of magnesium hydroxide has great effects on the subsequent filtr...Magnesium hydroxide is an important chemi- cal, and is usually obtained from seawater or brine via precipitation process. The particle size distribution of magnesium hydroxide has great effects on the subsequent filtration and drying processes. In this paper, micron-sized magnesium hydroxide with high purity, large particle size and low water content in filter cake was synthesized via simple wet precipitation in a mixed suspension mixed product removal （MSMPR） crystallizer. The effects of reactant concentration, residence time and impurities on the properties of magnesium hydroxide were investigated by X-Ray diffraction （XRD）, Scanning Electron Micro- scopy （SEM） and Malvem laser particle size analyzer. The results show that NaOH concentration and residence time have great effects on the water content and particle size of Mg（OH）2. The spherical Mg（OH）2 with uniform diameter of about 30 μm was obtained with purity higher than 99% and water content less than 31%. Furthermore, the crystallization kinetics based on the population balance theory was studied to provide the theoretical data for industrial enlargement, and the simulation coefficients （R2） based on ASL model and C-R model are 0.9962 and 0.9972, respectively, indicating that the crystal growth rate of magnesium hydroxide can be well simulated by the size- dependent growth models.展开更多
The development of high energy density LiNi_(0.5)Mn_(1.5)O_(4)(LNMO)cathode materials for lithium-ion batteries are challenged by capacity degradation,which becomes more aggravated particularly at elevated temperature...The development of high energy density LiNi_(0.5)Mn_(1.5)O_(4)(LNMO)cathode materials for lithium-ion batteries are challenged by capacity degradation,which becomes more aggravated particularly at elevated temperatures.Thus,the practical strategy with facile craft and the viability of large-scale preparation for industrialized applications should be developed urgently.In this work,a micron-sized LNMO single crystals is synthesized by a facile two-step method consisting of an alcohol gel solvent method and a segmented sintering reaction.Results show that the truncated polyhedron LNMO-900 sample,with the moderate D50 characteristic value of 4.429 mm and the highest tap density of 2.31 g cm^(-3),provides a stable structural and chemical stability even at elevated testing temperature due to its moderate specific surface area and the few Fd-3m phase.The LNMO/Li half-cells display more excellent capacity retention(87.3% at 1C and 25℃ after 500 cycles)and better thermal stability(76.65% at 1C and 55℃ after 200 cycles)than those of the single crystals of LNMO-850 and LNMO-950.Besides,the XPS,in-situ EIS and electrochemical tests results also prove that the LNMO-900 exhibits the lowest electrolyte decomposition degree,owing to a thin and effective solid-electrolyte interfacial film formed after cycles.展开更多
Cation-disordered rocksalt oxides(DRX)have been identified as promising cathode materials for high energy density applications owing to their variable elemental composition and cationic-anionic redox activity.However,...Cation-disordered rocksalt oxides(DRX)have been identified as promising cathode materials for high energy density applications owing to their variable elemental composition and cationic-anionic redox activity.However,their practical implementation has been impeded by unwanted phenomena such as irrepressible transition metal migration/dissolution and O_(2)/CO_(2)evolution,which arise due to parasitic reactions and densification-degradation mechanisms during extended cycling.To address these issues,a micron-sized DRX cathode Li_(1.2)Ni_(1/3)Ti_(1/3)W_(2/15)O_(1.85)F_(0.15)(SLNTWOF)with F substitution and ultrathin LiF coating layer is developed by alcohols assisted sol-gel method.Within this fluorination-induced integrated structure design(FISD)strategy,in-situ F substitution modifies the activity/reversibility of the cationic-anionic redox reaction,while the ultrathin LiF coating and single-crystal structure synergistically mitigate the cathode/electrolyte parasitic reaction and densification-degradation mechanism.Attributed to the multiple modifications and size effect in the FISD strategy,the SLNTWOF sample exhibits reversible cationic-anionic redox chemistry with a meliorated reversible capacity of 290.3 mA h g^(-1)at 0.05C(1C=200 mA g^(-1)),improved cycling stability of 78.5%capacity retention after 50 cycles at 0.5 C,and modified rate capability of 102.8 mA h g^(-1)at 2 C.This work reveals that the synergistic effects between bulk structure modification,surface regulation,and engineering particle size can effectively modulate the distribution and evolution of cationic-anionic redox activities in DRX cathodes.展开更多
文摘Magnesium hydroxide is an important chemi- cal, and is usually obtained from seawater or brine via precipitation process. The particle size distribution of magnesium hydroxide has great effects on the subsequent filtration and drying processes. In this paper, micron-sized magnesium hydroxide with high purity, large particle size and low water content in filter cake was synthesized via simple wet precipitation in a mixed suspension mixed product removal （MSMPR） crystallizer. The effects of reactant concentration, residence time and impurities on the properties of magnesium hydroxide were investigated by X-Ray diffraction （XRD）, Scanning Electron Micro- scopy （SEM） and Malvem laser particle size analyzer. The results show that NaOH concentration and residence time have great effects on the water content and particle size of Mg（OH）2. The spherical Mg（OH）2 with uniform diameter of about 30 μm was obtained with purity higher than 99% and water content less than 31%. Furthermore, the crystallization kinetics based on the population balance theory was studied to provide the theoretical data for industrial enlargement, and the simulation coefficients （R2） based on ASL model and C-R model are 0.9962 and 0.9972, respectively, indicating that the crystal growth rate of magnesium hydroxide can be well simulated by the size- dependent growth models.
基金This work was supported by the National Natural Science Foundation of China(no.51962019 and 21766017)the Gansu Province Science and Technology Major Project(no.18ZD2FA012)the Lanzhou University of Technology Hongliu First-class Discipline Construction Program.
文摘The development of high energy density LiNi_(0.5)Mn_(1.5)O_(4)(LNMO)cathode materials for lithium-ion batteries are challenged by capacity degradation,which becomes more aggravated particularly at elevated temperatures.Thus,the practical strategy with facile craft and the viability of large-scale preparation for industrialized applications should be developed urgently.In this work,a micron-sized LNMO single crystals is synthesized by a facile two-step method consisting of an alcohol gel solvent method and a segmented sintering reaction.Results show that the truncated polyhedron LNMO-900 sample,with the moderate D50 characteristic value of 4.429 mm and the highest tap density of 2.31 g cm^(-3),provides a stable structural and chemical stability even at elevated testing temperature due to its moderate specific surface area and the few Fd-3m phase.The LNMO/Li half-cells display more excellent capacity retention(87.3% at 1C and 25℃ after 500 cycles)and better thermal stability(76.65% at 1C and 55℃ after 200 cycles)than those of the single crystals of LNMO-850 and LNMO-950.Besides,the XPS,in-situ EIS and electrochemical tests results also prove that the LNMO-900 exhibits the lowest electrolyte decomposition degree,owing to a thin and effective solid-electrolyte interfacial film formed after cycles.
基金supported by the National Key R&D Program of China(2021YFB2401800)the National Natural Science Foundation of China(22179008,21875022)+2 种基金the Natural Science Foundation of Chongqing,China(cstc2020jcyj-msxmX0589,cstc2020jcyjmsxmX0654)the support from Beijing Institute of Technology Research Fund Program for Young Scholarsthe 4B7B beamlines radiation equipment of Beijing Synchrotron Radiation Facility(2021-BEPC-PT-005924,2021-BEPC-PT-005967)。
文摘Cation-disordered rocksalt oxides(DRX)have been identified as promising cathode materials for high energy density applications owing to their variable elemental composition and cationic-anionic redox activity.However,their practical implementation has been impeded by unwanted phenomena such as irrepressible transition metal migration/dissolution and O_(2)/CO_(2)evolution,which arise due to parasitic reactions and densification-degradation mechanisms during extended cycling.To address these issues,a micron-sized DRX cathode Li_(1.2)Ni_(1/3)Ti_(1/3)W_(2/15)O_(1.85)F_(0.15)(SLNTWOF)with F substitution and ultrathin LiF coating layer is developed by alcohols assisted sol-gel method.Within this fluorination-induced integrated structure design(FISD)strategy,in-situ F substitution modifies the activity/reversibility of the cationic-anionic redox reaction,while the ultrathin LiF coating and single-crystal structure synergistically mitigate the cathode/electrolyte parasitic reaction and densification-degradation mechanism.Attributed to the multiple modifications and size effect in the FISD strategy,the SLNTWOF sample exhibits reversible cationic-anionic redox chemistry with a meliorated reversible capacity of 290.3 mA h g^(-1)at 0.05C(1C=200 mA g^(-1)),improved cycling stability of 78.5%capacity retention after 50 cycles at 0.5 C,and modified rate capability of 102.8 mA h g^(-1)at 2 C.This work reveals that the synergistic effects between bulk structure modification,surface regulation,and engineering particle size can effectively modulate the distribution and evolution of cationic-anionic redox activities in DRX cathodes.
